Insight into atmospheric deposition and contamination of toxic Zinc in remote glacier regions of the Northwestern China

Zinc (Zn) plays an important role in biogeochemical cycles. Its excessive supplies, however, are detrimental to living organisms. To figure out Zn contamination and migration along the atmosphere-glacier-meltwater runoff path in various glaciers of central Asia, this work investigated the concentration, enrichment factors (EFs), deposition and meltwater release fluxes of Zn in large-scale glaciers and snowpacks of the Northwestern China. Results showed that the concentration and EF value of Zn exhibited a heterogeneous geographic distribution from west to east, with higher values in the Zhaosu snowpack in Tienshan Mountains of the west and Northeastern Tibetan Plateau (NETP) glaciers (e.g., Qiyi Glacier) of the east, and lower values in the central region. A compilation of EF data of Zn showed that glacier areas in the Northwestern China have experienced significant anthropogenic Zn pollution, which has spread to the glacier meltwater. We found that there were different degrees of Zn enrichment in the NETP glacial basins, with the highest enrichment observed in the terminus and upper reaches. Furthermore, the estimated Zn release flux from the Laohugou Glacier was 11 ± 2 t a−1, which was significantly higher than that of the non-glacial river (3.7 ± 3.3 t a−1). This highlights a substantial release of Zn from the glacial basins. Based on the HYSPLT model, we deduced that aeolian dust and anthropogenic aerosols originating from central Asia (e.g., Kazakhstan), Xinjiang province, and local sources are the probable sources of Zn deposition in glacier regions in the Northwestern China. A conceptual model was provided to illustrate the multiple origins and transport dynamics of Zn along the atmosphere-glacier-meltwater runoff pathway. Therefore, this work provides a more complete view and understanding of Zn distribution and biogeochemical cycle in high-altitude glacial areas of the Northwestern China.