NEW ORLEANS — An area in the Gulf of Mexico with too little oxygen to keep sea creatures alive is the 11th largest measured and nearly 18 percent bigger than predicted earlier this year.
It has gotten so big because heavy June rains throughout the Mississippi River watershed carried nutrient-rich runoff from farms and other human activities into the gulf, federal and state scientists said Tuesday.
Those nutrients, mainly nitrogen and phosphorus, feed algae and other one-celled plants that die and fall to the bottom, where their decomposition uses up oxygen.
This year's dead zone is about as big as Connecticut and Rhode Island combined, covering 6,474 square miles, said Nancy Rabalais, who has measured the low-oxygen area for 31 years and is now director of the Louisiana Universities Marine Consortium.
It also extends higher than usual above the bottom, and much of the area has even less oxygen than usual, she wrote in her annual report.
The cutoff for the low-oxygen condition, known as hypoxia, is less than 2 milligrams of oxygen per liter of water. Much of the hypoxic area had less than half that much, often very close to zero, Rabalais wrote.
The National Oceanic and Atmospheric Administration had predicted the hypoxic area would cover nearly 5,500 square miles, based on combining four models. The highest of those four predictions was low by nearly 500 square miles.
Last year's dead zone was about the size of Connecticut.
"In 2001, state and federal bureaucrats set a goal of reducing the size of the Dead Zone to 1,950 square miles by 2015," said Matt Rota, senior policy director for the nonprofit Gulf Restoration Network. "Well, here we are at 2015, and we are over three times that goal."
Rota's group and others sued the Environmental Protection Agency in 2012 for failing to set and enforce standards for nitrogen and phosphorus pollution nationwide. That suit is in federal court in New Orleans.
Early this year, an EPA-led task force postponed the deadline for shrinking the dead zone from 2015 to 2035, with an interim goal of a 20 percent nutrient reduction by 2025. Scientists estimated that a 45 percent cut is needed to reach the 1,950-square-mile goal, according to an EPA news release about that change.