Washington - This year's low-oxygen "dead zone" in the Gulf of Mexico is one of the largest ever, about the size of Massachusetts, and overlaps areas hit by oil from BP's broken Macondo well, Louisiana scientists report.
The area of hypoxia, or low levels of oxygen, covered 20 000 square kilometres of the bottom of the Gulf and extended far into Texas waters, researchers from the Louisiana Universities Marine Consortium said in a statement late on Sunday.
"This is the largest such area off the upper Texas coast that we have found since we began this work in 1985," said Nancy Rabalais, the consortium's executive director. "The total area probably would have been the largest if we had had enough time to completely map the western part (of the Gulf)."
The annual summer "dead zone" in the Gulf is fuelled by farm chemicals carried by the Mississippi and Atchafalaya rivers. Nitrogen and phosphorus in agricultural runoff stimulates algae growth in the Gulf.
When these tiny plants or fecal matter from animals that eat them settles to the bottom waters, decomposition of this organic material by bacteria consumes oxygen in the water, the consortium said.
The result, the researchers said, is oxygen depletion that forces many types of fish, shrimp and crabs to leave the area or suffocate. Animals that live in the sediments that can survive with little oxygen will die if the oxygen level falls toward zero.
To be considered hypoxic, oxygen content in the bottom waters of the Gulf must reach the level of two parts per million or less. By late July, large patches of the northern Gulf had reached that level, including one swath off Texas's Galveston Bay.
While the area of the BP oil spill overlaps some parts of the "dead zone", Rabalais said. "It would be difficult to link conditions seen this summer with oil from the BP spill in either a positive or negative way." - Reuters