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INCREASE IN NUTRIENTS, MERCURY, AND METHYLMERCURY AS A CONSEQUENCE OF ELEVATED SULFATE REDUCTION TO SULFIDE IN EXPERIMENTAL WETLAND MESOCOSMS
Myrbo, A., E.B. Swain, N.W. Johnson, D.R. Engstrom, J. Pastor, B. Dewey, P. Monson, et al.
Journal of Geophysical Research: Biogeosciences 122:2769-2785(2017)

In water-saturated wetland soils, which usually are anoxic, decomposition of dead plants and other organic matter is greatly retarded by the absence of oxygen. The addition of sulfate can allow bacteria that respire sulfate instead of oxygen to decompose organic matter that otherwise would not decay. This accelerated decay has multiple consequences that are concerning. The bacteria that respire sulfate "breathe out" hydrogen sulfide, analogous to the conversion or respiration of oxygen to CO2. Sulfide is very reactive with metals, which makes it toxic at higher concentrations. In addition to the release of sulfide, sulfate-accelerated decomposition of plants releases phosphorus and nitrogen, fertilizing the waterbody. Decomposition also mobilizes Hg (which is everywhere, thanks to atmospheric transport) into the surface water. The microbes that convert sulfate to sulfide also methylate Hg, producing methylmercury (MeHg), the form of Hg that contaminates fish. This study demonstrates that adding sulfate to a wetland can not only produce toxic levels of sulfide but also increase the surface water concentrations of nitrogen, phosphorus, Hg, and MeHg. https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017JG003788



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