Travis Lux / WWNO New Orleans, Public Radio 10 June 2019

The dead zone in the Gulf of Mexico is predicted to be the second biggest in history, according to a new forecast from the Louisiana Universities Marine Consortium (LUMCON).

The dead zone is mostly caused by agricultural run-off from the Mississippi River; nutrients from fertilizers like nitrogen and phosphorus enter the water, causing algae to bloom once it slows and heats up in the Gulf of Mexico. When the algae decays, it uses up oxygen in the water which can stress and kill some sea creatures. The condition of reduced oxygen is known as hypoxia.

LUMCON’s forecast predicts this summer’s dead zone to reach 8,717 square miles. That’s about the size of New Hampshire, and would be just smaller than the 8,776 square miles measured in 2017. The 5-year average is 5,770 square miles — still well above the Hypoxia Task Force’s target of shrinking the dead zone to 1,930 square miles.

LUMCON researcher Dr. Nancy Rabalais says a flooding Mississippi River and high nutrient load are the reasons for the near-record prediction. She and her team have been monitoring the Mississippi River discharge and nutrient levels since the first big pulse of flood water in the spring, so they “weren’t necessarily surprised” by the results of their models.

The model is based on data observed during the month of May, so the measured size typically differs slightly from the forecast.

Rabalais says the dead zone will likely be even bigger if the the Army Corps of Engineers opens the Morganza Flood Control Structure, commonly called the Morganza Spillway, to relieve the flooding Mississippi River. That would likely cause the dead zone to expand farther west.

Rabalais and her team will spend 10 days mapping this year’s dead zone at the end of July.