Scientists say warmer water is shrinking Gulf dead zone

According to two leading researchers, the Gulf of Mexico dead zone is shrinking due to warming waters, not due to reduced nitrate inflow from the Mississippi River.

Dr. Nancy Rabalais and Dr. Gene Turner, a husband-and-wife team and scientists at Louisiana State University, predicted last Thursday that the hypoxia zone will shrink significantly due to “much warmer” waters in the depths offshore. They estimated the size of the dead zone at 1,972 square miles in late July. That’s less than half the size predicted by the National Oceanic and Atmospheric Administration, which was estimated at 5,800 square miles.

Their model was not included in the NOAA estimate, so it was released separately. This is the first time the influence of water temperature has been included in a dead zone model. NOAA officials said they are reviewing how the LSU model might affect the government forecast.

If the dead zone size predicted by Rabalais and Turner is correct, it would meet the goals of the Mississippi River and Gulf of Mexico Hypoxia Working Group, led by Iowa Agriculture Secretary Mike Naig, whose goal is for the dead zone to be 1,900 square miles or less by 2035.

Dr. Nancy Rabalais studies gulf hypoxia at Louisiana State University.

Rabalais and Turner stressed that the decline is entirely due to water that has warmed rapidly in recent years. They point out that nitrate pollution in the river has not decreased. Fertilizer application has tripled from 1950 to 2015. It is believed that the dead zone did not exist before 1970. In the meantime, water temperatures off the continental shelf have risen by about 5 degrees Fahrenheit. This increase affects the entire deep ecosystem, from plankton to shrimp.

It speaks to their integrity as scientists that they want to publish their forecast model, even if it superficially undermines their argument of reducing nitrate pollution in the Gulf. Rabalais talks about the nitrogen cycle and the “nitrodollar” supply chain. She told me that voluntary nutrient reduction plans have not reduced nitrate pollution in the rivers or the Gulf, and that is consistent with observations by Iowa scientists like Dr. Chris Jones and others.

If the dead zone becomes less than 2,000 square miles, the agribusiness lobby will claim victory over surface water pollution. When drought dried up the drainage pipes and the flow of nitrates from the drainage pipes into the river decreased, the agribusiness industry cheered Iowa’s voluntary program. When the drainage pipes were put into operation this year, the Raccoon swelled again with nitrate.

We still have a nutrient problem. The dead zone this year is the size of Rhode Island at best. Iowa is experiencing an unexplained cancer explosion. Des Moines is struggling to get drinking water. Yet about 30% of our nitrogen supply is lost in the air and water, and we throw fertilizer on top of that. Nitrate and phosphorus do all kinds of bad things in the water. In the Gulf, they don’t work in isolation.

Rabalais said they don’t know how warming waters at depth will affect fishing and production. There are complicated interactions at play where microbial life peaks and then declines at a certain temperature. As the water warms, the Gulf swells and storms occur, threatening wetlands and shoals that protect the coast.

She will be monitoring the results of a scientific cruise later this month that will measure oxygen depletion off the Gulf Coast. Members of the Hypoxia Task Force will also be watching closely, no doubt hoping that the LSU model and forecast prove correct.

It’s an intriguing twist in a story that’s dragged on for decades, culminating in the Des Moines Waterworks’ 2015 lawsuit against Buena Vista, Sac and Calhoun counties over nitrate pollution of the Raccoon River from agricultural drainage systems. The lawsuit was dismissed, and the Midwest stuck with voluntary incentives to clean up the Gulf. A confirmed reduction in the size of the dead zone will be cause for celebration in West Des Moines offices and at the Capitol. It won’t mean much at the waterworks, which is restarting its nitrate removal system.