Terrestrial Mercury and Methylmercury Budgets for Scandinavia

Abstract

In Scandinavia 1979, measurements of Hg in air was started at the Swedish west-coast. This site, the Rorvik station, has since then been part of several Swedish and Nordic atmospheric Hg networks. The results from the measurements in these networks clearly demonstrate the existence of a decreasing south-north gradient over Scandinavia. A compilation of available data suggest a decrease in Hg concentrations in air starting in 1990. This coincides with drastically decreased Hg emissions following the closing down of large Hg emitters in the former GDR. Scandinavian measurements of total Hg in precipitation are available from 1987. The coupling between atmospheric Hg in Scandinavia and large continental emission sources, is supported by a clear decreasing south-north gradient and by the fact that the total Hg precipitation data also start to decline around 1990. MeHg in air has recently been measured, but the data set is still too limited to allow trend analysis. The MeHg precipitation data set is much larger, but a rather unclear south-north gardient is present and no coupling to the dramatic changes 1990 in Eastern Europe can be detected. By reviewing the seasonality and long-term changes in our atmospheric Hg data set, together with our Hg/MeHg budget calculation for forested ecosystems and changes in output rates, we try to derive any coupling between the load to a forested ecosystem and the output to surface waters. A lowered export rate of Hg and MeHg over time is indicated in catchment studies in south-western Sweden. However, it is not yet possible to statistically confirm the coupling between input and ouput fluxes of Hg/MeHg from a forested catchment.