The importance of microbial processes for the regulation of dissolved gaseous mercury (DGM) in deep freshwaters has not been previously investigated. In this study, we evaluated microbial mercury reductase and oxidase activities in depth profiles from Jack's Lake. In addition, detailed DGM depth profiles were determined for four sampling stations on Lake Ontario. Our results illustrate that microbial processes are an important factor regulating DGM in the hypolimnion. Levels of DGM in William's Bay in Jack's Lake were 6 times higher than that observed at Brooke's Bay. This was accompanied by a 10 fold reduction in mercury oxidase activity in William's Bay. When DGM concentrations are expressed on an aerial basis, DGM concentrations above the thermocline in Lake Ontario average 1.5 ng DGM m~(-2) and in small freshwater lakes it ranged between 0.1 and 0.8 ng DGM m~(-2). Further, it was demonstrated that the majority of DGM in large freshwater lakes such as Lake Ontario exists below the thermocline where photochemical oxidation and reduction processes cannot occur. The importance of this DGM to atmospheric flux rates is discussed.
展开▼
