ISSUE-- NUTRIENTS IN SURFACE WATER: Occurrence of fish kills, decline of seagrasses, and presence of foul odors and bacteria in waters of recreational areas motivate concerns about nutrient enrichment and algal blooms in estuaries that receive water from the study area.
Key Findings: All four river basins (Chowan, Roanoke, Tar, and Neuse Basins) in the Albemarle-Pamlico drainage area contain elevated concentrations of nitrogen and phosphorus that eventual1y reach the Sounds. Of the large river basins, total nitrogen concentrations were highest (1-3 milligrams per liter) in the Neuse and Tar Basins, and lowest (0.2-0.8 mg/L) in the Roanoke and Chowan Basins (from: Harned and others, 1995 and McMahon and Woodside,1994 ).
These four rivers carry at least 13,000 tons of nitrogen and 1,100 tons of phosphorus to the Sounds every year, with the Neuse Basin contributing the largest share.
Suspended-sediment, suspended solids and total solids concentrations have decreased throughout the Albemarle-Pamlico drainage system. Decreasing concentrations of suspended solids in the sounds and estuaries may result in clearer water and deeper light penetration in water, which in turn improve conditions for algal blooms in areas with nutrient enrichment.
Key Causal Factors
Agricultural fertilizer and livestock waste are major sources of nitrogen and phosphorus found in streams in all 4 basins, supplying 50 percent of the nitrogen and 75 percent of the phosphous originating in the basins.
Atmospheric inputs are a source of 27 percent of the nitrogen load and 21 percent of the phosphorus load in the basin.
Permitted point sources of nitrogen and phosphorus from municipal waste water treatment plants and industrial sources account for less than 5 percent of the nutrient source inputs in all basins. However, these sources go directly into streams and may constitute up to 20 percent of the in-stream nutrient load.
Decreases in sediment and solids concentrations are probably a result of (1) construction of new lakes and ponds in the basin, which trap solids, (2) improved agricultural soil management, including use of conservation tillage, (3) and improved wastewater management. Decreases in sediment and solids may improve water clarity. Improved clarity of the water allows greater light penetration, which may promote algal blooms, yet may have beneficial effects on other organisms with decreased silting of habitats.
Trends:
Phosphorus concentrations have generally declined since 1980 in all four basins. Part of this decrease may be due to improved agricultural practices and a phosphate ban in North Carolina, and Virginia since 1988.
Total nitrogen concentrations have generally declined since 1980 in all four basins, probably as a result of improved agricultural practices and enhanced waste-water treatment.
ISSUE-- NUTRIENTS IN GROUND WATER: Most rural residents use ground water for drinking water. Because high nitrate concentrations in ground water can cause health problems there is a need to evaluate nitrate concentrations in ground water.
Key findings: (from Spruill and others, 1996, Spruill, Eimers and Morey, 1996 , and Harned and others, 1995 ).
Based on the NAWQA random well sample, nitrate-nitrogen concentrations in the inner Coastal Plain are higher (median = 0.4 mg/L) than concentrations in the outer Coastal Plain (median = 0.05 mg/L).
About 10 percent of 20 shallow observation wells in agricultural areas of the inner Coastal Plain exceed the Environmental Protection Agency MCL of 10 mg/L, whereas none of the sampled wells exceed nitrate standards in the outer Coastal Plain. A maximum concentration of 11 mg/L occurred in water from one well.
Nitrate-nitrogen concentrations in ground water are generally less than 2 mg/L where dissolved organic carbon concentrations exceed 2-3 mg/L.
Ground water beneath sandy, well-drained soils, within the Albemarle-Pamlico Drainage and particularly near the Fall Line when nitrogen sources at the land surface are present, had generally higher nitrate-nitrogen concentrations than beneath moderately or poorly drained soils.
Key Causal Factors:
Ground water from shallow wells (less than 100 feet deep) in the Coastal Plain of the Albemarle-Pamlico Study Unit had higher nitrate concentrations and greater variability than wells deeper than 100 feet, indicating the presence of sources of nitrate.
Nitrate, the common water-soluble oxidized form of nitrogen from these sources, can enter ground water as a point (localized) source, such as leakage from a tank or pipe, or, more commonly, as a non-point (dispersed) source such as from areally applied fertilizer, biological fixation, animal waste, and precipitation.
When organic carbon is present in a low-oxygen environment, bacteria may utilize it to reduce nitrate dramatically and convert it to nitrogen gas, nitrogen oxides, or ammonia. Therefore, ground water with high DOC tends to have low nitrate concentrations.
Trends: There is not currently sufficient ground-water quality data over time to evaluate regional trends.
ISSUE-- PESTICIDES: Are pesticides in surface water, ground water, andaquatic organisms of the Albemarle-Pamlico Drainage?
Key findings: Pesticides and pesticide metabolites occur in most surface water samples, in many ground water, and in many of the aquatic organisms tested. With few exceptions, these detections do not exceed existing drinking water or aquatic health standards. (from Harned and others, 1995, Skrobialowski, 1996, Smith and Ruhl, Spruill and others, 1996, Woodside and Simerl 1996, and Woodside and McMahon, 1994).
Metolachlor was detected in 90 percent, atrazine in 80 percent, prometon in 70 percent, and alachlor in 60 percent of 233 stream samples from 65 sites in the Albemarle Pamlico Drainage. Only alachlor occurred at levels above the drinking water standard of 2 ug/L. Standards for drinking water or human health exist for only 50 percent of the individual compounds found, and no standards exist to evaluate pesticide combinations that are typically found in streams.
Herbicides and insecticides were generally not found in ground water, although several breakdown products from these pesticides were detected. There are no drinking water standards for the breakdown products detected. Of 47 pesticides analyzed, 11 were detected in ground water. Concentrations in ground water were generally less than 0.1 microgram per liter and never exceeded established MCL's for drinking water. Diazinon was the most frequently detected pesticide in ground water, although concentrations were just above the detection limit.
Despite the ban of DDT the pesticide and its metabolites DDD and DDE persist in the environment. In an examination of existing data from 1969-90, 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 associated with adverse biological effects on some benthic invertibrates. Elevated concentrations of DDD, DDE, and DDT also were detected at several sites in the Roanoke River Basin. Of 22 bed sediment sample collected in the Albemarle-Pamlico basin in 1992-93, 63 percent had detectable levels of DDT. There are no human health standards established for DDT in bed sediment.
DDD, DDE, DDT, dieldrin, trans-nonalachlor, PCB, and toxaphene were detected in Asiatic clam or redbreast sunfish at 11 of 19 sites sampled in 1992-93. DDE was the most common and widespread organochlorine compound detected. All but toxaphane were present in concentrations well below the National Academy of Sciences and National Academy of Engineering guidelines for the protection of fish-eating wildlife.
Key Causal Factors:
Pesticides in surface water come from cropland, surficial runoff from developed areas, and atmospheric deposition, not from ground water discharge.
Pesticide metabolites or breakdown compounds found in ground water originate from pesticides leached from the land surface to the water table.
Many of the pesticides that were detected; including DDT, Dieldrin,an Toxaphene; have been banned or restricted, yet their presence isediment and in organisms indicates their persistence in the environment.
Trends: NAWQA pesticide data form the baseline for future trend analysis. Intensive organonitrogen sampling in Chicod Creek in 1992-94 (in the Tar River Basin) indicated seasonal variation in pesticide concentrations. No relation between streamflow and pesticide concentrations was noted. Concentrations of atrazine increased in in late May and early June and decreased gradually until the renewed application the following spring.
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