Mean Soil Erosion Rate Research Articles

The Effect of Land Cover Change on Soil Erosion in Awach Kibuon Sub-basin, Kenya

Land cover change is a significant driver of soil erosion. While soil erosion is a natural process, human activities can significantly alter the landscape, making soil more vulnerable to erosion. This erosion reduces a watershed's capacity to sustain vital natural resources and ecosystem services. This study investigated the impact of these changes on soil erosion within four hydrological units (Awach Kibuon, Awach Owade, Awach Kasipul, and Awach Kabondo) of the Awach Kibuon sub-basin between 2018 and 2023. The specific objective of the study was to quantify the effect of land cover change on soil erosion rate and determine how specific land cover types affect soil erosion in the study area. This study employed a quasi-longitudinal design to assess the influence of land cover changes on soil erosion. Sentinel-2 NDVI satellite imagery provided land cover data. The land cover maps, soil data, rainfall data and the Digital Elevation Model were used in the Revised Universal Soil Loss Equation Model within a GIS environment to estimate soil erosion rates. The study revealed a consistent decline in vegetation cover across all hydrological units, as indicated by a decrease in NDVI. The mean NDVI decreased by 12.88%, 10.92%, 4.78%, and 11.92% in Awach Kibuon, Awach Owade, Awach Kasipul and Awach Kabondo respectively. Conversely, the mean soil erosion rate increased by 23.9% in Awach Kibuon, 17.85% in Awach Owade, 24.43% in Awach Kasipul, and 20.54% in Awach Kabondo. Sediment yield increased by 33% in Awach Kibuon, 18% in Awach Owade, 17% in Awach Kasipul, and 23% in Awach Kabondo. These findings suggest a direct relationship between reduced vegetation and elevated soil erosion. The relationship between land cover and erosion varies depending on the density of vegetation. Areas with dense vegetation cover have an inverse relationship, highlighting the protective role of vegetation cover. However, the study also observed that very dense vegetation areas which were also found in high-sloped areas experienced high soil erosion rates. The erosion rate increases even in areas that have experienced an increase in vegetation cover. This is because these areas are also found in high-sloped areas. The slope factor superseded the ability of vegetation cover to protect against soil loss. In conclusion, the change in land cover has significantly increased soil erosion in the Awach Kibuon Sub-basin, however, the slope factor also accelerated soil loss in the basin. Therefore, a holistic approach that combines promoting vegetation cover with land management techniques like terracing and drainage channels is crucial for mitigating soil degradation and water sedimentation in sub-basin.

Spatial Quantification of Cropland Soil Erosion Dynamics in the Yunnan Plateau Based on Sampling Survey and Multi-Source LUCC Data

The mapping and dynamic monitoring of large-scale cropland erosion rates are critical for agricultural planning but extremely challenging. In this study, using field investigation data collected from 20,155 land parcels in 2817 sample units in the National Soil Erosion Survey, as well as land use change data for two decades from the National Land Use/Cover Database of China (NLUD-C), we proposed a new point-to-surface approach to quantitatively assess long-term cropland erosion based on the CSLE model and non-homologous data voting. The results show that cropland in Yunnan suffers from serious problems, with an unsustainable mean soil erosion rate of 40.47 t/(ha·a) and an erosion ratio of 70.11%, which are significantly higher than those of other land types. Engineering control measures (ECMS) have a profound impact on reducing soil erosion; the soil erosion rates of cropland with and without ECMs differ more than five-fold. Over the past two decades, the cropland area in Yunnan has continued to decrease, with a net reduction of 7461.83 km2 and a ratio of −10.55%, causing a corresponding 0.32 × 108 t (12.12%) reduction in cropland soil loss. We also quantified the impact of different LUCC scenarios on cropland erosion, and extraordinarily high variability was found in soil loss in different basins and periods. Conversion from cropland to forest contributes the most to cropland erosion reduction, while conversion from grassland to cropland contributes 56.18% of the increase in soil erosion. Considering the current speed of cropland regulation, it is the sharp reduction in land area that leads to cropland erosion reduction rather than treatments. The choice between the Grain for Green Policy and Cropland Protecting Strategy in mountainous areas should be made carefully, with understanding and collaboration between different roles.

Understanding the linkages between land-use transitions and soil erosion/sediment deposition: A case study of the transboundary Sio-Malaba-Malakisi watershed in Kenya and Uganda

Soil erosion consequent of unsustainable land-use practices represents one of the world's most pressing environmental problems affecting many watersheds. An assessment of sediment sources and delivery paths is essential for the development of site-specific soil management strategies for curbing environmental degradation. The present study employed a physically-based lumped approach to estimate soil erosion and sediment deposition patterns across the transboundary Sio-Malaba-Malakisi (SMM) watershed. The Unit Stream Power-based Erosion Deposition (USPED) model was adopted for the study, and integrated with physically-based parameters derived in a Geographical Information System (GIS). A land-use map for 2017 was used for simulating the reference soil erosion and deposition status of the basin. Furthermore, the impacts of two land-use scenarios representing options for cropland expansion (Scenario-I), and land reclamation (Scenario-II), were evaluated for the period 2047, corresponding to a thirty-year period used in assessing catchment management planning for SMM. The annual soil erosion ranged between 0 and 460 t. ha−1yr−1, with a mean erosion rate of 160 t.ha−1yr−1 for the baseline condition. Deposition zones were mainly concentrated along stream banks and floodplain in low-lying sub-catchments. The mean soil erosion rate increased by 61 % and 16 % for scenarios I and II respectively. Overall, the modelled erosion/deposition values were correlated with available sediment data for the basin, realizing a coefficient determination (R2) value of 0.74. These results could serve as a benchmark against which future trends in land-use changes can be compared in the region and hence support the development of regional soil erosion conservation strategies.

How does straw-incorporation rate reduce runoff and erosion on sloping cropland of black soil region?

Straw-incorporation has been widely utilized as an important practice for agricultural soil carbon sequestration, but few studies have been performed to investigate its impact on cropland runoff and erosion. In this study, the relationships between straw-incorporation rate and cropland runoff and erosion were quantified through field observations in the black soil region of Northeast China. Runoff and erosion were significantly influenced by straw-incorporation rate. Compared to the treatment without straw-incorporation, the mean runoff depth and soil erosion rate of seven observed rainfall events reduced by − 0.04–0.72 mm and − 3.34–15.34 t km−2. Under different straw-incorporation rates, the runoff reduction percentage (RRP) and erosion reduction percentage (ERP) varied from 7.3% to 90.3% and − 4.2–92.5%, with the means of 62.5% and 61.4%. RRP was mainly attributed to plant coverage, root mass density and the maximum 30-minute rainfall intensity, while plant coverage, leaf area index and the maximum rainfall intensity of ten minute were identified as the main factors influencing ERP. These parameters could explain 47%, 6%, 47% and 45%, 44%, 11% of total variations of soil erosion and runoff, respectively. Overall, straw-incorporation was effective in mitigating runoff and erosion under non-extreme rainfall event when straw-incorporation rate was greater than 4.5 t hm−2. Straw-incorporation rate of 9 t hm−2 had the best benefits to control runoff and erosion, followed by 13.5 t hm−2, while 1.125 t hm−2 had the least benefits. Our results highlight an importance of straw-incorporation in reducing cropland runoff and erosion and the implication for controlling soil erosion and associated environment problems by selecting best crop straw managements in semi-humid region of the world.

Effect of climate change on soil erosion indicates a dominance of rainfall over LULC changes

Study regionMahanadi River Basin in India Study focusThis study explores the effect of climate change and human-induced farming and construction activities on soil erosion in a rainfed basin during two time periods viz. 1981–2000 and 2001–2019. This study assesses erosion using the Geographic Information System integrated Revised Universal Soil Loss Equation (GIS-integrated RUSLE) model. Three different analyses are designed to assess the effect i) combined effect of change in all the RUSLE factors over these two time periods, ii) effect of only land use/cover change (LULC), and iii) only rainfall change impact on erosion rate. A modified sediment delivery ratio (SDR) has been proposed and the model performances are validated using the observed Sediment Yield data. New hydrological insights for the regionThe results indicate an overall decrease in the erosion rate as a combined effect of change in all the factors, but at the same time, an increase in the spatial extent of the areas affected by soil erosion is noticed. The mean soil erosion rate varies between 37.02 tons ha⁻¹ yr⁻¹ in 1981–2000 and 31.89 tons ha⁻¹yr⁻¹ in 2001–2019, with a 40% decrease in the maximum erosion rate, while the total and mean erosion rates are both down 13.85% compared to 1981–2000. The analysis suggested overall effect of the change in rainfall is more profound on erosion than LULC change.

Impacts of Soil Erosion on Soil Quality and Agricultural Sustainability in the North-Western Himalayan Region of India

Erosion by water reduces soil quality and hence crop yield. Understanding the response of crop yields to soil erosion is vital in assessing agriculture’s vulnerability to erosion. However, these effects are difficult to quantify. The study presents a quantitative relationship between soil erosion and soil quality and productivity of rainfed wheat (Triticum aestivum) by comparing field plots with different degrees of erosion in some sub-tropical alfisols in the Doon Valley region of India. By comparing the topsoil depth with the reference site as the control, erosion severity was classified into different phases such as slight, moderate, severe, and very severe. A quantitative, weighted additive model was used to evaluate soil quality for different phases of erosion using soil clay content, water holding capacity, soil aggregate, soil organic carbon, pH, CEC, total N, available P, and available K. The synthesis of long-term experimental data revealed that the mean soil erosion rate varied from 5.5 Mg ha−1 yr−1 in slightly eroded plots to 33.4 Mg ha−1 yr−1 in very severely eroded plots. Compared with the reference forest, the soil organic carbon (SOC) declined by 81.4% and water holding capacity by 31% in severely eroded soils. A substantial loss of total N, extractable P, and available K was also observed. Water stable aggregates (WSA) decreased from 86% to 12.6%, and the cation exchange capacity (CEC) from 25 to 12.6 c mol(+) kg−1. The soil quality index was 0.7 in slightly eroded compared with 0.4 in severely eroded soil. Similarly, the sustainable yield index for wheat was 0.9 and 0.6 for slightly and severely eroded soils, respectively. Thus, there is a strong need to identify land management systems that reduce erosion risks, restore eroded soils, and enhance soil quality.

Agricultural practices drive elevated rates of topsoil decline across Kenya, but terracing and reduced tillage can reverse this

As agricultural land area increases to feed an expanding global population, soil erosion will likely accelerate, generating unsustainable losses of soil and nutrients. This is critical for Kenya where cropland expansion and nutrient loading from runoff and erosion is contributing to eutrophication of freshwater ecosystems and desertification. We used the Revised Universal Soil Loss Equation (RUSLE) to predict soil erosion rates under present land cover and potential natural vegetation nationally across Kenya. Simulating natural vegetation conditions allows the degree to which erosion rates are elevated under current land use practices to be determined. This methodology exploits new digital soil maps and two vegetation cover maps to model topsoil (top 20 cm) erosion rates, lifespans (the mass of topsoil divided by erosion rate), and lateral nutrient fluxes (nutrient concentration times erosion rate) under both scenarios. We estimated the mean soil erosion rate under current land cover at ~5.5 t ha−1 yr−1, ~3 times the rate estimated for natural vegetation cover (~1.8 t ha−1 yr−1), and equivalent to ~320 Mt yr−1 of topsoil lost nationwide. Under present erosion rates, ~8.8 Mt, ~315 Kt, and ~ 110 Kt of soil organic carbon, nitrogen and phosphorous are lost from soil every year, respectively. Further, 5.3 % of topsoils (~3.1 Mha), including at >25 % of croplands, have short lifespans (<100 years). Additional scenarios were tested that assume combinations of terracing and reduced tillage practices were adopted on croplands to mitigate erosion. Establishing bench terraces with zoned tillage could reduce soil losses by ≥75 %; up to 87.1 t ha−1 yr−1. These reductions are comparable to converting croplands to natural vegetation, demonstrating most agricultural soils can be conserved successfully. Extensive long-term monitoring of croplands with terraces and reduced tillage established is required to verify the efficacy of these agricultural support practices as indicated by our modelling.

Application of the Adapted Approach for Crop Management Factor to Assess Soil Erosion Risk in an Agricultural Area of Rwanda

Land use and land cover (LULC) management influences the severity of soil erosion risk. However, crop management (C) is one factor of the Revised Universal Soil Loss Equation (RUSLE) model that should be taken into account in its determination, as it influences soil loss rate estimations. Thus, the present study applied an adapted C-factor estimation approach (CvkA) modified from the former approach (Cvk) to assess the impact of LULC dynamics on soil erosion risk in an agricultural area of Rwanda taking the western province as a case study. The results disclosed that the formerly used Cvk was not suitable, as it tended to overestimate C-factor values compared with the values obtained from t CvkA. An approximated mean soil loss of 15.1 t ha−1 yr−1, 47.4 t ha−1 yr−1, 16.3 t ha−1 yr−1, 66.8 t ha−1 yr−1 and 15.3 t ha−1 yr−1 in 2000, 2005, 2010, 2015 and 2018, respectively, was found. The results also indicated that there was a small increase in mean annual soil loss from 15.1 t ha−1 yr−1 in 2000 to 15.3 t ha−1 yr−1 in 2018 (1.3%). Moreover, the soil erosion risk categories indicated that about 57.5%, 21.8%, 64.9%, 15.5% and 73.8% had a sustainable soil erosion rate tolerance (≤10 t ha−1 yr−1), while about 42.5%, 78.2%, 35.1%, 84.5% and 16.8% had an unsustainable mean soil erosion rate (&gt;10 t ha−1 yr−1) in 2000, 2005, 2010, 2015 and 2018, respectively. A major portion of the area fell under the high and very high probability zones, whereas only a small portion fell under the very low, low, moderate and extremely high probability zones. Therefore, the CvkA approach presents the most suitable alternative to estimate soil loss in the western province of Rwanda with reasonable soil loss prediction results. The study area needs urgent intervention for soil conservation planning, taking into account the implementation of effective conservation practices such as terracing for soil erosion control.

Projections of soil loss by water erosion in Europe by 2050

Changes in future soil erosion rates are driven by climatic conditions, land use patterns, socio-economic development, farmers’ choices, and importantly modified by agro-environmental policies. This study simulates the impact of expected climatic and land use change projections on future rates of soil erosion by water (sheet and rill processes) in 2050 within the agricultural areas of the European Union and the UK, compared to a current representative baseline (2016). We used the Revised Universal Soil Loss Equation (RUSLE) adjusted at continental scale with projections of future rainfall erosivity and land use change. Future rainfall erosivity is predicted using an average composite of 19 Global Climate Models (GCMs) from the Coupled Model Inter-comparison Projects (CMIP5) WorldClim dataset across three Representative Concentration Pathways (RCP2.6, RCP4.5 and RCP8.5). Concerning future land use change and crop dynamics, we used the projections provided by the Common Agricultural Policy Regional Impact Analysis (CAPRI) model.Depending on the RCP scenario, we estimate a +13 %-22.5 % increase in the mean soil erosion rate in the EU and UK, rising from an estimated 3.07 t ha−1 yr−1 (2016) to between 3.46 t ha−1 yr−1 (RCP2.6 scenario) and 3.76 t ha−1 yr−1 (RCP8.5 scenario). Here, we disentangle the impact of land use change and climate change in relation to future soil losses. Projected land use change in the EU and UK indicates an overall increase of pasture coverage in place of croplands. This land use change is estimated to reduce soil erosion rates (-3%). In contrast, the increases in future rainfall erosivity (+15.7 %–25.5 %) will force important increases of soil erosion requiring further targeted intervention measures.Given that agro-environmental policies will be the most effective mechanisms to offset this future increase in soil erosion rates, this study proposes soil conservation instruments foreseen in the EU Common Agricultural Policy (CAP) to run policy scenarios. A targeted application of cover crops in soil erosion hotspots combined with limited soil disturbance measures can partially or completely mitigate the effect of climate change on soil losses. Effective mitigation of future soil losses requires policy measures for soil conservation on at least 50 % of agricultural land with erosion rates above 5 t ha−1 yr−1.

Soil erosion and properties as affected by fire and time after fire events in steep rangelands using 137Cs technique

Post-fire erosion is a main concern to society because it has inflicted serious damages in managed ecosystems. In this study, the impacts of fire and time after fire events on soil erosion (as predicted using 137Cs technique) and on some soil chemical and physical properties were investigated in steep rangelands of western Iran. Three sites in rangelands with similar slope gradients and parent materials were selected, and within each site, the burnt (1, 5, and 10 years after the fire events) and the unburnt treatments were studied and soil samples were collected from five depths (0–2.5, 2.5–5, 5–10, 10–20, and 20–40 cm) with three replicates. The results indicated that soil organic matter (SOM), total nitrogen (TN), available phosphorus (Pava), available potassium (Kava), electrical conductivity (EC), and bulk density (BD) were significantly different between burnt and unburnt treatments for two times (1 and 5 years) after fire events. No significant difference by Duncan’s test was obtained for these properties between the 10 and 5 years after fire events. In addition, clay and sand contents and magnetic measures (χlf, χhf) were significantly different between burnt and unburnt treatments for all the three times after fire. The results of soil erosion by the 137Cs technique showed that profile distribution model (PDM) estimated the mean soil erosion rate of 38.9 and 23.02 Mg ha−1 year−1 in the three studied years in the burnt and the unburnt rangelands, respectively. Fire events increased soil erosion rate and altered soil physical, chemical, and magnetic properties in the studied steep rangelands. Overall, the results confirmed that the 137Cs technique could be used as a rapid and efficient model to determine soil degradation in the rangelands. The fire diminished soil organic matter and, subsequently, reduced aggregate stability, and increased soil erosion and degradation in the burnt rangelands. Hence, understanding historical contexts of fire occurrences is paramount to increase our capacity for ecological transformations and management in the face of the critical situation.

Modeling predictive assessment of soil erosion related hazards at the Uva province in Sri Lanka

At present, soil erosion is one of the most prominent environmental and socio-economic concerns in Sri Lanka and identification of soil erosion hazard zones is crucial for applying effective soil and water conservation measures. Thus, the study assessed the soil erosion and generated soil erosion hazard zonation map for the Uva province in Sri Lanka by means of the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) Sediment Delivery Ratio (SDR) model, which was developed as part of the Natural Capital Project, a partnership between Stanford University-USA, the Nature Conservancy (TNC), and the World Wildlife Fund (WWF), working with many other institutions. The estimated mean soil erosion rate of Uva province was 25.6 t ha−1 year−1 and which is ~ 3 times greater than the soil loss tolerance in Sri Lanka. However, the soil erosion rates of the major basins in the province ranged between 0.9 and 117.8 t ha−1 year−1. Based on this study, province was classified into five soil erosion hazard classes viz. low (0–5 t ha−1 year−1), moderate (5–12 t ha−1 year−1), high (12–25 t ha−1 year−1), very high (25–60 t ha−1 year−1), and extremely high (60 < t ha−1 year−1) and the study revealed that under the existing land use scenario, 73.5% of the land area falls into low soil erosion hazard category while 11.7%, 2.1%, 1.6% and 11.10% of the areas falls into moderate, high, very high and extremely high soil erosion hazard categories respectively. Moreover, the soil erosion hazard status of the Uva province clearly indicates that the soil erosion occurring in the province are related to the improper land use practices and resulted in copious environmental and socio-economics problems. Hence, the findings of the study suggest that the implementation of sustainable watershed management options is crucial to mitigate present soil erosion and to enhance the quality of the watershed.

Space-Time Drought Dynamics and Soil Erosion in Puruliya District of West Bengal, India: A Conceptual Design

This paper integrates drought and soil erosion problems of Puruliya district of West Bengal. The space-time dynamics of vegetative drought is assessed based on the mean monthly time-series MODIS data for the period of 2000–2013. The drought recurrence ranges from 0 to 29 months, and the mean frequency was assessed to be 7.09 months for the entire period under deliberation. The potential soil disintegration of the district was estimated using the Revised Universal Soil Loss Equation in the geo-spatial environment. The locale has been arranged into six potential soil erosion classes ranging from low-to-severe risk depending upon the computed soil erosion amount. The mean soil erosion rate of the district was anticipated as 76.29 t ha−1 year−1. The erosion amount is high in gently sloping grounds covering mainly harvested agricultural fields and open fields. These areas contribute mostly the soil erosion in this district. It is found that in this area the slope length-steepness factor is the major erosion-controlling factor. About one-fourth of the total area comes under the threat of a very high-to-severe erosion zone. Also, it was observed that the drought condition of the district is strongly correlated with the soil moisture condition in the drought-affected months and the precipitation amount. The study likewise distinguished the conceivable interrelationship between the soil erosion problem and drought frequency for better monitoring and policy decision making. A considerable increasing trend is observed in mean soil erosion with increasing frequency of drought-affected months for the study period.

Quantifying farmland shelterbelt impacts on catchment soil erosion and sediment yield for the black soil region, northeastern China

AbstractAs one part of the ‘Three Norths’ forest protection system, dense farmland shelterbelt networks in northeastern China could greatly modify water and sediment flows. In this paper, catchment soil erosion rate and sediment yield (SY) that are impacted by farmland shelterbelts were estimated using WaTEM/SEDEM model. The shelterbelts reduced catchment soil erosion and SY to some extent. The mean soil erosion rate and specific sediment yield (SSY; defined as the ratio of SY to catchment area; t km−2 yr−1) of the 25 reservoir catchments decreased from 351.6 and 93.9 t km−2 yr−1 under the supposed scenario without shelterbelts to 331.1 t km−2 yr−1 and 86.3% t km−2 yr−1 under the current situation with shelterbelts. The sediment trap efficiencies (STEs) varied from 0.01% to 23.6% with an average value of 7.6%. The STEs were significantly correlated with shelterbelt density, catchment perimeter, topographic factors, RUSLEP‐factor and land use patterns including patch density (PD), patch cohesion index (COHESION), Shannon's diversity index (SHDI) and aggregation index (AI). The multiple regression equation involving factors of catchment's topography and morphology and land use pattern has a satisfactory performance, and mean slope gradient (MSG) and AI explained most of the variability of shelterbelts’ STE. This information can help land managers to better design shelterbelts and to reduce water‐derived soil loss at catchment scale.

Estimation of Soil Erosion in Nepal Using a RUSLE Modeling and Geospatial Tool

Soil erosion is a major issue, causing the loss of topsoil and fertility in agricultural land in mountainous terrain. Estimation of soil erosion in Nepal is essential because of its agriculture-dependent economy (contributing 36% to national GDP) and for preparing erosion control plans. The present study, for the first time, attempts to estimate the soil loss of Nepal through the application of the Revised Universal Soil Loss Equation (RUSLE) model. In addition, it analyzes the effect of Land Use and Land Cover (LULC) and slope ( β ) exposition on soil erosion. Nation-wide mean annual soil loss of Nepal is estimated at 25 t ha−1 yr−1 with a total of 369 million tonnes (mT) of potential soil loss. Soil erosion based on the physiographic region of the country shows that the Middle Mountains, High Mountains, High Himal, Chure, and Terai have mean erosion rates of 38.0, 32.0, 28.0, 7.0, and 0.1 t ha−1 yr−1. The soil erosion rate by basins showed that the annual erosions of the Karnali, Gandaki, Koshi, and Mahakali River basins are 135, 96, 79, and 15 mT, respectively. The mean soil erosion rate was significantly high (34 t ha−1 yr−1) for steep slopes (β &gt; 26.8%) and the low (3 t ha−1 yr−1) for gentle slopes (β &lt; 5%). Based on LULC, the mean erosion rate for barren land was the highest (40 t ha−1 yr−1), followed by agricultural land (29 t ha−1 yr−1), shrubland (25 t ha−1 yr−1), grassland (23 t ha−1 yr−1), and forests (22 t ha−1 yr−1). The entire area had been categorized into 6 erosion classes based on the erosion severity, and 11% of the area was found to be under a very severe erosion risk (&gt; 80 t ha−1 yr−1) that urgently required reducing the risk of erosion.

Holocene evolution of closed depressions and its relation to landscape dynamics in the loess areas of Poland

Past Pleistocene topography of the loess uplands is rich in local sinks (closed depressions (CDs)) influencing sediment fluxes. Soil-sediment sequences from CDs constituting geoarchives where landscape changes under natural and anthropogenic conditions have been recorded. Pedo-sedimentary archives from 10 CDs in the Polish loess belt and human settlements were analysed. Phases of the Holocene evolution of the CDs were correlated with landscape dynamics in loess areas in Poland and Central Europe. Phases of infilling of CDs occurring (2) from the late Boreal/early Atlantic Period until the (middle) late Bronze Age/early Iron Age and (4) since the early Middle Ages until today were documented. These were phases of long-term soil erosion and colluviation corresponding to the increasing agricultural land use of Polish loess uplands. Phases of soil formation related to geomorphic stabilization of CDs occurred (1) from the late Vistulian until the late Boreal/early Atlantic Period and (3) from the late Bronze Age/early Iron Age until the early/high Middle Ages. These were phases of decreased soil erosion and landform conservation in a considerable part of Poland’s loess areas. Pedo-sedimentary archives from the CDs have recorded soil erosion strongly related with human-induced land-use changes. The mean soil erosion rate in the catchment of CDs was 0.33 t·ha−1·yr−1 during prehistory and 4.0 t·ha−1·yr−1 during the last approximately 1000 years. Phases of CD evolution are representative for the main phases of sediment and landscape dynamics in Poland’s loess areas recorded in various archives, and are not synchronous with some of these phases in Central Europe.

Reconstructing recent changes in sediment yields from a typical karst watershed in southwest China

Southwest China is characterized by shallow soils with low soil loss tolerance (30–68 t km−2 yr-1), and this region is one of the largest contiguous karst areas in the world, notorious for its highly eroded landscapes. However, reliable information on soil erosion rates in these karst watersheds is limited due to the highly heterogonous landscape. Karst depressions are a unique geomorphologic pattern in southwest China which can trap eroded sediment similar to a reservoir or dam, and may provide a great opportunity for sediment yield estimation if the sediment chronology can be properly determined. This study used karst depression sediment deposits to reconstruct the changes in sediment yields over the past 60 years from a typical karst watershed in southwest China. Three sediment cores were collected from the depression to measure the changes in 137Cs and 210Pbex, clay, silt, and sand contents, and soil organic carbon at different depths. The results indicated that the three common 210Pbex dating models - Constant Sedimentation (CFCS), Constant Initial Concentration (CIC), and Constant Rate of Supply (CRS) - were not applicable to karst depressions, while a modified CRS model that used 137Cs age marker as reference improved determination of the sediment chronology. From 1949 to 2015, the sediment yields initially increased and then sharply decreased to a low value, which might represent a general trend of soil erosion dynamics in karst watershed of southwest China. It was noteworthy that the mean soil erosion rate after the “Grain for Green” project of 1999 was only 80 t km−2 yr-1, which also is greater than the soil loss tolerance in karst regions. This study demonstrates the potential for use of 137Cs and 210Pbex to evaluate the temporal variation in sediment yield in a typical karst watershed of southwest China and may improve karst watershed management.

Impacts of land use changes and land cover alteration on soil erosion rates and vulnerability of tropical mountain ranges in Borneo

The evaluation of the impact of changes in land use on soil erosion rates and vulnerability was carried out in a tropical rainforest region of Sarawak, Borneo. Although tropical rainforest covers over 88% of the study area, supervised classification of Landsat 8 Optical Land Imager (OLI) images identified eight other classes of land cover (LC) (mixed agriculture, hill paddy, wet paddy, bushes/shrubs/grasses, exposed barren land, artificial surface, pebbles / cobbles and waterbody) with an overall classification accuracy above 80%. Maximum rate of soil loss estimated from the study area through Revised Universal Soil Loss Equation (RUSLE) was 1312 t ha−1y−1 and the result aided the identification of regions with critical soil erosion vulnerability. Mean soil erosion rate in the study area was assessed to be 27 t ha−1 y−1. The zones with higher soil erosion rates exceed 25 t ha−1y−1 and amounted to a total area of 11%. Critical erosion zones (> 50 t ha−1 y−1) were found to cover 8% and show linear characteristics which is innate of logging roads and skid trails. At the same time, over 64% of the study area showed low erosion risk with soil losses lower than 5 t ha−1 y−1. Assessment made through geospatial overlay indicates dominance of four LC classes in contributing to soil erosion vulnerability and erosion rates. These are exposed barren land, secondary forest, bushes/shrubs and mixed agriculture. Field assessments confirmed the critical role of logging and hill paddy cultivation, which alter the natural terrain conditions and remove the forest cover. Although forest clearing for hill paddy cultivation removes vegetation and hence decreases protection against erosive rainfall, the sediment delivery will be relatively low due to less terrain alteration. Logging and associated activities induce the formation of soil erosion hotspots, which remain as such for several years. Logging activities generate exposed barren land which although only covers over 4% of the study area contributes more than 28% of the total soil loss.

An improved RUSLE/SDR model for the evaluation of soil erosion

The accurate assessment of soil erosion is key to assess environmental parameters, such as the reduction in soil fertility, the increase in flood risk, the loss of nutrients, and degradation of water quality. In this study, we developed a methodology using the Revised Universal Soil Loss Equation (RUSLE) with the sediment delivery ratio (SDR) to estimate the annual amount of soil erosion and sediment yield in the Nozhian watershed (western Iran). The weighted total least-squares (WTLS) algorithm was applied to generate the rainfall–runoff erosivity surface using rainfall data and a digital elevation model (DEM) instead of traditional interpolation methods. The results demonstrated that the obtained sediment yield by the RUSLE/SDR model was approximately 802,000 tons per year. More than half of the watershed (61.6%) belonged to the high and severe erosion classes (20–100 t/ha year), and the mean soil erosion rate in the study area was 89.32 t/ha year. Several landslides extracted using a Google Earth map by expert interpretation were exactly consistent with areas that had high erosion rates based on the RUSLE results. This compatibility implies the compatibility between the results and reality. According to the statistical analysis, topographic features, especially slope steepness, had the greatest effect on the rate of soil erosion in the region. The results of our RUSLE/SDR analysis were also compared with the reported results from the Modify Pacific Southwest Interagency Committee (MPSIAC), Erosion Potential method (EPM), and Hydrophysical model. In situ data from the measured annual sediment yield during a 40-year interval from a hydrometric station were used for the accuracy analysis. The comparison indicated improvement in the accuracy of our approach by up to 65% in comparison to other reported results. These results can surely aid in the implementation of soil management and conservation practices to reduce soil erosion in the Nozhian watershed.

Extent of Cropland and Related Soil Erosion Risk in Rwanda

Land conversion to cropland is one of the major causes of severe soil erosion in Africa. This study assesses the current cropland extent and the related soil erosion risk in Rwanda, a country that experienced the most rapid population growth and cropland expansion in Africa over the last decade. The land cover land use (LCLU) map of Rwanda in 2015 was developed using Landsat-8 imagery. Based on the obtained LCLU map and the spatial datasets of precipitation, soil properties and elevation, the soil erosion rate of Rwanda was assessed at 30-m spatial resolution, using the Revised Universal Soil Loss Equation (RUSLE) model. According to the results, the mean soil erosion rate was 250 t·ha−1·a−1 over the entire country, with a total soil loss rate of approximately 595 million tons per year. The mean soil erosion rate over cropland, which occupied 56% of the national land area, was estimated at 421 t·ha−1·a−1 and was responsible for about 95% of the national soil loss. About 24% of the croplands in Rwanda had a soil erosion rate larger than 300 t·ha−1·a−1, indicating their unsuitability for cultivation. With a mean soil erosion rate of 1642 t·ha−1·a−1, these unsuitable croplands were responsible for 90% of the national soil loss. Most of the unsuitable croplands are distributed in the Congo Nile Ridge, Volcanic Range mountain areas in the west and the Buberuka highlands in the north, regions characterized by steep slopes (&gt;30%) and strong rainfall. Soil conservation practices, such as the terracing cultivation method, are paramount to preserve the soil. According to our assessment, terracing alone could reduce the mean cropland soil erosion rate and the national soil loss by 79% and 75%, respectively. After terracing, only a small proportion of 7.6% of the current croplands would still be exposed to extreme soil erosion with a rate &gt;300 t·ha−1·a−1. These irremediable cropland areas should be returned to mountain forest to foster environmental sustainability or further sustainable alternative erosion control techniques may be applied, such as applying Vetiver Eco-engineering Technology due to its economical soil erosion control and stabilization of steep slopes and the construction of erosion control dams to absorb and break down excess runoff from unusually intense storms in various parts of the watersheds.

Assessment of soil erosion sensitivity and post-timber-harvesting erosion response in a mountain environment of Central Italy

This study aimed to assess the effects of forest management on the occurrence of accelerated soil erosion by water. The study site is located in a mountainous area of the Italian Central Apennines. Here, forest harvesting is a widespread forestry activity and is mainly performed on the moderate to steep slopes of the highlands. Through modeling operations based on data on soil properties and direct monitoring of changes in the post-forest-harvesting soil surface level at the hillslope scale, we show that the observed site became prone to soil erosion after human intervention. Indeed, the measured mean soil erosion rate of 49tha−1yr−1 for the harvested watershed is about 21 times higher than the rate measured in its neighboring undisturbed forested watershed (2.3tha−1yr−1). The erosive response is greatly aggravated by exposing the just-harvested forest, with very limited herbaceous plant cover, to the aggressive attack of the heaviest annual rainfall without adopting any conservation practices. The erosivity of the storms during the first four months of field measurements was 1571MJmmh−1ha−1 in total (i.e., from September to December 2008). At the end of the experiment (16months), 18.8%, 26.1% and 55.1% of the erosion monitoring sites in the harvested watershed recorded variations equal or greater than 0–5, 5–10 and >10mm, respectively. This study also provides a quantification of Italian forestland surfaces with the same pedo-lithological characteristics exploited for wood supply. Within a period of ten years (2002–2011), about 9891ha of coppice forest changes were identified and their potential soil erosion rates modeled.