After flooding, iron reduction in riverine wetlands may cause the release of large quantities of phosphorus. As phosphorus is an important nutrient causing eutrophication in aquatic systems, it is important to have a tool to predict this potential release. In this study we examined the P release to the soil pore water in soil cores from floodplains in the Netherlands and from less anthropogenically influenced floodplains from Poland. During the inundation experiment, concentrations of P in the pore water rose to 2–90 times the initial concentrations. P release was not directly related to the geographic origin of the soils. An important predictor variable of P release was found in the ratio between the concentration of iron-bound P and amorphous iron. This ratio may provide a practical tool for the selection of new areas for wetland creation, and for impact assessment of plans for riverine wetland restoration and floodwater storage. Mobilisation of phosphorus in floodplain wetland soils can be predicted with easily measurable soil characteristics.

Historic and current agricultural and industrial activities have resulted in accumulation of Cd, Cu, Pb and Zn in soil. To estimate potential risks for ecosystems, agriculture and water quality, an integrated risk assessment was performed for The Netherlands. Risks of metal contamination were assessed on a national scale by comparing present soil concentrations of Cd, Pb, Cu and Zn with critical concentrations of those metals in view of agricultural impacts, ecological impacts and impacts on the quality of groundwater and surface waters. Results show that present soil metal concentrations cause few risks for agriculture or ecosystems; for less than 2% of the surface area present metal levels exceed critical limits. Critical limits for groundwater are only significantly exceeded for Pb (17% of the area), but critical limits for surface water are exceeded throughout the country for Cu and Zn. Taking critical limits used in The Netherlands, the area where exceedances take place is nearly negligible for Cd and low for Pb (less than 3%), but much larger (between 40% and 50%) for both Cu and Zn. Results from this study suggest that accumulation of heavy metals in Dutch soils at present primarily affects the quality of surface waters. This stresses the need for harmonization of soil and water policy. Measures to reduce the load in surface waters to meet target levels, under conditions like those prevailing in The Netherlands, are bound to have an impact on land management.

A critical load data base was developed for Europe and Northern Asia using the latest data bases on soils, vegetation, climate and forest growth. Critical loads for acidity and nutrient nitrogen for terrestrial ecosystems were computed with the Simple Mass Balance model. The resulting critical loads are in accordance with critical loads from previous global empirical studies, but have a much higher spatial resolution. Critical loads of acidity are sensitive to both the chemical criterion and the critical limit chosen. Therefore a sensitivity analysis of critical loads was performed by employing different chemical criteria. A critical limit based on an acid neutralizing capacity (ANC) of zero resulted in critical loads that protect ecosystems against toxic concentrations of aluminium and unfavourable Al/Bc ratios, suggesting that ANC could be an alternative to the commonly used Al/Bc ratio. Critical loads of nutrient nitrogen are sensitive to the specified critical nitrate concentration, especially in areas with a high precipitation surplus. If limits of 3¿6 mg N l¿1 are used for Western Europe instead of the widely used 0.2 mg N l¿1, critical loads double on average. In low precipitation areas, the increase is less than 50%. The strong dependence on precipitation surplus is a consequence of the simple modelling approach. Future models should explore other nitrogen parameters (such as nitrogen availability) instead of leaching as the factor influencing vegetation changes in terrestrial ecosystems.