Researchers traveled more than 1,400 miles throughout the Gulf over a five day period, the first ever focusing on the month of June.

The size of the dead zone off coastal Louisiana has been routinely monitored for about 25 years and shows nitrogen levels in the Gulf related to human activities have tripled over the past half century.


Hypoxia is most severe around the Louisiana coast but still exists farther west toward Texas, notably in the Galveston area. (Credit: Texas A&M)
During the past five years, the dead zone has averaged about 5,800 square miles. It is predicted to exceed 9,400 square miles this year, which would make it one of the largest ever recorded, according to the Louisiana Universities Marine Consortium.

Hypoxia occurs when oxygen levels in seawater drop to dangerously low levels. Severe hypoxia can potentially harm marine life resulting in fish kills and creating a “dead zone” of life in that particular area.

Because of record amounts of water flowing from the Mississippi River into the Gulf, there is keen interest in the dead zone areas this year, says Steve DiMarco, professor of oceanography at Texas A&M University.

The size of this year’s dead zone could still change because large amounts of water are still flowing into the Gulf of Mexico from the Mississippi River.

“This was the first-ever research cruise conducted to specifically target the size of hypoxia in the month of June,” DiMarco says.

“We found three distinct hypoxic areas. One was near the Barataria and Terrebonne region off the Louisiana coast, the second was south of Marsh Island (also Louisiana), and the third was off the Galveston coast. We found no hypoxia in the 10 stations we visited east of the Mississippi delta.

“The largest areas of hypoxia are still around the Louisiana coast, where you would expect them because of the huge amounts of fresh water still coming down from the Mississippi River,” he says.

“The hypoxic area extends about 50 miles off the coast. The farther you go west toward Texas, there is still hypoxia, but less severe. However, we did see noticeable hypoxia near the Galveston area.”

DiMarco plans to examine the area again on Aug. 8 and will visit many of the same locations for additional data.

The Mississippi is the largest river in the United States, draining 40 percent of the land area of the country. It also accounts for almost 90 percent of the freshwater runoff into the Gulf of Mexico.

The research was funded by the NOAA Center for Sponsored Coastal Ocean Research and Texas Sea Grant.

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