Table of Contents
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BACKGROUND
DESCRIPTION OF THE MISSISSIPPI EMBAYMENT STUDY UNIT
MAJOR WATER-QUALITY ISSUES
COMMUNICATION AND COORDINATION
BACKGROUND
In 1991, the U.S. Geological Survey (USGS) began the National Water-Quality Assessment (NAWQA) Program. The long-term goals of the NAWQA Program are to describe the status of and trends in the quality of a large part of the Nation's water resources and to identify the major natural and human factors that affect the quality of these resources. In addressing these goals, the program will produce a wealth of water-quality and ancillary information that will be useful to policymakers and managers at national, State, and local levels.The emphasis of the NAWQA Program is on regional scale water-quality problems. The program will not diminish the need for the studies and monitoring presently designed and conducted by national, State, and local agencies to meet their individual needs. The NAWQA Program, however, will provide a large-scale framework for conducting many of these activities and an understanding about regional and national water-quality conditions that cannot be acquired from individual, more localized programs and studies.
Studies of 60 hydrologic systems that include parts of most major river basins and aquifer systems (study-unit investigations) are the building blocks of the national assessment. The 60 study units range in size from 1,000 to more than 60,000 square miles and represent from 60 to 70 percent of the Nation's water use and population served by public water supplies. Twenty study-unit investigations were started in 1991, 20 additional started in 1994, and 20 are planned to start in 1997. The Mississippi Embayment study unit was selected to begin assessment activities in 1994. This study will be managed from the Mississippi District office of the U.S. Geological Survey in Jackson, Mississippi.
DESCRIPTION OF THE MISSISSIPPI EMBAYMENT STUDY
UNIT
The Mississippi Embayment study area covers approximately 48,500
square miles and includes parts of Arkansas, Kentucky, Louisiana,
Mississippi, Missouri, and Tennessee. The drainage area extends downstream
from the confluence of the Mississippi and the Ohio Rivers to a point on
the Mississippi River south of Vicksburg, Mississippi, and includes, in
order within the study area, the drainage basins of the Yazoo, the
Hatchie-Obion, the St. Francis-Lower White, and the Bayou
Bartholomew-Tensas Rivers.
The study area has a humid subtropical to temperate climate. Climatic
variations are largely governed by the presence of the extensive land mass
to the north and the Gulf of Mexico to the south; these produce
alternating flows of cold air moving southward and warm, moist air moving
northward, respectively. Mean annual air temperature ranges from about
58° F in the northern part of the area to about 66°
F in the southern part. Mean annual precipitation ranges from about
48 inches near Little Rock, Arkansas, which is in the west-central part
of the area, to about 56 inches in Louisiana, which is in the southern
part of the area. Precipitation is unevenly distributed throughout the
year. The greatest mean precipitation occurs in
the winter and early spring, and the least occurs in the fall. Droughts
are common during the summer and fall.
More than 75 percent of land use in the study area consists of
cropland with interspersed pasture, forest, and woodland. The area
underlain by the Mississippi River alluvium produces large amounts of
cotton, soybeans, and rice. Aquaculture, specifically the farming of
catfish in Mississippi and crawfish in Louisiana, also is an important
economic activity in the study area. About 20 percent of the land use
consists of woodlands with interspersed croplands and pasture. About 5
percent of the study area
consists of forested wetlands of the Mississippi River. In the mid
1900's, probably one-half of the area consisted of forested wetlands. The
conversion of these forested wetlands to cropland over the past century
has been, perhaps, the most dramatic ecological change in the study area.
The loss of wetlands has implications for water quality because they act
as traps for sediment and nutrient deposition and provide flood-water
retention, which reduces suspended sediment load. Loss of wetlands also
has caused profound changes in the habitat and fauna assemblages of the
area.
Ground-water contamination from point sources generally is localized
and limited to areas that range in size from a few acres to several square
miles. Common point sources of contamination are petroleum storage tanks,
industrial chemical leaks and spills, and application of wastewater to
the land. Ground-water contamination from nonpoint sources has not been
extensively investigated. Specific water-quality issues include the
following:
National Program
Location of the Mississippi Embayment study unit.MAJOR WATER-QUALITY ISSUES
Potential nonpoint sources of pollution are irrigated and
nonirrigated agriculture, grazing, and recreation. Potential point sources
of pollution are agriculture-related industry, aquaculture, municipal
wastewater-treatment facilities, and landfills.
Anthropogenic water-quality effects on lakes and reservoirs in the study
area result primarily from activities related to agriculture and
aquaculture.
COMMUNICATION AND COORDINATION
Communication and coordination between the USGS and water-management
or other related scientific organizations are critical components of
the NAWQA Program. A study-unit liaison committee that comprises
representatives from Federal, State, and local agencies, universities,
and the private sector who have water-resources responsibilities has been
established to aid in this communication process. Specific activities of
the liaison committee include the following:
-Michael J. Mallory
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