The amount of oxygen within Chesapeake Bay waters plunged last month, a setback for a environmental barometer that had started the summer at a promising level. In just one month, oxygen levels in the estuary went from among the highest in a generation to among the lowest.
From The Baltimore Sun,
State environmental officials blamed a heat wave for the decline. Warm water holds less oyxgen than cold water does.
Levels of dissolved oxygen are an important indicator of bay health because they are vital for creatures such as blue crabs, striped bass and anchovies.
Deeper portions of the bay can contain low levels of oxygen, or become devoid of it, in the summer. Pollutants such as nitrogen and phosphorus fertilize algae blooms, and when those blooms die and decompose, they strip oxygen from the water.
The dead zones can kill large numbers of fish and other creatures.
In June, a dead zone from the Bay Bridge south to the mouths of the Patuxent and Potomac rivers was at 40 percent of its historic volume, its smallest size for that time of year since 1985.
In late July, 1.65 cubic miles of water along the bottom of the bay contained little or no oxygen, more than an average of 1.29 cubic miles for late July from 1985 to 2015.
“A prolonged heat wave likely exasperated low oxygen conditions, as warmer waters hold and mix less oxygen,” state Department of Natural Resources officials wrote. “A lack of significant winds also prevented surface oxygen from mixing with bottom waters.”
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