OutdoorNebraska

9 Siltation Excess sediment will have an impact on freshwater mussels which is often species dependent. Some species like the Giant floater and Mapleleaf were tolerant whereas others like the Wabash pigtoe or Black sandshell were not. The first two are doing quite well in Nebraska while the later two may be extirpated. Iowa mussel populations declined with loss of streamside woodlands, high siltation, and intensive agricultural land use. Removal of forest vegetation increases stream runoff. Increased runoff can activate the stream bed and results in increased scour and altered deposition of sediment. Streambeds degrading in one area with aggrade in another downstream. Aggradation results in increased width/depth ratios and increased bedload transport. In the end, habitat complexity declines. 17, 32, 40 Stream Channelization Streams naturally adjust to natural variations in flow and, over time, develop a quasi-equilibrium. Channelization destroys this equilibrium by reducing stream length and increasing gradient. As a result the stream will degrade, eroding downwards and outwards, eliminating meanders, filling pools and burying riffles while also removing riparian vegetation and snags. It reduces the total stream area and eliminates the natural diversity of a stream's flow and substrate. Channelization also results in lower low flows and higher high flows. In a comparison of channelized and unchannelized streams in Iowa, the unchannelized streams had more diversity of habitat and supported more centrarchids and ictalurids. The result is the direct loss of mussels during the channelization process and the loss of the hosts needed for reproduction and the loss of the habitats needed for recovery. This is especially notable in Nebraska's Nemaha River basin where many species of mussels have been extirpated due to the extensive channelization of the basin's streams. 11, 27, 42, 44 Pollutants, Pesticides and Contaminants Freshwater mussels are more sensitive to pesticides than many other animals. The effects of pesticides are species-specific but, in general, sub-lethal levels inhibit respiratory efficiency and accumulate in the tissues. Mussels, especially juveniles, are sensitive to heavy metals. River reaches downstream of wastewater treatment plants are often devoid of freshwater mussels as their

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