Mercury inputs, outputs, cycling, and ambient concentrations under the forest canopy in the Adirondacks of New York.

摘要

This study investigated the mercury input, output, and cycling, and interactions between deposition and emission and atmospheric conditions at the Huntington Wildlife Forest of Newcomb, New York (43.97° N, -74.22° W) during 2005 and 2006. Atmospheric Hg species concentrations were measured continuously and the total Hg concentration in wet deposition and deciduous throughfall were composited on a weekly basis. Hg0 emissions were measured under the deciduous forest canopy numerous times throughout the study period.;Ambient air concentrations of gaseous elemental Hg (GEM), reactive gaseous Hg (RGM), and particulate Hg (HgP) were measured using a Tekran speciation system (Models 2537A, 1130, and 1135) at Huntington Forest in the Adirondacks, New York from June 2006 to May 2007. The average concentrations of GEM, RGM, and HgP were 1.39 +/- 0.36 ng m-3, 1.77 +/- 2.20 pg m-3, and 3.22 +/- 3.73 pg m-3, respectively. Potential source contribution function (PSCF) was used with GEM, RGM, and HgP to identify possible Hg sources. The model results indicate that Pennsylvania, West Virginia, Ohio, Kentucky, Texas, Indiana, and Missouri were major Hg sources that have a potential to contribute the high concentrations of mercury (Hg) observed at the Huntington Forest in the Adirondacks. These identified sources agreed well with sources identified in the Hg emissions inventory.;Hg wet deposition and deciduous throughfall were collected in the Adirondacks for two years from December 2004 to December 2006. During this study, the volume-weighted mean (VWM) total Hg concentration in throughfall (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 mug m-1) was very similar to precipitation (11.6 mug m-2) due to relatively lower precipitation depths in throughfall. The total deposited cumulative flux in precipitation and deciduous throughfall were very similar (11.6 mug m-2 and 12.0 mug m-2, respectively) because the higher concentrations in throughfall were offset by smaller throughfall depths. Meteorological analysis indicated the precipitation events resulting in the highest Hg fluxes were associated with trajectories that passed through regions of Midwest where major Hg sources including coal/oil-fired power plants and waste incinerators are located.;The emission flux of gaseous elemental mercury (Hg0) from the forest floor of the Adirondack in New York (USA) was measured using a polycarbonate dynamic flux chamber (DFC). The Hg emission flux ranged between -2.5 ng m-2 hr-1 and 27.2 ng m-2 hr-1. The measured Hg emission flux was highest in spring, and summer, and lowest in winter. During leaf-off periods, the Hg emission flux was highly dependent on solar radiation and less dependent on temperature. During leaf-on periods, the Hg emission flux was fairly constant because the forest canopy was shading the forest floor. The empirical models estimated the cumulative emission flux was 6.3 mug Hg0 m-2 year-1.;The yearly estimated Hg inputs into the forest canopy include throughfall (6.5 mug m-2 year), litterfall (18.3 mug m-2 year-1), and dry deposition during leaf-off periods (0.4 mug m-2 year). The yearly estimated Hg outputs from the forest canopy include emission from the forest floor (6.3 mug m-2 year-1), soil water (0.6 mug m-2 year -1), and Hg loss via evaporation or overland flow during snow melt (1.0 mug m-2 year). Litterfall represented the most significant input of Hg to this forest ecosystem. Based on this mass balance, 17.3 mug m-2 of Hg is accumulating in the forest floor every year.