The U.S. Geological Survey's National Water-Quality Assessment (NAWQA) program was established to answer the question " Is the Nation's water quality getting better, worse or staying the same?" The Albemarle-Pamlico Study Unit (fig. 1) was one of 20 study areas, called study units, established in 1991 to help address this important question. By 1997, as many as 60 study units are targeted to be established on a national basis.
Location map of the ALBE basin.
The Albemarle-Pamlico study unit provides the United States Congress, natural resources managers, and the public with an assessment of water quality within each study unit by analysis of historical (pre-1992) and current (1992-95) water quality information. The environmental characteristics of the Albemarle-Pamlico Study Unit have been described in McMahon and Lloyd (1995). Analysis of historical data in the Study Unit was published in Harned, McMahon, Spruill, and Woodside (1995). A brief description of the background and design of the study was presented in Spruill, Harned, and McMahon (1995).
Surface-water samples collected from the Coastal Plain and Piedmont and ground-water samples from the Coastal Plain of the Albemarle-Pamlico Drainage were analyzed to characterize current water-quality conditions in the basin and identify potential problems in the study area. Because of potential human health and environmental implications, plant nutrients (nitrogen, ammonia, and phosphorus) and pesticides have been the primary national water-quality focus of the NAWQA effort
The Albemarle-Pamlico Drainage Study Unit is located in portions of Virginia and North Carolina and includes four major river basins, the Chowan, Roanoke, Tar-Pamlico and Neuse. More than 65 surface water sites were sampled between 1993 and 1995 for nutrients, pesticides and other chemical constituents. More than 57 ground water sites were sampled for these same constituents during the same period. Wells were less than 50 feet in depth and located in the surficial aquifer of the Coastal Plain. Wells in the surficial and Yorktown aquifers were selected because the these aquifers are the shallowest and are the most likely to become contaminated by human activities on the land surface.
The quality of water resources in the Albemarle-Pamlico drainage study area is influenced by the environmental setting-an interrelated set of natural, cultural, and hydrologic factors. Natural factors include physiography, geology, and soils; cultural factors include land use and population distribution; and hydrologic factors include climate and the amount and distribution of surface-water runoff and ground-water discharge.
The physiography, geology, and soils form the container over and through which surface and ground water flows. The kind and amount of rock, soil, and the land-surface slope influence the kind and amount of mineral matter in water. In the mountains where slopes are steep, surface and ground water move fast and have less opportunity to dissolve rock and soil; consequently, the water generally contains very little dissolved mineral matter. In the Piedmont and Coastal Plain, slopes are flatter and water moves more slowly; consequently, surface water generally has two to three times the mineral content of surface and ground waters in the mountains.
Land use and land cover; population distribution, and manmade reservoirs have significant influences on water quality in the area. In general, the study area is dominated by a patchwork of forested (50 percent of the area) and agricultural (more than 30 percent) land, with large tracts of wetlands (about 15 percent) in the eastern Coastal Plain. Less than 5 percent of the overall basin area contains developed land.
Agricultural and developed areas have the greatest potential to influence water quality because these land uses introduce the greatest amounts of nutrients, sediments, and pesticides into the hydrologic system. The agricultural sector is devoted to growing corn, soybeans, cotton, peanuts, tobacco, grains, and potatoes, and raising chickens, turkeys, hogs, and cattle.
About 3 million people live in the Albemarle-Pamlico drainage area, with urban areas located in the Upper Roanoke and Upper Neuse River Basins. Wetlands and man-made reservoirs have a beneficial effect on water quality because they slow water flow, thus allowing the deposition of suspended sediments and their sorbed compounds and providing an opportunity for aquatic vegetation to use mineral matter dissolved in the water.
Characteristics of climate, topography, geology, and soil influence water quality and control the amount and routing of freshwater resources in the study area. Annual precipitation (1961-90) ranged from 36 to 52 in. in the mountains, from 40 to 44 in. in the Piedmont, and from 44 in. at the Piedmont/Coastal Plain boundary to 52 in. near the coast. Evapotranspiration consumes about 30 in. (about 55 percent) of average annual precipitation in the mountains, where the average annual temperature is about 52 degrees F. Evapotranspiration consumes about 36 in. (about 70 percent) of average annual precipitation in the southeastern part of the area, where the average annual temperature is about 62 degrees F.About one-third of the remaining precipitation reaches streams by overland runoff; the remainder recharges the the water-table aquifer, where much of the water eventually discharges to streams as ground water. Thus, ground-water quality has a substantial infuence on surface-water quality.
On average, more than half of the water that reaches streams first infiltrates the land surface, percolates through soil to the water table, and moves through the aquifers as ground water before it is discharged to the streams. Thus, the quality of ground water has substantial influence on surface-water quality. Major aquifers in the Valley and Ridge, Blue Ridge, and Piedmont Provinces are consolidated, fractured rocks; in the Coastal Plain Province, they are primarily unconsolidated sands with some consolidated to partly consolidated limestone and sandy limestone.
Approximately 250 permitted point sources discharged about 410 Mga1/d of treated effluent throughout the study area in 1990, along with 5,800 tons of nitrogen and 1,800 tons of phosphorus. Deposition of nitrogen from the atmosphere was 50,500 tons during 1990. Crop-related nutrients and manure produced by livestock are also important potential non point sources of nitrogen and phosphorus. A total of about 153,000 tons of nitrogen and 10,500 tons of phosphorus were used as fertilizer or fixed by leguminous crops in 1990. About 43,500 tons of nitrogen and 12,200 tons of phosphorus were produced as animal wastes in the area in 1987.
About 2.5 million pounds of selected herbicides and 800,000 pounds of selected insecticides were used in the study area in 1990. Alachlor, atrazine, metolachlor, butylate, eptam, pendimethalin, carbaryl, ethoprop, and carbofuran were each used at annual rates exceeding 100,000 pounds. Alachlor and atrazine were the most used herbicides-about 670,000 and 330,000 pounds per year, respectively-and carbaryl was the most used insecticide-about 20,000 pounds per year.
To facilitate study of the relation between the environmental-setting factors and water-quality issues, all land in the study area was classified into 12 strata, using a geographic information system. Each stratum represents homogeneous combinations of natural, cultural, and hydrologic factors. The classification reveals large areas of poorly drained agricultural lands and wetlands in the Coastal Plain that can have significant general influences on water quality. Large areas of agricultural and forested land and smaller areas of developed land can exert a significant influence on Piedmont water quality due to associated point-source discharges.
Water quality in the Albemarle-Pamlico drainage study area is influenced by natural, cultural, and hydrologic factors. These factors define the environmental setting of the study area and influence the occurrence and spatial distribution of sediments, nutrients, and pesticides.
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