Production and Loss of Methylmercury and Loss of Total Mercury from Boreal Forest Catchments Containing Different Types of Wetlands

Abstract

Four terrestrial boreal forest catchments containing different types of wetlands were studied to determine their strength as sources or sinks of methylmercury (MeHg) and total mercury (THg) to downstream ecosystems and to determine if patterns seen in one year were consistent over several years. All catchments were sinks for THg. The wetland type, percentage wetland area (0−25%), or annual water yield did not appear to have a consistent effect on the magnitude of this retention. Wetland areas of the catchments were always net sources of MeHg. Unlike for THg, there were large and consistent differences in the source strength among wetland types for MeHg. These differences appeared to be related to differences in the internal hydrology of the wetlands. All types of wetlands were greater sources of MeHg during years of high water yield, but even during years of low flow all wetland types were sources of MeHg. Thus, we conclude that wetlands are important sites of MeHg production in boreal ecosystems on the l...