Distribution Characteristics and Ecological Risk Assessment of Soil Heavy Metals in Typical Watersheds of the Qinghai-Tibet Plateau

Abstract

The Qinghai-Tibet Plateau is an extremely vulnerable area that is sensitive to human activities. In recent years, more and more human disturbances have been detected in this area. This study analyzed the spatial distribution and ecological risks of 7 heavy metals (Cr, Ni, Cu, Zn, As, Cd, and Pb) in two regions, namely the Bailong River and Yellow River and their two tributaries (BY region) in Gannan and the Yarlung Zangbo River and its two tributaries (YZ region) in Tibet. In terms of spatial distribution, concentrations of the seven heavy metals were higher in the east and lower in the west of the BY region. The average concentrations all exceeded the background value of the Qinghai-Tibet Plateau, especially for Cd (4.50 times) and As (2.83 times). High Pb concentrations were mainly found in water, urban and rural residential land, and industrial and construction land. In the YZ region, heavy metal concentrations were lower along the river, while high-altitude areas exhibited higher heavy metal concentrations. The average concentrations of Ni, Zn, As, and Cd exceeded the background values of the Qinghai-Tibet Plateau, especially that of Cd (3.13 times), which mostly exhibited high values in water coverage areas. The geo-accumulation index method and the potential ecological risk index method show that the degree of As and Cd pollution was relatively high in the BY region in Gannan, with the greatest potential ecological risk occurring in the water coverage area. In the YZ region in Tibet, the degree of Cd pollution was high, with the highest potential ecological risk also occurring in the water coverage area. This study provides significant guidance for the environmental protection, sustainable development, and utilization of soil under different types of land use in the Qinghai-Tibet Plateau.