This year’s area of low oxygen in the Gulf of Mexico is larger than average, the National Oceanic and Atmospheric Administration (NOAA) announced on Thursday.
The “dead zone” is approximately 6,705 square miles, as measured last week. Within NOAA’s 38 years of measuring the dead zone, this year’s assessment marks the 12th-largest area of low- to no oxygen, which can kill fish and marine life.
NOAA had forecast at the beginning of the summer that the dead zone would be above average. But the measurement announced this week is even larger than anticipated.
Experts fault upriver conservation efforts that are not keeping pace.
Scientists at Louisiana State University and the Louisiana Universities Marine Consortium (LUMCON) conducted the 2024 dead zone survey aboard the research vessel Pelican from July 21 to 26.
The annual survey helps keep track of the progress made through the efforts of the Environmental Protection Agency’s Mississippi River/Gulf of Mexico Hypoxia Task Force, a state-federal partnership that is working toward a long-term goal of reducing the five-year average dead zone to fewer than about 1,900 square miles by 2035.
Today, the five-year average – which accounts for extremely wet and dry years becoming more common with climate change – is 4,298 square miles, more than twice the Task Force’s goal.
The dead zone occurs every summer and is caused in large part by nutrient runoff from the overapplication of fertilizer on Midwestern farms. During rains or flooding, water carries the fertilizer’s nitrogen and phosphorus from fields into the Mississippi River and its tributaries.
When the nutrients reach the Gulf, either from the Mississippi or the adjacent Atchafalaya River, they ignite an overgrowth of algae. As the algae dies, it decomposes and sinks to the bottom, depleting oxygen from the water.
When this happens, animals like fish and shrimp will leave. Some commercially harvested species such as shrimp will concentrate around the edges of the affected area, forcing local fishermen to travel outside the dead zone to cast their nets.
Bottom-dwelling creatures, such as clams and burrowing crabs, aren’t as mobile. They cannot leave the dead zone and will suffocate and die.
“The hypoxic zones lead to habitat loss for several ecologically and economically important species in the Gulf: I’m talking about shrimp, menhaden and a variety of other species,” said Sean Corson, director of NOAA’s National Centers for Coastal Ocean Science.
In 2020, the Union of Concerned Scientists estimated the dead zone’s average annual cost in damages to fisheries and marine habitats at $2.4 billion. This year’s dead zone impacts a swath of marine habitat roughly the size of New Jersey, stretching from south Louisiana almost to Galveston, Texas.
Though the dead zone is larger than NOAA had anticipated with its early-summer forecast, it falls within the range experienced over the last four decades of monitoring, said LSU professor Nancy Rabalais, the co-chief scientist for the research cruise.
Still, researchers are never quite sure where the dead zone will hit hardest and what its size will be at the height of summer, said Rabalais. “We continue to be surprised each summer at the variability in size and distribution,” she said.
But the high five-year average is not surprising to most dead zone experts, who point upriver to the Midwest, where there’s been a lag in farmers adopting agricultural practices that reduce nutrient runoff.
“After nearly four decades of experience with the Gulf dead zone, it should be clear that we can’t continue to rely on the same policy tools to manage fertilizer pollution and expect a different result,” wrote Karen Perry Stillerman, deputy director of the Food and Environment Program at the Union of Concerned Scientists.
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“Instead, we should demand a new approach, one that not only helps farmers to shift their practices but also insists that they do so,” she said.
In June 2022, the EPA established the Gulf Hypoxia Program to support the work of nutrient-reduction programs. The Bipartisan Infrastructure Law committed $60 million to support state-driven strategies to reduce nutrient runoff within the Mississippi River Basin. This funding will be spread across 12 states over the next five years.
A preliminary goal for the EPA’s Hypoxia Task Force is to reduce nitrogen and phosphorus loads in the river by 20% by 2025. In May 2024, the U.S. Geological Survey found that while nitrogen loads had fallen 7% since 1980, phosphorus had increased by 22%.
Some experts have linked this excess phosphorus to wastewater from municipalities that don’t remove the nutrient from otherwise-clean sewage discharged into the river and its streams.
By the time the water reaches Louisiana, it’s already loaded with nutrients from upriver. So, from a lower-river perspective, putting more resources into efforts across the basin has helped, but further policy changes must be enacted soon to reduce the size of the dead zone, said LSU research scientist Doug Daigle, who coordinates the Louisiana Hypoxia Working Group.
Without changes to current nutrient reduction programs, the task force will be hard-pressed to meet its 2035 goals, Daigle said.
This story is a product of the Mississippi River Basin Ag & Water Desk, an independent reporting network based at the University of Missouri in partnership with Report for America, with major funding from the Walton Family Foundation.