CHANGES IN WATER QUALITY OF STREAMS IN THE SOUTHEASTERN UNITED STATES (Invited Presentation)

Results from the U.S. Geological Survey (USGS) National Water Quality Assessment study show an evolving anthropogenic effect on water quality of streams draining to, and in the Coastal Plain of the Southeastern United States. Forty-four USGS sites across the Southeast were examined for trends in water quality from 1973 to 2005. Concentrations of dissolved major ions have increased in the Southeast during the last 30 years. Specific conductance increased at 62 percent and decreased at 3 percent of the USGS sites, and pH increased at 31 percent and decreased at 11 percent of the sites. The 44 USGS sites and an additional 290 sites from the U.S. Environmental Protection Agency Storage and Retrieval database were tested for trends over 1975-2004 in total nitrogen and total phosphorus concentrations. Decreasing trends in total nitrogen were detected at 49 percent of the sites, and increasing trends were detected at 10 percent of the sites. Ammonia concentrations decreased at 27 percent of the sites and increased at 6 percent of the sites. Nitrite plus nitrate concentrations increased at 29 percent of the sites and decreased at 10 percent of the sites. These results indicate that the changes in stream nitrogen concentrations generally coincided with improved municipal wastewater-treatment methods. Long-term decreasing trends in total phosphorus were detected at 56 percent of the sites, and increasing trends were detected at 8 percent of the sites. The decrease of phosphorus over the last 35 years coincides with phosphate-detergent bans, improvements in wastewater treatment, and implementation of agricultural best management practices to reduce erosion following passage of the Federal Water Pollution Control Act of 1972.

Multiple-regression analysis indicated a relation between changes in atmospheric inputs and agricultural practices, and changes in water quality. Model results of the SPARROW (SPAtially Referenced Regressions On Watersheds) can be used to estimate the contribution share from different natural and anthropogenic source categories to in-stream nutrient load in each stream reach in the Southeastern United States. http://pubs.usgs.gov/sir/2009/5268/