Surviving and growing in dynamic floodplains : Habitat heterogeneity drives communities of young fish in the lower river Rhine

Abstract

Lowland river-floodplain systems, such as the Rhine, contain a complex gradient of aquatic and terrestrial habitats that contribute to a high level of biological and structural diversity, ranking them among the most diverse and productive freshwater ecosystems in the world (Welcomme 1979;Junk et al. 1989;Ward et al. 1999). The ecological importance of the Rhine was however hardly recognised until the 1970s. In the past, poor water quality as a result of water pollutants (Wolff 1978), regulated discharges (Cowx & Welcomme 1998), and extensive river modifications resulted in a major decline in floodplain habitat diversity, availability, and quality. This had a major impact on its ecological functioning (Van Urk & Smit 1989; Van den Brink et al. 1996;Middelkoop 1997). Numerous ecological groups, especially (migratory) riverine fishes, are sensitive to changes in water quality and habitat availability, and their populations have severely declined as a result (