Accumulation of Pollutants in Proglacial Lake Sediments: Impacts of Glacial Meltwater and Anthropogenic Activities

With global warming, the melting of glaciers can result in the release of pollutants into the environment. For remote Alpine lakes, both atmosphere-deposited anthropogenic pollutants and glacier-released pollutants can eventually sink in the sediment. To date, there has, to the best of our knowledge, been no attempt at quantifying the contributions of these processes to the accumulation of pollutants in glacial lake sediment. To fill this gap, a semi-enclosed proglacial lake located in the southern Tibetan Plateau was chosen and a 28 cm sediment core, which can be dated back to 1836, was used to explore the temporal trends of trace elements, Hg, and black carbon (BC) during the past two centuries. Geochemical indicators (Rb/Sr, Ti-Zr-Hf, and sedimentary rate) in sediment showed an overall continuous warming of the lake, while the temporal trends of fluxes of toxic elements and BC were broadly associated with their emission patterns. By using a positive matrix factorization model, the contribution of the anthropogenic source rose from <10% in the 1850s to >40% after the 1980s. However, the signal of glacial meltwater release was also distinct, and the greatest contribution of ice-snow meltwater reached up to 61% in the 1950s. Regarding the most recent two decades, 90% of pollutant deposition in the Tibetan sediment can be attributed to the combined forces of primary emissions and glacial release.