玉米種植過量 墨西哥灣「死海區」近2/3台灣面積

This year's dead zone in the Gulf of Mexico is likely to be the largest on record and growing U.S. corn production is a primary cause of the worsening conditions, federal and state scientists said Tuesday.

The research team predicts that the dead zone - a stretch of water without enough oxygen to support marine life - could cover some 8,800 square miles this summer, an area roughly the size of the state of New Jersey.

The forecast was announced today by scientists with the U.S. National Oceanic Atmospheric Administration, NOAA, Louisiana Universities Marine Consortium and Louisiana State University, LSU, who predicted the dead zone would be the largest since official monitoring began in 1985.

The dead zone forms annually off the coasts of Louisiana and Texas, fed by nutrient heavy water from the Mississippi River. The country's largest river drains some 40 percent of the United States, including much of its agricultural heartland and its corn belt.

From as far north as Minnesota, runoff water laden with fertilizer nutrients nitrogen and phosphorous flows into river and into the Gulf, stimulating an overgrowth of algae. When the algae die, they sink to the bottom and decompose, depleting oxygen levels in the water and choking out marine life.

"The strong link between nutrients and the dead zone indicates that excess nutrients from the Mississippi River watershed during the spring are the primary human-influenced factor behind the expansion of the dead zone," said Rob Magnien, director of the NOAA Center for Sponsored Coastal Ocean Research. Last year's dead zone reached some 7,900 square miles, but the record came in 2002, when the area totalled nearly 8,500 square miles.

Record corn harvests throughout the Midwest are clearly adding to the problem, according to Eugene Turner, a scientist with LSU, and leader of the research team.

U.S. farmers are planting "an awful lot of corn and soybeans," he told reporters, adding that both crops leach nitrogen easily into soil and groundwater.

Corn production in the United States has shot up dramatically in recent years, driven by demand for corn-based ethanol. The U.S. Agriculture Department estimates some 87 million acres of corn were planted this year.

Some 817,000 tons of nitrogen, roughly 35-45 percent above normal, seeped into the Gulf between April and June, according to the U.S. Geological Survey, USGS.

Added to the mix is a record amount of phosphorous flowing into the Gulf.

The USGS reported that 85,000 tons of phosphorous entered the Gulf from April through June, some 85 percent above normal levels.

"It is going to have to come from changes in land use," Turner said. "We will have to reduce the amount of nitrogen coming off the watershed."

He suggested farmers move away from perennial crops that leave the land barren and susceptible to flooding, but warned that reductions in nutrient runoff will not yield instant results. Nitrogen is stored in the soil and can continue leaching for many years.

In February, NCGA corn growers, conservation organizations and companies throughout the agriculture supply chain teamed up to launch a first-of-its-kind working group to help establish sustainable outcomes for agriculture.