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USGS North Carolina Water Science Center Publication
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Suspended Sediment and Nutrients in the Upper Cape Fear River Basin, North Carolina, 2002–04, with an Analysis of Temporal Changes, 1976–2004

Prepared in cooperation with the Upper Cape Fear River Basin Association

Scientific Investigations Report 2005–5271
By Timothy B. Spruill, Phillip S. Jen, and Ryan B. Rasmussen


Complete report in PDF (50 pages, 3.1 MB)


Abstract

An investigation of suspended sediment and nutrients was conducted in the Haw River near Bynum and in the Deep River at Moncure, North Carolina, to characterize water quality based on data collected weekly or biweekly between August 2002 and August 2004. Samples were collected five times per year for selected major ions and trace elements to help in characterizing the water quality at these sampling sites. Sediment and nutrient data collected from 1976 to 2004 also were analyzed to evaluate whether loads and concentrations changed significantly over this period.

The water chemistry in the Haw and Deep Rivers is of mixed ionic composition, although the water chemistry in the Haw River is more variable. Water types in both rivers generally shifted from calcium and bicarbonate in the winter and spring months and during high flows to sodium and chloride during low flows in the summer. Sediment and nutrient loads were estimated for calendar years 2002 and 2003 using the nutrient and suspended-sediment concentration data collected between 2002 and 2004 for calibration of regression load models. Sediment and nutrient loads generally were greater in 2003, an unusually wet year, than in 2002. Annual constituent yields generally were higher in the Deep River with the exception of dissolved nitrate and nitrite. Phosphorus loads and concentrations were significantly higher in the Deep River as a result of substantial continuous-discharge sources of phosphorus, particularly near High Point, North Carolina. More stringent wastewater-treatment requirements in the Haw River primarily are responsible for much lower phosphorus concentrations and loads compared with those in the Deep River. Seasonal loads were evaluated at both sites for the period September 2002 through August 2004. Primary transport of nutrients and sediment occurred during spring 2003 and winter 2004.

Historical flow and water-quality data previously collected at both sites by the U.S. Geological Survey and the North Carolina Division of Water Quality were used to evaluate historical changes through time and to compare information from the two datasets. Historical water-quality changes between 1976 and 2004 were greatest in the Haw River near Bynum, which had a statistically significant (p is less than 0.05) decrease in sediment, total nitrogen, and total phosphorus concentrations and loads. Decreases in cultivated land, improved land-management practices, and improved wastewater-treatment processes since the 1980s are primary reasons for the observed improvement in water quality in the Haw River.

Because sampling was limited for nutrients (16 samples) and sediment (25 samples) in the Deep River, changes in concentrations between the early 1980s and 2002–04 were not statistically detectable (p is greater than 0.05) for suspended sediment, total nitrogen, or total phosphorus. Data from the North Carolina Division of Water Quality also indicated no change between 1992 and 2004. Calculated sediment loads, however, using the load-streamflow regression models calibrated for two separate periods, 1976–83 and 2002–04, indicate that sediment loads may be lower for 2002–04 compared with those in the early 1980s. Nutrient concentrations have remained relatively unchanged since the 1980s.

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