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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 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.

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.

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.

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.

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.

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.

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 5^o and 30^o. 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.

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.

Mediterranean mid-mountain areas have been subject to significant human pressure through deforestation, cultivation of steep slopes, fires and overgrazing. However, during the 20^th 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

            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.

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.

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.

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.

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.

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.

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.

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.

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.

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 26^th, 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.

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.

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.

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

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

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

References:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

References

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

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

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

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

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