Effects of Dams on Fish and Macroinvertebrate Communities in the Vermilion River, IL

Dams are a main source of anthropogenic disturbances on river systems and can affect rivers in a variety of ways. Dams have the ability to change rivers from lotic to lentic habitats, affect sediment transportation, connectivity, water quality, linkages with wetlands and the quality of in-stream and riparian habitats. The Danville Dam was constructed in 1914 on the Vermilion River in Danville, Illinois and is becoming a safety hazard for human recreation on the Vermilion River, resulting in three deaths in the last 10 years. The Illinois Department of Natural Resources in conjunction with the city of Danville has proposed to remove the Danville dam on the main channel fall 2015 and an additional low head dam, Ellsworth Dam, in its tributary the North Fork Vermilion in fall 2014. To assess the impacts of removing the Ellsworth and Danville dams on the aquatic biota and stream habitat quality. Beginning October 2012, we assessed the fish and macroinvertebrate assemblages in twelve, 100 meter long sections of river. Six of the 12 sites were located in the North Fork, referred to as Ellsworth Dam, and six sites in the Vermilion, referred to as Danville Dam sites. Each dam consisted of two sites below the dam and four sites above the dam. The above dam sites consisted of a site directly above the dam, the last 100 meters of the pool, the first 100 meters of the river and an upstream site (the farthest accessible upstream location). This sampling captures the community composition both above and below the dam (immediate impacts) and characteristics of sites above the dam\u27s influence. The effects of the dams were greatest seen at base flow, in the fall seasons. Data shows fall community composition demonstrates strong influences of both dams on fish assemblages and revealed compositional differences between the two drainages. In sharp contrast, a cluster analysis showed no separation in community composition between rivers or sites in the spring. Therefore base flow was used to assess the fish and macroinvertebrate community structure. Non-metric Multidimensional Scaling was used to assess the structure of fish and macroinvertebrate communities. Per-Manova analysis verified river, location, and their interaction to be significant on fish assemblages. Mantel tests showed there was an effect of habitat on fish community structure but no significant effect of physical distance on fish assemblages. Per-Manova reflected the complexity of compositional relationships with both river and the interaction of river and location to be significant on macroinvertebrate assemblages. Unlike the fish, macroinvertebrate assemblages were affected by distance but not by local environment. The Vermilion River system is one of the highest quality systems in Illinois. The removal of the dams will allow the main channel to reconnect and also provide access to upstream habitats in the North Fork tributary. Eliminating physical barriers will allow fish to move upstream allowing them to restore populations. Returning to a free flowing system will increase macroinvertebrate diversity increasing aquatic resources . The combination of these factors will increase the quality of the Vermilion River and return it to its natural environment. The goal of this study is to serve as a model to test the efficacy of dam removal in restoring the diversity and structure of river communities