A preliminary assessment of the potential for using 210Pbex measurement to estimate soil redistribution rates on cultivated slopes in the Sichuan Hilly Basin of China

In order to assess its potential for estimating soil redistribution rates, the naturally occurring fallout radionuclide Pb-210(ex) has been used in parallel with (CS)-C-137, derived from the atmospheric testing of nuclear weapon testing in the 1950s to 1970s, to estimate rates of soil redistribution on a sloping field with traditional erosion control measures located near Jiajia Village, Jianyang County, in the Sichuan Hilly Basin of China. The local Pb-210(ex) reference inventory of 12,860 Bq m(-2) is higher than those reported for many other areas of the world and may reflect the influence of cloudy weather in preventing Pb-210 released to the atmosphere across the local region moving up into the upper troposphere, where is would be more widely dispersed. The mean Pb-210(ex) and Cs-137 inventories measured in cores collected from the upper part of the field with an average slope of 10 degrees were 8028 Bq m(-2) and 993 Bq m(-2), respectively, and the equivalent values for the lower part of the field, where the slopes are steeper (20 degrees) were 11,388 Bq m(-2) and 1299 Bq m(-2). The pattern of post-fallout Pb-210(ex) and Cs-137 redistribution on the sloping field reflects not only the effects of water erosion and redistribution by tillage, but also the local traditional practice of Tiaoshamiantu, whereby sediment trapped in the ditches is returned to the fields by the fanner. The estimates of annual rates of soil loss provided by the Pb-210(ex) measurement are closely comparable with those derived from the Cs-137 measurements and are consistent with existing knowledge for the study area. The results obtained from this study confirm the potential for using Pb-210(ex) measurement to estimate soil erosion rates over medium-term timescale of 50-100 years. By combining the estimates of erosion rates provided by the Pb-210(ex) and Cs-137 measurements, the weighted mean net soil loss was estimated to be 48.7 t ha(-1) year(-1) from the upper subfield and 16.9 t ha(-1) year 1 from the lower subfield. These rates are considerably lower than the erosion rates obtained from runoff plot measurements in the local area. It is suggested that the traditional erosion control practices and the practice of Tiaoshamiantu have a significant effect in reducing soil loss and conserving valuable cultivated soil on sloping fields in the Sichuan Hilly Basin. (c) 2006 Elsevier B.V. All rights reserved.