NOAA FORECASTS LARGER THAN NORMAL "DEAD ZONE" FOR GULF THIS SUMMER
July 24, 2006 — A team of scientists from the NOAA National Centers for Coastal Ocean Science, Louisiana Universities Marine Consortium and Louisiana State University is forecasting that the "Dead Zone" off the coast of Louisiana and Texas this summer will be larger than the average size since 1990. (Click NOAA image for larger view of Bottom Dissolved Oxygen Contours in the Gulf of Mexico taken July 14-16, 2006. Click here for high resolution version. Please credit “NOAA.”)
This NOAA supported modeling effort, led by Eugene Turner, Ph.D., of LSU, predicts this summer's "Dead Zone" will be 6,700 square miles, an area the half the size of the state of Maryland. Since 1990 the average annual hypoxia-affected area has been approximately 4,800 square miles. The forecast is based on nitrate loads from the Mississippi and Atchafalaya rivers in May and incorporates the previous year's load to the system. The nitrogen data are provided by the U.S. Geological Survey. NOAA funds research cruises to track development of hypoxia.
The "Dead Zone" is an area in the Gulf of Mexico where seasonal oxygen levels drop too low to support most life in bottom and near-bottom waters. 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.
There are multiple models of the size of the hypoxic zone that are useful in evaluating the influence of nitrogen load and variations in ocean currents on the size of the "Dead Zone." These models do not always produce similar results, and model improvement is one focus of ongoing research. Over the past four years, NOAA and its collaborators have compared two independent models. The LSU model is the most accurate model based on past performance, but it is still in the experimental stages. Additional research for model improvement is required before this annual prediction can become an operational forecast.
"We are anticipating a larger hypoxic zone this summer because the nitrate loading this May, a critical month influencing the size of the area, is higher than last year," said Turner, explaining the NOAA forecast. "The result is that we will have some additional key information about the relative contribution of stratification and nutrient concentrations in different years which should help us better understand the causes behind this annual event."
"This prediction is an example of the ecological forecasting capabilities of NOAA and its partners," said David Whitall, Ph.D., a NOAA scientist involved in the project. "We believe such forecasts will become important tools for coastal managers in the coming years."
Research 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.
These research, observational and modeling studies are part of a larger NOAA sponsored effort to develop a fundamental understanding of the northern Gulf of Mexico ecosystem with a focus on the causes and effects of the hypoxic zone over the Louisiana continental shelf and the prediction of its future extent and impacts to ecologically and commercially important aquatic species.
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