In the 1970s, the U.S. Environmental Protection Agency (EPA) initiated a decade-long study that was focused on reducing sediment and nutrient inputs into the bay (Horton and Eichbaum, 1991). The first Chesapeake Bay Agreement (1983) formally recognized the need for cooperative efforts to reduce pollution (including nutrient enrichment) and enhance bay productivity (Appendix D). A second agreement in 1987 expanded upon the first and committed to a 40% reduction in nitrogen and phosphorus entering the mainstem of the bay by 2000. Although the goal has not been met, nutrient levels have declined despite increased population growth and development in the watershed. The model of the Chesapeake Bay watershed used by the Chesapeake Bay Program (CBP) to estimate nutrient input suggests that nitrogen loads have decreased by 51 million pounds/year between 1985 and 2000 (from 300 million pounds/year to 249 million pounds/year) and that phosphorus loads have declined by 8 million lbs/year (from 25 million pounds/year to 17 million pounds/ year) over the same time (Chesapeake Bay Program, 2000). U.S. Geological Survey measurements at nine river input monitoring stations provide more detailed and site-specific data. Nutrient levels computed using actual water quality data collected between 1985 and 1998 at these stations showed no statistically significant trends in either total nitrogen or total phosphorus loads at six of the nine stations. Some of the difference is attributable to high streamflows, which can lead to higher nutrient loads even if nutrient concentrations have maintained status quo or declined. Adjustment of the data to account for this variation resulted in downward trends for nitrogen concentrations (at six of the nine sites) and phosphorus concentrations (at seven of the nine sites; Belval and Sprague, 1999; Sprague et al., 2000). A further analysis of nutrient data from 31 sites in the nontidal portions of the Chesapeake Bay basin from 1985 to 1999 showed that flow-adjusted concentrations of total nitrogen and total phosphorus trended downward at 23 of 31 sites. This suggests that management actions are working in reducing nutrient concentrations (Langland et al., 2001; U.S. EPA, 2002). The Chesapeake 2000 Agreement reaffirms the commitment of its signatories to achieve and maintain the 40% nutrient reduction goal agreed to in 1987 and further strives to correct all nutrient-and sediment-related problems in the bay and its tidal tributaries by 2010 (Chesapeake Bay Program, 2000).

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