Quantifying post-dam anthropogenic mercury accumulation in three gorges reservoir sediments using mercury isotopic...

The Three Gorges Reservoir (TGR) is the largest hydroelectric power facility in the world. Mercury (Hg) accumulation in sediment of the TGR has been highly concerned because of its far-reaching impacts on aquatic safety and human health. However, effects of hydrological modification on Hg accumulation processes after the full operation of the Three Gorges Dam (TGD) remain elusive. Here, we explored the dynamic accumulation of Hg in the mainstream sediment of water-level fluctuation zone in the whole TGR region during 2016-2020 and quantified the anthropogenic contribution to Hg accumulation by Hg stable isotopes. We found that the Hg concentration in sediment increased by ∼50 % when compared with the level before full operation of TGD. Furthermore, ∼7.0 Mg yr^-1 of Hg has been trapped in sediment since the year of 2016. Anthropogenic release directly contributed to 37 ± 15 % of Hg accumulation in sediment of the whole TGR region, of which up to 62 ± 19 % originated from the nearby megacity of Chongqing City. Results indicate that the long-term monitoring of Hg in sediment of the TGR and regulating industrial discharges from Chongqing are needed to avoid negative impacts on aquatic safety, specifically under the context of continuous sediment trapping and extreme climate.