Inputs, outputs, and pool sizes of total mercury (Hg) were measured in a forested 10 ha watershed consisting of a 7 ha hardwood-dominated upland surrounding a 3 ha conifer-dominated peatland. Hydrologic inputs via throughfall and stemflow, 13±0.4 μg m-2 yr-1 over the entire watershed, were about double precipitation inputs in the open and were significantly higher in the peatland than in the upland (19.6 vs. 9.8 μg m-2 yr-1). Inputs of Hg via litterfall were 12.3±0.7 μg m-2 yr-1, not different in the peatland and upland (11.7 vs. 12.5 μg m-2 yr-1). Hydrologic outputs via streamflow were 2.8±0.3 μg m-2 yr-1 and the contribution from the peatland was higher despite its smaller area. The sum of Hg inputs were less than that in the overstory trees, 33±3 μg m-2 above-ground, and much less than either that in the upland soil, 5250±520 μg m-2, or in the peat, 3900±100 μg m-2 in the upper 50 cm. The annual flux of Hg measured in streamflow and the calculated annual accumulation in the peatland are consistent with values reported by others. A sink for Hg of about 20 μg m-2 yr-1 apparently exists in the upland, and could be due to either or both storage in the soil or volatilization.
Bibliographical noteFunding Information:
We would like to thank Carissa Pang and Bruce Cook for their helpful discussions, insights, and data. We would also like to thank Sandy Verry, Art Elling, and Deacon Kylander of the USDA Forest Service for their help in sample collection. Partially supported by a grant from the Legislative Commission on Minnesota Resources to the Minnesota Pollution Control Agency, by grants from the U.S. Geological Survey through the Water Resources Center of the University of Minnesota, and by projects 25-054 and 25-032 of the University of Minnesota Agricultural Experiment Station. Published as article 991250077 in the Scientific Journal Series of the Minnesota Agricultural Experiment Station.
- Atmospheric deposition
- Mercury cycling