This past summer’s dead zone in the Chesapeake Bay was the second-smallest over the past 35 years, Maryland’s Department of Natural Resources says.
Dead zones, areas with insufficient dissolved oxygen levels to support marine life, can be caused by nutrient pollution. When excess nutrients — from fertilizers and sewage, for instance — flow into bodies of water, they can overstimulate the growth of algae, which blocks sunlight from reaching plant life below and sucks up oxygen as it decomposes.
This year, the average dead zone calculated during monitoring trips to the bay was .63 cubic miles. Between 1985 and 2019, the average was .84 cubic miles. In that period, only 2012 scored better than 2020, with .62 cubic miles worth of dead zones.
The data shows that the bay is rebounding from a disastrous 2019, when record rainfall yielded algal blooms, which decomposed quickly during a hot summer, starving the bay of oxygen. Last year was the third-worst on record since 1985, according to the Department of Natural Resources.
In mid-June, a team of researchers from the Environmental Protection Agency’s Chesapeake Bay Program and the University of Maryland Center for Environmental Science, among other institutions, predicted slightly better than average dead zone measurements, based on lower water and nitrogen flows into the bay from January to May. This year’s cool spring may have been a contributor, too, researchers say.
The department’s 2020 findings are supported by similar readings from Virginia’s portion of the bay. The Virginia Institute of Marine Science found that this summer’s dead zone, or hypoxic zone, was smaller than in 80% of the years since 1985.
Maryland’s Department of Natural Resources takes its dead zone measurements during the summer because, generally, during the colder months, researchers observe less hypoxia, as inclement weather stirs the bay and sends more oxygen toward the bay’s murky depths.
Conditions were better than average during seven out of the department’s eight monitoring trips this summer. They were only worse than average in late July. Researchers didn’t observe any anoxic zones — areas with hardly any dissolved oxygen at all — in the mainstream bay in Maryland or Virginia this year. Plus, the department’s September monitoring effort didn’t find any dead zones in the mainstream bay, although it took place about a week later than normal this year due to windy conditions, which also likely stirred the waters and spread dissolved oxygen.
Scientists at the Chesapeake Bay Foundation cheered the summer’s results, which were released Wednesday.
“This year’s small dead zone is another positive sign that watershed-wide Chesapeake Bay cleanup efforts are working,” wrote the foundation’s Director of Science Beth McGee in a statement.
This comes as a 2025 deadline for reducing pollution levels in the bay, set by 2010′s Chesapeake Clean Water Blueprint, draws ever closer.
“As the 2025 deadline looms, we’re encouraging states to figure out new ways to reach pollution reduction goals, including by adding more natural filters to the landscape such as trees, grass pastures, and wetlands,” McGee wrote.
Wednesday’s announcement about oxygen levels comes on the heels of a fairly strong crabbing season, and at the beginning of what experts anticipate will be a strong oyster season, too.
“A smaller dead zone means more areas for oysters, crabs and fish to thrive in the Bay," McGee wrote. “This is good news.”