Bay ‘dead zone’ still bad in ’09, But scientists have new knowledge of how it works
By PAMELA WOOD, Staff Writer11/27/09, The Capital, Annapolis, MD
Courtesy photo
Unusual weather conditions – dry weather in Pennsylvania and New York and a wet summer in Maryland and Virginia – threw off scientists’ predictions, but gave them new understanding into how the dead zone works.
"It was a pretty insightful year for us," said Bill Dennison, a University of Maryland Center for Environmental Science professor and vice president who leads the research team.
The dead zone is caused when the nutrients nitrogen and phosphorus flow into creeks, rivers and the bay from sewage plants, septic systems, farms and stormwater runoff.
In the water, the nutrients fuel the growth of algae blooms, which suck life-sustaining oxygen from the water when they decompose. The result is that vast stretches of the bay’s water is inhospitable to fish, crabs and shellfish.
Nutrients flowing in from all parts of the bay contribute to the dead zone, but scientists have figured out that fluctuations in spring rains and stream flows in the Susquehanna River can cause a measurable shift in how big the dead zone is.
But this year, the Susquehanna watershed in Pennsylvania and New York was dry, meaning fewer nutrients flowed south into the bay.
There was still a significant dead zone, however, which Dennison and his team attribute to nutrients flowing into the bay from Maryland and Virginia rivers during the rainy summer.
In other words, "We got to average in a different way," Dennison said.
And the message to people who live in the bay’s watershed and to decision-makers is that nutrients matter to the health of the bay, no matter where they are coming from, Dennison said.
Beth McGee, a scientists with the nonprofit Chesapeake Bay Foundation, said the dead zone data shows that the bay continues to be unhealthy.
"The bottom line is it fluctuates a little bit, but it’s all unacceptable," McGee said.
She said another year with another big dead zone shows the importance of the federal government’s effort to create a "pollution budget" for the bay and for Congress to pass legislation to ramp up bay restoration efforts.
"We need to do things differently," she said.
To measure the dead zone, scientists from the university and government agencies test water at more than 160 locations around the bay. They sample at different depths at each location.
There are distinctions within the dead zone. Hypoxia, or low oxygen, is 2 mg of oxygen per liter of water or below. Anoxia, the most truly dead water, is 0.2 mg/l or below.
In 2009, the hypoxic zone was larger than average, while the anoxic zone was just slightly smaller than average. Both measurements were deemed "moderate" by scientists.
Rockfish, shad, perch and clams need at least 5 mg/l, spot can survive at 2 mg/l, crabs need 3 mg/l and worms need 1 mg/l.
When faced with a lack of oxygen, fish and crabs will move to healthier waters. But oysters are stuck on the bottom, where they can die.
The University of Maryland teams don’t venture up into the bay’s rivers to test for oxygen. But riverkeepers and other advocates say they find the same dead zone phenomenon in the rivers, too.
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