U.S. Water News Online
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.
"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.
Larry Simns, president of the Maryland Watermen's Association, said the low oxygen levels are much harder on oysters than on striped bass (rockfish). These fish are being caught in good numbers this summer, because they can swim away from the dead zones to survive.
"The only reason this isn't the worst summer ever is that there's been very little rain," said Simns, a commercial fisherman. "If we had a lot of rainfall in June and July, we'd be in really worse shape," he said, saying that more rain washes more pollutants into the bay.
Beth McGee, senior scientist with Chesapeake Bay Foundation, said the last few years of poor oxygen levels mean that the state should approve more funding to help reduce farm runoff, the No. 1 source of pollution.
"Until we have significant increases in funding to help farmers reduce agricultural runoff, this trend will only get worse," McGee said.
Delaware, Maryland, New York, Pennsylvania, Virginia, West Virginia and the District of Columbia are in the Chesapeake Bay's 64,000-square-mile watershed.
Those states agreed earlier this year to limit outflows of nitrogen and phosphorous from wastewater treatment plants that drain into the Chesapeake Bay in an effort to reduce such biological "dead zones."
The U.S. Environmental Protection Agency estimated that the new limits would stop about 17.5 million pounds of nitrogen and 1 million pounds of phosphorus from entering the bay each year.
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