Effects of a hydropeaking dam on river health and benthic macroinvertebrate secondary production in a Northern Great Plains river

Hydroelectric dams represent an ever-growing portion of the global energy grid, and the number of operations practicing hydropeaking is on the rise. Early research shows that dams affect benthic macroinvertebrates (BMIs). In contrast, our knowledge of the impacts of hydropeaking on BMIs is limited; this contributes to gaps in our understanding of how hydropeaking affects structural and functional aspects of lotic ecosystem health. This is especially apparent in the large rivers of the Northern Great Plains where aquatic health and function are rarely measured. River health is often scored using metrics such as biotic indices (BI) and the ratio of Ephemeroptera, Plecoptera, and Trichoptera to Chironomidae (EPT/C), whereas functional measures include calculating secondary production are far less common. This dissertation sought to explore the effects of the hydropeaking E. B. Campbell dam on downstream BMI assemblages in the Saskatchewan River using BI, EPT/C, and estimating BMI mean daily secondary production while considering seasonality as a key factor. BMI communities downstream of the dam had higher proportions of tolerant taxa relative to upstream sites regardless of season. This was reflected in elevated BI and lower EPT/C scores observed downstream. Canonical correspondence analysis (CCA) showed clear differences between upstream and downstream sites, and an analysis of similarities (ANOSIM) found the downstream BMI assemblage was significantly different than the one found upstream. A similarity percentages (SIMPER) analysis revealed that Sigara lineata (Hemiptera: Corixidae), Hydropsyche sp. (Trichoptera: Hydropsychidae), and Chironomidae (Diptera) were among the taxa that contributed most to differences between upstream and downstream locations. Estimated mean daily secondary production and mean instantaneous growth rates for Chironomidae, Sigara lineata, Hydropsyche sp., and Stenonema sp. (Ephemeroptera: Heptageniidae) ranged between 0.083 - 0.996 mg m-2 day-1 and 0.004 - 0.021 upstream, and 0.059 - 23.402 mg m-2 day-1 and 0.021 - 0.046 downstream, respectively. High production in downstream Hydropsyche sp. may be attributed to their proximity to the reservoir. This dissertation demonstrated that hydropeaking may alter downstream BMI community composition and production, resulting in degraded river health. It was shown that seasonality can play a key role in dictating hydropeaking effects. Continued monitoring of downstream BMI assemblages will provide valuable information that can mitigate the impacts of hydropeaking operations on the downstream environment