NOAA Predicts Summer Dead Zone in the Gulf of Mexico

NOAA Predicts Summer "Dead Zone" in the Gulf of Mexico

Hypoxia research could improve gulf assessments
29 July 2004

The oxygen-starved zone off the coast of Louisiana and Texas this summer is predicted to remain between 10,619 and 16,835 square kilometers, about the same size as it has been since 1990, according to a team of U.S. government scientists, the Louisiana Universities Marine Consortium and Louisiana State University. The dead zone is an area in the Gulf of Mexico where oxygen levels are too low to support most life. It is caused by a seasonal change in the growth of algae that is stimulated by input of nutrients like nitrogen and phosphorus from the Mississippi and Atchafalaya rivers. The algae settle and decay in the bottom waters, where they consume oxygen faster than it can be replenished from the surface. This leads to hypoxia, or decreased levels of dissolved oxygen.The Mississippi River system drains all or parts of 31 states and 6,086 square kilometers before reaching the Gulf of Mexico; the Atchafalaya River, an outlet for the Mississippi River, arises in central Louisiana and flows south 362 kilometers to Atchafalaya Bay.

National Oceanic and Atmospheric Administration (NOAA) funds research cruises to track the development of hypoxia. These have been conducted monthly since January and will be completed by the end of July. The forecast about the size of this summer's dead zone is based on nutrient loads from the Mississippi and Atchafalaya rivers in May and June provided by the U.S. Geological Survey.

Research from the team indicates that nearly tripling the nitrogen load into the gulf over the past 50 years has increased hypoxia there. The latest research could help improve assessments of hypoxic effects under various gulf coast oceanographic conditions.

The northern Gulf of Mexico's bottom-water summer hypoxic zone in recent years has extended roughly 604 kilometers westward from the mouth of the Mississippi River across the Louisiana-Texas border.

Further information is available at http://www.ncddc.noaa.gov/Habitat/coastwatch

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National Oceanic and Atmospheric Administration
U.S. Department of Commerce

NOAA News Online

NOAA, LOUISIANA SCIENTISTS ISSUE "DEAD ZONE" FORECAST

July 26, 2004 — A team of NOAA scientists, the Louisiana Universities Marine Consortium and Louisiana State University is forecasting that the "Dead Zone" off the coast of Louisiana and Texas this summer should be roughly the same size as it has been since 1990. This summer's Dead Zone is predicted to be between 4,100 and 6,500 square miles, an area the size of Connecticut and Rhode Island combined. The average annual hypoxia-affected area since 1990 has been approximately 5,700 square miles. The forecast is based on nutrient loads from the Mississippi and Atchafalaya rivers in May and June provided by the U.S. Geological Survey.

NOAA funds research cruises to track development of hypoxia. These have been conducted monthly since January and will be completed by the end of July.

"This effort is an example of an innovative environmental service—officially referred to as 'ecological forecasting'—that NOAA scientists believe will become an important tool in coming years for both decision makers and the public," according to Richard Spinrad, Ph.D., assistant administrator of the NOAA Ocean Service.

The Dead Zone is an area in the Gulf of Mexico where oxygen levels are too low to support most life. It is caused by a seasonal change where algal growth, stimulated by input of nutrients such as nitrogen and phosphorus from the Mississippi and Atchafalaya rivers, settles and decays in the bottom waters. The decaying algae consume oxygen faster than it can be replenished from the surface, leading to decreased levels of dissolved oxygen.

Research from the team indicates that nearly tripling the nitrogen load into the Gulf over the past 50 years has led to the heightened Gulf of Mexico hypoxia problem. The scientists say their research will improve assessments of hypoxic effects under various Gulf Coast oceanographic conditions. Multiple models of the size of the hypoxic zone are useful in evaluating the influence of nitrogen load and variations in ocean currents on the size of the Dead Zone.

"By using river-dissolved-oxygen model based on Mississippi River nutrient loadings in the northern Gulf of Mexico, our research team was also able to look back more than 30 years and determine that these now virtually perennial events were uncommon before the mid-1970s," said Donald Scavia, professor of natural resources and environment at the University of Michigan and former chief scientist of the NOAA Ocean Service.

Last year, the scientific team made the first advance forecast of the annual hypoxic event in the Gulf of Mexico. This year, scientists used two independent models to make this forecast. Despite differences in the way the different models function, each model predicted roughly the same size of the Dead Zone for this year.

The modeling effort led by Eugene Turner of LSU predicts that the Dead Zone will be 5,600 square miles and the modeling effort led by NOAA scientists predicts the size will be 5,400 square miles (with a range of 4,100 to 6,500).

"Algal blooms that fuel the eventual summer hypoxia events were abundant this spring when the Mississippi River discharge peaked multiple times with a prolonged summer peak in June through early July," said Nancy Rabalais, chief scientist for hypoxia research at LUMCON. "The additional input of freshwater and nutrients in the summer contributed to further algal blooms and an intensification of stratification."

The northern Gulf of Mexico's bottom-water summer hypoxic zone in recent years has extended roughly 375 miles westward from the mouth of the Mississippi River across the Louisiana/Texas border.

The NOAA Ocean Service is dedicated to exploring, understanding, conserving and restoring the nation's coasts and oceans. It balances environmental protection with economic prosperity in fulfilling its mission of promoting safe navigation, supporting coastal communities, sustaining coastal habitats and mitigating coastal hazards.

NOAA is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and providing environmental stewardship of the nation's coastal and marine resources. NOAA is part of the U.S. Department of Commerce.

Relevant Web Sites

NOAA Hypoxia Watch System for the Gulf of Mexico http://www.ncddc.noaa.gov/Habitat/coastwatch

NOAA Coastal Ecosystem Program

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