Chesapeake Bay's 'Dead Zone' Is Smallest On Record


The Maryland Department of Natural Resources said this year’s dead zone, or area with low oxygen, was the smallest on record in the Cheaspeake Bay. The bay is pictured above in Baltimore County. (Jacob Baumgart/Patch)

Patch manager Deb Belt wrote this story.

MARYLAND — The area of low oxygen, or dead zone, in the Chesapeake Bay is the smallest it's been since experts began tracking the condition 39 years ago. That's good news for fish, crab and oyster habitat, said a new report by the Maryland Department of Natural Resources.

Water monitoring data collected by the DNR and Old Dominion University show that dissolved oxygen conditions in the Chesapeake Bay mainstem of Maryland and Virginia were much better than average for May through October 2023.

The size of the dead zone averaged 0.52 cubic miles this summer, compared to the historical average (1985-2022) of 0.97 cubic miles.

“This year’s Chesapeake Bay dissolved oxygen conditions are the best on record, and it is encouraging news,” said Mark Trice, program chief of water quality informatics with Maryland DNR’s Resource Assessment Service, in a news release. “These results illustrate that nutrient input reductions can produce a significant improvement for fish, crab and oyster habitats, and that we need to continue and advance our management efforts throughout the watershed.”

Dissolved oxygen was better than average in May through August, with early August having the lowest volume of hypoxia (low oxygen levels) ever measured during that time period. Hypoxia remained into September with worse than average conditions of 0.84 cubic miles observed versus a September historical average of 0.45. No hypoxia was observed in October.

Seasonal hypoxia in the Chesapeake Bay mainstem is based on freshwater flow into the Bay from January through May. Freshwater flow is an indicator of how much nutrient (nitrogen and phosphorus) runoff may be entering the Bay; Maryland had rainfall near average this summer, while the report said Pennsylvania saw rainfall 3.4 inches above the 129-year state average, with most of the excess occurring in July and August.

Crabs, fish, oysters, and other creatures in the Chesapeake Bay require oxygen to survive. Scientists and natural resource managers study the volume and duration of Bay hypoxia to determine possible impacts to bay life, and track improvements due to nutrient management efforts.

The total loads of nitrogen and phosphorus have not yet been monitored for 2023, the Chesapeake Bay Program said. Each jurisdiction with water flowing into the Bay implements pollution-reducing practices across the landscape to limit nutrient runoff. It’s estimated that between 2009 and 2022, the six watershed states and the District of Columbia met 51% of the goal to reduce nitrogen and 60% of the goal to reduce phosphorus by 2025.

Each year, DNR computes hypoxia volumes from the water quality data collected by DNR and Virginia Department of Environmental Quality. Water quality data collection occurs year round, and is funded by these states and the Chesapeake Bay Program. Bay hypoxia reporting will resume in May 2023. Additional Maryland water quality data and information, including DNR’s hypoxic volume calculation methods, can be found at DNR’s Eyes on the Bay website.

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