USE OF CS-137 AND PB-210 RADIONUCLIDES AS TRACERS TO INVESTIGATE SEDIMENT SOURCES 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 Sichuan 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 Bq·kg~(-1) ± 0.40 Bq·kg~(-1) and 162.01 Bq·kg~(-1) ± 3.86 Bq·kg~(-1), 4.01 Bq·kg~(-1) ± 0.31 Bq·kg~(-1) and 70.96 Bq·kg~(-1) ± 2.65 Bq·kg~(-1), and 0 and 15.12 Bq·kg~(-1) ? 1.22 Bq·kg~(-1), respectively, while those concentrations in the recently deposited sediments in the reservoir were 3.06 Bq·kg~(-1) ± 0.23 Bq·kg~(-1) and 72.66 Bq·kg~(-1) ± 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 t·km~(-2)·a~(-1) and 886 t·km~(-2)·a~(-1), respectively.