133A—Southern Coastal Plain

This MLRA (shown in orange in the figure above) is in Alabama (26 percent), Mississippi (24 percent), Georgia (21 percent), Florida (8 percent), North Carolina (7 percent), Virginia (5 percent), South Carolina (4 percent), Tennessee (4 percent), and Louisiana (1 percent). It makes up about 106,485 square miles (275,930 square kilometers). It is the largest MLRA in the U.S. The city of Alexandria, Virginia, is at the northernmost tip of the area. The MLRA also includes Fredericksburg, Richmond, and Petersburg, Virginia; Rocky Mount, Goldsboro, Fayetteville, and Lumberton, North Carolina; Florence, Sumter, and Orangeburg, South Carolina; Albany and Tifton, Georgia; Tallahassee, Florida; Tuskegee, Eufaula, Selma, and Tuscaloosa, Alabama; Savannah, Tennessee; Corinth, Starkville, Grenada, Meridian, Hattiesburg, and McComb, Mississippi; and Bogalusa, Louisiana. Interstates 95, 64, 85, 40, 20, 20/59, 26, 16, 75, 10, 65, 59, and 55 cross this area from north to south.

Forts Belvoir and A.P. Hill, Cameron Station Military Reservation, and Quantico Marine Corps Combat Development Command are in the part of this area in Virginia. The MLRA also includes Fort Bragg and Pope Air Force Base near Fayetteville, North Carolina; a small part of Fort Gordon and Fort Stewart in Georgia; Maxwell Air Force Base and Fort Rucker in Alabama; Whiting Naval Air Station and Eglin Air Force Base in Florida; the National Aeronautics and Space Administration’s National Space Technology Center in Mississippi; and the western edge of the Department of Energy’s nuclear materials production facility at the Savannah River Site in South Carolina.

Mt. Vernon, George Washington’s Birthplace National Monument, and Robert E. Lee’s birthplace are in the part of this MLRA in Virginia. A number of national wildlife refuges, State forests, and State parks are throughout this area. A number of national forests and National Wild and Scenic Rivers are in the southern part of the area. The Choctaw Indian Reservation is in the part of the area in Mississippi.

Physiography

This area extends from Virginia to Louisiana and Mississippi, but it is almost entirely within three sections of the Coastal Plain Province of the Atlantic Plain. The northern part is in the Embayed Section, the middle part is in the Sea Island Section, and the southern part is in the East Gulf Coastal Plain Section. This MLRA is strongly dissected into nearly level and gently undulating valleys and gently sloping to steep uplands. Stream valleys generally are narrow in their upper reaches but become broad and have widely meandering stream channels as they approach the coast. Elevation ranges from 80 to 655 feet (25 to 200 meters), increasing gradually from the lower Coastal Plain northward. Local relief is mainly 10 to 20 feet (3 to 6 meters), but it is 80 to 165 feet (25 to 50 meters) in some of the more deeply dissected areas.

The extent of the major Hydrologic Unit Areas (identified by four-digit numbers) that make up this MLRA is as follows: Mobile-Tombigbee (0316), 12 percent; Choctawhatchee-Escambia (0314), 12 percent; Apalachicola (0313), 10 percent; Pascagoula (0317), 9 percent; Altamaha-St. Marys (0307), 7 percent; Alabama (0315), 6 percent; Pearl (0318), 6 percent; Suwannee (0311), 4 percent; Ogeechee-Savannah (0306), 4 percent; Pee Dee (0304), 4 percent; Lower Mississippi-Yazoo (0803), 4 percent; Lower Chesapeake (0208), 3 percent; Cape Fear (0303), 3 percent; Ochlockonee (0312), 2 percent; Neuse-Pamlico (0302), 2 percent; Lower Mississippi-Hatchie (0801), 2 percent; Lower Tennessee (0604), 2 percent; Chowan-Roanoke (0301), 2 percent; Edisto-Santee (0305), 2 percent; Middle Tennessee-Elk (0603), 1 percent; Lower Mississippi-Lake Maurepas (0807), 1 percent; Lower Mississippi-Big Black (0806), 1 percent; and Potomac (0207), 1 percent. This MLRA stretches from the Chesapeake Bay in the north to just short of the Mississippi River in Louisiana and Mississippi. A great number of major rivers originating in the Appalachian Mountains west of this area cross the MLRA and empty into the Atlantic Ocean or the Gulf of Mexico.

Geology

This MLRA is bordered on the west and north by the “fall line.” This line of water falls marks the western and northern extent of the unconsolidated Coastal Plain sediments. It is an erosional scarp formed when this area was the Atlantic Ocean shore in Mesozoic time. The MLRA is underlain by eroded igneous and metamorphic bedrock. Rivers and streams draining the Appalachians deposited a thick wedge of silt, sand, and gravel east and south of the fall line as delta deposits in the Atlantic Ocean. These Jurassic and Cretaceous river sediments were eventually exposed as the Coastal Plain uplifted and the sea level changed. When the sea level rose again, the Coastal Plain was submerged and covered by a thin layer of Cretaceous sands in the eastern half of the area. In the western part of the area, the water was deeper and limestone, dolomite, and calcareous sands were deposited. As the Coastal Plain continued to uplift and the sea level dropped again, Quaternary material consisting of unconsolidated clay, silt, sand, and gravel was deposited over the Tertiary sand and carbonates. Subsequent changes in the sea level created terraces in these younger deposits along many of the streams and rivers draining this area. Much of the MLRA has a “benched” appearance because of the cycles of erosion and deposition that occurred as the area was exposed and submerged numerous times in its geologic history.

Climate

The average annual precipitation in most of this area is 41 to 60 inches (1,040 to 1,525 millimeters), increasing from north to south. It is typically 61 to 72 inches (1,550 to 1,830 millimeters) in the extreme southwest part of the area, inland along the Gulf Coast. The minimum precipitation occurs in autumn throughout the area. The maximum precipitation occurs during midsummer in the eastern part of the area and during winter and spring in the western part. Rainfall typically occurs as high-intensity, convective thunderstorms during the summer, but moderate-intensity tropical storms can produce large amounts of rainfall during winter in the eastern and southwestern parts of the area. Snowfall does not occur in the southern part of the area, and it occasionally occurs in the northern part. The average annual temperature is 55 to 68 degrees F (13 to 20 degrees C), increasing from north to south. The freeze-free period averages 250 days and ranges from 200 to 305 days, increasing in length from north to south.

Water

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

Public supply—surface water, 6.1%; ground water, 5.1%
Livestock—surface water, 1.9%; ground water, 4.4%
Irrigation—surface water, 3.9%; ground water, 4.5%
Other—surface water, 69.7%; ground water, 4.4%

The total withdrawals average 7,030 million gallons per day (26,610 million liters per day). This MLRA is among the top 10 MLRAs in total amount of water used. About 18 percent is from ground water sources, and 82 percent is from surface water sources. Precipitation and perennial streams provide an abundance of water. Water for livestock is primarily obtained from perennial streams and small farm ponds. The many perennial streams have the potential for supplying water for municipal use, human consumption, and farming but have been little used for these purposes. A few large reservoirs are available for recreation and other uses. Most of the surface water in this area is used for cooling thermoelectric power plants. The surface water is suitable for all uses.

Domestic water supplies in this area are obtained mainly from shallow wells. In most areas one or more aquifers provide ample ground water for irrigation and for municipal and industrial uses. The Floridan aquifer (limestone, dolomite, and calcareous sand) is heavily used in the southern part of the area, and the Cretaceous sand aquifer is extensively used throughout the area. Both of these aquifers have some of the best quality water in the area. The level of total dissolved solids generally is less than 250 parts per million (milligrams per liter), and the water is typically soft or moderately hard. A number of more minor aquifers are used for ground water throughout the area. Mississippi, for example, obtains water from 12 of the 14 principal aquifers in that State. Since the ground water is shallow throughout the area, nitrate contamination from barnyards, confined animal-feeding operations, septic systems, and poor nutrient management practices is always a potential problem. Some ground water in Mississippi has naturally high levels of iron, and many wells in South Carolina pump water that exceeds the national drinking water standard for sodium. Brine water is commonly encountered in wells in the part of this area in Louisiana. The brine originates from salt domes and moves up to the shallow aquifers along faults created by the upward migration of the domes.

Soils

The dominant soil orders in this MLRA are Ultisols, Entisols, and Inceptisols. The soils in the area dominantly have a thermic soil temperature regime, a udic or aquic soil moisture regime, and siliceous or kaolinitic mineralogy. They generally are very deep, somewhat excessively drained to poorly drained, and loamy. Hapludults formed in marine sediments (Luverne and Sweatman series) and mixed marine sediments and alluvium (Smithdale series) on hills and ridges. Kandiudults formed in marine sediments (Dothan, Fuquay, Norfolk, and Orangeburg series) and mixed marine and fluvial sediments (Troup series) on hills and ridges. Fragiudults (Ora and Savannah series) and Paleudults (Ruston series) formed in mixed marine and fluvial sediments on uplands and stream terraces. Fluvaquents (Bibb series) and Endoaquepts (Mantachie series) formed in alluvium on flood plains. Quartzipsamments (Lakeland series) formed in sandy eolian or marine material on uplands. Paleaquults (Rains series) formed in marine and fluvial sediments on terraces.

Biological Resources

This area supports mixed oak-pine vegetation. Loblolly pine, longleaf pine, slash pine, shortleaf pine, sweetgum, yellow-poplar, red oak, and white oak are the major overstory species. Dogwood, gallberry, and farkleberry are the major understory species. Common sweetleaf, American holly, greenbrier, southern bayberry, little bluestem, Elliott bluestem, threeawn, grassleaf goldaster, native lespedezas, and low panicums are other understory species.

Some of the major wildlife species in this area are white-tailed deer, turkey, rabbit, squirrel, bobwhite quail, and mourning dove. The species of fish in the area include bass, bluegill, and channel catfish.

Land Use

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

Cropland—private, 17%
Grassland—private, 8%
Forest—private, 61%; Federal, 3%
Urban development—private, 6%
Water—private, 3%
Other—private, 2%

Timber production, cash-grain crops, and forage production are important in this MLRA. Soybeans, cotton, corn, and wheat are the major crops grown throughout the area. Pastures are grazed mainly by beef cattle, but some dairy cattle and hogs are raised in the area.

The major resource concerns are water erosion, maintenance of the content of organic matter and productivity of the soils, control of surface water, artificial drainage, and management of surface compaction and soil moisture. 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. The most important conservation practice in pastured areas is prescribed grazing. Pastures commonly are overseeded with small grains and/or legumes to supplement forage production during winter. Haying also helps to provide supplemental feed during the long winters. Critically eroding areas and areas where animals congregate should be monitored and treated.

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