ANN ARBOR, Mich., June 28 (UPI) -- The Gulf of Mexico's oxygen-starved "dead zone" will be larger than average this year and threatens the region's $659 million fishing industry, scientists say.
The 2010 dead zone could be between 6,500 and 7,800 square miles, an area roughly the size of Lake Ontario, says a forecast released Monday by the U.S. National Oceanic and Atmospheric Administration.
The average size of the zone over the past five years has been 6,000 square miles, NOAA said.
Farmland runoff of fertilizers and livestock waste is the main cause of the annual Gulf of Mexico hypoxia zone. In late spring and summer, these nutrients flow down the Mississippi River and into the gulf, feeding explosive algae blooms.
When the algae die and sink, bottom-dwelling bacteria break down the organic matter, consuming oxygen in the process. The result is an oxygen-starved region in bottom and near-bottom waters: the dead zone.
The possible additional impact of the Deepwater Horizon oil spill on this year's dead zone is difficult to predict, experts say. (The spill began after an explosion on the drilling rig April 20 and oil continues to spew into the gulf.)
"We're not certain how this will play out," University of Michigan aquatic ecologist Donald Scavia said.
"But one fact is clear: The combination of summer hypoxia and toxic-oil impacts on mortality, spawning and recruitment is a one-two punch that could seriously diminish valuable Gulf commercial and recreational fisheries."