NCCOS: Ecosystems - Estuaries: Mississippi River

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Estuaries

Estuaries are highly dynamic places. Winds, tides, and freshwater flowing into an estuarine area sculpt the landscape and create constantly changing physical and chemical conditions. In some areas, such as the birdfoot delta where the Mississippi River flows into the Gulf of Mexico, the change can be quite rapid. New land can be created or existing areas wiped away even within the course of a single major storm. Despite this instability, and probably because of it, estuarine areas are highly productive. These areas support great populations of plants and animals, but only those that can tolerate changes in characteristics such as salinity and temperature.

Estuaries can be home to a range of habitats, from freshwater swamps to seagrass beds adjacent to barrier islands. The diversity and complexity of these habitats provide feeding and breeding grounds for many animals, including endangered species. In addition, many commerically and recreationally important fisheries species spend all or part of their life cycle in a habitat within an estuary.

People have lived along the shores of estuaries long before recorded history. These areas have provided human communities with easy access to food, resources, and transportation. Our use of these areas can come at a significant cost, though. Overharvesting has resulted in declining populations of some estuarine animals. Changes made to the movement of water through these estuarine systems, such as when canals are built through marshes, has resulted in the rapid loss of some types of habitat. Runoff from our roads, lawns, and fields has introduced chemicals into estuaries that can change the way the ecosystem functions. We're working hard now to restore habitat that has been lost or changed as a means of replacing lost functions within the estuary.

Estuaries can be found from the tropics to polar regions. This range of latitude, coupled with a great diversity in tidal height, currents, and the physical shape of bays, means that an estuary can take any of a variety of forms. They can be a shallow lagoon between a barrier island and the mainland. Estuaries can be deep cuts into the bedrock, formed when glaciers ground their way across the land. A bay can be an ancient river valley that was flooded as the sea level rose thousands of years ago.

Estuaries have been used as a method of transportation for thousands of years. Native people used dugout canoes to reach estuarine resources such as oyster beds, as well as to move from village to village. Over the years, the size of vessels has greatly increased. In some estuaries, the water is naturally deep enough to accommodate large ships. In others, such as the estuaries of the northwestern Gulf of Mexico, ship channels have to be dredged and maintained to accomodate shipping. In some estuarine areas, these channels can fundamentally change how water flows within the ecosystem and may impact organisms that live in those areas.

Estuaries directly support human communities. They provide food, income, and improve the basic quality of life. People must take care, however, to use estuaries in a way that is sustainable to allow the ecosystem, as well as human cultures and economies, to continue well into the future.

Estuaries play an important role in a diverse group of American cultures, from the Cajuns of South Louisiana to the watermen of Maryland's Eastern Shore. Estuarine creeks, bayous, sloughs, and branches wind their way through art, folklore, cuisines, and traditional economies. Preserving and restoring estuaries not only provides valuable ecological benefits, it helps to perserve disappearing features of human life.

NOAA's National Centers for Coastal Ocean Science

Estuaries