Environmental stress in five aquatic ecosystems in the floodplain of the River Rhine

General theories of stress ecology were applied to aquatic communities in the floodplain of the polluted River Rhine. These communities inhabited (i) a brackish section of the Ems-Dollard estuary with large intertidal flats, (ii) the coastal waters of the North Sea and the adjacent Wadden Sea, (iii) a former estuary of the Rivers Rhine and Meuse: the newly endiked Lake Grevelingen, (iv) the shallow Loosdrecht Lakes, and (v) the lower River Rhine. These systems are characterized by natural perturbations, such as suspension of sediments and flushing of the shallow waters. Organic pollution, eutrophication and chemical pollution reinforce the natural tendency to severe selection in the communities, in extreme cases leading to an abundance of small and opportunistic species participating in relatively simple food chains. Signs of ecosystem distress, as defined by Rapport et al., were detectable in all five ecosystems. The application of the theory of Odum et al. on stimulation and inhibition of ecosystems helped in identifying the positive impact of man. The role of stress in natural aquatic ecosystems in the delta, together with observations on ecological recovery under reduced man-made perturbation, suggest that there is scope for effective water management that exploits the resilience of these ecosystems.