Content:

SSS – Soil System Sciences

SSS2.4 – Gully, rill and piping erosion: recent advancements and novel approaches

EGU2020-10940 | Displays | SSS2.4

Ephemeral Gully Erosion Advancements within the AnnAGNPS Watershed Simulation Model

Ronald Bingner, Robert Wells, and Henrique Momm

Concentrated runoff increases erosion and moves fine sediment and associated agrichemicals from upland areas to stream channels. Ephemeral gully erosion on croplands in the U.S. may contribute more of the sediment delivered to the edge of the field then from sheet and rill erosion. Typically, conservation practices developed for sheet and rill erosion are also expected to treat ephemeral gully erosion, but science and technology are needed to account for the separate benefits and effects of practices on each of the various sediment sources.

Watershed modeling technology has been widely developed to aid in evaluating conservation practices implemented as part of a management plan, but typically lacks the capability to identify how a source, such as sheet and rill erosion, ephemeral gully erosion, or channel erosion, is specifically controlled by a practice or integrated practices. The U.S. Department of Agriculture’s Annualized Agricultural Non-Point Source pollutant loading model, AnnAGNPS, has been developed to determine the effects of conservation management plans on erosion and provide sediment tracking from all sources within the watershed, including sheet and rill, ephemeral gully, and channel erosion. 

This study describes the ephemeral gully erosion capabilities within the AnnAGNPS model and discusses research needs to further improve these components for integrated conservation management planning.  Conservation management planning by agencies within the U.S. and by international organizations requires a systematic approach when determining the extent of ephemeral gully erosion impacts on a field, watershed, or national basis, and/or to predict recurring or new locations of ephemeral gullies prior to their development.  This technology provides the capability to separate the impact of ephemeral gullies on erosion from other sources and then evaluate the impact of targeted practices to control erosion at the source and subsequent downstream resources.

How to cite: Bingner, R., Wells, R., and Momm, H.: Ephemeral Gully Erosion Advancements within the AnnAGNPS Watershed Simulation Model , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10940, https://doi.org/10.5194/egusphere-egu2020-10940, 2020.

EGU2020-1701 | Displays | SSS2.4

Small permanent gullies: modelling and application to a semiarid region

Pedro Henrique Lima Alencar, José Carlos de Araújo, and Adunias dos Santos Teixeira

Gullies are key drivers of land degradation, are important sources of sediment and increase sediment and pollutant connectivity in the catchment. They also play an important role in desertification areas, changing the water-table height and in farmlands, reducing productive areas. In this study, we attempted to model small permanent gullies, common in the Brazilian Semiarid Region, where the shallow soils limit the size of gullies cross-sections to a depth of no more than one meter. To model this process, we coupled the models of Foster and Lane (1983) and Sidorchuk (1999), in order to consider the effect of permanent gullies not considered in the first. Both models need as input the discharge peak and its duration, however, these data are frequently not available. We tested four different rain intensities (average, 60-minute, 30-minute and 15-minute), finding that the most intense 30 minutes represent the best the effects of the storms over gully erosion. The coupling of the two models is defined by a threshold that indicates when the equations for sidewall erosion proposed by Sidorchuk should be applied. To validate the model, we measured three gullies in the Brazilian Semiarid Region. The gullies were initiated in 1958 after the construction of a country road and have drainage area below 1 ha. The model yielded a Nash-Sutcliffe coefficient of 0.85.

How to cite: Lima Alencar, P. H., de Araújo, J. C., and dos Santos Teixeira, A.: Small permanent gullies: modelling and application to a semiarid region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1701, https://doi.org/10.5194/egusphere-egu2020-1701, 2020.

EGU2020-11469 | Displays | SSS2.4

Evaluation of CCHE2D hydrodynamic and sediment transport model to simulate erosional sources in row crop agriculture in Midwest US

Robert Wells, Yafei Jia, Henrique Momm, Carlos Castillo, Dalmo Vieira, Ronald Bingner, Sean Bennett, and Martin Locke

Soil erosion due to rainfall and overland flow can be detrimental to agricultural management and long-term agricultural sustainability. Although numerous conservation measures and planning strategies have greatly reduced the amount of sediment moving within the landscape, there are still unresolved questions concerning initiation of particle motion, susceptibility to erosion, total soil loss, sediment transport and general measurement theory. Within agricultural fields, ephemeral erosion is particularly harmful because these sources can accelerate sediment transport, often yield more sediment than interrill sources and are more challenging to mitigate. In this study, terrain data were collected by aerial photogrammetry using an unmanned aerial system (UAS) following planting and approximately one month later, while climate variables during the period were collected using NexRad radar. Imagery was captured within seven agricultural fields (six in Iowa and one in Minnesota), ranging in size from 0.6 to 3.6 hectare (1.6 to 8.8 acre). Considering the small scale in topographic variation between two surveys, extreme efforts were applied to image processing and geospatial registration. Advanced models for camera calibration utilizing Micmac open-source photogrammetry software package were used to account for complex distortion patterns in the raw image data set. The undistorted images were then processed using Agisoft Photoscan for camera alignment, model georeferencing and dense point cloud generation (millions to billions of points per survey), from which digital elevation models (DEMs; 10 to 57 million cells) were produced. A physically-based finite element hydrodynamic and sediment transport model (CCHE2D, developed at the National Center for Computational Hydroscience and Engineering) was applied to simulate hydrological (runoff), sediment detachment (raindrop splash, sheet flow, and concentrated flow erosion) and sediment transport/deposition landscape evolution processes. Simulated geomorphological and sediment budget results over time were compared to field observations for model input parameter adjustment and consequently quantification of estimates. Integration of high-resolution spatial and temporal topographic measurements with physically-based numerical models support the development and validation of dynamic landscape evolution models needed for accurate prediction and quantification of gully initiation, evolution and impact on total soil loss and effective conservation management planning.

How to cite: Wells, R., Jia, Y., Momm, H., Castillo, C., Vieira, D., Bingner, R., Bennett, S., and Locke, M.: Evaluation of CCHE2D hydrodynamic and sediment transport model to simulate erosional sources in row crop agriculture in Midwest US, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11469, https://doi.org/10.5194/egusphere-egu2020-11469, 2020.

EGU2020-4380 | Displays | SSS2.4

Simulation of Loess Gully Evolution Based on Geographic Cellular Automata

Lanhua Luo and Fayuan Li

Gully development is an important topic in the evolution of modern geomorphology. The study of the development process of gullies is key to explain the genesis, mechanism and spatial differentiation of loess geomorphology. Geographic cellular automata (Geo-CA) can simulate complex geographical phenomena by expanding and elements of Cellular automata (CA). This study explores the mechanism of the development process of loess gullies while taking into account the dynamic factors of head-cut erosion. Based on geographic cellular automata (Geo-CA), the transition rules for gully evolution are designed, including the rules of gully head region, the rules of water infiltration, flow direction rule, flow rules, and sediment transport rules. Based on the small simulated Loess watershed under artificial rainfall, the simulation model of loess gully evolution is constructed and implemented. In order to evaluate the accuracy of the simulation results, the negative terrain, Hypsometric Integral (HI) and a gully head confusion matrix of the simulated results and the measured data are compared. The evaluation produces encouraging results in terms of numeric accuracy and spatial distribution, in agreement with the evolution of the loess gully. In addition, the simulation model of loess gully evolution this study proposed is applied to the evolution of a natural watershed, the Madigou watershed located in Jingbian County, Yulin City, Shaanxi Province. The comparison between the simulated results of the model and the measured data is used to verify the validity of the model. All the results show that the evolution model of loess gully based on Geo-CA is satisfactory in simulating the process of loess gully evolution, which provides a new research method and ideas for in-depth study of the process of gully evolution. 

How to cite: Luo, L. and Li, F.: Simulation of Loess Gully Evolution Based on Geographic Cellular Automata, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4380, https://doi.org/10.5194/egusphere-egu2020-4380, 2020.

EGU2020-8661 | Displays | SSS2.4

Process-oriented gully density modelling at the continental scale of Africa: first insights

Sofie De Geeter, Matthias Vanmaercke, Gert Verstraeten, and Jean Poesen

Gully erosion is an important land degradation process, threatening soil and water resources worldwide. However, contrary to sheet and rill erosion, our ability to simulate and predict gully erosion remains limited, especially at the continental scale. Nevertheless, such models are essential for the development of suitable land management strategies, but also to better quantify the role of gully erosion in continental sediment budgets. We aim to bridge this gap by developing a first spatially explicit and process-oriented model that simulates average gully erosion rates at the continental scale of Africa.

We are currently developing a spatially explicit model that (i) allows to simulate the spatial patterns of gully density at high resolution (30-90 m); (ii) is based on the physical principles that control the gully erosion process; (iii) uses GIS and data sources that are available at the continental scale. Our model structure is based on the threshold-dependent character of the gully-initiation process where a proxy of flow shear stress is weighted against a proxy of local shear resistance at the pixel scale. To calibrate and validate this model, we make use of an extensive database of 44 000 gully heads mapped over 1680 sites that are randomly distributed across Africa. The exact location of all gully heads was manually mapped by trained experts, using high resolution optical imagery available in Google Earth. This allows to extract very detailed information at the level of the gully head, such as the local slope and the area draining to the gully head. Based on these variables, we simulate indices for peak runoff (based on the Curve Number method), the shear stress of the concentrated runoff and the critical shear stress of the soil. The combination of these indices reflects the process leading to gully initiation and therefore provides an accurate indication of the susceptibility of that location to gully initiation.

Preliminary results indicate that it is feasible to model gully head locations and densities using this process-oriented approach. However, important trade-offs exist between an accurate description of the (threshold-dependent) gully initiation process and the uncertainties on the GIS data used to describe this process. One important issue is the resolution of the digital elevation model (DEM) used to extract local slopes (S) and to delineate contributing areas (A).  Comparing S- and A-values obtained from 30m SRTM-data with those obtained from higher resolution DEMs (5-12m) showed that SRTM data allows to obtain reasonable proxies of S and A but that uncertainties can be significant and correction factors are needed to avoid biases.

Overall, our results indicate that modelling gully densities using a process-oriented and spatially explicit approach has (conceptual and pragmatic) advantages as compared to a purely empirical ‘black-box’ modelling approach and offers opportunities to better quantify this important land degradation process at the global scale.

How to cite: De Geeter, S., Vanmaercke, M., Verstraeten, G., and Poesen, J.: Process-oriented gully density modelling at the continental scale of Africa: first insights, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8661, https://doi.org/10.5194/egusphere-egu2020-8661, 2020.

EGU2020-147 | Displays | SSS2.4

Spatial variation of gully density and morphology and their controlling factors at a regional scale: a case study for the Chinese Loess Plateau

Yixian Chen, Juying Jiao, Matthias Vanmaercke, Xiqin Yan, and Jianjun Li

Gully erosion is a major cause of land degradation in many regions worldwide. Recent research shows that the challenges posed by gully erosion are likely to further increase as a result of climate change and increasing land use pressure. Nonetheless, our understanding of this process remains limited in many ways. While numerous studies have focused on the occurrence and morphology of gullies at local (catchment) scale, relatively little research has explored their spatial variations at regional to continental scales. As a result, the factors controlling the density, size and morphology of gullies at such scales remain poorly understood. This is especially the case for the role of climate/weather conditions. Here we aim to advance our understanding on this topic by studying gully densities and gully morphology in the Chinese Loess Plateau (CLP), a region severely affected by gully erosion. 
We selected five representative catchments in the CLP that are relatively similar in size (7-30 km²), topographic context, soil characteristics and land use but represent a large gradient in rainfall conditions. We mapped 2511 gullies in these catchments, using Pleiades-1B (panchromatic resolution at 0.5 m) and WorldView-3 images (panchromatic resolution at 0.31 m). For each of the gullies, we calculated a range of morphological parameters including the gully length, width, surface area, length-width ratio and shape index. Next, we explored to what extent differences in gully density and morphology are correlated to contrasts in rainfall and other environmental factors.
Overall, the gullies showed large variations in gully length (2.1-308 m, average 38.1 m), width (1.3-87 m, average 11.5 m) and density (0-4.8 km/km², average 2.3 km/km²). Gully densities showed a negative correlation with rainfall amounts. This is likely partly attributable to feedbacks between rainfall amounts and vegetation cover. However, also contrasts in rainfall intensity and regime likely play an important role. Also variations in gully width appear strongly correlated with rainfall patterns (with more humid catchments resulting in overall wider gullies). Surprisingly, gully lengths (a first indicator of gully headcut retreat) showed no clear correlation with rainfall patterns. Overall, our results indicate that contrasts in rainfall regime are crucial to understand gully erosion dynamics at regional to continental scales. This is true for their initiation but also for their subsequent expansion (and especially gully widening). These findings have important implications for the development of models aiming to predict gully erosion at regional to continental scales.

How to cite: Chen, Y., Jiao, J., Vanmaercke, M., Yan, X., and Li, J.: Spatial variation of gully density and morphology and their controlling factors at a regional scale: a case study for the Chinese Loess Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-147, https://doi.org/10.5194/egusphere-egu2020-147, 2020.

Soil erosion constitutes a major problem in the European loess belt. From England to Eastern Europe, loess-derived soils are particularly susceptible to water and tillage erosion. This is certainly the case for the Aa River Basin (Nord-Pas-de-Calais, northern France), where a relatively thin Pleistocene loess cover is present on top of a substrate of clay-with-flints and Cretaceous chalk. This research aimed at quantifying the amount of soil eroded since its initiation. Making a gross balance of the soil erosion and sedimentation processes intends to study the evolution of the soil surface and the effects of different types of erosion over longer periods of time, and quantify erosion rates in agricultural areas.

The extent and amount of eroded soil was mapped in the Lauwerdal, a 63 ha large catchment in the headwaters of the Aa River Basin (Northern France). Based on four soil profiles, described and sampled along a topographic transect, and 256 augerings spaced along a grid, the original soil surface level was reconstructed. The current topographic surface was analysed based on a Digital Terrain Model obtained from UAV aerial photographs. The organic matter present in the filling of a former erosion channel, observed in one of the soil profiles, was dated by 14C as an indication of the onset of the erosion and sedimentation process.

Water and tillage erosion are the main processes characterizing the study area: eroded soils (Nudiargic Luvisols) dominate the upper reaches of the study area with colluvium at the footslopes (Colluvic Regosols). The sediment budget reveals that the bulk of the sediments are discharged from the headwater catchment as the quantity of eroded soil (0.87 × 106 tonnes) is more than a ten-fold higher than the deposition (0.068 × 106 tonnes). The 14C dating indicates that the erosion channels started filling up between the Early Iron Age and the Roman period, ca. 1200 years BP. The historical erosion rates are estimated at 491.4 t/km2 per year, and deposition rates at 91.8 t/km2 per year.

Our findings illustrate how the amount of soil eroded over a long time span can be estimated from soil morphologic features in combination with a detailed Digital Terrain Model. Indeed, human induced soil erosion dates back at least to Early Iron Age, when forest clearing for agricultural expanded. Surely, the mechanization and upscaling of agriculture in the 20th century will have exacerbated this process. The results also show that sediments are evacuated from headwater catchments and, consequently, must accumulate in the lower alluvial plains. Our findings corroborate research findings from the silt-loess belt of central Belgium where it was shown that soil erosion started in the same period and also led to the formation of wide alluvial valleys.

How to cite: Krekelbergh, N., Frankl, A., and Dondeyne, S.: Understanding soil profiles and sediment redistribution over long time scales in an agrarian setting: the case of Lauwerdal (Northern France), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14026, https://doi.org/10.5194/egusphere-egu2020-14026, 2020.

Ephemeral gullies (EG) are linear erosion features located in swales where runoff concentrates during or immediately after rainfall events. EG are temporary because they are easily filled by conventional machinery and cause important soil losses in cultivated areas. Casalí et al. (1999) distinguished three types of EG: “classical”, formed by concentrated runoff flows within the same field where runoff started; “drainage”, created by concentrated flows draining areas upstream from the field; “discontinuity”, found in places where management practices create a sudden change in slope. There is still a great lack of knowledge about the true extent and importance of this EG. In this sense, the information obtained from aerial photographs can be of great value. The main objective of this work is to evaluate the possibility of making an exhaustive characterization of the space-time evolution of ephemeral gullies in a relatively large area from color aerial photographs. The effect of precipitation on the EG will be also analyzed.

The 570 ha study area is almost completely cultivated with winter cereals and located in the Pitillas district (Navarre). Climate is Continental Mediterranean (on average 550  mm yr-1). Soil (upper horizons) are loam–silty loam in texture.

EG within cultivated fields were located, classified and digitized using GIS interfaces over seven colour orthophotos (1:5000 with 0.5mx0.5m resolution) taken between 2003 and 2014. Gully length was determined after locating EG down and upstream ends. EG drainage areas and slopes were determined using a 2 m resolution DEM.

To determine EG volumes, an empirical power model for the study area defining the relationship between EG lengths and volumes was first obtained from previous field measurement, and then used for the EG lengths from this study. The corresponding erosion rates were also calculated.

57 small watersheds affected by EGs were identified, being 39 of them classified as drainage EGs, and the remaining 18 EGs as classic. 70% of the small watersheds were affected by EG only once. In remaining watersheds EG reappeared from twice to seven times. Therefore, it seems that the repeatability is not as high as thought.

The average erosion rate in classical EG is about 1.1 Kg m-2 year-1. Previous assessments using accurate direct methods reported an average value of 0.8 Kg m-2 year-1 for very similar watersheds in the same area. Although it is not a conclusive proof, this findings indicate that both methods provide similar results.

A very high correlation (r2= 0.84) has been found between the length of the gullies formed in the study area and the total annual precipitation. It would follow that EG erosion would also be controlled by the overall amount of rainfall also in Mediterranean climates, and not only by high intensity-low frequency events.

References

  1. Casalí, J. J. López, J. V. Giráldez, 1999. Ephemeral gully erosion in Southern Navarra (Spain). CATENA 36: 65-84.

How to cite: Chahor, Y., Casalí, J., and Giménez, R.: Analysis and assessment of ephemeral gully erosion in wide areas of Navarre (Spain) from routinely obtained ortophotographs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10866, https://doi.org/10.5194/egusphere-egu2020-10866, 2020.

EGU2020-19925 | Displays | SSS2.4

Using GIS techniques for automatic mapping of gullies in the Moldavian Plateau, Romania

Ionut - Costel Codru and Lilian Niacsu

Gully erosion represents one of the major environmental problems within the agricultural hilly areas of Moldavian Plateau, Romania. Deforestations, made in the last two centuries, and unsustainable agricultural techniques made the Moldavian Plateau a very susceptible area especially to soil erosion, gullying and landsliding. Beside the human influence that accelerated the process, gully erosion is a natural hazard that occurred from heavy rain falls and water concentrations in catchment areas. The most important natural induced factors that influenced gully head retreat in the Moldavian Plateau are the landform features, favorable lithology, land cover changes under improper human impact on the background of specific climacteric conditions such as heavy rain falls, snow melt and or freeze-thaw phenomenon. The Moldavian Plateau is the area that has one of the biggest densities of gullies in Europe, and, because of its large population of gullies and lack of materials, techniques and time no comprehensive inventory was made. Due to the appearance of high resolution LIDAR images and the evolution of GIS software in recent years, a lot of researchers, from all around the world, tried to identify gullies and quantify them using these modern techniques. For this research, morphometric features (e.g. profile curvature and a 360⁰ hillshading grid with eight points of lightening distributed at a distance of 45 azimuth degrees) derived from LIDAR were used for a more facile mapping of gullies. These morphometric features were classified using different classification method. To evaluate the quality of the results, a shapefile with gully contours had been created by digitizing the banks of the gully. The results of the manually digitized shapefile were confronted with the results of the automatic morphometric features obtained in this research. The combination of hillshading grids that were used in this research covered a very big part of the surfaces occupied by gullies, excepting the gullies affected by landslides that were hardly recognized. Also, the derived profile curvature identified the banks of the gully in a very accurate way.

How to cite: Codru, I.-C. and Niacsu, L.: Using GIS techniques for automatic mapping of gullies in the Moldavian Plateau, Romania, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19925, https://doi.org/10.5194/egusphere-egu2020-19925, 2020.

EGU2020-168 | Displays | SSS2.4

The gullies of southeast Nigeria: an ecogeomorphic investigation

Ikenna Osumgborogwu, John Wainwright, and Laura Turnbull-Lloyd

Gully erosion was unknown in the Orlu area of Southeast Nigeria before the Nigerian civil war (from 1967 to 1970) but has now become endemic and continues to present day.  Human activities are central to this acceleration of erosion due to their intervention with ecogeomorphic processes. This paper aims to improve understanding of ecogeomorphic drivers of gully erosion using case studies from the Orlu area of southeast Nigeria, and to achieve this aim, focus-group meetings and analyses of remotely sensed data were adopted. High-resolution (0.61 – 5 m) satellite imagery for 2009 and 2018 were acquired from different platforms and used for gully mapping and monitoring while ASTAR DEM was used to estimate topological parameters. Upslope contributing areas were produced for two gullies; A and U, while gully evolutions between 2009 and 2018 were related to changes in contributing areas during same time span. Ecogeomorphic and climatic drivers such as vegetation-cover change, slope angle, elevation, rainfall, and nearness to roads and rivers were studied and their associations with gullying established. Vegetation cover was classified into three: non-vegetated, open vegetation and trees while daily surface runoff between 2009 and 2018 was estimated for these vegetation classes using the Curve Number approach. Results from focus-group meetings show that both gullies started in 1969 during the civil war as a result of increase in population density arising from the influx of refugees as well as other military activities. Gully growth was sustained after the civil war was a result of land use changes. Average gully headcut retreat rate between 2009 and 2018 was 64 m yr-1 and 12.2 m yr-1 for gully A and U respectively, while a positive correlation was recorded between change in vegetation cover in contributing areas and increase in gullied area with Pearson’s correlation of 0.6 and r2 of 0.4. The runoff model predicted runoff for only the non-vegetated areas with runoff coefficients ranging from 11.5 % to 22 %. Slope angle, profile and plan curvature had positive associations with gullies while elevation, nearness to rivers and nearness to roads recorded negative correlations with gullies. In conclusion, while geomorphic drivers such as slope angle are preparatory factors, human activities including civil wars and land-use changes are forcing factors of gully erosion. This study has implications for gully remediation especially as regards land use management of upslope contributing areas.

Keywords: Gully erosion, Ecogeomorphology, upslope contributing area, south east Nigeria

How to cite: Osumgborogwu, I., Wainwright, J., and Turnbull-Lloyd, L.: The gullies of southeast Nigeria: an ecogeomorphic investigation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-168, https://doi.org/10.5194/egusphere-egu2020-168, 2020.

EGU2020-10791 | Displays | SSS2.4

Assessing the impacts of urban gullying in the Democratic Republic of Congo

Guy Ilombe Mawe, Eric Lutete Landu, Fils Makanzu Imwangana, Charles Nzolang, Robert Wazi Nandefo, Jean Poesen, Charles Bielders, Olivier Dewitte, and Matthias Vanmaercke

Urban gullies cause major infrastructural damages and often claim casualties in many tropical cities of the Global South. Nonetheless, our understanding of this hazard is currently limited to some case studies while the overall impacts remain poorly quantified. Here, we aim to bridge this gap by making a first quantification of the number of persons and buildings affected by urban gullies at the scale of the Democratic Republic of Congo (DRC). We used Google Earth imagery to identify and map urban gullies for cities in the DRC and evaluate their expansion rate and the resulting damages where possible. In total, more than one thousand urban gullies were mapped across 22 affected cities. Over 80% of these gullies were active and, by analyzing their expansion, we identified 1463 houses and 386 roads destroyed. Nonetheless, the actual impacts are likely much larger since the limited amount of imagery available does not allow to quantify all impacts.

We therefore also made an estimate of the total number of persons directly affected by urban gullies (i.e. displaced due to the destruction of their house). For this, we calculated the areal fraction of urban gullies in affected cities (which ranged from 0.12% to 4.66%) and combined these fractions with the urban population density. From this, we estimate that a total of 212 000 people have been affected. The problem is especially acute in the cities of Kinshasa, Mbujimayi, Tshikapa, Kananga, Kabinda, and Kikwit. Given that these gullies are linked to recent urban growth and typically less than 30 years old, we estimate that at least 7000 people/year lose their house as a result of urban gullies in DRC. This is likely an underestimation since (i) not all urban gullies are detectable; (ii) urban gullies may disappear and reappear over time; and (iii) many of these gullies are likely more recent than 30 years. Furthermore, this assessment does not take into account numerous other indirect impacts of urban gullies (e.g. impacts on traffic and sanitation, increased flood risks, real estate value loss and intangible impacts like fear or stress). 

Overall, this research shows that urban gullying is a serious problem in DRC, but likely also in many other tropical countries. More research is needed to better understand this processes and, ultimately, to prevent and mitigate its impacts. The results and the database of this study provide an important first step in this direction.

How to cite: Ilombe Mawe, G., Lutete Landu, E., Makanzu Imwangana, F., Nzolang, C., Wazi Nandefo, R., Poesen, J., Bielders, C., Dewitte, O., and Vanmaercke, M.: Assessing the impacts of urban gullying in the Democratic Republic of Congo , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10791, https://doi.org/10.5194/egusphere-egu2020-10791, 2020.

EGU2020-10706 | Displays | SSS2.4

Analysis of ephemeral gully erosion in small agricultural watersheds in Iowa (USA)

Eduardo Luquin, Richard M. Cruse, Karl R. Gesch, Matthew J. Helmers, Henrique G. Momm, Robert R. Wells, Miguel A. Campo, and Javier Casalí

Ephemeral gullies (EG) are linear erosion features located in swales where surface and/or subsurface runoff concentrate during or immediately after rainfall events. As its name states, EGs are temporary because they are easily filled by conventional machinery, but when filled they reform if the area is not appropriately managed. Downstream water quality issues and decreased soil productivity are the main environmental impacts. EGs are frequently identified as (the most) relevant sediment sources in agricultural areas but their dimensions and particular contribution to the total erosion under different temporal, spatial, climate and land use condition is still unknown. Therefore, the objective of this study is to obtain ephemeral gully erosion rates and estimate the main morphological characteristics of the ephemeral gullies (width, length and depth) and their evolution both in relation to time and position on the landscape.

The studied EGs, B6 with a 0.94 ha watershed and I3 with a 0.95 ha watershed formed in two fields located in the Walnut Creek watershed, Iowa (US). The field-sized watersheds are less than 1.5 Km apart and have similar topography and soils. The cropping system consists of a two-year corn-soybean rotation managed by one farmer using no-till and other standard management practices. EG were measured using close range photogrammetry techniques. In order to achieve a suitable characterization of the EG evolution over time and space, EGs were divided in three sections (bottom, middle and top) of equal length. Photographs were taken at least once in 2013, 2014 and 2018 (a total of five in I3 and three in B6). Cross section profiles along the EG perpendicular to the flow path direction were selected and their width, area and depth were determined from a graphical representation of the cross sections. EG volumes were estimated by the sum of interpolating sequential cross-section areas and multiplying by the distance between them.

Average EG erosion rates during 2013-2014 were 3.19 Mg ha-1 year-1 for B6 and 3.63 Mg ha-1 year-1 for I3. Values in agreement with rates estimated by the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) of 0.49 to 5.18 Mg ha-1 year-1 across the USA and other simulated values of 4.00 ± 1.76 Mg ha-1 year-1 for no till systems in the state of Iowa. The current study shows evidences that EG in no till systems may not stabilize after their formation. EG dimensions (depth, width and length, thus volume) varied over time and space during the continuously monitored period. In general, volumes tend to increase in the middle position while depths decrease in the bottom position. When the EG was filled, it reformed again in approximately the same location showing similar dimensions to that which existed prior to filling.

How to cite: Luquin, E., Cruse, R. M., Gesch, K. R., Helmers, M. J., Momm, H. G., Wells, R. R., Campo, M. A., and Casalí, J.: Analysis of ephemeral gully erosion in small agricultural watersheds in Iowa (USA), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10706, https://doi.org/10.5194/egusphere-egu2020-10706, 2020.

EGU2020-4034 | Displays | SSS2.4

Channel widening quantification under laboratory conditions

Chao Qin, Fenli Zheng, and Robert Wells

Channel widening constitutes about 80% of total soil loss, especially in the presence of a plow pan which manifests a less or nonerodible soil layer. Channel bank erosion quantification is prerequisite to couple effectively the bank sediment supply system with fluvial sediment transport fluxes. The objectives of this study were to: 1) describe and evaluate methods for monitoring and data post-analysis of channel widening and 2) investigate how inflow rate, slope gradient and initial channel width affect channel widening processes in the presence of a non-erodible layer. Technology was developed to capture 5-cm spaced cross-sections along a soil flume at 3-s time intervals. Two off-the-shelf digital cameras were positioned 3-m above the soil bed and controlled by a program to trigger simultaneously and download images to the computer. Methods utilizing color differences in images and elevation differences in DEMs were applied to detect discontinuities between channel walls and the soil bed. Channel widths were calculated by differentiating the coordinates of these surface discontinuities. A volumetric method was used to calculate flow velocity with measurements of flow depths obtained from ultrasonic depth sensors. Sediment concentration was determined by manual sampling.

The results showed that different channel width calculation methods exhibited comparable outcomes and achieved satisfactory accuracy. Sediment discharge showed a significant positive linear correlation with channel widening rate, while exhibiting a 5 to 25-s time lag compared to the peak of channel widening rate. Total sediment discharge calculated by photogrammetry was 3.1% lower than that calculated by manual sampling. Flow velocity decreased with time and showed a significant negative power correlation with channel width. Sediment delivery and channel width increased with the increase of inflow rate, bed slope and the decrease of initial channel width. Exponential equations were used to predict the channel width time series. Toe scour, crack development, sidewall failure and block detachment and transport, in sequence, were the four main processes of channel widening. Basal scour arc length, tension crack length and width decreased with initial channel width and increased with time, flow discharge and bed slope. Basal scour arcs were divided into three patterns according to different shapes in comparison to the failure arcs. Sediment delivery equations based on the disaggregation of concentrated flow entrainment and mass failure were also fitted. Advantages of the described methodology include automated high spatial and temporal monitoring resolution, semi-automated data post-processing, and the potential to be generalized to large scale river/reservoir bank failure monitoring. This study provides new insight on improving channel widening measurements and prediction technology.

How to cite: Qin, C., Zheng, F., and Wells, R.: Channel widening quantification under laboratory conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4034, https://doi.org/10.5194/egusphere-egu2020-4034, 2020.

EGU2020-2199 | Displays | SSS2.4

Evaluation of the magnetite as a magnetic tracer of eroded sediment from ephemeral gullies: conditioning factors of magnetic susceptibility

Elena Zubieta, Juan Larrasoaña, Rafael Giménez, Alaitz Aldaz, and Javier Casalí

In gully erosion, the soil detached by the action of the erosive flow can be transported over long distances along the drainage network of the watershed. In this long way, the eroded material can be redistributed and/or deposited on the soil surface, and then eventually buried by eroded material from subsequent erosion events. Likewise, the variability of the soil (i.e., in texture and moisture content) over which this material moves can be considerable. The presence of the eroded material could be detected through magnetic tracers attached/mixed with the eroded soil. In this experiment, the degree to which the magnetic signal of the magnetite is conditioned by (i) the burying tracer depth, (ii) the texture and moisture content of the soil covering the tracer and (iii) the tracer concentration was evaluated.

The study was carried out in the lab in different containers (0.5 x 0.5 x 0.3 m3). Each container was filled with a given soil. In the filling process, a 0.5-cm layer of a soil-magnetite mixture of a certain concentration was interspersed in the soil profile at a certain depth. Overall, 3 different soil:tracer concentrations (1000:1, 200:1, 100:1), 4 tracer burying depths (0 cm, 3 cm, 5 cm and 10 cm from soil surface), and  2 contrasting soils (silty clay and sandy clay loam) were used. In each case, the magnetic susceptibility was measured with a magnetometer (MS3 by Bartington Instruments). Experiments were repeated with different soil moisture contents (from field capacity to dry soil).

If the tracer is located under the soil surface a minimum soil:tracer concentration of 200:1 is required for its correct  detection from the surface using a magnetometer. The intensity of the magnetic signal decreases dramatically with the vertical distance  of the tracer from the soil  surface (burying depth). The maximum detection depth of the tracer magnetic signal is strongly dependent on the natural magnetic susceptibility of the soil which hides the own tracer signal. Variation in soil moisture content does not significantly affect the magnetic signal. For extensive field studies the soil-tracer volume to be handled would be very high. Therefore, it is necessary to explore new tracer application techniques.

How to cite: Zubieta, E., Larrasoaña, J., Giménez, R., Aldaz, A., and Casalí, J.: Evaluation of the magnetite as a magnetic tracer of eroded sediment from ephemeral gullies: conditioning factors of magnetic susceptibility, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2199, https://doi.org/10.5194/egusphere-egu2020-2199, 2020.

EGU2020-13446 | Displays | SSS2.4

Particle and aggregates size distribution of soil transported due to surface runoff and rill erosion

Romana Kubínová, Petr Kavka, Martin Neumann, and Tomáš Laburda

In this contribution the grain size distributions of the soil sediment obtained from soil erosion experiments were analysed. All the tests were done on arable topsoil’s, separately the size distribution of the soil aggregates and individual soil particles were evaluated. Soil erosion was initiated under the controlled conditions in the laboratories. The rainfall was artificially generated with use of a nozzle type rainfall simulator. The sediment transported due to the surface runoff and rill erosion was collected from the discharge of the inclined soil erosion plots (slopes 20 – 34°, slope length 4 m).

The soil sediment was collected in four sampling times. The first and the second were collected in fifteen and thirty minutes from the beginning of the simulation, then followed fifteen minutes long pause without raining and then the simulation continued and soil samples were collected again in fifteen and thirty minutes from the beginning of the rain. After ten days long pause whole process were repeated at the same experimental plot contains rills from previous simulation. Experimental plots were vertically divided into two parts. On one part was an eel and on the second part were different types of rolled erosion control products (RECPs) – Enkamat 7010, Biomac-C, coir fibres K700 and K400, jute, Macmat 8.1 with soil, mulch, hay and nonwoven. The influence of RECPs to the grain size distribution was investigated.

Laser diffraction has been selected as a method to determine grain size distribution and device Mastersizer 3000 was used. By the comparison of the grain size distribution, of more than five hundreds samples, the different response to the soil erosion mechanism and the influence of external factors (experimental plot slope, sampling time from the surface runoff and presence of RECPs) on the grain size distribution and soil aggregates content in eroded sediment were investigated. It has been found that both the particle size and aggregates size distribution of the eroded sediment changes considerably in time.

This research is funded by the TH02030428 - „Design of technical measures for slopes stabilization and soil erosion prevention”.

How to cite: Kubínová, R., Kavka, P., Neumann, M., and Laburda, T.: Particle and aggregates size distribution of soil transported due to surface runoff and rill erosion , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13446, https://doi.org/10.5194/egusphere-egu2020-13446, 2020.

EGU2020-22509 | Displays | SSS2.4

Grass species selection to control for concentrated flow erosion in grassed waterways.

Corina Lees, Robert Simmons, and Jane Rickson

Grassed waterways reduce water runoff, prevent scouring and encourage sediment deposition from erosion prone land. The aim of this study was to assess the efficacy of conventional and novel grass species (as monocultures and mixtures) to control erosion, at an early establishment stage (6 weeks), within grassed waterways. The experimental treatments included bare soil (B), a conventional mix of Lolium perenne and Festuca rubra (C), Festulolium cv prior (F1), Festulolium cv prior and Festulolium bx511 (F1+F2), and all grass species combined (F1+F2+C). F1 is adapted to flooded conditions, whilst F2 is adapted to drought conditions. With climate change in the UK likely to result in drier summers and wetter winters these Festulolium species will be adapted to future climatic conditions. However, little is known about their efficacy within grassed waterways. The grasses were established in 1.2 x 1 x 0.5m macrocosms in a sandy clay loam soil during June-Aug, 2019. A sub sample of each experimental treatment was taken (0.3 x 0.1 x 0.1m) from the macrocosms within a stainless steel box. Tests were replicated in quadruplicate.
The following above ground trait (Stem area density) and the following below ground traits (Total root length of fine roots <0.25mm, root diameter and root surface area) were determined for each experimental replicate. Prior to testing, the grass was cut to circa 3.0 cm height to represent a mowed grass sward before being placed into a fully instrumented hydraulic flume. The hydraulic flume simulated a concentrated flow event and treatment performance was assessed in terms of turbidity, sediment concentration, soil loss and flow velocity.
The effects of roots+shoots and of roots only on performance indicators were determined to quantify the relative contribution of above ground vs below ground traits in controlling erosion. One set of replicates was tested only with roots whilst another set of replicates was tested with roots+shoots and then with roots only. This was done to isolate the effect of below ground and above ground traits.
All replicates were subjected to a concentrated flow event with increasing incremental flow velocities from 0.2-0.6l s-1 for bare soil, 0.2-0.8l s-1 for roots+shoots treatments and 0.2-1.4l s-1 for roots only treatments. Each flow rate velocity was run for 60 seconds. For each flow rate, duplicate water samples were taken downslope of the treatment and water depth was measured, upstream of the treatment, in the centre of the treatment and downstream of the treatment.  The water samples were used to determine sediment concentrations. The water depth measurements were used to determine runoff velocity. Furthermore, a turbidity meter continuously measured turbidity during the concentrated flow event. Soil detachment and transport rates were significantly reduced for all experimental treatments as compared to the bare soil (p<0.05). Final treatment efficacy will be assessed based on a ranking of the key performance indicators. The knowledge gained from this research can be used and applied to other grassed soil erosion mitigation features such as in field and riparian buffer strips, swales as well as grassed waterways.

 

How to cite: Lees, C., Simmons, R., and Rickson, J.: Grass species selection to control for concentrated flow erosion in grassed waterways., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22509, https://doi.org/10.5194/egusphere-egu2020-22509, 2020.

EGU2020-1497 | Displays | SSS2.4

Internal Erosion of Soil Pipes: Still More Questions Than Answers

Glenn Wilson, Anita Bernatek-Jakiel, John L. Nieber, and Garey A. Fox

Internal erosion of soil pipes can be a very important process in gully erosion as well as other mass failure events such as sinkholes, landslides and levee/dam breaching. Flow through preferential flow paths such as macropores can be rapid enough to exceed the soil critical shear stress and cause detachment of particles from the walls of the flow path, i.e. internal erosion. Development of a soil pipe from enlargement of a macropore results in more rapid flow and thus greater internal erosion, particularly mass failure of aggregates from pipe walls and roofs. If the sediment transport capacity of the pipe is exceeded, the pipe will plug causing back-pressure to build up within the soil pipe, which can foster hillslope instability. However, limited research has been conducted on particle and aggregate detachment within soil pipes as well as transport of sediment through soil pipes. The objective of this paper is to present observations of little known and poorly described processes involved in pipeflow and the resulting internal erosion of soil pipes. Many of the processes involved in internal erosion of soil pipes are assumed based upon processes observed in surface and stream erosion studies but are so poorly quantified for soil pipes that they are yet to be transferable. For example, the role of solution chemistry on sediment detachment from pipe walls has been quantified to a limited extent but little has been done on the effects of seepage forces on particle detachment in pipes and even less done on sediment transport capacity of soil pipes. Recent advances have included: development of suspended sediment and bedload rating curves for soil pipeflows but the results are crude and warrant further study. Quantification of the interactive effects of surface flow in channels with flow through soil pipes below channels on headcut migration and gully widening is in its infancy. Other processes, such as air-entrapment in creating or temporarily plugging pipes, have been suggested as important but lack quantification. These processes and others combine to result in internal erosion of soil pipes but they must be better understood and quantified in order to develop the next generation of soil erosion models and landscape morphology prediction technologies.

How to cite: Wilson, G., Bernatek-Jakiel, A., Nieber, J. L., and Fox, G. A.: Internal Erosion of Soil Pipes: Still More Questions Than Answers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1497, https://doi.org/10.5194/egusphere-egu2020-1497, 2020.

EGU2020-665 | Displays | SSS2.4

New insights on controls of piping distribution in degraded blanket bog

Taco Regensburg, Joseph Holden, Pippa Chapman, Michael Pilkington, and Martin Evans

As part of the EU-funded MoorLIFE2020 project, which examines strategies to restore degraded blanket bog in the Peak District of northern England, we investigated natural soil pipes. These pipes are a cause of concern to peatland restoration practitioners who are unsure whether to block them to reduce erosion and flood risk when conducting restoration work. Soil pipes often occur in complex networks with varying channel sizes, undulating through the soil profile. Their prevalence is often linked to controls such as topographic location, slope, aspect, vegetation cover, climate, and properties of the surrounding soil. Such relationships are poorly understood for degraded blanket bog. A before-after-control treatment study was designed to examine the effects of pipe blocking on fluvial carbon removal and streamflow in Upper North Grain (UNG), a small headwater catchment located between 490 m and 541 m above sea level. The catchment has a blanket peat cover up to four meters thick at places, with a branching network of deep gullies that incise into the bedrock. This experimental design was envisaged to address the following hypotheses: (i) the severity of degradation of UNG is a dominant control on pipe density; (ii) blocking of pipe outlets impairs pipe-to-stream connectivity. Our results point towards a rejection of both hypotheses. An initial field survey used to locate and characterize pipe outlets, resulted in 353 individual outlet recordings with a density of 13.79 per km of surveyed gully bank. Southeast, south, southwest and west-facing gully banks accounted for more than 75% of identified pipe outlets. The experimental design compares water and aquatic carbon fluxes in two streams - in one catchment the active pipe outlets (n=25) were blocked by closing off the void behind the pipe outlet with peat and stones, wooden screens or plastic pilling, while in the other catchment the pipes were left open. Areas on the gully bank around original outlets were photographed every two weeks. This analysis showed that within the first month after blocking, all treated pipes had formed bypass routes around the block and initiated new pipe outlets. New outlets were found both above and below the original pipe outlet at distances up to 1 meter from the original pipe outlet regardless of bank aspect, suggesting the networks behind a pipe outlet to be a porous system that connects in both vertical and horizontal directions when issuing onto gully banks. Further results will be presented from the ongoing monitoring showing effects of pipe blocking on streamflow storm responses and the export of particulate and dissolved organic carbon from pipes and streams.

How to cite: Regensburg, T., Holden, J., Chapman, P., Pilkington, M., and Evans, M.: New insights on controls of piping distribution in degraded blanket bog, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-665, https://doi.org/10.5194/egusphere-egu2020-665, 2020.

EGU2020-2017 | Displays | SSS2.4

ERT and GPR Characterization from Soil Pipe System in Brazilian Tropical Soil

Felipe Jesus, Wellington Silva, Jorge Porsani, and Marcelo Stangari

A Soil Pipe System (SPS) were identified in Candói region, located in the Paraná state, southern Brazil. This region is constituted of intensive agriculture and cattle raising. SPS correspond to a structure associated to an erosive processes stage in downhill slope that tend to increase over time. The growth of the SPS results in instability to the terrain and the possibility of collapse, in this case the collapse can be accelerated by external factors, such as the overload of agricultural machinery and animals that circulate around the site, may leading to the machinery loss, animal’s death or even risk to worker safety. Frequently, the SPS are identified by surface methods that don’t provide parameters such as shape, distribution and depth. In this research, Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) were used to obtain a 3D characterization of the SPS identified in a farm in Candói region to estimate the soil cover over the structure, the subsurface channels distribution and identify potential collapse risk portions. Seven ERT profiles using dipole-dipole array and twenty-one GPR profiles of 200 MHz antenna were acquired, covering an area of 900 m². The results were combined in a block diagram, which enabled: i) identify the subsurface channels distribution and direction, ii) estimate the average soil cover thickness, with 1.5 m over the whole structure. The possible connection between subsurface secondary and primary channels has also been suggested in results interpretation through of identification of a channel parallel to acquisition profiles direction. It was verified that in structure portions closer to the river next to the slope, the SPS ceiling has larger dimensions than the walls, suggesting areas with increased vertical tension, which was classified as potential collapse risk areas.

How to cite: Jesus, F., Silva, W., Porsani, J., and Stangari, M.: ERT and GPR Characterization from Soil Pipe System in Brazilian Tropical Soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2017, https://doi.org/10.5194/egusphere-egu2020-2017, 2020.

EGU2020-7410 | Displays | SSS2.4

Time dependent backward piping erosion 2D modeling with laminar flow transport equations

Juan Pablo Aguilar-Lopez, Manuel Wewer, Thom Bogaard, and Matthijs Kok

Backward piping erosion (BEP) is a highly complex erosive process which occurs on granular soils when large head differences are exerted. This process represents a significant threat to dams and levees stability and therefore a large part of the design and reliability assessment of these water retaining structures is devoted to this single process. Several authors have achieved great accuracy in predicting the critical head difference that triggers the process but not so much has been studied regarding the time of occurrence and the duration of the erosive process.  In the present study we propose a 2D finite element model for which not only the critical head difference can be predicted but also the development of the erosive process in time. This was achieved by coupling the 2D Darcy partial differential equation with Exner’s 1D sediment transport mass conservation equation. Different laminar sediment transport rate empirical models were tested and used as inputs in the coupled model. To test the performance of the proposed model, the IJkdijk real scale experiment for piping erosion was simulated. The results show that the model is capable of predicting not only the critical head and its progression in time but also specific events of the process such as the instants of start of the erosion and the  complete seepage length development . An important conclusion of the study is that from several transport empirical formulas tested, the model from Yalin which is widely recognized by the sediment transport community performs the best.

How to cite: Aguilar-Lopez, J. P., Wewer, M., Bogaard, T., and Kok, M.: Time dependent backward piping erosion 2D modeling with laminar flow transport equations , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7410, https://doi.org/10.5194/egusphere-egu2020-7410, 2020.

EGU2020-7465 | Displays | SSS2.4

Backward piping erosion detection in levees by fiber optic acoustic sensing

Juan Pablo Aguilar-López, Andres Garcia-Ruiz, Thom Bogaard, and Miguel Gonzalez-Herraez

Backward piping erosion (BEP) is considered the most dangerous failure mode for levees due to its unpredictable nature. This erosive process happens most of the time underneath the impermeable layers on which levees are commonly founded. This makes it very difficult to detect as conventional geophysical methods are either too expensive or too imprecise for real time monitoring of longitudinal soil made structures such as Dams or levees. Fiber optic based distributed acoustic sensing (DAS) is an innovative technology which allows to retrieve information from an acoustic propagating medium in a spatially dense manner by using a fiber optic cable. The present study aimed to explore the potential of DAS for early detection of BEP  under levees based on the frictional emissions of the sand grains during the erosive process. The tests were performed in the lab under controlled ambient noise conditions. The technology was tested by embedding fiber optic based microphones underneath and outside a laboratory scaled aquifer set up capable of recreating BEP. The results show that indeed the process emits certain characteristic frequencies which may be located between 1200 to 1600 Hz and and that they can easily be captured by the fiber optic cables.

How to cite: Aguilar-López, J. P., Garcia-Ruiz, A., Bogaard, T., and Gonzalez-Herraez, M.: Backward piping erosion detection in levees by fiber optic acoustic sensing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7465, https://doi.org/10.5194/egusphere-egu2020-7465, 2020.

Piping is an erosion process in which cracks and macropores extend into channels with a diameter of cm or more. This process is important for the formation of highly permeable porosity, failure of the levees, formation of gullies and intense erosion of agricultural soil. In this research we studied the evolution of conduits in Střeleč locked sand (SLS). This material composes mainly of quartz and resembles friable sandstone. Study was done in Střeleč quarry (Czech Republic), where depression in the regional water table (decrease of water table by ~20 m) due to the water pumping causes fast flow (up to 40 cm/s) through fractures in the SLS body. Large conduit systems developed along fracture zones that divide the SLS body into subvertical blocks with a width of cm to tens of cm in each fracture zone. Erosion starts at water table and blocks bordered by fractures are eroded by the fast water flow, especially the parts that are in stress shadows due to inefficient loading from the surrounding sandstone mass. Blocks whose base is eroded tend to collapse, which leads to the creation of free space above the water table and also possibly destabilization of the sides. Empty space propagates upward mostly meters but sometimes tens of meters toward ground surface. Experiments showed that the SLS is prone to erosion when it is under low gravity induced stress. In addition to observation of the existing conduits, the experiments focused on the evolution of transversal section of conduits in SLS were performed. Experimental erosion was done on fracture systems exposed in quarry by the flow of water from the hose. Sequence of photos of fracture zones evolving into conduit during experiments was taken and the evolution of the transverse section of conduits was observed. By this method the blocks were eroded to a depth of several decimeters. Based on field experiments and time-laps photos two erosion mechanisms are responsible for conduits evolution. While the less thick blocks are eroded mainly by rapid water flow, thicker blocks are eroded by tension failures (gravity driven wasting). The tension failure dominates, forming about 65 % of total erosion.

Many thanks to the management of Střeleč Quarry for enabling of the field documentation and experiments. The research was supported by Charles University Grant Agency (GAUK #1292119).

How to cite: Vojtisek, J., Bruthans, J., and Slavik, M.: Combination of stress-controlled erosion and tensile failures during development of piping conduits in locked sand, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10628, https://doi.org/10.5194/egusphere-egu2020-10628, 2020.

EGU2020-20163 | Displays | SSS2.4

Spatial distribution and geophysical characterization of natural pipes in Ultisols

Miguel Cooper, Renata Cristina Bovi, Cesar Augusto Moreira, Raquel Stucchi Boschi, Lucas Moreira Furlan, and Fernanda Teles Gomes Rosa

Piping is a type of subsurface erosion caused by subsurface water and is considered one of the most difficult erosive processes to study. The nature of this erosion process makes it very difficult to study and quantify.  The aim of this study was to characterize the surface and subsurface distribution of the pipes and to understand the network architecture of pipe systems in tropical forested areas.The study area is situated at the Experimental Station of Tupi, state of São Paulo, Brazil. We conducted a Digital Elevation Model allied to a superficial pipe mapping, and 2D and 3D geophysical surveys. The subsurface erosion identified by surface mapping and geophysical surveys appeared at two depths: one more superficial, in the upper part of the study area, and one at greater depth, in the lower part of the study area. The higher topographical positions presented the pipes at less developed stages (closed depressions and simple sinkholes), while the lower topographical positions showed the most advanced features (multiple sinkholes and blind gullies). The method of electroresistivity showed zones where low resistivity values correspond to water saturation (~ 70 omh m) and high values (> 4040 ohm m) that define the pipe; this method was efficient in detecting the presence of collapsed and non-collapsed pipes. We concluded that the use of different methods (superficial and subsuperficial) was essential for the characterization of pipe systems. The integrated analysis of the results obtained from the superficial and 2D subsurface mapping allowed us to infer the spatial continuity of the pipes. The 3D geophysical survey was efficient in mapping soil pipe and the connectivity in situ. The 3D modeling of the pipes revealed the connection and connectivity of the pipe network’s complexity and morphology.

How to cite: Cooper, M., Bovi, R. C., Moreira, C. A., Stucchi Boschi, R., Moreira Furlan, L., and Teles Gomes Rosa, F.: Spatial distribution and geophysical characterization of natural pipes in Ultisols, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20163, https://doi.org/10.5194/egusphere-egu2020-20163, 2020.

EGU2020-1875 | Displays | SSS2.4

The Role of Soil Pipes and Pipeflow in Headcut Migration Processes

Ximeng Xu, Glenn V. Wilson, Fenli Zheng, and Qiuhong Tang

Headcut formation and migration is sometimes mistaken as the result of overland flow without realizing that the headcut was formed by or significantly influenced by flow through soil pipes into the headcut. To determine the effects of a soil pipe and flow through a soil pipe on headcut migration, laboratory experiments were conducted under free-drainage conditions and conditions of a shallow water table. Soil beds with a 3-cm deep initial headcut were formed in a flume with a 1.5-cm diameter soil pipe 15 cm below the bed surface. Overland flow and flow into the soil pipe was applied at a constant rate of 68 L/min and 1 L/min, respectively, at the upper end of the flume. The headcut migration rate and sediment concentrations in both surface (channel) and subsurface (soil pipe) flows were measured with time. The typical response without a soil pipe was the formation of a headcut that extended in depth until an equilibrium scour hole was established at which time the headcut migrated upslope. The presence of a soil pipe below the channel, and particularly the phenomena of flow through a soil pipe and into the headcut, whether by seepage from a shallow water table or upslope inflow, significantly impacted the headcut migration. Pipeflow caused erosion inside of the soil pipe at the same time that runoff was causing a scour hole to deepen and migrate. When the headcut extended to the depth of the soil pipe, surface runoff entering the scour hole interacted with flow from the soil pipe also entering the scour hole. This interaction dramatically altered the headcut processes, greatly accelerated the headcut migration rates and sediment concentrations. Conditions in which a perched water table provided seepage into the soil pipe in addition to pipeflow increased the sediment concentration by 42% and the headcut migration rate by 47% compared with pipeflow under free-drainage conditions. The time that overland flow converged with subsurface flow was advanced under seepage conditions by 2.3 and 5.0 minutes compared with free-drainage condition. This study confirmed that pipeflow dramatically accelerates headcut migration especially under conditions of shallow perched water tables and highlights the importance of understanding these processes in headcut migration processes.

How to cite: Xu, X., Wilson, G. V., Zheng, F., and Tang, Q.: The Role of Soil Pipes and Pipeflow in Headcut Migration Processes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1875, https://doi.org/10.5194/egusphere-egu2020-1875, 2020.

SSS2.5 – Soil erosion and driving factors of soil carbon distribution: a worldwide threat

EGU2020-11546 | Displays | SSS2.5 | Highlight

Soil erosion leads to significant mobilisation of terrestrial organic and inorganic carbon

Laura Turnbull and John Wainwright

Soil carbon content is greatly affected by soil degradation – in particular erosional processes – which cannot be ignored in the context of the global C cycle. Soil degradation, driven largely by wind and water erosion, affects up to 66% of Earth’s terrestrial surface. Understanding how soil degradation affects soil organic carbon (SOC) and soil inorganic carbon (SIC) stocks is an essential component of understanding global C cycling and global C budgets, and is essential for improved C management and climate-change mitigation policies.

In this study, we quantify the distribution of SOC and SIC, and estimate their combined effects on carbon mobilisation via water and wind-driven erosion. We estimate spatially variable water-driven erosion rates for different land-use systems and degradation severities using values obtained from a meta-analysis of soil erosion rates, and undertake stochastic simulations to account for possible uncertainty in our estimates. For wind-driven soil erosion rates we use modelled dust emission rates from AeroCom Phase III model experiments for the 2010 control year, for 14 different models. We use the Harmonized World Soil Database v1.2 to calculate SOC and SIC stocks, the GLASOD map of soil degradation to estimate soil degradation severities and the Land Use Systems of the World database to estimate water-driven erosion rates associated with different land-use systems.  

We find that 651 Pg SOC and 306 Pg SIC (in the top 1-m of soil) is located in degrading soils. We estimate global water-driven soil erosion to be 216.4 Pg yr-1, which results in the mobilisation of ~2.9536 Pg OC yr-1. Accounting for the enrichment of organic carbon in eroded sediment increases these estimates up to 12.2 Pg SOC yr-1. A minimum estimate of SIC mobilisation by water erosion is ~0.5592 Pg IC yr-1. Dust emission model ensemble results indicate that ~19.8 Pg soil is eroded for the 2010 AeroCom reference year, with ~11.1 Pg deposited via dry deposition and ~7.2  Pg deposited via wet deposition. The total amount of SOC and SIC mobilised by water-driven erosion is greater than wind-driven erosion, and the spatial patterns of SIC and SOC mobilisation by wind and water vary considerably. Across all land-use types, water-driven carbon mobilisation is higher than wind. Water-driven SOC mobilisation is highest in cropland (~ 2.6602 Pg OC yr-1) where high erosion rates coincide with average SOC content of 68.4 tonnes ha-1. SIC mobilisation follows the same pattern in relation to land use, with highest water-driven mobilisation in cropland (~0.4660 Pg IC yr-1) and highest wind-driven mobilisation in bare areas (0.05 Pg IC yr-1). Overall, wind-driven erosion mobilises more IC than OC.

Future land-use change has great potential to affect global soil carbon stocks further, especially with increases in the severity of soil degradation as human pressures on agricultural systems increase.

How to cite: Turnbull, L. and Wainwright, J.: Soil erosion leads to significant mobilisation of terrestrial organic and inorganic carbon , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11546, https://doi.org/10.5194/egusphere-egu2020-11546, 2020.

Soil erosion and deposition patterns can affect the fate of soil organic carbon (SOC) in agroecosystems. Topographic constraints affect soil redistribution processes and create spatial structure in SOC density. We combined isoscape (isotopic landscape) analyses for δ13C and cesium-137 (137Cs) inventory via digital terrain analysis quantifying SOC dynamics and soil redistribution patterns to gain insight on their responses to topographic constraints in an Iowa cropland field under soybean/maize (C3/C4) production. Additionally, historic bare soil orthophotos were used to determine soil carbon distribution before the 1960s (prior to global 137CS fallout). Topography‐based models were developed to estimate 137Cs inventory, SOC density, and δ13C distributions using stepwise principal component regression. Findings showed that spatial patterns of SOC were similar to soil erosion/deposition patterns with high SOC density in depositional areas and low SOC density in eroded areas. Soil redistribution, SOC density, and δ13C signature of SOC were all highly correlated with topographic metrics indicating that topographic constraints determined the spatial variability in erosion and SOC dynamics. The δ13C isoscape indicated that C3‐derived SOC density was strongly controlled by topographic metrics whereas C4‐derived SOC density showed much weaker expression of spatial pattern and poor correlation to topographic metrics. The resulting topography‐based models captured more than 60% of the variability in total SOC density and C3‐derived SOC density but could not reliably predict C4‐derived SOC density. This study demonstrated the utility of exploring relationships between δ13C and 137Cs isoscapes to gain insight on fate of SOC within eroding agricultural landscapes.

How to cite: McCarty, G. and Li, X.: Soil Organic Carbon Distribution and Isotope Composition Response to Erosion in Cropland under Soybean/Maize Production, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5833, https://doi.org/10.5194/egusphere-egu2020-5833, 2020.

EGU2020-11147 | Displays | SSS2.5

Visual assessments and model estimations of soil erosion and relations to soil organic carbon

Hakan Djuma, Adriana Bruggeman, and Marinos Eliades

Visual soil erosion assessment methods and erosion models are widely applied around the globe. The objective of this research is to assess the relation between soil organic carbon (SOC) concentrations (sampled) and two different soil erosion estimates (visual assessment and model). For the visual assessment, the method of the World Overview of Conservation Approaches and Technologies (WOCAT) was used, which is based on expert field observations per land cover unit. For the model assessment, the Pan-European Soil Erosion Risk Assessment (PESERA) model was used to simulate hill slope soil loss based on land cover, soil texture, meteorological data and slope profile. The research was conducted in Peristerona watershed in Cyprus (surface area: 106.4 km2, elevation: 300 to 1,540 m above sea level, average annual precipitation: 270 mm downstream and 750 mm upstream). The WOCAT questionnaires were completed by a trained specialist during site visits for 79 mapping units in 15 different land cover types. These results were compared with SOC concentrations from 29 points in the same watershed (0-25 cm depth, grid-based sampling, variety of land covers). For erosion modelling comparison, SOC concentrations from 11 paired sites of productive and abandoned terraced vineyards (0-10 cm depth, random sampling) were compared to the PESERA estimates of the same sites. A transect was drawn from the slope top to the SOC sampling point and erosion was estimated for the slope section where sampling was performed. Both the visual assessment and the modelling method showed that SOC concentrations were lower for areas with higher soil erosion. The mean SOC concentration was 1.7% (n=19) for areas ranked as “light erosion” in the WOCAT assessment and was 0.8% (n=10) for areas ranked as “moderate erosion”. Similarly, the abandoned sites that showed higher PESERA estimated erosion than the productive sites (more than 10 times higher erosion rate (n=2)) had lower SOC concentrations than their productive counterpart (half the SOC concentrations). The SOC concentrations almost doubled for abandoned sites compared to the productive sites when PESERA estimated erosion went from 10 times more to 5 times more (n=6) for the abandoned sites. Results from both methods indicate that soil erosion rates and top soil SOC concentrations are related and need to be considered in erosion models. 

How to cite: Djuma, H., Bruggeman, A., and Eliades, M.: Visual assessments and model estimations of soil erosion and relations to soil organic carbon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11147, https://doi.org/10.5194/egusphere-egu2020-11147, 2020.

EGU2020-3947 | Displays | SSS2.5

Soil erosion and sediment transport in South Africa: an overview

John Boardman and Ian Foster

We have few direct measurements of erosion in the country and those that we have are for relatively small areas (badlands) or for experimental plots. We therefore have to rely on sediment yields from rivers and reservoirs, mapping based on remote sensing (gullies) and some modelling. All methods have their disadvantages. With sediment yields the problem of scale is acute and estimates range from <5 to > 11,000 t km-2 yr-1. The great range of estimates partly reflects rainfall/runoff variability but it also strongly reflects the intensity of land use and connectivity or dis-connectivity within catchments.  Elements in the landscape such as gullies (dongas) were initiated under conditions in the past of intense land-use (overstocking) and perhaps climatic pressure. Many gullies are inactive at the present day but have been shown to improve landscape connectivity. However, overgrazed land continues to contribute large quantities of sediment to freshwater systems and to the infilling of reservoirs. The protection of inadequate water resources, threatened by erosion, is a currently urgent problem. More information is needed about the origin of sediments using techniques such as fingerprinting.

How to cite: Boardman, J. and Foster, I.: Soil erosion and sediment transport in South Africa: an overview, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3947, https://doi.org/10.5194/egusphere-egu2020-3947, 2020.

EGU2020-8802 | Displays | SSS2.5

South Africa’s agricultural dust sources and events from the MSG SEVIRI record

Frank Eckardt, Johanna Von Holdt, Nickolaus Kuhn, Anthony Palmer, and Jonathan Murray

Our aim was to determine South Africa’s major dust sources using the MSG (Meteosat Second Generation) SEVIRI (Spinning Enhanced Visible and Infra-red Imager) image record from 2006-2016. A total of 334497 images were examined, which revealed 178 discrete dust plumes on 75 dust-producing days. These originated largely from the Free State to the north of Bloemfontein. Landsat derived National Geospatial data suggests that emission areas consist mostly of grass and low shrublands as well as commercial rainfed agriculture.

The dust emission season from June to January overlaps with the dry season and coincides with the maize harvest period. 2015 and 2016 saw almost half of all event days in the 11-year record, which is matched by a severe drought index (SPEI Standardised Precipitation-Evapotranspiration Index) and strong winds (ERA5). This period is also accompanied by a below average NDVI (Normalized Difference Vegetation Index) response for cropland areas, while DAFF (Department: Agriculture, Forestry and Fisheries) crop data reports a notable decline in Free State maize cover from 1.2 to 0.6 million hectares and a pronounced increase in fallow land from 140 thousand to 790 thousand hectares over the same time span.

Dust events adhere to distinct diurnal patterns, are almost entirely midday occurrences and are accompanied by hourly average windspeeds of up to 11 m s-1. HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory) suggests that aerosols would largely head towards the Indian Ocean with the passing of cold fronts. South Africa’s major dust sources in the SEVIRI record appear to be mostly anthropogenic in nature and a function of both land cover and land management practices associated with rainfed agriculture on soils rich in silt and sand. The soil textures in the Free State, especially those associated with arenosols extend into the wider drier interior, including the Kalahari, where future climate scenarios have predicted increases in dust emissions from both soils and dunes. Notwithstanding other land-use practices, we would argue that the 2015-2016 dust season in South Africa provides an insight into potential future regional scenarios, given increases in drought, associated bare cover and an increase in windiness.

How to cite: Eckardt, F., Von Holdt, J., Kuhn, N., Palmer, A., and Murray, J.: South Africa’s agricultural dust sources and events from the MSG SEVIRI record, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8802, https://doi.org/10.5194/egusphere-egu2020-8802, 2020.

EGU2020-3913 | Displays | SSS2.5

Determining Sub-Catchment Contributions to the Suspended Sediment load of the Tsitsa River, Eastern Cape, South Africa

Laura Bannatyne, Ian Foster, Ian Meiklejohn, and Bennie van der Waal

In South Africa, as in many developing countries, the suspended sediment (SS) data required to support catchment scale hillslope restoration and rehabilitation programmes are typically scarce or absent, leading to a reliance on modelled SS loads and yields that are generally not validated by measured SS data. An exception is the Tsitsa River catchment in the Eastern Cape Province, where modelled SS yields were high (21 – 50 t/ha/yr), leading to the establishment of a Citizen Technician-based monitoring programme (2015 – 2019) that has provided flood-focused, sub-catchment scale SS data at sub-daily timestep for 11 sites throughout the 4000 km2 catchment.

A confluence-based SS fingerprinting and tracing exercise was undertaken in the catchment (2018). Analysis of the distinctive physicochemical properties of resuspended fine sediment sampled above and below major confluences allowed the percentage of SS contributed by each tributary to be apportioned, and compared with findings from both the SS monitoring campaign and from existing models.

How to cite: Bannatyne, L., Foster, I., Meiklejohn, I., and van der Waal, B.: Determining Sub-Catchment Contributions to the Suspended Sediment load of the Tsitsa River, Eastern Cape, South Africa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3913, https://doi.org/10.5194/egusphere-egu2020-3913, 2020.

EGU2020-1186 | Displays | SSS2.5

Gully Initiation on the Quartzite Ridges of Ibadan, South West, Nigeria

Olutoyin Fashae, Rotimi Obateru, and Adeyemi Olusola

Gullies are morphological evidences that reflect the impact of environmental changes on landscape. In an attempt to emphasize the importance of topography on gully initiation and development in an area of uniform geology, this study examined the morphological characteristics of hillslope and the role of topographic mechanism in gully initiation on a quartzite terrain of Ibadan, South western Nigeria. Four prominent quartzite ridges exist in Ibadan namely Mokola, Mapo, Eleyele and Ojoo, each of which except the latter is characterized with significant gully systems. Field measurement was carried out to determine the gully morphological characteristics such as length, width, depth, area and depth of gully head, width/depth ratio, gully sinuosity and gully shape while Digital Elevation model (DEM) was used to examine the slope-area relationship. The slope-drainage area threshold was established for each of the gully systems.  

The average gully density of the study area is 2.48km/km2 and the gully frequency is 9.72 gullies/km2. Although an investigation into the variation of the gully morphology and initiation show that human activities and vegetation are contributary factors to their development. However, topographic characteristics exhibit a dominant role in the gullying process. The ridges were observed to trend in NNW-SSE direction with slope angles ranging between 5o and 30o. The inverse relationship derived between the topography and gully dimension (r = 0.462), suggested that gully initiation processes are dominant on gently sloping ridges due to extensive surface area on a deeply weathered regolith that enhances fluvial processes of material detachment on the one hand and anthropogenic conditions on the other hand. Thus, further geomorphological assessment of landform units in Ibadan is necessary with a view of identifying potential geomorphic risk prone areas, an essential component of risk management for dense urban areas of the tropics.

How to cite: Fashae, O., Obateru, R., and Olusola, A.: Gully Initiation on the Quartzite Ridges of Ibadan, South West, Nigeria, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1186, https://doi.org/10.5194/egusphere-egu2020-1186, 2020.

EGU2020-3065 | Displays | SSS2.5 | Highlight

Accumulation of soil carbon and nutrients along a 127-yr soil chronosequence in the Hailuogou Glacier retreat area

Shouqin Sun, Genxu Wang, and Xinbao Zhang

Climate change is resulting in accelerated retreat of glaciers worldwide, leaving behind bare soil and succeeding vegetation at ecological sites that share similar attributes but represent different ages across chronosequences of primary succession. These glacial succession chronosequences provide a space for time exchange opportunity to investigate the development of soil and vegetation from the very beginning. In this study we investigated how soil carbon (C), nitrogen (N) and phosphorus (P) nutrients were accumulated along a 127-yr primary successional chronosequence on Hailuogou glacier, China, where the soil samples were collected at 1-cm depth interval from 9 sectioned profiles with ages ranged from 27 yr to 127 yr on the glacial retreated area. Soil organic C (SOC) and TN showed an increasing trend along the chronosequence. The organic C and N accumulation was minimal after 27 yr of succession; with succession the soil had slightly C and N accumulation at the surface 0-1 cm depth after 45 to 53 years, and had obvious accumulation at the 0-2 cm depth after 59-72 years; the SOC and N accumulation extended to the 0-5 cm depth after 87 yr and to the 0-10 cm depth after 102 yrs. In contrast soil total P exhibited a depleting trend along the succession. Results indicated that the C and N accumulation along a glacier retreat chronosequence is not linear, but a slow increase in accumulating rates in the first 72 years, followed by a sharp increase between 72 to 87 years and then slow down with succession proceeded.

How to cite: Sun, S., Wang, G., and Zhang, X.: Accumulation of soil carbon and nutrients along a 127-yr soil chronosequence in the Hailuogou Glacier retreat area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3065, https://doi.org/10.5194/egusphere-egu2020-3065, 2020.

Land use change can significant impact on carbon dynamics by directly changing the carbon stock on soil and biomass and by controlling the magnitude of soil erosion which indirectly influences the erosion-induced carbon sink or sources. Whether land use change causes a net carbon sink or source to the atmosphere, an integrated analysis that considers both the direct effects of land use changes on vertical fluxes as well as its effects on the erosion-induced carbon sink is therefore necessary.

The Chinese Loess Plateau (CLP) is an ideal case for an integrated assessment of the influence of land use change on OC dynamic, given that CLP has experienced significant land use change during last two decades and is the most eroded regions in the world which potentially target the relative higher magnitude of erosion-induced carbon sink. Therefore, the objectives of this study are to carry out an integrated analysis of the influence of land use change and soil erosion on regional carbon dynamics during 1990-2010.

Our results indicated that CLP experienced two inverse tendencies of land use change and carbon dynamics between 1990 and 2010. During 1990 to 2000, a net decrease of vegetation cover land (grass and woodland) has happened on the CLP which induced a carbon loss by 4.85 Tg C yr-1 on soil and biomass, which was mainly due to the cutting of native forest and the conversion of grassland to arable land. While, based on the assumes that 50% of the mobilised carbon is finally buried and that full replacement takes place at the erosion sites, the erosion-induced sink would compensate about 55% of the carbon loss due to land use change. Thus, between 1990 and 2000 the CLP was a net carbon source to atmosphere. Due to the implementation of the Grain for Green Project, permanent vegetation cover land has gradually increased between 2000 and 2010. The net rise of vegetation cover land resulted in an annual carbon sink of soil and biomass by 1.67 Tg C yr-1. Meanwhile, soil conservation measures (terrace) and land use change constrained the strength of erosion-induced carbon sink. The total amount of carbon mobilised declined to ca. 5.00 Tg C yr-1 and the erosion-induced carbon sink was ca. 2.50 Tg C yr-1 (based on the same assumes of carbon replacement rate and carbon burial efficiency). Therefore, CLP was a carbon sinks during 2000-2010. Again, changes in land-atmosphere carbon fluxes due to land use change were far more important than changes due to erosion reduction.

There are large uncertainties in our estimations, especially because the extent of land use change due to the Grain for Green Project remains uncertain. Meanwhile, the magnitude of the erosion-induced carbon sink is also uncertain, and estimates need to be further refined and constrained by more accurate data and the use of more explicit models. Nevertheless, our current understanding allows us to clearly identify the direction of change in carbon fluxes brought about by the combined effects of land use change and erosion reduction.

How to cite: Zhao, J.: Coupling of land use change, soil erosion and carbon dynamic on the Chinese Loess Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6349, https://doi.org/10.5194/egusphere-egu2020-6349, 2020.

EGU2020-494 | Displays | SSS2.5 | Highlight

Are human activities main drivers of soil organic carbon losses in mountain rainfed agroecosystems?

Ivan Lizaga, Leticia Gaspar, Laura Quijano, Maria Concepción Ramos, and Ana Navas

One of the principal soil degradation problems affecting European agroecosystems is the loss of topsoil by water erosion. In dry climates, soil erosion is led by two main factors, human activities such as agriculture and extreme episodic rainfalls. However, agriculture plays a crucial role in leaving the soils unprotected during part of the year. Thus, extreme rainfall can easily remove the topsoil with the subsequent removal of nutrients in surface soil layers and the reduction of soil quality.

To assess the effects of extreme storms in rainfed agriculture catchments on soil organic carbon removal, surface soil samples from different land uses were collected in a medium-sized catchment at the foot of Santo Domingo range. The study area was mostly cultivated at the beginning of the 19th century but changed to rangeland and afforestation forest in the last 50 years. The remaining cropland area is mostly rainfed agriculture that leaves soils unprotected in periods when erosive storms occur (autumn convective rainfalls). The main land uses are croplands, pine afforestation, scrubland and Mediterranean forest. To track the export of soil organic carbon associated to mobilised sediment occurring under storm events, channel bed sediment samples were collected along the principal streams of the drainage network during regular flow, after a regular storm event, and after an extreme storm event. The contents of soil organic carbon (SOC), SOC fractions and grain size were analysed and compared for the three sampling campaigns.  The results show a gradual decrease of the fine fraction from regular flood samples to samples collected after the extreme event. However, the SOC showed a sharp decrease in the post-extreme event samples, with higher decreases in the active carbon fraction (ACF) than in the stable carbon fraction (SCF).

Our findings highlight the substantial in situ hazards of extreme rainfall events removing soil organic carbon from topsoils and exporting fine sediment and nutrients out of the catchment with important indirect impacts on water resources both quantity and quality.

How to cite: Lizaga, I., Gaspar, L., Quijano, L., Ramos, M. C., and Navas, A.: Are human activities main drivers of soil organic carbon losses in mountain rainfed agroecosystems?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-494, https://doi.org/10.5194/egusphere-egu2020-494, 2020.

EGU2020-18475 | Displays | SSS2.5

Soil organic carbon and soil total nitrogen stocks, soil quality and vegetation composition during natural revegetation processes in a Mediterranean mid-mountain area

Estela Nadal Romero, Pedro Sánchez Navarrete, Makki Khorchani, Luis Miguel Medrano-Moreno, and Teodoro Lasanta

Mediterranean mid-mountain areas have been subject to significant human pressure through deforestation, cultivation of steep slopes, fires and overgrazing. However, during the 20th century, the mountainous areas of the northern rim of the Mediterranean region were affected by abandonment of cultivated fields and natural revegetation processes. Natural revegetation occurred in most of the lands where human activity (farming on steep slopes, grazing) declined in intensity or was abandoned, resulting in the expansion of shrubs, bushes and forests. What are the consequences of such processes on soil quality, soil organic carbon (SOC) and soil total nitrogen (TN) stocks and vegetation composition? What are the differences between the different land uses and land covers (LULCs)? The general aim of this study is to study the effects of natural revegetation processes after land abandonment on soil quality, SOC and soil TN stocks and vegetation composition in the Leza Valley (Iberian System, Spain). We hypothesized that natural revegetation processes improves soil quality and higher SOC and TN stocks. For this purpose, we analyzed 60 soil samples, from 5 LULCs and four depths (0-10, 10-20, 20-30, 30-40 cm): pasture, shrubs characterized by the presence of Cistus laurifolius, bushed characterized by the presence of Juniperus communis, Young forest (Quercus faginea), and old forest or dehesa. In addition, plant species inventories were carried out in each LULC.

The results related to physico-chemical soil properties indicated: (i) significant differences in soil quality between the first stages of natural revegetation (pasture and shrubs) and young forest (limited to the first 20 cm between shrub and young forest); (ii)  significant differences in SOC stocks between the first stage of natural revegetation (pasture) and young and old forests; (iii) significant differences in soil TN stocks between pasture and shrubs and young and old forests; and (iv) significant differences between the shrub families. Final results obtained through a Principal Component Analysis with all the variables differentiate forests from shrubs, bushes and pastures confirming our first hypothesis. We can conclude that natural revegetation is an effective strategy to improve soil quality and increase SOC and soil TN stocks.

How to cite: Nadal Romero, E., Sánchez Navarrete, P., Khorchani, M., Medrano-Moreno, L. M., and Lasanta, T.: Soil organic carbon and soil total nitrogen stocks, soil quality and vegetation composition during natural revegetation processes in a Mediterranean mid-mountain area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18475, https://doi.org/10.5194/egusphere-egu2020-18475, 2020.

Erosion is the most widespread process that cause land degradation. It produces changes in soil properties and contribute to the depletion of organic matter content as well as to the loss of nutrients. The changes have an additional effect on the infiltration and on water retention capacity, which all together influence crop productivity. Water erosion occurs due to natural forces rainfall. But in areas with Mediterranean climate, most of erosion losses occur in a reduced number of events of high intensity. In this research, the effect of high intensity rainfalls on soil carbon mobilization was analysed in a vineyard, which is maintained with scarce soil cover most of the year. The research was carried out under simulated rainfall in a commercial vineyard located in Raimat, Costers del Segre Denomination of Origin, Lleida, NE Spain). The soil type in the analysed plot is classified as Haploxeralf fluventic located in a gentle slope (about 5%). Soil samples from 0-2 cm were collected in two locations in the field, before the rainfall simulation for texture characterization and chemical analysis. Plots 1m length*0.5 m width were delimited in the field at each location and subjected to simulated rainfall using a rainfall simulator consisted, which had a dropper system placed 2.5 m above the ground. The rainfall intensity was fixed for the experiment in 60 mm/h. The simulations were done in triplicate. Runoff was collected every 10 minutes during 1h and the sediment transported by runoff was separated and weighted after dried. Total organic carbon (TOC) was analysed in the soil before and after the simulation. In addition, in the original soil and in the sediments recorded in each simulation, the particulate organic carbon (POC) and the mineral-associated organic carbon (MOC) (Cambardella and Elliott, 1992), as well as the water extractable organic carbon (WEOC) (Gigliotti et al., 2002) were analysed. The soils had 50.2 and 49.5% of silt, 25.5 and 23.2% of clay and 24.3 and 27.3% of sand, respectively. Runoff started between 4.5 and 7 min after the beginning of the simulations, and runoff rates were of about 50% after the first 20 minutes of rainfall. Sediment concentration in runoff ranged between 13 and 18 gL-1 in the three simulations. The TOC in the original soils were 14.09±0.67 gkg-1 and 13.56±0.8 gkg-1, respectively, while after the simulation the TOC was near 10% lower. In the sediments, TOC were 12.29±1.13 gkg-1 and 12.84±1.19 gkg-1, respectively in both soils. The POC and the MOC represented 24.7% and 75.3% of TOC in the original soil, and no significant changes were observed in the sediment transported by runoff (values ranging between 25.90 to 28.47 % for POC and between 71.5 and 74.1% for MOC). However, the WEOC fractions were higher in the sediment (7.7 and 7.5%) than in the original soil (5.26%).

References

Cambardella CA, Elliott ET. 1992. Soil Sci. Soc. Am. J. 56,777-783.

Gigliotti G, Kaiser K, Guggenberger G, Haumaier L. 2002. Biology and Fertility of Soils, 36,321-329.

How to cite: Ramos, M. C.: Particulate, mineral fraction and water extractable organic carbon in the soil and in the sediments transported by runoff, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3108, https://doi.org/10.5194/egusphere-egu2020-3108, 2020.

EGU2020-10221 | Displays | SSS2.5

Temporal variability in soil organic carbon in response to erosion in mountain agricultural landscapes

Jessica Vasil’chuk, Leticia Gaspar, Ivan Lizaga, and Ana Navas

Soil erosion leads to the loss of fertile topsoil, resulting in one of the principal soil degradation problems in agricultural landscapes worldwide. Soil redistribution processes affect the spatial and temporal variability of soil properties and nutrients, as soil organic carbon (SOC) which is linked to soil quality and soil functions. In the context of climate change mitigation as well as soil fertility and food security, there has been considerable interest in monitoring soil and carbon loss, especially in erosion-affected agricultural landscapes.

In this study, we attempt to evaluate the temporal variation of SOC and carbon fractions in a Mediterranean mountain agroecosystem. To this purpose, repeating soil sampling and carbon measurements within the same sites was undertaken in 2003 and in 2016. The sampling sites were located in agricultural areas where erosion or deposition preferably occurs based on soil redistribution rates obtained by using 137Cs measurements. The content of soil organic carbon (SOC) and the active and stable SOC fractions, (ACF and SCF, respectively) contents were measured by the dry combustion method using LECO RC-612 equipment.

Although statistically significant differences between the two surveys were not found, the mean content of SOC, ACF and SCF were slightly lower in the survey taken in 2016 than the one in 2013. Repeated topsoil sampling (0-5 cm) after 13 years reveals SOC and ACF losses for almost all the agricultural soils selected in this research. It’s important to highlight that the biggest differences between the two surveys are identified in the sites located in areas with steep slopes, while small variations occurred in the sites located in gentle slopes where deposition processes predominate. However, even if SCF losses were detected, especially in the erosive sites located in steep slopes, the content of SCF slightly increases for the second survey in sites located in depositional areas. To date, there have been few attempts to monitor soil carbon in Mediterranean soils, and this study represents a preliminary investigation that may be suitable for tracking absolute changes in SOC and carbon fractions in agricultural landscapes.

How to cite: Vasil’chuk, J., Gaspar, L., Lizaga, I., and Navas, A.: Temporal variability in soil organic carbon in response to erosion in mountain agricultural landscapes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10221, https://doi.org/10.5194/egusphere-egu2020-10221, 2020.

EGU2020-17676 | Displays | SSS2.5

Lateral transport of SOC induced by water erosion in a Spanish agroecosystem

Leticia Gaspar, Lionel Mabit, Ivan Lizaga, and Ana Navas

The main route for the lateral movement of soil organic carbon (SOC) is water erosion. Awareness of the distribution and magnitude of land carbon mobilization is important both for improving models of the carbon cycle and for management practices aimed to preserve carbon stocks and enhance carbon sinks. There is a need to consider the global significance of soil erosion from soil organic carbon cycling schemes and for this reason, the movement of SOC during erosion processes should be elucidated.

Our study aims to estimate the SOC redistribution induced by water erosion during a 40 years period in an agroforestry mountain ecosystem located in northern Spain. To this purpose, topographically driven transects were selected with mixed land uses to i) assess what factors modify the runoff patterns with impact on soil and carbon redistribution and ii) evaluate the mobilization of topsoil organic carbon along the transects.

The lateral movement of SOC shows similar spatial patterns with that of soil erosion. To identify whether erosional or depositional processes have been predominant in the sampling sites we used 137Cs inventories and the characterization of terrain attributes of the study with a detailed analysis of the main runoff pathways. Results indicate that SOC losses were related to an increase in water flow accumulation, while the highest SOC gains were recorded at concave positions. Soil erosion processes and the content of SOC in soils are the two main factors controlling carbon budgets. The topographical and geomorphological characteristics of the transects, the spatial distribution of land uses and the presence of landscape linear elements such as terraces or paths, affect runoff and determine the sediment connectivity and carbon dynamics along the slopes.

The interactions between topography and land use produce significant positive or negative effects on SOC accumulation, particularly in areas with complex topography, as the results obtained in our study sustain. Even though the effect of topography and land use/land cover and their interactions on the horizontal distributions of carbon remains largely unknown, our approach contributes to better understand the pattern of gains and losses of soil organic and inorganic carbon induced by water erosion.

How to cite: Gaspar, L., Mabit, L., Lizaga, I., and Navas, A.: Lateral transport of SOC induced by water erosion in a Spanish agroecosystem, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17676, https://doi.org/10.5194/egusphere-egu2020-17676, 2020.

EGU2020-5593 | Displays | SSS2.5

Linking soil C pools and N in radiotraced soils of Grey lake area (Torres del Paine, Chilean Patagonia)

Alejandra Castillo, Leticia Gaspar, Ivan Lizaga, Gerd Dercon, and Ana Navas

The Grey Glacier, located in the Torres del Paine region, belongs to the Patagonian ice sheet that suffered several glacial fluctuations during the Quaternary resulting in spectacular glacial landscapes. Similar as in other world mountains, glaciers in the Andean Patagonia are declining and the Grey Glacier has experienced during the last 80 years a clear retreat. Important ice mass collapses occurred in 1996 and recently in 2017 and 2019. In the proglacial environment of Grey Lake, the most characteristic glacial landforms are the Last Glacial Maximum moraine belts while landforms of the Little Ice Age reveal the advance of ice in modern times in the lake surroundings. At present the most active formations are composed of glacial deposits exposed after the recent retreat of Grey glacier. In this rapidly changing environment new soils are developing becoming a relevant framework to assess the trends in the pedogenesis dynamic and the variations of nutrient pools.

During a 15 days field campaign in the frame of the IAEA INT5153 project main proglacial landforms were identified and soil sampling was undertaken to assess if there were differences in the soil status and the nutrients pools in function of the geomorphic characteristics. Previous research in the area (Navas et al., 2019) revealed the usefulness of combining 137Cs with soil organic carbon (SOC) for deriving information on soils generated on recently exposed glacial deposits linked to soil redistribution patterns. Our study aims to evaluate what is the status of the SOC pool in soils formed in the Grey Lake area in relation to 137Cs proxies of soil stability. Analyses of 137Cs (Bqkg-1), and of contents of SOC and its fractions, and nitrogen (N) were done for characterizing the soils of the study landforms. We found that the most recent glacial deposits that are highly unstable in this paraglacial environment had the lowest contents of SOC and N along with negligible activities of 137Cs. In parallel with the highest 137Cs activity found in more developed soils on forest slopes, high SOC and N contents though less than in swamps indicated higher soil stability in forest slopes than in recently exposed glacial deposits. In the C pool, the stable fraction was most abundant in soils on forest slopes and on vegetated moraines in accordance with more abundant vegetation cover on relatively more developed soils. Though all landforms had much higher proportion of the active fraction, specially swamps, the contribution of the active fraction to SOC was also much higher in swamps, followed by forest and vegetated moraines. However, in comparison with the rest of glacial deposits and forest slopes, swamps presented the lowest contribution of the stable fraction to SOC evidencing their fragility to degradation processes that would rapidly eliminate the more labile fraction disrupting the natural cycle of C towards more stable fractions. Our results show that combination of 137Cs derived information with data from nutrients pools can be an important aid for interpreting changes in paraglacial landscapes where soils are forming on recently exposed glacial deposits.

How to cite: Castillo, A., Gaspar, L., Lizaga, I., Dercon, G., and Navas, A.: Linking soil C pools and N in radiotraced soils of Grey lake area (Torres del Paine, Chilean Patagonia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5593, https://doi.org/10.5194/egusphere-egu2020-5593, 2020.

EGU2020-9621 | Displays | SSS2.5 | Highlight

Distribution of nutrient pools in recently formed soils of Andean high wetlands (Huayna-Potosí, Bolivia)

Michele Nuñez-Quiroga, Edson Ramírez, Gerd Dercon, and Ana Navas

The Andean glaciers are experiencing since 1980 an accelerated decline associated with an increase in air temperature across the region. Encompassing the shrinking of mountain glaciers new soils are formed as deglaciation facilitates biogeochemical processes and the subsequent development of vegetation. Under extreme environmental conditions high-altitude soils are constrained by climate, substrate and geomorphological characteristics of recently deglaciated surfaces that control soil features in high mountains. At the foot of Huayna-Potosí, the glacier retreat is gradually exposing mineral substrate, which is being colonised by soil biota and plants. The subsequent accumulation of organic matter is progressing rapidly especially in wetlands developed in the proglacial area thus accelerating the processes of soil formation. The characterization of soil organic carbon (SOC) pools is necessary to understand SOC dynamics in soils and a relative measure of C stability in soils.

In this study we attempt to evaluate the distribution of SOC, C fractions and nitrogen in glacial deposits and high altitude wetlands to relate it with that of 137Cs as indicator of soil stability. To this purpose topsoil sampling of moraines, colluvium and peat soil in wetlands was undertaken during a two weeks expedition to Huayna-Potosí Glacier area in the frame of IAEA INT5153 project in May 2017 and contents of SOC and its fractions (i.e. active and stable carbon fractions), nitrogen and 137Cs activity (Bq kg-1) were determined.

The high wetlands both at favourable flat topographic positions and slopes have high organic rich soils showing large carbon sink capacity. More abundant depleted values of 137Cs in moraines and colluvium indicate greater impact of soil erosion processes in comparison to wetlands, whereas a higher 137Cs content is related to higher carbon contents and more abundant vegetation that would preserve soil from erosion. The size of the nutrient pool such as carbon and nitrogen is much higher in wetlands than in glacial deposits. In the carbon pool, the active fraction is more abundant than the stable fraction but in wetlands the ratio active/stable is much higher (mean: 31) than in glacial deposits (mean: 5). The contribution of the active fraction to SOC is also higher in wetlands (c.a. 1), while the opposite was found for the stable fraction contribution to SOC with almost a ratio of 0 in wetlands compared to 0.24 in glacial deposits. Paralleling the evolution of vegetation the enrichment in soil nutrients affects carbon (C) dynamics in the new soils that all are in the early forming stages with low C stability. Despite wetlands soils having the largest SOC content, the imbalance in the proportions of the C fractions with almost negligible stable C evidence the risk of interrupting the C cycle by loosing the more labile fraction. Therefore, focus should be directed to preserve the fragile new forming soils but specially wetlands because their key role in regulating the hydrological system and maintaining high altitude ecosystems.

How to cite: Nuñez-Quiroga, M., Ramírez, E., Dercon, G., and Navas, A.: Distribution of nutrient pools in recently formed soils of Andean high wetlands (Huayna-Potosí, Bolivia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9621, https://doi.org/10.5194/egusphere-egu2020-9621, 2020.

EGU2020-10027 | Displays | SSS2.5

Erosion and sediment enrichment ratio in volcanic soils

Ludmila La Manna, César Mario Rostagno, Manuela Tarabini, Federico Gomez, and Ana Navas

Patagonian Andean region is widespread affected by soil degradation and erosion processes. The subhumid sector, which corresponds to the transition (ecotone) between the Andean forests and the Patagonian steppe, has suffered the highest human pressure and overgrazing, accelerating the soil erosion processes.

Near Esquel town (Subhumid sector of Chubut province, Argentina), where soils are mainly developed from volcanic ashes, erosion studies based on fallout radionuclides (Caesium-137) and simulated rainfalls were performed. Studies based on Caesium-137 showed that soil losses in the last 50 years were higher than 30 m3 ha-1 year-1 under different land uses.

Rainfall simulation experiments, carried out under the same conditions (Rain fall intensity: 100 mm h-1 for 30 minutes; Drop diameter: 2.5 mm; Drop velocity: 5.3 m s-1) showed that erosion rates are highly affected by land use. Potential erosion rates in degraded rangelands varied between 143 and 750 g m-2, depending on soil characteristics (such as texture and presence of non-crystalline materials), soil cover and slope. In mature exotic conifer afforestations, with soil completely covered by litter, soil erosion was negligible, varying between 0 and 10 g m-2. Erosion rates increased both in young afforestations with open canopies (8 a 44 g m-2), and in mature afforestations where fresh litter and duff layers were removed (35 a 200 g m-2).

In the different studied systems, soil losses involved not the detachment of individual particles, but of soil micro aggregates rich in organic matter. Sediments enrichment ratio was always higher than 1, varying between 1.2 and 1.8. These results show that the sediments were enriched with organic matter, as compared to the contributing soils, indicating its selective removal. The erosion studies performed evidence the high erodibility of volcanic soils when their cover is lost, and the close link between erosion and carbon losses in these systems.

How to cite: La Manna, L., Mario Rostagno, C., Tarabini, M., Gomez, F., and Navas, A.: Erosion and sediment enrichment ratio in volcanic soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10027, https://doi.org/10.5194/egusphere-egu2020-10027, 2020.

EGU2020-18155 | Displays | SSS2.5

Simulating heavy rainfall events for parameterizing a first application of the physically based soil erosion model EROSION3D in South Africa

Andreas Kaiser, Michael Geißler, Jay Le Roux, Marike Stander, George van Zijl, and Jussi Baade

Soil erosion is a frequently tackled field of research and plays a major role in land degradation. Representing a discontinuous process soil loss is strongly determined by single events, which leads to high demands on modelling approaches.

Here we present a first application of the physically-based soil erosion model EROSION3D in a South African setting within the framework of the project SALDi (South African Land Degradation Monitor). Parameterization of the model requires intensive field work in accordance to land use and management patterns, soil types and topography. The experimental determination of physical and hydrological processes for selected sites allows for an improvement of the modelling results. Thus, rainfall and runoff simulation campaigns were carried out on various sites with a 3 x 1 m² mobile rainfall simulator. Additionally, UAV and TLS surveying, soil sampling, laboratory analysis and digital soil mapping complemented the approach. The created datasets are firstly handled in EROSION2D to calibrate soil erosivity and hydraulic conductivity and then introduced to EROSION3D for including land use, precipitation, elevation, multi-layered soil properties, organic carbon content and additional model input parameters.

The modelling procedure was applied within the boundaries of a research catchment close to Ladybrand in the Free State for first test runs. Furthermore, the same approach showed distinct differences on a conventionally tilled field vs. a conservational approach. An upscaling to larger catchments will then be carried out in basins with protected soils within Kruger National Park to directly compare them to results from intensively cultivated agricultural sites adjacent to the park boundaries.

How to cite: Kaiser, A., Geißler, M., Le Roux, J., Stander, M., van Zijl, G., and Baade, J.: Simulating heavy rainfall events for parameterizing a first application of the physically based soil erosion model EROSION3D in South Africa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18155, https://doi.org/10.5194/egusphere-egu2020-18155, 2020.

EGU2020-1208 | Displays | SSS2.5

Pragmatic, fast and easy to use Model for Predicting Susceptibility to Concentrated Flow Erosion in a GIS in data-sparse regions

Liberty Lazarus Orapine Mgbanyi, Matthew Johnson, and Colin Thorne

Less Economically Developed Countries (LEDCs) are at particular risk of gullying due to climate change, land-use change, poor agricultural practices and widespread farming intensification, but in these areas, the data required to apply most predictive models are usually unavailable. Therefore, an urgent need for a practical and rapid predictive tool for assessing gullying potential in data-sparse regions, to inform planning, agricultural practices and environmental management decision-making is required. Given the difficulty in applying existing empirical models to developing areas, where input data is sparse, but the risk of gullying is high, alternative methods need to be developed to identify areas susceptible to gullying. Here it is hypothesised that detailed data is required to apply existing models of soil loss from agricultural areas because they focus on predicting the quantities of sediment lost after agriculture has commenced. The data requirements for successful model application could be less if the focus were instead on identifying areas that are susceptible to gullying.  The decision to avoiding soil loss by either protecting them from agricultural development or at least applying soil conservation measures from the outset, without attempting to predict the extents or the specific metre-scale locations of individual gully channels will come much handy. The Compound Topography Index (CTI) meets the criteria for that candidate predictive model for concentrated flow erosion in the data-sparse regions. The CTI, however, required quality and high-resolution data(<5m LiDAR DEMs) available in data-rich regions to perform, but with weak quality and low-resolution data(30m DEM) found in the data-sparse regions, fuzzy logic data applied to this data before using it as input into the CTI model to at least on identifying areas that are susceptible to gullying. The accuracy of the model was moderately improved when used with high-resolution data, and consistent in prediction for coarse resolution DEMs. A key finding is that the fuzzy CTI reveals that much of the landscape has the potential to suffer gullying – i.e. there is sufficient planform and profile curvature to concentrate and accelerate overland flow. Soil degradation and loss of soil structure, or removal of natural vegetation and, especially forests, could exacerbate the condition rapidly lead to widespread gullying based on the occurrence of concentrated overland flow driven by the topography, while the incorporation of soil structural stability index in the fuzzy CTI slightly improved it performance as per modelling concentrated flow erosion. The calculation of CTI is easy, repeatable, require less comprehensive, sophisticated data collection and not over extended periods and could widely be an applicable predictor of gullying, for use in sparse data regions.

How to cite: Mgbanyi, L. L. O., Johnson, M., and Thorne, C.: Pragmatic, fast and easy to use Model for Predicting Susceptibility to Concentrated Flow Erosion in a GIS in data-sparse regions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1208, https://doi.org/10.5194/egusphere-egu2020-1208, 2020.

EGU2020-2228 | Displays | SSS2.5

Quantitative assessment of gully erosion dynamics using a GIS implementation of Sidorchuks' DYNGUL model in Southern KwaZulu-Natal, South Africa

adel omran, Dietrich Schroeder, Christian Sommer, Volker Hochschild, Aleksey Sidorchuk, and Michael Maerker

Soil erosion is considered as one of the main threats affecting both rural and urban areas in many different parts all over the world. Therefore, increasing attention has been attributed to soil erosion in the last decades. This can also be documented by an increasing number of studies targeting soil erosion assessment using qualitative and quantitative models. However, gully erosion phenomena have been widely neglected in erosion modelling due to the nature and complexity of the related processes and hence, it is also more difficult to simulate, predict and to visualize its effects. Sidorchuk (1999) established a Fortran based dynamic erosion model called DYNGUL to describe the first quick stage of gully development, coinciding with the main changes in gully morphology; like changes in volume, area and elevation of the longitudinal profile. The DYNGUL model is based on the solution of the equations of mass conservation and gully bed deformation. The model of straight slope stability was used to predict gully side wall inclination and of the finite morphology of the gully. The objective of this contribution is to establish a GIS tool for a quantitative gully erosion assessment and to predict gully evolution over time. The tool will help: i) to cope with or mitigate gully erosion processes and ii) to plan measures to stabilize the landscape affected by gully erosion. Therefore, we developed a Python-based tool that can be applied in a GIS environment. The model was tested its performance and the sensitivity of physical parameters with data from a gully in the Drakensberg Mountains, KwaZulu-Natal, South Africa. The results of the gully erosion model showed that their sensitivity to lithological and hydrological factors is rather high.

How to cite: omran, A., Schroeder, D., Sommer, C., Hochschild, V., Sidorchuk, A., and Maerker, M.: Quantitative assessment of gully erosion dynamics using a GIS implementation of Sidorchuks' DYNGUL model in Southern KwaZulu-Natal, South Africa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2228, https://doi.org/10.5194/egusphere-egu2020-2228, 2020.

EGU2020-11249 | Displays | SSS2.5

Soil Degradation in Argan Woodlands, South Morocco

Mario Kirchhoff, Lars Engelmann, Lutz Leroy Zimmermann, Irene Marzolff, Manuel Seeger, Ali Aït Hssaine, and Johannes B. Ries

The argan tree (Argania spinosa) populations, endemic to South Morocco, have been highly degraded. Although the argan tree is the source of the valuable argan oil and is protected by law, overbrowsing and -grazing as well as the intensification and expansion of agricultural land lead to tree and soil degradation. Young stands cannot establish themselves; undergrowth is scarce due to the semiarid/arid climate and thus, goats, sheep and dromedaries continually browse the trees. Canopy-covered areas decrease and are degraded while areas without vegetation cover between the argan trees increase.

On 30 test sites, 60 soil samples of tree and intertree areas were studied on their soil physical and chemical properties. 36 rainfall simulations and 60 single-ring infiltration measurements were conducted to measure potential differences between tree/intertree areas in their runoff/erosion and infiltration properties. Significant differences using a t-test were found for the studied parameters saturated hydraulic conductivity, pH, electric conductivity, percolation stability, total C-content, total N-content, K-content, Na-content and Mg-content. Surface runoff and soil erosion were not statistically significant, but showed similar trends due to the higher complexity of runoff formation. The soil covered by argan trees generally showed less signs of degradation than intertree areas. With ever-expanding intertree areas due to the lack of rejuvenation of argan trees a further degradation of the soil can be assumed.

How to cite: Kirchhoff, M., Engelmann, L., Zimmermann, L. L., Marzolff, I., Seeger, M., Aït Hssaine, A., and Ries, J. B.: Soil Degradation in Argan Woodlands, South Morocco, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11249, https://doi.org/10.5194/egusphere-egu2020-11249, 2020.

EGU2020-831 | Displays | SSS2.5

Gully Erosion: A Threat to Livable Cities in Developing Countries

Adeyemi Olusola and Samuel Yakubu

The United Nations Centre for Human Settlement in 2007 estimated that out of about 6 billion people in the world, 3 billion (50%) live in urban cities. A projection of about 61% of the total world population will be living in urban cities by 2030. As these cities grow, certain aspects of the urban space are significantly affected due to this unavoidable growth especially in developing countries. Aspects such as demographic, environmental and economic are severely altered. This study employs a ‘mixed approach’ to explaining how gully erosion, is a threat to liveable settlements/cities in the 21st century. The first part of the study is a meta-research on gully erosion and how it affects human settlements in Nigeria, then a field study on gullies within Osogbo Metropolis, southwestern Nigeria, its morphology and distribution. The morphology (width and depth) of each of the identified gully was determined using standard instruments. Structures around the gullies were also identified spatially using a handheld GPS (Global Positioning System). Gully clusters were analysed using Moran I index. The identified gullies within Osogbo Metropolis at its deepest section are about 10metres, while the widest of the gullies is 2.5metres. On the average the measured gullies are about 0.7meteres wide and 1.7meteres deep. All the measured gullies are still undergoing downcutting and almost all of them are affecting one structure or the other within their catchment area. Given a z-score of -0.40 and -1.15 Moran I index I, the pattern does not appear to be significantly different than random. Hence, the occurrence of these gullies cannot be said to be associated with natural factors like lithology or soil properties. Out of the twelve major gullies identified, nine (9) were as a result of poor engineering, largely due to the on-going urban renewal process. Osogbo and elsewhere in Nigeria suffer from the havocs of gully erosion. Urban sprawl coupled with urban renewal processses in many parts Nigeira (particularly in the Third World) leads to the rapid development of large gully channels (urban gullies) endangering the bearing function of soils and causing damage to infrastructure and private property. The implication of the result is that, as good as the renewal process being carried out mostly in southwestern cities is a good one especially to achieve livable cities in the 21st century, there is the need for such planning to ensure that most engineering works adhere to best practices. The government at all levels in Nigeria and stakeholders in environmental management should ensure proper planning and make it a duty to create cities that are livable and healthy.

How to cite: Olusola, A. and Yakubu, S.: Gully Erosion: A Threat to Livable Cities in Developing Countries, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-831, https://doi.org/10.5194/egusphere-egu2020-831, 2020.

EGU2020-10739 | Displays | SSS2.5

Understanding the effectiveness of measures aiming to stabilize urban mega gullies in Kinshasa

Eric Lutete Landu, Guy Ilombe Mawe, Charles Bielders, Fils Makanzu Imwangana, Olivier Dewitte, Jean Poesen, and Matthias Vanmaercke

Kinshasa, the capital of the D.R. Congo, is strongly affected by urban mega gullies. There are currently hundreds of such gullies, having a total length of >100 km. Many of these gullies (typically tens of meters wide and deep) continue to expand, causing major damage to houses and other infrastructure and often claiming human casualties. To mitigate these impacts numerous efforts are being implemented. The type and scale of these measures varies widely: from large structural measures like retention ponds to local initiatives of stabilizing gully heads with waste material. Nonetheless, earlier work indicates that an estimated 50% of the existing urban gullies continue to expand, despite the implementation of such measures. As such, we currently have very limited insight into the effectiveness of these measures and the overall best strategies to prevent and mitigate urban gullies. One reason for this is that gully erosion is typically very episodic with long periods of stability, followed by sudden expansion events. As a result, understanding the dynamics of gully expansion in urban environments requires observations over sufficiently long time periods. However, most current initiatives to stabilize urban gullies happen on a rather isolated basis and are rarely evaluated afterwards.

This work aims to improve our understanding of this issue by constructing a large inventory of measures implemented to stabilize urban gullies in Kinshasa and statistically confronting these measures with observed vegetation recovery and long-term gully expansion rates (derived from high-resolution imagery over a period of >10 years). Our preliminary results (based on a dataset of > 140 urban gullies) shows that the most commonly applied measures are revegetation and reinforcement of gully heads with sandbags or household waste material (implemented in around 50% of the cases). Also retention ponds and water storage tanks are frequently implemented (around 30% of the cases). Surprisingly, our results indicate that urban gullies with higher expansion rates tend to have more measures implemented in their upstream catchment. While this seems counterintuitive, it may point to the fact that more actively retreating gullies create a larger sense of urgency and therefore instigates a higher number of (often ineffective) initiatives. More research is needed to confirm this. Furthermore, the stability of gullies seems to be strongly linked to vegetation cover in the gully. Nonetheless, it is not always clear if vegetation is the cause or the result of this stability. Overall, this study provides one of the first large scale assessments of the effectiveness of gully control measures in urban tropical environments. With this study, we hope to contribute to a better prevention and mitigation of this problem that affects many cities of the tropical Global South.

How to cite: Lutete Landu, E., Ilombe Mawe, G., Bielders, C., Makanzu Imwangana, F., Dewitte, O., Poesen, J., and Vanmaercke, M.: Understanding the effectiveness of measures aiming to stabilize urban mega gullies in Kinshasa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10739, https://doi.org/10.5194/egusphere-egu2020-10739, 2020.

EGU2020-14073 | Displays | SSS2.5

Soil erosion on Mauritius

Paul Sumner

EGU2020-9864 | Displays | SSS2.5

A Study of Sediment Yield in the Deji Reservoir Watershed Using Risk Analysis

Wen Wei Chang and Chao Yuan Lin

Deji Reservoir Watershed was used as a sample site to understand the sediment yield using risk analysis. The historic typhoon and/or torrential storm events were collected to estimate the excessive runoff for each event. The distribution of SCS-CN is obtained by combining the maps of land use and soil texture, and the excess rainfall (Pe) and the maximum water storage (S) for each event were then calculated according to SCS-CN. Regression analysis shows that there is a good relationship between estimated runoff (x) and measured runoff (y); y=0.9561x+3*106, R2= 0.9414. Topographic wetness index (TWI) and sediment delivery ratio (SDR) were derived from DEM. The risk model developed to assess the sediment yield is calculated from the multiplication of hazard (Pe), vulnerability (TWI), and exposure (SDR). The total siltation amount of Deji Reservoir from 2009 to 2017 was taken as the measured value, and the estimated amount of sediment yield was calculated from the aforementioned formula  to obtain the potential index of sediment yield. The results show that there is also a good relationship between estimated sediment yield (x') and measured sediment yield (y') annually; y'=10-11x'2-0.0223x'+9*106 , R2= 0.74.

Keywords: Risk Analysis, Curve Number, Sediment Delivery Ratio

How to cite: Chang, W. W. and Lin, C. Y.: A Study of Sediment Yield in the Deji Reservoir Watershed Using Risk Analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9864, https://doi.org/10.5194/egusphere-egu2020-9864, 2020.

SSS2.7 – Advancements in modeling and remote sensing assessments in soil and water degradation processes

EGU2020-22200 | Displays | SSS2.7

Visualizing resource dependencies of the urban system at multiple scales: a hydrological case study

Héctor Angarita, Vishal Mehta, and Efraín Dominguez

Freshwater is one key component of the resource dependency of urban areas, linking concentrated population centers to geophysical and ecosystem processes operating at regional and global scales. Resources like water, food, biofuels, fibers or energy that sustain cities directly depend on the productive or assimilative capacities of the hydrological system, operating at multiple nested scales (from catchment to river basins) —areas orders of magnitude greater than the extent of the built-up urban areas.

Although the freshwater systems–urban population relationship has a broad regional and sectorial scope, the quantification of the extent of regional and global impacts of cities’ resource demands, and more importantly, their integration into decision-support frameworks continues to be overlooked in water-management and urban planning practice. A key limitation of understanding the scope of impacts of urban systems is the characterization of the distributed and non-linear nature of the regional relationship of water and cities, wherein a given region can simultaneously supply resources to—or be affected by—multiple urban areas (and vice-versa), and the heterogeneity of physical and biotic processes of freshwater systems.

Here we introduce a novel approach to assess and visualize the interactions between urban resource demands and the freshwater system. We propose a set of indicators that make use of freshwater drainage structure to incorporate the cumulative effects and concurrent resource dependency of urban areas across multiple nested scales. The cumulative character of the proposed indexes aims to replace the fixed control boundary (i.e. basin, sub-basin, etc -the current practice in water resources appraisals), with the (topological) integral of the process across the multiple nested scales present in a river basin. This approach allows: (i) visualizing how factors like patterns of size, spatial distribution and interconnection of urban resource demands or the nested and hierarchical character of freshwater systems, influence the cumulative pressure exerted or a urban system on the freshwater system, (ii) mapping the spatial patterns of resource import and export across different scales and regions of a freshwater system, and (iii) quantifying the scales of the process required to sustain the resource supply of the multiple cities sharing the same provisioning freshwater system. The presented advances can inform regional urban planning to determine options to avoid, minimize or offset regional impacts of urban populations. An example of this proposed approach is presented for the Magdalena River Basin (Colombia).

How to cite: Angarita, H., Mehta, V., and Dominguez, E.: Visualizing resource dependencies of the urban system at multiple scales: a hydrological case study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22200, https://doi.org/10.5194/egusphere-egu2020-22200, 2020.

EGU2020-12287 | Displays | SSS2.7

Modelling the responses of extreme events hydrometeorological events in the landslides and floods of the Combeima river basin.

Laura Viviana Garzon Useche, German Ricardo Santos Granados, and Gerald Augusto Corzo Perez

The village of Juntas has a periodic sequence of hydrometeorological extreme events. The region present a tropical vegetation with a highly dynamic weather. Currently modelling of hydrological events have been limited to the use of conventional rainfall runoff models, that fail to represent accurately the moment when landslides start to occur, as well as to not be able to provide a clear spatial sensitivity of the relationship between landslide event and precipitation. This research presents a contribution in the linking of various modelling concepts to understand more the influence of the spatial variability of rain in the generation of the events. The data avaialable was daily precipitation during 15 years from de satelital imagine and the discharge of geotechnical characterizations, hydraulic analysis, ecological structures, cartography, vulnerability, flood and torrential risk maps.

The analysis is done by combining the information available in remote sensing rasters and the overall temporal relation of events is mapped with a spatiotemporal analysis of the extremes. The current methodology is expected to contribute to the understanding of the sensitivity of landslides due to the spatiotemporal variation of rain in the region.

How to cite: Garzon Useche, L. V., Santos Granados, G. R., and Corzo Perez, G. A.: Modelling the responses of extreme events hydrometeorological events in the landslides and floods of the Combeima river basin., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12287, https://doi.org/10.5194/egusphere-egu2020-12287, 2020.

Spatio temporal visualization of soil critical sources areas to assess the dynamics of source pollution in agricultural management practices

always changes aim at the reduction of nutrient pollution. Critical identification of areas that are the sources of pollution is crucial for identifying which practices provide the most substantial contamination. The dynamics of agricultural practices are complex and the precise determination of pollution concentration requires a comprehensive model. In this research, we present the results of analysing via a new visualisation technique were the critical source areas using a spatiotemporal methodology that allows for a georeferenced identification of changes. The proposed method in this research used a radial diagram to evaluate the changes in regions of pollution and makes a radial diagram formulation of intensities, location and frequency. For this location and intensity identification, a clustering process, using the Non-contiguous drought areas method and the Contrigous drought area method. This clustering groups by first mapping in one dimension the threshold that defines a change in the state of the CSA, and then groups if by its neighbours and soil characteristics. To obtain a spatially distributed data, a SWAT model was set up for two types of crops, mainly potato and tomato tree, aside, we added also Kikuyu grass as it is one of the most important in the region. The simulation period for our experiment was in an area of 103434 Ha, using daily data from 1995 to 2015.  Two steps calibration was done, first with streamflow and second with an analysis of monthly nutrients. Results show a definite change in location, which will imply that a significant error could be present if the spatiotemporal relation is not analysed. The current work is part of a PhD thesis and the partial results presented here contribute to a broader formulation of the optimisation of agricultural practices to reduce the impact of the Critical Source Areas in nutrients pollution. 

 

How to cite: Uribe, N. and Corzo P, G. A.: Spatio temporal visualization of soil critical sources areas to assess the dynamics of source pollution in agricultural management practices, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22024, https://doi.org/10.5194/egusphere-egu2020-22024, 2020.

EGU2020-8212 | Displays | SSS2.7

Large-scale Groundwater Simulation using Artificial Neural Networks in the Danube River Basin

Illias Landros, Ioannis Trichakis, Emmanouil Varouchakis, and George P. Karatzas

In recent years, Artificial Neural Networks (ANNs) have proven their merit in being able to simulate the changes in groundwater levels, using as inputs other parameters of the water budget, e.g. precipitation, temperature, etc.. In this study, ANNs have been used to simulate hydraulic head in a large number of wells throughout the Danube River Basin, taking as inputs, precipitation, temperature, and evapotranspiration data in the region. Different ANN architectures have been examined, to minimize the simulation error of the testing data-set. Among the different training algorithms, Levenberg-Marquardt and Bayesian Regularization are used to train the ANNs, while the different activation functions of the neurons that were deployed include tangent sigmoid, logarithmic sigmoid and linear. The initial application comprised of data from 128 wells between 1 January 2000 and 31 October 2014. The best performance was achieved by the algorithm Bayesian Regularization with a error of the order  based on all observation wells. A second application, compared the results of the first one, with the results of an ANN used to simulate a single well. The pros and cons of the two approaches, and the synergies of using both of them is further discussed in order to distinguish the differences, and guide researchers in the field for further applications.

How to cite: Landros, I., Trichakis, I., Varouchakis, E., and Karatzas, G. P.: Large-scale Groundwater Simulation using Artificial Neural Networks in the Danube River Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8212, https://doi.org/10.5194/egusphere-egu2020-8212, 2020.

Soil erosion in agricultural landscapes reduces crop yields and influences the global carbon cycle. However, the magnitude of historical topsoil loss remains poorly quantified at large, regional spatial scales, hindering predictions of economic losses to farmers and quantification of the role soil erosion plays in the carbon cycle. We focus on one of the world’s most productive agricultural regions, the Corn Belt of the Midwestern United States and use a novel spectral remote sensing method to map areas of complete topsoil loss in agricultural fields. Using high-resolution satellite images and the association between topsoil loss and topographic curvature, we use high resolution LiDAR topographic data to scale-up soil loss predictions to 3.7x105 km2 of the Corn Belt. Our results indicate 34±12% of the region has completely lost topsoil as a result of agriculturally-accelerated erosion. Soil loss is most prevalent on convex slopes, and hilltops throughout the region are often completely denuded of topsoil indicating that tillage is a major driver of erosion, yet tillage erosion is not simulated in models used to assess soil loss trends in the U.S. We estimate that soil regenerative farming practices could restore 16±4.4 Pg of carbon to the exposed subsoil in the region. Soil regeneration would offset at least $2.5±0.3 billion in annual economic losses to farmers while generating a carbon sink equivalent to 8±3 years of U.S. CO2 emissions, or ~14% of the global soil carbon lost since the advent of agriculture.  

How to cite: Larsen, I., Thaler, E., and Yu, Q.: A remote sensing approach for evaluating regional-scale topsoil loss in the Midwestern United States, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4340, https://doi.org/10.5194/egusphere-egu2020-4340, 2020.

EGU2020-22225 | Displays | SSS2.7

Identifying the impact of human activities on soil erosion- the case of Jiangxi Province, China

Yanqing Lang, Xiaohuan Yang, and Hongyan Cai

Soil erosion is the results of the combined effects of natural factors and human activities. Since modern times, human activities are the main causes of soil erosion and plays a key role in the process of soil erosion, both promoting and inhibiting. Therefore, identifying the impact of human activities on soil erosion is of great significance to control and transform the impact of human activities reasonably and effectively. In this study, Jiangxi province is taken as the study area, the main patterns of human activities affecting soil erosion are sorted out and the spatial distribution of human activities is identified, and the impact of human activities on soil erosion is assessed. This study aims to reveal the temporal and spatial distribution of different human activities affecting soil erosion and explore the relationships between different human activities and soil erosion, and to provide data support, scientific reference and policy suggestions for soil erosion control and land resources management in Jiangxi province.

How to cite: Lang, Y., Yang, X., and Cai, H.: Identifying the impact of human activities on soil erosion- the case of Jiangxi Province, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22225, https://doi.org/10.5194/egusphere-egu2020-22225, 2020.

EGU2020-17972 | Displays | SSS2.7

Forecasting landslides using a spatiotemporal analysis of remote sensing data

Carlos Alfredo Mesa Zuluaga, German Ricardo Santos Granados, and Gerald Augusto Corzo Perez

Forecasting landslides is highly dependent in the weather conditions and the land-soil characteristics and its state. The uncertainty present in the evaluation of precipitation and its continuous variation is always a challenge for having accurate forecast, of primary importance for risks reduction. Currently, the landslides generate an impact on the imbalance of ecosystems and their occurrence is increasing which leads to an increase in the vulnerability of man on earth. The complexity of the landslide systems requires detailed analysis of the highly dynamic information of the rain and in turn the form as the hydrology response. Being able to combine hydrological models forced by satellite information systems and put them with a soil cohesion analysis system could help improve monitoring and in a particular case forecast landslide events.

The Combeima river located at the village of Juntas with canyon type land relief currently, faces a vital challenge in the face of winter times where precipitation threaten urban zones. Current researchers have explored risk factors, however, results still are quite far from optimal.

This study develops a methodology to identify the water volume that can cause landslides over the canyon type land relief, and use it as a trigger for forecasting. Remote sensing data at the present time and projected from past data will be used to simulate forecasting situations (hidcasting). A coupled Mike SHE models and data from Google earth platform are used to analyze a period of twenty years. Local information from events and its analysis in the satellite images are used to validate the events. Finally, the results of past conditions that led to the generation of floods are used to identify the state of the soil and the volumes. A calibration and validation of a neural network model is done feeding the volumes and states. The results of the model allow us to specifically characterize the saturation limits of the soil and the maximum rainfall intensities that a soil may contain before collapsing. With this information a high performance and a design of a system to forecast in real time was proposed. This work is part of an ongoing research and partial results will be presented.

How to cite: Mesa Zuluaga, C. A., Santos Granados, G. R., and Corzo Perez, G. A.: Forecasting landslides using a spatiotemporal analysis of remote sensing data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17972, https://doi.org/10.5194/egusphere-egu2020-17972, 2020.

EGU2020-21326 | Displays | SSS2.7

Estimating badland denudation with pin measurements and high resolution Digital Elevation Models derived from UAV image analysis

Brigitte Kuhn, Nikolaus Kuhn, John Boardman, and Vincent Schneider

The denudation of soil or soft rock surfaces by non-concentrated flow is mostly estimated by relating the sediment discharge observed at the outlet of a plot or natural micro-catchment to their respective surface areas. This approach generates an average denudation rate, but ignores spatial patterns of erosion and deposition. A well established approach to capture such spatial differences are pins, which deliver a highly precise point measurement of surface elevation change. Advances in the development of Unmanned Aerial Vehicles (UAVs) and imagine processing in the past decades offer an additional tool for mapping erosion and deposition at millimetre scale for continuous surfaces. In this study, pin and UAV-derived erosion data for a badland area in the Karoo rangelands, South Africa, are compared. The results show that typical annual erosion rates in the study area are lower than the differences between two DEMs generated a year apart. This illustrates that in situations where erosion rates are low, pins still offer the faster and more reliable results. For their extrapolation, on the other hand, UAV-derived DEMs provide suitable topographic data.

How to cite: Kuhn, B., Kuhn, N., Boardman, J., and Schneider, V.: Estimating badland denudation with pin measurements and high resolution Digital Elevation Models derived from UAV image analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21326, https://doi.org/10.5194/egusphere-egu2020-21326, 2020.

The Universal Soil Loss Equation (USLE) is a standard model to assess soil erosion by water. The model equation quantifies long-term average annual soil loss as a product of the rainfall erosivity R, soil erodibility K, slope length and slope steepness LS, the soil cover C and support measures P. Several methods exist to derive each of the model inputs from readily available data. The estimated values of a model input, however, can strongly differ depending on the method that was applied. The multiplication of the input factors with the USLE eventually results in large uncertainties for the soil loss estimates. A comparison of the estimated soil loss to observation data can potentially reduce the uncertainties. Yet, for large scale soil loss estimations, in-field observations are rare and their comparability to long-term soil estimates is limited. This work puts a focus on uncertainty and sensitivity analysis in large scale soil loss estimation employing the USLE with different realizations of the USLE input factors.

In a systematic analysis we developed different representations of the USLE inputs for the study domain of Kenya and Uganda with a spatial resolution of 90 m. All combinations of the generated USLE inputs resulted in 756 USLE model setups. We assessed the resulting distributions in soil loss, both spatially distributed and on district level for Kenya and Uganda. In a sensitivity analysis we analyzed the contributions of the USLE model inputs to the ranges in soil loss and analyzed their spatial patterns. We compared the calculated USLE ensemble soil estimates to available in-field data and other study results and addressed possibilities and limitations of the USLE model evaluation.

The USLE model ensemble resulted in wide ranges of estimated soil loss, exceeding the mean soil loss by over an order of magnitude particularly in hilly topographies. The study implies that a soil loss assessment with the USLE is highly uncertain and strongly depends on the realizations of the model input factors. The employed sensitivity analysis enabled us to identify spatial patterns in the importance of the USLE input factors. The C and K factors showed large scale patterns of importance in the densely vegetated part of Uganda and the dry north of Kenya, respectively. The LS factor estimates were mostly relevant in small scale heterogeneous patterns. Major challenges for the evaluation of the estimated soil losses with in-field data were due to spatial and temporal limitations of the observation data, but also due to measured soil losses describing processes that are different to the ones that are represented by the USLE.

Reference: Schürz, C., Mehdi, B., Kiesel, J., Schulz, K., and Herrnegger, M.: A systematic assessment of uncertainties in large scale soil loss estimation from different representations of USLE input factors – A case study for Kenya and Uganda, Hydrol. Earth Syst. Sci. Discuss., https://doi.org/10.5194/hess-2019-602, in review, 2019. 

How to cite: Schürz, C., Mehdi, B., Kiesel, J., Schulz, K., and Herrnegger, M.: A systematic assessment of uncertainties in large scale soil loss estimation from different representations of USLE input factors – A case study for Kenya and Uganda, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13787, https://doi.org/10.5194/egusphere-egu2020-13787, 2020.

EGU2020-17539 | Displays | SSS2.7

Photogrammetricaly measured sheet and rill erosion on steep slopes

Tomas Laburda, Petr Kavka, Romana Kubínová, Martin Neumann, Ondřej Marek, and Adam Tejkl

Soil erosion is a long-term problem that causes the degradation of the earth's surface depending on geomorphological and climatic conditions. Adverse combinations of these conditions can create situations where not only sheet erosion occurs, but also rill processes begin to occur due to the concentration of surface runoff. Erosion processes become undesirable and dangerous when they occur on construction sites. The presented project is basically focused on the effectiveness of protective geotextiles against soil erosion, but processes related to sheer and rill erosion were also investigated. The research was carried out on experimental plots of 4x1 meters, which were placed in the outdoor laboratory in Jirkov. These three plots were set at slopes from 22° to 34° and artificial rain was simulated on them using a rainfall simulator. A second experimental area of ​​the same size was available at the laboratory rainfall simulator at the CTU in Prague, where a modern facility was created for the purpose of soil erosion testing on steep slopes. This device can create slopes up to 40°.

The photogrammetric method „Structure from Motion“ was used for monitoring soil surface before and after each simulation. Orthophotos and digital elevation models were compared with each other to get digital elevation models of difference. Calculation of the ratio between sheet and rill erosion was done by manually creating rill polygons and by calculating the volume changes above the polygons of these rills and over the whole surface. According to preliminary results on these 4 m long slopes, the rill volume represented approximately 30 % compared to the overall volume change.

Shifts of stabilizing natural geotextiles by surface runoff and eroded material were also monitored using photogrammetric methods. Deformations and displacements were measured from differences in the detailed images before and after the simulation. Transversal veins and their shift along the slope were evaluated.

This research is funded by the TA CR  - TH02030428.

How to cite: Laburda, T., Kavka, P., Kubínová, R., Neumann, M., Marek, O., and Tejkl, A.: Photogrammetricaly measured sheet and rill erosion on steep slopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17539, https://doi.org/10.5194/egusphere-egu2020-17539, 2020.

EGU2020-10023 | Displays | SSS2.7

Spatiotemporal assessment of ephemeral gully characteristics using low altitude aerial imagery: an approach for quantifying

Henrique Momm, Robert Wells, Carlos Castillo, and Ronald Bingner

In agricultural fields, ephemeral gullies are defined as erosional channels formed primarily by overland flow from rainfall events. These channels are characterized by small dimensions, approximately 0.5 to 25 cm in depth, which allows their removal during regular farming operations. This dynamic characteristic coupled with their small size often can conceal soil losses by ephemeral gullies and poses challenges to efforts devised for soil loss quantification and mitigation. In this study, novel surveying and data processing techniques were employed to capture the small scale in topographic variation between two surveys and to assure that changes were due to erosional processes rather than survey miss-alignment. An agricultural field located in Iowa, U.S.A. with an area of approximately 54,500 m2 was surveyed twice: right after the field was planted with corn and approximately one month later, following several rainfall events. A static benchmark point was established at the edge of the field and tied to public geodesic locations. A set of removable ground control points were spread throughout the field and surveyed in relation to the benchmark point. Low altitude aerial images were collected using a quadcopter UAS. Ground control points were used to aid in geospatial registration and to assess final survey accuracy. Standard off-the-shelf commercial software packages were unable compensate for less distortion and a new procedure using Micmac open-source photogrammetry software package was used to account for complex distortion patterns in the raw image data set. The undistorted images were then processed using Agisoft Photoscan for camera alignment, model georeferencing, and dense point cloud generation. Each point cloud representing a time period contained over 1 billion of points (file size > 100GB) and was processed using custom algorithms for filtering outliers and rasterization into a 2.5 cm raster grid (DEM). Analysis of differences between the two high spatial resolution DEMs revealed changes in the landscape due to natural (erosion/deposition) and anthropogenic (farming activities) factors. Specifically, for ephemeral gully analysis, morphological features in the form of headcut position and size, channel incision, sinuosity, lateral expansion, and depositional patterns were easily identified. Findings of this study shed light on potential pitfalls inherent to the utilization of off-the-shelf commercial software packages for such fine scale multi-temporal analysis, describe the need for standardization of procedures that assure accurate erosional response amongst different studies, and support the generation of accurate datasets critical in advancing our understanding of ephemeral gully processes needed for improved model development and validation.

How to cite: Momm, H., Wells, R., Castillo, C., and Bingner, R.: Spatiotemporal assessment of ephemeral gully characteristics using low altitude aerial imagery: an approach for quantifying, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10023, https://doi.org/10.5194/egusphere-egu2020-10023, 2020.

EGU2020-12788 | Displays | SSS2.7

Impact on wheat production of anthropic soil erosion by recent gully filling at the Campiña landscape in Southern Spain

Carlos Castillo, Rafael Pérez, and Miguel Vallejo Orti

            Gully erosion is one of the main drivers of environmental degradation on intensively managed agricultural fields in Southern Spain. Ephemeral and permanent gullies develop after intense rainfall events, which leads to significant loss of arable land. In the study area, productivity is also affected atn gully surroundings since gully filling (by using the top soil scraped from the vicinity of the gully) is a common practice among local farmers.

            The aim of this communication is to analyze the impact of gully filling practices on wheat production during two growing years (2017 and 2019) in a medium-sized catchment (94 ha) at the Galapagares watershed. The study area is close to the city of Córdoba (Spain) and belongs to the Campiña landscape (rolling landscape on vertic soils). The catchment under study is divided in five subcatchments, two of them not affected by gully filling in the last eight years while in the other three, the soil was scraped and displaced into the gully within the study period (last two years).

            Firstly, a series of topographic and spatial factors (insolation, topographic index, slope, aspect, drainage area, distance to the gully) and a soil-related variable calculated prior to the growing season (soil color from the Sentinel-2 visible band) were selected as posible explanatory factors for remote sensing-based Vegetation Indexes (VI) derived from Sentinel-2 (the Normalized Difference Vegetation Index - NDVI and Enhanced Vegetation Index - EVI). Both indexes were considered potential proxies for crop yield for 2017 and 2019 campaigns. Furthermore, the differences in VI were compared between potentially affected areas by soil scraping close to gullies and non-affected areas. At last, a field survey on crop production (kg of wheat grain per ha, 15 % moisture) was carried out during the harvest period to determine the relation between vegetation indexes and crop yield.

            Results show that the most relevant explanatory factors for NDVI and EVI variance were solar irradiation, topographic index, aspect (positively correlated), soil colour (inverse correlation) and distance to the gully (positive correlation), in this order of importance. A general linear model explained 40% of NDVI and 55% of the EVI variances Nevertheless, when gully adjacent (<30m to the gully) and non adjacent (>30m) areas were analyzed separately, significant diferences were detected. Non-adjacent areas presented higher VI values and homogeinity pixelwise. Moreover, the distance to the gully became the second most significant explanatory factor for VI in adjacent areas (with higher VI values for more distant locations), whereas it remained non significant for non-adjacent pixels. In addition, those subcatchments impacted by recent gully filling showed larger variability in VI values before and after the operations as compared to non-affected subcatchments.

How to cite: Castillo, C., Pérez, R., and Vallejo Orti, M.: Impact on wheat production of anthropic soil erosion by recent gully filling at the Campiña landscape in Southern Spain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12788, https://doi.org/10.5194/egusphere-egu2020-12788, 2020.

EGU2020-8325 | Displays | SSS2.7

Soil Cohesion Development under Different Pore and Size Characteristics

Cagla Temiz, Fikret Ari, Selen Deviren Saygin, Sefika Arslan, Mehmet Altay Unal, and Gunay Erpul

Soil cohesion (Co) is one of the most important physical soil characteristics and it is closely related to the basic soil properties and physical distribution forces (e.g. particle size distribution, pore sizes, shear strength) and so it is mostly determined by experimentally approaches with the help of other soil properties in general terms. Instead of using these assumptions, the fluidized bed approach provides an opportunity for direct measurement of intrinsic soil cohesion. In this study, soil cohesion development for different soil types was investigated with the fluid-bed method by which pressure drop in soil mass measures under increasing water pressures until the cohesion between particles disappears. For this purpose, 20 different soils varying with a wide range of relevant soil physical properties were sampled; such that clay, silt and sand contents varied between 2% and 56%, 1% and 50%, and 1% and 97%, respectively while porosity values were between 0.38 and 0.92. By those textural diversities of the soils, obtained cohesion values changed between 5203 N m-3 and 212276 N m-3. Given results from regression analysis, a significant relationship was found between cohesion values of the soils and their porosity and silt fractions (R2: 86.6).These findings confirm that the method has a high potential to reflect differential conditions and show that soil cohesion could be modeled by such basic and easily obtainable parameters as particle size distribution and porosity, as well. 

Key words; Mechanical soil cohesion, particle size distribution, fluidized bed approach, porosity

How to cite: Temiz, C., Ari, F., Deviren Saygin, S., Arslan, S., Unal, M. A., and Erpul, G.: Soil Cohesion Development under Different Pore and Size Characteristics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8325, https://doi.org/10.5194/egusphere-egu2020-8325, 2020.

EGU2020-3619 | Displays | SSS2.7

Estimation of the Rates of Particle Aggregation and Disaggregation in the Mesopelagic Zone of the Eastern North Pacific

Vinicius Amaral, Olivier Marchal, Phoebe Lam, Jong-Mi Lee, Ken Buesseler, and Montserrat Roca Marti

The processes of particle aggregation and disaggregation are of paramount importance for ocean biogeochemical cycles. Particle aggregation leads to a transfer of particulate material and of their chemical constituents into large size fractions that can settle rapidly through the water column, thereby contributing to the ocean biological pump. In contrast, particle disaggregation redistributes material into smaller size classes and places limits on the size of the largest aggregates. In spite of their preeminent importance for ocean biogeochemistry, rates of particle (dis)aggregation in the ocean cannot be measured directly and are notoriously difficult to constrain. Indeed, current estimates obtained in a variety of oceanographic environments range over several orders of magnitude and suffer from appreciable uncertainties.

The goal of the Export Processes in the Ocean from Remote Sensing (EXPORTS) program is to develop a predictive understanding of the export and fate of global ocean net primary production for present and future climates. As part of this program, an extensive oceanographic campaign took place in summer 2018 in the Gulf of Alaska, during which various measuring and sampling platforms including a large-volume filtration (LVF) system have been deployed at different depths in the euphotic and mesopelagic zones at stations centered around a drifting Lagrangian float. Here we present the status of our ongoing effort to estimate the rates of particle (dis)aggregation in the mesopelagic zone of EXPORTS stations based on concomitant measurements of the concentration of particulate organic carbon (POC), lithogenic elements (Al and Ti), and thorium-234 (a naturally-occurring particle-reactive radionuclide), in different size fractions sampled from LVF and bottles. The rates of particle (dis)aggregation, as well as remineralization and sinking, are estimated from the quantitative combination of this diverse dataset with a simplified model of the cycling of POC, Al, Ti, and Th-234 in the upper water column using a least-squares procedure that accounts for both data and model errors. Rate estimates and their errors obtained at different stations and at different depths in the upper 500 m are presented and discussed in the context of independent measurements bearing on the mesopelagic ecosystem of the eastern North Pacific.

How to cite: Amaral, V., Marchal, O., Lam, P., Lee, J.-M., Buesseler, K., and Roca Marti, M.: Estimation of the Rates of Particle Aggregation and Disaggregation in the Mesopelagic Zone of the Eastern North Pacific, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3619, https://doi.org/10.5194/egusphere-egu2020-3619, 2020.

EGU2020-13427 | Displays | SSS2.7

Evaluation of olive grove management on various soils at the micro-catchment scale with the AnnAGNPS model to quantify their impacts on organic carbon

Encarnación Taguas, Ronald L. Bingner, Henrique Momm, Robert R. Wells, and Martin Locke

Soil organic carbon (SOC) stock changes are crucial to identify the risk of desertification in fragile areas such as the Mediterranean Basin and to fulfill environmental protection global conventions. In Spain, 48% of the world’s olive oil is produced with 2.6 Mha dedicated to the crop and there is clear concern over the carbon balance in the context of climate change and the resulting loss of productivity. In this work, 108 scenarios were prepared with the model AnnAGNPS in a small catchment of extensive olive groves by considering the impact of soil type and management using 6 different soil types (with textures sandy, S; sandy loam, Slo; loam, L; clay loam, Clo; silty loam clay, SiLoC; clay, C), 3 different managements (no till, NT; conventional tillage, CT, and cover crop, SC), 3 types of fertilization (two organic with different rates, F2 and F3,  and another inorganic F1) and 2 contrasting reach organic carbon half-life time (0.1 day-730 days). The consistency of the simulated values of annual OC attached to the sediments and of variations of ground SOC (h=200 mm) were evaluated and compared in the context of the region of Andalusia.

There were significant differences of annual values of the sediment OC for the scenarios of soil and management with a range variation between 0.0 kg.ha-1 and 368.9 kg.ha-1. In addition, S and SC showed the lowest variability intervals while Clo and NT had the highest sediment OC and variation ranges. For the SOC pools, the effects of soil and fertilization types were more evident than of the management. The combination C-SC-F3 presented the maximum increase of SOC (0.150 mg OC.g-1soil.y-1) while the combination Slo-NT-F1 presented the minimum (0.080 mg OC.g-1soil.y-1). Despite specific calibrations needed to quantify OC balances, the consistency of the hydrological and erosive parameterization based on the abundance of experimental studies supports the use of AnnAGNPS for simulating the OC loss in agricultural catchments.

How to cite: Taguas, E., Bingner, R. L., Momm, H., Wells, R. R., and Locke, M.: Evaluation of olive grove management on various soils at the micro-catchment scale with the AnnAGNPS model to quantify their impacts on organic carbon , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13427, https://doi.org/10.5194/egusphere-egu2020-13427, 2020.

SSS2.8 – Soil Erosion and Conservation

EGU2020-18653 | Displays | SSS2.8

Cycles of gully incision and infill in agricultural landscapes of Central European Russia: natural and anthropogenic factors

Yulia Kuznetsova, Vladimir Belyaev, Sergey Kharchenko, and Anna Semochkina

Gullies are traditionally considered as one of the most active landforms in agricultural areas. In many places gully erosion leads to massive loss of fertile soil, decline of areas available for cultivation and a number of other land use complications. In addition, gullies in many cases act as the most effective runoff and sediment routing pathways, promoting better connectivity and increasing sediment delivery from cultivated hillslopes into fluvial network. Hence, gully network development may also cause significant detrimental off-site effects, including small river degradation, reservoir siltation, particle-bound pollutants concentration, etc. On the other hand, this process is often not progressive and unidirectional, but rather includes cycles of incision and head retreat alternating with infill periods. Understanding this dynamics and knowing its control factors may help to predict the future process trends for different climate and land use change scenarios, save fragile soil and water resources and design sustainable agricultural activity in changing environment.

We analyzed five different small river basins in Central European Russia to investigate the cycles of gully growth and infill. The main approach was to acquire gully network structure from topographic maps or by manual visual interpretation of satellite images. A set of topographic maps was used to map the spatial structure of gullies over the case study areas for several time intervals from mid XIX century to the end of XX century. In addition, recent satellite images were used to investigate the up-to-date (2018-2019) gully network structure and distinguish its possible latest changes related to climate or land use changes.

It is common to consider agriculture as the main factor of gully erosion activation in this area. We found that land use changes over the last 150 years lead not only to erosion rates shifts, but to incision and infill cycles. Besides, morphometric parameters of individual gullies, spatial patterns of gully network and gully density within different catchments strongly depend on local topography. Particularly important controls are topographic ranges, long profile and planform shapes of catchment slopes. Recent studies also showed that planform structure of upper parts of gully network (especially small tributary gullies of larger gully systems), as well as smooth slope depressions and periodically formed ephemeral gullies on cultivated hillslopes are in many cases strongly related to relic cryogenic features (RCF) of the Late Pleistocene cold stages. Evidence of partly infilled gullies incised into the RCFs such as ice or ice-ground wedge pseudomorphs are widely observed both on satellite and airborne images and in natural (undercut gully or small valley banks) or anthropogenic (quarries) exposures.

Interaction of climatic impact, intrinsic gully headcut retreat threshold and recent land use changes determine modern gully network conditions. The main presently observed tendency is stabilization or gradual infill of most of the small- and medium-sized gullies by sediments transported by sheet wash, rill and ephemeral gully erosion from arable fields. At the same time, small discontinuous bottom gullies are developed in larger gully systems.

This study is supported by the Russian Foundation for Basic Research (Project No. 18-05-01118a).

How to cite: Kuznetsova, Y., Belyaev, V., Kharchenko, S., and Semochkina, A.: Cycles of gully incision and infill in agricultural landscapes of Central European Russia: natural and anthropogenic factors, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18653, https://doi.org/10.5194/egusphere-egu2020-18653, 2020.

EGU2020-12909 | Displays | SSS2.8 | Highlight

Development of Web GIS based Surface Soil Erosion Prediction System

Dongjun Lee, Jae E Yang, Kyoung Jae Lim, Jonggun Kim, and Won Seok Jang

This study is to develop the Web GIS-based surface soil erosion prediction system that informs soil information such as daily potential soil erosion, soil quality, and best management practices (BMPs). The system involves three functions that are: 1) to predict daily potential soil erosion in the study areas (e.g., Jaun-Cheon, Bukhan-Gang, Namhan-Gang, and Gyoungan-Cheon); 2) to provide the current levels of soil qualities at field scale; 3) to recommend BMPs which can improve soil qualities. This study developed a module based on MUSLE and assessed the availability of the module comparing with the measured data at sample fields (3%, 9% slope). After verification of the module, the Web GIS-based system was developed using a user-friendly interface. The users can obtain the visualized soil erosion information through the interface and compare the amount of soil erosion using the single field or multi-fields analysis tool developed in this study. Moreover, the users can find the current level of soil qualities at fields they selected and gain various applicable BMPs information. The system enables to inform non-experts to soil information without using a complex model and equation. Therefore, the system can play a significant role in recognizing the importance of soil resources and enacting laws relative to soil conservation.

How to cite: Lee, D., Yang, J. E., Lim, K. J., Kim, J., and Jang, W. S.: Development of Web GIS based Surface Soil Erosion Prediction System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12909, https://doi.org/10.5194/egusphere-egu2020-12909, 2020.

EGU2020-21695 | Displays | SSS2.8

Soil erosion in Austria – National calculations using regional data delivering local results for the ÖPUL programme

Elmar Schmaltz, Georg Dersch, Christine Weinberger, Carmen Krammer, and Peter Strauss

Empirical models, such as the Revised Universal Soil Loss Equation (RUSLE) are in use since the 1950s to estimate the mean annual soil loss for single agricultural fields or spatially-distributed for larger areas (municipalities, regions or states). A particular focus on the computation of the RUSLE lies in the calculation of the respective factors on which the equation is built on and represent the erosivity of rainfall events, the erodibility of soils, the topography and land management. However, the RUSLE is highly susceptible to large errors in the prediction of the erosion rates of single agricultural parcels, due to the high variability of these factors in large areas (e.g. on national scale).

In this study, we present a parcel-sharp erosion map for the entire territory of Austria. We discuss frequent error sources of the factor computations and their consequences for the representativeness of erosion maps at nation-scale. Based on our results we discuss furthermore regional erosion hotspots and evaluate nationally funded management practices for soil erosion reduction as they are defined in the Austrian programme for an environmentally responsible agriculture (ÖPUL).

Since our approach depicts a novelty for Austria, we further describe opportunities for analysis of our results and highlight potential sources of errors, as well as regional and legal discrepancies of the distribution of national funds for soil conservation.

How to cite: Schmaltz, E., Dersch, G., Weinberger, C., Krammer, C., and Strauss, P.: Soil erosion in Austria – National calculations using regional data delivering local results for the ÖPUL programme, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21695, https://doi.org/10.5194/egusphere-egu2020-21695, 2020.

Climate models project increased extreme precipitation for the coming decades, which may lead to higher soil erosion in many locations worldwide. The impact of climate change on soil erosion is most often assessed by applying a soil erosion model forced by bias-corrected climate model output. A literature review among more than 100 papers showed that many studies use different soil erosion models, bias-correction methods and climate model ensembles. In this study, we assessed how these differences affect the outcome of climate change impact assessments on soil erosion. The study was performed in two contrasting Mediterranean catchments (SE Spain), where climate change is projected to lead to a decrease in annual precipitation sum and an increase in extreme precipitation, based on the RCP8.5 emission scenario. First, we assessed the impact of soil erosion model selection using the three most widely used model concepts, i.e. a model forced by precipitation (RUSLE), a model forced by runoff (MUSLE), and a model forced by precipitation and runoff (MMF). Depending on the model, soil erosion in the study area is projected to decrease (RUSLE) or increase (MUSLE and MMF). The differences between the model projections are inherently a result of their model conceptualization, such as a decrease of soil loss due to decreased annual precipitation sum (RUSLE) and an increase of soil loss due to increased extreme precipitation and, consequently, increased runoff (MUSLE). An intermediate result is obtained with MMF, where a projected decrease in detachment by raindrop impact is counteracted by a projected increase in detachment by runoff. Second, we evaluated the implications of three bias‐correction methods, i.e. delta change, quantile mapping and scaled distribution mapping. Scaled distribution mapping best reproduces the raw climate change signal, in particular for extreme precipitation. Depending on the bias‐correction method, soil erosion is projected to decrease (delta change) or increase (quantile mapping and scaled distribution mapping). Finally, we assessed the effect of climate model ensembles on soil erosion projections. We showed that individual climate models may project opposite changes with respect to the ensemble average, hence, climate model ensembles are essential in soil erosion impact assessments to account for climate model uncertainty. We conclude that in climate change impact assessments it is important to select a soil erosion model that is forced by both precipitation and runoff, which under climate change may have a contrasting effect on soil erosion. Furthermore, the impact of climate change on soil erosion can only accurately be assessed with a bias‐correction method that best reproduces the projected climate change signal, in combination with a representative ensemble of climate models.

How to cite: de Vente, J. and Eekhout, J.: The implications of soil erosion model conceptualization, bias-correction methods and climate model ensembles on soil erosion projections under climate change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8158, https://doi.org/10.5194/egusphere-egu2020-8158, 2020.

EGU2020-1432 | Displays | SSS2.8

Erosion assessment in the desertification site of Gilbues, Brazil

José Carlos de Araújo, Antonio Álisson Simplício, Francisco Jairo Pereira, and Carlos Alexandre Gomes Costa

The Gilbués Desertification Site (GDS) is an 8,000-km² area located in the Northeast of Brazil. It comprises large continuous areas with deep (up to 30 m), wide (up to 50 m), and long (up to 6 km) gullies, as well as severe inter-rill erosion. Inside the GDS there is an experimental site, in which almost 100 check dams were constructed a decade ago to assess their feasibility as a soil-restoration initiative. For two years (2018 and 2019) we have monitored a 15-ha watershed that contains 52 check dams so as to estimate the main erosion-related parameters as well as to assess the effectiveness of the check dams. The monitoring program consisted of (i) a climate station; (ii) four hillslopes with pins every m², measured monthly to quantify gross erosion; (iii) five flights with an accurate unmanned aerial vehicle (UAV) to identify the siltation of the check dams and to parameterize the rainfall-runoff behavior; (iv) 92 soil samples in the hillslopes and inside the check dams; and (v) four infiltration experiments. The results show that (i) the gross erosion is 8 mm.yr-1, or 10² Mg.ha-1.yr-1, a value ten times higher than the region average; (ii) based on the silting of the check dams, the sediment yield averaged 85 Mg.ha-1.yr-1, 20 times higher than the regional mean value, which is partially explained by the small size of the watersheds (10²-10³ m²); (iii) the Wischmeier vegetation C factor is 0.9, showing high degree of vegetative-cover degradation; and (iv) the sediment delivery ratio was 0.8, which could be satisfactorily represented by the Maner equation. These results show that, although the GDS corresponds to only 10% of the Boa Esperança (5,000 hm³) hydroelectric power plant basin, it may cause 60% of the reservoir silting. The GDS soil has also shown specific properties: 71% of the soil mass has a diameter of ~ 0.1 mm; there is a high rate of open macro-pores when the soil is dry (they close shortly after a moderate rainfall event ~ 40 mm); and it is prone to form gravel-like particles that silt in the reservoir delta (despite its fine diameter). Last, we observed that the check dams – as they were built – are not a sustainable solution: after a decade, nearly 10% are spilling due to the high siltation rates, causing dam-wall erosion and instability; and three dams have presented piping, with discharges (0.2 – 0.7 L.s-1) one thousand times higher than the expected percolation flow through the dams.

How to cite: de Araújo, J. C., Simplício, A. Á., Pereira, F. J., and Gomes Costa, C. A.: Erosion assessment in the desertification site of Gilbues, Brazil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1432, https://doi.org/10.5194/egusphere-egu2020-1432, 2020.

EGU2020-9571 | Displays | SSS2.8

Variance based sensitivity analysis of the RUSLE model in the E.U. parameter space

Enrico Balugani, Andrea Rava, and Diego Marazza

Soil degradation through erosion is a major issue on a global scale, especially as the pressure on soils increases with increasing population, changing diets, and increase in land use changes. Measurements are plot specific and expensive, so most of the erosion assessment are done through modelling. The most used model for estimating soil water erosion worldwide is the Revised Universal Soil Loss Equation (RUSLE), which is an “ensemble” model with semi-empirical factors that can be determined using different equations, depending on scale of interest, geographical location, data availability. The –joint Research Centre (JRC) uses RUSLE to estimate water erosion potential in EU using spatial datasets collected by the European Soil Data Centre (ESDAC), as explained in a series of published articles. Model sensitivity analyses are a powerful tool for analysts and policy makers, especially for empirical and semi-empirical models like RUSLE, to assess model robustness, factor prioritization, and variance cutting. A sensitivity analysis was conducted on RUSLE by Estrada-Carmona et al. (2017) on a global (dishomogenous) parameter space using a Random Forest approach to calculate the relative relevance index. However, sensitivity analyses are dependent on the extent of the parameter space analysed and, especially for non-linear non-additive models like RUSLE, variance based methods are usually preferred.

Therefore, we performed a global sensitivity analysis of the RUSLE model as used by the JRC, using variance based methods and over the parameter space of the EU. The objective were to: (a) check the robustness of RUSLE in the EU parameter space, (b) define the most relevant factors on which to concentrate the attention (policy assessment) and (c) assess the interaction between these factors.

We analysed the spatial data provided by ESDAC to define the probability distribution of the model factors (the parameter space). We then sampled the parameter space with a low-discrepancy method and run the model on the whole dataset. We used the model output to: (a) plot the behaviour of the model to changes in single factors with scatterplots, (b) calculate the variance sensitivity index first order, (c) calculate the total sensitivity order, (d) analyse the relevant interactions between factors, first looking at the sensitivity indices, then using visual methods to show the model behaviour.

The results show that the C factor has the greater influence on the erosion estimates, followed by R and Kst, accounting for ~0.35, ~0.21 and ~0.0.04 of the erosion estimates variance, respectively. This is especially interesting, since it is possible to act on C and, hence, control erosion processes. The dependence on R, however, is troubling, since its average value will probably increase in time due to climate change. Kst can be affected only partially by increasing soil organic matter or soil stoniness. The analysis of the total effects show that C, R and Kst are all interacting between them. The P factor seems hardly relevant at this scale, hence it could be simply fixed, something already done in some studies, e.g. Gianinetto et al. 2019.

How to cite: Balugani, E., Rava, A., and Marazza, D.: Variance based sensitivity analysis of the RUSLE model in the E.U. parameter space, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9571, https://doi.org/10.5194/egusphere-egu2020-9571, 2020.

EGU2020-17768 | Displays | SSS2.8

Erosion effects on soil carbon and nutrient distribution: a meta-analysis

Maire Holz and Jürgen Augustin

Soil erosion has for a long time been considered as a process causing soil organic matter (SOM) loss, however, recent studies pointed out that erosion may increase soil carbon sequestration because only 10-30% of eroded topsoil material is transported into water bodies while the remaining 70-90% are transported in depositional settings. Soil erosion leads to variation in topsoil thickness and soil characteristics and leads to two different main types of erosion states develop along hillslope: the eroding and the depositional landform position. Disruption of aggregates and the transport of soil during erosion, likely leads to SOM loss in the eroding slope. In contrast, after deposition, the eroded material can be protected if it is incorporated into soil aggregates or sorbed to mineral surfaces, leading to an increase in SOM in the depositional landform position.

So far, there has been no study evaluating literature results on the effect of erosion on carbon and nutrient distribution in soils. We therefore reviewed the literature for the influence of erosion on carbon/nutrient contents and stocks in erosion affected landscapes. While 32 studies reported results on the enrichment of eroding sediments in carbon (C), nitrogen (N) and phosphorus (P), 39 studies reported results on carbon/nutrient contents and stocks in erosion affected landscapes.

The average C enrichment ratio (sediment C/soil C) was 1.56 while N enrichment ratio was 1.54 and P-enrichment ratio was 1.77. This indicates that the fine soil fractions, that carbon and nutrients are mostly associated to, were preferentially moved during soil erosion. High element contents in the original soils, resulted in relatively low enrichment ratios which may allow the conclusion that in low C- and nutrient soils, a relatively high portion of the elements are stored in the fine soil fraction. C and N enrichment ratios showed a significant positive relation (R2=0.61), pointing to the strong ecological link of both elements.

Carbon and nutrient contents were comparable for all landscape positons (upslope, backslope, footslope, depositional). This indicates that carbon and nutrients, lost during an erosion event, are replenished relatively fast in the eroded slopes. In contrast, erosion induced C, N and P stocks increased from the upper towards the depositional soil site, resulting in a 1.6, a 1.4 and 2.2 time increase in C, N and P stocks for the depositional site, compared to the upslope position.

In conclusion, this meta-analysis indicates that carbon and nutrients are preferentially moved during soil erosion which might lead to loss in soil fertility and crop productivity after erosion events. However, similar C and nutrient contents along hillslopes indicate that elements are replenished relatively fast in eroded soils after the occurrence of an erosion event. Increased soil stocks toward the depositional site can therefore be explained by increased soil depths in lower hillslope positions. Changes in soil depth, rather than changes in C and nutrient contents are therefore more likely to explain soil fertility losses in eroding slopes compared to depositional sites.

 

How to cite: Holz, M. and Augustin, J.: Erosion effects on soil carbon and nutrient distribution: a meta-analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17768, https://doi.org/10.5194/egusphere-egu2020-17768, 2020.

EGU2020-5103 | Displays | SSS2.8

Splash erosion experiments with silt loam and loamy sand soil under simulated rainfall produced by two types of rainfall simulators

Nives Zambon, Lisbeth Lolk Johannsen, Peter Strauss, Tomáš Dostál, David Zumr, Thomas A. Cochrane, and Andreas Klik

Soil erosion by water is globally the main soil degradation process which leaves serious consequences on agricultural land and water aquifers. Splash erosion is the initial stage of soil erosion by water, resulting from the destructive force of rain drops acting on soil surface aggregates. Splash erosion studies conducted in laboratories use rainfall simulators. They produce artificial rainfall which can vary according to type of the rainfall simulator. In this study the aim was to quantify the differences in splash erosion rates affected by rainfall produced by two different rainfall simulators on two silt loam and one loamy sand soil. Splash erosion was measured using modified Morgan splash cups and the rainfall simulators were equipped with four VeeJet or one FullJet nozzle. The soil samples placed under simulated rainfall were exposed to intensity range from 28 to 54 mm h-1 and from 35 to 81 mm h-1, depending on the rainfall simulator. Rainfall characteristics such as drop size and velocity distribution were measured with an optical laser disdrometer Weather Sensor OTT Parsivel Version 1 (Parsivel) by OTT Messtechnik. Rainfall simulator with VeeJet nozzles produced smaller drops but higher drop velocity which resulted in higher kinetic energy per mm of rainfall compared to rainfall simulator with FullJet nozzles. For the same intensity rate measured kinetic energy under the rainfall simulator with VeeJet nozzles was 45% higher than rainfall kinetic energy from rainfall simulator with FullJet nozzles. Accordingly, the average splash erosion rate was 45 and 59% higher under the rainfall simulator with VeeJet nozzles for one silt loam and loamy sand soil, respectively. Splash erosion was found to be a linear or power function of the rainfall kinetic energy, depending on rainfall simulator. The obtained results highlight the sensitivity of the splash erosion process to rainfall characteristics produced by different rainfall simulators. The heterogeneity of rainfall characteristics between different types of rainfall simulators makes a direct comparison of results obtained from similar erosion studies difficult. Further experiments including comparison between more rainfall simulators could define influencing rainfall parameters on splash erosion under controlled laboratory conditions.

How to cite: Zambon, N., Lolk Johannsen, L., Strauss, P., Dostál, T., Zumr, D., A. Cochrane, T., and Klik, A.: Splash erosion experiments with silt loam and loamy sand soil under simulated rainfall produced by two types of rainfall simulators , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5103, https://doi.org/10.5194/egusphere-egu2020-5103, 2020.

EGU2020-3689 | Displays | SSS2.8 | Highlight

SOiLUTION SYSTEM: innovative solutions for soil erosion risk mitigation and better management of vineyards in hills and mountain landscapes

Paolo Tarolli, Eugenio Straffelini, Chiara Maria Mattiello, and Aldo Lorenzoni

Cultivating in high-steep slope hilly and mountainous landscapes, requires a great effort in terms of economic and human resources, especially if the territory is particularly complex from a geomorphological point of view and historically affected by landslides such as the Italian peninsula. This fragility is also combined with two other factors. The first is linked to agricultural mechanization, which causes soil compaction and a consequent alteration of its draining capacity. The second is related to climate change, responsible for an increase of extreme rainfall events characterized by intense, shorter and localized precipitations. The combination of these elements makes agricultural terraced landscapes at risk and prestigious vineyards, particularly important for historical, cultural, landscaping and economic reasons, increasingly sensitive to soil erosion processes.

In response to these problems, the project SOiLUTION SYSTEM is proposed (www.soilutionsystem.com),  aiming to identify an integrated system of environmentally and economically sustainable interventions able to reduce the risk of erosion and improve soil management in the terraced area of Soave (Veneto region), one of the two Italian GIAHS-FAO site. Indeed, in such terraced areas, the hydrogeological risk is high due to the steep-slope where heroic vineyards are cultivated. The project is also focused on multidisciplinary, capable of combining expertise from the academic world, farmers and other stakeholders, in order to promote a sustainable production approach to ensure greater soil resilience, as well as to protect biodiversity.

In the first phase, several terraced study areas historically threatened by erosion have been selected. Within them were organized topographic surveys using a low-cost commercial drone in combination with an RTK-GPS for the 3D reconstruction of the terrain using the Structure-From-Motion photogrammetric technique. The point cloud obtained was subsequently processed, filtered and interpolated in order to create high-resolution digital terrain models (DTM) with cells of resolution less than 50cm. Based on the obtained data, some geomorphological indicators were calculated to identify areas potentially susceptible to erosion. In order then to understand the processes that take place at a larger scale than the single areas detected by drone, geomorphological analyses were also performed on a 1m DTM elaborated from airborne LIDAR data, granted by the Italian Ministry for Environment, Land and Sea (MATTM).

The goals of the project are 1) to provide innovative survey techniques using low-cost commercial drone to better understand erosion processes in vineyards; 2) to install innovative tools for the monitoring of surface runoff in the field; 3) to test new mechanization prototypes with low impact on the soil and able to work on steep slopes; 4) to provide an innovative technique for the consolidation of dry stone walls; 5) to introduce the “conservative agriculture” for improving soil management; 6) to analyze the role of native herbaceous species as grass cover in erosion reduction; 7) to evaluate the efficiency of the proposed management model in considering biodiversity conservation purposes.

How to cite: Tarolli, P., Straffelini, E., Mattiello, C. M., and Lorenzoni, A.: SOiLUTION SYSTEM: innovative solutions for soil erosion risk mitigation and better management of vineyards in hills and mountain landscapes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3689, https://doi.org/10.5194/egusphere-egu2020-3689, 2020.

EGU2020-1471 | Displays | SSS2.8

Gully erosion susceptibility modelling for avoided degradation planning

Jay Le Roux and Bennie Van der Waal

Gully erosion can reach alarming dimensions and contribute significantly to soil loss and sediment yield in a catchment.  Since restoration resources are usually limited, strategic information on sensitive and erosion susceptible areas are needed to avoid future degradation.  Although the mapping of areas susceptible to gully formation is not a new concept, this study has potential in the Mzimvubu River Catchment, the only large river network in South Africa without a large reservoir.  The Tsitsa tributary’s catchment, where two large reservoirs are planned, consists of large areas of highly erodible soils with widespread gully erosion evident.  It is important to prevent further gully erosion in the catchment due to the presence of duplex and dispersive soils. Therefore, this study modelled areas that are susceptible to gully development in the Tsitsa River Catchment, as well as estimated the sediment yield potential from the susceptible areas if gully development occurs.  This was achieved by mapping gully-free areas in a GIS that have the same DEM-derived topographical variables, soil associations and land cover than gullied areas, followed by scenario analysis of the potential sediment yield.  More than 30 000 ha (7%) of the catchment is intrinsically susceptible to further gully development, consisting of drainage paths with a large contributing area and erodible duplex soils.  If not protected, these susceptible areas could contribute an additional 300 million m3 of sediment to the river network, reducing the volumes of both reservoirs by more than 50%. 

How to cite: Le Roux, J. and Van der Waal, B.: Gully erosion susceptibility modelling for avoided degradation planning, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1471, https://doi.org/10.5194/egusphere-egu2020-1471, 2020.

EGU2020-9285 | Displays | SSS2.8 | Highlight

A first data-driven gully head density map of the world

Matthias Vanmaercke, Yixian Chen, Sofie De Geeter, Jean Poesen, and Benjamin Campforts

Gully erosion has been recognized as a main driver of soil erosion and land degradation. While numerous studies have focussed on understanding gully erosion at local scales, we have very little insights into the patterns and controlling factors of gully erosion at a global scale. Overall, this process remains notoriously difficult to simulate and predict. A main reason for this is that the complex and threshold-dependent nature of gully formation leads to very high data requirements when aiming to simulate this process over larger areas.

Here we help bridging this gap by presenting the first data-driven analysis of gully head densities at a global scale.  We developed a grid-based scoring method that allows to quickly assess the range of gully head densities in a given area based on Google Earth imagery. Using this approach, we constructed a global database of mapped gully head densities for currently >7400 sites worldwide. Based on this dataset and globally available data layers on relevant environmental factors (topography, soil characteristics, land use) we explored which factors are dominant in explaining global patterns of gully head densities and propose a first global gully head density map.

Our results indicate that there are ca. 1.7 to 2 billion gully heads worldwide. This estimate might underestimate the actual numbers of gully heads since ephemeral gullies (in cropland) and gullies under forest remain difficult to map. Our database and analyses further reveal clear regional patterns in the presence of gullies. Around 27% of the terrestrial surface (excluding Antarctica and Greenland) has a density of > 1 gully head/km², while an estimated 14% has a density of > 10 gully heads/km² and 4% has even a density of > 100 gully heads/km². Major hotspots (with > 50 gully heads/km²) include the Chinese loess plateau, but also Iran, large parts of the Sahara Desert, the Andes and Madagascar. In addition, gully erosion also frequently occurs (with typical densities of 1-50 gully heads/km²) in the Mid-West USA, the African Rift, SE-Brazil, India, New-Zealand and Australia.

These regional patterns are mainly explained by topography and climate in interaction with vegetation cover. Overall, the highest gully densities occur in regions with some topography and a (semi-)arid climate. Nonetheless, it is important to point out that not all gully heads are still actively retreating. Building on earlier insights into the magnitude and controlling factors of gully head retreat rates, we explore what our current results imply for assessing actual gully erosion rates at a global scale.

How to cite: Vanmaercke, M., Chen, Y., De Geeter, S., Poesen, J., and Campforts, B.: A first data-driven gully head density map of the world, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9285, https://doi.org/10.5194/egusphere-egu2020-9285, 2020.

EGU2020-3536 | Displays | SSS2.8 | Highlight

Desertification and Development: some broader contexts

Mike Kirkby

The dominant direct physical processes responsible for desertification are water erosion, wind erosion and salinization.  Other threats that degrade the soil  include loss of biodiversity, loss of soil organic matter, fire, changing water resources, soil compaction, soil sealing and contamination. Soil management inevitably combines  human and physical effects.  Climate, which is the most important driver of the physical systems, is now being rapidly modified by human action, and at a scale which is much coarser than any local remedial action. 

  

In a model of near-subsistence systems, productivity is limited by climate and available labour, with some options for additional inputs through improved seed, fertilizer or tillage equipment. Optimum solutions in a particular environment depend on both climate and access to markets.  Agricultural surpluses, if any, allow investment in infrastructure – some of it directly  supporting agriculture through irrigation and market systems, some less directly useful through, for example, warfare or pyramid building.

 

Today some traditional drivers of desertification may no longer be relevant, as land, particularly in the global South, is grabbed for intensive irrigated farming, and populations move into mega-cities. The dominant drivers may become soil sealing around cities and transfers of urban and irrigation water.  In semi-arid areas this will lead to competition for the best land – for urban expansion and agricultural land with irrigation potential.  Desertification then becomes an issue increasingly focussed on abandoned marginal land, maintaining biodiversity, managing regional water resources and controlling erosion in the face of global climate change.

How to cite: Kirkby, M.: Desertification and Development: some broader contexts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3536, https://doi.org/10.5194/egusphere-egu2020-3536, 2020.

EGU2020-12814 | Displays | SSS2.8

The joint application of digital modeling and field soil survey data for improvement of the accuracy in soil erosion mapping

Andrey Zhidkin, Mikhail Komissarov, and Evgeny Zazdravnykh

We used the data from field surveys with more than 2500 soil sampling points at 4 research sites in various regions of Russia. The study sites are located in the European part of Russia in the most contrasting physical-geographical and socio-historical conditions of soil erosion: in the Moscow, Kursk, Belgorod regions and in the Republic of Bashkortostan. The digital modeling was carried out with using of the WATEM / SEDEM model based on digital elevation models of detailed scale (1:10 000) on a total area more than 2000 km2. An analysis of the sediment balance in small catchments showed, that the digital modeling of soil erosion (in case of a certain quality level of input parameters) at an acceptable level reflects on the average long-term erosion rates in the valley-beam relief. The authors developed an original method in soil erosion mapping. It consists in revealing statistical relationships between the calculated erosion rates by WATEM / SEDEM model and the actual data of soils humus horizons thicknesses. Based on these dependencies, the probability of participation of soils with varying degrees on erosion in each pixel is calculated.

The specific in formation of soil erosion at the Moscow region is largely due to the complex stage history of agricultural land development. For this key site, a detailed study of historical maps was carried out (with digitization in the GIS of the sites boundaries with a different land use history) for 8 periods, starting from 1797 to the present. Also, the history of crop rotation was studied in detail. Based on the analysis of maps and digital modeling of erosion-accumulation processes in this territory, a very high dynamics of arable land and soil erosion over the past few centuries was revealed, which significantly influenced on the formation of soil cover. At research sites in the Belgorod and Kursk regions, the features in formation of erosion-accumulative soil cover structures are due to the large area of agricultural land development. The comparison of soil cover erosion maps produced in accordance to the traditional method and the author’s approach is revealed a high convergence of results and the perspective of digital modeling using. The indisputable advantage of the digital method is the ability to formalize the procedure for assessing soil erosion, minimizing the contribution of subjective factors. Detailed studies in the Republic of Bashkortostan revealed the features in the formation of soil erosion  due to the developed denudation processes and karst microrelief. A detailed mapping of the soil cover and topographic mapping of the relief in key areas was carried out. It was revealed, that the using of a digital elevation model with very high accuracy (scale 1: 1000 and higher) allows to qualitatively simulate and estimate the rates of erosion and accumulation even in conditions of pronounced karst microrelief.

Acknowledgement
This research was supported by the Russian Foundation for Basic Research (RFBR) within the scientific project No. 18–35–20011.

 

How to cite: Zhidkin, A., Komissarov, M., and Zazdravnykh, E.: The joint application of digital modeling and field soil survey data for improvement of the accuracy in soil erosion mapping, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12814, https://doi.org/10.5194/egusphere-egu2020-12814, 2020.

EGU2020-7985 | Displays | SSS2.8

Fluidized-bed: As an alternative method for rill erodibility modeling

Selen Deviren Saygin, Fikret Ari, Cagla Temiz, Sefika Arslan, Mehmet Altay Unal, and Gunay Erpul

Rill erodibility (Kr), which is a measure of the resistance of soil particles against disintegration in a rill under concentrated flow conditions, is a significant characteristic for rill initiation in a field.  The Process-based WEPP (Water Erosion Prediction Project) originally models Kr by linear excess shear stress (τ), and it is mostly obtained from mini-flume experiments at laboratory conditions. Alternatively, a critical value of flow stress (τcr) that points to fragmentation in rills can be modeled by a fluidized bed approach that quantifies the conditions in terms of cohesion (Co) and flow velocity (Vf) by considering the soil as a cohesive material. In there, the water as a fluid applies pressure on solid particle proportional to flow rate of the fluid (v). But, performed related studies on it were mostly tested for the limited soil types. The objectives of this study were to test these relationships and model the rill characteristic for the heavy textures of different soil types and investigate the role of basic soil properties on rill initiation. Experimental results showed that the stronger regression coefficient (R2=0.78) was found between Kr and flow velocity (Vf) monitored at the fluidization stage than that between Co & τcr at the studied soil conditions. However, correlations between constant and dynamic soil properties and the measured Kr, τcr, Co and Vf values were also quite remarkable (p<0.01) for next-generation modeling studies in terms of rill dynamics. It is believed that the fluidized-bed approach has a great potential to model Kr and encouragingly it is worth to be tested with wider data-sets under different soil-moisture conditions.

Keywords: Rill erodibility, Soil Cohesion, Fluidized bed approach, WEPP

How to cite: Deviren Saygin, S., Ari, F., Temiz, C., Arslan, S., Unal, M. A., and Erpul, G.: Fluidized-bed: As an alternative method for rill erodibility modeling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7985, https://doi.org/10.5194/egusphere-egu2020-7985, 2020.

Over the last two decades, geospatial technologies such as Geographic Information System and spatial interpolation methods have facilitated the development of increasingly accurate spatially explicit assessments of soil erosion. Despite these advances, current modelling approaches in Europe rest on (i) an insufficient definition of the proportion of arable land that is exploited for crop production, (ii) a neglect of the intra‐annual variability of soil cover conditions in arable land, and (iii) offer little understanding of the spatio-temporal trends of soil erosion. Here, we represent the recent developments of two methods tested to overcome current limitations and move towards the implementation of new modelling approaches in Europe.

The Object-oriented Soil Erosion Modelling and Monitoring v2.0 (O-SEMM) (Land degradation & development, 29, 1270-1281, 2018) combines highly accurate agricultural parcel information systems (LPIS) with crop statistics, Landsat 8 and Sentinel 2 satellite data and high temporal resolution rainfall data to assess soil erosion events at parcel level.

The Daily Erosion Project (DEP) (Earth Surface Processes and Landforms, 43, 1105-1117, 2018), developed by the Iowa State University, estimates soil erosion and water runoff occurring on hill slopes using the WEPP erosion prediction model.

References

Borrelli, P., Meusburger, K., Ballabio, C., Panagos, P., & Alewell, C. (2018). Object‐oriented soil erosion modelling: A possible paradigm shift from potential to actual risk assessments in agricultural environments. Land degradation & development, 29(4), 1270-1281.

Gelder, B., Sklenar, T., James, D., Herzmann, D., Cruse, R., Gesch, K., & Laflen, J. (2018). The Daily Erosion Project–daily estimates of water runoff, soil detachment, and erosion. Earth Surface Processes and Landforms, 43(5), 1105-1117.

How to cite: Borrelli, P., Cruse, R., Gelder, B., and Panagos, P.: Object‐oriented Soil Erosion Modelling and Daily Erosion Project: Laying the foundation for a new generation of soil erosion assessments in Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13575, https://doi.org/10.5194/egusphere-egu2020-13575, 2020.

Soil erosion by water is a serious problem in the coastal region of Syria. Annually, a hundred tons of soil are eroded from different ecosystems in the study area. Recently, The USDA-WEPP (Water Erosion Prediction Project erosion model) was widely used to estimate soil loss by water erosion. Unfortunately, detailed studies about the WEPP-model performance in the eastern Mediterranean in general and Syria, in particular, are still lacking. Within this context, this research undertook an assessment of the WEPP-model performance in the coastal region of Syria.

The study area is characterized by complex topography (slope ranges between 2% and 45%), heavy precipitation within short time intervals, and mixed land cover. On other hand, the most exposed ecosystems to soil erosion are agricultural (AG), burned forest (BF) and forest (FO). For this reason, experimental plots with 3 replicants in 9 different representative locations for each ecosystem were set up (81 experimental plots in total) to measure soil erosion by water. In the next step, the WEPP input files were prepared and run for each location. Finally, the WEPP performance was tested by using four statistical indexes: Pearson's correlation coefficient (r), the Nash-Sutcliffe coefficient (NSE), the percent bias (PBIAS), and RSR (the ratio of root mean square error (RMSE) to the standard deviation of the measured data).

The results showed that observed soil erosion ranges between 32 ton/h/year and 165 ton/h/year in the AG, while it ranges from 3 ton/h/year to 8 ton/h/year in the FO. Similarly, WEPP results range between 32 ton/h/year and 152 ton/h/year in the AG, while they range from 1.4 ton/h/year to 15 ton/h/year in the FO. The model performance showed a good agreement between measured and estimated values for AG systems (R =0.96, NSE=0.84; RSR=0.39; PBAIS=13.05), and a less satisfactory one for both forest and burned forest.

How to cite: Mohammed, S.: Sediment Yield Modeling in The Coastal Region of Syria Using the WEPP-Model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-97, https://doi.org/10.5194/egusphere-egu2020-97, 2020.

EGU2020-217 | Displays | SSS2.8

Adopting soil properties of compacted tramlines into soil erosion modelling: A field-scale approach

Philipp Saggau, Michael Kuhwald, and Rainer Duttmann

Soil erosion by water is recognized as the most threatening land degradation process worldwide, reducing natural soil fertility and productivity especially on arable land. Despite advances in soil erosion modelling, one major process, which is rarely investigated, is the effect of soil compaction from field management induced wheel tracks. However, tramlines noticeably contribute to the amount of soil eroded inside a field. To quantify these effects we incorporate high-resolution spatial tramline data into modelling. For simulation, we used the process-based soil erosion model EROSION3D, which has been applied on different fields for a single rainfall event. Model results were compared against measured soil loss. Our investigation showed that i) grid-based models like E3D are able to integrate tramlines, ii) the share of measured erosion between tramline and cultivated areas fits well with measurements for resolution ≤ 1 m, iii) tramline erosion showed a high dependency to the slope angle and iv) soil loss and runoff are generated quicker within tramlines during the erosion event. The results indicate that the integration of tramlines in soil erosion modelling improves the spatial prediction accuracy, and therefore, can be important for soil conservation planning.

How to cite: Saggau, P., Kuhwald, M., and Duttmann, R.: Adopting soil properties of compacted tramlines into soil erosion modelling: A field-scale approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-217, https://doi.org/10.5194/egusphere-egu2020-217, 2020.

EGU2020-793 | Displays | SSS2.8

Mechanical Properties of Native Tree Species for Soil Bioengineering in Northeastern Mexico

Rebeca Zavala, Israel Cantú, Laura Sánchez, Humberto González, Eduardo Estrada, and Tetsuya Kubota

In recent years, the effect of soil bioengineering has played a very important role on slope stability. However, our area of study is constantly under the influence of small-scale earthquakes and extreme events of heavy rainfall which cause potentially unstable conditions on the slopes. The mechanical properties of the root systems tensile strength (Ts) and modulus of elasticity (Eroot) of four native species were analyzed for a potential use as soil bioengineering elements. We investigated if tensile strength (N/mm2) and modulus of elasticity of roots (N/mm2) was different between studied species: Cercis canadensis, Celtis laevigata, Quercus rysophylla and Ligustrum lucidum. The species considered were selected based on their native characteristics and widespread existence on the slopes. Regarding tree forest species, the tests were conducted with the Universal Testing Machine Shimadzu type SLFL-100KN. The relationships among root diameter, tensile strength (Ts), and modulus of elasticity (Eroot) was negative and could be fitted with a power regression equation, showing highly significant   values p<0.01.Celtis laevigata showed the maximum value of tensile strength (Ts) 28.11 N/mm2 while the minimum value of tensile strength was observed in Ligustrum lucidum 5.27 N/mm2. For the variable modulus of elasticity (Eroot) Celtis laevigata  showed the maximum value of 90.01N/mm2 while the minimum value of modulus of elasticity was observed in Ligustrum lucidum 29.16 N/mm2.Results of mechanical proprieties are showed the following ascending order: Ligustrum lucidum < Quercus rysophylla < Cercis canadensis < Celtis laevigata. Likewise, Celtis laevigata showed the highest tensile strength and modulus of elasticity of all investigated species.

 

Key words: root, tensile strength, modulus or elasticity.

 

 

How to cite: Zavala, R., Cantú, I., Sánchez, L., González, H., Estrada, E., and Kubota, T.: Mechanical Properties of Native Tree Species for Soil Bioengineering in Northeastern Mexico, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-793, https://doi.org/10.5194/egusphere-egu2020-793, 2020.

EGU2020-863 | Displays | SSS2.8

Evaluation of changes in soil erosion rates in Andalucia between 1990 and 2018

Filippo Milazzo, Tom Vanwalleghem, Pilar Fernández, Rebollo, and Jesus Fernández-Habas

Land use and land management changes impact significantly on soil erosion rates. The Mediterranean, and in particular Southern Spain, has been affected by important shifts in the last decades. This area is currently identified as a hotspot for soil erosion by water. In the effort to achieve the SDG Target 15, we aim to show the effect of land management change, assessing soil erosion rate based on historical data. We analyzed the evolution of land use from historical aerial photographs between 1990 and 2018. We then calculated soil erosion with RUSLE. For this, we first determined the distribution frequency of cover-management factors for each land use class, comparing current land use maps with the European Soil Erosion Map (Panagos et al., 2015). Past C factors where then assigned using a Monte Carlo approach, based on the obtained frequency distributions. 

How to cite: Milazzo, F., Vanwalleghem, T., Fernández, Rebollo, P., and Fernández-Habas, J.: Evaluation of changes in soil erosion rates in Andalucia between 1990 and 2018, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-863, https://doi.org/10.5194/egusphere-egu2020-863, 2020.

Digital modeling of soil erosion has been actively developed in recent decades, including for solving practical problems of agriculture. This paper presents a new approach to mapping the degree of erosion of the soil cover based on a detailed retrospective analysis of the history of land use over the last 300 years.

The study site is located in the Moscow region, characterized by a stage history of plowing. The analysis of the boundaries of arable land was carried out using the digitization of maps for 1797, 1860, 1871, 1931, 1954, 1985, 2000 and 2018 years.

Erosion processes were simulated using the WATEM / SEDEM. LS factor was calculated based on a digital elevation model based on the digitized detail topographic map. Soil erodibility factor was calculated according to the formula [1] based on our own analytical data on soil properties (K=0.065–0.090 kg*h*MJ-1mm-1). The rain erosivity factor was taken from the [2]. The crop erosivity factor was taken from regional data, taking into account a detailed analysis of the history of crop rotation.

Soil erosion was calculated for each of 8 periods. Estimated rates were multiplied by the duration of the periods. The soil loss volumes were summarized using the raster calculator. The authors have database of soil surveys at 1567 points. The obtained estimated long-term volumes of soil loss were correlated with the data of a field survey of soils. Based on the obtained dependencies between the calculated soil loss volumes and the field survey data, a map of the erosion soil cover structures was constructed.

In the territory, the volume of soil loss varied from 0.02 tons to 1170 tons. The average volume of soil loss over 300 years was about 63.33 tons. It was revealed that the volume of soil loss is determined not only by the area of ​​arable land, but also by the location and topography of the plowed plots and the composition of crop rotation. The most intense erosion was observed in the first decades after the abolition of serfdom law (after 1860).

Despite the long period of land use, the soil cover of the study area is not very eroded, primarily due to the low erosion potential of the relief. However, the territory is divided into sections, to a different degree, transformed by soil erosion due to plowing of different duration and the composition of crop rotation.

This work was supported by the Russian Foundation for Basic Research (project for young scientists no. 18-35-20011)

[1] Renard K., Foster G., Weesies G., McCool D., Yoder D. (1997) Predicting soil erosion by water: a guide to conservation planning with the Revised Universal Soil Loss Equation (RUSLE). USDA Agriculture Handbook â„–703, 384 p.

[2] Panagos P, Borrelli P, Meusburger K, et al. Global rainfall erosivity assessment based on high-temporal resolution rainfall records. Sci Rep. 2017;7(1):4175.

How to cite: Fomicheva, D. and Zhidkin, A.: Digital modeling of erosion soil cover patterns development over the last 300 years (Moscow region, Russia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-969, https://doi.org/10.5194/egusphere-egu2020-969, 2020.

The magnitude of soil erosion and sediment reduction efficiency of check dams under extreme rainstorms are long-standing concerns. This paper aims to use check dams to deduce the amount of soil erosion under extreme rainstorms in watersheds and to identify the difference of sediment intercepting efficiency of different types of check dams. Based on the sediment deposition of 12 check dams with 100% sediment intercepting efficiency and sub-catchment clustering by taking 12 check dams-controlled catchments as standard separately, the amount of soil erosion caused by an extreme rainstorm event on July 26th, 2017 (named “7·26” extreme rainstorm) was deduced in the Chabagou watershed in the hill and gully region of the Loess Plateau. The differences of sediment intercepting efficiency among check dams in the watershed were analysed according to the field observation 17 check dams. The results showed that the average erosion intensity under the ‘7·26’ extreme rainstorm was approximately 2.03×104 t·km-2, which was 5 times that in the second erosive rainfall in 2017 (4.15×103 t·km-2) and 11-384 times that in 2018 (0.53×102 t·km-2 - 1.81×103 t·km-2). Under the ‘7·26’ extreme rainstorm, the amount of soil erosion in the Chabagou watershed above Caoping hydrological station was 4.20×106 tons. The sediment intercepting efficiencies check dams with drainage canals (including the destroyed check dams) and with drainage culverts was 6.48% and 39.49%, respectively. The total actual sediment amount trapped by the check dam was 1.11×106 tons, accounting for 26.36% of the total soil erosion amount. In contrast, 3.09×106 tons of sediment was inputted to the downstream channel, and the sediment deposition in the channel was 2.23×106 tons, accounting for 53.15% of the total amount of soil erosion. The amount of sediment transport at the hydrological station was 8.60×105 tons. The sediment delivery ratio (SDR) under the “7·26” extreme rainstorm was 0.21. The results indicated that the amount of soil erosion was huge, and the sediment intercepting efficiency of check dams was greatly reduced under extreme rainstorms. It is necessary to strengthen the management and construction technology standards of check dams to improve the sediment intercepting efficiency and flood safety in the watershed.

How to cite: bai, L.: Soil erosion and sediment interception by check dam in watershed under extreme rainstorm on the Loess Plateau, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1227, https://doi.org/10.5194/egusphere-egu2020-1227, 2020.

Although numerous studies have acknowledged that vegetation can reduce erosion, few process-based studies have examined how vegetation cover affect runoff hydraulics and erosion processes. We present field observations of overland flow hydraulics using rainfall simulations in a typical semi-arid area in China. Field plots (5 m × 2 m) were constructed on a loess hillslope (25°), including bare soil plot as control and three plots with planted forage species as treatments—Astragalus adsurgens (A. adsurgens), Medicago sativa (M. sativa) and Cosmos bipinnatus (C. bipinnatus). Both simulated rainfall and simulated rainfall + inflow were applied. Forages reduced soil loss by 55–85% and decreased overland flow rate by 12–37%. Forages significantly increased flow hydraulic resistance expressed by Darcy-Weisbach friction factor by 188–202% and expressed by Manning’s friction factor by 66–75%; and decreased overland flow velocity by 28–30%. The upslope inflow significantly increased overland flow velocity by 67% and stream power by 449%, resulting in increased sediment yield rate by 108%. Erosion rate exhibited a significant linear relationship with stream power. M. sativa exhibited the best in reducing soil loss which probably resulted from its role in reducing stream power. Forages on the downslope performed better at reducing sediment yield than upslope due to decreased rill formation and stream power. The findings contribute to an improved understanding of using vegetation to control water and soil loss and land degradation in semi-arid environments.

How to cite: Li, C. and Pan, C.: Overland runoff erosion dynamics on steep slopes with forages under field simulated rainfall and inflow, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1694, https://doi.org/10.5194/egusphere-egu2020-1694, 2020.

EGU2020-3369 | Displays | SSS2.8

Evaluation of the water storage capacity of soil management practices in basin scale

Zhenyu Lv, Tianling Qin, Hanjiang Nie, and Jianwei Wang

Abstract: Soil management practices, such as Terrace (TE), Contour Ridge (CR), Conservation Tillage (CT), Green Manure (GM) and Straw Mulching (SM), have been widely applied all over the word, due to their positive effects on enhancing Water Storage Capacity (WSC for short) of soil and improving the effectiveness of local precipitation.  However, there are few studies focus on the assessment of WSC of soil management practices in basin scale. In this study, a series of empirical equations for evaluating the WSC of different types of soil management practices were established, based on the fundamental assumption of SCS-CN model, and the geometric parameters of TE and CR. Taking the Sihe River Basin as an example, the current construction area of soil management practices and the potential of the design scenarios were input into the equations, to calculate the existing and potential WSC of various soil management practices. The results show that the construction area of soil management practices in the basin was 679.73 km2 in 2015, and the WSC reached 61.85 Million m3. Thereinto, the WSC of the SM was the largest, which was 19.83 Million m3; that of the GM was the smallest, which was 2.08 Million m3. The total potential construction area of soil management practices in each design scenario was 1797.13 km2. Scenario I gave priority to the TE and the CR construction, the WSC of soil management practices in the basin was 174.84 Million m3, which was 182.68% higher than that of in 2015. The WSC of soil management practices in Scenario II who gave priority to the SM, CT and CR construction, was 171.84 Million m3, which was 177.84% higher than that of in 2015. This research further compared the water storage efficiency of various soil management practices and discussed the uncertainty of the equations. The results could provide some references for integrated soil water management.

How to cite: Lv, Z., Qin, T., Nie, H., and Wang, J.: Evaluation of the water storage capacity of soil management practices in basin scale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3369, https://doi.org/10.5194/egusphere-egu2020-3369, 2020.

The development of karst landforms in southwest China has resulted in surface and underground dual hydrogeological structure. The characteristics of the mechanism of soil erosion and its environmental effects are different from those in non-karst regions. This study aims to monitor sediment load and identify the main sediment source in a typical karst plateau agroforestry catchment, to estimate the relative contribution rates of surface and underground river sediment sources. The results show that the annual sediment transport modulus in catchment is very low (5.1 Mg km-2 a-1) in this carbonate agroforestry catchment compare to deforestation 20 years ago (20 Mg km-2 a-1). Sediment Fluxes in the underground river and surface river account for 19.7% and 80.3% respectively. Soil leakage is an important way but not a main way of soil erosion in typical karst watershed. There is no obvious soil erosion on the hillsides (less than 1 Mg km-2 a-1), but the sediment sources results shows sediment sources of surface and underground river are different in 2017 and 2018, In 2017, it indicate that carbonate surface soil contributes 16.2% and 11.9% of the total suspended sediment to the surface and underground river respectively, and the clastic rock pieces are the primary source of both surface and underground river sediments, 79.5% and 60.8% respectively. Subsurface soil contributes a smaller fraction to the total sediment load, 4.3% to surface rivers and 27.3% to underground rivers. The 137Cs values for some suspended sediments in 2018 were outside the range all of the soil source samples, it attributed to re-mobilization of old sediment stored in karst underground conduits during the deforestation, and these “old sediments” could generate to the surface again when with the rainfall erosivity above 49 J·mm·m-2·h-1.

How to cite: Peng, T., Cheng, Q., and Cao, L.: Monitoring of suspended sediment load and Sediment Sources in a Karst Plateau Catchment of Southwest China., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6497, https://doi.org/10.5194/egusphere-egu2020-6497, 2020.

EGU2020-6578 | Displays | SSS2.8

Monitoring and Estimating Soil Loss in Agricultural Areas - Case Studies in Chania, Crete, Greece

Anthi Eirini Vozinaki, Dimitris Alexakis, and Ioannis Tsanis

Olive and vine orchards in the island of Crete suffer from extreme soil erosion due to intense rainfall, farm slope and/or the intensification of tilling processes. This research aims to assess the impacts of agricultural practices, land use, and vegetation cover on the quantity of erosion processes in three study areas located in Western Crete. These areas provide the case studies of soil loss (erosion/deposition) monitoring analysis and assessment process. Advanced research treatments of Soil Improving Cropping Systems (SICS) are implemented and tested in three different crop types: (1) Crop cover treatment (i.e. seed with vetch) applied in vineyards (Vitis vinifera) in Alikampos; (2) Tilled treatment applied in Olive orchards (Olea europaea cv. Koroneiki) in Astrikas; and (3) Crop switch treatment from Orange trees to Avocados applied in Koufos. It is notable that an avocado farm, besides providing financial benefits, can also maintain a superior overall soil quality. Soil erosion has not been measured yet for avocados, however, avocado plantations are proposed as a sustainable alternative. Soil loss is estimated for the aforementioned case studies, by comparing the results from treatments applied in SICS areas, with the Control areas, where no treatment has taken place. Three different methodologies are used in order to identify soil loss amount: (a) Sediment traps (all sites); (b) Cross sections measurement (Alikampos and Astrikas) and (c) Soil deposition reference sticks (Alikampos and Koufos). Preliminary results show that soil loss values (tn/ha), are absolute values of erosion/deposition, and range from 2.33 to 16.41 tn/ha for vineyards with no vetch (Control), from 1.64 to 13.46 tn/ha for vineyards with vetch (SICS), from 2.21 to 15.66 tn/ha for no tilled olive orchards (Control), from 0.43 to 5.8 tn/ha for tilled olive orchards (SICS), from 2.63 to 10.05 tn/ha for orange orchards (Control), and from 2.24 to 8.95 tn/ha for avocado orchards (SICS). In addition, the ongoing research has already yielded the following yearly average soil loss rates (tn/ha/yr): vineyards – Control 6.883 tn/ha/yr versus vineyards – SICS 6.587 tn/ha/yr; olive orchards -  Control 7.019 tn/ha/yr versus olive orchards – SICS 3.215 tn/ha/yr; and orange orchards – Control 6.406 tn/ha/yr versus avocados – SICS 5.386 tn/ha/yr. The above field results are also in general agreement with the yearly average soil erosion rates in the island of Crete, modeled by several researchers. All study sites show mitigation of soil loss and improvement of soil quality from the application of SICS treatments. Therefore, it is recommended to raise farmers’ awareness about their effectiveness in order to confront the consequences of soil degradation.

Keywords: Soil Loss; Sediment Traps; Soil Improving Cropping Systems; Crete

The research leading to these results is funded by H2020 program under grant agreement n° 633814 (SOILCARE).

How to cite: Vozinaki, A. E., Alexakis, D., and Tsanis, I.: Monitoring and Estimating Soil Loss in Agricultural Areas - Case Studies in Chania, Crete, Greece, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6578, https://doi.org/10.5194/egusphere-egu2020-6578, 2020.

EGU2020-8078 | Displays | SSS2.8

Studying soil erosion rates through landscape fragmentation. A case study in Crete, Greece.

Dimitrios D. Alexakis, Christos Polykretis, and Manolis G. Grillakis

The regular patterns of soil erosion tend to change at different scales of observation, affecting the mechanism of soil erosion and its evolution characteristics. Fragmentation and land loss are two critical, interrelated processes that influence the entire landscape. In this study, we examine how the relationship between landscape fragmentation and soil loss is diversified in different scales and contexts. Thus, different Earth Observation (EO) products, in terms of spatial analysis, such as Landsat 8, Sentinel 2 and Planetscope imageries are utilized to search the influence of scale effect in fragmentation rate. Land use / Land Cover (LULC) maps were developed in different scales through the use of sophisticated classification algorithms. Following, FRAGSTATS software was employed to calculate spatial metrics in order to capture important aspects of landscape patterns such as edge density, largest patch index, number of patches, contagion etc. In this context we calculated fractal dimensions and Moran’s I spatial autocorellation statistics and used them to represent the degree of landscape fragmentation. Soil loss data, estimated in different scales were incorporated in the overall study as derived from RUSLE (Revised Universal Soil Loss Estimation) soil loss estimation model. Ordinary least square (OLS) and Geographical Weighted Regression (GWR) methodologies were applied in order to correlate both spatially and quantitavely soil loss rates with landscape fragmentation The results denoted the fact that areas of larger patches with least fragmentation suffer less from soil loss phenomena. The overall approach can be used as a road map in order to extract crucial conclusions about landscape’s diachronic evolution and how this is affected both from natural and anthropogenic interventions.

How to cite: Alexakis, D. D., Polykretis, C., and Grillakis, M. G.: Studying soil erosion rates through landscape fragmentation. A case study in Crete, Greece., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8078, https://doi.org/10.5194/egusphere-egu2020-8078, 2020.

EGU2020-15394 | Displays | SSS2.8

The use of high-speed camera technique for observation of soil splash phenomena

Michał Beczek, Magdalena Ryżak, Rafał Mazur, Agata Sochan, Cezary Polakowski, and Andrzej Bieganowski

Soil, i.e. the natural outer layer of the lithosphere and an important component of many ecosystems, may be subjected to various degradation processes dependent on different factors. One of the forms of degradation is water erosion, where the first stage is the splash phenomenon. This process is caused by water drops hitting the soil surface during rainfall, which results in detachment and ejection of splashed material and transport thereof over different distances. The aim of this study was to present the application of the high-speed camera technique for investigations of surface phenomena (effects) influenced by the impact of a single water-drop onto the soil surface.

The measurements were conducted on types of soil differentiated in terms of texture and variants of initial moisture content, which helped to observe different aspects of the soil splash phenomenon. Water drops with a diameter of 4.2 mm fell on soil samples with various kinetic energy values depending on the height of the drop fall (up to 7m). Phantom Miro M310 high-speed cameras were used to observe the effects of the drop impact. The devices registered images with a speed of 3260 fps (frames per second) at the highest available resolution (1280x800 pixels). The following phenomena were observed: I) ejection of splashed particles (including solid soil particles, water droplets, solid particles within the water sheath); II) crown formation – when the drop impacting onto wet soil surface forces the liquid layer to rise up and form a crown (important for the mode and amount of transferred material); III) micro-crater formation – the deformation of the surface and formation of a shallow pool after the drop impact.          

 

This work was partly financed from the National Science Centre, Poland; project no. 2018/31/N/ST10/01757.

 

References:

  1. Beczek M., Ryżak M., Sochan A., Mazur R., Bieganowski A.: The mass ratio of splashed particles during raindrop splash phenomenon on soil surface. GEODERMA 347, 40-48, 2019
  2. Beczek M., Ryżak M., Lamorski K., Sochan A., Mazur R., Bieganowski A.: Application of X-ray computed microtomography to soil craters formed by raindrop splash. Geomorphology 303, 357-361, 2018
  3. Beczek M., Ryżak M., Sochan A., Mazur R., Polakowski C., Bieganowski A.: The differences in crown formation during the splash on the thin water layers formed on the saturated soil surface and model surface. PLoS ONE 12, 2017

How to cite: Beczek, M., Ryżak, M., Mazur, R., Sochan, A., Polakowski, C., and Bieganowski, A.: The use of high-speed camera technique for observation of soil splash phenomena, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15394, https://doi.org/10.5194/egusphere-egu2020-15394, 2020.

 Desertification is one of the main environmental problems in arid and semi-arid areas. In Otindag sandy land, the activation of fixed sand dunes caused by climate change and human activities is the main reason of the development of desertification, and the activation of fixed sand dunes is first manifested by the formation and evolution of blowouts. In recent years, with the increase of high-resolution image data, it has become possible to make use of dynamic monitoring of terrain and landscape changes in small areas, so as to accurately analyze the interaction between terrains and influencing factors on smaller landscape scales, especially dune-interdune scale. We use the high-resolution satellite image data in 2010, 2013, 2016 and 2019 with the ground survey data as the data source, as well as the ArcGIS software to adopt the visual interpretation method. According to the different developmental positions, the shapes of the blowouts can be divided into saucer, bowl, groove, dustpan and irregular shaped. In the study area, the ways of changes in blowout are mainly based on expansion and amalgamation between 2010 and 2019. The area of blowout increased by 6.47hm2 from 2010 to 2013. During 2013-2016, the area increased by 4.89hm2, following by the next three years, it continued growing by 3.04hm2. With little disturbance of human activity, the growth of blowouts in this area is largely affected by the change of climate factors. As the dynamic factor of blowouts, the reduction in sand drift potential, only decreases the development rate and slows down the process. The shapes of the blowout themselves also work as the main influencing factor.

How to cite: Hu, R., Hasi, E., and Yin, J.: Dynamic changes of blowout in the fixed dune on the southeastern fringe of Otindag sandy land in recent decade, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21021, https://doi.org/10.5194/egusphere-egu2020-21021, 2020.

Wind erosion is one of the main factors of soil degradation and air pollution in arid and semiarid regions. In recent years, dust storms have become ever more important sources of air pollution in large areas of Iran. Dust storms previously were confined to the summer season and to western Iran. Nowadays, dust storms occur during eight months of the year and extend to the central regions and the entire south of Iran. This is causing increasing problems for the residents of the affected areas, threatening their health and impairing social, economic and agricultural activities. Ahvaz, the capital of Khuzestan Province, is the city that is most seriously affected by these problems in Iran.

Wind erosion is a multifaceted phenomenon influenced by a variety of factors. One of these factors that has changed considerably in recent time in Iran is land use/cover and land management. To investigate the impact of these changes on wind erosion potential in southwestern Iran we applied an empirical model of the Iran Research Institute of Forest and Rangeland (IRIFR) to remote sensing data extracted from Landsat ETM+ and Landsat 8 imagery of 2010 and 2019. Relationships between changes in wind erosion and land use/cover were determined by cross-tabulation, combining the original spectral bands with synthetic bands and using Maximum Likelihood classification.

The results indicate major changes in wind erosion potential over the last decade in the study area. Interestingly, while areas with a low, medium, and high sediment yield potential decreased, areas with a very high sediment yield potential have increased. Increasing soil erosion potential was primarily related to the conversion of rangeland to agricultural cropland Moreover, the results indicate an increase in desertification in the study area which is also a clear evidence of increasing in soil erosion.

How to cite: Nikseresht, F. and Rainer, S.: Influence of changing land use/cover and land management on wind erosion potential in southwestern Iran, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22440, https://doi.org/10.5194/egusphere-egu2020-22440, 2020.

EGU2020-9661 | Displays | SSS2.8

Linking regional modelling with field measurements to evaluate effectiveness of living windbreaks as measures against wind erosion

Thomas Weninger, Nathan King, Karl Gartner, Barbara Kitzler, Simon Scheper, Peter Strauss, and Kerstin Michel

The degrading impact of wind on agricultural soils has been observed throughout centuries in the Pannonian region of central Europe. Nevertheless, soil loss was not yet quantified and the extent or relevance of the problem are unknown for this agriculturally important region. Especially dry soil surface is highly prone to erosion and as drought periods are expected to become more frequent and severe with changing climate, the risk of wind erosion will increase accordingly. Living windbreaks and similar agro-forestry systems are supposed to be highly effective measures against wind erosion. In an extensive research project, multiple approaches are integrated to obtain a broad view onto the relevance of soil degradation by wind on plot scale and its regional distribution.

More in detail, case studies are conducted where the soil loss by wind erosion is measured in sediment traps. Data about driving and stabilizing factors like wind speed, soil moisture, vegetation density etc. are measured in high spatial and temporal resolution. The measurements started in December 2019. Besides, wind erosion risk is modelled and mapped on regional scale applying state-of-the-art model procedures. The measurement results are used in an attempt to down-scale the model application and thus create a link to ground-truth data. Information about spatial and temporal variability of the driving factors is used for implementation of stochastic calculation procedures in a sensitivity study which determines the most relevant factors for wind erosion mitigation.

The used modelling approach also includes the effects of wind shelters what enables a partly evaluation of the existing network of such elements in the Pannonian region. There, the Authority of Land Reform has been supporting and documenting the installation of wind shelters for more than 60 years. Incorporating this data base, quantitative and qualitative statements will be developed about the state of the shelter belts and their relevance concerning erosion rates. Additionally, the potential and actual value of living windbreaks will be determined with special regards to physiological and ecological characteristics, stability under future climate conditions and further ecosystem services in agricultural landscapes.

How to cite: Weninger, T., King, N., Gartner, K., Kitzler, B., Scheper, S., Strauss, P., and Michel, K.: Linking regional modelling with field measurements to evaluate effectiveness of living windbreaks as measures against wind erosion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9661, https://doi.org/10.5194/egusphere-egu2020-9661, 2020.

SSS2.9 – Soil and water conservation techniques to monitor, evaluate and mitigate the impacts of soil erosion from hillslopes to watershed scale

Linking landscape patterns to specific ecological processes has been and will continue to be a key topic in landscape ecology. However, the traditional landscape pattern analysis by landscape metrics inspired by patch-matrix model (PMM) may be difficult to reach such a requirement, and thus landscape pattern analysis to denote the significance of ecological process is strongly hindered. To find conceptual and methodological innovations integrating ecological processes with landscape patterns is important. In this paper, we proposed a conceptual model, i.e., the source-pathway-sink model (SPSM) by defining the role of each landscape unit to a specific process before conducting landscape pattern analysis. The traditional landscape matrices derived from the patch-matrix model is visual- or geometrical-oriented but lack of linkage to ecological significance. The source-pathway-sink model is process-oriented, dynamic, and scale dependent. This model as a complementary to the patch-corridor-matrix model can provide a simple and dynamic perspective on landscape pattern analysis. Based on the SPSM model, a landscape index was developed in term of the process of soil erosion, and further testified by using on-site measurements. It was found the new landscape index based on SPSM is useful in evaluating the risk of soil erosion from landscape pattern at watershed. Finally, a case study was conducted in the loess hilly areas to define the risk area of soil erosion that will be useful for sustainable land use management and optimization in future.

How to cite: Chen, L.: To link landscape pattern with soil erosion risk at watershed scale based on SPSM model in the loess hilly area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4995, https://doi.org/10.5194/egusphere-egu2020-4995, 2020.

EGU2020-1236 | Displays | SSS2.9

Influence of Check Dams on Flood and Erosion Dynamic Processes of a Small Watershed in the Loss Plateau

Shuilong Yuan, Guoce Xu, Peng Shi, and Kexin Lu

As an important soil and water conservation engineering measure, check dams have been constructed on a large scale in the Loess Plateau of China. However, their effects on runoff and sediment processes in the basin are still unclear. In this study, the hydrodynamic processes of the Wangmaogou watershed located in the Loess Plateau were simulated, and the influence of check dams on the flood and erosion dynamic processes in this watershed were also evaluated. The results showed that the check dams obviously reduced the flood peak and flood volume and mitigated the flood process. After the dam system was completed, the flood peak and flood volume were reduced by 65.34% and 58.67%, respectively. The erosion dynamic distribution of the main channel in the small watershed was changed to different extents by the different dam type combinations, and the erosion dynamic parameters of the channel decreased most after the dam system was completed, when the velocity and runoff shear stress of the outlet section were reduced by 10.69% and 31.08%, respectively. Additionally, the benefits of sediment reduction were most obvious after the check dam system was completed, with the sediment discharge in the watershed being reduced by 83.92%. The results of this study would provide specific implications for construction and management of check dams in the Loess plateau.

How to cite: Yuan, S., Xu, G., Shi, P., and Lu, K.: Influence of Check Dams on Flood and Erosion Dynamic Processes of a Small Watershed in the Loss Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1236, https://doi.org/10.5194/egusphere-egu2020-1236, 2020.

EGU2020-1361 | Displays | SSS2.9

Understorey vegetation drives surface runoff and soil loss in teak plantation-based system of Northern Laos

Layheang Song, Laurie Boithias, Oloth Sengtaheuanghoung, Chantha Oeurng, Christian Valentin, Phabvilay Sounyafong, Anneke de Rouw, Bounsamai Soulileuth, Norbert Silvera, Alain Pierret, and Olivier Ribolzi

Humid tropical mountainous area experiences serious soil erosion due to rapid changes in landuse, sometimes implying erosion prone management practices. In this study, we hypothesized that keeping understorey in teak tree plantation would protect soil and avoid soil erosion. We assessed the effects of 4 management practices in teak tree plantation area on water and soil losses using 6 replicated 1-m2 microplots in four plantations situated in Northern Laos during the wet season of 2017. The landuses in the four plantations were teak without understorey (TNU), teak with low density of understorey (TLU), teak with high density of understorey (THU), and teak with broom grass, Thysanolaena latifolia (TBG). During the wet season of 2017, we monitored surface runoff and soil loss for 22 rainfall events. We also measured some of the teak tree and understorey characteristics (i.e. height and percentage of cover) and the percentage areas of soil surface features (i.e. litter, free aggregates, crusting, etc.). Relationships among these variables was estimated through multiple statistics and regression analyses. We found that runoff coefficient and soil loss were the smallest for THU and TBG: runoff coefficient was 23% for both treatments, and soil losses were 465 and 381 g m-2, respectively. Runoff coefficient and soil loss for TLU were 35% and 1115 g m-2, respectively. We observed the highest runoff coefficient and soil loss under TNU (60%, 5455 g m-2) associated to the highest crusting rate (82%). High runoff coefficient and soil loss under TNU was explained by the kinetic energy of rain drops falling from the broad leaves of the tall teak trees down to bare soil, devoid of plant residues, thus leading to severe soil surface crusting and detachment. Overall, promoting understorey such as broom grass in teak tree plantations would (1) limit surface runoff and improve soil infiltrability, thus increase the soil water stock available for both root absorption and groundwater recharge, and (2) mitigate soil loss and favour soil fertility conservation.

How to cite: Song, L., Boithias, L., Sengtaheuanghoung, O., Oeurng, C., Valentin, C., Sounyafong, P., de Rouw, A., Soulileuth, B., Silvera, N., Pierret, A., and Ribolzi, O.: Understorey vegetation drives surface runoff and soil loss in teak plantation-based system of Northern Laos, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1361, https://doi.org/10.5194/egusphere-egu2020-1361, 2020.

Gravity erosion is one of the most remarkable natural hazards in mountainous regions, especially on the Loess Plateau of China. Nevertheless, the measurement of failure mass is very difficult because gravity erosion usually occurs randomly and it combines with hydraulic erosion. Here we present a novel testing technique that could quantitatively measure time-variable gravity erosion on the steep loess slopes. A structured light 3D surface measuring apparatus, the Topography Meter, was designed and manufactured in our laboratory. Dynamic variation of the steep slope relief was monitored under rainfall simulation and the slope deforming process was recorded by a computer video technology. With the help of laser marking, plane figures were vectorially transformed into 3D graphs, thus the shape of target surface was accurately computed. By comparing the slope geometries in the moments before and after the erosion incident on the snapshot images at a particular time, we could obtain the volume of gravity erosion and many other erosion data, including the volume of slide mass, the amount of soil loss eroded by overland flow, etc. A series of calibration tests were conducted and the results showed that the accuracy of this technique was high and sufficient for exploring the mechanism of slope erosion. More than 120 rainfall simulation events were subsequently tested with the apparatus, further confirming its feasibility and reliability.

How to cite: Xu, X., Xu, F. X., Guo, W., and Zhao, C.: The Topography Meter: a measurement system applicable for gravity-erosion experiments using a novel 3D surface measuring technique, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1690, https://doi.org/10.5194/egusphere-egu2020-1690, 2020.

EGU2020-2066 | Displays | SSS2.9

Distribution of soil organic carbon impacted by land-use change and check dam on the Loess Plateau of China

Peng Shi, Yan Zhang, Kexin Lu, Zhaohong Feng, and Yang Yu

Vegetation restoration, terrace and check dam construction are the major measures for soil and water conservation on the Loess Plateau. These effective measures of stabilizing soils have significant impacts on soil organic carbon (SOC) distribution. To understand the impact of land-use changes combined with check dam construction on SOC distribution, 1060 soil samples were collected across a watershed on the Loess Plateau. Forestland, shrubland and terrace had significant higher SOC concentrations in the 0-20 cm soil layer than that of sloping cropland.    Land use change affects the process of runoff and sediment transportation, which has an impact on the migration and transformation of soil carbon. The soil erosion of sloping farmland is the most serious, and the maximum annual erosion rate is as high as 10853.56 t·km-2. Carbon sedimented in the dam land was mainly from sloping cropland, and this source percentage was 65%. The application of hydrological controls to hillslopes and along river channels should be considered when assessing carbon sequestration within the soil erosion subsystem. 

How to cite: Shi, P., Zhang, Y., Lu, K., Feng, Z., and Yu, Y.: Distribution of soil organic carbon impacted by land-use change and check dam on the Loess Plateau of China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2066, https://doi.org/10.5194/egusphere-egu2020-2066, 2020.

EGU2020-2851 | Displays | SSS2.9

Planning method and application case of debris-flow check dams in water and soil conservation

Jiangang Chen, Huayong Chen, and Xiaoqing Chen

Check dams are transverse structures build across gullies and they are very important engineering measure in soil restoration hazard mitigation. After three successive earthquakes in China, a considerable number of solid material was deposited in gullies. With the extreme rainfall, a numerous of flood and debris flow events were trigged, some of them caused serious secondary disasters. In the past 12 years after the Wenchuan earthquake, based on the debris-flow prevention method by controlling debris-flow magnitude and avoiding blocking river, a series of check dams were constructed to regulate the water and soil erosion. The operation status of check dams needs to be investigated and summarize the engineering practice experience. Based on the results of field investigation, the shape and size characteristics of the dam opening were analyzed, and then established a classification system of the opening clogging types. Moreover, in August 20, 2019, Flash floods and mudslides occurred in Wenchuan County, causing more than 30 people dead, buried the G213 highway, and damaged a bridge. These disasters bring new thinking for future hazard mitigation. Geotechnical measures can quickly reduce the disaster risk of flash flood and debris flow, and now it has formed a set of perfect design standards. However, the disaster mitigation effect of the vegetation measures are not fully studied. Thus, the integrated disaster mitigation effect of the above two methods will be investigated in the future work.

How to cite: Chen, J., Chen, H., and Chen, X.: Planning method and application case of debris-flow check dams in water and soil conservation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2851, https://doi.org/10.5194/egusphere-egu2020-2851, 2020.

EGU2020-4738 | Displays | SSS2.9

Alternative approach for works controlling stony debris flows

Carlo Gregoretti, Matteo Barbini, Martino Bernard, and Mauro Boreggio

Many sites of the Dolomites are threatened by channelized debris flows: solid-liquid surges initiated by the entrainment of large quantities of sediments into the abundant runoff at the head of channel incised on fans, can dramatically increase their volume along the downstream routing. This is the case of the Rovina di Cancia site where solid-liquid surges forming in the upper part of the basin can increase their volume up and over 50000 m3, seriously impacting the downstream village of Borca di Cadore. The debris-flow channel ends just upstream the village that in the past was hit by four debris flows (three in the recent years) that caused victims and destructions. Control works built until now are not sufficient to protect the village from high magnitude debris flows and a definitive solution calls to be planned. Present works are a flat deposition area, 300 m downstream the initiation area, an open dam under construction downstream it, and  two retention basins at the end of the channel. Between the open dam and the upstream retention basin, there are the rest of eight check-dams made of gabions, built in the 60s and progressively damaged or destroyed by the debris flows occurred after their construction. This series of check-dams limited the entrainment of solid material and the occurrence of localized scours. The initial plan is the substitution of the check-dams with concrete structures and the widening of the dowsntream retention basin through the raising of high elevation embankment downstream it and the following demolition of the actual dyke. Finally, a channel crossing the village and national route on the valley bottom will deliver the fluid phase from the widened basin to the Boite river. All these control works have a very high cost for construction and maintenance and severely impact the village with the presence of a non-negligible residual risk. These drawbacks call for an alternative solution that is searched looking at to the morphology. Downstream of the open dam and on its right side, there is a deep impluvium that ends on a large grass sloping area. The novel solution requires the construction of a channel through the right high bank that deviates the debris flow into the impluvium. The impluvium, widened through the excavation of the surrounding slopes, is closed at the outlet by  an open dam. Downstream the open dam, a channel will lead to a retention basin, where most of storage volume is obtained from the excavation of the grass sloping area, limiting the elevation of the dykes At the end of this basin an open dam will deliver the debris-flow fluid part to a channel passing under the national route and joining the Boite river. Such a solution composed of a deviatory channel, two retention basins (the deep impluvium and that excavated on the sloping grass area) and the channels between and downstream them, has quite a lower costs of construction and maintenance, eliminating the impact on the village because occupying uninhabited areas without interrupting the main roads.

How to cite: Gregoretti, C., Barbini, M., Bernard, M., and Boreggio, M.: Alternative approach for works controlling stony debris flows, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4738, https://doi.org/10.5194/egusphere-egu2020-4738, 2020.

Soil erosion, a widely-occurring phenomenon in the terrestrial environment, affects land productivity and infrastructure security negatively both on-site and off-site. Therefore, soil erosion control services (SECS) are one of the most fundamental ecosystem services for human well-being. Although previous SECS assessments elaborate the benefits from preventing on-site soil erosion and soil loss comprehensively, the off-site benefits remain vague. They are usually estimated only through multiplying the capacity of on-site soil erosion prevention by a land-use-based, and spatially consistent, allocation coefficient. The corresponding overestimation, item omission, and inability to represent the spatial heterogeneity of SECS may lead to great uncertainties. In addition, the SECS decay with travel distance is not well represented, because of a neglect of the cascading nature of SECS formation and its delivery. Here, to address these deficiencies, a cascade framework for SECS assessment is developed that incorporates the concept of sedimentological connectivity over the landscape. This approach quantifies both the on-site soil erosion prevention and mitigation of sediment delivery over the landscape, based on an understanding of the cascading nature of soil erosion and sediment delivery, by referring to the framework of WATEM/SEDEM that potentially reveals the sedimentological connectivity over landscape. A monetized valuation of SECS delivered to local communities was derived by employing a land-use based replacement cost technique, which takes cultivated land units as a SECS receiver and conveyer. The approach was applied in a loess catchment located in the middle Yellow River basin, China as a case study. For this watershed, with an area of 54.2 km2, the gross soil erosion reduction was up to 156.93 × 104 t; the reduction of sediment input was 11.28 × 104 t; and the reduction in gross sediment export is up to 181.34 × 104 t. The monetized value delivered to utilized land units was 910.13 × 104 CNY. The approach described provides a tool that specifically addresses the SECSs directly useful to humans, contributes to quantifying the soil erosion control services provided by the landscape, and improves the reliability of evaluating SECS.

How to cite: Liu, Y., Zhao, L., and Yu, X.: A sedimentological connectivity approach for assessing on-site and off-site soil erosion control services, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13203, https://doi.org/10.5194/egusphere-egu2020-13203, 2020.

EGU2020-17159 | Displays | SSS2.9

Testing the Slake mobile app at the local scale to explore the spatial variability of soil structural stability

Sebastien Salvador-Blanes, Clément Girault, Thomas Rochereau, Arthur Gaillot, Frédéric Darboux, Blandine Lemercier, Didier Michot, and Nicolas Saby

The Slake mobile app measures the aggregate stability by rapid immersion in water. It is a particularly interesting tool to allow a cost-efficient determination of soil structural stability. The Slake app has proven its efficiency at large scale (New South Wales state, Australia). Its application at a more local level (e.g. small watersheds) could be of particular interest to farmers and local stakeholders to identify areas of sensitivity to soil slaking, in order to implement mitigation strategies in the most appropriate areas to prevent from soil erosion. The aim of this study was to test the Slake app at the plot and the watershed scales to test its applicability and robustness. The studied watershed is the 25 km² Louroux catchment, located in central France. This catchment is typical of intensively cultivated lowland catchments. Despite a very low slope (<0.4%), erosion processes have been shown as significant, either through soil surface erosion or tile drainage exports. Slaking values have been measured in the laboratory on undisturbed soil surface aggregates collected at 52 locations within the catchment, using a balanced sampling. The same methodology has been applied within a 5 ha plot on 52 sampling points. The aggregate stability was measured with the app simultaneously on three aggregates. This measurement was repeated 3 times for each sampling location. Therefore, 9 slaking indices can be extracted for each soil sampling location, allowing for a computation of the index variability at each sampling location. Besides, 13 samples for the plot and the catchment have been selected to measure soil structural stability by a normalized method (Mean Weight Diameter of soil aggregates after wet sieving, ISO 10930). Preliminary results show a variable heterogeneity of the slaking index measured at a single location. The origin of this heterogeneity (measurement errors, sample variability…) is discussed. The correlation with the normalized method is explored and the spatial structure of the slaking index over the two studied scales is presented.

How to cite: Salvador-Blanes, S., Girault, C., Rochereau, T., Gaillot, A., Darboux, F., Lemercier, B., Michot, D., and Saby, N.: Testing the Slake mobile app at the local scale to explore the spatial variability of soil structural stability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17159, https://doi.org/10.5194/egusphere-egu2020-17159, 2020.

EGU2020-7441 | Displays | SSS2.9

Soil water flow behavior of abandoned farmland restored with different vegetation communities in the Loess Plateau of China
not presented

Rui Wang, Zhengchao Zhou, Ning Wang, Zhijing Xue, and Liguo Cao

Natural vegetation succession in abandoned farmlands simulate the changes in near surface soil characcteristics over the Loess Plateau of China, and hence likely induce temporal variation in the distribution and the movement of soil water in soil layers. In order to assess the effect of the natural vegetation succession on soil water flow behavior, four vegetation communities at different stages of sucession (Artemisia scoparia, Artemisia sacrorum, Bothriochloa ischaemum, Periploca sepium Bunge) in Fangta watershed of Yan River were selected and dye tracer experiments were performed. Both the soil physicochemical properties (e.g., soil bulk density, the particle size, water stable aggregate (>0.25 mm) content, and soil organic matter) and the root systems (e.g., root mean diameter, root mass density, root surface area, and root volume density) tended to increase along with vegetation sucessional development. Results of the dye tracer experiment and the image analysis indicated that the preferential flow was the dominant type in the four field sites. Compared to the site in early stage of sucession, the preferential flow proportion (FFP), preferential infiltration volume (PIV), and the contribution of the preferential infiltration to the total infiltration (Con) in the late stage enhanced by 6.65-7.34 times, 2.73-4.08 times, and 2.52-3.75 times, respectively. Correlation analysis suggested that the plant roots and their morphometric features played more important role on the preferential flow in comparison with the soil physicochemical properties. The abundant lateral root and the steeper slope may have caused the presence of lateral flow. Along with increasing degree of preferential flow, the spatial variability of the soil water through the vertical soil profiles increase during the process of restoration and succession of vegetation communities. Our study demonstrated the improvement of the preferential flow in the abandoned farmland during natural vegetation restoration helped soil water storage in the deep soil layer.

 

How to cite: Wang, R., Zhou, Z., Wang, N., Xue, Z., and Cao, L.: Soil water flow behavior of abandoned farmland restored with different vegetation communities in the Loess Plateau of China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7441, https://doi.org/10.5194/egusphere-egu2020-7441, 2020.

The stability of soil aggregates is an indicator of restoration of soil in degraded ecosystems. A multitude of factors such as properties of plant roots and soil have been suggested to contribute to aggregate stability, but little information is available on the relative importance of these factors in temperate grass zones. We examined how root and soil properties modified aggregate stability along a gradient of secondary succession grassland on the Loess Plateau in China. We selected three cropland abandoned for 3, 10, and 16-year and measured the distribution of aggregates, mean weight diameter (MWD), bulk and aggregate-associated soil organic carbon (SOC) and glomalin-related soil protein (GRSP) contents, root biomass density, root length density, and specific root length (SRL). Compared with 3-year site, the amount of large macroaggregates (>2 mm) and aggregate stability (indicated by MWD) at 16-year site increased by 25.6% and 8.5%. The higher MWD contributed the most to the accumulation of SOC in large and small macroaggregates and to the accumulation of GRSPs in microaggregates (<0.25 mm). SRL was significantly positively correlated with MWD. Redundancy analysis (RDA) showed that soil and plant variables together explained 89.1% of the aggregate distribution variation. Partial RDA further revealed that soil variables solely explained 6.4% of the variation, plant root variables explained 47.9% of the variation, and interaction of soil and plant variables accounted for 34.8% of the variation. Our study indicated that increased soil aggregate stability during plant secondary succession depended on both plant roots and aggregate-associated SOC and GRSPs, and plant root exerted a stronger influence on soil aggregate stability than soil. Allowing secondary succession may be a promising strategy for restoring degraded ecosystems on the plateau.

How to cite: xiao, L. and Li, P.: Plant root exerted a stronger positive effect on aggregate stability than soil during plant secondary succession on the Loess Plateau, China , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1388, https://doi.org/10.5194/egusphere-egu2020-1388, 2020.

The characteristics of soil erosion under extreme rainstorm conditions can reflect the effect of ecological restoration measures and the rationality of land use patterns in the region. 12 dam-controlled catchments was selected after an extreme rainstorm event occurred in the northern Shaanxi Province on 25-26 July 2017 (called “7.26” rainstorm). Soil erosion intensity in the 12 catchments was obtained by digging up the sedimentation profiles and measuring the sedimentation areas. Using digital orthophoto map and digital terrain model by Unmanned Aerial Vehicle to obtain land-use types and their areas, slope gradients and the distance along the flow path to the edge of the downslope and dam-land. Stepwise regression method was used to analyze the main factors affecting catchment erosion intensity. The results showed that the average sedimentation thickness in the 12 damlands ranged from 0.16 m to 1.67 m and the intensity of soil erosion of the 12 catchments varied from 10295 t km-2 to 49227 t km-2. Soil erosion caused by this rainstorm was 10-50 times of the allowable amount of soil erosion in the Loess Plateau region (1000 t km-2.a) issued by Ministry of Water Resource of the People’s Republic of China (MWR). Stepwise regression analysis shows that, the closer the shape of a catchment to the circle is, the larger the area of slope-cropland in inter-gully land is or the closer the distance between slope-cropland and the dam-land is, the larger the erosion modulus in the catchment would be. What’s more, the presence of cement road up the valleys shoulder line reduced the modulus of soil erosion. Theses findings indicated that the existing ecological conditions in the dam-controlled catchments are not able to resist extreme rainstorm erosion effectively. Optimizing the distribution of land use types in catchments should be the focus of soil erosion control.

How to cite: Wang, N. and Jiao, J.: The magnitude of soil erosion of small catchments with different land use patterns under an extreme rainstorm on the Northern Loess Plateau, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-737, https://doi.org/10.5194/egusphere-egu2020-737, 2020.

EGU2020-1232 | Displays | SSS2.9

Quantitative assessment of check dam system impacts on catchment hydrological response - a case in the Loess Plateau, China

Tian Wang, Zhanbin Li, Jingming Hou, Shengdong Cheng, Lie Xiao, and Kexin Lu

The purpose of this study is to investigate the impact of check dams on catchment hydrological response in a small catchment on the Chinese Loess Plateau by applying a GAST (GPU Accelerated Surface-water and Transport model) numerical model at 2 m resolution DEM. The results showed that check dams significantly increase the so-called runoff lag times (lag to generation, lag to peak and lag to end of runoff) at the channel outlet compared to catchments without check dams. Furthermore, the peak runoff discharge at the catchment outlet without check dams decreased by 93.0% compared to with check dams. The total outlet discharge, surface water stored, and infiltration were respectively 20.1%, 74.9% and 5.0% of the total precipitation in the check dam catchment, while 75.4%, 22.6% and 2.0% in the system without check dams. Installation of check dams also altered the spatial water distribution of maximum discharge, moving the occurrences of maximum discharge further upstream and, thus, increasing safety downstream. Channel connectivity was found to have a direct relationship with peak discharge and with discharge volume at the basin mouth. In conclusion, implementing check dams significantly and effectively mitigated flood processes and increased runoff infiltration upstream.

How to cite: Wang, T., Li, Z., Hou, J., Cheng, S., Xiao, L., and Lu, K.: Quantitative assessment of check dam system impacts on catchment hydrological response - a case in the Loess Plateau, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1232, https://doi.org/10.5194/egusphere-egu2020-1232, 2020.

Water is the most essential resource for the ecological and biological survival of organisms as well as being an important strategic socio-economic factor. Stable isotopes of δD and δ18O in water are important indicators of hydrological and ecological process. In this study, temporal and spatial variations in δD and δ18O and transformations between three water bodies (precipitation, stream water, and groundwater) under ecological construction were studied in two contrasting watersheds of the Wuding River, China. In order to understanding the spatial and temporal variation of stable isotopes and water transmission times (WTT) under ecological construction, a total of 1028 water samples were collected from the 30 sites, and 79 precipitation samples were collected at the weather station. The results show that variation range of three water bodies occurred in the order
precipitation>stream water>groundwater, the local meteoric water line was above the level of the last two, and the isotopic composition of stream water and groundwater in controlling watershed is more enriched than that in natural watershed. WTT from precipitation to stream water in Jiuyuangou were 1.53 times those of Peijiamao. Similarly, WTT from precipitation to groundwater was about 7.6 times than that form precipitation to stream water. Supply ratios exhibited obvious seasonal variation. Precipitation and groundwater recharged stream water mostly in the dry season, while precipitation and stream water recharged groundwater during the wet season. Overall, this study shows that ecological construction measures extend WTTs and enhance water evaporation and fractionation. The results of this research are significant as they enhance our understanding of water transformation on the Loess Plateau under ecological construction.

How to cite: Zhao, B. and Li, Z.: Effects of ecological construction on the transformation of different water types on Loess Plateau, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1234, https://doi.org/10.5194/egusphere-egu2020-1234, 2020.

Check dam is widely used in the soil erosion control in the gully on the Loess Plateau of China. Check dam has significant effects in sedimentation, erosion control, land formation, water storage, and vegetation restoration. This result shows that the main dams and medium-sized dams on the Loess Plateau had deposited 5.12 million tons of sediment by the end of 2011, reducing sediment transportation to the Yellow River. The check dam system decreases the probability of gravity erosion. Check dams increases cropland in the gully-hilly area of the Loess Plateau, thus increases grain production. The check dam project is a carbon pool. On the Loess Plateau, 123 million tons of soil carbon is storaged in the check dam, accounting for 17.08% of the carbon sequestration in afforestation projects in China from 1994 to 1998. Check dam construction increases regional vegetational coverage, and the NDVI in the Dali River watershed increased by 28.4% after the dam project. The results provide a scientific basis for the assessment of the eco-environmental benefit of check dam on the Loess Plateau of China.

How to cite: Li, P., Yu, K., and Xiao, L.: Check dam is an effective engineering for soil and water conservation, carbon sequastration on the Loess Plateau of China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2262, https://doi.org/10.5194/egusphere-egu2020-2262, 2020.

China has implemented an ambitious ecological project Grain for Green Project (GGP) on the Loess Plateau (LP) at the end of last century. The GGP was to increase vegetation coverage, reduce soil and water erosion and store Carbon by converting croplands on steep slopes barren hills and wasteland to forests. Assessing the ecological effects of GGP correctly could improve vegetation restoration activities worldwide. In this study, two major ecological indicators (vegetation restoration and soil & water conservation) were used to evaluate the ecological benefits of GGP from 1982 to 2017. Our results show that the vegetation growth for most pixels of LP region have significantly increased at 21 century, annual growth rates of fraction of absorbed photosynthetically active Radiation (FPAR) in spring, summer, autumn and active growing season are 1.39, 4.49, 2.14 and 1.47, respectively. For leaf area index (LAI), these growth rates are 6.01, 20.06, 8.11 and 6.90, respectively. And for normalized difference vegetation index (NDVI), growth rates are 6.30, 25.46, 7.99 and 20.43, respectively. While the soil and water condition has differently changed, annual growth rates of soil moisture (SM) are 4.46, 2.79 and 2.30 for summer, active growing season and whole year, respectively. The coordinated responses of vegetation and soil & water condition suggest that the interaction between organisms (vegetation, animal and human) and environment (soil, water and so on) in the process of vegetation restoration should be further recognized to evaluate the benefits of ecological engineering more comprehensively.

How to cite: Gao, H. and Liu, S.: The trade-off between vegetation restoration and soil & water conservation in Loess Plateau, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13809, https://doi.org/10.5194/egusphere-egu2020-13809, 2020.

EGU2020-4779 | Displays | SSS2.9

Adaptation of the MMF (Morgan-Morgan-Finney) model to Mediterranean forests subject to wildfire and post-fire rehabilitation measures

Demetrio Antonio Zema, Joao Pedro Nunes, and Manuel Esteban Lucas-Borja

The hydrological effects of wildfire are very difficult to predict in Mediterranean forests, due their intrinsic semi-arid climate and soil characteristics. The Morgan-Morgan-Finney (MMF) model has shown generally accuracy and reliability in predicting surface runoff and soil erosion in several environmental contexts. In spite of its ease use and limited input requirements, few applications exist in Mediterranean forests with or without post-fire rehabilitation measures; therefore, its applicability to those conditions may be questionable without purposed verifications.

To fill this gap, the MMF model has been verified at the seasonal and plot scales in areas affected by a wildfire of a Mediterranean forest, with and without post-fire straw mulch treatment. The application of MMF with input parameters set up according to the original guidelines of the model’s developers led to poor performance in every soil condition. Subsequently, the model has been adapted to burned soils and Mediterranean climate characteristics, introducing changes in input data for both the hydrological and erosive components (seasonal values of evapotranspiration, reduction of the soil hydrological depth, including soil water repellency effects in burned soils, and modelling erosive precipitation only). By these adaptations, MMF was able to predict seasonal runoff volumes and soil loss with good reliability in all the experimented conditions.  

This modelling experiment has shown the capacity of the MMF model to simulate the seasonal hydrological response of the burned and mulched soils of Mediterranean forests. Therefore, the potential applicability of the model is promising as a management tool for predicting and controlling the erosion risk in semi-arid forest ecosystems threatened by wildfire as well as to evaluate the efficiency of post-fire treatments.

How to cite: Zema, D. A., Nunes, J. P., and Lucas-Borja, M. E.: Adaptation of the MMF (Morgan-Morgan-Finney) model to Mediterranean forests subject to wildfire and post-fire rehabilitation measures, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4779, https://doi.org/10.5194/egusphere-egu2020-4779, 2020.

EGU2020-1745 | Displays | SSS2.9

Characteristics of blown sand activities in sandy land on the eastern shore of the Qinghai Lake

Dengshan Zhang, Haijiao Wang, and Lihui Tian

Wind regime, sand drift potential and sand transport amount are important indicators to evaluate regional blown sand activities. This paper took Ketu sandy land on the eastern shore of Qinghai Lake as study area. The sand transport amount data were collected monthly in 2013-2014 and 2016-2017 with 16-azimuth sand collector, and data of local wind velocity and direction were used to compare and analyze the typical blown sand activities. The results were as follows: (1) In 2013-2014, the mean wind velocity in the study area was 2.79m/s and the frequency of sand-driving wind was 6.76%. While they were 2.63m/s and 6.13% in 2016-2017, respectively. (2) The directions of the sand-driving wind in two years were similar, clearly from WSW-WNW and ESE-SSE. The frequency of western wind increased whereas the frequency of southeastern wind decreased. (3) The seasonal variation of sand drift potential in two years were similar with the largest in spring and the smallest in summer. According to the annual variation trend of sand drift potential, the study area was belonging to low wind energy environment. (4) There is a significant difference in sand transport amount between the two years. The amount in 2016-2017 was 77.18kg less than that in 2013-2014, while the distribution of sand transport amount was similar. The increase of vegetation coverage in this area is the main reason for the decrease of sand transport amount.

How to cite: Zhang, D., Wang, H., and Tian, L.: Characteristics of blown sand activities in sandy land on the eastern shore of the Qinghai Lake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1745, https://doi.org/10.5194/egusphere-egu2020-1745, 2020.

EGU2020-2481 | Displays | SSS2.9

Effects of vegetation restoration on soil organic carbon redistribution along the Loess slope

Xiaoxia Zhang, Xiang Li, Yipeng Liang, and Tonggang Zha

Soil organic carbon (SOC) redistribution along the Loess slope under the effect of soil erosion plays an important role in understanding mechanism of SOC spatial distribution and turnover, hence to its effects on global carbon cycle. Vegetation restoration has been taken as an effective method to alleviate soil erosion on the Loess Plateau, while little research focused on the impact of vegetation restoration on the redistribution processes, especially the spatial distribution and stability of SOC. Here, we quantified the SOC stock and pool distribution on the loess slopes along geomorphic gradients under naturally regenerating forests (NF) and artificial black locust plantation (BP), using corn field as a control (CK).The results were as follows:  (1) vegetation restoration, especially NF, effectively slowed down the migration of SOC resulting from soil erosion and reduced the heterogeneity of SOC distribution. The ratios of topsoil SOC in the sedimentary area to the stable area were 109%, 143%, and 210% under the NF, BP, and CK, respectively. And (2) Vegetation restoration reduced the loss of labile organic carbon by alleviating the loss of dissolved organic carbon (DOC) and easily oxidized organic carbon (EOC) during migration. Both DOC/SOC and EOC/SOC ratios under NF and BP presented far less differences between the sedimentary and erosion zones than CK.A schematic diagram of SOC cycle patterns and redistribution along the loess slope under vegetation restoration based on our findings and discussions. The results suggested that vegetation restoration in the Loess slope, NF in particular, was an effective means for alleviating the redistribution and spatial heterogeneity of SOC and reducing soil erosion. Information from this study is useful for understanding the carbon cycles in restored ecosystems and evaluating the ecosystem services of natural and managed forests in soil erosion control and carbon sequestration.

How to cite: Zhang, X., Li, X., Liang, Y., and Zha, T.: Effects of vegetation restoration on soil organic carbon redistribution along the Loess slope, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2481, https://doi.org/10.5194/egusphere-egu2020-2481, 2020.

EGU2020-3080 | Displays | SSS2.9

Change in water discharge and sediment load on the Loess Plateau, China

Haiyan Zheng and Chiyuan Miao

Over the past 50 years, a series of soil and water conservation measures have been implemented on the Loess Plateau, including biological, engineering, and agricultural measures. As a result, water discharge and sediment load on the plateau have undergone significant changes. In this study, we compared the water discharge and sediment load at more than 100 hydrological stations across the Loess Plateau during the period 2008–2016 (P2) with the water discharge and sediment load during the period 1971–1987 (P1), and detected the main sources of sediment in each of the two periods. We then performed an attribution analysis to quantify the influence of different factors on the changes in sediment load. We found the following results: (1) Water discharge was reduced by 22% in P2 compared with P1, whereas the sediment load was reduced by 74%. (2) Sediment resources are mainly concentrated between Toudaoguai and Tongguan stations: this region contributed more than 88% of the total sediment load at the terminal station (Huayuankou station) in both P1 and P2. (3) When considering only the changes in sediment concentration on the Loess Plateau, we conclude that the contribution of human activities was greater than 72%. This study provides a detailed description of the temporal and spatial variations in water and sediment across the Loess Plateau, providing a reliable reference for the future development of ecological soil and water conservation measures on the Loess Plateau.

How to cite: Zheng, H. and Miao, C.: Change in water discharge and sediment load on the Loess Plateau, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3080, https://doi.org/10.5194/egusphere-egu2020-3080, 2020.

Soil moisture is the foundation of ecosystem sustainability in arid and semi-arid regions, and the spatial–temporal details of soil moisture dynamics of afforested areas can benefit for land use management in watershortage regions such as the Loess Plateau of China. In this study, spatial–temporal variations in soil moisture under Robinia pseudoacacia plantations on the Loess Plateau were analyzed. A total of 147 observations of soil moisture content (SMC) data to a depth of 500 cm soil profile were collected in 23 counties via field transect surveys and analyses of published literature. The results suggested that (1) the depth-averaged SMC was generally lower under forest sites than under cropland, both in the shallow layers and in the deep profiles. This finding implied that, compared with the native vegetation, the introduced R. pseudoacacia plantations caused intense reductions in soil moisture. (2) SMC was positively correlated with climatic factors (mean annual precipitation (MAP), mean annual temperature (MAT), and the Palmer drought severity index (PDSI)), indicating that the SMC under R. pseudoacacia plantations was highly consistent with the hydrothermal conditions at the regional scale. (3) The decreasing amplitude of SMC was linearly related to the increasing number of restoration years, especially in the areas below the 500–550 mm precipitation threshold. This finding showed that the restoration ageing sequence was an influential factor that affected the regional SMC variation in R. pseudoacacia plantations on the Loess Plateau. Our results suggest that afforestation activities should be avoided if the local total precipitation is insufficient for replenishing the soil moisture and that local tree species with a lower demand for water resources should be considered a top priority for further afforestation of the Loess Plateau.

How to cite: Liang, H. and Li, Z.: Soil moisture decline following the plantation of Robinia pseudoacacia forests: Evidence from the Loess Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4096, https://doi.org/10.5194/egusphere-egu2020-4096, 2020.

Soil moisture is a key factor affecting vegetation growth and survival in arid and semi-arid regions. Knowledge of deep soil moisture dynamics is very important for guiding vegetation restoration and for improving land management practices on the water-limited Loess Plateau. Temporal changes and vertical variations in deep soil moisture (at soil depths of 0–600 cm) combined with soil moisture availability were monitored in situ under Caragana korshinskii shrubs of different ages (named CK-10a, CK-20a and CK-35a) in the Loess hilly region during the growing season of 2013. The soil moisture content (SMC) under C. korshinskii shrubs of different ages was highly consistent with the seasonal precipitation variations and generally decreased as follows: CK-10a > CK-20a > abandoned land > CK-35a. The SMC varied greatly over time during the growing season (P < 0.01), decreasing from April to May and then slowly increasing with some fluctuation from June to October. The SMC drastically decreased with depth from 0–300 cm and then gradually increased with some fluctuation from 300–600 cm. A critical turning point and transition zone connecting the shallow and deep soil moisture occurred at 200–300 cm. Therefore, the soil profile was divided into active, secondary active and relatively steady soil layers in terms of soil moisture. The SMC fluctuated at depths of 0–100 cm and 300–400 cm and was relatively stable in the deeper soil layers. The amount of available soil moisture gradually decreased as the forest stand age increased, especially at CK-35a, where most of the soil moisture was unavailable for plant use. In addition, our study indicates that a large-scale restoration strategy with pure shrubland or woodland may not be suitable for soil moisture recovery in arid environments.

How to cite: Li, Z. and Liang, H.: Soil moisture dynamics under Caragana korshinskii shrubs of different ages in Wuzhai County on the Loess Plateau, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4107, https://doi.org/10.5194/egusphere-egu2020-4107, 2020.

EGU2020-1247 | Displays | SSS2.9

Effects of dynamic factors of erosion on soil nitrogen and phosphorus loss under freeze-thaw conditions

yuting cheng, peng li, Guoce Xu, and yixin zhang

Soil erosion is one of the primary environmental problems in China, and it can lead to serious water, soil, and nutrient losses. However, the mechanism of action of the dynamic factors of erosion on nitrogen (N) and phosphorus (P) loss remains unclear. In this study, a series of laboratory experiments were carried out to characterize the N and P loss and its influencing factors under freeze–thaw conditions. Two slope treatments (i.e. LS: loess and FTS: freeze–thaw soil) and five soil water content (SWC) (i.e. 10%, 15%, 20%, 25% and 30%) were considered. The results showed that the total runoff was higher under 30% SWC and lower under 20% SWC for the LS and FTS treatments. The freeze–thaw action caused higher sediment loss under low water content (10% and 15%). The runoff-associated total nitrogen (RTN), runoff-associated total phosphorus (RTP), and sediment-associated total phosphorus (STP) loss rate showed a larger fluctuation for FTS than for LS. The freeze–thaw action not only caused the instability of the nitrogen and phosphorus loss behavior but also caused increased diversity among individual samples. The soil erodibility, runoff energy, and runoff power were important dynamic factors associated with erosion, and the freeze–thaw action has a very large impact on these factors. For the LS treatments, the SWC could explain 60% of the variation in RTN loss and 63% of the variation in RTP; the runoff and infiltration both explained 90% of the variation in STN loss and the runoff time explained 97% of the variation in STP. For the FTS treatments, the runoff time explained 63% of the variation in STN and 53% of the variation in STP. The results enable us to understand further the relationship between dynamic factors of rainfall erosion and nitrogen and phosphorus loss under freeze–thaw conditions.

How to cite: cheng, Y., li, P., Xu, G., and zhang, Y.: Effects of dynamic factors of erosion on soil nitrogen and phosphorus loss under freeze-thaw conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1247, https://doi.org/10.5194/egusphere-egu2020-1247, 2020.

Soil conservation and water retention are important metrics for designating key ecological functional areas. However, research on the quantitative identification of dominant environmental factors in different ecological functional areas remains relatively inadequate, which is unfavorable for zone-based management of key ecological functional areas. This paper presents a case study of Beijing’s key ecological functional areas. In order to objectively reflect the ecological characteristics of key ecological functional areas in Beijing which is mainly dominated by mountainous areas, the application of remote sensing data about high resolution is important for the improvement of model calculation and spatial heterogeneity. Based on multi-source remote sensing data, meteorological and soil observations, soil erosion and water yield were calculated using the Revised Universal Soil Loss Equation (RUSLE) and Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model. Combining the influencing factors, including slope, precipitation, land use type, vegetation coverage, geomorphological type and elevation, a quantitative attribution analysis was performed on soil erosion and water yield in Beijing’s key ecological functional areas using the geographical detector. The power of each influencing factor and their interaction factors in explaining the spatial distribution of soil erosion or water yield varied significantly among different key ecological function areas. Vegetation coverage was the dominant factor affecting soil erosion in Beijing’s key ecological function areas, explaining greater than 30% of its spatial heterogeneity. Land use type can explain the spatial heterogeneity of water yield more than 60%. In addition, the combination of vegetation coverage and slope was found to significantly enhance the spatial distribution of soil erosion (>55% in various key ecological functional areas). The superposition of land use type and slope explained greater than 70% of the spatial distribution for water yield in key ecological functional areas. The geographical detector results indicated that the high soil erosion risk areas and high water yield areas varied significantly among different ecological functional areas. Thus, in efforts to enhance key ecological functional areas protection, focus should be placed on the spatial heterogeneity of soil erosion and water yield in different ecological functional areas.

How to cite: Gao, J. and Jiang, Y.: Identification of Dominant Factors Affecting Soil Erosion and Water Yield within Key Ecological Functional Areas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6839, https://doi.org/10.5194/egusphere-egu2020-6839, 2020.

As the population has grown and human activities have intensified (predominantly agriculture) in the Three Gorges Reservoir area (TGRA) since the 1980s, the substantial areas of arable land on the steep slopes are the main living and farming space for people. Chinese government implemented the Conversion of Cropland to Forest Program from 2001, because of increasing erosion hazard by excessive cultivation and over-felling. To investigate the efficiency of a range of widely recommended program for soil conservation, long-term monitoring in the Heigou watershed was initiated from 2009. Surface runoff, sediment and nutrient transport were measured at watershed. Monitoring has been done to collect sufficient baseline data about soil erosion rate, runoff rate and quantity of soil nutrients (the sum of nutrients in sediment and runoff) in the watershed. The results showed that the soil erosion modulus varied from 138.26 to 355.28 t·km-2·a-1 among between 2016 and 2019, while average soil erosion modulus was 265.8 t·km-2·a-1, lower than the allowable soil loss in this area. The average runoff coefficient, average loss load of total nitrogen and total phosphorus were 53.9%, 11.24 t·km-2·a-1 and 0.19 t·km-2·a-1. Runoff contributed more than 90% of nitrogen loss, and sediment contributed 82.7% of total phosphorus loss. The soil erosion modulus decreased significantly from 2054.06 t·km-2·a-1 to 265.8 t·km-2·a-1 by returning farmland to forest, which was a severe erosion before. Loss load of soil nutrient diversion was high, and TN was excessive for surface water. The ratio of nitrogen to phosphorus would encourage algae growth and eutrophication in TGRA.

How to cite: Huang, Z., Ma, L., Wang, T., and Zeng, L.: Benefit evaluation and annual change of soil and water conservation after converting farmland to forest in Lanlingxi watershed, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7984, https://doi.org/10.5194/egusphere-egu2020-7984, 2020.

EGU2020-12124 | Displays | SSS2.9

Characteristics of Soil nutrient loss under different rainfall pattern in slope plots

Tian Wang, Zhilin Huang, Liang Ma, and Lixiong Zeng

Rainfall intensity and duration directly affect the process of soil nutrient loss. In this paper, long-term, low-intensity rainfall (LL) (58.4mm rainfall, 605min duration) and short-term, high-intensity rainfall (SH) (59.2mm rainfall, 287min duration) were selected to study the pathway for soil nitrogen and phosphorus loss and load differentiation under different rainfall modes by using a slope experiment plot. The results indicated that: (1) The difference between the runoff duration of LL (3410min) and that of SH (410min) was obvious, and the runoff rate was 14.44% and 28.55%, respectively; (2) There were different nutrient concentration distributions. On one hand, the concentration of TN in the surface flow was lower than that in the interflow. The average TN concentration in the surface flow of LL and SH was 13.7 and 16.94 mg·L-1, respectively. The average TN concentration in the interflow of LL and SH was 59.25 and 50.89 mg·L-1, respectively. On the other hand, the concentration of TP in the surface flow was higher than that in the interflow. The concentration of TP ranged from 0.42 to 1.44 mg·L-1 in the surface flow, and from 0.21 to 0.91 mg·L-1 in the interflow; (3) The interflow is the main pathway of nitrogen loss, while the surface flow is the main pathway of phosphorus loss. The respective TN load of LL and SH runoff was 4.04 and 8.49 kg·hm-2, of which the contribution rate of the interflow was 88.49% and 85.54%, respectively. Additionally, the respective TP load of LL and SH runoff was 0.11 and 0.33 kg·hm-2, of which the contribution rate of the surface flow was 65.79% and 70.67%, respectively; (4) The amount of rainfall was almost the same but its intensity was different. High intensity rainfall would cause greater soil nutrient loss. The amount of total nitrogen and phosphorus loss in a sloppy land due to SH rainfall was 2-3 times higher than that due to LL rainfall.

How to cite: Wang, T., Huang, Z., Ma, L., and Zeng, L.: Characteristics of Soil nutrient loss under different rainfall pattern in slope plots, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12124, https://doi.org/10.5194/egusphere-egu2020-12124, 2020.

Introducing and establishing sand-binding vegetation, as one of important approaches for combating desertification, has already applied in the ecological restoration and recovery in Mu Us sandy land for more than 60 years. Study on the dynamics of vegetation coverage in Mu Us Sandy Land and its influencing factors is thus a crucial requirement for guiding and establishing sand-binding vegetation. Based on MOD13A2 NDVI time-series data from 2000 to 2015,annual average temperature, annual precipitation, annual growth season precipitation, the land-use/land-cover (LULC) data, and topographic data, explored its dynamics during 2000–2015 and detected their influencing factors by the geo-detector method. The results showed that: (1) the vegetation coverage decrease from east to west in the Mu Us sandy land; (2) from 2000 to 2015,the vegetation coverage in the Mu Us sandy land has been increasing generally, the growth rate was 0.006 /a; (3) the number of pixels with significant increase in vegetation coverage accounted for 33.24% of the study area, meanwhile there was obvious spatial difference, the areas with significant or extremely significant increase of vegetation coverage were mainly distribute in eastern parts; (4) the main influencing factors of vegetation coverage change were annual precipitation, annual growth season precipitation, annual average temperature and LULC. Results indicate that, the influence of climate factors on Mu Us sandy land vegetation coverage was higher than LULC. It is necessary to put forward a suitable vegetation restoration plan under the projected climate change.

How to cite: Gao, Y.: Vegetation Coverage change and its influencing factors in the Mu Us Sandy Land from 2000 to 2015, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8545, https://doi.org/10.5194/egusphere-egu2020-8545, 2020.

It is well known that soils are vulnerable to water erosion in the hilly and ravine region of the Loess Plateau. The soil and water losses induced by water erosion have both the on-site and off-site impacts in this region, which causes the on-site decline of soil fertility and reductions of crop yields on sloping farmlands, and drains the generated overland runoff and transports the eroded soils/sediments to the off-site valleys or rivers to threaten the safety of the river systems. Constructing the check dam in the valley has the long history and is regarded as one of the powerful measures to control the soil and water losses in a watershed in this region. On the one hand, the check dam plays the vital roles in trapping the large amounts of sediment generated from the sloping lands and buffering the drainage of runoff yielded form the slopes. On the other hand, the silted sediments or eroded soils by the check dam can develop the relatively flat lands in the valleys. The check dam-trapped lands can be utilized to grow the crops and become the farmlands in a watershed. The investigation indicates that the contents of soil organic matter, nutrients and soil moisture of he check dam-trapped farmlands are higher than those of the sloping farmlands or the terraces. According to the analysis on the survey data on the crop yield evolutions in the watershed in this region, the crop yields of check dam-trapped farmlands have been significantly higher than those of the sloping farmlands and terraces in the scenario of the similar fertilizer input and crop cultivars due to the optimum soil moisture condition in the check dam-trapped farmlands. However, the check dam-trapped farmlands face some challenges under the climate change. Some of the check dam-trapped farmlands or the grown crops in these kinds of lands are susceptible to the damage arose from extreme rainstorms because of the outdated measures of soil and water conservation for these kinds of farmlands. In some watersheds, the check dam-trapped farmlands are prone to salinization due to the outdated management. Therefore,the protective measures and techniques of harnessing salinization for the check dam-trapped farmlands should be updated over time in order to keep the check dam-trapped farmlands safe and maintain the higher crop yields in those farmlands in the hilly and ravine region of the Loess Plateau.

How to cite: Dang, W., Wang, B., and Dang, T.: Check Dam-Trapped Farmlands on the Hilly and Ravine Region of the Loess Plateau: Soil Fertility, Crop Yields and Faced Challenges, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21134, https://doi.org/10.5194/egusphere-egu2020-21134, 2020.

EGU2020-9921 | Displays | SSS2.9

Check dams effects on plant and soil interface immediately after wildfire

Bruno Timóteo Rodrigues, Manuel Esteban Lucas-Borja, Demetrio Antonio Zema, and Yang Yu

Installation of check dams is one of the approaches for erosion mitigation on watersheds all around the world, among others soil and vegetation restoration tools. National, regional and local governments have spent in the past, and still currently spend, important funds for basin scale erosion-control schemes (maintenance and new implementations) using numerous check dams. The functions of these structures are diverse and vary depending on the geomorphic context where the structures are built. However, with the number of check-dams increasing to control floods, regulate sediment transport, reduce upstream reach slopes, and stabilize torrent beds, some projects experience disappointing results and project objectives are not achieved due to many different circumstances. Causes of failure include poor construction quality, inadequate check dam location and lack of adequate design criteria. These failures lead to reduced confidence in using check-dams as restoration tools. Moreover, construction of dense networks of check-dams, or alternatively of a few large open structures, implies major economic investments, but a comprehensive evaluation of their long-term effectiveness is still lacking. This work aims to analyse the effect of check dam over soil and plant interface inmediatelly after wildfires. The proposed work pretends to share scientific  evidence of this effect using a study case located in the Mediterranean basin.

How to cite: Timóteo Rodrigues, B., Esteban Lucas-Borja, M., Antonio Zema, D., and Yu, Y.: Check dams effects on plant and soil interface immediately after wildfire, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9921, https://doi.org/10.5194/egusphere-egu2020-9921, 2020.

The present study is an attempt to describe the gross anatomy and histology of the alimentary canal of the economically important Nile fish, Hydrocyon lineatus, which is exclusively a carnivorous fish. The genus Hydrocyan is a member of the family Characidae. The family Characidae is a very generalized group confined to the fresh waters of Africa and South America. The species number about 500, of which only one-fifth are African. Of the twenty African genera only eight are represented in the Nile system. Living specimens of Hydrocyon lineatus were used during this work to study some aspects of the anatomy and histology of the alimentary canal. The general organization and structure of the different layers was found to confirm to the case found in general chordate organization. Nonetheless, it was thought pertinent to conclude that similarity in structure of the caeca to that of the intestine would justify replacement of the old nomenclature from pyloric caeca to intestinal caeca. Again, the presence of an intestinal mucosal fold could possibly be a characteristic diagnostic feature of the group in as much as it could be pleisiomorphic characteristic only occurring in lower groups of chordates.

How to cite: Ahmed, F.: Some Aspects on the Anatomy and Histology of the Alimentary Canal of Hydrocyon lineatus, White Nile, Sudan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11053, https://doi.org/10.5194/egusphere-egu2020-11053, 2020.

EGU2020-10009 | Displays | SSS2.9

Are site characteristics and channel hydro-morphology related with check dam functioning? A case study in México

Manuel Esteban Lucas-Borja, Bruno Gianmarco Carrà, Demetrio Antonio Zema, and Yang Yu

This study presents a comprehensive evaluation of the influence of channel geometry, check dam size, and stream hydrology, as well as site or check dam characteristics including sediment retention capacity and structural conditions of more than 200 check dams recently installed in a large river of Mexico. Analysis was completed using a combination of statistical multivariate techniques (ANOVA and PCA). ANOVA has shown that (i) only check dam material and vegetation cover of the contributing sub-watershed significantly influence check dam conditions and sediment retention capacity, respectively, and (ii) soil type? texture? may play an important role in these check dam characteristics. Conversely, other variables, such as land use and longitudinal slopes of the drained sub-watersheds as well as check dam location have   less influence on check dam sediment storage. PCA has provided two derivative variables related to channel dimensions and vegetation cover , thus demonstrating the influence of these watershed? features on sediment retention behind check dams.

How to cite: Esteban Lucas-Borja, M., Gianmarco Carrà, B., Antonio Zema, D., and Yu, Y.: Are site characteristics and channel hydro-morphology related with check dam functioning? A case study in México, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10009, https://doi.org/10.5194/egusphere-egu2020-10009, 2020.

SSS3.4 – Pedogenic processes of soils and palaeosols across scales - influence of various factors, including imprints of human activities

EGU2020-8786 | Displays | SSS3.4

Mapping and Classification of upland soils formed from sand stone and micaceous schist in Koko/Besse Area in North western Nigeria.

Olufunmilayo Ande, Kayode Are, Olateju Adeyolanu, Adebayo Oke, Oluremi Ojo, Olubunmi Denton, Gabriel Oluwatosin, Omodele Taiwo, Adelabu Lucas, and James Adediran

The study was set up to characterize upland soils of Koko/Besse Local Government Area  in North western Nigeria for sustainable intensification of cropped land. Soil units were identified using flexible grid method. Based on the geology, morphology and  physical  properties the soil units were identified provisional  Soil map was produced in a GIS environment using combination of DEM and field boundary parameters. The major pedogenic processes included ferruginisation, lessivage,  and mineralization. All these processes combined to form ferrallitic soils with  low organic matter content. The soil units on sand stone were generally low in  Cation Exchange Capacity (CEC) (0.88-3.82cmol/kg) while the soils formed from metamorphic rock had low to high CEC (2.92-12.44) The Phosphorus distribution was generally low (0.71–6.96 mg/kg) while Nitrogen content was less than or equal to 0.07%in all the units Soil organic carbon ranged from 0.21-0.95%.  The major pedogenetic processes included, cummilization and  gleization at the lower slopes while ferrolyses and lessivage and ferruginisation with formation of iron stone rubbles and plinthite was dominant at upper slope position of the soils formed from sand stone. While mineralization, salinisation and lessivage were dominant processes with basement complex. The soil units were classified using USDA classification system. The soils on sand stone include  Plinthustults, Kandiustults, Dystrochrept. Natrustalf and Kandiustalf dominated areas underlain by micaceous ferromagnessiun rock. Based on the characterization, sustainable land use will involve use of fortified organic fertilizers, green manure, leguminous cover crops and erosion control measures such as vetiver grass strips

How to cite: Ande, O., Are, K., Adeyolanu, O., Oke, A., Ojo, O., Denton, O., Oluwatosin, G., Taiwo, O., Lucas, A., and Adediran, J.: Mapping and Classification of upland soils formed from sand stone and micaceous schist in Koko/Besse Area in North western Nigeria., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8786, https://doi.org/10.5194/egusphere-egu2020-8786, 2020.

EGU2020-370 | Displays | SSS3.4

Genesis and Evolution of Black Soil in the Eastern Mediterranean

Hussam Hag Mohamed Husein, Wahib Sahwan, Bernhard Lucke, and Rupert Bäumler

Abstract

Knowledge about the genesis and evolution of black soils in the Eastern Mediterranean is vital for sustainable land management as well as for revealing the current and past climate conditions that were decisive for their evolution and development. Hence, it is important to study this type of soil as it only occurs very rarely in the semi-arid region. Answers on the conditions of formation and type of paleoclimate that prevailed during its development can be found in the surrounding environment. In this study, the black soils that currently occur in the Eastern Mediterranean were analyzed in different bioclimatic zones and were found to genetically belong to two soil types: 1-Calcareous black soil (ProperRendzina-Typic Rendolls), 2-Hydromorphic black soil (Haploxerolls). The impact of the relief was obvious on both thickness of the solum and the mollic horizon. Proper Rendzina (Typic Rendolls) occurs on toe slopes and feet slopes, Para-Rendzina (Lithic Rendolls) on shoulders and Chernozems on a flat plain. Regarding the Rendzina, the color reflects the origin of the prevailing parent material from which they are derived: Proper Rendzina forms on limestone, chalk, sandstone, conglomerates, and claystone; Reddish Rendzina on Dolomite and hard limestone, and Grayish Rendzina on Serpentine. It was also found that the Hydromorphic black soils (Haploxerolls, Calcic Chernozems) only occur on calcic marl and lacustrine deposits under saturation conditions and bad drainage in the depressions that formed by the Dead Sea faults. The soil has a thick dark mollic horizon with a high content of organic matter.

Keywords: semi-arid, black soil, Rendzina, Chernozems, eastern Mediterranean.

 

How to cite: Hag Mohamed Husein, H., Sahwan, W., Lucke, B., and Bäumler, R.: Genesis and Evolution of Black Soil in the Eastern Mediterranean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-370, https://doi.org/10.5194/egusphere-egu2020-370, 2020.

Soil formation is controlled by climate, vegetation, organisms, topography, parent material and time. There are various hypotheses on the relative importance of these individual soil-forming factors. The quantitative influence of each soil-forming factor on the expression and rates of soil-forming processes, and in particular the influence of the different factors in combination, have not yet been sufficiently analyzed. The aim of this study was to quantify the influence of the soil-forming factors on the rates of podzolization. For this purpose, we compiled published data from 46 soil chronosequence studies in a database. These studies contained altogether 231 soil profiles of known age, on which we tested existing hypotheses on the influence of different soil-forming factors. The formation of an E horizon and its increase in thickness over time is one of the characteristic features of Podzol formation. As it is one of the few features that was described in all 46 studies, we used it as an indicator of progressive podzolization. Through statistical analysis, we investigated how E horizon thickness is affected by latitude, longitude, mean annual precipitation, mean annual temperature, range between minimum and maximum monthly temperature, annual number of days with frost, vegetation class (pioneer, deciduous and coniferous), sand content, clay content, and soil age.

Since E horizon thickness exhibited a zero-inflated (semi-)continuous distribution, we opted for a zero-altered gamma (ZAG) model, consisting of a Bernoulli and a Gamma part. The Bernoulli part shows, how the probability of the presence of an E horizon changes with soil age and environmental conditions. The Gamma part of the ZAG model allows for capturing the effects of the covariates on E horizon thickness. Our results indicate that vegetation is the most important factor for both (1) the soil age at which podzolization starts (used indicator: first occurrence of an E horizon), and (2) the rates of podzolization thereafter (used measure: increase of E horizon thickness with soil age). Climatic factors such as mean annual precipitation and range of temperature play subordinate roles. They are important for the soil age at which podzolization starts but less important for the rates of podzolization. We did not identify a significant influence of sand content, neither on the start nor the rates of podzolization. Thus, this statistical assessment of global data provides new insights into the relative importance of the individual soil-forming factors on the onset and temporal course of podzolization.

How to cite: Zwanzig, L., Zwanzig, M., and Sauer, D.: Outcomes of a quantitative analysis of 46 soil chronosequence studies: Vegetation plays the key role for rates of podzolization in most environments., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3154, https://doi.org/10.5194/egusphere-egu2020-3154, 2020.

EGU2020-20494 | Displays | SSS3.4

Aeolian inputs as parent materials for Podzols and terra-rossa soils in a dolomitic landscape in the Italian Alps (Salmezza, BG, Italy)

Michele D'Amico, Enrico Casati, Marco Barcella, and Franco Previtali

On an unglaciated karst landscape in the Lombard Pre-Alps (Salmezza, Bergamo, Italy), an extremely high pedodiversity occurs across a few hectares on Norian dolostone. The rock is locally enriched in well crystallized sand-grained quartz. The climate of the area is suboceanic, with >1500 mm of annual rainfall, and an average temperature around 6-8°C. Rendzic Leptosols and Phaeozems are developed on the steepest slopes, Podzols, Cambisols and Luvisols on flatter areas, while Rhodic Luvisols/Alisols (Terra-Rossa soils) are found in doline cracks and crevices. The sand-grained quartz content of the parent rock seems to be the main soil differentiating factor: where it is abundant (ca. 10-20% in volume), it is responsible for the genesis of Podzols.

We sampled and analyzed 9 soil profiles from the Salmezza area, thus characterizing all pedogenic processes active in the area. In particular, we analyzed standard soil chemical properties (pH, organic carbon, base status and Cation Exchange Capacity, dithionite and oxalate-extractable Fe and Al); we performed a total elemental analysis on most samples and on substrate samples, in order to calculate mass balance and element loss and enrichment; we observed thin sections and performed XRD analysis in powder samples and on the clay fraction of most pedogenic horizons as well.

The parent material is a rather pure dolostone, composed of dolomite, locally enriched in quartz. No other minerals have been observed. Very little amounts of Fe, Al and other elements are thus included in the parent rock (almost completely composed of Ca, Mg and Si), often very close to the analytical detection limit. Ca and Mg were almost completely lost during most soil forming processes in this temperate humid climate, while the enrichment in Si, Fe, Al varies broadly amidst the different soils, thanks to different pedogenic processes. Fe and Al, in particular, were up to 120 times more concentrated in Bt and Bhs horizons than in the parent rock. The ratios between stable elements in rocks and soils verifies important inputs of aeolian materials. The values are, however, different also amidst different soils, so an univocal origin of aeolian materials cannot be hypothesized. The mineralogy of the clay fraction is also strongly modified by pedogenesis, so that each soil type is characterized by a different mineralogical assemblage, making it difficult to detect signatures of specific aeolian origins as well.

How to cite: D'Amico, M., Casati, E., Barcella, M., and Previtali, F.: Aeolian inputs as parent materials for Podzols and terra-rossa soils in a dolomitic landscape in the Italian Alps (Salmezza, BG, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20494, https://doi.org/10.5194/egusphere-egu2020-20494, 2020.

EGU2020-501 | Displays | SSS3.4

Influence of environmental parameters on bacterial lipids in soils from the French Alps: implications for paleo-reconstructions

Pierre Véquaud, Sylvie Derenne, Sylvie Collin, Christelle Anquetil, Jérôme Poulenard, Pierre Sabatier, and Arnaud Huguet

Microorganisms can modify the composition of their lipid membrane in response to variations in environmental parameters. This is the case for bacterial lipids such as glycerol dialkyl tetraethers (GDGT) and 3-hydroxy fatty acids (3-OH FAs), both used for temperature and pH reconstructions in terrestrial paleoenvironmental studies. However, a major concern with these proxies is that their structure may be influenced by other environmental parameters than temperature or pH. The present study aimed at identifying and quantifying the influence of environmental parameters such as soil moisture, vegetation types and soil types on bacterial GDGTs and 3-OH FAs. These lipids were analyzed in 49 soil samples collected between 200 m and 3,000 m altitude in the French Alps. The soils cover a wide range of temperature (0 °C to 15 °C) and pH (3 to 8) and are representative of the diversity of soils and vegetation encountered along the investigated altitudinal transects. Using this new well-documented and unique dataset, the GDGT-pH correlation was confirmed, but the one between 3-OH FAs and pH was lower than in previous studies. For the temperature, correlations were lower than in previous studies for the GDGTs and absent for the 3-OH FAs. These observations could be explained thanks to different statistical analyses. Redundancy analysis (RDA) showed that pH is the main driver of the variability of 3-OH FAs and GDGTs, explaining 20.5 % and 56 % of the distribution of these bacterial lipids, respectively, followed by the altitude (8 % influence on the distribution of 3-OH FAs, and 11 % on GDGTs) and granulometry (5 % impact on 3-OH FAs and 7.5 % on GDGTs). Taken together, these results highlight the major influence of the vegetation cover and soil types on the distribution of bacterial lipids. Indeed, we quantified and explained for the first time the impact of the different environmental factors (temperature, vegetation, soil type…) on the distribution of bacterial lipids. This novel comprehension of the impacts of environmental parameters will allow to refine the use of proxies based on these compounds. These results pave the way for new types of applications of GDGTs and 3-OH FAs as environmental proxies in paleosoils, peat or lacustrine sediments.

How to cite: Véquaud, P., Derenne, S., Collin, S., Anquetil, C., Poulenard, J., Sabatier, P., and Huguet, A.: Influence of environmental parameters on bacterial lipids in soils from the French Alps: implications for paleo-reconstructions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-501, https://doi.org/10.5194/egusphere-egu2020-501, 2020.

EGU2020-15848 | Displays | SSS3.4

Complex soil mass redistribution along a catena using meteoric and in-situ 10Be as tracers

Francesca Calitri, Markus Egli, Michael Sommer, Dmitry Tikhomirov, and Marcus Christl

In hilly and mountainous landscapes, the bedrock is actively converted to a continuous soil mantle. The bedrock-soil interface lowers spatially at the soil production rate, and the soil acts as a layer removing sediment produced locally and transported from upslope. Forested soils of a hummocky ground moraine landscape in Northern Germany exhibit strongly varying soil thicknesses with very shallow soils on crest positions and buried soils at the footslope. We explored the explanatory power of both 10Be forms (in situ and meteoric) for forest soils on a hillslope to shed light into the complex mass redistribution. Our main research questions were: how do meteoric and in-situ 10Be compare to each other? What do they really indicate in terms of soil processes (erosion, sedimentation, reworking)? By using both types of 10Be, the dynamics of soils and related mass transports should be better traceable. Both 10Be forms were measured along three profiles at different slope positions: Hydro1 (summit), Hydro3 (shoulder), Hydro4 (backslope). Furthermore, a buried horizon was found in the profile Hydro4 at 160 cm depth and 14C-dated. The distribution pattern of meteoric 10Be of Hydro4 shows an inverse exponential depth profile, and an almost uniform content of in-situ 10Be along the profile. Meteoric 10Be indicates on the one hand that a new soil was put on top of an older, now buried soil. On the other hand, meteoric 10Be is involved in pedogenetic processes and clearly exhibits clay eluviation in the topsoil and clay illuviation in the subsoil. The uniform content of the in situ 10Be shows soil mixing that must have occurred during erosion and sedimentation. The14C dated buried soil horizon indicates a deposition of eroded soil material about 7 ka BP. Consequently, an increase in the in-situ 10Be content towards the surface should be expect which however was not the case. The reason for this is so far unknown. Radiocarbon dating and 10Be data demonstrate that strong events of soil mass redistribution in Melzower Forest are mainly a result of ancient natural events. Further measurements of fallout radionuclides (239+240Pu) showed no erosion for the last few decades in the same catchment.

How to cite: Calitri, F., Egli, M., Sommer, M., Tikhomirov, D., and Christl, M.: Complex soil mass redistribution along a catena using meteoric and in-situ 10Be as tracers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15848, https://doi.org/10.5194/egusphere-egu2020-15848, 2020.

EGU2020-7116 | Displays | SSS3.4

Ending the Cinderella Status of Terraces and Lynchets in Europe

Daniel Fallu, Tony Brown, Kevin Walsh, Sara Cucchiaro, Paolo Tarolli, Pengzhi Zhao, Kristof van Oost, Lisa Snape, Andreas Lang, Rosa-Maria Albert, Inger Alsos, and Clive Waddington

Terraces and lynchets are not only ubiquitous worldwide and within Europe but can provide increasingly important Ecosystem Services (ESs), which may be able to mitigate aspects of climate change. They are also probably a major cause of non-linearity between climate and erosion rates in agricultural systems as noted from alluvial and colluvial studies. In this paper we review the theoretical background of terraces and lynchets, present a modified classification, and show how new techniques are transforming the study of these widespread and often ancient anthropogenic landforms. Indeed the problems of dating terraces and also the time-consuming nature and costly surveys has held back the archaeological study of terraces until now. The applicable suite of techniques available now includes the creation of Digital Terrain Models (DTMs) from Structure from Motion (SfM) photogrammetry, Airborne and Terrestrial Laser Scanning (ALS-TLS); the use of OSL and pOSL, pXRF, FTIR, phytoliths, calcium oxalates from plants and potentially sedaDNA. Examples will be drawn from a recently started ERC project (TerrACE; ERC-2017-ADG: 787790, 2018-2023; https://www.terrace.no/) which is working at over 10 sites in Europe ranging from Norway to Greece.

This paper explains the development of a new holistic approach to terrace archaeology driven by a modern conceptualisation of human-landscape relationships, and facilitated by new scientific developments. We explain the rationale for our choice of case study areas, for example, the range of bio-climatic zones. In addition, this multi-regional approach allows us to address contingent regional and local historical/socioeconomic processes; from demographic fluctuations to the development of specific forms of agricultural techniques. Examples of DTM creation, field analyses and selected results will be given from Martleburg in Belgium and sites in Italy. We will then move on to explain how this combination of a comprehensive suite of modern field and laboratory methods and an interpretive strategy informed by the environmental humanities will yield exciting and groundbreaking results.

How to cite: Fallu, D., Brown, T., Walsh, K., Cucchiaro, S., Tarolli, P., Zhao, P., van Oost, K., Snape, L., Lang, A., Albert, R.-M., Alsos, I., and Waddington, C.: Ending the Cinderella Status of Terraces and Lynchets in Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7116, https://doi.org/10.5194/egusphere-egu2020-7116, 2020.

EGU2020-12908 | Displays | SSS3.4

Palaeoenvironmental insights into Pliocene palaeosols of Tuscany (Italy).

Anna Andreetta, Marco Benvenuti, and Stefano Carnicelli

Pliocene has a key role in assessing future climate impact and specifically, the mid-Piacenzian is considered the most recent period in Earth’s history in which temperatures reached values similar to those predicted for the end of the 21st century, about 2°–3°C warmer globally on average than today. Palaeopedology offers a great potential for elucidating high resolution, deep time palaeoclimate records. Thus, we aimed to investigate palaeosols as suitable archives for reconstructing surface processes, paleo-ecosystem structures and local- to global-scale paleoclimate patterns in the Pliocene.

A favourable opportunity to study soils developed in the Early and in the Late Pliocene was provided on two alluvial sediments in Tuscany (Central Italy). Piacenzian palaeosol-stratigraphic sequences were compared with previously known Zanclean stratigraphic records. A multi-proxy approach, combining stratigraphic and paleopedological evidence, was adopted to produce more robust palaeoenvironmental insights. Field observations were related with quantitative techniques based on geochemical and isotopic analysis, to evaluate pedogenic processes, past-climate and palaeovegetation.

Pedological evidence of two contrasting environments were present at the two sequences. Strong redoximorphic features such as low-grade plinthite were observed in the Zanclean-age soil, suggesting that these soils evolved in humid palaeoclimate in a time span of a few thousand years. On the other hand, the Piacenzian-age soils of central Tuscany represented rhythmic and short intervals of pedogenesis, connected with sea level highstands. The best developed palaeosols show very well-expressed Calcic horizon. Pedogenic carbonates are typically associated with well-drained soil profiles in sub-humid, semi-arid and arid climates characterized by relatively low rainfall and high evapotranspiration. This suggest that Mediterranean-type rainfall patterns may have prevailed in the warmest intervals of Late Pliocene. The studied Piacenzian soils with carbonates were weak- to moderated-developed based on the characteristics of carbonate accumulation that are II and III stage moving from the ancient to the recent ones, suggesting a range of development from 103 to 104 years.

The estimates of the mean annual precipitation (MAP), based on weathering indices (CIA-K) and geochemical climofunctions, further allowed us to solidly inferred that substantial differences in climate conditions leaded to the divergent pedogenesis pathways, even considering the large difference in time as a factor (about one order of magnitude) between the two outcrops.

How to cite: Andreetta, A., Benvenuti, M., and Carnicelli, S.: Palaeoenvironmental insights into Pliocene palaeosols of Tuscany (Italy)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12908, https://doi.org/10.5194/egusphere-egu2020-12908, 2020.

EGU2020-18674 | Displays | SSS3.4

When appearances lie: micropedology of palaeosol markers in a Pleistocene sedimentary record from central Po Plain

Guido Stefano Mariani, Giovanni Muttoni, Gianluca Norini, Fulvia S. Aghib, Roberto De Franco, Andrea Piccin, and Andrea Zerboni

Environmental and time-scale reconstructions of deep sedimentary sequences are based on a wide variety of markers to highlight and characterise environmental variations within a homogeneous sedimentary setting. Moreover, in the lack of reliable age constrain, it is often the only way to highlight timelines and correlations between sequences collected in different places. Within this set of potential markers, palaeosols developed on terrestrial sedimentary beds during biostasy conditions stand out. These evidences are often useful for both their visibility within a core and their strong environmental implications. In continental basins characterized by glacial contributions, they also represent potential time information linked to the fluctuation of glacial and interglacial periods. However, the interpretation of sedimentary markers in cores using visual identification to the naked eye can possibly lead to the wrong conclusions: this method for palaeosol identification is not straightforward and prone to the production of false positives. We conducted detailed micromorphological investigations on a series of markers in a core from the central-northern portion of the Po Plain foreland basin, proximal to the Southern Italian Alps which fed the basin during the Pleistocene.

Seventeen sedimentary anomalies were identified during the visual description on the basis of colours and textures as potential palaeosols and were sampled to be studied in thin section. The study allowed to recognise evidences of soil-forming processes, which could characterise the past pedogenesis as well as their environment. From micromorphological analysis, only 4 samples showed visible signs of pedogenesis or post depositional weathering caused by proximity to the surface. Observed elements range from pedoplasmation to pedogenetic features related to redoximorphic processes and clay illuviation, thus allowing to interpreted them as truncated palaeosols. Conversely, 6 samples showed forms of transport of soil material, either sedimentary or in solution, but did not represent soils formed in situ; these can be interpreted as pedorelicts. Of the remaining samples, 5 were calcrete potentially related to groundwaters, and 2 represented accumulations of Fe/Mn oxides in wetland conditions (“bog iron”). These results suggest a reconsideration of the role of palaeosols as stratigraphic markers in the study of subsurface sedimentary sequences. Precise identification and microstructure characterization are necessary to avoid possible misinterpretations and correlations among cores.

How to cite: Mariani, G. S., Muttoni, G., Norini, G., Aghib, F. S., De Franco, R., Piccin, A., and Zerboni, A.: When appearances lie: micropedology of palaeosol markers in a Pleistocene sedimentary record from central Po Plain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18674, https://doi.org/10.5194/egusphere-egu2020-18674, 2020.

EGU2020-16957 | Displays | SSS3.4

Luminescence age constraints on the Pleistocene-Holocene transition recorded in loess sequences

Daniela Constantin, Stefana-Madalina Sacaciu, Viorica Tecsa, Anca Avram, Robert Begy, Szabolcs Kelemen, Daniel Veres, Cristian Panaiotu, Liping Zhou, Joseph Mason, Slobodan Marković, Ulrich Hambach, Natalia Gerasimenko, and Alida Timar-Gabor

Here we investigate the timing of the last glacial loess - Holocene soil transition recorded in loess-paleosol sequences across the Chinese Loess Plateau, the SE European loess belt and the Central Great Plains, Nebraska, USA by applying comparative luminescence dating techniques on quartz and feldspars. Equivalent dose measurements were carried out using the single-aliquot regenerative-dose (SAR) protocol on silt (4–11 μm) and sand-sized (63–90 μm and coarser fraction when available) quartz. Feldspar infrared stimulated luminescence (IRSL) emitted by 4–11 μm polymineral grains was measured using the post IR-IRSL290 technique.

The paleoenvironmental transition from the last glacial loess to the current interglacial soil was characterized using magnetic susceptibility and its frequency dependence. Based on the OSL ages and the threshold of the magnetic signal enhancement the onset of soil formation started around Termination 1 (~17 ka in the North Atlantic) as observed in radiocarbon-dated regional benthic δ18O stacks (Stern and Lisiecki, 2014) but before the stratigraphic Pleistocene/Holocene transition dated at 11.7 ka in ice core records (Svensson et al., 2008).

No major hiatuses in ages are identified in the investigated sites. A change in the sedimentation rate is generally observed at the Pleistocene-Holocene transition and no significant sedimentation change during the Holocene. Sedimentation rates of around 6 cm/ka are determined for the Holocene soil in most of the sites investigated.

The magnetic susceptibility indicates a gradual increase in pedogenesis after Termination 1 (∼17 ka in the North Atlantic). Based on this, we infer that the upbuilding soil formation prevailed over topdown soil formation during the Pleistocene-Holocene transition in the investigated sites (Roberts, 2008).

 

References

Roberts, H.M., 2008. The development and application of luminescence dating to loess deposits: a perspective on the past, present and future. Boreas 37, 483-507.

Svensson, A., Andersen, K.K., Bigler, M., Clausen, H.B., Dahl-Jensen, D., Davies, S.M., Johnsen, S.J., Muscheler, R., Parrenin, F., Rasmussen, S.O., Röthlisberger, R., Seierstad, I., Steffensen, J.P., Vinther, B.M., 2008.A 60 000 year Greenland stratigraphic ice core chronology. Climate of the Past 4, 47-57.

Stern, J.V., Lisiecki, L.E., 2014. Termination 1 timing in radiocarbon-dated regional benthic δ18O stacks. Paleoceanography 29, 1127-1142.

 

This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme ERC-2015-STG (grant agreement No [678106]).

How to cite: Constantin, D., Sacaciu, S.-M., Tecsa, V., Avram, A., Begy, R., Kelemen, S., Veres, D., Panaiotu, C., Zhou, L., Mason, J., Marković, S., Hambach, U., Gerasimenko, N., and Timar-Gabor, A.: Luminescence age constraints on the Pleistocene-Holocene transition recorded in loess sequences, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16957, https://doi.org/10.5194/egusphere-egu2020-16957, 2020.

EGU2020-11167 | Displays | SSS3.4

A New Continuous Terrestrial Archive of Environmental Change during the Last Interglacial/Glacial Cycle – The Loess-Palaeosol-Sequences of the Schwalbenberg (Middle Rhine Valley, Germany)

Peter Fischer, Olaf Jöris, Andreas Vött, Kathryn Fitzsimmons, Mathias Vinnepand, Ulrich Hambach, Charlotte Prud'homme, Philipp Schulte, Frank Lehmkuhl, Christian Zeeden, and Wolfgang Schirmer

Over the last interglacial/glacial cycle climate variability and forcing in the northern hemisphere is best documented in high resolution from marine and ice core records. The response of land surface processes to climate over this period, however, remains poorly defined. Understanding landscape response to climate change is nevertheless of critical importance not only because as humans we live on and interact with the land, but also in order to identify potential feedbacks and forcings between land and atmosphere which cannot be ascertained from marine and ice core records. In this context, Loess-Palaeosol-Sequences (LPS) are outstanding terrestrial archives allowing detailed reconstruction of palaeoclimate and palaeo­environ­mental changes. However, regarding their complexity, LPS represent polygenetic and multiphase archives over different spatial and temporal scales. Consequently, a solid understanding of geomorphological and pedogenic processes involved in LPS formation, and the interplay with changes in ecological conditions, must be considered before LPS can be correlated with other archives.

Against this background, extensive fieldwork has been carried out at the Schwalbenberg site near Remagen (Middle Rhine valley, Germany) combining geophysical exploration with Direct Push borehole geophysical measurements and sediment coring. We will present a first comprehensive data set for the Schwalbenberg key area based on a transect from up- to downslope. The integration of grain size, organic carbon and weathering indices from long sediment cores (up to 30 m) and profile sections contribute to a better understanding of processes involved in the Schwalbenberg LPS formation. These data combined with age constraints based on radiocarbon and luminescence dating lead to a first robust chronostratigraphic model of the Last Interglacial/Glacial Cycle suggesting the Schwalbenberg LPS to be a terrestrial archive of palaeoclimate variations in phase with northern hemispheric ice and marine records.

How to cite: Fischer, P., Jöris, O., Vött, A., Fitzsimmons, K., Vinnepand, M., Hambach, U., Prud'homme, C., Schulte, P., Lehmkuhl, F., Zeeden, C., and Schirmer, W.: A New Continuous Terrestrial Archive of Environmental Change during the Last Interglacial/Glacial Cycle – The Loess-Palaeosol-Sequences of the Schwalbenberg (Middle Rhine Valley, Germany), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11167, https://doi.org/10.5194/egusphere-egu2020-11167, 2020.

EGU2020-19814 | Displays | SSS3.4

Soil record of the Holocene paleofires at the north of European Russia

Nikita Mergelov, Dmitry Petrov, Andrey Dolgikh, and Elya Zazovskaya

Soils and sediments serve as complementary sources of detailed information on paleofires in various ecosystems. Despite the abundance of charcoal material entrapped in soils they remain relatively less studied pyrogenic archives in comparison to the sedimentary paleofire records (e.g. lacustrine and peat deposits), and that is especially the case for the most territory of Russia. We report here on the numerous soil archives of the Holocene forest fires at the Kola Peninsula (66.347°N, 37.948°E) and the north of Arkhangelsk region (64.747°N, 43.387°E) in Russia. Series of buried Podzols (up to ten successive profiles) separated by the distinct charcoal layers were revealed in specific geomorphological traps like the thermokarst depressions inherited from the early stages of moraine sediments formation (Kola Peninsula), as well as in active and paleokarst sinkholes in carbonate and sulfate rocks (Arkhangelsk region). The maximum temporal depth of archives was estimated as 10261±40 cal yr BP for the key site in Arkhangelsk region, with up to 12 major pyrogenic events recorded at the local scale. Soil formation at the inter-pyrogenic stages maintained a uniform direction for at least 10 thousand years and profiles of Podzols were regularly replicated at all the key sites. We employ here a combination of soil morphological hierarchical analysis, study of geomorphological processes leading to the burial of pyrogenic carbon, 14C dating of charcoal and TOC derived from the soil organic matter, carbon and nitrogen isotope ratio mass spectrometry and anthracomass concentrations analysis to extract a set of paleoenvironmental information from these soil archives. The study of complementary pyrogenic archives in the three-component system of the karst landscape (including bottom and slopes of the funnels, as well as the flat elevated areas between them) helped to mitigate overestimation or underestimation of the anthracomass concentration and allowed to acquire a detailed dataset on paleopyrogenic events at the local scale. This study is supported by the Russian Foundation for Basic Research, Project No. 19-29-05238.

How to cite: Mergelov, N., Petrov, D., Dolgikh, A., and Zazovskaya, E.: Soil record of the Holocene paleofires at the north of European Russia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19814, https://doi.org/10.5194/egusphere-egu2020-19814, 2020.

EGU2020-270 | Displays | SSS3.4

Soils in archaeological structures of the southern Levant: archives of Holocene dust dynamics

Bernhard Lucke, Amir Sandler, Kim André Vanselow, Hendrik Bruins, Nizar Abu-Jaber, and Rupert Bäumler

Ruins and archaeological structures in the southern Levant are often covered by initial soils that developed on debris. The fine grain size fractions of these soils may stem from aeolian sediments, and the ruins could serve as effective dust traps. The physical parameters and chemical composition of archaeological soils in hilltop ruins, cleanout spoils of cisterns, and ancient runoff-collecting terraces were determined in the Petra region in southern Jordan and the northern Negev in Israel. Different types of ruins could not be distinguished with regard to substrate composition. This indicates a predominance of aeolian processes for primary sedimentation, while fluvial processes only re-distribute aeolian material. In the Petra region, a significant local contribution from associated weathered rocks could be observed. Compared to modern settled dust, archaeological soils in southern Jordan are enriched with various major and trace elements associated with clays and oxide coatings of fine silt particles. In-situ weathering seems minimal, but preferential fixation of silt and clay by surface crusts (similar to desert pavements), and a role of moisture in sedimentation processes lead to increased sedimentation of calcareous silt. Contribution of rocks is negligible in the Negev due to greater rock hardness and abundant biological crusts sealing surfaces. Archaeological soils in the Negev and current settled dust consist of complex mixtures of local and remote sources, including significant portions of recycled material from paleosols. Archaeological soils in the southern Levant are archives of Holocene dust sources and aeolian sedimentation processes, with accretion rates exceeding those of Pleistocene hilltop loess in the Negev. Comparison with Pleistocene paleosols suggests that dust sources did not change significantly, but disappearance of snow could have reduced dust accumulation during the Holocene.

How to cite: Lucke, B., Sandler, A., Vanselow, K. A., Bruins, H., Abu-Jaber, N., and Bäumler, R.: Soils in archaeological structures of the southern Levant: archives of Holocene dust dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-270, https://doi.org/10.5194/egusphere-egu2020-270, 2020.

EGU2020-17507 | Displays | SSS3.4

Soils and landscapes as legacies of the sugar industry land use

Raisa Gracheva, Igor Zamotaev, Yulia Konoplyanikova, Natalia Telnova, and Elena Belonovskaya

The sugar industry has been widespread in the world for centuries, accumulating huge amounts of production waste. The development of modern technologies for sugar beet processing has led to the abandonment of dumps and sumps; not all of them were remediated later. In Russia, the industrial production of sugar from sugar beets was established in the early 19th century. For the first time, soils and landscapes formed on abandoned sites of sugar production waste in the Chernozem zone of Russia were studied. The distribution and chronological sequence of abandoned sites were identified using space images and field observation. Sugar production wastes discharged into sumps and landfills contained mainly carbonic lime (СаСО3), caustic lime Ca(OH)2 and organic material, and an admixture of nitrogen, phosphorus potassium and sulfur (about 1-3%). It was revealed that in about 50 years, alkaline soil- geochemical landscapes were formed, which are unusual in the study area. Series of ponds temporarily filled with rainwater – former waste sumps – are covered with dense reed beds (Phragmítes austrális); there, strongly alkaline (pH ≥9), rich in organic matter and bioturbated soils with a thickness of up to 50-60 cm are formed. They can be attributed to Garbic Technosols (Carbonic), but their classification position in WRB needs to be clarified. Reed has spread widely in the surrounding water bodies and rivers; newly formed landscapes enrich waters with nutrients, contributing to their eutrophication. Soil mantle is also complicated by Technosols of industrial sites of sugar factories, soils in the remediated and no-remediated landfills, and soils irrigated with sugar mills' wastewater. All these soils are repositories of large volumes of organic carbon. The study of newly formed soils and landscapes, overgrowing of dumps and sumps is extremely important both for nature conservation and for understanding the seasonal patterns of carbon dioxide emissions from accumulations of organic substances. Integrated soil-geochemical and geobotanical studies of areas affected by the sugar industry can be pioneers, among other things, to expand the horizons of soil and geobotanical classification.

The work was financially supported by the Russian Foundation for Basic Research, project № 19-29-05025-mk.

How to cite: Gracheva, R., Zamotaev, I., Konoplyanikova, Y., Telnova, N., and Belonovskaya, E.: Soils and landscapes as legacies of the sugar industry land use, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17507, https://doi.org/10.5194/egusphere-egu2020-17507, 2020.

EGU2020-2622 | Displays | SSS3.4

Harmonisation of a large-scale historical database with the principles of the World Reference Base for Soil Resources

Tereza Zádorová, Jan Skála, Vít Penížek, Daniel Žížala, and Aleš Vaněk

The possibility of an adequate use of data and maps from historical soil surveys depends, to a large measure, on their harmonisation. Legacy data originating from a large-scale national mapping campaign, “Systematic soil survey of agricultural soils in Czechoslovakia (SSS, 1961–1971)”, were harmonised and converted according to the World Reference Base 2014 (WRB). Applying three different methods of taxonomic distance computation and quantitative analysis and reclassification of the selected soil properties, the conversion of so-called Basic soil representatives (BSR) – mapping soil units providing information about soil (type, subtype, variety) and lithology (parent material, texture, soil depth, skeleton content) – to their counterparts in the WRB has been effectuated. The results proved the good potential of the used methods for soil data harmonisation. The values of taxonomic distance correspond to the different concepts and settings of the soil classes in the harmonized soil classifications. Classes with specific and narrowly defined diagnostics, often with one or few strong and distinctive features, show close distances with their counterparts, and, often, have only one relevant counterpart. On the contrary, soils with variable soil properties were approximating several related units. The additional information on the soil skeleton content, texture, depth and parent material showed the potential in the specification of some units, though the harmonisation of the soil texture turned out to be problematic due to the different categorisation of soil particles. The resulting soil classes have been presented for each polygon (so-called soil district) as i) one to one conversion, when each BSR is converted to one, most probable, WRB soil class (Reference soil group, RSG) and ii) soil association corresponding to the three closest RSGs. The validation of the results in the study region showed an average overall accuracy for a one-to-one (59.4 %) conversion and a very good accuracy (83.8 %) for the polygons presented as soil associations. The conversion accuracy differed significantly in the individual soil units, and ranged from 92 % in Fluvizems to 0 % in Technosols and Histosols. The extreme cases of a complete mis-classification can be attributed to inconsistencies originating in the historical database and maps. The study showed the potential of modern quantitative methods in the legacy data harmonisation and also the necessity of a critical approach to historical databases and maps.

Supported by the Ministry of Agriculture of the Czech Republic, Project No. QK1820389.

How to cite: Zádorová, T., Skála, J., Penížek, V., Žížala, D., and Vaněk, A.: Harmonisation of a large-scale historical database with the principles of the World Reference Base for Soil Resources, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2622, https://doi.org/10.5194/egusphere-egu2020-2622, 2020.

EGU2020-4178 | Displays | SSS3.4

Soils and relief relationships in subalpine grasslands in the Central Pyrenees (NE, Spain)

David Badía-Villas, Lucía Buendía-García, Luis Alberto Longares-Aladrén, José Luis Peña-Monné, and Clara Martí-Dalmau

On two accumulation levels, separated by an unevenness up to 2 m, two contrasted plant communities can be differentiated in subalpine stage of the Pyrenees: the dense tussock-forming grass Nardus stricta, at the upper level (L1), and the open chalk grasslands at the lower level (L2). In order to confirm the soil-relief-grasslands relationships, we analyzed and compared soil pedogenesis and properties in both accumulation levels. In addition, we classify the soils following WRB and ST systems and we discuss the finesse of both taxonomies in these high mountain environments. The work has been carried out at 1900 masl, in the Ordesa and Monte Perdido National Park (PNOMP), in the summer grasslands site of La Estiva (Fanlo, Central Pyrenees, NE Spain). Five soil pits were studied in every accumulation level (L1 and L2) for a side-by-side comparison.

            The study of soils in the two levels of accumulation reveals a series of differences in their genesis, properties and soil classification. The accumulation of organic matter and lixiviation are the dominant edafogenetic processes in L1, to which we must add the rejuvenation by gully erosion in L2. Soils at L1 and L2 shared many physical properties as a fine granulometry, with a homogeneous particle-size distribution with depth. In both levels, the soils lack carbonates, even though limestones are the parental material. The soils in L1 have a greater thickness and, thus, a higher water holding capacity than in L2. In relation to chemical properties, soils in L1 have a significantly lower pH, a lower base saturation, and lower available calcium content than in L2, reflecting a more intense leaching process, consistent with a longer period of slope stability. Over L1 with Nardus mat-grasslands, the main soil is classified as Orthoeutric Cambisols (Clayic, Humic), and the soil over L2, with chalk-grasslands, as Hypereutric Leptosols (Loamic, Ochric). Soil taxonomy System (USDA), giving more weight to the temperature regime, classify both soils as Haplocryept, at the level of great group, separating them at the subgroup level as Typic Haplocryept (L1) and Lithic Haplocryept (L2), according to the depth at which limestone appears (lithic contact). Definitely, the microtopograhy and geomorphologic context, is linked to the pedodiversity, which goes hand in hand with plant diversity in this subalpine environment.

How to cite: Badía-Villas, D., Buendía-García, L., Longares-Aladrén, L. A., Peña-Monné, J. L., and Martí-Dalmau, C.: Soils and relief relationships in subalpine grasslands in the Central Pyrenees (NE, Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4178, https://doi.org/10.5194/egusphere-egu2020-4178, 2020.

EGU2020-5661 | Displays | SSS3.4

The presence of silty mantles in Northcentral Appalachian, USA soils and their relevance to pedology

Patrick Drohan, Thomas Raab, and Florian Hirsch

Across the northcentral Appalachians, USA, high silt content soils are found as silty mantles or deep, high silt content pedons. The origin of such soils can be attributed to additions of wind-blown dust deposits (WBD) or local parent materials (i.e. shales or siltstone lithology). Previous research on silt soils originating specifically from WBD attributed to late marine isotope stage (MIS) 2 loess has often been isolated to drainageways receiving outwash from deglaciation. We hypothesize that thin (<25-50 cm) silty mantles, and some deep silt soils occurring farther from outwash systems, are also indicative of post MIS 2 WBD and their extent is widespread. To test this hypothesis, we evaluated over 900 pedons from an ~119,280 km2 area of the northcentral Appalachians, USA to: (i) develop a particle size signature indicative of soils largely derived from WBD versus local parent materials, (ii) determine the potential depth of WBD additions to soils, and (iii) document the spatial extent of WBD versus deep, high-silt content soils across part of the region. Results suggest that silty mantles are prevalent across the study area and have a particle size signature indicative of loess and the mean depth of WBD additions to soils is ~50 cm.  Below 50 cm, local lithology or pedogenesis more influences particle size trends.  Pedon results were applied in a spatial modeling effort using the USA Soil Survey Geographic Database (SSURGO) to document the extent of silty mantles (over non-silt sourced parent materials) and deep, high silt content soils.  Model results indicate silty mantles are common on stable landscape positions or positions that accumulate sediments (depressions or valleys). Aspect dependent deposition appears tied to sources of WBD deposits, and deposits correspond strongly to regional studies of WBD deposits derived from loess. Last, proximity to topography, which can act as a trap for WBD, appears to be a key variable explaining silty mantle and deep, high-silt content soil occurrence. 

How to cite: Drohan, P., Raab, T., and Hirsch, F.: The presence of silty mantles in Northcentral Appalachian, USA soils and their relevance to pedology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5661, https://doi.org/10.5194/egusphere-egu2020-5661, 2020.

EGU2020-21440 | Displays | SSS3.4

Development of Podzols in relation to Jenny's soil formation factors

Tiina Törmänen, Antti-Jussi Lindroos, Hannu Ilvesniemi, and Mike Starr

Podzols are considered to be the most common upland forest soil type in Finland. However, there have only been a few studies that have examined the degree of podsolization in Finnish soils. More detailed information about this dominating process in our soils can be utilized in other kinds of environmental research such as the impacts of climate change, carbon and nutrient cycling, and the degradation of soil and water systems.

We studied how the intensity of podsolization is related to Jenny’s classic five soil formation factors: climate, parent material, topography, biotic and time. The degree of podzolization of 86 soil profiles distributed over the whole of Finland was described using four podzolization indices: E-horizon thickness, B-horizon rubification, profile Al+Fe oxide eluviation-illuviation, and their sum (Podzolization Development Index, PDI). The soil profiles, selected out of over 600 soil profiles in a national database, met the World Reference Base for Soil Resources (WRB) criteria for them to be classified as Podzols. The relationship between the podzolization indices and a number of site and soil variables (continuous and categorical) describing Jenny’s soil formation factors were then evaluated. While podzolization intensity was found to be related to soil profile age, elevation, longitude, forest site type, aspect, Sphagnum moss cover and B-horizon texture, the individual relationships were weak. However, looking at the combined effect of all the variables using Partial Least Squares regression analysis, which is unaffected by multicollinearity among the predictor variables, nearly 70% of the measured PDI index could be explained.

How to cite: Törmänen, T., Lindroos, A.-J., Ilvesniemi, H., and Starr, M.: Development of Podzols in relation to Jenny's soil formation factors, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21440, https://doi.org/10.5194/egusphere-egu2020-21440, 2020.

EGU2020-21125 | Displays | SSS3.4

Recovery of forest patches in central Mongolia after fire: Which role does soil hydrology play?

Florian Schneider, Michael Klinge, Jannik Brodthuhn, and Daniela Sauer

The distribution of forest patches in the foreststeppe of central Mongolia reflects the interplay of several environmental factors that together control the vegetation pattern of the landscape. Since the mean annual precipitation of this semiarid area rarely exceeds 300 mm, the existence of forest strongly depends on the hydrological properties of the system. Only north-facing slopes provide suitable conditions for the growth of larch trees (Larix sibirica Ledeb.) due to their reduced evapotranspiration. Plains and south-facing slopes are covered by open steppe.However, after disturbance of the forest patches by fire, the regrowth of larch trees does not proceed equally in all areas. During fieldworkat the northern edge of the Khangai Mountains, we identified areas that seemed to havesimilar site conditions but neverthelessshowed different regrowth of larch trees after fire, ranging from intensive regrowth to no regrowth at all.Thisobservation stimulated us to carry out a comprehensive study of soils, vegetation and landscape development in field campaigns in 2017 and 2018, followed by laboratory analyses of soil samples.Through this work, we aimed at identifying the role of soil hydrology for forest succession in this sensitive ecotone.

We described and sampled 57 soil profiles, including sites (i) under forest, (ii) under steppe, (iii) on sites with succession after forest fire, (iv) on sites without succession after forest fire. In the field, we carried out measurements of water conductivity (by use of a compact constant head permeameter). In the laboratory, we analyzed particle size distribution and carried outkfand pF measurements.

These analyses showed that the dominant grain size of the soils was sand, whereby soils with forest regrowth had slightly loamier texture than those without regrowth. We concluded that already slightly loamier texture may be important for water storage during dry periods and thus for forest regrowth.Soils with forest regrowth had higher hydraulic conductivity in the first 25 cm and lower conductivity below.Soils without forest regrowth showeda reverse depth pattern of hydraulic conductivity. We concluded that quick drainage through the upper horizons supports forest regrowth, as it reduces competition for water with grass roots in the upper part of the soil.Soils with forest regrowth hadgreater plant-available water capacity than those without regrowth. We conclude that under the given climatic conditions, storage of plant-available water is a key factor for regrowth / no regrowth of forest after disturbance.

How to cite: Schneider, F., Klinge, M., Brodthuhn, J., and Sauer, D.: Recovery of forest patches in central Mongolia after fire: Which role does soil hydrology play?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21125, https://doi.org/10.5194/egusphere-egu2020-21125, 2020.

EGU2020-13174 | Displays | SSS3.4

Archives of Holocene geomorphological development in the Khangai Mountains, Mongolia

Daniela Sauer, Michael Klinge, Manfred Frechen, and Yan Li

The aim of this work was to obtain a deeper understanding of the factors triggering geomorphological processes in the semi-arid mountain forest-steppe of the Khangai Mountains in central northern Mongolia. We hypothesized that the pattern of geomorphological processes in this region is strongly influenced by (i) the spatial distribution of aeolian sediments and (ii) forest fires. We further assumed that the spatial and functional relationships between these two geomorphological factors lead to various types of sediment-soil archives of landscape evolution in different relief positions. These different types of archives should have recorded different pieces of information, which might be combined into a reconstruction of the landscape evolution in this area. We intended to use these different archives to reconstruct the Holocene landscape evolution, and in particular, to identify the roles of aeolian sediment distribution and forest fires on the geomorphological processes that took place over the Holocene.

The area is dominated by steppe vegetation. Only the north-facing slopes of the mountains, where reduced evapotranspiration leads to somewhat increased soil moisture, have forest. The bedrock on the slopes is overlain by Pleistocene periglacial slope deposits (PPSD), consisting of rock debris, which is mixed with fine sand in its upper part. These PPSD are widely covered by an aeolian sand sheet, which is usually more than one meter thick. IRSL ages indicate that the main deposition of these sediments took place 13-11 ka ago. Sediments at the toe slopes and on the valley bottom consist of layered, dark and lighter-colored, silty and sandy material with cryoturbation features. They apparently originate from soil material that has accumulated at the toe slopes and in the valleys by colluvial, fluvial and aeolian processes.

On the slopes under forest, charcoal commonly occurs in the upper 20 cm of the soils and provides calibrated 14C ages of up to 2 ka. Calibrated 14C ages of charcoal and soil organic carbon of the sediments at the toe slopes are generally older (up to 4.4 ka). This difference suggests that the charcoal produced by earlier forest fires, together with the sediment in which it is embedded, has been washed from the upper and mid slopes down to the toe slopes and valleys. Charcoal of later fires is at least partially still in the place of its origin, on the slopes.

Based on a set of 25 14C and 24 IRSL ages, we distinguish three main periods, i.e., (1) a period of extensive aeolian transport and deposition during the late glacial period, 16-11 ka ago, (2) a period of geomorphological stability from early until mid-Holocene, and (3) a period of enhanced aeolian, colluvial, and alluvial processes since 4.5 ka. The abundance of charcoal, indicating frequent forest fires during the late Holocene, points to a severe change of environmental conditions and geomorphological dynamics. It is not yet clear whether this change is due to more arid climate or human activities. Therefore, our further research will focus on distinguishing natural and human influence on the landscape evolution in Mongolia since the mid-Holocene.

How to cite: Sauer, D., Klinge, M., Frechen, M., and Li, Y.: Archives of Holocene geomorphological development in the Khangai Mountains, Mongolia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13174, https://doi.org/10.5194/egusphere-egu2020-13174, 2020.

EGU2020-7457 | Displays | SSS3.4

Unraveling the origin of the loess of the lower ebro river basin

Jose Manuel Plata, Carles Balasch, Rafael Rodriguez, Rosa Maria Poch, and Jaume Boixadera

Loess deposits related to the lower course of the Ebro river occupy about 2,000 km2, between the border of the Ebro depression and the Móra d’Ebre basin. They are the largest loess area in the Iberian Peninsula. The detailed study of these deposits has been intensified since the first decade of this century and now the first cartography of their spatial distribution is available. In parallel, the mineral composition, texture and physicochemical properties have been studied and the soils developed on them have been described and analyzed (mainly Calcic Haploxerept, Typic Xerorthent, Typic Calcixeroll). The most modern units have been dated with optically stimulated luminescence (OSL) and would have been deposited between 17 and 34 ky in relation to the Last Glacial Maximum and the oldest (few outcrops) would exceed 115 ky.

They form very discontinuous covers with average thicknesses of about 3-4 m, preferably located on the sheltered slopes of the prevailing W-NW winds and subsequently accumulated in the valley bottoms of the network of rivers and tributaries of the Ebro River. Their generally coarse grain size, with the predominance of very fine sand (50-100 µm) followed by the coarse sand fraction (20-50 µm), classifies them as sandy loess, and this feature has been interpreted as an effect of the proximity of the source areas of the particles, which according to the literature would be less than one hundred km.

Their mineral composition reflects a clear dominance of quartz and calcite (plus dolomite) in similar proportions and feldspar, mica and opaques as secondary minerals. In many of the outcrops, gypsum (up to 20%, average: 3.1%) appears as a companion mineral, which is redistributed in the profiles, preferably in the lower half, as gypsum infillings and crystal intergrowths, up to 1 cm size). It also gives a different response regarding magnetic susceptibility.

The direction of the prevailing winds, the arrangement of the outcrops, the coarse texture and the mineral composition are key indications of the proximal origin of the aeolian materials. Among the candidate areas are the alluvial plains of the Ebro river, which at that time would suffer the deflation of the extensive T-2 terrace (about 8-10 km wide and 20-30 m above the current talweg) and the interfluvial areas with Tertiary outcrops containing gypsum. Heavy minerals could serve as tracers of the origin of river sediments and gypsum (non-existent in river sediments) could be used as a marker of sedimentary materials with Oligocene and Miocene gypsum of the Ebro Depression, which is absent in the Móra d'Ebre basin.

Gypsum loess appears frequently and preferentially on the outcrops of the Ebro Depression. However, in the Móra d’Ebre basin they are seldom, which would indicate the isolation and independence between the two units of accumulation of loess by the Catalan Precoastal Range that would act as a first order orographic barrier against clouds with aeolian dust from the Ebro Depression.

How to cite: Plata, J. M., Balasch, C., Rodriguez, R., Poch, R. M., and Boixadera, J.: Unraveling the origin of the loess of the lower ebro river basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7457, https://doi.org/10.5194/egusphere-egu2020-7457, 2020.

EGU2020-7170 | Displays | SSS3.4

Investigation of spectral properties of different Quaternary paleosols and parent materials

József Szeberényi, Gabriella Barta, Ágnes Novothny, Diána Csonka, István Viczián, Erzsébet Horváth, and Tamás Végh

Diffuse Reflectance Spectroscopy (DRS) is a rapid method for analysing sediments and paleosols, which is a relatively new approach in Quaternary research. This method take into account the clay mineral content, the amount of Fe-bearing minerals and the grain size composition of samples at the same time.

Continuing our earlier research (Szeberényi et al. 2019), this paper reveals the relationship between the DRS curves of paleosols and their parent material. The basis of recent research was the most variable curve sections (between 400-1460 nm wavelength range) of entire measurement range (between 240-2000 nm). The goal of the actual study was to quantify the significant differences between original reflectance curves of paleosols and their parent materials in the case of different quaternary sediment successsions.

Different Quaternary sediment samples were chosen for characterization and comparison their reflectance curves, hereby detection and quantify the most important spectral properties of different paleosols and parent materials. Samples of different sediment types and paleosol variants were investigated from a loess-paleosol sequence at Malá nad Hronom (Slovakia) and a fluvial-aeolian sediment complex at Pilismarót (Hungary).

Five investigated curve sections were separated as the best indicators of reflectance properties of DRS curves. To compaire of spectral properties of samples was used the length of investigated curve sections. It could be explain by ΔR% value, which was shown the difference of reflectance intensity between end points of investigated curve sections.

This investigation showed the quantifiable differences between the units of pleistocene sediment successions, based on the reflectance properties. The influence of pedogenic processes were good detectable. Significant discrepancies were observed between reflectance curves of well-developed paleosols and parent material samples in the VIS-NIR range. Only in the visible range were observed differences between the weak developed paleosol layers and their parent materials. It could be separated from each other the fine sand, the sandy silt and the loess materials based on the intensity of entire reflectance curves.

 

How to cite: Szeberényi, J., Barta, G., Novothny, Á., Csonka, D., Viczián, I., Horváth, E., and Végh, T.: Investigation of spectral properties of different Quaternary paleosols and parent materials, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7170, https://doi.org/10.5194/egusphere-egu2020-7170, 2020.

Granulometric composition and magnetic susceptibility are important indicators of the genesis of paleosols, loesses and other newest sediments. Along with other characteristics, they make it possible to reconstruct evolution, surrounding landscapes and climatic changes in the past. The stratotypic section "Alexandrovsky quarry" (natural monument in Kursk, 51°35′31″N, 36°3′21″E) reveals the most complete structure of the Late Pleistocene for the periglacial zone of the East European Plain. Soil-sediment stratum with a thickness of more than 10 m represents the filling of a small buried valley. The formation of the stratum took place practically without interruptions during the last 130 thousand years. It includes two interglacial paleosols: Holocene (Marine Isotope Stage 1) and Ryshkovo (MIS 5е); four interstadial paleosols: Kukuevka (MIS 5с), Streletsa (MIS 5а), Alexandrovka (MIS 3.1), Bryansk (MIS 3.2), and also loess, pedo-sediment and other deposits that have periodically experienced exposuring to cryogenesis [Sycheva, 2012]. The particle size distribution and the magnitude of the magnetic susceptibility reflect the complex history of the stratum formation and reveal detailed climate changes in the Late Pleistocene. The particle size distribution was determined with fractionation method by Kaczynski and by instrumental laser-diffractometry method on a "Malvern Mastersizer 3000" particle size analyzer. The magnetic susceptibility was determined by a SatisGeo KM-7m field capameter with triplicate measurements for every 6 cm.
A change in the granulometric composition from Ryshkovo (MIS 5e) medium loamy deposits to heavy loamy soils and loess belonging to MIS 3.1 was established. The largest value of the clay fraction (<0.001 mm) is characteristic of the MIS 3 paleosols. Significant values of this fraction are also characteristic of the humus horizons of paleosols and Bt horizon Ryshkovo paleosol (MIS 5e). The lowest clay content is observed in loess, especially in their upper parts and in the eluvial horizon of the Rushkovo paleosol (MIS 5е). The data gained by instrumental method of particle size determination is different from such as data gained by the Kaczynski method for the upper heavy loam stratum (MIS 3-1). The predominant fraction is fine dust, in contrast to the lower sediments MIS 5-4, where the coarse silt fraction prevails. Whereas according to data gained by Kaczynski method, the coarse silt fraction prevails in the entire studied thickness of the loess-soil sequence.
Magnetic susceptibility (MS) depends on the content of superparamagnetic mineral in each of the samples and represents levels of pedogenesis in loess deposits. The highest MS values are characteristic of the humus horizon of the interglacial Ryshkovo paleosol (MIS 5e). Followed by Ah horizon of the Streletsa paleosol (MIS 5a) and underlying loess. Smaller values are characteristic of the Kukuevka (MIS 5c) paleosol. But they are more eroded and represented by transitional AB horizons. Loess is characterized by the lowest values of magnetic susceptibility.
The study was funded by RFBR according to the research project № 19-29-05024.

How to cite: Zakharov, A., Sycheva, S., and Panin, P.: Granulometric composition and magnetic susceptibility of the Late Pleistocene loess-soil sequence of the stratotype section (Alexandrovsky quarry, Kursk, Russia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11396, https://doi.org/10.5194/egusphere-egu2020-11396, 2020.

A catena of the Holocene soils and interstadial Bryansk paleosol has been studied within a small closed depression in the Kazatskaya Steppe on the Central Russian Upland. This depression is located on the territory of the Central Chernozem Biospheric Reserve named after V.V. Alekhin, Kursk oblast, Russia and presumably originated from suffosion processes. The main objective of the work is to find out how the Bryansk paleosol (final phase of MIS 3) changes under the influence of not only the cryogenesis of the Valdai glaciation maximum (MIS 2), but also Holocene soil formation (MIS 1) under different conditions of the modern microrelief within the studied catena. We studied the macro- and micromorphological characteristics, certain physical and chemical properties of the Bryansk paleosol on one hand and those of the superimposed Holocene soil on another, taking into consideration various conditions of the present-day microrelief. The studied catena is a typical component of the landscape and soil cover structure for watersheds of the Central Russian Upland. On the micro-elevation rising 80 cm above the micro-depression bottom, theHaplic Chernozems are developed, on the slope – the Luvic Chernozems, and at the bottom – theStagnic Chernozems. The change of the "normal" profile of paleosol of warm interstadial in final phase of MIS 3 started already in the last stages of its formation. The Bryansk soil is heavily deformed by cryogenic processes during the Valday glaciation maximum (the Vladimir cryogenic horizon, MIS 2). The secondary diagenesis of the Bryansk paleosol is related to the Holocene soil-forming processes. The Holocene soils are superimposed on the Middle Valday Bryansk paleosol, transforming it in different ways in different sectors of catena. On micro-elevation the Holocene diagenesis is minimal and consists in fragmentation by mesofauna, additional penetration of carbonates in the upper horizon of the paleosol. The micromorphological analysis showed that the fragmentation of soil mass by mezofauna is very significant, humus is abundant in the form of brown spots (organo-mineral complexes), and calcite is completely immersed into the clay fine material. The largest in size but rare grains of sparite have an unusual shape and probably biogenic origin. At the bottom of the micro-depression the Bryansk paleosol is the most transformed, and the entire profile of the Bryansk soil turned into illuvial horizon of the Holocene meadow-chernozem soil. At the micro-level of observation the clay fine material of the Bryansk soil is strongly consolidated (close c/f related distribution), has signs of anisotropy: circular, grano- and crosstriated b-fabric, the mineral grains are almost invisible and have the dimension of fine dust, very thin Fe- clay coatings in the pores, Fe spots are scattered over the fine clay material, and very characteristic of the presence of many black and sometimes transparent with a black border cube-shaped minerals (whewellite, weddellite?) which fill plant residues in the pores. This work was supported by the Russian Foundation for Basic Research; project N 19-29-05024 mk.

How to cite: Sycheva, S. and Khokhlova, O.: The diagenesis of the Bryansk paleosol (MIS 3) in a suffusion micro-depression at the center of the Russian Upland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1897, https://doi.org/10.5194/egusphere-egu2020-1897, 2020.

The loess-paleosols sections (LPS) situated on flat interfluves integrally reflect the zonal characteristics of paleolandscapes and climate change of large-scale rank such as interglacial-glaciation, megainterstadial-stadial. However, they do not reflect small-scale climatic fluctuations and the local diversity of paleoecological conditions. Geochemical combinations of soils and sediments along the slopes of the paleo-relief, i.e., paleo-catenas, make it possible to supplement the missing links of the paleogeographic history and to detail the paleogeographic events.

In support of this idea, we show the results of study of paleo-catenas of the Ryshkovo pedo-litho-complex formed in the Mikulino interglacial (MIS 5e) and presented in the Alexandrov quarry near the city of Kursk, the Central Russian Upland. The Ryshkovo paleocatenas are analyzed along the slopes of the northern and southern expositions in the paleo-balka’s upper course. The variability of the Ryshkovo paleosols fits into the framework of one genetic soil type. Its closest analogue is sod-podzolic soil of mixed forests (Luvic Retisols). The main differences between the soils developed in the paleo-catenas are related to the degree of detail of the evolutionary development record due to various combinations of soil forming and denudation-sedimentation processes. Paleo-catena 1 along the slope facing to south is distinguished by the simplicity of soil profiles. Paleo-catena 2 of the northern exposition slope is more diverse in the completeness of the structure of paleosol profiles. It is complicated by micro-catena along a buried coastal ravine. Based on the study of the Ryshkovo paleo-catenas, the following stages of soil development in the Mikulino interglacial (130-117 ka BP) are reconstructed: 1) the lower meadow soil (the first soil stage) is read throughout the paleo-catena 2, i.e., in the bottom and on the paleo-balka slope; 2) the formation of bottom and coastal ravines, their subsequent filling with material of a humus horizon, carried away from the slopes during the climatic cooling within the interglacial (the first morpholithogenic stage); 3) the formation of the of sod-podzolic soil profile (the second soil stage) is recorded in the fillings of the coastal ravine; 4) subsequent erosion and accumulation of humus material in the bottom of the balka and ravine (the second morpholithogenic stage); 5) sod-podzolic soil (the third soil stage) is detected throughout the catena; 6) stressful restructuring of the paleoecological situation before burial is recorded in traces of a strong fire and a post-fire storm erosion at the end of the interglacial period when the climate became cooler (the third morpholithogenic stage). Thus, in the catena along the northern exposition slope and especially in the bottoms of the ravine and the main channel of the balka, the detailed change in the stages of development of local landscapes is reflected: three soil-forming stages separated by two erosion stages, and the most intense final (third) erosion stage. A complex combination of soil and relief-forming processes is reflected in the physicochemical properties of the Ryshkovo pedo-litho-complex, especially in its upper humus-accumulative and eluvial parts. This work was supported by the Russian Foundation for Basic Research; project N 19-29-05024 mk.

How to cite: Pushkina, P. and Sycheva, S.: Paleo-catenas of the Ryshkovsky pedo-litho-complex (130-117 KA BP) of the Central Russian Upland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7240, https://doi.org/10.5194/egusphere-egu2020-7240, 2020.

EGU2020-3070 | Displays | SSS3.4

A Field-, GIS- and FTIR based approach to assess the distribution and development of soils affected by historical charcoal production in western Connecticut, USA

Alexander Bonhage, Florian Hirsch, Thomas Raab, Anna Schneider, Alexandra Raab, and William Ouimet

The effects of historical charcoal production on forest soil properties are increasingly well studied on sites in Europe and the northern USA. The most obvious effect of this past forest use practice is the addition of large quantities of charcoal into the soil at sites of former charcoal production. These so called relict charcoal hearth (RCH) sites are mapped in expansive numbers due to the rising availability of high-resolution LiDAR data. However, studies determining the impact of RCHs on more than a field plot scale are rare, so far. To transform results from specific RCH sites to a landscape scale, we sampled and measured 52 RCH sites on a 0.7 km² area in the Litchfield Hills in western Connecticut, USA.

In this study we combine field based measurements of RCH site stratigraphy and geometry, GIS-based spatial analysis of site locations, laboratory determination of soil organic and pyrogenic carbon and FTIR-based analysis of soil carbon. We aim at assessing the soil distribution and soil development in an RCH affected landscape, i.e. the distribution of three typical soils commonly found in these landscapes: natural forest soils, technogenic soils of RCH platforms and soils buried below technogenic soils. Furthermore, we determine the distribution of organic and pyrogenic carbon in these soils and specifically the variation of carbon contents within the technogenic RCH soil stratigraphy.

Preliminary results suggest that RCH site occurrence does not depend on relief position, i.e. RCH site abundance is not correlated with slopes, plateau or flatland positions. However, RCHs with multiple layers of technogenic substrates are more abundant on slope positions. RCH soils have a significantly increased content in total carbon compared  to unaffected forest soils. Multi-layered RCHs have a heterogeneous vertical distribution of pyrogenic carbon and a possibly modern enrichment of organic matter in the surface soil. Wet chemical digestion of RCH soil samples coupled with FTIR analysis shows an increased presence of aromatic compounds and therefore pyrogenic carbon. However, the majority  of carbon in RCH soils seems to be of non-pyrogenic origin. As of now it is unclear, whether  the content of pyrogenic carbon is underestimated by analytical uncertainties or if pedogenic processes are responsible for an enrichment of labile- and semi-labile organic carbon in the charcoal-rich RCH soil.

How to cite: Bonhage, A., Hirsch, F., Raab, T., Schneider, A., Raab, A., and Ouimet, W.: A Field-, GIS- and FTIR based approach to assess the distribution and development of soils affected by historical charcoal production in western Connecticut, USA, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3070, https://doi.org/10.5194/egusphere-egu2020-3070, 2020.

EGU2020-5744 | Displays | SSS3.4

Relic charcoal hearth geomorphology and hydrology across the northcentral Appalachians, USA

Samuel Bayuzick, Patrick Drohan, Thomas Raab, and Florian Hirsch

Throughout the northeastern United States and Europe, relic charcoal hearths (RCHs) are more regularly being discovered in proximity to furnaces used for iron or quick-lime production; charcoal was used as a primary fuel source in the furnaces.  RCHs have been found across parts of Europe and Connecticut, USA in different hillslope positions, on vary degrees of slope and aspect, all of which can be a factor affecting the shape of the RCH.  Their usage for charcoal production varied with time period furnaces were in operation with some hearths being used once and older ones (such as in Europe) being used multiple times. RCHs across the northcentral Appalachians, USA have been minimally investigated, thus determining where they occur on the landscape, their shape, and their morphologic positions will be useful in discerning their effect on surface hydrology and soil development. Our study focuses on developing a repeatable process for: finding RCHs, classifying the different shapes or styles of the hearths in relation to their geomorphic positions and quantifying how RCHs may alter surface hydrology.  

We used a combination of processed LiDAR to create hillshades of varying light angles and altitude, and slope gradient maps derived from the same LiDAR, to visually digitize > 6,100 hearths. A subset of the mapped hearths was ground-truthed for accuracy of the methodology. For our study, three areas in the mid-Appalachian region of Pennsylvania were chosen for study in order to reflect different historical time periods of construction and environments. A goal of our study is to determine the age of hearths. We hypothesize that using a calculated 3D distance to nearby furnaces, hearths closer to furnaces will be the oldest and have a higher likelihood of being used multiple times resulting in multiple layers of charcoal-enriched substrate. An initial analysis of RCHs indicates a relationship between slope gradient and hearth shape. Hearths constructed on flatter slope gradients are seemingly more circular in shape and have more equal axes whereas steep slopes have a more oval shape being elongated in one axis and shortened on the other.  Likewise, there may be a relationship between hillslope position and the shape of the RCHs such as more circular hearths are on or near flatter hillslope positions (such as on summits or shoulders) whereas oval shaped hearths are on steeper hillslope positions (like backslopes). We also modeled the effect of RCHs on hydrology.  Based on a combination of topographic wetness index data and geomorphology, hearths are not acting as sinks for surface flow but instead often cause water to flow around them leading to slightly drier conditions within RCHs. Future work will address site-specific monitoring of hearth temperature and moisture, and hearth carbon decomposition dynamics in relation to temp and moisture conditions.

How to cite: Bayuzick, S., Drohan, P., Raab, T., and Hirsch, F.: Relic charcoal hearth geomorphology and hydrology across the northcentral Appalachians, USA , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5744, https://doi.org/10.5194/egusphere-egu2020-5744, 2020.

EGU2020-2339 | Displays | SSS3.4

The temperature and moisture regime of charcoal-enriched land use legacy soils

Anna Schneider, Florian Hirsch, Alexander Bonhage, Alexandra Raab, and Thomas Raab

The stratigraphy and properties of soils can be significantly altered by past land use, even in areas that have been continuously used for forestry. Soils on relict charcoal hearths (RCHs) are a widespread example of such a pedological legacy of past forest use. RCH soils occur in many forest areas and receive increasing attention as model sites to study long-term effects of soil amendment with biochars, however, their physical properties have hardly been studied. The objective of our study was to characterize the soil temperature and moisture regime of RCH soils through comparison to reference forest soils on sandy substrates in woodlands in Brandenburg, Germany. We combined laboratory analyses of bulk density, pore size distribution, thermal conductivity and saturated hydraulic conductivity with sensor-based monitoring of soil temperature, moisture contents and matric potentials. 

The results of laboratory analysis reveal high soil organic matter (SOM) contents, a low bulk density and high porosity of the RCH substrates. Associated with this RCH specific soil structure, RCHs exhibit clearly lower thermal conductivity. However, the higher total porosity of RCH substrates does not necessarily imply higher water retention and plant-available water contents in the RCH soils than in the topsoil horizons of undisturbed forest soils.  The monitoring results reveal distinct differences between the temperature regimes of the RCH and reference profiles, with the RCH soil exhibiting higher daily and seasonal temperature variations within the topmost horizon, but lower variations in deeper parts of the profiles. Soil moisture monitoring shows higher water contents in RCH soils under relatively wet conditions and lower water contents under dry conditions, and increased spatial variation in soil moisture in RCH soils. Overall, the results show increased spatial and temporal variability of soil temperature and moisture on RCHs, which implies an increased variability in ecological site conditions in historic charcoal production areas.

 

How to cite: Schneider, A., Hirsch, F., Bonhage, A., Raab, A., and Raab, T.: The temperature and moisture regime of charcoal-enriched land use legacy soils , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2339, https://doi.org/10.5194/egusphere-egu2020-2339, 2020.

EGU2020-10808 | Displays | SSS3.4

Agrarian landforms in Czechia and their future value

Jitka Elznicová, Johana Vardarman, Jan Pacina, Iva Machova, Jiri Stojdl, Jiri Riezner, and Tomas Matys Grygar

Mountane and submontane hilly landscapes, mainly around the borders of the former Czech Kingdom were used for farming just rarely.  During the High Middle Ages these remote regions were colonized by mostly German speaking settlers invited by Bohemian King. Their villages were established and agricultural plots were divided into parallelly or fan-like ordered parcels, partially separated by agrarian walls. Parts of the historic settlements were continually used for agriculture for many centuries, sometimes with no problems with soil erosion. The traces of these landscape structures were best preserved around villages, which were not too suitable for farming and thus were not included into process of agriculture collectivization in the second half of the 20th Century. The historical landscape structures has thus preserved mainly in areas of high altitudes, steep slopes, low settlement density. Those areas with the traces, bearers of landscape memory, has been continually swallowed by forest and shrubs regrowth as noticeable in aerial images.

We mapped the preserved historical structures in the region of the Czechia based on the linear non-forest woody vegetation in current orthophotos and by use of topographic map and DTM based on LiDAR mapping. This examination showed a surprisingly large spatial extent of the historical landscape pattern, well framed bywoody vegetation. For our study, we used also old maps, archival aerial photographs and digital terrain models created from newly acquired airborne LiDAR imaging. We performed imaging of the wall structures by geophysical means (electromagnetic imaging EMI using a DEMP instrument). We focused particularly on terraced fields and agrarian walls.

The stone walls situated more-or-less perpendicular the slope gradient resulted in nearly terrace-like surface topography. Even in areas with a mean original slope higher than 10° the final slope of the fields decreased to a few degrees. Most agrarian walls were constructed from stones; their bases are usually a bit deeper than current terrain level at the wall foot according to the EMI images. Some walls are higher and wider than 1 m and their upper edge is buried by topsoil washed from upper parts of the fields. The topsoils on the fields have comparable grain size distribution in upslope, middle and downslope parts, showing the minimal net transfer of fine particles by erosion. No traces of deep erosion or soil degradation were observed, which could be attributed to the skeletal character of soils in well-preserved historical terrace fields.

We examined also local plant cover, which showed preservation of meadow species even after re-forestation of the former historical settlements and considerable differences in vegetation species composition of the agrarian wall and in surrounding agricultural parcels. Aconsiderable part of the still preserved historical agrarian, may play a positive future role in biodiversity of montane areas by presence of contrasting biotopes, e.g. including tree species more resistant to the global change than widespread spruce monocultures.

How to cite: Elznicová, J., Vardarman, J., Pacina, J., Machova, I., Stojdl, J., Riezner, J., and Matys Grygar, T.: Agrarian landforms in Czechia and their future value, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10808, https://doi.org/10.5194/egusphere-egu2020-10808, 2020.

EGU2020-20363 | Displays | SSS3.4

Effects of land use history on heavy metals concentration in agricultural soils

Giulio Genova, Georg Niedrist, Stefano Della Chiesa, Erich Tasser, Luigimaria Borruso, Stefano Cesco, and Tanja Mimmo

Intensive agricultural management can have significant impacts on soil properties. Such effects and their degree are often related to the history of land use and to the agronomic practices. When legacy soil data are missing, historical land use maps can help to describe how crop management might have changed the concentration of certain elements in soils. In this study, we prove how permanent crop management (vineyards and apple orchards) influenced heavy metal concentration in agricultural soils in South Tyrol, Italy. We selected areas where land-use change was unidirectional going from forests, grasslands and arable lands to apple orchards or vineyards. We hypothesize that the heavy metal accumulation in the soil starts when a parcel is converted to intensive permanent crops. This hypothesis allows us to see if there are any significant differences between parcels with a longer or shorter intensive agriculture history. We used approx. 6000 soil samples analyzed between 2006 and 2016 and coupled them with historical land use maps dating from the 1850s until today. Soils that have been cultivated as apple orchards or vineyards since the 1850s are characterized by higher concentrations of Cu. The oldest vineyards have much higher soil Cu concentrations than apple orchards of the same age with a median content of 342 mg kg–1 and 212 mg kg–1 of Cu respectively. Similar patterns, but with smaller extent can be described also for Zn concentration. Comparing the age of vineyards with today’s concentration we estimate an accumulation rate of 2.4 mg kg–1 year–1 of Cu. We conclude that historical land use maps are extremely helpful in understanding today’s soil characteristics especially with not degradable pollutants such as heavy metals. High concentrations of Cu in vineyards reveal the widespread and abundant use of this metal in viticulture for plant defense programs through time. The accumulation trend proves that further research and monitoring is needed to understand spatial and temporal pattern of Cu and Zn pollution in intensively managed permanent crops and to estimate their impact on taxonomical and functional fungal and bacterial diversity. These aspects are of pivotal role in determining the soil fertility levels of our cultivated soils.

How to cite: Genova, G., Niedrist, G., Della Chiesa, S., Tasser, E., Borruso, L., Cesco, S., and Mimmo, T.: Effects of land use history on heavy metals concentration in agricultural soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20363, https://doi.org/10.5194/egusphere-egu2020-20363, 2020.

SSS4.2 – Soil biological capacity, greenhouse gases’ emission and carbon stocks of SUITMA and croplands: assessment and best-management practices

EGU2020-11475 | Displays | SSS4.2

Diffusive limitation to photosynthesis and plant-microbe N competition dominate the urban lawn response to secondary salinization

Dario Liberati, Ramilla Brykova, Maria Cristina Moscatelli, Stefano Moscatello, Emanuele Pallozzi, and Olga Gavrichkova

Release of de-icing agents is the main cause of increasing soil salinization in urban and rural areas.  Grasses are the dominant vegetation in urban lawns and are exposed to different rates of soil salinization depending on the distance to the paved salt-affected surfaces. The capacity of these ecosystems to maintain C sequestration and nutrient cycling functioning depends on the sensitivity to salinization of the main players: primary producers and their interaction with microbial community.

In this mesocosm study we aimed to evaluating the impact of soil secondary salinization rates on the functioning of Lolium perenne. Salinization treatments were applied for two months in spring, irrigating the mesocosms with the commonly used de-icing agent NaCl at two concentration, 30 mM (low salinity treatment) and 90 mM (moderate salinity treatment). The leaf physiological  responses of Lolium were assessed monitoring photosynthetic rates (A), stomatal conductance (gs)  mesophyll conductance (gm), carboxylation capacity (Vcmax). Quantitative limitation analysis (QLA) was applied to calculate the relative contribution of diffusive and biochemical limitation to photosynthesis under salinization. Productivity was estimated by regular mowing of plants to 4cm height. Finally, plants were harvested and analyzed on leaf mass per area (LMA), leaf N content and 15N isotope composition. Rhizosphere soil was sampled and analyzed on the activity of enzymes involved in the cycling of C, N, S and P. 

Salinity increased LMA and leaf N, reducing  Lolium aboveground productivity. Photosynthetic rates were almost halved under both salinity treatments. QLA shows that photosynthesis was mainly limited by gm, limitation accounting for 68% and 54% of the total limitation in 30mM and 90mM, respectively. gs reduction significantly limited photosynthesis only in 90 mM (32% of total limitation), while biochemical limitations (due to a reduction in Vcmax) remained below 20% of the total limitation in both treatments.

Mesophyll conductance to CO2 depends on leaf anatomical and biochemical traits and is usually negatively related to LMA. The increased LMA observed under salinity treatments suggests that changes in the leaf structure (like increased cell wall thickness) could be responsible for most of the A (and consequently productivity) reduction.  On the other hand, the increased leaf N content is in agreement with the lack of significant reduction in Vcmax. Accumulation of N compounds in leaves in response to salinization was accompanied by a decline in soil extracellular enzymes involved in N and other cycles. Over-competing of the microbial pool in access to nutrients by vegetation could be suggested in conditions of salinization. Because the belowground biomass was not affected, decline in C losses with salinization could be hypothesize which should balance the shortage in C inputs.     

In conclusion, salinization mainly limited A through gm limitation, probably associated  to the increased LMA. At the same time, altering the capacity of the microbial pool to compete for N,  it increased leaf N, possibly reducing  the impact of biochemical limitation on A and avoiding a further A and productivity decline.

Experiment was financially supported by the Russian Science Foundation, project No.17-77-20046.

How to cite: Liberati, D., Brykova, R., Moscatelli, M. C., Moscatello, S., Pallozzi, E., and Gavrichkova, O.: Diffusive limitation to photosynthesis and plant-microbe N competition dominate the urban lawn response to secondary salinization, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11475, https://doi.org/10.5194/egusphere-egu2020-11475, 2020.

Understanding the interactions among different soil microbial species and how they responded to disturbances are essential to ecological restoration and resilience in the damaged mining areas. This information, however, remains unclear and poorly understood. In this study, we investigated the bacterial distribution in disturbed mining areas across three provinces of China, and constructed molecular ecological networks to reveal the interactions among soil bacterial communities. Furthermore, we examined the relationship between the microbial network topology and environmental factors to show if there is a correlation between the resilience of bacterial community and external pressure. Bacterial community composition differed dramatically among the different disturbed mining areas, and bacterial diversity decreased as microbial networks became more complex. Additionally, based on the network topology, we distinguished key microbial populations among the different mining areas, such as Proteobacteria, Acidobacteria, Actinobacteria, and Chloroflexi. Moreover, the network structure was significantly correlated with soil properties (e.g., pH value, electrical conductivity value, and available phosphorus value), which suggested that microbial network interactions might change the soil resilience, then affect soil ecosystem functions. Overall, our findings provided insight into the ways in which microorganisms responded to mining activities and change the resilience by regulating their interactions in different ecosystems.

How to cite: Ma, J. and Chen, F.: Molecular ecological network complexity drives stand resilience of soil bacteria to mining disturbances among typical damaged ecosystems in China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6286, https://doi.org/10.5194/egusphere-egu2020-6286, 2020.

EGU2020-9869 | Displays | SSS4.2 | Highlight

Are Collembola flying onto green roofs?

Sophie Joimel, Laure Vieublé-Gonod, Baptiste Grard, and Claire Chenu

Are Collembola flying onto green roofs?  

With a worldwide urban population projected to reach 5 billion by 2030 (Véron, 2007), the roles and benefits of urban green spaces cannot be denied, like climate regulation by trees or water flow regulation (Gómez-Baggethun and Barton, 2013). If green spaces are among the new societal expectations of urban people, they also play a crucial role in preserving biodiversity in urban areas. Among them, green roofs are a great opportunity to create green space in cities as they represent 32% of cities’ horizontal surfaces (Frazer, 2005). Their installation is also perceived as a possible way to preserve biodiversity in cities. However, the effectiveness of green roofs in supporting biodiversity, especially soil biodiversity, has rarely been studied.

Thanks to different research programmes (TROL, SEMOIRS and T4P), we investigated the taxonomic and functional collembolan biodiversity in both extensive and productive green roofs as well as in ground-level urban microfarms in order to (i) evaluate the effectiveness of green roofs in supporting soil biodiversity, (ii) identify the mechanisms of colonisation by soil organisms and (iii) separate the effect of landscape and soil conditions on collembolan communities assemblages.

Surprisingly, green roofs are supporting high levels of soil biodiversity. Despite various soil characteristics (organic matter and water avaibility), no difference was found between extensive roofs and rooftop gardens concerning the taxonomical structures of collembolan communities (e.g. species richness, abundances). In contrast, there are differences concerning both taxonomic and functional compositions. Two ways of colonisation are suggested: a passive wind dispersal − the “flying” collembolans − and a settlement through compost inputs. We conclude that stakeholders should take into account the spatial connections of green roofs with other green spaces in order to support urban soil biodiversity.

How to cite: Joimel, S., Vieublé-Gonod, L., Grard, B., and Chenu, C.: Are Collembola flying onto green roofs?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9869, https://doi.org/10.5194/egusphere-egu2020-9869, 2020.

EGU2020-2062 | Displays | SSS4.2

Urban Soils Mycobiota of the Subarctic (Apatity, Murmansk region, Russia)

Maria Korneykova, Dmitriy Nikitin, Andrey Dolgikh, and Anastasia Soshina

The soils mycobiota of Apatity was first characterized. Significant differences in quantitative and qualitative parameters of urban soils fungal complexes of the Subarctic zone in comparison with zonal soils were revealed. It was shown that the biomass of fungi in the soil of the residential area of Umbric Leptic Entic Podzol (Arenic, Neocambic) is 0.18 – 0.20 mg/g, in the background forest soil Folic Leptic Albic Podzol (Arenic) – 0.31 mg/g. The smallest values (0.04 – 0.08 mg / g) are typical for areas with no vegetation and a densely compacted surface (playground - Leptic Entic Podzol (Arenic, Neocambic, Technic), unpaved pedestrian walkway – Umbric Leptic Entic Podzol (Arenic, Neocambic).

In the soils of recreational and forest areas, fungi were mainly in the form of mycelium (66-70% of the total biomass), while in the soils of residential and agricultural areas in the form of spores. Spores are mainly represented by small forms up to 3 microns. The amount of large spores is insignificant, but they were mainly detected in the soil of the residential area.

The number of copies of ITS rRNA genes of fungi in soils of different functional zones varies from 4.0×109 to 1.14×1010 copies/g of soil, with the highest values in the natural Podzol of the forest zone and Podzol of the unpaved pedestrian walkway.

The number of micromycetes CFU in the upper soil horizon ranges from 1×103 to 9×104 CFU/g of soil, reaching maximum values in the soil of the Umbric Leptic Entic Podzol recreation zone (Arenic, Neocambic, Technic). The features of cultivated forms of micromycetes distribution on the soil profile in different functional zones were revealed: in the Podzol of the residential area, the maximum accumulation of fungi was noted in the lower horizons, while in the soil of the recreational, agricultural and forest areas, their maximum number was noted in the top horizon. However, the first two differed from the background one in the absence of a second maximum accumulation of micromycetes in the illuvial Bs horizon.

In general, urban soils were characterized by a low species diversity of micromycetes complexes and a specific structure significantly different from the background soils. The genus Penicillium is characterized by maximum species diversity. Trichocladium griseum and Penicillium dierckxii dominate in the communities of microscopic fungi in the soil of the residential zone, P. melinii in the soil of the recreational areas and in the playground, in the soil of agricultural area Plaggic Entic Podzol (Arenic) - micromycetes of the genus Fusarium, and in the background forest soil - P. decumbens.

How to cite: Korneykova, M., Nikitin, D., Dolgikh, A., and Soshina, A.: Urban Soils Mycobiota of the Subarctic (Apatity, Murmansk region, Russia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2062, https://doi.org/10.5194/egusphere-egu2020-2062, 2020.

EGU2020-3333 | Displays | SSS4.2

Long-term impacts of inter-cropping and reduced tillage on ecosystem services in dryland agriculture

María Martínez-Mena, Elvira Díaz-Pereira, Noelia García-Franco, Carolina Boix-Fayos, and Maria Almagro

We assess the long-term environmental impacts and delivery of several ecosystem services of crop diversification (inter-crop with legumes/cereal) in two rainfed almond (Prunus dulcis Mill.) orchards under semiarid Mediterranean conditions. In addition, the effect of the intensity of tillage practices (conventional tillage vs. reduced tillage) in the almond monocultures was also tested. The study was carried out in two farms located in the province of Murcia (South East Spain) and the experimental design consisted of nine plots (49 m long and 7 m wide) in a randomized-block design, with three replicates for each treatment: inter-crop, (IRT), monoculture under conventional tillage (MCT), and monoculture under reduced tillage (MRT). Each plot comprised five almond trees: the three central trees were used for soil measurements and the other two trees constituted guard rows (a buffer zone to avoid edge effects). The conventional tillage consists in a chisel plowing to 15 cm depth using a cultivator between three and five times a year while the reduced tillage treatments (MRT and IRT) implies ploughing only twice a year (autumn and spring), to control weeds. The tillage affects the whole plot area, including the area around the trunk base. In the monoculture, weeds are the only vegetation present between the rows. The inter-crop consists of a mix (3:1) of common vetch (Vicia sativa L.) and common oat (Avena sativa L.), sown annually during early autumn at 150 kg seeds ha-1 and mowed in May. After manually mowing, it is incorporated into the soil using a cultivator.

During ten years (2009-2018) the effects of crop diversification and reduced tillage on a range of soil quality indicators (including soil physical, chemical and biological properties) were monitored allowing the evaluation of different support, regulating and provisioning ecosystem services (e.g. carbon sequestration, water availability, crop yield).

An improvement in soil quality with the inter-crop management (IRT) was detected after three years from its implementation, after which it was maintained or slightly increased for ten years. When comparing the inter-cropping system with the monoculture one, an improvement in soil quality indicators for regulating and supporting ecosystem services was observed at the plow layer (e.g., soil bulk density decrease, as well as increases in soil water retention capacity, plant water availability, infiltration capacity, fertility, microbial activity, and OC stabilized in aggregates). During the first seven years of inter-cropping implementation, an average reduction of about 30% in the crop yield (provisioning ecosystem service) in the inter-crop treatment respect to the monoculture was observed. However, those differences decreased, or even were reversed after eight years, suggesting that the observed positive effect on crop production with inter-crops does not occur at the same time than the improvement on soil quality but several years after that. All together, these results highlight the potential of inter-cropping in woody crops as a good option to be adopted by farmers and for climate change mitigation and adaptation.

How to cite: Martínez-Mena, M., Díaz-Pereira, E., García-Franco, N., Boix-Fayos, C., and Almagro, M.: Long-term impacts of inter-cropping and reduced tillage on ecosystem services in dryland agriculture, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3333, https://doi.org/10.5194/egusphere-egu2020-3333, 2020.

EGU2020-20118 | Displays | SSS4.2

Changes in soil carbon stocks and distribution under perennial and annual bioenergy crops

Fabien Ferchaud, Bruno Mary, Thidarat Rupngam, and Claire Chenu

Bioenergy crops are expected to provide biomass to replace fossil resources and reduce greenhouse gas emissions. In this context, their effect on soil carbon sequestration is of primary importance. There is a wide range of candidate crops including perennial C4 crops or annual crops but their impact on soil organic carbon (SOC) stocks remain very uncertain as shown by the wild variability in published experimental results.

In this study, we measured the changes in SOC stocks under perennial (miscanthus and switchgrass), semi-perennial (fescue and alfalfa) and annual (triticale and sorghum or maize) bioenergy crops managed with two N fertilisation rates. The experiment called “Biomass & Environment” is located in northern France on a deep loamy soil (Haplic Luvisol) and was set up in 2006. The soil was sampled at the start of the experiment, in 2011-2012 and again in 2018 (0-60 cm, 5 layers). SOC stocks were calculated at equivalent soil mass and δ13C was systematically measured and used to calculate changes in new and old SOC stocks. In 2018, the SOC distribution in different soil particle-size fractions was also characterized for some treatments.

After 12 years, there was a large increase in SOC concentration (+7.6 g kg-1 on average) under perennial crops in the surface layer (≈ 0-5 cm) but a slight decrease in deeper layers. Changes in δ13C also showed that more than half of the new SOC accumulated in the surface layer. In addition, the additional SOC storage in the first layer was found in coarse organic fractions (50-200 and 200-2000 μm) but also in the more stabilised 0-50 μm fraction. SOC concentration under semi-perennial crops increased in the two first layers (≈ 0-20 cm), from 10.2 g kg-1 in 2006 to 11.6 g kg-1 in 2018 on average and slightly decreased below. Under annual crops, a decrease in SOC concentration was observed in all layers and particularly in the third layer (≈ 20-33 cm). There was no significant effect of the N fertilisation. Over the old ploughed layer (≈ 0-33 cm), SOC stocks increased between 2006 and 2018 under perennial and semi-perennial bioenergy crops (by 3 and 2 t C ha-1 on average respectively) and decreased by 7 t C ha-1 on average under annual crops.

This study show that different bioenergy crops can have contrasted impacts on SOC stocks but also on SOC distribution in the soil profile.

How to cite: Ferchaud, F., Mary, B., Rupngam, T., and Chenu, C.: Changes in soil carbon stocks and distribution under perennial and annual bioenergy crops, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20118, https://doi.org/10.5194/egusphere-egu2020-20118, 2020.

EGU2020-11058 | Displays | SSS4.2

Intercropping fava bean with broccoli can improve soil properties while maintaining crop production under Mediterranean conditions

Mariano Marcos-Pérez, Virginia Sánchez-Navarro, and Raúl Zornoza

Including legumes in intercropping systems may be regarded as a sustainable way to improve soil quality, fertility and land productivity, mostly due to facilitation processes and high rhizospheric activity which can mobilize soil nutrients for plants. Improvements in production and soil quality depend on inherent soil properties, climatic conditions, adopted management practices and fertilization, among others. The aim of this study was to assess the effect of the association between broccoli (Brassica oleracea var italica) and fava bean (Vicia fava) grown under different intercropping patterns on crop production, soil organic carbon (SOC), total nitrogen (Nt), soil aggregate stability (SAS) and soil fertility, compared to a broccoli monocrop. We defined a randomised block field experiment with three replications assessing the effect of monocropping, row 1:1 intercropping, row 2:1 intercropping and mix intercropping, with 30% reduction in fertilization in intercropped systems compared to monocrop. Soil sampling took place at harvest in February 2019. Results showed that the broccoli-fava bean intercropping significantly increased the general land production, with similar broccoli yield of 20000 kg ha-1 in all treatments, plus 8000 kg ha-1 coming from fava bean. Crop diversification and fava bean cultivation even in monocrop significantly increased SOC and Nt compared to broccoli monocrop. SOC and Nt were 1.06% and 0.09%, respectively, for broccoli monocrop, while they had average values of 1.29% and 0.12%, respectively for the intercropped systems. SAS was also significantly affected by crop diversification, with increases in the proportion of the macroaggregates (size >2 mm) with intercropping. Broccoli monocrop showed an average proportion of these macroaggregates of 9.19%, while they increased up to 17.51% in intercropped systems. CEC was not significantly affected by intercropping SAS showing almost same percentage of aggregates independently of the treatment. Available P significantly increased in intercropped systems, likely due to increased microbial activity with the simultaneous growth of the two crop species. However, no significant effect of intercropping was observed with any other nutrient (Ca, Mg, K, Mn, Cu, Fe, Zn and B), suggesting that microbial communities activated by the crop association are highly related to P mobilization but not so intensively involved in other nutrients. Thus, intercropping systems like broccoli-fava bean association can be regarded as a viable alternative for sustainable crop production while increasing soil fertility despite reducing the addition of external fertilization. However, more crop cycles are needed to confirm this trend.

How to cite: Marcos-Pérez, M., Sánchez-Navarro, V., and Zornoza, R.: Intercropping fava bean with broccoli can improve soil properties while maintaining crop production under Mediterranean conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11058, https://doi.org/10.5194/egusphere-egu2020-11058, 2020.

EGU2020-116 | Displays | SSS4.2

Management Practices Influenced Corn Grain Yield and Soil Chemical Properties

Maysoon Mikha and Alan Schlegel

Land sustainability could be influenced by management decisions, soil nutrients content, and soil erosion potential. This study evaluates the management that consist on two sources of nitrogen (cattle beef manure, M; and synthetic fertilizer, F) and two levels of residue removal (0% and 80%) on corn yield and soil chemical properties in a no-tillage irrigated field. The study was initiated in 2011 in Tribune, Kansas where the nitrogen treatments and residue removal were organized in randomized strip design with four replications. After Seven years of annual M addition, corn yield and soil chemical properties significantly increased compared with synthetic fertilizer. Annual residue removal at 80% level greatly reduced soil chemical properties measured especially STN, SOC, and soil P availability for subsequent crops. Residue removal at 80% show a potential to decrease soil EC compared with 0% removal, but the EC reduction was not significant. The data generated from this study shows that soil nutrients content was reduced with removing the residue even in irrigated and well fertilized field unless organic amendment was accompanied the residue removal practice.

How to cite: Mikha, M. and Schlegel, A.: Management Practices Influenced Corn Grain Yield and Soil Chemical Properties, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-116, https://doi.org/10.5194/egusphere-egu2020-116, 2020.

EGU2020-663 | Displays | SSS4.2

Soil organic carbon stability of urban soils and of floodplain soils under different hydrothermal conditions

Inna Brianskaia, Vyacheslav Vasenev, and Ramilla Brykova

Пожалуйста, вставьте свой абстрактный HTHigh anthropogenic impact and the rate of urbanization result in a decrease of urban soils’ capacity to perform ecosystem services. Carbon sequestration is an important soil-based ecosystem service, which can be assessed through quantity and quality soil carbon stocks. The stability of soil organic matter (SOM) is characterized by the resistance of its constituent components to biological, chemical and physical destruction. In the study, SOME stability in peat-sand mixture used for urban soils’ construction; floodplain soil was analyzed in response to temperature-moisture conditions. The decomposition rate of various soils was assessed. Decomposition was assessed through studying microbial production of CO2. In the research the CO2 emissions were studied under following temperatures and moisture conditions: temperature – 7°C, 22°C, 30°C and 40°C and moisture – 0.2 WHC, 0.4 WHC, 0.6 WHC, 0.8 WHC, 1 WHC. Moisture affects the amount and activity of microbial biomass, controls the availability of oxygen to microorganisms, causes periods of water microbial stress and also can destabilize organic matter, resulting in increased availability of carbon to soil microorganisms. Different patterns of moisture and temperature impacts on the soil organic carbon (SOC) decomposition rates were observed. It was concluded that, depending on the qualitative composition of carbon, the impact of hydrothermal conditions on the emission of carbon dioxide changed.ML здесь.

How to cite: Brianskaia, I., Vasenev, V., and Brykova, R.: Soil organic carbon stability of urban soils and of floodplain soils under different hydrothermal conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-663, https://doi.org/10.5194/egusphere-egu2020-663, 2020.

EGU2020-1064 | Displays | SSS4.2

Soil microbial biomass, community level physiological profiles relate to tree species and its state in urban environment

Alexandra Seleznyova, Alexey Yaroslavtcev, Olga Gavrichkova, Alexey Ryazanov, Julia Kovaleva, Nadezhda Ananyeva, and Riccardo Valentini

Urban trees and soil microbial communities are the key ecosystem components to provide the supporting, provisioning and regulating services that define citizen’s well-being. Understanding the relationships between physiological states, age, species of trees and microbial functional properties are needed for a management of urban areas and landscapes' engineering. The research focuses on finding linkages between a wide range of trees’ properties monitored by smart TreeTalker technology and soil functional microbial indexes in Moscow megapolis.

The study was carried out on the RUDN University campus area (Moscow, Russia), where six tree species were selected (Pinus sylvestris, Populus tremula, Acer platanoides, Tilia cordata, Picea abies, Betula pendula). TreeTalker device was installed on the preselected five trees of each species for monitoring the sap flux, vertical stability (according to digital accelerometer), spectrums of canopy reflectance, trunk and canopy air temperature and humidity. Monitoring started in May 2019. The composite soil samples (0-10) were taken under each tree at the 0.5 m distance from its stand by augering in October 2019. In the samples, the microbial biomass carbon (MBC, SIR-method), basal respiration (BR), community level physiological profile (CLPP, MicroResp) and Shannon microbial diversity index (H’) based on CLPP were determined.

Soil MBC content was significantly depended on tree species, increasing from A.platanoides to T.cordata (from 538 to 1445 µg C g-1). The microbial diversity index was lowest in soil under A.platanoides (H’=2.1) and the highest for B.pendula (H’=2.4). The soil CLPP for A.platanoides was mainly shifted to microbial response on carboxylic acids with the low reaction on amino and phenolic acids compared to other trees species (e.g. B.pendula). Soil qCO2 (BR/MBC ratio) was positively related to trees’ age (r=0.8). Response to carboxylic acids (especially oxalic) had the highest correlation with physiological properties of the trees: trunk moisture, photochemical reflectance index and vertical stability (r > -0.5).

Current research was financially supported by Russian Science Foundation [No 19-77-30012].

How to cite: Seleznyova, A., Yaroslavtcev, A., Gavrichkova, O., Ryazanov, A., Kovaleva, J., Ananyeva, N., and Valentini, R.: Soil microbial biomass, community level physiological profiles relate to tree species and its state in urban environment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1064, https://doi.org/10.5194/egusphere-egu2020-1064, 2020.

EGU2020-1499 | Displays | SSS4.2

Do diverse mixtures of cover crop residues alter the soil microbial community and increase soil function?

Xin Shu, Yiran Zou, Liz Shaw, Lindsay Todman, Mark Tibbett, and Tom Sizmur

Cover crops are a contemporary tool to sustainably manage agricultural soils by boosting fertility, suppressing weeds and disease, and benefiting cash crop yields, thus securing future food supply. Due to the different chemical composition of crop residues from different plant families, we hypothesised that a mixture of cover crop residues may have a greater potential to improve soil health than the sum of the parts. Our experiment focused on the impact of four cover crops (clover, sunflower, radish and buckwheat) and their quaternary mixture on soil respiration and the soil microbial community in an 84-day microcosm experiment. On average adding cover crop residues significantly (P < 0.001) increased soil respiration from 29 to 343 µg C g-1 h-1 and microbial biomass from 18 to 60 µg C g-1, compared to the unamended control during 84 days’ incubation. Cover crop addition resulted in a significant (P < 0.001) alteration of the soil microbial community structure compared to that of the control. The quaternary mixture of cover crop residues significantly (P = 0.011) increased soil respiration rate by 23.79 µg C g-1 h-1 during the period 30 to 84 days after residue incorporation, compared to the average of the four individual residues. However, no significant difference in the size of the microbial biomass was found between the mixture and the average of the four individuals, indicating the mixture may invest resources which transit dormant microbial species into a metabolically active state and thus boost microbial respiration. Analysis of similarity of microbial community composition (ANOSIM) demonstrated the mixture significantly (P = 0.001) shifted microbial community structure away from buckwheat (R = 0.847), clover (R = 0.688), radish (R = 0.285) and sunflower (R = 0.785), respectively. This implies cover crop residues provide a niche specialization and differentiation on a selection of microbial communities that favour certain plant compounds. While applying cover crop residues has positive impacts on soil function, we found that applying a mixture of cover crop residues may provide greater potential to select for microorganisms or activate dormant microbial species which result in higher soil function. The outcome of this study will help seed suppliers to design, and farmers to select, novel cover crop mixtures which enhance soil function synergistically, leading to a greater potential to sustainably improve soil health.

How to cite: Shu, X., Zou, Y., Shaw, L., Todman, L., Tibbett, M., and Sizmur, T.: Do diverse mixtures of cover crop residues alter the soil microbial community and increase soil function?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1499, https://doi.org/10.5194/egusphere-egu2020-1499, 2020.

EGU2020-3155 | Displays | SSS4.2 | Highlight

Development of plant-available water in soil-like substrate derived from urban wastes and processed by earthworm Dendrobaena veneta

Moreen Willaredt, Susanne Ulrich, Thomas Nehls, and Loes van Scheik

Topsoil and peat are often taken from intact rural ecosystems to supply the urban demand for fertile soils and soil-like substrates. One way of reducing this exploitation is to recycle suitable urban wastes to produce Technosols and technogenic soil-like sub­strates. In this study we investigate the role earthworms can play in improving the hydraulic properties of such a soil-like substrate.

In a four-month microcosm experiment, the influence of the earthworm species D.veneta on the hy­draulic properties of brick-compost mixture was examined. Of the ten boxes filled with ca. 11 dm³ of ground bricks (0.7 cm³ cm-3) and green waste compost (0.3 cm³ cm-3), five contained earthworms (W-boxes) and the re­maining five were used as controls (C-boxes). The substrate was periodically irrigated and the weight of the boxes and of the drained water was monitored. At the same time, images were taken from the front of the boxes to quantify the activity of the earthworms by image analysis. Before and after the experiment, water retention curves were determined from disturbed samples of the substrate using the simplified evaporation method.

After six weeks, differences between the C- and the W-boxes were evident. Micrographs showed brick-compost aggregates only for the substrates processed by earthworms. The earthworm activity leads to reduced evaporation and an increased water content in the respec­tive microcosms. The effect persists even after disturbing the substrate. The propor­tion of plant-available soil water is about 0.02 cm³ cm-3 higher for the substrate processed by earthworms (0.250 ±0.009 cm³ cm-3) compared to the control (0.230 ±0.008 cm³ cm-3).

This study shows that earthworms are capable of ingesting and processing crushed bricks together with compost. The earthworms produced aggregates which persisted after disturbance and had a positive influence on the water retention capacity of such a soil-like substrate constructed from waste.

How to cite: Willaredt, M., Ulrich, S., Nehls, T., and van Scheik, L.: Development of plant-available water in soil-like substrate derived from urban wastes and processed by earthworm Dendrobaena veneta, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3155, https://doi.org/10.5194/egusphere-egu2020-3155, 2020.

EGU2020-3832 | Displays | SSS4.2

The effect of urban heat island and other mesoclimatic anomalies on soil C stocks and fluxes in Moscow megapolis

Viacheslav Vasenev, Andrey Dolgikh, Olga Romzaykina, Inna Brianskaia, Mikhail Varentsov, Pavel Konstantinov, and Riccardo Valentini

Urbanization is a global tendency, which social-economic and environmental role will increase coming decades. Urbanization has a multiple effect on climate, vegetation and soils and these effects are interrelated. Specific features urban meteorological regimes including but not limited to urban heat island alters biogeochemical processes in urban vegetation and soils. Natural vegetation in cities is to a large extent substituted by introduced species. Urban soils are dominated by artificial constructions, engineered from substrates rich in organic carbon. A complex effect of the mesoclimatic anomalies in cities alter biogeochemical processes in urban soil-plat-air systems with a crucial effect on carbon balance.

This study aims to study relationships between carbon stocks and greenhouse gases’ emissions from urban soils and climatic conditions in Moscow megapolis, considering its spatial heterogeneity and history. Moscow is among the largest cities in the world, Rapid urbanization of recent decades has evoked complex and ambiguous effects on soil C stocks and emissions. Soil sealing resulted from building and road construction directly reduces C stock in topsoils and indirectly effects soil respiration by salinization, pollution and over-compaction. On the other hand, establishment of new green zones brings an additional input of C through adding C-rich materials for engineering urban soils and stimulating production of root biomass by fertilization, irrigation and other practices maintaining urban green infrastructure. The research included several steps. At first, an intensive soil survey was organized in Moscow on summer 2019. Sampling scheme covered all the megapolis area and considered different functional and historical zones. Mixed topsoil (0-20 cm) samples were collected in total 240 locations. Total, organic and inorganic C was measured at the collected samples and C stocks were estimated. Second, microbial respiration in contrast soil moistures (4-5 points on water saturation curve) and temperatures (10, 20, 30 and 40ºC) were measured in standard lab conditions by gas chromatography. The multiple regression equations relating C stocks and microbial respiration to soil temperature, moisture and adjustment soil properties were developed. Finally, a regional climate model COSMO-CLM was adapted to the case of Moscow megapolis to estimate dynamics of soil temperature and moisture regimes. The investigated relationships were used to generate maps of C stocks and microbial respiration of urban soils in Moscow as affected by mesoclimatic anomalies.

Acknowledgements The experimental research was performed with the support of Russian Science Foundation project № 19-77-30012. The modelling part was carried out with the support of Russian Science Foundation project № 18-35-20052.

How to cite: Vasenev, V., Dolgikh, A., Romzaykina, O., Brianskaia, I., Varentsov, M., Konstantinov, P., and Valentini, R.: The effect of urban heat island and other mesoclimatic anomalies on soil C stocks and fluxes in Moscow megapolis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3832, https://doi.org/10.5194/egusphere-egu2020-3832, 2020.

EGU2020-5105 | Displays | SSS4.2

Water-soluble organic matter and enzymatic activity of urban soils of Rostov aglomeration

Gorbov Sergey, Skripnikov Pavel, and Bezuglova Olga

Soil water-soluble organic matter (WSOM) is the most dynamic and least stable component of humus. It takes a direct part both in leading soil processes and in the formation of effective soil fertility. Its components are involved in the creation of a water-resistant structure, also exhibit physiological activity, and be of service as energy material by microorganisms. The total content of organic matter in the soils of the Rostov agglomeration varies widely: from 1.5 to 7.0%. Long-term studies of soils of the Rostov agglomeration forest-park zones showed that the organic carbon content in these soils increases under tree vegetation. This is due to changes in microclimate conditions and the associated longer period of vegetation of herbaceous vegetation. The WSOM content was obtained by summing the results of cold and hot extraction in natural soils. Its gradually decreases with depth repeating the profile dynamics of the organic carbon content in general. The surface horizons of native chernozems in a forest park and in a virgin land have the highest content of WSOM. It can be concluded that the WSOM pool is directly proportional to the stock of incoming plant residues. The maximum of extracellular enzymes activity was obtained in upper most biogenic soil horizons in the natural city soils. The highest activity was record for the enzyme, which is responsible for the nitrogen cycle (arginine-aminopeptidase (Agr)) and for the phosphorus cycle (acid phosphatase (Pho)). The enzymes activity decreases down the soil profile. 

For anthropogenically transformed soils, the WSOM profile distribution indicates a peculiar two-member structure of soil profile. The transformed upper urbiс horizons was demonstrate the absence of any patterns in its distribution. In the buried horizons of Technosols, were have the same profile trends and the same absolute values of the organic carbon content such us presented in native chernozems. Despite the high humus content in natural soils (5–7%), most of it is strongly associated with calcium ions. As a result, WSOM has values not exceeding 0.14% of the soil as a whole, or 4% in terms of organic carbon. For the urban horizons of anthropogenically transformed soils, WSOM values are not exceeding 0.04% of the soil, or about 2% in terms of organic carbon. The inversions of enzyme activity are often observed in anthropogenically transformed soils. The enzymatic activity is higher in buried humus-accumulative horizons of urbostratozems than in overlying horizons of the urbic. 

How to cite: Sergey, G., Pavel, S., and Olga, B.: Water-soluble organic matter and enzymatic activity of urban soils of Rostov aglomeration , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5105, https://doi.org/10.5194/egusphere-egu2020-5105, 2020.

EGU2020-5973 | Displays | SSS4.2

Crop residues amendments quality and effect on greenhouse gas emissions and aggregate stability

Gheorghe Stegarescu, Jordi Escuer, Karin Kauer, and Endla Reintam

The organic residues amendments have been widely studied for their essential role of enriching the soil with organic matter. Although the pathways of the fresh organic matter additions are very complex, so is the effect. Thus, the quality of the crop residues incorporated into the soil is a valuable attribute when deciding to switch to conservation agriculture. The different C/N ratio and biochemical composition of the crop residues will affect in various ways soil CO2, N2O and CH4 emissions and soil structural stability. The study explores the effect of different crop residues incorporated in the soil on greenhouse gas emissions and aggregate stability. The incubation experiment consisted of five treatments: control (just soil), sand (as reference), soil mixed with wheat straw, soil mixed with green fresh rye residues and soil mixed with green fresh oilseed rape residues. The residues were applied into the soil at a rate of 6 g C kg-1 of soil. The pots of all the treatments were placed for incubation for 105 days at approximately 23 oC and covered with dark plastic bags. The wetting procedure was done five times at 0-11-26-46-75 days to bring the soil to field capacity for water. The sampling for the gas emissions and aggregate stability was done before wetting and after wetting. The gas emissions were sampled using the chamber method and analysed in a Gas Chromatographer. The water-stable aggregates were analysed using the wet sieving method. The plant material was chemically analysed for total carbon and nitrogen and the biochemical composition on Fourier Transform Infrared Spectroscopy. The results revealed that the cumulative CO2 emissions in oilseed rape were 8% higher than in rye treatment. Also, it was 76% higher than in wheat straw treatment and 95 % higher than in control treatment. The highest cumulative N2O emissions were registered in rye treatment 18.79 (±0.48) mg m-2 h-1. Oilseed rape treatment had 19% lower cumulative emissions compared to rye and 98 % higher compared to control and wheat straw treatments. Both rye and oilseed rape had a low C/N ratio 12 and 10, respectively whereas wheat straw had 98 C/N ratio. From a biochemical point of view, the wheat straw was richer in stable compounds such as lignin, cellulose and hemicellulose followed by rye and oilseed rape which had a higher content of labile compounds such as sugars and easily decomposable proteins. In general mean aggregate stability increased significantly only in the wheat straw treatment being 34.69% ±1.35. 

In conclusion, this study showed that crop residues with low C/N ratio have a negative effect on greenhouse emissions. But do not have a long term effect on the increase of aggregate stability. On the contrary, the wheat straw has a positive impact on greenhouse gases, and it increased aggregate stability. 

How to cite: Stegarescu, G., Escuer, J., Kauer, K., and Reintam, E.: Crop residues amendments quality and effect on greenhouse gas emissions and aggregate stability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5973, https://doi.org/10.5194/egusphere-egu2020-5973, 2020.

EGU2020-7564 | Displays | SSS4.2

Effects of mechanical weed control in organic soybean cultivation on weed biomass and diversity in Luxembourg

David Richard, Laura Leimbrock, Gilles Rock, René Diederich, Guy Reiland, and Stéphanie Zimmer

With a high protein content (± 40 %) and an optimal amino acid composition, soybean (Glycine max (L.) Merr.), a member of the family Leguminosae, is one of the most important feed protein sources in animal nutrition. By signing the European Soy Declaration in 2017, Luxembourg aims to promote the regional cultivation of protein crops, e.g. soybean. Organic soybean cultivation in Luxembourg is still in its initial stage, with knowledge gaps mainly in mechanical weed control. The aim of the project “Sustainable and resource-efficient protein production using various mechanical weed control methods in grain legume cultivation, using soybean as an example” (LeguTec) is to investigate the efficiency of the selected mechanical systems under consideration of, inter alia, weed biomass.

In 2018 and 2019, field trials took place on two organic farms in Luxembourg (in Manternach and Hostert). Five mechanical methods were tested in soybean cultivation (variety Merlin), including A) harrow, B) interrow cultivator with duck-foot shares, C) interrow cultivator with duck-foot shares and finger-weeder, D) a combination of treatments A and C, and E) mixed cropping of soybean and camelina in combination with harrow. A positive control F) weeded by hand and a negative control G) not weeded are also implemented. Field trials were set as one-factorial-exact-trial with four replicates. Weeds were counted and identified and biomass cut before and after each weed control run as well as at flowering. Weed diversity was estimated by means of the Shannon index.  Data were analysed using ANOVA (p<0.05) and appropriated pairwise comparison Tuckey tests.

In 2018, significant less weed biomass is observed in Hostert for D in comparison to A and E, and for B, C and D in comparison to A and E, in 2019. Biomass in Manternach in 2019 is significantly lower in treatment D. Globally, weed biomass at flowering tends to be lower in the hoeing treatments (B, C and D) than in the harrowing treatments. High weed pressure from the beginning on in all treatments in Hostert has limited the efficiency of weeding but with a tendency in favour of the interrow cultivator.  At the Manternach site, weed pressure was low in 2018, allowing good regulation resulting in low diversity in all treatments. Values of the Shannon index tend to be negatively affected by mechanical weeding across all field trials. In 2019, significant lower Shannon index is observed in Hostert for treatments C and D, as well as for treatment C in Manternach. Hoeing generally tends to lower the most weed diversity in addition to weed biomass. Low abundant species were more likely to disappear, while 1 to 4 species became over-dominant in each treatment.

The increased interest in regional soybean cultivation in Luxembourg due to the LeguTec project shows the need of further research on soybean cultivation to reach the long-term goal of overcoming cultivation barriers and promoting a sustainable, resource-efficient protein production in Luxembourg.

How to cite: Richard, D., Leimbrock, L., Rock, G., Diederich, R., Reiland, G., and Zimmer, S.: Effects of mechanical weed control in organic soybean cultivation on weed biomass and diversity in Luxembourg, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7564, https://doi.org/10.5194/egusphere-egu2020-7564, 2020.

EGU2020-10594 | Displays | SSS4.2

Mycobiota in urban soils of Russian North

Inna Vaseneva, Elena Kuznetsova, and Fluza Khabibullina

Microbilogical properties of urban soils were studied in Syktyvkar town (Komi Republic), in the taiga zone of Russia. Within the settlement, two different types of functional zones were compared: transport (roadside areas with limited influence of traffic and highway area) and recreation areas (parks). The soils of parks are man-changed urban soils, whereas the soils of roadside areas were mainly man-made or considerably disturbed. The investigated soils were formed on the cultural layer or buried soils and sediments of various genesis. The soil profiles included a humus-accumulative horizon in the top part, followed by an anthropogenically transformed part, underlain by a slightly modified parent rock.

The highest number of species was determined in the soils of recreational areas, including 33 species of microscopic fungi. Soils of the transport area contained 22 species. The higher number of species is associated with the development of specific for urban zone fungal complex and partial preservation of natural zonal species of fungi, mainly representatives of Penicilliumgenus. Non-typical for the taiga zone species from Aspergillus and Fusariumgenera were frequently noted. Highway areas with intensive traffic were characterized by the dominance of dark-colored melanin-containing fungi, which are conditional pathogens for humans, and increasing presence of sterile mycelium – indicator of soil disturbance. Stenotopic species which are typical for undisturbed zonal conditions were rarely isolated.

Acknowledgements The experimental research was partly supported by Russian Science Foundation project № 19-77-30012.

How to cite: Vaseneva, I., Kuznetsova, E., and Khabibullina, F.: Mycobiota in urban soils of Russian North, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10594, https://doi.org/10.5194/egusphere-egu2020-10594, 2020.

EGU2020-13415 | Displays | SSS4.2

A comparison between vegetable intercropping systems and monocultures in greenhouse gas emissions under organic management

Virginia Sánchez-Navarro, Mariano Marcos-Pérez, and Raúl Zornoza

Legume crops have been proposed as a way of reducing greenhouse gas (GHG) emissions because both, their rhizosphere behaviour and their ability to fix atmospheric N reducing the need of external N fertilizer. Moreover, the establishment of organic agriculture has been proposed as a sustainable strategy to enhance the delivery of ecosystem services, including mitigation of climate change by decreases in GHG emissions and increases in soil C sequestration. The aim of this study was to assess the effect of the association between cowpea (Vigna unguiculata L.) and melon (Cucumis melo L.) growing in different intercropping patterns on soil CO2 and N2O emissions compared to cowpea and melon monocultures under organic management as a possible strategy for climate change mitigation. Soil CO2 and N2O emissions were weekly measured in melon and cowpea rows using the dynamic chamber method during one cropping cycle in 2019. Results indicated that melon growing as monoculture was related to increases in O cumulative emissions (0.431 g m-2) compared to the average of the rest of treatments (0.036 g m-2). Cowpea growing as monoculture was related to decreases in CO2 cumulative emissions (390 g m-2) compared with the other treatments (512 g m-2 average). However, N2O and CO2 emission patterns did not directly follow soil moisture patterns in the experimental period, with no significant correlations. Finally there were no significant differences among intercropping treatments with regard to NO2 and CO2 emissions. Further measurements are needed to monitor the evolution of GHG emissions under these cropping systems and confirm the trend observed.

How to cite: Sánchez-Navarro, V., Marcos-Pérez, M., and Zornoza, R.: A comparison between vegetable intercropping systems and monocultures in greenhouse gas emissions under organic management, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13415, https://doi.org/10.5194/egusphere-egu2020-13415, 2020.

EGU2020-13890 | Displays | SSS4.2

Soil Carbon Dioxide Emission in Extreme Environment of the Center of Moscow Megapolis

Andrey Dolgikh, Dmitriy Petrov, Inna Brianskaia, Soryia Demina, Ksenia Mahinya, Olga Romzaikina, and Aleksandr Dobrianskii

Moscow is the largest megapolis in Europe. The area of sealed areas in the center of Moscow is more than 50% (without hydrological objects). Anti-icing mixtures, car traffic, aerosols, dust, trampling - all this leads to the maximum stress of ecosystems in an urban environment Soil emission is the largest component of Gross Respiration in terrestrial ecosystems, including cities. Field measurements of emission allow estimating and comparing the state of both the underground tier and the entire ecosystem in different functional zones of a city with different types of vegetation. Soil emission is the easiest to measure, as compared to other fluxes of С-exchange. In 2019, field measurements of carbon dioxide emissions were carried out at 15 key sites (15 times, 1 per 2 weeks), which showed that in the historic center, not only the temperature at different depths of the soil, soil moisture, carbon content, particle size distribution, but also the diversity of factors combined into a group of "land use", namely: human tillage, irrigation, lawn mowing, garbage removal, sprinkling peat-compost mixture, trampling, bringing anti-icing reagents, etc., have a contrasting effect on carbon dioxide emissions from urban soils. In some cases, the emission is below the conditional background values (urban forest), in other cases, it is higher up to several times, which allows a new assessment of soils of unsealed (open) areas of the center of a megapolis as an important component of the (micro-) regional C-cycle. The data obtained allow comparing the current state of the upper part of the underground tier of urban ecosystems under the maximum anthropogenic load in the territory of a modern large city, where the share of open surfaces is minimal. The territories, where the ground layer is represented by cultivated lawn, are characterized by the maximum values of soil carbon dioxide emission.

The study was supported by the Russian Research Foundation #19-77-30012 (field measurements in the periphery of Moscow) and the Russian Foundation for Basic Research #18-35-20052 (field measurements in the historic center of Moscow).

How to cite: Dolgikh, A., Petrov, D., Brianskaia, I., Demina, S., Mahinya, K., Romzaikina, O., and Dobrianskii, A.: Soil Carbon Dioxide Emission in Extreme Environment of the Center of Moscow Megapolis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13890, https://doi.org/10.5194/egusphere-egu2020-13890, 2020.

EGU2020-17496 | Displays | SSS4.2

From natural land to irrigated crops: impact of land use change and crop diversification on interrill erosion

Efraín Carrillo López, Carolina Boix-Fayos, Niek Verschaeren, Jesús Lucas Parra, Elvira Díaz Pereira, Noelia García-Franco, María Almagro, Pedro Pérez Cutillas, and María Martínez-Mena

Soil erosion is one of the most important processes of soil degradation, especially vulnerable are many agricultural systems of SE Spain which are being transformed from a rainfed to irrigated agriculture. Crop diversification has been raised as a possible management measure with multiple benefits to combat soil degradation. Interrill soil erosion rates and processes were assessed in three land uses in SE Spain next to each other, with the same basic characteristics (climate, lithology and soils)  representing a gradient of land use change: natural shrubland, rainfed almond crop (Prunus dulcis) on terraces and levelled citrus crops (Citrus reticulata) with street-ridge morphology. The experimental design included two diversifications in the rainfed almond: intercropping Capparis spinosa and Thymus hyemalis, respectively, while in the citrus irrigated area a rotation with Hordeum vulgare and Vicia sativa (from February to July) or Vicia faba (from October to January) were intercropped in the streets.

In the rainfed and natural area interill erosion was measured using erosion pins with a 2 or 3 x 3 x 3 scheme (2 or 3 plots of 1 m2 with 9 pins at two diversifications and control, at three different agricultural terraces). In the natural area two pin plots were set up. At the irrigated area the experimental design was a 2 x 2 x 2 scheme (2 plots (ridge; street) x 2 replicates x 2 (bare, vegetated). Pins were measured after each rain event or each month during 14 months, identifying detachment (positive values) and sedimentation (negative values) within the erosion process.

The preliminary results indicate significant higher erosion rates in the irrigated areas than in the traditional rainfed terraces (83.6±147.4 t ha-1 versus 9.59±170.34 t ha-1, respectively). Shrubland natural areas show significant higher deposition rates (-74.97±43.08 t ha-1) than recent diversified plots with Capparis and Thymus (-52.56±227.06 and -28.29±85.94 t ha-1, respectively). Neither differences within diversification type (Capparis versus Thymus) nor between control and diversifications in the rainfed almond area have been yet detected. In the Citrus irrigated area erosion rates under Hordeum vulgare and Vicia sativa were significantly higher than under Vicia faba (129.58±94.43 and 25.61±87.79 t ha-1, respectively).

So far, those preliminary results indicate that natural shrubland and traditional rainfed crop systems facilitate sedimentation rates and are effective systems for soil conservation. However, the conversion from rainfed to irrigated crops mean a significant increase of erosion rates due to a system that does not facilitate retention of detached soils. Within this temporal framework, crop diversifications, both in rainfed and irrigated systems, have not yet significantly reduced erosion rates. A longer experimentation period is necessary to determine the effect of crop diversifications on soil erosion.

How to cite: Carrillo López, E., Boix-Fayos, C., Verschaeren, N., Lucas Parra, J., Díaz Pereira, E., García-Franco, N., Almagro, M., Pérez Cutillas, P., and Martínez-Mena, M.: From natural land to irrigated crops: impact of land use change and crop diversification on interrill erosion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17496, https://doi.org/10.5194/egusphere-egu2020-17496, 2020.

EGU2020-17745 | Displays | SSS4.2

Environmental impact of crop diversification in steep vineyards

Thomas Iserloh, Felix Dittrich, Cord-Heinrich Treseler, Katharina Frey-Treseler, Roman Hüppi, Johann Six, Sören Thiele-Bruhn, and Manuel Seeger

The intensification of European agriculture leads to soil degradation, reduction of biodiversity and an increased economic risk for the farmers. An approach towards solving this problem is crop diversification and the optimized use of resources. Increasing agricultural efficiency/resilience through diversification and the associated falling environmental costs could contribute to the growth of the European agricultural sector by adapting the entire value chain.

The EU-funded project DIVERFARMING (Horizon 2020 no 728003) aims to develop and deploy innovative farming and agribusiness models based on crop diversification. Germany is involved with a broad-based study in organic steep slope viticulture in Wawern (Saar Valley).

A fundamental issue of steep slope viticulture is related to vegetation management below the vines. In order to overcome problems of soil erosion and soil organic matter depletion, an increasing number of winemakers is establishing cover crops such as grasses and legumes in driving lanes. On the contrary, the area underneath the vines is typically kept free of vegetation to avoid fungal diseases and competition on water. As cover crops do not benefit to the value chain and may compete with vines on water or have other adverse effects on vine performance, an alternative strategy for vegetation management underneath vines in steep slope viticulture is required.

Therefore, intercropping vines with perennial herbs like Thyme and Oregano growing underneath is a promising cropping practice to address the abovementioned issues. Both herbs are economically valuable and originate from dry and warm environments, which are typical for most viticultural areas. Furthermore, their relatively low need for water and flat-growing habitus is assumed to be suitable to cover the soil underneath the vines in order to protect against erosion and suppress weeds without having adverse effects on vine growth and -health. They can be marketed directly or indirectly as a concentrate for cosmetics, perfumes, nutritional supplements and food.

During the 5-year project, we will investigate impacts on and interactions between crops, soil ecological and physicochemical properties as well as erosion and emission of greenhouse gases to evaluate ecological benefits of crop diversification. Selected results obtained within the first two years of investigation will be presented.

How to cite: Iserloh, T., Dittrich, F., Treseler, C.-H., Frey-Treseler, K., Hüppi, R., Six, J., Thiele-Bruhn, S., and Seeger, M.: Environmental impact of crop diversification in steep vineyards, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17745, https://doi.org/10.5194/egusphere-egu2020-17745, 2020.

EGU2020-19676 | Displays | SSS4.2

Soils of abandoned industrial wastes disposal sites: properties, processes, functioning

Igor Zamotaev, Natalia Telnova, Alexander Alexandrovskiy, Raisa Gracheva, Andrey Dolgikh, Dmitry Karelin, Yulia Konoplyanikova, Pavel Mikheev, Alexander Dobrianskiy, and Eleonora Belova

Soils formed at once abandoned and recultivated industrial waste dumping sites are key research objects both as models of soil-forming processes in underdeveloped soils and indicators of persistent or potential environmental hazards of dumps themselves. Our studies of technogenic surface-like soil formations (TSF) and soils were conducted on a closed landfill and two abandoned filtration fields from sugar factories  in Kursk region, central part of European Russia.

Key properties of TSF and soils were defined with the assessments of their ecological, microbiological state and gas-geochemical condition. Set of methods (mesomorphological and micromorphological analysis, soil chemical and physico-chemical analysis, comparatively geographical method) was used for the detection of current elementary soil processes. Seasonal dynamics of carbon dioxide, methane and nitrous oxide emissions from soils to the atmosphere was also under consideration. Main used methodology is a research of sustainable properties of soil solid-phase (“soil memory”) together with soil functioning.

Long-term time series of high-detailed remote sensing data (from archive aerial photos of 1950s to actual satellite images and UAV optical photogrammetry) provided the possibility for the retrospective remote monitoring of the all abandoned dumps in study and reconstruction of their life cycles and land cover patterns.

As a result for the three industrial waste dumping sites of different types and the varying age of abandonment and recultivation history there were elaborated schemes of chrono-functional zoning. Each chrono-functional zone is characterized by the specific set of TSF and soils. Among them, it was described technogenic surface-like soil formations of closed landfill, calcareous technosols with several thick organic layers at the bottom of abandoned field filtration cells, calcic anthrosols of field filtration cells spontaneously used for agriculture after the abandonment of sugar factories.

The study is financially supported by RFBR project № 19–29–05025–mk.

How to cite: Zamotaev, I., Telnova, N., Alexandrovskiy, A., Gracheva, R., Dolgikh, A., Karelin, D., Konoplyanikova, Y., Mikheev, P., Dobrianskiy, A., and Belova, E.: Soils of abandoned industrial wastes disposal sites: properties, processes, functioning, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19676, https://doi.org/10.5194/egusphere-egu2020-19676, 2020.

EGU2020-20635 | Displays | SSS4.2

Effects of management on soil organic carbon and structural stability in olive grove toposequences in Mediterranean areas.

Manuel González-Rosado, Jesús Aguilera Huertas, Beatriz Lozano-García, and Luis Parras-Alcántara

Carbon sequestration in agricultural soils has been defined as a positive strategy to mitigate the climate change effects. To implement this strategy, it is necessary to reduce the soil physical disturbances that encourage its degradation. It is therefore essential to analyze the consequences that conventional tillage practices have on agrosystems as a first step towards developing sustainable management practices that are in line with strategies to combat climate change. In order to evaluate the conventional tillage impact in olive groves, a toposequence was carried out where three profiles of 50 cm depth each were opened in three topographical positions: summit, backslope and toeslope. The physical and chemical soil properties were analyzed, including soil organic carbon (SOC) and mean weight diameter (MWD) of the aggregates, which showed a plot scale low SOC levels and low MWD being subject to erosive processes which negatively impacts on its SOC storage capacity.

How to cite: González-Rosado, M., Aguilera Huertas, J., Lozano-García, B., and Parras-Alcántara, L.: Effects of management on soil organic carbon and structural stability in olive grove toposequences in Mediterranean areas., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20635, https://doi.org/10.5194/egusphere-egu2020-20635, 2020.

EGU2020-20661 | Displays | SSS4.2

History and geography of land productivity to assess the challenges for food security

Marta Tuninetti, Luca Ridolfi, and Francesco Laio

Increasing population and changing diets toward larger proportion of meat products have driven agricultural production increase over the past decades and will probably push it in the upcoming years. The analysis of the agricultural production increase is at the centre of the international debate since the 1800-century Malthusian prediction of exponentially growing population outstripping linearly increasing production.

In this study, we show how agriculture has changed over the past decades through the concept of a newly developed land productivity (LP) indicator, which measures the amount of calories, proteins, and fats produced per hectare of land and merges the variegate macronutrients spectrum of a 140-crops production basket. Land productivity indicator adds to the more widespread (crop specific) yield indicator the nutrient content of each product.

We find that the global LP has increased by 2.6-2.9% per year over 1961-2016 for calorie and protein, and 3.7% for fat. This confirms an important boost of the global productive regime whose growing rate has been able to overcome that of population. Humans can rely on larger amounts of calories (+1640 kcal/cap/day), proteins (+69 g/cap/day), and fats (+55 g/cap/day) supply. In this global picture, different macro-regions exhibit relevant heterogeneities. In particular, we found that Eastern Asian and Latin American countries could escape the Malthusian trap around the Nineties through both LP increase and ad hoc variation in the composition of their basket of products. However, this transition seems far to happen in Sub-Saharan Africa and South Asia, where the daily productive regime has remained stable since the Sixties, despite the variation of the basket composition.

How to cite: Tuninetti, M., Ridolfi, L., and Laio, F.: History and geography of land productivity to assess the challenges for food security, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20661, https://doi.org/10.5194/egusphere-egu2020-20661, 2020.

In conditions of on-going urbanization, urban parks play a key role in the sustainable development of urban space. New Moscow, the territory attached to Moscow in 2012, is currently the largest area in Russia experiencing rapid and intensive urban development. New Moscow is a unique area in which over the past five years, starting in 2012, rapid urbanization has been observed, including the formation of new recreational areas in the former forest, fallow and arable territories. There are currently more than 70 parks with a different land use history on this territory. Most of them have been created or reconstructed in the last 7 years. The aim of our study is to study the state of soils and green spaces of the recreational zones of New Moscow and the impact of anthropogenic factors on them, taking into account the different history of land use. For analysis, we selected 4 parks. Two parks are formed on the site of the former arable territory, and two parks in the forest zone. At the same time, one park from a couple was closer to the old borders of Moscow, and the second at a distance of more than 15 km. In the selected territories, we conduct physical, chemical and microbiological analysis of soils, as well as assess the state of green spaces. In each of the parks, 9 or 10 points were selected in various functional areas (territories near sports and playgrounds, in the walking area, barbecue area, etc.). The selection was carried out to a depth of 50-100 cm. The top layer (0-10 cm) was selected for analysis of the carbon content in the microbial biomass (Cmic), basal respiration (BR) and CO2 production. To carry out the pH, C / N analysis, as well as the content of heavy metals in the soil, the samples were taken horizontally to a depth of 100 cm. The second stage of the study was to assess the state of woody vegetation within a radius of 20 meters from each point selected for soil analysis. Thus, we plan to obtain a comprehensive analysis of the physical, chemical and microbiological condition of the soils of the recreational zones and green spaces with a different land use history and to identify the influence of the anthropogenic factor on them.

How to cite: Mahinya, K., Demina, S., Vasenev, V., and Brianskaia, I.: Analysis of the impact of urbanization on the microbiological, chemical and morphological properties of the soil in the recreational areas of the New Moscow with a different land-use history, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21658, https://doi.org/10.5194/egusphere-egu2020-21658, 2020.

EGU2020-21474 | Displays | SSS4.2

Biogeochemical characterization of soils affected by more than 100 years of lead mining activity.

José María Esbrí, Sara Gallego, JuanAntonio Campos, Fabrice Martin-Laurent, Jesus Peco, and Pablo Higueras

Mining has an adverse effect on soil quality as it is a source of heavy metal environmental pollution with direct consequences on its ecosystem services, especially those related to microbial activity. The magnitude and diversity of the impact produced by pollution is linked to the complexity and diversity of mining processes that share the same mining area. The soil will be modified, not only in the physicochemical characteristics but also physical alterations of varied typology will occur. All these changes and alterations related to mining activity are accompanied by changes in the composition, diversity and activity of soil microorganisms..
A study was carried out on a mine site showing variable degrees of contaminations with metals, to estimate the impact of mining works on the geochemistry of soils, and the activity and diversity of soil microorganisms.  The aim is to characterize the level of disturbance on the “soil health” due to the presence of different metals, related physicochemical factors, and typology of the wastes affecting the soil. Besides, the process of bacterial colonization of the wastes has been also subject of interest to our work.
The selected study area was originally a lead-silver mine. Later, a mineral treatment plant was established in the area in order to recover Zn from the primary gangue dumps. In addition spills of olive mill residues were later deposited in the area. Four composite samples from the five distinct sites differing in their characteristics were selected: tailings, dumps, olive mill residues, contaminated soil and reference soil. A range of various analyses was done on these samples including pH, electrical conductivity, organic matter, multi-elemental contents, enzymatic activity and bacterial biodiversity (16S rRNA amplicon sequencing).
Selected sampling sites have contrasted physicochemical characteristics: acidic pH was observed in dumps (3.8 in average) and neutral in tailings and soils (~6); highest conductivity was recorded in dumps (2282 microS cm-1 in average) and lowest in soils (62 microS cm-1 in average); the highest organic matter value was measured in soils amended with olive mill residues (60% in average). Heavy metals were detected in higher concentrations in dumps and olive mill residues than in tailings or soils. It is noteworthy in dump samples the maximum concentrations of metals reach 6.8% with significant amounts of Zn, Cu, Sb, Hg, Ni, Co and Mn. Highest enzymatic activities were measured in contaminated and non-contaminated soils, while lowest values were obtained in dumps and tailings soils, in accordance with the concentration of metal measured in the matrix. Next generation sequencing analysis of 16S rRNA amplicon lead to the discrimination on the different sites sampled according to bacterial composition and diversity. Most abundant bacterial phyla were Proteobacteria, Actinobacteria, Chloroflexi, Acidobacteria, Gemmatimonadetes, Bacteriodetes, TM7, Firmicutes, Cyanobacteria and Verrucomicrobia.
As a conclusion, we have found evidences of the intense affection of the metal pollution to the microbiological biodiversity, particularly that related with the presence of high Pb concentrations.

How to cite: Esbrí, J. M., Gallego, S., Campos, J., Martin-Laurent, F., Peco, J., and Higueras, P.: Biogeochemical characterization of soils affected by more than 100 years of lead mining activity., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21474, https://doi.org/10.5194/egusphere-egu2020-21474, 2020.

SSS4.3 – Plant-Microorganism-Soil interactions in the rhizosphere: from chemical, biological, and physical perspectives to an interlinked understanding of processes

EGU2020-4634 | Displays | SSS4.3 | Highlight

Multimodal Imaging of Plant-Soil Interaction for Better and More Predictive Modelling of Rhizosphere Processes

Tiina Roose, Siul Ruiz, Dan McKay Fletcher, Katy Williams, Chiara Petroselli, Callum Scotson, and Arjen van Veelen

We rely on soil to support the crops on which we depend. Less obviously we also rely on soil for a host of 'free services' from which we benefit. For example, soil buffers the hydrological system greatly reducing the risk of flooding after heavy rain; soil contains very large quantities of carbon, which would otherwise be released into the atmosphere where it would contribute to climate change. Given its importance it is not surprising that soil, especially its interaction with plant roots, has been a focus of many researchers. However the complex and opaque nature of soil has always made it a difficult medium to study.

In this talk I will show how we can build a state of the art image based model of the physical and chemical properties of soil and soil-root interactions, i.e., a quantitative, model of the rhizosphere based on fundamental scientific laws.
This will be realised by a combination of innovative, data rich fusion of structural and chemical imaging methods, integration of experimental efforts to both support and challenge modelling capabilities at the scale of underpinning bio-physical processes, and application of mathematically sound homogenisation/scale-up techniques to translate knowledge from rhizosphere to field scale. The specific science questions I will address with these

techniques are: (1) how does the soil around the root, the rhizosphere, function and influence the soil ecosystems at multiple scales, (2) what is the role of root- soil interface micro morphology on plant nutrient uptake, (3) what is the effect of plant exuded mucilage on the soil morphology, mechanics and resulting field and ecosystem scale soil function and (4) how to translate this knowledge from the single root scale to root system, field and ecosystem scale in order to predict how the climate change, different soil management strategies and plant breeding will influence the soil fertility.

How to cite: Roose, T., Ruiz, S., McKay Fletcher, D., Williams, K., Petroselli, C., Scotson, C., and van Veelen, A.: Multimodal Imaging of Plant-Soil Interaction for Better and More Predictive Modelling of Rhizosphere Processes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4634, https://doi.org/10.5194/egusphere-egu2020-4634, 2020.

EGU2020-7925 | Displays | SSS4.3

A micro-macroscale approach coupling processes that shape rhizosphere diffusivity and permeability

Alice Lieu, Alexander Prechtel, Nadja Ray, and Raphael Schulz

A novel, comprehensive modeling approach extending (Ray et al., 2017, Rupp et al., 2018, Rupp et al., 2019) is used to study the interplay between biogeochemical processes in the rhizosphere. Understanding these local interactions is crucial for the habitat as they influence processes in the root-soil system such as the water and nutrient uptake by the roots. The mechanistic model explicitly represents the pore structure and allows for dynamic structural organization of the rhizosphere at the single root scale.

At this microscale, the movement of interacting entities - nutrients, bacteria and possibly charged chemicals - in the fluid is described by means of the diffusion and Nernst-Planck equations with a Henry transmission condition at the liquid/gas interfaces. A biomass phase can develop from agglomerations of bacteria and stabilising sticky agents may grow or decay at the solid surfaces. To take into account specific properties of the rhizosphere, root cells and an explicit phase of exudated mucilage as well as root hairs are included. In addition to solving the continuous partial differential equations, a discrete cellular automaton method (Tang and Valocchi 2013, Ray et al. 2017, Rupp et al., 2019) is used, enabling structural changes in the solid and mucilage phases at each time step. The partial differential equations are discretised with a local discontinuous Galerkin method which is able to handle discontinuities induced by the evolving geometry.

The microscale model is not amenable to large scale computations because of its high complexity. Upscaling techniques enable the incorporation of information from the rhizosphere scale to the macroscale. We apply these techniques to dynamically evolving microstructures taking the spatiotemporal evolution of the rhizosphere into account. Although the setting is periodic, the underlying geometries can be arbitrarily complex. The resulting hydraulic properties (e.g. diffusion coefficient, permeability) are an important input for existing root-water uptake models, involving e.g., the effect of mucilage.

In this study, we use two- and three-dimensional CT scans of maize root, and show how mucilage concentration as well as its distribution in the pore space result in changes of macroscopic soil hydraulic properties. The access of nutrients in small pores for the root is assessed in simulation studies and its effect on effective diffusivity is evaluated.

N. Ray, A. Rupp and A. Prechtel (2017): Discrete-continuum multiscale model for transport, biomass development and solid restructuring in porous media. Advances in Water Resources 107, 393-404.

A. Rupp and K. Totsche and A. Prechtel and N. Ray (2018): Discrete-continuum multiphase model for structure formation in soils including electrostatic effects. Frontiers in Environmental Science, 6, 96.

A. Rupp, T. Guhra, A. Meier, A. Prechtel, T. Ritschel, N. Ray, K.U. Totsche (2019): Application of a cellular automaton method to model the structure formation in soils under saturated conditions: A mechanistic approach. Frontiers in Environmental Science 7, 170.

Y. Tang and A.J. Valocchi (2013): An improved cellular automaton method to model multispecies biofilms. Water Research 47 (15), 5729-5742.

How to cite: Lieu, A., Prechtel, A., Ray, N., and Schulz, R.: A micro-macroscale approach coupling processes that shape rhizosphere diffusivity and permeability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7925, https://doi.org/10.5194/egusphere-egu2020-7925, 2020.

EGU2020-8612 | Displays | SSS4.3

Root system architecture with and without root hairs: Consequences for nutrient and water uptake efficiency and related spatio-temporal patterns

Eva Lippold, Maxime Phalempin, Steffen Schlüter, Robert Mikutta, and Doris Vetterlein

Root hairs substantially contribute to the acquisition of nutrients and potentially also to water uptake. Hence, they might have a strong impact on plant growth under nutrient- or water-limited conditions. As little information presently exists about differences in matter uptake to plants either with or without root hairs, we hypothesize that the absence of root hairs will be compensated by an increase in root growth to overcome the hair-less handicap. Within the DFG-funded Priority Program 2089, we compare two different genotypes (i.e. Zea mays “Wild Type” and its corresponding hair-less mutant “rth3”) grown in two different substrates (loam and sand) in column experiments. X-ray computed tomography (X-ray CT) was used to investigate the spatial-temporal change of root architecture during growth. Additionally, total root length was measured after destructive sampling at harvest with WinRhizo. Contrary to our expectation, the reduced root surface area available for water and nutrient uptake in case of the hair-less cultivar was not compensated by more intensive root growth. The substrate had a higher impact on root growth than the presence or absence of root-hairs. For shoot growth (shoot biomass), both factors (genotype, substrate) had a significant impact. As a consequence, nutrient uptake efficiency (uptake per unit root length) was clearly increased by the presence of root-hairs, irrespective of the substrate. Water uptake efficiency did not show any difference between genotypes under the well-watered conditions studied. In general, water uptake per unit root length was higher in sand compared to loam. Differences in nutrient uptake efficiency should be reflected in the extent of nutrient depletion gradients around roots. To address such biochemical gradients we develop a new subsampling scheme based on extraction of undisturbed subsamples. Subsamples will be imaged with micro X-ray fluorescence (μXRF) for elemental mapping. The 2D µXRF image will be registered into the 3D X-ray CT image to relate the extent of gradients to the age of the respective root segment.

 

This project was carried out in the framework of the priority programme 2089 “Rhizosphere spatiotemporal organisation - a key to rhizosphere functions” funded by DFG (project number 403640293).

How to cite: Lippold, E., Phalempin, M., Schlüter, S., Mikutta, R., and Vetterlein, D.: Root system architecture with and without root hairs: Consequences for nutrient and water uptake efficiency and related spatio-temporal patterns, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8612, https://doi.org/10.5194/egusphere-egu2020-8612, 2020.

EGU2020-14310 | Displays | SSS4.3

The effect of root exudates on soil nitrogen availability - an evaluation using microdialysis

Scott Buckley, Richard Brackin, Torgny Näsholm, Susanne Schmidt, and Sandra Jämtgård

Plant root exudates are believed to increase root capture of nutrients (including nitrogen) by encouraging development of a rhizosphere root community, and providing them with an energy source to facilitate degradation of litter and soil organic matter. However, observing the consequences of root exudation on nutrient cycling and microbial activity is challenging with current methods, given the small scales involved. We investigated the effect of root exudation on nitrogen (N) availability by simulating root exudation with microdialysis. This novel technique enables continuous release of synthetic solutions of root exudates via diffusion in situ in soil by using a root-sized permeable membrane. Importantly, it also allows for simultaneously monitoring the effects on inorganic N fluxes. To emulate growth of a root tip through a specific soil region, sucrose was released for seven days before substituting sucrose with water for a further 7 days. We investigated boreal forest soils with and without litter amendments (ground pea shoots) to attain different C/N ratios and we used two rates of exudation by retrodialysing with either 0.5 or 5 mM sucrose solution. We observed that pea litter promoted significant N immobilisation, along with greater rates of sucrose release from microdialysis probes - peaking at 90.7 ± 8 µg sucrose m-2 s-1 using the 5 mM sucrose solution after three days. This suggests that greater root exudation may be driven by microbial demand for both C and N, with no short-term nutritional benefit for plant roots, even after exudation has ceased within a specific soil region. Glucose and fructose fluxes (breakdown products of sucrose) were also greatest in the litter treatment, indicating enzyme activity was promoted by the availability of both sucrose and litter. CO2 respiration measurements indicated significant differences between litter and control soils, but there was no detectable effect of sucrose exudation, suggesting that the small amounts of C supplied and the limited area influenced by the diffusion of sucrose had little impact on overall microcosm respiration. We conclude that short-term C exudation presented no immediate benefit for plant nutrition in our experiment. Future studies can benefit from using microdialysis to investigate the influence of more complex root exudate solutions, as well as the mechanistic roles of transpiration-induced mass flow on plant N availability in the rhizosphere.

How to cite: Buckley, S., Brackin, R., Näsholm, T., Schmidt, S., and Jämtgård, S.: The effect of root exudates on soil nitrogen availability - an evaluation using microdialysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14310, https://doi.org/10.5194/egusphere-egu2020-14310, 2020.

EGU2020-12304 | Displays | SSS4.3

Deciphering taxonomic carbon exchange between plants and microorganisms using proteomics coupled with 13C tracers and spatially resolved protein extraction

James Moran, Vivian Lin, Ying Zhu, Nikola Tolic, Samuel Purvine, Joshua Rosnow, and Mary Lipton

Clear elucidation of plant-microbe interactions within the rhizosphere and how these relationships change over time can be confounded by the large microbial biodiversity, shifting microenvironmental conditions, and extensive spatial constraints within these complex systems. Proteomics analysis of root or soil samples, when linked with metagenomic interpretation, can provide key insights to both the taxonomy and functional capability of microbial populations within a sample. Yet, existing proteomic approaches may not always be able to provide the needed temporal and spatial resolution to capture fine-scale and short-term interactions between plants and microorganisms. To remedy this limitation, we are developing a suite of methodological adaptations intended to leverage proteomic analysis to help identify key interactions between rhizosphere microorganisms and their host plant.

First, we are employing 13C tracers coupled with automated data analysis to identify specific organisms consuming both simulated and natural root exudates. We are specifically exploring microcosms constructed from natural soil (Kellogg Biological Station, Hickory Corners, Michigan, USA) and planted with switchgrass as a platform for developing the techniques. Multiple previous studies have linked key interactions between both free-living and epiphytic microbial members with improved performance of a switchgrass host under nutrient-depleted, natural field conditions. Providing evaluation of the amount and taxonomic recipient of switchgrass-supplied carbon under varying conditions may help link key taxonomic groups with improved plant performance and biomass production.

Second, we are leveraging a membrane extraction technique coupled with specialized sample digestion, purification, and analysis to enable non-destructive, spatially-resolved protein extraction from the root-soil interface within our constructed microcosms. Through its non-destructive nature, this approach permits timeseries analysis for tracking specific taxa and, in some cases, functions associated with rhizosphere processes both before and after a system perturbation as well as variations over plant growth phases during a growing season. The high sensitivity of this system enables spatial analysis at the one to two mm scale where samples can be manually selected based on proximity to specific root structure, metabolic hotspots in the system, or other parameter of choice. Spatial analysis can be leveraged to track taxonomic distribution within the rhizospheres associated with roots at different growth stages or levels of maturity.

How to cite: Moran, J., Lin, V., Zhu, Y., Tolic, N., Purvine, S., Rosnow, J., and Lipton, M.: Deciphering taxonomic carbon exchange between plants and microorganisms using proteomics coupled with 13C tracers and spatially resolved protein extraction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12304, https://doi.org/10.5194/egusphere-egu2020-12304, 2020.

EGU2020-6171 | Displays | SSS4.3

Rhizosphere legacy: amelioration of MicroBioPhysical properties of compacted soil

Bahar S. Razavi, Nicole Rudolph-Mohr, and Christoph Tebbe

Soil compaction is a multi-disciplinary problem in which soil, plant, and air operations play an important role and may have dramatic environmental consequences throughout the world. In compacted soils, the increase in bulk density, and the accompanying decrease in porosity hinders the exchange of oxygen, carbon dioxide and other gases, thereby causing hypoxic stress in plant roots. Hypoxic stress can effects root physiological functions, reduce soil enzyme activity, hence reducing soil fertility. For the first time we applied a unique combination of two imaging techniques, zymography and optodes sensors with molecular microbial community analysis to illuminate the rhizosphere self-regulation for amelioration of microbiophysical properties of compacted soil. To this end maize in compacted and uncompacted soil under control condition for 2 weeks was planted.

Soil oxygen map and β-glucosidase activity in compacted maize treatment overlaid with the extracted root system demonstrated more than 65% positive correlation between hotspots of enzymatic activity and localities with high oxygen concentration –which were mostly in association with root. Similarly, extend of rhizosphere for oxygen concentration and enzyme activity across the root of compacted soil was 1mm broader than the uncompacted.

Based on root morphology analysis, compacted maize reduced roots diameter and increased the distribution. Which resulted in 30% higher ratio of rhizosheath mass in compacted than uncompacted soil. Rhizosheath formation changed porosity and aggregation around the root, thus, improved oxygen exchange. Accordingly, bacterial abundance and alpha diversity in hotspots of compacted soils were higher than the one of uncompacted. Thus, microorganisms localized in hotspots (rhizosheath) respond to better aeration, new carbon inputs compared to those inhabiting in the bulk soil. This confirms the distinguished role of rhizosphere-self organization for enzymatic mobilization of nutrients, and point out on the importance of aeration for rhizospheric microbial functionality (such as, enzyme expression for nutrients mining).

How to cite: Razavi, B. S., Rudolph-Mohr, N., and Tebbe, C.: Rhizosphere legacy: amelioration of MicroBioPhysical properties of compacted soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6171, https://doi.org/10.5194/egusphere-egu2020-6171, 2020.

EGU2020-22488 | Displays | SSS4.3

Studying deep rooting and its value for crops

Kristian Thorup-Kristensen

Water and nutrients are distributed throughout the soil volume, and their ability to move towards the plant roots is highly restricted, in most cases to a few mm or less. This mean, that unlike the aboveground resources of light and CO2 moving to the plants, roots need to grow towards the resources. Thus, for efficient resource uptake, roots need to be well distributed in the soil, both locally within the root zone and to grow deep to increase the overall volume of soil exploited. In crop production, deep rooting has been shown to be highly important for water and nitrogen use, and deep rooting is expected to contribute specifically to soil C sequestration.

Research into deep rooting and its functions is strongly restricted by the difficulties of studying roots hidden deeply in the soil. It is very laborious to access them, and even more difficult to set up experiments giving frequent and non-destructive measurements of the relevant parameters.  

In previous experiments, we have studied deep rooting of crops and cover crops and its effect on deep nitrogen uptake. By measuring roots and soil nitrogen to 2.5 m depth, we found that deep rooting was a main factor in nitrogen uptake and the reduction of nitrogen leaching loss. This showed how deep rooted species can be used to develop nitrogen efficient cropping systems. Further, it was shown that inclusion of deeper soil layers in the studies were critical for the conclusions to be drawn. Increasing the depth of study from e.g. 1 m to 2.5 m did not just moderate the conclusions and quantitative estimates, in several studies it basically changed conclusions that could be drawn.

Since 2015, we have built three new research platforms dedicated to detailed study of deep root growth and function. We have built a rhizobox facility consisting of 24 rhizoboxes each 4 m deep. The rhizoboxes are equipped with soil water sensors, and give access to observe the roots, take soil and root samples and inject tracers along the whole soil profile. In the field, we have built a platform, aimed at giving similar research possibilities, using long minirhizotrons, soil water sensors and metal access tubes for inserting ingrowth cores, all together giving valuable opportunities, though we cannot achieve the same easy access to the root zone as in the rhizoboxes. Finally, we have built a deep root phenotyping facility, using minirhizotrons to allow screening of 600 plant lines for root growth down to 3 meters depth, and allowing us to measure root activity of the lines by deep placement of isotope tracers.

These new facilities, and the research opportunities they give will be discussed, together with some of the first research results on deep roots we have obtained there.

How to cite: Thorup-Kristensen, K.: Studying deep rooting and its value for crops, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22488, https://doi.org/10.5194/egusphere-egu2020-22488, 2020.

EGU2020-5061 | Displays | SSS4.3

Spatio-temporal dynamics of root system architecture of maize in a field trial during a growing season

Doris Vetterlein, Susanne Schreiter, Eva Lippold, Maxime Phalempin, Sebastian Blaser, and Steffen Schlüter

A better understanding of how roots explore soil is crucial for plant breeding, yield increase and sustainable agriculture. This requires detailed knowledge about the temporal dynamics of root system architecture under field conditions, which is hard to achieve as sampling of roots with unconstrained growth (no root windows) is very laborious. 
Here we present the results of a major undertaking to sample maize roots in a field experiments at four growth stages in various depths (0-20, 20-40, 40-60 cm) with two different methods: a) destructive sampling with a root corer and root washing vs. b) undisturbed sampling combined with root detection in X-ray CT images. The first method results in root length data with a higher number of technical replicates per depth and plot, whereas the second provides more details of small-scale rooting patterns and plant-soil interactions in intact soil for a smaller number of samples.
The aim of the study was to explore differences in spatio-temporal root growth patterns between two different maize genotypes (wild type vs. root hairless mutant) growing in two different homogenized substrates (sand vs. loam). For disturbed sampling we found that for both genotypes root growth was more vigorous in sand during the entire growing season. This was remarkable since shoot biomass was larger on the loam plot. As drought developed during the growing season, root length density profiles reversed in loam, but not on sandy substrate. For intact cores we find the same trends so that they can now be analyzed towards inter-root distances at shorter scales.
In loam the absence of root hairs and the associated reduction of available surface for water and nutrient uptake resulted in a 50% reduction in shoot biomass, whereas root length profiles did not differ in the root corer data. In sand differences in shoot biomass between genotypes were comparable, but here root length densities were lower for the root hairless mutant in the root corer data. Unexpectedly there was no compensation of lacking root hairs by enhanced root growth. The root length data in intact samples showed higher variation due to smaller sampled volumes which disguised possible trends between genotypes.
In summary, the different hydraulic properties of the substrates had a strong effect on root growth and root distribution with depth, whereas the genotype governed shoot biomass supposedly through differences in nutrient and/or water uptake efficiency mediated by the presence or absence of root hairs. As the next steps, these observations will be underpinned by transpiration and soil moisture monitoring data as well as plant nutrient uptake data.

How to cite: Vetterlein, D., Schreiter, S., Lippold, E., Phalempin, M., Blaser, S., and Schlüter, S.: Spatio-temporal dynamics of root system architecture of maize in a field trial during a growing season, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5061, https://doi.org/10.5194/egusphere-egu2020-5061, 2020.

EGU2020-5225 | Displays | SSS4.3

An improved method for the segmentation of roots from X-Ray computed tomography 3D images: Rootine v.2

Maxime Phalempin, Eva Lippold, Doris Vetterlein, and Steffen Schlueter

X-ray computed tomography (CT) is acknowledged as a powerful tool for the study of root system architecture (RSA) of plants grown in soil. The study of the root system properties is however only possible after performing root segmentation, i.e. the binarization of all root voxels. Root segmentation is often regarded as a tedious and difficult task as its success depends on several factors such as the image resolution, the signal to noise during image acquisition and the gray value contrast between the roots and all other surrounding features. Here, we present an improved method for the segmentation of roots from X-Ray computed tomography 3D images. The algorithm Rootine (Gao et al. 2019) does not detect roots by their gray values but by their characteristic tubular shape. This algorithm was further developed in order to improve the root recovery rate and to reduce the number of parameters involved during the segmentation process. This was achieved by adding two key steps: (1) an absolute difference transform and (2) an automatic calculation of the parameters used during the Gaussian smoothing. The first step allows for targeting specific features based on a gray value criteria contained within a user-defined gray value range in order to better distinguish roots from pores whereas the second step allows for targeting root segments of specific diameters. On the benchmark dataset of Gao et al. 2019, the newly called “Rootine v.2” was able to recover 34 % more roots as compared to its preceding version. Moreover, the number of parameters was reduced from 10 down to 5 which allows for a faster calibration and an overall better usability of the algorithm. The presented method also allows for a more reliable estimation of root diameter derived from X-Ray CT images. This work was carried out in the framework of the priority programme 2089 “Rhizosphere spatiotemporal organization - a key to rhizosphere functions” funded by DFG (project number 403640293).

How to cite: Phalempin, M., Lippold, E., Vetterlein, D., and Schlueter, S.: An improved method for the segmentation of roots from X-Ray computed tomography 3D images: Rootine v.2, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5225, https://doi.org/10.5194/egusphere-egu2020-5225, 2020.

EGU2020-9707 | Displays | SSS4.3

Spatial sampling approach to unravel the impact of soil texture and root genotype on maize root gene expression profiles

Minh Ganther, Marie-Lara Bouffaud, Lucie Gebauer, François Buscot, Doris Vetterlein, Anna Heintz-Buschart, and Mika Tarkka

The complex interactions between plant roots and soil microbes enable a range of beneficial functions such as nutrient acquisition, defense against pathogens and production of plant growth hormones. The role of soil type and plant genotype in shaping rhizosphere communities has been explored in the past, but often without spatial context. The spatial resolution of rhizosphere processes enables us to observe pattern formation in the rhizosphere and investigate how spatial soil organization is shaped through soil–plant–microbiome interactions.

We applied spatial sampling in a standardized soil column experiment with two maize genotypes (wildtype vs. roothairless3) and two different soil textures (loam vs. sand) in order to investigate how in particular functions of the maize roots relating to nutrient/water uptake, immunity/defense, stress and exudation are affected. RNA sequencing and differential gene expression analysis were used to dissect impact of soil texture, root genotype and sampling depth. Our results indicate that variance in gene expression is predominantly explained by soil texture as well as sampling depth, whereas genotype appears to play a less pronounced role at the analyzed depths. Gene Ontology enrichment analysis of differentially expressed genes between soil textures revealed several functional categories and pathways relating to phytohormone-mediated signaling, cell growth, secondary metabolism, and water homeostasis. Community analysis of rhizosphere derived ACC deaminase active (acdS gene including) plant beneficial bacteria, which suppress the phytohormone ethylene production, suggests that soil texture and column depth are the major factors that affect acdS community composition.

From the comprehensive gene expression analyses we aim to identify maize marker genes from the relevant core functional groups. These marker genes will be potentially useful for future experiments; such as field plot experiments for investigation of later-emerging plant properties.

This research was conducted within the research program “Rhizosphere Spatiotemporal Organisation – a Key to Rhizosphere Functions” of the German Science Foundation (TA 290/5-1).

How to cite: Ganther, M., Bouffaud, M.-L., Gebauer, L., Buscot, F., Vetterlein, D., Heintz-Buschart, A., and Tarkka, M.: Spatial sampling approach to unravel the impact of soil texture and root genotype on maize root gene expression profiles, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9707, https://doi.org/10.5194/egusphere-egu2020-9707, 2020.

EGU2020-10412 | Displays | SSS4.3

Implications of root exudates on the formation of rhizosheaths

Riffat Rahim, Adrian Haupenthal, and Eva Kroener

Root exudates stimulate microbial activity and functions as a binding and adhesive agent that increases aggregate stability in the rhizosphere. The exudates produced from plant roots and microorganisms in the rhizosphere play a significant role in the formation of rhizosheath. Rhizosheaths comprises the soil that adheres to the roots with the help of root hair and mucilage even when it is removed from the surrounding soil. Low surface tension and great viscosity stabilize soil aggregates in surrounding root and develop rhizosheath formation. To our knowledge, no investigations are made on the influence of root exudates in soil rhizosheath formation, although it is well documented the formation and stabilization of rhizosheath of maize plants under various soil water contents but the influence of root exudates on the rhizosheath formation associated with other rheological properties is still missing. Such knowledge will greatly enhance the understanding of how rhizosheath is formed under different root and seed exudates and the effect of their physiochemical properties on the adhesion properties of mucilage will be studied in this project.

The aim of this study is to provide the first combined quantitative data on how root and seed exudates of different plants affect rhizosheath formation. We hypothesized that mucilage will contribute to the formation of rhizosheaths.  For this, we will use the mucilage of chia seeds which acts as a modelled plant root mucilage and mix it with soil in five different concentrations. After preparing the soil with mucilage, artificial roots (flax cords) will be incorporated in this soil and after drying and wetting cycles roots will be removed and the mucilage adhesion, simulation and rheological properties will be investigated under various soil water contents, soil texture, soil type, and soil compaction.

Key words:

                   Rhizosheath, mucilage, drying and wetting cycles and soil structure

 

How to cite: Rahim, R., Haupenthal, A., and Kroener, E.: Implications of root exudates on the formation of rhizosheaths, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10412, https://doi.org/10.5194/egusphere-egu2020-10412, 2020.

EGU2020-6428 | Displays | SSS4.3

Rhizosphere effect of woody plants: A meta-analysis

Dayong Gan, Jiguang Feng, and Biao Zhu

Interactions among plants, soil and microbiota play an important role in maintaining the function of terrestrial ecosystems, which often occur in rhizosphere. The rhizosphere effect is defined as the difference in soil properties and biogeochemical processes between rhizosphere and root-free bulk soil. Despite its importance in controlling soil biogeochemical cycling, quantitative assessments of the rhizosphere effects of woody plants are still rare. In this study, we synthesized the rhizosphere effects of woody plants on soil physicochemical properties, microbial biomass and community structure, enzyme activities, and carbon (C) and nitrogen (N) mineralization rates. We also explored the controls of rhizosphere effects by functional traits (eg. leaf life form, mycorrhizal type), environmental and experimental variables (eg. soil sampling method).

Our results showed that the rhizosphere effects on most soil physicochemical variables were positive (except pH). For example, the rhizosphere stimulated C mineralization rate by 56.7%, gross N mineralization rate by 57.9%, and net N mineralization by 60.9% on average compared to the root-free bulk soil. Moreover, for enzyme activities and C mineralization rate, the rhizosphere effects were generally higher in shrubs than in trees. For C mineralization rate, the rhizosphere effects of evergreen species were stronger than those of deciduous species. However, the rhizosphere effects did not vary significantly between species associated two mycorrhizal types (arbuscular mycorrhizal, AM vs. ectomycorrhizal ECM), with few exceptions for NO3-, NH4+, bacteria and fungi biomass. Overall, this meta-analysis comprehensively assessed the rhizosphere effects of woody plants (187 species and 29 variables) on global scale and strengthened our understanding of the effect of living roots on soil C and nutrient cycling in the rhizosphere.

How to cite: Gan, D., Feng, J., and Zhu, B.: Rhizosphere effect of woody plants: A meta-analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6428, https://doi.org/10.5194/egusphere-egu2020-6428, 2020.

EGU2020-8363 | Displays | SSS4.3

Land use effect on microbial growth and respiration under future climate

Vusal Guliyev, Melissa Pfeiffer, Maria Udovenko, Christina Fasching, Thomas Reitz, and Evgenia Blagodatskaya

Fresh input of organic material in soil is continuously transformed and processed by growing microorganisms using this organic input as a substrate. Therefore, the quality and quantity of soil organic C stock is strongly dependent on the intensity of mineralization processes through microbial respiration and growth. We aimed to prove the sensitivity of microbial respiration and growth parameters to indicate an interactive effect of land use and climate warming. For this we used Global Change Experimental Facility in Bad Lauchstädt, UFZ, Halle, Germany. This long-term experiment is designed in 5 land use strategies (Organic Farming, Conventional Farming, Intensive Meadow, Extensive Meadow, and Extensive Pasture) and 2 climate scenarios (ambient and future). We determined basal respiration by CO2 emission, microbial growth parameters by substrate-induced growth respiration (SIGR), and the quality of soil organic matter by Fourier-transformed infrared spectroscopy (FTIR). The effect of biotic (vegetation type) and abiotic (temperature and moisture) factors on microbial attributes and on chemical composition of soil organic matter will be compared.

How to cite: Guliyev, V., Pfeiffer, M., Udovenko, M., Fasching, C., Reitz, T., and Blagodatskaya, E.: Land use effect on microbial growth and respiration under future climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8363, https://doi.org/10.5194/egusphere-egu2020-8363, 2020.

EGU2020-8403 | Displays | SSS4.3

Interactive effect of vegetation and climate warming on total microbial and fungal biomass in soil

Maria Udovenko, Vusal Guliyev, and Evgenia Blagodatskaya

Soil microbiota ensuring sustainable functioning of terrestrial ecosystems is strongly dependent on climatic conditions and vegetation type. Even within the same climatic zone, active land use alters the size, structure and functioning of the microbial community. We hypothesized that land use effect on soil microbial biomass will be more pronounced under impact of global warming. We also tested whether the biomass of specific microbial group (e.g., fungi) is more sensitive to environmental changes than total microbial biomass.

We proved these hypotheses in the experiments based on Global Change Experimental Facility platform, located at the field research station of the Helmholtz-Centre for Environmental Research in Bad Lauchstädt near Halle, Saxon-Anhalt, Germany. Experimental setup included 50 plots, located in 10 blocks (5 plots per block). Five blocks are under ambient climate and the rest 5 blocks are subjected to a realistic climate change treatment (under conditions predicted by several models of climate change in Central Germany for 2050–2080 period). Five land use types were established in every block: conventional farming; organic farming; intensively used meadow, extensively used meadow and extensively used pasture. We determined soil microbial biomass and its fungal component by chloroform fumigation-extraction method and by ergosterol content, respectively. We found that fungal biomass was more sensitive to intensive land use for crop production than to climate change. The possible mechanisms of such a sensitivity will be discussed.

How to cite: Udovenko, M., Guliyev, V., and Blagodatskaya, E.: Interactive effect of vegetation and climate warming on total microbial and fungal biomass in soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8403, https://doi.org/10.5194/egusphere-egu2020-8403, 2020.

The H2020 project Excalibur will be presented. It has the ambition of making the road to a biodiversity-driven change in the soil management of crops through the acknowledgement of the important role of soil biodiversity conservation and exploitation. The project applies integrated approach of research, development and field implementation to achieve its goals. Excalibur will deploy the knowledge gained by new molecular techniques, such as genomic sequences characteristics to specific groups of microorganisms and functions, in the creation of tools, indicators and evaluation systems. Co- innovation is fostered by collaboration of researchers with farmers and manufacturers, with a mutual exchange of information and feedback. Project’s results will bring new insights and practical solutions to stakeholders, validated by process analysis. For this purpose Excalibur plans to: 1) focus on multiscale plant-soil-microbes interactions be to exploit the potential of multifunctional bio-inocula and bio-effectors; 2) optimize the formulation and the application methods of these products based on native soil biodiversity dynamics; 3) develop a strategy to improve the exploitation of soil biodiversity interactions with bio-effectors and bio-inocula by assessing their impacts on crops and biodiversity under contrasting agricultural management practices (conventional, organic) and biotic/abiotic stress conditions; 4) to build a multi-criteria model to assess soil biodiversity status of cropping systems for a more efficient use of bio-effectors and bio-inocula; 5) develop technical tools to monitor the persistence and dispersion of bio-inocula under field conditions for eco-toxicological and agronomical purposes; 6) evaluate the effects of the new strategy on economy, environment quality and ecosystem functions; 7) disseminate results to all stakeholders with a dynamic and comprehensive methodology and encourage the adoption of best practices derived from the new strategy at local, regional and global level.

How to cite: Mocali, S., Canfora, L., Pinzari, F., and Malusà, E.: The EXCALIBUR project: novel microbial-based bioproducts improving soil biodiversity and the effectiveness of biocontrol and biofertilization practices in horticulture, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11850, https://doi.org/10.5194/egusphere-egu2020-11850, 2020.

Forests plants affect the biological and chemical properties of the soil through the root exudation, input of leaf and root litter. This study investigates the relationships between the species composition of plant communities, microbial properties and content of elements of the upper soil horizon in boreal forest ecosystems (using NMS analysis).

It is hypothesized that 1) microbial biomass and chemical properties relates to the species diversity of plants, 2) microbial biomass and chemical properties relates to certain plant communities, 3) microbial biomass and chemical properties linked to altitude gradient, 4) types of communities differ due to the composition of the grass cover.

Plots were chosen in the foothills of the Ural Mountains, Russia, in Pechoro-Ilych Nature Reserve, 62-63°N, 58-59°E, to small altitude gradient 250-400 m above sea level. Plant, litter and soil were taken from five spruce - fir forests (Picea obovate together with Abies sibirica) with siberian pine and birch (hereinafter “spruce forest”). The peculiarity of the territory is that in a small area five different grassy communities were formed.  They represented by both species-rich tall grasses forests and poor species, moss and large fern forests.

Types of forests: boreal-tall grass (3 plots), small grass – green moss (3 plots), bilberry-green moss (3 plots), shrub - haircap moss (4 plots) and large fern (3 plots). The plots (10×10 m) were selected for plant biodiversity describing. Topsoil samples (0-5 cm) were taken from sub-plots in July 2018 (n=48). In the collected samples, microbial biomass carbon (MBC), basal respiration (BR), pH and content of elements (S, P, Ca, Mg, K, Si, Ti, Mn) were measured.

We distinguished a group of communities with high microbial biomass (small grass-green moss and boreal-tall grass spruce forests) and a group with low microbial biomass (shrub-long moss, bilberry-green moss, large fern spruce forests). The high biological activity of the soil is weak confined to plant communities.

No strong relationship between MBC, BR, plant species richness and altitude was found.

Microbial biomass is strongly related to species of boreal-tall grasses (Aconitum septentrionale Koelle, Crepispaludosa (L.) Moench, Rubussaxatilis L., Thalictrum minus L., Valerianaofficinalis L., Filipendulaulmaria (L.) common species, Geranium spp. Species L.) albiflorumLedeb., Paris quadrifolia L.). These types of grass indicate an increase in soil pH, increase the content of Ca, Mg and S in the soil, and a decrease the content of Si and Ti. Opposite, the content of Si and Ti increased in the moss communities. K increased in the soil of large fern and boreal-tall grass communities. Thus, the content of microbial biomass, S, Ca, Mg, pH increased together in the direction of boreal tall grass community. The research was financial supported by grant RFBR mol_a No. 18-34-00987.

How to cite: Kvitkina, A.: Plant biodiversity linked with microbial biomass and chemical soil properties in boreal forests, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10420, https://doi.org/10.5194/egusphere-egu2020-10420, 2020.

Until the early nineteenth century, the Belgian landscape was characterized mainly by the presence of heathland, a typical cultural landscape with important ecosystem services. Since then, urbanisation has led to the conversion of large stretches of heathland to be converted to forest, arable land or cities. Increased concentrations of exhaust gasses result in elevated concentrations of nitrogen (N) in the atmosphere. Through rainfall this N enters the soil and is fixed via precipitation reactions, which in turn leads to higher N soil concentrations. Because Calluna vulgaris (common heather; the dominant plant species in heathlands) thrives on soil containing low nutrient concentrations,  it is now being outcompeted by plant species more suited to these altered nutrient levels. As a result, the heathland is slowly evolving into grassland and, consequently, its ecosystem services and soil nutrient cycling are changing.

Here, we present the preliminary results of our investigation into the influence of grass encroachment on nutrient cycling in heathlands. For this research question, we set up a gradient of 14 plots of increasing grass cover from 0 to 100%. The woody structures of heather contain high concentrations of lignin, consequently the 100% heather plots have a more recalcitrant organic input. It is therefore hypothesized that the nutrient turnover in these plots are lower than in the 100% grass plots since grass has lower lignin concentrations and thus higher litter quality. We set up a series of measurements on pooled and homogenized soil samples of these 14 plots. We measured N mineralization and nitrification, 2 enzymes and relevant soil parameters. Interestingly, there were no significant results found for the N mineralization and nitrification. The measurement of the enzymes chitinase and phosphatase showed a significant correlation, indicating the impact of vegetation on the enzymatic activity, and therefore on the soil nutrient cycle.

How to cite: Arnauts, N.: Influence of grass invasion on soil parameters in a Belgian heathland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8330, https://doi.org/10.5194/egusphere-egu2020-8330, 2020.

EGU2020-21598 | Displays | SSS4.3

On-line nano-solid phase extraction Fourier-transform ion cyclotron resonance mass spectrometry workflow to analyse soil solution organic matter gradients in the rhizosphere

Martin Lohse, Sebastian Blaser, Doris Vetterlein, Steffen Schlüter, Eva Oburger, Thorsten Reemtsma, and Oliver Lechtenfeld

Plant-microbe interplay in the rhizosphere generates multi-faceted chemical gradients. The soil solution is a crucial component of the rhizosphere, where chemical gradients of organic molecules first develop upon growth of roots, introduction of plant-derived carbon and microbial turnover. Studying these gradients requires high resolution both in time and space as well as high chemical specificity to resolve the multitude of compounds. Existing methods to probe the rhizosphere soil solution were mostly limited to bulk chemical parameters, inorganic ions or targeted analysis of organic molecules. However, to decipher organic carbon turnover in the rhizosphere the characterization of the complex pool of soil solution organic matter is needed.

Here we present a novel method that combines time-resolved collection of soil solution samples via micro-suction cups in the rhizosphere with ultrahigh chemical resolution provided by Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to unravel developing pattern of soil solution organic matter.

Zea mays plants were grown in soil columns for three weeks and soil solution samples of undisturbed root-soil system were collected once a week. Growth of the root system and hence position of sampling locations in relation to the distance from the root, were followed by X-ray computed tomography (X-ray CT).

The online sample preparation was optimised to extract and desalt the organic matter from a few microliters of soil solution. The downscaling to a nano-liquid chromatography system for the on-line extraction allowed the analysis of only minute amounts of organic carbon within the samples (down to 10 ng). Given the high background concentration of soil-derived organic carbon, the high mass resolution and sensitivity of FT-ICR-MS enabled to distinguish root derived molecules from soil organic matter based on their exact masses. Molecular formulas of the root derived molecules could be calculated showing distinct chemical characteristics as compared to the bulk soil solution. X-ray CT analyses enabled relating the results from the chemical analysis to distance from the root and root age. With increasing influence of the roots higher molecular masses and an increasing degree of oxygenation of the molecules could be observed.

Our method is thus capable to show the changing small scale pattern of soil solution organic matter during the early rhizosphere development, closing the knowledge gap between root exudates, soil chemistry and microbial processes.

How to cite: Lohse, M., Blaser, S., Vetterlein, D., Schlüter, S., Oburger, E., Reemtsma, T., and Lechtenfeld, O.: On-line nano-solid phase extraction Fourier-transform ion cyclotron resonance mass spectrometry workflow to analyse soil solution organic matter gradients in the rhizosphere , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21598, https://doi.org/10.5194/egusphere-egu2020-21598, 2020.

EGU2020-10640 | Displays | SSS4.3

Succession between living and dead roots drives the fate of soil carbon pools

Pedro Paulo de C. Teixeira, Ana Paula M. Teixeira, Luís Fernando J. Almeida, Luís Carlos Colocho Hurtarte, Ivan F. de Souza, Danilo H. S. da Silva, Carsten W. Mueller, Alix Vidal, and Ivo R. da Silva

There is growing evidence that belowground plant carbon (C) inputs displays a major role for soil organic matter (SOM) dynamics. During the root life-cycle, there is a sequential shift from C inputs from living to dead roots, which might affect the conversion of these specific compound classes to SOM. However, this successional effect has yet not been investigated. In this study, we aimed to evaluate (i) the short-term impacts of living root-derived C on SOM formation and composition and (ii) how the succession between living and dead roots impacts their respective fate in soil. For this purpose, we set up a two-step experiment that simulated the shift between living and dead roots C inputs. In the first step, Eucalyptus spp. plants were cultivated in pots under controlled conditions for 66 days. In order to isolate the living root-derived C, we inserted in each pot 4 cylinders (0.5 cm high, 4.75 cm diameter) capped with a nylon membrane (pore size 5 μm) and filled with soil (clayey Rhodic Ferrasol) at the start of the experiment. Half of the pots were periodically pulse-labeled with 13C-CO2 (10 pulses of 10 h, 0.46 g of 13C plant-1), while the remaining ones were used as controls (unlabeled treatments). After 66 days, all pots were harvested, and one cylinder per pot was used to depict the living root effects on SOM pools. Those cylinders were separated in layers according to the distance from the roots (0-4, 4-8, 8-15 and 15-25 mm) and analyzed for organic carbon, nitrogen, as well as δ13C. We quantified and characterized the microbial communities using phospholipid fatty acid (PLFA), and extracted the pedogenic oxides (iron and aluminum) to highlight potential alterations in organo-mineral complexes and short-range order phases. Using density/size fractionation, we further gained elemental and isotopic information of specific SOM pools, i.e. particulate, occluded and mineral-associated organic matter. The remaining cylinders were incubated for 84 days in two treatments, with and without dead roots. Heterotrophic respiration rates were measured periodically together with the 13C enrichment of the CO2 produced. Carbon derived from living roots was mainly recovered in the first millimeters from the root source, as occluded or mineral-associated SOM. Close to the roots, we detected a shift in the microbial communities and a decrease of organo-mineral complexes and short-range order phases. Carbon derived from living roots was rapidly mineralized and the δ13C from the respired CO2 returned to natural abundance ranges after 84 days of incubation. The presence of dead roots did not affect the mineralization C derived from living roots. Our work highlights the importance of C inputs from living roots for the formation of SOM. However, the compounds deposited by living roots exhibit also a transient nature which challenges the assumption that living root-derived C is necessarely a precursor of stable SOM formation.

How to cite: de C. Teixeira, P. P., Teixeira, A. P. M., Almeida, L. F. J., Colocho Hurtarte, L. C., Souza, I. F. D., Silva, D. H. S. D., Mueller, C. W., Vidal, A., and Silva, I. R. D.: Succession between living and dead roots drives the fate of soil carbon pools, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10640, https://doi.org/10.5194/egusphere-egu2020-10640, 2020.

EGU2020-20202 | Displays | SSS4.3

Effect of tree native species assemblages on C, N & P contents of burned soils

Natalia Aguilera, Felipe Aburto, Francisco Salazar, Marcela Bustamante, Manuel Acevedo, Marta Gonzalez, Ulrike Schwerdtner, and Yvonne Oelmann

Keywords: Assemblage, Interaction, nutrients

Forest fires can cause a temporary nutrient deficiency or imbalance in the soil. Post fire forest restauration could be enhance by simulating process of vegetation succession taking advantage of beneficial interaction between species (e.g. facilitation and complementarity), which could help coping with nutrient imbalances. To determine the type of interactions and their effects on soil nutrients affected by fires and on the acquisition of nutrients by plants, a meso-cosmos experiment was established under controlled conditions, using surface soils affected by the Cayumanque megafire (Región del Biobio). Seven assemblages of three species with different nutrient acquisition strategies were established: Nothofagus obliqua (mycorrhizae), Lomatia dentata (proteiform roots) and Sophora cassioides (nodules). In a complete factorial design of two blocks (with and without complementary fertilization). The main interactions resulted in competition between N. obliqua from S. cassioides and L. dentata, while S. cassioides was not be significantly affected by the presence of L. dentate, suggesting complementarity. Fertilization did not interact with assemblages or reduce competition, but increased plant growth in all assemblages. Available soil nitrogen (NO3-) increased significantly in the presence of S. cassioides (6.88±3.10) and decreased in the presence of L. dentata (2.67±0.84). Finally, N. obliqua increased its nitrogen acquisition by 44% in the presence of L. dentata and decreased by 5% in the presence of S. cassioides. Although no significant differences were observed in POlsen, the fraction of inorganic phosphorus was significantly lower in the presence of proteacea (122.24±20.99). In addition, enzyme analysis showed no significant differences for microbial biomass and LAP activity. However, the combination of N.O. and L.D. showed significantly high phosphatase activity (16.36±5.57).

Finally, further isotopic and enzymes work is in process to study nutrient pools in plants and soil either of L. hirsuta and N. obliqua individuals growing alone or in combination. Because native Nothofagus spec. forests have been affected by forestry fires and replaced by plantations of exotic tree species throughout Chile, knowledge on interactions among native species affecting tree nutrition is lacking. Therefore, the results of our research support the use of plant assemblages as a potentially effective restoration strategy in post-fire soils with low nutrient content.

Acknowledgement: Special thanks to National forestry institute, BayCEER and Yvonne Oelmann’s laboratory for contribute to this research and make it possible at an international scale.   

 

How to cite: Aguilera, N., Aburto, F., Salazar, F., Bustamante, M., Acevedo, M., Gonzalez, M., Schwerdtner, U., and Oelmann, Y.: Effect of tree native species assemblages on C, N & P contents of burned soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20202, https://doi.org/10.5194/egusphere-egu2020-20202, 2020.

EGU2020-5784 | Displays | SSS4.3

Towards soil micro-zymography: comparison of staining and impregnation strategies

Negar Ghaderi, Andrey Guber, Hannes Schmidt, and Evgenia Blagodatskaya

Enzymes are produced by microorganisms either intracellularly in cell’s cytoplasm and periplasm or extracellularly either as attached to outer surface of cell membranes or released to the soil microhabitats. The distribution of microhabitats in soil is highly heterogeneous with high abundance of microorganisms in the small volume of soil hotspots, e.g., in the rhizosphere - the most important plant-soil interface with very dynamic interactions between roots and microorganisms. Soil zymography is one of the most realistic methods developed to visualize enzyme activity in undisturbed soil at the mesoscale (mm-cm) level using substrate-saturated membranes. However, visualization of enzymatic processes at the micro-scale level remains a challenge. We tested several impregnation strategies of soil sample (e.g., by agarose gel, silicon spray and super transparent silicon mixture) for their suitability for micro-zymography, i.e., for visualization of enzyme activity in undisturbed soil particles at the microscopic level combining fluorogenic substrates with epifluorescence microscopy. The pros- and cons- of various combinations of impregnation and staining of micro-sized soil samples will be discussed.

Keywords: enzyme activity, zymography, fluorogenic substrates

How to cite: Ghaderi, N., Guber, A., Schmidt, H., and Blagodatskaya, E.: Towards soil micro-zymography: comparison of staining and impregnation strategies , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5784, https://doi.org/10.5194/egusphere-egu2020-5784, 2020.

SSS4.4 – Diving into the soil microhabitat - Impacts of the soil physical structure on soil biota and vice-versa

EGU2020-18396 | Displays | SSS4.4

Microbes meet Structure - Soil Ecology in Microengineered Soil Chips

Edith Hammer, Micaela Paola Mafla Endara, Carlos G. C. Arellano, Kristin Aleklett, Milda Pucetaite, and Pelle Ohlsson

Many soil processes are governed by microbes, and biological and physical processes influence each other. We recently developed microfluidic model systems that simulate the spatial microstructure of soil microbial habitats in a transparent material, which we call Soil Chips. They allow us to study the impact of soil physical microstructures on microbes, and vice versa, the influence of microbes on soil physical properties: such as Microbial behavior and interactions in response to a spatially refined habitat, or wettability and water retention, soil aggregate formation and changes in the pore space.

We inoculated our chips with fluorescent lab cultures or natural whole soil inocula. Through the chips we observed via microscopy processes in real-time and at the scale of the microbial cells.

We could study fungi, bacteria, protists and nematodes as well as the distribution of soil minerals and soil solution in the chips. We subjected the adjacent soil to drying-rewetting processes, which was visible in water movements inside the chip. We studied the development of preferential water flow paths, and water retention in smaller pores and as a consequence of microbial exudates. Also the microbes themselves influenced the formation of microhabitats, where fungal hyphae both blocked connections and pushed through existing borders, and single-celled protozoa opened passages through existing aggregates. We found that the presence of fungal hyphae in a pore space system increased both the presence of bacteria and the likelihood of water in the pores, and thus allowing us to study fungal highways in a more realistic soil setting.

The chips act like a window into the soil, through which we can eaves-drop on a world that otherwise is largely hidden to us: Jostling protists, tsunami-like drying-rewetting events, and fungi with character. Beyond the scientific potential, the chips can also bring soils closer to people and hopefully increase engagement in soil health conservation.

How to cite: Hammer, E., Mafla Endara, M. P., Arellano, C. G. C., Aleklett, K., Pucetaite, M., and Ohlsson, P.: Microbes meet Structure - Soil Ecology in Microengineered Soil Chips, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18396, https://doi.org/10.5194/egusphere-egu2020-18396, 2020.

EGU2020-9512 | Displays | SSS4.4

Manufactured Soil Aggregates for Studying Microhabitats

Harry Harvey, Ricky Wildman, Sacha Mooney, and Simon Avery

Environmental perturbation, anthropogenic or otherwise, can have a profound effect on soil microbiota and essential biogeochemical processes. The general resistance and adaptation of yeasts and other fungi to stressors has been well studied in vitro however, the influence of key physical variables, such as how soil structure regulates fungal response to perturbation, is poorly understood. In this study, we developed an approach to manufacture soil macroaggregates that are characteristically similar to their natural counterpart (determined by X-ray CT) and with defined microbial composition. This new tool allowed us to examine the influence of soil aggregation on fungal stress response by manufacturing aggregates with yeast cells either within, or on, the aggregate surface. Environmental stressors including heavy metals, anoxia, and heat stress were applied to these aggregates to capture an array of environmental stressors and assay differences in survival between exo-and-endo aggregate cells. Results generated with this new tool indicate that the location of yeast cells in soil macroaggregates can impact on their survival, in a stressor- and time-dependent manner.

How to cite: Harvey, H., Wildman, R., Mooney, S., and Avery, S.: Manufactured Soil Aggregates for Studying Microhabitats, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9512, https://doi.org/10.5194/egusphere-egu2020-9512, 2020.

Soil structure is the organisation of soil particles in aggregates with increasing hierarchical levels, from nano- to macro-architectures. Several processes and the functioning of the entire soil ecosystem fundamentally depends on soil structure. Soil is also a very heterogeneous and complex matrix to study because of several components with different nature (mineral, organic and biological), physics and chemistry comprise it. Its study often involves techniques that profoundly alter its natural composition or destroy its original 3D arrangement, including the pore distribution and organisation, which is crucial in preserving a suitable habitat for soil ecology and functioning.

Microbial life has been discovered in the last decades to exist in biofilms, 3D spatial organisations of microbial communities adhering to solid surfaces. In these well-organised assemblages of one or more different microbial species, extracellular polymeric substances (EPS) play remarkable functions for microorganisms in biofilms and facilitate aggregation of soil particles.

As a model system, a self-standing polymer biodegradable nanostructured scaffolds (NS) composed of a mixture of nano- to microfibres and microbeads mimicking the fibrous materials and particles comprising the main morphological types of soil (organic matter and mineral particles) and the relative spatial architecture at the micro- and nanoscale were created by electrospinning. Electrospinning is a nanotechnology producing 2D and 3D nano- and microfibrous scaffolds under an electric field. The resulting NS were characterised by considerable porosity and extensive surface area. A PGPR species was employed as a model microbial type to test the capacity of similar NS of supporting the biofilm development. Incubation was performed under stirring to stimulate only stable interactions between microorganisms and the various morphological types of the NS, and also to assess the stability of the NS mimicking the soil aggregates. To shed some light into the nexus between microorganisms and soil structure and the reciprocal influence, combination of imaging techniques such as optical, SEM and TEM microscopy were used to observe “in situ” associations of microbes with mineral and organic materials at nano- and microscale and the consequent effects on porosity usually destroyed under investigations.

The typical phases of conditioning film release, initial and stable adhesion mediated by appendages and EPS release, micro- and macrocolony formation until a mature biofilm development were observed. Morphological modifications of bacteria and the involvement of other components in the mentioned stages were also detected. The bacteria growth rate, the overall respiratory activity and its spatial distribution throughout the NS were recorded.

Hence, the tools here proposed can have high potentials in reproducing the spatial and temporal dynamics of microbial hotspots of activity typically present in the rhizosphere, the sphere of soil surrounding roots, which is of central importance for the entire soil ecosystem functioning. 

Similar 3D NS can also provide the opportunity of zooming in microbial lifestyle observing microbes at work, from the dynamics of interactions with organic matter and particle surfaces to their spatial distribution and colony formation, then linking biological processes to specific physical and chemical features of soil at different scales (from nm to mm).

How to cite: De Cesare, F., Di Mattia, E., and Macagnano, A.: Developing 3D polymer nanostructured fabric as a soil-like model for studying interactions between microorganisms and soil structure - The case of bacterial biofilm development, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19304, https://doi.org/10.5194/egusphere-egu2020-19304, 2020.

EGU2020-7588 | Displays | SSS4.4

Pore connectivity across scales and resolutions

Maik Lucas, Doris Vetterlein, Hans-Jörg Vogel, and Steffen Schlüter

An important parameter to quantify pore structure and link it to soil functions is connectivity. When quantifying connectivity with X-ray microtomography (X-ray-µCT), one of the major drawbacks is that high resolution can only be achieved in small samples. In these samples, the small pores can be described, but the connectivity of larger pores cannot be quantified reasonably.

Here we explore changes in pore connectivity with changing sample size covering a range of analyzed pore diameters of more than three orders of magnitude. Soil columns with a diameter of 10 cm were taken in two different depths (0 - 20 cm and 40 - 60 cm) at different sites of an agricultural chronosequence ranging in age from 0 to 24 years. X-ray CT was used for scanning the original columns as well as undisturbed subsamples of 3 and 0.7 cm diameter. This enabled us to detect characteristic traces in certain connectivity metrics on the chronosequence, caused by different pore types and thus different processes. In detail, we determined the connection probability of two random points within the pore system, i.e. the Γ-indicator and the Euler number, χ as a function of minimum pore diameter.

Our results revealed that scale artifacts in the connectivity functions overlap with characteristic signatures of certain pore types. For the very first time a new method for a joint-Γ-curve was developed that merges information from three samples sizes, as the Γ-indicator gives highly biased information in small samples. In contrast, χ does not require such a scale fusion and is helpful to define characteristic size ranges for pore types. Overall, findings suggest a joint evaluation of both connectivity metrics to identify the contribution of different pore types to the total pore connectivity with Γ and to disentangle different pore types with χ.

For the samples of the chronosequence such an evaluation revealed that biopores mainly connect pores of diameters between 0.1 and 0.5 mm. However, this was not necessarily coupled with increasing porosity. Tillage, conversely, lead to an increase in porosity due to a shift of pores of diameter >0.05 mm towards pores of diameter >0.20 mm and therefore increased connectivity of pores >0.20 mm.

The current study is part of the DFG-Project Soil Structure (AOBJ: 628683). 

How to cite: Lucas, M., Vetterlein, D., Vogel, H.-J., and Schlüter, S.: Pore connectivity across scales and resolutions , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7588, https://doi.org/10.5194/egusphere-egu2020-7588, 2020.

EGU2020-18948 | Displays | SSS4.4

Potential of combined neutron and X-ray imaging to quantify local carbon contents in soil

Genoveva Burca, Stephen Hillier, Pawala Ariyathilaka, Jumpei Fukumasu, Anke Herrmann, Mats Larsbo, Oxana Magdysyuk, and John Koestel

Soil organic carbon (SOC) is of key importance for soil functioning. It strongly impacts soil fertility, greenhouse gas emissions, nutrient retention, and contaminant degradation. The soil pore network determines how oxygen, water and nutrients are transported and exchanged in soil, and the architecture of the soil is therefore equally fundamental to soil functions. For a thorough understanding of the microbial habitat, the soil pore network architecture needs to be evaluated alongside with the spatial distribution of SOC, but the challenge ahead is the 3-D visualization of organic carbon at the micro-scale. At present, such visualizations are undertaken using staining agents, but their non-specific binding to other features in the soil aggravates evaluation of organic carbon at the micro-scale.

In the present study, we investigated the potential and limitations of using joint white-beam neutron and X-ray imaging for mapping the 3-dimensional organic carbon distribution in soil. This approach is viable because neutron and X-ray beams have complementary attenuation properties. Soil minerals consist to a large part of silicon and aluminium, elements which are relatively translucent to neutrons but attenuate X-rays. In contrast, attenuation of neutrons is strong for hydrogen, which is abundant in SOC, while hydrogen barely attenuates X-rays. When considering dried soil samples, the complementary attenuation for neutrons and X-rays may be used to quantify the fractions of air, SOC and minerals for any imaged voxel in a bi-modal 3-dimensional image, i.e. a combined neutron and X-ray image.

We collected neutron data at the IMAT beamline at the ISIS facility and X-ray data at the I12 beamline at the Diamond Light source, both located within the Rutherford Appleton Laboratory, Harwell, UK. The neutron image clearly showed variations in neutron attenuation within soil aggregates at approximately constant X-ray attenuations. This indicates a constant bulk density with varying organic matter and/or mineralogy. For samples with identical mineral composition, neutron attenuation data of sieved and repacked soil samples exhibited a large coefficient of determination (R2) in a regression between volumetric SOC content and neutron attenuation (0.9). Even larger R2 (0.93) were obtained when the volumetric clay content was also included into the regression. However, when comparing soil samples with different mineralogy, R2 dropped to 0.24 and 0.37, depending whether the clay content was considered or not. To improve the method, it is necessary to include specifics of the soil mineralogy. Here, analysing the time-of-flight neutron attenuation data collected at the IMAT beamline will provide further insights. In summary, our approach yielded promising results. We anticipate that quantitative 3-D imaging of organic carbon contents in soil will be possible in the near future.

How to cite: Burca, G., Hillier, S., Ariyathilaka, P., Fukumasu, J., Herrmann, A., Larsbo, M., Magdysyuk, O., and Koestel, J.: Potential of combined neutron and X-ray imaging to quantify local carbon contents in soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18948, https://doi.org/10.5194/egusphere-egu2020-18948, 2020.

EGU2020-12324 | Displays | SSS4.4

X-ray computed microtomography to predict CO2 emissions in casts of 6 earthworm species (Lumbricidae)

Guillaume Le Mer, Nicolas Bottinelli, Marie-France Dignac, Arnaud Mazurier, Laurent Caner, and Cornelia Rumpel

Plant residues are the main precursors of soil organic matter (SOM) and soil macrofauna is an important driver of ecological processes involved in the sequestration of carbon (C) in soils. In particular, earthworms are one of the largest contributors to soil matter formation in most terrestrial ecosystems. In the short term, they may increase the rate of OM turnover by mineralization, fragmentation and stimulation of microbial activity. On the other hand they may reduce OM degradability by forming stable aggregates and organo-mineral complexes protecting C from mineralization for longer time scales. Earthworms are classified in three main ecological groups depending on their behaviors and on their morpho-functional traits. However, their intra- or inter- ecological group effect on C stabilization needs to be investigated.

In this study, we explored the impact of earthworm diversity (composed of several species belonging to different ecological groups) on the physicochemical properties of casts, related to CO2 emissions. We hypothesized that C mineralization in casts would be related to the ecological category.

We studied casts of 6 species (2 anecic species: Lumbricus terrestris & Aporectodea nocturna, 2 endogeic species: Allolobophora icterica & Aporrectodea caliginosa and 2 epigeic species: Lumbricus castaneus & Eisenia fetida) produced in a silty subsoil with addition of plant litter. Casts were incubated for 140 days under similar laboratory conditions. We measured CO2 mineralization, pH, elemental composition and physical cast organization by X-ray microtomography (resolution of 9.49 µm voxel) at 7, 42, and 140 days.

Our results showed lower CO2 mineralization in aggregates produced without earthworms than all earthworm casts. In the beginning of the incubation casts showed similar CO2 emissions and specific physicochemical properties as OC content and pH. After 140 days, CO2 emissions were earthworm species specific with Aporectodea nocturna showing highest CO2 emissions, and Aporrectodea caliginosa the lowest values. Microtomographic analyses showed that this is due to an increase of cast porosity with increasing cast age coupled with a concurrent decrease particulate organic matter (POM) structures. Our first results seemed to suggest that earthworms belonging to the same ecological category influence similarly C mineralization through their impact on the cast organization.

How to cite: Le Mer, G., Bottinelli, N., Dignac, M.-F., Mazurier, A., Caner, L., and Rumpel, C.: X-ray computed microtomography to predict CO2 emissions in casts of 6 earthworm species (Lumbricidae), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12324, https://doi.org/10.5194/egusphere-egu2020-12324, 2020.

EGU2020-20330 | Displays | SSS4.4

Soil texture determines the microbial processing from litter to POM and MAOM in the detritussphere

Kristina Witzgall, Alix Vidal, David Schubert, Carmen Höschen, Steffen Schweizer, Franz Bruegger, Valerie Pouteau, Hirte Juliane, Claire Chenu, and Mueller Carsten W

Soil texture and microorganisms are key drivers controlling the fate of organic matter (OM) originating from decaying plant litter, and thus the stabilization of soil organic matter (SOM). However, the understanding of the mutual interactions between microbial litter decay and soil structure formation controlled by different soil textures remains incomplete. We monitored the fate of litter-derived OM (using 13C isotopic enrichment) from decaying litter (shredded maize leaves) to microorganisms and SOM in two differently textured soils (sand and loam). The two soils were incubated with litter mixed in the top layer in microcosms for 95 days during which regular CO2 and 13CO2 measurements were conducted. After the incubation, each microcosm was divided in three to separate a top, center and bottom layer. Using a physical soil fractionation scheme, we assessed the fate of litter-derived OM to free and occluded particulate OM (POM), as well as mineral associated OM (MAOM). All SOM fractions were analysed with respect to their mass distribution, C, N, and 13C contents, and for their chemical composition using compound-specific 13C-CPMAS NMR spectroscopy. The effects of contrasting textures on the total microbial community structure were studied using phospholipid fatty acids (PLFA) and the incorporation of litter-derived C into individual PLFAs was assessed via 13C-PLFA. Lastly, scanning electron microscopy and nano scale secondary ion mass spectroscopy (NanoSIMS) analysis of free POM of both textures enabled qualitative insights directly at the biogeochemical interface of the microbial hot spot of decaying plant litter.

We were able to clearly demonstrate higher contents of litter-derived OM still residing as free POM in the loamy textured soil after the 95 day-incubation, while higher contents were found in occluded and MAOM in the sandy textured soil. This indicated that the overall litter decomposition was refrained in the finer-textured soil, whereas microbial alteration and allocation of litter-derived compounds was promoted in the coarser textured soil. This was further corroborated by higher respiration and higher amounts of respired litter-derived CO2-C in the sandy soil. The PLFA analysis showed a coherent pattern between the textures, with similar community structures in all treatments and significant increases in microbial abundance in the top layers induced by litter addition. This increase was found most pronounced in fungal biomarkers, which was in line with the 13C-PLFA measurements revealing over 90% of fungal biomarkers to be of litter-origin (compared to 30-40% in the other microbial groups). The labelled PLFA profiles also confirmed the importance of fungi as a vector for litter-derived OM into deeper layers of the soil columns, with significantly higher litter-derived fungal markers also in center and bottom layers. The NanoSIMS measurements verified the high 13C enrichment in fungal hyphae and further revealed clay minerals embedded in enriched microbial-derived extracellular polymeric substances and intertwined with hyphae directly on top of the POM. Based on this comprehensive data, we highlight that regardless of the texture, plant litter in association with microbial-derived products represent a hot spot for soil structure formation by harbouring a core for aggregation and MAOM formation.

How to cite: Witzgall, K., Vidal, A., Schubert, D., Höschen, C., Schweizer, S., Bruegger, F., Pouteau, V., Juliane, H., Chenu, C., and Carsten W, M.: Soil texture determines the microbial processing from litter to POM and MAOM in the detritussphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20330, https://doi.org/10.5194/egusphere-egu2020-20330, 2020.

EGU2020-13565 | Displays | SSS4.4

The role of prokaryotes and their extracellular polymeric substances on soil aggregation in carbonate containing semiarid grasslands

Jeroen Zethof, Antje Bettermann, Cordula Vogel, Doreen Babin, Erik Cammeraat, Albert Solé-Benet, Roberto Lázaro, Lourdes Luna, Joseph Nesme, Susanne Woche, Søren Sørensen, Kornelia Smalla, and Karsten Kalbitz

Individual plant species form so-called resource islands in the barren semiarid landscape, whereby many soil properties are enhanced including soil structure. Within the soil structure, mostly studied as soil aggregates, microaggregates (<250µm) form fundamental components, reducing potential erosion of finer particles and subsequent loss of nutrients. Extracellular polymeric substances (EPS) are considered an important glue determining aggregation in addition to inorganic binding agents such as carbonates and clay minerals. However, the role of the soil prokaryotic community in EPS formation and consequently for microaggregation in natural environments has not been clarified yet. EPS should be particularly important under semiarid conditions as they form a protection mechanism of the prokaryotes against desiccation. Therefore, we examined the influence of the prokaryotic community on soil EPS content and subsequently on soil aggregation in semiarid grasslands, with respect to the parent material of soil formation, common plant species and the distance to the plant.

During two sampling campaigns in spring 2017 and 2018, soil samples were taken over a distance gradient from two major semiarid grassland plant species in Southern Spain, the legume shrub Anthyllis cytisoides and the grass tussock Macrochloa tenacissima, to the surrounding bare soil. While topsoil was sampled in five distances to the plant during the first sampling campaign, the second one focused stronger on the root influence, hence rhizoplane and rhizosphere were sampled. Additionally, two sites with different parent materials were chosen to scale the effect of EPS on soil aggregation in the presence of inorganic binding agents (here carbonates). Total community DNA and EPS were extracted, followed by quantification of EPS-saccharides and bacterial abundance, as well as examination of the prokaryotic community composition by Illumina amplicon sequencing of the 16S rRNA genes. Further, the particle size distribution of (micro)aggregates in water was determined, with and without ultrasound treatment, as a measure of soil aggregate size distribution and stability.

Based on the first sampling campaign, we found that the overall prokaryotic community composition differed between the two sites, but not between plant species. Interdependencies between the community composition and EPS content were revealed, whereby soil organic matter (SOM) seems to be a regulating factor as increasing SOM contents resulted in more EPS-saccharides. Soil microaggregation in the topsoil was enhanced by the plant canopy, especially at the edge of Macrochloa tussocks. Contrary to the expectation that increasing inorganic C contents would diminish the importance of EPS, the parent material richest in inorganic C results in a significant effect of EPS-saccharides on microaggregation.

First results of the second sampling campaign indicate that even in the rhizoplane and rhizosphere, parent material had a dominating influence on the prokaryotic community composition. As EPS-saccharide contents and soil aggregation followed a similar decreasing trend with distance to the roots and canopy cover, interdependencies are expected.

From the outcomes until now, we can conclude that the availability of decomposable OM influences the prokaryotic community composition and thereby triggers EPS production, whereas large contents of polyvalent cations from carbonates promote the stabilizing effect of EPS on microaggregates.

How to cite: Zethof, J., Bettermann, A., Vogel, C., Babin, D., Cammeraat, E., Solé-Benet, A., Lázaro, R., Luna, L., Nesme, J., Woche, S., Sørensen, S., Smalla, K., and Kalbitz, K.: The role of prokaryotes and their extracellular polymeric substances on soil aggregation in carbonate containing semiarid grasslands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13565, https://doi.org/10.5194/egusphere-egu2020-13565, 2020.

EGU2020-10286 | Displays | SSS4.4

Effects of carbon to nitrogen ratios on amounts and composition of Bacillus subtilis biofilms

Natalia Cortes Osorio, Robert Endrika, Karsten Kalbitz, and Cordula Vogel

In natural environments, bacteria can be found as multicellular communities exhibiting a high degree of structure, denominated biofilms. Biofilms are composed of microbial cells, often of multiple species, embedded within a matrix of extracellular polymeric substances (EPS). The exact composition, physical and chemical properties, and amounts of these components varies depending on their growth conditions. However, it remains unclear how nutrient availability drives the allocation into cell growth or EPS production, especially under conditions found in soils. Here we aimed to evaluate the effect of various C/N ratios on Bacillus subtilis biofilm growth (spatial expansion and structure) and their EPS composition. We hypothesized that the largest biofilm development and highest EPS production by Bacillus subtilis would be caused by a nutrient imbalance reflected in C/N ratios, especially high C availability. Biofilms were grown on membranes on MSgg agar plates with C/N ratios of 1:1, 10:1, 25:1 and 100:1. Several methods from macroscopic observations over EPS extraction and determination up to various microscopic visualisation techniques were used. The radial expansion of the biofilm was measured, followed by EPS extraction to quantify EPS-proteins and EPS-polysaccharides. Hydrated biofilm samples were studied regarding their biofilm structures by scanning electron microscopy (SEM) within the environmental mode at approximately 97% humidity. Fixed, dehydrated and embedded samples were used to evaluate the biofilm height and internal structure with SEM in high vacuum mode. Low C/N ratio (1:1) resulted in the smallest biofilms in terms of radial expansion and biofilm height, with densely packed layers of cells and low amounts of EPS. Our first results revealed that the highest biofilm productions were observed at C/N ratio of 10:1 and 25:1. The microscopic approaches indicated that biofilms growing at C/N ratios of 100:1 produced the highest amount of EPS. Furthermore, changes in the microscopical features of the biofilms were detected with different structures along the biofilm regions affected by the nutrient conditions. These results suggest that the C/N ratio has a large impact on the biofilm development and structure, with different allocations into microbial cells and EPS. Overall, the results obtained until now allowed us to accept the initial hypothesis, indicating that higher C/N ratios induce a higher EPS production. This suggests that environments containing a high ratio between carbon and the limiting nutrient, often nitrogen, may favour polysaccharide production, probably because energy from the carbon excess is used for polysaccharide biosynthesis.

How to cite: Cortes Osorio, N., Endrika, R., Kalbitz, K., and Vogel, C.: Effects of carbon to nitrogen ratios on amounts and composition of Bacillus subtilis biofilms, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10286, https://doi.org/10.5194/egusphere-egu2020-10286, 2020.

EGU2020-11651 | Displays | SSS4.4

Rhizobacteria Mediated Changes in Soil Physical and Hydrological Properties

Yan Jin, Saiqi Zeng, Fatema Kaniz, Wenjuan Zheng, Jacob LaManna, and Harsh Bais

Large communities of microbes are associated with plant roots in the rhizosphere, which is a critical interface supporting the exchange of water and nutrients between plants and their associated soil environment. The diverse communities of rhizobacteria mediate plant-soil feedback through a multitude of interactions including those that contribute to plant abiotic stresses. For example, enhancement of plant drought stress tolerance by plant growth promoting rhizobacteria (PGPR) has been increasingly documented in the literature, however, investigations to date have been largely focused on PGPR-root/plant interactions and related plant responses to PGPR activities that induce drought tolerance. Comparatively, much less is known about PGPR’s role in mediating physiochemical and hydrological changes in the rhizospheric soil that may also impact plant drought stress tolerance. Using UD1022, aka Bacillus subtilis FB17, as a model bacterium, we demonstrated via soil water characteristic measurements that UD1022-treated soil samples retained more water, had lower hydraulic conductivity than its controls. In addition, we investigated the effects of UD1022 on soil water evaporation via combined neutron radiography, neutron tomography, and X-ray tomography imaging techniques. Neutron radiography images confirmed greater water retention in UD1022-treated soil samples than their controls due to reduced water evaporation. Combined neutron and X-ray tomography 3D images revealed that water distribution in UD1022-treated soil samples was heterogeneous, i.e., there were more disconnected water pockets compared with the controls where water was distributed more uniformly. Our study provides pore-scale mechanistic explanation for increased water retention and reduced evaporation rate from UD1022-treated soil samples, which is mainly attributed to the production of extracellular polymeric substances (EPS) by UD1022 due to EPS’ hygroscopic and chemical properties (viscosity and surface tension). However, our latest experiments showed similar effects by a UD1022 mutant with eps-producing genes removed, suggesting that the beneficial impacts of rhizobacteria may not be limited to their ability to EPS production alone. These findings have practical implications in, for example, “rhizosphere engineering” to improve/restore soil structure, support sustainable agricultural production, and mitigate climate change.

How to cite: Jin, Y., Zeng, S., Kaniz, F., Zheng, W., LaManna, J., and Bais, H.: Rhizobacteria Mediated Changes in Soil Physical and Hydrological Properties, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11651, https://doi.org/10.5194/egusphere-egu2020-11651, 2020.

EGU2020-15917 | Displays | SSS4.4

Inoculation of bacteria for the amelioration of sandy soil under drought

Violeta Carmen Angulo Fernández, Mariet Hefting, and George Kowalchuk

Soil degradation represents a pressing worldwide problem that is being accelerated by processes of erosion, depletion of soil organic matter, soil compaction, acidification, salinization, and drought. Soil microorganisms can influence soil aggregation via a range of mechanisms such as the production of exopolysaccharides and other extracellular matrix polymers such those involved in biofilm formation. In this study, we south to use bacteria harboring specific traits to enhance soil aggregation. To this end, 120 bacterial strains were isolated from an experiment field under drought conditions and tested for their ability to grow under drought, salinity tolerance, rapid growth, biofilm, and exopolysacharides production. Based upon this trait assessment, 24 strains were further tested at two moisture levels for their ability to impact soil structure after 8 weeks of incubation at 25ºC. The mean weight diameter (MWD) of water-stable aggregates and carbohydrates were determined for treated soils. Three strains were shown to impact soil aggregate properties at the higher moisture content: one affiliated with Bacillus niacini, one affiliated with Paenarthrobacter nitroguajacolicus and one of unclear classification. The first of these strains also affected soil structure at the lower moisture level. This B. niacini strain also increased the carbohydrate content of the soil, as did two other strains, related to B. wiedmannii and B. aryabhattai, respectively. However, no positive correlation was observed between the MWD and the production of carbohydrates in soil. Our results suggest that soil inoculation with specific microbial strains can improve soil structure.

How to cite: Angulo Fernández, V. C., Hefting, M., and Kowalchuk, G.: Inoculation of bacteria for the amelioration of sandy soil under drought, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15917, https://doi.org/10.5194/egusphere-egu2020-15917, 2020.

EGU2020-4126 | Displays | SSS4.4

Interplay between water adsorption and viscosity determines the spatial configuration of EPS during soil drying

Andrea Carminati, Pascal Benard, Judith Schepers, Margherita Crosta, and Mohsen Zarebanadkouki

Bacteria alter the physical properties of soil hotspots by secreting extracellular polymeric substances EPS. Despite the biogeochemical importance of these alterations is well accepted, the physical mechanisms by which EPS shapes the properties of the soil solution and its interactions with the soil matrix are not well understood.

Here we show that upon drying in porous media EPS forms one-dimensional filaments and two-dimensional interconnected structures spanning across multiple pores. Unlike water, primarily shaped by surface tension, EPS remains connected upon drying thanks to its high extensional viscosity. The integrity of one-dimensional structures is explained by the interplay of viscosity and surface tension forces (characterized by the Ohnesorge number), while the formation of two-dimensional structures requires consideration of the interaction of EPS with the solid surfaces and external drivers, such as the drying rate. During drying, the viscosity of EPS increases and, at a critical point, when the friction between polymers and solid surfaces overcomes the water adsorption of the polymers, the concentration of the polymer solution at the liquid-gas interface increases asymptotically and the polymers can no longer follow the retreating gas-water interface. At this critical point the polymers do not move any longer and are deposited as two-dimensional surfaces, such as hollow cylinders or interconnected surfaces. EPS viscosity, specific soil surface and drying rates are the key parameters determining the transition from one- to two-dimensional structures.

The high viscosity of EPS maintains the connectivity of the liquid phase during drying in soil hotspots, such as bacterial colonies, the rhizosphere and biological soil crusts.

How to cite: Carminati, A., Benard, P., Schepers, J., Crosta, M., and Zarebanadkouki, M.: Interplay between water adsorption and viscosity determines the spatial configuration of EPS during soil drying, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4126, https://doi.org/10.5194/egusphere-egu2020-4126, 2020.

Structural stability in agricultural soils is said to be maintained through production of ‘biological binding agents’, including temporary binding agents (fungi, roots), transient binding agents (EPS), and persistent binding agents (of less certain origin). We sampled soils from a long-term field trial, comprising previous grassland, arable and fallow land-uses in factorial combination with current land-uses of the same type: previous 3 land-uses  x current 3 land-uses = 9 treatments (Redmile-Gordon et al., 2020). Total soil organic carbon (SOC), EPS (including protein, and polysaccharide fractions; Redmile-Gordon et al., 2014), and mean weight diameter (MWD) of water stable aggregates (Le Bissonnais, 1996) were quantified.

Both EPS and MWD were correlated, and were both strongly influenced by current land-use (implemented 2.5 years before sampling), but not by previous land-use (implemented > 50 years ago, terminated 2.5 years before sampling). While exopolysaccharides were significantly correlated to the soil’s structural stability (p = 0.027), proteinaceous EPS were more closely related to the associated gains in soil aggregate stability (p = 0.002).

In contrast to EPS and soil stability, total soil organic carbon (SOC) was strongly influenced by previous land-use. Importantly, this indicates that any capacity for relatively stable organic matter to contribute to the soil’s structural stability is overwhelmed by temporary/transient effects owed to current land-use. This is cause for optimism, as it seems the physical quality of soils might be improved by short-term application of managements that favour EPS production. This approach would represent a qualitative step beyond that of building total SOC, which can be difficult for land-managers to achieve. This study is the first to simultaneously assess the effects of land-use on proteinaceous and polysaccharide content of EPS, and link this to the structural stability of soils. Further understanding surrounding the ecology of EPS production, and disentangling the contributions of temporary (largely physical) vs. transient (biochemical) binding agents is hoped to contribute to the development of more efficient land-management strategies.

 

References:

Le Bissonnais, Y., 1996. Aggregate stability and assessment of soil crustability and erodibility.
1. Theory and methodology. Eur. J. Soil Sci. 47, 425–437.

Redmile-Gordon, M., Brookes, P.C., Evershed, R.P., Goulding, K.W.T., Hirsch, P.R., 2014. Measuring the soil-microbial interface: extraction of extracellular polymeric substances (EPS) from soil biofilms. Soil Biol. Biochem. 72, 163–171.

Redmile-Gordon, M., Gregory, A.S., White, R.P., Watts, C.W. 2020. Soil organic carbon, extracellular polymeric substances (EPS), and soil structural stability as affected by previous and current land-use. Geoderma, 363. https://doi.org/10.1016/j.geoderma.2019.114143

How to cite: Redmile-Gordon, M.: Soil Structural Stability and Extracellular Polymeric Substances (EPS): transient binding agents affected by land-use., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5742, https://doi.org/10.5194/egusphere-egu2020-5742, 2020.

SSS4.8 – Life in soil hotspots: Microbial activity, carbon and nutrient cycling and functions

EGU2020-4089 | Displays | SSS4.8

High viscosity of polymer solutions supports life in soil hotspots

Andrea Carminati, Pascal Benard, Mohsen Zarebanadkouki, and Mutez A Ahmed

Plant roots and bacteria alter the soil properties by releasing a polymeric blend of substances (e.g. mucilage and extracellular polymeric substances EPS). Despite extensive knowledge of their ecological importance, the physical mechanisms by which these polymers alter the spatial configuration of the liquid phase and the related hydraulic and biogeochemical properties remain unclear.

Here we show that upon drying in porous media polymer solutions form one-dimensional filaments and two-dimensional interconnected structures spanning across multiple pores. Unlike water, primarily shaped by surface tension, these structures remain connected upon drying thanks to their high viscosity. The integrity of one-dimensional structures is explained by the high viscosity and low surface tension of the polymer solutions (elegantly characterized by the Ohnesorge number). The formation of two-dimensional structures requires consideration of the interaction of the polymer solution with the solid surfaces and external drivers, such as the drying rate.

The implications of these physical processes for life in soils are manifold. After their deposition they enhance water retention by acting as a new solid matrix delaying the air entry, they maintain the connectivity of the liquid phase, thus enhancing the unsaturated hydraulic conductivity, diffusion and enzyme activity. Upon rewetting, the formation of extensive two-dimensional structures corresponds to a sudden increase in soil water repellency, which reduces the rewetting kinetics and maintains gas diffusion preventing sudden water saturation. In summary, these structures buffer fluctuations in soil water contents, protecting roots and soil microorganisms against severe drying and sudden rewetting in soil hotspots.

How to cite: Carminati, A., Benard, P., Zarebanadkouki, M., and Ahmed, M. A.: High viscosity of polymer solutions supports life in soil hotspots, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4089, https://doi.org/10.5194/egusphere-egu2020-4089, 2020.

EGU2020-19045 | Displays | SSS4.8

Zooming in: a single-cell perspective on nitrogen fixation in the rhizosphere of rice

Hannes Schmidt, Stefan Gorka, David Seki, Arno Schintlmeister, and Dagmar Woebken

Our current understanding of microbial hotspots such as the rhizosphere mainly stems from observations through measurements at the macroscopic scale, integrating a multitude of microbial cells and taxa into a few measured variables. Consequently, we still lack an understanding of the individual participants that actively contribute to processes. Identifying microorganisms and relating their activity to these processes within the soil-plant interface on a microscopic scale represent a missing link in understanding nutrient flux in agriculturally important ecosystems such as rice cultivation.

I will present a novel workflow for single-cell isotope imaging in the rhizosphere that combines fluorescence in situ hybridization, gold-targeted secondary electron microscopy, and nano-scale secondary ion mass spectrometry. Based on correlative microscopy and hotspot detection, this approach now allows to (i) identify single bacteria on root surfaces that actively incorporate stable isotopes, (ii) quantify their contribution to processes of interest within a given population, and (iii) potentially trace nutrient fluxes among plants and bacteria on a microscale.

Illuminating plant-microorganism interactions on a microscale provides the potential to evaluate the actual impact of bio-inoculants applied as fertilizers and to engineer plant-microorganism associations which may be essential to increase the production of major staple crops for a growing world population.

How to cite: Schmidt, H., Gorka, S., Seki, D., Schintlmeister, A., and Woebken, D.: Zooming in: a single-cell perspective on nitrogen fixation in the rhizosphere of rice, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19045, https://doi.org/10.5194/egusphere-egu2020-19045, 2020.

EGU2020-20074 | Displays | SSS4.8

Imaging biogeochemical gradients in the rhizosphere

Nicole Rudolph-Mohr, Sarah Bereswill, Christian Tötzke, Nikolay Kardjilov, and Sascha E. Oswald

Dynamic processes occurring at the soil-root interface crucially influence soil physical, chemical, and biological properties at local scale around the roots that are technically challenging to capture in situ. Combining 2D optodes and 3D neutron laminography, we developed a new imaging approach capable of simultaneously quantifying H2O-, O2-, and pH-distribution around living plant roots while additionally capturing the root system architecture in 3D. The interrelated patterns of root growth and distribution in soil, root respiration, root exudation, and root water uptake can be studied non-destructively at high temporal and spatial resolution.

Neutron computed laminography (NCL), a tomographic approach specially adapted to samples with large lateral extension (here 15 x 15 x 1.5 cm) was applied to visualize the root architecture and soil water content three-dimensionally. Optodes, sensitive to pH and O2 changes, were attached at the inner-sides of thin boron-less glass-containers where one maize plant was grown in each container. Knowledge about the distance of the roots from the container walls and thus from the optodes, support the interpretation of the optical images.

Neutron laminography made it possible to visualize and quantify the 3D root system architecture in association with the observed H2O, pH and oxygen patterns. The older part of the root system with higher root length density was associated with fast decrease of water content and rapid change in oxygen concentration. Lateral roots acidified their rhizosphere by a quarter of a pH unit and crown root even induced acidification of up to one pH unit compared to bulk soil. The benefit of neutron laminography is that we can extract the root structure in 3D, identify root age and root types and relate this to spatiotemporal changes in water content distribution, oxygen concentration and pH values.

How to cite: Rudolph-Mohr, N., Bereswill, S., Tötzke, C., Kardjilov, N., and Oswald, S. E.: Imaging biogeochemical gradients in the rhizosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20074, https://doi.org/10.5194/egusphere-egu2020-20074, 2020.

EGU2020-8648 | Displays | SSS4.8

Image-based model quantification of pore-scale nitrogen diffusion and potential microbial ‘dead zones’ induced by fertilization application

Siul Ruiz, Daniel McKay Fletcher, Andrea Boghi, Katherine Williams, Simon Duncan, Callum Scotson, Chiara Petroselli, Tiago Dias, Dave Chadwick, David Jones, and Tiina Roose

Soil microbial communities contribute many ecosystem services including soil structure maintenance, crop synergy, and carbon sequestration. However, it is not fully understood how the health of microbial communities is effected by fertilization at the pore scale. This study investigates the nature of nitrogen (N) transport and reactions at the soil pore scale in order to better understand the influence of soil structure and moisture content on microbial community health. Using X-ray Computed Tomography (XRCT) scans, we reconstructed a microscale description of a dry soil-pore geometry as a computational mesh. Solving two-phase water/air models produced pore-scale water distributions at 15, 30 and 70% water-filled pore volume. The model considers ammonium (NH4+), nitrate (NO3-) and dissolved organic N (DON), and includes N immobilization, ammonification and nitrification processes, as well as diffusion in soil-solution. We simulated the dissolution of a fertilizer pellet and a pore scale N cycle at the three different water saturation conditions. To aid interpretation of the model results, microbial activity at a range of N concentrations was quantified experimentally using labelled C to infer microbial activity based on CO2 respiration measurements in bulk soil. The pore-scale model showed that the diffusion and concentration of N in water films is critically dependent upon soil moisture and N species. We predicted that the maximum NH4+ and NO3- concentrations in soil solution around the pellet under low water saturation conditions (15%) are in the order of 1x103 and 1x104 mol m-3 respectively (1-10 M), and under higher water saturation conditions (70%) where on the order of 2x102 and 1x103 mol m-3, respectively (0.1-1 M). Supporting experimental evidence regarding microbial respiration suggests that these concentrations at the pore-scale would be sufficient to reduce microbial activity in the zone immediately around the fertilizer pellet (ranging from 0.9 to 3.8 mm depending on soil moisture status), causing a major loss of soil biological activity by up to 90%. This model demonstrates the importance of pore-scale processes in regulating N movement in soil with special capability to predict the effects of fertilizers on rhizosphere-scale processes and the root microbiome.

How to cite: Ruiz, S., McKay Fletcher, D., Boghi, A., Williams, K., Duncan, S., Scotson, C., Petroselli, C., Dias, T., Chadwick, D., Jones, D., and Roose, T.: Image-based model quantification of pore-scale nitrogen diffusion and potential microbial ‘dead zones’ induced by fertilization application , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8648, https://doi.org/10.5194/egusphere-egu2020-8648, 2020.

EGU2020-5352 | Displays | SSS4.8

Limiting factors for soil microbial growth in climate change simulation treatments in the Subarctic

Mingyue Yuan, Meng Na, Lettice Hicks, and Johannes Rousk

Soil microorganisms play a crucial role in the regulation of nutrient cycling, and are thought to be either limited by low nutrient availability, or by labile carbon supplied by nutrient limited plant productivity. It remains unknown how climate change will affect the rate-limiting resources for decomposer microorganisms in the Arctic, rendering feedbacks to climate change highly uncertain. In this study, we focused on the responses of soil microbial community processes to simulated climate change in a subarctic tundra system in Abisko, Sweden, using litter additions to represent arctic greening and inorganic N fertilizer additions to represent a faster nutrient cycling due to arctic warming. We hypothesized that 1) the plant community would shift and plant productivity would increase in response to N fertilization, 2) microbial process rates would be stimulated by both plant litter and fertilizer additions, and 3) the growth limiting factors for decomposer microorganisms would shift toward nutrient limitation in response to higher plant material input, and towards C-limitation in response to N-fertilizer additions.

 

We assessed the responses of the plant community composition (vegetation surveys) and productivity (NDVI), microbial processes (bacterial growth, fungal growth, C and N mineralization) along with an assessment of the limiting factors for fungal and bacterial growth. The growth-limiting factors were determined by full factorial additions of nutrients (C, N, P), with measurement of microbial growth and respiration following brief incubations in the laboratory. We found that plant productivity was ca. 15% higher in the N fertilized plots. However, field-treatments had limited effects on bacterial growth, fungal growth and the fungal-to-bacterial growth ratio in soils. Field-treatments also had no significant effect on the rate of soil C mineralization, but did affect rates of gross N mineralization. Gross N mineralization was twice as high in N fertilized plots compared to the control. In control soils, bacterial growth increased 4-fold in response to C, indicating that bacterial growth was C limited. Bacterial growth remained C limited in soils from all field-treatments. However, in the N fertilized soils, the C limitation was 1.8-times greater than the control, while in soils with litter input, the C limitation was 0.83-times the control, suggesting that the N fertilized soils were moving towards stronger C-limitation and the litter addition soils were becoming less C-limited. The limiting factor for fungal growth was difficult to resolve. We presumed that the competition of fungi with bacteria decreased our resolution to detect the limiting factor. Therefore, factorial nutrient addition were combined with low amount of bacterial specific inhibitors.

How to cite: Yuan, M., Na, M., Hicks, L., and Rousk, J.: Limiting factors for soil microbial growth in climate change simulation treatments in the Subarctic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5352, https://doi.org/10.5194/egusphere-egu2020-5352, 2020.

EGU2020-21605 | Displays | SSS4.8

Revealing how nitrogen fertilisation regulates the fluxes of COS and CO2 between soil communities and the atmosphere using a functional metagenomic and metatranscriptomic approach

Evert van Schaik, Samuel Mondy, Melanie Lelievre, Marine Martin, Solene Perrin, Laura Meredith, Aurore Kaisermann, Samuel Jones, Olivier Rue, Valentin Loux, and Lisa Wingate

Recent interest in the seasonal and spatial variability of atmospheric COS has intensified as its use as an atmospheric tracer of biosphere productivity in the carbon cycle has recently been demonstrated. The key link between the COS and CO2 cycles in the biosphere is a family of enzymes called the carbonic anhydrases (CA) that catalyse both the hydration of CO2 and the hydrolysis of COS in both plants and soil microbes. Recently studies have demonstrated that the variability in soil COS and CO2 fluxes are modified significantly by fertilisation with inorganic N, indicating a strong coupling between soil carbon (C), nitrogen (N) and sulphur (S) cycling (Kaisermann et al., 2018). However, it is currently not clear whether the observed changes in COS and CO2 gas exchange were principally driven by important shifts in the microbial community size, structure or function or some combination of the three.

To elucidate the underlying mechanism(s) we used a functional metagenomic and metatranscriptomic approach coupled with climate controlled gas exchange measurements on soils. A set of 6 soils collected from boreal and temperate sites were sieved and re-packed in microcosms and incubated in the lab for 2 weeks at 23oC and 30% water holding capacity in the dark. For each site half the microcosms were fertilised with 5 mg N in the form of NH4NO3 at the start of the incubation period. At the end of the incubation period soil COS, CO2 fluxes were measured, and soil samples transported at -80oC to the Genosol platform for DNA and RNA extraction.  For each soil microcosm we quantified the abundance of bacterial, fungal and algal genes in each community using 16S, 18S and 23S amplicon sequencing. After assembling and cross-mapping the metagenomes and metatranscriptomes we used a HMM model (Meredith et al. 2018) to estimate and comparatively assess the abundance of CA genes between the different sites and treatments.

Our results indicate that the N treatment caused a relative increase in the abundance of fungi in N treated soils compared to those in the control. Generally, we also found that the total number of CAs in soils shifted when treated with N compared to the controls and that the β-D CA sub-family were the most prevalent CAs in all of the soils. In our presentation we will demonstrate how both the community structure and the abundance of CAs were modified upon N fertilisation and provide vital clues on the most likely mechanism(s) controlling COS and CO2 fluxes in soil communities and the significance of these results for interpreting atmospheric signals.

Kaisermann, Aurore, Sam P. Jones, Steven Wohl, Jérôme Ogée, and Lisa Wingate. 2018 Nitrogen Fertilization Reduces the Capacity of Soils to take up Atmospheric Carbonyl Sulphide. Soil Systems 2 (4), 62 doi.org/10.3390/soilsystems2040062

Meredith, Laura K, Jérôme Ogée, Kristin Boye, Esther Singer, Lisa Wingate, Christian von Sperber, Aditi Sengupta, et al. 2018. “Soil Exchange Rates of COS and CO18O Differ with the Diversity of Microbial Communities and Their Carbonic Anhydrase Enzymes.” ISME Journal, 2018. https://doi.org/10.1038/s41396-018-0270-2.

How to cite: van Schaik, E., Mondy, S., Lelievre, M., Martin, M., Perrin, S., Meredith, L., Kaisermann, A., Jones, S., Rue, O., Loux, V., and Wingate, L.: Revealing how nitrogen fertilisation regulates the fluxes of COS and CO2 between soil communities and the atmosphere using a functional metagenomic and metatranscriptomic approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21605, https://doi.org/10.5194/egusphere-egu2020-21605, 2020.

The projected global warming risks due to high emissions of greenhouse gases, mainly from anthropogenic activities, increases the need for an agricultural practice with high carbon sink capacity and low water requirements without compromising on environment and productivity. On one hand, it’s well accepted that soil moisture directly affects microbial activity, whereas on the other hand, drought stress was recently postulated to increase root exudates, which in turn will accelerate soil organic matter mineralization “priming effects”. Thus, the objective of this study was to investigate the interplay between soil moisture (well-watered and drought stressed) and maize (Zea mays L.) root exudates on soil CO2 efflux. The experiment consisted of three treatments, which are well-watered, drought stressed maize plus a control (without plants) lysimeters (1 m3), Soil CO2 efflux, soil temperature and moisture content were measured weekly during the growing season (April to September) and monthly in the fallow period. Under well-watered conditions, the annual average of CO2 efflux was 0.12 g CO2-C m-2 hr-1, which was 24.5 and 20% significantly higher than under drought stressed and the control, respectively. Moreover, well-watered treatment had significantly greater primed carbon than drought stressed maize. Soil temperature in deeper soil layers (25, 50 and 75 cm) correlated positively (with the CO2 efflux, while soil moisture correlated negatively at the 5 cm and 25 cm. Overall, these results suggested that the root exudates decreased under drought conditions, which decreasing soil respiration. Drought tolerance varieties could be an option to decrease soil respiration and maintain productivity.

How to cite: Abdalla, K., Ahmed, M., and Pausch, J.: Does rhizosphere priming effect explain the greater soil respiration in well-watered and drought stressed maize? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18874, https://doi.org/10.5194/egusphere-egu2020-18874, 2020.

EGU2020-17859 | Displays | SSS4.8

Management of hotspots for sustainable crop production: hotter, deeper, or simply more?

Michaela Dippold, Sara Halicki, Mutez Ahmed, Hongcui Dai, Jie Zhou, Natalyia Bilyera, Xuechen Zhang, Sandra Spielvogel, Duyen Hoang, and Callum Banfield

Hotspots in agricultural soils, which include rhizosphere, detritusphere and drilosphere, are characterized by strongly different dynamics than those of natural ecosystems. This involves hotspot properties such as element cycling intensity, microbial activation, lifetime or spatial extension. Evidence from studies around the globe suggests that key hotspot characteristics intensify or increase under strongly limiting cropping conditions e.g. low-input agriculture: i) nutrient mining is more intensive around roots in infertile soils, ii) root exudates decompose more slowly under water limitation, and iii) the rhizo-hyphosphere forms a more spatially extended hyphal network under P deficiency. These examples suggest that smart management of hotspots might be a sustainable strategy to overcome soil limitations, not only for crop production on marginal soils but also as a strategy to save resources for future agriculture.

Here, we will present a set of studies applying management strategies, which actively modify hotspot intensity, lifetime or spatial extension with the aim to manipulate biogeochemical cycles of the respective agroecosystem. Most traditional, tillage enlarges the topsoil detritusphere or moves it to lower soil depths. Rather novel but increasingly studied approaches seek to modify rhizosphere properties: applying genotypes with i) specific root traits such as an optimized root morphology (e.g. modified root hairs or deeper fine root system) or ii) modified root exudate compositions and resulting rhizosphere microbiomes. Such approaches need to be applied site- and agroecosystem-specifically to optimize resource utilization. Moreover, as agroecosystems are under long-term controls, hotspot management strategies are not limited to one growing season but can stretch over years of cultivation. The generation of specific biopores – the root channels - created by e.g. tap-rooted or deep-rooting cover crops is a management practise inducing a rhizosphere-detritusphere-rhizosphere transition over time. ‘Re-activated’ hotspots feature unique biogeochemical conditions for young roots as well as microbial communities. Such ‘highways to subsoil’ foster rhizosphere establishment in subsoils, where i) hotspots remain moist and thus active under drought and ii) where gradients from hotspots to bulk soils are for magnitudes higher compared to topsoils. All these aspects present a unique, however largely unexploited potential for future agriculture, yet.

By a novel set of methodological approaches and their combinations, comprising multi-isotope applications, in-situ imaging techniques, biomarkers and microbial activity measures with high spatial resolution, we will provide new insights into the potential of hotspot management in agroecosystems. We will discuss implications for crop production under resource limitation up to the potential for a sustainable development of future agricultural production systems especially in the face of projected climate change.

How to cite: Dippold, M., Halicki, S., Ahmed, M., Dai, H., Zhou, J., Bilyera, N., Zhang, X., Spielvogel, S., Hoang, D., and Banfield, C.: Management of hotspots for sustainable crop production: hotter, deeper, or simply more?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17859, https://doi.org/10.5194/egusphere-egu2020-17859, 2020.

EGU2020-93 | Displays | SSS4.8 | Highlight

Global maps of current and future nitrogen mineralization

Julia Maschler, Daniel S. Maynard, Devin Routh, Johan van den Hoogen, Zhaolei Li, Shuli Niu, and Thomas W. Crowther

Soil nitrogen is a prominent determinant of plant growth, with nitrogen (N) availability being a key driver of terrestrial carbon sequestration. The local availability of soil N is thus crucial to our understanding of broad-scale trends in soil fertility, productivity, and carbon dynamics. Here, we provide global, high-resolution maps of current and future (2050) potential net nitrogen mineralization (N-min), revealing global patterns in soil N availability. Highest mineralization rates are found in warm and moist tropical regions, leading to a strong latitudinal gradient in N-min. We observed a positive correlation of N-min rates with human population density and net primary productivity. Projected climate conditions for 2050 suggest that N availability will further decrease in areas of low N availability and increase in areas of high N availability, thereby intensifying current global trends. These results shed light on the core processes governing productivity at a global scale, providing an opportunity to improve the accuracy of plant biomass and climate models.

How to cite: Maschler, J., Maynard, D. S., Routh, D., van den Hoogen, J., Li, Z., Niu, S., and Crowther, T. W.: Global maps of current and future nitrogen mineralization, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-93, https://doi.org/10.5194/egusphere-egu2020-93, 2020.

The biogeochemical interfaces are hotspots for organic matter (OM) transformation. However, direct and continuouxiacis tracing of OM transformations and N and P degradation processes are lacking due to the heterogeneous and opaque nature of soil microenvironment. To investigate these processes, a new soil microarray technology (SoilChips) was developed and used. Homogeneous 2-mm-diameter SoilChips were constructed by depositing a dispersed paddy soils with high and low soil organic carbon (SOC) content. A horizon suspension on a patterned glass. Dissolved organic matter from the original soil was added on the SoilChips to mimic biogeochemical processes on interfaces. The chemical composition of biogeochemical interfaces were evaluated via X-ray photoelectron spectroscopy (XPS) and the two-dimensional distribution of enzyme activities in SoilChips were evaluated by zymography. Over 30 days, soil with high SOC content increases microbial nutrition (N and P) requirements than soil with low SOC evidenced by higher hotspots of β-1,4-N-acetaminophen glucosidase, and acid phosphomonoesterases and higher 16S rRNA gene copies. The degree of humification in dissolved organic matter (DOM) was higher and the bioavailability of DOM was poorer in soil with high SOC than soil with low SOC. The poorest bioavailability of DOM was detected at the end of incubation in soil with high SOC. Molecular modeling of OM composition showed that low SOC mainly facilitated the microbial production of glucans but high SOC mainly facilitated the microbial production of proteins. We demonstrated that SOC content or DOM availability for microorganisms modifies the specific OM molecular processing and N and P degradation processes, thereby providing a direct insight into biogeochemical transformation of OM at micro-scale.

How to cite: Wei, L.: Organic matter content controls the N and P degradation process on biogeochemical interfaces: A micro-ecosystem scale study based on SoilChips-XPS-Zymography integrated technique in paddy soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2963, https://doi.org/10.5194/egusphere-egu2020-2963, 2020.

Earthworm catalyzes soil organic matter (SOM) decomposition through their burrowing activity, gut processing of carbon (C) inputs and microorganism stimulation. Specific enzyme is characterized for the decomposition, which is denoted in enzyme activity, substrate turnover and turnover rate of the decomposition. To demonstrate the interaction between earthworms and microbial activities, 14C-labelled plant litter was placed on a soil surface of a mesocosm (10 x 2 x 50 cm) prior to placing earthworms into soil, control soil was set up in mesocosms without earthworms. After 1 month of earthworm presence, soil materials coated on the biopore walls were excavated for another soil incubation to define C turnover by trapping respired CO2 in NaOH 1M. While another subsample was used to define activity of cellobiohydrolase (a cellulolytic enzyme) and its turnover rate. The hypotheses were that i) C turnover by incubation is associated with enzymatic turnover rate but ii) these two turnover rates are depth dependent.

Consequently, activity of cellobiohydrolase was higher in earthworm biopores than control soil regardless of soil depth. The difference in enzyme kinetics between biopores and control soil showed a shift of enzyme system toward higher substrate affinity in the topsoil but lower in the subsoil. This finding can be explained by the distinction in microbial community between topsoil and subsoil in both earthworm biopore and control soil. Substrate turnover time calculated based on saturated substrate concentration and maximum reaction rate velocity. The turnover
rate of substrate decomposition was faster in biopores than bulk soil. The substrate turnover time is depth dependent. We concluded that earthworm biopores are microbial hotspots with demonstrated interactions between microbial functions and microscale features. The decrease of enzyme activities with depth, accompanied by the decrease of catalytic efficiency, implies the microbial production of more efficient enzymes in the top- than in the subsoil. Bioturbation induced by earthworms leads to localization of microorganisms and litter within biopores and plays a crucial role for organic matter processing, its microbial utilization, and turnover. This has direct consequences for C and nutrient cycling.

How to cite: Hoang Thi Thu, D.: Carbon turnover and Turnover rate of enzyme cellobiohydrolase in earthworm biopores, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6080, https://doi.org/10.5194/egusphere-egu2020-6080, 2020.

EGU2020-10838 | Displays | SSS4.8

Contrasting responses of soil fungal communities and soil respiration to the above‐ and below‐ground plant C inputs in a subtropical forest

Lingling Shi, Wenting Feng, Xin Jing, Huadong Zang, Peter Edward Mortimer, and Xiaoming Zhou

The roles of soil fungal diversity and community composition in regulating soil respiration when above‐ and below‐ground plant carbon (C) inputs are excluded remain unclear. In the present study, we aimed to examine: (i) how does the exclusion of above‐ and below‐ground plant C inputs affect soil respiration and soil fungi singly and in combination? and (ii) are changes in soil fungal diversity aligned with changes in soil respiration? A field experiment with manipulation of plant C inputs was established in a subtropical forest in southwest China in 2004 with litter removal and tree stem‐girdling to exclude inputs of the above‐ and below‐ground plant C, respectively. In 2009, we measured the rates of soil respiration with an infrared gas analyser and soil fungal community structure using Illumina sequencing. We found that the rates of soil respiration were reduced significantly by litter removal and girdling, by similar magnitudes. However, they were not decreased further by the combination of these two treatments compared to either treatment alone. In contrast, litter removal increased the diversity of soil fungal communities, whereas girdling decreased the abundance of symbiotrophic fungi but increased the abundance of saptrotrophic and pathotrophic fungi. These changes in soil fungal community might initiate CO2 emission from soil C decomposition, offsetting further decline in soil respiration when plant C inputs are excluded. These results revealed that the exclusion of the above‐ and below‐ground plant C inputs led to contrasting soil fungal communities but similar soil function. Our findings suggest that both above‐ and below‐ground plant C are important in regulating soil respiration in subtropical forests, by limiting substrates for soil fungal growth and altering the diversity and composition of soil fungal community.

How to cite: Shi, L., Feng, W., Jing, X., Zang, H., Mortimer, P. E., and Zhou, X.: Contrasting responses of soil fungal communities and soil respiration to the above‐ and below‐ground plant C inputs in a subtropical forest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10838, https://doi.org/10.5194/egusphere-egu2020-10838, 2020.

EGU2020-16574 | Displays | SSS4.8

Re-colonization of sterile soil samples during long term field exposure

Michael Herre, Bernd Marschner, and Sven Marhan

The distribution of soil organic matter and microbial biomass in subsoils is much more heterogeneous than in the topsoil due to a more localized input of fresh substrate and nutrients from rhizodeposition and preferential flow paths forming hotspots of microbial activity. However, the remaining bulk soil also contains substantial amounts of labile substrates that are readily mineralized during lab incubation experiments. We therefore hypothesized that one reason for this is that potential consumers are spatially separated from these substrates due to the low microbial densities in subsoils. Consequently, hotspots are not only formed through high substrate inputs but also through a higher abundance and diversity of microorganisms compared to the bulk soil due to inputs of cells and spores with the soil solution or through hyphal growth. However, little is known about the colonization potential or dynamics of microorganisms in the subsoil.

In November 2018, we started a field experiment to investigate the re-colonization potential of microorganisms by exposing 24-well microplates containing sterilized soil samples in the field at two different depths (topsoil: 10 cm, subsoil 60 cm) at a beech forest site in northern Germany. After 6 and 12 months, samples from each well and from the intact soil compartments above each well were analyzed for enzyme activities (hydrolytic enzymes using MUF and AMC substrates), microbial activity parameters (soil respiration and SIR using the MicroResp®) and the microbial community structure (quantitative PCR).

We expect (1) different temporal dynamics of re-colonization between top- and subsoil samples; (2) that the recolonization potential is related to the microbial activity in the soil compartments above the exposed samples and (3) that the heterogeneous re-colonization is maintained throughout the field exposure and thus indicates the relevance of preferential flow paths for microbial transport especially in subsoils.

First results of the SIR assays after 6 months of field exposure show that in the topsoil microbial activity has been re-established in all of the wells, but is still below the mean activity in the undisturbed soil above the sterilized samples. In all subsoil samples, the re-established microbial activity was much lower and even below detection limit in some of the wells. In both depths, the SIR assays show a very patchy distribution of wells with higher microbial activities indicating that the influx of organisms is limited to small areas from the soil above the exposed containers.

How to cite: Herre, M., Marschner, B., and Marhan, S.: Re-colonization of sterile soil samples during long term field exposure , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16574, https://doi.org/10.5194/egusphere-egu2020-16574, 2020.

  With the increasing of nitrogen(N) deposition and changing of precipitation patterns worldwide, large amounts of N are loaded in terrestrial ecosystem, resulting in soil nutrient imbalance and soil nitrous oxide(N2O) flux change. Nitrification and denitrification in soil are two major sources of N2O emission mediated by microorganisms. However, It is still unclear how the soil N2O flux and the abundance of nitrifiers and denitrifiers might change under the addition of N and water(W) in temperate semi-arid steppe. In this study, we established a one-year-long field experiment investigating how soil N2O flux, the abundance of nitrifiers and denitrifiers, and environmental properties, including soil pH, soil moisture, soil dissolved organic carbon content(DOC) and soil available N content responsed when N(NH4NO3 was applied at a rate of 4 g N·m-2·yr-1, which is equivalent to one time the annual nitrogen deposition) and/or W(water was applied at a rate of 112.5 mm·yr-1, which is equivalent to 30% of the annual rainfall) were added to temperate semi-arid steppe in northern China with the natural condition without any treatment as control. Quantitative PCR was used to analyze the abundance of ammonia oxidizers(ammonia-oxidizing bacteria and archaea amoA) and denitrifiers(nirS/nirK and nosZ). Our experimental results demonstrated that soil N2O emission decreased when W was added and W and N were added in temperate semi-arid steppe in northern China. The abundance of nirS and nosZ genes increased when W and N were added. Compared with AOA/AOBamoA and nirK genes, the abundance of nirS and nosZ genes is more sensitive to the addition of N and W. Soil N2O flux was negatively correlated with the abundance of nirS-denitrifier. The nirS gene abundance, soil pH and DOC were the main controls on soil N2O flux and totally explained 78.2% of the variation of soil N2O flux. The results of this study provide a theoretical basis for N cycle mechanism mediated by microorganisms and have practical significance for the prediction of N2O flux change in temperate semi-arid steppe under the background of global change.

How to cite: Jiaqi, Z. and Yinghui, L.: Environmental properties and microbial abundance explain soil nitrous oxide flux variation synergistically under the addition of nitrogen and water in temperate semi-arid steppe , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6270, https://doi.org/10.5194/egusphere-egu2020-6270, 2020.

EGU2020-4140 | Displays | SSS4.8

Rhizosphere hotspots: root hairs and warming control microbial efficiency, carbon utilization and energy production

Xuechen Zhang, Yakov Kuzyakov, Huadong Zang, Michaela A. Dippold, Lingling Shi, Sandra Spielvogel, and Bahar S. Razavi

Among the factors controlling root exudation, root hair proliferation and warming strongly influence exudate release, microbial substrate utilization and enzyme activities. The interactions of these two factors are important but poorly known in the rhizosphere. To clarify these interactions, two maize varieties – a wild type with root hairs and a hairless mutant – were grown at 20 and 30 °C for 2 weeks. We applied a unique combination of zymography to localize hotspots of β-glucosidase with microcalorimetry and substrate-induced respiration from soil sampled in hotspots. This approach enabled monitoring exudate effects on microbial growth strategy, enzyme kinetics (Vmax and Km), heat release and CO2 production in the hotspots in response to warming.

Root hair effects on enzyme activity and efficiency were pronounced only at the elevated temperature: i) β-glucosidase activity of the wild type at 30 °C was higher than that of the hairless maize; ii) temperature shifted the microbial growth strategy, whereas root hairs (i.e. C input) promoted the fraction of growing microbial biomass; iii) Km and the activation energy for β-glucosidase under the hairless mutant was lower than that under wild maize. These results suggest that microorganisms inhabiting hotspots of the wild type synthesized more enzymes to fulfill their higher energy and nutrient demands than those of the hairless mutant. In contrast, at higher temperature the hairless maize produced an enzyme pool with higher efficiencies rather than higher enzyme production, enabling metabolic needs to be met at lower cost. These changes in enzyme kinetics and metabolic shifts confirmed evolutionary theory on tradeoffs of enzyme structure–function and thermal–substrate under warming at the soil hotspot level. We conclude that, if microbial and enzymatic activities are stimulated by more substrate input under warming, then this shift in the microbial community and in enzyme systems to a lower efficiency could offset C losses.

How to cite: Zhang, X., Kuzyakov, Y., Zang, H., Dippold, M. A., Shi, L., Spielvogel, S., and Razavi, B. S.: Rhizosphere hotspots: root hairs and warming control microbial efficiency, carbon utilization and energy production, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4140, https://doi.org/10.5194/egusphere-egu2020-4140, 2020.

EGU2020-730 | Displays | SSS4.8

Effect of Vaccinium vitis-idaea L. and moisture on mountain-meadow soils

Rida Sabirova, Michael Makarov, and Maxim Kadulin

Against the climate change there has been an overgrowing of phytocenoses of alpine lichen heath and arctic tundra with dwarf shrubs and shrubs over the past 40 years. Dwarf shrubs roots of Vaccinium vitis-idaea L. forms symbiosis with ericoid mycorrhiza, which may lead to change of soil properties. Mycorrhizal fungi regulate nitrogen, phosphorus and carbon cycles by secretion of active enzymes which depolymerize and mineralize soil organic matter and increase available of mineral nutrition elements for vegetation and microorganisms.

Moreover, in the previous research it was found that moisture was greater under shrubs than under alpine lichen heath. It is known that moisture plays key role in microbial processes in the soil, affect on enzyme activity, nitrification, mineralization and so on. Therefore, the objective of this research is to evaluate the influence of both dwarf shrubs and moisture on the soil characteristics.

Research area is located around 2750 m a.s.l. in the alpine heath of Teberda Nature Reserve, North Caucasus, Karachay-Cherkess Republic where 3 areas with different moisture (15, 21 and 27%) were chosen. In each area samples of mountain-meadow soil were collected from under dwarf shrubs and alpine lichen heath without dwarf shrubs (control) during 10 days of the second part of July and then frozen until laboratory analysis. Firstly, there were analyzed chemical (soil pH, mineral P, organic N, C, inorganic N) and biological (C and N of microbial biomass, basal respiration, mineralization, nitrification and activity of glucosidase, phosphatase, chitinase and leucinaminopeptidase) properties of the soil samples. Furthermore, it was made statistical analysis in Statistica 8.0 program.

 It was found that increase in moisture is accompanied by increase in concentrations of inorganic forms of nitrogen, C and N of microbial biomass, basal respiration and nitrification activity in heath without shrubs, which indicates a growth of microbiota activity. However concentrations of labile organic carbon and nitrogen, and enzymatic activity decrease at the same conditions. Such changes indicate a shift from a community of heath with herbal vegetation to communities dominated by ericoid mycorrhizal plants.

The investigation also revealed that soil acidity is significantly higher under V. vitis-idaea L., however, there is a noticeable decrease in nitrification activity, inorganic nitrogen concentrations, which indicates minor dependence of the dwarf shrubs on mineral compounds in nitrogen nutrition.

Thus, both the presence of V. vitis-idaea L. and various moisture have a significant effect on the soil characteristics. Moreover, the moisture under control plays an essential role, while under the dwarf shrubs many soil properties remain unchanged, therefore, V. vitis-idaea L. creates a microclimate in the soil among roots where moisture has no effect.

How to cite: Sabirova, R., Makarov, M., and Kadulin, M.: Effect of Vaccinium vitis-idaea L. and moisture on mountain-meadow soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-730, https://doi.org/10.5194/egusphere-egu2020-730, 2020.

EGU2020-5344 | Displays | SSS4.8

Tea Bag Index as potential indicator for soil microbial activity.

Gera Van Os, Karin Pepers, Jaap Bloem, Joeke Postma, and Johnny Visser

Worldwide there is an enormous interest in microbial indicators for soil quality, since this reflects the potential capacity for soil ecosystem functions i.e. nutrient cycles, carbon storage, biodiversity and resilience to climate change. Farmers are anxious to measure the effects of different soil management practices in order to improve soil quality and attain sustainable food production. Despite the rapid developments in (molecular) measurement techniques, adequately validated and affordable methods for field measurements on soil microbial activity are still lacking. Nowadays, farmers participate in campaigns to bury cotton undies in order to measure biological activity in their fields (Soil your undies).  If there’s not much left of the undies after a couple of months, this supposedly indicates good soil health. Of course this is by no means a quantitative nor validated indicator.

An elegant, cheap and simple method to measure biological activity in soil is the Tea Bag Index (TBI). This method was developed to determine the global variation in decomposition rate of organic matter by the soil microflora as influenced by abiotic circumstances. The TBI consists of two parameters describing decomposition and stabilization of organic matter by measuring weight loss of green tea and rooibos tea bags that have been buried in the soil for three months. The method is designed to discriminate contrasting ecosystems and, within ecosystems, differences in factors such as soil temperature and moisture content (Keuskamp et al. 2013, doi: 10.1111/2041-210X.12097).

Our research aimed to assess the possibility to use the TBI as an indicator for soil microbial activity, considering its sensitivity and robustness to discriminate between agricultural soil management practices that are known to have a significant impact on soil microbial diversity and activity. The responsiveness to soil pasteurization and organic amendments was investigated under both controlled and field conditions. The TBI decomposition rate differed significantly between both tea varieties (green tea > rooibos tea). Organic amendments had little or no effect. The TBI-results were plotted against some more established biochemical indicators which are sensitive to soil management and often related to microbial biomass, i.e. hot water extractable carbon, potentially mineralizable nitrogen and fungal biomass. Results are discussed, as well as factors which complicate the interpretation of TBI data with respect to soil microbial activity.

How to cite: Van Os, G., Pepers, K., Bloem, J., Postma, J., and Visser, J.: Tea Bag Index as potential indicator for soil microbial activity., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5344, https://doi.org/10.5194/egusphere-egu2020-5344, 2020.

EGU2020-1148 | Displays | SSS4.8

Pore size effect on soil carbon dynamics during decomposition of switchgrass

Kyungmin Kim, Andrey Guber, and Alexandra Kravchenko

Soil pore size distribution (PSD) regulates oxygen diffusion and transport of water/mineralized nutrients. Microbial activity, which drives the carbon (C) cycle in the soil system, can react to these physical factors regulated by PSD. In this study, we investigated the contribution of PSD to C-related microbial activity during the switchgrass decomposition. We used two types of soils, which have controlled PSD (dominant pore size of < 10um and > 30 um). 13C labeled switchgrass leaf and root were incorporated into different PSD of soils and incubated for 21 days under 50% water-filled pore space. During the incubation, microbial activity was assessed with several indicators. i) Fate and transport of mineralized switchgrass, ii) Priming effect, iii) Spatial distribution of b-glucosidase and phenol oxidase, and iv) Microbial biomass. Our preliminary results showed that CO2 emission from switchgrass leaf was greater in the soil dominated by < 10 um pores. Higher b -glucosidase activity and mineralized C from switchgrass leaf supported greater C-related activity in such soil. However, interestingly, we observed a greater priming effect in the soil dominated by > 30 um pores. Due to the less mineralization and transport of switchgrass-derived C in such pores, enzymes targeting more complex substrate could be more active in such soil stimulating mineralization of native soil C. Our full results of phenol oxidase, microbial biomass, and more detailed analysis on 13C and C dynamics will help understanding how PSD can affect biochemical reactions in plant decomposition system.

How to cite: Kim, K., Guber, A., and Kravchenko, A.: Pore size effect on soil carbon dynamics during decomposition of switchgrass, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1148, https://doi.org/10.5194/egusphere-egu2020-1148, 2020.

Climate change represents a key challenge to the sustainability of global ecosystems and human prosperity in the twenty-first century. The impacts of climate change combined with natural climate variability are predominantly adverse, and often exacerbate other environmental challenges such as degradation of ecosystems, loss of biodiversity, and air, water and land pollution. Besides, rapid industrialization and increasing adaption of agrochemical based crop production practices since green revolution have considerably increased the heavy metal contaminations in the environment.

Assessing the impacts of climate change on our planet and addressing risks and opportunities is essential for taking decisions that will remain robust under future conditions, when many climate change impacts are expected to become more significant.

Here, we established a review survey to assess the impact of biochar amendment and agroforstry system on CO2 sequestration and methaloid remediation.

Our data base showed that Agroforestry-based solutions for carbon dioxide capture and sequestration for climate change mitigation and adaptation in long-term is more practical and realistic options for a sustainable ecosystem and decreasing negative effect of climate change. This was more supported in arid and semi-arid regions as well as area with saline and alkaline soil (20%).

From a soil remediation standpoint, the general trend has been shifting from reduction of the total concentration to reduction of the physic-chemically and/or biologically available fractions of metals. This regulatory shift represents a tremendous saving in remediation cost. While metals are not degradable, their speciation and binding with soil through biochar amending reduced their solubility, mobility, and bioavailability. While agroforestry showed high efficiency in C sequestration (32%), biochar amendment raveled significant mitigation in heavymetals bioavailability (42%). However, studies which coupled both approaches are limited. Thus, we conclude that combined Agroforestry and biochar amendment regulates C sequestration and metalloids remediation more efficiently.

How to cite: Feizi, A. and Razavi, B.: Climate change mitigation and adaptation by biochar: mechanisms and regulatory trend in the rhizosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22654, https://doi.org/10.5194/egusphere-egu2020-22654, 2020.

EGU2020-5468 | Displays | SSS4.8

How 'hot' are the hotspots: Statistical approach to localize the high activity areas on soil images

Nataliya Bilyera, Irina Kuzyakova, Bahar S. Razavi, Sandra Spielvogel, and Yakov Kuzyakov

The recently raised topic of microbial hotspots in soil needs not only visualizations of their spatial distribution and biochemical analyses, but also statistical approaches to segregate these hotspots and separate them from the background.  We hypothesized that each type of hotspots (e.g. hotspots of root exudation, enzyme activities, root water uptake, pesticides accumulation in plant) is a result of processes driven by biotic or abiotic factors, and consequently corresponds to a statistical distribution follows of a composite functions (e.g. normal/Gaussian), which is significantly different from the background. Consequently, the elucidation of microbial hotspots should be based on statistical separation of the distributions or segregate of maximal values within one distribution. As examples, we collected 3 groups of published images: 1) 14C images on carbon input by roots into the rhizosphere, 14C localization in roots and glyphosate accumulation in the plant, 2) zymogram on leucine aminopeptidase, 3) neutron image on root water uptake. Each of the images was analyzed for statistical distribution of activity and its area. In the next step, respective distribution parameters (means and standard deviations) were calculated, the modeled distribution was fit, and the background was removed. For the parameters with one distribution, we identified hotspots as the areas outside of the “Mean+2SD” values (corresponding to the upper ~ 2.5% of activity being over 95.5 % of background values). Finally, images of solely hotspots locations were visualised. Comparison with previously used decisions of the hotspot intensity (i.e. Top-25% intensity) thresholding showed advantages of the “Mean+2SD” approach. The advantages (suitable for “time-specific” hotspots in temporal sequence of images, identification of hotspots with different level of activity, unification of thresholding approach for several imaging methods with different principles of activities distribution) and limitations (loss of hotspot areas at low quality images, several thresholding rounds for two or more distributions at on image) of the suggested approach and the potentials of its further development were discussed. We conclude that objective elucidation and separation of the hotspots is case specific and should be based on statistical tools of distribution analysis, which will also help to understand the processes responsible for the highest activities.

How to cite: Bilyera, N., Kuzyakova, I., S. Razavi, B., Spielvogel, S., and Kuzyakov, Y.: How 'hot' are the hotspots: Statistical approach to localize the high activity areas on soil images, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5468, https://doi.org/10.5194/egusphere-egu2020-5468, 2020.

The roles of multiple global change are expected for many terrestrial ecosystems in future. As two main global change factors, the impact of drought and nitrogen deposition and their interaction on soil respiration and its components (R) remains unclear. To explore the responses of soil respiration (Rs), autotrophic respiration (Ra) and heterotrophic respiration (Rh) to multiple global change factors, we established a field experiment of throughfall reduction and nitrogen additions in a subtropical Moso bamboo (Phyllostachys heterocycla) forest in the Southwest China, using a 4 × 4 completely randomized design. Results showed that bivariate exponential equation with soil temperature (T) and soil moisture (SWC) (R=a.ebT.SWCc) was fitted to predict Rs, Ra and Rh. Throughfall reduction, nitrogen additions and their interaction had no effect on annual mean Rs and Ra, but nitrogen additions significantly depressed annual mean Rh. Nitrogen additions significantly decreased contribution of Rh to Rs and increased contribution of Ra to Rs, however, the contributions were non-responsive under throughfall reduction. The more positive effect of nitrogen additions on the contribution of Ra to Rs was appeared compared with that of throughfall reduction, thereby more negative effect on the contribution of Rh to Rs. The fine root biomass, fine root carbon and nitrogen storage regulated Rs, while fine root phosphorus storage determined Ra. The Rh was negatively correlated with vector lengths, thus suggesting that microbial carbon limitation caused the decline of Rh. Our findings demonstrate that the nitrogen additions played overriding role than throughfall reduction in affecting the contribution of Ra and Rh to Rs. Moreover, the negative response of temperature sensitivity of Rs and Rh to nitrogen additions, suggesting that that the nitrogen additions may weaken the positive response of soil CO2 emission to global climate warming. Our study highlights asymmetrical responses of Rs, Ra and Rh to throughfall reduction and nitrogen additions and could enhance accurate predictions of soil carbon dynamics in response to multiple global climate change in future.

How to cite: Wang, Y., Liu, S., and Luan, J.: Soil respiration and its components respond asymmetrically to throughfall reduction and nitrogen additions in a subtropical Moso bamboo forest in the Southwest China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6262, https://doi.org/10.5194/egusphere-egu2020-6262, 2020.

EGU2020-6227 | Displays | SSS4.8 | Highlight

Nitrous oxide production and sources in response to a simulated fall-freeze-thaw cycle

Sisi Lin and Guillermo Hernandez Ramirez

Thaw-induced N2O emissions have been shown to account for 30-90% of N2O emissions in agricultural fields. Due to the climate change, increased precipitatio is expected in fall and winter seasons for certain regions. As a result, this would in turn enhance the thaw-induced N2O emissions and aggravate climate change. A mesocosm study was conducted to investigate N2O production and sources from soils under elevated soil moisture contents in response to a simulated fall-freeze-thaw cycle. Treatments included two levels of N addition (urea versus control) and two different management histories [with (SW) and without (CT) manure additions]. Our results showed that at least 92% of the N2O emissions during the study were produced during the simulated thawing across all treatments. The thaw-induced N2O emissions increased with increasing soil water content. The fall-applied urea increased the soil-derived N2O emissions during thawing, indicating an excessive mineralization of soil organic N. Compared to the CT soils, the SW soils induced more soil-derived N2O emissions. This could be because the SW soil had more easily decomposable organic matter which was likely due to historical manure additions. Regarding to the daily primed N2O fluxes, different soil water contents impacted the dynamics of daily priming effect. At the high water content, the soils experienced a shift in daily primed N2O fluxes from positive to negative and eventually back to positive throughout the simulated thawing, while the soils at lower water contents underwent positive primed fluxes in general. The shift in daily primed fluxes was probably driven by the preference of soil microbes on the labile N substrates. When the microbes switched from easily to moderately decomposed substrates (e.g., from dissolved organic N to plant residuals), they started to uptake inorganic N from the soil due to a relatively high C:N ratio of plant residuals. Therefore, a net N immobilization and negative primed N2O production occur in the short term in the soils at the high water content.

How to cite: Lin, S. and Ramirez, G. H.: Nitrous oxide production and sources in response to a simulated fall-freeze-thaw cycle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6227, https://doi.org/10.5194/egusphere-egu2020-6227, 2020.

EGU2020-6893 | Displays | SSS4.8

Combined application of manure and mineral fertilizers weakens the impact of manure on soil biochemical properties

Shibin Liu, Yakov Kuzyakov, Shengyan Pu, and Bahar Razavi

Manure application has been considerably emphasized to mitigate global soil degradation and improve soil fertility. Though there have been investigations on the contribution of manure application on soil properties in comparison with mineral fertilization, a comprehensive understanding of manure application on soil organic matter (SOM), total nitrogen (TN), microbial biomass carbon (MBC) and nitrogen (MBN) and activities of 7 enzymes is yet to be identified. This study extensively quantified the response of soil biochemical properties to manure application based on a meta-analysis of 83 articles including 460 observations with time span from days to years. The impact of explanatory factors (i.e. climatic factors, experimental types, soil properties and manure characteristics) was also elucidated. Manure application increased SOM, TN, MBC and MBN by 27 ± 3% and 41 ± 5.3%, 87 ± 4.3% and 88 ± 6.7 %. Soil C/N ratio did not vary but MBC/MBN ratio decreased after manure application, indicating a shift in microbial community. The activities of β-glucosidase, dehydrogenase, acid phosphatase, alkaline phosphatase, N-acetyl-β-D-glucosaminidase, urease and sulfatase were also elevated by 150%, 110%, 40%, 110%, 59%, 106% and 221%, respectively. Besides, all soils were neutralized following manure application, suggesting that manure accelerates soil nutrient cycling by adjusting pH to optimum. When mean annual temperature is within the range of 10-20 °C or initial soil pH within 6-8, the highest increase of enzyme activities was revealed. Furthermore, composting manure has stronger impact on soil enzyme activities compared to non-composted manure, which was attributed to beneficial microbial community composition as well as favourable soil organic compound composition in the compost. Contrarily, combined application of manure with mineral fertilizers induces an antagonistic effect and weakens the impact of manure on soil biochemical properties as compared to only manure application. This weakening effect may mitigate the competition between microbes and plant roots for nutrients. In conclusion, necessary differentiation of only manure and manure + chemical fertilizers application is required when developing and modeling the influence of management practices on arable lands.

How to cite: Liu, S., Kuzyakov, Y., Pu, S., and Razavi, B.: Combined application of manure and mineral fertilizers weakens the impact of manure on soil biochemical properties, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6893, https://doi.org/10.5194/egusphere-egu2020-6893, 2020.

EGU2020-11995 | Displays | SSS4.8

Land use change and management of a Duric Histic Placaquand in Southern Chile: effects on biological properties and greenhouse gas emissions

Leandro Paulino, Nelson Beas, Dorota Dec, Felipe Zúñiga, Oscar Thiers, Oscar Martínez, and José Dörner

Aquands are shallow depth and frequently waterlogged volcanic ash soils, presenting seasonal dynamics of water content in the soil profile. Land use change and management are expected to alter the Aquands biological activity due to their impact to water/air relationships as well as nutrient dynamics and greenhouse gases emissions. In southern Chile (41°26’S;73°07’W; 70 m a.s.l.), soil biological processes related to C- and N cycles, as well as greenhouse gas effluxes were assessed in relation to historical land use change and a drainage set in a naturalized grassland for animal husbandry. Disturbed soil samples were obtained in order to evaluate soil respiration, N mineral dynamics (NH4+ and NO3-), denitrification, nitrate reductase activity. Static-closed chambers were installed in the field to assess fluxes of CO2, N2O and CH4 from the soil surface at different seasons of the year with contrasting water table depths. Soil respiration responded to the historical land use change and draining effects. The aerobic and anaerobic biological processes related to soil nitrogen dynamics were less sensitive than respiration, and showed arbitrary effects according to the current use and management of the Aquand. Soil surface fluxes of greenhouse gases showed similar patterns, where CO2 emissions responded temporarily to land use, while N2O and CH4 did not respond conclusively. The content of soil organic carbon associated to the structural changes derived from land use change (e.g. fire clearance) and soil management (e.g. animal trampling) are plausible parameters to explain the variations of CO2 emissions from Aquand soils surface, while other elements such as microbial community and the ferrous wheel hypothesis, should be investigated in order to explain the biological responses and trace greenhouse gases emissions.

How to cite: Paulino, L., Beas, N., Dec, D., Zúñiga, F., Thiers, O., Martínez, O., and Dörner, J.: Land use change and management of a Duric Histic Placaquand in Southern Chile: effects on biological properties and greenhouse gas emissions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11995, https://doi.org/10.5194/egusphere-egu2020-11995, 2020.

EGU2020-9434 | Displays | SSS4.8

Hotspots created by earthworms, and their contribution to soil nitrogen cycling

Joann Whalen and Hicham Benslim

Earthworms create hotspots that support microbial diversity and activity in soil. These hotspots may be internal to the earthworm, such as in their intestinal tract, or external to the earthworm in the biopores, casts and middens they create on the soil surface and within the soil profile. This presentation summarizes some of the key hotspots associated with earthworms, and how the biostimulated microbial community in these areas contributes to soil nitrogen cycling. We will present observations about the diversity and activity of nitrogen-cycling microorganisms that live within the earthworm and in its built environments, as well as the population- and community-level contributions of earthworms to denitrification, nitrogen mineralization, and the soil nitrogen supply in temperate agroecosystems.

How to cite: Whalen, J. and Benslim, H.: Hotspots created by earthworms, and their contribution to soil nitrogen cycling , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9434, https://doi.org/10.5194/egusphere-egu2020-9434, 2020.

Annually, millions of tons of antibiotics in the world are used in medicine, veterinary and agriculture, and their excessive application have negative impacts on soil microorganisms and biological processes. In the present study, the effect of releasing the mostly used antibiotic in veterinary and ameliorative impact of organic and non-organic amendments was studied in which treatments include (control (without antibiotic), gentamicin, oxytetracycline and penicillin) and different concentrations (50, 100 and 200 mg/kg dry soil) with and without organic and mineral conditioners (cow manure, biochar and nano-zeolite) on soil urease (URE) and alkaline phosphatase (ALP) enzyme activity and their resistance and resilience indices at three time periods including 1-7, 7-30 and 30-90 days during a 90-day incubation time in a split-factorial design which soil conditioners were considered as the main plots and antibiotic types and concentration were as experimental factors. Resistance (RS) and resilience (RL) indices were calculated for enzymes activity. Results showed that in control treatment (without conditioner), application of gentamicin at 200 mg/kg caused a 68.9 percent decrease in soil ALP activity compared to control (without antibiotic), while a decrease in ALP activity in tetracycline-treated soils compared to control (without conditioner), manure, biochar, and nano-zeolite was 17.5, 13.8, 17.5 and 16 percent, respectively. URE enzyme activity at 30-90-days during incubation the period had an increasing trend from 1-7 days and the highest enzyme activity was measured on the 90th day of incubation. According to results, soil enzymes responded differently to antibiotics and conditioners in soil, so that penicillin and oxytetracycline had no considerable negative impact on ALP enzyme activity, while gentamicin and oxytetracycline at all applied concentrations significantly decreased URE activity. To sum up, findings showed that application of soil conditioners could alleviate negative impacts of antibiotics in soil and could improve resistance and resilience indexes of soil enzymes activities in soil.

How to cite: Rashtbari, M. and Safari Sinegani, A. A.: Enzymes Activity in Response to Veterinary Antibiotics in Presence of Organic (Biochar and Manure) and Mineral (Nano-Zeolite) amendment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10264, https://doi.org/10.5194/egusphere-egu2020-10264, 2020.

EGU2020-10754 | Displays | SSS4.8

Microbial necromass shaped plant traits in a warmer condition

Wioleta Stelmach-Kardel, Magdalena Frąc, Agata Gryta, and Bahar S. Razavi

Among many factors controlling root exudation, root hairs proliferation and warming have strong influence on exudate release as well as microbial substrate utilization and enzyme activities. Thus, the interactions of these two factors are important but least known in the rhizosphere. Phosphorus (P) is the most important growth limiting nutrient in soils. Concerns about a depleting supply of P as fertilizer has boosted research efforts on understanding P cycling and fluxes, as a breakdown of P availability would have disastrous global consequences. Efficient P recycling in temperate ecosystems provides an excellent possibility to study all kind of biogeochemical P transformations – those mobilizing low available P species and those recycling available P – maintaining a high level of microbial biomass P in the ecosystem. Such microbial cycling has been successfully shown for individual C compounds or within compound classes. P recycling, especially within microbial communities, has not been investigated so far. Microbial necromass as a source of available C and N affect microbial P utilization. However, the mechanisms underlying this alteration of biogeochemical transformations within the P cycle are not understood. To clarify these interactions for 21 days, rhizoboxes with Maize wildtype and mutant (rth3, no root hairs) under 20 and 30 °C, with and without necromass addition were incubated. The spatial distribution of acid phosphatase was assessed with MUF-based Zymography. Phosphatase activity as well as enzyme kinetics parameters (Vmax and Km) were determined in bulk and rhizosphere soil of all treatments. 
Our result showed that necromass addition accelerated microbial activity and phosphates hotspots at high temperature ranges. Necromass had no influence on rhizosphere size but increased hotspots independent of temperature. In treatment without necromass amendment, root-hairs effects on enzyme activity and efficiency was pronounced only at elevated temperature. Necromass addition caused formation of roots with special morphology comparable to root hairs in mutant type (hairless root). This was plant strategy to compensate P limitation and acquire more P under competition with soil microbiome. Consequently, P content in plant biomass after changes of root morphology increased while MBP decreased. This, shows that microbial necromass was decomposed and used as a source of P by plant. Thus, plant by adaptation of their morphology over compete microorganisms for more efficient P uptake.

How to cite: Stelmach-Kardel, W., Frąc, M., Gryta, A., and S. Razavi, B.: Microbial necromass shaped plant traits in a warmer condition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10754, https://doi.org/10.5194/egusphere-egu2020-10754, 2020.

EGU2020-13985 | Displays | SSS4.8

Soil warming leads to an up-regulation of genes involved in the decomposition of organic N in a subarctic grassland

Joana Séneca, Andrea Söllinger, Alexander Tveit, Petra Pjevac, Craig Herbold, Tim Urich, Josep Peñuelas, Ivan Janssens, Michael Wagner, Bjarni Sigurdsson, and Andreas Richter

Soil microorganisms control the breakdown (depolymerization) of high molecular weight organic matter in soil and its mineralization and release as CO2 to the atmosphere. The enzymatic reactions involved in these steps are known to be temperature sensitive. Therefore, increasing global temperatures are expected to accelerate microbial activity and ecosystem processes and stimulate further CO2 emissions, potentially causing a positive feedback to climate change. On the other hand, higher turnover rates demand an increased amount of energy allocated for growth, enzyme production and maintenance, which can progressively deplete soils from substrate, forcing a reduction of microbial biomass and/or activity and a higher metabolic investment in resource acquisition.

The response of ecosystems to warming has been shown to be related with its duration and magnitude. In this study, we analyzed soils from long-term (>50 years) and short-term (8 years) warmed plots at the natural geothermal warming experiment ForHot (https://forhot.is), located in a sub-arctic grassland in Iceland. Previous studies at this warming experiment have shown an accelerated C cycle in response to warming, with decreased soil carbon stocks, and higher rates of decomposition of labile and recalcitrant organic matter, regardless of the warming duration. In addition to carbon losses, increased N losses from soils were found, but no change in the N content of the vegetation along the temperature gradient. Additionally, both ammonification and nitrification rates were shown to increase under warming, pointing to higher N losses from warmed soils.

In this study, we tested the hypothesis that under warming microorganisms become progressively limited in organic substrates, leading to a higher microbial investment in organic N decomposing enzymes to mine the existing organic N sources present in their surroundings. This hypothesis is based on previous data, that showed that microbial turnover was increased in the warmed plots. Under this assumption, we expected to observe higher expression levels of genes coding for organic N mining extracellular enzymes in warmed plots.

We analyzed the metatranscriptome from a total of 16 soil samples representative of ambient (n=4) and +6°C warmed (n=4) soils, for both grassland types. Additionally, we sequenced the metagenomes of 4 soil samples, representative of each condition, to allow for transcript mapping and differential gene expression analysis.

We used Hidden Markov models to screen the assembled metatranscriptomes for genes involved in the degradation of chitin, proteinaceous compounds, nucleic acids and microbial cell walls. The subcellular location and presence/absence of signal peptides was assessed with Psort and SignalP to discriminate transcripts involved in internal recycling from those targeted for secretion. First results show a general up-regulation of all transcripts involved in organic N degradation in the grassland subjected to long-term warming, whereas this trend is less clear in the short-term warmed grassland. Further work includes cross-referencing gene expression patterns with potential changes in active community composition.

We conclude that an acceleration in microbial turnover rates in response to warming is coupled to a higher investment in N acquisition enzymes, as indicated by an up-regulation of genes involved in upstream processes of organic N degradation.

How to cite: Séneca, J., Söllinger, A., Tveit, A., Pjevac, P., Herbold, C., Urich, T., Peñuelas, J., Janssens, I., Wagner, M., Sigurdsson, B., and Richter, A.: Soil warming leads to an up-regulation of genes involved in the decomposition of organic N in a subarctic grassland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13985, https://doi.org/10.5194/egusphere-egu2020-13985, 2020.

How agroforestry systems influence the abundance of nitrogen-cycle contributing microbial genes under Mediterranean conditions?

 

Onurcan Özbolat *,1, Irene Ollio1, Eva Lloret1, Marcos Egea2, Raul Zornoza1

 

1 Sustainable Use, Management and Reclamation of Soil and Water Research Group, Universidad Politécnica de Cartagena, Paseo Alfonso XIII, 48, 30203 Cartagena, Spain.

 

2 Institute of Plant Biotechnology (IBV), Campus Muralla del Mar, Edificio I+D+I, Universidad Politécnica de Cartagena, 30202, Cartagena, Spain.

 

*

 

ABSTRACT

 

Agroforestry systems represent cropping systems in which woody crops are intercropped with alley crops to increase land productivity and enhance the delivery of ecosystem services. Avoiding bare soils in the alleys and cultivation of different annual or perennial species, with shifts in tillage and/or irrigation patterns, will have an influence in organic matter turnover and nutrient cycling, mostly carbon and nitrogen, mediated by soil microbial communities. The ability of the soil to conduct a healthy relation with the microbiome and the crops is one of the most important soil quality indicators. In this study, soil samples from two different case studies where different diversification systems were applied are examined in perspective of ammonia oxidizing (amoA) and denitrifying (nirK and narG) gene abundances through quantitative-PCR assays to assess how nitrogen cycle can be modified by agroforestry systems compared to tree monocultures. The first case study included an almond orchard intercropped weather with Capparis spinosa or Thymus hyemalis. The second case study represented a mandarin orchard intercropped with a rotation of fava bean and vetch/barley or a rotation of several vegetables and vetch/barley. Abundances of amoA, nirK and narG genes significantly decreased in all intercropped systems with respect to monocultures. Thus, the special root-microorganisms and plant-plant interactions in the diversified systems contributed to soil N-cycle by decreasing the functional gene abundances. Decreasing nitrification and denitrification through management is desirable to decrease N losses and increase N fertilizer use efficiency. Thus, agroforestry systems seem more efficient in N turnover than tree monocultures where alleys remain bare most of the year.

How to cite: Ozbolat, O.: How agroforestry systems influence the abundance of nitrogen-cycle contributing microbial genes under Mediterranean conditions?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21485, https://doi.org/10.5194/egusphere-egu2020-21485, 2020.

EGU2020-22683 | Displays | SSS4.8

Effects of snow cover on CO 2 production and microbial composition in a thin topsoil layer

Dalia López, Francisco Matus, and Carolina Merino

Temperate rain forest soils (>8000 mm yr -1 ) of south of Chile in the East Andes range are
intensively affected by increasing freezing and thawing cycles (FTC) due to increasing
climate variability in the last 20 years. Most of these volcanic forests soils are unpolluted
(pristine) and receive seasonal snow-cover. In spite of pollutant free precipitations, the
snow cover in these ecosystems contains aerosols, nutrients and microorganisms from
circumpolar south west winds. These inputs and FTC generate specific conditions at the
shallow layer at the soil surface for soil microbiology and biochemistry. The objectives of
the study were to compare (micro)biological and chemical properties of topsoil and snow
cover in an pristine forest and after clear-cut. The organic matter mineralization was
monitored in a microcosm experiment to explore the effects of FTC and snow melting on
redox potential and other topsoil parameters. FTC for soil+snow released more CO 2 in
closed forest (81.9 mg CO 2 kg -1 ) than that after clear-cut (20.5 mg CO 2 kg -1 ). Soil texture
and soil organic matter accumulation played a crucial role for organic matter mineralization
and CO 2 fluxes. Gradually increase of temperature after freezing reveled that loamy soils
with certain amount of available C maintain active microbial population that response very
fast to temperature change. Sandy soils with very low C content showed the opposite
results – very slow response of microbial community and CO 2 fluxes. In conclusion,
microbial community structure and functions have distinct transition from snow to the soil
in temperate snow-covered forest ecosystem. FTC showed that different microbial groups

are responsible for organic matter mineralization in soil under forest and clear-cut, because
the pH and redox potential are influenced by snow melting.

How to cite: López, D., Matus, F., and Merino, C.: Effects of snow cover on CO 2 production and microbial composition in a thin topsoil layer, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22683, https://doi.org/10.5194/egusphere-egu2020-22683, 2020.

Hummock-hollow microtopography is a common feature in northern peatlands. It
creates microsites of variable hydrology, vegetation, and soil biogeochemistry, thus affect soil C
cycling in peatlands at the local scale. This study investigated effects of microtopography on soil
enzyme (β-1,4-glucosidase (βG), β-1,4-N-acetylglucosaminidase (NAG), acid phosphatase (AP)
and peroxidase (PER)) activities and environment variables as well as their relationships in a
typical sedge peatland in Changbai Mountain, northeast of China. Our results showed that the
enzyme activities in the sedge peatland significantly varied across seasons and microtopographical
positions. Soil enzyme activities in hummocks exhibited more obvious seasonal variation than
hollows, with the βG, AP and PER activities presented a distinct valley in summer and the
maximum values occurred in Spring or Autumn. Soil hydrolase (βG, NAG and AP) activities in
hummocks were significantly higher compared to hollows, while soil oxidase (PER enzyme)
activity in hollows was higher than hummocks. The NMDS analysis revealed that the influence
degree of microtopography on the enzyme activities was higher than that of seasonal variation.
Redundancy analysis (RDA) indicated that the variations of soil enzyme activities in the peatland
were related to environmental variables, especially to water table depth (WTD), soil temperature
(ST), SOC, N availability and P availability. Furthermore, correlation analysis showed that the
three hydrolase (BG, NAG and AP) activities were positively correlated with soil TN, SOC and
C/N, and negatively correlated with WTD and TP. On the contrast, the PER activities were
positively correlated with TP, and negatively correlated with ST, SOC and C/N. The present
study demonstrated that small scale topographic heterogeneity created by hummock cause habitat
heterogeneity and thus lead to significant difference of soil enzyme activity between hummock
and hollow in the sedge peatlands. This finding provides further evidence of the importance of
peatland microtopography to C cycling and has direct implications for scaling biogeochemical
processes to the ecosystem level.

How to cite: Wang, M.: The response of soil enzyme activity to seasonal and microtopographical variations in the sedge peatlands in Changbai Mountain, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22531, https://doi.org/10.5194/egusphere-egu2020-22531, 2020.

SSS4.11 – Responses of terrestrial biogeochemical cycles to climate change

EGU2020-8424 | Displays | SSS4.11

Linking microbial communities to soil carbon cycling under anthropogenic change using a trait-based framework

Ashish Malik, Robert Griffiths, and Steven Allison

Microbial physiology may be critical for projecting future changes in soil carbon. Still, predicting the ecosystem implications of microbial processes remains a challenge. We argue that this challenge can be met by identifying microbial life history strategies based on their phenotypic characteristics, or traits, and representing these strategies in models simulating different environmental conditions. By adapting several theories from macroecology, we define microbial high yield (Y), resource acquisition (A), and stress tolerance (S) strategies. Using multi-omics and carbon stable isotope probing tools, we empirically validated our Y-A-S framework by studying variations in community traits along gradients of resource availability and abiotic conditions arising from anthropogenic change. Across a Britain-wide land use intensity gradient, we used isotope tracing and metaproteomics to show that microbial resource acquisition and stress tolerance traits trade off with growth yield measured as carbon use efficiency. Reduced community growth yield with intensification was linked to decreased microbial biomass and increased biomass-specific respiration which subsequently translated into lower organic carbon storage in such soil systems. We concluded that less-intensive management practices have more potential for carbon storage through increased microbial growth yield by greater channelling of substrates into biomass synthesis. In Californian grass and shrub ecosystems, we used metatranscriptomics and metabolomics to infer traits of in situ microbial communities on plant leaf litter in response to long-term drought. This experimental set-up provided gradients of resource availability and water stress. We observed that drought causes greater microbial allocation to stress tolerance. The most discernable physiological adaptations to drought in litter communities were production or uptake of compatible solutes like trehalose and ectoine as well as inorganic ions to maintain cellular osmotic balance. Grass communities also increased expression of genes for synthesis of capsular and extracellular polymeric substances possibly as a mechanism to retain water. These results showed a clear functional response to drought in grass litter communities with greater allocation to survival relative to growth that reduced decomposition under drought. In contrast, communities on chemically complex shrub litter had smaller differences in gene expression and metabolite profiles in response to drought, suggesting that the drought stress response is constrained by litter chemistry which also reduces decomposition rates. Overall, our findings suggest trade-offs between drought stress tolerance, resource acquisition and growth yield in communities across different ecosystems. These empirical studies demonstrate how trade-offs in key microbial traits can have consequences on soil carbon decomposition and storage. We recommend the use of our Y-A-S framework in experimental and modelling studies to mechanistically link microbial communities to system-level processes.

How to cite: Malik, A., Griffiths, R., and Allison, S.: Linking microbial communities to soil carbon cycling under anthropogenic change using a trait-based framework, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8424, https://doi.org/10.5194/egusphere-egu2020-8424, 2020.

EGU2020-8695 | Displays | SSS4.11

Drought stress memory in filamentous soil fungi

Alexander Guhr

Drought is a common stressor for soil organisms. One adaptive mechanism is “stress priming”, the ability to cope with a severe stress (“triggering”) by retaining a memory from a previous mild stress event (“priming”). While plants have been extensively investigated for drought memory, only scare information is available for filamentous soil fungi and its implications for soil microbial communities. We investigated the potential for drought-induced stress priming on single species as well its effect on microbial communities in forest A-horizons. Batch experiments with 4 treatments were conducted: exposure to priming and/or triggering as well as non-stressed controls. A priming stress was caused by desiccation to pF 4. The samples were then rewetted and after a recovery time of up to 14 days triggered (pF 6). After triggering, microbial biomass and activity as well as microbial communities by rDNA sequencing were analysed.

Some filamentous fungi show the potential for drought-induced stress priming leading to increased survival rates and activity under severe stress events. Yet, the effect seems to be species specific with potentially high impact on composition and activity of microbial communities considering the expected increase of drought events. Especially receptive to stress priming seem to be species within the fungal classes Mortierellomycetes, Pezizomycetes, and Tremellomycetes. Shifts in the microbial community compositions could be observed in some cases in response to stress priming. In general, the nature of the response depends on the original composition of the microbial community and the occurrence of a subsequent triggering event. For example, species investing high amounts of resources into the primed state only prevail if a triggering occurs (especially noteworthy was Byssonectria fusispora).

How to cite: Guhr, A.: Drought stress memory in filamentous soil fungi, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8695, https://doi.org/10.5194/egusphere-egu2020-8695, 2020.

EGU2020-269 | Displays | SSS4.11

The magnitude of temperature increase matters: how will soil organic mineralization respond to future climate warming?

Jie Zhou, Yuan Wen, Lingling Shi, Michaela Dippold, Yakov Kuzyakov, Huadong Zang, Davey Jones, and Evgenia Blagodatskaya

The Paris climate agreement is pursuing efforts to limit the increase in global temperature to below 2 °C above pre-industrial level. The overall consequence of relatively slight warming (~2 °C), on soil C and N stocks will be dependent on microorganisms decomposing organic matter through release of extracellular enzymes. Therefore, the capacity of soil microbial community to buffer climate warming in long-term and the self-regulatory mechanisms mediating soil C and N cycling through enzyme activity and microbial growth require a detailed comparative study. Here, microbial growth and the dynamics of enzyme activity (involved in C and N cycling) in response to 8 years warming (ambient, +1.6 °C, +3.2 °C) were investigated to identify shifts in soil and microbial functioning. A slight temperature increase (+1.6 °C) only altered microbial properties, but had no effect on either hydrolytic enzyme activity or basic soil properties. Stronger warming (+3.2 °C) increased the specific growth rate (μm) of the microbial community, indicating an alteration in their ecological strategy, i.e. a shift towards fast-growing microorganisms and accelerated microbial turnover. Warming strongly changed microbial physiological state, as indicated by a 1.4-fold increase in the fraction of growing microorganisms (GMB) and 2 times decrease in lag-time with warming. This reduced total microbial biomass but increased specific enzyme activity to be ready to decompose increased rhizodeposition, as supported by the higher potential activitiy (Vmax) and lower affinity to substrates (higher Km) of enzymes hydrolyzing cellobiose and proteins cleavage in warmed soil. In other words, stronger warming magnitude (+3.2 °C) changed microbial communities, and was sufficient to benefit fast-growing microbial populations with enzyme functions that specific to degrade labile SOM. Combining with 48 literature observations, we confirmed that the slight magnitude of temperature increase (< 2 °C) only altered microbial properties, but further temperature increases (2-4 °C) was sufficient to change almost all soil, microbial, and enzyme properties and related processes. As a consequence, the revealed microbial regulatory mechanism of stability of soil C storage is strongly depended on the magnitude of future climate warming.

How to cite: Zhou, J., Wen, Y., Shi, L., Dippold, M., Kuzyakov, Y., Zang, H., Jones, D., and Blagodatskaya, E.: The magnitude of temperature increase matters: how will soil organic mineralization respond to future climate warming?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-269, https://doi.org/10.5194/egusphere-egu2020-269, 2020.

EGU2020-11631 | Displays | SSS4.11

Effect of forest soil warming on the rate and temperature sensitivity of microbial C and N processes in a temperate mountain forest

Carolina Urbina Malo, Ye Tian, Chupei Shi, Shasha Zhang, Marilena Heitger, Steve Kwatcho, Werner Borken, Jakob Heinzle, Andreas Schindlbacher, and Wolfgang Wanek

Despite the intensified efforts to understand the impacts of climate change on forest soil C dynamics, few studies have addressed the long term effects of warming on microbially mediated soil C and nutrient processes. In the few long-term soil warming experiments the initial stimulation of soil C cycling diminished with time, due to thermal acclimation of the microbial community or due to depletion of labile soil C as the major substrate for heterotrophic soil microbes. Thermal acclimation can arise as a consequence of prolonged warming and is defined as the direct organism response to elevated temperature across annual to decadal time-scales which manifest as a physiological change of the soil microbial community. This mechanism is clearly different from apparent thermal acclimation, where the attenuated response of soil microbial processes to warming is due to the exhaustion of the labile soil C pool.

The Achenkirch experiment, situated in the Northern Limestone Alps, Austria (47°34’ 50’’ N; 11°38’ 21’’ E; 910 m a.s.l.) is a long term (>15 yrs) soil warming experiment that has provided key insights into the effects of global warming on the forest soil C cycle. At the Achenkirch site, we have observed a sustained positive response of heterotrophic soil respiration and of soil CO2 efflux to warming after nine years (2013), making it an appropriate setting for testing hypotheses about continued or decreasing warming effects at decadal scales. We collected soil from six warmed and six control plots in October 2019, from 0-10 cm and 10-20 cm depth, and incubated them at three different temperatures: ambient, +4, and +10 °C. We measured potential soil enzyme activities with fluorimetric assays, gross rates of protein depolymerization, N mineralization, and nitrification with 15N isotope pool dilution approaches, and microbial growth, respiration, and C use efficiency (CUE) based on the 18O incorporation in DNA and gas analysis.  Our preliminary results show that potential enzyme activities of aminopeptidase, N-acetylglucosaminidase, b-glucosidase, and acid phosphatase were stimulated by decadal soil warming by 1.7- to 3.5-fold, measured at the same i.e. ambient temperature. In contrast, the temperature sensitivity (Q10) remained unaltered between warmed and control soils for all enzyme activities (Q10=1.63-2.28), except for aminopeptidase where we observed a decrease in Q10 by 25% in warmed topsoils (0-10 cm). Aminopeptidase also had the highest temperature-sensitivity (Q10=2.39), causing a decrease of the enzymatic C: N acquisition ratio with warming. These results indicate an increasing investment in microbial N acquisition with warming. We will follow these trends based on results on gross rates of soil C and N processes, allowing to delineate decadal soil warming effects on soil microbial biogeochemistry and to understand their effect on the cross-talk between organic C and N cycling in calcareous forest soils.

How to cite: Urbina Malo, C., Tian, Y., Shi, C., Zhang, S., Heitger, M., Kwatcho, S., Borken, W., Heinzle, J., Schindlbacher, A., and Wanek, W.: Effect of forest soil warming on the rate and temperature sensitivity of microbial C and N processes in a temperate mountain forest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11631, https://doi.org/10.5194/egusphere-egu2020-11631, 2020.

EGU2020-21256 | Displays | SSS4.11

The effect of drought on functional traits and diversity in Douglas Fir: snapshots before, during, and after the summer 2018 European drought event

Rosaleen March, Marjolein Paardekooper, Joris Timmermans, Celine Huisman, Manouk van der Aa, Qi Chen, Amie Corbin, and Peter van Bodegom

The summer of 2018 brought a record-breaking heat wave and record low rainfall, resulting in a severe drought in much of northern and central Europe. In the following year, precipitation increased but in many locations remained below average. A temporal study that began in 2017 in a temperate evergreen forest in the Netherlands allowed the opportunity examine the effects of this drought on functional traits before, during, and after the event. This gave us new trait-based insight into the resistance, resilience, and recovery abilities of the Douglas Fir to drought. During the growing season of 2017-2019, leaves were collected every 2-4 weeks. Functional traits were derived, including total chlorophyll, carotenoids, specific leaf area, and leaf dry matter content. Functional diversity metrics were also derived to examine response to drought. Using ANOVA to compare trait values during the same parts of the season, we found all traits showed significant changes at some point, but chlorophyll and carotenoids had the largest responses to the drought. Chlorophyll concentrations showed a continued decrease into 2019. Carotenoid concentration increased across the years, which has been shown to be an indication of plant stress. Though Douglas Fir has been considered drought resistant, this study reveals that the intensity of the 2018 drought had an impact on its traits and its resilience without sufficient soil moisture relief in the following year. Much attention has been paid to extreme events with climate change; however, it is these events paired with a lack of adequate recovery conditions that can push ecosystems past their tipping point.

How to cite: March, R., Paardekooper, M., Timmermans, J., Huisman, C., van der Aa, M., Chen, Q., Corbin, A., and van Bodegom, P.: The effect of drought on functional traits and diversity in Douglas Fir: snapshots before, during, and after the summer 2018 European drought event, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21256, https://doi.org/10.5194/egusphere-egu2020-21256, 2020.

Soil moisture and temperature collectively regulate the production and consumption of carbon in soils. With expected changes in both the soil thermal and hydrological regimes globally, experimental data on carbon turnover under these changes in contrasting ecosystems are important for constraining predictive models of soil carbon turnover. We investigated the effect of changes in soil water and temperature on heterotrophic respiration (Rh) and net methane uptake (MU) in soils from grassland ecosystems in Arctic, temperate and subtropical climates.
The temperature sensitivity of RH increased with decreasing mean annual temperature, but there was no indication of a site-specific response of Rh to changes in soil moisture. All sites displayed MU, primarily controlled by the soil water content with little temperature dependence. Thus, the optimum temperature for MU did not differ between sites despite the differences in the climate. However, the optimal soil water content for the relative maximum MU decreased with increasing mean annual temperature at the sites.
These results point to site-specific adaptation of the microbial community that governs the sensitivity of Rh to temperature, but not soil moisture and the dependency of MU to soil moisture alone. We would also like to discuss how this insight can be used to inform ecosystem models.

How to cite: Hessilt, T., Lyberth Hauptmann, D., and Riis Christiansen, J.: Response of heterotrophic respiration and oxidation of atmospheric CH4 to changes in soil moisture and temperature in drylands across a global climate and ecosystem gradient, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18064, https://doi.org/10.5194/egusphere-egu2020-18064, 2020.

EGU2020-3736 | Displays | SSS4.11

Modelling respiration pulses at rewetting as a stochastic process

Stefano Manzoni, Arjun Chakrawal, Thomas Fischer, Amilcare Porporato, and Giulia Vico

Respiration pulses at rewetting are prominent features of soil responses to soil moisture fluctuations. These pulses are much larger compared to respiration rates under constant soil moisture, pointing to variations in water availability as drivers of the enhanced CO2 production. Moreover, the respiration pulses tend to be larger when soil moisture before rewetting is lower. Thus, both the pre-rainfall soil moisture and the variation in soil moisture control the size of the respiration pulse. While these patterns are known from empirical studies, models have struggled to capture the relations between rainfall statistical properties (frequency of occurrence and rain event depths) and the occurrence and size of respiration pulses, framing the scope of this contribution. Specifically, we ask – how are the statistical properties of respiration pulses related to rainfall statistics?

Because rainfall can be regarded as a stochastic process generating variations in soil moisture, also respiration pulses at rewetting can be modelled through a probabilistic model. Here we develop such a model based on the premises that rainfall can be described as a marked Poisson process, and that respiration pulses increase with increasing variations of soil moisture (i.e., larger pulses after larger rain events) and decreasing pre-rain soil moisture (i.e., larger pulses after a long dry period). This model provides analytical relations between the statistical properties of soil respiration (e.g., long-term mean and standard deviation) and those of rainfall, allowing to study in a probabilistic framework how respiration varies along existing climatic gradients or in response to climatic changes that affect rainfall statistics.

Results show that the long-term mean CO2 production during respiration pulses increases with increasing frequency and depth of rainfall events. However, the relative contribution of respiration pulses to the total microbial respiration decreases with rainfall frequency and depth. Similarly, also the variability of the size of respiration pulses, as measured by their standard deviation, decreases with increasing rainfall frequency and depth. As a consequence, climatic changes exacerbating rainfall intermittency – longer dry periods and more intense rain events – are predicted to increase both the relative contribution of respiration pulses to total microbial respiration and the variability of the pulse sizes.

How to cite: Manzoni, S., Chakrawal, A., Fischer, T., Porporato, A., and Vico, G.: Modelling respiration pulses at rewetting as a stochastic process, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3736, https://doi.org/10.5194/egusphere-egu2020-3736, 2020.

EGU2020-776 | Displays | SSS4.11

Do microbial communities adapt to the temperature of their climate?

Daniel Tajmel, Carla Cruz Paredes, and Johannes Rousk

Terrestrial biogeochemical cycles are regulated by soil microorganisms. The microbial carbon release due to respiration and carbon sequestration through microbial growth determine whether soils become sources or sinks for carbon. Temperature i​s one of the most important environmental factors controlling both microbial growth and respiration. Therefore, to understand the influence of temperature on microbial processes is crucial. One strategy to predict how ecosystems will respond to warming is to use geographical ecosystem differences, in space-for-time (SFT) substitution approaches. We hypothesized (1) that microbes should be adapted to their environmental temperature leading to microbial communities with warm-shifted temperature relationships in warmer environments, and vice versa. Furthermore, we hypothesized  (2) that other factors should not influence microbial temperature relationships, and (3) that the temperature sensitivity of microbial processes (Q10) should be linked to the microbial temperature relationships.

 

In this project, we investigated the effects of environmental temperature on microbial temperature relationships for microbial growth and respiration along a natural climate gradient along a transect across Europe to predict the impact of a warming climate. The transect was characterized by mean annual temperature (MAT) ranging from - 4 degrees Celsius (Greenland) to 18 degrees Celsius (Southern Spain), while other environmental factor ranges were broad and unrelated to climate, including pH from 4.0 to 8.8, C/N ratio from 7 to 50, SOM from 4% to 94% and plant communities ranging from arctic tundra to Mediterranean grasslands. More than 56 soil samples were analyzed and microbial temperature relationships were determined using controlled short-term laboratory incubations from 0 degrees Celsius to 45 degrees Celsius. The link between microbial temperature relationship and the climate was assessed by using the relationship between the environmental temperature and indices for microbial temperature relationships including the minimum (Tmin), optimum (Topt) and maximum temperature (Tmax) for microbial growth as well as for respiration. To estimate the Tmin, Topt and Tmax the square root equation, the Ratkowsky model was used.

 

We found that microbial communities were adapted to their environmental temperature. The microbial temperature relationship was stronger for microbial growth than for respiration. For 1 degrees Celsius rise in MAT, Tmin increased 0.22 degrees Celsius for bacterial and 0.28 degrees Celsius for fungal growth, while Tmin for respiration increased by 0.16 per 1 degrees Celsius rise. Tmin was also found to be universally linked to Q10, such that higher Tmin resulted in higher Q10. Other environmental factors (pH, C/N ratio, SOM, vegetation cover) did not influence the temperature relationships. By incorporating the determined relationships between environmental temperature and microbial growth and respiration into large scale ecosystem models, we can get a better understanding of the influence of microbial adaptation to warmer climate on the C-exchange between soils and atmosphere.

How to cite: Tajmel, D., Cruz Paredes, C., and Rousk, J.: Do microbial communities adapt to the temperature of their climate?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-776, https://doi.org/10.5194/egusphere-egu2020-776, 2020.

EGU2020-11341 | Displays | SSS4.11

Does long-term soil warming affect microbial element limitation? A test by short-term assays of microbial growth responses to labile C, N and P additions

Chupei Shi, Carolina Urbina Malo, Ye Tian, Shasha Zhang, Marilena Heitger, Steve Kwatcho Kengdo, Werner Borken, Jakob Heinzle, Andreas Schindlbacher, and Wolfgang Wanek

Human activities have caused global warming by 0.95 °C since the industrial revolution, and average temperatures in Austria have risen by almost 2 °C since 1880. Increased global mean temperatures have been reported to accelerate carbon (C) cycling, but also to promote nitrogen (N) and phosphorus (P) dynamics in terrestrial ecosystems. However, the extent of warming-induced increases in soil C, N and P processes can differ, causing an eventual uncoupling of biogeochemical C, N and P cycles, and leading to altered elemental imbalances between available plant and soil resources and soil microbial communities. The altered dynamics in soil C and nutrient availability caused by increased soil temperature could shift the growth-limiting element for soil microorganisms, with strong repercussions on the decomposition, mineralization and sequestration of organic C and nutrients. The latter relates to the conservative cycling of limiting elements while elements in excess are mineralized and released at greater rates by microbial communities.

Despite the many laboratory and in situ studies investigating factors that limit soil microbial activity, most of them explored nutrient addition effects on soil respiration or soil enzyme activities. A critical assessment, however, clearly indicated the inappropriateness of these measures to deduce growth-limiting nutrients for soil microbes. Similar to studies of plant nutrient limitation, unequivocal assessment of soil microbial element limitation can only be derived from the response of microbial growth to element amendments. To our knowledge this has not been performed on soils undergoing long-term soil warming.

In this study, we therefore investigated the effect of long-term soil warming on microbial nutrient limitation based on microbial growth measurements in a temperate calcareous forest soil. Soil samples were taken from two soil depths (0-10, 10-20 cm) in both control and heated plots in the Achenkirch soil warming project (>15 yrs soil warming by + 4 °C). Soil samples were pre-incubated at their corresponding field temperature after sieving and removal of visible roots. The soils were amended with different combinations of glucose-C, inorganic/organic N and inorganic/organic P in a full factorial design, the nutrients being dissolved in 18O-water. After 24 hours of incubation, microbial growth was measured based on the 18O incorporation into genomic DNA. Nutrient (co)limitation was determined by comparing microbial growth responses upon C and nutrient additions relative to unamended controls. Basal respiration was also measured based on the increase in headspace CO2, allowing to estimate microbial C use efficiency (CUE). The fate of C and nutrient amendments was finally traced by measurements of inorganic and organic extractable and microbial biomass C, N and P. This study will thereby provide key insights into potential shifts in limiting nutrients for microbial growth under long-term soil warming, and into concomitant effects on soil C and nutrient cycles.

How to cite: Shi, C., Malo, C. U., Tian, Y., Zhang, S., Heitger, M., Kengdo, S. K., Borken, W., Heinzle, J., Schindlbacher, A., and Wanek, W.: Does long-term soil warming affect microbial element limitation? A test by short-term assays of microbial growth responses to labile C, N and P additions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11341, https://doi.org/10.5194/egusphere-egu2020-11341, 2020.

EGU2020-11362 | Displays | SSS4.11

Changes in soil warming effects on microbial C, N and P cycling across seasons in a temperate calcareous mixed forest

Ye Tian, Carolina Urbina Malo, Chupei Shi, Shasha Zhang, Marilena Heitger, Steve Kwatcho Kengdo, Werner Borken, Jakob Heinzle, Andreas Schindlbacher, and Wolfgang Wanek

Global warming may accelerate soil carbon (C) and nutrient cycling as higher temperatures accelerate soil microbial and enzymatic activities. However, this enhanced soil C cycling can diminish with time due to the depletion of labile soil C or due to thermal acclimation of soil microbes, while the increased N cycling may be dampened over time in N-rich soils. Moreover, soil climate as well as the quality and quantity of plant inputs change between seasons, which could influence the C: nitrogen (N): phosphorus (P) stoichiometry of resources available for microbes and thereby alter the warming effect on microbial activities and nutrient cycling between seasons. Such seasonal changes caused inconsistent warming effects on extracellular enzyme activities and on soil respiration in some experiments, with warming effects turning from positive to negative between seasons, yet the underlying controls of these adverse effects are far from being well understood. In this study, we therefore aimed to investigate soil warming and seasonal effects on soil C, N, and P pools and processes in a temperate calcareous mixed forest. We collected soil samples in spring, summer and fall (May, August, and October 2019) from a long-term (>15 yrs) soil warming experiment in Achenkirch, Northern Limestone Alps, Austria (47°34’ 50’’ N; 11°38’ 21’’ E; 910 m a.s.l.). The samples were incubated at the corresponding in-situ temperatures in the laboratory. Microbial growth, respiration and C use efficiency were determined by following 18O-H2O incorporation in DNA and by gas analysis. 15N pool dilution assays were applied to quantify gross rates of protein depolymerization, N mineralization, and nitrification, whilst gross rates of soil inorganic P mobilization were measured by a 33P pool dilution assay. Moreover, we measured the potential soil enzyme activities of four hydrolases and two oxidases, and determined contents of labile (extractable) and microbial biomass C, N, and P. This study will thereby provide a comprehensive insight into how soil warming influences soil microbial C, N, and P cycling in a temperate calcareous mixed forest as well as into their energetic, stoichiometric and soil microclimatic constraints. The long-term nature of this soil warming experiment will therefore allow predictions of the future biogeochemical behavior of calcareous forest soils, and deduce potential feed-backs on forest productivity, atmospheric composition and climate change.

How to cite: Tian, Y., Urbina Malo, C., Shi, C., Zhang, S., Heitger, M., Kwatcho Kengdo, S., Borken, W., Heinzle, J., Schindlbacher, A., and Wanek, W.: Changes in soil warming effects on microbial C, N and P cycling across seasons in a temperate calcareous mixed forest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11362, https://doi.org/10.5194/egusphere-egu2020-11362, 2020.

EGU2020-18383 | Displays | SSS4.11

The influence of short-term and long-term warming on physical soil carbon pools

Moritz Mohrlok, Victoria Martin, Niel Verbrigghe, Lucia Fuchslueger, Christopher Poeplau, Bjarni D. Sigurdsson, Ivan Janssens, and Andreas Richter

Soils store more carbon than the atmosphere and total land plant biomass combined. Soil organic matter (SOM) can be classified into different physical pools characterized by their degree of protection and turnover rates. Usually, these pools are isolated by dividing soils in different water-stable aggregate size classes and, inside these classes, SOM fractions with differing densities and properties: Stable mineral-associated organic matter (MOM) and labile particulate organic matter (POM). Increasing temperatures are known to initially enhance microbial decomposition rates, releasing C from soils which could further accelerate climate change. The magnitude of this feedback depends on which C pool is affected the most by increased decomposition. Since MOM, thought to be the best protected carbon pool, holds most of the soil C, losses from this pool would potentially have the biggest impact on global climate. Experimental results are inconclusive so far, as most studies are based on short-term field warming (years rather than decades), leaving the ecosystem response to decades to century of warming uncertain.

We made use of a geothermal warming platform in Iceland (ForHot; https://forhot.is/) to compare the effect of short-term (STW, 5-8 years) and long-term (LTW, more than 50 years) warming on soil organic carbon and nitrogen (SOC, SON) and its carbon and nitrogen isotope composition (δ13C and δ15N) in soil aggregates of different sizes in a subarctic grassland. OM fractions were isolated via density fractionation and ultrasonication both in macro- and microaggregates: Inter-aggregate free POM (fPOM), POM occluded within aggregates (iPOM) and MOM.

MOM, containing most of the SOC and SON, showed a similar response to warming for both macro- and microaggregates. Compared to LTW plots, STW plots overall had higher C and N stocks. But warming reduced the carbon content more strongly in STW plot than in LTW plots. δ13C of MOM soil increased with temperature on the STW sites, indicating higher overall SOM turnover rates at higher temperatures, in line with the higher SOC losses. For LTW, δ13C decreased with warming except for the most extreme treatment (+16°C). Warming duration had no impact on iPOM-C. fPOM-C decreased in STW sites with increasing temperature, while it increased on the LTW sites.

Overall our results demonstrate warming-induced C losses from the MOM-C-pool, thought to be most stable soil carbon pool. Thus, warming stimulated microbes to decompose both labile fPOM and more stable MOM. After decades of warming, C losses are less pronounced compared to the short-term warmed plots, pointing to a replenishment of the carbon pools at higher temperatures in the long-term. This might be explained by adaptations of the primary productivity and/or substrate-limitation of microbial growth.

 

How to cite: Mohrlok, M., Martin, V., Verbrigghe, N., Fuchslueger, L., Poeplau, C., Sigurdsson, B. D., Janssens, I., and Richter, A.: The influence of short-term and long-term warming on physical soil carbon pools , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18383, https://doi.org/10.5194/egusphere-egu2020-18383, 2020.

EGU2020-7551 | Displays | SSS4.11

Effects of long-term soil warming on nitrogen fluxes in forest soils

Erich Inselsbacher, Jakob Heinzle, and Andreas Schindlbacher

Forests are the main contributors to the global terrestrial carbon (C) sink but several studies suggest that global warming could significantly reduce their CO2 mitigation potential. The capacity of forest plants to sequester C is closely linked to soil nitrogen (N) availability, a major control of plant growth and ecosystem functioning. An increase of soil temperature caused by global change is critically affecting soil N supply rates, both directly by increasing diffusive N fluxes in the soil solution and indirectly by accelerating soil N turn-over rates. In recent short-term laboratory incubation studies, an increase in soil temperature has not only led to a significant increase in diffusive N fluxes but also to a concomitant shift in N quality available for plant uptake towards a higher portion of inorganic N forms compared to small organic N forms such as amino acids. However, until now long-term effects of soil warming on soil N fluxes have not been studied. Here, we present first results from a study on soil N availabilities at the long-term soil warming experimental site Achenkirch (Austria) in the Limestone Alps. This site is one of the few in situ climate manipulation experiments operational for more than 10 years and has already provided a wealth of novel insights into the potential effects of global warming on forest ecosystem responses. Applying in situ microdialysis, we estimated diffusive fluxes of inorganic N and amino acids along the growing season in soils warmed by resistance heating cables since 2005 (+4 °C compared to control plots) and control soils. Fluxes of all N forms were highly variable within each subplot (2 x 2 m) and reflected the high heterogeneity of soils at this forest site. Interestingly, fluxes of amino acids were less variable than of nitrate or ammonium throughout the year, indicating comparably stable protein depolymerization rates. In summary, long-term soil warming affected diffusive N fluxes but less than other factors operating on smaller (< 1 cm) scales.

How to cite: Inselsbacher, E., Heinzle, J., and Schindlbacher, A.: Effects of long-term soil warming on nitrogen fluxes in forest soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7551, https://doi.org/10.5194/egusphere-egu2020-7551, 2020.

EGU2020-19555 | Displays | SSS4.11

The impacts of long-term, high intensity N addition on the chemical composition of soil organic matter in a boreal forest

Shun Hasegawa, John Marshall, Torgny Näsholm, and Mark Bonner

The intense use of fertilisers for agricultural and forest management purposes as well as atmospheric nitrogen (N) deposition has changed ecosystem stoichiometry in some parts of the planet, drawing great attention to the long-term impacts of N additions on carbon (C) sequestration. Soil organic matters (SOMs) are the major sink of C in terrestrial ecosystems and hence it is essential to understand the impacts of N addition on SOM not only quantitatively but also qualitatively. In temperate and boreal forests, chronic N addition generally suppresses SOM decomposition and increases C accumulation. The potential mechanisms for this have long been discussed and yet to be unearthed.

Here, we examined the impacts of long-term N addition on the chemical composition of SOMs in boreal forests situated in northern Sweden under two vegetation types (Norway spruce or Scots pine) and a range of N addition regimes where N addition rates varied between 3 and 70 kg N ha-1 year-1, duration between 12 and 32 years and total added amount between 50 and 2000 kg N ha-1. Soil samples were collected from the organic layer (litter and humus layers) and analysed for the chemical composition of SOMs using two metrics: pyrolysis gas chromatography–mass spectrometry (GC/MS) and solid-state 13C nuclear magnetic resonance spectroscopy (13C-NMR).

We found that the chemical composition of SOMs shifted with soil C:N ratios regardless of vegetation types, or duration and rates of N addition. Preliminary results suggest that the observed shift in chemical composition in SOMs may have been attributed to altered decomposition of lignin and carbohydrate-derived compounds. This was in line with previous research conducted in the same study sites that demonstrated added-N enhanced non-enzymatic brown-rot lignin oxidation relative to enzymatic white-lot lignin mineralisation. Here, the comprehensive examination of SOM chemical composition demonstrates altered molecular characteristics of SOMs with soil C:N conditions. This may help us to elucidate the mechanisms by which N addition alters the balance of decomposition and accumulation of SOMs.

How to cite: Hasegawa, S., Marshall, J., Näsholm, T., and Bonner, M.: The impacts of long-term, high intensity N addition on the chemical composition of soil organic matter in a boreal forest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19555, https://doi.org/10.5194/egusphere-egu2020-19555, 2020.

EGU2020-18405 | Displays | SSS4.11

Using N2O to detect if a tipping point has been crossed in tropical soils after droughts

Simone Kilian Salas, Elisa Díaz García, Alberto Andrino, Katharina H. E. Meurer, Diana Boy, Marcus Horn, Jens Boy, and Hermann Jungkunst

The western Amazon is particularly sensitive to drought since precipitation is common even during "dry season". The combination of increasing land use pressure and droughts due to climate change makes the scenario of this ecosystem likely to cross or having crossed tipping points. We argue that nitrous oxide (N2O) emissions can be used to identify the crossing of tipping points in soils, particularly those related to N-cycling. This hypothesis is being tested within the BMBF funded Project PRODIGY, which will show that under stress microbial functional diversity in soils are a safety-net for ecosystems. The survey area (MAP) spreads across three countries (Peru, Brazil and Bolivia). Lab and field experiments are used to test our hypothesis based on the observations that N2O emission under tropical pasture shift after 10 years in use. Pre-measurement modeling is used to optimize measurement designs. Replicated above-ground biodiversity levels (n=4) will be sampled in each country. The soil will also be used for lab drought manipulation experiments to unravel underlying mechanisms. Measured values have shown to be lower than expected and simulated rates. Maybe because tipping points at different spacial and temporal scales are crossed faster than in temperate regions and biogeochemistry is less understood? Results from this investigation will allow the improvement of N2O models for tropical soils.

How to cite: Kilian Salas, S., Díaz García, E., Andrino, A., Meurer, K. H. E., Boy, D., Horn, M., Boy, J., and Jungkunst, H.: Using N2O to detect if a tipping point has been crossed in tropical soils after droughts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18405, https://doi.org/10.5194/egusphere-egu2020-18405, 2020.

EGU2020-10376 | Displays | SSS4.11

Effects of a simulated drying-rewetting cycle on microbial activity in soils degraded by post-fire erosion

Elena Fernández Boy, M. Belén Herrador, Violeta Ordoñez, Laura Morales, Oscar González-Pelayo, Jan Jacob Keizer, and María T. Domínguez

Large forest fires are expected to occur more frequently in some areas in the Iberian Peninsula with the current climate change predictions. Post-fire soil erosion is an important issue because of its potential large impact on soil carbon stocks and functioning. Addition of mulching to burnt soils has been proved as an effective measure to reduce post-fire erosion. This measure could also increase the stability of microbial activity to drought events, which are also expected to be more frequent in the region.

This study analyzes the response of three measurements of soil microbial activity (dehydrogenase activity, respiration rates and DNA concentration, as an index of microbial biomass) to a drying-rewetting cycle in soils that were burnt during large wildfires and that have been treated with different mitigation measures to prevent post-fire erosion.

Soil samples were collected from two field experiments on post-fire mitigation in Portugal, one in a Maritime Pine plantation over a Humic cambisol and one in a Strawberry tree stand over a Umbric leptosol. These sites were affected by large wildfires in june and october 2017, respectively. At the pine site, three treatments were compared: 1) control plots, where no treatment was applied and post-fire erosion rates were highest; 2) SM plots (Spontaneuos Mulching), in which spontaneous needle cast from the scorched pine crowns occurred (at an average rate of 0.5 kg m-2); 3) HM plots (Human Mulching), in which pine needles (were applied manually at a rate of 0.2 kg m-2. In addition, a nearby unburned Maritime Pine plantation was sampled (Unburnt). At the Strawberry tree site, control plots were compared with plots mulched with wheat straw (WM) at an application rate of 0.2 kg m-2. Sampling involved the organic surface horizon as well as the upper 15 cm of the Ah horizon.

Samples were preincubated during 28 days at 25°C and at 70% of field capacity. Afterwards, they were divided into two sets; one set was subjected to a drought event for 30 days that reduced soil moisture contents to 5-10% of field capacity. Subsequently, the drought replicates were rehydrated until they reached their initial moisture content, which was maintained for 14 days.

Dehydrogenase activity differed significantly between the burnt and unburnt soils, both for the drying and the re-wetting period. The burnt soils generally were more vulnerable to the drought episode than the unburnt soil. By contrast, dehydrogenase activity did not reveal significant impacts of the different mulching treatments compared to the untreated burnt soils. This was the case for both the organic surface horizon and the subsurface horizon. Respiration rates and DNA concentrations revealed basically the same results.

The three indicators of microbial activity studied here discriminated between burnt and unburnt soils, but they did not suggest any significant improvement in the response to drought by any of the post-fire emergency stabilization measures. Further research on the impacts of such measures on the resistance and resilience of microbial activity to drought should consider other soil quality indicators such as labile organic matter fractions.

How to cite: Fernández Boy, E., Herrador, M. B., Ordoñez, V., Morales, L., González-Pelayo, O., Keizer, J. J., and Domínguez, M. T.: Effects of a simulated drying-rewetting cycle on microbial activity in soils degraded by post-fire erosion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10376, https://doi.org/10.5194/egusphere-egu2020-10376, 2020.

EGU2020-1180 | Displays | SSS4.11

Effects of simulated drought and warming on microbial responses to drying and rewetting in contrasting land-uses

Ainara Leizeaga, Lettice C. Hicks, Albert C. Brangarí, Menale Wondie, Hans Sandén, and Johannes Rousk

Climate change will increase temperatures and the frequency and intensity of extreme drought and rainfall events. When a drought period is followed by a rainfall event, there is a big CO2 pulse from soil to the atmosphere which is regulated by soil microorganisms. In the present study, we set out to investigate how simulated drought and warming affects the soil microbial responses to drying and rewetting (DRW), and how those responses will interact with the level of land degradation. Previous work has shown that exposure DRW cycles in the laboratory and in the field can induce changes in the microbial community such that it resumes growth rates faster after a DRW cycle. In addition, it has been observed that a history of drought in both a humid heathland ecosystem in Northern Europe and in semi-arid grasslands in Texas can select for microorganisms with a higher carbon use efficiency (CUE) during DRW. In this study we tested if these observations could be extended to subtropical environments.

Rain shelters and open top chambers (OTC) were installed in Northwestern Ethiopia in two contrasting land-uses; a degraded cropland and a pristine forest. Soils were sampled (>1-year field treatments) and exposed to a DRW cycle in the laboratory. Microbial growth and respiration responses were followed with high temporal resolution over 3 weeks. We hypothesized that (i) simulated drought would result in more resilient and efficient microbial communities to DRW, while (ii) simulated warming should leave microbial community traits linked to moisture unchanged. In addition, (iii) we hypothesized that microbial communities would recover growth rates faster in the cropland since that ecosystem is more prone to DRW events.

Microbial responses in both land-uses and treatments universally showed a highly resilient type of community response with both bacterial growth and fungal growth increasing immediately upon rewetting, linked with the expected respiration pulse. The field treatments simulating drought and warming did not affect the already high resilience of soil microbial communities to DRW cycles. However, differences between the rates of recovery between fungi and bacteria were observed. Fungal growth recovered faster than bacterial growth, peaking c. 15 h in comparison to bacteria that peaked at c.20h after rewetting. Simulated drought reduced the microbial CUE during rewetting in croplands without affecting the forest soils. The CUE was also elevated in the warming treatments in both land-uses, and generally higher in croplands than in forest soils. Taken together, the responses in microbial CUE during the rewetting of dry soils were likely linked to either (i) differences in resource availability which were higher in warming treatments and in croplands compared to forests, or (ii) selection of  more efficient microbial communities due to a higher exposure to DRW events driven by the higher temperatures in the cropland, and increased evapotranspiration in the warming treatments.

 

How to cite: Leizeaga, A., Hicks, L. C., Brangarí, A. C., Wondie, M., Sandén, H., and Rousk, J.: Effects of simulated drought and warming on microbial responses to drying and rewetting in contrasting land-uses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1180, https://doi.org/10.5194/egusphere-egu2020-1180, 2020.

EGU2020-20220 | Displays | SSS4.11

Current knowledge and future perspectives on soil drying and rewetting, by the scientific community

Albert C. Brangarí, Lettice Hicks, Ainara Leizeaga, and Johannes Rousk

Drying and rewetting events induce enormous dynamics in soil biogeochemistry, known as the “Birch effect”. A series of laboratory studies have shown that during this phenomenon, respiration and microbial growth are uncoupled. In addition, it has been found that soil microorganisms exhibit one of two different response-patterns, the dynamics of which are strongly regulated by the harshness of the moisture disturbance experienced by soil microbes. Despite the potential significance of these responses for the global carbon cycle, the characteristics and mechanisms underlying them are still unclear.

In order to shed some light on the current status of research in this field, we will present the outcomes of an international workshop organized in Lund in November 2019. During it, we integrated researchers from different environments in order to identify knowledge-gaps and tackle outstanding and new challenges in this field. We will review the characteristics of the growth and respiration responses to moisture fluctuations and the putative mechanisms and factors governing them. We will also discuss the advantages of combining empirical and modelling approaches by using our own group experience as a case example.

How to cite: Brangarí, A. C., Hicks, L., Leizeaga, A., and Rousk, J.: Current knowledge and future perspectives on soil drying and rewetting, by the scientific community, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20220, https://doi.org/10.5194/egusphere-egu2020-20220, 2020.

EGU2020-16648 | Displays | SSS4.11

Is microbial resilience to drying-rewetting driven by selection for quick colonizers?

Lettice Hicks, Simon Lin, and Johannes Rousk

Climate change is exposing terrestrial ecosystems to more extreme drought and rainfall events, resulting in an increased frequency and intensity of drying-rewetting (D/RW) events in soils. Rewetting a dry soil induces enormous dynamics in both microbial growth and biogeochemistry, including a large pulse of COrelease to the atmosphere. Upon D/RW, two different microbial growth responses have been identified; a more resilient response where bacteria start growing immediately with a quick recovery after rewetting and a less resilient response where there is a lag-period of up to 30 hours of near-zero growth before bacteria start to grow. The resilience of microbial growth following D/RW has important implications for the ecosystem C budget, since an extended lag-period of no growth during a time of high COrelease will result in net soil C loss. In natural systems, it has been found that a legacy of drought led to a more resilient bacterial growth response upon rewetting, with a reduced lag-period before the onset of growth. Exposing soils to repeated cycles of D/RW in the laboratory has also been shown to shift bacterial growth responses to a more resilient type. We hypothesised that this shift in response is explained by selection for a microbial community which is quick at colonizing the labile C resources made available upon D/RW.  

In order to test our hypothesis, we pre-treated soils by exposing them to either (i) three cycles of D/RW, (ii) three pulses of glucose addition or (iii) three pulses of litter addition. The substrate additions were used to simulate the labile C release in soils during D/RW, thereby enabling us to investigate if the colonization of new substrate is the causal mechanism explaining the observed shift in bacterial resilience in soils with a history of D/RW. The pre-treated soils – along with an unamended control soil – were then exposed to the same D/RW event, with bacterial growth, fungal growth and respiration responses measured at high temporal resolution over 4 days. As previously reported, exposing the soil to a series of D/RW events resulted in a more resilient bacterial growth response, with the lag-period reduced from ca. 30 hours to an immediate initiation of growth. Pre-treating the soils with glucose reduced the lag-period before the onset of bacterial growth by ca. 50% whereas pre-treatment with litter induced only a marginally (< 10%) more resilient bacterial growth response to D/RW. Interestingly, pre-treatment of the soils with glucose and litter both induced a more resilient fungal growth response, with the responses resembling the shift in fungal resilience induced by exposing the soils to repeated cycles of D/RW. Overall, our results show that selection for quick colonizers partly explains the shift to more resilient microbial growth in soils exposed to repeated D/RW events, but further investigation is required to identify additional factors contributing to the shift in resilience.

How to cite: Hicks, L., Lin, S., and Rousk, J.: Is microbial resilience to drying-rewetting driven by selection for quick colonizers? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16648, https://doi.org/10.5194/egusphere-egu2020-16648, 2020.

The influence of drought on terrestrial carbon cycling has received great attention because of the increasing frequency of extreme drought events in climate scenarios. In the CLIMAITE experiment, we have exposed plots to reduced precipitation since 2006. During the first years, precipitation was only reduced for 4-6 weeks during spring/early summer. In order to increase our focus on finding thresholds for functional and structural change in the ecosystem, the experiment was redesigned towards more extreme manipulations in June 2016 using a new gradient design continuously removing 40, 50, and 66% of ambient precipitation with permanent rainout shelters.

Rates of net ecosystem exchange (NEE), ecosystem respiration (RE) and soil respiration (Rs) are measured inside treatment plots using an LI-6400 connected to a custom-built 210L transparent chamber (for NEE) that can be darkened (for RE) as well as a 1L dark chamber (for Rs). In addition, environmental variables such as soil temperature, precipitation, soil water content and photosynthetically active radiation (PAR) are recorded continuously at the plot or site level. In addition, soil cores from the different treatments will be collected and analyzed for soil substrate (e.g. soil organic carbon) and incubated in the lab for analysis of Q10.  Using the observations from the field and the lab together we will develop a new multiple regression model to fit the CO2 fluxes under severe precipitation removal treatments.

 

To obtain more reliable and accurate estimates of the seasonal and annual responses of soil carbon flux exchange under precipitation change scenarios, the change in soil water content and temperature, the soil substrate availability as well as the variation of the frequency and timing of precipitation events are included in the carbon flux model. The fitting of models to the observational data will reveal if functional/structural thresholds for the carbon exchange have been exceeded in the ecosystem, thus providing novel experimental and modeling evidence for such thresholds.

How to cite: Li, Q., Larsen, K. S., and Gundersen, P.: Long-term effects of precipitation removal manipulations on soil carbon balance and exchange in a Danish heathland/grassland ecosystem, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13404, https://doi.org/10.5194/egusphere-egu2020-13404, 2020.

EGU2020-12125 | Displays | SSS4.11

Exploring The Birch Effect In The Subsurface Using Diffusive Soil Probes

Joseph Roscioli, Joanne Shorter, Jordan Krechmer, Laura Meredith, and Juliana Gil Loaiza

Soil gases are efficient messengers of the subsurface biogeochemical processes that underlie important nutrient cycles.  Recent advances in subsurface gas sampling techniques can be combined with high precision trace gas instrumentation to yield novel insights into these processes and their mechanisms.

We present measurements of a wide range of trace gases before, during, and after a simulated rainfall upon northeastern US temperature forest soil in meso-scale columns.  Subsurface concentrations and above-ground fluxes of N2O and its isotopes, CH4 and its isotopes, CO2, NO, NO2, NH3, and a wide range of volatile organic compounds (e.g. monoterpenes, sesquiterpenes, isoprene, acetonitrile, aromatics) were quantified in real time with 30 minute temporal resolution.  Small molecules were measured using Aerodyne TILDAS instruments, while VOCs were measured using a Vocus mass spectrometer.

Addition of water to the dried soil column produced a classic Birch effect pulse of both C and N species, including for VOCs.  We explore correlations between responses of trace gases above- and below-ground, and relate the small molecule pulses to the larger VOC responses.  In addition, we demonstrate the value of isotopic signatures for these studies, with the observation of fast, large isotopic shifts in the 15N2O isotopomers.  We compare these isotopic signatures to simple kinetic models to provide insight into the mechanisms underlying the nitrogen Birch effect.

How to cite: Roscioli, J., Shorter, J., Krechmer, J., Meredith, L., and Gil Loaiza, J.: Exploring The Birch Effect In The Subsurface Using Diffusive Soil Probes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12125, https://doi.org/10.5194/egusphere-egu2020-12125, 2020.

EGU2020-12151 | Displays | SSS4.11

Effect of Drought and Recovery on Microbial, Fungal, and Crop Response in a Diverse Multi-Crop Rotation

Songul Senturklu, Douglas Landblom, and Joshua Steffan

Soil nutrient availability is essential for adequate crop production and drought conditions that result in abnormally low amounts of precipitation for extended periods of time have a substantial impact on soil microbial activity and therefore nutrient cycling. The northern Great Plains region of the USA suffered an extended period of time in which effective precipitation for crop production was severely reduced and based on the USA Drought Monitor the drought during the growing season from April through October 2017 was classified as exceptional drought. At the NDSU – Dickinson Research Extension Center, a long-term integrated system that includes a diverse multi-crop rotation (spring wheat, cover crop, corn, pea-barley intercrop, and sunflower), beef cattle grazing of the pea-barley, corn, and a 13-specie cover crop within the rotation, is being utilized to monitor the effects soil microbial and fungal activity have on production over time and space in this crop and animal production system. Moreover, the overall effects of increased soil health indices on production are being monitored. Research results have previously been reported showing that soil organic matter (SOM) mineralization has resulted in reduced nitrogen fertilizer application. Regression analysis of SOM and potential nitrogen mineralization suggests that 8.4 mg N/kg are mineralized for each 1% increase in SOM. However, during periods of restricted precipitation on rain-fed crops, soil microbial respiration and fungal activity are negatively impacted, and crop production and animal grazing days are sharply reduced. Soil microbial biomass was correlated to overall production with the exception of spring wheat in rotation which may be due to increased water use by the previous crop (sunflower). Further analysis indicated that most soil microbial organisms recovered two years post drought with the exception of Rhizobia spp. populations which did not recover two years post drought. However, compared to the pre-drought 2016 production year, overall crop production yields had not fully recovered by 2019. Compared to the 2016 crop production, overall crop production in the rotation was reduced 64% in 2017, recovered to 54% of 2016 in 2018, and recovered to 66% of 2016 by the 2019 crop year. Whether crop yields are on par with 2016 by the end of the 2020 crop year is still to be determined. These yield observations point to the amount of time needed to fully recover from the long-term effects of exceptional drought on crop production.

How to cite: Senturklu, S., Landblom, D., and Steffan, J.: Effect of Drought and Recovery on Microbial, Fungal, and Crop Response in a Diverse Multi-Crop Rotation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12151, https://doi.org/10.5194/egusphere-egu2020-12151, 2020.

EGU2020-20312 | Displays | SSS4.11

Vaccinium vitis-idaea decreases the dependence of alpine soil properties from soil moisture

Mikhail Makarov, Tatiana Malysheva, Maksim Kadulin, and Rida Sabirova

Climatic and plant community changes are observed in the alpine belt of the Teberda Reserve (the Northwest Caucasus) in the last decades. Increase of average monthly temperature in the summer months in 2006-2018 was 1.8-2.2 ºC in comparison with 1966-1990. For the last 13 years, the maximum temperature in July and August reached 22.1-23.2 ºC vs. 20.5 ºC in 1966-1990, and minimum temperature during these months did not fall lower than -1.8 ºC whereas in 1966-1990 it fell up to -7.0 ºC. At the same time decrease of summer precipitation, especially in July and August is observed (average 80-100 mm per month vs. 150-160 mm in 1966-1990). Against this climatic background, a significant increase of dwarf shrub with ericoid mycorrhizal symbiosis (Vaccinium vitis-idaea) occurs in plant community of alpine lichen heath. As ericoid mycorrhiza is characterized by high enzymatic activity capable to transform and mobilize soil organic matter, we assume that the appearance of Vaccinium vitis-idaea in grass ecosystems can change soil properties. Simultaneously the observed tendency to decrease the amount of summer atmospheric precipitation in mountain regions can change soil moisture which is also highly important to control soil microbial activity and organic matter transformation.

The properties of the mountain-meadow soil of the alpine lichen heath, characterizing labile forms of carbon, nitrogen and phosphorus, as well as biological activity at different soil moisture and in the presence or absence of Vaccinium vitis-idaea in the plant community, have been studied. It has been shown that under V. vitis-idaea soil is characterized by greater acidity and less responsive to changes in soil moisture. Differences in properties in the presence and absence of V. vitis-idaea are predominantly determined by the expressed response of the soil to changes in moisture in the absence of dwarf shrub. Under herbal vegetation, when soil moisture decreases, concentrations of inorganic nitrogen, activity of N-mineralization and nitrification, microbial biomass and soil respiration decrease, but concentrations of labile organic carbon and nitrogen, and enzymatic activity increase. Such changes indicate a shift in organic matter transformation from mineralization to depolymerization, more characteristic of ectomycorrhizal and ericoid mycorrhizal dominated ecosystems. Thus, both factors (soil moisture and invasions of ericoid mycorrhizal plant species) should be taken into account in predicting changes of alpine ecosystems functioning.

This study was supported by Russian Science Foundation (16-14-10208).

How to cite: Makarov, M., Malysheva, T., Kadulin, M., and Sabirova, R.: Vaccinium vitis-idaea decreases the dependence of alpine soil properties from soil moisture, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20312, https://doi.org/10.5194/egusphere-egu2020-20312, 2020.

Beef cattle grazing, soil microbial respiration, and Rhizobia spp. populations serve important roles in soil nutrient cycling and during periods of drought, when abnormal precipitation declines, forage production for animal grazing and performance are negatively impacted. Soil nutrient availability is essential for adequate crop production and extended drought reduces soil microbial activity and therefore nutrient cycling. During the 2017 growing season between April and October in the northern Great Plains region of the USA, effective precipitation for crop production and animal grazing was severely reduced due an exceptional drought as classified by the US Drought Monitor. At the NDSU – Dickinson Research Extension Center, Dickinson, North Dakota, USA, a long-term integrated system that includes yearling steer grazing within a diverse multi-crop rotation (spring wheat, cover crop, corn, pea-barley intercrop, and sunflower). Within the rotation of cash and forage crops, beef cattle graze the pea-barley, corn, and cover crop (13-specie) within the rotation and is being utilized to monitor the effects of animal, microbial and fungal activity over time and space in the crop and animal production system. Nitrogen fertilizer has been replaced in the system by soil microbial and fungal activity (Potential Mineralizable Nitrogen: 8.4 mg N/kg) such that for each 1% increase in SOM there is a corresponding increase of 18.8 kg of potential nitrogen mineralized per ha. Animal grazing days are severely reduced when precipitation is inadequate for soil microbial respiration to occur. What is even more concerning, when relying on microbial activity to supply plant nutrients, is recovery time for microbial activity to fully recover from exceptional drought as was the case in this research project. Compared to the 2016 crop production year that preceded the 2017 drought, cover crop (13-specie), pea-barley, and corn yields were reduced 86, 33, and 64% during the 2017 drought. This decline in crop production reduced the number of days of grazing by an average 50% and average daily gains were also reduced. Steer average daily gains were 1.05 0.95, and 0.83 kg/steer/day in 2017 when grazing pea-barley, corn, and cover crop, respectively. For this research that relies on soil derived plant nutrients soil analysis for microbial and Rhizobia spp. biomass began recovery in 2018 and continued into 2019 as evidenced by large percentage increases in organism biomass; however, complete production recovery did not occur by the end of the 2019 grazing season in which days of grazing were reduced compared to the 2016 grazing season. Biological animal, crop, microbial, fungal, and nutrient replacement recovery will be presented in the poster.

How to cite: Landblom, D. and Senturklu, S.: Effect of Drought and Recovery on Grazing Animal, Microbial, and Fungal Response in a Diverse Multi-Crop Rotation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20195, https://doi.org/10.5194/egusphere-egu2020-20195, 2020.

Changes in climate and land-use are altering soil respiration patterns and thus affecting C sequestration rates globally. This study aims to understand the effect of revegetation induced land-use change on the response of soil respiration to precipitation pulses during an extreme-drying-and-rewetting period. Soil respiration (SR) in cropland, grassland, shrubland, and orchard were intensively monitored along with environmental variables during an extreme drought period with precipitation pulse on China’s Loess Plateau. SR was strongly correlated to soil water content for all land-uses. However, the relationship was highly dependent on land-use types: SR was only strongly suppressed in cropland and orchard when moisture content exceeded 10.8% and 13.7%, respectively, whereas no clear suppression was observed under other land-uses. As a result, the C loss in grassland and shrubland was 49.1-78.9% higher than in cropland following significant precipitation events. In addition, SR was negatively and weakly correlated with soil temperature, indicating the change in the dominant control on SR due to extreme drought. Land-use change alters the response of soil respiration to soil moisture during extreme-drying-and-rewetting periods in this revegetated ecosystem. Its effect on respiration pulses will amplify as extreme climate events increase in the future, which may potentially alter the existing C balance.

How to cite: Sun, W.: Revegetation modifies patterns of temporal soil respiration responses to extreme-drying-and-rewetting in a semiarid ecosystem, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6591, https://doi.org/10.5194/egusphere-egu2020-6591, 2020.

EGU2020-4454 | Displays | SSS4.11

Climatological study of the Boundary-layer air Stagnation Index for China and its relationship with air pollution

Qianqian Huang, Xuhui Cai, Jian Wang, Yu Song, and Tong Zhu

The Air Stagnation Index (ASI) is a vital meteorological measure of the atmosphere’s ability to dilute air pollutants. The original metric adopted by the US National Climatic Data Center (NCDC) is found to be not very suitable for China, because the decoupling between the upper and lower atmospheric layers results in a weak link between the near-surface air pollution and upper-air wind speed. Therefore, a new threshold for the ASI–Boundary-layer air Stagnation Index (BSI) is proposed, consisting of daily maximal ventilation in the atmospheric boundary layer, precipitation, and real latent instability. In the present study, the climatological features of the BSI are investigated. It shows that the spatial distribution of the BSI is similar to the ASI; that is, annual mean stagnations occur most often in the northwestern and southwestern basins, i.e., the Xinjiang and Sichuan basins (more than 180 days), and least over plateaus, i.e., the Qinghai–Tibet and Yunnan plateaus (less than 40 days). However, the seasonal cycle of the BSI is changed. Stagnation days under the new metric are observed to be maximal in winter and minimal in summer, which is positively correlated with the air pollution index (API) during 2000–2012. The correlations between the BSI and the concentration of fine particulate matter (PM2.5) during January 2013 and November to December in 2015–2017 of Beijing are also investigated. It shows that the BSI matches the day-by-day variation of PM2.5 concentration very well and is able to catch the haze episodes.

How to cite: Huang, Q., Cai, X., Wang, J., Song, Y., and Zhu, T.: Climatological study of the Boundary-layer air Stagnation Index for China and its relationship with air pollution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4454, https://doi.org/10.5194/egusphere-egu2020-4454, 2020.

SSS4.13 – Soil biodiversity and microbial turnover

EGU2020-6545 | Displays | SSS4.13

Soil fauna regulates the ecosystem service/disservice balance in mulched soils

Christine van Capelle, Friederike Meyer-Wolfarth, Torsten Meiners, Mignon Sandor, and Stefan Schrader

A sustainable agricultural management can contribute to promoting soil biodiversity performance, thereby preserving soil functions and ensuring the provision of soil biota-induced ecosystem services. In order to make the best possible use of these services for the benefit of agricultural production, a better understanding of interlinkages between management measures, ecosystem service/disservice balance and soil self-regulation potential is essential. In this context, it is well known that the reduction of soil tillage intensity combined with mulching techniques, on the one hand, promote the survival, development and spread of plant pathogenic mycotoxin-producing soil-borne fungi, but, on the other hand, enhance the diversity of antagonistic mycotoxin-degrading fungivorous soil animals. However, up to now it is still unclear, which ecosystem service/disservice balance results from both pathways and which self-regulation mechanisms are involved.

 

To analyse and assess the bioregulation potential of fungivorous soil faunal key species (earthworms: Lumbricus terrestris, collembolans: Proisotoma minuta, enchytraeids: Enchytraeus crypticus and E. christenseni) on economically relevant plant pathogenic species of the fungal genus Fusarium (F. graminearum, F. culmorum, F. verticillioides) and its mycotoxins (deoxynivalenol (DON), zearalenon (ZEN), 3-acetyl-deoxynivalenol (3AcDON) and fumonisin B1 (FB1)) in maize residues, field and laboratory experiments were performed as part of the EU BiodivERsA project SoilMan. Based on these studies the following hypotheses were tested: (1) soil faunal key organisms supress Fusarium species and reduce their mycotoxins in maize residues, (2) the bioregulation potential depends on substrate size and soil texture (3) interactions between fungivorous key species affect their bioregulation potential, (4) leaching of mycotoxins represents a potential risk for arable soils.

 

The results reflect that soil faunal key species regulate amounts of F. graminearum and F. culmorum in maize residues depending on substrate size and soil texture, but did not affect amounts of F. verticillioides. Fungivorous soil animals significantly accelerate degradation rates of Fusarium mycotoxins by up to 300%, depending on soil faunal species, respective mycotoxin and soil texture. In particular, primary decomposers within the earthworm community (L. terrestris) are pivotal for the bioregulation of Fusarium species and their mycotoxins in the mulch layer. The bioregulation potential of the mesofauna (collembolans and enchytraeids) strongly depends on soil faunal interactions. The findings further indicate that the mycotoxins DON and ZEN leach from infected maize residues.

 

The present studies contribute to improve understanding of the complex interrelations between arable management and ecosystem service/disservice balance in agroecosystems.

How to cite: van Capelle, C., Meyer-Wolfarth, F., Meiners, T., Sandor, M., and Schrader, S.: Soil fauna regulates the ecosystem service/disservice balance in mulched soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6545, https://doi.org/10.5194/egusphere-egu2020-6545, 2020.

EGU2020-274 | Displays | SSS4.13

Local, landscape and continental scale factors controlling earthworm community structure

Ashley Cameron, Robert Bradley, Petra Benetkova, Agnieszka Józefowska, Gabriel Boilard, Miloslav Šimek, Joann Whalen, and Naresh Thevathasan

Past studies have praised earthworms for improving soil structure and fertility, but criticized earthworms for increasing the leaching of nutrients and soil greenhouse gas emissions. Therefore, in order to maximize the environmental benefits and reduce the environmental costs of earthworms, it is important to determine the factors controlling the structure of earthworm communities at local, landscape and continental scales. We first hypothesized that forested riparian buffer strips (FRBS) within agricultural landscapes would be a refuge for earthworms, due to higher soil moisture and organic matter compared to adjacent agricultural fields (“treatment” = FRBS vs. Field).  Within sites, we hypothesized that earthworms would be most abundant where the chemical quality of above- and belowground plant litter is high, or where soil disturbance is low. At the continental scale, we hypothesized that total summer precipitation interacts with regional and local scale factors in controlling earthworm community structure.  A field survey was conducted to quantify earthworm species abundances in FRBS and adjacent agricultural fields across Eastern Canada and Central Europe (two “bioregions” differing in rainfall). At each of 77 sites, we collected and identified earthworms from three plots within FRBS and adjacent agricultural fields, and noted the tree species, understory vegetation, drainage class, agricultural crop as well as five soil physicochemical variables (texture, pH, total C, total N and % organic matter). In each bioregion and treatment, we found proportionately more endogeic than anecic or epigeic earthworm species. In Eastern Canada there were proportionately fewer anecic and more epigeic individuals in FRBS than in fields, whereas in Central Europe there were fewer endogeic and more anecic earthworms in FRBS than in fields. We also found significant interactions between bioregion and treatment on total earthworm abundance and biomass, and on soil moisture. More specifically, in Eastern Canada we found higher earthworm abundance and biomass, soil moisture and organic matter in FRBS. Conversely, in Central Europe we found higher earthworm abundance and biomass in fields, no treatment effects on soil moisture, and higher soil organic matter in FRBS. The different earthworm distribution patterns in each bioregion were not related to the types of agricultural crops, but rather to differences in precipitation and soil moisture across bioregions. Within FRBS in Eastern Canada, earthworm abundance in deciduous and mixedwood stands were higher than in coniferous stands; in Central Europe, earthworm abundance was higher in deciduous stands only. Within FRBS in Eastern Canada, the abundance of the prominent endogeic species Apporectodia rosea was correlated with herbaceous plants, notably ferns and graminoids. Conditional regression tree analysis revealed positive relationships between earthworms and soil clay content, pH, moisture and organic matter. Our results suggest that local and landscape patterns in earthworm diversity can be predicted by soil and vegetation attributes, but the relative importance of these factors change across continual scales due to climate.  Comparing the distributions of earthworms across different scales provides insights into the potential of different species to spread into new habitats with climate change.

How to cite: Cameron, A., Bradley, R., Benetkova, P., Józefowska, A., Boilard, G., Šimek, M., Whalen, J., and Thevathasan, N.: Local, landscape and continental scale factors controlling earthworm community structure, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-274, https://doi.org/10.5194/egusphere-egu2020-274, 2020.

EGU2020-9043 | Displays | SSS4.13

Long-term effects of tillage intensity on the distribution of microbial biomass and activity in four arable field-sites across Europe

Ilka Schmoock, Deborah Linsler, Mignon Sandor, Rainer Georg Joergensen, and Martin Potthoff

Over the last decades, reduced tillage became more and more important as a suitable soil management practice. Moreover, reduced tillage is expected to promote a healthy and active soil life as a feature of sustainable agricultural. The determination of soil microbial biomass and microbial indices are suitable indicators for estimating soil quality. This study follows a regional approach and focusses at four different countries with varying environmental conditions at long-term experimental field-sites (LTE´s) across Europe. Soil microbial biomass carbon (SMB-C), the metabolic quotient (qCO2) and the ratio of SMB-C to soil organic carbon (SOC) were measured as microbial properties.

Our contribution to the ongoing discussion of the effectiveness of non-conventional tillage systems is (i) the comparison between conventional ploughing (CT) and minimum tillage (MT), (ii) the comparison of inversion vs. not inversion tillage at the same working depth, (iii) the comparison of ploughing vs. no-tillage (NT), (iv) the comparison between reduced tillage systems with each other (MT vs. NT).

We found a significant difference of SMB-C for CT and MT between 0 and 10 cm in Germany and Sweden, but no difference between tillage treatments for the sampled soil profile (0-30 cm). We highlight that tillage changed the vertical distribution of SMB-C, showing similar values among soil depths under CT and a depth gradient with decreasing values for MT.

The comparison of inversion vs. not inversion tillage at the same working depth in Romania showed no differences between CT and MT at all. This suggests that humus-rich soils seem to be more resistant to tillage-related disturbances. The working depth might have a greater impact for both, inversion and non-inversion tillage than the type of the tillage system itself.

For the comparison of CT and NT, we used the field-sites in Spain and Sweden. In Spain, NT was clearly of advantage for microbial biomass and activity, compared to CT. This was true for the whole sampled soil profile (0-30 cm) whereas in Sweden differences could only be detected between SMB-C levels in two soil depths. Our results indicate that the effect of tillage seems to be smaller in cold-temperate areas.

Comparing MT and NT in Sweden, we found no difference in SMB-C between these two forms of conservation tillage, neither in the first centimeters, nor in the whole sampled profile. Consequently, minimum tillage seems to be an alternative in cold and moist regions if no-tillage is not possible to apply without reducing soil quality or crop yields.

We conclude that even if minimum and no-tillage are generally beneficial for microorganisms, there is a big variance between the different forms of reduced tillage systems. Thus, statements cannot be made across different soils and machine types, but have to be made on a regional scale.

 

How to cite: Schmoock, I., Linsler, D., Sandor, M., Joergensen, R. G., and Potthoff, M.: Long-term effects of tillage intensity on the distribution of microbial biomass and activity in four arable field-sites across Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9043, https://doi.org/10.5194/egusphere-egu2020-9043, 2020.

EGU2020-11209 | Displays | SSS4.13

Organic matter additions to soil and effects on microbially mediated carbon cycling

Rachel hasler, Mark pawlett, Jim harris, Helen bostock, and Marc redmile-gordon

The type of soil organic amendment selected can have profound implications for carbon cycling processes in soils. Understanding the link between this choice and its effect on the soil microbiome will improve our understanding of the capacity of these materials to improve carbon sequestration and cycling dynamics. Understanding and facilitating the lifestyle strategies of microorganisms processing organic matter is essential to improving our understanding of the terrestrial carbon cycle. This research focuses on utilising organic amendments to alter the indigenous soil microbial community composition and function to improve the capacity of the soil to cycle and store carbon in horticultural soils.  The effects of annual application of various organic fertilisers (peat, bracken, bark, horse manure, garden compost) in a long-term (10year) field experiment were explored. Sampling was completed pre and post application of organic matter within one season (following 10 years of applications) to identify which organic amendment was more effective in producing benefits to plants through improved soil organic matter and which amendments provide the greatest legacy effect on carbon cycling. The response of the soil microbial community composition (phospholipid fatty acid analysis) and carbon functional cycling dynamics (respiration using MicroResp™) were determined with a view to improving our understanding of the interaction between the materials applied and microbial processes. PCA of the MicroResp™ data identified that all treatments had a different functional profile compared to the control[PM1]  with peat being significantly different from all other treatments. Horse manure and bark differed significantly within a single growing season; prior and post organic matter addition in spring 2019.  Microbial biomass measurements for garden compost and horse manure were significantly higher following organic matter addition compared to all other treatments and the control[PM2] .  All treatments had a significant effect [PM3] on hot water extractable carbon and total carbon. Peat had a significantly different effect[PM4] , when compared to other treatments, on the soil PLFA profile and bark application significantly increased [PM5] the neutral lipid (NLFA) biomarker 16:1ω5.  Bark and horse manure application both significantly increased PLFA fungal biomarker 18:2ω6,9. No significant differences were found between the fungal/bacterial ratios of the organic matter additions prior to being added to the soil. These findings show that altering the resources available to the soil microbial community has a significant impact on soil microbial community composition and microbially mediated carbon cycling functionality. Increasing our understanding of how soil functions are altered by land management decisions will enable better informed predictions of the long-term benefits of organic matter applications on carbon sequestration and cycling dynamics.

How to cite: hasler, R., pawlett, M., harris, J., bostock, H., and redmile-gordon, M.: Organic matter additions to soil and effects on microbially mediated carbon cycling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11209, https://doi.org/10.5194/egusphere-egu2020-11209, 2020.

EGU2020-10283 | Displays | SSS4.13

From soil degradation to restoration via soil microorganisms

Oksana Coban, Gerlinde de Deyn, and Martine van der Ploeg

Soil, the living skin of the Earth, provides ecosystem services critical for life: soil acts as a water filter and a growing medium, offers habitat for billions of organisms, and supplies most of the antibiotics. In places, it may take a hundred years to form one cm of soil, but it can be degraded only in a few years or less by a number of natural and anthropogenic factors, including climate change. Presently, one third of all land is degraded to some extent, and fertile soil is lost every year. Droughts are becoming more common, also in humid climates, and the combination of erratic weather patterns with an increased pressure on land by human activities leads to soil degradation. Soil degradation results in a loss of fertile topsoil, thereby altering the soil hydrology completely. As the consequences, soil water holding capacity decreases, hydrophobicity increases, and more runoff is observed, that leads to further soil degradation. Thus, soil hydrology is the key for a healthy functioning topsoil/soil ecosystem. We are in urgent need for novel solutions for improving soil hydraulic properties that will lead to restoration of degraded soils.

In this study we investigate a possibility of restoring degraded soil using microorganisms. The hypothesis is that microorganisms can improve soil hydraulic properties such as infiltration and water retention, and reduce hydrophobicity that will facilitate further ecosystem restoration. Such strategy is based on combining the research fields of microbiology and soil physics that to date have hardly been combined. To test this hypothesis, we have inoculated sandy soil with a bacterium Bacillus mycoides and then measured its hydraulic properties using evaporation and pressure plate methods. We have also made efforts of standardizing this methodology by testing incubation time and inoculum concentrations on the hydraulic properties of the soil. Evaluation of an effect of bacteria addition on the soil water holding capacities and unsaturated water conductivity have been conducted as a comparison between inoculated soil and uninoculated (control). Results of this ongoing study will be presented here.

How to cite: Coban, O., de Deyn, G., and van der Ploeg, M.: From soil degradation to restoration via soil microorganisms, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10283, https://doi.org/10.5194/egusphere-egu2020-10283, 2020.

The high diversity of densely packed organisms occurring in small volumes of soils has long been intriguing and we still poorly understand what drives such diversity. Exploring the role of small scale physical structure of the soil, constituting the habitat of these organisms offers unprecedented clues for explaining how organisms interact, notably through trophic interactions and how, in turn, these interactions drive this extraordinary diversity. We review here how restrictions on soil organisms’ ability to sense (e.g. volatiles) and access food resources/prey imposed by the soil physical structure and aqueous habitats within are important drivers for trophic interactions, and consequently, of soil biodiversity. Examples from micro- to macrofauna are presented, focusing on organisms unable to create their own pore space, such as bacteria, fungi, protists, nematodes and microarthropods. Finally, we discuss interdisciplinary challenges to develop research merging soil physics and soil food web ecology.

How to cite: Erktan, A., Or, D., and Scheu, S.: Into the soil labyrinth: soil physical structure as a driver of trophic interactions and soil biodiversity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4802, https://doi.org/10.5194/egusphere-egu2020-4802, 2020.

EGU2020-19246 | Displays | SSS4.13

Towards standardized experimentation in soil research – a synthetic ecology approach

Hannes Schmidt, Julia Horak, K. Dimitri Kits, Alberto Canarini, Leila Hadziabdic, and Andreas Richter

Soils contain a vast diversity of microorganisms including millions of cells and thousands of species. Many of those species encode for similar functions which is known as functional redundancy. From an ecosystem perspective, it remains unknown how many of such species are contributing to processes and are actually necessary to perform functions. Not knowing about the number and type of taxa of a soil sample a priori, let alone of the interaction between those taxa or the chemical environment of their habitats, hampers the reproducibility of soil ecological research and renders a targeted experimentation virtually impossible. This is one of the most important reasons why linking microbial identity to processes at the soil scale has proven to be everything but easy.

A promising avenue to overcome these limitations are model ecosystems that allow to identify principles of community functioning via standardised experimentation. Here, we will present a synthetic ecology approach using artificial soil mimicking the structural and chemical complexity of a soil and a synthetic microbial community to investigate microbial functioning in soil. Our approach includes genome-guided in silico design of synthetic communities to reproduce the functionality of soil heterotrophic bacteria and fungi, while largely decreasing the number of individual taxa for laboratory experimentation.

Initial experiments suggested that our synthetic community was able to establish in artificial soil and sterilized natural soil and to perform a range of simple soil processes, as evident through potential enzymatic activities, heterotrophic respiration, and changes in organic and inorganic soil components. Molecular analysis of the community composition over time demonstrated high similarities of the established community among replicates, indicating low effects of stochasticity on community assembly, a major requirement for reproducible experimentation. These promising preliminary data indicate that our model system could indeed represent the experimental platform for targeted experimentation in soil ecological research in the future.

How to cite: Schmidt, H., Horak, J., Kits, K. D., Canarini, A., Hadziabdic, L., and Richter, A.: Towards standardized experimentation in soil research – a synthetic ecology approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19246, https://doi.org/10.5194/egusphere-egu2020-19246, 2020.

EGU2020-16475 | Displays | SSS4.13

Modelling the role of selection and complementarity in ecosystem function under climate change

Rebecca Millington, Peter M. Cox, Francisca C. García, and Gabriel Yvon-Durocher

Understanding how ecosystem function depends on temperature is important in understanding ecosystem resilience to climate change. The response to warming at a species level is relatively well understood, through the metabolic theory of ecology, which captures the temperature dependence of biological processes. However, when multiple species are present, interactions between the species are important too. Therefore, to understand community function, we must understand the response of the individual species, and the interactions between them. These interactions may depend on temperature, and can be split into two main mechanisms: selection and complementarity. Both of these processes are likely to depend on the number of species present; the biodiversity of the ecosystem. Currently, the response of communities to temperature change, and how changes in diversity may increase or buffer impacts, is poorly understood.

 

Our understanding of ecosystem function can be improved by using mathematical models to constrain the mechanisms underlying key processes. Using data from laboratory experiments, we model communities of heterotrophs responding to temperature change. To model selection, we use a simple model of a community sharing a resource, with parameters measured empirically. Without complementarity, the model underestimates community function. Complementarity is included through a single parameter, which determines to what extent different taxa share the same resource pool. This parameter is difficult to measure directly, so must be fitted using empirical community function data. Through our model, we show that the strength of complementarity within a community depends on both diversity and temperature. Interestingly, we also find that complementarity is strongest at higher and lower temperatures, and more dependent on diversity at medium temperatures.

How to cite: Millington, R., Cox, P. M., García, F. C., and Yvon-Durocher, G.: Modelling the role of selection and complementarity in ecosystem function under climate change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16475, https://doi.org/10.5194/egusphere-egu2020-16475, 2020.

EGU2020-13094 | Displays | SSS4.13

Microbial necromass as a source for soil organic matter formation - implications for soil processes

Anja Miltner, Tiantian Zheng, Chao Liang, and Matthias Kästner

The vital role of soil microorganisms as catalysts for soil organic matter (SOM) formation has long been recognised. Plant residues are now considered to be transformed by soil microorganisms who use the plant litter as a carbon source for microbial biomass formation. How much carbon is retained as microbial biomass during transformation of plant material, critically depends on substrate availability, carbon use efficiency of the microorganisms, and maximum microbial growth. In addition, microorganisms presumably recycle biomass building blocks from plant or microbial material to avoid energy expenditure for biomass synthesis. After cell death, a part of the microbial necromass is cycling through the microbial food web; the other part is stabilised in soil (Miltner et al., 2012). Potential stabilisation mechanisms are similar to those for SOM in general, with organo-mineral interactions, in particular encapsulation and physical isolation, being important mechanisms. Independent of which pathway the plant-derived carbon goes, SOM constitutes a continuum of plant and microbial necromass at various stages of decay. The contribution of microbial necromass to the topsoil organic matter pool has recently been estimated to range from 30 to 60% (Liang et al., 2019). Such high contributions of microbial necromass have a number of important implications for understanding SOM transformation and sequestration processes. Most obviously, the chemical identity of the organic material changes. For example, while retaining a substantial part of the carbon, the elemental stoichiometry changes substantially. Some microbial necromass materials are rather long-lasting in soil. In general, cell envelope residues have a higher stability than bulk biomass carbon. Proteins have also been shown to be rather persistent in soil, presumably due to conformational changes and the spatial arrangement of microbial necromass material, e.g. fragments of cell envelopes presumably pile up in multiple layers and the material forms clusters of macromolecular size. Residual electron-shuttle biomolecules (e.g. oxidoreductases, Fe-S-cluster, quinoid complexes of respiratory chains) may persist and retain some activity and thus contribute to redox reactions in soil. In addition, the necromass is expected to cover soil particle surfaces and thus determine the surface properties of these particles. In particular, these materials contribute to the water storage potential. They affect water retention and nutrient diffusion as well as microbial motility. Adaption of microbes to water stress changes their cell surface properties and molecular composition and thus may determine overall soil wettability. Knowledge on the contribution of microbial necromass to SOM would thus be essential for modelling SOM formation and optimising soil management practices for maintaining soil functions.

 

References:

Miltner A, Bombach P, Schmidt-Brücken B, Kästner M (2012) SOM genesis: Microbial biomass as a significant source. Biogeochemistry 111: 41-55.

Liang C, Amelung W, Lehmann J, Kästner M (2019) Quantitative assessment of microbial necromass contribution to soil organic matter. Global Change Biology 25: 3578-3590.

How to cite: Miltner, A., Zheng, T., Liang, C., and Kästner, M.: Microbial necromass as a source for soil organic matter formation - implications for soil processes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13094, https://doi.org/10.5194/egusphere-egu2020-13094, 2020.

During the decomposition of organic matter (OM), microorganisms use the assimilated carbon (C) for biomass production or respiration, and the fraction of growth to total assimilation defines the microbial carbon-use efficiency (CUE). Therefore, microbial CUEs have direct consequences for the balance of C between atmosphere and soil, and is as such a central parameter to represent the global C cycle well in Global Cycling Models (GCMs). Despite its enormous leverage this factor remains critically underexplored. Based on the physiology of cultured microorganisms, it is anticipated that (H1) high nutrient availabilities will increase microbial CUE, (H2) that higher quality substrate will increase microbial CUE, (H3) that microbial communities more dominated by fungi will have higher CUE, and (H4) that microbial CUE will decrease in response to environmental stress. We combined extensive field surveys with experimental treatments in microcosms to assess our hypotheses. We sampled temperate forest soils, temperate agricultural soils, and subarctic forest soils, encompassing a wide range of soil pHs (4.0-7.1), nutrient availabilities (10<soil C/N<33), and soil OM qualities (7-fold differences in respiration per SOM). We also surveyed environmental pollution gradients where metallurgy had contaminated soil with high heavy metal concentrations in boreal forest and temperate grassland sites. We also subjected selected soils to microcosm experiments where soil pH (liming), mineral N (50 kg N ha-1), OM quality (plant litter), or heavy metal stress were manipulated and the resulting bacterial and fungal growth, respiration, and CUE were monitored over the course of 2 months.

 

Fungal-to-bacterial growth ratios (F:B) ranged from 0.02 to 0.44 across the studied ecosystems, and that the fungal dominance was higher in soils with lower C:N ratio and higher C-quality. CUE ranged from 0.03 to 0.30, and values clustered most strongly according to site rather than level of soil N. CUE was higher in soil with high C:N ratios and high C-qualities. However, within each land-use type, a high mineral N-content did result in lower F:B and higher resulting CUE. In the microcosm experiments, plant litter addition stimulated the growth of fungi more than bacteria, while increasing soil pH stimulated bacteria more than fungi. Mineral N additions inhibited bacterial growth and stimulated fungal growth. This resulted in microbial CUE estimates in real time that ranged from ca 0.05 to 0.55, and where increased pH and litter increased values while mineral N supplements decreased values. Long-term exposure to heavy metals decreased microbial CUE, but only marginally, even at very high rates of metal exposure. Short-term exposure to metal stimulated microbial CUE in soil from contaminated sites, while CUE was reduced in soil with no history of metal contamination. In conclusion, a higher site soil C-quality coincided with lower F:B and higher CUE across the surveyed sites, while a higher N availability did not. A higher site N availability resulted in higher CUE and lower F:B within each site, while mineral N supplements in the microcosm induced the opposite response, suggesting that site-specific differences associated with fertility such as the effect of plant communities, overrode the influence of mineral N-availability.

How to cite: Rousk, J.: Soil microbial growth and carbon-use efficiency: ecological control mechanisms, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2166, https://doi.org/10.5194/egusphere-egu2020-2166, 2020.

EGU2020-20248 | Displays | SSS4.13

Microbial diversity drives carbon use efficiency in a model soil

Luiz A. Domeignoz-Horta, Grace Pold, Xiao-jun A. Liu, Serita D. Frey, Jerry M. Melillo, and Kristen M. DeAngelis

Empirical evidence for the response of soil carbon cycling to the combined effects of warming, drought and diversity loss is scarce. Microbial carbon use efficiency (CUE) plays a central role in regulating the flow of carbon through soil, yet how biotic and abiotic factors interact to drive it remains unclear. Here, we combined distinct community inocula (biotic factor) with different temperature and moisture conditions (abiotic factors) to manipulate microbial diversity and community structure within a model soil system. Abiotic factors indirectly influenced CUE through their impacts on diversity and community structure, which were the strongest predictors of CUE. We also found that abiotic factors modulated the relationship between diversity and CUE, with CUE being positively correlated with bacterial diversity under high moisture. Altogether these results indicate that drier soils diminished the synergistic effect between diversity and CUE, with potential consequences for the fate of C in soils.

How to cite: Domeignoz-Horta, L. A., Pold, G., Liu, X.-A., Frey, S. D., Melillo, J. M., and DeAngelis, K. M.: Microbial diversity drives carbon use efficiency in a model soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20248, https://doi.org/10.5194/egusphere-egu2020-20248, 2020.

EGU2020-13148 | Displays | SSS4.13

How drought modulates carbon-use efficiency and soil carbon formation in rhizosphere, detritusphere, and bulk soils

Noah Sokol, Steve Blazewicz, Megan Foley, Alex Greenlon, and Jennifer Pett-Ridge

Carbon use efficiency (CUE) is theorized to be positively associated with the formation of microbially-derived, mineral-associated soil carbon.  Yet few empirical studies have directly tested this relationship. Moreover, it is unclear: (1) how differences between distinct soil microbial communities (for example, differences in competitive interactions and/or growth rate among rhizosphere, detritusphere, and bulk soil communities) may yield different relationships between carbon-use efficiency and soil carbon formation, and (2) how microbial ecophysiology – such as physiological changes induced by drought – may modulate the strength and/or direction of the CUE-soil carbon relationship.

To investigate these questions, we conducted a 12-week 13C tracer study to track the movement of two dominant sources of plant carbon – rhizodeposition and root detritus – into soil microbial communities and carbon pools under normal moisture vs drought conditions. Using a continuous 13CO2-labeling system, we grew the Mediterranean annual grass Avena barbata in controlled growth chambers and measured the formation of organic matter from 13C-enriched rhizodeposition. As the plants grew, we harvested rhizosphere and bulk soil at three time points (4, 8, and 12 weeks) to capture changes in soil carbon pools and microbial community dynamics. In parallel microcosms, we tracked the formation of soil carbon derived from 13C-enriched A. barbata root detritus during 12 weeks of decomposition; harvesting detritusphere and bulk soil at 4,8, and 12 weeks. In all microcosms, we manipulated soil moisture to generate drought (7.8 ± 2.1 % soil moisture) and ‘normal moisture’ (15.1 ± 4.2 % soil moisture) treatments.

In all samples (over 150 observations), we measured CUE via the 18O-H2O method, and quantified the formation of different 13C-soil organic carbon pools via density fractionation. Here we will present data on how soil moisture influences CUE in rhizosphere, detritusphere, and bulk soil communities, and whether differences in CUE are correlated with the formation of mineral-associated soil organic carbon. These results will help to illustrate whether CUE acts as a lynchpin variable with predictive power for stable soil carbon formation, or whether other microbial traits may require consideration.

 

 

How to cite: Sokol, N., Blazewicz, S., Foley, M., Greenlon, A., and Pett-Ridge, J.: How drought modulates carbon-use efficiency and soil carbon formation in rhizosphere, detritusphere, and bulk soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13148, https://doi.org/10.5194/egusphere-egu2020-13148, 2020.

EGU2020-9254 | Displays | SSS4.13

Impact of soil sample pre-treatment on microbial carbon use efficiency and associated parameters

Julia Schroeder, Lisa Kammann, Christoph C. Tebbe, and Christopher Poeplau

The 18O-labelling method is a powerful tool for studying soil microbial carbon use efficiency (CUE), as the label itself does not affect the soil microbial carbon metabolism. Beside parameters of soil microbial activity, the DNA extracted within this method can be used to gain information on soil microbial metagenome, e.g. community composition. Amongst others, the 18O-CUE method can support studies on the impact of land use change on the soil microbial metabolism and thus soil carbon dynamics.

As soil sample handling and length of incubation prior to analysis have been shown to affect measured parameters of soil microbial activity (e.g. Birch-effect) and community, different sample preparation measures are recommended in the literature depending on the focus of the study. However, so far the sensitivity of CUE and associated parameters to sample pre-treatment is unknown. We therefore tested i) how different sample pre-treatments (freezing, drying, and fresh) affect the parameters of soil microbial metabolism and community measured within the 18O-CUE method. In order to determine the potential to use the 18O-CUE in land use change studies we tested ii) if mentioned parameters of the two compared systems forest and cropland were - if applicable -affected in a similar way.

Based on five different paired sites (cropland and forest each), we evaluated the effects on the CUE and associated parameters (respiration, soil microbial biomass C, DNA extracted, abundance of fungi, bacteria and archaea) of six pre-treatments for soil samples via the 18O-CUE method: (i) direct analysis of field-fresh soil samples, analysis after pre-incubation of (ii) field-fresh, (iii) air-dried, (iv) oven-dried, (v) frozen at -20°C and (vi) in-situ frozen soil samples (dry ice and subsequently liquid N2).

Among all pre-treatments, the pre- incubation of 14 days as such had the strongest effect on metabolic parameters. Furthermore, while individual parameters (respiration, microbial biomass C) were influenced by the pre-treatment the 18O-CUE was relatively insensitive. We therefore conclude that not only fresh but also archived, dried soil samples can be used to obtain representative CUE values. Drying soil samples and rewetting led to increased fungal abundance in the forest soil, while this was not the case for croplands.

How to cite: Schroeder, J., Kammann, L., Tebbe, C. C., and Poeplau, C.: Impact of soil sample pre-treatment on microbial carbon use efficiency and associated parameters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9254, https://doi.org/10.5194/egusphere-egu2020-9254, 2020.

EGU2020-14553 | Displays | SSS4.13

Quantifying microbial growth and carbon use efficiency in dry soil environments via 18O water vapor equilibration

Alberto Canarini, Wolfgang Wanek, Margarete Watzka, Taru Sandén, Heide Spiegel, Stefanie Imminger, Dagmar Woebken, Jiří Šantrůček, and Jörg Schnecker

As the global hydrological cycle intensifies with future warming, more severe droughts will alter the terrestrial biogeochemical carbon (C) cycle. As soil microbial physiology controls the large fluxes of C from soil to the atmosphere, improving our ability to accurately quantify microbial physiological parameters in soil is essential. However, currently available methods to determine microbial C metabolism in soil require the addition of water, which makes it practically impossible to measure microbial physiology in dry soil samples without stimulating microbial growth and respiration (namely, the “Birch effect”).

We developed a new method based on in vivo 18O water vapor equilibration to minimize soil re-wetting effects. This method allows the isotopic labelling of soil water without any liquid water or dissolved substrate addition to the sample. This was compared to the main current method (18O-water application method) in soil samples either at near-optimal water holding capacity or in air dry soils. We generated time curves of the isotopic equilibration between liquid soil water and water vapor and calculated the average atom percent 18O excess over incubation time, which is necessary to calculate microbial growth rates. We tested isotopic equilibration patterns in nine different soils (natural and artificially constructed ones) covering a wide range of soil texture and organic matter content. We then measured microbial growth, respiration and carbon use efficiency in three natural soils (either dry or at near-optimal water holding capacity). The proposed 18O vapor equilibration method provides similar results as the currently widely used method of liquid 18O water addition to determine microbial growth when used a near-optimal water holding capacity. However, when applied to dry soils the liquid 18O water addition method overestimated growth by up to 250%, respiration by up to 500%, and underestimated carbon use efficiency by up to 40%.

Finally, we applied the new method to undisturbed biocrust samples, at field water content (1-3%), and show for the first time real microbial growth rates and CUE values in such arid ecosystems. We describe new insights into biogeochemical cycling of C that the new method can help uncover and consider the wide range of questions regarding microbial physiology and its response to global change that can now be proposed and addressed.

How to cite: Canarini, A., Wanek, W., Watzka, M., Sandén, T., Spiegel, H., Imminger, S., Woebken, D., Šantrůček, J., and Schnecker, J.: Quantifying microbial growth and carbon use efficiency in dry soil environments via 18O water vapor equilibration, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14553, https://doi.org/10.5194/egusphere-egu2020-14553, 2020.

EGU2020-5450 | Displays | SSS4.13

New insights on carbon use efficiency using calorespirometry – a bioenergetics-based model

Arjun Chakrawal, Anke M. Herrmann, and Stefano Manzoni

Soil organic carbon (SOC) represents both a source of energy (catabolism) and a building material for biosynthesis (anabolism) for microorganisms. Microbial carbon use efficiency (CUE) – the ratio of C used for biosynthesis over C consumed – measures the partitioning between anabolic and catabolic processes. While most work on CUE has been based on C mass flows, the role of SOC energy content, microbial energy demand, and general energy flows on CUE have been rarely considered. Thus, a bioenergetics perspective on CUE could provide new insights on how microorganisms utilize C substrates and ultimately allow C to be stabilized in soils.

The microbial growth reactions are generally associated with a negative enthalpy change, which results in heat dissipation from the system. This heat can be measured using an isothermal calorimeter, which is often coupled with respiration measurements. This coupled system allows studying energy and C exchanges, and calculating their ratio referred to as the calorespirometric ratio (CR). Here, we formulate a coupled mass and energy balance model for microbial growth and provide a generalized relationship between CUE and CR. In the model, we consider two types of organic C in soils, the added substrate (i.e., glucose) and the native SOC. Furthermore, we assume that glucose is taken up via aerobic (AE) and two fermentation metabolic pathways – glucose to ethanol (F1) and glucose to lactic acid (F2); for simplicity, only aerobic growth on the native SOC was adopted. We use this model as a framework to generalize previous formulations and generate hypotheses on the expected variations in CR as a function of substrate type, metabolic pathways, and microbial properties (specifically CUE). In turn, the same equations can be used to estimate CUE from measured CR.

Our results show that in a non-growing system, CR depends only on the rates of different metabolic pathways (AE, F1, and F2). While in growing systems, CR is a function of rates as well as growth yields for these metabolic pathways. Under purely aerobic conditions, our model predicts that CUE increases with increasing CR when the degree of reduction of the substrate is higher than that of the microbial biomass. Similarly, CUE decreases with increasing CR when the degree of reduction of substrate is lower than that of the biomass. In the case of combined metabolism – aerobic and fermentation simultaneously – CUE is not only a function of CR and the degree of reduction of substrates but also the rates and growth yields of all metabolic pathways involved. To summarize, in this contribution we illustrate how calorespirometry can become an efficient tool to evaluate CUE and the role of different metabolic pathways in soil systems.

How to cite: Chakrawal, A., M. Herrmann, A., and Manzoni, S.: New insights on carbon use efficiency using calorespirometry – a bioenergetics-based model , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5450, https://doi.org/10.5194/egusphere-egu2020-5450, 2020.

Energy crops are grown at low cost and low maintenance used in making biofuels, such as bioethanol, or combusted to generate electricity or heat. Production of energy crops as an alternative to fossil fuels will help to reduce CO2 emission, thus leading to large scale changes in agricultural landscapes. Increase in the cultivation of annual energy crops such as maize (Zea mays) is assumed to decrease biodiversity in the agrarian landscape. This may lead to changes in soil properties, thereby affecting the soil biodiversity and its ecosystem functions and services like for instance soil microarthropod communities and their contribution to decomposition of plant litter. Perennial crops such as field grass (a mixture of Festulolium,  Dactylis glomerate, Loliuim perenne, Festuca pratensis and Festuca arundinacea) and cup plant (Silphium perfoliatum) are assumed to protect and promote soil biodiversity through less intensive management. The relationship between decomposer diversity and ecosystem functioning is little understood. So far, the role of soil microarthropods in decomposition is the most disputed aspect due to scarce empirical data.

The main aim of this field study was to assess the effect of soil microarthropods on litter of maize, field grass and cup plant, via decomposition using litter bags with 2 different mesh sizes (0.02 mm and 0.5 mm) for a period of 3 months during the vegetation period. At the end of the experiment, the decomposition rate was higher in cup plant followed by maize and field grass in the coarse mesh size, and higher in the cup plant followed by field grass and maize in the fine mesh size. A total of 55,464 soil microarthropods (73% mites, 25% collembola and 2% others) were extracted from the litter bags. The diversity and abundance of soil microarthropods was higher under cup plant cultivation followed by field grass and maize.

How to cite: Dioh Lobe, P. and Schrader, S.: How energy crops (Maize, Field grass, Cup Plant) affect soil microarthropods and their decomposition services, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6624, https://doi.org/10.5194/egusphere-egu2020-6624, 2020.

EGU2020-7128 | Displays | SSS4.13

Dynamics of selected chemical and microbiological properties changes in soils after application of ultra-fine powdered calcium carbonate – incubation studies

Karolina Woźnica, Michał Gąsiorek, Justyna Sokołowska, Agnieszka Józefowska, and Tomasz Zaleski

Soil acidification is a serious problem on a global scale, about 30% of land surface is occupied by acidic soils (pH≤ 5.5). Recent research indicates, that more than 50% of arable soils in Poland have too low pH. Acid soils are characterised the ability to mobilize toxic metals and increased plant uptake as well as decreased microbial activity in the soil. Progressive acidification leads to degradation of soils and caused that they are marginal for agricultural production. Soil acidification is a naturally occurring process, but only when natural factors are supported by intensive human activity, especially by nitrogen fertilisers application, intensive degradation is observed. Traditionally method to increase soil pH is the application of lime materials e.g. calcite, burnt lime or dolomite. The liming efficiency depends on lime material type (primarily chemical form of calcium compounds), the neutralising value, lime application method, soil properties and the particle size distribution of lime. The aim of this research was to determine the rate of action and influence of ultra-fine powdered calcium carbonate on selected chemical and microbiological soil properties.

The incubation studies were conducted on the three soils (G1, G2 – silt loam and G3 – sandy loam). Soil samples were taken from the 0-20 cm layer. Soil properties were measured after 7, 14, 30, 60 and 120 days of incubation. The liming factor was ultra-fine powdered calcium carbonate with particle size distribution < 0.08 mm. The application dose was calculated for 0.5 soil hydrolytic acidity. In the soil samples pHKCl, buffer capacity, microbial biomass carbon and dissolved organic carbon content were measured.

Application of lime caused an increase of pH value in all studied soils. The highest increase of the pHKCl was noted between 0 to 7th day of incubation. Afterward, the pHKCl decreased slowly for the soil G1 and G2. However, in the soil G3 significantly decreased just after 7th to 14th day, and afterward, the pHKCl decreased slowly to the end of the incubation period. As a result of liming long-term changes in soil buffer capacity were not noted. The studied soils were characterised by the higher buffer capacity in alkaline than in acidic range. The microbial biomass carbon content was varied during the incubation in all studied soils. The dissolved organic carbon content increased during the incubation, starting from the 7th to the 120th day of incubation for G2 and G3 soils and from 14th to last day of incubation for G1 soil. Application of lime caused an increase of the dissolved organic carbon content in all studied soils. These studies show that application of ultra-fine powdered calcium carbonate is an effective and fast way to improve soil properties.

How to cite: Woźnica, K., Gąsiorek, M., Sokołowska, J., Józefowska, A., and Zaleski, T.: Dynamics of selected chemical and microbiological properties changes in soils after application of ultra-fine powdered calcium carbonate – incubation studies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7128, https://doi.org/10.5194/egusphere-egu2020-7128, 2020.

EGU2020-7130 | Displays | SSS4.13

The effects of natural forest succession on soil respiration in Bieszczady National Park (south-eastern Poland)

Justyna Sokołowska, Agnieszka Józefowska, Karolina Woźnica, and Tomasz Zaleski

The Polish Carpathian Mountains characterise the unique landscape containing high valuable seminatural mountain meadows. However, due to land abonnement, especially decrease agriculture and pasture activity, land cover changes occur. As a result of such changes, natural forest succession in the Carpathians become more and more widespread process. Despite, landscape transformations the natural forest succession is an important issue of science in the context of carbon sequestration. It is well known, that soil organic carbon is the largest terrestrial organic carbon pool in the world. Land cover transformations are regarded as the most dynamic factors of soil organic carbon changes. So far, studies have presented no clear organic carbon accumulation pattern, there is a lack of study covered different land use conversions.

Soil microbiota is the major factor influence on decomposition and transformation of organic matter in the soil. One of the predominantly measured parameters of microbial activity is soil respiration. Moreover, soil respiration is widely used as an indicator of soil quality, degree of development and especially the carbon cycling dynamics. Furthermore, understanding the mechanism controlling microbial respiration is critical to efforts to model carbon cycling at a regional and global scale. The purpose of this study was to investigate the influence of natural forest succession on microbial respiration.

The study area was located in Bieszczady National Park in south-eastern Poland. The samples from two layers (0-10 cm and 10-20 cm) in the four transects each consisted of a meadow, a succession (covered by 30-60 years trees) and a forest (more than 150 years old trees) were taken. Microbial respiration was determined by the incubation method. Respiration was measured for 5 weeks in closed vials. During the three days, the soil was carried in the vial with the small baker containing NaOH and hermetically closed. After this period the baker was removed and trapped CO2 was quantified by titration with HCl and with participation BaCl2. Additionally, based on the first-order kinetic model of microbial respiration cumulative respiration, the content of carbon available for microbial respiration present at the start of the experiment and the rate constant were calculated. Moreover, other microbiological, chemical and physical soil properties were determined in previous research.

Soil respiration C-CO2 after the first week of incubation was significantly higher in the 0-10 cm layer compare to 10-20 cm, however, after the fifth week of incubation differences between investigated layers were no significant differences. In the 0-10 cm layer, the highest cumulative respiration was observed in succession (74.9 mgC-CO2 g-1 h-24) and the lowest in forest (51.9 mgC-CO2 g-1 h-24). However, in the 10-20 cm layer meadow characterised the highest cumulative respiration (42.0 mgC-CO2 g-1 h-24) and forest the lowest (26.8 mgC-CO2 g-1 h-24). Following cumulative respiration, significant the highest content of carbon available for microbial respiration was observed in succession and meadow, in the 0-10 and 10-20 cm layers respectively. Cumulative respiration of investigated soils was positively correlated with total nitrogen content, microbial biomass carbon as well as dehydrogenase and cellulase activity.

How to cite: Sokołowska, J., Józefowska, A., Woźnica, K., and Zaleski, T.: The effects of natural forest succession on soil respiration in Bieszczady National Park (south-eastern Poland), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7130, https://doi.org/10.5194/egusphere-egu2020-7130, 2020.

Maize (Zea mays) is the most commonly cultivated energy crop throughout Europe. However, its cultivation has severe negative effects such as loss of biodiversity and its delivery of ecosystem services, soil compaction and enhanced greenhouse gas emissions. These negative effects tend to be even more pronounced in wet soils such as pseudogleys. As an alternative to annual maize, the perennial cup plant (Silphium perfoliatum) is known to produce a similar yield, especially under waterlogging conditions, while management impacts of its cultivation are assumed to be less harmful to soil biota. Therefore, the aim of the present study was to quantify the provision of ecosystem services (here: control of the soil water balance) delivered by earthworm communities in wet soils under cultivation of cup plant compared with maize and to assess the ecological impact of both energy crops.

Fieldwork was conducted cup plant and maize fields (n = 4) in South Western Germany in spring and autumn 2019. The overall soil type was pseudo gleyic luvisol. All fields are managed for commercial purposes by farmers in the area. Sampling included earthworm extraction with allyl isothiocyanate (AITC) while the infiltration rate was measured simultaneously. Afterwards, hand sorting completed the earthworm sampling. Earthworm species, their abundance and biomass (live weight) were determined.

On average, earthworm abundance and biomass were higher in cup plant fields than in maize fields. In addition, variations in earthworm communities were found. While endogeic earthworms, especially of the genus Aporrectodea, were present in all fields, anecic earthworms were more abundant in cup plant fields. Higher infiltration rates were measured in maize fields. Hints to a correlation between the infiltration rates and the functional earthworm groups were found.

Our results suggest that cup plant fields host overall more diverse earthworm communities. These communities are able to produce a wider range of ecosystem services, even though the link between the infiltration and the crops studied in this stud is not yet validated.

How to cite: Wöhl, L. and Schrader, S.: Effects of earthworm communities on water infiltration in wet soils with energy crops, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7628, https://doi.org/10.5194/egusphere-egu2020-7628, 2020.

EGU2020-8773 | Displays | SSS4.13

Automatic detection and mapping of European ground squirrel burrows on UAV-based multi- and hyperspectral imagery with classification methods

Mátyás Árvai, János Mészáros, Zsófia Kovács, Eric C. Brevik, László Pásztor, and Csongor I. Gedeon

European ground squirrels (EGS) are members of the soil megafauna and part of the ecosystem engineers that shape physical, chemical, and biological characteristics of soil ecosystems in European grasslands. Thanks to their strict protection their abundance and distribution have been surveyed systematically and annually in Hungary. The results of their 20 year monitoring indicate that their population is declining, there are sudden extinctions of local populations, and a desynchronized variation of the abundance of local populations occur either spatially or temporally.

The monitoring protocol involves the estimation of their abundance in each colony by a strip-transect method and the habitat-colony area by visual observations or digital maps. Both approaches use animal burrows as proxies for either their presence (colony area) or density (colony size). These estimation methods, however, consist of systematical errors: first, they consider the animals’ density to be even over the entire habitat-area, second, they conjecture that animals occupy the habitable area completely, and third, evenly. If we were able to survey distribution and abundance of EGS more accurately, frequently, and efficiently, we could better intervene in time when local populations begin to decline or before they disappear. In addition, we could better estimate the effects (+ or -) of management strategies in real time.

The primary aims of our study were to develop a non-invasive, semi-automated method for (1) estimating abundance of EGS in the area of occupation of a colony, and (2) delineating their occupancy within the habitable area. We have defined burrow openings and mounds as quantitative proxies for the presence of animals. We have started to develop a monitoring technique to identify, locate, and count objects of interest in images automatically and to delineate the area of occupancy by identifying those objects of interest from the surroundings. To survey EGS colonies and habitats we have used a multirotor platform UAV equipped with either an RGB visible-range or a hyperspectral sensor.

To test our method several pilot areas with different vegetation and relief were surveyed. Acquired aerial images have been processed by photogrammetric software and resulting high spatial resolution orthomosaics are classified by machine-learning algorithms (randomforest, CART, C5.0) implemented in a custom R script. As detection of mounds and openings are visually restricted by vegetation height (e.g. grass, shrubs, weeds, herbs), we have studied the effect of grass height on detection success. Preliminary results suggest that successful classification can be performed either on RGB visible-range and hyperspectral images. However, the appropriate spatial resolution (below cm range) and the presence of high grass are more important key factors than number of spectral bands.

Detecting EGS burrow openings and mounds is based on surface characteristics of EGS burrow openings and mounds consequently the method is being developed for EGS specifically but can be modified to the characteristics of other burrowing mammals of this size (e.g. mole-rats, moles).

How to cite: Árvai, M., Mészáros, J., Kovács, Z., Brevik, E. C., Pásztor, L., and Gedeon, C. I.: Automatic detection and mapping of European ground squirrel burrows on UAV-based multi- and hyperspectral imagery with classification methods, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8773, https://doi.org/10.5194/egusphere-egu2020-8773, 2020.

EGU2020-10240 | Displays | SSS4.13

Microbial properties in European arable soils with different tillage systems

Deborah Linsler, Jacqueline Gerigk, Ilka Schmoock, Rainer Georg Jörgensen, and Martin Potthoff

Reduced tillage is assumed to be a suitable practice to maintain and promote microbial biomass and microbial activity in the soil. The microbial biomass in particular is considered as a sensitive indicator for detecting soil disturbances. The objective of this study was to quantify the influence of different tillage practices on microbial parameters in the soil. Furthermore, we analyzed the relation of those microbial parameters with site-specific conditions.

To get a deeper insight in that topic, soils from different fields of agricultural farms with different tillage practices in France (12 fields), Romania (15 fields) and Sweden (17 fields) were examined within the “SoilMan project”. The tillage practices were no-tillage (absence of any tillage), minimum tillage (non-inversion tillage for instance by chisel plough or cultivator) and conventional tillage (inversion tillage by ploughing), all of which were carried out for at least five years prior to sampling. Soil samples were taken in spring 2018 from all fields under winter wheat (Triticum aestivum) at three soil depths (0-10 cm, 10-20 cm, 20-30 cm). As microbial parameters we measured microbial biomass carbon and nitrogen contents, ergosterol contents (as proxy for fungi) and basal respiration rates. For site-specific conditions we measured soil organic carbon, total nitrogen and total phosphorus contents, texture, pH and the soil water content.

Results show that microbial biomass carbon and nitrogen were more affected by soil type and soil texture as well as climatic conditions (mean precipitation and temperature) than by tillage practices. For instance, an increased clay content had a positive effect on the microbial biomass and, in addition to the higher average annual temperature, explained the generally low values ​​in France. The lack of inversion tillage primarily led to stratified levels of soil organic carbon, microbial biomass carbon and ergosterol contents, which can be explained by the lack of crop residue incorporation. There were hardly any differences in microbial indicators between the tillage intensities when looking at the whole of the sampled soil profile (0-30 cm). In France, the microbial biomass carbon / soil organic carbon ratio was lower for no-tillage than for conventional tillage, which may indicate, among other things, that the mechanically ground organic matter incorporated into the soil under conventional tillage was better colonized by microorganisms. However, this effect could not be confirmed in the other countries. The metabolic quotient was generally increased at the lowest sampled depth (20-30 cm), irrespective of the cultivation.

We can conclude that the soil tillage intensity influenced the distribution of microbial biomass carbon and soil organic carbon contents more strongly than the total amounts in the sampled soil profile and that the soil texture had a greater impact on microbial soil properties than the agricultural management practice.

How to cite: Linsler, D., Gerigk, J., Schmoock, I., Jörgensen, R. G., and Potthoff, M.: Microbial properties in European arable soils with different tillage systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10240, https://doi.org/10.5194/egusphere-egu2020-10240, 2020.

EGU2020-11299 | Displays | SSS4.13

Effects of agricultural soil management practices on soil microbiota across Europe – investigations in seven long term field experiments

Luis F. Arias, Gema Guzmán, José A. Gómez, Manuel Anguita-Maeso, Dumitria Dascalu, Deborah Linsler, Thierry Morvan, Maarja Öpik, Guénola Pérès, Martin Potthoff, Mignon Sandor, Astrid Taylor, Kaisa Torppa, Tanel Vahter, and Blanca B. Landa

Traditionally, soil quality has been assessed through physical, chemical and biological properties without paying attention to soil biota and the different associated ecosystem services provided (Tyler, 2019). To fill that gap, the european BiodivERsA “SoilMan” project (Ecosystem services driven by the diversity of soil biota – understanding and management in agriculture) is focused on the relations among soil management, soil biodiversity, and ecosystem services, at seven different management gradients in agricultural long term observations (LTO’s) trials across Europe (France “SOERE-PROs EFELE” and “SOERE-ACBB Lusigan”, Romania “Turda”, Sweden “Angermanland” and “Säby-Uppland”, Germany “Garte Süd” and Spain “La Hampa”). Management gradients covered different tillage regimes (zero, minimum and conventional) and different crop rotations (crop types and duration).

In the present study, we characterised the bacterial and fungal communities of soils from the different countries and agricultural managements in arable land. The samplings were carried out following the same methodology in all the countries during 2017-2018 when wheat was sown in the LTO’s. The soil DNA was extracted and subjected to metabarcoding analysis of 16S and Internal Transcribed Spacer (ITS) ribosomal RNA (rRNA) for bacterial and fungal community analysis, respectively.

Different alpha diversity metrics, including number of OTUs, Simpsons and Shannon indexes, as well as beta diversity distances (weighted and unweighted UNIFRAC, Jaccard and Bray-Curtis) were calculated. Multidimensional Scaling ordination plots (PCoA) were used to visualize the existence of community gradients among locations and soil managements. All the statistical data  procedure  was analysed using the vegan R package (Oksanen, 2011).

In general terms, results show that alpha diversity for both bacteria and fungi, clearly differs among countries while soil management effects are less defined among and within countries. Concerning the beta diversity indexes, communities tend to cluster more according to the spatial location than due to the soil management regimen. This is especially true for fungal communities. Further analysis will identify possible correlations of bacterial and fungal communities with environmental variables and other physicochemical and biological soil properties.

References:

Oksanen, J. (2011). Multivariate Analysis of Ecological Communities in R: vegan tutorial.

Tyler, H. L. (2019). Bacterial community composition under long-term reduced tillage and no till management. Journal of Applied Microbiology, 126(6), 1797–1807. https://doi.org/10.1111/jam.14267

How to cite: Arias, L. F., Guzmán, G., Gómez, J. A., Anguita-Maeso, M., Dascalu, D., Linsler, D., Morvan, T., Öpik, M., Pérès, G., Potthoff, M., Sandor, M., Taylor, A., Torppa, K., Vahter, T., and Landa, B. B.: Effects of agricultural soil management practices on soil microbiota across Europe – investigations in seven long term field experiments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11299, https://doi.org/10.5194/egusphere-egu2020-11299, 2020.

EGU2020-21058 | Displays | SSS4.13

Evaluation of the enzymatic activity and diversity of soil microorganism in Andean temperate forests degradation gradient

Alejandro Atenas, Felipe Aburto, Rodrigo Hasbun, and Carolina Merino

Soil microorganism are an essential component of forest ecosystem. Microbes and plant release enzymes that catalyse reactions needed to decomposed soil organic matter and crucial to release nutrient in available forms. Therefore, soil enzymes are relevant indicators of microbial activity and nutrient cycling in forest ecosystems. Anthropic disturbances in natural forest, such as logging and exotic livestock, modify the structure and composition of forest thereby altering the structure and activities of soil microbial communities.

Here we determine the effect of these disturbances on the enzymatic activity (Dehydrogenase-DHA; Phosphatase Acid-AP; Ureasa-UA) and the microbial diversity using a forest degradation gradient of native temperate forest dominated by Nothofagus dombeyi, Nothofagus obliqua and Nothofagus alpina. In addition we quantify C:N:P nutrient reservoirs, stoichiometry and available pools. Preliminary results suggest a higher activity of the DHA enzyme in degraded forest dominated by N. obliqua. AP and UA showed no relationship with the phosphorus and total nitrogen reservoirs. Forest degradation modify microbial communities, C:N:P stoichiometry, total and available nutrient pools, where the biggest pool of total C and N was registered on low degraded condition and decrease as degradation condition increase from medium to high degraded forest (74.44%; 65.35%; 48.05% for total C and 3.71; 3.41; 3.24 for total N respectively). Inverse relation was registered for total P pool were the highest pool was registered on high degraded condition (14963ppm; 13092ppm and 11299ppm from high to low degraded condition). Degraded sites were dominated mainly by members of Gammaproteobacteria, Alfaproteobacteria, Acidobacteria and Bacteroidia. Chitinophagaceae and Burkholderiacea were not detected in degraded plots, which suggest that some of the specialised functions carried by this groups could be lost. With respect to fungi Ascomycota and Basidomicota Phylum dominated the soil profiles. A species of the genus Clonostachys (Bionectriaceae) was identified, an endophyte fungus that acts as a saprophyte, also known to be a parasite of other fungi and some nematodes.

This research contributes to a better understanding of the direct effects of anthropic disturbances on the biogeochemical functioning of temperate forests and their relationship to the activity and composition of microbial communities.

Acknowledgment: Proyecto Reforestación Enel – UdeC

How to cite: Atenas, A., Aburto, F., Hasbun, R., and Merino, C.: Evaluation of the enzymatic activity and diversity of soil microorganism in Andean temperate forests degradation gradient, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21058, https://doi.org/10.5194/egusphere-egu2020-21058, 2020.

EGU2020-21272 | Displays | SSS4.13

Soil microbial functional diversity along an elevation gradient in Northwestern Caucasus

Kristina Ivashchenko, Alexandra Seleznyova, Sofia Sushko, Anna Zhuravleva, Alexander Tronin, Nadezhda Ananyeva, and Valery Kudeyarov

In contrast to taxonomic diversity of soil microbiome, the distribution patterns of functional diversity for various ecosystems, including along an altitudinal gradient, is poorly understood. Consequently, the study focuses on finding out the spatial distribution features of microbial functional diversity in mountainous soils along elevation through forests and meadows ecosystems. We hypothesized that soil microbial functional diversity is increasing along the altitudinal gradient in conjunction with plant diversity. In Northwestern Caucasus (Karachay-Cherkess Republic, Russia) the north-eastern mountain slope was studied across mixed, fir and deciduous forests, subalpine and alpine meadows located from 1260 to 2480 m above sea level. Twelve plots (0.25 m2 each) were randomly chosen within each ecosystem (total 60). Plant species composition and Shannon plant diversity index (H) were assessed for the plots. Topsoil samples (0-10 cm) were taken from the plots in August for assessment microbial functional diversity through community level physiological profile (CLPP). It was determined by microbial respiration response on amino, carboxylic, phenolic acids and carbohydrates (MicroResp). Shannon's functional diversity index based on the CLPP (HCLPP) was calculated. Edaphic properties as moisture, temperature, pH, total carbon (C) and nitrogen (N) contents were determined as possible drivers of CLPP. As expected, plant diversity was increased along the elevation gradient with the lowest H value in the mixed forest (0.6) and the highest – in the alpine meadow (1.9). The HCLPP did not differ among studied ecosystems and reached on average 2.4 for each. Microbial respiration response on amino acids was mainly contributed to dissimilarities between studied ecosystems and increased on average by 1.3 times with elevation from mixed to fir and deciduous forests. Along this elevation row, the soil N content was the most significant driver compared to other edaphic properties. Among subalpine and alpine meadows the differences between microbial responses on studied carbon substrates were not found.

Considering that elevation didn’t contribute to distribution patterns of soil HCLPP at the inter-ecosystems level, consequently, the hypothesis of our study was rejected. Plant diversity was not related to HCLPP as expected. Meanwhile, the distribution patterns of soil microbial community, utilizing amino acids, along the altitudinal gradient was found.

The current research was financially supported by RFBR No 20-34-70121

How to cite: Ivashchenko, K., Seleznyova, A., Sushko, S., Zhuravleva, A., Tronin, A., Ananyeva, N., and Kudeyarov, V.: Soil microbial functional diversity along an elevation gradient in Northwestern Caucasus, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21272, https://doi.org/10.5194/egusphere-egu2020-21272, 2020.

EGU2020-22032 | Displays | SSS4.13

Microbiological and FTIR applications in Atlantic forest regeneration areas

Laura Borma, Breno Pupin, and Kumiko Sakani

Soil regulates plant productivity in terrestrial ecosystems and maintains the balance of biogeochemical cycles through biotransformations mediated by living organisms, which are responsible for 80 to 90% of these functions. Therefore, it is necessary to evaluate whether restoration/natural regeneration processes in land degraded areas may allow the soil to partially or fully recover its microbial functions reflecting thus, in the fertility of these soils and consequently in the regeneration of forests. The use of microbiological attributes combined with infrared spectroscopy (FTIR) offers many opportunities to understand temporal dynamics and spatial variability in the recovery of important ecosystems during forest regeneration stages.The present work aims to evaluate the evolution of microbial quality in soils under three Atlantic Forest areas at different stages of regeneration (R40 - advanced, R12 - intermediate and RP - early regeneration pasture area) located in São Paulo state, Brazil. We used as indicators of the soil microbial quality the number of colony-forming units (CFU) of total bacteria and fungi, spore density and root colonization by arbuscular mycorrhizal fungi (AMF). We also analyzed these soils by Fourier Transform Infrared Spectroscopy (FTIR-UATR). For each area, seven soil samples and plant roots were randomly collected at a depth of 0-20 cm at the end of the dry season (October 2019). In terms of dry soil, the CFU bacteria for each area was, respectively, 7.7, 4.6 and 3.2 x 105 CFU g-1; fungi, 1.2, 1.0 and 0.6 x 103 g-1, and AMF spore density, 39, 33 and 27 spores 50 ml-1. On average, AMF root colonization was 26 (R40), 25 (R12) and 21% (PR). For the FTIR spectrum, the major bands and their assignments were identified as a 3.370 cm-1 wide band assigned to the O-H groupings; a peak at 1.635 cm-1 attributed to aromatic C=C vibration, with contribution of C=O of the COO- and a peak at 1.072 cm-1 attributed to the carbohydrate C-O bond. No difference was attributed to the composition of the main functional groups (O-H, C=O, COO- and C-O) between the soils from R40 and R12, but this difference was more evident when compared to the RP area.  The microbiological results show good similarity between the tree areas in terms of spores, fungi and root colonization. However, in terms of bacteria, there is a more pronounced difference between the recent (RP) and the older regeneration areas (R12 and RP). Similar pattern was pointed by the FTIR results. Considering pasture as a strongly degrading area, these results are interesting since they show the differences in the soil quality between the three areas is not highly pronounced. They also show that in twelve years of regeneration, in many aspects’ soils become similar to the area with forty years regeneration. Given these results, a further investigation on soil physics of these areas is being developed to relate soil regeneration processes and soil physical properties such as porosity, density and water retention capacity, all of them important to the maintenance of vegetation and ecosystem services of water and climate regulation.

How to cite: Borma, L., Pupin, B., and Sakani, K.: Microbiological and FTIR applications in Atlantic forest regeneration areas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22032, https://doi.org/10.5194/egusphere-egu2020-22032, 2020.

EGU2020-16110 | Displays | SSS4.13

Fertilization effects on the fungal biomass in grasslands

Ana Barreiro, Aaron Fox, Andreas Lüscher, Franco Widmer, and Linda-Maria Dimitrova Mårtersson

Fertilisation is a common practise in grass production systems performed to increase primary production, a supporting ecosystem service essential for other services. However, different fungal groups, like saprothropic fungi (SF) and the obligate symbionts arbuscular mycorrhizal fungi (AMF), have potential differential response to the fertilizer concentration and composition. Three controlled field experiments were utilised in our study, two medium-term (6 years) in the south of Sweden (SE) and one long-term experiment (46 year) in Switzerland (CH), all sampled in 2018. The Swedish sites included the same two factor treatment, i.e. four different plant mixtures and two (SE-Lanna) or three (SE-Alnarp) nitrogen fertilization levels (0, 60, 120 kg ha-1 yr-1); while the Swiss experiment  included different proportions of N, P and K fertilization under different cutting regimes (CH-Bremgarten). The PLFA and NLFA (phospholipid- and neutral lipid fatty acid) analysis was used to estimate the fungal biomass (SF+AMF). The application of N was associated with a decrease in the AMF biomass, with significant effects with the application of 60 and 120 kg N ha-1 in SE-Alnarp, and 75 and 150 kg N ha-1 in CH-Bremgarten. On the other hand, the SF biomass was only negatively affected by the N fertilization in SE-Lanna (60 kg N ha-1) under the plant mixture that showed the biggest SF biomass in the unfertilized plot; and by the highest application of N in CH-Bremgarten. Our findings indicate that nitrogen fertilization influences microbial community structure and reduces the abundance of AMF, with these being more sensitive than SF to fertilizer application.

How to cite: Barreiro, A., Fox, A., Lüscher, A., Widmer, F., and Dimitrova Mårtersson, L.-M.: Fertilization effects on the fungal biomass in grasslands , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16110, https://doi.org/10.5194/egusphere-egu2020-16110, 2020.

Studying the soil seed bank is a time and space-consuming task, and therefore only a small fraction of the soil is sampled. It is then critical to optimize sampling effort to reliably estimate soil seed bank properties. Here, we test whether the spatial patterns of species richness in the soil seed bank differ under increasing sampling effort. For this, we used data of germination from soils in a mediterranean shrubland in Central Spain. Two data sets were used, one of the seedlings emerging after heating the soil to break dormancy, and one with the combined germinations of heated and non-heated soil subsamples. We simulated increased sampling effort with sample-based rarefaction curves, extrapolating the species richness corresponding to a 2x and 3x increase in the number of individuals (seedlings) per sample. We then analyzed the spatial pattern of the original and extrapolated species richness using linear regression and semivariograms. Species richness increased by 34% and 52% in the 2x and 3x estimations, however the spatial pattern of species richness remained largely unchanged. For the long-distance spatial pattern, the slope of the plot-scale trend (i.e., the regression coefficient) increased only slightly with increasing sampling effort, while the adjusted R-squared of the regression decreased with increasing sampling effort. For the short-distance spatial pattern we could only fit spherical model semivariograms to the data from soils exposed to a heat shock, and the intensity of the spatial pattern (spatial dependence) increased very slightly with increased sampling effort. These results suggest that even with a doubled or tripled sampling effort, as provided by the simulations, the spatial pattern of species richness would have remained unchanged. We argue that increased effort in detecting species in the seed bank needs not necessarily improve the detection of spatial pattern.

How to cite: Torres, I. and Moreno, J. M.: Relating sampling effort to the detection of spatial patterns of species richness in the soil seed bank of a mediterranean shrubland., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18218, https://doi.org/10.5194/egusphere-egu2020-18218, 2020.

EGU2020-4224 | Displays | SSS4.13

Soil microbial communities from olive cultivars are shaped by seasonality and geographical scales

Manuel Anguita-Maeso, Juan C. Rivas, Guillermo León, Cristina Estudillo, Juan A. Navas-Cortés, and Blanca B. Landa

Soil biodiversity is essential to sustain healthy ecosystems supporting the maintenance of the environment and agricultural practices. Soils provide vital habitat for microorganisms which play determinant roles through organic matter transformation and nutrient cycling, which have a great impact in agriculture and food production and climate regulation. Understanding soil microbiome is becoming a relevant matter for supporting plant productivity and plant health. Unravelling the function and structure of microbial communities prevailing in soils is essential for a better understanding of plant development. However, the vast majority of soil microorganisms remain unknown and their variability at regional and temporal seasonal scale is still an unexplored field. In this study, soils associated to the rhizosphere of three olive varieties were sampled during autumn 2018 and spring 2019 in three olive orchards with differences in physicochemical soil characteristics and climate, located in the provinces of Jaén, Córdoba and Málaga, in Andalusia, Southern Spain. Bacterial and fungal populations were analysed using Illumina MiSeq platform to determine the structure and diversity of soil microbial communities and how those environmental factors may affect them. Sequencing data resulted in a total of 730 bacteria OTUs, distributed in 23 phyla and 312 genera while there were 553 fungal OTUs divided in 8 phyla and 280 genera. Proteobacteria was the most abundant bacterial phylum across olive orchard location (30.37%-5.52%) followed by Actinobacteria (10.72%-5.49%) and Bacteroidetes (7.73%-0.89%). There was circa 50% abundance reduction of these phyla on samples taken in autumn compared to that sampled in the spring. Unique bacterial genera differed according to field location in Jaén (72), Córdoba (45) and Málaga (48) while the shared bacteria genera among plots was 82. Fungi results showed Ascomycota (49.13%-3.13%) and Basidiomycota (25.64%-2.79%) as the two most abundant phyla in all olive orchards. A reduction on the abundance of Ascomycota was noticed on samples from autumn to spring (37.84% and 20.42%, respectively), while Basidiomycota displayed a distinct behavior (11.89% to 20.27%). Exclusive fungal genera varied from Jaén (50), Córdoba (7) and Málaga (14), whereas the core fungal genera among fields was 28. This information can contribute to generate new knowledge regarding temporal and spatial scale insights on soil microbiome associated to olive crop that may be considered to increase plant health and soil biodiversity.

Study supported by Projects 01LC1620 SOILMAN, XF-ACTORS 727987 (EU-H2020) and AGL2016-75606-R (MICINN Spain and FEDER-EU).

How to cite: Anguita-Maeso, M., Rivas, J. C., León, G., Estudillo, C., Navas-Cortés, J. A., and Landa, B. B.: Soil microbial communities from olive cultivars are shaped by seasonality and geographical scales, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4224, https://doi.org/10.5194/egusphere-egu2020-4224, 2020.

EGU2020-6297 | Displays | SSS4.13

Litter decomposition under drought related with litter and decomposer diversity

Junwei Luan, Shirong Liu, Siyu Li, Yi Wang, Haibo Lu, Junhui Zhang, Shijie Han, Hui Wang, Lin Chen, Wenjun Zhou, and Yiping Zhang

Litter decomposition is a crucial ecosystem process that driven carbon and nutrient cycling, which can be determined by the diversity of biota that involved in decomposition process. Forest ecosystems at globally have been or being expected to experience drought stress and cause dieback, consequently may lead losses of tree species and soil biota. However, how projected drought affect litter decomposition and its relationship with biodiversity is less understood. We hypothesize that 1) drought depressed the activity of soil biota and retard litter decomposition, while biodiversity loss at both plant and soil organism levels exacerbated the drought induced retarding of litter decomposition; 2) soil biota interaction or the top down control of ecosystem process can be relieved under drought stress. In our study, throughfall reduction experiments were conducted in five locations representing different forest types (i.e., temperate broadleaf-Korean pine mixed forest, warm-temperate oak forest, subtropical bamboo forest, south subtropical evergreen forest, tropical rainforest) along a climate gradient in China. In each location, leaf litter from 4 common native plants and 11 mixtures of these litter types were enclosed in three types of nylon mesh screens litterbags, and were placed in the field of throughfall reduction and control treatments replicated five times. Different combination of litter types represent diversity of litters, and mesh size of litterbags represent diversity of functional group of soil biota (i.e., microorganism, medium-sized fauna, large-bodied fauna) participate into decomposition. The litterbags were incubated in situ for a period of time and were collected, all litter samples were separated into the constituent species immediately after litter retrieval, mass loss, C and N loss of each sample was determined. Thereby the hypothesizes can be testified.

How to cite: Luan, J., Liu, S., Li, S., Wang, Y., Lu, H., Zhang, J., Han, S., Wang, H., Chen, L., Zhou, W., and Zhang, Y.: Litter decomposition under drought related with litter and decomposer diversity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6297, https://doi.org/10.5194/egusphere-egu2020-6297, 2020.

EGU2020-12665 | Displays | SSS4.13

Microbial and abiotic interactions driven higher microbial anabolism on organic carbon accumulation during 2000 years of paddy soil development in the Yangtze River Delta, China

Qingfang Bi, Xianyong Lin, Wolfgang Wanek, Shasha Zhang, Alberto Canarini, Andreas Richter, and Yong-Guan Zhu

Paddy soil as a major component of cropland, plays an important role in the global carbon (C) cycle and favors carbon sequestration especially in southern China. Soil microorganisms are central to the conversion of organic matter into SOC, yet the mechanisms underlying the paddy management at long time scales remain largely unknown, including microbial enzyme and functional potential kinetics, microbial growth and turnover. Here, using observations from a 2000-year-old paddy chronosequence since reclamation from tidal wetland at two different soil depths (0-20 cm and 20-50 cm) in the Yangtze River Delta, China, we show how paddy soil C sequestration is driven by the relationship between short-term responses in microbial physiology and long-term changes in biogeochemical soil properties. The samples were analyzed for nutrient pools, microbial biomass and growth, microbial activity and community composition, functional gene abundances, as well as microbially mediated nitrogen (N) cycling rate to determine how these microbial functionalities and processes affect microbial carbon use efficiency (CUE), an important indicator for microbial C sequestration. Across multiple time-scales ranging from decades to millennia, SOC in topsoil was increased by 65% during the first 50 years and reached the steady-state condition until 700-year, then was largely accumulated by 169% and 125% in 1000- and 2000-year, respectively, while C loss appeared in subsoil after 700 years of paddy cultivation. For topsoil and subsoil, microbial CUE reached to the highest values in 1000- and 700-year (0.46 and 0.36, respectively, while only 0.20 in the tidal wetland), along with microbial growth which both increased 5.2- and 3.3-fold in 1000-year, respectively. We found the similar increasing trends between microbial CUE and soil C:P and N:P ratios, the reduction of N limitation and functional potentials including N- and P-cycling, C degradation, C-fixation (acsA gene), microbial community homogenization and microbial biomass across soil chronosequence in topsoil. Moreover, the structural equation model revealed that with longer paddy management, the decline in soil pH had positive effects on microbial functional potentials and microbial biomass carbon. The enhanced functional potentials directly positively affected microbial growth, and thereby on microbial biomass carbon. Finally, the prolonged paddy cultivation increased SOC content via its direct positive effect and indirect positive influence on microbial biomass carbon. We conclude that longer paddy management captures the cumulative microbial anabolism on SOC sequestration in the plough layer, with the shifts in abiotic and biotic conditions towards increased nutrient availability and homogenous microbial community with higher functional potentials.

How to cite: Bi, Q., Lin, X., Wanek, W., Zhang, S., Canarini, A., Richter, A., and Zhu, Y.-G.: Microbial and abiotic interactions driven higher microbial anabolism on organic carbon accumulation during 2000 years of paddy soil development in the Yangtze River Delta, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12665, https://doi.org/10.5194/egusphere-egu2020-12665, 2020.

SSS5.2 – Mechanisms of soil organic matter stabilization and carbon sequestration

Soils are continuously exposed to recurrent cycles of drying and rewetting, for instance, when extended periods of drought are followed by rainfall events. For nearly a century it has been known that the balance of the soil C budget is affected by these moisture fluctuations, which is characterized by very large mineralization losses when dry soils are rewetted. In some ecosystems, the soil C losses resulting from this phenomenon (“the Birch effect”) even represent a dominant fraction of the annual C-transfer from soils to the atmosphere. However, to balance the soil C budget, the microbial control of C input to the soil during these events also needs to be known. It was recently discovered that the growth of microorganisms, driving C stabilization in soils, has a far slower response to rewetting than does respiration. This results in a pronounced and dynamic disconnection between the mechanisms controlling microbial respiration and growth. Despite the significance of this decoupling for the C budget and the long-term balance of soil C stocks, this feature has so far been entirely overlooked by biogeochemical models, potentially leading to a failure to capture the capacity of soils to mitigate the effects of climate change.

To close this knowledge gap, we developed a new process-based soil microbial model that includes a wide range of physical, chemical and biological mechanisms to explore the nature of soil C dynamics induced by moisture changes. The model was validated using respiration data from soils exposed to repeated cycles of drying and rewetting which has been frequently studied (Miller et al., 2005, Soil Biol Biochem) and compared to other models existing in the literature. The proposed model was able to capture, at once and for the first time, the respiration data and the decoupled behaviour of growth. Simulation results identified the drought-legacy effects on C use efficiency and microbial physiology as the main mechanisms controlling the soil responses to moisture fluctuations. This represents a critical step towards unravelling the C sequestration capacity of soils, its drivers and feedback on climate.

How to cite: Brangarí, A. C., Manzoni, S., and Rousk, J.: Uncovering the diverging factors that control microbial carbon sequestration and respiration in soils exposed to moisture fluctuations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-415, https://doi.org/10.5194/egusphere-egu2020-415, 2020.

EGU2020-514 | Displays | SSS5.2 | Highlight

The chemical and physical stability soil organic carbon in the top 1 m of the soil profile under different land uses in the UK

Dedy Antony, Jo Clark, Chris Collins, and Tom Sizmur

Soils are the largest terrestrial pool of organic carbon and it is now known that as much as 50% of soil organic carbon (SOC) can be stored below 30 cm. Therefore, knowledge of the mechanisms by which soil organic carbon is stabilised at depth and how land use affects this is important.

This study aimed to characterise topsoil and subsoil SOC and other soil properties under different land uses to determine the SOC stabilisation mechanisms and the degree to which SOC is vulnerable to decomposition. Samples were collected under three different land uses: arable, grassland and deciduous woodland on a silty-clay loam soil and analysed for TOC, pH, C/N ratio and texture down the first one metre of the soil profile. Soil organic matter (SOM) physical fractionation and the extent of fresh mineral surfaces were also analysed to elucidate SOM stabilisation processes.

Results showed that soil texture was similar among land uses and tended to become more fine down the soil profile, but pH did not significantly change with soil depth. Total C, total N and C/N ratio decreased down the soil profile and were affected by land use in the order woodland > grassland > arable. SOM fractionation revealed that the free particulate organic matter (fPOM) fraction was significantly greater in both the topsoil and subsoil under woodland than under grassland or arable. The mineral associated OC (MinOC) fraction was proportionally greater in the subsoil compared to topsoil under all land uses: arable > grassland > woodland. Clay, Fe and Mn availability play a significant role (R2=0.87) in organic carbon storage in the top 1 m of the soil profile.

It is evidently clear from the findings that land use change has a significant effect on the dynamics of the SOC pool at depth, related to litter inputs to the system.

How to cite: Antony, D., Clark, J., Collins, C., and Sizmur, T.: The chemical and physical stability soil organic carbon in the top 1 m of the soil profile under different land uses in the UK, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-514, https://doi.org/10.5194/egusphere-egu2020-514, 2020.

It has long been known that processes that determine soil carbon dynamics are spatially heterogeneous. However, the spatially heterogeneous mechanisms have not been well characterized nor incorporated into Earth system models for predicting soil carbon sequestration in response to climate change. This presentation shows our recent results from an integrated approach that combines deep learning, data assimilation, big data with >100,000 vertical soil organic carbon (SOC) profiles worldwide, and the Community Land Model version 5 (CLM5) to optimize the model representation of SOC over the world. Our results indicate that CLM5 that is trained by >100,000 data via data assimilation alone is constrained with spatially homogeneous parameter values over the globe. However, CLM5 that is not only trained by data assimilation but also optimized by deep learning from the big data is constrained with spatially heterogeneous parameter values. Our further analysis suggests that those parameters representing microbial carbon use efficiency greatly vary across space. The spatial heterogeneity in carbon use efficiency is caused by interactions of edaphic, climate and vegetation factors. When the spatially heterogenous parameterization is applied to simulation over time with temporal variation, CLM5 predicts substantial carbon sequestration under climate change. In contrast, CLM5 with the spatially homogeneous parameters predicts carbon loss. Our study demonstrates the importance to uncover and represent spatially heterogeneous mechanisms underlying soil carbon sequestration in order to realistically predict SOC dynamics in the future.

How to cite: Luo, Y., Tao, F., and Huang, X.: Spatially heterogeneous mechanisms underlying soil carbon sequestration as revealed via big data-driven Earth system modelling and deep learning, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2473, https://doi.org/10.5194/egusphere-egu2020-2473, 2020.

EGU2020-3613 | Displays | SSS5.2

Modelling dynamic interactions between soil structure and soil organic matter

Nicholas Jarvis, Elsa Coucheney, Claire Chenu, Anke Herrmann, Thomas Keller, Thomas Kätterer, and Katharina Meurer

The aggregated structure of soil is known to reduce rates of soil organic matter (SOM) decomposition and therefore influence the potential for long-term carbon sequestration. In turn, the storage and turnover of SOM strongly determines soil aggregation and thus the physical properties of soil. The two-way nature of these interactions has not yet been explicitly considered in soil organic matter models. In this study, we present and describe a new model of these dynamic feedbacks between SOM storage, soil pore structure and soil physical properties. We show the results of a test of the model against measurements made during 61 years in a field trial located near Uppsala (Sweden) in two treatments with different OM inputs (bare fallow, animal manure). The model was able to successfully reproduce long-term trends in soil bulk density and organic carbon content (SOC), as well as match limited data on soil pore size distribution and surface elevation. The results suggest that the model approach presented here could prove useful in analyses of the effects of soil and crop management practices and climate change on the long-term potential for soil organic carbon sequestration.

How to cite: Jarvis, N., Coucheney, E., Chenu, C., Herrmann, A., Keller, T., Kätterer, T., and Meurer, K.: Modelling dynamic interactions between soil structure and soil organic matter, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3613, https://doi.org/10.5194/egusphere-egu2020-3613, 2020.

Microbial transformation of organic substances is a key process of soil organic matter (SOM) formation. Carbon (C) entering the soil can be transformed in three main directions: i) stabilization over long period without relevant microbial utilization, ii) recycling by microorganisms for production of new and reparation of old cells, and iii) microbial utilization for energy production leading to C losses from soil as CO2. So, individual compounds within huge diversity of the organic substances entering the soil will follow predominantly one of these directions, depending on the substance chemistry, soil properties, microbial activities and environmental conditions. Therefore, organic substances can have two general trends: i) they converge from any initially distinct compounds (e.g. in litter or rhizodeposition) to completely mixed, so that it is impossible to trace back their origin; or ii) divergence: the substances maintain their differences despite microbial transformations by SOM formation.

We proved two opposite hypotheses that convergence and divergence of the fate of organic substances depends on microbial utilization at two levels: 1) intermolecular: high recycling intensity leads to convergence, whereas stabilization leads to divergence of the C originated from various organic compounds, and 2) incorporation of C from various molecule positions into microbial metabolic cycles define the C fate at intramolecular level. We tested the first hypothesis based on own and literature data to the fate of polymeric substances: sugars, proteins, lipids and lignin. The second hypothesis was tested by the C atoms from various positions of pentoses and hexoses by position-specific 13C and 14C labeling.

The polymeric substances as well as monomers from the same chemical group clearly converge to three groups stabilization, recycling and losses. Carboxylic acids will be nearly completely mineralized and are lost from soil. The fate and functions organic compounds depend mainly on microbial recycling. Proteins, amino acids and sugars - key components of microbial biomass - are intensively recycled and e.g. proteins remain relatively long in soil.

For the intramolecular differences, we traced the fate of position-specific 13C labeled glucose and ribose under field conditions for 800 days. Both sugars were simultaneously metabolized via glycolysis and pentose phosphate pathway. The similarity between position-specific 13C recovery in microbial biomass and soil reflected high contribution of microbial necromass to SOM. The mean residence time of uniformly labeled 13C ribose in the soil was 3 times longer than that of glucose. Consequently, ribose and glucose were incorporated into different cellular components, defining their long-term fate in soil. The convergence of glucose C positions in soil and microbial biomass revealed that recycling dominated glucose transformation. In contrast, divergence of ribose C positions in soil revealed that intact ribose-derived cell components are reused or preserved in SOM.

Thus, convergence vs. divergence distinguished the two general trends explaining the long persistence of C at inter- and intra-molecular levels: microbial recycling leads to convergence, whereas slow decomposition and preservation define the divergence of C pathways in soil.

How to cite: Kuzyakov, Y., Bore, E., and Dippold, M.: Soil organic matter formation: Convergence and divergence of three carbon pathways: Stabilization, recycling and losses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6174, https://doi.org/10.5194/egusphere-egu2020-6174, 2020.

Improvements in management practices can prevent the decline of soil organic carbon (SOC) storage caused by conventional tillage practice in Northeast China. Density and size fractionation can track the transformation of plant residue into SOC and its location in soil matrix. We used a long-term field study in China to evaluate these changes as a result of improved management involving tillage and cropping systems. Experimental treatments included no-till (NT) and moldboard ploughing (MP) under monoculture maize (Zea mays L.) (MM) and maize-soybean (Glycine max Merr.) rotation (MS); these were compared to the traditional management involving conventional tillage (CT) under MM. An incubation study was conducted to evaluate mineralization and the biodegradability of SOC. The soils were also physically fractionated by density (light fraction, LF) and size (sand, silt, clay). With improved management, the SOC storage in the clay showed the largest increase across all fractions. This increase was greater for MS than MM. The NTMS treatment resulted in a decline in silt-OC storage compared to CTMM. The SOC mineralization (mg CO2-C g-1 soil) was affected by tillage and driven by LF-OC and was observed in the order: NTMM (2.06) > MPMM (1.72) ≈ NTMS (1.71) > CTMM (1.52) ≈ MPMS (1.41). Both cropping and depth affected the biodegradability of SOC. Considering the plough layer (0-20 cm), treatments under MM had larger proportion of biodegradable SOC than under MS. We conclude that the significant differences in SOC storage in physical fractions and SOC biodegradation were caused by differences in soil management.

How to cite: Zhang, Y.: Tillage and cropping effects on soil organic carbon: biodegradation and storage in density and size fractions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8186, https://doi.org/10.5194/egusphere-egu2020-8186, 2020.

Aggregation of mineral and organic particles is a key process of soil development, which promotes carbon (C) stabilization by hindering decomposition of plant and microbial residues. All microbial utilization and C stabilization processes lead to 13C fractionation and consequently to various δ13C values of organic matter in aggregate size classes, sand, silt, and clay-sized particles, as well as density fractions. Differences in δ13C within the aggregates and density fractions may have two reasons: 1) preferential stabilization of organic compounds with light or heavy δ13C and/or 2) stabilization of organic materials after passing one or more microbial utilization cycles, leading to respiring of 13C depleted CO2 and heavier δ13C in remaining C. Assuming these two reasons, the new approach based on the natural differences in stable C isotopic composition between SOM fractions was proposed and tested on soils developed solely under C3 vegetation (arable, coniferous and deciduous forests) in boreal climate (Gunina and Kuzyakov, 2014). This approach assumes that: 1) 13C enrichment between the SOM fractions corresponds to successive steps of SOM formation; 2) 13C fractionation (but not the δ13C signature) depends mainly on the transformation steps and not on the C precursors. Consequently, 13C enrichment of SOM fractions allows reconstructing the SOM formation pathways. To prove these initial results we reviewed  δ13C values of soils globally and focused on the i) estimation of the validity of this approach for soils developed under various climatic conditions and parent materials, and depending on fertilization, and ii) C flows not only between aggregate size classes and density fractions but also between various particle size classes of the soils (i.e. sand, silt, and clay) and iii) on revealing the intensities of natural 13C fractionation during the stabilization of litter C in aggregates, particle size classes, and density fractions. Results showed that density fractions were 13C enriched in the order: free particulate organic matter (POM) < light occluded POM < heavy occluded POM < mineral fraction, with the strongest increase between the light occluded and heavy occluded POM. The maximum 13C fractionation during stabilization of litter C in density fractions and aggregate size classes was < 2‰. Δ13C enrichment of the SOM fractions showed that the main direction of C flows within the aggregates and SOM fractions was from the macroaggregate-free POM to the mineral microaggregate fraction. Thus, despite some limitations, δ13C natural abundance approach based on 13C fractionation within individual steps of SOM formation is very useful and probably the sole approach to estimate C flows under steady-state without labeling.

How to cite: Gunina, A. and Kuzyakov, Y.: Carbon flows by soil organic matter formation: A review based on 13C natural abundance, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10730, https://doi.org/10.5194/egusphere-egu2020-10730, 2020.

EGU2020-18700 | Displays | SSS5.2

Impact of soil wetness on plant litter decomposition using low-cost soil moisture sensors and off-the-shelf tea bags

Angelika Xaver, Taru Sandén, Heide Spiegel, Luca Zappa, Gerhard Rab, Drew Hemment, and Wouter Dorigo

Soil organic matter plays a key role within the nutrient cycle, serves as an agent to improve soil structure, and is also known to impact concentrations of greenhouse gases and stabilize soil pollutants. Thus, the soil organic matter content and its potential losses through decomposition are of high interest, especially in the light of a changing climate. As the decomposition process is significantly influenced by climatic conditions, it is important to understand the relationship between decomposition and environmental variables. Previous studies primarily focused on determining the influence of air temperature and precipitation on litter decomposition, but the impact of soil moisture has hardly been investigated.

In this study, we evaluate the relationship between plant litter decomposition, using commercial tea bags (Green and Rooibos tea) as standardized plant litter, and soil moisture, observed with low-cost sensors used within the European citizen science project GROW Observatory (GROW; https://growobservatory.org/). The low-cost soil moisture sensors were placed alongside the tea bags at eight different locations, covering four different land cover types, within the Hydrological Open Air Laboratory (HOAL), a small agricultural catchment in Petzenkirchen, Austria. Data has been collected for two years providing decomposition rates (k) and stabilization factors (S) for the four different seasons of both years. Apart from soil moisture, we investigate air and soil temperature, precipitation and soil parameters as drivers for litter decomposition.

We will show preliminary results on the relationship between decomposition and different environmental variables, in particular soil moisture, throughout all seasons and various land cover classes.

 

This study was funded by the GROW Observatory project of the European Union’s Horizon 2020 research and innovation programme (https://growobservatory.org/).

How to cite: Xaver, A., Sandén, T., Spiegel, H., Zappa, L., Rab, G., Hemment, D., and Dorigo, W.: Impact of soil wetness on plant litter decomposition using low-cost soil moisture sensors and off-the-shelf tea bags, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18700, https://doi.org/10.5194/egusphere-egu2020-18700, 2020.

Studies of the distribution of soil organic matter (SOM) below intensively cultivated fields on clayey sediments of Quaternary age in Denmark show three markedly different zones from the surface and down to about 10 meters below surface. Each zone reflects the balance between input and losses of since the last glaciation.

The upper zone makes up the uppermost few meters below the soil surface. Here, the inherited bioavailable pool of SOM has mineralized and only small amounts of not-bioavailable SOM are present. The largest pool of SOM is renewable and derives from crops grown in the field.

In the underlying middle zone, the content of inherited SOM is very low and seems well protected against biological decomposition (not-bioavailable). No renewable source of SOM from the crops seems to reach down to this middle zone.

In the third and deepest zone, only inherited SOM is present. The SOM origins from the sediments deposited during the last glaciation, about 12,000 years ago.

Typically, the lowest contents of SOM is in the middle zone.

Zonation by content, composition, and bioavailability of the organic matter in soils and deeper sediments is important for the fate of many environmentally substances and for the quality of soil water as well of the quality of other parts of the aquatic environment. In addition, the SOM- pools of different composition in the three zones will most likely behave different to future changes in atmospheric CO2 and climate change adoption.

How to cite: Ernstsen, V.: Postglacial zonation of soil organic matter in clayey till sediments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20704, https://doi.org/10.5194/egusphere-egu2020-20704, 2020.

EGU2020-21025 | Displays | SSS5.2

Fractionation of soil organic carbon under different land management in dry tropics, south India

Eito Nonomura, Soh Sugihara, Mayuko Seki, Hidetoshi Miyazaki, Muniandi Jegadeesan, Pandian Kannan, and Haruo Tanaka

An understanding of the mechanisms of soil organic carbon (SOC) stabilization is essential to develop the appropriate management for C sequestration and soil health. In southern India, where neutral-alkaline soils are mainly distributed, soil C stocks are inherently low in cropland, despite relatively high clay contents (Clay>ca. 30%, OC<ca. 5 g C kg-1 soil). To consider this reason of low SOC in this area, we evaluated the fractionated C contents and its controlling factors, by measuring the particulate organic matter (POM). The objective of this study was to evaluate the effect of land management on the amount and composition of each fraction of soil in southern India. We collected the surface soils (0-10 cm) from two representative sites of southern India; Vertisols with alkaline soil pH (8.4-8.8) and Alfisols with neutral soil pH (6.0-7.0). At each site, two different land management were selected; forest and cropland of Vertisols, and cropland with no organic matter application (no-OM) and with manure application (with-OM) of Alfisols. Soils were separated into the four fractions; (1) Light Fraction; LF (<1.7 g cm-3) , (2) Coarse POM; cPOM (>1.7 g cm-3, 250-2000 µm), (3) Fine POM; fPOM(>1.7 g cm-3, 53-250 µm), and (4) Silt+Clay; S+C (>1.7 g cm-3, <53 µm). Each fraction was analyzed by elemental analysis (C, N) and CPMAS 13C NMR spectroscopy. In Vertisols, C contents of cPOM, fPOM, S+C were significantly higher in forest (0.65, 0.91, 4.8 g kg-1 soil, respectively) than those of cropland (0.17, 0.22, 4.1 g kg-1 soil, respectively), causing the higher total SOC in forest (7.8 g kg-1 soil) than in cropland (4.5 g kg-1 soil). C concentration of cPOM, fPOM, and S+C fractions were also significantly higher in forest (3.7, 7.6, 6.7 g kg-1 fraction, respectively) than those of cropland (1.0, 2.7, 5.4 g kg-1 fraction, respectively). In particular, increasing rates in cPOM and fPOM (180-280 %) were greater than S+C (24 %), possibly suggesting that forest management should increase the relatively active and intermediate SOC pools through the C accumulation in cPOM and fPOM fractions of Vertisols. In Alfisols, C contents in LF and S+C were significantly higher in with-OM (1.1 and 5.2 g kg-1 soil, respectively) than in no-OM (0.76 and 4.7 g kg-1 soil, respectively). C concentration of S+C fraction was significantly higher in with-OM (14 g kg-1 fraction) than in no-OM (11 g kg-1 fraction), but not of cPOM and fPOM fractions. It suggests that the OM application to cropland should increase the slow SOC pool through the C accumulation in S+C fractions of Alfisols. These results indicate that different fraction may contribute to SOC stabilization between Vertisols and Alfisols in southern India.

How to cite: Nonomura, E., Sugihara, S., Seki, M., Miyazaki, H., Jegadeesan, M., Kannan, P., and Tanaka, H.: Fractionation of soil organic carbon under different land management in dry tropics, south India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21025, https://doi.org/10.5194/egusphere-egu2020-21025, 2020.

EGU2020-6731 | Displays | SSS5.2

Interaction of exogenous microbial inoculum with soil organic matter fractions

Luciano Beneduce, Cesar Plaza, Stefano Trotta, and Claudio Zaccone

In a previous study (Zaccone et al., 2018. Appl. Soil Ecol. 130, 134-142), we evaluated the potential ecological partition of microbial and plant DNA across soil organic matter (SOM) fractions linked to conceptual stabilization mechanisms. We found that different microbial taxa (bacterial and fungal) seem to be specifically associated to SOM fractions. In the present work we investigated the short-term distribution of exogenous microbial population in SOM fractions following inoculation, in order to track the fate of bacterial DNA (in the form of spores) artificially spiked in bulk soils. The main hypothesis was that the colonization of external organisms proceeds from the unprotected fraction (FR) towards those protected physically and/or chemically by soil minerals from decomposition (i.e., into macro and micro-aggregates [MA, MI] or interacting with mineral surfaces [MIN]).

Three different soils with different pH, SOM content and texture were used in the experiment. One aliquot of soil was spiked with approx. 8 Log cfu of spore of Bacillus clausii from a commercial preparation of 4 strains. DNA was extracted from soil and recovered from SOM pools isolated using a physical fractionation method [Plaza et al., 2012. CLEAN-Soil Air Water 40, 134-139] and quantified by fluorescence (Qubit).

DNA recovered from spiked vs. non-spiked samples followed two different patterns of distribution, according to the SOM fractions. Total DNA in the bulk soils varied according to the soil types and the effect of spiking 8 cfu was negligible. In the SOM fractions, while MI and MIN showed different concentration according to the soil type (no apparent influence of spiking), total DNA in FR was clearly higher for spiked samples, while MA had a putative interaction between soil type and spiking. Even if very preliminary, our results point out a possible mechanism of short-term distribution of exogenous DNA (through spores and potential vegetative forms of B. clausii germinated during the incubation) from the free SOM to the macroaggregates, with no apparent influence on MI and MIN yet.

Further analyses (e.g., PCR-ARISA and qPCR) will allow to disclose whether indigenous vs. exogenous bacterial DNA are differentially distributed in SOM, possibly enhancing the description of the mechanisms underlying the distribution of microbial communities in soil, according to the different organization of the SOM in soil aggregates.

How to cite: Beneduce, L., Plaza, C., Trotta, S., and Zaccone, C.: Interaction of exogenous microbial inoculum with soil organic matter fractions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6731, https://doi.org/10.5194/egusphere-egu2020-6731, 2020.

EGU2020-6997 | Displays | SSS5.2

Characterizing soil organic matter differences among extracts and the solid phase – the role of conservation tillage

Gergely Jakab, Tibor Filep, Csilla Király, Balázs Madarász, Dóra Zacháry, Marianna Ringer, Anna Vancsik, Malihe Masoudi, and Zoltán Szalai

Soil organic matter (SOM) is in the focus of research as it plays crucial role in soil fertility, carbon sequestration, and all adsorption related processes in the soil. Nevertheless, its compound and the methods to investigate it are rather diverse. Some approach prefers to define different theoretical carbon pools in the soil based on input and mineralization dynamics using mean residence times. Other studies apply physical and/or chemical fractionations of the soil to separate the various eg. mineral phase associated or aggregate occluded carbon pools to gain less heterogeneous material. However, in practice, these two approaches are hardly met each other. As a considerable part of SOM is strongly associated with the mineral colloid fraction or even cations its investigation reveals the question of extractions. Traditional methods aimed to extract pure SOM fractions such as fulvic and humic acids (FA; HA)  and characterized the whole SOM based on them, even though these pure fractions represented only a small part of the total SOM and were not present under natural conditions. Recent methods try to characterize the SOM using in situ samples where the role of organic mineral complexes is still not fully understood. As a result, findings based on several approaches are hardly comparable with each other. The present study aims to characterize SOM based on parallel in situ solid-phase investigation FA separation, and water dissolved organic matter extraction. The study site is a haplic Luvisol under plowing and conservation tillage. Fourier transform infrared spectroscopy on the solid phase fractions resulted in an inverse proportion between organic carbon content and aromaticity independently from tillage. The aggregate occluded SOM was characterized by the lack of aliphatic components, whereas the fine fraction, and the bulk soil associated SOM seemed to be rich in them. The water-soluble SOM revealed molecular size increase in both the fine fraction related and the aggregate occluded organic matter owing to plowing, nonetheless, aggregates occluded the same sized OM molecules as those attached to the fine fraction. In general, FA fractions provided more humified organic matter, whereas water dissolved SOM showed a more intensive microbiome origin. The photometric properties of the FA fractions did not differ between the tillage systems, except for the SUVA254, which provided higher aromaticity under conservation tillage due to the lack of plowing. Also, the water-soluble part of SOM showed more humified composition and increased aromaticity under conservation tillage compared to plowing tillage. As a consequence, beneath the fingerprint of recent microbial activity, DOM reflects soil organic matter composition as well, therefore it seems to be suitable as a direct SOM proxy. The present research was supported by the Hungarian National Research and Innovation Office (NKFIH) K-123953, which is kindly acknowledged.

How to cite: Jakab, G., Filep, T., Király, C., Madarász, B., Zacháry, D., Ringer, M., Vancsik, A., Masoudi, M., and Szalai, Z.: Characterizing soil organic matter differences among extracts and the solid phase – the role of conservation tillage, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6997, https://doi.org/10.5194/egusphere-egu2020-6997, 2020.

EGU2020-9794 | Displays | SSS5.2

Influences of repeated application of organic waste products on soil organic carbon content and stability assessed using Rock-Eval 6® thermal analysis

Amicie Delahaie, Pierre Barré, Lauric Cécillon, François Baudin, Camille Resseguier, Thierry Morvan, Denis Montenach, Florence Savignac, Aurélia Michaud, Florent Levavasseur, and Sabine Houot

The term Organic Waste Products (OWPs) encompasses a wide range of byproducts such as manure, sewage sludge or green waste compost. The use of OWPs impacts soil quality and functioning, agricultural yields, carbon (C) sequestration, biogeochemical cycles of nutrients like nitrogen (N) or phosphorus, and organic matter (OM) dynamics. These impacts likely depend on the considered OWP.

Taking advantage of 3 mid to long-term experimental trials (6 to 20 years) located in the Northern part of France (Paris region; Brittany; Alsace), we investigated the impact of 16 different OWPs on C content and stability. To do so, surface soil samples from replicated plots amended with the different OWPs used either alone or in addition with mineral N fertilization and appropriated control treatments were analyzed using Rock-Eval 6® thermal analyses. Samples taken up at the onset of the experiment and after 6, 18 and 20 years for the 3 sites respectively were analyzed. It resulted in the analyses of 248 different samples whose Rock-Eval 6® (RE6) signature can be used as a proxy for soil organic carbon (SOC) biogeochemical stability. In particular, we determined 2 RE6 parameters that were related to SOC biogeochemical stability in previous studies (e.g. Barré et al., 2016): HI (the amount of hydrogen-rich effluents formed during the pyrolysis phase of RE6; mgCH.g-1 SOC), and T50 CO2 oxidation (the temperature at which 50% of the residual organic C was oxidized to CO2 during the RE6 oxidation phase; °C). We also computed the amount of centennially stable SOC from RE6 parameters using the model developed in Cécillon et al. (2018).  

 

Our results showed that no clear effect of OWPs addition can be established for the youngest site (6 years). On the contrary, OWPs amendments had a clear effect on SOC quantity and quality at the sites having experienced 18 and 20 years of OWPs addition. For these sites, OWPs amendments increased SOC content, decreased SOC thermal stability (T50 CO2 oxidation) and increased the Rock-Eval 6® Hydrogen Index (HI) compared to control plots. OWPs amendments tended to increase slightly the amount of centennially stable SOC at the sites having experienced 20 years of repeated OWPs application. Our results suggest that if OWPs addition does increase SOC content, at least in the long run, the majority of this additional SOC is labile and may be quickly lost if OWPs additions are stopped.

 

References:

Barré P., Plante A.F., Cécillon L., Lutfalla S., Baudin F., Bernard S., Christensen B.T., Eglin T., Fernandez J.M., Houot S., Kätterer T., Le Guillou C., Macdonald A., van Oort F. & Chenu C. (2016) The energetic and chemical signatures of persistent soil organic matter. Biogeochemistry, 130: 1-12.

Cécillon L., Baudin F., Chenu C., Houot S., Jolivet R., Kätterer T., Lutfalla S., Macdonald A.J., van Oort F., Plante A.F., Savignac F., Soucémarianadin L.N. & Barré P. (2018) A model based on Rock-Eval thermal analysis to quantify the size of the centennially persistent organic carbon pool in temperate soils. Biogeosciences, 15, 2835-2849.

How to cite: Delahaie, A., Barré, P., Cécillon, L., Baudin, F., Resseguier, C., Morvan, T., Montenach, D., Savignac, F., Michaud, A., Levavasseur, F., and Houot, S.: Influences of repeated application of organic waste products on soil organic carbon content and stability assessed using Rock-Eval 6® thermal analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9794, https://doi.org/10.5194/egusphere-egu2020-9794, 2020.

EGU2020-11972 | Displays | SSS5.2

Larger contribution of non-protonated aromatics for organic matter in subsoil than topsoil horizons in Brazilian Ferralsols

Ivan F. Souza, Aline A. Vasconcelos, Robert L. Johnson, Luis Fernando J. Almeida, Emanuelle M. B. Soares, Klaus Schmidt-Rohr, and Ivo R. Silva

Several processes are involved in soil organic matter (SOM) formation and turnover across the soil profile. Interestingly, while deep soil C appears to turn over very slowly, it remains unclear whether this trend is related to the molecular chemistry of SOM retained therein or its interaction with the mineral matrix. Besides, the extent to which the molecular chemistry of SOM is related to the chemistry, amount, and frequency of C inputs in topsoil and subsoil horizons remains unclear. We addressed these questions by collecting soil samples from three deep Ferralsols (a Gibbsic, a Ferritic, and a Haplic Ferralsol) across the Brazilian Cerrado to include samples with distinct texture classes and mineralogical combinations. Interestingly, the vegetation of the Brazilian Cerrado is characterized by different proportions of trees and grasses, implying different depth of rooting. Moreover, the Cerrado biome is subjected to frequent fire events, which could affect the input rate and the chemistry of C added to the soils. At each site, samples were taken from topsoil (0–10 cm) and subsoil horizons (60–100 cm) and incubated with a double-labeled (13C and 15N) eucalypt litter for 12 months under laboratory conditions. After the incubation, the samples were submitted to physical fractionationation to isolate SOM within the particle-size fractions (PSF) greater and smaller than 53 µm. Subsequently, we quantified the total C and N remaining in these PSF. Subsamples of the clay+silt fraction (<53 µm) were treated with a 10% HF solution to concentrate SOM. The molecular composition of SOM within the HF-insoluble fraction was assessed by 13C/15N Nuclear Magnetic Resonance (NMR) spectroscopy by applying a multi/cross-polarization (multi/CP) pulse sequence, yielding a quantitative solid-state magic-angle spinning (MAS) 13C/15N NMR. After the incubation, litter-C was retained at approximate proportions in both PSF evaluated, while a larger fraction of the litter-N was concentrated within the clay+silt fraction. Based on the multi-CP MAS NMR results, carbohydrates (65–110 ppm) accounted for most of the total C forms identified in the HF-insoluble fraction, regardless of soil type, soil depth, and plant litter addition. In topsoil, differences in the molecular chemistry of SOM between samples treated with plant litter and the controls were small. Otherwise, plant litter inputs to subsoil led to major changes in the chemistry of SOM, with a substantial reduction in the proportion of non-protonated aromatics and the aromaticity degree of SOM. Although observed in the topsoil, this effect was much less pronounced for the three Ferralsols evaluated. In addition, following eucalypt litter addition the molecular composition of SOM in topsoil and subsoil tended to converge, becoming enriched in alkyl-C (0–46 ppm), carboxylic and/or amide groups (160–190 ppm for 13C and 120 ppm for 15N-NMR). Our results suggest that in topsoil, SOM molecular chemistry is consistent with a continuous supply of fresh plant litter. Otherwise, the deep burial of plant litter appears to be less relevant for SOM formation in subsoil horizons, where the accumulation of charred/pyrogenic materials are significant.

How to cite: F. Souza, I., A. Vasconcelos, A., L. Johnson, R., J. Almeida, L. F., M. B. Soares, E., Schmidt-Rohr, K., and R. Silva, I.: Larger contribution of non-protonated aromatics for organic matter in subsoil than topsoil horizons in Brazilian Ferralsols, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11972, https://doi.org/10.5194/egusphere-egu2020-11972, 2020.

EGU2020-18999 | Displays | SSS5.2

Does soil disturbance result in soil carbon losses? – A case study on bioturbation effects of wild boar

Axel Don, Christina Hagen, Erik Grüneberg, and Cora Vos

Soil disturbance and disruption is assumed to enhance mineralisation and cause losses of soil organic carbon. Therefore, no tillage is promoted as soil carbon sequestration measure. However, the experimental evidence of enhanced carbon turnover due to soil disturbance is rare.  We investigated soil disturbance in forest ecosystems with simulated bioturbation of wild boar. Wild boar are effective at mixing and grubbing in the soil and wild boar populations are increasing dramatically in many parts of the world. In a six-year field study, we investigated the effect of wild boar bioturbation on the stocks and stability of soil organic carbon in two forest areas at 23 plots. The organic layer and mineral soil down to 15 cm depth were sampled in the disturbed plots and adjacent undisturbed reference plots.

No significant changes in soil organic carbon stocks were detected in the bioturbation plots compared with non-disturbed reference plots. However, around 50% of forest floor carbon was transferred with bioturbation to mineral soil carbon and the stock of stabilised mineral-associated carbon increased by 28%. Thus, a large proportion of the labile carbon in the forest floor was transformed into more stable carbon. Carbon saturation of mineral surfaces was not detected, but carbon loading per unit mineral surface increased by on average 66% due to bioturbation. This indicates that mineral forest soils have non-used capacity to stabilise and store more carbon.

Our results indicate that soil disturbance and bioturbation alone does not affect soil carbon turnover and stocks, but only change the distribution of carbon in the soil profile. This is in line with results from no-tillage experiments. The prevailing effect is a redistribution of carbon in the soil profile with no changes in total soil carbon stocks. We discuss these findings in the light of soils as potential sinks for carbon.

 

How to cite: Don, A., Hagen, C., Grüneberg, E., and Vos, C.: Does soil disturbance result in soil carbon losses? – A case study on bioturbation effects of wild boar , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18999, https://doi.org/10.5194/egusphere-egu2020-18999, 2020.

EGU2020-983 | Displays | SSS5.2

Soil microstructure is sensible to ecosystem and land use changes: simple approach to monitoring C pools

Anna Yudina, Dmitriy Fomin, Yulian Farkhodov, Polina Tregubova, Konstantin Abrosimov, and Vladimir Cheptsov

Soil organic matter (SOM) as one of the main aggregation factors supports the hierarchy structure organization of soils. Structure organization at the micro-level (µm-mm) is based on soil primary particles, composite building units and microaggregates characterized by different SOM composition, stabilization mechanisms and dynamics (Yudina et al., 2018; Yudina & Kuzyakov, 2019). This presentation aims to show the specifics in composition and sensitivity of soil microstructure to ecosystem type and land use changes. The studied objects are Haplic Chernozems (Kursk region, Russia) under 6 land use types differing in vegetation: natural steppe, natural forest, conventional arable field, long-term bare fallow, and afforestation. Separation of C pools associated with particle size distribution (PSD) were obtained with high resolution by laser diffraction technique. Mathematical computations with PSD's allow to find localization of particles sensitive to the chosen factor. Two parameters (mean volume diameter MVD, µm and content of particles, %) for each of the three particle types (organo-mineral OMp, particulate organic matter POM, microaggregates µA) can be calculated. POM is the smallest (3 or less %) but the most labile solid phase C pool and very sensitive indicator to changes in land use and C accumulation with the soil depth. OMp is sensitive to long-term factors and were the lowest in bare fallow soil. Since Chernozems are well-structured soils, the content of µA is less sensitive than MVD, which vary from 50 µm under bare fallow to 170 µm in forest soil. Presented indicators in combination with C storage characterize role of SOM in soil microstructure organization. We have supposed that the differences in dynamics between OMp, POp and µA is attributable to internal particle structure and microbial availability of SOM. The marking particle types were separated for physical and biological justification of suggested indicators. Their thermal stability, specific surface area, microporosity, microbial activity and composition were characterized. Following hypotheses were tested: 1) content of the thermostable organic C fraction will increase from POM to µA and OMp; 2) value of specific surface area and porosity will be higher in µA compare to OMp. The proposed approach to describe C dynamics based on combination of high-resolution PSD data is a simple, sensitive and effective tool for monitoring of SOM pools dynamics.

Yudina, A. V., Fomin, D. S., Kotelnikova, A. D., & Milanovskii, E. Y. (2018). From the Notion of Elementary Soil Particle to the Particle-Size and Microaggregate-Size Distribution Analyses: A Review. Eurasian soil science, 51(11), 1326-1347. DOI: 10.1134/S1064229318110091

Yudina, A., & Kuzyakov, Y. (2019). Saving the face of soil aggregates. Global change biology, 25(11), 3574-3577. DOI: 10.1111/gcb.14779

The reported study was funded by Russian Foundation for Basic Research according to the research project No 18-34-00825.

How to cite: Yudina, A., Fomin, D., Farkhodov, Y., Tregubova, P., Abrosimov, K., and Cheptsov, V.: Soil microstructure is sensible to ecosystem and land use changes: simple approach to monitoring C pools, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-983, https://doi.org/10.5194/egusphere-egu2020-983, 2020.

EGU2020-1058 | Displays | SSS5.2

Soil organic matter in soils of the Russian Arctic: insights from 13C-NMR spectroscopy

Ivan Alekseev and Evgeny Abakumov

Polar soils play a key role in global carbon circulation and stabilization as they contain maximum stocks of soil organic matter (SOM) within the whole pedosphere. Cold climate and active layer dynamics result in the stabilization of essential amounts of organic matter in soils, biosediments, and grounds of the polar biome. Chemical composition of soil organic carbon (SOC) determines its decomposability and may affect soil organic matter stabilization (SOM) rate (Beyer, 1995). This is quite important for understanding variability in SOC pools and stabilization rate in context of changes in plant cover or climate (Rossi et al. 2016). 13C nuclear magnetic resonance spectroscopy, which provides detailed information on diversity of structural composition of humic acids and SOM, may also be used to study the SOM dynamics under decomposition and humification proceses (Kogel-Knabner, 1997; Zech et al., 1997). This study aims to characterize molecular organization of the humic acids, isolated from various permafrost-affected soils of Yamal region and to assess the potential vulnerability of soils organic matter in context of possible mineralization processes. Organic carbon stocks for studied area were 7.85 ± 2.24 kg m-2 (for 0-10 cm layer), 14.97 ± 5.53 kg m-2 (for 0-30 cm), 23.99 ± 8.00 kg m-2 (for 0-100 cm). Results of solid-state 13C-NMR spectrometry showed low amounts of aromatic components in studied soils. All studied humic powders are characterized by predominance of aliphatic structures, and also carbohydrates, polysaccharides, ethers and amino acids. High content of aliphatic fragments in studied humic acids shows their similarity fulvic acids. Low level of aromaticity reflects the accumulation in soil of lowly decomposed organic matter due to cold temperatures. Our results provide further evidence of high vulnerability and sensitivity of permafrost-affected soils organic matter to Arctic warming. Consequently, these soils may play a crucial role in global carbon balance under effects of climate warming.

How to cite: Alekseev, I. and Abakumov, E.: Soil organic matter in soils of the Russian Arctic: insights from 13C-NMR spectroscopy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1058, https://doi.org/10.5194/egusphere-egu2020-1058, 2020.

As the climate emergency gathers pace there is a growing imperative to reduce carbon emissions and move to a low carbon economy. Such shifts in global economics and politics will inevitably take time and therefore there is also a pressing need to identify immediate actions that can help limit or reduce carbon emissions.

 

Soils store large quantities of carbon. However, chemical, physical and biological properties limit the amount of carbon that any particular soil can store. It may be possible to alter soil properties such that the carbon sequestration potential of a soil is increased without causing a reduction in (or even increasing) other important ecosystem services delivered by the soil.

 

Soil aggregates are widely acknowledged to play an important role in the storage of carbon in soil. One limiting factor for aggregate formation in some soils is the amount of iron oxide present; the iron oxide is an important binding agent, holding aggregates together.

 

Ochres comprise a variety of poorly crystalline iron (III) oxides and form in a number of environments such as mine drainage when water moves to increasingly oxygenated environments and dissolved iron (II) is oxidised and precipitates from solution. In many countries these ochres are treated as wastes and are landfilled.

 

In batch experiments in which soil was amended with 0, 0.5 or 5% by mass ochre and shaken with water in a ratio of c. 1:5 (g:mL) ochre amendments reduced the concentration of dissolved organic carbon released into solution by almost a factor of 2. In experiments that are more realistic of field deployment of ochre amendments to increase soil carbon sequestration in which soils were amended with 0, 0.5 or 5% by mass ochre and kept moist for c. 9 weeks with treatments comprising presence/absence wheat and presence/absence earthworms, ochre amendments reduced the concentration of cold water extractable carbon by a factor of 2 and hot water extractable carbon by a factor of 1.3.


In this presentation the above results together with additional results relating to impacts on other soil properties will be presented. The data confirm the potential of waste iron ochres as a soil amendment to increase soil carbon sequestration though further work with more soil types and a variety of ochres is needed and the carbon footpring of applying the amendments needs to be calculated. Whilst methods such as these may provide vital time to transition to low carbon lifestyles, it is the move to such lifestyles that must be the ultimate solution to the climate emergency.

How to cite: Hodson, M. E.: Ochre amendments as a means of increasing carbon sequestration in soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1653, https://doi.org/10.5194/egusphere-egu2020-1653, 2020.

EGU2020-3020 | Displays | SSS5.2

Biotic and abiotic controls on carbon storage in aggregates from grassland soils in the Northern Limestone Alps of Germany

Noelia Garcia-Franco, Martin Wiesmeier, Roswitha Walter, Luis Carlos Colocho-Hurtarte, Vincent Buness, Bernd Josef Berauer, Marcus Zistl-schlingmann, Ralf Kiese, Michael Dannenmann, and Ingrid Kögel-Knabner

Alpine and pre-alpine grassland soils in Bavaria provide important ecosystem services and are hotspots for soil organic carbon (SOC) storage.  However, information on the underlying factors that control SOC stabilization via soil aggregation is limited. In three grassland soils with the same parent material but at different elevation (Fendt: 600 m.a.s.l, Graswang: 860 m a.s.l and Esterberg: 1,260 m a.s.l), we studied the soil aggregate distribution and associated SOC according to aggregate size classes (large-macroaggregates > 2,000 µm, small-macroaggregates 250-2000 µm, microaggregates 63-250 µm, silt plus clay particles <63 µm). Furthermore, the biomass and abundance of different ecological groups of earthworms were determined. Our results showed an increase in SOC contents and aggregate stability with elevation. SOC and N stocks of bulk soils showed the same trend as OC contents in aggregates.  Principal component analysis revealed that carbonates, SOC, aboveground plant biomass and the earthworm biomass are the main facilitating agents of aggregation and SOC and N storage in grassland soils of the Northern Limestone Alps of Germany

How to cite: Garcia-Franco, N., Wiesmeier, M., Walter, R., Colocho-Hurtarte, L. C., Buness, V., Berauer, B. J., Zistl-schlingmann, M., Kiese, R., Dannenmann, M., and Kögel-Knabner, I.: Biotic and abiotic controls on carbon storage in aggregates from grassland soils in the Northern Limestone Alps of Germany, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3020, https://doi.org/10.5194/egusphere-egu2020-3020, 2020.

EGU2020-11229 | Displays | SSS5.2

Does agricultural practices impact the quantity and the forms of organic carbon stored in cultivated soils of the Senegal groundnut basin? A Rock-Eval approach

Oscar Pascal Malou, David Sebag, Patricia Moulin, Tiphaine Chevallier, Yacine Badiane Ndour, Abou Thiam, and Lydie Chapuis-Lardy

Soil organic carbon (SOC) is a key element in the functioning of agrosystems. It ensures soil quality and productivity of cultivated systems in the Sahelian region. This study uses Rock-Eval pyrolysis to examine how cultural practices impact SOC quantity and quality of cultivated sandy soils in the Senegal groundnut basin. Such thermal analysis method provides cost-effective information on SOC thermal stability that has been shown to be qualitatively related to SOC biogeochemical stability. Soils were sampled within 2 villages agricultural plots representative of local agricultural systems and for local preserved areas. Total SOC concentrations ranged from 1.8 to 18.5 g.kg-1 soil (mean ± standard deviation: 5.6 ± 0.4 g.kg-1 soil) in the surface layer (0-10 cm) and from 1.5 to 11.3 g.kg-1 soil (mean ± standard deviation: 3.3 ± 0.2 g.kg-1 soil) in 10-30 cm deep layer. SOC of cultivated soils significantly (p-value < 0.0001) decreased according to treatments in the following order: +organic wastes > +manure > +millet residues > no input. Our results show that the quantity and the quality of SOC are linked to each other and both depend on land-use and agricultural practices, especially the nature of organic inputs. This correlation is very strong in the tree plantation (R² = 0.98) and in the protected shrubby savanna (R² = 0.97). It remains important for cultivated soils receiving organic wastes (R² = 0.82), manure (R² > 0.75), or millet residues (R2 = 0.91) but it’s no more significant in no-input situations. The Rock-Eval based indexes were depicted in a I/R diagram that illustrate the level of SOC stabilization and plotted against comparable results from literature. The Senegalese sandy soils have thermal signatures showing an inversion of the I and the R indexes compared to data from the literature and highlighting SOC stabilization as a function of soil depth. Indeed, the studied soils were characterized by a more abundant refractory pool (A5 which ranged from 7.7 to 21.3 % in 0-10 cm layer and from 12.5 to 24.3 % in 10-30 cm, respectively) compared to other tropical soils. The SOC in these sandy soils while positively affected by organic inputs is dominated by labile forms that mineralize quickly which is excellent for the needs of productivity of these agrosystems but not for mitigation of climate change.

Keywords: Soil organic carbon; Organic inputs; Thermal analysis; Agrosystems; West Africa

How to cite: Malou, O. P., Sebag, D., Moulin, P., Chevallier, T., Badiane Ndour, Y., Thiam, A., and Chapuis-Lardy, L.: Does agricultural practices impact the quantity and the forms of organic carbon stored in cultivated soils of the Senegal groundnut basin? A Rock-Eval approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11229, https://doi.org/10.5194/egusphere-egu2020-11229, 2020.

EGU2020-13082 | Displays | SSS5.2

The potential for full inversion tillage to increase soil carbon storage following pasture renewal in New Zealand

Mike Beare, Erin Lawrence-Smith, Denis Curtin, Sam McNally, Frank Kelliher, Roberto Calvelo-Pereira, and Mike Hedley

EGU2020-13609 | Displays | SSS5.2

Soil carbon respiration in tropical forest soils along geomorphic and geochemical gradients

Benjamin Bukombe, Laurent Kidinda, Alison Hoyt, Cordula Vogel, Marijn Bauters, Florian Wilken, Karsten Kalbitz, Peter Fiener, and Sebastian Doetterl

Tropical ecosystems and the soils therein have been reported as one of the most important and largest terrestrial carbon (C) pools and are considered important climate regulator. Carbon stabilization mechanisms in these ecosystems are often complex, as these mechanisms crucially rely on the interplay of geology, topography, climate, and biology. Future predictions of the perturbation of the soil carbon pool ultimately depend on our mechanistic understanding of these complex interactions.

Using laboratory incubation experiments, we investigated if carbon release from soils through heterotrophic respiration in the African highland forests of the Eastern Congo Basin follows predictable patterns related to topography, soil depth or geochemical soil properties that can be described at the landscape scale and ultimately be used to improve the spatial accuracy of soil C respiration in mechanistic models. In general, soils developed on basalt and granite parent material (mafic and felsic geochemistry of parent material) showed significantly (p <0.05) higher specific respiration than soils developed on sedimentary rocks (mixed geochemistry) with highest rates measured for soils developed on granite. For soils developed on basalt, specific respiration decreased two-fold with soil depth, but not for soils developed on granite or sedimentary rocks. No significant differences in respiration under tropical forest were found in relation to topography for any soil and geochemical background.

Using a non-linear,  stochastic gradient boosting machine learning approach we show that soil biological, physical and chemical properties can predict the pattern of specific soil respiration (R2=0.41, p<0.05). An assessment of the relative importance of the included predictors for soil respiration resulted in 43 % of the model being driven by geochemistry (pedogenic oxides, nutrient availability), 12 % driven by soil texture and clay mineralogy, 34 % by microbial biomass, C:N, and C:P ratios and 11 % by topographic indices. 

We conclude that, in order to explain soil C respiration patterns in tropical forests, a complex set of variables need to be considered that differs depending on the local bedrock chemistry. Its effect is likely related to the varying strength of C stabilization with minerals as well as nutrient availability that might drive C input patterns and microbial turnover.

How to cite: Bukombe, B., Kidinda, L., Hoyt, A., Vogel, C., Bauters, M., Wilken, F., Kalbitz, K., Fiener, P., and Doetterl, S.: Soil carbon respiration in tropical forest soils along geomorphic and geochemical gradients, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13609, https://doi.org/10.5194/egusphere-egu2020-13609, 2020.

Agricultural soils in Germany store about 2.5 Pg (1 Pg = 1015 g) of organic carbon in 0-100 cm depth. If this carbon was all powdered charcoal, it would fill a train with 61 million carriages, extending 2.5 times the distance to the moon. This study aimed at better understanding the origin of the organic carbon contained in mineral soils under agricultural use. For this, total organic carbon (TOC), C:N ratios and particulate organic carbon (POC) of 2,939 crop- and grassland sites scattered in a 8x8 km grid across Germany were evaluated. RandomForest algorithms were trained to predict TOC, C:N, POC and their respective depth gradients down to 100 cm based on pedology, geology, climate, land-use and management data. The data originated from the first German Agricultural Soil Inventory, which was completed in 2018, comprising 14,420 mineral soil samples and 36,163 years of reported management.

In 0-10 cm, land-use and/or texture were the major drivers for TOC, C:N and POC. At larger depths, the effect of current land-use vanished while soil texture remained important. Additionally, with increasing depth, soil parent materials and/or pedogenic processes gained in importance for explaining TOC, C:N and POC. Colluvial material, buried topsoil, fluvio-marine deposits and loess showed significantly higher TOC and POC contents and a higher C:N ratios than soil that developed from other parent material. Also, Podzols and Chernozems showed significantly higher TOC and POC contents and a higher C:N ratio in the subsoil than other soil types at similar depths because of illuvial organic matter deposits and bioturbation, respectively. In 30-70 cm depth, many sandy sites in north-western Germany showed TOC, POC and C:N values above average, which was a legacy of historic peat- and heathland cover. The depth gradients of TOC, POC and C:N showed only little dependence on soil texture suggesting that they were robust towards differences in carbon stabilization due to organo-mineral associations. Instead, these depth gradients were largely driven by land-use (redistribution of carbon in cropland by ploughing) and variables describing historic carbon inputs (e.g. information on topsoil burial). Hardpans with packing densities > 1.75 g cm-3 intensified the depth gradients of TOC, POC and C:N significantly, suggesting that such densely packed layers restricted the elongation of deep roots and therefore reduced organic carbon inputs into the subsoil.

Today’s soil organic carbon stocks reflect past organic carbon inputs. Considering that in 0-10 cm, current land-use superseded the effect of past land-cover on TOC while land-use showed no effect on POC and C:N, we conclude that topsoil carbon stocks derived from relatively recent carbon inputs (< 100 years) with high turnover. In the subsoil, however, most carbon originated from the soil parent material or was translocated from the topsoil during soil formation. High C:N ratios and POC content of buried topsoils confirm low turnover rates of subsoil carbon. The contribution of recent, root-derived carbon inputs to subsoils was small but significant. Loosening of wide-spread hardpans could facilitate deeper rooting and increase carbon stocks along with crop yield.

How to cite: Schneider, F. and Don, A.: What do carbon fractions and C:N ratios tell us about the origin of carbon in German agricultural soils?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18540, https://doi.org/10.5194/egusphere-egu2020-18540, 2020.

SSS5.5 – Biomass and waste valorization within a circular economy: from urban mining to soil amendments

EGU2020-22161 | Displays | SSS5.5 | Highlight

Evaluating phosphorus availability from sewage sludge derived pyrochar and hydrochar in European agriculture

Maria Pimenta, Ruben Sakrabani, Wilfred Otten, Gabriel Gasco, and Ana Maria Mendez

Currently, phosphorus (P) mine reserves are monopolised by several countries and its market price variations represents a challenge for modern agriculture systems. Consequently relying on alternative renewable sources of P such as sewage sludge (SS) is timely as its supply is expected to increase with population worldwide. However, this has to be carefully managed to ensure potential pollutant transport when applied to soils.

However, alternative treatment options can reduce this risk and create greater value from SS as a P-fertiliser. By carbonizing the residues through Pyrolysis or Hydrothermal Carbonization (HTC), organic pollutants can be significantly decomposed, and its volume reduced, which ease enormously its management (R. Huang & Tang, 2015). Different characteristics will be obtained depending on the thermal process and the conditions to which the sample is subjected, differentiating the potential applications of the pyrochar/hydrochar obtained respectively. Nevertheless, the data gathered for yield crop responses from sewage sludge thermal derivatives is still very scarce and hence more information needs to be produced.

The aim of this research is to evaluate interactions in phosphorus availability of spring wheat from SS and its thermally treated derivatives, when added on its own and in combination with raw SS as soil amendment. Two pyrochars were produced at the Polytechnic University of Madrid though pyrolysis at 400⁰C-1h and 300⁰C-1h using pre-oven dried (105⁰C-48h) sewage sludge from Spain.  Two hydrochars were obtained through Hydrothermal Carbonization in another reactor at 180⁰C-4h and 240⁰C-4h using raw sludge adjusted to 15% d.m. All samples were analyzed for physical-chemical changes and applied to the soil in a glasshouse experiment.

Results confirmed different degrees of carbonization through the selected treatments, gaining similar characteristics to sub-bituminous coals after pyrolysis and midpoint after HTC. A germination test indicated that the phytotoxicity of the raw material was reduced after all thermal treatments, with the best effect being through pyrolysis. However, P availability was reduced in all derivatives, 65.6% in Pyrochars and 41.5% HTC from the original SS.

 A 136 pots study with amended soils at different rates showed that despite P availability on initial conditions, after 3 months P became more available, being at least twice the amount found in the original soil, higher if the treatments were combined with additional wet SS (1:1). It also revealed a reduction of pHinitial=[7-8] to pHfinal=[6-7] after harvesting and a slight increment on the Electrical Conductivity [0.15-6.7]µS/cm (max value 16.6µS/cm) probably due the different mineralization of the derivatives amendments and the washing of the materials through the soil profiles.

The data gathered with this research to date suggests that, the addition of the sewage sludge derivatives on their own indeed decreases the production of grain. However, with the combination of a commercialized sludge (SS2) at the highest rate, no negative effects have been reported after the first crop season. Derived pyrochar and hydrochar offer an alternative source of available phosphorus to mitigate the growing demand of mineral phosphorus reserves whilst providing at the same time a good base of organic matter for low fertile soils.

How to cite: Pimenta, M., Sakrabani, R., Otten, W., Gasco, G., and Mendez, A. M.: Evaluating phosphorus availability from sewage sludge derived pyrochar and hydrochar in European agriculture, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22161, https://doi.org/10.5194/egusphere-egu2020-22161, 2020.

EGU2020-6817 | Displays | SSS5.5

Conifer wood biochar as an amendment for agricultural soils in South-Tyrol: impact on greenhouse gases emissions and soil carbon stocks

Irene Criscuoli, Maurizio Ventura, Katja Wiedner, Bruno Glaser, Pietro Panzacchi, Christian Ceccon, Marta Petrillo, Damiano Zanotelli, Carlo Andreotti, and Giustino Tonon

Biochar is a carbonaceous material produced through the pyro-gasification of biomass. In the last decade, biochar has been proposed as a soil amendment because it can improve soil physico-chemical properties and carbon stocks, contributing to climate change mitigation.

In the framework of the Wood-Up project (Optimization of WOOD gasification chain in South Tyrol to prodUce bioenergy and other high-value green Products to enhance soil fertility and mitigate climate change, FESR1028), we studied the impact of conifer wood biochar on the emissions of the main greenhouse gases (GHGs) from the soil: carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4), as well as on the soil carbon stock of agricultural fields in South Tyrol.

In May 2017, 25 and 50 t ha-1 of pure biochar and biochar mixed with compost (45 t ha-1), were applied to the soil of a vineyard near Merano (South-Tyrol, northern Italy) following a randomized block experimental design with four replicates per treatment.

Soil GHGs fluxes were monitored from June 2017 until December 2019. Fluxes were measured, in real time, with a high-resolution portable multi-gas analyzer based on cavity ring-down spectroscopy technology (Picarro inc., Santa Clara, CA, USA) connected to an automated dynamic chambers system (Eosense Inc., Dartmouth, NS, Canada). Gas emissions were measured monthly and were related to soil temperature and moisture to evaluate the impact of treatments on the sensitivity of GHGs fluxes to environmental parameters. The stability of conifer wood biochar in soil was assessed through the quantification of the Benzene PolyCarboxylic Acids (BPCA), specific biomarkers of black carbon, over time. The BPCA content in the soil was measured before the application of biochar and compost, three weeks after the application and two years later.

During the first year of experiment, in biochar-amended soils, we observed a reduction of the temperature sensitivity of all GHGs fluxes in comparison to treatments without biochar (control and compost alone). In the second and third year an opposite trend was observed, with an increase of temperature sensitivity of GHGs fluxes in biochar-treated soil. The change of biochar effect over time might be linked to biochar ageing in soil. However, a role of soil moisture cannot be excluded, as it was higher in the first year of experiment. The experimental results will be presented in the broader context of the Wood-Up project.

How to cite: Criscuoli, I., Ventura, M., Wiedner, K., Glaser, B., Panzacchi, P., Ceccon, C., Petrillo, M., Zanotelli, D., Andreotti, C., and Tonon, G.: Conifer wood biochar as an amendment for agricultural soils in South-Tyrol: impact on greenhouse gases emissions and soil carbon stocks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6817, https://doi.org/10.5194/egusphere-egu2020-6817, 2020.

EGU2020-856 | Displays | SSS5.5

Effect of biochar application at a trace-elements polluted area on soil carbon stability

Paloma Campos Díaz de Mayorga, Ana Z. Miller, Heike Knicker, Águeda Sánchez-Martín, Elena Fernández-Boy, and José María De la Rosa

Biochar, the solid carbonaceous material produced by pyrolysis of biomass, is a promising alternative for restoring degraded soils [1]. Specifically, biochar has been reported to increase agronomic productivity of acidic soils. Nevertheless, the theoretical high stability and recalcitrance of biochar is being questioned by recent studies [2]. In addition, the alterations on biochar C after its application into low C soil is still under debate. Thus, this study intends to evaluate the changes in carbon stability when biochars from different feedstock are applied into trace element polluted soils.

For this purpose, biochars were produced from rice husk-RHB, olive pit-OPB and almond shell-ASB using a steel batch reactor (temperature of 500 ºC; reaction time of 2 h under N2 atmosphere with a heating rate of 20 ºC min-1). A certified wood biochar (CWB) was also studied for comparative purposes. Two soils with a moderate and a high concentration of trace elements (called MPS and HPS respectively) were sampled for this study. Mixtures of each soil and 10 % (w/w) of the biochars were prepared in triplicates. Each pot was inoculated with 1 ml of a standard microbial suspension, the moisture was adjusted to 50 % of the water holding capacity and incubated in the automatic respirometer Respicond (Nordgren Innovations, Sweden) at 25 ºC for 60 days similarly to the procedure described by De la Rosa et al (2018) [2]. The CO2 released was measured automatically every 6 h and the kinetics of the biological decomposition of the materials were fitted by a double exponential model. Results showed that the feedstock nature influenced the decomposition rates. Thus, the biochar stability of the tested materials followed the order ASB>RHB>OPB according to MTR2.

Soil respiration showed a different C decomposition rate in both soils, having greater mean residence time in HPS (MTR2=14.9 years) than in MPS (MTR2=5.7 years). Our findings suggest that biochar addition increased the MTR2 of the slow C pool in both soils.

References:

[1] Lehmann, J., Joseph, S., 2015. Biochar for environmental management: science and technology. 2nd ed. London & New York: Earthscan from Routledge.

[2] De la Rosa, J.M., Rosado, M., Paneque, M., Miller, A.Z., Knicker, H., 2018. Effects of aging under field conditions on biochar structure and composition: Implications for biochar stability in soils. Science of the Total Environment 613-614, 969-976.

Acknowledgements:

The former Spanish Ministry of Economy, Industry and Competitiveness (MINEICO) and AEI/FEDER are thanked for funding the projects CGL2016-76498-R and GL2015-64811-P. P. Campos thanks the “Fundación Tatiana Pérez de Guzmán el Bueno” for funding her PhD.

How to cite: Campos Díaz de Mayorga, P., Miller, A. Z., Knicker, H., Sánchez-Martín, Á., Fernández-Boy, E., and De la Rosa, J. M.: Effect of biochar application at a trace-elements polluted area on soil carbon stability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-856, https://doi.org/10.5194/egusphere-egu2020-856, 2020.

EGU2020-2880 | Displays | SSS5.5

Biochar from sugarcane residues: An overview of its sequestration potential in Sao Paulo, Brazil

David Lefebvre, Jeroen Meersmans, Guy Kirk, and Adrian Williams

Harvesting sugarcane (Saccharum officinarum) produces large quantities of biomass residues. We investigated the potential for converting these residues into biochar (recalcitrant carbon rich material) for soil carbon (C) sequestration. We modified a version of the RothC soil carbon model to follow changes in soil C stocks considering different amounts of fresh sugarcane residues and biochar (including recalcitrant and labile biochar fractions). We used Sao Paulo State (Brazil) as a case study due to its large sugarcane production and associated soil C sequestration potential.

Mechanical harvesting of sugarcane fields leaves behind > 10 t dry matter of trash (leaves) ha-1 year-1. Although trash blanketing increases soil fertility, an excessive amount is detrimental and reduces the subsequent crop yield. After the optimal trash blanketing amount, sugarcane cultivation still produces 5.9 t C ha-1 year-1 of excess trash and bagasse (processing residues) which are available for subsequent use.

The available residues could produce 2.5 t of slow-pyrolysis (550°C) biochar C ha-1 year-1. The model predicts this could increase sugarcane field soil C stock on average by 2.4 ± 0.4 t C ha‑1 year‑1, after accounting for the climate and soil type variability across the State. Comparing different scenarios, we found that applying fresh residues into the field results in a smaller increase in soil C stock compared to the biochar because the soil C approaches a new equilibrium. For instance, adding 1.2 t of biochar C ha‑1 year‑1 along with 3.2 t of fresh residue C ha‑1 year‑1 increased the soil C stock by 1.8 t C ha‑1 year‑1 after 10 years of repeated applications. In contrast, adding 0.62 t of biochar C ha‑1 year‑1 with 4.5 t of fresh sugarcane residues C ha‑1 year‑1 increased the soil carbon soil stock by 1.4 t C ha‑1 year‑1 after 10 years of application. These are reductions 25% and 40% of the potential soil C accumulation rates compared with applying available residues as biochar.   

We also tested the sensitivity of the model to biochar-induced positive priming (i.e. increased mineralization of soil organic C) using published values. This showed that the C sequestration balance remains positive over the long term, even considering an extremely high positive-priming factor. Upscaling our results to the total 5 Mha of sugarcane in Sao Paulo State, biochar application could sequester up to 50 Mt of CO2 equivalent per year, representing 31% of the emissions attributed to the State in 2016.

This study provides first insights into the sequestration potential of biochar application on sugarcane fields. Measurements of changes in soil C stocks in sugarcane field experiments are needed to further validate the model, and the emissions to implement the practice at large scale need to be taken into account. As the climate crisis grows, the need for greenhouse gas removal technologies becomes crucial. Assessing the net effectiveness of readily available technologies is essential to guide policy makers.  

How to cite: Lefebvre, D., Meersmans, J., Kirk, G., and Williams, A.: Biochar from sugarcane residues: An overview of its sequestration potential in Sao Paulo, Brazil , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2880, https://doi.org/10.5194/egusphere-egu2020-2880, 2020.

Biochar is extensively used in environmental pollutant remediation because of its diverse property, however the effect of biochar on microbial nitrate reduction and electrochemical behavior of biochar remain unknown. Also electron transfer from the microbial cells to electron donor or acceptor have been transport across the extracellular polymeric substances (EPS), however it was unclear whether extracellular polymeric substances captured or enhance the electrons.  Hence, aim of the present study is to investigate the electrochemical behavior of biochar and its effects on microbial nitrate reduction and elucidate the role of extracellular polymeric substances in extracellular electron transfer (EET).  The biochar was prepared at different pyrolysis temperatures (400 °C, 500 °C and 600 °C) and their electrochemical behavior was characterized by electrochemical analysis (cyclic voltammetry, electrochemical impedance spectrum, chronoamperometry). Results demonstrated that all the biochars could donate and accept the electrons, impact of biochar on microbial nitrate reduction was studied and the results showed that biochar prepared at 400 °C significantly enhances microbial nitrate reduction process. Phenol O-H and quinone C=O surface functional groups on the biochar contributes in the overall electron exchange which accelerated the nitrate reduction. The role of EPS in EET by electrochemical analysis results reveals that outer membrane c-type cytochrome and flavin protein from the biofilm was involved in electron transfer process, and EPS act as transient media for microbial EET. Overall, present study suggested that biochar could be used as eco-friendly material for the enhancement of microbial denitrification.

How to cite: Sathishkumar, K., Li, Y., and Ikram, R. M. A.: Wood derived biochar as electron donor and its influence on microbial denitrification: Role of extracellular polymeric substances in extracellular electron transfer , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3824, https://doi.org/10.5194/egusphere-egu2020-3824, 2020.

EGU2020-20731 | Displays | SSS5.5

The Biochar challenge in Mediterranean viticulture: results from 10 years of field experiment

Silvia Baronti, Anita Maienza, Fabrizio Ungaro, Antonio,Antonello Montagnoli, Lorenzo Genesio, Alessandro, Girolamo Rombolà, Laura Giagnoni, and Francesco, Primo Vaccari

There are extensive reports and scientific articles in literature on the applicability of biochar as soil amendment in agriculture and on the benefits that this practice can bring in terms of soil improvement and optimization of water resources. The use of biochar as a soil amendment in agriculture is a suitable option that helps to mitigate the effects of climate change. Biochar has an approximate mean residence time in the soil over 1,000 years and this long-term stability is a fundamental prerequisite for considering biochar as a suitable method for carbon sequestration. Unfortunately, most literature provides results based on one-year trials. Not enough for a soil amendment to be able to claim effectiveness for many decades and not enough for a soil treatment to be considered irreversible. An effective option to fill this knowledge gap is represented by long-term field experiments. In this study, we investigated the effect of biochar application on plant water relations and soil properties during 10 years in a field experiment in Central Italy on Vitis vinifera. Biochar was applied at a rate of 22 t ha-1 in two consecutive growing seasons: 2009 and 2010. The results obtained during these years on biochar treatment compared to the control treatment are exciting: we demonstrated an increase in grape production, up to 66%, without a decrease of the grape quality, an increase in plant-soil water relations, no effects on the concentrations of soil PAHs, no eco-toxicity soil effect and a positive effect on soil chemical and biological parameters. Surprisingly, after 10 years the biochar effect continued to demonstrate significant differences among treatments, in particular: a significant increase of soil biological quality, decrease in soil bulk density coupled with a corresponding increase in saturated hydraulic conductivity, an enhance in soil available water content and a significant improvement of plant water status. The modification of plant water availability induced by biochar application increase the resilience of vineyards to droughts, as demonstrated by the lower leaf potential and higher stomatal conductance. This effect has a significant impact on quantity and quality of grape production after 10 years. Moreover, in the long-term perspective the biochar demonstrates to have an effect on soil biological communities that resulted sensitive to biochar with positive increase of abundance of species related to soil moisture content and enhance of biodiversity index. According to these results, the viticulture is now in the position to provide an effective contribution to mitigate climate change and we expect that this will be an example for other Mediterranean countries.

How to cite: Baronti, S., Maienza, A., Ungaro, F., Montagnoli, A., Genesio, L., Rombolà, A. G., Giagnoni, L., and Vaccari, F. P.: The Biochar challenge in Mediterranean viticulture: results from 10 years of field experiment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20731, https://doi.org/10.5194/egusphere-egu2020-20731, 2020.

Soil organic carbon management is a key element in solving such urgent global-scale challenges as overcoming degradation of soils and mitigating climate change. Organic fertilizers application has a significant potential for sequestering C in soils, but their efficiency depends on decomposition characteristics. Firstly, it noted the dependence of resynthesis of humic compounds in a soil on a quality of organic inputs, secondly - a need for zonal approach to fertilizers production based on amphiphile properties of macromolecules.

The present study was conducted in long-term field experiment on black soil in Forrest-Steppe zone of Ukraine. The technology of production of organo-mineral fertilizers (OMFs) was based on the regulated processing of livestock waste with mineral components to stabilize it with hydrophobic bonds. OMFs in amorphous and granular form were compared in case of broadcast and band method of incorporation. The dose of OMF input was equivalent 350 C kg ha-1 and 80 N, 80 P, 80 K kg ha-1. Organic carbon content in soil was determined by Turin method. Different organic matter fractions were isolated: humic acids (HA), fulvic acids (FA), and humin.

The soil C accumulation rates in OMF treatment was by 15 % higher than in manure treatment and up to 70 % higher than in chemical fertilizer treatment, respectively. The soil C accumulation was strongly influenced by the form of OMF and method of their application. The highest TOC level was found over band application of amorphous OMF, accumulating 6.2 t C ha–1 yr–1 in 0-20 cm soil layer. Lower efficiency of broadcast incorporation OMFs could be explained by more intensive mineralization due to higher aeration. Taking into account the effect of OMFs on C stock an advantage of amorphous form versus granulated OMF with similar composition was proven. Black soil on control plot (without fertilization) had almost equal ratio between HA, FA and humin in humus composition. The content of humic compound increased in all treatments. Applying OMF significantly increased HA content in black soil compared to applying mineral fertilizer. OMFs application promoted the increase of the degree of condensation of organic matter. The highest HA/FA was found under the effect of broadcast incorporation OMF. That means that low molecular weight compounds were rapidly degraded while more resistant to mineralization HA were formed in soil. There was no significant difference in humus composition between amorphous and granulated OMF.

How to cite: Hetmanenko, V., Skrylnyk, I., and Kutova, A.: Soil Organic Carbon Accumulation under Different Forms of Organo-Mineral Fertilizers and Methods of Their Application on Ukrainian Black Soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3282, https://doi.org/10.5194/egusphere-egu2020-3282, 2020.

Biochar is a carbon-rich black stable solid substance that when utilized as soil amendment can effectively mitigate greenhouse gas (GHG) emission. However, during the pyrolysis process of organic feedstock (i.e. manure) greenhouse gases are released as the feedstock undergo thermochemical degradation. Many studies were reported with regards to the effectiveness of biochar to mitigate greenhouse gas emission and to maintain soil quality via carbon sequestration. However, no clear investigation was done regarding biochar utilization on reducing GHG emission in an integrated perspective that starts from pyrolysis (production) to field application (utilization). To evaluate the integrated influence of biochar utilization on the overall Global Warming Potential (GWP) and (Greenhouse Gas Intensity) GHGI at different temperature, the fluxes of GHGs during feedstock pyrolysis to soil application were calculated. The key components include GHGs released during production processes and biogenic GHG emissions taking place in the soil via short-term incubation experiment in lowland and upland condition treated with biochar pyrolyzed at different temperature. Highest pyrolysis temperature of 700oC emitted 6.92 Mg CO2-eq ton-1 biochar, wherein 8.7% and 91.2% was contributed by Carbon dioxide (CO2) and Methane (CH4) effluxes, respectively, during pyrolysis. This GHG emission during pyrolysis at 700oC was 5.6, 2.2, and 1.5 times higher than at 400oC, 500oC and 600oC, respectively. Meanwhile, biochar produced at lowest temperature (Biochar400) when utilized as soil amendment emitted 43.4 and 38.2 Mg CO2-eq ha-1 in lowland and upland condition, respectively. In addition, this emission value under lowland (and upland) condition was 1.38 (1.36), 1.51 (1.56) and 1.86 (1.91) times higher than Biochar500, Biochar600 and Biochar700, respectively. Combining the GWP during the production and the utilization processes in lowland and upland condition reveal that at 400oC emanates the lowest overall GWP of 93.3 and 88.1 Mg CO2-eq ha-1, respectively.  Moreover, under lowland (and upland) condition, overall GWP at 400oC was noted to be 65.7% (71.7%), 131.6% (140.4%) and 221.9% (237.1%), lower than at 500oC, 600oC and 700oC, respectively. In conclusion, the use of lower temperature during biomass pyrolysis and utilization of its derived biochar could be a practical approach to mitigate GHG emissions.

 

Keywords: Biochar, Pyrolysis, Greenhouse gas, Methane, Global warming potential, Greenhouse gas intensity

How to cite: Canatoy, R., Jeong, S. T., and Kim, P. J.: Biochar production under low pyrolysis temperature leads to lesser overall global warming potential and greenhouse gas intensity under lowland and upland short-term condition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6273, https://doi.org/10.5194/egusphere-egu2020-6273, 2020.

EGU2020-9632 | Displays | SSS5.5

Effect of biochar addition to compost on biological stability of the mixture

Aubertin Marie-Liesse, Girardin Cyril, Houot Sabine, Le Brech Yann, Bena Sarah, and Rumpel Cornelia

Application of biochar, a solid product produced from biomass pyrolysis under low oxygen conditions, has been suggested as a low emission technology capable of increasing soil C sequestration to mitigate climate change. Its combined application with compost may be a promising avenue to ameliorate soil quality while increasing C sequestration. We hypothesized that biochar addition to compost reduces the mineralization of the mixture compared to compost alone. The study aimed to compare the mineralization rate of six biochar-compost mixtures differentiated by biochar feedstocks. Biochars were produced at temperatures ranging from 450 to 650°C for 10 minutes. Our conceptual approach included incubation of fresh and artificially aged biochar-compost mixtures. Physical ageing of the mixtures was performed with successive cycles of humidification/drying and freezing/thawing. We evaluated elemental composition and biological stability of the fresh and aged mixtures after incubation with a soil inoculum for 1 year. We monitored components of biochar-compost mixtures decomposition when biochar were produced from C4 feedstock by determination of the 13C signature of emitted CO2.

Combination of compost with biochar induced synergistic effects in terms of the mixtures stability. Isotopic analyses showed that carbon mineralization from compost was greatly reduced, while biochar mineralization was increased. Physical ageing induced a strong leaching of water-soluble compounds of both substrates. Carbon mineralization of aged material was however not reduced as much as expected when comparing with mineralization rates of single compounds of the mixture. Furthermore, isotopic signatures showed that compost, when amended with biochar, mineralized better after ageing. We thus suggest that the water-soluble fraction of biochar may induce an inhibitive effect on the mineralization of compost. The intensity of this effect seems to be dependent upon the feedstock of the biochar in the mixture.

We conclude that biochar addition to compost may reduce the mineralization of the mixture depending on biochar feedstock and that this effect may be alleviated after ageing.

How to cite: Marie-Liesse, A., Cyril, G., Sabine, H., Yann, L. B., Sarah, B., and Cornelia, R.: Effect of biochar addition to compost on biological stability of the mixture, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9632, https://doi.org/10.5194/egusphere-egu2020-9632, 2020.

Biochar is related to multiple greenhouse gas (GHG) mitigation potentials, namely nitrous oxide (N2O) mitigation, carbon (C) sequestration and the possible green electricity produced in the pyrolysis process. Whereas the mechanisms behind potential N2O mitigation effects of biochar are still unclear, the mechanisms behind C sequestration is agreed to be caused by C compound conversion towards aromatic structures in the biochar C as a consequence of the heating treatment in the pyrolysis process. The specific recalcitrance of the biochar is, however, difficult to estimate. The possible electricity production from the syn-gas and bio-oil pyrolysis products depends on the feedstock and process temperature, and can contribute considerably to total system GHG mitigation. However, the multiple effects on GHG balances of biochar and pyrolysis represent a complexity, which may best be analysed by a life cycle assessment (LCA) approach. In this study, the average Danish oilseed rape cultivation was set as the reference scenario in an LCA of cultivation related GHG emissions. The reference was compared with two scenarios with theoretical inclusion of pyrolysis and biochar, meaning that the oilseed straw residue was transported to a pyrolysis plant and the biochar was returned to the field in a corresponding amount (ca. 1 Mg ha-1). Transportation, additional field operations, N2O mitigation, electricity production and C sequestration was included, and the latter was calculated by using the concept of avoided atmospheric CO2 load. The latter approach resulted in larger mitigation effects than derived from calculations of just the remaining C in soil. In total, GHG emissions were reduced by 73 to 83% in the two biochar scenarios as compared with the reference scenario, mainly due to increased C sequestration. The study suggests that even low application rates and rather conservative biochar C recalcitrance estimates lead to considerably reductions in GHG emissions from oilseed rape and expectedly other crops.

How to cite: Thers, H., Njakou Djomo, S., Elsgaard, L., and Trydeman Knudsen, M.: Biochar reduces total greenhouse gas emissions from oilseed rape cultivation, mainly due to C sequestration quantified by the concept of avoided atmospheric CO2 load – a theoretical life cycle assessment study., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20412, https://doi.org/10.5194/egusphere-egu2020-20412, 2020.

EGU2020-17771 | Displays | SSS5.5

The use of MSW-compost on land, a study of metal and nutrient leaching
not presented

Jessica Graca, Brian Kelleher, and Brian Murphy

It is estimated that up to 138 million tonnes of bio-waste are produced in Europe annually, with only 25% being recycled into high-quality compost and digestate. Currently, residual organic waste is generated as by-product of municipal solid waste treatment. Its reuse options vary across EU countries, due to the lack of clear guidance at European level. In some countries, compost derived from municipal solid waste (MSW – compost) is restricted to being used as landfill cover or in land reclamation, under the premises of meeting national legal criteria. Other countries, have regulated its used as marketable compost if it meets defined compost standards. However, for many countries the value-added use of MSW derived compost is uncertain.

The restricted use of MSW - compost is linked to the organic and inorganic contamination associated with such a heterogeneous material. Despite this, under the European view of the Circular Economy, MSW-compost has great potential to be reused and recycled for the benefit of all. Controlled use on land would off-set carbon emissions by diverting the material from a waste that is largely incinerated or added to landfill to a carbon positive soil additive that increases soil quality particularly in restoration sites. 

Our study aims to risk-assess the use of MSW-compost as a soil amendment by monitoring resulting water run-off for metal and nutrient content. Leaching trials, conducted over 6 months were performed in a forest soil (20 cm depth) with a history of Sitka Spruce plantation (c.a 20 years). Adapted water storage tanks were set-up to conduct the trials. Leachate was collected weekly in the first two months, and monthly thereafter. Four treatments 1) control, 2) sewage sludge chemically stabilized (10 t/ha), 3) MSW-compost (10 t/ha) and 4) MSW-compost (25 t/ha) were established in duplicate. Sewage sludge was used as a comparison material, due to its current legal status allowing for controlled land spreading. Leachate samples were analysed for nitrate, ammonium and the metals aluminium, cadmium, copper, total chromium, mercury, nickel, zinc and lead. 

Preliminary results from the first 6 weeks show that metals concentrations in the leachate from all trials were below threshold criteria in surface water quality regulations. Levels of ammonium above detection limits were only detected at week one and surpassed 0.2 mg/L. Nitrate concentration in the leachates was found to be below 50 mg/L and it peaked in the sewage sludge and MSW-compost (25 t/ha) at week 2.

Results gathered so far show that the use MSW-compost in land compares to sewage sludge application in relation to their potential for water pollution. MSW-compost could be used as a soil improver under a regulatory alignment similar to the sewage sludge regulations, aligned with the current European Circular Economy goals.

How to cite: Graca, J., Kelleher, B., and Murphy, B.: The use of MSW-compost on land, a study of metal and nutrient leaching , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17771, https://doi.org/10.5194/egusphere-egu2020-17771, 2020.

EGU2020-11376 | Displays | SSS5.5

Long Term Experiment Platform (LTEP) to establish the effectiveness of biochar applications: a case study in vineyards at Tebano, Ravenna, Italy.

Nicolas Greggio, Carlotta Carlini, Francesco Vaccari, Silvia Baronti, Andrea Contin, and Diego Marazza

In the recent years many papers explored the potentiality of biochar as soil improver as for water retention capacity and chemical and biological fertility. Many of these studies are 1-2 years lab-scale to study the biochar short term effects.

Although is well known that the behavior of biochar in soil changes with the progress of time, few are the open-field 5 years longer experiments which we propose to consider as Long Term Experiments (LTE). Furthermore the few current LTE experiments repeat the same experimental design, changing every time biochar (feedstocks and pyrolysis parameters), soil type and crop.

In this context, there is an evident need for a common platform where assembling information e where new experiments can be designed to progress and demonstrate biochar effectiveness.

The ICHAR (the Italian Biochar Association) and the University of Bologna - CIRSA Department are launching a Long-Term Experiment Platform (LTEP) aiming to be the house for all the Italian LTE for agronomic applications of the biochar. The LTEP is currently based on data from more than 15 experiments in Italy, looking for include also other European trials and it is preparing an identity card with a) a description of the project and its objectives, b) site description, c) tested biochar and substrates, d) published results, e) a working group description.

As an example of application and identity card, we present the experiment started in Tebano during 2019. Differently from the other operating LTEs, it brought biochar in a new vineyard field, amending soil before the shoot transplanting and just in proximity of the rows, exactly at root depth. The applied biochar has been produced by local the vineyard pruning residues with the purpose to establish a closed circular pattern in grape cultivation. Biochar was applied to soil as such and blended with a fertilizing sludge-based compost, produced by a company owned by a winery cooperative.  The compost, labelled as ACFa in accordance to the Italian legislation, is obtained mixing ligno-cellulosic biomass and centrifuged-sludge from digestate from anaerobic digestion plants, in a ratio 6:4, respectively. Biochar as such and 3 blends were distributed, four replica each one, in a randomized design experiment. Each of the 20 treated parcels includes 15 grape plants. Soil characterization, before the amending and yearly at the end of the growing season is planned. Plant biomass, leaf nutrient content, quantity and quality of the production of grape and wine will be monitored. Weathering of the amending matrices, especially biochar will be investigated every year. From last summer, 4 stations for continuous monitoring of water content, electrical conductivity and temperature are operating for all the matrices.

The working group involved in the project is multidisciplinary including environmental scientist, chemists, soil experts, agronomic experts, grape and winery expert, as well as personnel of a regional research center for agronomic studies and personnel from the industry and winery cooperative of compost suppliers.

How to cite: Greggio, N., Carlini, C., Vaccari, F., Baronti, S., Contin, A., and Marazza, D.: Long Term Experiment Platform (LTEP) to establish the effectiveness of biochar applications: a case study in vineyards at Tebano, Ravenna, Italy., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11376, https://doi.org/10.5194/egusphere-egu2020-11376, 2020.

EGU2020-7464 | Displays | SSS5.5

Persisting effects of ligneous organic soil amendments on CO2, N2O and CH4 emissions in relation to moisture content in northern agricultural clay soil

Kenneth Peltokangas, Jimi Havisalmi, Jussi Heinonsalo, Kristiina Karhu, Liisa Kulmala, Jari Liski, and Mari Pihlatie

In agriculture, organic soil amendments are envisioned to mitigate climate change through carbon sequestration. However, the full impact of the organic amendments on soil physico-chemical dynamics is still poorly understood. We conducted a laboratory incubation to assess the net climate effect of four ligneous organic amendments: two biochars (willow and spruce) and two fiber byproducts of paper and pulp industry. Soil samples were collected from a soil-amendment field experiment at Qvidja farm, South-West of Finland. Soil samples were sieved, air-dried and adjusted to 30%, 50%, 80% and 110% of water holding capacity (WHC), and incubated for 32 days in standard laboratory conditions. Greenhouse gas (GHG) emissions were measured after 1, 5, 12, 20 and 33 days. 

The carbon dioxide (CO2) emissions were highest at 80% WHC, and lowest at severely water stressed conditions at 30% WHC. The organic amendments did not have an observable effect on CO2 dynamics. The CO2 emissions correlated linearly with soil moisture and microbial biomass nitrogen. Nitrous oxide (N2O) emissions were systematically lower in the amended soils compared to the control soil, and independent of soil nitrate concentrations. Without organic amendments, N2O emissions increased exponentially with soil moisture content. Methane (CH4) emissions fluctuated throughout the incubation, exhibiting mostly negative values. Consequently, CH4 emissions played only a minor role in the GHG budget.

CO2, N2O and CH4 emissions, calculated as CO2 equivalent, exhibited a linear correlation with the moisture gradient. CO2 dominated the GHG budget up to a moisture of 80% WHC, but was superseded by N2O emissions at 110% WHC. The results indicate that soil moisture content is critically affecting the GHG emissions and that while organic soil amendments may have persisting effects on GHG exchange, they primarily occur through N2O dynamics.

How to cite: Peltokangas, K., Havisalmi, J., Heinonsalo, J., Karhu, K., Kulmala, L., Liski, J., and Pihlatie, M.: Persisting effects of ligneous organic soil amendments on CO2, N2O and CH4 emissions in relation to moisture content in northern agricultural clay soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7464, https://doi.org/10.5194/egusphere-egu2020-7464, 2020.

EGU2020-21932 | Displays | SSS5.5

Graphene oxide modified magnetic sludge biochar as a green adsorbent for environmental concentration level of pesticide removal

Zulin Zhang, Yongfei Ma, Siyu Chen, Tingmei Lu, Lie Yang, and Li Wu

In addition to the advantage for resource utilization of municipal sludge which is an important solution to reduce the secondary pollution (e.g. landfill and incineration) to the environment, biochar derived from municipal sludge displayed a potential adsorption capacity for emerging contaminants, particularly with appropriate modification. This study synthesized a green adsorbent (Graphene oxide modified magnetic sludge biochar, GO/CoFe2O4-SBC), which showed the superiority of low cost, effective adsorption and separation for the environmental concentration level of pesticide (Imidacloprid, IMI) removal from water. The results suggested that higher dose and temperature would facilitate the contaminant removal. The optimum removal rate of IMI obtained at pH=6 was due to the weakest electrostatic repulsion. Pseudo-second kinetic, Freundlich and Temkin isotherm models fitted the experimental data, which indicated that both physisorption and chemisorption were involved in the adsorption process. The maximum adsorption capacity of sludge biochar (SBC), magnetic sludge biochar (CoFe2O4-SBC) and GO/CoFe2O4-SBC were 3.11×103, 5.99×103 and 8.92×103 μg g-1, respectively. Physicochemical characteristics, kinetics, isotherms and thermodynamics analysis suggested that the better adsorption performance for GO/CoFe2O4-SBC was attributed to pore filling, π-π electron donor-acceptor and oxygen-containing functional groups (e.g. C=O, C-O, -OH, Fe-O and Co-O) interaction. IMI adsorption was a spontaneous endothermic process and GO/CoFe2O4-SBC exhibited the greater spontaneous. Ethanol extraction increased the regeneration of adsorbents and maintained more than 90% of adsorption capacity in the recycles (1-5 cycles) of the fresh. The leaching concentrations of Fe and Co of adsorbent (GO/CoFe2O4-SBC) were below drinking water standard (0.5 mg L-1) in the range of pH 3 to 12. In conclusion, this work not only provided a promising biochar (e.g. GO/CoFe2O4-SBC) with superior removal capacity for pesticides in water at low concentrations, but also offered a sustainable and cost-effective way for the resource utilization of municipal sludge.

How to cite: Zhang, Z., Ma, Y., Chen, S., Lu, T., Yang, L., and Wu, L.: Graphene oxide modified magnetic sludge biochar as a green adsorbent for environmental concentration level of pesticide removal, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21932, https://doi.org/10.5194/egusphere-egu2020-21932, 2020.

EGU2020-6953 | Displays | SSS5.5

Effect of sewage sludge biochar on tomato plant (Solanum lycopersicum L.) cultivation

Evan Diamadopoulos, Paraskevi Velli, and Ioanna Manolikaki

The present study refers to biochar production, its application to soil with or without combining it with compost, as well as its effect on tomato (Solanum Lycopersicum L.) cultivation. The feedstock selected for biochar production was a mixture of primary and secondary sewage sludge, which had previously been anaerobically digested and thermally dehydrated. Sewage sludge pyrolysis was conducted at 300 °C. The produced biochar was initially characterized and subsequently applied to soil, in order to study its effect on Solanum Lycopersicum L. cultivation. Pot trials which included four treatments, each comprising of three replicates, were carried out during a period of three months, using pots with a 10 kg capacity. More specifically, the following treatments were studied: i) Control (soil without biochar addition), ii) soil with biochar at a rate of 2% w/w (BC-SS), iii) soil with compost at a rate of 2% w/w (Compost), and iv) soil with a mixture of biochar and compost at a total rate of 2% w/w (BC-SS+Compost). The aim of the study was to examine whether sewage sludge biochar with or without compost affects: a) the dry weight and morphological characteristics of the plant, b) the concentrations of macronutrients, micronutrients and heavy metals in aboveground and belowground plant tissues, c) soil properties, including nutrients and heavy metals.

With biochar application a number of soil properties exhibited substantial improvement. Specifically, significant increases were noticed for TOC (67% - 85% increase), NO3–N (55% increase) and ΝΗ4–Ν (145% increase). Moreover, biochar with or without compost, substantially improved plant growth (25% – 34% increase in the first 40 days), and led to a significant increase of the dry weight of aboveground and belowground plant tissues. Heavy metal concentrations in plant tissues were quite low. Specifically, traces of Cr, Ni and Co were found only in plant roots, while Si was present in plant roots and stems. As, Mo and Pb were present in all plant tissues, albeit without exceeding the permissible levels established for vegetables. Finally, no traces of Hg, Se and Cd were found in any of the tissues.

Generally, sewage sludge biochar addition to soil, with or without compost, improved soil characteristics and increased plant yield. Moreover, heavy metal concentrations within permissible levels do not raise any concerns regarding safe consumption of tomato fruits.

 

How to cite: Diamadopoulos, E., Velli, P., and Manolikaki, I.: Effect of sewage sludge biochar on tomato plant (Solanum lycopersicum L.) cultivation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6953, https://doi.org/10.5194/egusphere-egu2020-6953, 2020.

EGU2020-7268 | Displays | SSS5.5

Environmental and Hydrological Implications of Innovative Sprayable Biodegradable Polymer Membrane: First Results

Vilim Filipović, Lana Filipović, Yusong Wang, Michael V. Braunack, Raju Adhikari, George Freischmidt, Priscilla Johnston, Phil S. Casey, and Keith L. Bristow

Agricultural management techniques like plastic mulch films are widely used to enhance crop production by conserving soil water and increasing temperature with the ability to suppress weeds. However, the use of plastic represents large environmental concern since the recovery of plastics from soils and its persistence in the environment is causing global problems. The EU in leading in policy with ban on single use plastics and it is a matter of time when conventional plastic mulch films will be banned as well. To solve the problem, researchers have turned their attention to biodegradable products while lately sprayable biodegradable polymer membrane (SBPM) technology was introduced. Here, we present first results of glasshouse study and in-field experiments with SBPM technology in Australia where with the use of subsurface drip irrigation we could improve water use efficiency of crops with reducing evaporation. First results indicate that SBPM technology could limit soil evaporation, reduce irrigation needs and prevent weed emergence while at the same time providing environmentally sustainable agricultural practice through its biodegradability, nontoxicity and sprayability nature. This innovative technology shows large potential even at this early development stage with the need for further improvement of SBPM formulation, management and properties.

How to cite: Filipović, V., Filipović, L., Wang, Y., Braunack, M. V., Adhikari, R., Freischmidt, G., Johnston, P., Casey, P. S., and Bristow, K. L.: Environmental and Hydrological Implications of Innovative Sprayable Biodegradable Polymer Membrane: First Results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7268, https://doi.org/10.5194/egusphere-egu2020-7268, 2020.

EGU2020-1114 | Displays | SSS5.5

Impacts of different treatment methods on spread of pathogens from organic wastes to vegetable crops in Nigeria

Vince Chukwu, Jo Smith, Norval Strachan, Lisa Avery, and Smart Obiekezie

Organic wastes, such as cattle manure, are widely used as organic amendments but may constitute a potential risk to human and animal health if they are not properly treated before application to agricultural soil. This study investigated the impact of different common household treatment methods on the reduction of pathogens in organic wastes and the spread of pathogens to food crops. Fresh cattle manure was subjected to three different treatments available to households; anaerobic digestion, burning and composting. Sub-samples were screened for E. coli contents using standard plating and IDEXX Colilert Quanti-Tray 2000 system. The numbers of organisms were used to assess the effectiveness of the treatment methods in the reduction of pathogens in the organic wastes. The E. coli count of the cattle manure was 391.42 CFU/g before treatment. After treatment, there was significant reduction in the E. coli in all treatments. Burning was most effective at reducing pathogens in the cattle manure (95%) followed by anaerobic digestion (50%) and composting (40%). Ash, bioslurry, compost and untreated manure were all significantly different in the ratio of pathogens to nitrogen. Bioslurry contained more nitrogen than ash, compost and untreated manure. Application of the recommended nitrogen dose of 120 kg/ha as bioslurry resulted in significantly lower contamination of soil (4.19 most probable number (MPN) per g) than ash (9.73 MPN/g), compost (6.89 MPN/g) or untreated manure (13.77 MPN/g). The E. coli content of lettuce grown on soil amended with ash, bioslurry or compost at recommended rates was significantly lower than lettuce crop grown on soil amended with untreated cattle manure. The results from this study provide information on the transmission of the pathogens remaining in the treated and untreated wastes when applied as organic fertilizer to food crops. This information will help to reduce the potential risks associated with the use of organic manures in growing food crops, as well as determining the optimum rate of application of organic waste after treatment.

How to cite: Chukwu, V., Smith, J., Strachan, N., Avery, L., and Obiekezie, S.: Impacts of different treatment methods on spread of pathogens from organic wastes to vegetable crops in Nigeria, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1114, https://doi.org/10.5194/egusphere-egu2020-1114, 2020.

The present study aimed to investigate the effect of the waste lemon extract on the flushing treatment of the copper-contaminated soil collected from contaminated farmland, in which the copper concentration was measured as high as 2487 mg/kg. The soil flushing solution was prepared using the extract from collected waste lemons. The soil flushing treatment using the solution containing commercial citric acids was also conducted for comparison. Additionally, the waste lemon was used for soil rehabilitation after composting treatment.

The soil copper concentration treated with the solution containing waste lemon extract decreased more than that treated by the commercial citric acid solution at the comparable citric acid concentration. This is because the waste lemon extract solution contains additional co-dissolved organic substances other than citric acid and the flushing treatment had a higher retention time. For the treatment with lemon extract, the soil pH values were 4.56, 5.70 and 6.29 before, after lemon extract flushing and after compost treatment. The copper plant availability dropped from 677 mg/kg for the soil before flushing to 156 mg/kg after stabilization with composted waste lemon. Therefore, the citric acid flushing combined with stabilization was found effective for heavy metal removal in the soil environment.

How to cite: Fan, C., Chang, P.-W., and Huang, Y.-Z.: Application of waste lemon extract to rehabilitate the copper-contaminated farmland through gravitational soil flushing and stabilization, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2681, https://doi.org/10.5194/egusphere-egu2020-2681, 2020.

EGU2020-2762 | Displays | SSS5.5

Iron-based water treatment residuals as sorbent of heavy metals and metalloids

Magdalena Wołowiec, Małgorzata Komorowska-Kaufman, Alina Pruss, Grzegorz Rzepa, and Tomasz Bajda

The ever-increasing water pollution caused by an increase in industrial activity in developing countries is a major worldwide problem. Heavy metal contamination is particularly dangerous because of their toxic and carcinogenic nature as well as harmful effects on human and animal health. Over the past decades, considerable efforts have been made to develop effective technologies for removing heavy metals from water. Adsorption seems to be the most promising out of the many methods. Conventional adsorbents used to remove heavy metals include activated carbon or clay minerals. However, due to the need for waste management, waste products have recently become very popular, especially industrial wastes containing iron and/or aluminum oxides. One of the possible sorbent are water treatment residuals (WTRs) which are generated during drinking water treatment process. The aim of this work was to examine the possibility of using residuals from deironing of underground water (G-WTRs) as effective sorbents of Cd (II), Pb(II), Zn(II), Cu(II), Cr(III), Cr(VI) P(V), and As(V) as a function of initial concentration, pH, temperature and time.

The G-WTRs were poorly crystalline and composed predominantly of ferrihydrite with minor calcite and quartz admixture. The main chemical components were iron (32%) and calcium (17%). Specific surface area was 144 m2/g with a total pore volume of 0.181 cm3/g. The proportion of micropores was 29%, mesopores occupied the greatest volume – 54%, while micropores the lowest volume – 17%.

Cation sorption efficiecy was almost 100%, in the case of anions it ranges between 50 – 100%. Sorption capacity increased with an increase in the initial pollutant concentration. Adsorption of the metal cations was higher with and increasing pH of the solution and the best results were obtained for pH 6.0 to 7.0. While anions were preferably sorbed in lower pH. Sorption was the efficient in the temperature range of 20-40 ℃. The greatest differences in the sorption efficiency were observed within the first 2 – 4 h. The possible sorption mechanism was chemisorption.

The results showed that G-WTRs can be effective and cheap sorbents of heavy metals and metalloids. However, further research including desorption process as well as the long-term stability of formed metal-G-WTRs complexes.

Acknowledgments: This work was financed by the National Science Centre, Poland Grant No. 2017/27/N/ST10/00713.

How to cite: Wołowiec, M., Komorowska-Kaufman, M., Pruss, A., Rzepa, G., and Bajda, T.: Iron-based water treatment residuals as sorbent of heavy metals and metalloids, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2762, https://doi.org/10.5194/egusphere-egu2020-2762, 2020.

Reclaimed land in Korea is increasingly being used for horticulture, grains, livestock, etc. However, soil reclaimed land located in coastal lowland have so high salinity, poor fertility, high possibility of pollution that farming is difficult. Therefore, it is needed to reduce environmental burden and to promote fertility of soil through natural circulation farming. Therefore, we presented sustainable eco-friendly natural circulation model of agricultural resources in reclaimed land. It promotes desalination and fertility of soil through eco-friendly circular farming by integrating horticulture and livestock. To demonstrate the model, the test complex is planned to apply energy and resources circulation between horticulture and livestock focusing on Hanwoo, Korean-bred cattle. Basically high-technical plastic greenhouse-type horticultural complexes and livestock complexes including fuel facility using manure pellet are planned. Additionally, agricultural product processing, sales and distribution centers, themed landscape agricultural complexes, ecological parks, agricultural tourism facilities, and observation facilities were arranged.

How to cite: Seo, D.: A Study on Development of Test Complex for Natural Circulation Agriculture in Reclaimed Land, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8532, https://doi.org/10.5194/egusphere-egu2020-8532, 2020.

EGU2020-9370 | Displays | SSS5.5

Innovative Drone-based Hyperspectral Detection of Heavy Metals (Ni, Zn, and Cu) in Plants cultivated for Phytomining

Friederike Klos, Magdalena Sut-Lohmann, Thomas Raab, and Florian Hirsch

Natural and anthropogenic activities can result in soil contamination and thus disturb their important functions for the abiotic and biotic environment, e.g. filtering, buffering or plant growth. Specific remediation measures are already taken for such environmental issues including phytoremediation using plants that are able to reduce heavy metal concentrations in the pedosphere and accumulate these heavy metals in their biomass. A fast monitoring system for a large-scale and area-wide mapping of metal contents in plants is still missing. However, such a monitoring system would be a very helpful tool to the recycling of heavy metals and supports the development of environmentally friendly processes for metal recovery. We present the concept of the innovative HyPhy project, which studies the possibility of monitoring heavy metal accumulation in hyperaccumulators with drone-based hyperspectral sensors. The phytoscreening considered here can be used to profitably mine raw materials such as nickel, zinc and copper using hyperaccumulating plants. Method will be validated using green house and field measurements based on hyperspectral sensors supported by drones. Two sensors will be used, the VNIR hyperspectral sensor from Cubert GmbH (450-950nm) and the SWIR hyperspectral sensor HySpex from the Norwegian company NEO (1000-2500nm). The two optical sensors are validated with the point spectrometer PSR+ from Spectral Evolution (350-2500nm). This presentation will show background, methods and first results of our project.

 

How to cite: Klos, F., Sut-Lohmann, M., Raab, T., and Hirsch, F.: Innovative Drone-based Hyperspectral Detection of Heavy Metals (Ni, Zn, and Cu) in Plants cultivated for Phytomining, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9370, https://doi.org/10.5194/egusphere-egu2020-9370, 2020.

EGU2020-9436 | Displays | SSS5.5

Detailed monitoring of groundwater quality near municipal solid waste landfills. Case study in Valencia region (Spain)

Javier Rodrigo-Ilarri and María-Elena Rodrigo-Clavero

Municipal solid waste landfills are one of the most relevant soil and groundwater pollution sources. Monitoring networks should be designed on the preliminary phases to guarantee that groundwater quality control is performed periodically over both the operation and post-closure phase of the landfill.

This work shows the results of a groundwater quality detailed monitoring campaign developed on a municipal solid waste landfill in Valencia Region (Spain). The sampling campaign included the continuous analysis over 11 boreholes of the following parameters: mineral oil, As, B, Ba, Cd, Chlorine, electric conductivity, TOC, total Cr, Cr VI, Cu, COD, phenols, fluorine, total P, Hg, hydrocarbons, Mo, total N, Ni, Pb, pH, Sb, Se, suspended solids, sulphates and Zn. Besides, the piezometric levels around the landfill were also controlled.

Despite there is no clear Spanish legislation concerning groundwater quality, results show that the evolution of groundwater quality over time is satisfactory, fulfilling the requirements of the American (USEPA) and European (Dutch) legislation standards.

How to cite: Rodrigo-Ilarri, J. and Rodrigo-Clavero, M.-E.: Detailed monitoring of groundwater quality near municipal solid waste landfills. Case study in Valencia region (Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9436, https://doi.org/10.5194/egusphere-egu2020-9436, 2020.

EGU2020-9437 | Displays | SSS5.5

Evaluation of future municipal solid waste production. Case study in Valencia region (Spain)

María-Luisa Carnero-Pousa, Javier Rodrigo-Ilarri, and María-Elena Rodrigo-Clavero

Municipal Solid Waste (MSW) management activities are an important tasks of both national and municipal governments as they can induce significant impacts on the environment, the economy and the living quality of the population involved.

The optimal design of a MSW management plan depends greatly on the waste production values and its distribution over the territory. This production depends mainly on the socioeconomic level of its inhabitants. On the scientific literature several studies have already been carried out, concluding that there exist a direct relationship between the waste production of a certain country or region and its Gross Domestic Product (GDP). Therefore, if GDP increases, so will the rate of waste production, although not necessarily at the same rate.

The objective of the work was to carry out an evaluation of the future production of (MSW) within the V5 production area inside Valencia Region (Spain) in the 2012-2034 time horizon. The year 2011 was used as the starting point for the simulation as this was the last year in which the population census was taken. The correlation between the evolution of the economic growth indicators and the waste production indicators was analyzed. Results showed a linear correlation between all the variables studied so that variations in one of them are reflected in the same direction in the others.

How to cite: Carnero-Pousa, M.-L., Rodrigo-Ilarri, J., and Rodrigo-Clavero, M.-E.: Evaluation of future municipal solid waste production. Case study in Valencia region (Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9437, https://doi.org/10.5194/egusphere-egu2020-9437, 2020.

EGU2020-9694 | Displays | SSS5.5

Biochar production from waste biomass: Characterization and evaluation for potential applications

Frantseska-Maria Pellera, Panagiotis Regkouzas, Ioanna Manolikaki, and Evan Diamadopoulos

In the last years, global focus has been directing towards the circular economy model. In this framework materials that had so far been regarded as waste, are now considered as valuable resources for both energy and added-value materials recovery. In this context, more and more valorization methods and technologies are being developed for waste valorization, with biomass materials of municipal and agroindustrial origin constituting ideal options, due to both composition and availability.

Biochar generation from waste biomass is a method with high potential for effectively valorizing such residual resources, by providing not only a waste management option, but also multiple agronomic and environmental benefits. In fact, biochar materials are characterized by high versatility as far as their applications are concerned. Due to their wide variety of properties, biochars can be used in various applications, such the use as an adsorbent for contaminant removal from water or wastewater, or the use as an amendment for improving soil characteristics and remediating contaminated sites.

In the present study, six different waste biomass feedstocks, specifically three of municipal origin, namely two types of sewage sludge and the organic fraction of municipal solid waste, and three of agroindustrial origin, namely grape pomace, rice husks and exhausted olive pomace, were used to generate biochar through pyrolysis at two different temperatures, i.e. 400 and 600 °C. The resulting carbonaceous materials were then characterized through a series of analyses. Based on both physical and chemical biochar properties, it was able to evaluate their potential use in different applications, for agronomic or environmental purposes.

How to cite: Pellera, F.-M., Regkouzas, P., Manolikaki, I., and Diamadopoulos, E.: Biochar production from waste biomass: Characterization and evaluation for potential applications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9694, https://doi.org/10.5194/egusphere-egu2020-9694, 2020.

EGU2020-10568 | Displays | SSS5.5

Construction and demolition waste in Macedonia, a study financed by the know-how exchange program SAMCODE promoted by the Central European Initiative

Gianluca Bianchini, Ristovski Igor, Milcov Igor, Zupanc Alojz, Natali Claudio, Salani Gian Marco, Marchina Chiara, and Valentina Brombin

Construction and Demolition (C&D) waste is the solid debris resulting from construction and demolition activities. Recycling of this solid waste may result in substantial economic and environmental benefits. Unfortunately, is some Balkan countries such as Macedonia C&D recycling awareness is not developed yet. In this country, C&D are often dumped without control. According to the Macedonian landfill operator "Drisla" the estimated amounts of C&D waste generated per year in the Skopje surroundings approach 150.000 tons, but nothing is known on their composition. On this basis, a know-how exchange programme (KEP) called SAMCODE was financed by the Central European Initiative (CEI) and specifically dedicated to the characterization of C&D waste in Macedonia. GAYA operators sampled C&D landfills in the surroundings of Skopje, verified the absence of radioactivity, and then crushed the C&D down to the grain size of two millimetres. Crushed C&D chips were sent to the Department of Physics and Earth Sciences of the University of Ferrara, where the materials were powdered and analysed by X-ray fluorescence (XRF). Moreover, to characterize elemental mobility leaching tests on the C&D powders were carried out according to the following protocol: 1g of C&D powder has been soaked with 10 ml of deionized water, for 24 h. Subsequently the solutions have been centrifuged, filtered (at 45 mm) and analyzed by inductively coupled plasma mass spectrometry (ICP-MS). XRF analyses showed that – although variable - silica, calcium and aluminium are always the dominant components (SiO2 between 32 and 60 wt%, CaO between 7 and 30 wt%, Al2O3 between 7 and 16%) suggesting possible recycling in the ceramic/cement industrial processes. However, the real re-use of these materials in industrial processes is hampered by the lack of homogeneity, a feature required by the industries. The analysis of trace elements emphasized another critical aspect: Macedonian C&Ds often contain anomalously high concentrations of elements potentially hazardous, especially chromium (Cr), nickel (Ni), lead (Pb) and zinc (Zn). Note that the high concentrations of Cr, Ni, Zn and Pb do not necessarily recall the presence of contaminants, as these elements can be present in natural raw materials used in the country. Noteworthy, in Macedonia there are rocks included in the ophiolite sequences such as peridotites, serpentinites, pyroxenites and chromitites that can contain thousand(s) ppm of chromium and nickel, and also mining areas where there are sulphides of lead (galena) and zinc (sphalerite). If similar rocks are used as raw materials in the building activity, it is not strange to have C&D anomalously enriched in Cr, Ni, Pb, Zn. This hypothesis is confirmed by soil studies retrieved in the literature that highlighted that Macedonian soils can contain anomalous content of these elements. ICP-MS analyses of leachates show negligible concentrations of Ni, Pb and Zn, but significant concentrations of Cr. The results indicate that to foresee effective recycling Macedonian C&D have to be preliminarily screened to eliminate Cr-bearing components, crushed and sorted to obtain a better homogenization.

How to cite: Bianchini, G., Igor, R., Igor, M., Alojz, Z., Claudio, N., Gian Marco, S., Chiara, M., and Brombin, V.: Construction and demolition waste in Macedonia, a study financed by the know-how exchange program SAMCODE promoted by the Central European Initiative, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10568, https://doi.org/10.5194/egusphere-egu2020-10568, 2020.

EGU2020-16760 | Displays | SSS5.5

Study of pre-treatments of fly ashes aimed to the reuse as construction materials: chemical and mineralogical characterization

Enrico Destefanis, Caterina Caviglia, Davide Bernasconi, Costanza Bonadiman, Giorgia Confalonieri, Linda Pastero, Renzo Tassinari, and Alessandro Pavese

The management of waste and its sustainable reuse is one of the most important concern in our society in recent years, together with the increasing need to find primary materials without resorting to new extraction of resources. In this context, the thermovalorization of municipal solid waste (MSW) is currently the method that is spreading and replacing landfill disposal; the thermal treatment allows to reduce the volumes significantly, producing energy and returning bottom ashes (BA) and fly ashes (FA) in the measure of 20% and 5% of the total waste respectively.
The MSW incineration BA are classified as non-hazardous waste and can be reused as a raw material after some physical-chemical treatments.
The FA, on the contrary, are classified as hazardous waste and according to current legislation, they are usually subjected to vitrification treatments and stored in dedicated landfills. The hazard is due to the high content of soluble salts (chlorides and sulfates) and heavy metals (mainly Zn and Pb). Therefore, for their possible reuse as construction materials (e.g. ceramic, cement, concrete aggregates) or base roads, a preliminary stabilization step is required which often requires the use of significant quantities of energy.
In the present work, low energy cost methods are considered to reduce the dangerousness of FA and consequently make them more easily treatable for their reintegration into the production cycles.
Among the methods, washing of FA with water is examined, to find the lowest L / S ratio in the reduction of salts and heavy metals, analyzing the dissolution kinetics and the mineralogical content of fly ash before and after each washing treatment.
For a better definition of the kinetics, the FA are previously submitted to particle size separation to understand in which fractions the most dangerous substances are concentrated.
Washing treatments can be useful to remove or reduce soluble salts, in particular chlorides, by using a different liquid / solid (L / S) ratio, in order to obtain a more suitable material for the solidification / stabilization treatments carried out by geopolymerization or in cement.
The eluates of washing are also taken into consideration to evaluate the recovery of elemental species of interest and the purification of the liquid phase with biochar.

How to cite: Destefanis, E., Caviglia, C., Bernasconi, D., Bonadiman, C., Confalonieri, G., Pastero, L., Tassinari, R., and Pavese, A.: Study of pre-treatments of fly ashes aimed to the reuse as construction materials: chemical and mineralogical characterization, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16760, https://doi.org/10.5194/egusphere-egu2020-16760, 2020.

EGU2020-19514 | Displays | SSS5.5

Do different organic amendments effectively improve the soil biochemical activity of very poor arid soils from Tunisia?

Houda Oueriemmi, Petra S Kidd, Ángeles Prieto-Fernández, Beatriz Rodriguez-Garrido, Mohamed Moussa, and Carmen Trasar-Cepeda

Soils from arid and semi-arid ecosystems are generally very low in organic matter content, poor in nutrients and typically with sandy texture.  The application of different organic amendments has been proposed as an adequate approach to improve the quality of these soils for their use in agriculture. The use of organic wastes of different origins (agricultural, industrial, urban, etc.) as soil amendments has a dual goal: i) improving soil fertility and quality, ii) reducing the environmental problem that poses the disposal of these residues. However, despite of the beneficial effects of these residues, undesirable changes may also occur in agricultural soils after their addition. For example, the presence of various pollutants of anthropogenic origin in organic wastes may cause adverse effects on soil microbiota.  Generally, the arid and semi-arid soils of Tunisia are well characterised. However, the use of organic amendments to improve the quality of these soils has been scarcely investigated. Soil biochemical properties, and specifically soil enzyme activities, have been often used to investigate the impact of different amendments on soil quality, because they are highly sensitive to human or environmental perturbations.

In this work, the results of a field trial established for investigating the effectiveness of three organic residues (composted municipal solid waste, composted sewage sludge and farmyard manure) to improve the quality of one agricultural soil from Tunisia are reported. The soil had a sandy texture, alkaline pH (pH 8.3) and was very poor in organic matter (0.21 and 0.03% of total C and N, respectively). Each of the organic residues was applied in triplicate at three different doses in nine sub-plots randomly distributed; three untreated sub-plots were also established for comparison. One, 6 and 18 months after the soil amendments, surface (0-20 cm) soil samples were collected from all the treated and untreated subplots. The soil samples were analysed for the enzyme activities of four hydrolases involved in the C, N, P and S cycles and for an oxidoreductase (dehydrogenase) reflecting soil microbial activity. All the soil samples were also characterised for their main physicochemical properties.

Addition of the three organic amendments induced slight increases of the total organic carbon and nutrients content; however, the improvements observed were generally not related with the amount of applied residue. The activity of the enzymes increased after the application of the three residues, but these increments were not correlated with the dose of residue and did not consistently varied with the time elapsed after residue application. Generally, the highest increases in absolute values were observed for manure-amended soils, but when the activities were considered in relation to the total organic C of the soils, the sludge amended soils appeared to be the most favoured. The results are discussed with regards to their implications for improving very poor agricultural soils.

Acknowledgements: This research was financially supported by the Xunta de Galicia (IN607A 2017/6), UE Interreg-Sudoe program (SOE1/P5/E0189) and the Tunisian Ministry of Higher Education and Scientific Research. H. Oueriemmi thanks founding support of Erasmus plus program for her stay at the IIAG-CSIC.

How to cite: Oueriemmi, H., Kidd, P. S., Prieto-Fernández, Á., Rodriguez-Garrido, B., Moussa, M., and Trasar-Cepeda, C.: Do different organic amendments effectively improve the soil biochemical activity of very poor arid soils from Tunisia?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19514, https://doi.org/10.5194/egusphere-egu2020-19514, 2020.

EGU2020-19535 | Displays | SSS5.5

The effect of lignin application on plant growth and soil biological quality

Mesfin Gebremikael, Ramon Vandendaele, Marta Alarcon, Ruben Torregrosa, and Stefaan De Neve

There is a wide variety of agricultural waste co- and by-products that could potentially be valorised in high-value applications. One of such products is lignin, the second most abundant organic biopolymer after cellulose. Because of the large amounts of pruning wastes in the Mediterranean regions, lignin extraction can be one of the possibilities for valorisation and sustainable management of agricultural wastes. Research on the application of lignin, particularly lignosulfonates, is limited to its use as a biostimulant for root growth under controlled laboratory conditions and as a complexing agent in micronutrient foliar fertilizer formulations. Little is known about the impacts of lignin extracted from various feedstock on plant growth and soil quality.

 

We investigated the potential of lignin as plant biostimulator and soil conditioner in a pot experiment with fresh soil and lignin extracts obtained from three types of pruning wastes (urban trees, fruit and forest trees) using ryegrass as a test plant, under laboratory conditions. Two doses of lignin extracts (equivalent to 5 and 20 kg lignin-C ha-1) were applied to assess whether the effect on plant growth and soil quality depends on the rate of application. Soil and plant parameters were determined seven weeks after the grass was planted at 17 °C and 16 h photoperiod. 

 

Root biomass significantly increased (62-152%) in treatments with lignin addition, particularly lignin from urban and forest pruning wastes compared to the control. However, the increase in root biomass did not result in a simultaneous increase in shoot biomass or N uptake showing the need to apply additional plant nutrient. The microbial biomass C did not significantly respond to the application of lignin. A significantly higher dehydrogenase enzyme activity was recorded in samples with the high dose of lignin extracted from the urban wastes compared to the lower dose. Urban waste lignin extract contains 15-18 times more total N compared to the lignin extracts from forest and fruit trees, which could explain its significant effect on enzymatic activities and root biomass.

 

The findings show that differences in feedstock properties may influence the plant growth stimulating activity of the lignin. Further research is needed to improve the plant growth-stimulating effect of lignin, to investigate the simultaneous application of the major plant nutrients and the response of the microbial community to lignin application.   

 

How to cite: Gebremikael, M., Vandendaele, R., Alarcon, M., Torregrosa, R., and De Neve, S.: The effect of lignin application on plant growth and soil biological quality, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19535, https://doi.org/10.5194/egusphere-egu2020-19535, 2020.

EGU2020-19906 | Displays | SSS5.5

Recovery of metals from mining tailings by eco-friendly hydrometallurgical processes

Gabriel Gascó, Ignacio Sánchez, José Manuel Fidalgo, Antonio Saa, Jorge Paz-Ferreiro, and Ana Méndez

Metal´s demand and price are increasing due to the global trend towards urbanisation and industrialisation. Metals and raw materials are crucial to Europe’s society, economy and industry. However, some of them show a high-supply risk due to high dependence of imports, being necessary to find alternative materials or new sources for their recovery. Additionally, the overall global reserves of high-grade ores are close to depletion. In this context, low-grade, complex ores like sulphide minerals and old waste deposits related to past mining activities have received much more attention in recent years as new metal sources. The main objective of the present work is the recovery of metals from mining tailings, mainly post-flotation wastes, by eco-friendly hydrometallurgical processes. The presence of low-grade minerals hinders metal extraction by traditional pyrometallurgical processes. Spanish mining tailings show different compositions depending on their origin. However, complex ores like sulphide minerals (pyrite; sphalerite; chalcopyrite; arsenopyrite and other polymetallic sulphides) are generally present. It is known that metals in the form of complex sulphide precludes their chemical leaching.  For this reason, some carbon materials have been studied during last years as efficient catalysts for the leaching of metals from complex sulphides. The present work will be performed during the project RTI2018-096695-B-C31 (Ministerio de Economía y Competitividad). Different mining taillings will be selected from Spanish mining areas and mix with corresponding carbon catalysts. Leaching experiments will be performed during 96 hours at 60 and 90ºC under continuous agitation. The results obtained in the project will contribute to better understanding of the influence of catalysts in the leaching of metals from mineral sulphides. 
Authors wish to thank Spanish Ministerio de Economía y Competitividad for economic support (RTI2018-096695-B-C31)

How to cite: Gascó, G., Sánchez, I., Fidalgo, J. M., Saa, A., Paz-Ferreiro, J., and Méndez, A.: Recovery of metals from mining tailings by eco-friendly hydrometallurgical processes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19906, https://doi.org/10.5194/egusphere-egu2020-19906, 2020.

EGU2020-21181 | Displays | SSS5.5

Soil respiration and soil organic matter pools in soils amended for 7 years with biochar combined with mineral and organic fertilizers

Iria Benavente-Ferraces, Fátima Esteban, Denis Courtier-Murias, Ana Rey, Claudio Zaccone, Eduardo Moreno-Jiménez, Gabriel Gascó, Marco Panettieri, María del Mar Delgado, Juan C. García-Gil, and César Plaza

Biochar application is now considered to be one of the most promising agricultural practices to mitigate climate change. However, to fully assess the benefits of biochar, we still need to better understand its effects on soil properties, and particularly on native soil organic matter (SOM) dynamics.

In this work, we investigated soil respiration and changes in SOM pools (mineral-free, intra-aggregate, and mineral-associated SOM) as affected by the application of 20 t / ha per year of biochar alone or combined with mineral fertilizer, municipal solid waste compost, or sewage sludge. The experiment was run for 7 years in a semiarid agricultural soil. We found that biochar had no effect on soil respiration with respect to mineral fertilization and no amendment (control), and tended to decrease CO2 emissions from soils amended with municipal solid waste compost and sewage sludge. Biochar accumulated mainly in the mineral-free SOM fraction and its addition, especially in combination with municipal solid waste compost, promoted the amount of SOM occluded with aggregates and associated to mineral surfaces.

Acknowledgments: to the Spanish MICINN (MINECO, AEI, FEDER, EU) for supporting the research project AGL2016-75762-R.

How to cite: Benavente-Ferraces, I., Esteban, F., Courtier-Murias, D., Rey, A., Zaccone, C., Moreno-Jiménez, E., Gascó, G., Panettieri, M., Delgado, M. M., García-Gil, J. C., and Plaza, C.: Soil respiration and soil organic matter pools in soils amended for 7 years with biochar combined with mineral and organic fertilizers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21181, https://doi.org/10.5194/egusphere-egu2020-21181, 2020.

EGU2020-21238 | Displays | SSS5.5

The Potential for Biochar to Mitigate the Impact of Climate Change

Naeema Al Nofeli and Fred Worrall

The date palm tree has been mainly used as a source of food in the MENA (Middle East North Africa) region. Specifically, in the United Arab Emirates produces over 44 million date palm trees yearly, each tree generates approximately 20 Kilograms of palm frond waste per year and this waste is currently sent to landfills. In this study, we proposed that in the arid soil conditions found in the UAE, this date palm waste could be converted to biochar and used to improve the water holding capacity of UAE soils. Therefore, the aim of this study was to test whether amendments of date palm frond (DPF) and its biochar could improve the water holding capacity of soils. A mesocosm design and a plant growth experiment were used to assess the treatments at summer temperature conditions. For the mesocosm, there were 6 different biochar and DPF treatments (1%, 3%, 6%, 12%, 15% and 18% biochar or DPF in soil) along with the controls (sharp sand, DPF biochar and DPF). The experiment was divided into 3 cycles (wet, dry, and dry with a water bowl (waw)). The impact of the experimental treatments was assessed using ANOVA. Both Biochar and DPF had no significant effect during the first two cycles (wet and dry) but during the third cycle, the DPF appeared to have better water holding capacity than Biochar. A plant growth experiment was conducted with 6 different treatment (controls - sand, DPF and Biochar; and Biochar at 1%, 6%,15% and 18%). Cat grass was used for measuring its temperature, height, moisture and pH. Water was irrigated during the first 3 weeks then the soil treatments left to dry. The results of the greatest growth for 1% Biochar. Further investigations are being processed using thermal gravimetric analysis (TGA), Carbon, Nitrogen, Hydrogen & Oxygen (CHNO), Brunauer-Emmett-Teller (BET), Scanning Electron Microscopy (SEM) & Computerized tomography (CT) scan. This is to assess water binding capacity and physiochemical properties of the Biochar, DPF and soil.  

How to cite: Al Nofeli, N. and Worrall, F.: The Potential for Biochar to Mitigate the Impact of Climate Change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21238, https://doi.org/10.5194/egusphere-egu2020-21238, 2020.

EGU2020-21430 | Displays | SSS5.5

Nanominerals and biochar as additives in the composting of agricultural waste: effects on GHG emissions, composition and biodegradability of end-products on grassland soils.

Jorge Medina, Marcela Calabi-Floody, Marco Panettieri, Pablo Cornejo, Fernando Borie, and Heike Knicker

The utilization of additives is a strategy commonly used in composting operations to enhance the physicochemical properties and optimize the process. However, little is known about the impact of nanominerals, biochar and their combination during composting. The objective of this research was to evaluate the effects of iron oxide/halloysite nanominerals and oat hull-biochar as additives in the physicochemical properties of an aerobic composting process, the emission of greenhouse gases (GHG) and the composition of end-products. In order to analyze the biodegradability of composting end-products in grassland soils, an incubation experiment was also carried out. Wheat straw, lupine and beef manure were mixed (C/N: ~25) with iron oxide (Fe) or halloysite (Ha) nanoparticles (2% w/w), oat hull-biochar (B) (7% w/w) and their combination (BFe, BHa). pH, EC, C/N ratio, NH4-NO3 contents and the emission of CO2 and CH4 were analyzed. After 128 days of aerobic composting process, the end-products and their NaOH soluble fraction were characterized by using spectroscopic analysis that included E4/E6 ratio and solid state nuclear magnetic resonance (13CNMR). To analyze the biodegradability of produced compost in grassland soils, a respiration experiment (60 days) using Respicond Apparatus IV, combined with δ13C isotopic analysis was conducted. A decrease of final C/N ratio was observed in all treatments that was lower in B treated compost. Nitrate concentration increased as composting progressed, and compost supplied with Ha showed the higher final content of NO3 (5800 mg kg-1) and NH4 (220 mg kg-1). The addition of B significantly decreased the mean emission of both CO2 (~400 g CO2 m2 d-1) and CH4 (~4.5 g CH4 m2 d-1). Nanominerals significantly decreased the final E4/E6 ratio (<6) and the addition of B increased the aromaticity (twice), the alkyl-C/O alkyl-C ratio and the hydrophobicity which are parameters associated to stabilized end-products. In soil, the incorporation of additives reduced the loss of C (<5% after 60 days of incubation). Treatments supplied with B and Ha showed a higher mean residence time (8 and 5 years respectively) than compost without additives. These results suggest that the addition of halloysite and biochar to composting operations have significant effects on C stabilization and biodegradability of compost in grassland soils, that is relevant in the production of C sequestrant amendments. Acknowledgments to FONDECYT N° 3170677.

How to cite: Medina, J., Calabi-Floody, M., Panettieri, M., Cornejo, P., Borie, F., and Knicker, H.: Nanominerals and biochar as additives in the composting of agricultural waste: effects on GHG emissions, composition and biodegradability of end-products on grassland soils., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21430, https://doi.org/10.5194/egusphere-egu2020-21430, 2020.

EGU2020-21625 | Displays | SSS5.5

Design and experimental production of organic fertilizers from biogas digestates and secondary materials for horticultural purposes

Frank Repmann, Nils Dietrich, Florian Hirsch, and Thomas Raab

An ever growing quantity of digestates produced from agricultural biogas facilities puts alternative use options, other than spreading those residues on agricultural land, into focus, particularly to protect the ground water from nitrogen leaching in intensively used regions. Within the framework of the FNR funded project Skarabäus, Brandenburg University of Technology (BTU) together with partners from the Institute of Agricultural and Urban Ecological Projects affiliated to Humboldt University Berlin (IASP) and the Humboldt University Berlin (HU) investigate whether biogas digestates could be converted to fertilizer products of defined composition to be used outside agricultural production particularly for gardening and landscaping. The project rationale is to agglomerate the separated digestates to produce a fertilizer which is flexible in the design of properties, easy to handle for application and  effective to plant’s growth. Basically the tumble agglomeration was considered as the main process. The properties of the fertilizer product, particularly the nutrient content with respect to nitrogen, phosphorus and potassium, was thought to be adjusted by adding nutrient rich secondary materials like meat and bone meal, replaced powders from fire extinguishers and recycled material originating from waste water treatment during the agglomeration process.

Experiments revealed that separated digestates could hardly be agglomerated due to the high amount of relatively large and inflexible fiber contained. The addition of binding agents like clay minerals strongly improved the agglomeration process. However, so far best results were achieved when separated digestates were composted prior to the agglomeration process. In this way no binding agents were necessary. Agglomerates produced from composted digestates showed a reasonable particle size distribution and nutrient- and organic matter content generally suitable for application in horticulture, given that future greenhouse and field experiments could also demonstrate the beneficial application.

How to cite: Repmann, F., Dietrich, N., Hirsch, F., and Raab, T.: Design and experimental production of organic fertilizers from biogas digestates and secondary materials for horticultural purposes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21625, https://doi.org/10.5194/egusphere-egu2020-21625, 2020.

The use of biochar as a soil amendment has been proposed to increase the carbon (C) sequestration in soils. However, a more rapid soil organic matter turnover after biochar application might reduce the effectiveness of biochar applications for C sequestration. Data on the effects of biochar on soil C turnover is particularly important in boreal forests where large quantities of forest harvest residues would be available as feedstock for biochar production. To better understand the effects of biochar on boreal forest soil, we established a split-plot experiment where two spruce biochar produced with different temperatures (500°C and 650°C) were applied at a rate of 1.0 kg m-2 and 0.5 kg m-2 in a young xeric Scots pine forest in southern Finland. Measurement of soil CO2 effluxes and microbial biomass were used to investigate changes in soil C dynamics. Biochar application increased the rate of soil CO2 efflux by 10.6% across all biochar treatments and significantly (P<0.05) in 1.0 kg m-2 treatments. Soil microbial biomass remained unchanged. Soil temperature was 0.1 to 0.5°C higher in the biochar-amended treatments. Further analysis revealed that when soil CO2 efflux was corrected for the changes in soil temperature and soil moisture, there were no significant differences between treatments. We conclude that increase in soil CO2 efflux was attributed to warmer soils at the initial stage after biochar application to the soil surface; changes in soil chemical properties did not have any detectable effect on soil respiration.

How to cite: Zhu, X.: Short-term effects of biochar on soil CO2 efflux in boreal Scots pine forests, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21914, https://doi.org/10.5194/egusphere-egu2020-21914, 2020.

EGU2020-21730 | Displays | SSS5.5

Effects of liquid organic fertilisers on selected soil quality indicators

Susanne Eich-Greatorex, Annbjørg Øverli Kristoffersen, Jan Stabbetorp, Svein Jarle Horn, Trond Børresen, and Trine Aulstad Sogn

Anaerobic digestion of organic household waste as a means of energy production leaves considerable amounts of organic residues. These biogas digestates may represent a valuable source of nutrients and organic material, especially in areas with little application of animal manure to arable land. However, due to a typically high amount of available nitrogen and a low dry matter content, only small amounts of organic material are added with untreated digestates, also compared to other liquid organic fertilisers such as cattle slurry. The main objective of the study was to determine how the quality of liquid organic fertilisers affects soil properties. In soil samples from three field experiments in south-eastern Norway, aggregate stability, water retention characteristics, and selected chemical properties were determined. After three to seven years of application, the organic fertiliser treatments showed a positive effect on aggregate stability and pH compared to inorganic or no fertiliser, as well as a trend to higher carbon concentrations especially in soils with relatively low organic matter content. Effects on water retention characteristics depended on the quality of the organic fertilisers: Cattle slurry addition increased the number of medium-sized pores and thus plant-available water, whereas digestate addition instead increased the number of small pores in the soil.

How to cite: Eich-Greatorex, S., Kristoffersen, A. Ø., Stabbetorp, J., Horn, S. J., Børresen, T., and Sogn, T. A.: Effects of liquid organic fertilisers on selected soil quality indicators, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21730, https://doi.org/10.5194/egusphere-egu2020-21730, 2020.

EGU2020-21013 | Displays | SSS5.5

Nutrient Recovery from Agricultural Wastewater by Integrated Electrokinetic Processes

Shu-Yuan Pan, Chao-Yu Wei, Anwar Jamaal Wade, and Po-Chih Tseng

Agricultural wastewater including anaerobic digestate is annually generated in a huge quantity in Taiwan. The management of agricultural wastewater should be emphasized on the recovery and production of value-added resources, such as macronutrients (nitrogen, phosphorus, and potassium), for realizing the circular bioeconomy. In this paper, we will illustrate the development of energy-efficient electrokinetic processes for nutrient recovery from agricultural wastewater. First, we evaluate the performance of electrokinetic separations processes for recovery of macronutrients. We also discuss major challenges in managing nutrient reuse by the developed electrokinetic methods. Then, we elucidate the process chemistry and reaction kinetics by the processes. Lastly, we consider the interconnectivity among water, energy and the produced macronutrients in the context of large-scale deployment.

How to cite: Pan, S.-Y., Wei, C.-Y., Wade, A. J., and Tseng, P.-C.: Nutrient Recovery from Agricultural Wastewater by Integrated Electrokinetic Processes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21013, https://doi.org/10.5194/egusphere-egu2020-21013, 2020.

SSS5.6 – Organo-mineral associations and microaggregates in soil: Dynamics and functions

EGU2020-17147 | Displays | SSS5.6 | Highlight

Elucidating the 3D structure of soil microaggregate and the fate of organic matter

Tianyi Wu, Alexander Ost, Jean-Nicolas Audinot, Tom Wirtz, Franz Buegger, Carmen Höschen, and Carsten W. Mueller

Soil microaggregates play an important role for the long-term sequestration of soil organic matter (SOM) and are the nucleus of larger soil structures. However, it is still not well understood how the interplay of microaggregate structure and composition determine their functionality. This is especially due to analytical limitations that lead to the fact that the 3D architecture of microaggregates in conjunction with the fate of OM at the sub-micron scale is still hard to analyze. Combining microscopic and spectroscopic techniques with high sensitivity and high spatial resolution enables the correlation of microscale topographic information together with elemental and isotopic composition. In the present study we use novel imaging techniques at a previously unresolved spatial resolution to analyze and reconstruct the 3D architecture of microaggregates and the associated SOM.

In this study, isotope labelling was used to understand the fate of fresh C and N within newly developed soil microstructures. To explore the role of the inherited carbon content, soils from three different management practices, namely bare fallow, three-field and direct drilling, with different OM content, from an agricultural cropland research farm were used. To investigate the impact of fresh OM differing in C/N ratio on the 3D architecture of new formed soil microstructures, we performed an amendment with a substrate lacking N (highly labelled glucose (>99% 13C) ) and a substrate containing N (amino acid mixture (>98% 13C, >98% 15N) . After the incubation, all bulk soils and fractions were measured by Isotope-ratio mass spectrometry (IRMS) for 13C and 15N abundances. Microaggregates, clay and fine silt after 24 hours incubation were analyzed using Helium Ion Microscope (HIM) coupled with Secondary Ion Mass Spectrometer (SIMS) system and Nano Secondary Ion Mass Spectrometry (NanoSIMS) instrument for topography and elements/isotopes distribution, respectively. HIM-SIMS produced secondary electron images with a high resolution down to 0.5 nm and SIMS images of 24Mg, 27Al, 39K and 56Fe with a sub 20 nm resolution. NanoSIMS was capable to locate 12C2, 12C13C, 12C14N and 12C15N for organic matter and 16O, 27Al16O and 56Fe16O as mineral phases at a submicron scale.

Significant (p < 0.01) difference found between clay and fine silt fractions in amino acid treatment shows that the clay plays a more important role in fresh OM sequestration than fine silt, as more 13C and 15N were detected on mineral surfaces in the clay sized fraction. Interestingly, no difference between fractions were observed for the glucose (C added only) treatments, here N can be assumed to act as a limiting factor. By correlative image registration of HIM-SIMS with NanoSIMS data, the 3D architectural buildup soil microaggregates was reconstructed. The combination of HIM-SIMS and NanoSIMS analyses allows a considerable step forward in the capability to investigate soil microaggregate and their organo-mineral associations at a previously unresolved sub-micron scale. The ongoing work points to the chemical composition of the mineral microaggregate constituents as being decisive for the spatial arrangement of the organo-mineral associated OM.

How to cite: Wu, T., Ost, A., Audinot, J.-N., Wirtz, T., Buegger, F., Höschen, C., and Mueller, C. W.: Elucidating the 3D structure of soil microaggregate and the fate of organic matter, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17147, https://doi.org/10.5194/egusphere-egu2020-17147, 2020.

EGU2020-11335 | Displays | SSS5.6

Processing of organic matter input influences aggregate formation in artificial soils with different texture

Franziska Bucka, Shu-Yin Tung, and Ingrid Kögel-Knabner

Aggregate formation and stabilization depends on the interaction of minerals and soil organic matter (SOM). So far, little is known about the interplay of individual organic matter qualities and soil texture within this process. We developed an experimental set-up to study early soil development and aggregate formation within a controlled lab environment. We designed artificial soil microcosms with different texture, mimicking natural soils, and added organic carbon (OC) derived from particulate organic matter (POM, milled hay litter), dissolved organic matter (DOM, solution derived from hay), and bacterial necromass (Bacillus subtilis). We performed a short-term incubation for 30 days under constant water tension and investigated microbial activity, soil structure development and OC allocation compared to a control that did not receive additional OC input. 

OC input led to the formation of mostly large, water-stable macroaggregates (3000-630 µm) and some small microaggregates (<63 µm) in all microcosms as effect of microbial processing of the added OM. The addition and microbial decay of litter pieces led to physical occlusion of the particles into mainly large (3000-630 µm), OC-rich macroaggregates independent of the texture. The addition of DOM solution also induced the formation of large macroaggregates besides small microaggregates, although the OC input was much lower. Here, the aggregate formation was impaired by higher sand content in the mixtures. The addition of bacterial necromass led to the highest microbial activity, but relatively low aggregate formation, which might be a result of less physically active organic matter nuclei.

The results show that our experimental design allows to specifically investigate selected process complexes of soil structure formation defined by the addition of OM and soil texture.

How to cite: Bucka, F., Tung, S.-Y., and Kögel-Knabner, I.: Processing of organic matter input influences aggregate formation in artificial soils with different texture, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11335, https://doi.org/10.5194/egusphere-egu2020-11335, 2020.

EGU2020-9493 | Displays | SSS5.6

Microaggregation of goethite and illite: Linking mechanistic modeling and laboratory experiments

Alexander Prechtel, Simon Zech, Stefan Dultz, Georg Guggenberger, and Nadja Ray

Microaggregates are the fundamental building blocks of soils and thus important for their structure, properties, and functions. Hence, experimental aggregate formation studies (Dultz et al. 2019) were conducted to reveal the mechanisms leading to the establishment of soil microaggregates from mixtures of the mineral building units goethite and illite. Mathematically based modeling can further illuminate the mechanisms and factors behind structure formation as well as facilitate this understanding, even if the experimental capability is limited.

To this end, we present and extend a mechanistic modeling approach (Rupp et al. 2018, Rupp et al. 2019) which is based on a cellular automaton method that resolves explicitely particles at the micrometer scale. Thus it is capable to represent structural changes originating from (electrostatic) interaction of building units (aggregate forming materials). As prototypic building units goethite and illite with needle like and platy shapes of different size and charge are implemented. The operational, comprehensive model allows studying structure formation as a function of composition and charge of such mineral mixtures. Along this line, homoaggregation as well as heteroaggregation scenarios are investigated. The resulting microaggregates are investigated with respect to size, structure, and stability. Moreover, the role of the aspect ratio for stability, the point of zero charge for aggregation, and the amount of excess particles with respect to time is illustrated. Finally, the results are evaluated and compared to experimental data given in Dultz et al. (2019), and extend the scenarios studied there

S. Dultz, S.K. Woche, R. Mikutta, M. Schrapel, G. Guggenberger (2019): Size and charge constraints in microaggregation: Model experiments with mineral particle size fractions. Applied Clay Science 170, 29-40.

A. Rupp and K. Totsche and A. Prechtel and N. Ray (2018): Discrete-continuum multiphase model for structure formation in soils including electrostatic effects. Frontiers in Environmental Science, 6, 96.

A. Rupp, T. Guhra, A. Meier, A. Prechtel, T. Ritschel, N. Ray, K.U. Totsche (2019): Application of a cellular automaton method to model the structure formation in soils under saturated conditions: A mechanistic approach. Frontiers in Environmental Science 7, 170.

How to cite: Prechtel, A., Zech, S., Dultz, S., Guggenberger, G., and Ray, N.: Microaggregation of goethite and illite: Linking mechanistic modeling and laboratory experiments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9493, https://doi.org/10.5194/egusphere-egu2020-9493, 2020.

EGU2020-17611 | Displays | SSS5.6

The contribution of earthworms to soil aggregate formation

Tom Guhra, Katharina Stolze, Thomas Ritschel, and Kai Uwe Totsche

Anecic and endogeic earthworm species are known as “ecosystem engineers” that significantly contribute to the porosity and coherence of soil as well as soil water infiltration and the turnover rates of organic matter (OM). Additionally, earthworms actively excrete nutrient rich mucus, release bacteria within casts and translocate litter into the subsurface. In this way, earthworms not only shape the structure of soils but also the chemical milieu of the drilosphere where mucus forms a prominent fraction of OM. Furthermore, other biogenic extracellular polymeric substances (EPS) are known to form organo-mineral associations, which suggests that earthworms also facilitate their further attachment into soil aggregates.

With this study, we investigated how earthworms contribute to soil aggregate formation and impact aggregate properties by OM translocation and incorporation in the drilosphere. At vertically sampled burrow walls predominantly formed by Lumbricus terrestris, a patchy and depth dependent distribution of hydrophobic and hydrophilic regions was found with the water drop penetration time (WDPT) test. In the hydrophobic regions, we identified an enrichment of carbon and aggregate surface coatings containing plant residuals, bacteria, OM screenings and enmeshments by scanning electron microscopy (SEM) and elemental analysis. These structures were further investigated by factor analysis of Fourier transform infrared (FTIR) spectra that permitted the FTIR-band extraction of earthworm typical aggregation agents as, e.g., bacterial EPS, earthworm mucus and plant components (leaves, roots and sprout). Furthermore, with sorption experiments to typical minerals of temperate soils (e.g. illite and goethite), we found a mineral-specific adsorption of earthworm cutaneous mucus (of Lumbricus terrestris and Aporrectodea caliginosa) and bacterial EPS (of Bacillus subtilis). Specifically, a preferential adsorption of phosphorus containing constituents of mucus and bacterial EPS to goethite has been observed. The resulting formation of organo-mineral associations characterized by screened mineral surface charges was shown by zeta potential measurements.

We show that besides the active incorporation of particulate OM, as e.g. plant residuals and microorganisms, the mineral specific adsorption of EPS formed by earthworms and bacteria induce the formation of organo-mineral associations and alteration of the physico-chemical properties of earthworm-formed structures and soil aggregates.

How to cite: Guhra, T., Stolze, K., Ritschel, T., and Totsche, K. U.: The contribution of earthworms to soil aggregate formation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17611, https://doi.org/10.5194/egusphere-egu2020-17611, 2020.

EGU2020-16496 | Displays | SSS5.6

Free soil colloids and colloidal building units of soil aggregates

Ni Tang, Nina Siebers, and Erwin Klumpp

Nanosized mineral particles and organic matter (<100 nm) ,as well as their associations, belong to the most important ingredients for the formation of the soil aggregate structure being a hierarchically organized system. Colloids (< 220 nm) including nanoparticles can be occluded as primary building units of soil aggregates. Nevertheless, a large proportion of these colloids is mobile and presents in the solution phase (as “free”) within the soil matrix. However, the differences between “free” and occluded colloids remain unclear.

Here, both occluded and free colloids were isolated from soil samples of an arable field with different clay contents (19% and 34%) using wet sieving and centrifugation. The release of occluded colloids from soil macroaggregates (>250 µm) was carried out with ultrasonic treatment at 1000 J mL-1. The free and occluded colloidal fractions were then characterized for their size-resolved elemental composition using flow field-flow fractionation inductively coupled plasma mass spectrometry and organic carbon detector (FFF-ICP-MS/OCD). In addition, selected samples were also subjected to transmission electron microscopy as well as pyrolysis field ionization mass spectrometry (Py-FIMS).

Both, free and occluded colloids were composed of three size fractions: nanoparticles <20 nm, medium-sized nanoparticles (20 nm–60 nm), and, fine colloids (60 nm–220 nm). The fine colloid fraction was the dominant size fraction in both free and occluded colloids, which mainly consist of organic carbon, Al, Si, and Fe, probably present as phyllosilicates and associations of Fe- and Al- (hydr)oxides and organic matter. However, the organic matter contents for all three size fractions were higher for the occluded colloids than for the free ones. The role of OM concentration and composition in these colloids will be discussed in the paper.

How to cite: Tang, N., Siebers, N., and Klumpp, E.: Free soil colloids and colloidal building units of soil aggregates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16496, https://doi.org/10.5194/egusphere-egu2020-16496, 2020.

EGU2020-10404 | Displays | SSS5.6

Imaging organo-mineral associations of creek sediments

Karin Eusterhues, Jürgen Thieme, Lars Lühl, Andreas Haidl, S. Johannes Heym, Konstantin Adrianov, Aurelie Dehlinger, Stefan Rehbein, Thomas Wilhein, Birgit Kanngießer, and Kai Uwe Totsche

Interactions of organic matter with mineral surfaces are seen as one of the important mechanisms to increase carbon preservation in soils. Often, the mineral associated organic matter is assumed to consist of microbial derived material, because of its small C/N ratio and its isotopic signature.

We sampled sediments and surface water flocs from a small creek (pH 6.4) to obtain natural samples with a much higher microbial versus plant derived organic matter input than expected for soils. The bulk material was investigated by CNS analysis, X-ray diffraction (XRD), and infrared spectroscopy (FTIR). Organo-mineral associations were imaged by a combination of atomic force microscopy (AFM), scanning electron microscopy (SEM), and X-ray fluorescence spectroscopy (STXM-XRF) at 2550 eV (S, P, Si, Al, Fe) and 320 eV (C) at a spatial resolution of 50 nm. The speciation of C and P was addressed by near edge X-ray absorption fine structure spectroscopy (STXM-NEXAFS). Synchrotron measurements were performed at the PO4 beamline at PETRA III using the Animax STXM endstation with a 4-channel fluorescence detector with a solid angle of detection of up to 1.1 sr.

Organic matter was mainly found on Fe oxides (ferrihydrite). However, the C concentration on the Fe oxides varied and some Fe oxides were not covered by organic matter. Clay minerals (mainly illite) were either free of organic matter or showed a lower concentration of organic matter than the Fe oxides. Phosphorus was only observed on some of the Fe oxides surfaces and its P K-edge NEXAFS spectrum usually showed a small pre-edge peak at ~2150 eV, which can be taken as evidence for inner-sphere Fe-O-P bonds. Although Fe oxides were often found in close proximity of bacterial cells, the Fe oxide-associated organic matter was rich in carbonyl C and O-alkyl C, but showed higher contributions of aryl C and/or alkyl C than pure extracellular polymeric substances (EPS) or bacterial cells.

Our observations confirm a high reactivity of Fe oxides towards organic matter and phosphate. However, the Fe oxides were not fully coated, i.e. saturated with organic matter. The mineral associated organic matter was not similar to EPS or bacterial cells.

How to cite: Eusterhues, K., Thieme, J., Lühl, L., Haidl, A., Heym, S. J., Adrianov, K., Dehlinger, A., Rehbein, S., Wilhein, T., Kanngießer, B., and Totsche, K. U.: Imaging organo-mineral associations of creek sediments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10404, https://doi.org/10.5194/egusphere-egu2020-10404, 2020.

EGU2020-11509 | Displays | SSS5.6

Investigation on organic matter-mineral interaction by confocal multispectral and time-resolved microscopy

Francisco E G Guimaraes, Carla P Morais, Amanda Tadini, Mauricio Falvo, Odemir Bruno, Hajjoul Housam, Roland Redon, Ladislau Martin Neto, Stéphane Mounier, and Debora M B P Milori

Organic matter makes up less than 5% of soil and sediment and is often linked to the particulate mineral fraction, forming an organo-mineral microsystem that certainly contributes to its stability in the natural environment. However, most of the techniques used to study and quantify organic matter necessarily require the separation of the organic phase from the mineral phase by chemical or physical extraction and, subsequently fractionation methods that destroy and/or degrade the original aggregate morphological structure. The present work demonstrates that Scanning Confocal Microscopy (MC) can be used as a non-destructive fluorescence technique capable of characterizing organic matter (OM) interacting with the surface of the mineral fraction in soils and sediments without prior sample preparation and use of extraction or chemical fractionation of its components. Organic matter (OM) interacts with the mineral surface through molecular stacking in the form of stable molecular aggregates. Besides that, aggregate states also favor energy transfer processes between aggregated molecules which strongly affects the dynamics of excited state producing spectral shifts to the red and changes in life-time that can be correlated to aggregate morphology and to molecular amount deposited on the surface. These features confer a high spectral and intensity contrast of the confocal images. Here, infrared 2-photon (2P) excitation proved to be adequate to selectively excite OM aggregate states in the visible region between 400 and 700 nm, which allows a direct access to the fundamental aspects of the organic matter-mineral interactions.

We will show that the use of confocal methodologies, together with image analysis, provide helpful tools to understand the complex OM interactions at a molecular level. Here, we studied the interaction of OM with sodium bicarbonate and sodium hydroxide surfaces that form fractal crystals. When a drop of water containing both soil and solubilized bicarbonate or hydroxide salts is dried on a glass surface, dendritic-type salt crystals are first formed on the glass surface within the water droplet. In a second step of the droplet drying process, suspended organic molecules deposit on the surface of these fractal crystals. We will show that the morphology and molecular packaging substantially change spectral and life-time properties which strongly depend on the amount of OM on the crystal surface. Special features can be obtained from linear unmixing of spectral images using 1P and 2P excitation at 375 nm and 750 nm respectively for OM interacting with powder bicarbonate. Therefore, molecular aggregates of interacting fluorescence-emitting species can be used to characterize OM regarding the morphological, molecular structure and interactions with inorganic surfaces. These properties determine the stability of the original OM packing and the limits for the molecular stacking on different active surfaces in nature.

How to cite: Guimaraes, F. E. G., Morais, C. P., Tadini, A., Falvo, M., Bruno, O., Housam, H., Redon, R., Martin Neto, L., Mounier, S., and Milori, D. M. B. P.: Investigation on organic matter-mineral interaction by confocal multispectral and time-resolved microscopy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11509, https://doi.org/10.5194/egusphere-egu2020-11509, 2020.

EGU2020-11295 | Displays | SSS5.6

Biological sources and molecular composition of iron oxides bound organic carbon in agricultural soils

Qiaoyun Huang, Wenli Chen, and Yurong Liu

A strong link exists between iron oxides and soil organic carbon (SOC). However, the role of iron oxides in the preservation of SOC in agricultural soil remains poorly understood. In this study we comprehensively examined the concentration, molecular composition and biological sources of iron oxide-bound organic carbon (Fe-bound OC) in arable soils collected from 12 sites in central and east China. The effect of elevated temperatures on Fe-bound OC in two contrasting soils was also investigated. The results indicated that 6.2 ~ 31.2% of the SOC was bound to iron oxides in agricultural soil, and that the binding mechanisms varied from adsorption in most soils to coprecipitation in those with a large content of organic carbon. The distribution of Fe-bound OC showed no clear variation in relation to site, but Fe-bound OC reached a peak in soils with an annual mean temperature of 16.4°C. Correlation analysis demonstrated that TOC might be the main determinant for the amount of Fe-bound OC, and that the binding mechanism is influenced by both TOC and the active Fe ratio. Analysis of C/N, 13C isotope, and synchrotron radiation-based Fourier transform infrared (SR-FTIR) spectroscopy showed that iron oxides selectively protected plant-derived aliphatic compounds and polysaccharides in agricultural soil. Warming decreased the content of Fe-bound OC from 3.46 g kg−1 to 1.99 g kg−1 in Ultisol, while enhanced that from 4.04 g kg−1 to 5.12 g kg−1 in Histosol. NMR results suggested that warming could alter the composition of soil organic matter by accelerating O-alkyl C degradation and increasing the sequestration of recalcitrant alkyl C and carboxyl C. It is supposed that warming promoted the association of iron oxides with microbial-derived polysaccharides and aliphatic compounds. This study revealed the quantitative characterization, biological sources and molecular composition of Fe-bound OC in arable soils, which provides useful information for evaluating and managing the global C cycle under the framework of climate change.

How to cite: Huang, Q., Chen, W., and Liu, Y.: Biological sources and molecular composition of iron oxides bound organic carbon in agricultural soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11295, https://doi.org/10.5194/egusphere-egu2020-11295, 2020.

EGU2020-4678 | Displays | SSS5.6

Nanoscale chemical imaging of soil organo-mineral associations.

Floriane Jamoteau, Nithavong Cam, Clément Levard, Thierry Woignier, Adrien Boulineau, Emmanuel Doelsch, Jérôme Rose, and Isabelle Basile-Doelsch

Organo-mineral associations drive organic matter (OM) stabilization in soils, but mechanisms controlling their dynamics are still not fully known at micro and nanoscale. Adsorption of OM on minerals’ surfaces is a prevalent viewpoint of OM stabilization processes (Kleber et al., 2007), but Basile-Doelsch et al., (2015) suggested that mineral alteration generating amorphous nanophases and cationic oligomers on minerals’ surfaces is also a driver of OM stabilization through coprecipitation processes. Lab experiments which mimic these processes showed that the nanosized co-precipitates (Nanosized Coprecipitates of inorganic oLIgomers with organiCs: nanoCLICs) are made of inorganic Fe, Al, Si oligomers associated with organic molecules (Tamrat et al., 2019). Andosols are known to have a high OM-stabilization capacity, mostly attributed to associations of OM with nanominerals (imogolite, allophane, proto-imogolite) (Basile-Doelsch et al., 2007; Levard et al., 2012). In the present study, we investigated the presence of nanoCLICs in Andosol fractions from La Martinique (French West Indies). We used Transmission Electron Microscopy (TEM, FEI Tecnai Osiris 200kV) coupled with 4 EDX detectors and EELS to semi-quantify and map major elements. TEM analyzed zones of interest ranged from 5 µm to 10 nm with pixel size from 500 to 1 nm. Few crystallized minerals, particulate OM and amorphous thin fibers that could not be definitively attributed to imogolite nanotubes were observed. However, we mainly observed totally amorphous phases to electron diffraction. Al, Si, C, Fe and O were the main component of the latter amorphous phases. Al, Si and Fe were systematically associated to C even at a size resolution down to 1 nm (semi-quantifications ranged from 11 to 41% of C, 4 to 7% of Fe, 34 to 36% of Al and 22 to 46% of Si). Similar high-resolution images were obtained for the andosol organo-mineral associations and the synthetic nanoCLICs. At the working TEM resolution, the nanoCLICs model proposed by Tamrat et al., (2019) is consistent with the structures observed on the andosol. Based on these results, the majority of C appears to be in nanoCLICs form in these Andosol fractions and confirms the hypothesis puts forward by Basile Doelsch et al., (2015).

Basile Doelsch et al., 2007. Mineral control of carbon pools in a volcanic soil horizon. Geoderma, 137 (3-4), 477-489. ISSN 0016-706.

Basile-Doelsch et al., 2015. Are Interactions between Organic Compounds and Nanoscale Weathering Minerals the Key Drivers of Carbon Storage in Soils? Environ. Sci. Technol. 49, 3997–3998.

Kleber et al., 2007. A Conceptual Model of Organo-Mineral Interactions in Soils: Self-Assembly of Organic Molecular Fragments into Zonal Structures on Mineral Surfaces. Biogeochemistry 85, nᵒ 1 (1 août 2007): 9‑24.

Levard et al., 2012. « Structure and distribution of allophanes, imogolite and proto-imogolite in volcanic soils ». Geoderma 183‑184 (1 août 2012): 100‑108. 

Tamrat et al., 2019. « Soil organo-mineral associations formed by co-precipitation of Fe, Si and Al in presence of organic ligands ». Geochimica et Cosmochimica Acta, 10 juin 2019. 

How to cite: Jamoteau, F., Cam, N., Levard, C., Woignier, T., Boulineau, A., Doelsch, E., Rose, J., and Basile-Doelsch, I.: Nanoscale chemical imaging of soil organo-mineral associations., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4678, https://doi.org/10.5194/egusphere-egu2020-4678, 2020.

EGU2020-12377 | Displays | SSS5.6

Long-term soil water content and exchangeable Ca interact to stabilize organic matter

Itamar Shabtai, Srabani Das, Thiago Inagaki, Ingrid Kogel-Knabner, and Johannes Lehmann

Organo-mineral interactions stabilize soil organic matter (SOM) by protecting from microbial enzymatic attack. Soil water content affects aggregation, mineral weathering, and microbial respiration, thus influencing the relative importance of SOM stabilization mechanisms. While the response of microbial respiration to momentary changes in water content is well established, it is unclear how microbial activity will impact stabilization mechanisms under different long-term moisture contents.

To understand how long-term soil moisture affects SOM stabilization mechanisms we studied fallow soils from upstate New York situated on a naturally occurring water content gradient. Wetter (but not saturated) soils contained more exchangeable Ca and had more strongly stabilized SOM, resulting in SOM accumulation. But it was not clear whether Ca-driven surface interactions or occlusion in micro-aggregates was more important, and if interactions with Fe and Al played a role in the Ca-poor soils. Also, the role of biotic drivers in SOM stabilization at different water contents was unknown.

We tested which mechanisms governed SOM stabilization by determining C and N contents and natural isotope abundances in particulate and mineral-associated organic matter fractions. We also extracted the C bound to Ca and to reactive Fe+Al phases. Wetter, Ca-rich soils had higher oPOM content, and in the heavy mineral fraction, higher relative concentrations of Ca-bound C, lower C:N values, and more oxidized C forms. In addition, wetter soils had greater microbial biomass. Together, these results showed that high long-term soil moisture increased microbial SOM cycling, and that processed SOM was better stabilized, in agreement with the recent notion that stable SOM consists of processed labile C. Additionally, higher soil moisture augmented the role of Ca in SOM stabilization over that of Al+Fe phases. We then manipulated the exchangeable Ca content and incubated soils with 13C15N labeled plant litter. Ca-amended soils emitted less CO2 while incubated with litter, confirming that Ca is instrumental in SOM stabilization. Tracing the labeled isotopes in the gaseous phase and soil fractions will allow us to gain a clearer understanding of how water content and soil Ca interact to stabilize SOM.  

How to cite: Shabtai, I., Das, S., Inagaki, T., Kogel-Knabner, I., and Lehmann, J.: Long-term soil water content and exchangeable Ca interact to stabilize organic matter, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12377, https://doi.org/10.5194/egusphere-egu2020-12377, 2020.

EGU2020-4559 | Displays | SSS5.6

Chemical complexity matters: differential mobilization of mineral-associated organic matter driven by functionally distinct rhizodeposits

Tobias Bölscher, Hui Li, Mariela Garcia Arredondo, Zoe G. Cardon, Carolyn M. Malmstrom, Matthew Winnick, and Marco Keiluweit

Protective mineral-organic associations are the quantitatively most important soil carbon storage mechanism, but their vulnerability to environmental change is largely uncertain. While it is well established that root growth can promote (or “prime”) the microbial decomposition of organic matter (OM), our mechanistic knowledge of the ability of roots to destabilize OM protected within mineral-organic associations remains limited. Here we examined how the composition of root-derived compounds (rhizodeposits) affects the stability of mineral-organic associations.

In model systems, we first tested the ability of functionally distinct low-molecular weight compounds (ligands, reductants, simple sugars) commonly observed in the rhizosphere to cause the mobilization and mineralization of isotopically labeled OM from different mineral types (Fe and Al hydroxides). Our results showed that all compounds stimulated mobilization and mineralization of previously mineral-associated OM. However, OM bound to Al hydroxide was less susceptible to mobilization than OM bound to Fe hydroxide. Further, sugars and reductants revealed a greater mobilization potential than ligands for both mineral types, suggesting that OM mobilization in soils may be microbially mediated, rather than driven by direct mineral dissolution. In complementary pot experiments, we investigated the effect of rhizodeposition on the mobilization of mineral-associated OM. We grew Avena sativa in soils amended with isotopically-labeled mineral-organic associations and followed mobilization dynamics over four weeks. First results indicated that rhizodeposition dynamics dictate the mobilization and mineralization of mineral-associated OM. Together, our results suggest a strong mechanistic linkage between the composition and functionality of rhizodeposits and their ability to destabilize mineral-associated OM.

How to cite: Bölscher, T., Li, H., Garcia Arredondo, M., Cardon, Z. G., Malmstrom, C. M., Winnick, M., and Keiluweit, M.: Chemical complexity matters: differential mobilization of mineral-associated organic matter driven by functionally distinct rhizodeposits, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4559, https://doi.org/10.5194/egusphere-egu2020-4559, 2020.

EGU2020-171 | Displays | SSS5.6

Soil organic matter and phosphate sorption on natural and synthetic Fe oxides under in situ conditions

Lydia Pohl, Kristof Dorau, Christopher Just, Carmen Höschen, Kristian Ufer, Tim Mansfeldt, and Carsten W. Mueller

In redoximorphic soils, iron (Fe) and manganese (Mn) oxides undergo reduction with subsequent oxidation of their reduced counterparts (Fe2+ and Mn2+) impacting nutrient sorption and the stability of soil organic matter (SOM). One tool to investigate the soil redox status is the indicator of reduction in soils (IRIS) method. Thereby, synthetic Fe and Mn oxides are coated onto polyvinyl chloride (PVC) bars, which are typically installed for an operator-defined period in the soil. After removal of the bars we studied organo-mineral associations, which have been formed under field conditions on the surface of the coated bars.

In this study, each one Mn and Fe oxide-coated redox bar were installed for 30 days in a Mollic Gleysol. A previous study revealed, that the Mn oxide coating facilitated a non-enzymatic redox reaction under anoxic conditions, while Fe2+ from the soil solution is oxidized to Fe3+ along the Mn oxide coating and Mn2+ is removed from the PVC surface [1]. In consequence, in situ Fe oxides formed along the Mn oxide coatings and were further considered as ‘natural’ Fe oxides. This enables us to differentiate between sorption occurring onto the surfaces of ‘synthetic’ Fe oxides from the Fe bar versus ‘natural’ formed Fe oxides along the Mn bar. They were analysed by nanoscale secondary ion mass spectrometry (NanoSIMS) to study the distribution of Fe (56Fe16O), SOM (12C14N), and phosphorus (31P16O2). NanoSIMS is a spectromicroscopic technique offering a high lateral resolution of about 100 nm, while having a great sensitivity for light elements. In contrast to classic bulk analysis, it offers the possibility to examine the spatial distribution of SOM and phosphorous at the microscale within the intact organo-mineral matrix. 

Image analysis of individual Fe oxide particles revealed a close association of Fe, SOM, and P resulting in coverage values up to 71% for synthetic and natural iron oxides. Furthermore, ion ratios between sorbent (56Fe16O) and sorbate (12C14N; 31P16O2) were smaller along the natural oxides when compared with those for synthetic Fe oxides. We conclude that both natural and synthetic Fe oxides rapidly sequestered SOM and P (i.e., within 30 days) but that newly, natural formed Fe oxides sorbed more SOM and P than synthetic Fe oxides.

 

[1] Dorau, K.; Eickmeier, M.; Mansfeldt, T. Comparison of Manganese and Iron Oxide-Coated Redox Bars for Characterization of the Redox Status in Wetland Soils. Wetlands 2016, 36, 133–144.

How to cite: Pohl, L., Dorau, K., Just, C., Höschen, C., Ufer, K., Mansfeldt, T., and Mueller, C. W.: Soil organic matter and phosphate sorption on natural and synthetic Fe oxides under in situ conditions , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-171, https://doi.org/10.5194/egusphere-egu2020-171, 2020.

EGU2020-18840 | Displays | SSS5.6

Redox-driven colloidal mobility and its effects on carbon cycling in temperate paddy soils

Daniel Said-Pullicino, Beatrice Giannetta, Beatrice Demeglio, Anna Missong, Nina Gottselig, Roland Bol, Erwin Klumpp, and Luisella Celi

Rice paddy soils are known to represent a large proportion of global terrestrial carbon (C) stocks (ca.10 Pg), accumulating organic C in the topsoil due to cultivation under submerged conditions. Apart from the limited mineralization under anoxic soil conditions resulting from frequent field flooding, other mechanisms involving the dynamic interactions between organic C and redox-active minerals particularly Fe (oxy)hydroxides, together with the transport of organic C to deep mineral horizons, can lead to long-term C stabilization. Our previous studies have shown that up to 30-50 g m-2 of dissolved organic C (DOC, defined as <450 nm) and 25-40 g m-2 of Fe2+ may be mobilized and translocated into the subsoil over a rice cropping season in temperate rice paddies, contributing to an increase in belowground C stocks. However, little is yet know on influence of frequent redox fluctuations on the contribution of colloidal organo-mineral associations to C mobilization and accrual in paddy subsoils.

We hypothesized that (i) redox fluctuations may lead to an overall increase in colloid dispersion (via reductive dissolution of Fe oxides, changes in soil pH, as well as neoformation of colloidal organo-mineral associations), and that (ii) colloidal mobility may represent an important C input to paddy subsoils. In order to evaluate the effects of redox fluctuations on colloid dynamics in situ, water-dispersible fine colloids (WDFC) were isolated from soils collected from different horizons along two profiles opened in adjacent plots under long-term paddy (P) and non-paddy (NP) management in NW Italy. Moreover, WDFC were also isolated from anaerobically-incubated topsoil samples to evaluate the changes in colloid dispersion under reducing conditions as a function of management. Colloidal size-fractionation and their elemental compositions were evaluated by asymmetric flow field-flow fractionation (AF4) coupled with OCD or ICP-MS. 

Our results evidenced that redox cycling favours colloidal stability in the topsoils, with a preferential dispersion of the smallest-sized colloidal C (<30 nm and 30-240 nm fractions), even though larger-sized colloidal C (>240 nm) contributes predominantly to the WDFC. Consequently, under long-term paddy management colloidal dispersion and transport along the soil profile were probably responsible for the lower amounts of colloidal C (and Fe) observed in the Ap topsoil horizons of P with respect to NP, as well as for the significant accumulation of colloidal C in correspondence with the Brd subsoil horizons just beneath the plough pan. These illuvial horizons were also particularly rich in small-sized (30-240 nm) colloidal Fe, Al and Si possibly due to mineral phase changes induced by redox fluctuations.

Our findings therefore indicate that downward mobilization of colloidal C associated with Fe (hydr)oxides (e.g. coprecipitates) or small aluminosilicate minerals, rather than dissolved organic C, may represent an important process driving organic C accrual in paddy subsoils. However, further insights are still required to entangle the contribution of the different mechanisms involved.

How to cite: Said-Pullicino, D., Giannetta, B., Demeglio, B., Missong, A., Gottselig, N., Bol, R., Klumpp, E., and Celi, L.: Redox-driven colloidal mobility and its effects on carbon cycling in temperate paddy soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18840, https://doi.org/10.5194/egusphere-egu2020-18840, 2020.

EGU2020-1107 * | Displays | SSS5.6 | Highlight

How much more carbon can be sorbed to soil?

Rose Abramoff, Katerina Georgiou, Bertrand Guenet, Margaret Torn, Yuanyuan Huang, Haicheng Zhang, Wenting Feng, Sindhu Jagadamma, Klaus Kaiser, Dolly Kothawala, Melanie Mayes, and Philippe Ciais

Quantifying the upper limit of stable soil carbon storage and relative saturation is essential for guiding policies designed to increase soil carbon storage, such as ‘4 per 1000’ sequestration initiative. Carbon stabilization processes are diverse, but one particular pool of carbon that is considered stable across climate zones and soil types is the mineral-associated fraction, measured using density or size fractionation. Some soil carbon decomposition models assume sorption to minerals is the main form of stabilization in this fraction. We estimate the global capacity of mineral soils in six soil orders to sorb additional dissolved organic carbon (DOC). We gathered data from 400 DOC sorption experiments representing 133 soil profiles across six soil orders. We used the relationship between DOC added and DOC sorbed to calibrate a modified Langmuir sorption equation, from which we quantified the DOC sorption potential in each soil. We found that the sorption potential is empirically related to climate variables (including mean annual temperature and mean annual precipitation) and soil geochemical variables (chiefly, percent clay, pH, and soil order). From this relationship, we then estimated the DOC sorption potential for 14631 profiles distributed globally. This amount was 1.4 (global median; 95% CI: 0.50, 2.8) kg C m-3, totaling 102 Pg C globally across six soil orders, representing up to a 7% increase in the existing total C stock. We show that there is greater capacity for additional DOC sorption in subsoils (30cm-1m) compared to top-soils (0-30cm). The gap between the modest potential of mineral sorption processes found in this study and the large total capacity of long-term organic matter stabilization (2541 Pg C for the six soil orders of this study) indicates that other mechanisms such as aggregation, the sorption of microbial necromass, layering, and co-precipitation also play a critical role in stable organic matter formation and persistence.

How to cite: Abramoff, R., Georgiou, K., Guenet, B., Torn, M., Huang, Y., Zhang, H., Feng, W., Jagadamma, S., Kaiser, K., Kothawala, D., Mayes, M., and Ciais, P.: How much more carbon can be sorbed to soil?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1107, https://doi.org/10.5194/egusphere-egu2020-1107, 2020.

Recent studies suggest significant control on pedogenic iron (Fe) and aluminum (Al) on organic matter (OM) storage and stability across a wide range of soils around the world. This information would be useful to improve or replace existing SOM models. On the other hand, metal extraction studies have shown that only minor portions of soil OM are directly bound to pedogenic Fe and Al. How can these metals control OM storage and stability without direct binding with bulk of OM? To answer this, an important step is to understand the location of the metals and OM within bulk soils. Sequential density fractionation is useful to examine their localizations because pure OM (e.g., plant detritus) and pure mineral particles (e.g., quartz, clay, Fe oxide) are the two endmembers along particle density gradient. We tested if Fe and Al released by chemical weathering are mainly present in association with OM using 22 soil samples from 11 sites spanning 5 climate zones, 5 soil orders (Andisols, Spodosols, Inceptisols, Mollisols, Ultisols), and including several subsurface horizons and both natural and managed (upland and paddy) soils. Across all the studied soil samples, meso-density fractions (1.8-2.4 g cm-3) accounted for major portions of OM and the metals extractable by pyrophosphate, acid oxalate, and dithionite. We also found a strong stoichiometric relationship between the extractable metals and co-dissolved OM. We discuss the biogeochemical processes that may cause the co-localization of the metals and OM at the mesodensity across the soils from a wide range of pedogenic environments.

How to cite: Wagai, R., Kajiura, M., and Asano, M.: Co-localization of iron and aluminum with organic matter across a range of soils: a density-based approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22089, https://doi.org/10.5194/egusphere-egu2020-22089, 2020.

Formation of Microaggregates and organo-mineral composite building units: Novel pathways in the soil-parent rock continuum

 

Summary

 

Microaggregates and organo-mineral composite building seem to be unique structural features of natural permeable media like soils, rocks and aquifers. Thee develop in response to various aggregation processes and mechanisms that result in a non-random spatial arrangement of the solid phase already at the submicron scale. Soil microaggregates are defined as compound structures smaller <0.25mm, comprising the colloidal-sized and nanoparticulate composite building units and the organo-mineral composites (Totsche et al. 2018). Noteworthy, microaggregates, may be present as suspended or colloidally-dispersed components of the mobile phase. As such, they are prone to transport with the seepage and may affect the surface and pore-space properties. Surface alteration by interactions of seepage components with immobile surfaces is likely an important, yet essentially unexplored pathway triggering formation of microaggregates in the soil-parent rock continuum. In matured soils, the commonly found associations of clays with other, often poorly crystallized but highly reactive minerals and organic matter is the consequence of nucleation in the chemically heterogeneous soil suspension. Both pathways coexist and can be studied in the soil-parent-rock transition zone were weathering and formation/alteration of secondary mineral phases are still in the early stage. The stability of microaggregates and their interactions are dependent on wetting-drying and in turn by hydration-dehydration cycles. Such moisture-related dynamics regularly take place in soils of the temperate regions even down to the soil-parent-rock transition zone and suggests that the hydraulic and osmotic stress and their history results in attachment, detachment, translocation and accumulation. The presentation will We focus on two so far vastly ignored formation pathways of microaggregates and composite building units, i.e., the “geochemical inheritance” and “heteroaggregation from suspension”, thereby considering the role of dynamic relocation of composite building units and microaggregate forming materials from upstream compartments.

 

Totsche K.U., Amelung W., Gerzabek M.H., Guggenberger G., Klumpp E., Knief C., Lehndorff E., Mikutta R., Peth S., Prechtel A., Ray N., Kögel-Knabner I. (2018) Microaggregates in soils. Journal of Plant Nutrition and Soil Science 181(1), 104-136.

How to cite: Totsche, K. U.: Formation of Microaggregates and organo-mineral composite building units: Novel pathways in the soil-parent rock continuum, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10220, https://doi.org/10.5194/egusphere-egu2020-10220, 2020.

EGU2020-8349 | Displays | SSS5.6

Role of bedrock weathering in microaggregate formation - limestone alteration in the aeration zone

Michaela Aehnelt, Thomas Ritschel, and Kai Uwe Totsche

During pedogenesis, the development of the soil aggregate system may be strongly dependent on weathering of bedrock in the vadose zone. There, periodic drying and flushing by meteoric waters provides alternating hydro- and biogeochemical conditions for fluid-rock interactions and provokes the dissolution, displacement and placement of minerals as well as the release or adsorption of colloids. As a result, the seepage suspension is enriched with mobile mineral and organic matter that infiltrates into the bedrock void system thereby fueling aggregate forming materials and composite building units to exposed surfaces of the bedrock. We aim to elucidate related bedrock alteration processes in dependence on water composition, seepage vs. saturation and the fracture network during weathering.

Our study combines the investigation of the weathering rim of natural bedrocks (outcrop analogue) with the simulation of the natural conditions by column experiments in the laboratory. Study object are Triassic limestones (Upper Muschelkalk) of the Hainich area in Thuringia (central Germany). The columns were filled with fresh, unaltered material, crushed into coarse gravel fraction size and percolated with artificial rainwater or soil litter extract over a runtime of 6 months. In order to mimic natural conditions percolation periods changed with periods of drying. Geochemical data of the liquid phase resemble very well the alternating periods of drying and flushing by systematic changes of the element concentration and milieu parameters. Generally, dissolved elements in the seepage are higher in concentration when litter extract is used pointing towards a significant impact on dissolution kinetics, especially after periods of longer water-rock interaction. Weathered natural bedrock surfaces (bedrock clasts in the covering soil and fractures and voids in the bedrock) exhibit carbonate dissolution (edge pits and dissolution vugs) and the formation of clay mineral coatings, in part with iron oxides. The same holds true for rock clasts after the column experiments. The alteration is macroscopically visible by brownish and beige coatings on formerly greyish pristine surfaces. This feature seems more pronounced on clasts percolated with liquids from soil litter extracts than on clasts treated with artificial rainwater indicating the formation of organo-mineral associations during solid-liquid interaction.

Generally in both, nature and experiment, facial aging features include the dissolution of carbonates, the formation of clay minerals as well as oxides and hydroxides of iron, but also the appearance of organic constituents. Our results contribute to a better mechanistic understanding of the role of bedrock alteration during weathering for (a) the provision of microaggregate forming materials and (b) the formation of composite building units and microaggregates from pristine environments.

 

How to cite: Aehnelt, M., Ritschel, T., and Totsche, K. U.: Role of bedrock weathering in microaggregate formation - limestone alteration in the aeration zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8349, https://doi.org/10.5194/egusphere-egu2020-8349, 2020.

EGU2020-5314 | Displays | SSS5.6

The role of mineral composition regulating the turnover of organic matter in 13 forest soils from Hungary

Dóra Zacháry, Gergely Jakab, Tibor Filep, Réka Balázs, and Zoltán Szalai

The organic matter stability is regulated by the different protection mechanisms of the soil matrix and soil minerals. In spite of that, beyond the determination of the amount of fine fractions, relatively little research studied the mineralogical composition of these fractions and their organic matter stabilizing effects. Therefore, the aim of my work was to investigate the influence of the soil mineral phases on the decomposition of soil organic carbon pools of soils under forest vegetation.

Maize residues were added to the 13 soil samples (depth of 0−20 cm) collected from Hungary. The samples were incubated at 20°C and 70% field capacity during 163 days. The soil respiration was measured at specified intervals (on day 3, 8, 15, 30, 51, 79, 107, 135 and 163) and trapped in 2M NaOH and quantified by titration with 1M HCl. Another aliquot of NaOH was mixed with 2MSrCl2 to get SrCO3 for δ13C analysis.

The samples were analysed with an X-ray diffractometer (Rigaku Miniflex 600), a microwave plasma-atomic emission spectrometer (4200, Agilent Technologies) and an isotope ratio mass spectrometer (Delta plus XP, Thermo Finnigan). Carbon mineralization kinetics was modelled by fitting a first-order two pools model.

The results showed that 1−6% and 2−18% of the organic carbon content of the soils was mineralized in the control and amended samples during the incubation, respectively. Carbon mineralization was mostly reduced by the illite content (R2=0,797; p<0,001), Al-oxide content (R2=0,708; p<0,001) and clay content (R2=0,475; p<0,05) of the soils. The decomposition rates of the two carbon pools were found to be influenced to the greatest extent by the illite and total Al-oxide content of the soils investigated. Whereas the decomposition rate constant of the slowly mineralizable C pool was only affected by the Al-oxide and illite content, the decomposition rate constant of the easily mineralizable carbon pool was also sensitive to the other soil parameters (aromaticity, Fe-oxide content, C/N ratio, pH and clay content).

The priming effect was found to be influenced to the greatest extent by the pH (R2=0,715; p<0,05), whereas weaker negative relationship with the content of non-swelling clay minerals (R2=0,396; p<0,05), illite content (R2=0,389; p<0,05) and the C/N ratio (R2=0,345; p<0,05) of the soils was also detected.

This work was supported by the Development and Innovation Fund of Hungary [Nr. NKFIH 123953].

How to cite: Zacháry, D., Jakab, G., Filep, T., Balázs, R., and Szalai, Z.: The role of mineral composition regulating the turnover of organic matter in 13 forest soils from Hungary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5314, https://doi.org/10.5194/egusphere-egu2020-5314, 2020.

EGU2020-6068 | Displays | SSS5.6

Impact of integrated crop-livestock system (ICLS) on endogenous organic matter in a subtropical Oxisol

Deborah Pinheiro Dick, Gabriel Garcia, Ibanor Anghinoni, and Paulo Cesar de Faccio Cravalho

In this work, soil organic matter (SOM) content and composition was investigated in a Brazilian Red Oxisol submitted to ICLS during 15 years. The experiment was conducted in a clayey Oxisol in South Brazil in randomized blocks (n=3) with different grazing intensities according to pasture height: 10 (P10), 20 (P20) and 40 cm (P40) cm). The ICLS system consisted of black oat (Avena strigosa) and ryegrass (Lolium multiflorum) in winter and soybean (Glycine max) in summer (C3 plants). Litter and soil samples were collected within 1 m depth from treatments and from secondary bush forest (SF) soil. Previous to experiment, the whole area had been used for conventional agriculture for about 45 years. Before that (circa 60 years ago), the area was under native pasture (Aristida pallens, C4 plant). C and N contents and isotopic signature δ13C were determined and SOM chemical composition was investigated in HF-concentrated samples by 13C NMR CP/MAS spectroscopy. δ13C from a modal profile under native vegetation was determined as well. Grazing intensity did not affect C contents, that varied from 31.5 g kg-1 in surface to 7.6 g kg-1 at 1 m depth in ICLS. The greatest C contents were observed under SF down to 20 cm depth (47.8 to 20 g kg-1), evidencing the more relevant contribution of forest vegetation on C sequestration in this area. C/N ratio under ICLS tended to increase with depth from 11 to 16. In contrast, no such trend was observed under SF, where C/N ratio was smaller than under ICLS in all analyzed layers. For SF and P40 soils, δ13C values were around -22 ‰ at 0-5 cm (typical for C3 plants SOM), changing abruptly to -17 ‰ at 5-10 cm layer and increasing steadily downward the profile to -14 ‰. In the modal profile, δ13C values were typical for C4 plants and varied from –12.4 ‰ in A horizon to -9.7 ‰ at Bw horizon. It follows that residues from past and recent agriculture use contributed relevantly to surface layer (0-5 cm) SOM, whereas below 5 cm, endogenous SOM was the main constituent. SOM chemical composition at 0-5 cm layer was dominated by O alkyl C groups (45-110 ppm) that contributed with 52 to 54 %, followed by alkyl C groups (0-45 ppm) with 18 to 26 % and aromatic C groups (110-160 ppm) with 9 to 16%. In all analyzed sites, alkyl C decreased and aromatic C proportions increased with depth, reaching 14 to 17 % and 19 to 23 %, respectively, at 80-100 cm layer. Nevertheless, at this depth, O alkyl C proportion tended to remain high (49 to 52%). Under P10, alkyl C/O alkyl C ratio at surface was lower than in P40, indicating that grazing affected SOM composition mainly at the surface layer. Our results suggest that in the studied Oxisol profile, endogenous SOM resists to be exchanged by “recent vegetation” SOM from ICLS due to stabilization via interactions with Fe-Oxides that also preserve biochemically labile C groups.

How to cite: Pinheiro Dick, D., Garcia, G., Anghinoni, I., and de Faccio Cravalho, P. C.: Impact of integrated crop-livestock system (ICLS) on endogenous organic matter in a subtropical Oxisol, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6068, https://doi.org/10.5194/egusphere-egu2020-6068, 2020.

EGU2020-7299 | Displays | SSS5.6

Impact of Feedstock on Biochar Surface Properties: Practical Application of Boehm’s and Potentiometric Titration

Agnieszka Tomczyk, Katarzyna Szewczuk-Karpisz, Zofia Sokołowska, Milena Kercheva, and Emil Dimitrov

Biochar is a material created through the pyrolysis of different kind of biomass. On the basis of last research reports, it was found, that the kind of used biomass influences on surface properties of biochar. These properties are of key importance in effectiveness of biochar as a soil sorbent.

The experiments were carried out using three biochars derived from: tobacco, sweet corn cobs and vineyard which are produced by the "double-barrel" method.

The aim of the research was an investigation the effects of feedstock kind on surface properties of biochar. The characteristics of selected surface properties of biochar included the determination of: functional group content by Boehm's acid-base titration method; determination of the variable surface charge and distribution of surface functional groups from potentiometric titration.

Biochar samples exhibit a high variable surface charge (Q) and content of surface functional groups. Tobacco has the highest Q and content of acidic groups, while sweet corn cobs - the lowest one. Variable surface charge provides information about the quantity of surface functional groups. The distribution of surface functional groups exhibits the existence of 3 peaks, which indicate the presence of acidic groups (carboxylic, lactonic and phenolic).

The biochar from tobacco, vineyard or sweet corn cobs possessed merit for the improvement pollution removal from soil.

Research was conducted under the project "Water in soil - satellite monitoring and improving the retention using biochar" no. BIOSTRATEG3/345940/7/NCBR/2017 which was financed by Polish National Centre for Research and Development in the framework of "Environment, agriculture and forestry" - BIOSTRATEG strategic R&D programme

How to cite: Tomczyk, A., Szewczuk-Karpisz, K., Sokołowska, Z., Kercheva, M., and Dimitrov, E.: Impact of Feedstock on Biochar Surface Properties: Practical Application of Boehm’s and Potentiometric Titration, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7299, https://doi.org/10.5194/egusphere-egu2020-7299, 2020.

EGU2020-7351 | Displays | SSS5.6

Biochar impact on tensile strength of Dystric Cambisol aggregates – a model study

Katarzyna Szewczuk-Karpisz, Agnieszka Tomczyk, Zofia Sokołowska, Marcin Turski, Marta Cybulak, and Kamil Skic

Aggregate tensile strength is a significant parameter of soil structure. Adequate mechanical stability of aggregates promotes long-term crop productivity due to, inter alia, maintaining gas diffusion, facilitating root penetration and improving water infiltration. Soil aggregates characterized by high tensile strength are also resistant to erosion. Nowadays, intensive agriculture and environmental pollution contribute to clear deterioration of soil condition. The soil structure is often destroyed. In order to limit the negative phenomena, various soil additives are used, e.g. biochar.

In this paper, the effect of wood waste biochar on tensile strength and porosity of Dystric Cambisol artificial aggregates was examined. The experiments were performed on dry-air and wet soil aggregates non-containing and containing 0.1% or 5% dose of biochar. Tensile strength of the probes was determined using strength testing device (Zwick/Roell), whereas porosity – by mercury intrusion porosimetry (Micrometrics). The obtained results indicated that the biochar addition decreases tensile strength of all examined aggregates. This effect was more significant for higher biochar dose – 5%. This phenomenon is probably connected with formation of macropores of larger sizes within aggregates after the biochar addition.

Research was conducted under the project "Water in soil - satellite monitoring and improving the retention using biochar" no. BIOSTRATEG3/345940/7/NCBR/2017 which was financed by Polish National Centre for Research and Development in the framework of "Environment, agriculture and forestry" - BIOSTRATEG strategic R&D programme.

How to cite: Szewczuk-Karpisz, K., Tomczyk, A., Sokołowska, Z., Turski, M., Cybulak, M., and Skic, K.: Biochar impact on tensile strength of Dystric Cambisol aggregates – a model study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7351, https://doi.org/10.5194/egusphere-egu2020-7351, 2020.

EGU2020-7673 | Displays | SSS5.6

Subsoil organo-mineral associations under contrasting climate conditions

Thiago M. Inagaki, Angela R. Possinger, Katherine E. Grant, Steffen A. Schweizer, Carsten W. Mueller, Louis A. Derry, Johannes Lehmann, and Ingrid Kögel-Knabner

Organo mineral associations intermediated by Fe and Al are considered one of the most important mechanisms for soil organic carbon (SOC) stabilization. However, since Fe and Al are normally mentioned together as stabilizing agents, we still lack knowledge about their relative role. In addition, this stabilization mechanism can be profoundly affected by climate differences, but the magnitude of this influence whether as a direct effect or an indirect consequence due to changes in soil mineralogy is not yet fully understood. In this study, we evaluated a series of subsoil samples throughout a climate gradient (1800–2400 mm precipitation year-1 and 15–24º C) on Kohala Mountain, Hawaii to understand the impact of climate differences on organic matter protection. We have used a combined approach of analyses at the bulk soil and microscale using NanoSIMS. At the bulk soil scale, we have observed a concurrent decline of subsoil Fe, Al (i.e., dithionite citrate and ammonium oxalate extractions) and SOC above a precipitation level of 2000 to 2200 mm year-1. This decline co-occurred with more reduced forms of Fe s (evaluated by Fe K-edge XANES) and declines in carboxyl-C (evaluated by CP-MAS 13C NMR). We found significant positive correlations between SOC with Fe and Al in the bulk soil throughout the gradient, and we could discern the relative role of Fe and Al in promoting organo-mineral associations in contrasting climate conditions (e.g., ~1800 and ~2300 mm year-1) using NanoSIMS. While Fe contributed to approximately 40% of the microscale organo-mineral associations in the lower precipitation site (assessed by co-localizations with OM segments), this contribution at the higher rainfall regime was only 5%. In contrast, the contribution of Al was approximately the same in both rainfall levels (approximately 30%). This fact indicates that Al may be more important than Fe in stabilizing SOC especially under high precipitation levels. The normalized CN:C ratio was higher when associated with Fe and Al especially in the high precipitation level, which demonstrates the importance of Fe and Al in stabilizing N-rich organic matter. Here we demonstrate that spatial relationships between Fe and Al with SOC at the microscale display a shift towards Al-dominated SOC associations at higher precipitation that could not be ascertained from bulk measurements alone. Thus, they are of great importance to understand the impact of climatic differences on SOC sequestration in organo-mineral associations.

 

How to cite: Inagaki, T. M., Possinger, A. R., Grant, K. E., Schweizer, S. A., Mueller, C. W., Derry, L. A., Lehmann, J., and Kögel-Knabner, I.: Subsoil organo-mineral associations under contrasting climate conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7673, https://doi.org/10.5194/egusphere-egu2020-7673, 2020.

EGU2020-8660 | Displays | SSS5.6

Colloidal iron and organic carbon control soil aggregate formation and stability

Liming Wang, Lars Krause, Erwin Klumpp, Ines Nofz, Anna Missong, Wulf Amelung, and Nina Siebers

Several beneficial soil functions are linked to aggregates, but how the formation and stability depend on the presence of colloidal building blocks is still understood poorly. Here, we sampled subsites from an arable toposequence with 190 and 340 g kg-1 clay, and isolated small soil microaggregates (small SMA; < 20 µm) from larger macroaggregate units (> 250 µm) using an ultrasonic dispersion energy of 60, 250, and 440 J mL-1 , respectively. We then allowed these small SMA to reaggregate after chemical removal of organic carbon (OC) as well as of Fe- and Al (hydr)oxides, respectively. The size distribution of the reaggregated small SMA and fine colloids (< 0.45 µm) was analyzed via laser diffraction and asymmetric flow field-flow fractionation coupled to inductively coupled plasma mass spectrometry and OC detection, respectively. We found elevated amount of both fine colloids and stable SMA at subsites with larger clay contents. The size distribution of small SMA was composed of two distinct fractions including colloids (< 1 µm) and SMA with an average size of 5 µm. The removal of Fe with Dithionite-Citrate-Bicarbonate (DCB) shifted the size of the small SMA to a larger equivalent diameter, while destruction of OC with NaOCl reduced it. After three wetting and drying cycles, the concentration of colloids declined, whereas the small SMA without chemical pre-treatments reaggregated to particles with larger average diameters up to 10 µm, with the size depending on the clay content. Intriguingly, the gain in size was more pronounced after Fe removal, but it was not affected by OC removal. We suggest that Fe (hydr)oxides impact the stability of small SMA primarily via cementing the aggregates to smaller size. In contrast, the effect of OC was restricted to the size of colloids, gluing them together to small SMAs within defined size ranges when OC was present but releasing these colloids when OC was absent.

How to cite: Wang, L., Krause, L., Klumpp, E., Nofz, I., Missong, A., Amelung, W., and Siebers, N.: Colloidal iron and organic carbon control soil aggregate formation and stability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8660, https://doi.org/10.5194/egusphere-egu2020-8660, 2020.

EGU2020-12457 | Displays | SSS5.6

Size-dependent organo-mineral interactions and dynamics in a seasonally-flooded wetland

Mohammad Afsar, Bruce Vasilas, and Yan Jin

Understanding the mechanisms governing the composition and stability of organo-mineral associations is critical to predicting the dynamics of soil organic matter (SOC) and the related global carbon cycling. Redox-induced biogeochemical transformations are the key processes that control the stabilization of SOC via association with metal oxides in terrestrial environments such as wetlands. Despite its high C content (20-30% of terrestrial C), size-dependent organo-mineral associations and their dynamic changes in the redox-dynamic wetlands are poorly understood. Here we present size distribution, concentration, and composition of organo-mineral associations in pore water samples from a depressional wetland located at the Delmarva Bay in Delaware, USA, as influenced by seasonal fluctuations in water table level. The samples were collected from piezometers installed at multiple depths (50 cm, 100 cm, and 200 cm) and in three zones (upland, transitional, and wetland), respectively. Four size fractions were analyzed: dissolved (<2.3 nm), natural nanoparticle (2.3-100 nm, NNP), fine colloid (100-450 nm), and particulate (450-100 nm). Our results revealed that dissolved, NNP, fine colloid and particulate fractions comprised 47 ± 4%, 37 ± 4%, 8 ± 3% and 8 ± 3% of  the bulk organic C (<1000 nm) concentration, respectively. Relative percentages of respective Al, Mn, and Fe were 47 ± 24%, 30 ± 22%, 50 ± 18% at 2.3-450 nm and 22 ± 16%, 17 ± 12%, 25 ± 19% at 450-1000 nm size fraction. The main finding from this study are 1) dissolved and NNP fractions contain higher amount of C than colloidal and particulate fractions and 2) organo-mineral associations have significant differences in their elemental concentrations among different size fractions within colloidal size range. Additionally, the results clearly indicate that the commonly used operational definition for dissolved organic matter (DOM, <450 nm) significantly overestimates the dissolved phase C concentration by including the NNP and colloidal fractions, which contain mineral-associated C. This has important implications in the estimation of SOC decomposition rate in soils, particularly in redox sensitive wetlands, thus in assessing terrestrial C cycling and the transport of OC as well as the associated elements.

How to cite: Afsar, M., Vasilas, B., and Jin, Y.: Size-dependent organo-mineral interactions and dynamics in a seasonally-flooded wetland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12457, https://doi.org/10.5194/egusphere-egu2020-12457, 2020.

EGU2020-13589 | Displays | SSS5.6

Pore space characteristics of soil microaggregates – Possible implications for functioning

Stefan Dultz, Vincent Felde, Susanne K. Woche, Robert Mikutta, Daniel Uteau, Stephan Peth, and Georg Guggenberger

Soil microaggregates (SMA) are characterized by a pronounced small-scale structural heterogeneity, with recognizable chemical differences between the aggregate`s interior and its surface. Latter suggests a deterministic spatial pattern with respect to C stabilization, element exchange, and habitat function for microorganisms. Here, a detailed characterization of the pore space is crucial for the understanding of element transfer and microbial colonization in SMA. In our study, the 53-250 µm size fraction of SMA isolated along a soil clay content gradient (19-35%) were investigated in terms of their pore space characteristics. For the visualization of connected “open” pore structures as well as “closed” pores, a modified Hg-porosimetry technique utilizing Wood´s metal was used (WIP). The molten alloy was pressed into accessible connective pores by applying an argon pressure of 55 MPa, filling up pores with a diameter down to ≈20 nm. After solidification of the alloy, polished sections of SMA were analyzed by laser scanning confocal microscopy (Keyence, VK-9700). To image and quantify open and closed pores, grayscale-histograms were segmented and three pore size classes (<10, 10-100, and >100 µm²) were distinguished for open and closed pore systems. Additionally, we scanned 27 samples with high-resolution X-ray tomography (CT, Zeiss Xradia 520 versa) to characterize the 3D pore features at resolutions between 480 and 928 nm. SMA typically consist of two different sections, where particle arrangements are loose or dense. Relatively coarse-sized aggregate-forming materials were observed in sections with loose particle arrangements, where pores appear well connected. To some extent, these coarse aggregate-forming materials are arranged in larger circular structures. In contrast, dense particle arrangements consist primarily of fine aggregate-forming materials. The total porosity of the SMA derived by WIP was highly variable with a maximum of 40 area-%. While CT aggregate volume and CT aggregate surface area did not change with clay content, CT-porosity (vol.-%) increased with increasing clay content. Maximum CT porosity of 27 % was found in the samples with the highest clay content. Maximum pore diameter was similar across all clay contents, but the share of macropores with diameters >10 µm increased with increasing clay content. The Euler number decreased with increasing clay content, which indicates an increased connectivity of the pore space. Another parameter that increased with increasing clay content was the CT aggregate volume / CT internal pore surface area ratio, signifying more accessible surfaces for element exchange and/or C storage. While pores exceeding 100 µm² had the highest share within the open pores, it was the pore system <10 µm² for the closed pores. The proportion of closed pores of total porosity was smaller for the finer SMA sizes within the 53-250 µm fraction, which confirms the CT results (increasing Euler number). Our WIP data reveal that higher shares of clay minerals in SMA cause a narrower pore size distribution with smaller average diameters and increased tortuosity. Consequently, element transport and habitation by microorganisms might be slowed down in smaller, more clay-rich SMA, potentially resulting in larger C conservation within the interior of smaller SMA.

How to cite: Dultz, S., Felde, V., Woche, S. K., Mikutta, R., Uteau, D., Peth, S., and Guggenberger, G.: Pore space characteristics of soil microaggregates – Possible implications for functioning, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13589, https://doi.org/10.5194/egusphere-egu2020-13589, 2020.

Soil microaggregates are considered to play an important role in soil functioning and soil organic carbon (SOC) is of great importance for the formation and stabilization of these aggregates. The loss of SOC can occur, for example, after a change in land use and may lead to a decreased aggregate stability, which makes soils vulnerable to various threats, such as erosion or compaction. It is therefore important to understand the effect of SOC loss on aggregate stability in order to better understand and preserve the functioning of healthy soils.

We sampled two adjacent plots from a loess soil in Selhausen (North Rhine-Westphalia, Germany) in November of 2019 and measured aggregate stability and architecture of soil microaggregates. One plot was kept free from vegetation by the application of herbicides and by tillage (to a depth of 5 cm) from 2005 on, while the other plot was used for agriculture (conventional tillage). Over the course of 11 years, the SOC concentration in the bulk soil was reduced from 12.2 to 10.1 g SOC kg-1 soil. We took 10 undisturbed soil cores from two depths of each plot (Ap and Bt horizons).

The stability of aggregates against hydraulic and mechanical stresses was tested using the widespread wet sieving approach and a newly developed dry crushing approach. Isolated microaggregates gained from the latter procedure were tested against tensile stress by adapting a crushing test in a load frame to the microaggregate scale. To shed light on the effect of a decreased SOC content on microaggregate structure, we scanned several microaggregates with a high-resolution computed tomography scanner (Zeiss Xradia 520 versa) at sub-micron resolutions and analyzed the features of their pore systems.

This will give us valuable insights into the interplay of mechanical and physicochemical stability, as well as the structural properties of microaggregates with regard to SOC depletion. The consequences for various soil functions provided by microaggregates, like the habitat function for microorganisms or their capacity to store and transport gas, water and nutrients, are discussed.

How to cite: Roosch, S., Felde, V., Uteau, D., and Peth, S.: Effect of soil organic carbon loss on the stability and structure of microaggregates: First insights from an organic carbon depletion field trial in a loess soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17358, https://doi.org/10.5194/egusphere-egu2020-17358, 2020.

EGU2020-22405 | Displays | SSS5.6

Spatial organization of soil microaggregates

Eva Lehndorff, Nele Meyer, Andrey Radionov, Lutz Plümmer, Peter Rottmann, Beate Spiering, Wulf Amelung, and Stefan Dultz

The physical arrangement of soil compounds in microaggregates is important in many ways, e.g. by controlling soil stability and C sequestration. However, little is known about the spatial arrangement of organic and inorganic compounds in soil microaggregates, due to the lack of in-situ analyses in undisturbed material. Here we hypothesize that microaggregates are spatially organized, resulting in deterministic, predictable spatial patterns of different organic matter and mineral phases and that this organization depends on the abundance of specific phases such as on clay mineral content. We separated the water stable, occluded large and small microaggregate fractions from Ap horizons of a sequence of sandy to loamy Luvisols (19 to 35% clay, Scheyern, Germany) and subjected in total 60 individual aggregates to elemental mapping by electron probe micro analysis (EPMA), which recorded C, N, P, Al, Fe, Ca, K, Cl, and Si contents at µm scale resolution. Spatial arrangements of soil organic matter and soil minerals were extracted using cluster analyses. We found a pronounced heterogeneity in aggregate structure and composition, which was not reproducible and largely independent from clay content in soil. However, neighborhood analyses revealed close spatial correlations between organic matter debris (C:N app. 100:10) and microbial organic matter (C:N app. 10:1) indicating a spatial relationship between source and consumer. There was no systematic relationship between soil minerals and organic matter, suggesting that well-established macroscale correlations between contents of pedogenic oxides and clay minerals with soil organic matter storage do not apply to soil microaggregates.

How to cite: Lehndorff, E., Meyer, N., Radionov, A., Plümmer, L., Rottmann, P., Spiering, B., Amelung, W., and Dultz, S.: Spatial organization of soil microaggregates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22405, https://doi.org/10.5194/egusphere-egu2020-22405, 2020.

EGU2020-13488 | Displays | SSS5.6

Aggregate formation dynamics driven by 3D fluid flow in natural porous media

Thomas Ritschel and Kai Totsche

Fluid flow and reactive transport in natural porous media take place in a three-dimensional, hierarchically organized network of voids and pores in the size range of sub-micrometers inside small aggregates to several millimeters in, e.g., earthworm burrows or cracks. Thus, fluid flow regimes are manifold with consequences not only for the transport of solutes, but also for the displacement of colloidal particles and organic matter and thus, for their inclusion into soil aggregates. Therefore, we incorporated the simulation of three-dimensional fluid flow in pore networks typical for natural porous media into our recent approach to model soil aggregate formation using DLVO theory and diffusion-limited aggregation to overcome its previous limitation to suspensions at rest. To visualize the model capabilities, we simulated aggregation in pore networks that were either synthetically designed to represent certain structural features such as pore junctions and dead-end pores, or taken directly from X-ray µ-CT measurements of undisturbed soil cores. We explored the development of structural aggregated features that evolve in response to flow, transport and the topology of the soil pore space. The resulting three-dimensional arrangement of compounds and the entire aggregates were classified according to their morphological metrics, e.g. the pore space distribution, and functional properties, e.g. the water retention capacity, that are provided by these structures. By this fusion of complementary modeling approaches, we significantly contribute to the fundamental mechanistic understanding of the complex interplay and feedback of structure, interactions and functions on the scale of (micro-)aggregates.

How to cite: Ritschel, T. and Totsche, K.: Aggregate formation dynamics driven by 3D fluid flow in natural porous media, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13488, https://doi.org/10.5194/egusphere-egu2020-13488, 2020.

EGU2020-7642 | Displays | SSS5.6

Glucose-stimulation of natural microbial activity causes transient aggregation and alteration of clay mineralogy in sandy and loamy sediments

Pavel Ivanov, Natalia Manucharova, Svetlana Nikolaeva, Alexey Safonov, Viktoria Krupskaya, Mikhail Chernov, Karin Eusterhues, and Kai Uwe Totsche

Subsurface sediments usually show limited microbial activity, however, inputs of nutrients due to anthropogenic spills or infiltration from the surface may quickly activate the native microbial communities, thereby changing composition, structure and properties of sediments. We studied the effect of glucose addition, an easily available carbon source, on mineralogy, microstructure and properties of several (0.5-35 m) loamy and sandy sediments over 30 days in laboratory experiments. We followed the time changes in biomass by direct cell count; respiratory activity by CO2 emission; clay mineralogy by X-ray diffraction (XRD); microaggregate size distribution by pipette analysis; and observed microbial binding via scanning electron microscopy (SEM).

Glucose addition caused transient buildup of respiratory activity and biomass with maximal values 3-10 times more than in control (water-treated) samples appearing around the 7th day after the treatment. The biomass of bacteria, archaea, actinomycetes and fungi increased. After that the biomass and the CO2 emission declined sharply and reached stable values about twice as much as in control samples.

On day 7, we noted an increase in the proportion of smectite layers in the disordered mixed layer illite-smectite minerals (MLM), yet no changes in content and composition of other clay and non-clay minerals. After 30 days of observation, XRD showed further transformation of MLM composition, as well as partial destruction of other clay minerals. We hypothesize that with abundant external nutrition, microbes mined the lacking K from illite layers of the MLM. After the consumption of glucose, all clay minerals were a source of essential elements.

The content of microaggregates of 0.1-0.05 mm in size increased in loams on the 7th day after the treatment, presumably due to microbial binding and gluing of aggregates by cells and EPS. With the decline of the biomass, the previously-formed microaggregates partially disintegrated. We assume that after the consumption of glucose, the microorganisms lived on biomass and EPS, thereby removing previously formed glue and meshes from the aggregates.

SEM performed on air dried sands collected during maximal microbial activity revealed biofilms consisting of microbial cells and EPS, attaching to the fine clay coatings around sand grains. SEM on lyophilized loams showed filamentous structures, which we interpret to be actinomycete mycelium that enmeshes particles into microaggregates.

Irreversible changes in clay mineralogy and transient aggregation caused temporary alteration of stress-strain properties: increased cohesion, and decreased friction and compressive strength.

Our data show that ongoing/continued microbial activity is crucial for the formation of aggregates as well as for the clay mineral paragenesis in sediments. Both processes affect sediment quality, e.g. in terms of soil organic matter stabilization or with respect to the overall mechanical properties.

How to cite: Ivanov, P., Manucharova, N., Nikolaeva, S., Safonov, A., Krupskaya, V., Chernov, M., Eusterhues, K., and Totsche, K. U.: Glucose-stimulation of natural microbial activity causes transient aggregation and alteration of clay mineralogy in sandy and loamy sediments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7642, https://doi.org/10.5194/egusphere-egu2020-7642, 2020.

EGU2020-13629 | Displays | SSS5.6

Effects of Flow Regime on DOM Retention in Soils: Continuous Flow vs. Flow Interruption

Jannis Florian Carstens, Georg Guggenberger, and Jörg Bachmann

Dissolved organic matter (DOM) is one of the most mobile components of the global carbon cycle. Corresponding transport processes in the environment have received plenty of attention in the context of carbon sequestration as well as the mobility of DOM-associated contaminants.

However, most previous transport studies have been conducted exclusively under continuous flow conditions, which are not comparable to real water flow characteristics in soil. The present study aims to address that gap in knowledge by systematically assessing the effect of defined flow interruption phases on the retention of DOM.

For that, the breakthrough behavior of DOM as affected by phases of flow interruption was investigated in an increasingly complex system of solid matrices rich in oxide mineral coatings: goethite coated quartz sand, disturbed Cambisol subsoil, and undisturbed Cambisol subsoil. The classic DLVO and extended DLVO (XDLVO) models including Lewis acid—base parameters were applied based on measurements of sessile drop contact angles and zeta potentials.  

DOM retention was increasing with the duration of flow interruption, and retention was considerably higher in the soils than in goethite coated sand. After 112 hours of flow stagnation, DOM release from the soils was reduced to 16 to 22 % as compared to continuous flow conditions. The retention in the different solid matrix materials was well correlated with the respective amounts of oxalate and dithionite extractable oxide mineral phases. The DLVO model was capable of correctly predicting the mobility of DOM in goethite coated sand, but not in the soils, due to the fact that soil surface charge heterogeneities could not be measured. The XDVLO model predicted short-range hydrophilic repulsive interactions that may have contributed to the distinct tailing of the DOM breakthrough curves.

We conclude that the significant DOM retention during phases of flow stagnation phases shows that more complex flow regimes need to be considered in order to assess the mobility of DOM in soils. In fact, many previous studies excluding phases of flow stagnation likely overestimated the mobility of DOM in the environment.

How to cite: Carstens, J. F., Guggenberger, G., and Bachmann, J.: Effects of Flow Regime on DOM Retention in Soils: Continuous Flow vs. Flow Interruption , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13629, https://doi.org/10.5194/egusphere-egu2020-13629, 2020.

Land use change can significantly influence both mineralogy and chemical soil properties. This conversion, particularly from forest to agricultural system occurs often in volcanic soils due to their favorable properties for food production. Under agriculture, minerals can weather faster than in natural vegetation and this also impacts soil functioning. We aim to assess the impact of land use on geochemical soil properties and soil organic carbon across soils of different age. This study was conducted in Mt. Tangkuban Perahu and Mt. Burangrang where the soils were derived from similar andesitic parent material and have different ages based on their lithology. Five sites were selected representing land uses that have been converted (pine forest and agricultural land) and one site of natural forest as the origin of land use. The results showed that land use management enhances the mineral transformation. Pine forest and agricultural sites displayed higher weathering degree than natural forests as indicated by higher clay content, iron crystallinity index and the presence of gibbsite. The weathering degree of soils in agricultural sites might result from the length of cultivation period and soil age. Land use conversion also altered chemical properties such as pH, CEC, basic cations, and the proportion of amorphous materials. Non-crystalline Al and Fe minerals as indicated by Alo+1/2Feo were highly correlated with organic carbon and specific surface area (SSA) in the subsoils of all land uses. However, we did not see the accumulation of organic carbon in subsoils compared to topsoils as the amount of non-crystalline Al and Fe minerals increases with depth, especially in agricultural lands where the organic fertilizer input is very high. In addition, a significant proportion of carbon was stored in sand aggregate fractions in agricultural land which have longer cultivation period, while it was more readily found in silt and clay fractions in the site with shorter period.

 

How to cite: Anindita, S., Finke, P., and Sleutel, S.: Land use effects on the geochemical soil properties and their control on organic carbon in volcanic soils, near Bandung area (Indonesia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5516, https://doi.org/10.5194/egusphere-egu2020-5516, 2020.

EGU2020-18375 | Displays | SSS5.6

FTIR spectral properties affected by OM-cation interactions

Ruth Ellerbrock and Horst H. Gerke

Soil organic matter (OM) interacts with cations like Ca by using C=O and OH functional groups. Such interactions are known to protect soil OM against decomposition. This process affects the bonding strength of functional groups. Changes in bonding strength are assumed to shift the wavenumber region of OH and C=O absorption band maxima in Fourier transform infrared (FTIR) spectra. The aim is to analyze the extent of such shifts to determine presence and strength of OM–cation interaction. Solutions of PGA and Chia seed mucilage were mixed at different ratios with CaCl2 solution. The mixtures were freeze dried. FTIR spectra of PGA–Ca, and mucilage-Ca mixtures indicate that the OH band is affected by the presence of Ca. However, the C=O band maximum and the CH/C=O ratio were not affected. For the PGA–Ca and mucilage-Ca mixtures the shift in OH band maxima relative to PGA and mucilage, respectively, increases with Ca content. Such shifts in OH band maxima are in a similar range as the ones observed for the outer compared to inner regions of an intact chia seed mucilage droplet. The results suggest that it is necessary to know the relation between OM-cation interactions and band shifts for the correct interpretation of the FTIR spectra of soil and rhizosphere samples.

How to cite: Ellerbrock, R. and Gerke, H. H.: FTIR spectral properties affected by OM-cation interactions , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18375, https://doi.org/10.5194/egusphere-egu2020-18375, 2020.

SSS5.7 – Mutual interaction of humic substances with heavy metals, pesticides and PAHs | Posters only

EGU2020-3110 | Displays | SSS5.7

Isolation of the humin fraction from soil: preliminary comments

Jerzy Weber, Elżbieta Jamroz, Andrzej Kocowicz, Magdalena Debicka, Aleksandra Ukalska-Jaruga, Lilla Mielnik, Romualda Bejger, Maria Jerzykiewicz, Jakub Bekier, and Irmina Ćwieląg-Piasecka

The organic matter is the most important component of soil material, which determines most soil properties. Among humic substances, humin fraction has been the least studied to date, although it usually constitutes over half of their composition. This is probably due to the fact, that humin fraction has highly hydrophobic properties and is insoluble at all pH values, which makes its isolation much more difficult, compared to humic (HA) and fulvic (FA) acid fractions. In addition, humin fraction forms very stable humic-clay complexes with mineral part of the soil (Stevenson 1994), which cannot be destructed during humic substances extraction. According to the literature, the methods of humin fraction isolation can be divided into two main groups: (1) extraction by different organic solvents, and (2) isolation by extraction of HA and FA followed by digestion of mineral soil components. Nevertheless, each of these methods has different limitations.

We investigated some modifications of the latter method, obtaining humin fraction from eight mollic horizons of Chernozems and Phaeozems, which differed in their physico-chemical properties.

The first step was to separate HA and FA according to IHSS method described by Swift (1996), however we adopted different shaking procedure. To asses differences, each supernatant obtained was analyzed for the carbon content concentration, which corresponded to HA and FA extracted.

HA and FA free residue was then digested to reduce the content of mineral components. We used several digestion with 10% HF/HCl , as higher concentrations of HF can result in structural alteration of the organic compounds (Hayes et al. 2017). To find the optimal time of the procedure, the ash content was determined following each digestion stage. After the HF/HCl treatment, the residue was rinsed with 10% HCl to eliminate secondary minerals. The residue was washed with distilled water until the neutral pH, then transferred to dialysis membranes and dialyzed with distilled water until a negative Cl test with AgNO3. Afterwards the humin fraction was freeze dried. 

Finally, obtained humin fraction contained various ash content, ranged from 6 to 30%, depending on the soil. The conducted test indicated that: (1) the concentration of carbon in supernatant considerably increased as shaking time was extended to 20 hours, and (2) longer than 4 weeks digestion with HF/HCl did not affect the reduction of the ash content of the humin fraction obtained.    

 

Literature

Hayes M.H.B., Mylotte R., Swift R.S. 2017. Humin: Its Composition and Importance in Soil Organic Matter. In: Sparks D.L. (ed) Advances in Agronomy, Vol. 143, Academic Press, Burlington, 47–138.

Stevenson F.J. 1994. Humus Chemistry; Genesis, Composition, Reaction. 2nd ed. John Wiley & Sons., New York.

Swift R.S. 1996. Organic matter characterization. In: Sparks, D.L., et al. (Ed.), Methods of Soil Analysis. Part 3. Chemical Methods - Soil Science Society of America, Book Series no 5,  1011-1069.

 

Acknowledgements

This work was supported by the National Science Center (NCN) Poland (project No 2018/31/B/ST10/00677 “Chemical and spectroscopic properties of soil humin fraction in relation to their mutual interaction with pesticides").

How to cite: Weber, J., Jamroz, E., Kocowicz, A., Debicka, M., Ukalska-Jaruga, A., Mielnik, L., Bejger, R., Jerzykiewicz, M., Bekier, J., and Ćwieląg-Piasecka, I.: Isolation of the humin fraction from soil: preliminary comments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3110, https://doi.org/10.5194/egusphere-egu2020-3110, 2020.

EGU2020-4609 | Displays | SSS5.7

Interaction of soil humin fraction with pesticides - a review

Aleksandra Ukalska-Jaruga, Romualda Bejger, Irmina Ćwieląg-Piasecka, Jerzy Weber, Elżbieta Jamroz, Magdalena Debicka, Lilla Mielnik, Maria Jerzykiewicz, Jakub Bekier, and Andrzej Kocowicz

The use of pesticides significantly influences the efficiency of agriculture production, but at the same time, their extensive and widespread use, raises serious concerns regarding the release of harmful substances into the environment [1,2]. The fate of pesticides in soil depends on many factors related mainly to the physico-chemical properties of these compounds as well as content and quality of organic matter [3]. Humin as the predominant fraction of organic matter, may significantly determine the behavior and transformations of pesticides in soil [5]. Therefore, the aim of this review was to present the state of the art of humin-pesticides mutual interactions.

Sorption-related studies showed that humin has dissimilar binding strengths with pesticides [4,5]. According to Pignatello [7], the sorption selectivity by humin has a number of potential causes: (1) preference for particular microdomains within fractions that are envisioned to segregate on the basis of functional group identity (aromatic, paraffinic, carbohydrate domains); (2) preference based on strong functional group interactions, such as hydrogen bonding and (3) preference based on the nature of the thermodynamic physical state of humin, namely the configurations and conformations of the molecules and strands at microstructural level.

Moreover, humin exhibits potentially different accumulation capacities for xenobiotics. Wang et al. [9] explained these relations with the limited accessibility to microporous domains of humin matrices for the larger-molecular-weight particles. The authors [9] observed a lower adsorbed mass of spatially developed compounds compared to compounds with small diameters. This process is probably most likely related to the structural rearrangement of the humin matrix under slow diffusion into microporous domains pronounced with the adsorption of large molecular weight compounds. Additionally, Pignatello [7] as well as Schaumann [4,5] indicated that the humin surface is covered with various polar and non-polar functionalities, which may efficiently interact with pesticides by van der Waals forces, hydrophobic attraction, hydrogen bonding, charge transfer or ligand exchange processes. Nevertheless, the chemical properties of pesticides as well as their coexistence with other chemical compounds i.e.: surfactants, coagulants, decomposition inhibitors and others [8] can modify the interactions of pesticides with humin in natural soil environment.

Literature:

[1] FAO, ITPS Global Assessment of the Impact of Plant Protection Products on Soil Functions and Soil Ecosystems. FAO, Rome 2017, 40 pp.

[2] Silva, V.; Mol, H.; Zomer, P.; Tienstra, M.; Ritsema, C.J.; Geissena, V. Sci. Total. Environ.  2019, 653, 1532–1545.

[3] Stolte, J.; Tesfai, M.; Øygarden, L.; Kværnø, S.; Keizer, J.; Verheijen, F.; et al. Soil Threats in Europe: Status, Methods, Drivers and Effects on Ecosystem 4 Services, 2016, Report

[4] Stevenson F. 1994, John Wiley & Sons, New York

[5] Schaumann G. 2006a, J Plant Nutr Soil Sci 169:145–156

[6] Schaumann G. 2006b, J Plant Nutr Soil Sci 169:157–167

[7] Pignatello J. 2012,  J Soils Sediments 12:1241–1256

[8] Ehlers, G.; Loibner, A. 2006, Environ. Pollut. 141, 494-512

[9] Wang X, Guo X, Yang Y, Tao S, Xing B. 2011, Environ Sci Technol 45:2124–2130

 

Acknowledgement: The studies were supported from the National Science Centre project no. 2018/31/B/ST10/00677 “Chemical and spectroscopic properties of soil humin fraction in relation to their mutual interaction with pesticides”

How to cite: Ukalska-Jaruga, A., Bejger, R., Ćwieląg-Piasecka, I., Weber, J., Jamroz, E., Debicka, M., Mielnik, L., Jerzykiewicz, M., Bekier, J., and Kocowicz, A.: Interaction of soil humin fraction with pesticides - a review, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4609, https://doi.org/10.5194/egusphere-egu2020-4609, 2020.

EGU2020-6844 | Displays | SSS5.7

The phytoextraction potential of selected vegetable plants on Kosovo contaminated soils

Teodoro Miano, Hana Voca, Lea Piscitelli, Anna Daniela Malerba, Donato Mondelli, and Valeria D'Orazio

Mining activities generate a great deal of particulate emissions and waste slag enriched in heavy metals that contaminate the surrounding, that is soil, water and air. Such effects are particularly serious and pose a severe ecological and human health risk, mainly if smelters are located in the proximity of urban areas. This is the case regarding the Kosovo, where from the 1930s the British company "Seltrust" founded Trepca Mining & Metallurgical Complex, causing a high level of pollution especially in the area of Mitrovicë, northern Kosovo. Two soils, A and B, have been sampled from two different sites in Mitrovicë municipality, showing a total content of Pb and Zn, respectively, of 2153 and 3087 mg kg-1, and 3214 and 4619 mg kg-1. A pot experiment was carried out aiming to understand the phytoremediation potential of two selected non-food crops (Sorghum bicolor L. Moench and Brassica napus cv. Westar) chosen for their economic importance and heavy metal accumulation capacities. Sorghum and canola plants were cultivated in polluted soils A and B. For both plant species, the accumulation of heavy metals proved to be higher in the roots. Indeed, in order to obtain an adequate phytoextraction, it is required that the metals be moved to the epigeal part of the plants, and plants with bioconcentration factor (BCF) and translocation factor (TF) values < 1 are not considered suitable for phytoextraction. The results obtained in this study indicate that, although canola was quite effective in translocating metals from roots to aerial parts, both sorghum and canola are not suitable for phytoextraction since their coefficient values were < 1. Anyway, both plants, especially canola ones, grew up in presence of high level of Pb and Zn pollution, thus they could be used for phytostabilisation process. Actually, the Tolerance Index (TI) values of the sorghum and canola clearly suggest, under the experimental conditions used in this study, a better performance of the canola in tolerating the presence of Pb and Zn in the soil, even if in soil B was not found the same efficiency shown by the same plants grown in soil A. Probably, since soil B has an absolute higher content of Pb and Zn and a lower pH, the availability of both metals is slightly higher, which may have induced in the plants that grow there a more intense condition of stress. This study shows that canola, unlike sorghum, can be an ideal choice for phytostabilization, and its breeding can represent an effective alternative to food crop. 

How to cite: Miano, T., Voca, H., Piscitelli, L., Malerba, A. D., Mondelli, D., and D'Orazio, V.: The phytoextraction potential of selected vegetable plants on Kosovo contaminated soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6844, https://doi.org/10.5194/egusphere-egu2020-6844, 2020.

EGU2020-7044 | Displays | SSS5.7

Olive husks biochar application in microbial remediation of pyrene polluted soil: a possible win-win solution

Lea Piscitelli, Anna Daniela Malerba, Giuseppe Natale Mezzapesa, Stefano Dumontet, Donato Mondelli, Teodoro Miano, and Giovanni Luigi Bruno

Human activities are negatively affecting ecosystems through the erosion and impoverishment of natural resources. Considering soil, global warming and unsustainable agricultural practices are reducing soil organic matter with consequent loss of fertility. An issue of major concern is also the soil pollution by organic and inorganic compounds affecting soil ability to generate ecosystem services. Polycyclic aromatic hydrocarbons are a large group of pollutants, made of two or more aromatic rings, widespread in the environment, soil included, and extremely toxicity for human and environmental health. Polycyclic aromatic hydrocarbons persistence in soil is an issue great concern that could be effectively faced by microbial remediation techniques.

In this work we studied the remediation of pyrene polluted soil through two parallel tests: bioremediation and biostimulatin techniques. The first involves inoculation into soil of exogenous microorganisms, in our case Trichoderma harzianum, whereas the latter was aimed at promoting the degrading ability of endogenous microorganisms. Moreover, in order to sustain microorganisms growth, we incorporated olive husk biochar in the two tested bioremediation systems.

Biochar is currently considered an excellent soil conditioner and its incorporation into soil seems to promote PAHs adsorption and to interact positively with soil microorganisms. Biochar is a carbonaceous matrix produced through thermal processing of organic biomasses at high temperature and at very low oxygen partial pressure. Here we converted olive husks, that is a potentially toxic by-product of olive oil extraction, by slow pyrolysis process with the aim of deprived this waste biomass of its noxious characteristics.

Soil samples were spiked with 50 ppm of pyrene, biochar was incorporated at a concentration of 13 g·kg–1 d.w. of soil and endogenous microbial growth, T. harzianum growth and microbial pyrene-degradation activity were measured weekly up to 28 days.

Pyrene concentration was reduced of approximately 70% in 28 days in both bioaugmentation and biostimulation remediation systems. T. harzianum did not display a distinctive ability in degrading pyrene and partially inhibited the endogenous soil microflora from degrading pyrene. Olive husks biochar application did not limited pyrene bioavailability or neither affected microbial pyrene degrading activity. However, our results underline that olive husks biochar increases T. harzianum growth and stimulates soil endogenous microorganisms.

How to cite: Piscitelli, L., Malerba, A. D., Mezzapesa, G. N., Dumontet, S., Mondelli, D., Miano, T., and Bruno, G. L.: Olive husks biochar application in microbial remediation of pyrene polluted soil: a possible win-win solution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7044, https://doi.org/10.5194/egusphere-egu2020-7044, 2020.

Soil contamination with arsenic in historical mining sites is a matter of considerable environmental concern, as the concentrations of As in those soils are locally as high as thousands mg/kg. Some of soils, particularly those affected in the past by tailings that were released from impoundments, are located in floodplains and used as grasslands. Those lands are periodically flooded, and the frequency and duration of flooding will probably increase in the future with changing climatic conditions. Reducing environment that develops upon soil flooding can cause a release of As from soil solid phase. This is an inherent effect of reductive dissolution of amorphous and crystalline iron hydroxides that are the main hosting components for metalloids. Changing redox conditions affect also the speciation of As in pore water, influencing its toxicity to soil biota. Moreover, soil fertilization with inorganic fertilizers that contain phosphates, or with organic fertilizers such as cattle manure, can accelerate As release from iron hydroxides, mainly via competitive desorption. The effects of all those processes are highly dependent on soil properties and still require a close examination.

Three kinds of soil material, containing up to 8000 mg/kg As, were collected from the tailings-affected floodplain of the Tująca river in Złoty Stok, a historical As mining centre. A laboratory incubation experiment with fertilized and non-fertilized soils was carried out to examine the changes in As concentrations in soil pore water, as well as to assess pore water ecotoxicity, determined in standard bioassays, including Microtox and Phytotox. Soil flooding resulted in a rapid release of As from soil solid phase. As concentrations in soil pore water in all samples exceeded 10 mg/L after a 2-day incubation, and tended to increase slowly with time. In some cases, after the 270-day incubation, As concentrations in pore water reached several hundred mg/L. Those effects resulted in a very high ecotoxicity of pore water, caused lethal effects to bacteria and springtails, and impeded plant germination. Soil amendment with manure was a factor that significantly enhanced those effects. The factors responsible for various effects that were reported from three soils were discussed.

How to cite: Szopka, K., Karczewska, A., Dradrach, A., and Gałka, B.: The effects of waterlogging on the solubility of arsenic and ecotoxicity of soil pore water in non-fertilized and fertilized soils in historical mining sites., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10576, https://doi.org/10.5194/egusphere-egu2020-10576, 2020.

EGU2020-17042 | Displays | SSS5.7

Colloidal Aspects of the Formation of the Interactions between Humic Substances and Surfactants

Michal Kalina, Tomas Duchacek, Jitka Krouska, Petr Sedlacek, and Jiri Smilek

Humic substances (HS) represent fascinating heterogeneous mixture of natural molecules, which possess a high potential to interact with various substances e.g. metals, surfactants, dyes, pesticides. This beneficial property allows their further utilization as the reactive part of sorbents with possible applications in remediation processes of soils and waste waters treatment plants. Surfactants represent a group of substances, which are artificially introduced in the nature by human driven applications causing the undesirable foaming of waters and enhancing the solubility of hydrophobic organic pollutants such as highly toxic polycyclic aromatic hydrocarbons. The present work is focused on the study of colloidal aspects of interactions between selected representatives of surfactants and humic substances, as the example of a promising sorbent and flocculant. For purposes of present work Hexadecyltrimethylammonium bromide, Tetradecyltrimethylammonium bromide, and Carbethoxypendecinium bromide were used as selected cationic surfactants, Sodium dodecyl sulphate as anionic and TWEEN-20 as a non-ionic. The interactions between the individual components were studied by using a combination of dynamic light scattering (determination of the changes in particle size distributions), electrophoretic light scattering (zeta potential – stability investigation) and isothermic titration calorimetry (thermodynamic parameters of interactions) in titration mode of measurement. This set-up provided us the determination of the critical aggregation concentrations of the surfactant-humic system, which corresponded to its phase separation. Moreover, the interactions between the components were confirmed also by routine physico-chemical methods (e.g. thermogravimetry and Fourier transform infrared spectroscopy).  We believe that the outcomes of our work will help to shed a new light on the phenomenon of the formation of the interaction between surfactants and humic substances and will provide the crucial insight in the broader utilization of specific fractions humic substances as the universal sorbent for surfactants mainly from the waste waters.

How to cite: Kalina, M., Duchacek, T., Krouska, J., Sedlacek, P., and Smilek, J.: Colloidal Aspects of the Formation of the Interactions between Humic Substances and Surfactants, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17042, https://doi.org/10.5194/egusphere-egu2020-17042, 2020.

In aquatic environments, Hg(II) is strongly reactive with the dissolved organic matter (DOM) and form complexes with acidic functional groups like carboxylic acids, phenols, ammonia, alcohol, and reduced sulfur ligands (Sred). It has been suggested, however, that both the concentration of Hg(II) and the composition of the DOM influence the potential for the removal of Hg(II) in water treatment.

Jar test experiments were performed at optimum coagulation conditions of pH and alum dose, using unfractionated DOM, humic substances (humic acids and fulvic acids) and different Hg(II) concentrations. Samples used in this work were obtained from the International Humic Substances Society (IHSS) and were selected based on the differences in aromatic carbon, reduced sulfur content, acidic functional groups concentration, geographical location, and commercial availability.

Results showed that good removal of Hg(II) can be achieved by alum coagulation under two circumstances: (1) when the DOM is low in Sred ligands but rich in aromatic content and (2) when the DOM is rich in Sred ligands and low in aromaticity. At low Hg/DOM ratio (0.05 μg Hg/mg DOM), Hg(II) removal can be as high as 95%, while at high Hg/DOM ratio (1.0 μg Hg/mg DOM) Hg removal can be as high as 73%. The aromaticity of the DOM and the presence of Hg(II)-binding ligands in the fraction of carbon that adsorbs to aluminum hydroxide flocs were the key variables that control the removal of mercury. All the same, the character of DOM determines the extent of the removal of carbon and the minimum amount of Hg(II) that can be removed from solution.

How to cite: Diaz, F., Katz, L., and Lawler, D.: Hg(II)-Dissolved Organic Matter (DOM) Interactions in Freshwater and their Removal in Conventional Water Treatment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20727, https://doi.org/10.5194/egusphere-egu2020-20727, 2020.

EGU2020-21642 | Displays | SSS5.7

The function of carboxyls in the structure of humic acids to binding of organic substances
not presented

Jiri Smilek, Anna Belusova, Michal Kalina, and Petr Sedlacek

The humic substances, the major and the most important part of soil organic matter, are responsible for the immobilization of organic compounds (e.g. heavy metal ions, organic dyes, surface active agents, etc.) in the soil. Unfortunately, there are a lot of gaps in the knowledge in the complex mechanism of binding of organic charged compounds by humic substances.

The unconventional diffusion and dialysis (transport) techniques have been developed for the purpose of study on the interactions between humic substances and organic charged substances.  In our contribution we are focusing on one fraction of humic substances – humic acids. The binding between humic acids with/without selectively blocking of carboxylic functional groups (methylation by –CH3) with organic charged compounds (e.g. organic dyes, surface active agents) has been studied by diffusion and dialysis approach using the spectroscopic techniques as analytical method. The strong impact of methylation on the positive affinity of humic acids towards organic compounds has been expected. These expectations were not confirmed by diffusion and dialysis techniques. The role of carboxyls in the structure of humic acids is not so essential as was expected and mentioned in the literature. The other effects (e.g. hydrophobic interactions, pi-pi stacking, etc.) are more important in the binding of organic compounds as was expected. The positive binding as well as kinetics of this process is also strongly depending on the physico-chemical circumstances of the system (e.g. pH, ionic strength, temperature, etc.).

How to cite: Smilek, J., Belusova, A., Kalina, M., and Sedlacek, P.: The function of carboxyls in the structure of humic acids to binding of organic substances, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21642, https://doi.org/10.5194/egusphere-egu2020-21642, 2020.

SSS5.8 – Soils and the Critical Zone: carbon, resilience, and change

EGU2020-12354 | Displays | SSS5.8

The chronosequence in context: Elevation-dependent dynamics of soil biogeochemistry during cloud forest succession

Nathaniel Looker, Andrew Margenot, Karis McFarlane, Ed Nater, Alain Plante, and Randy Kolka

In mountainous landscapes, rates of soil morphological and biogeochemical change during secondary forest succession (SFS) can vary widely with elevation due to gradients in water, energy, and mineral weathering status. Improved understanding of how elevation mediates the response of soils to SFS is critical not only for reducing the uncertainty of soil maps in complex terrain, but also for predicting the edaphic effects of SFS under future climatic conditions. Focusing on volcanic ash soils in Veracruz, Mexico, we sought to 1) quantify how elevation mediates the dynamics of soil organic carbon (SOC) and geochemistry during SFS and 2) disentangle the soil-forming processes responsible for altitudinal trends. We characterized 16 soil profiles (0-100 cm depth) at various stages of SFS after pasture abandonment at the lower and upper altitudinal limits of the cloud forest ecosystem (1350-1550 and 2050-2220 m) using a broad suite of analytical techniques. Elevation strongly affected the depth distributions of all measured inorganic elements and enhanced the rate of accumulation of biocycled elements (e.g., P, K, Ca, S, Mn) during SFS. Notwithstanding altitudinal differences in C inputs (namely, forest floor recovery rates), profile-level SOC composition and dynamics were more sensitive to mineral weathering status than to SFS stage or elevation per se. Differentiation of soil mineralogy and SOC dynamics contributed to variation of physical properties, consistent with local ‘folk’ soil taxonomy. Ongoing work addresses the interplay of climate, geology, and redistribution processes in determining the mineralogical properties and, ultimately, SOC dynamics of volcanic ash soils. Our findings underscore the importance of considering the complex environmental contingency of soil recovery rates during SFS.

How to cite: Looker, N., Margenot, A., McFarlane, K., Nater, E., Plante, A., and Kolka, R.: The chronosequence in context: Elevation-dependent dynamics of soil biogeochemistry during cloud forest succession, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12354, https://doi.org/10.5194/egusphere-egu2020-12354, 2020.

EGU2020-20675 | Displays | SSS5.8

Relationships between aboveground and belowground biomass stock – a case study from mountain area temperate forests in the northern Carpathians

Anna Zielonka, Marek Drewnik, Łukasz Musielok, Dariusz Struzik, Grzegorz Smułek, and Katarzyna Ostapowicz

The content of organic carbon in forest is partitioned between organic carbon accumulated in aboveground biomass (AGB) and belowground biomass (BGB) and is impacted by various natural and human factors. Growing interest in estimates of global biomass (and organic carbon) pools require research on a local scale in the context of potential environmental factors affecting their spatial distribution. Therefore, our aim of the research was to both derive and evaluate the relationship between aboveground biomass consisting mainly of European beech (Fagus sylvatica L.), spruce (Picea abies L. Karst) and fir (Abies alba Mill.) and BGB with particular emphasis on fine root biomass (FRB) as the most dynamic part of the root system and soil organic matter stock (SOM). Data were collected at 32 national forest inventory plots in mountainous temperate forests with different history of forest management located across the Carpathian range in Poland. All study plots were characterized with very similar soil properties (Cambisols). Moreover, numerous environmental factors affecting biomass distribution were taken under consideration. The largest aboveground biomass occurred in beech-dominated stands (~40 Mg ha-1 to over ~ 440 Mg ha-1). In the sampled depth layer (0-40 cm) the highest SOM stock was identified in soils under beech-dominated stands (median ~158 Mg ha-1). FRB was the highest under fir-dominated stands (median ~3.7 Mg ha-1). The amount of SOM and FRB differed also in the analyzed soil depth layers (10 cm interval up to 40 cm) reaching mostly the highest values at soil depths of 0-10 cm. The highest amount of biomass (both aboveground and the belowground) has been identified in beech-dominated forests. We examined relationships between AGB, FRB, and SOM, but were not able to identify clear significant correlations based only on vegetation parameters. Derived results illustrate the complexity of identifying significant relationships between aboveground and belowground biomass stocks. Employing the same models may be an erroneous strategy for different study sites because of local environmental factors that strongly determine aboveground and belowground biomass stock. Accordingly, creating biomass and carbon models at larger scales in northern Carpathians based on forest aboveground data may cause an over- or underestimation due to the significant impact of both abiotic and biotic factors. 

 

This research study was funded by the Polish National Science Centre (RS4FOR Project: Forest change detection and monitoring using passive and active remote sensing data (No. 2015/19/B/ST10/02127) and via Project No. UJ/IGiGP/K/DSC/004779.

How to cite: Zielonka, A., Drewnik, M., Musielok, Ł., Struzik, D., Smułek, G., and Ostapowicz, K.: Relationships between aboveground and belowground biomass stock – a case study from mountain area temperate forests in the northern Carpathians, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20675, https://doi.org/10.5194/egusphere-egu2020-20675, 2020.

EGU2020-3739 | Displays | SSS5.8

Scaling up microbial dynamics for soil carbon cycling models

Stefano Manzoni, Arjun Chakrawal, and Naoise Nunan

Soils are heterogeneous at all scales and so are the biogeochemical reactions driving the cycling of carbon (C) and nutrients in soils. While the microbial processes involved in these reactions occur at the pore scale, what we observe at the soil core or pedon scale depends on how micro-scale processes are integrated in space (and time). This integration step requires accounting for the inherent patchiness of soils, but models used to describe element cycling in soils typically assume that conditions are well-mixed and that kinetics laws developed for laboratory conditions hold. Similarly, the response functions used in models to capture the effects of environmental conditions on C and nutrient fluxes neglect the contribution of spatial heterogeneities, which might alter their shape. There is therefore a need to re-evaluate model structures to test whether they can account for micro-scale heterogeneities. Alternatively, one can ask why some models are clearly successful in capturing observations despite neglecting soil heterogeneities. In this contribution, we present examples of how soil heterogeneities – in particular the spatial placement of soil microorganisms and their substrate – may affect decomposition kinetics and microbial responses to soil drying. We show that the kinetics laws used in current models are different from the kinetics obtained by integrating microbial dynamics at the micro-scale, and that respiration responses to soil drying may vary depending on soil heterogeneity. These results thus highlight structural uncertainties in current models that we propose can be assessed using existing ‘scale-aware’ methods to derive macro-scale model formulations. Model advances will need to be supported by empirical evidence bridging the gap between pore and core (or larger) scales, but can also provide new theory-based hypotheses for novel experiments.

How to cite: Manzoni, S., Chakrawal, A., and Nunan, N.: Scaling up microbial dynamics for soil carbon cycling models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3739, https://doi.org/10.5194/egusphere-egu2020-3739, 2020.

EGU2020-11724 | Displays | SSS5.8

Controls of rainfall patterns on C and N emissions and stocks in Australian grasslands

Fiona Tang, William Riley, and Federico Maggi

In a warmer climate, regional and global climate models have projected Australia to experience an increase in the intensification of rainfall extremes, which range from heavy monsoon rains to long droughts. Here, we use a coupled carbon and nitrogen cycles mechanistic model (BAMS2) to investigate how the projected rainfall patterns affect carbon and nitrogen emissions, as well as the soil organic stocks in Australian grasslands located in different climatic regions.

                     The BAMS2 model (Tang et al., 2019) considers the depolymerization and mineralization of 11 soil organic matter (SOM) pools (i.e., lignin, cellulose, hemicellulose, peptidoglycans, monosaccharides, amino acids, amino sugars, organic acids, lipids, nucleotides, and phenols) and the transformation of inorganic nitrogen through fixation, nitrification, and denitrification. We explicitly model the growth, mortality, necromass decomposition, and water stress response of five microbial functional groups that mediate the carbon and nitrogen cycles. We include a simplified plant dynamics model to describe plant nutrient uptake, SOM inputs through root exudations and aboveground litter, and plant response to water stress. The BAMS2 reaction network is solved using a general-purpose multi-phase and multi-component bio-reactive transport simulator (BRTSim-v3.1a). We model the water flow along a vertical soil column using the Richards equation and the Brooks-Corey model for the water saturation-tension-permeability relationships, while the transport of dissolved chemicals is modeled using Darcy’s advection velocity and Fick’s diffusion. Aqueous complexation and gas dissolution are described using the mass action law, and SOM protection to soil is modeled using Langmuir’s kinetics.

                     Our multi-decadal simulations suggest a 30% increase in annual CO­2 emissions in tropical grasslands with a 20% decrease in annual rainfall amount, while temperate and semi-arid grasslands have opposite trends. A decreasing annual rainfall amount also results in a decrease in annual N­­2O emissions in the semi-arid grasslands, and a decrease in soil organic stocks in all grasslands. In tropical grasslands, a 20% decrease in annual rainfall results in approximately a 10% decrease in soil organic carbon stock and less than 1% decrease in soil organic nitrogen stock. Less frequent and more intense events in the semi-arid grasslands lead to increased soil moisture at greater depths where evapotranspiration rates are lower, hence reducing water loss to atmosphere and allowing the storage of water for plant growth. Our results show that changes in rainfall regimes alter both the emissions and the total amount of SOM. This study provides a modeling framework suitable for investigating SOM dynamics under various climatic and anthropogenic forcing.

Acknowledgement: This work is supported by SREI2020 EnviroSphere program, the University of Sydney.

Reference:

Tang, F. H.M., Riley, W. J., & Maggi, F. (2019). Hourly and daily rainfall intensification causes opposing effects on C and N emissions, storage, and leaching in dry and wet grasslands. Biogeochemistry, 1-18, https://doi.org/10.1007/s10533-019-00580-7.

How to cite: Tang, F., Riley, W., and Maggi, F.: Controls of rainfall patterns on C and N emissions and stocks in Australian grasslands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11724, https://doi.org/10.5194/egusphere-egu2020-11724, 2020.

EGU2020-244 | Displays | SSS5.8

High resilience of soils to re-grazing in a long-term abandoned alpine pasture

Alix Vidal, Anne Schucknecht, Paul Toechterle, Diana Rocio Andrade Linares, Noelia Garcia-Franco, Andreas von Heßberg, Alexander Krämer, Andrea Sierts, Alfred Fischer, Georg Willibald, Sarah Fuetterer, Jörg Ewald, Vera Baumert, Michael Weiss, Stefanie Schulz, Michael Schloter, Wolfgang Bogacki, Martin Wiesmeier, Carsten W. Mueller, and Michael Dannenmann

Grazed alpine pastures have shaped landscapes of the European Alps for millennia. However, especially steep alpine areas have largely been abandoned since the 1950s, resulting in a fast re-forestation of mountain pastures in the last decades, which is accelerated by climate change. Re-grazing of abandoned pastures could preserve the cultural landscape of the European Alps with its high species diversity, but there is a lack of information on the response of the soil system to re-grazing. We investigated short-term effects of re-grazing of an abandoned pasture in the German Alps on soil organic carbon and nitrogen biochemistry, soil microbial communities, and water quality. In May 2018, we set up a pilot grazing experiment at Brunnenkopfalm (1500-1700 m a.s.l.), abandoned since 1955. Four ha were fenced and a herd of rustic, local and endangered breeds (ca 1/ha) was introduced. Two and five months after the beginning of grazing, we investigated the short-term re-grazing effects, considering grazing-induced heterogeneity, as well as the distribution of vegetation types. In order to gain a functional understanding of soil responses to re-grazing, we used a wide array of techniques to characterize soil biogeochemical properties (salt-extractable and total organic carbon, gross nitrogen turnover rates, soil mineral nitrogen availability), as well as the abundance and characteristics of microbial communities (microbial biomass, phospholipid-derived fatty acids analysis, abundance of nitrogen-related microbial communities). A few months after re-grazing started, extractable organic carbon, gross nitrogen mineralisation rates and inorganic nitrogen concentrations were increased only in intensively grazing-affected areas with bare soil. Bare soils represented a small fraction of the study area (~ 1 %), and the grazing effects on these areas could at least partially also be driven by the initial site heterogeneity (soil and vegetation) rather than solely by recent grazing activities. Re-grazing did not affect the microbial abundance, but induced a community shift towards a smaller proportion of fungi compared to bacteria and an increase of ammonia oxidizers (archaea/bacteria). Concentrations of dissolved organic carbon and nitrate in the draining creek remained very low. Overall, re-grazing of pastures in the first season had very limited effects on microbial communities and associated carbon and nitrogen turnover and concentrations, highlighting the initial resilience of alpine soils to extensive re-grazing. However, a slight increase in nitrifier abundances at bare soil spots, as well as the low organic carbon:nitrogen ratios of soils suggest that a future increase in inorganic nitrogen accumulation is possible at least at bare soil areas. This could possibly endanger some biodiverse grassland biotopes via eutrophication and result in environmental nitrogen losses along hydrological or gaseous pathways. Thus, long-term studies are needed to verify whether soils are also resilient to re-grazing in the long-term. On the short-term, undesired re-grazing effects can be avoided by extensive, guided grazing with adapted cattle breeds targeted to avoid trampling-induced bare soil areas.

How to cite: Vidal, A., Schucknecht, A., Toechterle, P., Andrade Linares, D. R., Garcia-Franco, N., von Heßberg, A., Krämer, A., Sierts, A., Fischer, A., Willibald, G., Fuetterer, S., Ewald, J., Baumert, V., Weiss, M., Schulz, S., Schloter, M., Bogacki, W., Wiesmeier, M., Mueller, C. W., and Dannenmann, M.: High resilience of soils to re-grazing in a long-term abandoned alpine pasture , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-244, https://doi.org/10.5194/egusphere-egu2020-244, 2020.

EGU2020-22308 | Displays | SSS5.8

Linking molecular properties of soil organic carbon to emergent ecosystem functions in a tidally influenced landscape of the Pacific Northwest

Aditi Sengupta, Ben Bond-Lamberty, Albert Rivas-Ubach, Jianqiu Zheng, Pubudu Handakumbura, Steven Yabusaki, Vanessa Bailey, Nicholas Ward, and James Stegen

Coastal landscapes and their terrestrial-aquatic interface (TAI) will be increasingly exposed to short-term tidal inundation due to sea level rise and extreme weather events. These events can generate hot moments of biogeochemical activity and also alter ecosystem structure if occuring frequently. However, such responses of these vulnerable ecosystems to environmental perturbations are poorly understood, limiting our ability to evaluate the contribution of local processes on global scale carbon and nutrient budgets. Here, we evaluated whether and to what degree seawater inundation impacts biogeochemical responses in soils collected along a naturally variable salinity gradient in a first order tidal stream floodplain in the Pacific Northwest. A laboratory incubation experiment simulating episodic inundation was performed to detect the impacts on soil carbon chemistry. We characterized carbon before and after inundation using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICR-MS), metabolite signatures via Liquid Chromatography-Mass Spectrometry (LC-MS), and high-frequency carbon dioxide (CO2) and methane (CH4) gas fluxes from intact soil cores. Following three inundation events, we observed significant decreases in the thermodynamic favorability of the remaining organic compounds in soils with high natural salinity as compared to low salinity soils. Low salinity soils showed higher average flux compared to high salinity soils following periodic inundation events. Seawater inundation led to distinct metabolite features in low salinity soils, with surficial soil preferentially getting enriched in phenolic compounds. Biogeochemical transformations inferred from FTICR-MS data showed an increase in total transformations with increasing salinity for soil cores from naturally low salinity exposure sites, likely suggesting higher microbial activity. In conclusion, ecosystem responses in a tidal landscape frequently experiencing seawater inundation preferentially influences terrestrial soils to behave as a carbon source. This response is likely a function of historical salinity gradient-driven molecular-level organic carbon characteristics.

How to cite: Sengupta, A., Bond-Lamberty, B., Rivas-Ubach, A., Zheng, J., Handakumbura, P., Yabusaki, S., Bailey, V., Ward, N., and Stegen, J.: Linking molecular properties of soil organic carbon to emergent ecosystem functions in a tidally influenced landscape of the Pacific Northwest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22308, https://doi.org/10.5194/egusphere-egu2020-22308, 2020.

Soil organic carbon (SOC) is a valuable resource for mediating global climate change and securing food production. Despite an alarming rate of global plant diversity loss, uncertainties concerning the effects of plant diversity on SOC remain, because plant diversity not only stimulates litter inputs via increased productivity, thus enhancing SOC, but also stimulates microbial respiration, thus reducing SOC. By analysing 1001 paired observations of plant mixtures and corresponding monocultures from 121 publications, we show that both SOC content and stock are on average 5 and 8% higher in species mixtures than in monocultures. These positive mixture effects increase over time and are more pronounced in deeper soils. Microbial biomass carbon, an indicator of SOC release and formation, also increases, but the proportion of microbial biomass carbon in SOC is lower in mixtures. Moreover, these species‐mixture effects are consistent across forest, grassland, and cropland systems and are independent of background climates. Our results indicate that converting 50% of global forests from mixtures to monocultures would release an average of 2.70 Pg C from soil annually over a period of 20 years: about 30% of global annual fossil‐fuel emissions. Our study highlights the importance of plant diversity preservation for the maintenance of soil carbon sequestration in discussions of global climate change policy.

How to cite: Chen, H.: Effects of plant diversity on soil carbon in diverse ecosystems: a global meta-analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1425, https://doi.org/10.5194/egusphere-egu2020-1425, 2020.

EGU2020-20273 | Displays | SSS5.8

Soil systems as critical infrastructure: do we know enough about soil system resilience and vulnerability to secure our soils?

Jessica Davies, Pedro Batista, Victoria Janes-Bassett, Roisin O'Riordan, John Quinton, and Dmitry Yumashev

Soils provide us with multiple essential services, such as food production, water flow regulation, and climate regulation. The loss of soil function endangers provision of these services, in turn endangering the local, regional and global societies and economies that rely on these. Soils, therefore, are in effect a critical infrastructure, which can be defined as an asset, system or process, the loss or compromise of which could result in a major detrimental impact on the availability, integrity or delivery of essential services, with significant economic or social impacts. Conceptualising soil as a critical infrastructure changes the way we as a society need to approach its management. For example, government authorities have a responsibility to reduce the vulnerability of critical infrastructure, and strengthen their security and resilience. To meet this responsibility there is a need to assess infrastructure resilience, identify critical vulnerabilities, and identify and implement strategies for increasing resilience. There has been growing interest and research on soil resilience, particularly drawing on ecological resilience concepts. In this contribution, we will consider our current understanding of soil system resilience from a critical infrastructure perspective and discuss where further science is needed.

How to cite: Davies, J., Batista, P., Janes-Bassett, V., O'Riordan, R., Quinton, J., and Yumashev, D.: Soil systems as critical infrastructure: do we know enough about soil system resilience and vulnerability to secure our soils?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20273, https://doi.org/10.5194/egusphere-egu2020-20273, 2020.

EGU2020-11818 | Displays | SSS5.8 | Highlight

The impacts of urbanisation on urban soil carbon – a study from Manchester, UK

Roisin ORiordan, Jess Davies, Carly Stevens, John Quinton, and Christopher Boyko

The study of anthropogenic soils is a growing area of interest, and as cities continue to expand, urban soils are heavily influenced by human activities. Urbanisation exhibits a wide range of impacts on soil, from buried horizons, compaction, sealing with impervious surfaces, additions of anthropogenic material to being largely man-made soils, or technosols. The properties of urban soil are further complicated by the addition of fertilisers, management strategies in greenspaces and the treatments of soil, including topsoil removal, during construction projects. Therefore, the properties and functions of anthropogenic soils differ notably to that of natural soils, and as such, there is a need to understand the dynamics of soil carbon in urban areas.

Research on urban soil carbon has been relatively limited, however there is recent growth in this area due to its importance, firstly, as a carbon store contributing to climate regulation, and secondly, in relation to the potential of urban soil to support numerous ecosystem services. Urban soils are highly heterogeneous and anthropogenic carbon additions can come from many current or historical sources, such as charcoal used in old roads, coal ash from power stations, carbon from car tyres, as well as inorganic carbonates in limestone road foundations. Understanding the current stores of carbon, as well as how stable it is, is important to understand likely carbon dynamics and storage potential.

This work presents a field study across Manchester (UK) where soil carbon data has been collected from soils across urban parks, greenspaces and from under sealed surfaces (roads and pavements). It provides carbon data for a variety of urban contexts and with high spatial variability. We will build on previous work from this field study by presenting i) a typology of urban soils according to anthropogenic content, ii) data for physical size fractionation to understand soil physical properties and texture, and iii) the carbon content of the size fractions to provide a proxy for understanding how labile or stable the carbon is. This will allow us to understand the impacts of soil sealing on the carbon content and build a picture of soil carbon stability across a range of urban situations.

This research will contribute to the much-needed understanding on how soil carbon behaves in urban areas, and the implications of this for carbon storage in both sealed and urban greenspace soils. 

How to cite: ORiordan, R., Davies, J., Stevens, C., Quinton, J., and Boyko, C.: The impacts of urbanisation on urban soil carbon – a study from Manchester, UK, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11818, https://doi.org/10.5194/egusphere-egu2020-11818, 2020.

EGU2020-16870 * | Displays | SSS5.8 | Highlight

Impact of antibiotic pollution from wastewater irrigation on soils and agroecosystems

James Stockdale, Brett Sallach, Andrew Zealand, Clare McCann, Ergun Bey, Fin Ring-Hrubesh, David Graham, Alistair Boxall, and Sylvia Toet

Growing global demand of water use, and regional changes in precipitation in many regions, has resulted in increasing long-term irrigation of agricultural soils with post-treatment waste water. Overlaying this trend with the rising use of pharmaceuticals has created a new pathway for these pollutants, including biologically active compounds such as antibiotics, to enter the soil environment. We present results from a new interdisciplinary study of the response of an agroecosystem which was repeatedly contaminated with a typical combination of antibiotics at a representative concentration found in waste water effluent. Results from this experimental manipulation, show the impact of different concentrations of antibiotics in the soil and the unexpected repercussions throughout the agroecosystem. This includes effects on soil microbial communities, microbial function (anti-microbial resistance), abiotic soil condition, antibiotic persistence in the soil, ecosystem function (greenhouse gas exchange) and the effect on the arable crop itself. Implications of this study are relevant to fully understanding the impact of this land management technique on the sustainability of food production.

This study was funded through the UK’s N8AgriFood Programme.

How to cite: Stockdale, J., Sallach, B., Zealand, A., McCann, C., Bey, E., Ring-Hrubesh, F., Graham, D., Boxall, A., and Toet, S.: Impact of antibiotic pollution from wastewater irrigation on soils and agroecosystems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16870, https://doi.org/10.5194/egusphere-egu2020-16870, 2020.

EGU2020-6875 | Displays | SSS5.8

Modeling of soil carbon dynamics, with focus on microbial activity

Elin Ristorp Aas, Terje Koren Berntsen, Alexander Eiler, and Helge Hellevang

The representation of soil carbon dynamics is a major source of uncertainty in Earth System Models (ESMs). The terrestrial carbon pool is more than twice the size of the atmospheric pool. Therefore, the role of soil carbon as a source or a sink of atmospheric carbon, and in feedback loops is important to quantify in a changing climate. Decomposition processes of organic matter in soil have often been represented by first order decay equations, which make comparison and validation against observations difficult. Therefore, quantification of the uncertainties  and validation of improved parameterizations are problematic. An emerging approach to tackle these challenges is to represent microbial soil processes explicitly in the models. Following this approach, we have built a process based module that represent the carbon fluxes during soil decomposition, from aboveground litter to soil organic matter (SOM). The role of saprotrophs and mycorrhizal fungi is explicitly represented with separate carbon pools with associated fluxes. On a site level, we compare initial results from the stand alone module with both existing models and observations of carbon pools and fluxes. The observations are from the Norwegian Dovre Mountains, with data from three different alpine communities. These geographic areas are important, because they are subject to changes due to shrubification. In addition, these ecosystems can store large amounts of carbon. By modeling these sites, we gain more insight in the most important processes in soil decomposition, and how different microbial communities affect the carbon dynamics. We will further refine the module by expanding our study with more sites. The long-term objective is to develop an improved module that can be used to represent soil processes in ESMs, and thereby reduce the uncertainty connected to the exchange of carbon between land and atmosphere.

How to cite: Ristorp Aas, E., Koren Berntsen, T., Eiler, A., and Hellevang, H.: Modeling of soil carbon dynamics, with focus on microbial activity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6875, https://doi.org/10.5194/egusphere-egu2020-6875, 2020.

EGU2020-22627 | Displays | SSS5.8

A model for three-way carbon flux partitioning in calcareous soils using stable isotope measurements

Guy Kirk, Chris McCloskey, Wilfred Otten, and Eric Paterson

In order to understand and model soil carbon (C) dynamics it is essential that we are able to partition net ecosystem C exchange by individual organic and inorganic fluxes under field conditions. Stable isotope methods provide a reliable means to separate fluxes from two sources, such as plant respiration and soil organic matter (SOM) mineralisation. In many soils, however, plant and soil respiration are not the only sources of C efflux, as breakdown of carbonate minerals provide a third, inorganic, C source. We currently lack methods and models to allow us to untangle plant, inorganic soil, and organic soil C fluxes in the field. This limits our ability to gather field-scale plant and soil C flux data to soils without inorganic carbonates, rendering calcareous soils a major gap in our understanding of, and ability to model, soil C dynamics.

To remedy this we have developed a novel three-way partitioning model to account for inorganic carbonate dissolution in a planted soil. Analysis of a mechanistic model of lime (CaCO3) dissolution showed differences in CO2 pressure in the soil, arising from differences in soil respiration as influenced by differences in temperature and moisture, to be a major control on dissolution rates. The thee-way partitioning model we have developed derives the CO2 flux from CaCO3 dissolution from SOM mineralisation and below-ground plant respiration fluxes.

To test this model we used cavity ring-down spectroscopy to measure CO2 fluxes from soil mesocosms containing C3-origin SOM and planted with a C4 grass, both with and without CaCO3, and unplanted soil mesocosms containing CaCO3. As previously field measurements revealed temperature to be the strongest control on soil respiration this was carried out at four temperatures (15, 20, 25, and 30oC). Using the distinct δ13C values for CaCO3 dissolution, C4 grass respiration, and C3 SOM mineralisation, fluxes were partitioned from mesocosms containing two C fluxes to parameterise the model. The model was tested through application to flux data from mesocosms containing C fluxes from CaCO3, SOM, and plants in order to assess its suitability for generating novel field datasets of C fluxes from calcareous soils.

How to cite: Kirk, G., McCloskey, C., Otten, W., and Paterson, E.: A model for three-way carbon flux partitioning in calcareous soils using stable isotope measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22627, https://doi.org/10.5194/egusphere-egu2020-22627, 2020.

In the northern ecosystems’ soils, the carbon stock is preserved in peat soils which includes frozen peat. It is vulnerable to any climate changes. The permafrost degradation can affect both the quantity and the composition of dissolved organic carbon of permafrost-affected soils, especially peat soils.

The main aim of our study was to determine the relationship among peat type, water regime and the quantity and composition of water borne carbon export. The research site was located in the discontinuous permafrost zone (N65º18’, E72º52’). Monoliths of various peat soils were collected in summer 2019 for a laboratory experiment.

The experiments were carried out with 6 types of monoliths (oligotrophic fibric peat; oligotrophic hemic peat with lichen debris; eutrophic hemic peat with reindeer moss debris; eutrophic sapric peat; eutrophic sapric peat with a burnt horizon; oligotrophic fibric peat, underlied with sand). We try to understand how organic matter is leached from peat soils with different constitution and different degree of decomposition. In the model experiment, we simulated 3 types of hydrological conditions. Soil monoliths were watered, and the contents of DOC and POC were determined in the collected soil waters.

  1. Simulation of the moderate rainfall (70 mm) by adding distilled water during the week. DOC in this case ranged from 44,2±3.0 mg/l in oligotrophic peat to 80,6±28,7 mg/l in eutrophic peat.
  2. The simultaneous flow of large quantities of water, simulating prolonged rainfall or spring snowmelt. In this case DOC content leaching from fibric oligotrophic peat didn`t change much while DOC leaching from sapric eutrophic peat decreased in comparison with moderate rainfall.
  3. During modeling short stagnant regimen (spring conditions) we observed increase DOC, especially in sapric eutrophic peat (up to 291,0±11,3 mg/l). The mineral horizon under the peat layer reduced the rate of leaching of organic substances from the soil.

Our results indicate the significant role of both the peat constitution and hydrological regime of soils on the rate and amount of organic matter entering the hydrological basin from peat permafrost-affected soils. The data can be used to simulate the dynamics of permafrost ecosystems with changing climatic parameters or with the activation of anthropogenic load.

This research was supported by the Russian Foundation for Basic Research (Grant 18-04-00952)

How to cite: Timofeeva, M., Goncharova, O., and Matyshak, G.: Hydrological conditions and peat constitution effect on DOC leaching from permafrost-affected soils: model experiment (Western Siberia, Russia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-590, https://doi.org/10.5194/egusphere-egu2020-590, 2020.

Freshwater flux transport large amount of carbon (dissolved and particulate, organic and inorganic) from the continent into the ocean, contributing significantly to the global carbon cycle. The present sources and sinks of natural as well as anthropogenically produced C compounds in the global carbon cycle remain enigmatic. Among the carbon sources in the river ecosystem, the dissolved inorganic carbon (DIC) constitutes a major component of carbon influx from land to ocean. These fluxes are significantly influenced by the terrestrial and estuary processes. The isotopic composition of DIC can be used to understand the sources and cycling of carbon in rivers and estuaries. In this study, δ13C values of DIC in river water of Ganga have been used to understand the sources of dissolved inorganic carbon into the river. The river Ganga (2500 km) is the largest river of the Indian subcontinent which originates from the Gangotri glacier and drains into the Bay of Bengal through its vast delta in the Sunderban. The Ganga river basin (GRB) covers an area of 106 km2 draining the carbon sources of the entire basin into the mainstream of river Ganga. The river transports nearly 0.2% of the global freshwater flux, 1% of global DIC flux and 5% of the global sediment flux into the ocean. Despite its significant importance to the global carbon transport, the understanding of the DIC sources in the complex Ganga river system remains enigmatic. Therefore to elucidate the carbon sources in the river Ganga, the δ13C DIC of river water were measured from source (Gomukh) to sink (Bay of Bengal) of the river Ganga for pre and late-monsoon period. The seasonal variation in the δ13C DIC shows enriched isotopic values in pre-monsoon compared to late-monsoon samples. The upper, middle and lower stretch of the river shows distinct enrichment factors for pre and late-monsoon samples. The variation in the δ13C DIC of river water might be indicating the DIC signature of the source water. The pre-monsoon samples show enrichment in the δ13C DIC values as we move downstream of the river, whereas the late-monsoon samples show a slight depletion trend. The difference between the pre and late- monsoon samples might be indicating the high input of soil CO2 during the late-monsoon season which is characterized by lower δ13C values.

How to cite: Kumar, A. and Sanyal, P.: Decrypting the sources of dissolved inorganic carbon in river water: Isotopic study from river Ganga, India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-724, https://doi.org/10.5194/egusphere-egu2020-724, 2020.

Studying the effects of droughts and heavy rain events on DOC in Scot pine in Belgium

Cristina Ariza-Carricondo(1,2), Marilyn Roland(1), Bert Gielen(1), Eric Struyf(1), Caroline Vincke(2) and Ivan Janssens(1).

(1) PLECO, University of Antwerp, Belgium. (2) Faculty of Bioscience Engineering & Earth and Life Institute, University of Louvain-la-Neuve, Louvain-la-Neuve, Belgium.

Climate extremes, including extreme rain events, are becoming more frequent and more extreme, and affect the carbon cycle of ecosystems. Very little is known about how Dissolved Organic Carbon (DOC) production and leaching are affected by such precipitation extremes while the relation between dissolved and gaseous exports of carbon under different precipitation regimes remains unexplored.

Hydrological conditions are the main driver of DOC leaching and alterations in precipitation patterns may cause large changes in the carbon balance of forests. To test the effects of precipitation extremes on DOC, we designed a manipulation experiment in a Scots pine forest in Belgium.

One of the challenges to estimate DOC export is the quantification of water drainage flow. In this study we used self-designed Zero Tension Lysimeters (ZTL) to capture leaching water and analyze its DOC-concentrations as well as other elements along profiles in the soil (up to 75cm depth), to study how DOC moves under different precipitation regimes. Different manipulation experiments were performed where we modified the precipitation regime simulating heavy rain events after different droughts as well as experiments where we modified the precipitation intensity over time. Leached water was collected at different depths at monthly intervals after natural rain events as well as after irrigations.

Preliminary results showed that drainage water transported DOC differently through the soil when different amounts of water were added. Furthermore, more frequent small rain events appear to favor the production of DOC as compared to less frequent high intensity rain events, while DOC production ceases during droughts.

How to cite: Ariza Carricondo, C.: Studying the effects of droughts and heavy rain events on DOC in Scot pine in Belgium, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5329, https://doi.org/10.5194/egusphere-egu2020-5329, 2020.

EGU2020-12470 | Displays | SSS5.8

The relative importance of environmental factors on the interannual variability of carbon fluxes in the boreal forest

Mariam El-Amine, Alexandre Roy, Pierre Legendre, and Oliver Sonnentag

As climate change will cause a more pronounced rise of air temperature in northern high latitudes than in other parts of the world, it is expected that the strength of the boreal forest carbon sink will be altered. To better understand and quantify these changes, we studied the influence of different environmental controls (e.g., air and soil temperatures, soil water content, photosynthetically active radiation, normalized difference vegetation index) on the timing of the start and end of the boreal forest growing season and the net carbon uptake period in Canada. The influence of these factors on the growing season carbon exchanges between the atmosphere and the boreal forest were also evaluated. There is a need to improve the understanding of the role of the length of the growing season and the net carbon uptake period on the strength of the boreal forest carbon sink, as an extension of these periods might not necessarily result in a stronger carbon sink if other environmental factors are not optimal for carbon sequestration or enhance respiration.

Here, we used 31 site-years of observation over three Canadian boreal forest stands: Eastern, Northern and Southern Old Black Spruce in Québec, Manitoba and Saskatchewan, respectively. Redundancy analyses were used to highlight the environmental controls that correlate the most with the annual net ecosystem productivity and the start and end of the growing season and the net carbon uptake period. Preliminary results show that the timing at which the air temperature becomes positive correlates the most strongly with the start of the net carbon uptake period (r = 0.70, p < 0.001) and the start of the growing season (r = 0.55, p < 0.01). Although the increase of the normalized difference vegetation index also correlates with the start of these periods, a thorough examination of this result shows that the latter happens well before the former. No dependency between any environmental control and the end of the net carbon uptake period was identified. Also, the annual net ecosystem productivity is highly correlated with the length of the net carbon uptake period (r = 0.54, p < 0.01). Other environmental controls such as annual precipitations, the mean annual soil temperature or the maximum yearly normalized difference vegetation index have a smaller impact on the annual net ecosystem productivity. By extending the dataset to include forest stands that represent a wider climate and permafrost variability, we will examine the generalizability of these results.

How to cite: El-Amine, M., Roy, A., Legendre, P., and Sonnentag, O.: The relative importance of environmental factors on the interannual variability of carbon fluxes in the boreal forest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12470, https://doi.org/10.5194/egusphere-egu2020-12470, 2020.

EGU2020-6099 | Displays | SSS5.8

Variations in soil chemical and physical properties explain basin-wide Amazon forest soil carbon concentrations

Carlos Alberto Quesada, Claudia Paz, Erick Oblitas, Oliver Phillips, Gustavo Saiz, and Jon Lloyd

We investigate the edaphic, mineralogical and climatic controls of soil organic carbon (SOC) concentration utilising data from 147 primary forest soils (0-30 cm depth) sampled in eight different countries across the Amazon Basin. Sampling across 14 different World Reference Base soil groups our data suggest that stabilisation mechanism varies with pedogenetic level. Specifically, although SOC concentrations in Ferralsols and Acrisols were best explained by simple variations in clay content – this presumably being due to their relatively uniform kaolinitic mineralogy – this was not the case for less weathered soils such as Alisols, Cambisols and Plinthosols for which interactions between Al species, soil pH and litter quality are argued to be much more important. Although for more strongly weathered soils the majority of SOC is located within the aggregate fraction, for the less weathered soils most of the SOC is located within the silt and clay fractions. It thus seems that for highly weathered soils SOC storage is mostly influenced by surface area variations arising from clay content, with physical protection inside aggregates rendering an additional level of protection against decomposition. On the other hand, most of SOC in less weathered soils are associated with the precipitation of aluminium-carbon complexes within the fine soil fraction, with this mechanism enhanced by the presence of high levels of aromatic, carboxyl-rich organic matter compounds. Also examined as part of this study were a relatively small number of arenic soils (viz. Arenosols and Podzols) for which there was a small but significant influence of clay and silt content variations on SOM storage and with fractionation studies showing that particulate organic matter may accounting for up to 0.60 of arenic soil SOC. In contrast to what were in all cases strong influences of soil and/or litter quality properties, after accounting for these effects neither wood productivity, above ground biomass nor precipitation/temperature variations were found to exert any significant influence on SOC stocks. These results have important implications for our understanding of how Amazon forest soils are likely to respond to ongoing and future climate changes.

How to cite: Quesada, C. A., Paz, C., Oblitas, E., Phillips, O., Saiz, G., and Lloyd, J.: Variations in soil chemical and physical properties explain basin-wide Amazon forest soil carbon concentrations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6099, https://doi.org/10.5194/egusphere-egu2020-6099, 2020.

EGU2020-7370 | Displays | SSS5.8

A review of the impacts of land use change, climate zone, forest type and age on soil organic carbon and other soil quality indicators following afforestation

Yang Guo, Mohamed Abdalla, Mikk Espenberg, Astley Hastings, Paul Hallett, and Pete Smith

The main aim of this global review and systematic analysis was to investigate the impacts of previous land use system, climate zone and forest type and age on soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP), in the different soil layers (0-20, 20-60 and 60-100 cm), following afforestation. We collected 85 publications on SOC, TN and TP stock changes, covering different countries and climate zones. The data were classified into groups depending on these investigated parameters and analyzed using R version 3.6.1. We found that afforestation significantly increased SOC and TN stocks in the 0-20 and 20-60 soil layers, with values of 45% and 44% for SOC, 30% and 22% for TN, respectively, but had no impact on TP stock. Previous land use systems had the largest influence on SOC, TN and TP stocks, with greater accumulations on barren land compared to cropland and grassland. Climate zone influenced SOC, TN and TP stocks, with significant accumulations in the moist than in the dry climate zone. Afforestation with broadleaf deciduous and broadleaf evergreen forests led to greater SOC, TN and TP accumulations in each soil layer throughout the investigated profile (0-100 cm), compared to coniferous forests. Afforestation for <20 years had significantly increased SOC and TN stocks only at the soil surface (0-20 cm) whilst afforestation for ≥ 20 years had significantly accumulated them up to 100 cm soil depth. TP stock did not change with the forest age, suggesting that it may become a limiting factor for carbon sequestration under the older-age forest. Following afforestation, the change of soil bulk density had inverse relationships with SOC or TN stocks changes but had no effect on TP stock change.

How to cite: Guo, Y., Abdalla, M., Espenberg, M., Hastings, A., Hallett, P., and Smith, P.: A review of the impacts of land use change, climate zone, forest type and age on soil organic carbon and other soil quality indicators following afforestation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7370, https://doi.org/10.5194/egusphere-egu2020-7370, 2020.

EGU2020-22639 | Displays | SSS5.8

Soil thinning and thickening: the fate of soil organic carbon

Andrew Tye and Daniel Evans

The redistribution of soil by humans has been demonstrated to rival that of geologic events. Moreover, the impact of some conventional, agricultural techniques has been shown to redistribute a significant proportion of soil organic carbon. On the more erosive areas of hillslopes, the resulting thinning of soil could make deep soil carbon more accessible and, ultimately, more susceptible to destabilisation. However, downslope colluviation can thicken soil profiles such that subsoil carbon pools become inaccessible to microbial decomposition. The fate of soil thinning and thickening on soil organic carbon has not been studied in the UK until now. In this work, we studied the distribution of organic and inorganic carbon down profiles surveyed at three landscape positions (midslope, backslope, and toeslope) on Mountfield Farm, in Somerset, UK. In this poster, we present the results of thermogravimetric analysis and laser-induced fluorescence spectroscopy, both of which we used to investigate the stability of soil organic carbon down each profile. We explore the relationships between soil depth and the stocks and stability of soil organic carbon fractions at each position, and suggest the implications of continued upslope soil thinning and downslope soil thickening.

How to cite: Tye, A. and Evans, D.: Soil thinning and thickening: the fate of soil organic carbon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22639, https://doi.org/10.5194/egusphere-egu2020-22639, 2020.

EGU2020-21158 | Displays | SSS5.8

Postagrogenic differentiation of the old-arable horizon of different-aged fallow soils

Leysan Fattakhova and Dilyara Kuzina

The study of different-aged fallow soils seems to be interesting from the point of view of changes in their conditions of genesis and functioning because a radical change of pedogenesis nature in time the removal of arable land to fallow leads to soil evolution. If the climax stages of postagrogenic successions are quite achievable, then the process of restoring the original climax vegetation should be associated with a reversible return of the soil to its original state. But pedogenesis is not limited only to the processes of converting organic residues into soil humus, binding it to mineral surfaces, humus, and biophilic elements accumulation. It also includes a slow chemical transformation of the parent rocks, due to the course of a number of reactions that rarely reach chemical equilibrium. And for soils that were once plowed, we can state with confidence that there is no identity between the component and phase compositions of fine mineral phases at the stages of involving virgin soil to cultivation and removing arable soil to fallow. Accordingly, the once homogeneous old-arable layer can be considered as a lithologically homogeneous soil-forming rock for the magnetic subprofile that is formed on it in the process of successional restoration of ecosystems. Therefore, the study of the magnetic properties of the upper part of the profile of different-aged fallow soils is appropriate in the aspect of the kinetic parameters of postagrogenic differentiation of the old-arable horizon. This work is devoted to studying magnetic properties of different-aged light-gray forest (30-35 years), dark grey forest (10-15 years) and sod-podzolic (12-17 years) fallow forest-steppe soils of the Republic of Tatarstan for the diagnosis of postagrogenic signs of differentiation of the old-arable horizon.

The work is performed according to the Russian Government Program of Competitive Growth of Kazan Federal University and with the support of the RFBR in the framework of the scientific project No. 19-35-50040.

How to cite: Fattakhova, L. and Kuzina, D.: Postagrogenic differentiation of the old-arable horizon of different-aged fallow soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21158, https://doi.org/10.5194/egusphere-egu2020-21158, 2020.

EGU2020-16387 | Displays | SSS5.8

The Nivolet CZ Ecosystem Observatory reveals rapid soil development in recently deglaciated alpine environments: Biotic weathering is the likely culprit

Ilaria Baneschi, Ashlee Dere, Emma Aronson, Ramona Balint, Sharon Billings, Silvia Giamberini, Marta Magnani, Pietro Mosca, Maddalena Pennisi, Antonello Provenzale, Brunella Raco, Pamela L. Sullivan, and Timothy White

Soils are a critical component of the Earth system in regulating many ecological processes that provide fundamental ecosystem services (Adhikari and Hartemink, 2016). Soil formation factors may be operating at faster timescales than is typically considered in recently deglaciated alpine environments, yielding important implications for critical zone services (e.g., water retention, the preservation of carbon (C) and nutrients, and chemical weathering fluxes). It remains unclear how variation in these properties are linked to soil development and soil organic C pools and fluxes, in part because sites varying in these characteristics also typically vary in vegetation and climate.

Here we leveraged the high-altitude alpine pastures of the Nivolet Critical Zone and Ecosystem Observatory, Gran Paradiso National Park (Italy) to examine biotic and abiotic dynamics and controlling factors of organic C and weathering under different topographic positions and geologic substrates in a small localized mountainous region. Soil profiles were sampled across a range of parent materials deposited after the Last Glacial Maximum, including gneiss glacial till, carbonate and calcschist/gneiss colluvium, and gneiss/carbonate/calcschist alluvium across ridgetop, midslope and footslope topographic positions. Organic C, C stable isotopes, major and trace element content, particle size distribution, and pH reveal how parent material and landscape position govern soil C storage and development. Even under the cold climate, limited season with liquid water, young-age deglaciated context, soils have developed incipient spodic horizons and calcschist clasts appears completely weathered in place.

Alkali and alkaline earth elements exhibit chemical depletion throughout the profiles, whereas in some profiles phosphorus concentrations reflects nutrient uplift processes (i.e., accumulating at the top of the profile and depleted in mid-horizons) likely driven by “biotic” cycling. Phosphorus is relatively high in uppermost horizons at carbonate and glacial sites, but is quite low in gneiss, even though TOC is relatively high, suggesting that plants underlain by gneiss are able to generate organic compounds with lower P availability. Though rooting depth distributions exhibit linear declines with depth, contrary the typically observed exponential decay behavior, our data suggest that roots serve as important biotic weathering agents prompting rapid soil development. All profiles have high organic carbon content at the surface, but

are twice as high in the footslope Gneiss profile as in the midslope Glacier and Carbonate profiles and in the floodplain Alluvial profile.

These data, in conjunction with microbial analysis and geochemical variation, suggest that biota are key agents promoting the observed high degree of soil development in these high altitude ecosystems. We demonstrate how in the early stages of soil development abiotic and biotic factors influence soil weathering and C storage across different parent material and topography.

 

Adhikari, K. and Hartemink, A. E.: Linking soils to ecosystem services – A global review, Geoderma, 262, 101–111, 2016

How to cite: Baneschi, I., Dere, A., Aronson, E., Balint, R., Billings, S., Giamberini, S., Magnani, M., Mosca, P., Pennisi, M., Provenzale, A., Raco, B., Sullivan, P. L., and White, T.: The Nivolet CZ Ecosystem Observatory reveals rapid soil development in recently deglaciated alpine environments: Biotic weathering is the likely culprit, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16387, https://doi.org/10.5194/egusphere-egu2020-16387, 2020.

EGU2020-22591 | Displays | SSS5.8

Detecting soil degradation and restoration through a novel coupled sensor and machine learning framework

John Quinton, Mike James, Jess Davies, Greg Whiting, Christopeher Nemeth, Rebecca Killick, Evan Thomas, Richard Bardgett, and Jason Neff

In this poster we will outline a new  ambitious cross-disciplinary project focused on detecting soil degradation and restoration through a novel multi-functional soil sensing platform that combines conventional and newly created sensors and a machine learning framework. Our work  aims to advance our understanding of dynamic soil processes that operate at different temporal/spatial scales. Through the creation of an innovative new approach to capturing and analyzing high frequency data from in-situ sensors, this project will predict the rate and direction of soil system functions for sites undergoing degradation or restoration. To do this, we will build and train a new mechanistically-informed machine learning system to turn high frequency data on multiple soil functions, such as water infiltration, CO2 production, and surface soil movement, into predictions of longer term changes in soil health including the status of microbial processes, soil organic matter (SOM) content, and other properties and processes. Such an approach could be transformative: a system that will allow short-term sensor data to be used to evaluate longer term soil transformations in key ecosystem functions. We will start our work with a suite of off-the-shelf sensors observing multiple soil functions that can be installed quickly. These data will allow us to rapidly initiate development and training of a novel mechanistically informed machine learning framework. In parallel we will develop two new soil health sensors focused on in-situ real time measurement of decomposition rates and transformation of soil color that reflects the accumulation or loss of SOM. We will then link these new sensors with a suite of conventional sensors in a novel data collection and networking system coupled to the Swarm satellite network to create a low cost sensor array that can be deployed in remote areas and used to support studies of soil degradation or progress toward restoration worldwide.

How to cite: Quinton, J., James, M., Davies, J., Whiting, G., Nemeth, C., Killick, R., Thomas, E., Bardgett, R., and Neff, J.: Detecting soil degradation and restoration through a novel coupled sensor and machine learning framework, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22591, https://doi.org/10.5194/egusphere-egu2020-22591, 2020.

SSS5.11 – Fate, recycling and functions of organic substances in soil as traced by biomarkers and isotopes

EGU2020-12072 | Displays | SSS5.11

What is respiration - response to glucose addition, presence of plant roots and differences across biomes

Paul Dijkstra, Peter F. Chuckran, Bruce A. Hungate, Egbert Schwartz, Tijana Glavina del Rio, and Emiley Eloe-Fadrosh

Respiration is likely the most often measured process in soil ecology. It is used as a general measurement of soil activity, and physiologically related to microbial maintenance requirements, growth, and soil organic matter production via biochemical efficiency and CUE.

Genomic tools are increasingly used in soil ecology for measurement of community composition, and functional analysis of communities, and when combined with stable isotopes, can be used to infer activities, either of the whole community or of individual taxa. However, relating genomic or gene-expressed functions to whole ecosystem processes, such as respiration, remains a conceptual and practical problem.

We analyzed the biochemical processes related to respiration and determine how, during a short soil incubation experiment in the presence of glucose, these processes change. Furthermore, we will show how gene and transcript abundances of respiratory processes vary across more than 4000 soil and rhizosphere samples in forests and grasslands and other biomes.  

Results illustrate the treasure trove of biochemical information available to us in the form of metagenomes and metatranscriptomes.

How to cite: Dijkstra, P., Chuckran, P. F., Hungate, B. A., Schwartz, E., Glavina del Rio, T., and Eloe-Fadrosh, E.: What is respiration - response to glucose addition, presence of plant roots and differences across biomes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12072, https://doi.org/10.5194/egusphere-egu2020-12072, 2020.

The controlling factors and role of different soil microorganisms in rhizosphere priming effects (PE) are not yet well understood, especially the link between microbial growth and their carbon use efficiency (CUE) and PE remains poorly understood. We hypothesized that the positive PE (enhanced SOM decomposition) results from microbes using the additional C/energy from added labile substrates to decompose recalcitrant materials to release N (“microbial N mining hypothesis”). High CUE could lead to efficient growth of microbes and thus more decomposition of SOM and higher PE.

To test these hypothesis we assessed PE along a boreal forest gradient ranging from Estonia to Northern Finland, with soil C:N ratios and fungal to bacterial ratios increasing towards north. The soils received daily additions of 13C-labelled glucose during one week (dissolved in heavy water, 5 at% D2O). Control soils received D2O only. Respiration of glucose and respiration of SOM were distinguished by continuously measuring 13CO2 using a Picarro analyzer. We also measured microbial incorporation (into PLFAs) of 13C and D to assess to which extent different microbial groups rely on labile C input (13C-labelled) and on SOM. We further used these results to calculate the CUE of glucose and of SOM decomposition.

Glucose additions induced PE (12-52% increase in SOM respiration) in all soils, but there was no linear relationship between PE and soil C:N ratio. Instead, cumulative PE (µg C g-1 SOM) and the relative magnitude of the PE (%) were positively correlated with the average C:N imbalance experienced by the microbes (calculated as soil C:N ratio/microbial biomass C:N ratio). There was a positive relationship between the potential activity of total oxidative enzymes and the cumulative SOM respiration, but the same enzyme concentration resulted in higher SOM respiration in the glucose treatment. We suggest that glucose additions increased the activity of these enzymes rather than their concentrations.

Microbial incorporation of D and 13C into in PLFAs demonstrated that glucose additions stimulated both fungal and bacterial growth. Our results indicate that increased growth of fungi on the added 13C glucose was especially important for the PE, since the magnitude of PE was correlated with the ratio of fungal/bacterial growth on glucose and on SOM. High C:N ratio soils were fungal dominated, and there was a clear positive relationship between glucose CUE and fungal to bacterial ratio, indicating that fungal dominated communities had higher CUE. Bacteria were more affected by low N availability, since total bacteria growth and 13C uptake were lower in the high C:N ratio soils. When fungal growth was high relative to bacterial growth CUE was consistently higher, whether it was the total CUE, CUE of glucose or SOM respiration. Our results indicate that if fungal dominated communities can efficiently grow on the added glucose, they will have excess resources for decomposing N releasing recalcitrant substrates. This releases bioavailable C and N that can also increase bacterial respiration of SOM derived C.

How to cite: Karhu, K., Alaei, S., Li, J., and Bengtson, P.: Microbial carbon use efficiency and priming of soil organic matter mineralization by glucose additions in boreal forest soils with different C:N ratios, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5775, https://doi.org/10.5194/egusphere-egu2020-5775, 2020.

Fertilization practices can influence the soil nutrients and fertility status, which subsequently induce changes in soil carbon (C):nitrogen (N) ratio and rebuilt C:N stoichiometric balances between microbial biomass and resources. In this study, we investigated how available resource C:N ratio can regulate the priming effect (PE) to maintain microbial C:N stoichiometric balance by adding 13C-labeled glucose to four long-term fertilized paddy soils [Control (no fertilization), NPK (fertilized with mineral NPK fertilizers) , NPKS (NPK combined with straw), NPKM (NPK combined with manure)]. Glucose addition significantly increased SOC mineralization and subsequently induced a positive priming effect at day 2 of incubation, whereas the PE became negative after 20 days. DOC contents were increased by more than 1000% with glucose addition at day 2, whereas they rapidly decreased to -10% to -50% compared with those in soils without glucose addition. With the changes in available and biomass C and N, the microbial C:N imbalance initially increased to 3.3–6.8, and then reduced to the level as that in the soils without glucose addition. At the end of incubation, the microbial C:N imbalance in the glucose-treated soils was ranked as Control < NPK < NPKM < NPKS. This suggested that, without organic fertilization, soils were highly susceptible to labile C and increased SOC mineralization, leading to C limitation. The PE was positively related to DOC and NH4+ ratio, but negatively associated with microbial C:N imbalance, suggesting that the labile C supplied stimulated microbial stoichiometric decomposition of SOM. Glucose addition modified enzyme activities after 20 days, to allow the microorganisms to break up complex C compounds for C source. Our findings suggested that soil microorganisms could regulate extracellular hydrolytic enzyme production and their relative stoichiometric ratios to obtain necessary elements, thereby adjusting the microbial biomass C:N to the resource stoichiometry.

How to cite: Ge, T., Zhu, Z., and Wu, J.: Soil available resource C:N ratio regulates the priming effect by maintaining microbial C:N stoichiometric balance in long-term fertilized paddy soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14449, https://doi.org/10.5194/egusphere-egu2020-14449, 2020.

Rhizosphere is the most biologically active region between the plant and the surrounding soil where plant release their fixed carbon into the soils. Depending on the availability and types of carbon compounds released from the plant, they can directly solubilize nutrient or indirectly influence nutrient cycling by promoting increased microbial activity in the rhizosphere. In this study we applied phosphate oxygen isotope ratios (d18OP) to determine how root exudate influences temporal variation in microbial activities and P cycling in the rhizosphere. Rhizoboxes were filled with soils, watered to 75% water holding capacity and equilibrated for 10 days. After equilibration labeled phosphate isotopes synthesized using 18O labeled water was applied. Then a mixed exudate (i.e., glucose, alanine, and oxalate in the ratio of 1:1:1) was introduced into the soil for 4, 10, and 20 days via an artificial root. We used a sequential extraction technique (i.e., resin-Pi, NaHCO3-P, NaOH-P, and HCl-P) to track the fate of applied P in bulk and rhizosphere soils. The root exudate effects on the rate of P cycling and microbial activity were investigated using phosphate oxygen isotope ratios in the resin-Pi pool. Microbial community structures was determined using phospholipid fatty acids (PLFA) profiles. After supplying root exudate for 4, 10, and 20 days, the results showed that bioavailable P (i.e., resin-Pi) concentration was always higher in the bulk soil compared to rhizosphere soil and originally bioavailable P transformed gradually into unavailable P (i.e., NaOH-P and HCl-P). After supplying exudate compound for 4 days, the applied PO4 was mostly in the resin-Pi pool and its isotopic composition was heavier than the equilibrium isotopic composition suggesting that this Pi pool was not completely cycled by the microorganisms. As we continue supplying exudate compounds, the concentration of resin-Pi gradually decreased and as microbial activities increased, its isotopic composition got closer to the equilibrium isotopic composition. Further the microbial community structure in the rhizosphere soil after supply of root exudate were distinctly different then the bulk soil. Using phosphate oxygen isotopes this study shows the influence of root exudates on the rate of P cycling in rhizosphere soils.

How to cite: Joshi, S. R. and McNear, D. H.: Root exudate induced microbial activities and phosphorus cycling in soil: An application of phosphate oxygen isotopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12719, https://doi.org/10.5194/egusphere-egu2020-12719, 2020.

EGU2020-7121 | Displays | SSS5.11

Stabilization of labile carbon in soil microbial biomass and necromass – A question of nitrogen deficiency?

Nele Meyer, Outi-Maaria Sietiö, Sylwia Adamczyk, Christina Biasi, Per Ambus, Kevin Mganga, Rashmi Shrestha, Subin Kalu, Angela Martin, Bruno Glaser, and Kristiina Karhu

It has been assumed for a long time that stable soil organic carbon (SOC) results from selective preservation of plant residues. Yet, a new paradigm points to a more active role of microorganisms in building SOC storage. In this context, even labile C, such as sugars, may persist in soil for a long time due to their incorporation into microbial biomass and ultimately necromass. The latter is considered as a relatively stable pool. However, little is known about the cycling of labile C through the microbial biomass and the turnover time of its residues. Unraveling the mechanisms and regulating factors would be critical for understanding SOC stabilization in soil.

We assume that the fate of labile C is mainly driven by microbial nitrogen (N) demand and supply. Specifically, we hypothesize that (1) high N demand forces microbes to decompose N-rich substances (“microbial N mining”), such as amino sugars, leading to a rapid turnover of microbial necromass, and that (2) labile C is stabilized in microbial necromass when N demand is met.

To investigate these hypotheses, we set up a greenhouse pot experiment including four treatments: (1) bare soil, (2) bare soil+N, (3) tree, and (4) tree+N. The soil is a sandy and nutrient poor forest soil from southern Finland. Trees are 1 m high pines (Pinus Sylvestris), which are supposed to induce microbial N deficiency by exuding easily degradable C compounds and by competing with microbes for mineral N. In order to follow to fate of labile C, we added trace amounts of 13C labeled glucose to the soil (4 replicates per treatment). As a control to account for background variations in 13C, we added 12C glucose to another set of pots (4 replicates per treatment). Up to now, we sampled the soil 1 day, 3 days, 8 days, 1 month, 3 months, 6 months, 9 months, and 1 year after glucose addition. Measurements of the 13C recovery in soil, microbial biomass, water extractable C, PLFA, amino sugars, and DNA are in progress.

First results indicate that the largest loss of 13C tracer occurred in the unfertilized tree treatment, i.e., where N demand was high but N supply was low. Here, only 22% of the 13C glucose remained after 3 month, whereas 40% remained in the fertilized tree treatment. Only small proportions of the recovered 13C were present in the pool of water extractable C (<1%) and in living microbial biomass (8±3%, 3 days after glucose addition). As protection by clay minerals and aggregates is likely not a relevant process in this sandy soil, we suspect the remaining 13C to be stabilized in microbial residues, but depending on N demand. We assume that microbial necromass accounts for a considerable proportion to total SOC storage, especially under conditions of adequate nitrogen supply.

How to cite: Meyer, N., Sietiö, O.-M., Adamczyk, S., Biasi, C., Ambus, P., Mganga, K., Shrestha, R., Kalu, S., Martin, A., Glaser, B., and Karhu, K.: Stabilization of labile carbon in soil microbial biomass and necromass – A question of nitrogen deficiency?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7121, https://doi.org/10.5194/egusphere-egu2020-7121, 2020.

EGU2020-10528 | Displays | SSS5.11 | Highlight

Soil carbon dynamic after freezing/thawing and drying/wetting in a temperate forest soil: Dual labeling of 13C and 14C

Francisco Nájera, Michaela Dippold, Jens Boy, Oscar Seguel, Moritz Köster, Svenja Stock, Carolina Merino, Yakov Kuzyakov, and Francisco Matus

Temperate forests in Chile have experienced increasing temperatures and extreme climatic events, such as severe drought and short winters in unique Araucaria araucana forest in Nahuelbuta National Park. Therefore, it is relevant to understand the impact of drying and rewetting (D/R) or freezing and thawing (F/T) on SOM turnover in these ecosystems. Particularly important is the destabilization of soil organic matter (SOM) by microbial activity, which is highly heterogeneous and influenced by soil properties and water cycles. Drying and rewetting or F/T cycles accelerate particulate organic matter (POM) decomposition by aggregate disruption, thereby, decreasing carbon (C) availability for soil microorganism. We hypothesized that frequent D/R and F/T cycles release labile organic C locked away in the aggregates for microbial consumption. We assumed that a repeated number of D/R and F/T cycles enhance the preferential C utilization of fresh organic substrate. In the present study an incubation experiment was conducted for 27 days to assess the effect of F/T (-18 ºC to room temperature) and D/R (-500 kPa to 33 kPa, field capacity) cycles on labelled 14C glucose and 13C lignocellulose decomposition, soil aggregates size and POM fractions distributions. CO2 efluxes and priming effect (PE), i.e. the turnover acceleration or retardation of native C mineralization, C use efficiency (CUE) and C allocation in soil aggregate classes as POM-light, POM-occluded and heavy fractions were also determined. Labelled glucose was mainly allocated in macro (> 250 mm) and microaggregates (< 250 mm) as part of the POM-light fraction. In contrast, labelled lignocellulose was allocated in microaggregate in the POM-occluded and heavy fraction. CUE was similar amongst all treatments. The PE was negative in soil with and without cycles and it was much more pronounced (-125 mg C kg-1 soil) for F/T cycles than D/R (-50 mg C kg-1 soil) at the end of incubation. The C:N ratio of soil following mining theory is further discussed. We conclude that D/R cycles clearly retarded the native C mineralization by preferential use of labelled 13C-lignocellulose, while F/T cycles led to preferential use of 14C-glucose.

How to cite: Nájera, F., Dippold, M., Boy, J., Seguel, O., Köster, M., Stock, S., Merino, C., Kuzyakov, Y., and Matus, F.: Soil carbon dynamic after freezing/thawing and drying/wetting in a temperate forest soil: Dual labeling of 13C and 14C, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10528, https://doi.org/10.5194/egusphere-egu2020-10528, 2020.

EGU2020-5530 | Displays | SSS5.11

The origin and fate of organic matter in circum-Arctic subglacial ecosystems

Petra Vinsova, Myrna J. Simpson, Tiange Yuan, Irka Hajdas, Lukas Falteisek, Tyler J. Kohler, Jacob C. Yde, Jakub D. Zarsky, and Marek Stibal

Glacier and ice sheet beds represent important yet underresearched cryospheric ecosystems. Life in the subglacial environment is mostly dependent on organic matter (OM) overridden by ice during times of glacier advance, and the nature of subglacial OM is, therefore, likely to drive the ecosystem functionality. Here we describe the origin, degradation stage and environmental context of OM present underneath glaciers in the circum-Arctic, and their effects on the resident microbial communities.

In total, 19 glaciers from Alaska, Greenland, Iceland, Svalbard, and Norway were sampled for subglacial sediments. Biomarker analysis of the sediment samples was conducted using total solvent extraction, and copper (II) oxide (CuO) oxidation techniques yielding lipids and lignin-derived phenols. The extracts were analyzed by GC-MS to characterize the molecular-level composition of OM present. The biomarker data were then placed in the context of other environmental data, such as radiocarbon age, nutrient contents, and microbial community composition. The majority of OM in the samples was plant-derived, suggested by the dominance of long-chain n-alkanols over the microbial-specific short-chain n-alkanols. The composition of long-chain n-alkanes (≥C20), used as biomarkers for vascular plant waxes, in the solvent extracts suggested grass sources for samples from most Greenland glaciers and conifer sources for some glaciers from Norway, Alaska, and Disko Island (Qeqertarsuaq) in West Greenland. The rest of the OM in the subglacial samples was identified to have more general tree sources. The carbon preference index (CPI) of long-chain n-alkanes suggested a high degradation stage in most samples and was correlated with the radiocarbon age of the sediments’ OC (r = -0.68). Sediments containing older and more degraded OM were found to host less diverse microbial communities compared to those of the younger sites.

In a rapidly warming climate, previously glacier-covered areas are being exposed as a consequence of glacier recession. This new land is standing at the onset of ecological succession and pedogenesis. Our results contribute to the understanding of the potential ecological function of subglacial OM as an important source of carbon and driver of microbial community development after deglaciation in the circum-Arctic region.

How to cite: Vinsova, P., Simpson, M. J., Yuan, T., Hajdas, I., Falteisek, L., Kohler, T. J., Yde, J. C., Zarsky, J. D., and Stibal, M.: The origin and fate of organic matter in circum-Arctic subglacial ecosystems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5530, https://doi.org/10.5194/egusphere-egu2020-5530, 2020.

EGU2020-3537 | Displays | SSS5.11

Dark microbial CO2 fixation in temperate forest soils increases with CO2 concentration

Marie Spohn, Karolin Müller, Carmen Höschen, Carsten W. Müller, and Sven Marhan

Dark, that is, nonphototrophic, microbial CO2 fixation occurs in a large range of soils.
However, it is still not known whether dark microbial CO2 fixation substantially contributes
to the C balance of soils and what factors control this process. Therefore,
the objective of this study was to quantitate dark microbial CO2 fixation in temperate
forest soils, to determine the relationship between the soil CO2 concentration and
dark microbial CO2 fixation, and to estimate the relative contribution of different
microbial groups to dark CO2 fixation. For this purpose, we conducted a 13C-CO2 labeling
experiment. We found that the rates of dark microbial CO2 fixation were positively
correlated with the CO2 concentration in all soils. Dark microbial CO2 fixation
amounted to up to 320 μg C kg−1 soil day−1 in the Ah horizon. The fixation rates were
2.8–8.9 times higher in the Ah horizon than in the Bw1 horizon. Although the rates of
dark microbial fixation were small compared to the respiration rate (1.2%–3.9% of the
respiration rate), our findings suggest that organic matter formed by microorganisms
from CO2 contributes to the soil organic matter pool, especially given that microbial
detritus is more stable in soil than plant detritus. Phospholipid fatty acid analyses
indicated that CO2 was mostly fixed by gram-positive bacteria, and not by fungi. In
conclusion, our study shows that the dark microbial CO2 fixation rate in temperate
forest soils increases in periods of high CO2 concentrations, that dark microbial CO2
fixation is mostly accomplished by gram-positive bacteria, and that dark microbial
CO2 fixation contributes to the formation of soil organic matter.

Reference

Spohn M, Müller K, Höschen C, Mueller CW, Marhan S. Dark microbial CO2 fixation in temperate forest soils increases with CO2 concentration.
Glob Change Biol. 2019;00:1–10. https ://doi.org/10.1111/gcb.14937

How to cite: Spohn, M., Müller, K., Höschen, C., Müller, C. W., and Marhan, S.: Dark microbial CO2 fixation in temperate forest soils increases with CO2 concentration, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3537, https://doi.org/10.5194/egusphere-egu2020-3537, 2020.

Grazing is an important human activity affecting grassland ecosystems. Many studies have shown that grazing changed the carbon (C) cycle of grasslands, but it is still not clear how grazing will affect the recent photosynthetic C allocation in the temperate grasslands. To clarify this question, a situ field 13C labeling experiment was carried out in the temperate grasslands of Inner Mongolia, North China, in 2015. In this study. Grazing included 3 intensities of no grazing, medium grazing and heavy grazing. Eighty-one days after the labeling, the plants allocated more recent assimilated 13C (6.52% of recovered 13C) to shoots under medium grazing than that of no grazing (5.60%) and heavy grazing (5.40%). The most 13C was allocated to the belowground (roots, soil and soil respiration) under no grazing (40.68%). However, within the belowground pools, 1.36% and 17.33% of 13C were stored in roots and soil under medium grazing which was twice than that under no grazing and heavy grazing, which could be explained by intermediate disturbance hypothesis. 13C labeling experiment demonstrated medium grazing increased C assimilates by two processes:(Ⅰ) the highest total C input into plants and soil and (Ⅱ)the least C loss by soil microbial respiration (3.20%) than no grazing grassland (5.19%) and heavy grazing grassland (3.47%). The turnover rate of soil assimilates under the no grazing (0.25 ± 0.07 day-1) was higher than that of grazing (medium grazing 0.059 ± 0.01 day-1; heavy grazing 0.064 ± 0.02 day-1). Overall, the no grazing isn’t the best for carbon accumulation and the medium grazing which promotes C input and C sequestration is the most suitable grazing intensity of temperate grassland in China.

How to cite: Zhao, Y. and Tian, Y.: Effect of grazing on photosynthetic carbon allocation in a temperate grassland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6814, https://doi.org/10.5194/egusphere-egu2020-6814, 2020.

Understanding the source partitioning of carbon dioxide (CO2) and nitrous oxide (N2O) fluxes from soil is integral for the characterization of total fluxes and the quantification of potential soil organic matter priming effects. Additionally, we utilized 15N-N2O site preference data to analyze the process priming of microbial nitrification and denitrification on subsequent N2O fluxes. A 32-day laboratory incubation was designed to examine the effects of artificial exudate, nitrogen fertilizer and their potential interactive effects on CO2 and N2O fluxes, soil organic matter source-priming and N2O process-priming. Artificial root exudate (ARE) consisting of a mixture of 99 atom% 13C labelled compounds at three addition rates (0, 6.2, 12.5 mg C kg-1 soil day-1) was applied daily for 21 days to microcosms with or without urea fertilizer, a subset of which was labelled with 5 atom % 15N. Measurements of CO2 and N2O fluxes, isotopic composition and N2O site preference were frequent throughout the duration of the experiment. Source partitioning of CO2 fluxes showed that soil organic carbon (SOM-C) positive priming was significantly altered by additions of artificial exudate and urea (p < 0.001 and 0.001, respectively). When applied concurrently, urea addition had an antagonistic interactive effect on SOM-C sourced CO2 fluxes (p < 0.001).  Source partitioning of N2O flux data revealed that soil organic matter nitrogen (SOM-N) was positively primed for N2O flux by the addition of urea fertilizer (p < 0.001), but positive SOM-N priming was reduced by an antagonistic interaction with artificial exudate application (p < 0.001). Further, examination of 15N-N2O site preference found that the main processes by which N2O is formed (nitrification and denitrification) were differentially process-primed by the addition or absence of ARE. Cumulative denitrification and nitrification contributions to total N2O flux were both positively primed in the soils receiving both ARE and urea inputs relative to a control (50.0 ± 10.1 and 28.2± 8.0 μg N2O-N kg-1, respectively). In soils receiving only ARE application, denitrification-derived N2O was negatively primed relative to a control and thus contributed less to overall N2O flux (-9.5 ± 12.4 μg N2O-N kg-1) but nitrification-derived N2O was positively primed (17.2 ± 9.0 μg N2O-N kg-1).

How to cite: Daly, E. and Hernandez Ramirez, G.: Source-process partitioning of soil N2O and CO2 production: nitrogen and simulated exudate additions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2221, https://doi.org/10.5194/egusphere-egu2020-2221, 2020.

EGU2020-20216 | Displays | SSS5.11

Composition of low molecular weight organic substances affect total soil microbial activity independently of community composition.

Louis J.P. Dufour, Anke. M. Herrmann, Julie Leloup, Cédric Przybylski, Luc Abbadie, and Naoise Nunan

EGU2020-22169 | Displays | SSS5.11

Activation of soil enzymes by addition of artificial root exudate combinations

Diane Hagmann, Jennifer Krumins, Bhagyashree Vaidya, and Nina Goodey

In vegetated soils,plants naturally release root exudates, consisting of sugars, organic acids, and amino acids, into the soil increasing soil enzymatic activity.  Liberty State Park, located in Jersey City, New Jersey, is an industrial brownfield contaminated with heavy metals and organic pollutants.  Some sites have soils that function poorly, as indicated by low soil enzymatic activity, and do not support plant growth.  This study will determine whether different combinations of artificial root exudates increase soil enzymatic activity in these contaminated and low functioning soils. Different combinations of sugars, organic acids, and amino acids and will be added to barren, poorly functioning soil.  Three soil enzymatic activities will be examined at several time points over 120 days to assess the impacts of different combinations of root exudates on soil function. Further, soil microbial community composition will be determined to examine whether different artificial exudate solutions result in changes in soil microbial community.  Preliminary results suggest that the combination of sugars, organic acids, and amino acids greatly increased phosphatase, cellobiohydrolase, and L-leucine amino peptidase activity over time in poorly-functioning, barren soil from Liberty State Park. The other combinations (sugars and organic acids, sugars and amino acids, organic acids and amino acids) also increase the three enzyme activities more than the individual groups. Dormant microbes in barren soil can possibly be revived with the addition of artificial root exudates to mimic the presence of plants in revitalizing the microbial communities and improving soil function. 

How to cite: Hagmann, D., Krumins, J., Vaidya, B., and Goodey, N.: Activation of soil enzymes by addition of artificial root exudate combinations , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22169, https://doi.org/10.5194/egusphere-egu2020-22169, 2020.

EGU2020-10898 | Displays | SSS5.11

Soil texture mediated microbial activity affects the transfer of litter-derived carbon to soil organic matter

Gerrit Angst, Jan Pokorný, Travis Meador, Tomáš Hajek, Jan Frouz, Isabel Prater, Carsten W Mueller, Gerard van Buiten, and Šárka Angst

Knowledge about the nexus between litter decomposition and soil organic matter formation is still scarce, likely because litter decomposition studies are often conducted in the absence of mineral soil. Even if mineral soil is considered, variations in soil texture, which should substantially influence decomposition and soil C sequestration via, e.g., different capacities to store C or host microbial communities, have been neglected. Here, we examined the effect of soil texture on litter decomposition and soil organic matter formation by incubating sand- and clay-rich soils. These soils, taken under C3 vegetation, were amended with C4 litter to trace the fate of organic matter newly entering the soil. While we found only small amounts of litter-derived carbon (C) in the mineral soils after our six-month experiment, the microbial activity and amount of remaining litter between the sand- and clay-rich soils substantially differed. A high microbial activity combined with higher amounts of litter-derived C and a higher remaining litter mass in the clay-rich soil indicate a more effective transformation of litter to soil organic matter as compared to the sand-rich soil. In the sand-rich soil, microbial activity was lower, less soil C was litter-derived, and the litter lost more of its mass. We explain the apparently contradictory results of higher microbial activity and concurrently higher C contents with a more effective microbial pathway of SOM formation in the clay-rich soil. Our results indicate that soil texture does not only play a role in the provision of reactive surfaces for the stabilization of C but will also affect the decomposition of litter via effects on microbial activity, ultimately determining if litter C is transferred to the soil or respired to the atmosphere.

How to cite: Angst, G., Pokorný, J., Meador, T., Hajek, T., Frouz, J., Prater, I., Mueller, C. W., van Buiten, G., and Angst, Š.: Soil texture mediated microbial activity affects the transfer of litter-derived carbon to soil organic matter, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10898, https://doi.org/10.5194/egusphere-egu2020-10898, 2020.

EGU2020-11168 | Displays | SSS5.11

Biochemistry of plant litter types drives differentiation into particulate and mineral-associated soil organic matter and determines the magnitude of priming effect

Luís Fernando Januário Almeida, Luis Carlos Colocho Hurtarte, Pedro Paulo Teixeira, Thiago M. Inagaki, Ivan Francisco de Souza, Ivo Ribeiro da Silva, and Carsten W. Mueller

Soil organic matter (SOM) originates predominantly from above and belowground OM inputs derived from plants. Although the formation of SOM is well studied, it still remains unclear how the biochemical composition of litter affects the formation of new SOM as well as the degradation of “native” SOM. In the present study we aimed to disentangle the effect of plant litter composition on C transference from different plant tissues into specific SOM fractions and to determine the magnitude of priming effect on native SOC caused by litter amendments. To this end, we individually incubated 13C enriched Eucalyptus spp. major litter types (bark, leaves, twigs and roots) in soil (0–20 cm) of a sandy-clay loam (Haplic Ferralsol - Brazil). Additionally, a soil sample without plant residue addition was incubated as a control. The samples were incubated at 80% of their water-holding capacity at 25 ºC for 200 days. Soil respiration was assessed along the incubation period through headspace gas sampling and 13C/12C–CO2 analysis in a cavity ring-down spectrometer. After the incubation, soil subsamples were physically fractionated using a combined density-particle size separation method. The total C and the δ 13C of each soil organic matter fraction were measured and the litter-C contribution for each SOM fraction was assessed using a two-end member isotope mixing model. The molecular composition of the incubated plant material and SOM fractions were determined by solid-state 13C-CPMAS-NMR spectroscopy. Interestingly, we found no significant differences for total SOM contents among the different treatments. Conversely, incubation without litter amendment (control treatment) resulted in lower total SOM contents, indicating mineralization of “native” SOM along the incubation period. The partitioning of litter-derived C into SOM fractions indicated that leaves litter were preferentially transferred to mineral associated organic matter (MAOM), while roots contributed more to particulate organic matter (POM). Cumulative C-CO2 evolution from the treatments over the incubation period increased in the following order: twigs > leaves > bark > roots > controls. Incubation with twigs, bark and roots significantly increased “native” SOM respiration, while the treatment with leaves addition did not differ from the control. When tracing the source of “native” SOM-derived CO2, we observed a similar amount of C being respired from MAOM, regardless the treatment, while incubation with twigs, bark and roots resulted in higher respiration of “native” SOM-derived C from POM. Our data demonstrates that the biochemical composition of plant litter determines the fate of newly formed organic matter (MAOM or POM) and controls the degradation of “native” SOM. Therefore, plant residues enriched in more easily degradable compounds (leaves) are preferentially transferred to MAOM and causes less native SOC priming. On the other hand, plant residues enriched in structural compounds (twigs, bark and roots), are preferentially respired or allocated into the POM, also resulting in higher priming effect intensity.

How to cite: Januário Almeida, L. F., Colocho Hurtarte, L. C., Teixeira, P. P., Inagaki, T. M., de Souza, I. F., da Silva, I. R., and Mueller, C. W.: Biochemistry of plant litter types drives differentiation into particulate and mineral-associated soil organic matter and determines the magnitude of priming effect, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11168, https://doi.org/10.5194/egusphere-egu2020-11168, 2020.

EGU2020-22306 | Displays | SSS5.11

C:N stoichiometry of stable and labile organic compounds determine priming patterns

Min Liu, Na Qiao, Xingliang Xu, Huajun Fang, Huimin Wang, and Yakov Kuzyakov

Approximately 50–70% of C stored in soil is derived from the roots or root-associated microorganisms, reflecting their importance for soil organic matter (SOM) formation. Microorganisms are the major driver for SOM decomposition and their activities are modified by the input of labile organics such as root exudates and low molecular weight organic substances derived from litter decomposition. Such short-term changes in the turnover of SOM caused by moderate organic additions into the soil were defined as priming effects (PE). Priming effects can influence global carbon (C) storage in soil and lead to climate feedbacks by accelerating the decomposition of organic matter (OM). In natural ecosystems, input of nitrate (NO3) and ammonium (NH4+) into the soil can be derived from nitrogen (N) deposition and biological N fixation. Although availability N can alter the magnitude and direction of priming, it remains unclear whether additions of NO3 and NH4+ have distinct effects on the decomposition of OM. Thus, the aims of this study were to investigate the responses of OM decomposition along a decay continuum (i.e. decreasing decomposition degree) to labile C and N inputs and determine the PE induced by the two N forms. Leaf litter, wood litter, organic soil horizon, and mineral soil, with a broad range of C:N ratios were collected along a decay continuum in a typical subtropical forest and incubated for 38 days with 13C labeled glucose and N (NO3) additions. Based on the very broad range of C:N ratios in OM in soil and inputs of labile C and N, we demonstrated the OM decomposition within a decay continuum as well as PE intensities and the thresholds for the switch of PE directions. In contrast to NH4+ additions, NO3 generally accelerated the decomposition of all OM. Priming of plant litter was dependent on the C:N ratios of the labile inputs. However, leaf litter decomposition was more controlled by N addition than wood litter. Glucose addition greatly increased the priming of OM decomposition, demonstrating energy limitation for microorganisms. Distinct priming patterns were observed between NO3 and NH4+ additions, both for the individual OM types and for all four types of OM. The PE induced by labile C and N inputs can increase or reduce C sequestration depending on C:N stoichiometric ratios of labile inputs. Net C losses caused by PE can be observed in organic soil and plant litter with low C and N additions, but all four OM substrates increased C sequestration under high C addition. Minor differences in priming along the continuum were observed where the OM C:N ratio was below 30 when NO3 was added and where the labile C:N ratio was less than 55 when NH4+ was added. Thus, changes in the composition of deposited N (atmospheric deposition and fertilization) may induce distinct climate feedbacks. Under future climatic conditions by global warming and elevated CO2, more labile C inputs via root exudates could accelerate litter decomposition. Effects of N however, depend on the N form: NH4+ to NO3 due to the energy necessary for microorganisms for NO3- reduction.

How to cite: Liu, M., Qiao, N., Xu, X., Fang, H., Wang, H., and Kuzyakov, Y.: C:N stoichiometry of stable and labile organic compounds determine priming patterns, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22306, https://doi.org/10.5194/egusphere-egu2020-22306, 2020.

EGU2020-11990 | Displays | SSS5.11

Glucose concentration controls priming effects and soil carbon storage under pasture and forest in volcanic ash soils of Hokkaido, Japan

Chie Hayakawa, Taichi Kobayashi, Kazumichi Fujii, Yoshiyuki Inagaki, and Keishi Senoo

Introduction & objectives: Over ten thousand years, soils have been formed through events of volcanic ash deposition in Hokkaido, Japan. The soil organic matter (SOM) in the past surface layer has been buried in the deeper soil. The buried humic horizons serve as a large carbon (C) reservoir. The SOM in the deeper soil horizons is preserved due to lower microbial activities and limited inputs of fresh organic matters. However, when the buried humic horizons are exposed to the surface by deep plowing and bottom plow tillage, decomposition of the exposed SOM may be accelerated through priming effects, due to the increased supply of low-molecular-weight (LMW) substances from fresh plant litter inputs. To test this, we examined glucose concentration dependency of priming effect and the change of SOC balance through priming effect using 13C tracer incubation.

Materials & methods: Soil samples were collected from the volcanic soil profiles in pasture site and adjacent forest sites in Hokkaido, Japan. The moist soils were sieved (< 4 mm) to eliminate plant debris and stones for the incubation study and the other analysis. A 13C-glucose solution (99 atom%; 0 – 3.9 mg glucose g-1) was added to moist soil (equivalent to 10 g oven-dried weight) and incubated at 20ºC in the dark for 30 days. The head space gas sample was periodically taken into the vial, and 13CO2 and 12CO2 concentrations were determined by GC-MS. Priming effect (PE) was calculated by subtraction between the amounts of 12CO2 with and without glucose. The head space gas in the bottle was flush out and replaced to CO2-free-air every sampling time. We also measured soil microbial biomass C (MBC) by chloroform fumigation method, bacterial and fungal biomass by 16S and 18S rRNA genes targeted real-time PCR, SOC concentrations, inorganic N concentrations (ammonium and nitrate) and the other physicochemical properties of the soil profiles.

Results & discussion: Glucose addition induced the positive PEs in the buried humic soil samples of both sites, and the magnitudes of PEs (cumulative primed-CO2 amounts) in the buried humic soil samples were 0.4 to 1.5 times as those in the surface soils. However, the negative PEs were detected in the forest surface soil, probably because of low soil pH and relatively high inorganic N concentration. The magnitudes of PEs were dependent on added glucose concentrations for all the soils, and the threshold between negative and positive PEs corresponded to 3.5 % of glucose-C relative to MBC in the forest surface soil. The positive correlation between evolution rates of primed-CO2 significantly and bacterial or fungal biomass suggests both bacteria and fungi contributes to PE in the soils studied. Even if glucose addition induced PE, total SOC after incubation increased when glucose-C was added more than 0.5 mg C g-1 in the all soils. This implies that the optimized fresh litter input can control priming effects and C sequestration in volcanic soils.

How to cite: Hayakawa, C., Kobayashi, T., Fujii, K., Inagaki, Y., and Senoo, K.: Glucose concentration controls priming effects and soil carbon storage under pasture and forest in volcanic ash soils of Hokkaido, Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11990, https://doi.org/10.5194/egusphere-egu2020-11990, 2020.

EGU2020-4817 | Displays | SSS5.11

How does simulated climate change affect the susceptibility of SOM to priming by LMWOS in the Subarctic?

Meng Na, Mingyue Yuan, Lettice Hicks, and Johannes Rousk

Soil organic matter (SOM) stabilization plays an important role in long-term storage of carbon (C). However, now many ecosystems are experiencing global climate change, which could change soil C balance through affecting the C input via plant community shifts, and C losses via SOM decomposition. In subarctic ecosystems, plant community composition and productivity are shifting because of climate change. This change of above-ground communities will affect rhizosphere input such as low molecular weight organic substances (LMWOS), which can affect microbial decomposer activities and subsequent contribution to SOM mineralization (priming effect). In the present study, we simulated climate change with N fertilization, to represent a warming enhanced nutrient cycling, and litter input, to simulate arctic greening, to evaluate the effect of a changing climate on subarctic ecosystems in Abisko, Sweden. The 6 sampled field treatments included three years of chronic N addition (5 g N m-2 y-1), three years of chronic litter addition (90 g m-2 y-1), three years of chronic N and litter additions, one year of high N addition (15 g N m-2 y-1), one year of high litter addition (270 g m-2 y-1) and a control treatment. All treatments were established in 1×1 m experimental squares and had 6 replicates. We resolved effects on plant community (NDVI), SOM mineralization, microbial composition, bacterial and fungal growth rates, and soil properties.

We found that N treatments changed plant community and stimulated productivity and that the associated increase in belowground LMWOS induced shifts in the soil microbial community. This coincided with a tendency for a shift towards bacterial dominated decomposition (low fungi/bacterial growth ratio) and a microbial community that had shifted from gram-positive bacteria to gram-negative bacteria; a shift often observed when comparing bulk with rhizosphere conditions. However, N treatments had no effect on SOC mineralization, but did increase soil gross N mineralization. This shift in the C/N of mineralisation might be because N treatments accelerated the growth of fast growing plant species with higher nutrient content, whose litter input provided microbes with fresh OM richer in N.

These responses in belowground community and processes driven by rhizosphere input prompted the next question: how did the simulated climate change affect the susceptibility of SOM to priming by LMWOS? To assess this question and explore the microbial mechanisms underpinning priming of SOM mineralization, we added a factorial set of additions including 13C-glucose with and without mineral N, and 13C-alanine semicontinously to simulate the effect of belowground LMWOS input on SOM mineralization and microbial activity, and investigate how the SOM priming was linked to the actively growing microorganisms. Therefore, we incubated these samples for 7 days, treated with 13C LMWOS, and measured SOC and SON mineralization to assess SOM priming, bacterial and fungal growth rates, microbial phospholipid fatty acids (PLFAs) and 13C-PLFA enrichment, as well as the microbial C use efficiencies to assess microbial responses to LMWOS additions.

How to cite: Na, M., Yuan, M., Hicks, L., and Rousk, J.: How does simulated climate change affect the susceptibility of SOM to priming by LMWOS in the Subarctic?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4817, https://doi.org/10.5194/egusphere-egu2020-4817, 2020.

Extreme precipitation events resulting from climate change have strong impact on structure and functions of grassland ecosystems. The extreme climate events may shift plant productivity and nutrient acquisition preferences by roots and microorganisms.We conducted an extreme precipitation simulation experiment and used in-situ 15N labeling of the three N forms to investigate N acquisition (N uptake rate, 15N recovery and preference for N form) by the dominant plant species Stipa grandis and soil microorganisms.Increased rain frequency raised the growth and N acquisition of S. grandis, while microbial N uptake remains unaffected. Microorganisms strongly outcompeted S. grandis for total 15N acquisition, however such superiority decreased in higher extreme precipitation frequency. Plant and microorganisms converged their N demands from distinct to similar preferences for N forms with high precipitation frequency. Such chemical niche partitioning by extreme precipitation effectively reduced root and microbial competition for each N form. Overall, important mechanistical insights into chemical niche differentiation by the effects of extreme climate events and their effects on structure, functions and plant-microbial interactions in temperate grasslands were explained.

How to cite: Tian, Y.: Extreme precipitation increases plant biomass through altering nitrogen acquisition by grasses and soil microorganisms, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3243, https://doi.org/10.5194/egusphere-egu2020-3243, 2020.

EGU2020-6271 | Displays | SSS5.11

Uptake of urea by “drunken” trees on permafrost

Kazumichi Fujii, Yojiro Matsuura, Yoshiyuki Inagaki, and Chie Hayakawa

Boreal forest productivity on permafrost is limited by availability of soil nitrogen (N) in the active layer. Low soil temperature and summer flooding limit microbial N mineralization on shallow permafrost table. Uptake of amino acids by plant root-mycorrhizal association is known to mitigate N limitation in boreal forest soils. However, amino acid hypothesis can not fully explain advantage of black spruce trees in drunken forests due to competition of amino acids between plants, bryophytes, and microbes. Based on the observation of urea accumulation in deeper soil, we test another hypothesis that black spruce trees take up intact urea in deeper soil. Mixture solutions (glutamic acid, urea, ammonium, nitrate), with only one N form labeled by 13C and/or 15N, was injected into the organic/mineral soil layers. We compared two black spruce forest sites with/without shallow permafrost table in northern Canada. We found that black spruce trees take up intact urea as well as amino acids in the shallow permafrost sites. Urea accumulation is explained by low microbial activities to mineralize 14C-labeled urea. The other plants or bryophyte compete with black spruce for amino acids, but not for urea. Since the other black spruce trees in the deeper soil sites rely on amino acids and inorganic N, urea uptake strategy is specific to black spruce trees on shallow permafrost table. The root expansion on hummocky microrelief provides opportunity for leaning trees to access urea. The uptake of intact urea could be one of strategy of black spruce trees to mitigate N limitation in permafrost-affected hummocky soils.

How to cite: Fujii, K., Matsuura, Y., Inagaki, Y., and Hayakawa, C.: Uptake of urea by “drunken” trees on permafrost , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6271, https://doi.org/10.5194/egusphere-egu2020-6271, 2020.

EGU2020-8246 | Displays | SSS5.11

Effect of Ph and vegetation cover in soil organic matter structure at a high-mountain ecosystem (Sierra Nevada National Park, Granada, Spain)

José A. González-Pérez, Gael Bárcenas.Moreno, Nicasio T Jiménez-Morillo, María Colchero-Asensio, Layla M. San Emeterio, and José M. de la Rosa

Keywords: Soil reaction, analytical pyrolysis, soil respiration, carbon stabilization

During the last decade, soil organic matter dynamics and its determining factors have received increased attention, mainly due to the evident implication of these parameters in climate change understanding, predictions and possible management. High-mountain soil could be considered as hotspot of climate change dynamic since its high carbon accumulation and low organic matter degradation rates could be seriously altered by slight changes in temperature and rainfall regimes associated to climate change effects. In the particular case of Sierra Nevada National Park, this threat could be even stronger due to its Southern character, although its elevated biodiversity could shed some light on how could we predict and manage climate change in the future.

In this study, a quantitative and qualitative organic matter characterization was performed and soil microbial activity measured to evaluate the implication of pH and vegetation in soil organic matter dynamics.

The sampling areas were selected according to vegetation and soil pH; with distinct soil pH (area A with pH<7 and area B with pH>7) and vegetation (high-mountain shrubs and pine reforested area). Soil samples were collected under the influence of several plant species representatives of each vegetation series. Six samples were finally obtained (five replicates each); three were collected in area A under Juniperus communis ssp. Nana (ENE), Genista versicolor (PIO) and Pinus sylvestris (PSI) and other three were collected in area B under Juniperus Sabina (SAB), Astragalus nevadensis (AST) and Pinus sylvestris (PCA).

Qualitative and quantitative analyses of soil organic matter were made to establish a possible relationship with microbial activity estimated by respiration rate (alkali trap) and fungi-to-bacteria ratio using a plate count method. Soil easily oxidizable organic carbon content was determined by the Walkley-Black method (SOC %) and organic matter amount was estimated by weight loss on ignition (LOI %). Analytical pyrolysis (Py-GC/MS) was used to analyse in detail the soil organic carbon composition.

Our results showed that the microbial and therefore the dynamics of organic matter is influenced by both, soil pH and soil of organic matter. So that the pH in acidic media prevail as a determining factor of microbial growth over soil organic matter composition conditioned by vegetation.

Acknowledgement: Ministerio de Ciencia Innovación y Universidades (MICIU) for INTERCARBON project (CGL2016-78937-R). N.T. Jiménez-Morillo and L. San Emeterio also thanks MICIU for funding FPI research grants (BES-2013-062573 and Ref. BES-2017-07968). Mrs Desiré Monis is acknowledged for technical assistance.

 

How to cite: González-Pérez, J. A., Bárcenas.Moreno, G., Jiménez-Morillo, N. T., Colchero-Asensio, M., San Emeterio, L. M., and de la Rosa, J. M.: Effect of Ph and vegetation cover in soil organic matter structure at a high-mountain ecosystem (Sierra Nevada National Park, Granada, Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8246, https://doi.org/10.5194/egusphere-egu2020-8246, 2020.

EGU2020-19705 | Displays | SSS5.11

Loss of available soil organic carbon from afforestation plots: effect of tree species composition and warming

Zhenhui Jiang, Anna Gunina, Lucas Merz, Yihe Yang, Yakov Kuzyakov, Davey Jones, Andrew R. Smith, and Bernard Ludwig

Afforestation with pure and mixed-species is an important strategy to improve soil organic carbon (SOC) stocks and restore degraded lands. However, what remains unclear is the stability of SOC to microbial degradation after afforestation and the effect of tree species composition. Moreover, it is important to reveal how sensitive the SOC in afforestation lands is to environmental changes, such as warming. To study the combined effects of warming and the tree species composition on decomposition of SOC by microorganisms and enzyme activities, soils were collected from the monocultural and mixtures of Silver birch (Betula Pendula) and European beech (Fagus Silvatica) (BangorDiversity, UK, 12 years since afforestation) and were incubated for 169 days at 0, 10, 20, 30 °C at 60 % of WHC. The field experiment is arranged into a completely randomized design with n=4. The CO2 efflux was measured constantly, whereas activities of β-glucosidase, chitinase and acid phosphatase, and content of microbial biomass C (MBC) were obtained at the end of the incubation. Results showed that soil cumulative CO2 efflux increased by 34.7–107% with the temperature. Potential enzyme activities were dependent on tree species composition. Warming, but not tree species exhibited a significant impact on the temperature sensitivity (Q10) of soil cumulative CO2 efflux and enzyme activities. The greatest temperature sensitivity (Q10) of total CO2 efflux was found at 10–20 °C and was 2.0–2.1, but that of enzyme activities were found as 0.9–1.1 at 0–10 °C. These results suggest that warming has an asynchronous effect on the SOC decomposition and enzyme activity, and enzymes cannot account for the temperature sensitivity of soil respiration. Thus, thermal adaptations of SOC mineralization is independent of the adaptation of the enzyme pool.

How to cite: Jiang, Z., Gunina, A., Merz, L., Yang, Y., Kuzyakov, Y., Jones, D., Smith, A. R., and Ludwig, B.: Loss of available soil organic carbon from afforestation plots: effect of tree species composition and warming, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19705, https://doi.org/10.5194/egusphere-egu2020-19705, 2020.

Soil microbial necromass represents a significant proportion (>50%) of soil organic matter (SOM). Microbial necromass consists mainly of particulate organic residues from fragmented cells walls and other slow turnover cytoplasmic components of dead fungi and bacteria. Some of the key components of microbial cell walls, such as peptides and amino sugar polymers, can remain and accumulate in the soil over prolonged times. Amino sugars have been used as biomarkers to quantify the contribution of microbial necromass to stabilized SOM. The different amino sugars present in polymeric form in soils can be released by acid hydrolysis and allow the estimation of the contribution of both fungal and bacterial necromass to the SOM pool. Among the amino sugars, hexosamine isomers (glucosamine, galactosamine, mannosamine) and muramic acid (the ether of lactic acid and glucosamine) are the most abundant ones. Muramic acid is specific to bacterial peptidoglycan while glucosamine is an abundant cell wall component of both, fungal chitin and bacterial peptidoglycan.

There are several chromatographic methods to measure free and bound amino sugars and amino acids in soil extracts and soil hydrolysates, but none of them allow the combined determination of amino sugar biomarkers and amino acids simultaneously in a single assay for rapid analysis. This is important as a large fraction of soil necromass N (>50%) consists of non-amino sugar-N, such as proteins and nucleic acids. In this study we therefore adopt a method based on 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AccQ.Tag) derivatization of amino compounds and optimized chromatographic (reversed phase) separation to simultaneously measure amino sugars (isomers) and amino acids in soil extracts and soil hydrolysates using ultra-high-performance liquid chromatography coupled to fluorescence or UV detection.

The use of this method allows for fast, robust and highly sensitive quantification of amino acids and amino sugars in environmental samples at sub-micromolar levels. This approach will help to improve our understanding of soil microbial necromass dynamics and their inherent effect on soil C and N sequestration. The AccQ.Tag chemistry also allows compound detection by electrospray ionization (ESI)-mass spectrometry, enabling isotope (13C, 15N) tracing applications.

How to cite: Salas, E., König, A., Kaiser, C., and Wanek, W.: A new method to measure amino sugar isomers and amino acids in soil extracts and soil hydrolysates based on AccQ.Tag-chemistry and reversed phase ultra-high-performance liquid chromatography, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8200, https://doi.org/10.5194/egusphere-egu2020-8200, 2020.

EGU2020-9150 | Displays | SSS5.11

A novel fluxomics approach to decipher the flux partitioning between anabolic and catabolic processes in soil microbial communities

Theresa Böckle, Yuntao Hu, Jörg Schnecker, and Wolfgang Wanek

The activities of soil microorganisms drive soil carbon (C) and nutrient cycling and therefore play an important role in local and global terrestrial C dynamics and nutrient cycles. Unfortunately, soil microbial activities have been defined mostly by measurements of heterotrophic respiration, potential enzyme activities, or net N processes. However, soil microbial activities comprise more than just catabolic processes such as respiration and N mineralization. Recently anabolic processes (biosynthesis and growth) and the partitioning between anabolic and catabolic processes in soil microbial metabolism have gained more attention as they control microbial soil organic matter formation. Understanding the controls on these processes allows an improved understanding of the key roles that soil microbes play in organic matter decomposition (catabolic processes) and soil organic matter sequestration (anabolic processes leading to growth, biomass and necromass formation), and their potential feedback to global change.

Generally, there are two approaches to study the metabolism of soil microbial communities: First, position-specific isotope labeling is a tool that allows the tracing of 13C-atoms in organic molecules on their way through the network of metabolic pathways and second, metabolomics and fluxomics approaches can enable disentangling the highly complex metabolic networks of microbial communities, which however have rarely (metabolomics) or never (fluxomics) been applied to soils.

In this study we developed a targeted soil metabolomics approach coupled to 13C isotope tracing (fluxomics), in which we extract, purify and measure a preselected set of key metabolites. Our aim was to cover the wide spectrum of soil microbial metabolic pathways based on the analysis of biomarker metabolites being unique to specific metabolic pathways such as  glycolysis/gluconeogenesis (e.g. fructose 1,6-bisphosphate), the pentose phosphate pathway (ribose-5-phosphate), the citric acid cycle (α-ketoglutaric acid), purine and pyrimidine metabolism (UMP, AMP, allantoin), amino acid biosynthesis and degradation (10proteinogenic amino acids and their intermediates), the urea cycle (ornithine), amino sugar metabolism (N-Acetyl-D-Glucosamine and –muramic acid) and the shikimate pathway (shikimate). The minute concentrations of these primary metabolites are extracted from soils by 1 M KCl including 5 % chloroform, salts are removed by freeze-drying, methanol dissolution and cation-/anion-exchange chromatography and the metabolites and their isotopomers quantified by UPLC-Orbitrap mass spectrometry. To cover the wide range of metabolites, compound separations are performed by  hydrophilic interaction chromatography (HILIC) for metabolites such as amino acids, (poly-)amines, nucleosides and nucleobases and by Ion chromatography (IC), to separate charged molecules like amino sugars, sugar phosphates and organic acids.  Here we will show fluxomics results from a laboratory soil warming experiment where we added 13C-glucose to a temperate forest soil as a proof of concept.

How to cite: Böckle, T., Hu, Y., Schnecker, J., and Wanek, W.: A novel fluxomics approach to decipher the flux partitioning between anabolic and catabolic processes in soil microbial communities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9150, https://doi.org/10.5194/egusphere-egu2020-9150, 2020.

EGU2020-17791 | Displays | SSS5.11

A unified protocol for the high-throughput measurement of PLFA, NLFA, GLFA and sterols from soil

Stefan Gorka, Alberto Canarini, Bruna Imai, Georg Teischinger, Sean Darcy, and Christina Kaiser

Phospholipid fatty acids (PLFA) are widely used as biomarkers for soil microbial biomass. In more recent years, neutral lipid fatty acids (NLFA) have additionally been used as storage biomarkers. Both lipid classes are usually separated via silica solid phase extraction (SPE) after extraction with a mixture of chloroform, methanol and citric acid buffer. However, in recent years several studies reported incomplete or inconsistent separation of lipid classes, depending on minor differences in the polarity of the eluents used during the SPE. Moreover, while PLFA profiles have been tested on microbial pure cultures, the taxonomic specificity of NLFA is only assumed to equal that of PLFA.

Complementary to fatty acid based biomarkers, many studies quantify ergosterol as a reliable indicator for fungal biomass because the fungal-specific PLFA 18:1ω9 and 18:2ω6,9 also occur in plants, which compromises their use for detecting fungal biomass in plant tissue (for example mycorrhizal fungi in plant roots). Measuring ergosterol requires an additional extraction method, but existing protocols include silylation for further gas chromatography analysis and are thus not compatible with determining 13C by IRMS.

Here, we aimed to quantify the recovery of polar and non-polar lipid classes as well as ergosterol following lipid extraction and silica SPE fractionation. We used pure standards of representative phospholipids, glycolipids and neutral lipids with unique fatty acid chain lengths for unambiguous identification of the lipid class after SPE. Lipid fractionation was tested on a 96-well SPE plate with different eluents. Subsequently, we applied the modified method to characterize lipid fractions in microbial pure cultures from bacteria (Proteobacteria, Firmicutes, Actinobacteria), and saprotrophic and ectomycorrhizal fungi (Ascomycota, Basidiomycota).

Separation of lipid classes was achieved by successively eluting NLFA and sterols with a mixture of chloroform and ethanol (v:v = 98:2), glycolipid fatty acids (GLFA) with acetone, and PLFA with a mixture of methanol, chloroform and water (v:v:v = 5:5:1). GLFA were partially recovered in the NLFA or PLFA fraction depending on the nature of the lipid, which should be considered when interpreting PLFA data. Ergosterol recovery was unaffected by subsequent mild alkaline methanolysis of the NLFA fraction in which it was collected, allowing further analysis of both lipid classes in the same mixture. The gas-chromatographic method may be extended to elute both NLFA and (non-silylated) sterols in one run, assuming that the concentration of ergosterol in soil samples is high enough. Therefore, the method can be optimized by using an internal standard added to the NLFA fraction and simultaneously quantify ergosterol. Finally, we show how different lipid classes and attached fatty acid chains distribute in pure cultures of soil micro-organisms.

How to cite: Gorka, S., Canarini, A., Imai, B., Teischinger, G., Darcy, S., and Kaiser, C.: A unified protocol for the high-throughput measurement of PLFA, NLFA, GLFA and sterols from soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17791, https://doi.org/10.5194/egusphere-egu2020-17791, 2020.

EGU2020-18526 | Displays | SSS5.11

Compound-specific isotopic analysis of fatty acids in three soil profiles to estimate organic matter turnover in agricultural soils.

Layla M. San-Emeterio, Ian D. Bull, Jens Holtvoeth, and José Antonio González-Pérez

Soil lipids encompass substances of mainly plant or microbial origin that are insoluble in water and soluble in organic solvents such as ether, hexane, benzene, chloroform or dichloromethane. This soil organic fraction is of great interest because it encompasses biomarkers associated to soil microbial communities, i.e. Gram positive/negative bacteria, mycorrhizae, actinomycetes, etc. and because of its transitory nature that provides insights into soil organic matter (SOM) dynamics and soil carbon turnover. Compound-specific isotope analysis (CSIA) have been used in biomarker studies to investigate the assimilation of carbon from external inputs into SOM. This study determined the distribution and d13C composition of fatty acids as dominant part of the soil lipid fraction to assess turnover times in agricultural practice.

Soil samples were taken from three depth intervals (0-5, 5-20, 20-40 cm) from a Mediterranean agricultural soil at “La Hampa” experimental station used for a crop rotation experiment with wheat (C3 plant) and maize (C4 plant). Using the C4 biosynthetic pathway, maize discriminates less strongly against 13C, i.e. d13C values of fatty acids originating from maize are less negative than those of fatty acids from wheat.

Soil lipids were extracted using a DCM:MeOH (3:1) solvent mixture. Fatty acids were transmethylated with MeOH:acetyl chloride (30:1) to form fatty acid methyl esters (FAMEs) while the hydroxy groups of hydroxy acids, alcohols, sterols and other compounds were silylated using BSTFA prior to analysis by gas-chromatography combustion chamber isotope ratio mass spectrometry (GC-C-IRMS) for carbon isotope ratios. Compounds were identified through their mass spectra by gas-chromatography mass spectrometry (GC-MS) and quantified by gas chromatography with flame ionization detection (GC-FID).

Only two maize harvests after wheat cultivation, a significant 13C enrichment of up to 2 ‰ was found in the saturated C20, C22 and C23 FAMEs and the mono-unsaturated C22 FAME and of up to 5 ‰ in the leaf wax-derived C29 and C31 n-alkanes relative to the control treatments without maize input. No significant differences, however, were found for alcohols and hydroxy acids. These differences may respond to the high specificity of the long-chain n-alkanes from plant origin, whereas the other compounds FAMEs, and mainly alcohols and hydroxyl acids are less specific plant markers and may have a diverse origin.

No significant differences in the isotopic composition were observed at different depths within treatments apart from a slight d13C enrichment of 1.5 ‰ in the upper soil layer (0-5 cm) in the maize plots relative to the deeper layers. It is worth noticing that SOM content remained very low (< 1.3%) over the entire duration of the experiment, with no significant differences despite the high amount of C4 biomass presumably added to the soil during the two growth periods. Together with the d13C enrichment observed in the maize plots, this points to high mineralization rates in these soils and implies both a rapid turnover of plant debris into the SOM.

Acknowledgement: Ministerio de Ciencia Innovación y Universidades (MICIU) for INTERCARBON project (CGL2016-78937-R). L. San Emeterio also thanks MICIU for funding FPI research grants (BES-2017-07968). Mrs Desiré Monis is acknowledged for technical assistance.

 

How to cite: M. San-Emeterio, L., Bull, I. D., Holtvoeth, J., and González-Pérez, J. A.: Compound-specific isotopic analysis of fatty acids in three soil profiles to estimate organic matter turnover in agricultural soils., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18526, https://doi.org/10.5194/egusphere-egu2020-18526, 2020.

EGU2020-19596 | Displays | SSS5.11

Direct soil organic matter compound specific δ13C analysis using pyrolysis (Py-CSIA): identification of biomarkers in a dehesa from Southern Spain

José A. González-Pérez, Lyla M. San Emeterio, Francisco J. González-Vila, María T. Domínguez-Núñez, and José M. de la Rosa

Dehesa are woodlands typical of southern Mediterranean climate species modified by human to seasonal wood-pastures adapted to the unpredictability of the Mediterranean climate. Changes in climatic and environmental conditions can affect both, plant biomass chemical and isotope composition that will eventually be reflected in soil organic matter (SOM). Nowadays, many ecological studies use bulk isotope values, which represent a weighted mean average of the different necromass compounds. An isotopic characterization of individual compounds is desirable to differentiate the isotopic composition of the main plant components. Soil organic matter is composed mainly of high MW biopolymers i.e. polysaccharides, polypeptides, polypeptides, polyesters, etc. not amenable to most chromatographic techniques without the use of intense extraction and sample preparation steps.

Here, an analytical pyrolysis technique combining Py-GC with a continuous flow isotope ratio mass spectrometer (IRMS) (Py-CSIA) is described and validated for the direct study of compound specific isotope composition in soil samples.

The consistency of the Py-CSIA was tested using a standard n-alkanes mixture (dissolved C16 to C30 series with increasing concentrations along three pentads, Indiana Univ. SIL mix. Type B). The values obtained fitted to a straight line (R2 > 0.999). No induced thermal cracking nor deviations from the acclaimed isotope composition (fractionation) was observed up to high pyrolysis temperature (< 500 °C).

Composite dehesa (Pozoblanco , Córdoba, Spain) surface soil samples were taken under evergreen oak canopy . A detailed SOM study was performed using conventional analytical pyrolysis (Py-GC/MS) and δ13C for specific compounds released after pyrolysis was done using Py-CSIA.

Well-resolved chromatograms were obtained by Py-GC/MS and a total of 40 pyrolysis compounds were detected that represented the chemical variability of soil organic matter and consisted mainly of polysaccharide, lignin-derived compounds (G- and S- units), fatty acids and n-alkanes. When coupling Py with GC-C-IRMS, many c peaks were well resolved and with a sufficient chromatographic separation to give accurate δ13C readings. Nonetheless, there were compounds with high δ13C standard deviations considered not sufficiently resolved for a reliable estimation of their isotope composition due to coelution and were discarded.

The δ13C for specific biomass compounds released by pyrolysis of soil was in line with the expected values for C3 plants i.e. Quercus spp. Polysaccharide derived products (furans, cyclopentanones), showed slightly enriched δ13C values (-26.0 ± 0.47 ‰) in accordance with their naturally 13C enriched composition. Although no statistical differences were found, lignin-derived units showed slightly depleted δ13C ( -27.4 ± 0.78 ‰). Accordingly, depleted δ13C values for lipids (-35.1 ± 2.41 ‰) and alkanes (-35.5 ± 2.20 ‰) were found, the latter with lighter isotope composition with increasing the hydrocarbon length.

Here we show the possibility of using this particular analytical pyrolysis technique (Py-CSIA) for the direct measurement of δ13C in relevant specific soil organic matter components including those from polysaccharides (cellulose/hemicellulose), lignin, lipid/waxes and also peptide/protein-derived compounds.

Acknowledgement: Ministerio de Ciencia Innovación y Universidades (MICIU) for INTERCARBON project (CGL2016-78937-R) DECAFUN (CGL2015-70123-R). L. San Emeterio also thanks MICIU for funding FPI research grants (BES-2017-07968). Mrs Desiré Monis & Mr Eduardo Gutiérrez González are acknowledged for technical assistance.

How to cite: González-Pérez, J. A., San Emeterio, L. M., González-Vila, F. J., Domínguez-Núñez, M. T., and de la Rosa, J. M.: Direct soil organic matter compound specific δ13C analysis using pyrolysis (Py-CSIA): identification of biomarkers in a dehesa from Southern Spain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19596, https://doi.org/10.5194/egusphere-egu2020-19596, 2020.

EGU2020-19738 | Displays | SSS5.11

Does C accessibility have an effect on the formation of microbial cell membranes?

Ziwei Zhao, Anna Gunina, and Michaela Dippold

It is well known, that phospholipid fatty acids (PLFAs) are very dynamic, and reflect the living microbial community. The vast majority of previous studies limited its turnover determination to the lipid moiety (“the tail”) of the phospholipids. Thus, it remains unclear how dynamic the head groups of phospholipids are, and whether environmental conditions, i.e. amount of available carbon (C) have an effect on the dynamics of parts of the phospholipid molecule. To answer these questions, the double-labeling 14C/33P-was used in the present experiment. 

The soil was collected from a 45-75 cm depth at the Klein-Altendorf experimental research station Bonn, Germany. The site is an agricultural field for more than 100 years. Formation of PLFA was traced for the two conditions: C limited (2.5 mg glucose-C kg-1 soil added, 1% from microbial biomass C) and C rich (250 glucose-C kg-1 soil added, 100% of MBC). For both conditions, 14C labeled glucose and 33P-K2HPO4 (12.5 mg P kg-1 soil) were added with 1 mL of water and supplemented with (NH4)2SO4 (25 mg N kg-1 soil). These ratios of C/P and C/N were chosen relative to a 100% glucose-C application to reach a ratio of C:P=20:1 and C:N=10:1. The soil was incubated for 10 d, and destructive samplings were performed after 5 h, 19 h, 1, 3, 5, 7 and 10 days, and each time four replicates were harvested. Soils were extracted for PLFAs in 2 steps: first PLFAs were obtained following the standard procedure, but both phospholipid tails and head groups were collected for further 14C and 33P counting. The second step included separate extraction and compound-specific PLFA analysis by GC-MS to reveal changes in the community composition induced by C, N, P addition that might explain de-novo formation of phospholipids.

The peak of 33P incorporation into headgroups under high glucose addition was after 19 h, and accounted 0.3% from the applied tracer, whereas it was up to 1% after low glucose addition and peaked in the middle of incubation time. Incorporation of 14C into the head groups and tails after high glucose addition showed an identical temporal dynamic and was 1.5 times higher in heads than in tails. Both, 33P and 14C incorporation into head and tail had a temporal minimum at day 3 and increased afterwards suggesting two different underlying processes: direct incorporation versus C recycling. After low glucose addition, 14C incorporation was maximum on day 5 but was 3 times lower compared to growth conditions. This shows that even under limited C supply microorganisms construct new phospholipids from available glucose. Irrespective of the C supply, the ratio of head to tail incorporation relative to the ratio of head-to-tail C atoms demonstrates a significantly higher turnover of headgroup C than lipid C, suggesting recycling as an important process to cover microbial lipid demand. Thus, for the first time the different dynamics of phospholipid heads and tails was found and suggest recycling as an important process for growth and maintenance lipid formation.

How to cite: Zhao, Z., Gunina, A., and Dippold, M.: Does C accessibility have an effect on the formation of microbial cell membranes?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19738, https://doi.org/10.5194/egusphere-egu2020-19738, 2020.

EGU2020-22358 | Displays | SSS5.11

VOC analysis in soils – Extending SPME to SPME-trap and SPME-trap with enrichment.

Robert Brown, Jan Peter Mayser, Caroline Widdowson, Dave Chadwick, and Davey Jones

The ability of an agricultural soil to function and sustainably provide an increasing food supply for a rapidly increasing global population has become of vital worldwide importance. Traditionally, soil health has been determined on a physico-chemical basis with biological characteristics often being ignored. Although several biological methods have been proposed, to date, none of these methods adequately indicate soil health. One method proposed to correct these circumstances is profiling or fingerprinting the volatile organic compounds (VOCs) from soil. VOCs in soils originate from a large variety of biological sources; microbial, fungal, animal- and plant-derived. These volatilomes are vital to plant/fungi-microbe and animal/human-microbe interactions and therefore offer a potential reactive, functional diagnostic tool to determine soil health by investigating the intra and interspecies interactions.

The standard methodology for VOC profiling has been solid phase microextraction (SPME). This automated VOC extraction method allows the monitoring of the community structure, physiological state, and activity of any microbial community in a soil without the need of manual extraction or cultivation procedures. Other common techniques that could be used to monitor the VOC fingerprints from soils include high capacity sorptive extraction (HCSE) or thermal desorption using sorbent-packed tubes for passive, in-situ sampling of soil gas.

Combining each of these techniques with an innovative cryogen-free focussing and pre-concentration trap has two main advantages:

  1. All extraction techniques can run on a single platform without the need to change the hardware.
  2. Single (SPME-trap) and multiple extractions (SPME-trap with enrichment) can be carried out automatically on a single sample to increase the analytical sensitivity, thus achieving a comprehensive VOC profile.

In this microcosm study, soils were treated in three different ways and their VOC profiles investigated. A ‘good’ soil comprised of brown earth and compost, a ‘medium’ soil of unaltered brown earth and a ‘bad’ soil of brown earth held under eutrophic anaerobic conditions. 2 g of each soil was analysed with SPME-trap, SPME-trap with enrichment, HCSE and sorbent tubes. Both a targeted (phenol, p-cresol, isophorone, indole and trans-β-ionone) and untargeted approach indicates that there are significant differences between the different soil types. By increasing the sensitivity of the untargeted approach with SPME-trap enrichment, this study was able to extend the number of VOCs identified, allowing a much more comprehensive VOC profile and possibility to determine the actual functions of specific VOC produced by the soil microbial community.

How to cite: Brown, R., Mayser, J. P., Widdowson, C., Chadwick, D., and Jones, D.: VOC analysis in soils – Extending SPME to SPME-trap and SPME-trap with enrichment., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22358, https://doi.org/10.5194/egusphere-egu2020-22358, 2020.

SSS6.4 – Soil water Infiltration: Measurements, assessment and modeling

EGU2020-20212 | Displays | SSS6.4

Infiltration experiments with ultra-high spatial and temporal resolution of saturation measurements

Greg Siemens, Chris Oldroyd, and Ryley Beddoe

Near surface hydrological processes whereby moisture exchange occurs between the vadose zone and above-ground weather systems occur on daily, seasonal, and long-term cycles. Well-controlled laboratory studies of near surface moisture migration are often limited due to number of measurement points of moisture content and pore pressure. This presentation will describe experimental and digital image analysis techniques incorporating a refractive index matched soil-pore fluid combination that increase spatial resolution of saturation measurements by over 6 orders of magnitude. The refractive index matched material changes color from black (Saturation=1) to white (Saturation=0) allowing for saturation measurements at the digital pixel scale. This visualization technique allows for direct observation of flow effects which affect boundary measurements and local flow mechanisms. The capabilities of unsaturated transparent soil are incorporated in a 2D infiltration apparatus to examine the influence of confined air on infiltration. 2D experiments agree with previous column infiltration results showing air confinement decreases infiltration rate by more than one half. The 2D apparatus allows a clear unstable wetting front to develop, visualization of dynamic moisture migration within the transmission zone. In addition, the high spatial resolution saturation measurements show detectable influence of thin heterogeneities on wetting front migration and the influence of flow direction on saturation distribution. The high-resolution saturation measurements will allow for calibration of computational models multi-phase flow and open up new insight into near surface processes to improve water balance calculations and soil-structure-climate interactions.

How to cite: Siemens, G., Oldroyd, C., and Beddoe, R.: Infiltration experiments with ultra-high spatial and temporal resolution of saturation measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20212, https://doi.org/10.5194/egusphere-egu2020-20212, 2020.

Classic soil physics relies heavily on the concept of representative elementary volume (REV), which is necessary to perform upscaling from the studied soil samples and parameterize continuum scale hydrological models (e.g., based on Richards equation). In this paper we explore the boundaries of the classic REV concept and conventional representativity studies that claim REV for a given physical property if its values converge to a steady value with increasing sample’s volume. We chose two conventional undisturbed soil samples from Ah and B horizons and performed pore-scale flow simulations based on their X-ray microtomography scans. The volumes of the simulation domains were 729 million of voxels with a physical volume within the order of magnitude of the whole soil core. Based on 3D pore geometry images and resulting flow velocity and pressure fields we performed REV analysis for saturated hydraulic conductivity and porosity. To further facilitate the REV analysis, we also evaluated the stationarity of pore structures by computing directional correlation functions for studied images. We concluded that neither of the studied samples can be considered to be representative due to its structural non-stationarity, which reflects on the behavior of Ksat values within the subcubes of different volume within the samples. In this contribution we extensively discuss the implications of such results. While it was possible to show that studied soil samples are not REVs for saturated hydraulic conductivity, we were unable to establish any relevant domain length scale. The latter may require tensorial flow property analysis with correct boundary conditions (Gerke et al., 2019), multi-scale soil structure imaging (Gerke et al., 2015; Karsanina et al., 2018; Karsanina and Gerke, 2018) and pore-scale simulations on fused multi-scale images (Miao et al., 2017; Gerke et al., 2018).

This work was supported by Russian Foundation for Basic Research grant 20-54-12030 ННИО_а and 18-34-20131 мол_а_вед.

References:

Karsanina, M. V., Gerke, K. M., Skvortsova, E. B., Ivanov, A. L., & Mallants, D. (2018). Enhancing image resolution of soils by stochastic multiscale image fusion. Geoderma, 314, 138-145.

Gerke, K. M., Karsanina, M. V., & Mallants, D. (2015). Universal stochastic multiscale image fusion: an example application for shale rock. Scientific reports, 5, 15880.

Gerke, K. M., Vasilyev, R. V., Khirevich, S., Collins, D., Karsanina, M. V., Sizonenko, T. O., Korost D.V., Lamontagne S., & Mallants, D. (2018). Finite-difference method Stokes solver (FDMSS) for 3D pore geometries: Software development, validation and case studies. Computers & Geosciences, 114, 41-58

Karsanina, M. V., & Gerke, K. M. (2018). Hierarchical Optimization: Fast and Robust Multiscale Stochastic Reconstructions with Rescaled Correlation Functions. Physical Review Letters, 121(26), 265501.

Miao, X., Gerke, K. M., & Sizonenko, T. O. (2017). A new way to parameterize hydraulic conductances of pore elements: A step towards creating pore-networks without pore shape simplifications. Advances in Water Resources, 105, 162-172.

Gerke, K. M., Karsanina, M. V., & Katsman, R. (2019). Calculation of tensorial flow properties on pore level: Exploring the influence of boundary conditions on the permeability of three-dimensional stochastic reconstructions. Physical Review E, 100(5), 053312.

How to cite: Gerke, K. and Karsanina, M.: How representative is the conventional undisturbed soil core sample in terms of fllow properties?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10841, https://doi.org/10.5194/egusphere-egu2020-10841, 2020.

Increase in impermeable area and frequency of intense rainfall cause flooding damages in urban areas. Permeable Interlocking Concrete Paver (PICP) system, which is a composite system comprised of soils and blocks, is considered as one of the solutions to improve the urban water environment, and its applications are increasing rapidly worldwide. It is important to evaluate the initial permeability and its reduction due to clogging. In this study, the permeability and effect of clogging were evaluated based on experimental methods developed. The equivalent permeability and its degradation of PICP systems were successfully evaluated using the prodecure developed, and the equation for equivalent permeability presented quite a good agreement with the experimental results.

ACKNOWLEDGEMENT : The authors would like to thank the Ministry of Land, Infrastructure, and Transport of Korean government for the grant from Technology Advancement Research Program (grant no. 20CTAP-C152124-02) and Basic Science Research Program (grant no. 2017R1D1A3B03034563) through the National Research Foundation of Korea (NRF) funded by the Ministry of Education.

How to cite: Ahn, J. and Lee, Y.: Experimental Evaluation of Equivalent Permeability for Permeable Interlocking Concrete Paver (Soil-Block) Composite System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7434, https://doi.org/10.5194/egusphere-egu2020-7434, 2020.

EGU2020-14653 | Displays | SSS6.4

Numerical assessment of chemical species infiltration in the Prosecco area

Leonardo Costa, Stefano Mazzega Ciamp, Alessandra Cardinali, Laura Carretta, Nicola Dal Ferro, Marta Mencaroni, Francesco Morari, Giuseppe Zanin, and Paolo Salandin

The multidisciplinary research project SWAT - Subsurface Water quality and Agricultural pracTices monitoring - has been set up to assess pesticides contamination risks for groundwater in the hills of Prosecco in the north-east of Italy. The unconfined aquifer underneath the typical Glera grape-variety vineyards of Valdobbiadene and Conegliano is used as water supply resource for human consumption. The principal aim of the project SWAT is to obtain a thorough information on the impact of contaminants coming from agricultural practices and infiltrating in the soil of well protection areas. Based on specifically designed field experiments, a study on water and solutes infiltration process is developed to understand the movement and evolution of chemical species in the vadose zone. A one-dimensional transport model for unsaturated media (BRTSim - Maggi, 2015) is used to simulate solute infiltration and estimate the soil hydraulic parameters. Monitoring activities started in November 2018 in two experimental sites (the Settolo site in Valdobbiadene and the Colnù site in Conegliano) near supply wells surrounded by vineyards. A mixture of Bromide and Glyphosate was identically applied on two parcels of 25 m2 for each experimental site to obtain information about spatial heterogeneity and to collect independently water and soil quality measurements. Porous cups, for the collection of infiltrating water, and capacitive sensors, to gauge temperature and Volumetric Water Content (VWC), were installed beneath the sectors at three depths (-0.1, -0.3, -0.7 m). In each site meteorological station provides hydrological data. At first, laboratory analysis on soil samples collected at the same depths gave a vertical distribution of the sector-specific soil texture that was used as input for Rosetta to obtain initial estimations of retention curve behaviour and the saturated hydraulic conductivity. These data allowed us to develop an open-loop simulation using the early meteorological observations as hydrological forcing. As the laboratory analysis on soil and water samples proceed and the number of in-situ measurements increases, different data windows are tested to improve the performances of the calibration procedure performed using PEST. In all tests a spin-up procedure is applied to mitigate the dependency of the results on the imposed initial data by repeating the first month of hydrological forcing three times. The results of the transport model using Rosetta parameters are already satisfactory in terms of VWC trends even if they are considerably shifted respect to the measured values. The calibration reduces the gap between model results and observations, but the behaviour seems to get worse in dry conditions. Improvements are achieved in the upper layer (-0.3 m) applying evapotranspiration along the root zone. The Bromide simulations agree with the infiltration behaviour: its movement is well represented up to -0.3 m, while at -0.7 m the observed values are overestimated. Ongoing investigations on the glyphosate dispersion process show limited infiltrating mass in the water collected samples.

How to cite: Costa, L., Mazzega Ciamp, S., Cardinali, A., Carretta, L., Dal Ferro, N., Mencaroni, M., Morari, F., Zanin, G., and Salandin, P.: Numerical assessment of chemical species infiltration in the Prosecco area,