“Dead zone” in the Gulf of Mexico expected to be larger than average this summer

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The “dead zone” forms in the Gulf of Mexico every summer. It is caused by nutrients such as nitrogen and phosphorus, mostly from agricultural fertilizers and municipal runoff, being carried into the Gulf via the Mississippi River. Algae feed on these nutrients and when they die, bacteria consume the oxygen in the water, causing marine life to die or avoid the area.

For this year, the National Oceanic and Atmospheric Administration predicts an area of ​​5,827 square miles, 5% more than the long-term average.

The prediction is based on the amount of nutrients monitored along the river by the United States Geological Survey. The agency also found that nitrate levels were below average and phosphorus levels were above average this year. Nitrates tend to have a greater impact on the dead zone.

To address this problem, a multi-state and multi-agency Mississippi River/Gulf of Mexico Hypoxia Task Force was formed in 1997. Since then, billions of dollars have been spent to reduce nutrient flows, with the goal of reducing the size of the dead zone to 1,900 square miles (4,800 square kilometers) by 2035.

“Even with the reduced loading volumes, the area is still expected to be much larger than the task force’s 2035 target,” said David Scheurer, an oceanographer at NOAA’s National Centers for Coastal Ocean Science.

Because most of the nutrients that cause the dead zone come from fertilizers used on farms in the upper Mississippi River basin, this requires a change in agricultural practices.

“The annual fluctuations in the dead zone are driven primarily by weather in the Corn Belt, but the long-term trends are driven by nutrient loading from agriculture,” said Don Scavia, professor emeritus at the University of Michigan’s School for Environment and Sustainability. Increased precipitation in the upper basin can lead to more runoff into the river, so climate plays a role every year.

“The lack of a downward trend in the dead zone demonstrates that current efforts to reduce these pressures have not been effective,” Scavia added in a press release. “Clearly, federal and state agencies and Congress continue to prioritize industrial agriculture over water quality.”

Alisha Renfro, a coastal scientist with the National Wildlife Federation, said that while there are numerous efforts in individual states to reduce runoff, they have not been very successful.

“I think it shows that we need to think bigger when it comes to managing the Mississippi,” she said.

She said states need to work more closely together to address the problem and agencies should consider a more comprehensive management plan for the entire river. Wetland restoration also plays a role in reducing hypoxia, as wetlands naturally filter out nutrients.

NOAA’s forecast is based on the amount of nutrients monitored by the USGS in the system, so depending on weather conditions and whether hurricanes stir up the waters in the Gulf this summer, scientists’ actual readings in August could vary. In fact, during its monitoring trip last year, NOAA found that the actual size of the dead zone was smaller than predicted.

“Over the last few years, our predictions have not really matched reality,” said Cassandra Glaspie, a professor in the Department of Oceanography and Coastal Sciences at Louisiana State University who is helping to survey the dead zone.

Another prediction from her colleagues at LSU, still under peer review, contradicts NOAA’s forecast and argues that rising ocean temperatures will reduce the size this year. Glaspie co-authored the study that underpinned that model. She said higher temperatures could affect the food web, which in turn could affect oxygen levels.

“It will be a good test case if we can get there in August and there are no bad storms or erratic winds or whatever,” she said.

She said it’s important to have research funding to continue that modeling. Although the bipartisan infrastructure bill includes more money for reducing nutrient pollution, the Biden administration is proposing cuts to NOAA funding for research into harmful algal blooms and hypoxia in fiscal year 2025.

She said this was particularly worrying given the impact of hypoxia on fisheries in the Gulf.

“I think it would be logical to spend our money intelligently on an evidence-based approach to maintaining and expanding sustainable fisheries in coastal areas,” she said. “Instead of simply cutting funding for monitoring and allowing these problems to fester.”

This story is a product of the Mississippi River Basin Agriculture and Water Departmentan independent reporting network based in University of Missouri In a relationship with Report for Americawith major support from the Walton Family Foundation. The National Wildlife Federation and LSU have also received funding from Walton.