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BATON ROUGE – A recent forecast of the size of the “Dead Zone” in the northern Gulf of Mexico for late July 2021 is that it will cover 4,761 square-miles of the bottom of the continental shelf off Louisiana and Texas. The Mississippi River discharge of nitrogen in May controls the size of this zone, which will likely be the 16th largest zone since systematic measurements began in 1985. The water mass with oxygen concentrations less than 2 parts per million forms in bottom waters each year primarily as a result of nitrogen loading from the Mississippi River watershed, which fertilizes the Gulf of Mexico’s surface waters to create excessive amounts of algal biomass. The decomposition of this plant material in the bottom layer leads to oxygen loss.

The low oxygen conditions in the Gulf of Mexico’s most productive waters stress organisms, threatening living resources, including fish, shrimp and crabs, and may even kill them. Low oxygen conditions started to appear 50 years ago when agricultural practices intensified in the Midwest. No reductions in the nitrate loading from the Mississippi River to the Gulf of Mexico has occurred in the last few decades.

            The predicted hypoxic area is about three times the land area of Rhode Island and about 2.5 times the size of the Hypoxia Action Plan goal established in 2001. This estimate assumes that there are no significant tropical storms in the two weeks before or during the annual monitoring cruise planned for July 25 to August 1. The estimate is made each year by LSU scientists R. Eugene Turner and Nancy Rabalais. The report is posted at https://gulfhypoxia.net/research/shelfwide-cruise/?y=2021&p=hypoxia_fc.