This NOAA-supported modeling effort 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 "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.
"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 LSU professor Eugene Turner. "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."
Research indicates that nearly tripling the nitrogen load into the Gulf over the past 50 years has led to the heightened hypoxia problem. The scientists say their research will improve assessments of hypoxic effects under various Gulf Coast oceanographic conditions.