The Gulf of Mexico’s hypoxic zone is predicted to be the largest ever recorded due to extreme flooding of the Mississippi River this spring, according to an annual forecast by a team of NOAA-supported scientists from the Louisiana Universities Marine Consortium, Louisiana State University and the University of Michigan. The forecast is based on Mississippi River nutrient inputs compiled annually by the U.S. Geological Survey (USGS).
Scientists are predicting the area could measure between 8,500 and 9,421 square miles, or an area roughly the size of New Hampshire. If it does reach those levels it will be the largest since mapping of the Gulf “dead zone” began in 1985. The largest hypoxic zone measured to date occurred in 2002 and encompassed more than 8,400 square miles.
Hypoxia is caused by excessive nutrient pollution, often from human activities such as agriculture that results in too little oxygen to support most marine life in bottom and near-bottom water. The hypoxic zone off the coast of Louisiana and Texas forms each summer and threatens valuable commercial and recreational Gulf fisheries. In 2009, the dockside value of commercial fisheries in the Gulf was $629 million. Nearly three million recreational fishers further contributed more than $1 billion to the Gulf economy taking 22 million fishing trips.
During May 2011 stream-flow rates in the Mississippi and Atchafalaya Rivers were nearly twice that of normal conditions. This significantly increased the amount of nitrogen transported by the rivers into the Gulf. According to USGS estimates, 164,000 metric tons of nitrogen (in the form of nitrite plus nitrate) were transported by the Mississippi and Atchafalaya Rivers to the northern Gulf. The amount of nitrogen transported to the Gulf in May 2011 was 35 percent higher than average May nitrogen loads estimated in the last 32 years.
The actual size of the 2011 hypoxic zone will be released following a NOAA-supported monitoring survey led by the Louisiana Universities Marine Consortium between July 25 and August 6. Collecting these data is an annual requirement of the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force Action Plan.