Assessment of sediment yield in a small karst catchment by using 137Cs tracer technique

Abstract

There is very thin soil layer in karst rocky desertification areas in Southwest China, sediment deposition and sediment yield in the karst area affects the development of vegetation greatly. In the present study, the 137Cs technique was used to assess the rate of sediment deposition and sediment yield in a small karst catchment. The 137Cs inventory within the depression varied between 800 m−2 and 2,200 Bq m−2, with the mean value of 1,500.1 Bq m−2. The 137Cs reference inventory at a nearby reference site was 805.9 Bq m−2. It could be inferred to that sediment deposition had occurred in the catchment. The mean depth of sediments deposition in the depression was 6 cm and the deposition rate was approximately 0.13 cm yr−1. The analysis of the topographic characteristics of the catchment revealed that the sediment deposition occurred mainly at the lower part of the small catchment. Although, there was a sinkhole in the depression, little sediment had drained out with runoff through the sinkhole, because the local people built ridges around the sinkholes for storing water. According to this, sediment yield rate in the small catchment was estimated to be approximately 19.25 to 27.5 t km−2 yr−1, and the extremely low sediment yield was maybe the main obstacle to vegetation restoration in karst rocky desertification areas.