| Summary: | Freshwater species are the most threatened group among terrestrial, marine and freshwater ecosystems globally. Riverine species are particularly at risk and their conservation is likely to require an enhanced understanding of the effects of alterations to natural flow regimes. Run-of-river (RoR) hydropower has the potential to affect natural flow regimes and is an increasing component of energy portfolios. In particular, increased sedimentation due to decreases in discharge below RoR weirs may have deleterious biological effects on primary production and associated aquatic species. I hypothesized that primary production would decrease with higher fine sediment deposition, and in turn impair growth and survival of Coastal Tailed Frog (Ascaphus truei) tadpoles. I conducted tadpole surveys and quantified biofilm above three RoR weirs and in the diversion reach of each installation in British Columbia, Canada, during peak summer productivity. I also conducted an in situ mesocosm experiment with three levels of fine sediment deposition to determine the effects of fine sediment on tadpole growth and survival. I found that fine sediment deposition on the top surfaces of stones was higher in the diversion reach of two rivers with RoR hydropower projects, but varied in magnitude depending on the river. Fine sediment was positively associated with higher chlorophyll a biomass and ash-free dry mass on all three rivers. Tadpole density was consistently lower by nearly 50% in the diversion reach for all three rivers with RoR hydropower projects. The results from my mesocosm experiment suggested that survival and average tadpole growth tends to be lower as fine sediment amount increases. Although our experimental results were not conclusive, if fine sediment does decrease growth and survival of Coastal Tailed Frog tadpoles, this may indicate that higher fine sediment deposition in the diversion reach of rivers where discharge is reduced have the potential to impact Coastal Tailed Frog populations in these watersheds. === Forestry, Faculty of === Graduate
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