Geostatistical analyses and co-occurrence correlations of heavy metals distribution with various types of land use within a watershed in eastern QingHai-Tibet Plateau, China.

Due to increasing anthropogenic disturbance, various pollutants have been frequently detected in QingHai-Tibet Plateau, where the environment is extremely fragile and sensitive to human activities. In this study, 51 sampling sites with different land covers were selected in a sub-basin in the Huangshui watershed in eastern QingHai-Tibet Plateau. A total of 102 soil samples were collected at surface (0-20 cm) and subsurface (20-40 cm) depths for studying on heavy metal pollution in this region. The relationships between land cover types and spatial distribution of five heavy metals Cr, Cu, Cd, Pb, and Zn were systematically analyzed combing field survey, remote-sensing database, and geostatistical methods. The relationships between soil physiochemical properties and heavy metals were assessed by geostatistics, co-occurrence network analysis and geographically weighted regression (GWR) model. The results indicated that the average concentrations of all five heavy metals in soil were higher than the local background values, indicating the influence of anthropogenic inputs of these elements into environment. Strong positive correlations were observed between some heavy metals and soil physic-chemical properties in different land covers, combined with the geoaccumulation index, human activities contribution can be interpolated. The Cr and Zn in surface soils are explainers for Cr and Zn in subsurface soils in the GWR models respectively, as well as the area of different land cover. Cd contamination was specifically analyzed due to its degree of contamination and then the sources of Cd were identified such as energy production as well as chemical fertilizers. The results of this study can provide basic data for long-term accumulation of heavy metals in soils under different land uses in QingHai-Tibet Plateau.