Hydroelectric Dams Affect Hyporheic Copepod Diversity

This study investigates the ecological impact of a small hydroelectric power plant (SHPP) on the hyporheic zone of the venacquaro stream (VEN), a low-order groundwater-fed stream in Central Italy. The hyporheic zone, a critical ecological interface where groundwater and surface water interact, plays a pivotal role in nutrient cycling, pollutant retention, and supporting aquatic biodiversity. However, hydrological alterations from activities such as damming pose significant threats to this zone. The research employs a three-pronged approach to assess the effect of a SHPP on hyporheic copepod communities. Copepods were selected as the focal group due to their dominance in this habitat. Initially, a generalized estimating equation (GEE) model was used to evaluate changes in copepod diversity, specifically alpha and beta diversity. The study then examines environmental shifts caused by the SHPP using permutational analysis of variance (PERMANOVA) and principal component analysis (PCA). Lastly, a multivariate species distribution model (mSDM) explores correlations between environmental variables and copepod abundances. Results reveal significant alterations in copepod assemblage structure and environmental variables downstream of the SHPP. The GEE model indicates a notable shift in beta diversity, primarily driven by disruptions in hyporheic connectivity rather than environmental changes alone. This disruption favours stygobitic species downstream, suggesting the influence of groundwater upwelling. Environmental analysis shows several differences between upstream and downstream sites, with changes in parameters such as pH, temperature, and dissolved organic carbon. The study highlights the need for effective management strategies to mitigate sediment accumulation and maintain habitat quality in SHPP-affected streams. Techniques like sediment bypass tunnels (SBTs) are recommended to preserve both economic and ecological values. This research contributes to the still limited understanding of SHPP impacts on hyporheic ecosystems, emphasizing the importance of considering these effects in hydropower development and riverine ecosystem conservation.