Experts forecast Chesapeake Bay dead zone to be near average in summer 2024

Researchers from the Chesapeake Bay Program, University of Maryland Center for Environmental Science, University of Michigan and U.S. Geological Survey announced today that they are predicting this year’s Chesapeake Bay dead zone to be just above the long-term average taken between 1985 and 2023, despite above-average rainfall in spring 2024 that led to relatively high water flows entering the Bay from around the watershed. Experts also noted that the dead zone likely began earlier this year due to warmer-than-normal temperatures throughout the spring as well as weaker winds.

Nitrogen and phosphorus (referred to together as “nutrients”) pollution that runs off from across the Bay watershed spurs 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.

Due to higher-than-average precipitation, stream and river flows to the Chesapeake Bay recorded from January—May 2024 were 63% higher than the previous year and 23% higher than the long-term average. Based on this information, researchers estimate that the total annual hypoxic volume for the Bay in 2024 will be just 4% higher than the historic long-term average.

Additionally, from January—May 2024, 131 million pounds of nitrogen entered the Bay as measured at the River Input Monitoring (RIM) stations located on the Chesapeake’s nine largest tributaries, representing about 78% of the total area of the watershed. The amount of nitrogen entering the Bay in 2024 was approximately 77% higher than last year, when below-average rainfall brought about 74 million pounds of nitrogen into the Chesapeake. However, the amount of nitrogen pollution entering the Bay in 2024 is roughly equal to the long-term average (1985-2023).

In the areas of the Bay not monitored by the RIM stations, additional pollution is reported from wastewater treatment plants and included in the forecast. In 2024, 4.7 million pounds of nitrogen were recorded flowing into the Chesapeake between January and May, which is less than the 5.2 million pounds recorded in 2023 and the 5.7 million pounds recorded in 2022.

The slightly above-average estimated hypoxic volume following a season of relatively high stream and river flows indicate that management efforts to keep nutrient runoff out of the Bay watershed is having the desired effect.

In the fall of 2024, researchers will follow up on this forecast with a Bay-wide assessment of the dead zone size and duration.

Facts

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—October, depending on weather conditions, to track summer hypoxia in the Bay. Water quality results from each monitoring cruise can be accessed through the Eyes on the Bay website for the Maryland portion of the Bay and the Virginia Estuarine and Coastal Observation System (VECOS) website for the Virginia portion. The U.S. Geological Survey monitors river flow, nutrients and sediment entering the Bay at the RIM stations located where non-tidal and tidal waters meet on the nine largest tributaries flowing into the Bay.

A statistical 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 RIM stations and every wastewater treatment plant that is located in the watershed area 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 RIM stations along the Appomattox, Choptank, James, Mattaponi, Pamunkey, Patuxent, Potomac, Rappahannock and Susquehanna rivers. 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.

This model and forecast is supported by the most up-to-date river flow and nutrient pollutants entering the Bay 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 as well as an annual assessment of hypoxia in the Chesapeake.

Funding for the models has come from the National Oceanic and Atmospheric Administration and data used by the models are provided by the U.S. Geological Survey, Maryland Department of Natural Resources, Virginia Department of Environmental Quality and Chesapeake Bay Program.

Issues

The dead zone is an area of little to no oxygen that forms when excess nutrients enter the water through polluted runoff and feed naturally-occurring algae. This drives the growth of algae blooms, which eventually die and decompose, removing oxygen from the surrounding waters faster than it can be replenished. In warmer months, the Bay separates into layers of warmer, fresher water near the surface and colder, saltier water down deep. The sinking algae collect in the bottom layer as they decompose, and the layers do not easily mix. Together, this situation creates low-oxygen—or hypoxic—conditions in deeper waters of the Bay. Plant and animal life are often unable to survive in this environment, which is why the area is sometimes referred to as a “dead zone”.

Pollution reducing practices used in backyards, cities and on farms can reduce the flow of nutrients into waterways. Management actions taken to decrease pollution from point sources (e.g., wastewater treatment plants) may immediately show detectable pollution changes, but the implementation of best management practices for non-point sources often results in a lag before their impact on improving water quality can be detected.

Weather conditions also play a role in the size and duration of the annual dead zone. Heavy rainfall can lead to strong river flows entering the Bay, which carries along increased amounts of nutrient and sediment pollution. Above average spring freshwater flows to the Bay, along with hot temperatures and weak winds in the summer, provide the ideal conditions for the dead zone to grow larger and last longer.

Quotes

“Forecasts for average summer hypoxia despite above average precipitation and temperatures continues to demonstrate the success of nutrient management efforts.”

• Dr. Marjy Friedrichs, Research Professor, Virginia Institute of Marine Science

“Dissolved oxygen levels are a key measure of Bay health, as sufficient oxygen is needed to support vital fish, crab and oyster populations, as well as a healthy ecosystem. Bay monitoring data collected by the Chesapeake Bay Program’s state and federal partners informs us of habitat conditions, advances our knowledge of Bay ecology and measures the progress of our efforts toward restoration and nutrient reduction goals.”

• Mark Trice, Chief, Water Quality Informatics Program, Resource Assessment Service, Department of Natural Resources, State of Maryland

“The accuracy of the forecasting is supported by our growing scientific understanding of how the Bay works. The long-term water quality monitoring program continues to provide high-quality data used to inform targeting of management actions, improve our models and effectively inform assessments of management progress showing the Bay’s responsiveness to nutrient management actions. “

• Dr. Peter Tango, Monitoring Coordinator, U.S. Geological Survey at the Chesapeake Bay Program

“This forecast of an average year for summer hypoxia is further good news, following on the last few years of near or below average amounts of hypoxia in the Chesapeake. Let’s hope weather during the summer helps the Chesapeake realize this forecast.”

• Aaron Bever, Senior Managing Scientist, Anchor QEA, Inc.