Identification of anthropogenic contributions to heavy metals in wetland soils of the Karuola Glacier in the Qinghai-Tibetan Plateau

Deciphering apportionments of natural and anthropogenic sources to metal concentrations are essential for better understanding impacts of human activities on metal element distribution in remote alpine wetlands. In the present work, we investigated heavy metal distribution patterns and identified the substantial contributions from anthropogenic sources on heavy metal concentrations in wetland soils of the Karuola Glacier in Tibet using a geochemical model and lead isotopes. Mean iron (Fe), aluminum (Al), and scandium (Sc) concentrations were similar to their background values and manganese (Mn) was lower than that. Concentrations of copper (Cu), cadmium (Cd), lead (Pb), zinc (Zn), and chromium (Cr) were much higher than their background values. Cd was the main contaminant because more than 87.7% of Cd was anthropogenic. Al, Pb, and Sc showed significant positive correlations between each other, Cr and Mn concentrations were significantly and negatively correlated with Fe concentrations. No significant correlations were observed among Fe, Pb, Cu, Cd, and Zn. Three components were extracted by factor analysis. Al, Fe, Sc, Cr, and Mn were related primarily to the parent material, Pb in soils was from both endogenous and exogenous sources, and Cd, Zn, and Cu were considerably or mostly from anthropogenic sources. Endogenous sources represented about 59.85%-81%, 69.3%, 12.3%, and 58.1% for total Pb, Cu, Cd, and Zn in soils. Metal accumulation fluxes have been increasing over the past 200 years. Lead isotopic features showed that most anthropogenic Pb was attributed to Pb-Zn ore smelting and coal consumption.