New England Coastal Basins Mercury Deposition Network

DISTINGUISHING CONTRIBUTIONS OF WET AND DRY MERCURY DEPOSITION IN NEW ENGLAND

National Atmospheric Deposition Program meeting, September 27-30, 2005, Jackson, WY

Ann Chalmers¹, Peter C. VanMetre², Mark Nilles³, David Krabbenhoft⁴, and Eric Prestbo⁵

¹ U.S. Geological Survey, P.O. Box 628, Montpelier, VT 05601, T: 802-828-4511; F: 802-828-4465; E: chalmers@usgs.gov
² U.S. Geological Survey, Austin, TX
³ U.S. Geological Survey, Office of Water Quality, Lakewood, CO
⁴ U.S. Geological Survey, Middleton, WI
⁵ Frontier Geosciences, Seattle, WA


Abstract

Atmospheric deposition is an important source of mercury (Hg) to terrestrial and aquatic ecosystems across the globe. However, despite substantial advances over the past decade in our understanding of the sources and transport pathways of Hg in the atmosphere, the relative contributions of wet and dry depositions to any particular location remains poorly understood. The east coast metropolitan corridor (Washington D.C. to Boston) is one of the few areas in the U.S. where models estimate greater rates of dry deposition than wet deposition. Hg in wet and dry deposition in New England was investigated using sediment cores and wet-deposition collectors. Sediment cores were collected in 2000 as a part of a national study of trends in particle-associated contaminants. Cores were collected from two lakes, one a remote reference site (Bethel, ME), and the other an urban reference site (near Boston, but with no development in the watershed). Wet-deposition was measured at two sites in rural Maine by the National Atmospheric Deposition Program Mercury Deposition Network (NADP-MDN) between 1996 and 2004, one rural site in New Hampshire by NADP-MDN and the U.S. Geological Survey (USGS) between 2001-2004, and three sites in the Boston metropolitan area (USGS) between 2002-2004. Total Hg deposition (wet plus dry) estimated from sediment cores and measured wet deposition, support the conclusion that dry deposition is much more important in the metropolitan corridor. The ten-year average total Hg deposition near Boston was estimated to be 95 µg/m²/yr, more than 10 times the median wet-deposition rate for metropolitan Boston of 8.9 µg/m²/yr. In contrast, total Hg deposition at the remote reference site was about 10 times less than near Boston at 10 µg/m²/yr, and dry deposition was estimated to be about one-third of the total deposition. These comparisons indicate that dry deposition can dominate (about 90% for this study) the atmospheric flux of Hg in urban settings.

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