Predicting soil erosion and deposition on sloping farmland with different shapes in northeast China by using 137Cs

Slope shape has an important influence on soil erosion. However, the distribution of erosion and deposition on sloping farmland with different shapes is still unclear. This severely restricts the soil loss evaluation and protection of Mollisol resources in northeast China, where sloping farmland (<10<degrees>) accounts for 60 % of the cultivated land. In this study, the 137Cs technique combined with wavelet analysis theory was employed to study the spatial distribution characteristics of erosion-deposition rates along three slopes with straight, convex, and concave shapes in northeast China. The results indicated that the average erosion rates of the three slopes were in the following order: convex > straight > concave. The soil erosion and deposition rates fluctuated along the slope length. The primary fluctuation periods in the straight slope, convex slope and concave slope were 45.1 m, 55.0 m, and 40.4 m, respectively. Three relationships of coupled effects of slope gradient and slope length on straight, convex and concave slope were established and verified. It can be concluded that the relationship between the soil erosion rate and slope length was not simple monotonous but showed a certain periodic fluctuation, which was related to the change in transport capacity of runoff on the slope. The change in the erosion-deposition rate with slope length in a straight slope shape can be described by the cosine function. The cumulative soil erosion-deposition rates along the slope had very significant binary power function relationships with both slope length and gradient on convex and concave slopes. The coupled effects of slope gradient and length on soil erosion-deposition for different slope shapes should be fully considered for soil erosion prediction. This study could provide theoretical support for improving erosion prediction models and a scientific basis for the rational arrangement of soil and water conservation measures on slopes at appropriate locations.