The Nature Conservancy - LMR -- The Alluvial Plain

The Lower Mississippi River Program

The Lower Mississippi River - Alluvial Plain

Along the more than 950 miles between the Mississippi River’s convergence with the Ohio River in southern Illinois and its mouth at the Gulf of Mexico lies a vast alluvial plain, in some places 125 miles wide. The Mississippi and its tributaries meandered for millennia depositing deep soils to create a nearly flat landscape containing more than 24 million acres of permanent and seasonal wetlands. The streams’ wanderings were generated mostly by winter and spring floods that nourished dense bottomland forests and a remarkable assemblage of plants and animals.

The freshwater ecosystems of the Lower Mississippi River (LMR) region shelter some 240 fish species and about 40 known species of mussels. More than 265 migratory bird species use LMR habitats to rest and recuperate during difficult trips each spring and fall between nesting grounds to the north and winter territories to the south. Other birds breed in the alluvial plain’s swampy woodlands and the region annually hosts the world’s largest wintering population of mallards.

In addition to its ecological significance, the LMR region long has been of economic importance. Virgin hardwood forests were harvested to provide lumber for a growing country, making way for abundant crops of cotton, rice, soybeans, sugar cane and feed grains. An estimated 55 to 60 percent of the region’s land now is used for agriculture.

As the region’s economic prominence grew, the nation began engineering the Mississippi and tributaries to improve navigable routes used to ship regional products, prevent flood damage, drain additional lands for agriculture and impound water to meet future needs. Dams and levees were constructed, waterways were dredged and straightened, dikes were built to direct flows, and revetments were added to harden banks. Such works altered the region’s seasonal flooding and water flow patterns.

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Centuries-old cypress
trees are found in forests throughout the lower Mississippi River region © Byron Jorjorian

Working with numerous governmental and private-sector partners, the Conservancy is now addressing ecological threats and conservation opportunities in the LMR alluvial plain at 18 priority conservation sites and by developing broader strategies to address region-wide threats.

LMR Program

Priority Sites