Water-quality trends for streams and reservoirs in the Research Triangle area of North Carolina, 1983-95

Abstract

This report presents the results of analyses of trends in concentrations of nitrogen, phosphorus, suspended sediment, suspended solids, sodium, chloride, iron, zinc, manganese, and chlorophyll a at 34 stream and reservoir sites that are part of the Triangle Area Water Supply Monitoring Project. Trend results are discussed in relation to broad-scale changes in land cover that have occurred in the area since the mid-1970s.Data used for trend analysis of stream sites are from samples collected by the U.S. Geological Survey (USGS) from 1982 through 1987 for a study for the U.S. Army Corps of Engineers (Garrett, I990a and b), by the North Carolina Division of Water Quality (DWQ) from 1982 through 1995 for the statewide ambient water-Quality monitoring network. USGS science for e changing worldand by the USGS from 1988 through 1995 for the Triangle Area Water Supply Monitoring Project (Childress and Treece. 1996; Ragland and others, 1996). These three sources provide stream water-Quality data, collected monthly, which are ideally suited for trend analysis. Using continuous streamflow data from USGS gages, stream water-Quality data were statistically adjusted to eliminate the effects of changing streamflow.

Triangle Area Water Supply Monitoring Project, North Carolina—Overview of hydrologic and water-quality monitoring activities and data quality assurance

“…A Water-Resources Investigations Report (WRIR) was published describing water and bed-material quality, summary statistics, annual loads and yields, and streamflow conditions of selected streams and reservoirs for the Triangle area for data from 1988 to 1994 (Childress and Treece, 1996). An additional WRIR was published presenting the results of a trends analysis for selected constituents and parameters in the TAWSMP study area for the period 1983-95 (Childress and Bathala, 1997). This water-quality trends report describes data collected by the USGS from 1982 to 1987 for a USACE study.…”

“…This water-quality trends report describes data collected by the USGS from 1982 to 1987 for a USACE study. The WRIR also includes data collected by the North Carolina Department of Environment and Natural Resources, Division of Water Quality, from 1982 to 1995 for the statewide ambient water-quality monitoring network, as well as data from the USGS for the TAWSMP from 1988 to 1995 (Childress and Bathala, 1997).…”