Hydrological and biogeochemical controls on mercury fate and transport in a southern Ontario forested wetland

grantor: University of TorontoThis study assessed linkages between wetland hydrology, total mercury (HgT) and methylmercury (MeHg) fate and transport in Beverly Swamp, a forested swamp in southern Ontario, Canada. The hydrologically distinct wetland reaches exhibited differences in wetland-stream connectivity. Confined reaches showed little interaction with the wetland during low water levels, but there was hydrological and biogeochemical evidence of increased interaction at high flow. The unconfined reach showed disconnected, effluent flow during periods of high flow, and an influent regime during low flow. HgT flux in both reaches was highest during connected flow. Increased flux of McHg in the confined reaches was found during high flow, high water table connected periods due to decreasing redox and soil flushing. The unconfined reach showed no relationship between McHg and discharge due to periods of flow cessation and localized McHg production in-stream. Overall, the wetland is a sink for HgT and a source for McHg.M.Sc