Recent Progress: Decrease
An estimated 33.1% of the Chesapeake Bay and its tidal tributaries met water quality standards during the 2017-2019 assessment period. This score is lower than the previous score of 38% received during the 2016-2018 assessment period and marks a consecutive decline in the assessment status since the record high of 42.2% achieved during the 2015-2017 assessment period.
Periods of improvement and decline in water quality correlate with significant climatic events in the region. Experts attribute the consecutive decline in the assessment status of the overall indicator for the periods 2016-2018 and 2017-2019 to unusually wet weather in 2018 and 2019. The 2017-2019 assessment saw specific declines in deep water and deep channel habitat for dissolved oxygen, and in chlorophyll a, which may have been a reflection of short-term weather fluctuations and associated river inputs that produced conditions that contributed to the lower assessment status.
Despite the record high river flow to the Bay in 2019, open water and deep channel habitats have showed significant improvements for dissolved oxygen attainment as well as water clarity and submerged aquatic vegetation attainment between 1985-1987 and 2017-2019, which may be an indication of increasing resilience in the bay ecosystem over the long term. Nonetheless, water quality estimates remain far below the 100% attainment necessary to fully support survival, growth and reproduction of its living resources, and 67% of tidal waters are estimated to be impaired during the 2017-2019 assessment period.
Outlook: Off Course
The Water Quality Standards Attainment and Monitoring Outcome is currently off course. Tidal monitoring has been recognized as insufficient to fully assess water quality standards since the criteria were established in 2003. Data collection in the Bay has declined each year. Nontidal monitoring has maintained a network of about 125 sites across the watershed for the last decade. However, annual funding shortfalls and a major monitoring gap in the Coastal Plan region, limits assessments of nitrogen and phosphorus pollution entering tidal waters.
The Bay and its tidal tributaries have been divided into 92 segments. Each of these segments contains up to five “designated uses” (also known as aquatic habitats), including deep channel, deep water, open water, shallow water and migratory fish spawning-and-nursery habitat. Each of these designated uses has its own set of criteria for dissolved oxygen, water clarity/underwater grasses and chlorophyll a (a measure of algae growth), which are designed to protect those uses. If the Bay and its tidal tributaries are 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 for each segment must be met simultaneously as defined in MD, VA and DE State’s and Washington DC water quality standards.
Bay water quality is influenced by a variety of factors including nutrient and sediment loads delivered from the watershed into the bay. Nutrient and sediment loads are influenced by land use, land management, and river flow. Between October 2018 and September 2019, a record river flow to the Bay was recorded for the period 1938 to the present. River flow to the Bay measured 84.5 billion gallons per day, which is 60% higher than the 1985-2019 average and almost a 20% increase from the previous year. Generally, when the watershed receives more rain and river flows increase, the water carries more sediment and nutrient pollution than usual. Greater flows increase pollution loads received by the Bay. Between October 2018 and September 2019 approximately 491 million pounds of nitrogen, 34.8 million pounds of phosphorus, and 26.6 billion pounds of sediment reached the Bay, which are 40%, 52%, and 25% higher than the 1985-2019 average, respectively. For the short term, nitrogen loads to the Bay were much higher than last year, which experts attribute mainly to the higher river flow. By contrast, phosphorus and sediment loads both decreased from the previous year, despite the increase in river flow. Experts suggest the decline in phosphorus and sediment could be a result of management actions on controlling nonpoint source pollution in the Bay watershed.
Efforts to assess reduction progress over time are complicated by the annual variation in nitrogen, phosphorus, and sediment loads delivered to the Bay from the watershed. After accounting for annual variability using established procedures described in the methods document, the nitrogen and phosphorus total loads to the Bay declined overall between 1985-2019, with sediment increasing during the same period, but none of these trends were shown to be significant. However, statistically significant reductions were achieved in the point source loads of all three components (i.e., nitrogen, phosphorus, and sediment), which are a result of substantial efforts to reduce loads from wastewater treatment facilities by implementing advanced treatment technologies and a phosphorus detergent ban. In addition, there was a statistically significant decline in atmospheric deposition of nitrogen to the tidal waters between 1985-2019, pointing to the unintended water-quality benefits from the Clean Air Act implementation.
Several changes in assessment methodology for determining the pollution loads to the bay occurred during the 2017-2019 assessment period. First, the starting year of the reported loads was extended back from 1990 to 1985 because loads from all relevant sources have been made available for water years starting with 1985. In addition, the Chesapeake Bay Program’s Watershed Model, CAST-2019, was used to replace CAST-2017 as the data source. For detailed information on the Chesapeake Bay Watershed Model, please visit the Chesapeake Assessment Scenario Tool (CAST) website.
In 2020, the USGS released its analysis of the long-term (1985 to 2019) and short-term (2009 to 2019) trends in nutrient and sediment loads at nine River Input Monitoring (RIM) stations. Together, these stations reflect the nutrient and sediment loads delivered to the Bay from 9 major tributaries representing 78 percent of its watershed. Long-term and short-term nutrient and sediment load trends are summarized in the table below. In the figure for pollution loads, an upward arrow indicates improving conditions (and downward trends in nutrient or sediment loads), while a downward arrow indicates degrading conditions (and upward trends in nutrient or sediment loads).
Pollution Loads by Monitoring Station
While the table describes the short-term and long-term trends at each monitoring station individually, in summary, over the long term, trends in nitrogen have improved at five stations including the four largest rivers and degraded at three stations. Phosphorus and sediment loads showed long-term improvements at three RIM stations across four different rivers. The remaining stations showed degraded trends or no change. Over the short term, nitrogen loads improved at three stations and degraded at three stations. Phosphorus loads improved at five stations, including the three largest rivers, and degraded at two stations. Sediment loads improved at four stations and degraded at three stations. The remaining stations showed no change in conditions.
Computer-simulated nitrogen, phosphorus and sediment loads (generated using the Chesapeake Bay Program’s Watershed Model plus wastewater discharge data reported by watershed jurisdictions and calibrated using monitoring data) are also used to track progress toward the 2025 Watershed Implementation Plans (WIPs) outcome.
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; and
- Adhering to the TMDL Accountability Framework.
Monitoring progress toward achieving the outcome will occur through model simulations of pollution-reducing practices and analysis of data collected from monitoring networks that track river flow; nitrogen, phosphorus and sediment in the watershed; air deposition; conditions in tidal waters relative to established water quality standards; conditions of tidal habitats; and the health of living resources.
As part of the Chesapeake Bay Program’s partnership-wide implementation of adaptive management, progress toward this outcome was reviewed and discussed by the Management Board in August of 2020. It will be reviewed and discussed by the Management Board again in August 2022.
Logic & Action Plan
Chesapeake Bay Program partners have committed to taking a series of specific actions that will support the management approaches listed above.
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