Annapolis, MD—Researchers from the Chesapeake Bay Program, the University of Maryland Center for Environmental Science, the University of Michigan, and the U.S. Geological Survey announced today that they are predicting this summer’s dead zone to be smaller than the long-term average taken between 1985 and 2021. This is due to the below-average amount of water entering the Bay from the watershed’s tributaries this past spring, as well as decreased nutrient and sediment pollution from jurisdictions within the watershed.
“The fact that hypoxia in the Bay is once again forecasted to be lower than the long-term average is clearly a positive sign for Bay restoration. When we consider that hypoxia is continually being exacerbated by marine heat waves and warmer Bay waters, this recent success of our nutrient management efforts is even more impressive,” says Dr. Marjy Friedrichs, Research Professor, Virginia Institute of Marine Science.
Areas of low oxygen, also known as hypoxic regions, are often considered to have dissolved oxygen concentrations less than 2 mg/L (milligrams per liter) and are primarily caused by excess nutrient pollution flowing into the Bay. These regions can result in the loss of habitat for various types of marine life, including fish, blue crabs, oysters, and underwater grasses.
“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. The forecast brings attention to our continued progress towards the implementation of nutrient reduction strategies to improve oxygen conditions. The Maryland Department of Natural Resources looks forward to working with our Chesapeake Bay Program partners to monitor and report on hypoxic levels throughout the summer,” said Mark Trice, Water Quality Program Manager, Department of Natural Resources, State of Maryland.
Compared to the previous 36 years, this year’s Chesapeake Bay hypoxic volume, or “dead zone”, is predicted to be 13% lower than average. This is similar to last year when the hypoxic volume was predicted to be 14% lower than the average. For the past three years, the dead zone has been forecasted to be lower than the long-term average—and in all cases, the forecasts proved accurate when compared to data collected throughout the summer.
In 2022, summer hypoxia also began later than it had in several previous years. In 2021, 2019, 2018, and 2017, hypoxic conditions began in mid to late May, but in 2022, hypoxia was not apparent in the Bay until early June. This late start is largely due to cooler temperatures in May when compared to other years.
The levels of pollution reaching the Chesapeake Bay each year vary due to the amount of spring rainfall impacting river flows, which flush excess nutrients and sediment into the water, as well as conservation practices implemented by jurisdictions to reduce and manage those pollutants.
Although different types of nutrients contribute to the annual dead zone, it is the amount of nitrogen that enters the Bay during spring that is a key driver in how hypoxic conditions can vary from year to year. The amount of nitrogen pollution entering the Bay during spring 2022 was 22% lower than the long-term average and included 102 million pounds of nitrogen recorded at nine river input monitoring stations and 5.7 million pounds from treated wastewater. There was 5% less water flowing into the Bay when compared to the long-term average.
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 for an 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 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, monitors 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 is also included in the model.
Each of these models and forecasts are supported by the most 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, produce daily real-time estimates of hypoxia volume that show levels beginning later in 2022 when compared to recent years, consistent with monitoring data.
A Bay-wide assessment of the 2022 dead zone will be available this fall.