An oxygen-starved hypoxic zone, commonly called a dead zone and shown in red, forms each summer in the Gulf of Mexico. Fish and shellfish either leave the oxygen-depleted waters or die, resulting in losses to commercial and sports fisheries. Image credit: NOAAANN ARBOR—A University of Michigan researcher and colleagues from several institutions forecast that this summer’s Gulf of Mexico “dead zone,” an area of low to no oxygen that can kill fish and other marine life, will be approximately 8,185 square miles, or about the size of New Jersey.

This would be the third-largest Gulf of Mexico dead zone recorded since monitoring began 32 years ago. The average gulf dead zone since then has been 5,309 square miles.

The gulf’s hypoxic (low-oxygen) and anoxic (oxygen-free) zones are caused by excess nutrient pollution, primarily from agriculture and wastewater. The excess nutrients stimulate an overgrowth of algae, which then sinks and decomposes in the water. The resulting low oxygen levels are insufficient to support most marine life and habitats in near-bottom waters, threatening the gulf’s fisheries.

The 2017 forecast was released today by the National Oceanic and Atmospheric Administration, which sponsors the work. The researchers said there is a 90 percent chance that this year’s dead zone will be between 5,323 and 11,535 square miles.

In its 2001 action plan—which was confirmed in 2008 and again in 2013—the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force set the goal of reducing the five-year running average areal extent of the gulf hypoxic zone to 1,950 square miles by 2015. The task force is a coalition of federal, state and tribal agencies.

But little progress has been made toward that goal, and the target has been moved to 2035. The most recent five-year average is 5,410 square miles.

“Even though the federal-state action plan calling for nutrient-load reductions has been in place since 2001, there has been little systematic reduction in those loads,” said U-M aquatic ecologist Don Scavia, a professor of natural resources and environmental engineering.

“The bottom line is that we will never reach the action plan’s goal of 1,950 square miles until more serious actions are taken to reduce the loss of Midwest fertilizers into the Mississippi River system.”

Scavia is a member of NOAA-funded teams that produce annual forecasts for the Gulf of Mexico, the Chesapeake Bay and Lake Erie. The 2017 Chesapeake Bay hypoxia forecast was released June 14 and called for a larger-than-average dead zone. The Lake Erie harmful algal bloom forecast will be issued in early July.

In the Gulf of Mexico, the dead zone may slow shrimp growth, leading to fewer large shrimp, according to a NOAA-funded study led by Duke University. This could mean higher costs for large shrimp at the marketplace and an economic ripple effect on gulf shrimp fisheries.

“The gulf’s summer hypoxic zone continues to put important habitats and valuable fisheries under intense stress,” said Rob Magnien, director of NOAA’s Center for Sponsored Coastal Ocean Research. “Although there is some progress in reducing nutrients, the effects of the dead zone may further threaten the region’s coastal economies if current levels remain.”

The NOAA-sponsored forecast is based on nutrient runoff and river discharge data from the U.S. Geological Survey. The forecast assumes typical weather conditions; the actual dead zone could be disrupted by hurricanes and tropical storms.

This year’s predicted large dead-zone size is due mainly to heavy May stream flows, which were about 34 percent above the long-term average and had higher-than-average nutrient loads. USGS estimates that 165,000 metric tons of nitrate—about 2,800 train cars of fertilizer—and 22,600 metric tons of phosphorus flowed down the Mississippi and Atchafalaya rivers into the Gulf of Mexico in May 2017.

The USGS operates more than 3,000 real-time stream gauges and 60 real-time nitrate sensors. The agency tracks trends in nutrient loads and concentrations throughout the Mississippi-Atchafalaya watershed, which drains parts or all of 31 states.

“As algal blooms and hypoxia become more widespread and their effects more pronounced, the USGS’s long-term monitoring and real-time sensors, coupled with watershed modeling, will continue to improve our understanding of their causes and the role they play in the gulf and in lakes and streams across the country,” said Don Cline, associate director for the USGS Water Mission Area.

The partners plan to confirm the size of the 2017 Gulf of Mexico dead zone in early August, following monitoring surveys.

The ensemble of models that are the foundation of the forecast was developed by NOAA-sponsored modeling research teams at the University of Michigan, Louisiana State University, Louisiana Universities Marine Consortium, Virginia Institute of Marine Sciences/College of William and Mary, Texas A&M University, North Carolina State University and USGS.

More information:

• 2017 U-M Gulf of Mexico hypoxia forecast