1/3 Of Chesapeake Bay Low-Oxygen Dead Zone During Month Of July

ANNAPOLIS, Md. - More than a third of the Chesapeake Bay was a low-oxygen "dead zone" during monitoring in July, meaning the nation's largest estuary is on pace to have one of its most unhealthy summers on record, according to data released Monday. "Dead zones" occur when fertilizer from farms and other pollutants high in nitrogen and phosphorus are washed by rain into the bay. They an explosive growth of algae, which die and rot. Bacteria devouring the decaying mass consume oxygen, suffocating marine life.

A research cruise from the bottom of the bay in Virginia to its origin at the Susquehanna River in northern Maryland from July 11 to July 15 found that about 36 percent of the bay's central stem had less than 5 milligrams per liter of dissolved oxygen - the level that rockfish and other aquatic life need. This figure, when combined with earlier readings, puts the bay on pace to have oxygen levels about the third- or fourth-worst they have been in the 20 years the numbers have been closely monitored, said David Jasinski, data analyst for the Chesapeake Bay Program, an agency that coordinates the monitoring.

"The things we love to eat out of the bay will not do well with this kind of summer," said Bill Dennison, an ecologist at the University of Maryland Center for Environmental Science. "Oxygen is a crucial part of the environment for the fish and crabs and oysters, and having low oxygen or no oxygen is just as devastating for them as bulldozing a forest is for other creatures." "It's a system that's been kicked out of whack," Jasinski said. "The fish and crabs are stressed by these low oxygen levels, but it doesn't necessarily sign their death warrant."

About 7 percent of the bay in early July had oxygen levels of less than 0.2 mg per liter of oxygen, classified as "anoxic" or almost zero-oxygen, Jasinski said. Much of the worst areas are at the deeper sections of the bay; water closer to the surface tends to be healthier.

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