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

Abstract

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 semienclosed 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.

Impact of global warming on regional cycling of mercury and persistent organic pollutants on the Tibetan Plateau: current progress and future prospects

“…For remote alpine lakes, likewise, the atmospheric deposited Hg and POPs released by glaciers can end up sinking into the sediments. [172][173][174] To ll this critical research gap, Zhu et al 103 selected a semi-closed preglacial lake in the southern part of the TP and reported profound anthropogenic contributions ranging from <10% in the 1850s to >40% aer the 1980s. Moreover, the observed contribution from meltwater release in the 1950s was 61%.…”

“…Over the past two decades, 90% of the pollutant deposition in the sediments can be attributed to the combined action of major pollutant discharge and glacial release. 103…”

Black carbon and organic carbon dataset over the Third Pole

“…As BC is chemically inert in the lake sediment cores, it can serve as an archive and reliable indicator to investigate the source and transport of BC in the past (Han et al, 2012). The BC investigation from lake sediment cores over the plateau revealed an increasing trend of BC concurrent with increased anthropogenic emissions since the 1950s (Cong et al, 2013;Han et al, 2015;Neupane et al, 2019;Zhu et al, 2020) and suggested that BC deposition in recent decades has increased about 2-3-fold compared to the background level.…”

APCC Data Report I: Black carbon and organic carbon dataset from atmosphere, glaciers, snow cover, precipitation, and lake sediment cores over the Third Pole

“…As BC is chemically inert in the lake sediment cores, it can serve as an archive and reliable indicator to investigate the source and transport of BC in the past (Han et al, 2012). The BC investigation from lake sediment cores over the plateau revealed an increasing trend of BC concurrent with increased anthropogenic emissions since the 1950s (Cong et al, 2013;Han et al, 2015;Neupane et al, 2019;Zhu et al, 2020), and suggested that BC deposition in recent decades have increased about 2−3 fold compared to the background level.…”