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Trends in Water Quality and Nutrient Sources and In-stream Nutrient Loads in the Southeastern United States

1Douglas Harned, 1Erik Staub, 1Kelly Peak, 1Kirsten Cassingham

1 U.S. Geological Survey 3916 Sunset Ridge Road Raleigh, NC, 27607 919-571-4024

Abstract

Water-quality data from U.S. Geological Survey (USGS) surface-water sampling sites in the Southeastern United States for the period 1973-2005 are being assessed for trends in concentrations of nutrients, sediment and major constituents, and nutrient transport. The study objectives include assessing water- quality trends for individual stations; characterizing regional patterns in the trends; defining the association of trends in agricultural nutrient sources, atmospheric inputs, urban land use, population, and trends in water-quality; evaluating nutrient loads; testing trends for specific time periods using regression load models; and providing input to a regional SPARROW (SPAtially Referenced Regressions On Watershed) attributes model. The study area includes river basins draining to the southern Atlantic, Gulf Coast, and the Tennessee River. This study is one of several major river basin (MRB) studies of the National Water-Quality Assessment (NAWQA) Program, which include the review of a common time period to assess national water-quality trends. Sampling sites with sufficient water-quality data and continuous streamflow record (approximately 100 sites) are being examined for all apparent monotonic trends using the seasonal Kendall trend test or Tobit regression. The constituents being examined include major ions, nutrients, and sediment concentrations. The seasonal Kendall trend test adjusts for seasonal variability by comparing seasonally grouped constituent concentrations adjusted for the effects of streamflow with LOWESS (LOcally WEighted Sum of Squares) smoothed curves. The Tobit test is appropriate for examining records that include reporting limits. Spatial patterns in trends for multiple stations are being analyzed in reference to regional landscape variables. The associations of trends in agricultural nutrient sources (annual variation of cropping and fertilizer use) with trends in water quality are being tested using principal components and multiple-regression analysis.

Harned, D.A. , Staub E., Peak, K., and Cassingham K., 2006, Trends in Water-Quality and Nutrient Sources and In-stream Nutrient Loads in the Southeastern United States: Proceedings of the National Water-Quality Monitoring Council National Monitoring Conference, May 8-12, 2006, San Jose CA.