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 Netherl ands 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 (TWINSPA N, FLEXCLUS, DCA) of relative abundance data of plankton. The phyto- a nd zooplankton community composition in floodplain lakes is clearly re lated to hydrology, relevant nutritional resources and habitat charact eristics, mainly via input of N and P from the eutrophic main channels during floods. The plankton species richness was related to the compl exity of habitats formed by the presence of aquatic vegetation. There was a good agreement between the ecological and the environmental char acterization of site groups. Cyanobacteria, Chlorophyta and filter-fee ding zooplankton taxa associated with open water are characteristic fo r 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 duratio n, high Si/N and Si/P ratios, and a well-developed aquatic vegetation. It is concluded that the restoration of connections between rarely fl ooded lakes and the highly eutrophic main channels of the Lower Rhine and Meuse will result in hypertrophic conditions and a reduced plankto n diversity in these lakes.