Gulf  'Dead Zone' Smaller, Still Larger Than Connecticut

By RICK SPILLMAN
Old Salt Blog
(Reprinted with permission)

The bad news is that the annual summer “hypoxic” or “dead zone” in the Gulf of Mexico this year may be larger than average. The good news is that it will be about 15 percent smaller than last year’s model prediction and roughly 20 percent smaller than the record “dead zone” in 2017. Nevertheless, at 6,700 square miles, this year’s “dead zone” is still larger than the State of Connecticut.
The “dead zone” forms every year due to an algae bloom which deprives the Gulf waters of oxygen. The little or no oxygen in the water can kill fish and other marine life.

 NOAA explains that the algae bloom is caused “by excess nutrient pollution from human activities, such as urbanization and agriculture, occurring throughout the Mississippi River watershed. Once the excess nutrients reach the Gulf they stimulate an overgrowth of algae, which eventually die, then sink and decompose in the water. The resulting low oxygen levels near the bottom are insufficient to support most marine life and have long-term impacts to living marine resources that are unable to leave the area. Considered one of the world’s largest, the Gulf of Mexico dead zone occurs every summer.

“A major factor contributing to this year’s above-average hypoxic zone are the high river flows and nutrient loads delivered to the Gulf this spring, primarily from the Mississippi and Atchafalaya rivers. In May 2020, discharge in the Mississippi and Atchafalaya rivers was about 30 percent above the long-term average between 1980 and 2019.”

There is also a good news/bad news story that may impact the actual size of the “dead zone.” NOAA also notes that “while the hypoxic zone forecast assumes typical coastal weather conditions, the measured dead zone size could be disrupted and its size could be changed by major weather events, such as hurricanes and tropical storms, which mix ocean waters.”
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So, the bad news is that current forecasts are predicting an unusually severe hurricane season this year. The good news is that a severe hurricane season could help mix ocean waters, reducing the size of the “dead zone.”