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'Dead zone' predicted to become 2nd largest on record in Gulf of Mexico this summer

By Chaffin Mitchell, AccuWeather staff writer
June 12, 2019, 2:20:38 PM EDT

Scientists from the National Oceanic and Atmospheric Administration (NOAA) predict that there will be a large area in the Gulf of Mexico, roughly the size of Massachusetts, of low to no oxygen that may kill fish and other marine life this summer.

This area is an annually recurring spot called the hypoxic zone or ‘dead zone’ where excessive nutrient pollution from the Mississippi River watershed spills into the Gulf of Mexico. The pollution stems from human activities coupled with other factors such as urbanization and agriculture, and it depletes the oxygen required to support most marine life.

Dead zone satellite

A satellite image shows the light colors of sediments and nutrients reaching deeper into the Gulf of Mexico waters, which can ultimately cause a dead zone. (NOAA)

High spring rainfall and river discharge into the Gulf are major contributors to how big a dead zone can become.

"This happens every year due to rainfall in the Mississippi River basin and snowmelt from the northern Plains and the Midwest," AccuWeather Senior Meteorologist Jack Boston said.

"Excess nutrient pollution" from areas upstream empty from the Mississippi River into the Gulf of Mexico, especially during the late spring and early summer when the flow of the Mississippi is at its strongest, Boston said.

When these nutrients reach the Gulf they trigger an overgrowth of algae. The algae then dies and decomposes in the water.

"This basically robs the water in this area of its natural oxygen, taking a toll on marine life and causing a good percentage of marine life to expire," Boston said.

Scientists are forecasting this summer’s Gulf of Mexico dead zone to be approximately 7,829 square miles. The annual prediction is based on U.S. Geological Survey river flow and nutrient data.

"Due to heavy rainfall and snowmelt upstream, this year's dead zone is expected to be bigger than average," Boston said.

The abnormally high amount of spring rainfall in many parts of the Mississippi River watershed led to record high river flows and thus will contribute to much larger nutrient loading in the Gulf of Mexico, Boston added.

This year's dead zone is expected to near the record size of 8,776 square miles, which was set in 2017. It's also predicted to be significantly larger than the five-year average measured size of 5,770 square miles.

GRAPHIC - dead zone - 06072019 - NOAA - 1120x534 - LANDSCAPE.jpg

Forecast of the dead zone in the Gulf of Mexico during summer of 2019. (NOAA)

“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," said Steve Thur, Ph.D., director of NOAA’s National Centers for Coastal Ocean Science.

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"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," Thur said.

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