Katherine D. Sheehan1, Ivan Fernandez1, Aria Amirbahman1, and Stephen J. Kahl2. (1) University of Maine, 5722 Deering Hall - Room 1, Orono, ME 04469-5722, (2) Plymouth State University, MSC #63, 213 Boyd Science Center, Plymouth, NH 03264
Mercury deposition to the landscape is typically evaluated using data from precipitation Hg deposition. Litterfall is also an important flux for Hg to soils in forested landscapes, yet much less is known about litterfall Hg. We measured litterfall Hg contributions to Hg deposition in two small forested research watersheds in Acadia National Park, Maine. Hadlock Brook and Cadillac Brook watersheds are of similar size, relief, and are exposed to the same climatic conditions, yet have differences in vegetative community composition due to a fire that burned the majority of the Cadillac watershed in 1947. Litterfall was collected at 39 sampling sites in 2003 and 2004 and analyzed for total Hg. Four vegetation classes were designated in this study as hardwoods, softwoods, mixed and scrub. The mean litter Hg concentration in softwoods (58.8 ±3.3 ng Hg g-1) was significantly greater than in mixed (41.7 ± 2.8 ng Hg g-1) and scrub (40.6 ± 2.7 ng Hg g-1), and significantly lower than in hardwoods (31.6 ± 2.6 ng Hg g-1). In contrast, the mean weighted litter Hg flux was not significantly different among vegetation classes. Landscape characteristics (i.e., aspect, elevation and canopy density) were significantly correlated with litter Hg concentrations and flux. A significant negative correlation was defined between litter C:N and litter Hg concentrations attributable to differences in woody litter components. The estimated annual deposition of Hg via litterfall in Hadlock Brook watershed (10.1 µg m-2) and Cadillac Brook watershed (10.0 µg m-2) was greater than precipitation Hg deposition and similar to or greater than the magnitude of Hg deposition via throughfall. These results demonstrate that litterfall Hg flux to forested landscapes is at least as important as precipitation Hg inputs and are an essential consideration in Hg mass balance calculations.
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