The annual Gulf of Mexico "dead zone" – a region of oxygen-depleted water off the Louisiana and Texas coasts that's harmful to sea life – will be the third-smallest on record this summer, federal scientists said in a report released Tuesday.
This year's zone should be about 2,116 square miles, which is slightly smaller than the size of Delaware. The average Gulf dead zone is about 5,309 square miles.
A dead zone occurs at the bottom of a body of water when there isn't enough oxygen in the water to support marine life. Also known as hypoxia, it's created by nutrient runoff, mostly from over-application of fertilizer on agricultural fields during the spring.
Nutrients such as nitrogen can spur the growth of algae, and when the algae die, their decay consumes oxygen faster than it can be brought down from the surface, NOAA said. As a result, fish, shrimp and crabs can suffocate.
This year's dead zone is smaller due to the passage of then-Tropical Storm Hanna in July, which brought high winds and waves that mixed oxygen into the water off Louisiana down to about 65 feet. (Hanna became a hurricane just before landfall in west Texas.)
Nancy Rabalais, professor at Louisiana State University and report lead author, said that waves also pushed the low-oxygen area deeper than it usually is found. “The map is very different this year,” she said.
However, she noted, “the low-oxygen area will redevelop as long as the winds stay lower and the water’s calm.”
Although smaller than usual, the five-year average size is still almost three times bigger than what experts hope for the dead zone size. "Despite Hanna’s effect, the dead zone this year is still larger than the Environmental Protection Agency’s Hypoxia Task Force long-term goal for reduction," noted economist Rebecca Boehm of the Union of Concerned Scientists. "So there really isn’t much to celebrate this year."
The Gulf of Mexico dead zone is one of the largest in the world, according to NOAA. There is also an annual dead zone in the Chesapeake Bay.
Weather – including wind speed, wind direction, precipitation and temperature – affect the size of the dead zone, which usually fades away by autumn.
The annual dead zone survey was led by scientists at Louisiana State University and the Louisiana Universities Marine Consortium during a research cruise from July 25 to Aug. 1.
Annual measurements of the Gulf dead zone began in 1985, though it likely started in the late 1950s, NOAA reported.
Contributing: The Associated Press
This article originally appeared on USA TODAY: Gulf of Mexico dead zone smaller in summer 2020 due to Hurricane Hanna