Dissolved oxygen levels low in Chesapeake Bay
Special from the Star Democrat
— A prolonged heat wave could be behind low dissolved oxygen levels in the Chesapeake Bay in late July, according to the Maryland Department of Natural Resources.
Each year between June and September, DNR computes data collected on the Bay’s dissolved oxygen.
Oysters, crabs, striped bass and other creatures in the Bay need dissolved oxygen in the water to survive. Little to no oxygen in the water is called hypoxia, often referred to as “dead zones.”
Hypoxic areas are caused by excess nutrient pollution, primarily from human activity like agriculture and wastewater. The nutrient pollution feeds algae blooms, and when the algae dies it settles to the bottom and absorbs the oxygen in the water, said Bruce Michael, director of resource assessment service at DNR, in a July interview.
The summer started off positive. Late June dissolved oxygen levels were the second best in the Chesapeake Bay since since 1985. But by late July, dissolved oxygen levels were the seventh worst since 1985, according
to DNR. However, officials in July did expect the dead zone to get larger as the summer continued.
According to DNR’s data on dissolved oxygen conditions in Maryland’s portion of the mainstem of the Bay, the hypoxic zone in late June was .42 cubic miles.
In the late July period, the hypoxic zone was approximately 1.65 cubic miles, which is greater than the late July 1985-2015 average of 1.29 cubic miles, according to DNR. Hypoxia extended south of the Patuxent and Potomac rivers, DNR stated.
“A prolonged heat wave likely exacerbated low oxygen conditions, as warmer waters hold and mix less oxygen,” DNR stated. “A lack of significant winds also prevented surface oxygen from mixing to bottom waters.”
In the beginning of June, scientists from the University of Maryland Center for Environmental Science, National Oceanic and Atmospheric Administration, U.S. Geological Survey and the University of Michigan released predictions for this summer’s Bay dead zone. They estimated that the dead zone will be either average or slightly smaller compared to previous summers.