Chemical composition of soil solution provides information on the availability of nutrients and potentially toxic substances to plant roots and
mycorrhizas. It is therefore used to monitor impacts of air pollutants on soils. In this study we examined two soil solution parameters, base cations/aluminium ratio (Bc/Altot ratio) and inorganic nitrogen concentration (N), in samples collected at 300 intensive monitoring plots of the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) from the early 1990s to 2006
in order to detect possible critical limit exceedances (CLimE). CLimE for Bc/Altot ratio indicating negative effects for tree growth were only rarely detected. Quite the contrary was observed in CLimE for inorganic N concentrations where the safety limits were frequently exceeded in parts of Europe. Especially noteworthy is the number of the plots where leaching of
N from forest soils occurred over the studied period.With ongoing high atmospheric N input into forest soils, we expect critical limits to be exceeded in the future as well.
