For 36 years scientists have monitored the size of the Gulf of Mexico dead zone or hypoxic zone, which forms every spring. National Oceanic and Atmospheric Administration (NOAA) scientists are forecasting this summer’s hypoxic area or “dead zone” — an area of low to no oxygen that can kill fish and other marine life — to be approximately 4,880 square miles. The 2021 forecasted area is smaller than, but close to the five-year average measured size of 5,400 square miles. The annual prediction is based on U.S. Geological Survey river-flow and nutrient data.
According to NOAA the hypoxic zone is caused by excess nutrient pollution, primarily from human activities, such as agriculture, wastewater treatment and urbanization occurring throughout the Mississippi River Watershed. The excess nutrients stimulate an overgrowth of algae, which eventually die, then sinks and decomposes in the water. The resulting low oxygen levels near the bottom of the Gulf cannot support most marine life. Fish, shrimp and crabs often swim out of the area, but animals that are unable to swim or move away are stressed or killed by the low oxygen. The nutrient pollution runs into rivers that eventually empty into the Gulf.
There are other impacts associated with high nutrient concentrations within watersheds that studies have found. These include high nitrates in groundwater, higher drinking and wastewater treatment costs and wasted fertilizer applications.
“Understanding the effects of hypoxia on valuable Gulf of Mexico resources has been a long-term focus of NOAA’s research,” said Nicole LeBoeuf, acting director of NOAA’s National Ocean Service. “These forecasting models inform us of the potential magnitude of the Gulf of Mexico hypoxic zone that might impact living marine resources and coastal economies.”
The predicted dead zone would be larger than the long-term goal set by the Interagency Mississippi River and Gulf of Mexico Hypoxia Task Force. The Task Force strives to reduce the Gulf dead zone by identifying and implementing collaborative nutrient reduction strategies across the Mississippi River watershed and has set a goal of reducing the size of the hypoxic zone to a five-year average measured size of 1,900 square miles.
Photo courtesy of Jim Alvis and Mike Manning/USGS
