123—Nashville Basin

This MLRA (shown in red in the figure above) is entirely in Tennessee. It makes up about 5,625 square miles (14,580 square kilometers). The cities of Nashville, Franklin, Hendersonville, Columbia, Murfreesboro, and Shelbyville are in this area. Interstates 24, 40, and 65 intersect in Nashville. The Cedars of Lebanon State Park and Forest are in the center of this area.

Physiography

Most of this area is in the Nashville Basin Section of the Interior Low Plateaus Province of the Interior Plains. A small part of the northeast corner and the western and southern fourth of the area are in the Highland Rim Section of the same province and division. Most of the outer part of the Nashville Basin is deeply dissected and consists of steep slopes between narrow, rolling ridgetops and narrow valleys. The inner part of the basin is dominantly undulating and rolling. In many areas the land surface is deeply pitted by limestone sinks, and outcrops of limestone are almost everywhere. Elevation generally is about 650 feet (200 meters), but it is 1,000 to 1,325 feet (305 to 405 meters) on isolated hills and is as low as 450 feet (135 meters) in some of the more deeply cut stream channels.

The extent of the major Hydrologic Unit Areas (identified by four-digit numbers) that make up this MLRA is as follows: Cumberland (0513), 56 percent; Lower Tennessee (0604), 25 percent; and Middle Tennessee-Elk (0603), 19 percent. The Cumberland River is in the northern part of this area. Two major tributaries of this river, the Harpeth and Stones Rivers, are in this MLRA. A portion of the Harpeth River in the middle of the western part of this area has been designated a National Wild and Scenic River.

Geology

The bedrock geology in this area consists of Ordovician limestone exposed by geologic erosion of the top of the Nashville Dome (a high part of the Cincinnati Arch) throughout this area. Sinkholes are common in the limestone and are either open to the subsurface or are covered by soils and colluvium that have collected in the depressions formed on the land surface above the sinkhole. Younger rocks occur as a rim just outside this area. Surficial deposits include loess on the less eroded landforms and alluvium along the rivers and streams.

Climate

The average annual precipitation in this area is 48 to 57 inches (1,220 to 1,450 millimeters). The maximum precipitation occurs in midwinter and early in spring, and the minimum occurs in autumn. Rainfall primarily occurs during high-intensity, convective thunderstorms. Some snow occurs in winter, but it does not remain on the ground for long periods. The average annual temperature is 56 to 60 degrees F (14 to 16 degrees C). The freeze-free period averages 210 days and ranges from 195 to 230 days. The longer freeze-free periods occur in the southern part of the area.

Water

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

Public supply—surface water, 8.6%; ground water, 0.3%
Livestock—surface water, 0.1%; ground water, 0.3%
Irrigation—surface water, 0.1%; ground water, 0.1%
Other—surface water, 89.0%; ground water, 1.4%

The total withdrawals average 2,660 million gallons per day (10,070 million liters per day). About 2 percent is from ground water sources, and 98 percent is from surface water sources. The moderately high precipitation generally provides adequate moisture for crops and pasture, but short periods of drought in summer reduce pasture and crop yields in some years. Permanent streams and lakes are important sources of water. The Cumberland River has dams for flood control, power production, navigation, and recreation. Farm ponds provide supplemental water, especially in areas where surface water is scarce because of limestone sinks.

Ground water from wells and springs is an important source of water for domestic use and for livestock. The water is in the Ordovician carbonate aquifer that underlies this area. It is hard and typically has a median level of total dissolved solids of less than 500 parts per million (milligrams per liter). The water is in solution openings in this aquifer and is susceptible to contamination from surface activities in karst areas. For example, septic systems have contaminated the shallow water in the part of this aquifer in the Nashville area.

Soils

Many of the soils in this MLRA are Udalfs. The moderately deep to very deep, well drained, clayey soils formed in limestone residuum. They are dominantly in rolling to steep areas of the “Outer Basin” (Mimosa, Braxton, Gladdice, and Hampshire series) and the undulating to hilly areas of the “Inner Basin” (Talbott and Bradyville series). The most agriculturally productive soils are the very deep, well drained, clayey or loamy soils that formed in alluvium and/or loess over alluvium or limestone residuum in nearly level to undulating areas (Armour, Cumberland, Harpeth, Lomond, and Maury series). The less extensive soils generally are moderately well drained to somewhat poorly drained and formed in loamy or clayey alluvium and/or residuum (Byler, Capshaw, Colbert, and Tupelo series). This MLRA has a significant acreage of Mollisols. Shallow or moderately deep, well drained, clayey Udolls (Ashwood and Barfield series) formed in limestone residuum dominantly in rolling to steep areas. Very shallow, well drained, clayey Rendolls (Gladeville series) formed in limestone residuum dominantly in undulating to rolling areas of the “Inner Basin.” Very deep, well drained or moderately well drained Udolls (Arrington, Egam, Lynnville, and Staser series) and somewhat poorly drained or poorly drained Aquolls (Agee, Godwin, and Lanton series) formed in loamy or clayey alluvium derived from limestone on flood plains. Most of the remaining soils on flood plains are moderately well drained or well drained Udepts (Lindell and Ocana series). Udults are of small extent in this area. Most are very deep, well drained, and loamy and formed in gravelly colluvium or colluvium and the underlying residuum on steep hillsides (Dellrose soils). Rock outcrops are common on uplands.

Biological Resources

This area supports stands of oak and hickory. Yellow-poplar grows on the north aspects, and eastern redcedar and cedar-hardwood stands grow in limestone glades and on rocky, clayey sites. The understory vegetation includes many grasses, forbs, vines, and shrubs. Broomsedge bluestem is the dominant grass species.

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

Land Use

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

Cropland—private, 14%
Grassland—private, 31%
Forest—private, 36%; Federal, 1%
Urban development—private, 13%
Water—private, 3%
Other—private, 2%

This densely populated area consists mostly of small and medium-size farms. Much of the farmland has been converted to residential use and to small estate-type farms, particularly around Nashville. Hay, pasture, and some grain for beef cattle and dairy cattle are the principal crops. Small acreages are used for burley tobacco, cotton, or soybeans. Some large rocky sites, commonly called “Glady Land,” support redcedar forest or redcedar-deciduous brush.

The major soil resource concerns in this area are water erosion, deposition of sediment, depletion of organic matter in the soils, surface compaction, and soil contaminants. Conservation practices on cropland generally include systems of crop residue management, especially no-till systems; cover crops; and nutrient management. The important conservation practice on pasture is prescribed grazing.

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