Effects of flow regulation on river bed dynamics and invertebrate communities in a Mediterranean river
Lobera Galán, Gemma
Muñoz Gràcia, Isabel
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Mediterranean rivers are hotspots for biodiversity, and riverine species are adapted to regular physical perturbations that affect channel morphology during flashy rainfall-runoff events. Dams alter flow regimes, changing flood magnitude and frequency; they also interrupt the continuity of sediment transport. Changes in both flood and sediment transport regimes affect downstream channel dynamics and the ecological functioning of fluvial systems. This paper examines the effects of flow regulation on bed disturbance, invertebrate assemblages and their biological traits in a Mediterranean river (the Siurana, NE Iberian Peninsula). Results are put in the broader context of the whole Ebro river catchment. The Siurana Reservoir causes a complete inversion of the seasonal flow regime and reduces flood magnitude notably. Upstream from the reservoir, torrential floods mobilize surface and subsurface bed materials, regularly disturbing the physical habitat; downstream, geomorphological activity in the channel is almost nonexistent. Altogether, damming causes significant differences in taxonomic composition of the benthic invertebrate communities; density and biomass increase notably below the dam although diversity decreases. At the broader scale taxa with active aerial dispersal traits dominate unregulated reaches in areas with marked Mediterranean hydro-climatic regimes, whereas reaches with more stable regimes are characterized by fully aquatic detritivore species.