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

Abstract

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 downstream. 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 sediment 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 importance in improving the biological quality of lotic environments 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 macroinvertebrate community in its structural and functional aspects, and tested the performance of two biomonitoring indexes, comparing their diagnostic ability. Our results demonstrated that sediment flushing significantly altered the structure and composition of benthic communities for more than 1 year. Flash floods exacerbated the overall biological quality, but we believe that this treatment was useful because, by removing 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 taxonomical and functional metrics, was more reliable than the generic one.

The River Continuum Concept: lessons from the past and perspectives for the future

“…Flow cessation results in the loss of the longitudinal connectivity and isolation of stream reaches with consequences on population survival, the diversity of aquatic communities, and transport and storage of organic matter subsidies (Datry et al 2016b;Doretto et al 2020). Such adverse conditions may be exacerbated by the effect of anthropogenic-induced hydromorphological alterations at the local scale, such as damming and water abstraction (Grubbs and Taylor 2004;Holt et al 2015;Doretto et al 2019;Piano et al 2019). Regardless of the nature of these alterations (i.e., natural or human-induced), RCC poorly adapts to lotic ecosystems experiencing changes in flow regime, with deviations from its predictions probably depending on the components of the flow regime that are mostly modified (i.e., magnitude, frequency, duration, timing, and flashiness).…”

Contribution of beta diversity in shaping stream macroinvertebrate communities among hydro-ecoregions

“…species or taxa) that live in a certain habitat (Colwell 2009), is a key definition in community ecology with direct applications for basic and applied research. Measures and indices of biodiversity are generally used to get insights on the variation of biological communities along environmental gradients (Bo et al 2016;Falasco et al 2018) and in response to anthropogenic pressures (Bona et al 2016;Doretto et al 2018Doretto et al , 2019.…”

The year after an extraordinary sedimentation event in a regulated Alpine river: The impact on benthic macroinvertebrate communities

“…In that case, the long recovery time was mainly associated to ash accumulation and remobilization from hillslopes, and was comparable to that observed after ashfall (Anderson, 1992;Dorava & Milner, 1999) or landslide (Cover et al, 2010;Danehy et al, 2012;Lamberti et al, 1991) episodes (i.e., in the order of years). Recovery times of about 2 years were also reported after small dam removal (Carlson et al, 2018;Tullos, Finn, & Walter, 2014) and after an uncontrolled sediment release (Doretto et al, 2019). Shorter recovery times of benthic communities were generally documented in regulated Alpine streams subjected to controlled sediment flushing operations, varying from a few months up to 1 year, and mostly depending to the persistence of riverbed alteration, to seasons, and to site specificities such as the provision of macroinvertebrates by undisturbed tributaries (Espa et al, 2019).…”

“…In contrast, Heptageniidae, Perlodidae and Nemouridae did not recover or displayed the longest recovery times within the monitored year. Several studies (e.g., Doretto et al, 2019;Kaller & Hartman, 2004) reported that members of EPT group, such as the families just mentioned, are particularly sensitive to sedimentation.…”