Trends of mercury and methylmercury in deposition,run-off water and sediments in relation to experimental manipulations and acidification

In the covered catchment at Lake Gårdsjön, the reversibility of acidification and the effects on Hg output of a decreased deposition of Hg and MeHg have been investigated since 1991. A first indication of a decreased from the covered catchment, caused by the artificial removal of Hg and MeHg input, has been observed. This has occurred in parallel with an overall decrease in Hg deposition fluxes in SW Sweden during 1990 to 1993. In the sediments of two acidified lakes, Lake Gårdsjön (limed) and Lake Härsevatten (acid), Hg concentrations decrease by 60% in the top cm, from the maximum around 1000 ng g^–1 at 5 cm depth indicating a decreasing deposition during the last 10 years. This decrease has occurred in parallel with decreasing atmospheric S-levels and is most likely caused by decreasing European Hg emissions. Decreasing trends of MeHg in run-off from two catchments has also been observed while the Hg output has remained somewhat more stable.