June 20, 2009|By TIM WHEELER
The Chesapeake Bay's fish, crabs and oysters could be breathing easier this summer - the oxygen-starved "dead zone" in the troubled estuary should be one of the smallest ever measured, a University of Michigan scientist predicts.
Aquatic ecologist Donald Scavia and his colleagues issued forecasts this week for the nation's two most infamous "dead zones," stretches of the Chesapeake Bay and Gulf of Mexico where fish and shellfish can't get enough oxygen to breathe because of nutrient pollution fouling the water.
Scavia had good news (of sorts) for the bay, but gloomy tidings for the gulf.
First, the good news - the dead zone in the Chesapeake is likely to be the smallest since 2001 and one of the smallest on record, Scavia predicted. He based his forecast on the dry spell that lasted from January through much of April, dumping relatively little rain and snow on the bay's vast watershed, which stretches from Virginia north to Cooperstown in New York and west into West Virginia.
It's only good news of a sort, because the expected improvement in water quality stems from the weather, not from anything that's been done to reduce the massive overdose of nutrients we've been feeding the bay from sewage, lawn and farm fertilizer and air pollution.
"The predicted 2009 dead-zone decline does not result from cutbacks in the use of nitrogen, which remains one of the key drivers of hypoxia [low oxygen levels] in the bay," Scavia said in a statement released with his predictions.
University of Maryland scientists make summer forecasts of their own for the bay, but a spokesman said this week that they aren't ready yet.
Here's how the weather affects the health of the bay and its fish: Whenever it rains, the runoff washes nutrient-rich fertilizer, animal waste and fallout from power plants and vehicle exhaust into streams and rivers emptying into the bay. Those nutrients - the same ones we feed our lawns and flowers to get them to grow - stimulate "blooms" of algae that cloud the water. When those masses of microscopic aquatic plants die and sink to the bottom, they suck the oxygen out of the water as they decay.
Rainy weather such as we've been having for the past six weeks or so tends to wash more nutrients off the land and pavement, stimulating a feeding frenzy of algae in the water. If it gets bad enough, there are fish kills when oxygen levels in the water crash. Baltimore residents saw - and smelled - an episode up close last month in the Inner Harbor; scientists reported similar algae blooms throughout the mid-bay.
While you might think the rainy spell we've been experiencing would undercut the Michigan scientist's forecast of a smaller dead zone in the bay, that isn't necessarily true, says Joel Blomquest, who monitors mid-Atlantic streams and rivers for the U.S. Geological Survey. Blomquest said the upper half of the bay watershed in Pennsylvania and New York did not experience the wet weather we've had here in Maryland. Consequently, despite our downpours, the overall flow of freshwater into the bay has not been high, he said.
Scavia acknowledged that freshwater flows have increased in recent weeks, though, and hedged his forecast. While he still expects the Chesapeake dead zone to be a lot smaller, he says it will probably be on the high end of the size range he predicted.
While things are looking up, however temporarily, for the Chesapeake Bay, Scavia predicts that the Gulf of Mexico's "dead zone" this summer is likely to be one of the largest ever measured. The Mississippi and Atchafalaya rivers ran 11 percent above average this spring, feeding heavy doses of nitrogen into the gulf. It hasn't helped, either, scientists say, that nitrogen concentrations in those rivers have nearly tripled over the past 50 years from human activities.
