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NOAA scientists report below average 'dead zone' for Gulf of Mexico this year

 The hypoxic zone measurement was made during an annual survey cruise in late July.
NOAA
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The hypoxic zone measurement was made during an annual survey cruise in late July.

In June, NOAA forecasted an average-sized "dead zone" in the Gulf of Mexico of 5,364 square miles, based primarily on Mississippi River discharge and nutrient runoff data from the U.S. Geological Survey.

Last week, scientists updated that figure after measuring the actual area of low to no oxygen — also known as a hypoxic zone — at 3,275 square miles. Though that is considered below average, scientists say it is still more than 2 million acres of habitat impacted by oxygen-consuming bacteria and decaying algae.

And David Scheurer, an oceanographer at NOAA, says the area is still more than two times larger than a reduction target of 1,900 square miles by 2035.

"So, that's a lot of runoff and nutrient inputs from farms, from wastewater treatment plants and people’s yards,” he said. “It's going to take a lot of effort across the Mississippi River watershed to reduce those nutrients."

Every year during the summer, several marine species in the Gulf die after being exposed to an overgrowth of algae and excess nutrients that create a lack of oxygen.

Exposure to hypoxic waters has also been found to alter fish diets, growth rates, habitat use and availability of commercially harvested species like shrimp.

Scheurer says the annual survey helps scientists determine progress in minimizing dead zones.

"It really lets us see trends over time as they develop and understand the processes that are involved and potential contributions from land-based sources and what people can do on a local level to help reduce those nutrients that would go into the water and negatively impact the ecosystems,” he said.

The largest dead zone occurred in 2017 when scientists recorded a hypoxic zone of about 8,700 square miles, approximately the size of New Jersey.

In June, the Environmental Protection Agency said it's directing 60 million dollars in funding over the next five years to nutrient reduction efforts.

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Cathy Carter is the education reporter for WUSF 89.7 and StateImpact Florida.