After having been whipsawed between unusually good—and extremely bad—water quality conditions over the past decade, scientists say the Bay is in for something different this summer: moderation.
While an oxygen-starved “dead zone” will appear, it shouldn’t be as bad as last year’s, which was the fourth worst on record. That, at least, is what scientists saw when they peered into their crystal ball to come up the Bay Program’s second annual Chesapeake summer forecast.
This year, they predict a dead zone covering 1.17 cubic kilometers, or about 2.3 percent of the mainstem of the Chesapeake.
That is about the same amount of anoxia—water with essentially no oxygen—as seen in 2001. That year, the anoxic “dead zone” stretched along the bottom of the Bay from the Bay Bridge to the Choptank River. It was the 12th worst year for anoxia in 21 years of Baywide water quality monitoring.
By contrast, last year’s dead zone—the fourth worst—covered 2.35 cubic kilometers, and stretched from the Bay Bridge to the Patuxent River.
The anoxia forecast is based on the historic relationship between spring flows from the Susquehanna River, nutrient loads from the upper Bay, and the amount of anoxic water in the Bay.
Susquehanna river flows help to create a barrier, known as the pycnocline, between fresh water on the surface and salty ocean water on the bottom of the Bay. The nutrients fuel the growth of algae, much of which die and sink to the bottom where they are consumed by bacteria, which in turn uses up oxygen. The pycnocline helps to prevent the bottom water from mixing with oxygen-rich water near the surface.
The prediction only covers the volume of anoxic water because of its strong relationship to springtime flows and nutrient inputs.
A much larger area of the Bay is not anoxic but has less oxygen than is needed to support aquatic life. The Bay Program estimates that only about 24 percent of the Chesapeake and its tidal tributaries met their water quality standards for dissolved oxygen last year.
Dave Jasinski, a University of Maryland Center for Environmental Science analyst who helped to develop the dissolved oxygen forecast, said factors that contribute to reduced anoxia should also reduce hypoxia—low oxygen conditions.
“You would expect they would be in some way correlated,” he said. “I would expect a smaller volume of hypoxia.”
High flows in 2004 contributed to it being the seventh worst year on record, while 2002—one of the driest years—had the lowest amount of anoxia, with only 0.49 cubic kilometers starved of oxygen.
Because little can be done to influence flows, the Bay Program is seeking huge nutrient reductions from the Chesapeake’s 64,000-square-mile watershed to reduce algae growth and improve water quality.
If the Bay Program’s nutrient reduction goals were achieved, computer models suggest that anoxia would become a rare event, showing up only in the most extreme weather conditions.
Scientists also expect to make a prediction for underwater grasses for the summer, and harmful algae blooms on the Potomac, but those predictions were not expected to be ready until June.
For information, and to keep track of field observations made by scientists this summer, visit the Bay Program’s Ecological Forecasting web page, http://www.chesapeakebay.net/bayforecast.htm