the Upper Mississippi River generate revenue estimated at more than $1 billion per year (USACE, 1993). The UMR-IWW supports a rich array of ecosystems, species, and biodiversity, including the Upper Mississippi River National Fish and Wildlife Refuge, which was authorized by Congress in 1924 and extends from Wabasha, Minnesota, to Rock Island, Illinois. The refuge has the largest annual public use of any unit in the U.S. national wildlife refuge system (Holland-Bartels, 1992). Floodplains along the river provide sites for hundreds of communities, contain large agricultural areas, and serve as important highway and railroad corridors. Many areas in these floodplains are subject to flooding. Record floods occurred throughout the region in the summer of 1993, and the river system also experiences many smaller floods.
The Upper Mississippi River and Illinois Waterway systems have long supported this wide variety of human and economic uses, and different users of these systems have had various and changing effects on one another. Nineteenth century steamboats on the Upper Mississippi, for example, had few large impacts on river ecology; in fact, given the problems posed to the steamboats by snags, currents, and shifting sandbars during the steamboating era, the river system may have had more impacts on navigation activities rather than vice versa (Merrick, 2001, provides an account of mid-nineteenth century Upper Mississippi River steamboating). Urban and industrial activities and waste products have affected river ecology for decades. For example, concerns regarding the impacts of water pollution on the Upper Mississippi River’s mussel fishery were expressed as early as 1898 (Smith, 1899; cited in Scarpino, 1985). Water quality continued to be a concern into the 1920s, when steadily declining mussel populations were attributed to not only aggressive harvesting practices, but also “stream pollution from the large cities along the rivers” (ibid.). There have been improvements in water quality since passage of the Federal Water Pollution Control Act Amendments of 1972 (amended in 1977 and known today as the Clean Water Act). Raw sewage, oil slicks, and phosphates are better controlled, but some aspects of water quality, such as sedimentation, have become a greater concern (Ellis, 1993). An important water quality issue today is fertilizer applications across the upper basin. These applications contribute to high flows of nutrients downstream in the Mississippi River, which contributes to hypoxia (an oxygen-deficient condition) in the Gulf of Mexico. These flows ultimately contribute to the creation of an area known as the “Dead Zone” in the Gulf of Mexico (Mitsch et al., 2001; Rabalais et al., 2002).
Commercial logging and increases in mechanized agriculture across the upper Midwest in the middle and late twentieth century changed the region’s vegetative cover, which has had important implications for soil ero-