Sediment source identification by using ^137Cs and ^210pb radionuclides in a small catchment of the Hilly Sichuan Basin, China

Double radionuclide tracers of ¹³⁷Cs and ²¹⁰Pb were used to investigate sediment sources in the Wujia Gully, a small catchment in the Hilly Sichuam Basin in 2002. Average ¹³⁷Cs and ²¹⁰Pb concentrations in the source soils of the steep forest slopes, gentle cultivated terraces and bare slopes were 7.15±0.40 and 162.01±3.86 Bq·kg^-1, 4.01±0.31 and 70.96±2.65 Bq·kg^-1, and 0 and 15.12±1.22 Bq·kg^-1, respectively, while those concentrations in the recently deposited sediments in the reservoir were 3.06±0.23 and 72.66±1.61 Bq·kg^-1, respectively. By using the mixing model, the relative sediment contributions from steep forest slopes, gentle cultivated terraces and bare slopes (including channel banks) were estimated to be 18%, 46% and 36%, respectively. Cultivated terraces and bare slopes (including channel banks) were the first and the second important sediment sources in catchment. Specific sediment yield in the catchment was 642 t·km^-2·a^-1 from the deposited sediment volume in the reservoir since 1956. Soil erosion rates for the forest slopes and cultivated terraces, which accounted for 2/3 and 1/3 of the drainage area in the catchment, were estimated to be 173 and 886 t·km^-2·a^-1, respectively.