Water-Quality Trends for Streams and Reservoirs in the Research Triangle Area of North Carolina, 1983-95

Significant Findings

The most significant regionwide water-quality trend was a decline in total phosphorus concentration after 1988 that coincided with substantial phosphorus removal measures at many municipal wastewater-treatment facilities in the region and the removal of phosphates in detergent. The decline in total phosphorus as P ranged from 25 to 81 percent.

Total nitrogen concentrations at most sites were stable from 1983 through 1995. Increasing concentrations occurred in the Neuse River at Clayton and at Smithfield. Decreasing concentrations occurred in headwater streams and small lakes, including the Eno River at Hillsborough, Little River and Little River Reservoir, Lake Michie, Swift Creek, Cane Creek Reservoir, and Morgan Creek near White Cross. Total nitrogen also decreased in the Cape Fear River near Brickhaven.

Nitrate concentrations at most sites were stable from 1983 through 1995; however, at all but one stream site where a trend was recorded, the trend was increasing. These sites --the Eno River near Durham, Knap of Reeds Creek, Neuse River near Clayton and at Smithfield, and New Hope Creek--drain basins with substantial population increases since 1980.

Organic nitrogen concentrations were either stable or declining from 1983 to 1995. Sites with declining concentrations were headwater sites (Cane Creek and Morgan Creek), sites downstream from impoundments (Swift Creek, Haw River near Moncure, and Neuse River near Falls), sites receiving WWTP effluents (Eno River near Weaver and Knap of Reeds Creek), and the Cape Fear River near Brickhaven.

Suspended-sediment concentrations were stable at all sites tested; suspended-solids concentrations also were stable except for decreasing concentrations at Knap of Reeds Creek and Haw River at Bynum.

Sodium concentrations have decreased at Neuse River at Smithfield and Cane Creek near Orange Grove, and increased in University Lake.

Chlorophyll a concentrations have increased by 17 to 52 percent per year from 1989 to 1995 at monitored lakes except Cane Creek Reservoir and Lake Michie. In the upper Neuse River Basin, increases coincide with stable or decreasing total phosphorus concentrations. The reasons for this apparent contradiction will require further, more detailed study.

No clear patterns emerged linking water-quality trends to development and growth patterns. Swift Creek is the most rapidly developing of the basins studied‹developed land cover increased from 30 to 75 percent from 1975 to 1988. Ellerbe Creek is the most populated watershed in terms of numbers of people per square mile. Continued monitoring of these small watersheds is needed to assess the effects of growth and development on water quality.

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