Dead Zone Pollution Is Growing Despite Decades of Work, So Who's the Culprit?
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Rabalais has been mapping hypoxia for almost 30 years. Her research helped spawn a state/federal task force, which set a goal of cutting the Gulf’s dead zone almost in half, to about 1,930 square miles, by 2015.
Yet the dead zone keeps growing fatter, like an obese patient unable to shed weight. Last year it was 6,800 square miles – more than triple the goal.
“We’re a long way from the target now – a very long way,” she said. “When that target was set, it didn’t seem impossible, but it’s just getting harder and harder.”
In addition to the 75 percent increase at Hermann, nitrate levels have increased 76 percent since 1980 along the upper Mississippi River at Clinton, Iowa, according to the USGS research. In all, nitrate runoff in the entire basin increased 9 percent over the past 30 years, and much of that increase came from the watershed upstream of Hermann and Clinton.
“This the first time anyone has been able to show the actual concentrations have either not changed or actually increased when we’re supposed to be reducing the loads,” said Don Scavia, a professor of environmental sustainability at the University of Michigan in Ann Arbor who studies the dead zone.
“Whatever conservation practices have been put in place are not enough,” he said.
The corn theory
One theory is that more fertilizer is washing into the watershed because corn acreage has skyrocketed. But urban runoff, livestock and other sources could play a role, too.“These are really large watersheds with a lot of things happening – changes in crop patterns, livestock use, human population,” said Lori Sprague, a USGS hydrologist based in Denver who was lead author of the nitrate study. “All of those things change water quality.”
Farm fertilizer and livestock manure are the two biggest sources of total nitrogen in the Missouri River watershed, together responsible for 70 percent, according to 2011 USGS data. A 2008 study of the entire Mississippi River watershed had similar findings, with agriculture contributing 70 percent of the nitrogen and phosphorous that ended up in the Gulf. Scientists in 2009 also reported a direct correlation between intensive crop production, particularly corn, and nitrate-nitrogen levels in rivers.
Nationally, consumption of nitrogen fertilizer has tripled since the 1960s, surging to 12.3 million tons in 2010, according to USDA data. The amount of nitrogen applied as farm fertilizer grew 18 percent between 1987 and 1997, according to a 2006 USGS study.
It sounds clear-cut. Many farmers, however, tell a different story.
In the Bootheel area of southern Missouri, farmer Mike Geske grows about 2,000 acres of corn, cotton, rice and soybeans near Matthews, Mo. The land lies flat as a plate, the northernmost reaches of the fertile Mississippi delta.
Geske, a third-generation farmer, said when he first started farming in the 1970s, he would lay a thick dose of fertilizer on his fields in the spring. “Anhydrous ammonia was so cheap, we put on 80 to100 pounds extra,” he said.
Today, he applies fertilizer three or four times throughout the year so plants can use it as they need it. He said he uses 20 to 25 percent less fertilizer these days, yet he gets 25 to 30 percent more bushels of corn per acre. He credits better seed technology and careful management of nutrients in the soil.
Farther upstream, fourth-generation farmer Ron Hardecke raises crops, hogs and cattle on 2,000 acres in Owensville, Mo., about 35 miles south of Hermann. He said he carefully monitors his nitrogen use.