III.

Economic Importance

Many cities and towns began along the Mississippi and continue to depend on the river for their economic base. Dredging and other engineering works in the channel have eliminated many of the hazards of navigation, making it possible for large vessels to use the river. Saint Paul and Minneapolis lie at the northern limit of navigability. Saint Paul rose to prominence as a grain-shipping port, where wheat grown in the northern Great Plains is loaded for shipment south. St. Louis, known as the Gateway to the West, is located near the junction of the Missouri and grew as a port linking the Mississippi with the Great Plains. The portion of the river south of Baton Rouge is navigable by oceangoing vessels, and Baton Rouge and New Orleans are seaports. About 282 million metric tons of freight are carried on the river each year. The most important cargoes on the river are bulk items such as coal, petroleum products, sand, gravel, and grain.

The Mississippi Valley has rich alluvial soils, formed by thousands of years of erosion and deposition by the meandering river. The floodplain supports agriculture, especially feed grains and soybeans in the north and cotton, groundnuts, and rice in the south.

Abundant in fish, the river is known especially for several varieties of catfish, some of which are harvested commercially. The upper valley once contained vast shellfish beds, which were the basis of an extensive fishery in the 19th and early 20th centuries, but these were severely depleted and are no longer commercially significant. The floodplain includes extensive wetlands, especially in the delta area, which is the largest area of wetlands in the United States. These wetlands form an important habitat for migratory birds.

The Mississippi's role as a major artery for the United States extends to waste removal, and the river carries a significant load of both sewage and industrial pollution from urban and rural sources. In 1993 the huge flood of the Mississippi carried toxic chemicals into the river, but most of the spilled substances were diluted to low levels by the flood. In general, pollutant concentrations in the Mississippi are not as high as in some smaller rivers because the volume of water is large.