Warmer water shrinking Gulf dead zone, scientists say

The dead zone in the Gulf of Mexico is shrinking because of warming water and not because of less nitrate flowing in from the Mississippi River complex, according to two leading researchers.

Dr. Nancy Rabalais and Dr. Gene Turner, a wife-husband team at Louisiana State University, forecast last Thursday that the hypoxia zone will shrink considerably because of “much warmer” water at the depths off the coastline. They pegged the dead zone at 1,972 square miles at the end of July. That’s less than half the size forecast by the National Oceanographic and Atmospheric Administration, which estimated the size at 5,800 square miles.

Their model was not included in the NOAA estimate, so they released it separately. This is the first time that water temperature’s influence was factored in to a dead zone model. NOAA officials said they are considering how the LSU model may impact the government forecast.

If accurate, the size of the dead zone forecast by Rabalais and Turner would be on track with goals set by the Mississippi River/Gulf of Mexico Hypoxia Task Force chaired by Iowa Secretary of Agriculture Mike Naig. Its goal is for the dead zone to be 1,900 square miles or smaller by 2035.

Rabalais and Turner stressed that the shrinkage is due entirely to water that has warmed rapidly in recent years. They note that nitrate loads to the river have not decreased. Fertilizer application tripled from 1950 to 2015. It is believed that the dead zone did not exist before 1970. Meanwhile, water temperature off the continental shelf increased about 5 degrees Fahrenheit. That rise affects the entire deep ecosystem from plankton to shrimp.

It speaks to their integrity as scientists that they want to get their forecast model out there even if it superficially erodes their argument about lessening nitrate loads to the Gulf. Rabalais talks about the nitrogen cycle and the “nitrodollar” supply chain. She told me that voluntary nutrient reduction plans have not cut nitrate loads to the rivers or Gulf, and that flows with what Iowa scientists like Dr. Chris Jones and others observe.

If the dead zone comes in under 2,000 square miles the agribusiness lobby will declare victory over surface water pollution. When drought dried up tile lines and reduced nitrate flow to the river from drainage tile, the agribusiness establishment cheered the Iowa voluntary program. When the tile lines started running this year, the Raccoon swelled with nitrate again.

We still have a nutrient problem. The dead zone at best is the size of Rhode Island this year. Iowa has an unexplained cancer explosion. Des Moines is chasing its tail for drinking water. Still, about 30% of our nitrogen application is lost to air and water, and we are putting manure on top for good measure. Nitrate and phosphorous do all sorts of nasty things in the water. In the Gulf, they do not act in isolation with just each other.

Rabalais said they do not know how warming water at depth will impact fisheries and production. Complicated interactions are going on whereby microbial life peaks and then drops off over a certain temperature. As water warms, the Gulf swells and storms, threatening wetlands and shallows that protect the coast.

She will watch results trickle in from a scientific ship cruise at the end of the month measuring oxygen deprivation off the Gulf coastline. Members of the hypoxia task force will be watching closely, too, no doubt hoping that the LSU model and forecast prove right.

It’s a fascinating twist in a storyline that has run for decades, highlighted by the Des Moines Waterworks 2015 lawsuit against Buena Vista, Sac and Calhoun counties over nitrate pollution of the Raccoon River by ag drainage systems. The lawsuit was dismissed, and the Upper Midwest has stuck to voluntary incentives to heal the Gulf. A confirmed reduction in the size of the dead zone will be cause for celebration in the offices of West Des Moines and the capitol. It won’t mean much at the waterworks, which is running its nitrate removal system again.