Is Cedar River segment impaired for nitrate? Experts disagree

CEDAR RAPIDS — The Cedar River flows through the heart of Cedar Rapids, where it supplies drinking water to the city’s population.

Its watershed historically has been impaired for nitrate — a form of nitrogen linked to blue baby syndrome, cancer and other negative health impacts. Nonetheless, Cedar Rapids’ treated drinking water always has met safe drinking water standards for the contaminant.

In October, the Iowa Department of Natural Resources proposed to withdraw the watershed’s water quality improvement plan created in 2006 to help keep the city’s drinking water safe — the first-ever proposal of its kind for the department. The announcement was met with backlash from researchers, including a former Iowa DNR supervisor who believes the withdrawal goes against federal law.

The department’s public notice states that the river segment in question hasn’t been impaired for nitrate since April, the month the department’s latest biennial water quality report was approved by the U.S. Environmental Protection Agency. The two most recent reports show that nitrate levels in the segment — which extends from Bear Creek in Palo to McLoud Run in Cedar Rapids — haven’t violated department standards since 2016.

Because of this, the waterway will not be placed back on the state’s impaired waters list, according to the notice.

The Gazette spoke with the Iowa DNR and researchers about the Cedar River, its historical and current nitrate levels, how the contaminant is measured and what they say about the waterway’s water quality. The result: The department’s determination that the river is no longer impaired is at odds with several expert opinions.

“That’s not really reflective of what we think we've seen in the rest of the state in terms of nitrate levels,” Mary Skopec, executive director of the state-owned Iowa Lakeside Laboratory, which offers science classes and research opportunities for university students. “I'm skeptical.”

Current and historical nitrate levels

A nitrate impairment was first listed for the Cedar River in 1998. The 2006 water quality improvement plan attributed 91 percent of the nitrogen pollution in the watershed to runoff from nonpoint sources like fertilizer, crops and manure — which is not regulated under the federal Clean Water Act.

The U.S. Geological Survey has tracked water quality in the Cedar River since at least the 1990s. It uses sensors that measure the amount of nitrate and other substances in the waterway every 15 minutes based on their light absorbance. Depending on the year, these sensors may be taken out of the water during the winter.

Staffers also collect monthly water samples and analyze them for constituents that sensors can’t measure, like pesticides and metals.

So far this year, sensor data revealed that nitrate levels in the Cedar River segment have exceeded the 10-milligrams-per-liter limit during as many as 47 days, said hydrologist Jessica Garrett of the USGS Central Midwest Water Science Center.

The city of Cedar Rapids uses wells to pull drinking water from beneath the river after it has filtered through sand and gravel, where microorganisms reduce the amount of nitrate. Still, the city has noted elevated levels of the contaminant this year.

“While nitrate concentrations in the Cedar River were lower from 2016 to 2021, we did notice an increased concentration of nitrate in untreated source water in 2022,” said Roy Hesemann, the Cedar Rapids utilities director. But when treated, the drinking water has never exceeded safe standards for nitrate.

Analyzing decadeslong trends for nitrate levels gets a bit trickier, Garrett said. It’s difficult to compare newer data with historical data that was measured differently and less frequently. Additionally, stream flows in the Midwest tend to be increasing over time. That makes it harder to calculate how contaminant concentrations may be changing.

Despite these challenges, existing USGS studies show that nitrate loads haven’t decreased in the river over the past few decades, Garrett said. The USGS is also completing a new report that includes assessments of nutrient trends in the Iowa River and Cedar River in the last 40 to 50 years.

Iowa DNR’s impairment determination

To support its conclusion that the Cedar River segment in question is no longer impaired, the Iowa DNR relied on its biennial integrated reports summaries that help track water quality in the state, said Katie Greenstein, the department’s supervisor of water quality monitoring and assessment.

The river segment’s use for drinking water was deemed “fully supported” in the 2020 and 2022 reports — which means that significantly more than 10 percent of the collected nitrate data did not violate the 10-milligrams-per-liter limit.

“There can still be some exceedances based on how water quality standards work,” Greenstein said. “But it essentially means that, for the majority of the time, the values were lower than that standard.”

Altogether, the data in both reports spanned from 2016 to 2020. It was gleaned from about 360 water samples taken in the river segment by the USGS and the Cedar Rapids water utility, most likely on a monthly or weekly basis.

Greenstein said the Iowa DNR uses direct measurements — like physical water samples — in its assessments instead of data pulled from nitrate sensors like the ones USGS uses.

“Nitrate sensors are not being used for assessments for nitrate for the (reports) because sensors indirectly estimate nitrate, and data are statistical estimates,” she said.

If the segment in question becomes impaired again, Greenstein said the department would write an updated and improved water quality improvement plan, which could take years to craft. The EPA won’t approve another plan for the river without a listed impairment.

Nitrate sensors vs. water samples

Several water quality experts told The Gazette they were concerned about the Iowa DNR’s determination that the Cedar River was no longer impaired for nitrate. They said it contradicts existing research and available data about the watershed’s water quality — including the USGS sensor data that wasn’t factored into the department’s decision.

Data collected from nitrate sensors is valuable and should be considered when assessing the Cedar River’s impairment status, said Chris Jones, a University of Iowa research engineer who studies water quality. He led a 2020 research study that showed nitrate sensor data is comparable to conventional lab samples.

“It’s disturbing that DNR would make statements that apparently attempt to discredit water quality data collected by the federal government’s top science agency,” he said.

Since the USGS sensors continuously collect data, they can track nitrate on a fine-scale timeline. This helps researchers better understand nutrient behavior and can act as an early warning system for high concentrations coming down the waterway.

Monthly or weekly sampling can miss peaks that vary from day to day, potentially resulting in an incomplete picture of a waterway’s nutrient load over time, said David Cwiertny, director of the University of Iowa’s Center for Health Effects of Environmental Contamination and collaborator on the 2020 research with Jones.

“The general concern, when you develop a sampling plan, is how representative are the samples of what's really going on?” he said. “More data is always better.”

The USGS completes extensive quality checks on its sensor data to make sure it’s as accurate as possible. It also publishes methods for all of its approved sensors. When compared with laboratory data, nitrate sensor data has proved to be reliable, Garrett said.

However, she said she could not comment on whether she thought the Cedar River should be labeled as impaired or not.

“While we do work with entities like the DNR, the city of Cedar Rapids and other municipalities and state and federal agencies looking at water resources, the USGS does not have a regulatory role in making determinations about whether a water body is impaired,” she said.

Droughts affect nitrate levels

Nitrate levels in waterways are shaped by precipitation levels. Rainfall and ice melt creates runoff that carries nutrients from agricultural and grazing areas to nearby bodies of water.

It’s less common for contaminants like nitrate to exceed safe standards in waterways during drought conditions, which Iowa has been experiencing on and off in the past decade. Because of this influence, several experts said they’re worried that the Iowa DNR’s data — and subsequent conclusion — is not reflective of longer-term nitrate trends in the Cedar River.

“The delisting of the Cedar River from the impaired waters list happened during a drought, so we don't actually think that there was improvement in the water quality,” said Alicia Vasto, the Iowa Environmental Council’s water program director. “There's reason to believe that the Cedar River could be put back on the impaired waters list, and that it could be a long time before there's a new (plan) written.”

Safe water thresholds are often exceeded more in the years following droughts, when precipitation pushes built-up stores of nutrients from land into waterways. Experts said they were concerned this could happen in the near future — when there could be no water quality improvement plan left in place.

In their 2020 paper, Jones and his collaborators used sensors to calculate the nitrate level in the Cedar River that could trigger a contamination violation at a Cedar Rapids treatment plant: 16.1 milligrams per liter, only 2.4 milligrams per liter more than the highest value measured this summer.

“ (That is) almost certainly a value that could be exceeded in a post-drought condition, such as what we could see in 2023,” Jones said.

Brittney J. Miller is an environmental reporter for The Gazette and a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues.

Comments: (319) 398-8370; brittney.miller@thegazette.com