Mercury Inputs, Outputs, Cycling, and Ambient Concentrations under the Forest Canopy in the Adirondacks of New York

This study investigated mercury inputs, outputs, cycling, and the interactions between deposition, emissions and atmospheric conditions in the Huntington Forest of the Adirondacks, New York. Continuous speciated mercury concentrations of gaseous elemental Hg (GEM), reactive gaseous Hg (RGM), and particulate Bound Hg (PBM) were made from June 2006 to May 2007. The average concentrations of GEM, RGM, and PBM were 1.4 ± 0.4 ng m-3, 1.8 ± 2.2 pg m-3, and 3.2 ± 3.7 pg m-3, respectively. A hybrid receptor modeling technique (potential source contribution function (PSCF)) was used with the speciated Hg concentrations to identify possible Hg sources. Major Hg sources that have a potential to contribute high Hg concentrations observed in the Adirondacks were found to be Pennsylvania, West Virginia, Ohio, Kentucky, Texas, Indiana, and Missouri. The volume-weighted mean (VWM) total Hg concentration in throughfall (Dec. 2004 to Dec. 2006) (6.6 ng L-1) was higher than in precipitation (4.9 ng L-1), while the total cumulative Hg flux in throughfall (12.0 µg m-2) was similar to precipitation (11.6 µg m-2). The emission flux of GEM from the forest floor measured using a polycarbonate dynamic flux chamber (DFC) was highest in spring, and summer, and lowest in winter. The yearly estimated Hg inputs into the forest canopy include throughfall (6.5 g m-2 year-1), litterfall (18.3 g m-2 year-1), and dry deposition during leaf-off periods (0.4g m-2 year-1). The yearly estimated Hg outputs from the forest canopy include emission from the forest floor (7.0g m-2 year-1), soil water (0.6 g m-2 year-1), and Hg loss via evaporation or overland flow during snow melt (1.0 g m-2 year-1). Litterfall represented the most significant input of Hg to this forest ecosystem. Based on this mass balance, 16.6 g m-2 of Hg is accumulating in the forest floor every year.