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Title: Downstream fish assemblage response to river impoundment varies with degree of hydrologic alteration

Author
item Taylor, Jason
item SEIHEIMER, TITUS - University Of Wisconsin
item FISHER, WILLIAM - University Of Wisconsin

Submitted to: Hydrobiologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2013
Publication Date: 2/14/2014
Publication URL: http://handle.nal.usda.gov/10113/58908
Citation: Taylor, J.M., Seiheimer, T.S., Fisher, W.L. 2014. Downstream fish assemblage response to river impoundment varies with degree of hydrologic alteration. Hydrobiologia. 728:23-39.

Interpretive Summary: Understanding relationships between changes in stream flow and ecological measures is critical to mitigating impacts of altered hydrology in rivers. We used long-term datasets spanning pre- and post-dam periods, to compare differences in downstream hydrology and fish communities in two different rivers in Oklahoma. Hydrology in the stream with more upstream storage behind dams was substantially altered and exhibited larger changes in fish communities. However, we also observed increases in species associated with lake environments within fish communities in both systems. These results suggest that downstream fish communities do respond to high levels of hydrologic alteration associated with dams on rivers. However, other factors including expansion of species stocked in reservoirs into rivers may also influence shifts in fish communities, particularly when hydrologic changes associated with dams is limited. Identifying relationships between reservoirs, flow alteration, and downstream ecological changes is an important step in helping water resource managers establish stream flows below reservoirs that limit impacts to ecological communities while meeting human demands for water storage and flood control.

Technical Abstract: River impoundments alter downstream hydrology and habitat, often resulting in significant changes in stream communities. The degree of impact of a river impoundment on downstream hydrology and biological communities can be dependent on many factors, including underlying natural hydrologic regimes and reservoir operation purpose and scope. We compared pre- and post-impoundment hydrologic patterns and fish assemblage structure at two sites below reservoirs differing in natural hydrologic regimes in Oklahoma. We observed significant shifts in fish assemblage structure downstream after stream impoundment at both sites. The Bird Creek flow regime shifted from a historically intermittent stream to one with stable perennial flows, and changes in fish assemblage structure covaried with changes in all five components of the flow regime; most species that increased in abundance require fluvial habitats and likely benefited from increased flows during historically low flow periods. In contrast, the Kiamichi River flow regime did not change significantly for most flow components despite shifts in fish assemblage structure; however, most species shifts were associated with lentic environments and were more likely related to proximity of reservoirs in the drainage system rather than changes in stream flow. Findings from this study suggest that downstream fish assemblage response to river impoundment can be associated with high levels of hydrologic alteration, but other factors including expansion of lentic species into lotic environments may also influence shifts in assemblage structure, particularly when hydrologic changes related to impoundment are limited.