Effects Of Soil Conservation Measures Research Articles

Risk mitigation measures for pesticide runoff: How effective are they?

One of the most important sources of pesticide pollution of surface waters is runoff and erosion from agricultural fields after rainfall. This study analyses the efficacy of different risk mitigation measures to reduce pesticide runoff and erosion inputs into surface waters from arable land excluding rice fields. Three groups of risk mitigation measures were quantitatively analyzed: vegetative filter strips, micro-dams in row crops and soil conservation measures. Their effectiveness was evaluated based on a meta-analysis of available experimental data using statistical methods such as classification and regression trees, and exploratory data analysis. Results confirmed the effectiveness of vegetative filter strips and micro-dams. Contrary to common assumption, the width of vegetative filter strips alone is not sufficient to predict their effectiveness. The effectiveness of soil conservation measures (especially mulch-tillage) varied widely. This was in part due to the heterogeneity of the available experimental data, probably resulting from the inconsistent implementation and the inadequate definitions of these measures. Both vegetative filter strips and micro-dams are effective and suitable, and can therefore be recommended for quantitative assessment of environmental pesticide exposure in surface waters. However, the processes of infiltration and sedimentation in vegetative filter strips should be simulated with a mechanistic model like Vegetative Filter Strip Modeling System, VFSMOD. The reduction effect of micro-dams can be modelled by reducing the runoff curve number, e.g., in the pesticide root zone model, PRZM. Soil conservation measures are in principle promising, but further well-documented data are needed to determine under which conditions they are effective. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Assessing the Impact of Engineering Measures and Vegetation Restoration on Soil Erosion: A Case Study in Osmancık, Türkiye

The prioritization of preventing soil loss in Türkiye’s watersheds has become a pressing concern for planners. Numerous mathematical models are presently utilized on a global scale for soil erosion prediction. One such model is the Revised Universal Soil Loss Equation (RUSLE), commonly used to estimate average soil loss. Recently, there has been an increased emphasis on utilizing USLE/RUSLE in conjunction with Geographic Information System (GIS) technology, enabling grid-based analysis for predicting soil erosion and facilitating control measures. This study evaluates the effectiveness of erosion and flood control initiatives started in the 1970s within the Emine Creek watershed and its tributary rivers in Osmancık, Türkiye, utilizing RUSLE/GIS technologies. Two distinct maps illustrating the potential erosion risks were produced for two distinct temporal intervals, and a comparative analysis was conducted to evaluate the alterations that transpired. The implementation of various measures such as terracing, afforestation, and rehabilitation in the watershed led to a notable prediction of decreasing soil loss in the watershed. From 1970 to 2020, the rate of estimated soil loss was reduced from 417 to 256 metric tons per hectare per year, demonstrating the effectiveness of soil conservation measures in a semi-arid and weakly vegetated area at reducing potential soil loss.

Preferential Erosion of Soil Organic Carbon and Fine-Grained Soil Particles—An Analysis of 82 Rainfall Simulations

Soil erosion by water causes the loss of soil mineral particles and soil organic carbon (SOC). For determining the effectiveness of soil conservation measures on arable land, rainfall simulations are regularly carried out in field trials in the Czech Republic. The objective of this study was to analyse a dataset from 82 rainfall simulations on bare fallow soils, containing information on slope inclination, soil texture, soil bulk density, SOC, and soil loss with respect to the preferential erosion of fine-grained soil particles and the enrichment of SOC in the eroded soil. Each rainfall simulation comprised a first rainfall period of 30 min and a second one of 15 min in duration. The rainfall intensity was 1 mm min−1 and the kinetic energy of the raindrops accounted for 8.78 J m−2 mm−1. Runoff samples were taken to determine the soil loss and SOC enrichment in the eroded material. Regression analyses revealed that on sites with <14% slope inclination, SOC mitigated soil loss in the first rainfall period. On sites with >14% slope inclination, soil loss was driven by preferential erosion of fine-grained particles in the first rainfall period. Low soil loss was generally coupled with high SOC enrichment and vice versa, indicating that preferential erosion of SOC occurred mainly in soils with low erosion susceptibility. In order to prevent erosion of SOC and maintain soil quality, soil conservation measures are important in all soil types.

Impact of Ten Years Conservation Tillage in Organic Farming on Soil Physical Properties in a Loess Soil—Northern Hesse, Germany

In conservation agriculture, conservation tillage potentially influences the physical, chemical, and biological quality of the soil. Although the effects of conservation agriculture on the soil’s physical properties have been studied in conventional management systems, studies on organic farming systems, especially concerning long-term changes, are scarce. This study summarizes the results of physical and mechanical soil parameters obtained over the initial 10 years of different conservation management treatments (plowing versus reduced tillage with and without compost application) in an organic field trial conducted in central Germany. Moreover, as a research objective, the effects of soil conservation measures on soil’s physical quality were evaluated. Differences in the soil’s physical quality during treatments were mainly detected in the topsoil. At a depth of 0.10–0.24 m, the total porosity and air capacity were lower, and the bulk density was higher in the reduced-tillage systems, compared to those of the plowed treatments. Additionally, the soil’s mechanical stability (precompression stress) was higher at a depth of 0.10 m for reduced-tillage systems combined with compost application. In addition, the soil’s aggregate stability was enhanced in the reduced-tillage systems (higher mean weight diameter, as determined via wet sieving). Overall, the reduced-tillage treatments did not exceed the critical physical values of the soil, nor affect the functionality of the soil (saturated hydraulic conductivity), thereby demonstrating its feasibility as a sustainable technique for organic farming. Future studies should include measures to ameliorate compaction zones in reduced-tillage treatments, e.g., by applying subsoiling techniques in combination with deep-rooting crops to prevent limited rooting space resulting from the high mechanical impedance, especially under dry soil conditions.

Sediment yields variation and response to the controlling factors in the Wei River Basin, China

Assessing regional sediment yield variation and their responses to the potential controlling factors are critical to develop specific strategies of soil conservation measures to adapt to future climate change. This study attempted to investigate the spatial–temporal variation of sediment load in the Wei River basin in the midstream of the Yellow River during 1961–2015 at 15 hydrological stations. The results indicated that annual sediment load in the past six decades decreased significantly (P < 0.01) with the changing trends of −6.43 × 104, −3.86 × 104, −4.6 × 104 t/a at Xianyang, Zhangjiashan, and Zhuangtou stations, respectively. Annual sediment load exhibited abrupt changes in the mid-1990s, which were largely attributed to the strong effects of soil conservation measures in the study area. The spatial pattern of soil erosion were characterized by high sediment yield in the north with sparse vegetation cover and well-developed gullies, and low sediment yield in the south with flat plain and good vegetation cover in the Wei River basin. The results of the partial least squares-structural equation model (PLS-SEM) showed that vegetation changes and rainfall variability explained 62.3%, 47.3%, and 40.1% of the variation in runoff at Xianyang, Zhuangtou, and Zhangjiashan stations, respectively, whereas 59.4%, 17.6% and 48% of the variation in sediment load were explained by the combining effects of rainfall variability, changes of vegetation and runoff. This study provides a deep insight for understanding the effects of driving forces on sediment yield changes, and can be useful to regional soil conservation planning in the region.

Erosion risk assessment through prioritization of sub-watersheds in Nyabarongo river catchment, Rwanda

Soil erosion is a multi-dimension problem that attracted the attention of researchers and planners worldwide. Literature reports, soil conservation strategies should be integrated with the priority assessment to deal with such a problem and taking up a focus according to the priority order. However, in spite of various forms of land and water degradation in Rwanda, a holistic investigation or multi-criteria based watersheds prioritization that integrate various aspects and methods has yet to be assessed. Thus, Nyabarongo River Catchment which is the major river catchment in Rwanda that drains about 33% of the total Rwanda coverage has been selected and sub-watersheds were grouped into three order clusters (C1, C2, and C3) using Hierarchical Cluster Analysis (HCA). The priority assessment was estimated using the combination of Compound parameter index (Ci) and Erosion Hazard Rate Index (EHRI) derived from the Analytical Hierarchy Process (AHP) in Geographic Information System (GIS) using remote sensing, soil and geology data. Based on the literature, the Ci technique, in general, considered four parameters viz. morphometric analysis dimensionally reduced using the Principal Component Analysis (PCA) together with land cover, soil, and geology. Whereas EHRI considered five Erosion Hazard Parameters (EHPs) viz. Soil Loss (SL), Sediment Production Rate (SPR), Sediment Transport Index (STI), Runoff Potential (RP), and Slope. The priority assessment was categorized into High, Moderate, and Low priority classes. The priority assessment based on Ci and EHRI provided the same outcome. They noticed high priority in sub-watersheds under cluster C2 account for (35.94%), those under cluster C3 comprise for (16.27%) were identified as a moderate priority, and sub-watersheds belonging to cluster C1 account for (47.8%) falling under low priority sub-watersheds for conservation measures. Therefore, effective soil conservation measures at a priority basis are needed for sustained productivity while minimizing undesirable effects on the environment.

The Effect of Soil Conservation Measures on Runoff, Soil Erosion, TN, and TP Losses Based on Experimental Runoff Plots in Northern China

Total nitrogen (TN) and total phosphorous (TP) are the main pollutants affecting the water quality of the Miyun Reservoir, Beijing. However, few studies have been conducted on their responses to implemented soil conservation measures at a slope scale in northern China. To explore the impact of soil conservation measures on TN and TP losses, field monitored data from 18 runoff plots under natural rainfalls were used to analyze the changing characteristics of runoff, soil loss, and nutrient losses during 2014–2019. The results indicated that runoff, soil erosion, as well a TN and TP losses from the plots varied significantly, depending on land use and soil conservation measures. Bare plots suffered the highest soil, TN, and TP losses, followed by cultivated plots without soil conservation measures, cultivated plots with contour tillage, and other plots. Event-averaged runoff and soil loss rates ranged from 0 to 7.9 mm and from 0 to 444.4 t km−2 yr−1, and event-averaged TN and TP losses from cultivated plots were the highest, with values of 39.8 and 3.0 kg km−2, respectively. Bare and cultivated plots were the main sediment and nutrient sources. Among the cultivated plots, the terraced plot had the lowest soil and nutrient losses. The vegetated plots had insignificantly lower soil and nutrient losses. Most TN and TP were lost in particulate status from the plots, especially from the plots with soil conservation measures. Soil conservation measures can effectively prevent TN and TP losses. To guarantee water resource use, contour tillage is preferred for the bare and cultivated lands in the study region.

Assessing the impact of climate change on soil erosion in East Africa using a convection-permitting climate model

East Africa is highly reliant on agriculture and has high rates of soil erosion which negatively impact agricultural yields. Climate projections suggest that rainfall intensity will increase in East Africa, which is likely to increase soil erosion. Soil erosion estimates require information on rainfall erosivity, which is calculated using sub-daily storm characteristics that are known to be biased in traditional parameterized convection climate models. Convection-permitting climate models, which are run at higher resolution to negate the need for convection parameterization, generally better represent rainfall intensity and frequency. We use a novel convection-permitting pan-Africa regional climate model (CP4A) to estimate rainfall erosivity in Tanzania and Malawi, and compare it to its parameterized counterpart (P25), to determine if there is a benefit to using convection-permitting climate models to look at rainfall erosivity. We use eight year historical and end-of-century (RCP8.5) climate simulations to examine the impact of climate change on soil erosion in Tanzania and Malawi based on rainfall erosivity estimates from CP4A and P25 applied to the Revised Universal Soil Loss Equation. The effectiveness of soil conservation measures was also evaluated. Rainfall erosivity was lower in P25 than in CP4A and was a poorer match to observational storm characteristics, even after bias-correction. These results suggest that parameterized convection regional and global climate models might under-estimate rainfall erosivity, and the associated soil erosion. We found high values of present day erosion in mountainous regions in Tanzania and Malawi in CP4A. Under climate change, areas at high risk of soil erosion expanded due to increases in rainfall intensity in CP4A. Terracing was less effective at reducing soil erosion risk in the future than in the present day, and more extensive soil management may be required to manage soil erosion and reduce the negative impacts of soil erosion on agriculture.

Linking soils and streams: Chemical composition and sources of eroded organic matter during rainfall events in a Loess hilly-gully region of China

Ascertaining the chemical compositions and sources of eroded organic matter (OM) is of significant importance for understanding the flux and fate of laterally transported OM at the catchment scale. Limited information, however, is available for the sources and dynamics of the eroded OM in bulk and soluble phases in relation to land-use types and rainfall events from an erosion prone landscape. In this study, we collected the top-soils from different land-uses and gully bank in uplands over seven rainfall events in 2016 to address this issue at two contrasting watersheds (with vs. without soil conservation measures) in the Loess hilly-gully region of China. Chemical compositions of eroded OM in bulk sediments and stream waters at the stream channels during rainfall processes were determined by spectroscopic analysis and source partition was inferred with the stable isotopic technique. Our results indicated that OM from forested soils had higher aromaticity, hydrophobic fraction, humification, molecular weight, and proportion of humic-like substance compared with other land-use types. The calculation with isotope mixing model indicated that the eroded bulk OM sources in sediments mainly originated from gully bank, orchard, and forests at the watershed coupled with soil conservation measures. Further, gully banks were the main contributor of eroded OM during rainfall events only at the watershed without conservation practices. Moreover, the principal component analysis suggested that the dissolved organic matter in stream waters were primarily derived from microbial OM sources (i.e. biological production of OM) in deep soils during rainfall events at both contrasting watersheds. Our findings highlight the effects of soil conservation measures and rainfall events on the nature and reactivity of eroded OM in various forms issuing from watersheds.

Effect of soil conservation measures and slope on runoff, soil, TN, and TP losses from cultivated lands in northern China

Soil and nutrient loss characteristics in cultivated lands are scarcely identified in northern China that could retard reasonable implementation of soil conservation measures. In the present study, seven-year of water, sediment, and nutrient data in 2014–2020 from five cultivated plots in the Miyun Reservoir, Beijing were used to explore runoff, soil, total nitrogen (TN) and total phosphorous (TP) loss characteristics and their responses to soil conservation measures, slope gradients, and rainfall characteristics. Annual soil loss rate (SLR) decreased from 3025.23 t km−2 yr−1 on the plot with no soil conservation measure to 3.47 t km−2 yr−1 on the terraced plot. Contour tillage on gentle slopes decreased soil and nutrient losses and allowed more runoff running downslope. Event-averaged SLR also presented the same trend. Runoff depth decreased insignificantly from 72.83 mm on plot with no soil conservation measure, 68.40 mm on contour tillage plots, to 3.35 mm on terraced plot. Annual TN and TP losses decreased from 344.82 and 27.21 kg km−2 yr−1 on cultivated plot with no soil conservation measure to 11.11 kg km−2 yr−1 and 0.47 kg km−2 yr−1 on terraced plot, respectively. Particulate TN and TP losses contributed over 50% of the total, depending on SLR. This study implies that contour tillage is preferred on gentle slopes, and steep slope should be implemented with terrace or other measures in the study region.

Understanding sediment connectivity from soil erosion perspective

Sediment connectivity is closely related to geomorphology, topography, ecological hydrology, soil erosion, nutrient and pollutant movement, and water quality conservation. As one of the hot topics in soil erosion research during the past decade, sediment connectivity is required to be fully examined from the perspective of soil erosion. Sediment connectivity describes the interactions of sediment cascades between different topographical and landscape units in a system which is usually quantified with the structural connectivity and functional connectivity in four dimensions, i.e., lateral, longitudinal, vertical and temporal. Its impacting factors include climate, lithology, geomorphology, watershed characteristics, topography, soil properties, vegetation, hydrological processes, soil erosion and human activities as well as their temporal and spatial variations. The specific influencing mechanisms vary among these factors and among different spatial scales, therefore resulting in distinct responses of sediment connectivity. Field survey and mapping, graph theory, index and model simulation are frequently applied to investigate and quantify sediment connectivity. The theories behind these methods are different, so do the required data, specific procedures, and the corresponding results. The index of connectivity (IC) is the most widely employed in the quantification of sediment connectivity. Nevertheless, IC well reflects the structural connectivity, rather than the functional connectivity. From the perspective of soil erosion, future studies regarding sediment connectivity should focus on the concept, influencing factors and their dynamic mechanisms, method comparison and index optimization, relationships of sediment connectivity with hydrological connectivity, soil erosion and sediment delivery ratio, as well as the effects of soil conservation measures on sediment connectivity and the corresponding mechanisms.

Effects of soil conservation measures on wind erosion control in China: A synthesis.

Soil conservation measures (SCM) are believed to be effective in terms of wind erosion control. Currently, most studies regarding the efficacy of SCM in erosion control are based on data of individual experimental sites. A comprehensive understanding of the effectiveness of SCM and related impacting factors at large scale is lacking. A synthesis was conducted in this study based on data compiled from field experiments in major eroded regions of China in order to fully evaluate the efficacy of various SCM practices in erosion reduction, and further assess how their efficacy varied under different environmental conditions. Two main SCM categories were identified, i.e. agricultural measures (AM) used for both crop production and erosion control, and vegetation measures (VM) used for erosion control only. The results showed that SCM could lead to a significant reduction of wind erosion by over a half (0.51). The reduction of wind erosion under VM (0.56) was significantly higher than AM (0.46). Specifically, most AM and all the VM investigated in this study were beneficial for wind erosion control. Multiple cropping was the only practice that significantly increased the wind erosion rate compared to the conventional treatment. We further found that the effectiveness of SCM highly dependent on precipitation, temperature, soil organic carbon concentration, soil water content, soil type, elevation, and vegetation coverage. The responses of the efficacy of AM and VM to these environmental conditions also differed. Another important finding is that the lowest efficacy of SCM in erosion control was observed in regions with the highest erosion risk, indicating the greater challenge in erosion reduction in these regions. The efficacy of SCM quantified in this study can be used as an essential reference for the adoption of SCM in China and the environmental conditions should also be considered carefully when designing a SCM application framework.

Channel erosion dominates sediment sources in an agricultural catchment in the Upper Yangtze basin of China: Evidence from geochemical fingerprints

A sediment fingerprinting approach was applied to identify dominant sediment sources in an area where soil conservation measures (i.e. terracing) had been carried out on steep, intensively cultivated lands but the outcome was unknown. The wider purpose was to provide scientific evidence to inform decisions on where erosion control and sediment mitigation strategies could be further targeted. Geochemical fingerprints were used to quantify sediment contributions from three potential sources, i.e. surface soil under cropland and woodland land use, and channel banks, in a managed small catchment in the Upper Yangtze River basin in southwestern China. In parallel, artificial mixtures with known source proportions were evaluated to examine the effects of grain size selection (<125 µm and < 63 µm) on the accuracy of modeled source contributions. Source apportionment results suggest that materials originating from incised and actively eroding channel banks were the most important source of sediment, which contribute over 80% of sediment to the catchment outlet. Sediment inputs from cropland (10–20%) and woodland (<10%) areas as a result of surface erosion were less important, since effective soil conservation measures have been implemented in this catchment. Although apportionment of sampled sediment provided comparable results for both coarser (<125 µm) and fine (<63 µm) size fractions, the artificial mixture results indicated that unmixing the coarse fraction alone could yield poor agreement between modeled source contributions and actual source proportions. The mean absolute error (MAE) for the coarse fraction mixtures ranged between 8.8% and 19.6%, with a mean of 13.6%, compared to the values of 4.0–7.4%, with a mean of 5.2% for the fine fractions. The results of this study highlight that channel bank materials constitute a significant fraction of suspended sediment exports in a heavily managed agricultural catchment, suggesting that future conservation works should be focused on drivers of erosion from this particular source type. Herein, it is surmised that reworking of legacy valley fill deposits is tempering the downstream benefits (e.g. reduced siltation) of recent upslope soil conservation, an important message for policy makers. The findings of this work also emphasize the methodological need to take account of potential uncertainties associate with source apportionments when using specific particle size fractions in fingerprinting studies.

Effects of soil conservation measures on soil erosion in the Yunnan Plateau, southwest China

Soil and water conservation (SWC) measures are among the most important ways to control soil erosion in mountainous areas. However, little is known about the application of SWC measures on soil erosion over large areas. We developed a new framework for investigating the distribution of engineering measures by using high-resolution remote sensing images at a large scale, and we assessed the soil conservation effects of those measures on the Yunnan Plateau (YP) in China using the Chinese Soil Loss Equation (CSLE). We detected 43,398 km2 of soil conservation measures on the YP, accounting for 53% of farmland. The area of conservation measures decreased with an increase in slope gradient. Different types of engineering measures had different spatial distribution patterns, and together they conserved 5.08 × 108 t of soil each year on the YP. The effects of engineering measures on soil erosion decreased with an increase in slope. Furthermore, more than 82% of soil loss from farmlands was attributed to areas without engineering measures, and steep-slope farmland without such measures was the main source of soil erosion on the YP. Our results suggest that engineering measures were effective in soil conservation, but the effects varied with topography on the YP. We suggest that further studies focus on the relationships between the soil erosion and grain supply of farmlands without engineering measures to provide a basis for the formulation of land use planning policy in China.

Soil carbon and nitrogen fraction dynamics affected by tillage erosion

Understanding the impact of tillage erosion on soil organic carbon (SOC) and nitrogen (N) fractions is essential for targeted soil conservation in mountainous and hilly areas. However, little is known about this issue. In this study, we selected a tillage erosion-dominated hillslope from the Sichuan Basin, China, to determine the effect of tillage erosion on particulate OC (POC), dissolved OC (DOC), light fraction OC (LFOC), ammonium N (NH4+-N), nitrate N (NO3−-N) and alkali-hydrolysable N (AN). Additionally, we investigated the microbial activities in relation to soil C and N dynamics, including soil microbial biomass, β-glucosidase and urease activities. Tillage erosion induced serious soil loss in upper slope positions and soil deposition in lower slope positions. The observations of the various labile OC fraction distributions across the hillslope suggest that tillage erosion exerts less impact on DOC and LFOC dynamics but a notable effect on POC. The distribution pattern in total organic carbon under tillage erosion mainly depends on POC redistribution. The POC redistribution is a major factor affecting microbial activities. The AN is more prone to the tillage erosion impact than NH4+-N and NO3−-N. Effective soil conservation measures should be taken to weaken the adverse impacts of tillage erosion on POC and AN redistribution in sloping farmlands.

The assessment of water erosion using Partial Least Squares-Path Modeling: A study in a legally protected area with environmental land use conflicts.

Water erosion has historically been assessed by various methods, with the purpose to help reducing this phenomenon. However, application of models capable to handle complex relationships between large numbers of variables is still relatively scarce. The method of Partial Least Squares-Path Modeling (PLS-PM), used in this study, was able to expose complex causal paths between soil erosion and potentially related factors, namely "Surface Runoff", "Environmental Land Use Conflicts", "Soil Fertility" and "Relief Factors", within the Environmental Protection Area of Uberaba River Basin (EPA) located in Minas Gerais state, Brazil. In the context of PLS-PM, soil erosion (dependent) and the related factors (independent) are called latent variables and described by measured or estimated parameters. For example, the "Relief Factors" were described by measured drainage density and topographic slope. These were linked to the corresponding latent variables through weights and the later joined to each other through paths. During the PLS-PM runs, weights and paths were quantified and latent variables interpreted in regard to their importance for soil erosion and spatial incidence. The spatial incidence was used to prioritize areas for soil conservation. To test the model, data were obtained from soil samples (texture and fertility parameters) or digitally extracted from cartographic products (e.g., maps of soil loss, land use, brightness index, topographic slope, drainage density), at 37 sites within the EPA. The PLS-PM results revealed that 70.2% of soil erosion is predicted by the independent variables (R2 = 0.702), and that "Soil Fertility" and "Environmental Land Use Conflicts" were the most influencing ones (β = -0.758 and β = 0.346, respectively). These variables can be managed by man, through implementation of effective soil conservation measures and respect for suitable land use. It is therefore urgent to act in these regard, considering the socioeconomic and environmental importance of the EPA.

Using 137Cs and 210Pbex measurements to explore the effectiveness of soil conservation measures in semi-arid lands: a case study in the Kouhin region of Iran

One of the most fragile agro-ecosystems in Iran is represented by dry farming lands on steep hillslopes that occupy ca. 54% of the national agricultural lands. Therefore, in order to reduce loss of fertile soil from these lands, it is important to apply effective soil conservation strategies. This study used cesium-137 (137Cs) and excess lead-210 (210Pbex) measurements to assess the effectiveness of soil conservation practices in controlling soil erosion in Kouhin, Qazvin Province of Iran. Soil samples were collected from two adjacent hillslopes with and without conservation agriculture practices. The managed site benefited from conservation practices, including controlled grazing, terraces, and contour farming for 50 years. The unmanaged site was under cultivation without agricultural conservation practices. At the managed site, both 137Cs and 210Pbex activities were measured. Only 137Cs activity was measured for the unmanaged site. Conservation practices performed at the managed site were effective in minimizing soil erosion, i.e., net soil erosion rates provided by 137Cs measurements were only 4.6 Mg ha−1 year−1 at the managed site, compared to 12 Mg ha−1 year−1 for the unmanaged site. By using the 210Pbex approach, net soil loss and sediment delivery ratio in the managed site were 12.3 Mg ha−1 year−1 and 60%, respectively. Soil redistribution magnitudes established from 137Cs inventories are associated with a period extending from 1963 to the time of sampling, while those obtained from 210Pbex measurements are related to the past 100 years. However, 210Pbex measurements are expected to be more sensitive to erosive events that occurred during the last 15 to 20 years and this could reflect the higher estimate of erosion rate provided by this radionuclide for the managed site. The increasing trend seems to suggest a possibility that the higher soil losses estimated by the 210Pbex measurements are a result of increasing climate variability during the last two decades. However, further investigation would be needed to confirm this hypothesis.

Hydrological Response to Precipitation and Human Activities-A Case Study in the Zuli River Basin, China.

Precipitation and human activities are two essential forcing dynamics that influence hydrological processes. Previous research has paid more attention to either climate and streamflow or vegetation cover and streamflow, but rarely do studies focus on the impact of climate and human activities on streamflow and sediment. To investigate those impacts, the Zuli River Basin (ZRB), a typical tributary basin of the Yellow River in China, was chosen to identify the impact of precipitation and human activities on runoff and sediment discharge. A double mass curve (DMC) analysis and test methods, including accumulated variance analysis, sequential cluster, Lee-Heghnian, and moving t-test methods, were utilized to determine the abrupt change points based on data from 1956 to 2015. Correlation formulas and multiple regression methods were used to calculate the runoff and sediment discharge reduction effects of soil conservation measures and to estimate the contribution rate of precipitation and soil conservation measures to runoff and sediment discharge. Our results show that the runoff reduction effect of soil conservation measures (45%) is greater than the sediment discharge reduction effect (32%). Soil conservation measures were the main factor controlling the 74.5% and 75.0% decrease in runoff and sediment discharge, respectively. Additionally, the contribution rate of vegetation measures was higher than that of engineering measures. This study provides scientific strategies for water resource management and soil conservation planning at catchment scale to face future hydrological variability.

Towards global applicability? Erosion source discrimination across catchments using compound-specific δ13C isotopes

Accurate identification of soil erosion hot spots across catchments of different sizes and agro-ecologies through the use of conventional tracing techniques has proven challenging. Since this problem hinders implementation of precise soil conservation measures by land managers and decision-making bodies, novel evidence-based techniques are needed. To meet this need, the International Atomic Energy Agency (IAEA, Vienna, Austria) initiated the Coordinated Research Project entitled “Integrated Isotopic Approaches for an Area-wide Precision Conservation to Control the Impacts of Agricultural Practices on Land Degradation and Soil Erosion – D1.20.11” in 2008. This project emphasized the application of isotopic approaches to identify hot spots of land degradation in agricultural catchments to develop effective soil conservation measures. As one key outcome of this project, we present here an aligned protocol to explore the potential of compound-specific stable isotope (CSSI) analysis of individual fatty acids (FA) combined with Bayesian statistics to discriminate sediment sources across six catchments of different sizes and agro-ecologies. The global applicability of the CSSI approach was first tested on the basis of major land use categories (i.e., forest, cultivated and non-cultivated land) as potential sediment sources in the studied catchments. These land use categories were then further resolved into specific land use types (e.g., cassava and maize fields, orchards) to assess the potential resolution threshold of the CSSI technique. In a final step, the influence of miscellaneous sources (e.g., roads, channel banks) that had the potential to distort proportional contributions to sediment deposition was assessed. The introduced aligned protocol of the CSSI technique was applied to discriminate individual erosion sources based on land use types of tested catchments. Merging catchment-specific land use types with broader land use categories made it possible to determine inter-catchment comparisons of isotopic signatures due to significant differences in δ13C values of fatty acids when cultivated land was present. Notably, no correlations were found between different catchment sizes, agro-ecologies, number and type of land use types, or soil organic carbon concentrations and the number of significant δ13C fatty acid values of the various land use types. Thus, we propose that the presented CSSI technique has the potential to identify soil erosion hot spots in contrasting catchments of different sizes and agro-ecologies.

Effects of topographic factors on runoff and soil loss in Southwest China

Soil erosion is a threat to sustainable agricultural and regional development in karst regions. In this study, field plot observation method was used to estimate the effects of slope gradient and length on runoff and soil loss in Guizhou, Southwest China. The results showed that runoff and soil loss is nonlinearly related to slope gradient. The increasing trends of runoff and soil loss declined after the slope gradient of 15°. This turning point was affected by both slope gradient and rock outcrops on the 20°–25° slopes, hence it is still unknown whether the slope gradient of 15° is a critical value. Runoff showed a trend of decrease-increase-decrease as slope length increased, and soil loss rate showed an increasing trend as slope length increased. There is a significantly positive linear relationship between soil loss and slope length (P<0.01). Runoff and soil loss were significantly correlated with rainfall amount (P) and the maximum 30 or 60min rainfall intensity (I30 or I60), which had power function with PI30 on gradient-changed slopes and PI60 on length-changed slopes. Moreover, soil loss has a power function relationship with slope gradient/length and runoff depth. This study is helpful to elucidate the effect of topographic factors on soil erosion and to take effective soil conservation measures in karst regions.