The impact of land use changes and erosion process on heavy metal distribution in the hilly area of the Loess Plateau, China

Land use change alters the hydrological process, which in turn affects the migration of heavy metals. However, analyses of the watershed-scale distribution of heavy metals from slope to dam fields have seldom been studied. In this study, three land-use types on the slope (cropland, shrubland, grassland) and dam land in the channel on the Loess Plateau were selected to analyze the relationship between the change of slope erosion rate and the migration process of Manganese (Mn), Chromium (Cr), Zinc (Zn), Vanadium (V), Nickel (Ni), Copper (Cu), Arsenic (As) and Cobalt (Co) in soil. Moreover, the sources of heavy metals in sediments and their historical deposition process were revealed. It was found that the concentrations of Cr and As were higher in cropland than that in grassland and shrubland. The soil erosion of cropland was the most serious, and the maximum annual erosion rate was as high as 10,853.56 t km-2. The distribution of heavy metals was related to erosion rate in the cropland. With soil erosion, Cr, V, As, Co and Zn in cropland were prone to runoff migration. Cr and As in dam sediments mainly originated from the agricultural activities in cropland. Cu, Co, Mn, Ni, V and Zn in the dam land were largely affected by soil parent material. Land use and soil erosion were important factors influencing the redistribution of heavy metals. By optimizing land use patterns and reducing soil erosion, it is possible to control the migration and accumulation of heavy metals in the watershed. The findings of this study can serve as important reference for reducing non-point source pollution.