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

Abstract

In order to assess its potential for estimating soil redistribution rates, the naturally occurring fallout radionuclide 210Pb ex has been used in parallel with 137Cs, 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 210Pb 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 210Pb released to the atmosphere across the local region moving up into the upper troposphere, where is would be more widely dispersed. The mean 210Pb ex and 137Cs inventories measured in cores collected from the upper part of the field with an average slope of 10° 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°) were 11,388 Bq m − 2 and 1299 Bq m − 2 . The pattern of post-fallout 210Pb ex and 137Cs 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 farmer. The estimates of annual rates of soil loss provided by the 210Pb ex measurement are closely comparable with those derived from the 137Cs measurements and are consistent with existing knowledge for the study area. The results obtained from this study confirm the potential for using 210Pb 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 210Pb ex and 137Cs 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.