The upper and lower watersheds of the Mississippi River extend 2,340 miles from the headwaters in Lake Itasca, Minnesota, to the Gulf of Mexico. With a drainage basin of 1.15 million square miles, the Mississippi River, known as the "Father of Waters," drains 40 percent of the continental United States and discharges an annual average flow of 640,000 cfs into the Gulf of Mexico. On the basis of drainage area and mean annual discharge, the Mississippi is the largest river in the United States (Iseri and Langbein, 1974) and is ranked by annual discharge as the sixth largest river in the world (Berner and Berner, 1996). Figure 12-1 highlights the location of the seven catalog units of Accounting Unit 070102 for the Upper Mississippi River case study in the vicinity of Minneapolis-St. Paul in Minnesota. The Twin Cities are one of the nation's many major urban areas characterized by water pollution problems during the 1950s and 1960s (see Table 4-2; FWPCA, 1966; USPHS, 1951; 1953). Federal enforcement conferences were convened in 1964 and 1967 to investigate water pollution problems in the Minnesota and Wisconsin sections of the Upper Mississippi River (Zwick and Benstock, 1971).
In this chapter, data and information are presented to characterize long-term trends in population, municipal wastewater infrastructure and effluent loading of pollutants, ambient water quality conditions, environmental resources, and uses of the Upper Mississippi River in the vicinity of the Twin Cities. Data sources included STORET, USEPA's national water quality database, USGS streamflow records (USGS, 1999a), published literature, unpublished data, newsletters, and technical reports obtained from the Metropolitan Council Environmental Services (MCES) in St. Paul and from other state, local, and federal agencies. Data have also been obtained from a validated water quality model of the Upper Mississippi River (Lung and Larson, 1995) to identify the progressive improvements in dissolved oxygen and other water quality parameters attributed to upgrades of the Metropolitan Wastewater Treatment Plant in St. Paul from primary to secondary and advanced secondary with nitrification (Lung, 1998).
The Twin Cities of Minneapolis and St. Paul are the major urban centers for more than 1,100 miles along the Mississippi River upstream of St. Louis, Missouri. About one-third of the population and a majority of the commercial and industrial activity of Minnesota are located within the Twin Cities metropolitan region. Outside the Twin Cities, the Upper Mississippi watershed is primarily rural and forested, with the population dispersed in small towns and farms. The glaciated topography of the wa-
tershed provides extensive habitat for fish and wildlife and also supports an economy historically based on agriculture and wood products. In addition to these economic sectors, industrial and manufacturing activities have become significant components of the overall economy.
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