The size of this year’s so-called dead zone in the Gulf of Mexico, which runs practically the entire coastline at 3,000 square miles, is smaller than forecasted, according to Nancy Rabalais, executive director of the Louisiana Universities Marine Consortium. However, she says the dead zone, which is usually limited to water just above the sea floor, was so severe where it did occur that it is extending closer to the surface – a new trend.
Earlier this summer, the National Oceanic and Atmospheric Association sponsored forecast models developed by a group of researchers and they predicted a larger-than-normal dead zone area of between 7,450 and 8,456 square miles. The forecast was driven primarily by the high nitrate loads and high freshwater flows from the Mississippi and Atchafalaya rivers in the spring, as measured by the U.S. Geological Survey.
Rabalais believes the smaller dead zone is due to unusual weather patterns that re-oxygenated the waters, among other factors. “The winds and waves were high in the area to the west of the Atchafalaya River delta and likely mixed oxygen into these shallower waters prior to the cruise, thus reducing the area of the zone in that region,” says Rabalais. “The variability we see within each summer highlights the continuing need for multiple surveys to measure the size of the dead zone in a more systematic fashion.”
The dead zone is fueled by nutrient runoff, principally from agricultural activity, which stimulates an overgrowth of algae that sinks, decomposes and consumes most of the life-giving oxygen supply in the water. The Gulf of Mexico dead zone is of particular concern because it threatens valuable commercial and recreational fisheries that generate about $2.8 billion annually.
The average size of the dead zone over the past five years is about 6,000 square miles. The interagency Gulf of Mexico/Mississippi River Watershed Nutrient Task Force has a goal to reduce this figure to 2,000 square miles or less by 2015.—Jeremy Alford
