08-05-2024

Gulf of Mexico’s dead zone is unusually large this year

Earth.com staff writer

The Gulf of Mexico’s “dead zone” – an area with dangerously low oxygen levels – currently covers approximately 6,705 square miles. This makes it 12th largest dead zone in the 38 years of recorded measurements.

This expanse, equivalent to over four million acres, represents significant loss of habitat for marine species. It particularly affects those living on the ocean floor.

Surveying the dead zone in the Gulf

The annual survey was conducted from July 21–26 by scientists from Louisiana State University and the Louisiana Universities Marine Consortium (LUMCON) aboard research vessel Pelican.

The research provides crucial data for the Mississippi River/Gulf of Mexico Hypoxia Task Force. This state and federal partnership aims to reduce the five-year average size of the dead zone to fewer than 1,900 square miles by 2035. The current five-year average however, stands at 4,298 square miles – more than double the target.

“It’s critical that we measure this region’s hypoxia as an indicator of ocean health, particularly under a changing climate and potential intensification of storms and increases in precipitation and runoff,” said Nicole LeBoeuf, assistant administrator of NOAA’s National Ocean Service.

According to LeBoeuf, this long-term data set can help decision makers while they adjust their strategies to reduce the dead zone and manage its impacts to coastal resources and communities.

Gulf dead zone is larger than expected

In June, NOAA had predicted an above-average dead zone size of 5,827 square miles, based on data from the U.S. Geological Survey regarding Mississippi River discharge and nutrient runoff.

The actual size measured fell within the forecast’s uncertainty range, confirming the accuracy of the predictive models used and their utility in informing nutrient reduction strategies.

“The area of bottom-water hypoxia was larger than predicted by the Mississippi River discharge and nitrogen load for 2024, but within the range experienced over the nearly four decades that this research cruise has been conducted,” said Nancy Rabalais, a professor at Louisiana State University and LUMCON, and co-chief scientist for the survey. “We continue to be surprised each summer at the variability in size and distribution.”

What causes dead zones?

Dead zones are mainly caused by excess nutrients – particularly nitrogen and phosphorus – entering the Gulf of Mexico through the Mississippi-Atchafalaya River Basin.

These nutrients stimulate algal blooms, and upon dying they decompose and consume oxygen in the water. This process creates hypoxic conditions. Such low oxygen levels force marine animals, like fish and shrimp to leave the area, which severely impacts their diets, growth rates, reproduction and habitat use.

In an attempt to overcome these hurdles, the Environmental Protection Agency (EPA) launched the Gulf Hypoxia Program in June 2022, which aims to accelerate nutrient reduction efforts by Hypoxia Task Force.

“Nutrient pollution impacts water bodies across the country and in the Gulf of Mexico it has resulted in a dead zone, where low to no oxygen does not support fish and marine life,” said Bruno Pigott, acting assistant administrator of EPA’s Office of Water.

“EPA is committed to its partnership with state and local governments and Tribes in the Mississippi-Atchafalaya River Basin, working together to reduce nutrient pollution and protect the health of the Gulf. In fact, thanks to President Biden’s Bipartisan Infrastructure Law, EPA is investing $60 million into this effort.”

Nutrient reduction strategies

The Hypoxia Task Force states are intensifying their nutrient reduction strategies while also enhancing climate resiliency and ensuring that the benefits of these actions extend to disadvantaged communities.

“The importance of the Mississippi River to the strength and growth of our states’ economies and communities cannot be understated,” said Mike Naig, Iowa Secretary of Agriculture.

“By implementing our nutrient reduction strategies, the Hypoxia Task Force states are individually and collectively demonstrating our commitment to protecting and enhancing this working river.”

Naig noted that weather and other factors will always introduce variability in the hypoxic zone measurement from year to year, but the focused conservation implementation work within each state is making a positive impact on our water quality.

“States, along with numerous public and private partners, are best positioned to address their specific geographies and we remain motivated to expand this proven water quality work in rural, suburban and urban landscapes in the years and decades to come.”

Efforts to monitor and understand dead zones

NOAA’s work extends beyond the annual hypoxia forecast and survey. The agency supports the development of monitoring technologies to better understand dead zones and studies the effects of hypoxia on fish and fisheries through various programs, including Coastal Hypoxia Research, Ocean Technology Transition, Uncrewed Systems, and Hypoxia Watch.

Additionally, NOAA collaborates with states to create new tools for predicting nutrient runoff and supports the Northern Gulf Institute in delivering technical assistance, observation, and monitoring capabilities.

This year, NOAA scientists are also exploring the use of autonomous surface vehicles (ASVs) as an emerging technology to map hypoxia in the Gulf of Mexico. Several ASVs were deployed in coordination with the measurement survey, and their data will be compared with traditional ship-based measurements to assess their efficacy.

The efforts by NOAA and its partners underscore the importance of comprehensive and sustained actions to address the dead zone in the Gulf of Mexico, a critical issue affecting marine ecosystems, fisheries, and coastal economies.