Atmosphere-Land Dynamics of Mercury in a Forest Landscape
of the Adirondack Region of New York

Hyun-Deok Choi, Thomas M. Holsen
Department of Civil and Environmental Engineering, Clarkson University, Postdam, NY

Atmosphere-land dynamics of mercury were investigated at the Huntington Forest in the central Adirondack region of New York. Measurements of mercury were made in air, wet deposition, throughfall, foliage, litter, and streamwater, and soil mercury evasion was characterized. Measurements show a slight enrichment of mercury in throughfall (6.83 µg/m2-yr) compared to wet deposition (5.79 µg/m2-yr) in this northern hardwood watershed. Large increases in concentrations of mercury were evident in foliage of the dominant hardwoods over the growing season, with accumulation of mercury in American beech significantly higher than in sugar maple or yellow birch. Concentrations of mercury in understory foliage were significantly greater than overstory foliage. Concentrations of mercury in hardwood litter were consistent with values observed in foliage. Litter flux of mercury (17.2 µg/m2-yr) greatly exceeded throughfall and was the major pathway of mercury deposited to the forest floor (24.0 µg/m2-yr). Soil evasion of mercury was highly variable across diurnal cycles and the annual cycle, and was highly dependent on environmental conditions (e.g., temperature, radiation). Our best estimate of mercury evasion from upland soil (10.4 µg/m2-yr) suggests that this flux exceeded throughfall, but is less than total mercury deposition. Stream fluxes (2.3 µg/m2-yr) indicated that most of the mercury deposited to the watershed is evaded back to the atmosphere or retained in soil. However, stream losses are a critical pathway of mercury supply to aquatic ecosystems and ultimately human and wildlife exposure. Stream mercury species flux increased greatly during storm events, driven by the increase in runoff. Source areas of mercury varied within events, with recently deposited mercury readily mobilized on the rising limb of the hydrograph before shifting to mercury derived from soil water as the hydrograph peaked. The form and source of mercury may have important implications for the bioavailability in downstream Arbutus Lake.