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Mississippi Flooding Predicted To Create Large Gulf Dead Zone

June 15, 2011

The Gulf of Mexico’s “dead zone” is predicted to be the largest ever recorded due to extreme flooding of the Mississippi River this spring, according to a team of scientists working through the support of the National Oceanic and Atmospheric Administration (NOAA).

The scientists, from the Louisiana Universities Marine Consortium, Louisiana State University and the University of Michigan, based their forecast on Mississippi River nutrient inputs compiled annually by the US Geological Survey (USGS).

The “dead zone” — or hypoxic zone — could command an area between 8,500 and 9,241 square miles, roughly the size of New Hampshire or Lake Erie. If that estimate holds up, it will be the largest since mapping the Gulf hypoxic zone began in 1985. The current largest dead zone occurred in 2002 and measured more than 8,400 square miles.

Over the past five years, the dead zone averaged about 6,000 square miles per year of affected waters, much larger than the Gulf of Mexico/Mississippi River Watershed Nutrient Task Force’s goal of 1,900 sq. miles.

The NOAA/USGS collaboration along with university scientists brings a better understanding of the link between activities in the Mississippi River watershed and downstream impacts to the Gulf waters. Long-term data sets on nutrient loads and the extent of the hypoxic zone have improved forecast models used by management agencies to understand the nutrient reductions required to reduce the size of the dead zone.

Each year when the nutrient-rich freshwater from both the Mississippi and Atchafalaya rivers pour into the Gulf of Mexico, it spawns massive algae blooms. Those blooms consume much of the oxygen available in the surrounding waters, creating the low oxygen conditions. Fish, shrimp and other marine life must escape the hypoxic zone or risk death.

Dead zone forecasts are usually quite accurate, although hurricanes, which are prone to the Gulf of Mexico, have faltered those forecasts in the past.

When the hypoxic zone forms each summer off the coast of Louisiana and Texas it threatens important commercial and recreational Gulf fisheries.

“This ecological forecast is a good example of NOAA applied science,” said Jane Lubchenco, Ph.D., undersecretary of commerce for oceans and atmosphere and NOAA administrator. “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.”

Eugene Turner, an oceanographer at Louisiana State University, said the dead zone has continually gotten larger and worse each year since it was first noticed in the 1970s.

The biggest contributor to the dead zone is the amount of fertilizer that winds up in the Mississippi River each spring. The nitrogen-rich fertilizer is “fertilizing the waters offshore,” said Turner, adding that little progress has been made to reduce the nutrient load in the Gulf of Mexico.

However, the governments, along with states in the Mississippi valley, are now attempting to reduce runoff from farms, lawns and cities, but the efforts have, so far, done little to curb the problem.

The USGS said the nitrogen load this year was 35 percent higher than the average amount flushed into the Gulf each May over the past 32 years. The Mississippi and Atchafalaya rivers dumped nearly twice as much water than normal in May, according to officials.

“As usual, the size of the low oxygen offshore is driven by both the freshwater and nitrogen levels in the Mississippi, so this year we have had floods and we have had more nitrate coming into the system,” Nancy Rabalais, executive director of the Louisiana Universities Marine Consortium, told The Associated Press (AP).

Rabalais, a lead researcher of the dead zone, says she expects the dead zone to extend more to the west toward Texas and farther offshore than in previous years.

The increased stream-flow rates in May significantly increased the amount of nitrogen transported by the rivers into the Gulf. USGS officials estimated that 164,000 metric tons of nitrogen were transported by the Mississippi and Atchafalaya Rivers to the northern Gulf.

“The USGS monitoring network and modeling activities for water quantity and quality helps us “Ëœconnect the dots’ to see how increased nutrient run-off in the Mississippi watershed during a historic spring flood event impacts the health of the ocean many hundreds of miles away,” said Marcia McNutt, Ph.D., USGS director.

Coastal and freshwater resource managers across the country require new and better integrated information and services to adapt to future climate and land-use changes, an aging water delivery infrastructure, and an increasing demand on limited resources.

NOAA, USGS, and US Army Corps of Engineers have signed an agreement that will further facilitate collaborative efforts in the future. These agencies, with missions in water science, observation, prediction and management, have formed this collaborative effort to unify their commitment to address the nation’s water resources information and management needs.

Scientists said this year’s large dead zone will complicate the Gulf’s recovery from last year’s massive BP oil disaster, which spewed more than 200 million gallons of oil into the Gulf. “This is an additional stressor,” said Rabalais.

The actual size of this year’s dead zone will be released between July 25 and August 6 by the NOAA. NOAA has been funding the yearly investigations and forecast developments into the dead zone since 1990 and currently oversees two national hypoxia programs authorized by the Harmful Algal Bloom and Hypoxia Research and Control Act.

Image 1: Sediment from the Mississippi River carries fertilizer to the Gulf of Mexico. Credit: NASA

Image 2: Long-term measured size of Gulf of Mexico hypoxic zone with 2011 forecast. Dark gray represents the range of ensemble forecast. Credit: Nancy Rabalais LUMCON/NOAA

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Mississippi Flooding Predicted To Create Large Gulf Dead


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