The Gulf of Mexico's hypoxic zone (dead zone) is predicted to be larger than average this year, due to extreme flooding of the Mississippi River this spring, according to an annual forecast released Tuesday by a team of NOAA (National Oceanic and Atmospheric Administration) -supported scientists.

Scientists from the Louisiana Universities Marine Consortium, Louisiana State University and the University of Michigan are predicting the area could measure between 8,500 and 9,421 square miles, or an area roughly the size of New Hampshire. The forecast is based on Mississippi River nutrient inputs compiled annually by the U.S. Geological Survey (USGS).

The largest hypoxic zone measured to date occurred in 2002 and encompassed more than 8,400 square miles. The average over the past five years is approximately 6,000 square miles of impacted waters, much larger than the 1,900 square miles which is the target goal set by the Gulf of Mexico/Mississippi River Watershed Nutrient Task Force.

"This ecological forecast is a good example of NOAA applied science," said Jane Lubchenco, NOAA administrator, in a statement. "While there is some uncertainty regarding the size, position and timing of this year's hypoxic zone in the Gulf, the forecast models are in overall agreement that hypoxia will be larger than we have typically seen in recent years."

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 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.

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 U.S. dollars. Nearly three million recreational fishers further contributed more than one billion to the Gulf economy taking 22 million fishing trips.

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