Each year a hypoxic water mass with oxygen concentrations ≤2 mg l-1 forms in bottom waters of the northern Gulf of Mexico continental shelf. The low oxygen conditions threaten living resources including humans that depend on fish, shrimp and crabs. Nutrients from the Mississippi River watershed, particularly nitrogen and phosphorus, fertilize the Gulf’s surface waters to create excessive amounts of algal biomass, whose decomposition in the bottom layer leads to oxygen distress and even organism death in the Gulf’s richest waters. Various models use the May nitrogen load of the Mississippi River as the main driving force to predict the size of this hypoxic zone in late July. This prediction is based on one of these models.

The June 2016 forecast of the size of the hypoxic zone in the northern Gulf of Mexico for late July 2016 is that it will cover 17,673 km2 (6,824 mi2) of the bottom of the continental shelf off Louisiana and Texas. The 95% confidence interval is that it will be between 12,609 and 22,013 km2 (4,868 and 8,499 mi2). This estimate is based on the assumption that there are no significant tropical storms occurring in the two weeks before the monitoring cruise, or during the cruise. If a storm does occur, then the size of the zone is predicted to be 70% of the predicted size without the storm, equivalent to 12,371 km2 (4,776 mi2).

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