May 17, 2016
The flow of nitrates from farm fertilizer and treated wastewater into the Illinois River that contributes to a dead zone in the Gulf of Mexico has fallen, a new study says. Researchers believe one likely factor, the use of newer, more robust varieties of corn, could make the drop a long-lasting one.
The study from the University of Illinois found that the level of nitrates dropped 10 percent between 2010 and 2014. Adding in data from 2015 that was not available when the study was being written, that level dropped by 15 percent, one co-author said.
“The varieties (of corn) that are planted these days and in the last few years are more robust in a lot of different ways,” co-author and agricultural engineering professor Greg McIsaac said, calling the reductions a “promising sign.”
The Illinois river drains almost half of Illinois, most of it primary corn-growing land in a state that produces about a sixth of the nation’s crop. The river also carries lightly treated wastewater from the Chicago area, which for more than a century has discharged it in through waterways that wind up in the Illinois to keep it out of Lake Michigan — a move that caused resentment further down the river.
The Illinois flows into the Mississippi River, which takes on additional nitrates and other chemicals that fuel the Gulf’s dead zone, a massive area of water with little to no oxygen that kills fish and other marine life. The dead zone has been a stubborn problem that federal officials want to address.
Data used in the study, which was published May 6 in the Journal of Environmental Quality, suggest that varieties of corn adopted in recent years grow more crop per acre and are better at resisting drought, disease and pests are making better use of nitrogen fertilizer. That means less is left in the field to wash away into the river, McIsaac said.
McIsaac cited the difference in corn crops in two drought years, 2012 and 1988. The 2012 crop, grown during the period of reduced nitrate flow, was “respectable” in spite of the drought.
“The corn yields in 1988 were pretty terrible, and that left a lot more nitrogen fertilizer in the fields — and a lot of that nitrogen fertilizer ended up in the river,” McIsaac said.
Experts on the effects of nitrates on water quality and aquatic life who were not involved in the study but read its findings say they are encouraging, and rare good news about the flow of chemicals into the Mississippi and the Gulf.
Watersheds in other states that feed the Mississippi, such as Iowa, have shown little or no improvement, said Nancy Rabalais, director of the Louisiana Universities Marine Consortium and a marine ecology professor whose research has focused on the dead zone since the 1980s.
“If this is a trend of some kind of reversal because of some kind of agricultural improvements, that’s wonderful,” Rabalais said.
Charles Driscoll, a professor of environmental systems at Syracuse University, agreed.
“There are, I guess, few success stories,” Driscoll said. “I think it shows that maybe we can do something about this problem.”
The U.S. Environmental Protection Agency wants to eventually reduce the amount of nitrates and phosphorus, another fertilizer component that contributes to the dead zone, by 45 percent.
A smaller but significant source of nitrates is the treated wastewater from the Water Reclamation District of Greater Chicago, which comes in through a canal and the Des Plaines River.
While the authors are fairly confident that crop improvements are a primary reason for the reductions they found, they say they are not sure about potential reasons for the decreases found in wastewater.
A spokeswoman for the district said it has worked over the past five years to reduce both the phosphorous and nitrates it discharges.
“Early efforts show a reduction of nitrogen in addition to the phosphorus of between 30 and 40 percent,” spokeswoman Allison Fore said in an email.
The study’s findings are also potentially good news for water quality within the Illinois River basin. The city Peoria and its 186,000 residents, for instance, use the river for part of their drinking-water supply.