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Understanding the relationship between soil erosion and the changes in landscape patterns is important for guiding the management and development of watersheds. The Nangou watershed in Ansai County, Shaanxi on the Loess Plateau, is an area with the implement of "Grain for Green", ecological agriculture, ecological tourism and the demonstration of science and technology for landscape management. We quantified the spatial and temporal variations of landscape pattern and soil erosion from 1981 to 2018 using the GIS and the universal soil loss equation (USLE). The relationship between the soil erosion modulus and nine landscape pattern indices in three categories was analyzed using the principal component analysis at both plot and landscape levels. The results showed that, among the five landscape types, the spatial and temporal changes of cultivated land and woodland dominated the evolution of landscape patterns, which affected the concentration and distribution degree of the whole watershed. Soil erosion in the Nangou watershed decreased annually, with erosion area, erosion modulus and soil erosion intensity decreasing by 29.7%, 61.2%, and 73.4% from 1981 to 2018, respectively. The variation of cultivated land and forest land areas determined the changes of soil erosion modulus of the whole watershed. The change trend of landscape pattern index was consistent with that of soil erosion. "Grain for Green" Project was the major dri-ving force for the changes in the landscape pattern and for the reduction of soil erosion. The characteristic development and management could weaken soil erosion intensity in parts of the study area. The rational configuration of landscape types could effectively control soil erosion in a watershed. The combination of rational configuration and characteristic management could help achieve the goals for sustainable and high quality development of the watershed.

Rapid and reliable methods for estimating the relative contribution of interrill and rill erosion during a rainfall event are needed to provide an improved understanding of soil erosion processes and to develop process-based soil erosion prediction models. Use of the radionuclide 7Be in controlled experiments provides a means of addressing this need and this paper reports an experimental study aimed at refining and testing procedures employed to estimate the relative contribution of the two components of erosion. Four experimental plots (area 5×2m and 10°, 15°, 20°, and 25° slope), filled with a loessial soil, manually tilled, and kept free of weeds with herbicides, were subjected to high intensity rainfall (91.8–120.6mmh−1), in order to induce rill development. The evolution of the rill network was documented photographically during the rainfall events and the runoff and sediment output from the plots were collected and measured. The sediment was recovered from the runoff and its mass and 7Be activity were measured. The Yang model, reported previously, was used to estimate the relative contributions of interrill and rill erosion from the 7Be activity of the exported sediment and this model was further refined to take account of the dynamic growth of the rills during the rainfall event. The results from the experiments were also used to develop a simple empirical linear model for estimating the relative contributions of interrill and rill erosion from the 7Be measurements. A comparison of the results provided by the three models showed some differences in the estimates of the magnitude of the relative contributions, although their trend during the event was similar. The estimates provided by the empirical linear model tended to be higher than those obtained using the refined model and lower than those generated by the Yang model, but were closer to those provided by the refined model which was seen as being theoretically the most accurate model. The basis of the empirical linear model was simpler than that of other models, since only a few, easily obtained parameters were required. In practical terms the empirical linear model therefore has important advantages and is judged to provide acceptable results. Further work is required to test its applicability under a wider range of conditions. [ABSTRACT FROM AUTHOR]

Existing interrill erosion equations based on mini-plot experiments have largely ignored the effects of slope length and plot size on interrill erosion rate. This paper describes a series of simulated rainfall experiments which were conducted according to a randomized factorial design for five slope lengths (0.4, 0.8, 1.2, 1.6, and 2 m) at a width of 0.4 m, five slope gradients (17%, 27%, 36%, 47%, and 58%), and five rainfall intensities (48, 62.4, 102, 149, and 170 mm h−1) to perform a systematic validation of existing interrill erosion equations based on mini-plots. The results indicated that the existing interrill erosion equations do not adequately describe the relationships between interrill erosion rate and its influencing factors with increasing slope length and rainfall intensity. Univariate analysis of variance showed that runoff rate, rainfall intensity, slope gradient, and slope length had significant effects on interrill erosion rate and that their interactions were significant at p = 0.01. An improved interrill erosion equation was constructed by analyzing the relationships of sediment concentration with rainfall intensity, slope length, and slope gradient. In the improved interrill erosion equation, the runoff rate and slope factor are the same as in the interrill erosion equation in the Water Erosion Prediction Project (WEPP), with the weight of rainfall intensity adjusted by an exponent of 0.22 and a slope length term added with an exponent of −0.25. Using experimental data from WEPP cropland soil field interrill erodibility experiments, it has been shown that the improved interrill erosion equation describes the relationship between interrill erosion rate and runoff rate, rainfall intensity, slope gradient, and slope length reasonably well and better than existing interrill erosion equations. [ABSTRACT FROM AUTHOR]

Abstract: Sandy loess from the Wind–Water Erosion Crisscross Region on the Loess Plateau of China, an area with severe wind erosion, was collected for use in a wind tunnel experiment, to explore the feasibility of using 7Be measurements to estimate the amount of soil lost through wind erosion. Wind erosion selectively removes the finer particles of soil. Use of procedures for estimating soil loss from 7Be measurements developed for water erosion, which do not take account of this selective removal of fines, is therefore likely to result in overestimation of the amount of soil lost through wind erosion, because 7Be is preferentially associated with the finer fractions of the soil. The results of the experiment, supplemented by measurements undertaken on two field plots in the study region demonstrated a well-defined power function relationship between S e/S o and ABe (where S e is the specific surface area of the soil at the eroded site; S o is the SSA of the original soil and ABe is the 7Be activity remaining at the eroded site), with an exponent of ∼0.75. It is proposed that a particle size correction factor P′, based on the term (S e /S o)0.75, can be incorporated into the procedure for estimating soil loss by wind erosion from 7Be measurements. The estimates of soil loss obtained using the refined procedure were in close agreement with the measured values. Use of the 7Be measurements to estimate soil loss without incorporating the particle size correction factor P′ resulted in over-estimation of the soil loss by ∼14%. When P′ was incorporated, the overestimation was reduced to ∼2%. [Copyright &y& Elsevier]

Abstract: An understanding of the spatial distribution of soil erosion and deposition in a catchment is important for designing soil and water conservation measures. Traditional monitoring techniques provide limited information on the spatial patterns of erosion and deposition. The fallout radionuclide 137Cs was used to document rates and patterns of soil redistribution within a small (0.17km2) gully catchment located near An''sai in Shaanxi Province, representative of the Loess Plateau of China. The local reference inventory was estimated to be 2266Bqm−2 and the 137Cs inventories of 198 soil cores collected from the catchment, ranged from 0 to 3849Bqm−2. The coefficient of variation of the inventories of the individual cores was 0.85, reflecting the complex pattern of 137Cs redistribution by soil erosion and deposition. Estimates of erosion rates derived from 137Cs measurement ranged from less than 25 to 150Mgha−1 year−1, with about 70% of the net soil loss from the catchment coming from the gully area. The 137Cs technique was shown to provide an effective means of documenting the spatial distribution of soil erosion and deposition within the small catchment. [Copyright &y& Elsevier]

The stable rare earth element (REE) tracer method was evaluated in this study as a new method for studying soil erosion. Erosion and sedimentation amounts for a slope section can be estimated for each rainfall event using multiple tracers. The REE tracer method can be used for quantitative estimates of the distribution of soil erosion from specific areas and for determining sources of sediment in a small watershed. [Copyright &y& Elsevier]