ANNAPOLIS, Md. — The Chesapeake Bay’s summer “dead zone” was the smallest it’s been since monitoring began in 1985, according to data released by the Chesapeake Bay Program’s monitoring partners: The Maryland Department of Natural Resources (MD DNR), Old Dominion University and Virginia Institute of Marine Science (VIMS).
“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,” said Mark Trice, program chief of water quality informatics with MD DNR’s Resource Assessment Service.
According to the Chesapeake Bay Program, dead zones are areas of low oxygen that form in deep Bay waters when nitrogen and phosphorus enter the water through polluted runoff and feed naturally-occurring algae. This drives the growth of algal blooms, which eventually die and decompose, removing oxygen from the surrounding waters faster than it can be replenished, creating low-oxygen — or hypoxic — conditions at the bottom of the Bay that limit habitat for crabs, oysters, fish and other wildlife.
Based on water quality data provided by MD DNR, the Virginia Department of Environmental Quality and Old Dominion University, MD DNR and VIMS individually estimated the size of the dead zone from May to October 2023 using separate methods, then calculate hypoxic volume within the Bay’s mainstem from that time period.
Both estimates are the lowest on record and much lower than the historical average taken from 1985-2022, according to the Chesapeake Bay Program, adding the dead zone was larger than average in September, but observations showed no hypoxic conditions in October. For the past four years, the summer dead zone has been below the long-term average size, as documented both by VIMS and MD DNR.
It noted rainfall plays an important role in the development of dead zones, and was below-average for most of 2023, but added the 2023 dead zone could have been even smaller if it weren’t for the season’s above-average temperatures and average wind speeds.
“The low levels of hypoxia in 2023, despite the high temperatures, are truly surprising,” said Dr. Marjy Friedrichs, research professor at the Virginia Institute of Marine Science. “This may finally be clear evidence that our nutrient reduction strategies are improving water quality and fish and shellfish habitats.”
The Chesapeake Bay Program said pollution-reducing practices put into place by Delaware, Maryland, New York, Pennsylvania, Virginia, West Virginia and the District of Columbia, help reduce the amount of nutrients that enter local waterways and the Chesapeake Bay from sources such as wastewater, agriculture and stormwater runoff. It is estimated that between 2009 and 2022, those entities have met 51% of the goal to reduce nitrogen and 60% of the goal to reduce phosphorus by 2025.
For more information, two reports are available based on these data: the Virginia Institute of Marine Science in their 2023 Chesapeake Bay Dead Zone Report Card, as well as the Maryland Department of Natural Resources in their 2023 Final Hypoxia Report.
