Scientists have determined this year’s Gulf of Mexico “dead zone,” an area of low oxygen that can kill fish and marine life, is 8,776 square miles, an area about the size of New Jersey. It is the largest measured since dead zone mapping began there in 1985. The measured size is close to the 8,185 square miles forecast by NOAA in June.
The annual forecast, generated from a suite of NOAA-sponsored models, is based on nutrient runoff data from the U.S. Geological Survey. Both NOAA’s June forecast and the actual size show the role of Mississippi River nutrient runoff in determining the size of the dead zone.
This large dead zone size shows that nutrient pollution, primarily from agriculture and developed land runoff in the Mississippi River watershed is continuing to affect the nation’s coastal resources and habitats in the Gulf.
These nutrients stimulate massive algal growth that eventually decomposes, which uses up the oxygen needed to support life in the Gulf. This loss of oxygen can cause the loss of fish habitat or force them to move to other areas to survive, decreased reproductive capabilities in fish species and a reduction in the average size of shrimp caught.
The Gulf dead zone may slow shrimp growth, leading to fewer large shrimp, according to a NOAA-funded study led by Duke University. The study also found the price of small shrimp went down and the price of large shrimp increased, which led to short-term economic ripples in the Gulf brown shrimp fishery.
A team of scientists led by Louisiana State University and the Louisiana Universities Marine Consortium collected data to determine the size of the dead zone during a survey mission from July 24 to 31 aboard the R/V Pelican.
“We expected one of the largest zones ever recorded because the Mississippi River discharge levels, and the May data indicated a high delivery of nutrients during this critical month which stimulates the mid-summer dead zone,” said Nancy Rabalais, Ph.D., research professor at LSU and LUMCON, who led the survey mission.
“Having a long-term record of the size of the Gulf of Mexico dead zone is vital in forecasting its size, trends and effects each year,” said Steven Thur, Ph.D., acting director of NOAA’s National Centers for Coastal Ocean Science. “These measurements ultimately inform the best strategies for managers to reduce both its size and its impacts on the sustainability and productivity of our coastal living resources and economy.”
Previously the largest Gulf of Mexico dead zone was measured in 2002, encompassing 8,497 square miles. The average size of the dead zone over the past five years has been about 5,806 square miles, three times larger than the Gulf Hypoxia Task Force target of 1,900 square miles.
NOAA funds monitoring and research efforts to understand the dead zone in the Gulf of Mexico through its Northern Gulf of Mexico Ecosystems & Hypoxia Assessment program, known as NGOMEX. The annual dead zone measurement is used by the Gulf of Mexico/Mississippi River Watershed Nutrient Task Force to determine whether efforts to reduce nutrient pollution in the Mississippi River basin are working. New initiatives such as the Runoff Risk Advisory Forecast are designed to help farmers apply fertilizer at optimum times to limit nutrient runoff to the Gulf.
The 2017 “Dead Zone” measured 22,720 square kilometers (8,776 square miles). This size is close to the forecast made in June as described below. The 2017 dead zone size is above the five-year average (15,032 sq km). It is also more than four times larger than the Hypoxia Task Force Goal of 5,000 square kilometers. Researchers suggest that the Mississippi River May discharge, which was well above average, provides an explanation for most of the large zone measurement. For more information, read the Louisiana Universities Marine Consortium (LUMCON) and the National Oceanic and Atmospheric Administration (NOAA)
NOAA, USGS and partners predict third largest Gulf of Mexico summer ‘dead zone’ ever
The Gulf’s hypoxic or low-oxygen zones are caused by excess nutrient pollution, primarily from human activities such as agriculture and wastewater treatment. 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 Gulf dead zone may also slow shrimp growth, leading to fewer large shrimp, according to a NOAA-funded study led by Duke University. This could mean higher costs of large shrimp at the marketplace and an economic ripple effect on the 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.”
This NOAA-sponsored forecast is based on nutrient runoff and river discharge data from the U.S. Geological Survey. The forecast assumes typical weather conditions, and the actual dead zone could be disrupted by hurricanes and tropical storms.
This year’s predicted large size is due mainly to heavy May stream flows, which were about 34 percent above the long-term average and carried higher-than-average nutrient loads. The 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.
The USGS operates more than 3,000 real-time stream gauges, 60 real-time nitrate sensors, and 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 dead zone in early August, following monitoring surveys.
The ensemble of models that are the foundation of the forecast was developed by NOAA-sponsored teams of researchers 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 the USGS.
To help reduce nutrient runoff, NOAA provides information to farmers through its Runoff Risk Advisory Forecasts, which tell them when to avoid applying fertilizers to their croplands.
2015 Gulf of Mexico Hypoxic Zone Size
The 2015 “Dead Zone” measured 16,760 square kilometers (6,474 square miles). This size is larger than the predicted range made in June as described below. The 2015 dead zone size is above the five-year average (14,024 sq km). It is also three times larger than the Hypoxia Task Force Goal of 5,000 square kilometers. Researchers suggest that heavy rains in June and high river discharges in July may provide an explanation for the larger zone measurement.
Measuring the Hypoxic Zone
The hypoxic zone in the northern Gulf of Mexico is an area along the Louisiana-Texas coast, where water near the bottom of the Gulf contains less than two parts per million of dissolved oxygen, causing a condition referred to as hypoxia.
Each summer, the size of the hypoxic zone is measured. The size of the zone is an important indicator of how much progress is being made to reduce nutrient inputs into the Gulf of Mexico. Sometimes the size of the zone is influenced by other factors, such as droughts or hurricanes that can reduce the size of the zone, or floods that can increase the size.