134—Southern Mississippi Valley Loess

This MLRA (shown in orange in the figure above) is in Mississippi (39 percent), Tennessee (23 percent), Louisiana (15 percent), Arkansas (11 percent), Kentucky (9 percent), Missouri (2 percent), and Illinois (1 percent). It makes up about 26,520 square miles (68,715 square kilometers). The northern part of the area includes Paducah and Murray, Kentucky; Paragould, Jonesboro, and Forrest City, Arkansas; and Memphis, Dyersburg, Bartlett, and Germantown, Tennessee. The southern part includes Yazoo City, Clinton, and Jackson, Mississippi, and Baton Rouge, Opelousas, Lafayette, and New Iberia, Louisiana. Interstates 24, 55, 40, 20, 12, 49, and 10 cross this area. The area includes the Homochitto National Forest in Mississippi, the St. Francis National Forest in Arkansas, and the Shawnee National Forest in Illinois. A number of State parks and a few national wildlife refuges are in the southern part of this MLRA.

Physiography

This area is in the Coastal Plain Province of the Atlantic Plain. Most of the part of the area east of the Mississippi River is in the East Gulf Coastal Plain Section of the province. Parts of the western edge of the area, the part of the area in Arkansas, and the isolated part in northern Louisiana are in the Mississippi Alluvial Plain Section. The farthest southwest part in Louisiana is in the West Gulf Coastal Plain Section. The sharply dissected plains in this MLRA have a loess mantle that is thick at the valley wall and thins rapidly as distance from the valley wall increases. Valley sides are hilly to steep, especially in the western part of the area. The intervening ridges generally are narrow and rolling, but some of the interfluves between the upper reaches of the valleys are broad and flat. Stream valleys are narrow in the upper reaches but broaden rapidly downstream and have wide, flat flood plains and meandering stream channels. Elevation ranges from 80 to 600 feet (25 to 185 meters). Local relief is mainly 10 to 20 feet (3 to 6 meters), but it can be 80 to 165 feet (25 to 50 meters).

The extent of the major Hydrologic Unit Areas (identified by four-digit numbers) that make up this MLRA is as follows: Lower Mississippi-Hatchie (0801), 28 percent; Lower Mississippi-Big Black (0806), 20 percent; Lower Mississippi-St. Francis (0802), 12 percent; Lower Mississippi-Yazoo (0803), 12 percent; Lower Mississippi-Lake Maurepas (0807), 9 percent; Boeuf-Tensas (0805), 5 percent; Louisiana Coastal (0808), 4 percent; Pearl (0318), 4 percent; Lower Tennessee (0604), 4 percent; and Lower Ohio (0514), 2 percent. There are no major rivers in the part of this area west of the Mississippi River. A tributary of the Tennessee River (and lake) is in the part of this area in the southwest corner of Kentucky. The Obion and Hatchie Rivers are in the part of the area in Tennessee. The Hatchie River is a National Wild and Scenic River. Many of the tributaries of the Yazoo River are in the part of the area in northern Mississippi. The Big Black River crosses this area in southern Mississippi. The Mississippi River is in the extreme southeast corner of the area, near Baton Rouge, Louisiana.

Geology

This area is mantled with loess, which varies in thickness. The area is underlain by unconsolidated sand, silt, and clay, mainly of marine origin. Crowley’s Ridge is underlain by Pliocene sand and gravel. The seas extended up the present-day valley of the Mississippi River in Tertiary time, when these sediments were deposited by rivers draining the surrounding uplands. Throughout Quaternary and Recent time, the valley floor received fine grained sediments each time the Mississippi River flooded. After these sediments dried, winds picked them up and deposited them as loess in the higher areas on each side of the valley. There are five known periods of loess deposition in the area. The surface deposit is the Peoria Loess, which is of Late Wisconsin age (about 10,000 years ago). Pre-Peorian Loess, which is of Middle Wisconsin age (about 20,000 to 40,000 years ago), occurs in some areas. This loess is thinner than the Peorian Loess and is generally redder or darker. Loveland-Sicily Island Loess, which is of pre-Wisconsin age (85,000 to 130,000 years ago), is at the surface in some areas in the southern part of this MLRA. It has a well developed reddish paleosol (buried soil). Two other loess deposits have been described on Crowley’s Ridge. They have been identified as Marianna Loess and Crowley’s Ridge Loess. These deposits are not exposed at the surface. They have well developed paleosols.

Climate

The average annual precipitation in this area increases from north to south. In most of this area, it is 47 to 60 inches (1,195 to 1,525 millimeters). It is 61 to 70 inches (1,550 to 1,780 millimeters) in parts of the extreme southern end of the area. The maximum precipitation occurs in winter and spring. The precipitation decreases gradually throughout the summer, except for a moderate increase in midsummer. Rainfall occurs primarily as high-intensity, convective thunderstorms, but moderate-intensity tropical storms can produce large amounts of rainfall during winter in the southern part of the area. Snowfall generally occurs in the northern part of the area. The average annual snowfall in Stoddard County, Missouri, is 11 inches (28 centimeters). South of the Missouri-Arkansas State line, snowfall occurs but is rare. The average annual temperature is 57 to 68 degrees F (14 to 20 degrees C), increasing from north to south. The freeze-free period averages 270 days and ranges from 215 to 325 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, 2.3%; ground water, 5.8%
Livestock—surface water, 0.7%; ground water, 2.0%
Irrigation—surface water, 5.1%; ground water, 18.1%
Other—surface water, 61.7%; ground water, 4.3%

The total withdrawals average 5,270 million gallons per day (19,945 million liters per day). About 30 percent is from ground water sources, and 70 percent is from surface water sources. Precipitation is abundant, but most streams are small and flow intermittently. They flow most of the time in winter and spring. In summer and autumn, however, they flow only during and immediately after storms. Reservoirs store water for use when flows in streams decline. In the uplands, ponds and rural water systems are the main sources of water for domestic use and livestock. The surface water in the area is suitable for almost all uses. Most of the water used is for cooling thermoelectric power plants.

Ground water is abundant in this area, but shallow wells provide small quantities of water. In the uplands, shallow wells are used to fill cisterns for domestic use and livestock. Deep wells in the underlying unconsolidated sand and gravel of Cretaceous and Tertiary age yield large quantities of water. Most of the ground water east of the Mississippi River is suitable for all uses. It is soft and generally has less than 200 parts per million (milligrams per liter) total dissolved solids. Some of the water in the part of this area in Kentucky requires treatment for high levels of iron if it is to be used as drinking water.

In the part of Louisiana west of the Mississippi River, water from the Chicot aquifer system exceeds the drinking water standards for iron and water from the alluvial aquifer generally is not suitable for drinking because of high levels of total dissolved solids and iron and hardness. In Arkansas, water from the alluvial aquifer is very hard and has a median level of iron of almost 4,000 parts per billion (micrograms per liter). Water from the Sparta and Wilcox aquifers is soft, but most samples tested show levels of iron exceeding the 300 parts per billion (micrograms per liter) secondary standard for drinking water. All of the water west of the Mississippi River is very fresh and has median levels of total dissolved solids in the range of 100 to 350 parts per million (milligrams per liter).

Soils

The dominant soil orders in this MLRA are Alfisols, Entisols, Inceptisols, and Ultisols. The soils in the area are very deep or deep, are medium textured, and have a thermic soil temperature regime, a udic soil moisture regime, and mixed mineralogy.

Well drained, nearly level to very steep Hapludalfs (Memphis series) are on uplands. Nearly level to steep, well drained Hapludalfs (Memphis, Coteau, and Feliciana series), moderately well drained and somewhat poorly drained Fraglossudalfs (Olivier, Grenada, and Calloway series), moderately well drained Fragiudalfs (Loring series), and well drained Eutrudepts (Natchez series) formed in thick deposits of loess. Nearly level to gently sloping, somewhat poorly drained Epiaqualfs (Patoutville series), moderately well drained Fragiudults (Gigger, Toula, and Tangi series), well drained to somewhat poorly drained Hapludalfs (Colyell and Dexter series), and well drained Paleudults (Lytle series) formed in deposits of loess 2 to 4 feet (1 meter) thick. Nearly level and very gently sloping, somewhat poorly drained and poorly drained Glossaqualfs (Calhoun, Encrow, and Frost series), somewhat poorly drained Glossudalfs (Egypt series), somewhat poorly drained Hapludalfs (Satsuma series), and somewhat poorly drained Argiaquolls (Jeanerette series) formed in a thin mantle of loess over loamy alluvium or mixed loess and loamy alluvium. Deep, gently sloping, well drained Eutrudepts (Weyanoke series), somewhat poorly drained Fragiudults (Bude series), and somewhat poorly drained Fraglossudalfs (Fluker series) formed in silty material or in a mantle of loess and the underlying late Pleistocene loamy terrace material.

In the eastern part of the area, where the loess mantle thins, well drained Paleudalfs (Lexington series), moderately well drained Fragiudalfs (Dulac and Providence series), well drained Hapludults (Brandon and Silerton series), and well drained Paleudults (Smithdale series), all of which are gently sloping to steep, are on ridgetops and side slopes. Well drained Dystrudepts (Ariel series), moderately well drained Udifluvents (Collins series), moderately well drained Dystrudepts (Oaklimeter series), and somewhat poorly drained Fluvaquents (Gillsburg series) are on flood plains.

Biological Resources

This area supports hardwood-pine vegetation. Cherrybark oak, Shumard oak, white oak, post oak, southern red oak, and southern magnolia are widely distributed. Loblolly pine and shortleaf pine are the dominant pines. Yellow-poplar, white ash, swamp chestnut, cottonwood, sweetgum, and black walnut are important species on the flood plains. Loblolly pine and shortleaf pine are on a wide variety of sites, mainly the eroded soils on uplands and ridges. Other hardwood species that commonly grow in this area are white oak, basswood, sweetgum, water oak, American elm, blackgum, sycamore, sassafras, southern red oak, chinkapin oak, American beech, and hickory. Beech-magnolia-holly forests are dominant on narrow ridges and in steep ravines in the Tunica Hills of Louisiana.

Some of the major wildlife species in this area are white-tailed deer, red fox, gray fox, raccoon, opossum, skunk, muskrat, cottontail, gray squirrel, fox squirrel, bobwhite quail, and mourning dove. The species of fish in the area include largemouth bass, bluegill, and bullhead.

Land Use

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

Cropland—private, 36%
Grassland—private, 13%
Forest—private, 38%; Federal, 2%
Urban development—private, 7%
Water—private, 2%
Other—private, 2%

Most of this area is in farms. A small acreage is federally owned. About one-third of the area is cropland, but the proportion varies greatly from county to county, depending on the soils and the topography. This is largely a cash-crop area. Cotton, corn, rice, soybeans, and wheat are the major crops. Strawberries are important in Louisiana. Feed grains and forage are grown on dairy farms. Less than 15 percent of the area is pasture or hayland. About two-fifths is forest of mixed pine and hardwoods. Lumber is the major forest product, and some pulpwood is harvested. The present trend is toward the conversion of pasture and forest to cropland. Some areas are used for urban development, which is expanding near the metropolitan areas.

The major soil resource concerns are water erosion, maintenance of the content of organic matter and productivity of the soils, and management of soil moisture. Water erosion is a hazard in sloping areas that are bare because of tree harvesting. Conservation practices on forestland generally include systems of tree residue management and reforestation. Conservation practices on cropland generally include crop residue management, which increases the content of organic matter in the soils, and applications of lime in areas of low pH. Many of the soils remain wet or have a high water table for some or most of the year. Measures that improve drainage should be applied, or the crops adapted to the wet conditions should be selected for planting.

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