Scientists release summer ‘dead zone’ estimates for Bay
ANNAPOLIS — This summer’s “dead zone” in the Chesapeake Bay is expected to be about average or slightly smaller, according to organizations that released the findings on Monday, June 13.
A dead zone is an area of the water with little or no oxygen that can kill fish and aquatic life.
Scientists predict the dead zone to be about 1.58 cubic miles, or about the volume of 2.3 million Olympic-size swimming pools, which is close to the long-term average as measured since 1950.
The anoxic portion of the zone, which contains no oxygen at all, is predicted to be about .28 cubic miles in early summer and grow to .31 cubic miles by late summer. Both are smaller than the average, due to low river flow and low nutrient loading from the Susquehanna and Potomac rivers this spring, scientists reported.
Jeremy Testa, assistant professor at the University of Mar yland Center for Environmental Science’s Chesapeake Biological Laborator y in Solomons who was involved in putting together the forecast, said numerous field and laboratory studies show that even modest hypoxia (low oxygen) can impact fish behavior, growth and overall health.
“Dead zones over the past 30 years have been higher than in the 1950s to 1970s,” Testa said. “The most severe dead zones in recent years have been in the summers of 2003 and 2011.”
Dead zones are caused by excess nutrient pollution, primarily from human activity like agriculture and wastewater, according to the National Oceanic and Atmospheric Administration.
Oxygen levels in dead zones are not high enough to support most marine life and habitats in waters near the bottom, and dead zones can threaten the Bay’s production of crabs, oysters and other fisheries, according to NOAA.
The model to estimate the dead zone is based on nutrient loading estimated from the U.S. Geological Survey, and developed by NOAAsponsored researchers at the University of Maryland Center for Environmental Science and the University of Michigan.
USGS estimated that the Susquehanna River, which runs from New York, through Pennsylvania and into the Chesapeake Bay, delivered 66.2 million pounds of nitrogen to the Bay from January through May 2016, which is 17 percent below average conditions, according to NOAA.
Testa said the recent rains, which struck the mid-Atlantic area throughout most of May, will result in additional new nutrient inputs to parts of the Chesapeake Bay. The dead zones estimates include the river flow and nutrient loads from May, “so we are accounting for some of the recent rain effects,” he said.
“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 it’s no reason to be complacent — we have a long way to go to finish the job.”
Chesapeake Bay Foundation Senior Scientist Beth McGee said in a statement released Monday that the link between the Susquehanna River pollution and the dead zone underscores the importance of reducing nitrogen pollution from Pennsylvania.
“The Commonwealth’s (Pennsylvania’s) efforts to reduce nitrogen pollution remain off track by millions of pounds.” McGee said. “CBF believes that an average sized dead zone is still unacceptable, and that Pennsylvania and the other Bay states must implement the plans they developed to reduce pollution and restore water quality in local rivers, streams and the Chesapeake Bay.”
Follow me on Twitter @ jboll_stardem.
Excessive nutrient pollution in the Chesapeake Bay threaten its commercially and recreationally important blue crab fishery through oxygen depletion.