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'Dead Zone' In Gulf Of Mexico Is Larger Than Average For 2021

A Gulf of Mexico map using red to point out the "dead zone," nd a bar graph underneath compares size of dead zones from 1985 through 2021.
National Ocean Service
National Oceanic and Atmospheric Administration
"At 6,334 square miles, the 2021 hypoxic zone in the Gulf of Mexico is the 16th largest ever measured in the 35-year record, measured from July 25 to Aug. 1. Red area denotes 2 milligrams per liter of oxygen or lower, the level which is considered hypoxic, at the bottom of the seafloor," according to NOAA.

Scientists say the area of little-to-no oxygen is about the size of Lake Ontario and Lake Erie put together.

This year's hypoxic zone, or "dead zone",in the Gulf of Mexico is larger than average, the National Oceanic and Atmospheric Administration and its partners announced during a virtual press conference Tuesday.

It is 6,334 square miles, or nearly 1,000 square miles more than the five-year average, according to four panelists who spoke about the area of low-to-no oxygen that can kill marine life.

It's caused by Mississippi River discharges and nutrient runoff. Those events grow algae, which is followed by algae decay — that process consumes the oxygen near the bottom of the Gulf, creating habitat loss for several species.

“As it relates to the flow of water, we know that this is increasingly uncertain because of climate change,” said Northern Gulf Institute's Paul Mickie, the panel moderator, during his introductions.

Nancy Rabalais, a professor at Louisiana State University, was the principal investigator on the Gulf research cruise from July 25 through Aug. 1. She said she was surprised at the distribution of the dead zone because they didn't find much low oxygen on the eastern side.

"Then when we got in the area of the Atchafalaya River plume, we started to pick up expansive areas of low oxygen and very low oxygen, sometimes close to zero," she said.

The size of the dead zone is consistent with the nitrogen load and the amount of water that comes from the Mississippi, according to Rabalais.

She said scientists do consider climate change factors when they make their dead zone predictions every year.

“We do know that some climate change effects will occur within the Mississippi River Watershed with… more precipitation in the upper part… which will generate more freshwater, which will then wash off the land and into the Gulf. We also know that the temperatures will increase over time. These two factors combined can affect the physics of the northern Gulf of Mexico,” said Rabalais.

Radhika Fox, with the U.S. Environmental Protection Agency, spoke about federal programs funding to reduce nutrient runoff under the Biden administration, including a farmer-to-farmer grant program and the Section 319 Nonpoint Source pollution program.

“These are great programs that allow us to partner with states, local governments, the agricultural community on voluntary efforts to reduce nutrients on farms and fields. And there are also a range of programs at USDA that support such efforts as well,” said Fox, who is co-chair of the Mississippi River/Gulf of Mexico Hypoxia Task Force.

The task force is made up of 12 states in the Mississippi River Basin, including Iowa, which is represented by Iowa Agriculture Secretary Mike Naig. He said each of the 12 states has developed science-based nutrient reduction strategies to address the needs of their local communities and their unique landscapes.

“We have conservation professionals who work alongside municipalities and farmers and landowners and they're working to enhance water quality in their communities. We have funding that's been dedicated to implement water quality practices, because we know that that change on the land leads to positive change in the water,” said Naig.

This year’s larger-than-average hypoxic zone event is occurring as toxic red tide blooms persist along Florida's Gulf coast beaches.

Dave Kidwell, with NOAA, said there's no evidence to suggest that there's any connection between the two phenomena. But he said if you look at the big picture in the Gulf of Mexico, there are an increasing number of areas that are stressed right now.

"So, organisms that would be perhaps highly migratory or otherwise are going to be potentially more impacted, but this is an area in terms of at a large scale like that, that, at least from our research group's perspective, we have not done much work on to look at the aggregate impacts,” said Kidwell.

My main role for WUSF is to report on climate change and the environment, while taking part in NPR’s High-Impact Climate Change Team. I’m also a participant of the Florida Climate Change Reporting Network.