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. Aver-age 137Cs and 210Pb concentrations in the source ...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. Aver-age 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 Bqkg-1, 4.01±0.31 and 70.96±2.65 Bq·kg-1, and 0 and 15.12±1.22 Bq·kg-1, re-spectively, while those concentrations in the recently depos-ited 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, gen-tle cultivated terraces and bare slopes (including channel banks) were estimated to be 18%, 46% and 36%, respec-tively. Cultivated terraces and bare slopes (including channel banks) were the first and the second important sediment sources in catchment. Specific sediment yield in the catch-ment 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 esti-mated to be 173 and 886 t·km-2·a-1, respectively.展开更多
Three soil cores collected from China and UK show the 210Pbex and 137Cs depth distribution on uncultivated and cultivated land. Depth distributions of the two nuclides are very similar. Those nuclide concentrations ar...Three soil cores collected from China and UK show the 210Pbex and 137Cs depth distribution on uncultivated and cultivated land. Depth distributions of the two nuclides are very similar. Those nuclide concentrations are higher in the top horizon and decrease exponentially with depth on uncultivated land while the concentrations are almost uni-form throughout the plough layer as a result of mixing asso-ciated with cultivation on cultivated land. 210Pbex reference inventory in the Loess Plateau is 573 mBq·cm-2, a little higher than 520.0 mBq·cm-2 in UK. Distribution of artificial fallout 137Cs, produced during the nuclear testing period of the late 1950s and 1960s, is in an unsteady state. In contrast, distribution of natural fallout 210Pbex is in a steady state un-der constant conditions of land environment and erosion processes for a long term, e.g. >100 years. Therefore, mass balances of 137Cs and 210Pbex in soil are different. According to its processes of continues deposition from the atmosphere, nature decay and losses with soil losses, 210Pbex steady state mass balance models for cultivated land as well as for uncul-tivated land are developed to estimate soil erosion rates in this paper. Besides, the proportion of freshly deposited 210Pbex fallout removed by erosion on cultivated land can also be calculated from 210Pbex depth distribution at a reference site of uneroded permanent grass land.展开更多
文摘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. Aver-age 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 Bqkg-1, 4.01±0.31 and 70.96±2.65 Bq·kg-1, and 0 and 15.12±1.22 Bq·kg-1, re-spectively, while those concentrations in the recently depos-ited 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, gen-tle cultivated terraces and bare slopes (including channel banks) were estimated to be 18%, 46% and 36%, respec-tively. Cultivated terraces and bare slopes (including channel banks) were the first and the second important sediment sources in catchment. Specific sediment yield in the catch-ment 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 esti-mated to be 173 and 886 t·km-2·a-1, respectively.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.40271015 and 900102017)the Stiate Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,the Chinese Acatemy of Sciences(CAS)(Grant No.SKLLQG0206)+1 种基金the Knowledge Innovation Project of Water Erosion Prediction Modeling of CAS(Grant No.KZCX3-SW-422)IAEA(12322/RO).
文摘Three soil cores collected from China and UK show the 210Pbex and 137Cs depth distribution on uncultivated and cultivated land. Depth distributions of the two nuclides are very similar. Those nuclide concentrations are higher in the top horizon and decrease exponentially with depth on uncultivated land while the concentrations are almost uni-form throughout the plough layer as a result of mixing asso-ciated with cultivation on cultivated land. 210Pbex reference inventory in the Loess Plateau is 573 mBq·cm-2, a little higher than 520.0 mBq·cm-2 in UK. Distribution of artificial fallout 137Cs, produced during the nuclear testing period of the late 1950s and 1960s, is in an unsteady state. In contrast, distribution of natural fallout 210Pbex is in a steady state un-der constant conditions of land environment and erosion processes for a long term, e.g. >100 years. Therefore, mass balances of 137Cs and 210Pbex in soil are different. According to its processes of continues deposition from the atmosphere, nature decay and losses with soil losses, 210Pbex steady state mass balance models for cultivated land as well as for uncul-tivated land are developed to estimate soil erosion rates in this paper. Besides, the proportion of freshly deposited 210Pbex fallout removed by erosion on cultivated land can also be calculated from 210Pbex depth distribution at a reference site of uneroded permanent grass land.
