The construction of dams and reservoirs to meet increasing water and electricity demands has significantly altered many natural river flows, posing threats to the ecological integrity of freshwater ecosystems. Environmental flows (e‐flows) have been advocated to mitigate the negative impacts of hydroelectric power generation and to maintain healthy river ecosystems. However, the relationship between e‐flow implementation and ecological response remains poorly understudied. Here we conducted a comprehensive 2‐year study monitoring macroinvertebrate biodiversity using both morphological identification and DNA metabarcoding to explore the effect of e‐flow recovery after 50 years of no flow contribution (the stream was basically dry) due to hydroelectric regulation in a small stream (Valseco). Our results revealed significant changes in macroinvertebrate diversity and ecological status following e‐flow restoration. Initial diversity values were low, but they progressively increased, with distinct recovery rates observed across different stream sites. Molecular analyses, which provided a higher taxonomic resolution that allowed the detection of differences in species composition, showed a slight decrease in oligochaete species and an increase in Ephemeroptera, Plecoptera, and Trichoptera species. Ecological status assessments showed a shift from bad to good status within 2 years post‐restoration. Notably, the farthest downstream site (i.e. that closest to the receiving river and farthest from the dam) reached good steady status in the first year. This study highlights the effectiveness of e‐flow restoration in recovering macroinvertebrate biodiversity and achieving good status of biological integrity, underscoring the importance of such management strategies in meeting the targets of the Water Framework Directive. Finally, it emphasizes the need for further research to understand early recolonization dynamics and evaluate ecological status assessment methodologies in similar restoration contexts.
Fueyo et al. (Thu,) studied this question.
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