152A—Eastern Gulf Coast Flatwoods

This MLRA (shown in red in the figure above) is in Florida (71 percent), Mississippi (12 percent), Alabama (9 percent), and Louisiana (8 percent). It makes up about 9,860 square miles (25,555 square kilometers). It includes Hammond and Covington, Louisiana; Gulfport, Biloxi, and Pascagoula, Mississippi; Mobile, Alabama; and Pensacola, Panama City, and Perry, Florida. Pascagoula, Mississippi, is one of the great ship-building centers of the world. Interstates 10, 12, 55, 59, and 65 and U.S. Highway 90 are in this area. The De Soto National Forest and the NASA National Space Technology Laboratories are in the part of this area in Mississippi. The Olf Summerdale Naval Military Reservation is in the part in Alabama. The San Marcos de Apalache State Historical Site, Apalachicola National Forest, and Gulf Islands National Seashore are in the part in Florida. The Tyndall and Eglin Air Force Bases and Pensacola Naval Air Station also are in the part in Florida. A number of national wildlife refuges and State parks and a few State forests are throughout this MLRA.

Physiography

Almost all of this area is in the East Gulf Coastal Plain Section of the Coastal Plain Province of the Atlantic Plain. The extreme southeast tip is in the Floridian Section of the same province and division. This MLRA is a nearly level, low coastal plain crossed by many large streams. The part of the area in Florida has many lakes and ponds. Elevation ranges from sea level to 80 feet (0 to 25 meters). Local relief is generally 10 to 20 feet (3 to 6 meters).

The extent of the major Hydrologic Unit Areas (identified by four-digit numbers) that make up this MLRA is as follows: Suwannee (0311), 31 percent; Choctawhatchee-Escambia (0314), 18 percent; Apalachicola (0313), 14 percent; Pascagoula (0317), 13 percent; Ochlockonee (0312), 10 percent; Mobile-Tombigbee (0316), 5 percent; Lower Mississippi (0809), 4 percent; Lower Mississippi-Lake Maurepas (0807), 3 percent; and Pearl (0318), 2 percent. Reaches of four rivers in the part of this area in Louisiana have been designated as National Wild and Scenic Rivers. These are the Amite, Tangipahoa, Tchefuncte, and Bogue Chitto Rivers. The Pearl River forms the boundary between Louisiana and Mississippi in this area. The Escatawpa River joins the Pascagoula River just before it empties into the Gulf of Mexico in the part of this area in Mississippi. The Tombigbee and Alabama Rivers join just outside this area to form the Mobile River in Alabama. The Perdido River forms the boundary between Alabama and Florida in this area. The major rivers that cross the part of this area in Florida on their way to the Gulf of Mexico are the Escambia, Yellow, Choctawhatchee, Apalachicola, Ochlockonee, and Suwannee Rivers.

Geology

Pleistocene-age terraces consisting of ancient Mississippi River deposits of unconsolidated fine sand, which grades to coarser sand and gravel at depth, are at the surface in the western end of this area, in Louisiana and Mississippi. The Citronelle Formation is at the surface in most of the parts of this area in Mississippi, Alabama, and the western panhandle of Florida. This formation is a thin layer of silt, sand, and gravel deposited by an ancient predecessor of the Mississippi River during Pliocene time. A thin veneer of Pleistocene-age sand covers the surface of this area farther to the east in Florida. Limestone and dolomite of the Floridan aquifer lie just beneath the sand in the rest of the area in Florida. Karst topography is common in Florida. Recent silt, sand, and gravel deposits fill the valleys along most of the major rivers in the area.

Climate

The average annual precipitation is 60 to 68 inches (1,525 to 1,725 millimeters) in most of the central part of this area. It is 47 to 60 inches (1,195 to 1,525 millimeters) in much of the area in Louisiana and Florida. The minimum precipitation usually occurs in the early and middle parts of autumn, increasing moderately in winter and early spring. Lesser amounts occur in May. The maximum precipitation usually occurs in summer. At the eastern end of this area, in Florida, rainfall usually occurs as high-intensity, convective thunderstorms in summer. In the rest of the area, it typically occurs as moderate-intensity, tropical storms that produce large amounts of rain in winter. The average annual temperature is 64 to 71 degrees F (18 to 21 degrees C). The freeze-free period averages 300 days and ranges from 250 to 350 days. It is longer closer to the Gulf of Mexico and to the south in Florida.

Water

Following are the estimated withdrawals of freshwater by use in this MLRA:

Public supply—surface water, 1.8%; ground water, 15.3%
Livestock—surface water, 0.5%; ground water, 1.4%
Irrigation—surface water, 0.1%; ground water, 0.0%
Other—surface water, 74.0%; ground water, 6.9%

The total withdrawals average 1,030 million gallons per day (3,899 million liters per day). About 24 percent is from ground water sources, and 76 percent is from surface water sources. The abundant rainfall and the many perennial streams are important sources of water. Generally, river water is suitable for most uses with some treatment. Surface waters have been polluted by municipal and industrial wastewater discharges and fecal coliform bacteria. Some improvement in water quality has occurred as communities and industries strive to clean their wastewater before discharging it into nearby rivers or lakes. Most of the surface water is used for municipal and industrial supply and for cooling thermoelectric power plants.

Ground water is plentiful in this area but is affected by salt in many areas near the coast. Soft ground water is obtained from the Pleistocene terraces in Louisiana, Mississippi, and Alabama. This water is generally low in total dissolved solids, but it may be contaminated by septic systems. Where faults occur, brine from salt-dome deposits can move up into the surface aquifers, making the water too salty for most uses. Where the ground water is not suitable, better quality water can be obtained from river valley alluvium. River flows tend to recharge these aquifers annually, so this water is usually suitable for most uses with some treatment. Ground water is plentiful in the Citronelle and Floridan aquifers, in the middle and eastern parts of this area. This water is soft and hard, respectively, and is suitable for most uses. Since these aquifers are close to the Gulf of Mexico, intrusion of seawater is a constant problem.

Soils

The dominant soil orders in this MLRA are Alfisols, Ultisols, Entisols, Spodosols, and Histosols. The soils in the area dominantly have a thermic or hyperthermic soil temperature regime, an aquic or udic soil moisture regime, and siliceous mineralogy. They generally are deep or very deep; are somewhat poorly drained to very poorly drained; and are loamy, mucky, or sandy. Alaquods (Chaires and Leon series) and Psammaquents (Scranton series) formed in sandy marine sediments on flats and in depressions. Haplosaprists formed in organic deposits in swamps and depressions (Dorovan and Pamlico series) and in marshes and swamps (Lafitte and Maurepas series). Sulfihemists (Handsboro series) and Sulfaquents (Axis series) formed in saltwater and brackish water marshes. Quartzipsamments (Newhan and Corolla series) and Psammaquents (Duckston series) formed on dunes and in interdunal swales on barrier islands. Glossaqualfs (Guyton series) and Hydraquents (Arat and Levy series) formed in alluvium on flood plains. Endoaqualfs (Meadowbrook and Wekiva series) and Albaqualfs (Tooles series) formed in loamy marine sediments on flats and flood plains and in depressions. Endoaquults (Myatt series) and Paleudults (Stough series) formed in mixed fluvial and marine sediments on flats and stream terraces. Paleaquults (Plummer and Bayou series) and Paleudults (Escambia and Ocilla series) formed in loamy and sandy sediments on marine terraces.

Biological Resources

This area supports pine forest vegetation and freshwater, brackish water, and saltwater marsh vegetation. Longleaf pine and slash pine are the major trees. Chalky bluestem, Indiangrass, and several species of panicum make up the understory. Palmetto, gallberry, and waxmyrtle are the dominant woody shrubs. Roseau, common reed, bulltongue, maidencane, cutgrass, and alligatorweed characterize the freshwater and intermediate water vegetation. Marshhay cordgrass, saltgrass, and Olney bulrush characterize the brackish water vegetation. Saltgrass, marshhay cordgrass, smooth cordgrass, and black needlerush are included in the saltwater vegetation.

Some of the major wildlife species in this area are white-tailed deer, feral hog, gray fox, red fox, bobcat, raccoon, skunk, opossum, otter, rabbit, squirrel, turkey, bobwhite quail, and mourning dove. The species of fish in the area include largemouth bass, channel catfish, bullhead catfish, bluegill, redear sunfish, spotted sunfish, warmouth, black crappie, chain pickerel, gar, bowfin, sucker, spotted trout, croaker, striped mullet, flounder, and red drum.

Land Use

Following are the various kinds of land use in this MLRA:

Cropland—private, 1.3%
Grassland—private, 1.9%
Forest—private, 55.6%; Federal, 11.5%
Urban development—private, 10.4%
Water—private, 12.0%; Federal, 3.0%
Other—private, 4.3%

Very little of this dominantly forested area is in farms. Much of it is in large holdings owned by pulp and paper companies. Pulpwood and lumber are the principal forest products. Some of the forestland is grazed. Some areas are in State and national forests or are used as game refuges or as military training sites. Only a very small acreage is cropped or pastured. Corn, peanuts, tobacco, and soybeans are the major crops.

The major soil resource concerns are water erosion, maintenance of the content of organic matter and productivity of the soils, surface compaction, and management of soil moisture. Conservation practices on forestland generally include forest stand improvement, forest trails and landings, prescribed burning, riparian forest buffers, forest site preparation, bedding, establishment of trees and shrubs, and management of upland wildlife habitat. The most important conservation practice on pasture is prescribed grazing. Over-seeding of pastures with small grains and/or legumes during winter commonly supplements forage production. Haying also provides additional feed during the long winters. Conservation practices on cropland generally include systems of crop residue management, cover crops, crop rotations, water disposal, subsoiling or deep tillage, pest management, and nutrient management. Critically eroding areas and areas where animals congregate must be monitored regularly and treated promptly.

< Back to Technical Resources