2014 Hypoxic (Dead Zone) Predicted To Be Nearly the Size of Connecticut
June 25, 2014
Each year a hypoxic water mass with oxygen concentrations < 2 mg/l 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 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 2014 forecast of the size of the hypoxic zone in the northern Gulf of Mexico for July 2014 is that it will cover 14,785 km2 (5,708 mi2) of the bottom of the continental shelf off Louisiana and Texas. The 95% confidence interval is that it will be between 12,078 and 17,378 km2 (4,663 and 6,710 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 10,350 km2 (7,245 mi2). The predicted volume without storms is 43.2 km3 with a 95% confidence interval between 35.1 and 52.1 km3. The predicted hypoxic area is about the area of Connecticut. If the area of hypoxia becomes this large, then it will equal about three times the size of the goal of the Hypoxia Action Plan (less than 5,000 km2).
Caveats: 1) This prediction discounts the effect of large storm events that temporarily disrupt the physical and biological system attributes promoting the formation of the low oxygen zone in bottom waters; 2) The potential space on the shelf where hypoxia occurs is limited by the bathymetry; 3)The predictions assume that there will be no abrupt changes in discharge from now through July; 4)Unusual weather patterns affecting coastal winds, as experienced in 2009 and 2011, may skew the prediction to be lower.