Monitoring the impact of small hydroelectric plants in the Alps: an interesting case study from NW Italy

Alpine streams are valuable ecosystems for biodiversity and ecological function but are highly vulnerable to global and local stressors. Climate change represents a major global threat, while the growing development of small hydropower plants (SHPs) poses a significant risk to the integrity of Alpine lotic systems. This study examined the construction and implementation of an SHP in the Cottian Alps (NW Italy), assessing environmental quality and biodiversity indicators (macroinvertebrates and fish) over time. The STAR_ICMi index (standardised) and the FlowT index (innovative) were applied to evaluate SHP impact but revealed no differences: the ecological status was consistently rated as “good”, and no post-operam changes related to flow alterations were observed among the three stations (S1 = upstream, S2 = tail, S3 = downstream) when analysing macroinvertebrate rheophilia. Environmental parameters measured also showed no significant variation over time. However, some biological parameters did reveal changes. Macroinvertebrate abundance was significantly lower at S2, while taxa richness differed between the ante-operam and post-operam phases. Functional feeding groups remained unchanged. For fish, total abundance increased, though density and biomass stayed stable. Although the indices retained suggest minimal impact, the study underscores the need to integrate specific biological parameters into monitoring programmes for a more precise ecological assessment.