151-Gulf Coast Marsh

21,030 sq km (8,120 sq mi)

Land use: Most of this area is in marsh vegetation and is used mainly for wildlife habitat. The area is almost treeless and uninhabited. It is part of the fertile and productive estuarine complex that supports marine life of the Gulf of Mexico. The area provides wintering ground for millions of ducks and geese and habitat for many fur-bearing animals and alligators. A significant acreage west of Vermillion Bay is firm enough to support livestock and is used for winter grazing of cattle. A small acreage of freshwater marsh is drained by pumping systems and is used for pasture and for the production of rice.

Elevation and topography: Elevation ranges from sea level to about 2 m. On beach ridges, canal spoil banks, and natural levees, elevation is as much as 3 m, and on the salt dome islands, it is as much as 50 m. The land east of Vermillion Bay, part of the Mississippi River deltaic plain, has a ragged shoreline and is made up of recent alluvial and marine sediments. The land west of Vermillion Bay is made up of older alluvial and marine sediments and has a smoother shoreline. Low, narrow, elongated sandy ridges characterize much of the area. There are many rivers, lakes, bayous, tidal channels, and manmade canals.

Climate: Average annual precipitation-1,225 to 1,650 mm, increasing from west to east. During the growing season, precipitation ranges from 900 to 1,150 mm. Average annual temperature-About 21 C. Average freeze-free period-280 to 350 days, increasing from north to south.

Water: This area contains many rivers, lakes, bayous, tidal channels, and manmade canals. About one-half of the marsh is fresh, and one-half is salty. Tidal channels provide free movement of salty water from the Gulf of Mexico into parts of the Gulf Coast Marsh adjacent to the Gulf. Most of the area is susceptible to flooding either by freshwater drained from lands adjacent to the marsh or by saltwater from the Gulf of Mexico. Daily tides flood some parts. Tides resulting from hurricanes or tropical storms are as much as 3 m above sea level and flood most of the area. Notable ground water is scarce east of Vermillion Bay. Hard ground water is available in moderate to large quantities west of Vermillion Bay.

Soils: The dominant soils are Aquolls, Saprists, Aquents, and Hemists. They have a thermic temperature regime and an aquic moisture regime. Most of the soils of the Gulf Coast Marsh are very poorly drained, and their water table is at or above the surface most of the time. These soils are susceptible to frequent flooding. They formed in alluvial and marine sediments and organic accumulations. The Aquolls are firm, but the other soils are soft and can sustain little weight. West of Vermillion Bay, Haplaquolls (Harris series) are dominant. Soils with a thin surface layer of peat or muck and Medisaprists (Kenner, Lafitte, and Allemands series), Hydraquents (Gentilly and Scatlake series), and floating Medihemists (Carlin series) are dominant.

Potential natural vegetation: This area supports freshwater and saltwater marsh vegetation of grasses, sedges, rushes, and other plants. Alligatorweed, spikerush, maidencane, cutgrass, and bulltongue characterize the freshwater vegetation. Roseau, common reed, bulltongue, and marshhay cordgrass characterize the intermediate water vegetation. Marshhay cordgrass, saltgrass, and Olney bulrush are typical of the brackish water vegetation. Saltgrass, marshhay cordgrass, smooth cordgrass, and black needlerush are included in the saline water vegetation.

(From "Land Resource Regions and Major Land Resource Areas of the United States". United States Department of Agriculture Soil Conservation Service Handbook 296. Dec. 1981. page 110 - 111.)