Janet McConnaughey / Associated Press 16 May 2019
NEW ORLEANS — The year’s widespread flooding has made it likely that a big, oxygen-starved “dead zone” off Louisiana’s coast will form this summer, the head of the National Centers for Coastal Ocean Science said Thursday.
Preliminary computer model runs “indicate a large to very large year,” for the area where there’s too little oxygen to support marine life, Steven Thur told the Mississippi River/Gulf of Mexico Hypoxia Task Force during a meeting livestreamed from Baton Rouge. Thur’s agency is part of the National Oceanic and Atmospheric Administration.
The task force coordinates work to cut the amount of nitrogen and phosphorus flowing into the Gulf. The nutrients feed algae and plankton which die and fall to the bottom. Their decomposition uses up oxygen from the bottom up, resulting in low oxygen levels, called hypoxia. Fish and shrimp can swim away, but starfish and other bottom-dwellers die.
A detailed forecast of the world’s second-largest human-caused dead zone usually comes out in June.
The spring floods are likely to mean significant amounts of the widely used fertilizers have run from farmland into waterways in the 31 states that feed the Mississippi River. Sewage treatment plants, manure, and other sources also contribute to the river’s nutrient load from 41% of the U.S. mainland.
Last year’s dead zone covered about 2,720 square miles (7,040 square kilometers), about 40% the average size that had been predicted, and was one of the smallest recorded since Louisiana researcher Nancy Rabalais began mapping them in 1985.
It was smaller than usual only because winds stirred up the Gulf just before the annual mapping cruise, mixing oxygen into the water, Thur said.
In recent years, Thur noted, mapping cruises overseen by Rabalais have run out of money and had to end before the entire area was covered.
He said money is allocated for mapping cruises this year and next, and the government is looking into whether underwater robots could map a wider area and get more information about the total volume of the dead zone. The technology has advanced greatly in the four years since the last attempt, he said.
The nutrients carried by the river and the size of the dead zone have changed little since the task force released its first action plan in 2001, Matt Rota, senior policy director for the nonprofit Healthy Gulf, said during a public comment period.
“Regretfully, nutrient loadings in the Gulf have increased — nitrogen by a little, phosphorus quite significantly, according to U.S. Geological Survey data. 2017 also gave us the largest dead zone ever measured, and last year’s (smaller area) was an anomaly,” Rota said.
He said one study has estimated that it would take about $1 billion a year to prompt enough voluntary action to reduce the dead zone.
“If this task force is going to dedicate themselves to promotion of voluntary mechanisms, we need to figure out a way to get a lot more money,” he said.