MECHANISMS OF DEPOSITION OF METHYLMERCURY AND MERCURY TO CONIFEROUS FORESTS

Deposition of methylmercury (MeHg) and mercury (Hg) to a coniferous forest have been investigated using field measurements. Samples of open field (OF) wet deposition, throughfall (TF) and litterfall (LF) have been collected and analyzed for MeHg and Hg during the period November 1991 to April 1994. Average concentrations in TF were 22.8 and 0.38 ng L(-1) for Hg and MeHg, respectively. Concentrations in OF precipitation were 11.9 and 0.37 ng L(-1), for Kg and MeHg, respectively, during the same period. Considerable differences were found for Hg in TF and OF which was attributed to a dry deposition of Hg, Hg in LF contributes a deposition of equal size as in TF. The relations between OF, TF and total Hg deposition were approximately 1:1.5:3. A decrease in OF Hg was found over the three year period studied. MeHg deposition in OF was also found to decrease during the same period whereas the TF MeHg showed a slight increase. Dry deposition of MeHg is also an important process in a coniferous forest although the flux to the forest floor is not via TF but rather as MeHg in LF.