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Mercury transformations and fluxes in sediments of a riverine wetland
Authors:Richard R Goulet  Jonathan Holmes  Laurier Poissant  David RS Lean  Marc Amyot
Institution:a INRS-ETE, Université du Québec, 490, rue de la Couronne, Québec, Que., Canada G1K 9A9
b Department of Biology, University of Ottawa, Box 450, Station A, Ottawa, Ont., Canada K1N 6N5
c Department of Chemistry and Department of Environment and Geography, University of Manitoba, Winnipeg, Man., Canada R3T 2N2
d Environment Canada, Science and Technology Branch, Centre Saint-Laurent, 105 rue McGill, 7e étage (Youville), Montréal, Que., Canada H2Y 2E7
e Department of Soil Science, 51 Campus Drive, University of Saskatchewan, Saskatoon, Sask., Canada S7N 5A8
f Departement des sciences biologiques, Pavillon Marie-Victorin, 90 Vincent d’indy, Université de Montréal, Montréal, Que., Canada H3C 3J7
Abstract:Porewater samples were obtained on five occasions during spring, summer and fall by in situ dialysis from three sites of a large freshwater wetland situated along the St. Lawrence River. These samples were analysed for total dissolved mercury (Hg]T) and methylmercury (MeHg]) concentrations and for complementary variables including dissolved sulfate, sulfide and elemental sulfur concentrations. Sediment cores were obtained on three occasions from one of these sites for the determination of total mercury ({Hg}T) and methylmercury ({MeHg}) concentration as well as mercury methyltransferase (HgMT) activity profiles. {MeHg} and HgMT activity varied with time and sediment depth. The porewater Hg]T and MeHg] depth profiles varied with time and among sites. Modeling the porewater MeHg] profiles with a one-dimensional reaction-transport equation allowed identification of the sediment depths where MeHg is produced or consumed, as well as an estimate of the net in situ MeHg production rates in the sediments. The model-predicted depths of MeHg production, as well as the sulfate concentration and the HgMT activity depth distributions are all consistent with the involvement of sulfate reducing bacteria in the production of MeHg.
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