Trends and status of flow, nutrients, and sediments for selected nontidal sites in the Chesapeake Bay Watershed, 1985-98
Data from 30 stream sites in nontidal portions of the Chesapeake Bay Watershed were analyzed to document annual nutrient and sediment loads and trends for the period 1985 through 1998 as part of an annual water-quality update for the Chesapeake Bay Program. Annual loads were estimated by use of the U.S. Geological Survey ESTIMATOR model and are available upon request. Trends were estimated by use of either linear regression, Seasonal Kendall, or Kendall-Theil tests. Trends were reported for monthly-mean flow, monthly load, flow-adjusted concentration, and flow-weighted concentration. Mean yields and median concentrations were calculated to help assess current water-quality status and to facilitate comparisons between basins. The trend in flow was upward at 12 of the 30 sites. Trends of nutrient and sediment load were upward at these same 12 sites. Trends in flow-adjusted and flow-weighted concentrations varied by species. Trends in flow-weighted concentrations were generally upward or not significant for the nitrogen species and parallel or not significant for phosphorus species. Trends in flow-adjusted concentrations were downward at nearly all sites for sediment and dissolved solids in the Susquehanna and Potomac River Basins and generally were not significant in the Virginia river basins.