Lemke says IDALS scientists from Iowa State University and other agricultural entities stressed the need to explore the cause of Gulf hypoxia far beyond fertilizer use. “Ocean scientists have tried to correlate fertilizer use to growth of the hypoxia zone since the 1960s,” he says. “But the issue is a lot more complicated than that.”

A National Corn Growers Association (NCGA) white paper shows that the trail of soil sediments and other materials merged into the Mississippi and other rivers goes far beyond farmers.

The document points out that from 1983 to 1990, about 25 sq. mi. of riverbank erosion resulted every year. “Erosion not only puts organic matter directly into the waters near the hypoxic zone, but it also intensifies summer stratification by increasing the volume of warm, fresh water delivered to the hypoxic zone,” according to the NCGA.

In addition, construction along the Missouri River — which accounts for 45% of the total flow of the Mississippi River past St. Louis — has also put organic matter into the waters. The NCGA paper says the Army Corps of Engineers sent over 5 million tons of soil into the Missouri, containing about 11 million pounds of N and 9.3 million pounds of P.

EVIDENCE FROM SEDIMENT samples in the area of the hypoxia indicate that the source of organic matter there is from phytoplankton production in the overlying waters, and not from continental organic runoff, says Nancy Rabelais, aquatic ecologist and executive director of LUMCON, which heads Gulf Coast hypoxia monitoring.

Farm Bureau, IDALS, NCGA and researchers at Texas A&M University stress that more research is needed to determine the dead zone's cause. A&M's Thomas Bianchi and Steven DiMarco, who study the Gulf hypoxia, say destruction of wetlands over the years has prevented filtration of nitrates and other contaminants from the Mississippi and other rivers.

They say that from 1930 to 1990, the Mississippi delta experienced about 80% of the nation's wetland loss — 690,000 acres. Artificial canal dredging, pond creation and natural creation caused the losses. The A&M group says the peak hypoxia situations correlate with the time periods of peak wetland losses.

Rabalais points out that “accounting of nutrients coming into the Mississippi River by the U.S. Geological Survey indicates that agriculture is not the single culprit, but clearly contributes most of the P and N to the Mississippi River.” She says the survey indicates that at least half the N and 25% of the P derives from corn and soybean crops.

There are no easy solutions. However, Lemke says strategically located and designed wetlands could certainly help. But the magnitude is huge.

“We could need 10,000-15,000 such target wetlands in Iowa alone,” he says. “That's not going to happen overnight — or by 2015 as the action plan calls for on N and P reductions in waterways.”

Rabalais says there are certainly differences in scientific opinion regarding the hypoxia, its cause and how to alleviate the problem. Lemke says these differences in opinion between agricultural forces and the non-ag scientific community will likely remain on the complex subject.