A slight drop in nutrient pollution and river flow from the Susquehanna and Potomac earlier this year likely means a bit smaller dead zone in the Chesapeake Bay this summer.
That’s according to scientists at the National Oceanic and Atmospheric Administration and the U.S. Geological Survey, who released their annual joint forecast Monday.
Scientists say they expect the bay’s low-oxygen dead zone to be 1.58 cubic miles this year, or roughly the volume of 2.3 million Olympic-size swimming pools. That’s also about 10 percent less than the long-term average of 1.8 cubic miles dating from 1985, but on par with the mean of 1.53 cubic miles dating from 1950.
Meanwhile, the area of the dead zone stripped of oxygen entirely is expected to be 0.28 cubic miles in early summer, spreading to 0.31 cubic miles by late summer — also just below the average.
This year’s mild improvement is credited in part to measures taken by Virginia and other bay states to curb harmful runoff. In fact, two recent studies indicated the overall health of the bay is improving after decades of pollution-fueled decline.
“There has been a recent trend toward less hypoxia later in the summer that may signal an emerging response to actual reductions in nutrient pollution,” Donald Boesch, president of the University of Maryland Center for Environmental Science, said in a statement announcing the forecast.
The center partners with USGS in providing the raw data for forecast modeling.
“But it’s no reason to be complacent,” Boesch added. “We have a long way to go to finish the job.”
Dead zones are blamed primarily on nutrient pollution — nitrogen and phosphorus — from human sources such as agricultural and wastewater runoff.
An overload of those nutrients leads to massive summertime algal blooms that decay and strip oxygen from the water.
The result is low-oxygen areas, called hypoxic zones, and more severe oxygen-depleted areas, called anoxic zones, that can kill fish and other marine life.
Bay states have made progress in curbing runoff under a federal pollution diet imposed in 2010, although studies show Pennsylvania lags behind in reduction measures.
The Susquehanna River runs through New York, Pennsylvania and Maryland, and it supplies half the freshwater to the bay.
“The link between Susquehanna pollution and the dead zone underscores the importance of reducing nitrogen pollution from Pennsylvania,” said Beth McGee, senior scientist with the Chesapeake Bay Foundation.
That state has fallen behind its own nitrogen-reduction goals by millions of pounds, McGee said.
Still, the USGS estimates the Susquehanna dumped 17 percent less nitrogen than average to the bay — 66.2 million pounds — between January and May. That reduction, along with a lower nutrient load and flow from the Potomac, led scientists to predict a smaller anoxic area.
Dietrich can be reached by phone at 757-247-7892.
