Scientists are predicting that this summer's oxygen-starved "dead zone" in the Chesapeake Bay will be unusually bad - fueled by a wet spring that washed a heavy dose of nitrogen into the bay from the Susquehanna River and other tributaries.
Donald Scavia, a University of Michigan aquatic ecologist, who makes annual forecasts of "dead zone" sizes in the Chesapeake and Gulf of Mexico, thinks the amount of bay water with little dissolved oxygen in it will be the largest since 2003 and the sixth largest ever recorded. See the UMich forecast here.
Nitrogen - from sewage plants, fertilizer washing off land and vehicle and power plant pollution falling out of the sky - is one of the key drivers of the bay's hypoxia, or low-oxygen condition. The amount getting into the bay has increased significantly since the 1950s, Scavia says, and this year's estimated load is the highest in more than a decade. Not surprising, since river gauges measured unusually strong spring flows down the Susquehanna - the single biggest water source for the bay.
Scavia's prediction tracks with the preliminary forecasts of bay scientists, who a few weeks ago foresaw a "moderately large" volume of water with no oxygen in it at all from spring into mid-July. If conditions don't change, they predicted this summer's dead zone could be the fourth largest in the past 26 years.
(Note that the Michigan and Maryland scientists are measuring slightly different things. Scavia tracks "hypoxic" water, which still has a little oxygen in it but not enough for fish and shellfish to do well, while the Maryland-based group has focused so far only on the truly "dead zone," anoxic water with no oxygen at all in it for crabs and other critters to breathe. Eco-Check, the Maryland-federal scientific partnership, has yet to issue its prediction for the broader hypoxic zone in the bay.)
Variations aside, the general forecast is tor a rough summer for striped bass, blue crabs and oysters, points out Beth McGee, senior scientist with the Chesapeake Bay Foundation. When oxygen levels in the water drop, fish and shellfish become stressed.
Some might wonder why the bay's dead zone can still be so bad given the billions of dollars spent on cleanup - this past fall, for instance, Maryland farmers planted a record number of acres in "cover crops" to soak up excess nitrogen in their fields that would otherwise wash into the bay in spring. McGee points out such efforts take years to influence water quality; much of the nitrogen from farm fields gets into the bay via ground water, she notes, and can take a decade or more to seep out into surface streams.