Summary of trends and status analysis for flow, nutrients, and sediments at selected nontidal sites, Chesapeake Bay basin, 1985-99

Abstract

Water-quality and flow data from 31 sites in nontidal portions of the Chesapeake Bay Basin were analyzed to document annual nutrient and sediment loads and trends for the period 1985 through 1999 as part of an annual reevaluation and reporting for the Chesapeake Bay Program. Annual loads were estimated by use of the U.S. Geological Survey ESTIMATOR model. Trends were estimated using linear regression. Trends were reported for monthly mean flow, monthly load, flow-adjusted concentration, and flowweighted concentration. Median yields and concentrations were calculated to help facilitate comparisons between basins. The drought of 1999 had pronounced effects on trend results. The trend in flow increased at 4 of the 31 sites, 8 fewer sites than in 1998. Ten less significant trends were estimated for nutrient and sediment loads compared to 1985-98. Trends in flow-weighted and flow-adjusted concentrations varied little by nutrient species and geographic location. Trends were generally downward or not significant for both the nitrogen and phosphorus species throughout the Chesapeake Bay Basin. Trends in flow-adjusted concentration indicated downward trends at most sites for nutrients and about half the sites for sediments, an indication that management actions are reducing nutrient and sediment concentrations.