News

Gulf 'dead zone' smaller than expected

Tropical Storm Barry may have dispersed nitrates

The National Oceanic and Atmospheric Administration research vessel Pelican has been used for decades for an eight-day cruise to map the size of the oxygen-deprived “dead zone” in the Gulf of Mexico off the Louisiana shore. Here it is docked Aug. 9, 2018, at Louisiana Universities Marine Consortium in Chauvin, La. (John Steppe/The Gazette)
The National Oceanic and Atmospheric Administration research vessel Pelican has been used for decades for an eight-day cruise to map the size of the oxygen-deprived “dead zone” in the Gulf of Mexico off the Louisiana shore. Here it is docked Aug. 9, 2018, at Louisiana Universities Marine Consortium in Chauvin, La. (John Steppe/The Gazette)

The size of the oxygen-deprived “dead zone” in the Gulf of Mexico is smaller this summer than expected, given the high level of nitrate measured in the Mississippi River in May, scientists reported Thursday.

The dead zone was 6,952 square miles, a little smaller than the size of New Jersey, when researchers measured the area July 23 to 29, according to a news release. Though smaller than expected, the area still is the eighth largest in the 33 years of mapping done by Louisiana State University researchers and funded by the National Oceanic and Atmospheric Administration and the National Centers for Coastal Ocean Science.

Scientists measure the dead zone each year to track the effects of fertilizer washing from Midwest farm fields into the Mississippi River and down to the gulf. Fish and other organisms must swim away from the water or die, which has hurt the shrimping industry in Louisiana and other Gulf Coast states.

During a four-month investigation last fall, The Gazette found little progress in 12 Midwestern states in reducing nitrate and phosphorus going into rivers and streams that go into the Mississippi River.

Nancy Rabalais and Eugene Turner, LSU professors who measure the dead zone each summer, predicted it would be 8,700 square miles based on the May nitrogen load in the Mississippi River. The river had two large peaks of discharge and nitrate load in March and again in May through July, the researchers reported.

The Mississippi River saw record flood levels this spring and early summer, inundating cities including Davenport and Burlington.

But those nitrate loads didn’t cause a near-record size dead zone because of Tropical Storm Barry, which hit Louisiana in early July, a week before the research trip, according to the LSU researchers.

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Waves from the storm likely mixed up the water and narrowed the area where hypoxia, or low oxygen, was found after the storm, they said in the news release.

Comments: (319) 339-3157; erin.jordan@thegazette.com

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