New England Coastal Basins Mercury Deposition Network

SUMMARY

(from OFR2005-1368)

The rate of atmospheric mercury (Hg) deposition predicted for New England is thought to be among the highest anywhere in the contiguous United States and is most likely the dominant source of Hg input to terrestrial and aquatic ecosystems. In New England, more than half of the deposition is estimated to come from sources within the region. To determine if there are regional scale variations in Hg wet-deposition around the Boston, Mass. metropolitan area (southeastern New Hampshire and eastern Massachusetts), the U.S. Geological Survey, in cooperation with the Town of Ipswich, Mass., and in collaboration with Frontier Geosciences, the New Hampshire Department of Environmental Services, and the Blue Hill Observatory, designed a four-site network to monitor Hg in wet deposition.

Atmospheric Hg wet-deposition was examined by the use of newly designed wet-deposition sampler. The new sampler design was evaluated to determine reliability and capture efficiency. High capture efficiency (median values of 0.95 and 1.01) occurred with the top-loading sampler, likely reflecting the enhanced collection efficiency of the optical infrared precipitation sensor during light precipitation, and the improved temperature distribution in the top-loading model. Wet-deposition samples collected from January 2002 to August 2004 were analyzed for total mercury (HgT), and a subset of samples from September 2003 to August 2004 were analyzed for methyl mercury (MeHg). Concentrations of HgT in precipitation ranged from 0.73 to 24.6 ng/L at the four sites, whereas MeHg concentrations at all sites were below the detection level of 0.04 ng/L. The Manchester site, in the most urban environment, had the highest precipitation-weighted HgT concentration (8.31 ng/L), and Blue Hill, the closest site to Boston, had the highest deposition rate (9.98 μg/m2/yr). The regional background site, in Laconia, N.H., had the lowest precipitation-weighted HgT concentration (6.87 ng/L) and the lowest deposition rate (6.56 μg/m2/yr). The average annual Hg wet-deposition rate at sites in metropolitan Boston (Manchester, Beverly, and Blue Hill) was 9.16 μg/m2; 28 percent higher than the Hg deposition rate at the regional background site.