Water Quality Standards Attainment and Monitoring
Continually improve our capacity to monitor and assess the effects of the management actions being taken to implement the Chesapeake Bay Total Maximum Daily Load (Bay TMDL) and improve water quality. Use monitoring results to report annual progress being made in attaining water quality standards and trends in reducing nutrients and sediment in the watershed.
According to preliminary data, an estimated 42 percent of the Chesapeake Bay and its tidal tributaries met water quality standards during the 2015 to 2017 assessment period: the highest estimate of water quality standards attainment since 1985. This five percent increase from the previous assessment period is due in large part to improvements in water clarity, improvements in chlorophyll a (a measure of algae growth) and improvements in dissolved oxygen in the open waters of the Bay. In 2018, research published in Science of the Total Environment described the “positive and statistically significant trend” observed in this indicator of environmental health. This suggests the Bay—and, in particular, its underwater grass beds—has recovered from damages sustained during Hurricane Irene and Tropical Storm Lee, and is improving not by chance but because of our decades-long effort to reduce nutrient pollution. However, water quality remains far below 100 percent attainment, and 58 percent of tidal waters are considered impaired.
Pollution Loads and River Flow to the Chesapeake Bay (1990-2017)
The Bay and its tidal tributaries can be 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. 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 water quality standards or criteria must be met.
Water quality is influenced by nutrient and sediment loads, which in turn are influenced by land use, land management and river flow. Between October 2016 and September 2017, river flow to the Bay measured a below-average 47.7 billion gallons per day. During this same time period, approximately 240 million pounds of nitrogen, 12.7 million pounds of phosphorus and 4.3 billion pounds of sediment reached the Bay: a 0.4 percent, seven percent and 14 percent decrease from the previous year, respectively. While the amount of nitrogen, phosphorus and sediment entering the Bay from its watershed can change dramatically from year to year—complicating efforts to analyze trends over time—the fact that nutrient and sediment loads decreased between 2016 and 2017 even as river flow increased could be a positive sign of progress toward controlling pollution.
In 2018, the USGS released its analysis of the long-term (1985 to 2017) and short-term (2008 to 2017) 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 78 percent of its watershed. Long-term and short-term nutrient and sediment trends are summarized in the table below. 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).
Over the long term, trends in both nitrogen and phosphorus loads have improved at three monitoring sites (including the James, Patuxent and Potomac rivers) and degraded at one (the Pamunkey). Seven sites show long-term improvements in nitrogen loads, while three show long-term improvements in phosphorus loads. Three sites (including the Choptank, Patuxent and Potomac rivers) show long-term improvements in sediment loads.
Computer-simulated nitrogen, phosphorus and sediment loads (generated using the Chesapeake Bay Program’s Watershed Model (Phase 5.3.2) and wastewater discharge data reported by watershed jurisdictions and calibrated using monitoring data) are used to track progress toward the 2017 and 2025 Watershed Implementation Plans (WIPs) outcome.
Enhancing Chesapeake Bay Program models using our improved understanding of water quality trends;
Informing management strategies to improve water quality;
Conducting a 2017 Midpoint Assessment; and
Adhering to the TMDL Accountability Framework.
Monitoring progress toward the outcome will occur through model simulations of pollution-reducing practices and 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. Monitoring and assessing progress toward the outcome will also occur through the 2017 Midpoint Assessment, which will review our progress, enhance our modeling tools and address emerging issues like climate change.
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 May of 2018.