Sediment source identification by using~(137)Cs and~(210)Pb radionuclides in a small catchment of the Hilly Sichuan Basin, China

摘要

Double radionuclide tracers of~(137)Cs and~(210)Pb were used to investigate sediment sources in the Wujia Gully, a small catchment in the Hilly Sichuam Basin in 2002. Average~(137)Cs and~(210)Pb 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 centre dot kg~(-1), 4.01+-0.31 and 70.96+-2.65 Bq centre dot kg~(-1), and 0 and 15.12+-1.22 Bq centre dot 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 centre dot 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 percent, 46 percent and 36 percent, 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 centre dot km~(-2) centre dot 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 centre dot km~(-2) centre dot a~(-1), respectively.