Biogeochemical Cycling of Mercury in Hongfeng Reservoir, Guizhou, China

Abstract

Mercury accumulation in aquatic food chains is a global public health concern because of the dangers of human exposure to methylmercury. Hongfeng reservoir, situated in Guizhou Province, southwestern China, is a water body that suffers from mercury pollution. Its source of mercury is anthropogenic and mainly includes industrial discharge from coal-fired power plants, chemical plants using mercury as a catalyst, and atmospheric deposition. Here, we report on the temporal and spatial distribution of different mercury species in the water of the reservoir and analyze possible effects of eutrophication on the biogeochemical cycling of mercury. Hyper-eutrophication of the reservoir affected the concentration and distribution of mercury species in the water through algal blooms. Microalgae have a large capacity to bind mercury, and represent a substantial pool of mercury in the aquatic system. Hyper-eutrophication results in low DO and high DOC that accelerates the formation of MeHg in the hypolimnion, especially in summer. Hongfeng reservoir is a large net sink of total mercury and a net source of MeHg. The mercury cycling at the sediment–water surface indicates that sediment dominates the fate of both total mercury and methylmercury, but the fluxes of mercury diffusing from pore water contribute only weakly to mercury in water. The MeHg-enriched water discharged from the anoxic hypolimnion poses a serious risk to downstream ecosystems.