Pools and fluxes of mercury and methylmercury in two forested catchments in Germany

Mercury Hg. and methylmercury CH3Hgq. are global pollutants, but little information is available on rates of atmospheric input, distribution and mobility in soils and catchments of central Europe. The objectives of this study were to investigate input and output fluxes of these compounds in a deciduous and a coniferous catchment in NE Bavaria Germany., and to estimate pools and mobility of total Hg Hgtot. and CH3Hgq at the catchment scale. Bulk precipitation, throughfall, litterfall and runoff were collected biweekly from April 1998 to April 1999. Several soil profiles were sampled to estimate pools of Hg compounds in the catchments. In both catchments highest contents of Hgtot were found in the Oa layer of the forest floor up to 500 ng gy1. and the soil storage of Hgtot calculated for a soil depth of 60 cm was approximately 890 g hay1 in the coniferous and 190 g hay1 in the deciduous catchment. Highest contents of CH3Hgq in upland soils were observed in the Oi layer of the forest floor, and soil storage of CH3Hgq was 4.35 g hay1 in the coniferous and 0.59 g hay1 in the deciduous catchment. The annual total deposition of Hgtot total deposition not measured directly but calculated from throughfall and litterfall. was 541 mg hay1 yeary1 in the coniferous and 618 mg hay1 yeary1 in the deciduous catchment. Total deposition rates of CH Hgq 3 were 3.5 and 2.6 mg hay1 yeary1. The contribution of litterfall to the total deposition of Hgtot and CH3Hgq was 55% in the deciduous catchment. In the coniferous catchment, the contribution of litterfall to total deposition was only 29% for Hgtot , but 55% for CH3Hgq. By far the largest proportion of the deposited CH3Hgq and Hgtot remained in the catchments 85% in the coniferous, 95% in the deciduous.. As compared to remote Swedish catchments, deposition and output via runoff of Hgtot were higher, but deposition and output of CH3Hgq were lower in our catchments. In contrast to other studies, the annual budget revealed no differences in the mobility between the two species at the catchment scale. However, temporal patterns of the runoff fluxes and converse gradients of CH3Hgq and Hgtot contents in the forest floor indicated differences in mobility on shorter time scales