137Cs budget during the period of 1960s in a small drainage basin on the Loess Plateau of China

A sediment profile with a thickness of 28.12 m in a failed reservoir in a small catchment of the Yuntaishan Gully in the Loess Plateau of China consisted of 44 flood couplets deposited during the period from 1960 to 1970 with total volume of 2.36 X 10(6) m(3). Specific sediment yields for a flood event varied from 300 t km(-2) to 14,400 t km(-2) and annual sediment yields varied from 2500 t km(-2) in 1966 to 40,000 t km(-2) in 1964 with a mean value of 12,700 t km(-2) a(-1) for the period. Average annual Cs-137 concentrations of the sediments increased from 0.92 Bq kg(-1) in 1960 to 4.82 Bq kg(-1) in 1963, then decreased to 1.53 Bq kg(-1) in 1970. The total Cs-137 activity in the reservoir sediments was 9.22 X 10(9) Bq, which accounted for 31.9% of the total Cs-137 fallout precipitation of 2.89 X 10(10) Bq within the catchment during the period. The proportion of the Cs-137 loss from the catchment to the Cs-137 fallout precipitation within the catchment in a year varied between 8.01% and 66.8%, and it was 20.9% for the peak Cs-137 deposition year of 1963 and 52.0% in 1964. By analysis of the Cs-137 budget in the catchment for the Cs-137 peak precipitation period from 1962 to 1964, the Cs-137 surface enrichment coefficient Gamma should be Much less than 0.23. And for calculation of soil losses on the cultivated land in the inter-gully area by using the Mass Balance Model 11, the value of Gamma should be 0.05-0.1. (C) 2005 Elsevier Ltd. All rights reserved.