Record-breaking spring rains and historic flooding in the Midwest were poised to create one of the biggest dead zones on record in the Gulf of Mexico this summer, researchers had estimated.
Instead, Hurricane Barry mixed up the waters, making the dead zone smaller than expected, scientists said during a National Oceanic and Atmospheric Administration press conference on Thursday.
Still, the dead zone in the Gulf of Mexico is 2.8 times larger than the goal set by the government this year, and the eighth largest in the 33 years with similarly mapped areas.
A dead zone is an area in the ocean that has a low amount of dissolved oxygen. Scientists call this ocean environment hypoxia. It can no longer support life that would typically call that area home. When it starts to appear in the spring in the northern part of the Gulf of Mexico, it often causes die-offs of corals, aquatic plants, shellfish and other fish.
Several bodies of water have dead zones, but the Gulf of Mexico has the largest in the world. For decades, researchers have tracked its size.
This year, the size of the dead zone was 6,952 square miles. That’s well below the 8,717 square miles some predicted, or the slightly smaller dead zone of 7,829 square miles that NOAA predicted.
“There is still a surprisingly large area” of the dead zone, said Nancy Rabalais, a marine ecologist who has been studying this phenomenon for over 34 years, “despite the mixing up by the storm.”
Rabalais, a professor at Louisiana State University and a MacArthur fellow, took the measurements and helped create the report. She predicts that the dead zone will be larger a week from now, but “we can only spend so much time on the water” taking the measurements.
Dead zones have changed in size over the years. The size of the zone largely depends on the environment. The “abnormally high amount of spring rainfall” as NOAA calls it, flooded hundreds of farms in the Midwest this spring. That rain washes the soil off farmers’ fields and straight into the Mississippi River, which dumps into the Gulf.
The runoff contains large quantities of nitrogen and phosphorus that stimulate the growth of phytoplankton in the water. The phytoplankton fall to the bottom of the ocean and decompose with bacteria there, using up all the oxygen and creating harmful algal blooms.
Human activity has made the Mississippi River more of a problem for the Gulf. The river now has three times the amount of nitrogen than in the 1950s, Rabalais said, and the amount of phosphorus has doubled.
In May, nitrate loads were about 18% above the long-term average, and phosphorus loads were about 49% above the long-term average, according to scientists at the University of Michigan, who are among those monitoring the issue.
Scientists first noticed these dead zones in the 1970s, and they’ve been growing in size ever since.
The largest dead zone in the Gulf of Mexico formed in 2017 and covered nearly 9,000 square miles.
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State governments, the US Environmental Protection Agency, and farmers have created working groups to figure out how to reduce the material running into the Mississippi. Farmers have started to use more cover crops to prevent runoff and to build embankments to contain the soil, but as the climate crisis has increased, heavy rains will continue to cause problems with flooding.
We are “glad to see this is less than what the projection was,” said Bill Northey, under secretary for farm production and conservation with the US Department of Agriculture, said Thursday.
But it “does not mean we achieved a tremendous amount of success,” improving the environment that creates these dead zones, Northey said. “We still have a long ways to go.”