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Trends and Modeling of the Total Gaseous Mercury Flux and Mercury Deposition in the Leaf
Litter Fall in a Northeastern Red Maple Canopy

Jesse O. Bash
NOAA Atmospheric Research Laboratory
U.S. EPA National Exposure Research Laboratory
MD-E243-04, Research Triangle Park, NC 27711


Net total gaseous mercury (TGM) exchange, mercury deposition in the leaf litter fall, and wet deposition fluxes were measured from the spring of 2004 through the summer of 2005 along with mercury concentrations in the atmosphere, soil, vegetation, and precipitation at sampling locations in and around a hardwood forest. TGM exchange over a closed red maple (Acer Rubrum) canopy and the litter fall flux were measured for the 2004 and second half of the 2005 growing seasons at the University of Connecticut’s research farm in Coventry, Connecticut. The wet deposition flux was measured at an uncultivated field site three miles from the forest experiment site. Seasonal trends were measured in the wet deposition volume weighted concentrations and in the direction and magnitude of the TGM flux. Net TGM evasion was dominant during the early spring and late summer. TGM concentrations in the wet deposition peaked in late spring and early summer. During the growing season there was a significant trend from net deposition after leaf out to net evasion in the late summer through the fall senescence. Evasion was dominant during periods when the canopy was wet from either dew or rainfall which was about 50% of the total time. Atmosphere – forest canopy compensation points in the TGM flux were measured in the range of background concentrations. Over the duration of the experiment the mean annual wet deposition was 6.57 µg m-2, the leaf litter deposition was 12.10 µg m-2, and the net canopy flux during the growing season was an evasion of 12.94 µg m-2. Mercury was found to accumulate in the organic matter of the soil and in vegetation foliage. The relationships between the foliar concentrations of mercury, the atmosphere-vegetation compensation point, and cycling of mercury in this forest stand are being investigated through the use of the EPA’s community multiscale air quality (CMAQ) model.