USGS science informs revised water-quality restoration plans for the Chesapeake Bay and its watershed

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Science Summary


A major goal of the Chesapeake Bay restoration effort is to improve water-quality conditions for shellfish and finfish. To reach this goal, the Chesapeake Bay Total Maximum Daily Load (TMDL), established by the U.S. Environmental Protection Agency (EPA) in 2010, calls for all pollution reduction practices to be in place by 2025. The watershed jurisdictions (Delaware, District of Columbia, Maryland, New York, Pennsylvania, Virginia, and West Virginia) have developed Watershed Implementation Plans (WIPs) to reduce the amount of nutrients (nitrogen and phosphorus) and sediment flowing into local rivers and streams and the Chesapeake Bay.  

A midpoint assessment of the TMDL was conducted to help inform the next iteration of jurisdictional WIPs. Over several years, the Chesapeake Bay Program (CBP) partnership reviewed the latest science, data, tools, and best management practices to consider all lessons learned since the advent of the Chesapeake Bay TMDL. These lessons, as well as additional local data, have been incorporated into the tools used by the jurisdictions and their local partners to develop the next round (Phase III) of WIPs and guide implementation through 2025. The outcomes of the midpoint assessment are intended to streamline implementation, overcome challenges to restoring local and Bay water quality as 2025 approaches, and prepare the jurisdictions for successful development and implementation of their Phase III WIPs.


Explaining water-quality patterns and change in the watershed

The U.S. Geological Survey (USGS), working with State and academic partners, leads the monitoring of nutrients and sediment at over 100 sites across the Chesapeake Bay watershed. A major focus of USGS research is to explain the patterns and changes of nutrients and sediment at these sites, including the influence of management efforts. 

Several synthesis products were prepared to summarize findings on these topics for the midpoint assessment:


Coordinating efforts to understand tidal water quality

To assess progress in the restoration effort, it is critical to understand how estuarine water-quality conditions respond to nutrient and sediment reduction efforts. Teams of researchers, including Federal, State, and academic partners, were formed under USGS leadership, with support from the EPA, to address these key topics for the midpoint assessment:

  • Developing and applying new techniques to evaluate trends in tidal waters.
  • Documenting recent advances in understanding estuarine water-quality and dissolved-oxygen responses to changes in nutrient inputs.
  • Developing an integrated understanding of drivers of changes in water clarity in different settings.
  • Quantifying factors controlling the distribution and abundance of submerged aquatic vegetation.
  • Linking watershed and estuarine changes in the Potomac River.


Contributing to improved models and land-cover information

The USGS has also contributed to the following modeling, land-cover, and enhanced monitoring efforts for the midpoint assessment:

  • Improved modeling tools—The new Phase 6 Watershed Model, which is used by the jurisdictions to inform development of WIPs, has a simpler structure than the previous version and includes improved nutrient data, cutting-edge, high-resolution land-cover data, and new and improved information about the efficiencies of pollution-reducing best management practices. Over 30 years’ worth of USGS monitoring data were used to calibrate or verify the accuracy of the model.
  • High-resolution land-cover data—USGS scientists guided the development of a 1-meter by 1-meter resolution land-cover dataset of the entire Chesapeake Bay watershed with a high degree of accuracy, providing 900 times the amount of information over the existing dataset.
  • Enhanced data gathered from local agricultural and municipal partners—The Phase 6 watershed model includes an additional decade of new science and data from hundreds of monitoring stations across the watershed, as well as local planning and zoning data gathered by working directly with counties and municipalities across the watershed.
  • Monitoring trends—The CBP partnership has increased the number of monitoring stations throughout the watershed, giving a more complete picture of real-time conditions and trends. Comprehensive data can provide new insights to visualize and explain the long-term trends observed in local streams and rivers. Jurisdictions and their local partners and stakeholders can use those new insights in planning for their Phase III WIPs.


USGS scientists recognized for efforts supporting the midpoint assessment

Several USGS scientists received a 2018 National U.S. Environmental Protection Agency Gold Medal for their outstanding efforts as members of the Chesapeake Bay TMDL Midpoint Assessment team. See additional information here.

For more information on USGS science for the midpoint assessment, contact Joel Blomquist ( or Jeni Keisman (


Publications by USGS authors to support the midpoint assessment include the following:

Ator, S.W., and Denver, J.M., 2015, Understanding nutrients in the Chesapeake Bay watershed and implications for management and restoration—The Eastern Shore (ver. 1.2, June 2015): U.S. Geological Survey Circular 1406, 72 p.,

Ator, S.W., and Garcia, A.M., 2016, Application of SPARROW modeling to understanding contaminant fate and transport from uplands to streams: Journal of the American Water Resources Association, v. 52, no. 3, p. 685–704,

Ator, S.W., García, A.M., Schwarz, G.E., Blomquist, J.D., and Sekellick, A.J., 2019, Toward explaining nitrogen and phosphorus trends in Chesapeake Bay tributaries, 1992–2012: Journal of the American Water Resources Association, 20 p.,

Chanat, J.G., Moyer, D.L., Blomquist, J.D., Hyer, K.E., and Langland, M.J., 2016, Application of a weighted regression model for reporting nutrient and sediment concentrations, fluxes, and trends in concentration and flux for the Chesapeake Bay Nontidal Water-Quality Monitoring Network, results through water year 2012: U.S. Geological Survey Scientific Investigations Report 2015–5133, 76 p.,

Chanat, J.G., and Yang, G., 2018, Exploring drivers of regional water-quality change using differential spatially referenced regression—A pilot study in the Chesapeake Bay watershed: Water Resources Research, v. 54, no. 10, p. 8120–8145,

Fanelli, R.M., Blomquist J.D., and Hirsch, R.M., 2019, Point sources and agricultural practices control spatial-temporal patterns of orthophosphate in tributaries to Chesapeake Bay: Science of the Total Environment, v. 652, p. 422–433,

Hively, W.D., Devereux, O.H., and Keisman, J.L.D., 2018, Agricultural conservation practice implementation in the Chesapeake Bay watershed supported by the U.S. Department of Agriculture: U.S. Geological Survey Data Series 1102, 46 p.,

Hyer, K.E., Denver, J.M., Langland, M.J., Webber, J.S., Böhlke, J.K., Hively, W.D, and Clune, J.W., 2016, Spatial and temporal variation of stream chemistry associated with contrasting geology and land-use patterns in the Chesapeake Bay watershed—Summary of results from Smith Creek, Virginia; Upper Chester River, Maryland; Conewago Creek, Pennsylvania; and Difficult Run, Virginia, 2010–2013: U.S. Geological Survey Scientific Investigations Report 2016–5093, 211 p.,

Keisman, J.L.D., Devereux, O.H., LaMotte, A.E., Sekellick, A.J., and Blomquist, J.D., 2018, Manure and fertilizer inputs to land in the Chesapeake Bay watershed, 1950–2012: U.S. Geological Survey Scientific Investigations Report 2018–5022, 37 p.,

Lefcheck, J.S., Orth, R.J., Dennison, W.C., Wilcox, D.J., Murphy, R.R., Keisman, J., Gurbisz, C., Hannam, M., Landry, J.B., Moore, K.A., Patrick, C.J., Testa, J., Weller, D.E., and Batiuk, R.A., 2018, Long-term nutrient reductions lead to the unprecedented recovery of a temperate coastal region: Proceedings of the National Academy of Sciences of the United States of America, v. 115, no. 14, p. 3658–3662,

Moyer, D.L., and Blomquist, J.D, 2017, Summary of nitrogen, phosphorus, and suspended-sediment loads and trends measured at the Chesapeake Bay Nontidal Network Stations—Water year 2016 update: Reston, Va., U.S. Geological Survey, 15 p.,

Murphy, R.R., Perry, E., Harcum, J., and Keisman, J., 2019, A Generalized Additive Model approach to evaluating water quality—Chesapeake Bay case study: Environmental Modelling & Software, v. 118, p. 1–13,

Sanford, W.E., Plummer, L.N., Casile, G., Busenberg, E., Nelms, D.L., and Schlosser, P., 2017, Using dual-domain advective-transport simulation to reconcile multiple-tracer ages and estimate dual-porosity transport parameters: Water Resources Research, v. 53, no. 6, p. 5002–5016,

Sekellick, A.J., Devereux, O.H., Keisman, J.L.D., Sweeney, J.S., and Blomquist, J.D., 2019, Spatial and temporal patterns of Best Management Practice implementation in the Chesapeake Bay watershed, 1985–2014: U.S. Geological Survey Scientific Investigations Report 2018–5171, 25 p.,

Zhang, Q., and Blomquist, J.D., 2018, Watershed export of fine sediment, organic carbon, and chlorophyll-a to Chesapeake Bay—Spatial and temporal patterns in 1984–2016: Science of the Total Environment, v. 619–620, p. 1066–1078,

Zhang, Q., Hirsch, R.M., and Ball, W.P., 2016, Long-term changes in sediment and nutrient delivery from Conowingo Dam to Chesapeake Bay—Effects of reservoir sedimentation: Environmental Science & Technology, v. 50, no. 4, p. 1877–1886,

Zhang, Q., Murphy, R.R., Tian, R., Forsyth, M.K., Trentacoste, E.M., Keisman, J., and Tango, P.J., 2018, Chesapeake Bay's water quality condition has been recovering—Insights from a multimetric indicator assessment of thirty years of tidal monitoring data: Science of the Total Environment, v. 637–638, p. 1617–1625,


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