Impacts from deposition on Swedish forest ecosystems identified by integrated monitoring

Integrated monitoring of ecosystems (IM) is an international co-operative p rogramme (ICP) to control effects of air pollution and climate change on wa ter, soil and biological systems. It is a part of the Convention on Long-Ra nge Transboundary Air Pollution (CLRTAP) of the United Nations Economic Com mission of Europe (UN/ECE). The ICP-IM is undertaken on sites/catchments to investigate acidification, eutrophication and heavy metals with an integra ted approach. In Sweden, long-term time series from forest ecosystems, with a long and stable continuity, will reveal trends and changes in processes and enable modelling to be undertaken. Investigations of acidity/alkalinity in relation to mineral and organic acids indicated the importance of atmos pheric deposition. Recent results show very high inorganic nitrogen retenti on (99%), a net loss of sulphur originating mainly from organic horizons, a nd a high inorganic aluminium content in the illuvial soil horizons which c ould be detrimental to forests. Forest deficiency could also be caused by a n observed ongoing translocation of Zn to deeper soil layers implying a mov ement towards increased release to surface waters.