US floods to create record ‘dead zone’
By Catherine Brahic17:59 15 July 2008–NewScientist.com news service
The floods may be over, but their effects are still being felt far from the US farms that were hit when the levees broke this summer.
Researchers say that the floods which devastated the Midwest in June could play a part in boosting a "dead zone" which annually emerges in the Gulf of Mexico.
As a result, this year’s dead zone could be larger than it has been since records began in 1985.
Each year, oxygen levels in part of the Gulf of Mexico become too low to support life on the sea floor. It is caused by an influx of nutrients – mainly nitrogen – which come from fertilisers flushed out of the Mississippi basin.
The nutrients give a sudden boost to algae growing in the surface waters. As the algae dies, it drops to the sea floor and decomposes. The decay sucks oxygen out of the water, making it impossible for other organisms to survive.
Eugene Taylor of Louisiana State University and colleagues have developed a computer model that predicts how big the dead zone will be, using data from the US Geological Survey on how much nitrogen reaches the Gulf of Mexico each spring.
This year, the team says more run-off than usual will have reached the Gulf. They calculate the dead zone will stretch over 28,000 square kilometres, making it roughly the size of New Jersey. That’s a 27% increase on the previous record of 22,000 km2 set in 2002.