Mercury and methylmercury in upland and wetland acid forest soils of a watershed in NE-Bavaria, Germany

Mercury (Hg) and methylmercury (CH3Hg+) are global pollutants, but little i nformation is available on their distribution and mobility in soils and cat chments of Central Europe. The objective of this study was to investigate t he pools and mobility of Hg and CH3Hg+ in different forest soils. Upland an d wetland forest soils, soil solutions and runoff were sampled. In upland s oils the highest contents of total-Hg were found in the Oh layer of the for est floor (> 400 ng g(-1)) and the storage of non geogenic total-Hg (calcul ated for 60 cm depth) was about 120 mg/m(2). The storage of total-Hg was on e order of magnitude lower in wetland soils as compared to the upland soils . By far the largest proportion of total-Hg in soils was bound in immobile fractions. The depth gradients of CH3Hg+ did not correspond to those of tot al-Hg and the highest contents of CH3Hg+ in upland soils were observed in t he litter layer of the forest floor and in the Bsv horizon. The CH3Hg+ cont ent of the wetland soils was generally much higher in comparison with uplan d soils. CH3Hg+ in solution was found in the forest floor percolates of upl and soils and in wetland soils, but not in soil solutions from mineral soil horizons. Gaseous losses of Hg as well as methylation of Hg are likely in wetland soils. The latter might be highly relevant for CH3Hg+ levels in run off.