A (137)Cs erosion model with moving boundary

The Combined Use of 137Cs Measurements and Zr-Methods for Estimating Soil Erosion and Weathering in Karst Areas of Southwestern China

Soil physical erosion and chemical weathering quantification at the slope scale are important to reveal the material cycle of the ecosystem in the karst region, because of the high heterogeneity due to the complex habitats. The Zr-based mass balance method has been widely used to quantify long-term physical erosion and chemical weathering at the slope scale, but the method is still in the exploratory research stage for quantifying short-term physical erosion and chemical weathering. In this paper, sloping fields (nine sampling sites and two sloping fields) in Zunyi, within the Guizhou karst region, were studied. We attempted to quantify the short-term physical erosion and chemical weathering rates by 137Cs combined with the Zr-based mass balance method, and an ideal distribution curve of the Zr concentration in the soil surface layer of a karst region is proposed. The results showed the following: (1) The average soil erosion rate on the slope of the study area is 580 t/(km2·a), which is equivalent to 14% of the average value of the Wujiang River basin in which it is located. This shows that the spatial distribution of soil erosion in this area varies significantly. (2) The Zr concentration in the erosion profile (EUC (1)) corresponds to 48% of that in the deposition profile (DUC (3)). This indicates that physical erosion in the study area survives chemical weathering, which is also consistent with the relationship model hypothesis. In addition, the vertical distribution characteristics of Zr concentration in all profiles are basically consistent with the ideal hypothesis curve. (3) The chemical weathering rate of the topsoil has been preliminarily estimated to be around 30 t/(km2·a), and the ratio between the physical soil erosion and chemical weathering is 20:1. The results show that the physical erosion is dominant over the chemical weathering of topsoil, and the chemical weathering rate was proportional to the physical erosion. This study provides a new method for quantifying short-term soil erosion and weathering erosion at the slope scale in karst regions, which is important for regional ecological restoration and sustainable development.

137Cs estimates of soil erosion rates in a small catchment on a channelized river floodplain in the lower reaches of Yangtze River, China

Channelization significantly affects soil erosion in river floodplains. The object of this study was to use ¹³⁷Cs as a tracer to determine the ¹³⁷Cs inventory and derived soil erosion rates under various land use types in a catchment on channelized river floodplain in the lower reaches of Yangtze River, China. Sampling was carried out to establish a¹³⁷Cs reference inventory in a 70-year old paddy field located on the shoulder-slope of a local hill. The mean reference inventory of ¹³⁷Cs was 1275 Bq m^-2, whereas the ¹³⁷Cs inventory within the catchment ranged from 284 to 1150 Bq m^-2 and the soil erosion rates from -33.3 to -2.4 t ha^-1 yr^-1, respectively. The dominated land use of paddy in cultivated soils contributed relative low soil erosion. Bamboo and castanea mollissima were preferential for local land uses in uncultivated soils in comparison with woodland and Pinnus massoniana. The rates of soil erosion rates in old tea garden were higher than that in new tea garden. Overall, severe soil erosion and no deposition in the entire catchment occurred in the entire catchment due to the human-induced channelization in the 1970s. Our results suggest that restricting farmland being returned to tea plantations, thereby maintaining the current land use types would reduce soil erosion in river floodplain in the future.