Dead crabs in oxygen-starved water

The Chesapeake Bay's "dead zone" grows so large in summer that crabs and fish sometimes can have a hard time escaping to healthier waters and suffocate. (Glen Fawcett, 2008 / June 26, 2014)

Scientists are predicting that the Chesapeake Bay's oxygen-starved "dead zone" will be slightly larger than average this summer.

Using computer modeling underwritten by the National Oceanic and Atmospheric Administration, researchers forecast that by next month, nearly 2 cubic miles of bay water will have inadequate oxygen dissolved in it for fish and crabs to thrive. That's roughly 12 percent of the water in the bay and its river tributaries, according to Caroline Wicks of the University of Maryland Center for Environmental Science.

If it follows the normal pattern, the dead zone will grow and intensify until mid-July, then slowly shrink. About a half cubic mile of bay water is expected to be virtually devoid of oxygen in early summer, researchers predict. By late summer, the oxygen-free "anoxic" zone should shrink to about a third of a cubic mile, scientists say, which is a little better than the long-term average.

The bay forecast was developed by researchers at the University of Michigan and the UM Center for Environmental Science. Scientists in Louisiana, Texas and Virginia also helped with the modeling.

A separate forecast for the Gulf of Mexico predicts its "dead zone" of oxygen-starved water will be "average" but still quite large, covering an area about the size of Connecticut.

Such massive dead zones are formed by excessive nutrient pollution, primarily from agriculture and wastewater. Weather and winds also influence the size and duration of the oxygen-starved regions.

Researchers will actually measure the size of both dead zones later this summer, but sampling done earlier this month by the Maryland Department of Natural Resources shows about 20 percent of the state's portion of the bay already has poor oxygen conditions, a slightly larger water volume than the long-term average.

While both dead zones are expected to be about average in size this summer, they're still much larger than research indicates they were historically. The Gulf zone affects nationally important commercial and recreational fisheries, while the bay zone undermines efforts to restore and maintain crabs, oysters and other fisheries.

Don Scavia, a University of Michigan aquatic ecologist involved in the forecasts, said they "remind federal and state policy makers that insufficient progress is being made" in reducing nutrient pollution.

“We are making progress at reducing the pollution in our nation’s water that leads to ‘dead zones,’ but there is more work to be done,” said Kathryn D. Sullivan, NOAA's administrator.