Water Quality in the Apalachicola-Chattahoochee-Flint River Basin, Georgia, Alabama, and Florida, 1992-95

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Summary of major issues and findings in the Apalachicola-Chattahoochee-Flint (ACF) River Basin

PESTICIDES IN STREAMS AND GROUND WATER

Pesticide concentrations in stream-water samples from all major land uses in the Study Unit were less than current drinking-water standards and guidelines for lifetime exposure. However, concentrations of one or more insecticides in streams draining areas of urban and suburban land use often exceeded chronic exposure criteria for protection of aquatic life. The highest measured pesticide concentrations in stream-water samples generally coincided with the growing season when most pesticides are applied. However, some pesticides were present at lower concentrations throughout the year (pages 10-11).
Herbicides that provide selective preemergence weed control are the predominant type of pesticide detected in small streams draining agricultural areas and in large rivers located in the Coastal Plain. Small streams draining urban and suburban areas, and large rivers located downstream from urban areas contain a more diverse mixture of pesticides including compounds used for insect control, selective preemergence and postemergence weed control, and nonselective weed control (page 10).
Storm runoff carries much of the total quantity of pesticides present in streams in both agricultural and urban areas of the Study Unit. However, the quantities of pesticides transported by streams are low relative to the quantities applied, because pesticides are retained in the soil, degraded, or transported by other pathways (page 12).
Pesticide (and VOC) concentrations in ground-water samples generally were less than U.S. Environmental Protection Agency (USEPA) drinking-water standards and guidelines. However, in water samples from shallow ground water in Metropolitan Atlanta 14 percent of dieldrin concentrations exceeded drinking-water guidelines (and 5 percent of benzene and PCE concentrations exceeded drinking-water standards). These exceedances indicate a potential water-quality concern for developing future public-drinking water supplies in the fractured-rock aquifer underlying Metropolitan Atlanta. Pesticides were detected least frequently in water samples from shallow ground-water monitoring wells located adjacent to cropland and most frequently in samples from springs and wells located in the recharge area to the Upper Floridan aquifer, a karst aquifer that is susceptible to contamination (pages 13 and 29).
Many pesticides detected in ground-water samples either are no longer in use or were in much greater use a decade or more prior to the sampling period. Because ground water moves slowly through the subsurface, pesticides currently detected in ground water lag changes in crop production and pesticide use patterns (page 13).

NUTRIENTS IN STREAMS AND GROUND WATER

Nutrient concentrations and yields in streams within the ACF River Basin are generally highest in tributaries draining watersheds predominated by poultry, urban, and suburban land use, particularly during stormflow conditions, and in the Chattahoochee River downstream from Atlanta. USEPA criteria for total-phosphorus was most often exceeded during storm-flow conditions at each of these settings. In general, lower nutrient concentrations and yields are indicative of good water quality in watersheds predominated by cropland and forests, the Chattahoochee River upstream from Atlanta, and the Apalachicola River near its mouth (pages 14-16).
In tributary streams studied, more than 60 percent of most nutrient yield occurs during stormflows. In the urban watershed, which has the highest percentage of impervious area, more than 80 percent of runoff and nutrient yields occur during stormflows. The predominance of stormflow transport is indicative of nonpoint sources of nutrients (pages 15-16).
Improvements to wastewater-treatment facilities and restrictions on the use of phosphate detergents have significantly decreased phosphorus loads in municipal-wastewater effluent discharged to the Chattahoochee River near and downstream from Atlanta and in reservoir sediments downstream from Atlanta. However, point sources of phosphorus from wastewater-treatment facilities to the Chattahoochee River and overflows from sanitary and combined sewer overflows to tributaries contribute to exceedances of USEPA criteria for total phosphorus. Nonpoint sources of phosphorus continue to increase throughout Metropolitan Atlanta as indicated by data upstream from Atlanta (page 16).
Although nitrate generally is present in low concentrations in ground water in most urban and agricultural areas and in the Upper Floridan aquifer, nitrate concentrations only rarely exceed the drinking-water standard. In the major crop-producing areas of the ACF River Basin, clay-rich upland soils and extensive flood plains reduce the risk of nitrate contamination of ground water and streams, respectively. Nitrate concentrations in tile drains are very high, and where tile drains are present, they represent an important pathway for transport of nitrate and other agricultural chemicals to streams (page 17).

TRACE ELEMENTS AND ORGANIC COMPOUNDS IN BED SEDIMENTS AND RESERVOIR CORES

The largest enrichments of trace elements and the highest concentrations of organic compounds in bed sediments are in the urban and suburban watersheds draining portions of Metropolitan Atlanta and Columbus, and in main-stem and reservoir settings on the Chattahoochee River downstream from Atlanta. Concentrations of mercury, cadmium, lead, and zinc in bed sediments of these urban and suburban watersheds increased in direct proportion to the amount of industrial land and transportation corridors in these watersheds. Much of the current pollutant load of trace elements and organic compounds is from stormwater runoff from impervious surfaces in urban and suburban areas and local and regional industrial emissions (pages 18-20).
In reservoirs located downstream from urban areas, concentrations of lead, zinc, chromium, and copper in sediment cores reached maximum concentrations during the late 1960's and mid-1970's in response to urban growth and industrial development, but have declined as a result of compliance with environmental laws enacted during the mid-1970's. This is particularly true for lead. Atmospheric sources of lead peaked in 1972, when use of leaded gasoline peaked, and have continued to decline to present. Concentrations of lead in cores from reservoirs downstream from Atlanta closely mirror changes in atmospheric sources and related storm-runoff sources of lead (page 22).
Concentrations of organochlorine insecticides, particularly DDT and chlordane, and PCB's in reservoir cores correlate with regional use patterns. Although, concentrations of these compounds have declined significantly since being banned, they continue to be present in sediments deposited as recently as 1994. The slow rate of decline of chlordane and PCB concentrations in sediments deposited in West Point Lake indicate that fish-consumption advisories in the Chattahoochee River downstream from Metropolitan Atlanta may continue into the future (page 23).

BIOLOGICAL INDICATORS OF WATER QUALITY

Within the Piedmont, the health and composition of fish communities are best in streams draining watersheds predominanted by forested land use; followed by streams draining watersheds predominated by poultry and suburban land use. Streams draining watersheds predominated by urban land use have severely degraded fish communities (page 24).
The macroinvertebrate status of streams draining watersheds predominated by poultry and forest land use were relatively good on the basis of the abundance of pollution-sensitive insects. High stormflows, poor habitat, and the presence of chemical contaminants such as insecticides, contribute to severely degraded macroinvertebrate communities in streams draining watersheds predominated by suburban and urban land use (page 24).

Although urban and suburban land use accounts for only 5 percent of the ACF River Basin, it has the most important effect on stream-water quality. The intensity of the land-use effect on water quality varies in proportion to various measures of urbanization such as impervious area, population density, and percent industrial and transportation land use. As the percentage of urban land use increases within a watershed, nutrients, pesticides, trace elements, and organic compounds are more prevalent and occur at higher concentrations in streams. Watersheds in the Piedmont with higher population densities generally are drained by streams dominated by a few species of pollution tolerant, mostly non-native fishes, indicating poorer biological condition and potentially poorer water quality. Data indicate that the continued urbanization of forested and pasture land surrounding Metropolitan Atlanta are likely to be accompanied by increasing detrimental effects on water quality in area streams, including the area's source of drinking water (pages 5, 10-12, 14-16, and 18-25).

In the Coastal Plain of the ACF River Basin, cropland and silvicultural land in upland areas are separated from streams by relatively undisturbed riparian flood-plain and wetland habitats. This is in contrast to many intensively farmed areas of the United States where wetlands have been drained, channelized or filled, and little or no riparian buffers remain between cropland and streams. Several water-quality implications that can partially be attributed to these wetland buffer areas to streams include (1) fewer pesticides detected and lower pesticide and nutrient concentrations in streams than in other areas of the Nation, (2) lower nitrate concentrations in ground water underlying forested flood plains than in ground water underlying upgradient cropland, and (3) reduced disturbance of fish communities during and after large floods (pages 5, 9, 11, 13, 17, and 25).

Despite widespread alteration of the ACF River Basin environment, the basin is noteworthy for its remaining biological diversity and support of commercial fisheries for oysters, shrimp, blue crabs, and a variety of fin fish in Apalachicola Bay (page 4).

U.S. Geological Survey Circular 1164

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Suggested citation:
Frick, E.A., Hippe, D.J., Buell, G.R., Couch, C.A., Hopkins, E.H., Wangsness, D.J., and Garrett, J.W., 1998, Water Quality in the Apalachicola-Chattahoochee-Flint River Basin, Georgia, Alabama, and Florida, 1992-95: U.S. Geological Survey Circular 1164, on line at <URL: https://water.usgs.gov/pubs/circ1164>, updated April 29, 1998 .

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