Scientists detect high levels of nitrogen in Midwest waterways

Aug 27, 2013

This spring and summer, U.S. Geological Survey scientists waded into 100 Midwest streams to test for hundreds of chemicals used in farming, including nutrients, pesticides like atrazine and glyphosate, and livestock hormones. The results from the study are trickling in. But preliminary findings indicate that from May through early July, 21 percent of the region’s streams contained very high levels of nitrogen in the form of nitrates.

The nitrate concentrations at these streams exceeded the Environmental Protection Agency’s standards for safe drinking water. And though these streams don’t often provide water for nearby populations, they still affect the water supply.

“People aren’t drinking water directly out of these streams,” said Peter Van Metre, a hydrologist with the U.S. Geological Survey. “They’re drinking water out of city water treatment facilities or water systems that are largely taking water from larger rivers or reservoirs downstream. But those larger streams are being affected by these high concentrations in the small streams as well.”

The highest nitrate concentrations were found in Iowa and Minnesota streams. In Iowa, 72 percent of the streams had nitrate levels that exceeded safe drinking water standards. The highest detected concentration in the state was in the South Fork Iowa River near Buckeye. In Minnesota, 66 percent of streams exceeded safe drinking water standards. In Illinois, 31 percent of the samples showed high nitrates.

The cost of removing nitrates from drinking water

Lately, high nitrate levels have caused major problems for water treatment plants in parts of the Midwest that draw source water from lakes, reservoirs and rivers. In Central Iowa, Des Moines Water Works paid $900,000 this summer to remove nitrates from its source water, the Raccoon and Des Moines Rivers. That hefty bill will get passed on to customers.

“The process of treating this polluted water to deliver it in a safe and fair fashion is very expensive,” said general manager Bill Stowe. “But it’s also raising great concerns among our consumers about the safety of their tap water.”

Stowe said when babies and pregnant women consume nitrates, serious health problems can follow.

“Our concern, obviously, is that once you shake customers' faith in the safety of tap water, you turn them to other sources like bottled water, which is ... certainly a competitor,” he said. “It changes our business model and puts us at risk in the long term as a viable utility.”

Last year’s drought is one reason nitrate levels in the water have been so high lately. It prevented some parched fields from absorbing fertilizers applied by farmers. Then, extremely wet weather this spring caused a higher than normal load of nitrates to flow into the water.

Nitrate runoff is, of course, cyclical. It tends to be at its annual peak in the early summer after farmers have planted their crops, applied fertilizers and subsequent rainfall washes nitrates into area waterways. In Iowa, for example, nitrate levels in the Raccoon and Des Moines Rivers no longer exceed safe drinking water standards. But that doesn’t mean Stowe’s concerns have abated.

“It’s a foreboding issue,” Stowe said. “We are uncertain and concerned about when we’ll face the same issue again.”

The impact of nitrates on the environment

Nitrates in Missouri streams sampled in the U.S. Geological Survey (USGS) study did not exceed drinking water standards. Still, other data show concentrations are rising on parts of the Missouri River, which supplies much of the state’s drinking water.

The USGS has been tracking nitrate runoff near Hermann, Mo., at a slight bend in the Missouri River for decades. Historic sampling data indicates that levels are at least 75 percent higher there now than they were in 1980. In the middle of June, nitrates clocked in at more than double what they were in early May.

Beyond drinking water concerns, high nitrates hurt the Gulf of Mexico by contributing to the so-called “Dead Zone,” which is now the size of Connecticut.

“Some scientists have related the size of that zone of low dissolved oxygen to the amount of nitrogen that comes out of the Mississippi River and it’s been getting larger over time,” said Richard Coupe , also a hydrologist with USGS. “And so eventually, there’s concern that it could destroy the fisheries in the Gulf of Mexico or adversely affect them.”

Coupe believes farmers must continue to feed the world but not at the expense of the environment or drinking water sources.

“As we learn more and we collect more data and we kind of put these models together, we see how certain types of landscape activities affect this and that we can kind of change things,” he said. “And we need to show people that we can change.”

Using precision agriculture to limit nitrate runoff

But how can farmers limit the amount of fertilizer they use – and therefore the amount of nitrates that wash into waterways – while still producing a bumper crop?

Some farmers believe they have an answer to that question in the form of a crop reflectance censor. These devices, when connected to a farmer’s sprayer, tell the applicator to put less nitrogen on healthy corn plants and more nitrogen on weaker ones. Newell Kitchen, a U.S. Department of Agriculture-Agricultural Research Survey soil scientist, has been researching the effectiveness of different kinds of crop reflectance censors on the market.

“You would actually take readings over the top of the corn,” Kitchen said. “And the light is shining down on the corn and it's reflecting back up and then it records the information of what it reads.”

With price tags of up to $10,000 each, these crop sensors aren’t cheap. Yet a recent national survey found that this year, 7 percent of farmers are now using them, up from 4 percent in 2011.

“One of the solid arguments for these technologies is if I do put the right rate at the right place, then there’s less nitrogen at the end of the growing season that might be there that can go into streams and rivers or can go off into the atmosphere as, like, a greenhouse gas. And so it is a win-win,” Kitchen said.

Other strategies for reducing nitrate runoff include planting cover crops and nitrogen-efficient crop varieties. But it’s at the farmers’ discretion. Because currently, few states have laws, and there is no federal law, limiting the amount of nitrogen that farmers can put on their fields. 

Video dispatch

Harvest Public Media's Abbie Fentress Swanson rode the Missouri River with scientists checking the water's quality.