ATMOSPHERIC CONCENTRATIONS AND DEPOSITION OF HG TO A DECIDUOUS FOREST AT WALKER BRANCH WATERSHED, TENNESSEE, USA

Aerosol and total vapor-phase Hg concentrations in air have been measured at Walker Branch Watershed, Tennessee for approximately 2 yr. Airborne Hg at this site is dominated by vapor forms which exhibit a strong seasonal cycle, with summer maxima that correspond to elevated air temperature. Concentrations in this forest are near background levels; however, concentrations at a site within 3 km are significantly elevated due to emissions from Hg-contaminated soils. The concentration data have been combined with a recently modified dry deposition model to estimate dry deposition fluxes to the deciduous forest at Walker Branch. Weekly mean modeled V(d) values for Hg-degrees ranged from < 0.01 (winter) to > 0.1 (summer) cm s-1. Weekly dry deposition fluxes ranged from < 0.1-mu-g m-2 during winter to > 1.0-mu-g m-2 in the summer. Our dry deposition estimates plus limited measurements of wet deposition in this area indicate that dry deposition may be the dominant input process in this forest, at least during the summer.