Regional differences in nutrient limitation in floodplains of selected European rivers: Implications for rehabilitation of characteristic floodplain vegetation

Extremely high river discharges in 1993 and 1995 along the Dutch rivers Rhine and Meuse have increased the public awareness of possible safety threats. As a result the 'Space for Rivers' program was implemented, aiming at restoring physical space for the rivers in combination with ecological rehabilitation. However, the development of species-rich vegetation types in these floodplain areas is lagging behind restoration targets and biogeochemical constraints may play a vital role in this. Biogeochemical, hydrological and vegetation data were collected in I I I plots in both rehabilitated and original floodplains in regulated and more pristine river systems in The Netherlands and Poland. Soil nutrient and soil pore water data were summarized by factor analysis and the subsequent principal components were compared to vegetation and hydrological data by correlation analysis. The correlation analyses between vegetation parameters including nutrient stoichiometry and the biogeochemical soil variables resulted in a remarkable difference between pristine and impacted river systems. The results suggest a clear N-limitation of plant growth in pristine floodplains, and apparent absence of limitation in regulated, impacted floodplains. In addition, results indicate that flooding events do not lead to one-way transport of sediment and nutrients from the river into the floodplains; rather they indicate that highly dynamic hydrological conditions prevent soils from accumulating organic matter and nutrients. This study shows that nutrient limitation in regulated floodplains shifted from distinctly N-limited plant growth to no nutrient limitation at all, probably due to decades of high fertilizer and manure application and nutrient input by the rivers during flooding. The consequence of our findings for rehabilitation activities is that it might be necessary to restore nitrogen limitation in floodplain systems in order to create opportunities for a species-rich floodplain vegetation, through nutrient removal by haymaking. Copyright (c) 2006 John Wiley & Sons, Ltd.