A comparative study of mercury speciation and the vertical movement of newly added mercury across the mercury methylation layer in three contrasting wetlands

Extensive studies have shown that wetland are areas of rapid methylmercury (MeHg) production, yet we are presently unable to predict the in situ production of MeHg in wetlands. We hypothesize that McHg is produced primarily in a thin "mercury methylation layer" (MML) in sediments under dedicate pH, sulfide and dissolved organic matter conditions which ultimately decide mercury speciation and bioavailability to mercury methylators (e.g. sulfate reducing bacteria).; To probe the relation between MeHg production and Hg speciation, high resolution profiling was conducted to uncover detailed overlying water and porewater chemistry (e.g. Hg, MeHg, pH, DOC, sulfide, and in one instance thiols) across the MML in three contrasting wetlands (Baie St. Francois in Quebec, Delta Marsh in Manitoba and Lake 632 in Ontario). 202Hg addition experiments using mesocosms were carried out in two of the wetlands (Delta Marsh and Lake 632) to further trace the development and dynamics of the MML. (Abstract shortened by UMI.)...