Mercury budget of an upland-peatland watershed

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.