Kristy Rogers

M.S., Limnology and Marine Sciences, 2005

Advisor: Emily Stanley

Abstract:   Algal and macroinvertebrate responses to removal of a small dam
Dam removal is becoming an increasingly popular choice for dealing with failing small dams, in part because it is often the least expensive option for a dam owner and because of the general opinion that removals will have beneficial effects on streams. However, we actually know fairly little about the ecological impacts of small dam removals. Dam removal alters the transport of sediments, nutrients and organic materials in stream systems. Consequent changes in substrate, ambient nutrient levels and sedimentation rates should all impact algae and aquatic insects. The focus of my research is to determine the effect of dam removal on algae and aquatic insects. Specifically, how does dam removal impact the total amount of algae and aquatic insects present in a stream? Also, how does dam removal impact the quality of algae in a stream (measured using cellular nitrogen to phosphorus ratios)? I addressed these questions in Boulder Creek, a second order stream in central Wisconsin where two small dams were removed. We sampled algae from ceramic tiles to assess cellular N/P ratios and chlorophyll a levels as well as aquatic insect abundance. Following the dam removals, an initial release of sediment buried benthic substrate creating a new surface for algal colonization. This burial led to reductions in chlorophyll concentration and aquatic insect abundance immediately below the dam in the week following removal, while no similar changes were observed in the upstream reference reach. However, effects on algae and aquatic insects appeared transitory in Boulder Creek with rapid recovery from this initial hit. This suggests that while small dam removal had a strong immediate effect on the ecosystem, recovery from this disturbance is rapid.

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