NUTRIENT TRENDS IN RIVERS ENTERING THE CHESAPEAKE BAY

The Chesapeake Bay, the Nation’s largest estuary, has been adversely impacted by excess nutrients. Excess nutrients have caused low dissolved oxygen levels leading to loss of fisheries and other living resources. The Chesapeake Bay Program (CBP) is leading an effort to reduce nutrient sources and loads in the Bay watershed to meet dissolved oxygen criteria in the Bay by 2010. The U.S. Geological Survey (USGS), in cooperation with several agencies, has monitored the concentration of nutrients entering the Bay since the late 1980’s. The data are used to assess trends in load and concentrations of nutrients in rivers entering the Bay and understand the factors affecting those trends. The trend analysis revealed a large variation in the annual nitrogen and phosphorus loads to the Bay due to changes in yearly streamflow with slow reductions of the nutrient concentrations. The primary factors affecting the trends in concentration were streamflow, changes in nutrient sources, and influence of watershed characteristics (including in-stream biogeochemical transformations and the influence of ground water). All these factors influence the lag time between implementing nutrient-reduction practices in the watershed and water quality improvements in the Bay. The CBP is using these results to help refine, and assess the effectiveness of, management strategies to reduce nutrients in the Bay watershed.