Effectiveness of artificial floods for benthic community recovery after sediment flushing from a dam

The number of dams is predicted to increase worldwide under the current global change scenario. A major environmental problem associated with dams is the release of large quantities of fine sediment down- stream. Therefore, future studies in river conservation will largely be focused on the management of sediments trapped by reservoirs. The aim of this study was to investigate the downstream ecological impacts of sedi- ment flushing from a dam and the effectiveness of artificial flash floods as a recovery strategy. Artificial flash floods have often been employed to remove large amounts of sediment from riverbeds, but their impor- tance in improving the biological quality of lotic envi- ronments is almost unknown. We carried out a series of quantitative macroinvertebrate samplings over a 2-year period that started before sediment release and included the artificial flushing events. We characterized the mac- roinvertebrate community in its structural and functional aspects and tested the performance of two biomonitor- ing indexes, comparing their diagnostic ability. Our results demonstrated that sediment flushing significantly altered the structure and composition of benthic com- munities for more than 1 year. Flash floods exacerbated the overall biological quality, but we believe that this treatme nt was useful beca use, by removi ng large amounts of sediment, the biological recovery process was accelerated. Finally, regarding the water quality assessment, we found that the biomonitoring index for siltation, composed of a selection of taxonom- ical and functional metrics, was more reliable than the generic one.