Restoration of the river-floodplain interaction: benefits for the fish community in the River Rhine
Grift, R.; Buijse, A.D.; Densen, W.L.T. van; Klein Breteler, J.G.P.
In the lower River Rhine, canalization of the river and disconnection of floodplains from the river bed lead to the present low diversity of habitats. Spawning conditions for especially rheophilic cyprinids have declined dramatically. Nowadays, eurytopic species dominate the riverine fish community. In 1989, river restoration started by connecting water bodies in the floodplains to the main channel permanently. To evaluate the effect of these restorations on the fish community, four water bodies, which differ in connectivity with the main channel, flow velocity and presence of aquatic vegetation, were sampled to investigate their functions as spawning and nursery areas for riverine fishes. The hypothesis that density of rheophilic cyprinids is in accordance with flow and connectivity was tested by analysis of presence-absence data, using a logistic model and by analysis of variance for abundance data using a generalized linear model. Presence and abundance of rheophilic cyprinids increased from the isolated oxbow lake (not connected, no flowing water present) to connected oxbow lake (permanently connected with the main channel, no flowing water present) and to both secondary channels (permanently connected with the main channel, flowing water present permanently). Connectivity of a water body with the main channel and the presence of flowing water are important factors driving the structure of the YOY fish community in floodplain water bodies. Only a few years after their creation, secondary channels provide a suitable habitat as nursery areas for rheophilic cyprinids.