The U.S. Geological Survey (USGS) began full scale implementation of the National Water-Quality Assessment (NAWQA) Program in 1991. The goals of the NAWQA Program are (1) to describe current water-quality conditions for a large number of the Nation's freshwater streams and aquifers; (2) to describe how water quality is changing over time; and (3) to improve understanding of the primary natural and human factors that affect water quality. To achieve these goals, water-quality investigations of 59 river basins and aquifer systems have been conducted or are currently ongoing (fig. 1). About 70 percent of the Nation's freshwater use is within these basins. The basins, referred to as study units, were selected to represent the diverse geography, water resources, and land and water use of the Nation. The lower Tennessee River Basin is one of the 59 river basins selected for a water-quality assessment.
The lower Tennessee River Basin NAWQA study unit extends from Chattanooga, Tennessee, to near Paducah, Kentucky (fig. 1), and encompasses about 19,500 square miles (mi²). Most of the study unit is in Middle Tennessee and northern Alabama, with smaller parts in southwestern Kentucky, northeastern Mississippi, and northwestern Georgia (fig. 1). Parts of the Coastal Plain, Interior Lowland Plateaus, and Appalachian Plateaus Physiographic Provinces are in the study unit (fig. 1). The main stem of the Tennessee River is highly regulated with few free-flowing stream reaches. Six large reservoirs are located on the main stem (fig. 1), and many additional reservoirs are located on tributaries to the main stem.
Project activities for the water-quality assessment of the lower Tennessee River Basin began in 1997. Initial activities for the study included characterizing the environmental setting of the study unit, subdividing the study unit into subunits with relatively homogeneous geology and physiography, and inventorying and analyzing historical water-quality data. The historical data analysis helped to identify water-quality issues in the study unit and to determine the spatial distribution of existing water-quality data.
The purpose of this report is to describe the environmental setting and water-quality issues of the lower Tennessee River Basin. The environmental setting includes the natural and cultural factors that affect water quality. Natural factors in the lower Tennessee River Basin include geology, physiography, soils, climate, and surface- and ground-water hydrology. Geology and physiography are the primary natural factors that were used to subdivide the study unit into nine subunits within which the effects of anthropogenic (cultural) factors on water quality can be evaluated. Cultural factors described in this report include wastewater discharge, water use, and land use. Land use can be used as a surrogate for the distribution of nonpoint-source inputs that affect water quality. This report also presents data for the distribution of major crops, livestock, and agricultural-chemical use for 1992. Historical water-quality data for two constituents (nutrients and bacteria) that are water-quality issues in the study unit are summarized.
The authors thank the following individuals for their thoughtful input and suggestions in the delineation of the subunits in the lower Tennessee River Basin--Danny Moore, Geological Survey of Alabama, for providing a technical review of the subunit boundaries; Glendon Smalley, formerly of the U.S. Forest Service, for providing guidance on the delineation of the Highland Rim subunits; John Jenkins, Natural Resources Conservation Service, Tennessee, for providing insight on the surficial deposits and soils; Jim Omernik, U.S. Environmental Protection Agency, and Glenn Griffith, Natural Resources Conservation Service, for their contribution to the conceptualization of the subunits through their work on delineating level IV ecoregions in Tennessee, and Glenn Griffith for providing a digital version of the level IV ecoregion boundaries; as well as Bob Kidd, Pat Hollyday, and Bill Wolfe of the U.S. Geological Survey for providing insight on the hydrogeologic and geomorphologic aspects of the subunits. We also thank Enid Bittner, Alabama Department of Environmental Management, Sydney DeJarnette, Geological Survey of Alabama, and Ken Nafe and Tim Thompson, Tennessee Department of Agriculture who provided water-quality data from ground-water studies.
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