Seasonal Variability in Gaseous Mercury Fluxes and Mercury Deposition to Dew

Seasonal patterns of atmospheric mercury (Hg) fluxes measured over vegetated terrestrial systems can provide insight into the underlying process controlling emission and deposition of Hg to vegetated surfaces. Gaseous elemental Hg fluxes were measured for week-long periods in each season (spring, summer, fall, and winter) over an uncontaminated high-elevation wetland meadow in Shenandoah National Park, Virginia using micrometeorological methods. Mean net deposition was observed in the spring (-4.8 ng m -2 h -1 ), emission in the summer (2.5 ng m -2 h -1 ), near zero flux in the fall (0.3 ng m -2 h -1 ), and emission in the winter (4.1 ng m -2 h -1 ). Nighttime deposition (when stomata are closed) and the poor correlation between Hg fluxes and canopy conductance during periods of active vegetation growth suggest that stomatal processes are not the dominant mechanism for ecosystem-level GEM exchange at this site. The strong springtime deposition relative to summer implies that young vegetation is better at scavenging Hg, with the highest deposition occurring at night possibly via a cuticular pathway.

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