METHYLMERCURY DYNAMICS IN THE POREWATERS OF AN OMBROTROPHIC PEATLAND

In this study, we examined the biogeochemistry of mercury and other metals in an ombrotrophic peatland watershed in 2010 and 2011. Mercury, methylmercury, and trace element concentrations were measured in the porewaters of the S2 peatland to identify important zones of methylmercury formation within the wetland. We also examined the transport of mercury and other metals from the upland to the peatland and examined how these factors related to the conversion of mercury to methylmercury within the peatland. Samples were collected from the S2 watershed at the Marcell Experimental Forest, MN, in the lagg area around the peatland, in subsurface runoff collectors, and in peat porewater transects extending from the lagg to the center bog area of the peatland. Along with basic water chemistry and dissolved organic carbon (DOD), samples were analyzed for trace metals, total mercury, and methyl mercury content using an ICP-MS. Results so far show that a significant amount of mercury and many metals enter the lagg area from the upland during rainfall events, while other metals that bind strongly to soil organic matter (e.g. lead and arsenic) have little input from the upland. Methylmercury levels in the upland were low relative to levels in the lagg and bog areas, as would be expected. The highest methylmercury levels were often found in distinct areas along the lagg margin that were also typically higher in total mercury, suggesting that mercury from the upland is possibly being methylated as it enters the lagg via upland runoff. Significant differences in methylmercury levels were also found between 2010 and 2011, pointing to the importance of hydrology influencing mercury transport and methylation conditions within the peatland.