Water-Quality Conditions in a National Context

White areas indicate other NAWQA Study Units sampled during 1992-95.

Seven major water-quality characteristics were evaluated for stream sites in each NAWQA Study Unit. Summary scores for each characteristic were computed for all sites that had adequate data. Scores for each site in the Georgia-Florida Coastal Plain were compared with scores for all sites sampled in the 20 NAWQA Study Units during 1992-95. Results are summarized by percentiles; higher percentile values generally indicate poorer quality compared with other NAWQA sites. Water-quality conditions at each site also are compared to established criteria for protection of aquatic life. Applicable criteria are limited to nutrients and pesticides in water, and semivolatile organic compounds, organochlorine pesticides and PCBs in sediment. (Methods used to compute rankings and evaluate aquatic-life criteria are described by Gilliom and others, in press.)

EXPLANATION

Ranking of stream quality relative to all NAWQA stream sites-- Darker colored circles generally indicate poorer quality. Bold outline indicates one or more aquatic-life criteria were exceeded.

Nutrient concentrations are less than the national median at all but one of nine sites intensively sampled. Three sites had nutrient concentrations in the lowest 25 percent of NAWQA sites. The only site with nutrient levels greater than the median of NAWQA sites nationally was in an agricultural area where the land use is gradually changing to urban.

At three of the four stream sites intensively sampled for pesticides, the number of pesticide detections was less than the median for NAWQA sites nationwide. The only site where pesticide detections were greater than the median for NAWQA sites nationwide was in a highly urbanized area. Most of the measured concentrations were very low and did not exceed any drinking-water standards.

PCBs were not detected at any of the nine sites sampled. Organochlorine pesticides in streambed sediments at five of nine sites sampled were higher than the median for NAWQA sites nationwide. Three of the nine sites were in the highest 25 percent of NAWQA sites. Concentrations of chlordane exceeded guidelines for protection of aquatic life at two of these sites, one located in a highly urbanized basin and one in an agricultural basin. Concentration of p,p´-DDE exceeded guidelines for protection of aquatic life at one agricultural site.

At five of the nine sites sampled trace element concentrations in streambed sediments were in the highest 25 percent of NAWQA sites nationwide. Concentrations of lead were highest in a highly urbanized basin and in a mixed land-use basin. Although some trace elements occur naturally in soils and stream sediments in the study area, the higher concentrations are probably related to urban and agricultural land-use activities.

At eight of nine sites sampled, SVOCs concentrations in stream- bed sediments were lower than the median for NAWQA sites nationwide. Four of the nine sites had levels in the lowest 25 percent of NAWQA sites. Concentrations at one site located in a highly urbanized basin, however, were in the highest 25 percent of NAWQA sites.

Fish communities at the six sites sampled in the study area were less affected by pollution and other effects on their ecosystems than in other NAWQA Study Units nationwide. At these sites, the number of diseased, pollution-tolerant, and non-native fish in the streams in the study area was less than the median for NAWQA sites around the country.

Stream habitats at the seven sites studied were ranked below the median for NAWQA sites nationwide, that is, they are providing better conditions to sustain aquatic organisms than many other streams around the country. Stream habitat, which includes the physical characteristics of streams and their banks (such as amount of bank vegetation, stability of bank soils, and stream depth and shape), strongly influences the capacity of streams to support biological communities.

CONCLUSIONS

In the Georgia-Florida Coastal Plain, compared to other NAWQA Study Units:

• Concentrations of nutrients and pesticides in streams and semivolatile organic compounds in streambed sediments were low.
• PCBs were not detected in sediments.
• Organochlorine pesticides and trace element concentrations in streambed sediments were high.
• Stream habitats and fish communities were less degraded.

White areas indicate other NAWQA Study Units sampled during 1992-95.

Five major water-quality characteristics were evaluated for ground-water studies in each NAWQA Study Unit. Ground-water resources were divided into two categories:
(1) drinking-water aquifers, and (2) shallow ground water underlying agricultural or urban areas. Summary scores were computed for each characteristic for all aquifers and shallow ground-water areas that had adequate data. Scores for each aquifer and shallow ground-water area in the Georgia-Florida Coastal Plain were compared with scores for all aquifers and shallow ground-water areas sampled in the 20 NAWQA Study Units
during 1992-95. Results are summarized by percentiles; higher percentile values generally indicate poorer quality compared with other NAWQA ground-water studies. Water-quality conditions for each drinking-water aquifer also are compared to established drinking-water standards and criteria for protection of human health. (Methods used to compute rankings and evaluate standards and criteria are described by Gilliom and others, in press.)

EXPLANATION

Shallow ground-water study areas

Ranking of ground-water quality relative to all NAWQA ground-water studies-- Darker colored circles generally indicate poorer quality.

Nitrate concentrations in the row-crop agricultural area were among the highest 25 percent of NAWQA studies nationwide. One-third of the ground-water samples collected in this area contained nitrate concentrations greater than the drinking-water standard of 10 milligrams per liter. However, the aquifer sampled is not a major source of drinking water. Nitrate concentrations in two urban areas and in domestic wells in rural areas were lower than the median of NAWQA studies.

Radon concentrations in ground water in the row-crop agricultural and urban study areas were in the highest 25 percent of NAWQA studies nationwide. Radon, a decay product of uranium-238, naturally occurs in the phosphate rocks and other sediments in the study area accounting for the high radon concentrations. There is currently no drinking-water standard or guideline for radon.

Concentrations of dissolved solids in the study area were in the lowest 25 percent of NAWQA studies nationwide. Dissolved solids are derived from the minerals present in the aquifer materials. The sandy sediments in the surficial aquifers sampled in the study area are less readily dissolved than sediments in other study areas.

The percentage of samples containing one or more VOCs was greater than the median of NAWQA studies nationwide. However, concentrations of individual compounds were quite low and few drinking-water standards were exceeded. No drinking-water supplies contained elevated VOC concentrations. Usually no more than one VOC was detected per sample. VOCs detected were at low levels. Only 11 of the 60 VOCs analyzed were detected in samples in the study area.

Pesticides were detected in ground water less frequently than in most other NAWQA studies nationwide. Detection frequencies in agricultural and urban samples were about equal, and concentrations were generally low. Prometon in the Ocala urban area and metolachlor in the row-crop agricultural area accounted for most of the pesticide detections.

CONCLUSIONS

In the Georgia-Florida Coastal Plain, Compared to other NAWQA Study Units:

• Nitrate concentrations exceeding the drinking- water standard in the row-crop agricultural area were the greatest ground-water quality problem in the study area. This area does not rely on the sampled aquifer for drinking water. The same area had very few pesticide detections and concentrations of detected compounds were quite low.
• Radon levels were elevated. Radon is naturally present in the aquifer sediments in the study area. There is currently no drinking-water standard or guideline for radon.
• Dissolved solids were low.
• Urban areas showed little contamination from volatile organic compounds. The percent of samples with VOC detections in urban areas was greater than the median of NAWQA studies nationwide, but most samples had only one VOC detection and concentrations were very low.
• Pesticide detections and concentrations were low.