Long-term integrated catchment monitoring within the Swedish Environmental Monitoring Programme (PMK) aims primarely at the fate and effects of pollutants in mature ecosystems, mainly protected boreal forests. The measurements that were conducted since the early eighties, with some variation, included deposition throughfall, litterfall and the chemistry of soil water, groundwater and runoff water. Together with, or perhaps partly due to acidification, accumulation and transport of heavy metals are a serious threat to the ecosystem and in the end to the health of human beings. This paper discuss the behaviour of Hg, Pb, Cd Zn and Cu based on the experiece gained from the studies in the small catchment areas. The importance of present deposition, soil storage and biogeochemical condition for metal mobility to the transport of metals is discussed. The storages of Hg and Pb have been built up during a long time span and are very large in comparison with the flux. The present atmospheric deposition have probably little impact can the nux,which rather is governed by the biogeochemical conditions. There is still a small accumulation of Cd but its great mobility under acidic conditions makes input and output almost in balance. A reduction in deposition will probably have an immediate effect on flux, which also is the case for Zn. Cu generally accumulates in soil The mobility and hence the flux are certainly regulated by the biogeochemical conditions, but more detailed studies are required to reveal the general mecanisms for Cu transport within the catchment.
