Abstract:
Mercury (Hg) and methylmercury (MeHg) are global pollutants, but little information is available on their biogeochemistry in forested catchments of Central Europe. The objectives of this study were to investigate input and output fluxes of total Hg (Hgtotal) and MeHg in a deciduous and a coniferous catchment in Bavaria (Germany), and to estimate pools and mobility of these compounds at the catchment scale, and particularly in the forest floor. Furthermore, the role of wetlands as internal sources of MeHg, and the bioaccumulation of Hgtotal and MeHg in aquatic biota were studied.
In both catchments, input and output fluxes of Hg compounds were investigated. Several soil profiles were sampled to estimate pools of Hg compounds in the catchments. In the coniferous catchment fluxes of Hgtotal and MeHg with forest floor percolates were measured. The potential of a wetland soil in the coniferous catchment to produce MeHg was investigated in a laboratory experiment under varying incubation conditions, using stable isotope addition and isotope-specific detection of MeHg. Mosses and insect larvae of a creek in the coniferous catchment were analyzed for contents of Hgtotal, MeHg, and isotope composition of carbon and nitrogen.
In summary it was shown that forested catchments act as a sink for both MeHg and Hgtotal, without considerable differences in the input/output ratio between the species Hgtotal and MeHg at the annual catchment scale. Nevertheless, differences in transport and mobility of both species were important at smaller scales, e.g. the forest floor. Pools of both compounds in the soils seem to be of higher importance for the output of MeHg and Hgtotal than the current deposition. Besides the large pools, transformation processes can strongly influence the output by runoff, especially of MeHg. Slight changes in runoff concentrations of both compounds can strongly affect the aquatic biota, due to high bioconcentration factors of MeHg and Hgtotal. |
