Assessment of chemical weathering and physical erosion along a hillslope, southwest China

Abstract

The chemical compositions and soil erosion characteristics of three soil profiles along a hillslope in karst area, southwest China were investigated. The material sources, element behavior and relationship between soil erosion and soil formation are discussed. Based on the 137Cs technique, the mean soil redistribution rates were found to be 11.88, −15.31 and −21.03 t ha−1 year−1 in the summit (DSD), shoulder (DSY) and toeslope (DSJ) profiles, respectively. The results show that the three profile soils are in situ weathering products of the underlying bedrocks and have inherited relationships. The Al, rare earth elements (REEs) and high field strength elements (HFSEs) contents increase with increasing clay content in DSY and DSJ profiles, indicating that these elements could be loss with clay particles via soil erosion. Coarse particles contained Si accumulates at the DSJ profile due to the migration of soil from upslope, resulting in Si enrichment. The REEs and HFSEs are mainly transported from the deposition profile DSD as solutes by chemical weathering and from the erosion profiles DSY and DSJ as particles by physical migration. The DSY profile has the thinnest soil layer and lowest clay contents, which facilitate the chemical reaction between minerals and soil water. Above all, we believe that at some intermediate soil erosion rate, that soils with the least input of fresh materials could experience the strongest chemical weathering, resulting in vast dissolution of minerals such as feldspar. These results suggested that soil texture, topographical features and vegetation coverage together affect the soil chemical weathering, physical erosion and element behaviors in karst hillslope.