U.S. Geological Survey

Factors Affecting Nutrient Trends in Major Rivers of the Chesapeake Bay Watershed

Water Resources Investigations Report 00-4218
Richmond, Virginia, 2000
By Lori A. Sprague, Michael J. Langland, Steven E. Yochum, Robert E. Edwards, Joel D. Blomquist, Scott W. Phillips, Gary W. Shenk, and Stephen D. Preston

Download the report in PDF  (For best results, use Adobe Acrobat 4.0)


Trends in nutrient loads and flow-adjusted concentrations in the major rivers entering Chesapeake Bay were computed on the basis of water-quality data collected between 1985 and 1998 at 29 monitoring stations in the Susquehanna, Potomac, James, Rappahannock, York, Patuxent, and Choptank River Basins. Two computer models—the Chesapeake Bay Watershed Model (WSM) and the U.S. Geological Survey’s "Spatially Referenced Regressions on Watershed attributes" (SPARROW) Model—were used to help explain the major factors affecting the trends. Results from WSM simulations provided information on temporal changes in contributions from major nutrient sources, and results from SPARROW model simulations provided spatial detail on the distribution of nutrient yields in these basins. Additional data on nutrient sources, basin characteristics, implementation of management practices, and ground-water inputs to surface water were analyzed to help explain the trends. 
The major factors affecting the trends were changes in nutrient sources and natural variations in streamflow. The dominant source of nitrogen and phosphorus from 1985 to 1998 in six of the seven tributary basins to Chesapeake Bay was determined to be agriculture. Because of the predominance of agricultural inputs, changes in agricultural nutrient sources such as manure and fertilizer, combined with decreases in agricultural acreage and implementation of best management practices (BMPs), had the greatest impact on the trends in flow-adjusted nutrient concentrations. Urban acreage and population, however, were noted to be increasing throughout the Chesapeake Bay Watershed, and as a result, delivered loads  of nutrients from urban areas increased during the study period. Overall, agricultural nutrient management, in combination with load decreases from point sources due to facility upgrades and the phosphate detergent ban, led to downward trends in flow-adjusted nutrient concentrations atmany of the monitoring stations in the watershed. The loads of nutrients, however, were not reduced significantly at most of the monitoring stations. This is due primarily to higher streamflow in the latter years of the monitoring period, which led to higher loading in those years.
Results of this study indicate a need for more detailed information on BMP effectiveness under a full range of hydrologic conditions and in different areas of the watershed; an internally consistent fertilizer data set; greater consideration of the effects of watershed processes on nutrient transport; a refinement of current modeling efforts; and an expansion of the non-tidal monitoring network in the Chesapeake Bay Watershed.

For more information, contact
Virginia District
U.S. Geological Survey
1730 E. Parham Road
Richmond, Virginia 23228
(804) 261-2600
Maryland District
U.S. Geological Survey
8987 Yellow Brick Road
Baltimore, Maryland 21237
(410) 238-4200

Pennsylvania District
U.S. Geological Survey
840 Market Street
Lemoyne, Pennsylvania 17043
(717) 730-6900

To order printed copies, contact
U.S. Geological Survey
Information Services
Box 25286, Federal Center
Denver, CO 80225

Return to the Virginia District Home Page

USGS Water Biology Geology Mapping On-Line Water Resources Investigations Reports On-Line Water-Resources Reports

U.S. Department of the Interior, U.S. Geological Survey
Maintainer: Virginia District Publications
Last update: 12:01:22 Fri 15 Dec 2000
Privacy Statement || Disclaimer
URL: http://va.water.usgs.gov/online_pubs/WRIR/00-4218.htm
FirstGov, 'Your First Click to the U. S. Government'