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The Mississippi River is the largest river in the United States and the sixth largest river in the world, draining 41% of the continental U.S. (Amon and Benner, 1997). The Mississippi River discharges a total of about 580 cubic kilometers per year into the Gulf of Mexico contributing more than 70% of Gulf of Mexico’s freshwater input (Meade). The Ohio River contributes 38% of this water (Antweiler and Taylor). This water carries with it large amounts of sediments and nutrients that have been picked up from the land along the way. Events that occur in the Mississippi River basin impact the river and the Gulf of Mexico even if hundreds of miles away.
The Mississippi River is divided into three sections. The area of the river that is above where it is joined by the Ohio River is referred to as the Upper Mississippi River. The majority of the river in this area flows through a valley created by glacial and riverine processes. The Lower Mississippi consists of the area below the joining of the Ohio River and flows through an alluvial plain. The third region is the region where the Mississippi meets the Gulf of Mexico (Meade). The Mississippi is a river that has been highly modified by human activity; the hydrology of the river has been changed for flood control, hydroelectric power and navigation. These modifications include a stretch of lock and damn structures between Minneapolis and St. Louis, wing dams which concentrate river flow into channels and dredging. Probably the largest modification of the Mississippi River is the diversion of about a quarter of the water to Atchaflaya River (Meade).