SPATIAL DISTRIBUTIONS AND YIELDS OF HG AND TRACE ELEMENTS FROM AN OMBROTROPHIC PEATLAND

In this study, we examined the biogeochemistry of mercury and other metals in a peatland watershed (S2 peatland, Marcell Experimental Forest, MN, USA) from 2010 to 2012. Mercury and trace element concentrations were measured in porewaters collected from multiple lagg and bog locations. Peat porewaters were sampled repeatedly over time along six transects extending from the upland to the lagg to the center bog area. Three transects were downstream of a convex upland area and three were adjacent to a concave upland area. We compare mercury and other metal concentrations in runoff waters from upland soils with outflowing stream water and atmospheric deposition. Along with basic water chemistry and dissolved organic carbon (DOC), samples were analyzed for trace metals, total mercury, and methyl mercury content using an ICP-MS. Results so far suggest 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. Differences between concave and convex topographies were noted, particularly following large rainfall events. Transects adjacent to convex landscapes typically had similar Hg porewater concentrations extending from the lagg towards the bog; transects adjacent to concave upland areas were characterized by decreasing Hg concentrations extending from the lagg towards the bog. After large rainfall events, however, both convex and concave transects exhibited Hg levels decreasing from the lagg towards the bog, suggesting significant inputs from the uplands. Conversely, Pb, for example, where transport from the upland to the bog is not as significant, porewater concentrations generally decreased extending from the lagg to the bog in both convex and concave transects. These results point towards the importance of hydrologic and landscape influences on trace element transport within the peatland watershed.