The fish-killing “dead zone” in the Gulf of Mexico this summer is the third-smallest in 34 years of surveys, said scientists supported by NOAA. At 2,116 square miles, the hypoxic region is about one-third the size of the forecast of 6,700 square miles, which was based on elevated nutrient runoff and water volume in the Mississippi River this spring.
Hurricane Hanna passed through the central and western Gulf of Mexico days before the annual research and water sampling voyage by scientists, which ran from July 25-Aug. 1. Storms disrupt the dead zone, though it normally forms again within days or weeks. This year, the low-oxygen area partially re-formed before the sampling occurred. Nancy Rabalais, a professor at Louisiana State University, said Hanna generated 5- to 6-foot waves “and mixed the water column down to about 15 to 20 meters.”
The dead zone is caused by nutrients from cities, farms, and other sources that are washed downstream into the Gulf, where they stimulate algal growth. The algae die and the bacteria that eat the algae consume oxygen in the water. The Mississippi River/Gulf of Mexico Watershed Nutrient Task Force has set a goal of reducing the dead zone to an average of 1,900 square miles or smaller by 2035. The current five-year average is 5,408 square miles.