This summer’s Gulf of Mexico dead zone is forecasted by federal scientists to be approximately 8,185 square miles, or about the size of New Jersey, making it the third largest the Gulf has seen.
According to NOAA, dead zones are hypoxic (low-oxygen) areas in the world’s oceans and large lakes, caused primarily by nitrogen, phosphorus and other nutrient pollution from human activities such as agriculture and wastewater treatment coupled with other factors that deplete the oxygen required to support most marine life in bottom and near-bottom water. The nutrient pollution runs into rivers that eventually empty into the Gulf.
Every year for the past 32 years scientists have monitored the size of the Gulf dead zone. During that time the hypoxic zones have averaged 5,300 square miles, about the size of Connecticut. This year’s forecast of 8,185 square miles is being blamed on heavy May stream flows, which were about 34 percent above the long-term average and carried higher than average nutrient loads. The nutrients feed plankton blooms that die and sink to the bottom, where their decay uses oxygen. The resulting low oxygen levels are insufficient to support most marine life and habitats in near bottom waters, threatening the Gulf’s fisheries.
The scientists are concerned that 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.
In a statement, Rob Magnien, director of NOAA’s Center for Sponsored Coastal Ocean Research said “The Gulf’s summer hypoxic zone continues to put important habitats and valuable fisheries under intense stress. 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 date from the U.S. Geological Survey (USGS). The forecast assumes typical weather conditions, and the actual dead zone could be disruted by hurricanes and tropical storms. 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 Atchafalya rivers into the Gulf of Mexico in May.
The size of the 2017 Gulf dead zone will be confirmed in early August following monitoring surveys.