Bay Dead Zone Shrinks

This year’s Chesapeake Bay “dead zone” was the 10th-smallest observed since 1985, according to findings released today by the Chesapeake Bay Program and its partners, including the University of Michigan.

The annual Chesapeake Bay dead zone is an area of low oxygen that forms in deep waters when excess nutrients, including both nitrogen and phosphorus, enter the water through polluted runoff and feed naturally occurring algae.

The findings announced today are on par with the forecast that researchers released in June, which estimated a 13% smaller-than-average dead zone due to lower amounts of winter and spring precipitation, which brought fewer nutrient and sediment pollutants into the bay from the surrounding watershed.

The annual forecast is developed by the University of Michigan and informed by data from the Chesapeake Bay Program, Maryland Department of Natural Resources, Virginia Department of Environmental Quality and U.S. Geological Survey.

“The fact that our June 2022 forecast and the measured size of this year’s dead zone are in close agreement lends credibility to our models,” said University of Michigan aquatic ecologist Don Scavia, who leads one of several research teams partnering with the federal government on the annual forecast.

Findings about the size of the 2022 Chesapeake Bay dead zone are based on research by the Virginia Institute of Marine Science and the Maryland Department of Natural Resources. The VIMS 2022 Chesapeake Bay Dead Zone Report Card and the MDNR 2022 Final Hypoxia Report both found this year’s dead zone to be the 10th-smallest observed since 1985.

The Maryland Department of Natural Resources, in conjunction with Old Dominion University, conducted nine water quality sampling 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.

Additionally, scientists at the Virginia Institute of Marine Science, in collaboration with Anchor QEA, use a computer model combined with local weather information, as well as regular estimates of how many nutrients are entering the bay from the surrounding watershed, to produce daily, real-time estimates of dead zone size throughout the summer.

The Chesapeake Bay Environmental Forecast System also provides daily estimates of other environmental conditions throughout the bay, including water temperature, salinity levels and acidification.

The U.S. Geological Survey reported that Water Year 2022 (Oct. 1, 2021, through Sept. 30, 2022) had river flows entering the Chesapeake Bay averaging 73,000 cubic feet per second, which is below the long-term water-year average of 79,000 cfs.

Rivers carry nutrients that drive the growth of algae blooms in the bay. The algae eventually die and decompose, removing oxygen from the surrounding waters faster than it can be replenished. This creates low-oxygen—or hypoxic—conditions at the bottom of the bay: the dead zone.

Cool and windy conditions in spring 2022 resulted in hypoxia first appearing in June, which is later than average. This year’s dead zone then grew to a more typical size through mid-August, due to moderate river flows, temperatures and winds throughout the region. Hypoxia was still observed in mid-September, but cooler temperatures and stronger winds allowed it to dissipate soon thereafter.

In fact, Virginia Institute of Marine Science models found that the duration of the 2022 dead zone was likely shorter than 95% of any since 1985.