ENVIRONMENTAL SETTING Urban land use within the Study Unit is defined as dense commercial areas and transportation networks associated primarily with the city of Atlanta. Urban watersheds contain substantial impervious areas that are connected to streams by storm sewers. Streams also receive inputs from combined sewers and leaking or overflowing sanitary sewers. Chemical and microbial contaminants from point and nonpoint sources are the primary water-quality issues within the urban watersheds.   Suburban land use within the Study Unit is defined as established and developing residential areas, associated commercial areas, and transportation networks. It differs from urban land use by the amount of impervious land cover and the lack of known point sources but has the same water-quality issues of contaminants from nonpoint sources.   Since the 1930's, large areas of agricultural land in the Piedmont have been abandoned and have reverted to forests. The remaining agricultural land currently is used for poultry production and livestock grazing. Nutrient inputs from poultry litter applied to sloping pasture land and soil erosion are water-quality issues in the headwaters of the Chattahoochee River.   Unlike parts of the United States where large, continuous tracts of land often are farmed to streambanks, cropland in the ACF River Basin generally is limited to well-drained upland areas. The long growing season and center-pivot irrigation support a broad range of cash crops and several plantings of some crops on the same fields during the year. Cropland commonly is bordered by extensive forested wetlands (inset). In this study, cropland was further subdivided into areas underlain by clastic deposits (sands and shales) and carbonate bedrock (karst) to investigate any differences in water quality that might be attributed to differences in hydrogeology. Excess nutrients and pesticides in ground water and streams are the primary water-quality issues within this land use. (Photograph of cotton field is by L. Elliott Jones, USGS.)   Most forested land in the ACF River Basin is silvicultural land owned and managed by individuals or corporations for pulp and lumber production. These mostly second-growth forests are the best available representation of background water-quality conditions in the Study Unit. Erosion, sedimentation, and release of nutrients following timber harvests are the primary water-quality issues in these forested watersheds. (Photograph of Chattahoochee National Forest is by Alan M. Cressler, USGS.)

Circular 1164 Table of Contents

Last updated Wednesday, 14-Feb-2001 18:19:00 EST
The URL for this page is http://ga.water.usgs.gov/publications/cir1164/p05_enviro_setting.html