Assessment of soil redistribution in a typical karst catchment using ¹³⁷Cs

An effective assessment of soil erosion and redistribution is a prerequisite for soil erosion control and is critical to achieving sustainable development goals. The most typical landscape in the karst region of Southwest China is found in the peak-cluster depression area, but little attention has been given to the soil redistribution here. A typical karst peak-cluster depression catchment water area in Southwest China was selected, and ¹³⁷Cs technology was used to evaluate the soil redistribution rate and soil erosion process along a total transect (hillslope, depression and sinkhole) in the catchment. The results showed that the distribution of ¹³⁷Cs had a high spatial variability on the total transect of the catchment (CV = 60.04%), the middle slope was the most severely eroded (highest erosion rate of 13.49 t ha^-1 yr^-1), and the area between the bottom slope and the depression was the primary sedimentary area on the surface in the catchment. The distribution of soil properties on the hillslope was affected by the process of soil redistribution. According to the distribution of the ¹³⁷Cs soil profile, the soil profile of the hillslope was uniform, and signs of historical tillage activities were evident; the historical tillage activities of depressions were in the range of 0-20 cm depth, while the ¹³⁷Cs in the sinkhole was mostly distributed in the shallow layers and decreased exponentially with depth, reflecting the depositional characteristics of noncultivated soil. In addition, this study found evidence of underground soil loss in sinkholes since the 1960s; the shallow sediment of these sinkholes mainly came from depressions, with an average deposition rate of 11.77 t ha^-1 yr^-1. Human disturbance and land-use change controlled recent changes in soil redistribution. The soil erosion rate of the hillslopes in catchments was extremely low (average erosion rate of 1.92 t ha^-1 yr^-1). The rocky desertification of hillslopes occurred before 1960; it was not a short-term contemporary process that occurred only during recent decades. This study showed that underground soil loss mainly occurred through sinkholes for a short period of time (100 years). These research results are of great significance for understanding the evolution of rocky desertification and the process of soil erosion.