A team of scientists from the National Oceanic and Atmospheric Administration (NOAA), Louisiana Universities Marine Consortium and Louisiana State University (LSU) is forecasting that a so-called dead zone off the coast of Louisiana and Texas has the potential to be the largest since shelf wide measurements began in 1985. The dead zone, an area where seasonal oxygen levels drop to low to support most life in bottom and near-bottom waters, is on track to be significantly larger this summer than in years past.

The dead zone modeling effort, led by R. Eugene Turner of LSU, predicts this summer's zone may be as large as 8,500 sq miles, an area the size of New Jersey. The average annual hypoxia-affected area has been approximately 4,800 sq miles since 1990, and last year's dead zone measured 6,662 sq miles.

Tropical storms and hurricanes can disrupt the physical structure of the water column and expose the bottom layer, and NOAA predicts an active hurricane season for 2007. Also, algal growth, stimulated by nutrient input from the Mississippi and Atchafalaya Rivers, settles and decays in bottom waters. Decaying algae consume oxygen faster than it can be replenished from the surface, decreasing dissolved oxygen levels and threatening the Gulf's valuable fishery.

The research team's forecast is based on May nitrate loads form the aforementioned rivers and incorporates 2006 conditions, as well. The nitrogen data are provided by the U.S. Geological Survey.

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 indicate the importance of nutrient loading to the development of hypoxia but do not always produce the same predictions for a given year. Model improvement is a major focus of ongoing research.

Over the past four years, NOAA and its collaborators have compared two independent models in an experimental forecast product. 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 needed before this annual prediction can become an operational forecast.

Research indicates that nearly tripling the nitrogen load into the Gulf over the past 50 years has led to the heightened hypoxia problem. Team scientists say their research will improve assessments of hypoxic effects under various Gulf Coast oceanographic conditions.

Source: National Oceanic & Atmospheric Administration (NOAA)