IMPACT OF HYDROLOGY ON PHYTOPLANKTON AND ZOOPLANKTON COMMUNITY COMPOSITION IN FLOODPLAIN LAKES ALONG THE LOWER RHINE AND MEUSE

Floodplain lakes along the rivers Lower Rhine and Meuse in The Netherlands can be categorized according to their hydrology and geomorphology. The impact of hydrology on the summer plankton community composition in 100 floodplain lakes was studied by multivariate analyses (TWINSPAN, FLEXCLUS, DCA) of relative abundance data of plankton. The phyto- and zooplankton community composition in floodplain lakes is clearly related to hydrology, relevant nutritional resources and habitat characteristics, mainly via input of N and P from the eutrophic main channels during floods. The plankton species richness was related to the complexity of habitats formed by the presence of aquatic vegetation. There was a good agreement between the ecological and the environmental characterization of site groups. Cyanobacteria, Chlorophyta and filter-feeding zooplankton taxa associated with open water are characteristic for floodplain lakes with a long annual flood duration, low Si/N and Si/P ratios, and a poorly developed aquatic vegetation. Bacillariophyceae and scraping zooplankton taxa associated with aquatic macrophytes are characteristic for floodplain lakes with a short annual flood duration, high Si/N and Si/P ratios, and a well-developed aquatic vegetation. It is concluded that the restoration of connections between rarely flooded lakes and the highly eutrophic main channels of the Lower Rhine and Meuse will result in hypertrophic conditions and a reduced plankton diversity in these lakes.