MONEY

The real story on nitrate levels in Iowa's rivers

Donnelle Eller
deller@dmreg.com
Chris Jones, an environmental specialist at the Iowa Soybean Association, agrees that nitrate levels in the Raccoon and Des Moines rivers have trended up over the past 40 years. But, he said, the data show little or no change from 1984 to 2014 and slight improvement when measuring from 1994 and 2004.

Nitrate levels in Iowa's major rivers have increased more than threefold since the 1950s, but have stabilized — and even slightly declined — in recent decades, according to an in-depth review of available research.

The increased levels directly correspond with Iowa's rise as an agriculture powerhouse. As production soared in the '60s, '70s and '80s, so did nitrates — climbing from an average of around 2 milligrams per liter from 1906-1954 to more than 7 milligrams per liter from 1954-2010, according to a Register analysis of water-quality research.

"It's unmistakable. The long-term trend is decidedly upward," said Keith Schilling, a research scientist at the Iowa Geological Survey at the University of Iowa, who has studied nitrate levels in the state's rivers.

Yet, that same research shows that nitrate levels, while still elevated, have shown signs of ebbing slightly in recent decades, potentially indicating Iowa farmers are doing a better job of employing conservation practices that can slow and capture nitrates before they get into streams and rivers.

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The studies lend credence to both sides of the ongoing argument over Iowa's water quality — farm groups that say Iowa's nitrate levels are improving vs. Des Moines Water Works' complaint it needs to spend millions of dollars in the years ahead to clean water to meet federal standards of no more than 10 milligrams of nitrates per liter.

Those historically higher levels — exacerbated by wet periods that can flush more nitrates into streams and rivers — prompted the Des Moines water utility to file a lawsuit against three farm-heavy counties in northern Iowa in January, claiming upstream drainage districts were sending high levels of nitrates into the Raccoon River, the source of drinking water for 500,000 residents.

The suit has raised critical questions about farming's effect on Iowa's water quality. And it has spotlighted the impact of nitrates, which can be harmful, or even fatal, to infants younger than 6 months without treatment.

Two factors have given rise to Iowa's high nitrate levels, research shows:

• Drainage tiles, which help make about 12 million acres of Iowa land farmable, enable nitrogen that's both applied and in the soil organically to move much more quickly into Iowa rivers and streams.

• Massive row-cropping, which has put roughly two-thirds of Iowa land into farm production, also is elevating nitrate concentration in the state's waterways, say Schilling and others. And the loss of perennial crops such as alfalfa in many farmers' rotation plays a role in those rising levels.

In essence, the very elements that have made Iowa farmers the most productive in the world are responsible for elevating nitrate levels in the state's waterways.

"Because of the sheer area ... farming is always going to be the No. 1 source" of nitrates, Schilling said.

But he and other experts warn that nitrate trends can be tricky, subject to large swings brought on by drought or heavy rains.

"Depending on the time period you pick, or the site you pick, you can get different numbers," he said.

Nitrates' shifting trends

The Des Moines utility says in its lawsuit that it has experienced record nitrates in the Raccoon River watershed in 2013, 2014 and 2015. And its data show nitrate levels in the Raccoon River have pushed upward since 1974.

The utility has spent about $1 million in recent years to remove nitrates from the water so it's safe to drink, with record high levels threatening to overwhelm its nitrate removal equipment, according to the complaint.

Chris Jones, an environmental specialist at the Iowa Soybean Association, agrees that nitrate levels in the Raccoon and Des Moines rivers have trended upward over the past 40 years. But, he said, the data show little or no change from 1984 to 2014 and slight improvement when measuring from 1994 and 2004.

Moreover, a study Jones recently completed with UI's Schilling shows that nitrate levels at 39 of 41 sites on tributaries flowing into the Raccoon River have declined from 1999 to 2014.

Tom Isenhart talked about t a new nitrate reduction practice called saturated buffers; it diverts water from drainage tiles, then relies on trees, shrubs to take up the nitrates before it hits waterways; it’s something of a superstar in reducing nitrates from the water that’s been diverted

However, Jones concedes: "Even with a downward trend, we can't deny that nitrate concentrations in the Raccoon and Des Moines rivers can still be very high, and can still be over the drinking water standard for extended periods of time."

The crux of the difference between farm groups and the utility, Jones said, is the decision to litigate vs. "working together to find solutions."

The role of farm production

Much of Iowa's nitrogen — and nitrates — are in the soil organically.

Iowa has about 10,000 pounds of organic nitrogen per acre, according to Iowa State University professors Matt Helmers and Michael Castellano. "To get a sense of scale, a farmer might apply 150 to 200 pounds of nitrogen per acre to a corn crop," said Castellano, an assistant professor of agronomy.

Each year, about 30 pounds of nitrogen per acre is lost, much of it from organic matter that's already in the soil, say Castellano and Helmers. Studies show about the same amount of nitrogen is lost regardless of whether farmers grow corn or soybeans, which requires no nitrogen application.

"There's no statistical difference," Castellano said.

Nitrates occur when Iowa's rich soils get warm and wet, and microbes convert nitrogen — both that farmers apply and what's available organically — into nitrates, which plants use to grow.

Problems occur, though, when there are no plants in the fields to soak up the nitrates — particularly in the spring and the fall — allowing them to seep into waterways, said Castellano and Helmers, an agricultural biosystems engineer.

It's why leaders have pressed farmers to adopt conservation practices such as cover crops. Cereal rye and other crops can help soak up nitrates before Iowa's massive corn and soybean crops are too young to do it in the spring — or ready to be harvested in the fall, the ISU professors say.

High organic soil matter is "one of the reasons why we have such high production in Iowa," Castellano said. "It's also one of the reasons we have nitrate losses."

Drainage tiles a two-edge sword

Drainage tiles are another culprit in Iowa's elevated nitrate levels, moving water and nitrates from fields into nearby waterways, said Schilling, the UI researcher.

Drainage tiles dry the soils, boosting yields. But the tiles pick up and carry nitrates "like sugar in water" to nearby ditches or streams, he said.

Schilling said a new study shows farming and drainage tiles move water about 150 times faster than before settlement.

But Schilling said it's difficult to accurately measure drainage tiles' impact on nitrate runoff, since farmers aren't required to report how much they install.

"We have no real clue how many miles and miles of tiles are out there in the Iowa landscape," Schilling said.

Even non-tiled areas get water and nitrates moving below the crop root zone to downstream waters" during large rains, said Matt Helmers, an Iowa State University agronomy professor.

Schilling said Iowa wouldn't have agriculture without tiling. "You can't remove tile from the system unless you want to go back to wetlands."

Changing nitrate levels

While drainage tiles are helping move nitrates from farm fields, research shows high upstream nitrate levels can decline by the time they reach Des Moines.

That complicates the picture of exactly where the nitrates are originating before they reach water utilities.

"There's so much processing that can occur in a river, I'm not sure the nitrate discharge from those drainage districts is a big contributor all the way at the mouth of the river in the Des Moines area," Schilling said.

Decreasing nitrate levels from upstream contributors is good news for water utilities such as Des Moines, he said. Reducing nitrate levels upstream 25 percent could be enough to keep Des Moines from exceeding safe drinking water standards, he said.

"You don't have to get to zero," he said.

Water Works' lawsuit targets Calhoun, Sac and Buena Vista counties, putting on trial upstream drainage districts and pushing to regulate them much like factories, wastewater plants and businesses. The outcome could impact districts, and indirectly farmers, across Iowa and the nation, since agricultural runoff is now exempt from federal clean water standards.

Bill Stowe, CEO of Des Moines Water Works, argues that it doesn't matter that high nitrate concentrations from northern counties could be diluted before reaching Des Moines.

"We believe those districts have completely shirked their responsibility" over their contribution to nitrate levels in the Raccoon River, he said. "You can't sidestep that and say, 'oh, there are diluted impacts beneath us, so we can do what we want.' "

The studies

Stability

Keith Schilling, a research scientist at the Iowa Geological Survey, and other University of Iowa researchers looked at nitrate levels across the state from 1998 to 2012 and discovered that 80 percent — or 37 of 46 sites tested — showed no statistically significant change in nitrate concentrations. Six sites running parallel with the Missouri River showed significantly increasing trends.

Raccoon impaired

The Raccoon River in Des Moines is considered impaired, due to high nitrate levels, although studies show that level slightly decreasing since 1987. Altogether, Iowa has 479 impaired rivers, lakes and streams. Schilling said 92 percent of the total nitrate loads for the Raccoon come from nonpoint sources, meaning areas such as farming.

What about phosphorus?

The state's nutrient reduction strategy also calls for reducing phosphorus, a fertilizer that's carried by soil through erosion and other losses into waterways. Schilling and other UI scientists looked at phosphorus trends at sites on 42 rivers and found eight sites trended slightly higher, although it wasn't statistically significant; 34 sites showed downward trends, and 12 sites showed statistically significant declines. "It's good news," he said. "Agriculture should get credit for doing something right."