Title: Estimation of soil erosion in the Xihanshui River Basin by using 137Cs technique

Abstract

The Cesium-137 technique was used to estimate soil erosion in the Xihanshui River Basin. More than 100 samples were taken from 10 sites and 20 hillslopes with a 10cm diameter hand-operated core driller. Each sample was 60 cm long. The 137Cs activity was analyzed by gamma spectrometry. The simplified mass balance model and the profile distribution model were used to calculate soil erosion and deposition rate. The local 137Cs reference ranged from 1,600 to 2,402 Bq m-2. The data shows an exponential decrease of mass concentration and amount with depth in an undisturbed soil profile. Soil erosion in the river basin is moderate or severe on cultivated land with annual erosion rates of 2,000-6,000 t km-2 yr-1. In general, very severe or severe soil erosion occurred at the upper slope sections, moderate or severe soil erosion at the middle section, and moderate or slight soil erosion at the lower slope sections. On the slopes with natural vegetation, consisting of herbaceous and wood species, the erosion rate is much lower or not detectable. On the lower section of slopes with well-developed vegetation however, there was no soil loss, instead deposition occurred at a rate of more than 300 t km-2 yr-1. The slope gradient and vegetation cover affected soil erosion and deposition rates. In general, the rate of soil erosion was proportional to the slope gradient and inversely proportional to the degree of vegetative cover.