Evaluating soil erosion and sediment deposition rates by 137Cs fingerprinting technique at different karst hillslope positions in Yunnan Province, southwest China

In karst environments, soil erosion is a  prominent environmental issue that can cause many other problems. Researching the erosion and deposition rates at the hillslope scale in small watersheds is important for designing efficient soil and water conservation measures for the small watersheds even the large scale areas. In our research, the closed watershed, a representative depression in karst gabin basin, located in the Yunnan province, Southwest China, was selected to assess the soil erosion and sediment mobilisation at different hillslope positions using the ¹³⁷Cs tracing technique. The results showed that the soil erosion rates in the shoulders, backslopes and footslopes were 0.87, 0.35 and 0.49 cm a^-1, respectively, meanwhile the soil sediment rate in depression bottom was 2.68 cm a^-1. The average annual soil erosion modulus of the complete hillslope was 632 t km^-2a^-1, which confirmed the serious gradation according to karst soil erosion standards. The sediment delivery ratio would summarize 0.82 in the whole catchment according to the square of hillslope and depression bottom. To identify which factor could play the most important role in influencing the estimations using ¹³⁷Cs, a linear correlation and Principal Component Analysis were conducted. The results showed ¹³⁷Cs concentration of different soil depth at different hillslope positions were significantly correlated with soil organic matter (SOM) and total nitrogen (TN) (P<0.05). As the typical karst geomorphological types, these findings are expected to provide data support for the whole watershed soil erosion management and ecological restoration in  fragile karst ecosystem.