June 13, 2016
A University of Michigan ecologist and colleagues from several institutions are forecasting a near-average Chesapeake Bay "dead zone" in 2016.
This year's forecast calls for an oxygen-depleted, or hypoxic, region of about 1.58 cubic miles, which is close to the long-term average measured since 1950.
The anoxic, or oxygen-free, portion of the zone is predicted to be 0.28 cubic miles in early summer, growing to 0.31 cubic miles by late summer. Low river flow and low nutrient loading from the Susquehanna and Potomac rivers this spring account for a smaller-than-average predicted size of the anoxic portion.
The forecast was released Monday by the National Oceanic and Atmospheric Administration.
The Chesapeake Bay's hypoxic and anoxic zones are caused by high levels of nutrients, primarily from activities such as industrialized agriculture and inadequate wastewater treatment. The low oxygen levels are insufficient to support most marine life and habitats in near-bottom waters and threaten the bay's production of crabs, oysters and other fisheries.
"While the latest forecast calls for a near-average dead zone in the Chesapeake Bay this year, it is important to recognize that these averages are unacceptable. They are considerably higher than those implied by the targets set under the Chesapeake Bay Total Maximum Daily Load agreement," said U-M aquatic ecologist Don Scavia, director of the Graham Sustainability Institute.
Scavia is a member of the NOAA-funded teams that produce annual forecasts for the Gulf of Mexico, the Chesapeake Bay and Lake Erie. This year's gulf forecast was issued last week and called for an average-size dead zone. The Lake Erie harmful algal bloom forecast will be released in early July.
The predicted size of the Chesapeake Bay dead zone is based on models that forecast three of its features: midsummer low-oxygen hypoxic zone, early summer oxygen-free anoxic zone and late-summer oxygen-free anoxic zone. The models were developed by NOAA-sponsored researchers at U-M and the University of Maryland. The modelers rely on nutrient-loading estimates from the U.S. Geological Survey.
"These improved forecasts help groups like the Chesapeake Bay Program protect the bay for the future," said Russell Callender, assistant NOAA administrator of the National Ocean Service. "They're also one of many tools NOAA and its partners are developing to better understand the environmental threats to the bay, and guide the bay restoration efforts."
The forecast relies on nutrient runoff data, as well as river and stream data, from USGS. The federal agency estimates that the Susquehanna and Potomac rivers delivered 42.2 million pounds of nitrogen to the bay from January to May 2016, which is 17 percent below average conditions.
The data are funded through a cooperative agreement between USGS and the Maryland Department of Natural Resources. USGS operates more than 400 real-time stream gauges and collect water-quality data at numerous long-term stations throughout the Chesapeake Bay basin to track how nutrient loads are changing over time.
"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," said Donald Boesch, president of the University of Maryland Center for Environmental Science. "But there's no reason to be complacent — we have a long way to go to finish the job."
Later this year, researchers will measure oxygen levels in the Chesapeake Bay, based on surveys by the Chesapeake Bay Program's partners from the Maryland Department of Natural Resources and the Virginia Department of Environmental Quality.