A simulation study of inorganic sulfur cycling in the water level fluctuation zone of the Three Gorges Reservoir, China and the implications for mercury methylation

• The water level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) in China experiences a drying and wetting rotation every, year, and the water level induced redox variation may influence inorganic sulfur speciation and mercury methylation. In this work, a simulative flooding and drying experiment and a sulfate added, flooding experiment were conducted to study this topic. The results showed that sulfate was reduced from the 10th d during the flooding period based on the detected sulfide in water and the increased elemental sulfur (S-0) in sediment. Sulfate reduction and sulfide re oxidation led to the increase of S-0 contents with the maximal values of 1.86 and 0.46 mg kg(-1) during the flooding and drying period, respectively. Methylmercury (MeHg) content in sediment displayed a rising trend (0.16-0.28 mu g kg(-1)) in the first 40 d during the flooding period, and then declined from 0.28 to 0.15 mu g kg(-1). A positive correlation between MeHg content and S-0 content in soil (r = 0.53, p < 0.05) was found during the flooding period, and a positive but not significant correlation between the percent of MeHg in THg (%MeHg) and S-0 content (r = 0.85, p = 0.08). In, sulfate added flooding simulation, MeHg content in sediment did not increase with the sulfate concentration increasing. The increased pyrite in high-sulfate treatment may fix mercury through adsorption process. This study demonstrated that inorganic sulfur species especially S-0 and chromium reducible sulfur (CRS) play an important role on mercury methylation in the WLFZ of the TGR. (C) 2016 Elsevier Ltd. All rights reserved.

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LANTBRUKSVETENSKAPER  -- Lantbruksvetenskap, skogsbruk och fiske -- Skogsvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Agriculture, Forestry and Fisheries -- Forest Science (hsv//eng)

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