Questions: How is restored inundation affecting the ground-water composition in a floodplain? To what extent has the floodplain plant community composition changed? What are the effects of flooding frequency and intensity and water quality on the floodplain vegetation changes?
Location: Demer river, Flanders, Belgium.
Methods: 75 10 m × 10 m plots were surveyed in 1997 and in 2003. Vegetation changes were quantified using a Detrended Correspondence Analysis on the combined 1997–2003 data-set. Groundwater quality in the floodplain was analysed on macro-ions. Inundation intensity and frequency were related to vegetation changes.
Results: The inundation water was rich in nutrients, although only for NH4 and ortho-PO4, and a significant increase was recorded in the groundwater. Plant species characteristic of very nutrient-rich herb vegetation disappeared or decreased while the cover and species richness of species from wet, moderately productive habitats increased. Very few new species colonized the floodplain.
Conclusion: Nutrient-rich flooding water does not necessarily result in increased abundance of species from nutrient-rich habitats, very likely because N becomes less available by denitrification and is transformed into biomass by tall herbs. Either micro-site limitation or dispersal limitation could explain the colonization problems of new species. The data do not allow distinction between these two mechanisms.