BIOLOGICAL TOOLS FOR WATER SECURITY IN THE NORTHERN GREAT PLAINS

Rivers and streams are a critical component of Northern Great Plains ecosystems and an extremely valuable source of surface water. Despite their importance, these waterbodies have traditionally received much less scientific attention than forested regions. This thesis provides insight into what best available natural communities may still exist, and how alterations in the physical characteristics of rivers and streams can push communities outside of their range of natural variation. Specifically, I show that since the construction of a hydroelectric dam on a large Northern Great Plains river densities of benthic macroinvertebrates have increased significantly through time in the river downstream relative to reference sites and pre-dam conditions. My findings indicate that although there is a notable loss in sensitive taxa such as mayflies and stoneflies, other midge taxa colonize this unique, cold water habitat and create a new community of benthic macroinvertebrates. Further, reaches downstream of the dam are significantly cooler than reference through the summer into August and do not reach the temperature optima of reference reaches. I use these results to develop a reference condition model that assesses current condition and can be used to monitor recovery through mitigation of these perturbations. My results have implications primarily for understanding and quantifying the ecosystem impacts of hydroelectric energy production, but also range expansion of cold-water tolerant taxa, the life-history of select groups of invertebrates, and ultimately the forage resources available to the fish assemblages of this river system. Further, as Northern Great Plains rivers are typified by considerable flow variability, particularly in the presence of water control structures, fine sediment (