Extent, and Landuse
The Nashville Basin extends from southern
Kentucky through central Tennessee, and into northern Alabama. This major
land resource area (MLRA 123) occupies a total land area of 1,458,200 ha
(Fig. 1). A variety of cropping systems are present and grazing is prevalent.
Tobacco and corn are grown on the alluvial soils and the residual limestone
soils are used primarily for hay land and pasture. There is significant
residential and urban development in the Nashville-Davidson County Metro
area near the center of this MLRA.
In the Central Basin, Paleozoic Era
rocks are from the Ordovician period. Shale and limestone outliers of Devonian-Mississippian
periods cap the many small hills around the edge of this MLRA. Phosphates
are the major resource of the Central Basin, but other products include
crushed limestone and Zinc (Miller, 1974).
A summary of the soil series in this
MLRA are given in Table 1. STATSGO soils
are depicted in Fig. 1. Pedons from Jackson and Lincoln counties are representative
of the Central Basin MLRA 123. Soil morphology, classification, and parent
materials are described for both pedons in this MLRA (Tables
2 and 3). Total elemental concentrations are given in Tables
4 and 5.
MLRA 123 lies in the Interior Low Plateaus
subregion of the Appalachian Plateaus and Valley and Ridge ground water
region of North America. The topography is generally mature and well-rounded,
with several major areas of karst. Altitudes within the subregion range
from 100 to 300 m above mean sea level. There are three conceptual models
required to cover the diversity of ground water occurrence with this area
(Back et al., 1988).
In areas of Mississippian rocks, the
regolith varies from a thickness of 10 m to more than 35 m; in these areas
the ground water occurrence varies from diffuse to conduit and the secondary
permeability and storage vary from very poorly to very well developed.
Ground water flow in these systems is generally limited to secondary permeability
in rocks within 100 m of the ground surface.
The Ordovician rocks found in this MLRA
dip gently or lie flat. Ground water in these rocks flows through shallow
vertical joints and openings in horizontal bedding planes. This flow is
usually concentrated in valleys and within 100 m of the surface.
The Knox aquifer which is part of a regional
freshwater flow system occurs in buried paleokarst. The depth of the aquifer
below the land surface varies from 100 to 460 m. The transmissivity of
the aquifer is homogeneous but quite low, with flow to wells of about 0.3
L s -1 . It is thought that the permeability of the rocks beneath the Knox
aquifer is extremely low.
The water of the shallow carbonate rock
aquifers in the MLRA is a calcium magnesium bicarbonate type that is typically
fresh (<1000 mg L -1 ) for depths less than 100 m (Brahana and Bradley,
1986a, 1986b). This suggests an interaction between the aquifers and water
from outside the aquifers. Salinity increases with depth, suggesting less
interaction with outside water sources as aquifer depths increase. Near
the Nashville Dome, saline water may be encountered at relatively shallow
depths, probably from isolated, stagnant flow cells that are in contact
with evaporites. Salinity within the Knox aquifer does not increase with
depth suggesting it is part of a deep regional flow system.
and Solute Transport
The prevalence of karst topography in
this MLRA makes water and solute transport quite variable.
Back, W., J.S. Rosenshein, and P.R.
Seaber, editors. 1988. Hydrogeology: The geology of North America, Volume
O-2. The Geological Society of America, Boulder, Colorado.
Brahana, J.V. and M.W. Bradley. 1986a.
Delineation and description of the regional aquifers of Tennessee; The
Central Basin aquifer system. p. 35. U.S. Geological Survey Water-Resources
Investigations Report 82-4001.
Brahana, J.V. and M.W. Bradley. 1986b.
Delineation and description of the regional aquifers of Tennessee; Highland
Rim aquifer system. p. 38. U.S. Geological Survey Water-Resources Investigations
Miller, R.A. 1974. The geological history
of Tennessee, Bulletin 74. Tennessee Department of Conservation, Division
of Geology, Nashville, Tennessee.
USDA-SCS. 1981. Land Resource Regions
and Major Land Resource Areas of the United States. Agriculture Handbook
296. Washington, DC.
Return to Home Page
Electronic document prepared by:
D.L. Nofziger, Oklahoma State University
Email address: email@example.com