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A spatial characterization of nutrient concentrations for the Albemarle-Pamlico drainage area, North Carolina and Virginia

American Geophysical Union 1994 Fall Meeting, Eos, November 1, 1994, p. 247.
By Douglas A. Harned

Abstract

Water-quality data for 66 riverine and 296 estuarine stations in the Albemarle-Pamlico drainage area in North Carolina and Virginia for 1980-90, collected by the U.S. Geological Survey, the North Carolina Department of Health, Environment, and Natural Resources, and the Virginia Department of Environmental Quality, were examined for spatial trends. These data provide the basis for spatial characterization of changes in nitrogen and phosphorus concentrations in the major river basins that reflects influences of point and nonpoint sources of nutrients.

Nutrient concentrations generally decreased downstream in the Roanoke River, which drains an 8,473-square-mile predominately forested and rural basin. The Roanoke River Basin is about 32-percent agricultural land and 5-percent developed land. The decrease in nutrient concentrations in the Roanoke River reflects the influence of several lakes downstream from major point-source nutrient contributions to the basin. These lakes trap phosphorus associated with particulate matter, and algae assimilate some of the dissolved nutrients.

Nutrient concentrations also increased downstream in the Tar River, which drains a 2,222-square-mile agricultural and urban basin, reflecting the intensity of farming in this basin. Cropland accounts for 38 percent of the Tar River Basin, and about 5 percent is developed.

The Neuse River Basin is approximately 37-percent agricultural land and 9-percent developed area. Nutrient concentrations in this river, which drains a 2,712-square-mile agricultural and urban basin, peaked downstream from Raleigh, N.C. The peak in nutrient concentrations in the Neuse River is probably due to nutrients from urban point sources.

Nutrient concentrations generally decreased downstream as these rivers drained into estuarine areas, indicating possible uptake of dissolved nitrogen in algal biomass. In the Pamlico River estuary, which is the receiving water body for the Tar River and which drains an additional 2,078 square miles of agricultural and forested land, total phosphorus concentrations peaked near a major point source in the estuary, and decreased downstream from that source. Phosphorus concentrations in the Pamlico River estuary are some of the highest measured nationally.

Harned, D.A., 1994, A spatial characterization of nutrient concentrations for the Albemarle-Pamlico Drainage Area, North Carolina and Virginia, American Geophysical Union 1994 Fall Meeting, Eos, November 1, 1994, p. 247.