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| Albemarle-Pamlico NAWQA |
| ALBE | NAWQA | DATA | PUBLICATIONS | CONTACTS |
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| Albemarle-Pamlico NAWQA |
| ALBE | NAWQA | DATA | PUBLICATIONS | CONTACTS |
ABSTRACT
INTRODUCTION
The 28,000 square mile Albemarle-Pamlico drainage basin (fig.1) includes the Roanoke, Dan, Chowan, Tar, and Neuse Rivers. The basin extends through four physiographic provinces in North Carolina and Virginia: Valley and Ridge, Blue Ridge, Piedmont and Coastal Plain. About 50 percent of the area is forested, more than 30 percent is in agriculture, 15 percent is wetland, and about 5 percent is developed. The basin population is approximately 3 million.
This web page is an abstract of a report by Harned, McMahon, Woodside and Spruill (1994) which summarizes the spatial and temporal trends in ground-water and riverine water quality in the study area, using readily available data sources. The primary data sources for this study included the U. S. Geological Survey Water Storage and Retrieval (WATSTORE) data base, the U.S. Environmental Protection Agency Storage and Retrieval data base (STORET), and results of investigations of pesticide occurrence. The principal water-quality constituents examined were suspended sediment, nutrients, and pesticides. The data examined generally spanned the period from 1950 to 1993.
SURFACE-WATER QUALITY
The distribution of available data is uneven. No suitable surface water stations are located in large areas of the Coastal Plain and the upper reaches of the Blackwater, Nottoway, Meherrin, Hyco, Otter, Pigg,and Dan River basins. Better coverage of the major trunks of the Roanoke, Dan, and Neuse Rivers is available.
Suspended sediment concentrations for the National Stream Quality Accounting Network (NASQAN) stations generally were less than 50 milligrams per liter except for the Dan River at Paces Virginia (d5). Kerr and Gaston Lakes serve as effective traps for sediment from the upper Roanoke River basin, as does Falls Lake for the Neuse River. Agricultural land use, particularly highly erosive corn and tobacco farming, and the high slopes of the Piedmont promote high sediment concentrations.
Total nitrogen concentrations at most of the larger stream sites are generally greater than 0.3 milligrams per liter, a level associated with potential nuisance growth of algae. Contentnea Creek at Hookerton, N.C. (n18) shows the highest total nitrogen values; followed by the Neuse River at Kinston, N.C. (n14); Tar River at Tarboro, N.C.(t8); Dan River at Paces, Va.(d5); Blackwater River near Franklin, Va. (c4); the other Chowan tributaries (c1 and c2); and the Roanoke River at Roanoke Rapids, N.C. (r15). In general, the most developed basins and those with the most intensive agriculture show the highest nitrogen values. Nitrogen concentrations generally decrease downstream for the Roanoke River (fig. 2), and increase downstream for the Tar River (fig. 3). The decrease in nitrogen concentrations in the Roanoke reflects the influence of the lakes downstream from the major inputs of nutrients to the basin in the area around Roanoke Virginia. The increase in nitrogen concentrations in the Tar River probably reflects the intensity of farming in the basin. Nitrogen concentrations in the Neuse River peak near the Smithfield station and decrease downstream (fig. 4).
Total phosphorus concentrations are relatively uniform in the Dan River (fig. 5), increase downstream in the Tar River (fig. 6), and peak in the Neuse River near Smithfield (fig. 7)in a manner similar to the pattern observed for other constituents. The concentrations of phosphorus in the Neuse River are some of the highest values for any of the Albemarle-Pamlico drainage study subbasins.
The highest nutrient concentrations were observed in Coastal Plain basins having considerable agriculture and poorly drained soils. Developed basins also had high nutrient concentrations (nitrogen: fig. 8a, phosphorus fig. 8b).
The most commonly detected pesticides in the STORET data base were atrazine and aldrin. The pesticide groups most frequently detected in the WATSTORE data set were the acetnalilide herbicides and the triazine and metabolite herbicides. Intensive organonitrogen herbicide sampling of Chicod Creek in 1992 showed seasonal variation in pesticide concentration. The most commonly detected herbicides were atrazine, alachlor, metolachlor, prometon, and metribuzin. No relation between streamflow and pesticide concentrations was evident. Concentrations of atrazine were elevated in late May and early June and decreased gradually until September.
TRENDS IN SURFACE-WATER QUALITY
The only significant trends in suspended sediment were detected for the three Chowan River tributary sites, which showed long-term decreases. Suspended- and total-solids concentrations have decreased throughout the Albemarle-Pamlico drainage basin (fig. 9). The decreases are probably a result of construction of new lakes and ponds in the basin which trap solids, improved agricultural soil management, and improved waste-water treatment.
Total nitrogen trends show a cluster of increases in the tributaries of the upstream end of Kerr Lake, and a cluster of decreases in the Neuse River Basin (fig.10). Trends observed for total organic plus ammonia nitrogen and for nitrate nitrogen were similar to those observed for total nitrogen (fig.11). In general, increasing trends in total phosphorus concentration were evident for the stations in Virginia, and decreasing trends were observed for the riverine stations in North Carolina (fig. 12). The effect of the 1988 phosphorus ban for both States is evident at several stations. All eight Virginia stations having total organic carbon data showed decreasing concentrations from 1980-89. Generalized decreases in organic carbon are consistent with decreases in solids concentrations as part of improved waste-water treatment. Increasing trends in potassium were detected in seven of the eight NASQAN stations.
GROUND-WATER QUALITY
The distribution of available ground-water data is uneven, as shown by the locations of wells with nitrate data in figure 13. Median concentrations of nitrate in ground water in four of seven geologic zones in the study area were less than 0.5 milligrams per liter (fig. 14). Median concentrations were largest and variability greatest in carbonated fractured rock aquifers of the Ridge and Valley Province and granitic rock aquifers of the Piedmont. Nitrate concentrations and variability are greatest in shallow (less than 100 feet deep) wells, compared to deeper wells. Median concentrations of nitrate are lowest in the Coastal Plain The highest median concentration (0.25 milligrams per liter) and the largest variability in total phosphorus were observed in the Coastal Plain probably because of the occurrences of natural phosphorites in Coastal Plain sediments.
In recent studies alachlor and atrazine were found in the largest percentage of shallow domestic wells in eastern North Carolina. In Duplin County, approximately one third of the 189 private wells sampled in 1991 for atrazine, alachlor, metalaxyl, and aldicarb had detectable concentrations, and 5 percent of the sampled wells had concentrations greater than one microgram per liter for at least one of these pesticides
LOADS
Nutrient loads from point sources are much less than loads from nonpoint nutrient input sources at the eight NASQAN basins . The greatest nitrogen inputs are associated with crop fertilizer and biological nitrogen fixation by soybeans and peanuts. Atmospheric and animal related nitrogen inputs are comparable in magnitude. The largest phosphorus inputs are associated with animal wastes.
Nitrogen loads (fig. 15) at the eight stations generally are directly related to the size of the nitrogen inputs. Phosphorus and sediment loads (fig. 16) are generally greater than loads reported for 14 national water-resource regions. Sediment yields are greatest in basins characterized by relatively steep slopes, erodible soils, and predominantly urban and agricultural land uses. Sediment yields at the basin outlet are mitigated by upstream reservoirs.
Figure 1.--The Albemarle-Pamlico drainage study area, with surface-water-sampling stations.
Figure 2.-- Boxplots of total nitrogen concentration for sites along the Roanoke River, indicating a general downstream decreasein concentration.
Figure 3.--Boxplots of total nitrogen concentration for sites along the Tar River, indicating a general downstream increase in concentration.
Figure 4.--Boxplots of total nitrogen concentration for sites along the Neuse River, indicating a peak in concentration near the Neuse River near Smithfield station (n8).
Figure 5.--Boxplots of total phosphorus concentrations for sites along the Dan River, indicating relatively uniform concentrations downstream. The lower concentrations for sites r15 and r15x are due to the retention of phosphorus by Kerr and Gaston lakes.
Figure 6.--Boxplots of total phosphorus concentration for sites along the Tar River, indicating a general downstream increase in concentration.
Figure 7.-- Boxplots of total phosphorus concentration for sites along the Neuse River, indicating a peak in concentration near the Neuse River near Smithfield station (n8).
Figure 8a.--Boxplots of total nitrogen and total phosphorus concentation by land-use category, indicating the highest nutrient concentrations in Coastal Plain agricultural basins.
Figure 8b.--Boxplots of total nitrogen and total phosphorus concentation by land-use category, indicating the highest nutrient concentrations in Coastal Plain agricultural basins.
Figure 9.--Locations of sites having statistically significant trends of decreasing suspended solids concentration., 1980-90.
Figure 10.--Locations of sites having statistically significant trends in total nitrogen concentration, 1980-90.
Figure 11.--Locations of sites having statistically significant trends in ammonia plus organic nitrogen concentration, 1980-90.
Figure 12.--Locations of sites having statistically significant trends in total phosphorus concentration, 1980-90.
Figure 13.-- Locations of wells with dissolved nitrate data.
Figure 14.--Boxplots of dissolved nitrate concentration in ground water by geologic zone.
Figure 15.-- Nitrogen Loads at the NASQAN sites, 1980-92.
Figure 16.--Sediment loads at the NASQAN site, 1980-92.
Harned, D.A., McMahon, Gerard, Spruill, T.B., and Woodside, M.D., 1995, Water-quality assessment of the Albemarle-Pamlico Drainage Basin, North Carolina and Virginia—Characterization of suspended sediment, nutrients, and pesticides: U.S. Geological Survey Open-File Report 95-191, 131 p.
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