Several of the scientists who worked on a two-year assessment of central Iowa's rivers shared key findings in Des Moines Monday evening. Over 600 people registered for the event, which was hosted by the Harkin Institute and Polk County.
Jennifer Terry, who led the project, asked the crowd how many times they have wondered: What’s in the water? Is the fish safe to eat? Will Central Iowa Water Works have enough clean water to serve a growing metro?
“Polk County, in 2023, decided to commission the most comprehensive analysis of our two vital rivers that flow into the metro, the Des Moines and the Raccoon river watersheds, in order to answer those sorts of questions,” Terry said.
Sixteen experts in hydrology, microbiology, chemistry, statistical modeling and ecology contributed to the 200-plus page Central Iowa Source Water Research Assessment (CISWRA).
Along with analyzing data, they suggested action steps at the local, regional and state levels to restore and protect the Des Moines and Raccoon rivers. Polk County Supervisors formally accepted the CISWRA findings in July.
River flow and quantity
The flow of water affects the quality, and those flows are changing, according to Larry Weber, director of the IIHR—Hydroscience and Engineering program and the Iowa Flood Center at the University of Iowa.
Annual precipitation in Polk County increased roughly 20% from 1950 to 2023, bumping up annual averages from 30 to 36 inches. But much of the rainfall is coming in shorter, heavier bursts.
Climate scientists predict more extended dry periods broken by intense rainfall in the Midwest.
“The most recent National Climate Assessment Report has indicated for our region that we could expect to see a 10% increase in the 5% rainiest days by 2050, and a 20% increase in that same 5% rainiest days by 2100,” Weber said.
More intense rainfall leads to greater runoff and flooding, especially from May through July.
Drinking water resources
Out of more than 2,000 rivers recently surveyed in the U.S., the Des Moines and Raccoon rivers are in the top 1% for nitrate concentrations, according to Jerald Schnoor, professor emeritus of civil and environmental engineering at the University of Iowa.
Most of the nitrate in the two rivers comes from agricultural land: 40% from fertilizers, 20% from manure applied to land, 20% from soybeans and other nitrogen-fixing legumes.
“About 18% of nitrate, believe it or not, is in our rain and our snow. So even that is contaminated with nitrate,” Schnoor said.
Wastewater and developed land contribute 2% of the nitrate in the two rivers.
Other drinking water challenges in the Des Moines and Raccoon watersheds include harmful algal blooms. Along with reducing oxygen for aquatic plants and animals, some types of algae release toxins, like microcystins. They can make people sick and affect their skin, liver and nervous systems.
Pesticides, PFAS, pharmaceuticals and personal care products contribute to the mixture of chemicals in Iowa’s source waters, Schnoor said.
Recreation and health
To measure recreational risks from waterborne diseases, scientists often rely on the presence of a subset of E. coli bacteria.
“What we see is that E. coli in our streams is overall much higher than at our beaches and that there are certain areas where the water exceeds the standard as much as 60-80% of the time,” said Claire Hruby, an assistant professor of environmental science and sustainability at Drake University.
She said bacteria levels are typically higher a few days after rain. But some streams are more at risk during very low flows, likely from an undiluted discharge of waste nearby.
Antibiotic-resistant bacteria are another concern.
“That antibiotic resistance can come from both human waste downstream of wastewater discharges, but also in our livestock industry,” Hruby said.
She added that genetic testing in some waters shows a higher amount of fecal material from humans in Polk County compared to upstream, but more research is needed.
Iowa Department of Natural Resources staff test state beaches weekly for E. coli and microcystins from Memorial Day to Labor Day. Some cities and counties also monitor their public beaches during the recreation season.
But water quality can change quickly, according to Hruby.
“If the water is pea-soup green or kind of blue-green, do not get in it, and don't let your pets in it either,” she said.
Beyond swimming and paddling, Hruby said water quality affects people who fish. Around 32,500 Polk County residents purchased fishing licenses in 2019, and nearly half of them catch fish for food.
“We need to do a better job of regularly testing those fish, because fish can bioaccumulate certain contaminants over time, especially the larger ones and the ones that feed off the bottom,” Hruby said.
More manure
Nutrients from manure can trigger harmful algal blooms and create the breeding ground for different types of pathogens. Manure spills can also cause fish kills, said Elliot Anderson, an assistant research scientist with IIHR—Hydroscience and Engineering and Iowa Geological Survey at the University of Iowa.
The average annual amount of nitrogen from manure produced in the Des Moines and Raccoon river watersheds is just over 300 million pounds. With phosphorus, it's about 55 million pounds.
“[Manure] has become a big area of concern over the last 20 years or so, because of two major trends that we see with the livestock industry,” Anderson said. “One is that the hog industry has really taken off. At around the turn of the millennium, we had about 15 million hogs within the state. Present day, that number is closer to 25 million.”
The second trend is consolidation. In 1997, hog operations in the Des Moines and Raccoon river watersheds had about 1,000 animals. Now, the average is more than 6,000 hogs per operation.
“If you have crops that can absorb the nutrients that are produced within this manure, that can be okay, but in many parts of the state, we just have too much manure and not enough crop ground to apply it on,” Anderson said.
Recommendations
The CISWRA includes a long list of recommendations to restore and protect the Des Moines and Raccoon river watersheds.
At the individual level, Anderson said this could be as simple as reporting fish kills to the DNR or volunteering to collect data.
Regional or watershed level actions include restoring and protecting freshwater and riparian habitats, planning for more variability in the drinking water supply and developing comprehensive watershed plans.
At the state level, the researchers recommend additional funding for upgrades at wastewater treatment systems. Developing a publicly available database to map land and inventory manure management plans, and partnerships to create a pollution list and benchmarks also fall under this category.
Schnoor said it’s possible to improve water quality with bipartisan support.
“We invested $100 billion in the '70s and '80s and '90s to clean up our point sources when the Cuyahoga River was burning, when Lake Erie was dead,” Schnoor said. “We invested and industry put in an equal amount, more than a $100 billion, and by God, we cleaned up the water.”
The same kind of investment needs to happen with non-point sources of pollution, like nutrient loss from farm fields, he said.
The scientists emphasized that data and robust monitoring are needed to identify hot spots, track trends and measure progress. A significant loss in state funding is expected to drop the number of nitrate sensors in rivers from 80 to 20, starting next year.
“I believe when it comes to water quality in Iowa, this is a step in the wrong direction, but there are many steps that we can take that are in the right direction,” Anderson said.
