Researchers from the Chesapeake Bay Program, University of Maryland Center for Environmental Science, University of Michigan, and U.S. Geological Survey announced today that the 2024 Chesapeake Bay dead zone is predicted to be slightly above the long-term average from 1985 to 2023. This forecast comes despite above-average spring rainfall, which led to high water flows into the Bay from the surrounding watershed.
Overview of the Dead Zone
Nitrogen and phosphorus pollution from the Bay watershed promotes algae blooms, which deplete oxygen from the water when they decompose. These low-oxygen areas, known as hypoxic zones or dead zones, can suffocate marine life, reducing habitat availability for fish, crabs, and other species.
Rainfall and Water Flows
Between January and May 2024, stream and river flows into the Chesapeake Bay were 63% higher than the previous year and 23% higher than the long-term average. This year's higher-than-average precipitation resulted in an estimated total annual hypoxic volume that is just 4% higher than the historic average.
Nitrogen Pollution
From January to May 2024, 131 million pounds of nitrogen entered the Bay, as recorded at River Input Monitoring (RIM) stations on the nine largest tributaries. This amount is 77% higher than the previous year, which saw below-average rainfall and only 74 million pounds of nitrogen. However, the nitrogen pollution in 2024 is roughly equal to the long-term average from 1985 to 2023.
Additional Pollution Sources
Wastewater treatment plants also contribute to the nitrogen levels. In 2024, these plants added 4.7 million pounds of nitrogen to the Bay between January and May, less than the 5.2 million pounds in 2023 and 5.7 million pounds in 2022.
Management Efforts and Future Assessments
The relatively stable hypoxic volume, despite increased stream and river flows, indicates effective nutrient management efforts in the Bay watershed. Researchers plan to follow up with a comprehensive Bay-wide assessment of the dead zone's size and duration in fall 2024.
Monitoring and Research
The Chesapeake Bay Monitoring Program involves several watershed jurisdictions, federal agencies, academic institutions, and over 30 scientists. The Maryland Department of Natural Resources and Virginia Department of Environmental Quality conduct multiple monitoring cruises between May and October to track summer hypoxia. Water quality results are accessible through the Eyes on the Bay and Virginia Estuarine and Coastal Observation System (VECOS) websites.
The University of Michigan has used a statistical model since 2007 to forecast summer hypoxia volumes. This model, enhanced in 2020, uses data from RIM stations and wastewater treatment plants to project average July, summer, and total annual hypoxic volumes. The U.S. Geological Survey, in partnership with Maryland and Virginia, monitors nitrogen and other pollutants entering the Bay from 78% of the watershed.
Model and Forecast Support
The National Oceanic and Atmospheric Administration funds the hypoxia forecast model, which uses data from the U.S. Geological Survey, Maryland Department of Natural Resources, Virginia Department of Environmental Quality, and Chesapeake Bay Program. The Virginia Institute of Marine Science and Anchor QEA produce daily real-time hypoxia estimates and annual assessments using a computer model.
Issues and Impacts
Dead zones form when excess nutrients feed algae, which deplete oxygen as they decompose. The Bay's water layers do not mix easily, leading to hypoxic conditions in deeper waters, where plant and animal life cannot survive. Pollution reduction practices in urban, suburban, and agricultural areas help mitigate nutrient runoff.
Weather Influence
Heavy rainfall increases nutrient and sediment pollution entering the Bay, while hot temperatures and weak winds during summer exacerbate dead zone conditions. The forecast of average summer hypoxia despite above-average precipitation and temperatures highlights the success of nutrient management efforts.
"Forecasts for average summer hypoxia despite above-average precipitation and temperatures continue to demonstrate the success of nutrient management efforts," said Dr. Marjy Friedrichs, Research Professor at Virginia Institute of Marine Science.
Mark Trice, Chief of the Water Quality Informatics Program at the Maryland Department of Natural Resources, emphasized the importance of dissolved oxygen levels for Bay health, supporting vital fish, crab, and oyster populations. He noted that monitoring data informs habitat conditions and measures restoration progress.
Dr. Peter Tango, Monitoring Coordinator at the U.S. Geological Survey, highlighted the value of long-term water quality monitoring in targeting management actions and improving models. He emphasized the Bay's responsiveness to nutrient management.
Aaron Bever, Senior Managing Scientist at Anchor QEA, called the forecast of an average year for summer hypoxia good news, following recent years of near or below average hypoxia levels.
While the Chesapeake Bay dead zone is expected to be slightly above average in 2024, the forecast reflects ongoing progress in nutrient management. Researchers and policymakers remain committed to improving the Bay's water quality and health through sustained monitoring and effective management practices.
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