摘要: The Upper Mississippi River (UMR) flows south about 1,300 miles from its headwaters in Minnesota to its confluence with the Ohio River at Cairo, Illinois. The river gains volume along its path as it drains nearly 190,000 square mi... 展开 The Upper Mississippi River (UMR) flows south about 1,300 miles from its headwaters in Minnesota to its confluence with the Ohio River at Cairo, Illinois. The river gains volume along its path as it drains nearly 190,000 square miles (490,000 km2) of land, extending over parts of South Dakota, Minnesota, Wisconsin, Iowa, Illinois, and Missouri (fig. 1). The UMR is valued as a multiple-use resource where commercial navigation, water supply, and recreational demands coexist with valued natural resources. Some 7%80 million tons of commodities are transported on the river annually. More than 30 million residents rely on river water for uses such as public and industrial supplies and power plant cooling. The river hosts about 12 million recreational visitors annually. When the public has been asked to identify priorities for the river, however, environmental uses were considered more important (Carlson, 1999). The river is home to a wide variety of wildlife, fish, and aquatic invertebrates. Added to these year- round residents are the many bird species that migrate through the corridor or stop seasonally to breed or overwinter (fig. 2). The fact that three major National Wildlife Refuge complexes and several National Park units have been established along the corridor of the UMR reflects the river's importance to the natural resources of the Nation. 收起