122—Highland Rim and Pennyroyal

This MLRA (shown in red in the figure above) is in Tennessee (47 percent), Kentucky (43 percent), Indiana (7 percent), and Alabama (3 percent). It makes up about 21,530 square miles (55,790 square kilometers). Bloomington, Indiana, is in the small part of this area that juts into southern Indiana. The towns of Bowling Green, Fort Knox, and Hopkinsville, Kentucky, Clarksville, Tennessee, and Athens, Alabama, are in this MLRA. Interstates 24, 40, and 65 cross this area. The historic Natchez Trace (Natchez Trace Parkway) crosses the southeast part of the area. Fort Knox and Fort Campbell Military Reservations are in this MLRA. The Arnold Engineering Development Center, which is a National Natural Landmark, and the Land Between the Lakes, which is a Biosphere Reserve, are in the part of this area in Kentucky. The Biosphere Reserve lies between Kentucky Lake and Lake Barkley, formed on the Tennessee and Cumberland Rivers by dams in Kentucky.

Physiography

This area is in the Highland Rim Section of the Interior Low Plateaus Province of the Interior Plains. It is a plateau consisting of low, rolling hills, upland flats, and narrow valleys. Steep slopes occur where the encircled Nashville Basin cuts into the area and along the western edge bordering the Coastal Plain. Elsewhere, except for steep walls and hillsides along deeply cut stream channels, the topography generally is gently rolling to strongly rolling and is interrupted in a few areas by broad upland flats and shallow basins. In many areas the land surface is pitted by limestone sinks. Elevation generally is 660 to 980 feet (200 to 300 meters). It ranges from about 330 feet (100 meters) along the deepest valley floors to about 1,310 feet (400 meters) on the crest of isolated hills.

The extent of the major Hydrologic Unit Areas (identified by four-digit numbers) that make up this MLRA is as follows: Cumberland (0513), 39 percent; Green (0511), 22 percent; Lower Tennessee (0604), 16 percent; Middle Tennessee-Elk (0603), 11 percent; Lower Ohio (0514), 9 percent; and Wabash (0512), 3 percent. The headwaters of the Kentucky, Green, and Cumberland Rivers occur in the part of this area in Kentucky. The Ohio River forms the boundary between Indiana and Kentucky in this MLRA. The Tennessee River follows the western edge of the part of this area in Tennessee. The Cumberland River also is in this area. The Buffalo River, in Tennessee, has been designated a National Wild and Scenic River.

Geology

Most of this area is underlain by Ordovician- to Mississippian-age limestone and dolomite that has been exposed through erosion of the Cincinnati Arch. Parts of these rocks are covered by a layer of clay as much as 80 feet thick. Karst areas are common where the layer of clay does not occur. In the northernmost part of the MLRA, in Indiana, a sizable area is underlain by shale, sandstone, and limestone. Much of the bedrock on uplands and ridges is covered by a loess cap. Significant sand and gravel deposits occur on the valley floor and on terraces along the major rivers.

Climate

The average annual precipitation in this area is 43 to 63 inches (1,090 to 1,600 millimeters), increasing to the south. The maximum precipitation occurs in winter and early in spring, and the minimum occurs in fall. Most of the rainfall occurs as high-intensity, convective thunderstorms. Snowfall may occur in winter. The average annual temperature is 52 to 60 degrees F (11 to 16 degrees C), increasing to the south. The freeze-free period averages 210 days and ranges from 185 to 235 days. The longer freeze-free periods occur in the more southerly parts of the area.

Water

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

Public supply—surface water, 4.0%; ground water, 1.6%
Livestock—surface water, 0.2%; ground water, 0.2%
Irrigation—surface water, 0.2%; ground water, 0.2%
Other—surface water, 90.2%; ground water, 3.4%

The total withdrawals average 2,055 million gallons per day (7,780 million liters per day). About 5 percent is from ground water sources, and 95 percent is from surface water sources. In most years precipitation is adequate for crops, but in some years yields are reduced by short dry periods early in summer. The numerous perennial streams and lakes supply abundant water to much of the area. The surface water generally is suitable for all uses. Several medium to large lakes constructed by the U.S. Army Corps of Engineers provide flood control, power production, opportunities for recreation, and water for municipalities. Water lines from metropolitan areas commonly extend far into the countryside in areas where surface water is scarce. Farm ponds provide supplemental water in areas where the supply of other surface water is low.

Most of the ground water used in this area is from a Mississippian-age carbonate aquifer system. The water occurs in solution openings and fractures in the limestone and dolomite. It is very hard but is otherwise of excellent quality. The median level of total dissolved solids is about 175 parts per million (milligrams per liter) in Tennessee and about 250 in Kentucky. In some areas high levels of iron, manganese, and sulfate can occur. In Indiana and other areas where the levels of iron are high, they may exceed the national secondary standard for drinking water, which is 300 parts per billion (micrograms per liter). The secondary standard is primarily esthetic, although the iron can stain ceramic and porcelain and precipitate in pipes. In karst areas this aquifer is susceptible to contamination from nonpoint sources of pollution in runoff.

Soils

The dominant soil orders in this MLRA are Alfisols, Inceptisols, and Ultisols. The soils in the area dominantly have a mesic soil temperature regime, a udic soil moisture regime, and mixed or siliceous mineralogy. They are moderately deep to very deep, generally moderately well drained or well drained, and loamy or clayey. Paleudalfs formed in residuum (Baxter and Vertrees series) and loess over residuum or old alluvium (Crider, Hammack, and Pembroke series) on hills and ridges. Hapludalfs (Caneyville series) and Hapludults (Frankstown series) formed in residuum on hills and ridges. Fragiudalfs (Bedford and Nicholson series) and Fragiudults (Dickson series) formed in loess over residuum on hills and ridges. Eutrudepts formed in residuum on hills (Garmon series) and in alluvium on flood plains (Nolin series). Paleudults formed in residuum on uplands (Frederick series) and in loess over residuum on ridges and plateaus (Mountview series). Fluvaquents (Newark series) formed in alluvium on flood plains.

Biological Resources

This area supports oak-hickory forests. Yellow-poplar is common on the deeper soils. Understory plants include a variety of grasses, forbs, vines, and shrubs. Little bluestem and broomsedge are the dominant grass species.

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

Land Use

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

Cropland—private, 23%
Grassland—private, 23%; Federal, 1%
Forest—private, 40%; Federal, 2%
Urban development—private, 6%
Water—private, 3%
Other—private, 2%

Most of this area consists of small and medium-size farms. Extensive forests are on the deeply dissected hills surrounding the Nashville Basin and along the western edge joining the Coastal Plain. Elsewhere, the forests consist mostly of small farm woodlots. Hay and pasture for beef cattle are the principal crops. Corn and soybeans, grown mostly on narrow strips of bottom land and on upland flats, are important locally. Tobacco, especially burley, is an important cash crop. Dark-fired tobacco is a high-value crop grown on the Tennessee-Kentucky line. Some areas are used for urban development.

The major soil resource concern is water erosion. Erosion is a hazard on cropland, streambanks, and construction sites. Minor erosion can occur on overgrazed pastures, and extreme overgrazing can result in gullies in areas of concentrated flow and heavy use. Maintenance of the content of organic matter and productivity of the soils and management of soil moisture are additional resource concerns in areas where long-term erosion has occurred.

Conservation practices on cropland generally include systems of crop residue management, especially no-till systems; cover crops; pest management; and nutrient management. Conservation practices on pasture generally include prescribed grazing, watering systems, protection of heavily used areas, nutrient management, and pest management. Conservation practices on hayland generally include forage harvest management, nutrient management, and pest management. Critical area planting helps to prevent gully erosion in all areas.

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