Dry deposition and foliar leaching of mercury and selected trace elements in deciduous forest throughfall

The estimated annual throughfall deposition flux of Hg in a northern mixed- hardwood forest in the Lake Huron Watershed was 10.5 +/- 1.0 mug m(-2) comp ared to an annual precipitation Hg flux of 8.7 +/- 0.5 mug m(-2) (June 1999 -June 1997). The source of this additional Hg in throughfall is often attri buted to wash-off of dry deposition, but foliar leaching of Hg may also be important. To determine the influence of both dry deposition and foliar lea ching of Hg and other elements in throughfall, we measured a suite of trace elements (Hg, Al, Mg, V, Mn, Cu, Zn, As, Rb, Sr, Cd, Ba, La, Ce, and Pb) i n throughfall, precipitation, and ambient air samples from a northern mixed -hardwood forest. Based on a multiple linear regression model, dry depositi on had the most important influence on Hg, Al, La, Ce, V, As, Cu, Zn, Cd, a nd Pb fluxes while foliar leaching strongly influenced Mg, Mn, Rb, Sr, and Ba fluxes in net: throughfall. The Hg dry deposition flux was estimated usi ng gaseous and aerosol Hg measurements and modeled deposition velocities. T he calculated dry deposition flux (similar to 12-14 mug m(-2)) of Hg to the canopy indicated that atmospheric deposition of Hg could easily account fo r all of the Hg deposited in net throughfall (1.9 +/- 0.1 mug m(-2)). Altho ugh there is a large uncertainty associated with these techniques, the mode ling estimates indicate that atmospheric Hg may account for all of the Hg d eposited in litterfall (11.4 d +/- 2.8 mug m(-2)). (C) 2001 Elsevier Scienc e Ltd. All rights reserved.