Timothy Scherbatskoy1 (email@example.com) & James B. Shanley2 (firstname.lastname@example.org)
1 School of Natural Resources, University of Vermont, Burlington, VT 05405-0088, U.S.A.
2 US Geological Survey, Box 628, Montpelier, VT 05601, U.S.A.
Total mercury (Hg) deposition and input/output relationships were investigated in an 11-ha deciduous forested catchment in northern Vermont as part of ongoing evaluations of Hg cycling and transport in the Lake Champlain basin. This research is being carried out in cooperation with the University of Michigan Air Quality Laboratory as part of a regional study on Hg deposition and cycling in the Great Waters. At our Vermont site, atmospheric Hg deposition (wet + dry) was 124 mg ha-1, during the one-year period, March 1994 through February 1995, and 146 mg ha-1 from March 1995 through February 1996. In the same period, stream export of total Hg was 33 mg ha-1 and 16 mg ha-1, respectively. Thus, there was a net retention of Hg by the catchment of 73 % the first year and 89 % the second year. In the first year, half of the annual stream export occurred on the single day of peak spring snow-melt in April. In contrast, the maximum daily export in the second year, when peak stream flows were considerably lower, was 1.9 mg ha-1 during a January thaw. The ultimate fate of the Hg retained by this forested catchment is not known at this time.
Dissolved Hg concentrations (<0.22 µm) in stream water ranged only from 0.5-2.6 mg L-1, even when total (unfiltered) concentrations were greater than 10 ng L-1 during high flow events. Total Hg concentrations in stream water were correlated with the total organic fraction of suspended sediment, suggesting the importance of organic material in Hg transport within the catchment. High flow events and transport with organic material may be especially important mechanisms for the movement of Hg through forested ecosystems.
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