Recent Progress: Increase
Analysis of tidal and nontidal water quality monitoring data are showing mixed results across the suite of key indicators that assess whether management actions are having the expected reduction in pollutant loads and corresponding improvements in water quality. Funding has been identified to address long-term funding shortfalls for the water quality monitoring program; however, additional funding is needed. Progress is increasing with new reports and scientific journal publications focused on Bay health improvements and watershed factors affecting trends in nutrient and sediment pollution. The 2024 release of the Chesapeake Bay Total Maximum Daily Load (TMDL) indicator, which uses a combination of monitoring and modeling data to estimate the progress of nitrogen and phosphorus load reductions in response to implemented management practices, also constitutes progress in assessing the effects of management actions on water quality.
Outlook: On Course
This outcome is on course as efforts continue to support the monitoring and annual reporting of water quality standards attainment and key trends in nutrients and sediment in the watershed. These efforts include sustaining the operation of 123 stations as a nontidal water quality monitoring network, including the nine RIM sites at major rivers that provide necessary data to assess the outcome’s indicators. The Scientific, Technical Assessment & Reporting (STAR) team conducted a monitoring review at the request of the Principals’ Staff Committee to identify resource needs for sustaining and expanding this network. The Water Quality Goal Implementation team updated grants and interagency agreements to increase funding and address inflation effects to sustain the nontidal network, along with receiving investments for maintenance and growth of the nontidal network.
While this outcome’s progress and outlook are not determined based on the levels of water quality standards attainment or pollution loads, the indicators associated with this outcome have their own set of targets outside of the outcome language. We, therefore, report on trends in standards attainment and pollution loads as part of the outcome goal.
Five indicators are used to assess change over time for measuring the effectiveness of our management actions to improve water quality:
- Water quality standards achievement for dissolved oxygen, water clarity/submerged aquatic vegetation and chlorophyll in tidal waters of the Bay.
- Annual total nutrient and sediment pollution loads delivered to the Bay.
- Long-term trends (i.e., since 1985) in nutrient and sediment pollution loads summarized for sites and river basins in the watershed.
- Short-term (i.e., 10-year) trends in nutrient and sediment pollution loads for sites and river basins in the watershed.
- TMDL progress, combining monitored and modeled data to estimate the progress of nitrogen and phosphorus load reductions in response to implemented management practices.
Water Quality Standards Achievement: Decline
The current Bay-wide attainment score is 28.1%, meaning that 28.1% of tidal waters are estimated to have met water quality standards during the 2019-2021 assessment period. This is a slight decrease from the estimated 28.9% from the 2018-2020 assessment period. The 28.1% score shows a continued decline in the assessment status since the record high of 42.2% was achieved during the 2015-2017 assessment period, in response to unusually wet weather in 2018 that increased nutrient and sediment loads to the Bay. Overall, however, the long-term trend is one of statistically significant improvement from 1985 to 2021.
Periods of improvement and decline in the combined measure of water quality correlate with significant changes in rainfall patterns across the region, the resulting nutrient and sediment loads delivered to the Bay, algal blooms that lead to poor water clarity, and low dissolved oxygen in bay habitats. Experts attribute the recent ongoing decline in the assessment status of the overall indicator to the impacts on water quality resulting from unusually wet weather. Higher than average river flows entering the Bay delivered abundant pollutant loads in 2018 and 2019 (see Pollution Loads and River Flow to the Chesapeake Bay (1990-2021)) and thus the decline in indicator score was anticipated.
The indicator score combines evaluations of dissolved oxygen conditions, water clarity with submerged aquatic vegetation, and chlorophyll a measures. Looking at the individual parameter assessments for 2019-2021, attainment for open water and migratory fish spawning, as well as for nursery dissolved oxygen, increased from the preceding assessment period. However, a major decline in attainment occurred with deep water dissolved oxygen. Shallow water bay grasses and water clarity attainment also declined relative to the preceding period. These declines in attainment values are likely to rebound in the near future as the effects of unusually wet weather in 2018 and 2019 diminish.
The estimated water quality standards attainment of 28.1% for 2019-2021 remains far below the 100% attainment necessary to fully support survival, growth, and reproduction of its living resources. For the Bay and its tidal tributaries to function as a healthy ecosystem and be taken off of the impaired waters listings under Section 303(d) of the Clean Water Act, all applicable water quality criteria must be met simultaneously as defined in the water quality standards of Maryland, Virginia, Delaware and Washington D.C.
Annual Nutrient and Sediment Pollution Loads to the Bay: Decline
During 2021, average river flow to the Bay measured 54.8 billion gallons per day, a 4.5 billion gallon per day increase from 2020, and a 9% increase from the 1985-2021 mean. The corresponding pollutant loads entering the Bay in 2021 were approximately 286 million pounds of nitrogen, 19.9 million pounds of phosphorus, and 17.7 billion pounds of sediment. While all of these are below the 1985-2021 mean, they are increases from 2020 (up 16%, 38%, and 19% respectively), and thus represent a decline from this indicator’s targets.
Nutrient and sediment loads delivered from the watershed into the Bay are one of many factors that influence water quality and are influenced by land use, land management, and river flow. Generally, when the watershed receives more rain and river flows increase, the water carries more sediment and nutrient pollution than usual, as shown by the high flows and pollutant loads to the Bay in 2018 and 2019.
The source of the information of loads and river flow to the Bay includes the loads from the nine River Input Monitoring (RIM) stations in nine major rivers entering the Bay, point source discharges into tidal waters, and an estimate of nonpoint source below the RIM stations from the Chesapeake Bay Program’s Watershed Model, CAST-2019.
Nutrient and Sediment Pollution Trends for the Nine Major Rivers Entering the Bay: Mixed
The nutrient and sediment load trends of the nine major rivers entering the Bay are updated every year based on data from the corresponding nine RIM stations. Together, these stations reflect the nutrient and sediment loads delivered to the Bay from 78 percent of its watershed.
In July 2021, the USGS released its analysis of the long-term (1985 to 2021) and 10-year (2012 to 2021) trends in nutrient and sediment loads at nine RIM stations. These nutrient and sediment load trends are summarized in the table below. The trend qualifiers “improving,” “degrading,” and “no trend” are based on Chesapeake Bay restoration goals for water quality attainment (i.e., reduction of nutrients and sediments) in the Bay. “No trend” indicates that an “improving” or “degrading” trend is about as likely to exist as it is not, based on the trend estimation approach.
Pollution Loads by Monitoring Station
In summary, over the long term, trends in nitrogen have improved at six stations including the four largest rivers (Susquehanna, Potomac, James, and Rappahannock), along with the Patuxent and Mattaponi, degraded at two stations (Choptank and Appomattox) and showed no discernable trend at one station (Pamunkey). Phosphorus loads showed long-term improvements at three stations (Patuxent, Potomac, and James), degrading conditions at four stations (Choptank, Rappahannock, Pamunkey, and Appomattox), and no discernable trend at two stations (Susquehanna and Mattaponi). Sediment loads improved at three stations and (Choptank, Patuxent, and Potomac), degraded at four stations (Susquehanna, Rappahannock, Pamunkey, and Appomattox), and showed no discernable trend at two stations (James and Mattaponi).
Trends in Nutrient and Sediment Pollution Loads in the Watershed: Mixed
Ten-year trends in nutrient and sediment loads are published for the nontidal network stations biennially. According to the latest assessment, nitrogen load trends were analyzed for 89 nontidal network sites, while suspended sediment and phosphorus are analyzed at 70 stations. For nitrogen, results between 2011-2020 showed 38% of the 89 sites had improving trends but 42% had degrading trends and the remainder had no trend. For phosphorus, 44% of the sites had improving trends, 23% had degrading trends, and the remainder had no trend. For suspended sediment, 19% of stations had improving trends, 46% had degrading trends, and the remainder had no trend. These results are used to assess the water quality response to nutrient and sediment restoration efforts and target where future restoration can be most effective. Additional information can be found here.
Chesapeake Bay Total Maximum Daily Load Indicator: Improvement
The TMDL indicator combines monitored and modeled data to estimate the progress of nitrogen and phosphorus annual loading rate reductions (millions of pounds per year) in response to implemented management practices. The indicator addresses the following questions:
- What reductions have been observed in the monitoring data?
- What reductions are expected from past management actions but have not been observed due known lags in implementation action and environmental response?
- What reductions are needed from planned future management actions?
- What reductions are expected but not yet observed in monitoring?
To provide quantitative answers to these questions, this indicator leverages modeling data from the Chesapeake Assessment Scenario Tool (CAST) along with monitoring data, including river discharge and water quality measurements, wastewater loads and atmospheric deposition (only nitrogen) to tidal waters. CAST integrates knowledge of land use, nutrient inputs and watershed processes to estimate load reductions in response to implemented management practices. However, the expected reductions often differ from the reductions observed in the rivers due to factors including uncertainty in CAST, uncertainty in monitored trends, natural lags between implementation of management practices and eventual achievement of water quality improvements, as well as the impacts of climate change and infill of Conowingo Reservoir. By quantifying the effects of some of these factors – lag times, climate change and infill of Conowingo Reservoir – this indicator can help bridge the gap between the monitored reduction and model-estimated reduction.
Also, a comprehensive effort has been made to compile and analyze data sets for the watersheds of the Chesapeake Bay Nontidal Network (NTN) stations, including 83 stations for nitrogen and 66 stations each for phosphorus and sediment. These station-level results, available through the Monitored and Expected Total Reduction Indicator for the Chesapeake (METRIC) tool, can help resource managers gauge expectations on the trajectory and pace of reduction progress at a localized scale.
The TMDL indicator uses 1995 as the baseline year because it marks the end of the 1993-1995 critical period used for assessing attainment of water quality standards in the TMDL. It divides the total annual loading rate reductions required to meet the TMDL planning targets into categories:
- Implemented and Realized refers to reductions due to actions in the Watershed Implementation Plans (WIPs) that have been both estimated in the models and seen in monitoring data.
- Implemented but Lagged refers to nitrogen and phosphorus reductions that are expected in the future due to actions that have already taken place, but not yet been realized due to natural lag times.
- RIM Expected but Not Seen refers to reductions in the RIM watershed due to actions in the WIPs that are estimated to have occurred in the models but have not been seen in the monitoring data.
- Future Implementation refers to expected nitrogen and phosphorus reductions planned in the WIPs, but not yet reported as implemented.
- WIP Shortfall refers to the difference between the nitrogen and phosphorus reduction goals under the Bay TMDL and the reductions the jurisdictions planned in their WIPs.
- Climate Adjustment refers to the additional reduction amount required to offset the impact of climate change, including increased delivery of nitrogen and phosphorus to the Bay and the decreased ability of the Bay to absorb nutrients while maintaining water quality standards.
- Conowingo Adjustment refers to the additional reduction amount required to offset the filling of the Conowingo reservoir that increased the throughput of nitrogen and phosphorus.
- Tidal Deposition Reduction Realized refers to observed nitrogen reductions in atmospheric deposition to tidal waters.
- Tidal Deposition Reduction Unimplemented refers to expected future nitrogen reductions in atmospheric deposition to tidal waters.
For nitrogen, a total reduction of the annual loading rate by 145.07 million pounds is required compared to 1995 to achieve the TMDL planning target. The TMDL planning target includes a 10.33 million pound per year increase to account for the increased delivery due to the Conowingo Reservoir infill (+6.01 million pounds) and climate change (+4.32 million pounds). As of 2021, implemented management actions are yielding annual load reductions of 77.64 million pounds per year (i.e., implemented and observed in the monitoring data). Implemented management actions are expected to yield additional annual load reductions of 13.92 million pounds per year, but these reductions have not yet been realized in the monitoring data due to natural lags between nutrient application and the subsequent delivery to streams. In addition, annual load reductions of 42.26 million pounds per year are expected from planned future implementation of management actions. The last total reduction of the annual loading rate required to meet the target is 7.92 million pounds per year from tidal atmospheric deposition, of which 6.50 million pounds per year have been realized in 2021.
From 1995 to 2021, the reduction of nitrogen loading rates has been trending toward meeting the TMDL planning target. Specifically, the category “implemented and realized” and “tidal deposition reduction realized” have increased over time, whereas the category “future implementation” has decreased over time as more of the planned actions to meet the TMDL planning target are completed.
For phosphorus, a total reduction of the annual loading rate by 9.31 million pounds is required compared to 1995 to achieve the TMDL planning target. The TMDL planning target includes a 0.78 million pounds per year increase to account for the increased delivery due to Conowingo Reservoir infill (+0.26 million pounds) and climate change (+0.52 million pounds). In 2021, implemented management actions are yielding annual load reductions of 2.95 million pounds per year (i.e., implemented and observed in the monitoring data). Implemented management actions are expected to yield additional annual load reductions of 1.85 million pounds per year, but these reductions have not yet been realized in the monitoring data due to natural lags. In addition, annual load reductions of 1.66 million pounds per year are expected from planned future implementation of management actions. Lastly, annual load reductions of 2.07 million pounds per year have been estimated by the model while accounting for lag times, but have not been observed in the monitoring data, which represents an unknown response gap and implies unknown sources and/or processes that may need to be examined and incorporated in the future refinements of CAST.
Like nitrogen, the reduction of phosphorus loading rates since 1995 has been trending toward meeting the TMDL planning target. Specifically, the category “implemented and realized” has increased over time, whereas the category “future implementation” has decreased over time as more of the planned actions to meet the TMDL planning target are completed.
There are multiple factors affecting attainment of water quality standards and response of nutrients to management actions in the watershed. The Chesapeake Bay Program water quality standards indicator showed a fourth consecutive year of degrading results, which is influenced by the amount of pollution washed into the Bay each year as well as management efforts to control nutrient pollution. However, the indicator showed an improving trend in the long term since the monitoring began 1985. There are mixed results in the watershed response to management actions based on the monitoring sites located throughout the watershed. Studies are improving the understanding of the factors affecting water quality response to nutrient reduction efforts in the watershed. Recent studies identified water quality improvements resulting from point source upgrades and reduced air deposition of nitrogen, but management challenges are recognized in addressing nonpoint sources of nutrients delivered to rivers and the Bay from agricultural and urban lands.
To achieve the Water Quality Standards Attainment and Monitoring outcome, participating partners have committed to:
- Analyzing water quality trends in the Chesapeake Bay and its watershed.
- Explaining the factors affecting water quality trends in the Bay and its watershed.
- Enhancing Chesapeake Bay Program models using our improved understanding of water quality trends.
- Informing management strategies to improve water quality.
- Adhering to the TMDL Accountability Framework.
- Investing in enhanced monitoring efforts in the Bay and its watershed.
Assessing progress toward achieving the outcome will occur through analysis of data collected from monitoring networks that track river flow, nitrogen, phosphorus and sediment in the watershed; air deposition of nitrogen and phosphorus; water quality conditions in tidal waters relative to established water quality standards; conditions of tidal habitats; changes in climate and the health of living resources.
Logic & Action Plan
Chesapeake Bay Program partners have committed to taking a series of specific actions that will support the management approaches listed above.
- Leading Best Management Practice (BMP) Verification.
- Supporting continued BMP implementation, tracking and reporting across all source sectors.
- Upgrading and enhancing wastewater treatment plants and septic systems.
- Guiding the development of jurisdictions’ trading and offset programs.
- Providing permit and enforcement oversight across all sectors.
- Improving assessment of temporal and regional patterns in nontidal waters and water quality criteria attainment in tidal waters.
- Coordinating the Chesapeake Bay Program Tidal and Nontidal Water Quality Monitoring Network.
- Addressing gaps in monitoring programs.
- Developing and applying new approaches for quantifying and explaining water quality trends in tidal waters.
- Explaining the drivers of water quality trends in the watershed.
- Communicating the factors affecting trends and understanding responses to management practices.
- Contributing to understanding of co-benefits of water-quality restoration to selected habitats and living resources.
- Conducted field investigation of factors affecting stream condition in southeastern Pennsylvania.
- Established continuous (measurements on an hourly basis) water quality monitoring in a nontidal network of nine major RIM Program sites.
- Deployed three water quality sensors in Chesapeake Bay for the summer season.
- Developed a two-year nutrient limitation project in the Bay.
- Developed a multiyear satellite-monitoring protocol development and regional test case project.
- Published studies on management results in nutrient and sediment reduction efforts and water quality impacts of climate change, land use and population growth.
- Conducted a field investigation of factors affecting stream conditions on the Eastern Shore of Maryland.
- Created a project team to create a tool that tracks water quality over space and time.
- Created the Hypoxia Collaborative Team, focused on enhanced high temporal frequency water quality monitoring in the Bay.
- Completed the 2021-2022 Monitoring Review, at the Principal’s Staff Committee request, to enhance core Bay Program monitoring networks.
- Successfully deployed seasonal testing for new investment in high temporal frequency water quality monitoring sensors in deep waters.
- Published studies on various topics related to trends in nutrient and nitrogen in the Bay watershed as well as impacts on hypoxia (see the Analysis & Methods document for publication details).
- Conducted field investigation of factors affecting stream conditions in the Shenandoah Valley.
- Published the STAC Workshop Report on satellite monitoring opportunities for submerged aquatic vegetation in Chesapeake Bay and a study on nutrient limitation patterns in the mainstem of the Bay.
- Developed and awarded new six-year funding for the EPA-funded Community Science program through the Chesapeake Monitoring Cooperative.
The Water Quality Goal Implementation Team leads the effort to achieve this outcome. It works in partnership with the Scientific, Technical Assessment and Reporting Team.
Participating partners include:
- State of Delaware
- State of Maryland
- State of New York
- Commonwealth of Pennsylvania
- Commonwealth of Virginia
- State of West Virginia
- District of Columbia
- Chesapeake Bay Commission
- Natural Resources Conservation Service (U.S. Department of Agriculture)
- U.S. Army Corps of Engineers
- U.S. Department of Defense
- U.S. Department of Homeland Security
- U.S. Environmental Protection Agency
- U.S. Geological Survey