SAN FRANCISCO -- A dramatic doubling in the size of a "dead zone" in the Gulf of Mexico near the mouth of the Mississippi River has raised new concerns among scientists and policy makers. The hypoxic region, where oxygen levels drop to two ppm or less, has expanded each summer since the record-breaking Midwest flood of 1993. Within that zone, which can be as large as the state of New Jersey, fish and other sea creatures become stressed and many die.
Because the gulf is a leading U.S. fishery, the ecological and economic stakes of a continuing hypoxic zone there are enormous. To confront the problem, an 18 month assessment, under the auspices of the White House Office of Science and Technology Policy is underway to prepare a thorough study of the issue. This assessment, conducted by the Committee on Environmental and Natural Resources, will characterize the hypoxia, investigate its sources and consequences, and evaluate the social and economic costs of various methods of reducing nutrient loads. The assessment will include an examination of the benefits that some nutrient enhancement may have for biological productivity. Hypoxia in the gulf also will be addressed by a high-level task force, which met as a full group for the first time in December.
Anecdotal evidence suggests that small pockets of hypoxia have been present in the gulf for several decades at least. But when the 1993 flood flushed nutrients from farms, cities, and industrial areas into the river system and down to the gulf, it caused a doubling of the size of the dead zone.
When nutrients hit the gulf, they stimulate algae blooms. Bacteria that feed on the algae and on the fecal matter of other organisms deplete the oxygen along the ocean bottom. The dead zone develops between February and October, peaks in the summer following freshwater pulses of nutrients, and dissipates in the fall when storms stir up the water. But each summer since 1993, the size of the dead zone has ballooned to between 15,540 and 18,300 square kilometers -- its size following the big flood. During the past 5 years, the zone has been two times as large as it was during the preceding 8 years. This dramatic increase might be due to residual effects from the 1993 flood or to continued high water volume -- nobody has a definitive answer.
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