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

The Hilly Sichuan Basin is one of the most populous agricultural regions in the Upper Yangtze River Basin and has an area of about 105000 km2. Cropland ratios and population densities vary between 0.3 and 0.7 and be-tween 400 and 800 people/km2, respectively, in the Si-chuan basin. The basin is considered as one of the most severely eroded regions in the Upper Yangtze River Basin as well in China. Soil erosion rates were reported mostly to be greater than 5000 t·km-2·a-1 by the first st…

Sediment source identification by using137Cs and210Pb 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.