Summary of Water-Quality Issues and Major Findings
Nutrients in streams
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Of four river basins studied in the Albemarle-Pamlico Drainage Basin--the Chowan, Roanoke, Tar, and Neuse--highest nitrogen and phosphorus yields occurred in the highly agricultural and urbanized Neuse Basin; lowest nutrient yields occurred in streams of the forested Chowan Basin (p. 7).
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Suspended-sediment, suspended-solids, and dissolved-solids concentrations have decreased throughout the Albemarle-Pamlico drainage system from 1980 to 1995. Decreasing concentrations of suspended solids in the sounds and estuaries may result in clearer water and deeper light penetration which, in turn, enhance conditions for algal blooms in nutrient-enriched areas. As a result, reduction of nutrients will be even more important in controlling eutrophication (p. 15).
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A 50-percent reduction of summertime nitrogen and phosphorus concentrations in the Neuse River and a 30-percent reduction of these same constituents in the Tar River and Contentnea Creek would be required to attain literature-based guidelines to reduce the incidence of nuisance algal blooms and fishkills (p. 14).
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Permitted point sources of nitrogen and phosphorus from municipal wastewater-treatment plants and industry account for less than 6 percent of the nitrogen source inputs and 16 percent of the phosphorus source inputs in all basins. However, nutrients from these point sources go directly into streams and may constitute more than 40 percent of the instream nutrient load (p. 6).
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Based on synoptic data collected in 1995, ground water contributes significantly to instream phosphorus loads of the Neuse River, Contentnea Creek, and other streams. Natural deposits of phosphate occur in Miocene and Cretaceous sediments of the Albemarle-Pamlico Drainage Basin and produce high concentrations (median = 0.2 milligram per liter [mg/L]) of phosphorus in ground water. Because of natural geologic sources, control of phosphorus concentrations in streams in these basins may be difficult for water managers (p. 12-14).
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Phosphorus and nitrogen concentrations in streams generally have declined since 1980 in all four basins. This decrease is probably the result of improved agricultural practices, a phosphate detergent ban in North Carolina and Virginia in 1988, and enhanced wastewater-treatment practices. However, phosphorus and nitrogen concentrations are still high enough in the Tar and Neuse River Basins to cause nuisance algal growths (p. 15).
Nutrients in ground water
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Water in about 4 percent of 49 shallow monitoring wells randomly placed in agricultural areas of the Coastal Plain exceeded the 10 mg/L drinking-water standard for nitrate (U.S. Environmental Protection Agency, 1986). Nitrate-nitrogen concentrations in shallow ground water of the inner Coastal Plain are significantly higher than nitrate-nitrogen concentrations in the outer Coastal Plain (p. 8
).
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Highest nitrate concentrations in shallow ground water are in well-drained, sandy soils in combination with intensive agricultural activity, such as crop or livestock production. Residents in Coastal Plain areas having high nitrate can avoid water with high nitrate concentrations by using water from deeper aquifers. Nitrate concentrations in shallow ground water can be decreased by limiting fertilizer and manure applications on crops in these areas (p. 14).
Pesticides
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Of 47 pesticides analyzed in stream samples, 45 were detected. Metolachlor, atrazine, alachlor, and prometon were the most commonly detected pesticides in streams. Highest incidence of pesticide detections occurred in the Tar River Basin (p. 16).
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During the 1993-95 pesticide sampling period, concentrations of atrazine, alachlor, metolachlor, and prometon in streams increased in late May and early June and decreased gradually through August until applications increased the following spring. Drinking-water standards for pesticides are most likely to be violated during May through July (p. 16-17).
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Of 47 pesticides analyzed in shallow ground-water samples, 14 were detected. Atrazine, deethylatrazine, and metalachlor were the most commonly detected pesticides. Concentrations in ground water generally were less than 0.1 mg/L and never exceeded drinking-water guidelines (U.S. Environmental Protection Agency, 1986). Breakdown products from atrazine were detected, but no drinking-water standards currently are established for these chemicals (p. 16).
Other organic compounds and trace elements
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Despite the 1972 ban against the use of the organochlorine pesticide DDT in the United States, the pesticide and its metabolites DDD and DDE persist in the environment. In an examination of data from 1969 to 1990, all sites sampled for bed sediment in the Tar River Basin for DDD, DDE, and DDT had concentrations greater than the effects range established by the National Oceanic and Atmospheric Administration (Long and Morgan, 1991) as being associated with adverse biological effects on some benthic invertebrates (p. 18).
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DDD, DDE, DDT, dieldrin, trans-nonalachlor, polychlorinated biphenyls (PCBs), and toxaphene were detected in Asiatic clam or redbreast sunfish collected at 11 of 19 sites during 1992-93. DDE was the most common and widespread organochlorine compound detected. Except for one detection of toxaphene, pesticide concentrations were well below guidelines for the protection of fish-eating wildlife (p. 18-19).
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All 10 of the U.S. Environmental Protection Agency trace-element priority pollutants were detected in either Asiatic clam or redbreast sunfish in relatively low concentrations. Mercury concentrations were highest in heavily stained blackwater streams (p. 19).
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Mercury was widely detected, being present in 29 of 30 tissue samples, but concentrations did not exceed the Federal Food and Drug Administration (FDA) action limit (Nowell and Resek, 1994) or a risk-based screening value for the general public (Cunningham and others, 1992) (p. 19).
Fish communities
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Differences in the numbers and kinds of fish in small Coastal Plain streams were strongly related to basinwide habitat characteristics, such as soil drainage, proportion of adjacent areas of forested wetlands to streams, amount of row-crop agriculture, and channelization. Differences in fish communities were more weakly related to site-specific habitat variables, such as the amount of instream woody cover. These results indicate that mitigation and restoration strategies, which are of local focus but neglect basinwide conditions, may not be fully successful (p. 21).
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Channelized streams in agricultural areas with well-drained soils tended to have the greater numbers of fish species associated with flowing water environments than with ponded environments (p. 21).
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Agricultural land use, channelization, and destruction of floodplain buffer zones affect fish communities by altering flow regimes, decreasing the amount of organic material entering the stream, increasing nutrient concentrations, and raising pH. Fish community composition responds to these changes by shifting toward species that prefer flowing, well-oxygenated water that is moderately to weakly acidic (p. 21).
Albemarle Sound, North Carolina
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