9781934874448-ch12

Fishery Resources, Environment, and Conservation in the Mississippi and Yangtze (Changjiang) River Basins

The Lower Mississippi River Floodplain Ecosystem: Current Status and Future Potential

Michael A. Eggleton, Quenton C. Fontenot, and John R. Jackson

doi: https://doi.org/10.47886/9781934874448.ch12

Abstract.—The lower Mississippi River encompasses the 1,535-km reach extending from the confluence with the Ohio River at Cairo, Illinois to the Gulf of Mexico. Waters of the lower Mississippi River have historically inundated vast areas of adjacent floodplain during spring flood pulses. Additionally, processes of land building within the river’s deltaic plain supported vast forests and diverse freshwater and salt-marsh habitats. Flood pulses provided a mechanism of lateral exchange of energy and nutrients between the aquatic and terrestrial habitats, while sediment loads continually rebuilt and supported the deltaic plain. As human populations and agriculture expanded throughout the lower Mississippi Valley, construction of flood-protection levee systems and commercial navigational structures severely decreased the connectivity between the lower Mississippi River and its floodplain. The current lower Mississippi River floodplain is more than 90% reduced in area compared to historical conditions. Fluvial dynamics, which are the driving forces that stimulate floodplain function and create diverse habitats, appear to have been altered throughout approximately 80% of the river. As a result, the hydrograph, thermograph, sedimentation patterns, nutrient dynamics, and vegetation communities within the lower Mississippi River floodplain have experienced major changes through time, with many large alterations occurring during the past century. In addition, because most of the sediment load of the lower Mississippi River now enters the northern Gulf of Mexico, land building and associated processes are much reduced in the river’s deltaic plain. This process has allowed intrusion of saltwater into coastal habitats, which has heavily impacted vegetation communities. This paper reviews the consequences of river modification to lower Mississippi River floodplain, current efforts towards restoring the floodplain and deltaic plain, and proposes future strategies towards restoring portions of the historical floodplain.