Distribution characteristics of heavy metals in Tibetan Plateau surface soils and its influencing factors
LIU Xiao-li1,2, Gao Wen-hua1, Wei Ting3, Dong Zhi-wen2, Shao Ya-ping4
1. College of Geography and Environmental Science, National Demonstration Center for Experimental Environment and Planning Education, Henan University, Kaifeng 475004, China; 2. School of Geography and Information Engineering, China University of Geosciences, Wuhan 430078, China; 3. State Key Laboratory of Cryosphere Sciences, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China; 4. Institute of Geophysics and Meteorology, University of Cologne, Germany
Abstract：Due to the delicate ecological balance of the Tibetan Plateau (TP) and its heightened vulnerability to human-induced impacts, there has been a growing scholarly focus on investigating heavy metal pollution in the plateau's environment in recent years. In this study, we conducted a comprehensive analysis of nine distinct heavy metal elements (HMs), including As, Cr, Co, Ni, Cu, Mo, Cd, Pb, and Sb, using topsoil samples collected from the TP during the period of 2021~2022. This analysis was complemented by evaluating snow and cryoconite samples obtained during the same timeframe. Our investigation revealed a significant disparity in HM content between TP topsoil (with an average of 256.5μg/g) and snow-cryoconite samples (with an average of 14.6μg/L). Specifically, the calculated average Igeo value for As indicated moderate pollution (1.32), while the remaining heavy metals in the soils showed predominantly non-polluted to lightly polluted levels. Clear differences in both composition and spatial distribution of HMs were evident between the topsoil and the snow-cryoconite matrix. Regarding spatial distribution, composition, and Enrichment Factors (EFs), congruence was observed among different regions in the topsoil samples. Through a triangulation of correlation analysis, principal component analysis, and the APCS-MLR method, our investigation identified three principal sources of HMs in the topsoil: coal combustion (42.3%), inherent natural sources within the surface soil (20.6%), and vehicular emissions (14.2%). Disparities in the composition and distribution of HMs within high-altitude glaciers and topsoil samples were attributed to local processes of natural weathering and anthropogenic influences on the topsoil. These factors tend to mask the influence of long-range transport (LRT) on HM content in topsoil. Conversely, HMs present in snow and cryoconite samples are more susceptible to the effects of LRT sources. This study provides a holistic overview of the composition of HMs in the extensive expanse of TP topsoil,highlighting significant enrichment of certain elements, such as As, while emphasizing an overall condition of relative purity in terms of HM content.
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