Quantifying small hydropower dam effects on habitats and multiple organism groups in forested rivers

Many studies have quantified dam impacts on riverine ecosystems, but few have compared the efficacy of using multiple organism groups to assess these impacts. Our study quantified impacts of small hydropower dams on forested river habitats. We used 3 organismal groups to examine above-impoundment and below-dam reaches in regulated rivers as putative impact sites and riffle habitats in unimpacted nearby rivers as reference sites. The regulated and reference rivers studied here were similar in their environmental characteristics, apart from differences in flow and substratum. Benthic invertebrate and macrophyte, but not diatom, assemblages differed between regulated and reference rivers, and analysis of traits aided in understanding the mechanisms underpinning these differences. Regulated rivers were characterised by benthic invertebrate and macrophyte traits indicative of fine-textured substrata, such as burrowing/boring invertebrates and emergent macrophytes, whereas benthic diatoms had a higher frequency of disturbance-resistant low-profile guilds. Correlation supported the importance of flow and substratum as predictors of benthic invertebrate and macrophyte assemblages. Based on our results and findings from other studies, we recommend the continued use of benthic invertebrate and macrophyte assemblages for assessing the effects of small dams on rivers and urge a greater focus on developing biological trait-based indices to better quantify land-use effects on flow and substratum.