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.