Hydropower regulation reshapes littoral invertebrate communities: functional traits reveal impacts beyond richness and abundance

Abstract

Freshwater lake ecosystems are increasingly affected by altered water level fluctuations (WLF) from hydropower regulation, yet impacts on lake biodiversity remain understudied. We investigated how regulation influences Ephemeroptera, Plecoptera and Trichoptera (EPT) communities in boreal lakes. Three regulated and three nearby control lakes were sampled eight times across 2023–2024. We analyzed differences in abundance and species richness while accounting for temporal and spatial variability. To gain deeper mechanistic insight, we assessed community responses through analysis of composition, beta diversity-partitioning, indicator species, and functional traits. Abundance and species richness showed directional decrease in regulated lakes, although there was substantial variability among lakes. Control lakes supported compositionally similar communities with diverse functional traits, whereas communities in regulated lakes were more variable and functionally constrained. In particular, species that were temporarily attached or that required vegetation for case building were less common in regulated lakes. The observed patterns are consistent with the hypothesis that water-level fluctuations (WLF) impose stress on less mobile taxa and contribute to environmental filtering associated with reduced habitat complexity. Although responses varied among regulated lakes, our findings suggest that moderate regulation amplitudes (4–6 m) can alter littoral EPT communities. We detected clear impacts on functional composition even where changes in abundance and richness were less pronounced, highlighting its potential value as a sensitive indicator of hydropower effects in lake ecosystems.