Chesapeake Bay’s dead zone predicted to be 33% smaller than average

July 5, 2023
Below-average rainfall and greater nutrient management have led researchers to predict that the Chesapeake Bay’s 2023 dead zone could be the smallest on record.

Researchers at predicting that the Chesapeake Bay’s 2023 dead zone will be significantly smaller than the long-term average taken between 1982 and 2022, according to a press release by the Chesapeake Bay Program.

Researchers from the Chesapeake Bay Program, the University of Maryland Center for Environmental Science, University of Michigan and U.S. Geological Survey predicted that the dead zone will be 33% smaller than the historic average.

If the forecast proves accurate, it would be the Bay’s smallest dead zone on record.

During the spring and summer, nutrient pollution spurs on the growth of algae blooms, which remove oxygen from the water when they die off. These low-oxygen sections of the Bay, known as hypoxic areas or “dead zones,” can suffocate marine life and shrink the habitat available to fish, crabs and other critters.

The small forecast size is due in large part to a lack of rainfall in the spring of 2023. Researchers working on the forecast calculated that from November 2022 to May 2023, river flows were 20% lower than the average. Less rainfall generally means a lower nutrient load from runoff.

As a result, the amount of nitrogen pollution flowing into the Bay from its watershed was 42% lower than the long-term average during January through May 2023. Scientists calculated 74 million pounds of nitrogen at nine river input monitoring (RIM) stations and 5.2 million pounds were tracked from wastewater treatment plants. This is a decrease from last year when researchers noted 102 million pounds from monitoring stations and 5.7 million pounds from wastewater treatment plants.

While rainfall plays a major role in the size of the dead zone, efforts to limit nutrient pollution in the watershed are also a factor. Maryland, Virginia, Pennsylvania, New York, Delaware, West Virginia and Washington, D.C., all implement best management practices to reduce nutrient runoff that enters the Bay from sources such as wastewater, agriculture and stormwater.

For the past three years, the Bay’s dead zone has been smaller than the long-term average, indicating progress is being made to manage nutrient pollution.

This year, hypoxic conditions began forming in the Bay in mid-May, which is typical. Warm weather increases the likelihood of hypoxic areas forming which is why dead zones tend to last from late May to early fall.

In the fall of 2023, researchers will follow up on the forecast with a Bay-wide assessment of the 2023 dead zone size and duration.

Throughout the year, researchers measure oxygen and nutrient levels as part of the Chesapeake Bay Monitoring Program, a Bay-wide cooperative effort involving watershed jurisdictions, several federal agencies, 10 academic institutions and over 30 scientists.

Among these institutions, the Maryland Department of Natural Resources and Virginia Department of Environmental Quality conduct 8-10 cruises between May and October to track summer hypoxia in the Bay. Results from each monitoring cruise can be accessed through the Eyes on the Bay website for the Maryland portion of the Bay and the VECOS website for the Virginia portion. The U.S. Geological Survey monitors river flow, nutrients and sediment entering the Bay at the nine river input monitoring stations.

A model developed by the University of Michigan has been used since 2007 to forecast the volume of summer hypoxia for the mainstem of the Chesapeake based on the amount of nitrogen pollution flowing into the Bay from nine river monitoring stations and the wastewater treatment plants that are located downstream of them. The hypoxia forecast model, enhanced in 2020, allows for projections of average July, average summer and the total annual hypoxic volume, and is based on the monitoring of nitrogen pollution and river flow at the nine river input monitoring stations.

Together, the U.S. Geological Survey, in partnership with Maryland and Virginia, monitor nitrogen pollution and other important pollutants, flowing into the Bay from 78% of the watershed. In the area not monitored by these stations, additional pollution reported from wastewater treatment plants are also included in the model.

Each of these models and forecasts are supported by up-to-date river flow and nutrient inputs from the U.S. Geological Survey. Scientists at the Virginia Institute of Marine Science, in collaboration with Anchor QEA, use a computer model to produce daily real-time estimates of hypoxia volume that show levels beginning in mid-May 2023.