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CHAPTER 5: RESTORING AQUATIC RESOURCES TO THE LOWER MISSOURI RIVER The Missouri River's course through highly erodible soils resulted in major changes in channel configuration during flooding. During nonnal flows, the channel was characterized by continuous bank erosion, a braided shifting configuration. and numerous sand islands and sandbars. Extensive channel migration in the lower river resulted in a floodplain width of 2.4-27.4 kilometers, averaging 8.1 kilo- meters (Hesse and others, 1989a). For example, about one- third of the floodplain of the lower Missouri River was reworked by the river between 1879 and 1930 (Schmudde, 1963). Erosional and depositional characteristics of this dynamic equilibrium resulted in a range of serial forest communities in the Missouri River floodplain (Bragg and Tatschl, 1977). Recently deposited and exposed sandbars are rapidly colonized by willows (Salix spp.) and succeeded by cottonwood (Populus deltoides), which dominates the canopy for up to 30 years. Box elder (Acer negundo), silver maple (Acer saccharinurn), red mulberry (Mows rubra), and American elm (Ulmus arnericana) replace cottonwood as an intermediate serial stage. Mature floodplain forests contain several species of oaks (Quercus spp.) and hickories (Carya spp.), plus hackberry (Celtis occidentalis), Ameri- can elm, black walnut (Juglans nigra), green ash (Fraxinus pennsylvanica), sycamore (Plan/anus occidentalis), bass- wood (Tilia arnericana), and-almost exclusively in old growth forests-pawpaw (Asirnina triloba) (Weaver, 1960; Bragg and Tatschl, 1977). Little light penetrates the dense canopy of mature Missouri River floodplain forests, result- ing in an understory dominated by climbing vines (Weaver, 1960), including poison ivy (Rhus radicans), Virginia creeper (Partenocissus quinquefolia), and wild grapes (Vitis spp.). Studies of the structural and functional biology of the Missouri River abound. Sowards and Maxwell (1985) list more than 600 Missouri River references, and Hesse and others (1982, I 989a) provide comprehensive reviews of phytoplankton, periphyton, invertebrates, fishes, and energy dynamics of the river and its main-stem reservoirs. Many of these studies deal with biota and processes and how they have been influenced by river alteration; these events are referenced in table 5- I. Fishes and fisheries of the lower Missouri River are treated in a separate section. AL TERA TIONS TO THE MISSOURI RIVER ECOSYSTEM Modifications to the integrity of the natural Missouri River-floodplain ecosystem have been immense and ongo- ing for more than 150 years (table 5-1). Presently, 35 percent (1,316 kilometers) of the river's length is impounded, 32 percent (1,212 kilometers) is channelized or stabilized, and the remaining 33 percent (1,241 kilometers) is free flowing (Schmulbach and others, 1992). Major civil 53 works projects involved channelization, channel mainte- nance, and impoundment and reservoir operation. Total cost for construction, operation. and maintenance of civil works projects through 1984 was nearly $6.2 billion (table 5-2) (Hesse, 1987). Agricultural, industrial, and urban develop- ment within the basin also significantly modified the Missouri River and produced extensive water pollution (table 5-1). CHANNELIZATION Abundant large woody debris (snags) in the river chan- nel, fluctuating water levels, and extensive channel migra- tion made early Missouri River navigation perilous. Modifications of the river to facilitate navigation consisted of snag removal, channel dredging, and construction and maintenance of dikes, revetments. and levees. Stabilizing a river channel contrasts sharply with the concept of dynamic equilibrium discussed earlier. Stabilized channels are static. They lack the successional pattern and periodic disturbance events that maintain physical habitat diversity. Conse- quently, structure and function of the biological system also become stabilized. Funk and Robinson (1974) described how channelization and associated activities were accom- plished in the lower Missouri River, and we summarize its chronology in table 5-1. Presently, all of the Missouri River from Sioux City, Iowa, to its mouth at SI. Louis, Missouri, is channelized. Even during flooding, only about 10 percent of the original floodplain is inundated, as high agricultural levees confine the river to a width of 183-335 meters (Schmulbach and others, 1992). Impacts of snag removal and channelization have been numerous and severe on the physical, chemical, and biological structure and function of the Missouri River and its floodplain (table 5-3). The most damaging of these alterations to aquatic communities has been the nearly complete isolation of the river from its floodplain, subsequent loss of floodplain habitat, drastic reduction in the area and diversity of river channel habitats, and increase in flow yelocity of the main channel. See Brookes (1988) for a further review of the general physical and biological impacts of river channelization. DAM CONSTRUCTION AND OPERATION Widespread flooding during the war years of 1942- 1944 was the impetus for passage of the 1944 Flood Control Act to construct a six-dam system of flood control on the main-stem Missouri River (Keenlyne, 1988). Called the Pick-Sloan Plan, the act would "...provide for the most effi- cient utilization of waters ofthe Missouri River Basin for all purposes including irrigation. navigation, power, domestic and sanitary purposes, wildlife. and recreation" (House Report 475, 78th Congress, 2d. Sess., 1944).