The Gulf of Mexico “dead zone” will approach near record levels this year according to the National Oceanic and Atmospheric Administration (NOAA). This year’s dead zone will be approximately 7,829 square miles – roughly the size of the state of Massachusets.
Each year, NOAA forecasts the size of the hypoxic zone in the Gulf of Mexico – an area where oxygen is low enough that it kills fish and marine life. Predictions are based on a number of factors, including the U.S. Geological Survey (USGS) river flow and nutrient data.
The Gulf of Mexico dead zone is one of the largest recurring dead zones in the world and is caused by excess nutrient pollution from human activities, particularly agriculture and urbanization. Agriculture runoff enters the Mississippi River and is carried to the Gulf, where it causes an overgrowth of algae. When the algae die, they sink and decompose in the water, causing low oxygen levels.
This year, heavy rains and flooding along the Mississippi River watershed have led to much higher than normal nutrient loading. According to the USGS, 156,000 metric tons of nitrate -about 18 percent above average – and 25,300 metric tons – about 49 percent above average – of phosphorus were carried into the Gulf this year.
The prediction assumes normal coastal weather conditions, but the size of the dead zone can be affected by things like tropical storms, hurricanes, and other wind major wind events.
The largest dead zone ever recorded was 8,776 square miles in 2017. While this year’s zone won’t quite reach that size, it is still far above the five-year average of 5,770 square miles. A NOAA-supported monitoring survey will be conducted in early August to confirm the size of the 2019 Gulf of Mexico dead zone in order to help test the accuracy of and refine the models used to predict the area.
“The models help predict how hypoxia in the Gulf of Mexico is linked to nutrient inputs coming from throughout the Mississippi River Basin,” said Dr. Steve Thur, director of NOAA’s National Centers for Coastal Ocean Science.
“This year’s historic and sustained river flows will test the accuracy of these models in extreme conditions, which are likely to occur more frequently in the future according to the latest National Climate Assessment. The assessment predicts an increase in the frequency of very heavy precipitation events in the Midwest, Great Plains, and Southeast regions, which would impact nutrient input to the northern Gulf of Mexico and the size of the hypoxic zone.”
According to Done Cline, associate director of the USGS Water Resources Mission Area, while phosphorus and nitrate loading has been decreasing in other coastal estuaries, that hasn’t been the case in the Gulf of Mexico.
The USGS uses more than 3,000 real-time stream gauges, 50 real-time nitrate sensors, and 35 long-term monitoring sites throughout the Mississippi-Atchafalaya watershed. That area drains all of the streams and rivers from 31 states and 31 Canadian provinces into the Gulf of Mexico.
Jenn Bentley is a freelance writer and editor whose work has been featured in publications such as The High Tech Society, FansShare, Yahoo News, Examiner.com, and others. Follow her on Twitter: @JennBentley_