WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT

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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 Albemarle-Pamlico Drainage Basin were compared to 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 to that of 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 of circle indicates one or more aquatic-life criteria were exceeded.

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Nutrient concentrations in the southern Coastal Plain of the basin are high compared to concentrations at other NAWQA sites nationwide. Intensive agriculture in the Coastal Plain, combined with wastewater-treatment discharges and runoff from urban areas in the Piedmont, provide major sources of nutrient concentrations in the Neuse and Tar River Basins. Phosphorus concentrations are particularly high in parts of the Tar and Neuse River Basins, partly because of a geologic source.

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Pesticides were present in low concentrations in most of the surface-water samples collected; the Tar River Basin had the highest concentrations. The herbicides metolachlor, atrazine, prometon, and alachlor were detected in over 60 percent of the stream samples. Pesticides in surface water are indicative of extensive agriculture in the Albemarle-Pamlico Drainage Basin.

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Relatively few organochlorine compounds were detected. Of those, DDE was the most common. Concentrations of the detected compounds are near or above the median at several sites when compared nationally. The highest values are associated with small basins in areas of intensive agriculture.

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Trace element concentrations in bed sediment at 6 of the 10 sites were above the national median. Based on 1992 sampling of 22 sites, highest concentrations of trace elements in bed sediment were usually associated with urban basins.

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SVOCs were generally low compared to those at other NAWQA sites nationwide. The sites with elevated concentrations are generally associated with urban areas.

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Fish communities in the Albemarle-Pamlico Drainage Basin were ranked as low to moderately degraded compared to other sites across the Nation; however, the metrics used to calculate the national rankings may not be appropriate for assessing fish community degradation in the Coastal Plain of North Carolina. The four national metrics are the percentage of individual fish belonging to species classified as (1) omnivorous, (2) non-native, (3) tolerant to human-caused stream degradation, and (4) having external physical anomalies.

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Based on stream modification, bank erosion, bank stability, and riparian vegetation density, sites in the Study Unit were moderately to highly degraded when compared to other sites in the Nation. This degradation reflects the presence of extensive and widespread channel modifications made in past decades to improve drainage and the presence of many areas susceptible to bank erosion.

CONCLUSIONS

Nutrient concentrations, organochlorine compounds, and trace elements in sdeiment at many of the sites in the Albemarle-Pamilico Drainage Basin were high compared to those at other NAWQA sites nationwide. The causes for the elevated concentrations are a combination of agricultural, urban, and natural sources.
Although stream habitats tended to be more degraded than the national norm, fish communities tended to be less degraded than the national norm. This inconsistency may occur because the fish community metrics used to calculate the national index are insensitive to changes in fish community composition that occur as a result of habitat degradation in the Coastal Plain.

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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 Albemarle-Pamlico Drainage Basin were compared to 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 to that of 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.)

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Nitrate concentrations in ground water were low relative to national conditions. However, certain areas of the Albemarle-Pamlico Drainage Basin have higher concentrations than others. The highest concentrations are associated with well-drained soils of the inner Coastal Plain. About 5 percent of the wells in shallow aquifers of the inner Coastal Plain and 3 percent in the outer Coastal Plain exceeded the 10-mg/L drinking-water standard (U.S. Environmental Protection Agency, 1986).

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Dissolved-solids concentrations in ground water were among the lowest relative to national conditions. The ground-water samples tested were from shallow, unconsolidated sedimentary units in the Coastal Plain, which contain relatively few easily dissolved minerals.

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Volatile organic compound detections in ground water were among the lowest in the Nation. Only four compounds were detected in ground water in three wells in the Coastal Plain, and these concentrations were below drinking-water standards. However, these compounds may be more common in urban areas not sampled in this study.

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Pesticide detections in the agricultural areas of the Coastal Plain were among the highest nationally. Three herbicides or their metabolites were detected at concentrations greater than 0.1 µg/L in shallow ground water. However, in general, pesticides applied to crops appeared in shallow ground water at concentrations less than drinking-water standards.

CONCLUSIONS