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Report: Plastics, road salt and farm runoff threaten Mississippi

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The river from Harriet Island Park
The Mississippi River as seen from Harriet Island Park near downtown St. Paul.
Evan Frost | MPR News file

Updated: 5:55 p.m. | Posted: 11:46 a.m.

Use sand on a slippery sidewalk, not salt. Embrace cotton over synthetic fabrics. Clean up after your dog.

The Mississippi River would be better off with less road salt, microplastics and E. coli bacteria, according to a report released Wednesday.

The State of the River report, from the National Park Service and Friends of the Mississippi River, looks at the 72 miles of the waterway that travel through the metro area.

Four years after the first State of the River report, some problems like invasive species and sediment and nitrate pollution from farming persist. But this year researchers looked at some emerging problems they know less about: chloride that gets into the river from road and sidewalk salt and microplastic fibers that come off the clothes we wear.

Water quality managers have noticed an upward trend in chloride from road salt in Minnesota lakes and rivers. If levels are high enough, it can affect the aquatic ecosystem. While the Mississippi isn't impaired because of chloride, the report shows several streams that flow into the river are.

Researchers have known about microplastics for a while now, but recent studies have given them more to think about. Before, the concern was plastic microbeads from face wash and other personal care products.

"What we found in research from the park, both in the water itself and also in sediment and fish and mussel tissue, is that it's microplastic fibers that are actually the dominant form of microplastics here in the Mississippi River," said Lark Weller of the National Park Service, who co-authored the report. "These are products that we link to synthetic clothing like microfleece, polyester, nylon."

Researchers found higher concentrations of the plastic fibers downstream from the metro wastewater treatment plant, Weller said. The findings correlate with other studies around the country, she said.

Just last week, the U.S. Geological Survey announced finding plastic fibers in tributaries that feed into the Great Lakes. This summer, chemistry professor Lorena Rios Mendoza of the University of Wisconsin-Superior collected samples from Lake Superior near wastewater treatment plants. Sure enough, she found plastic fibers, likely going down the drain when people wash their clothes. She has also found the fibers inside of fish. 

"They are floating in the water, and everything that's floating in the water is food," Rios said, adding that more research is needed to see what toxics are attaching themselves to the plastic. 

That will be a big question for the Mississippi because a variety of harmful pollutants wash into the river. Still, the river is much cleaner than it was 40 years ago, and the report notes it supports bald eagles, mussels and many fish species. A range of policy changes and cleanup efforts, including the Clean Water Act, have been credited for the improvements.

"The river is a complex, living ecosystem, and many factors affect its health.  You can have some indicators pointing down and some pointing up, and it's very dynamic and they change," said Whitney Clark, executive director of Friends of the Mississippi River.

Mercury and industrial chemicals have declined, leading to more wildlife and looser health guidelines on eating fish out of the river. 

One thing that hasn't changed for the better is pollution coming from farm fields. Nitrate has increased 44 percent since 1976, according to the report. And a study from the Minnesota Pollution Control Agency shows more than half of the nitrogen in the Mississippi and Minnesota rivers comes from cropland drainage — flexible plastic tubing installed under corn and soybean fields to improve drainage and boost yields. 

Clark says Minnesota should require permits for new tile drainage systems so the state has a better understanding of regional hydrology. He also said voluntary conservation efforts aren't cutting it. 

"We've been nibbling around the edges with voluntary measures in the past, and we're really not moving the needle. So we need new policies that have the potential to make big changes on the landscape," he said.

Researchers have found that agricultural drainage has changed hydrology along the Minnesota River, which feeds into the Mississippi, more so than changes in precipitation. 

Shawn Schottler, a senior scientist at the St. Croix Watershed Research Station, said changes in land use and drainage have resulted in a nearly 25 percent increase in flow since the 1930s. 

"Flow of the river is the pulse of the watershed," he said. "And just like your pulse is symptomatic of what's going on in your body, the flow of the river is symptomatic of what's going on in the watershed."

High flows aren't always bad, he said, but they can cause erosion and bring more pollutants into the river. 

"What's changing the flow, what's changing the pulse of the river, is also changing the delivery of the pollutants," Schottler said.

Better drainage systems might be one solution, but Schottler and others speaking at the Mississippi report's release say we also need different crops — perennials like alfalfa and switchgrass that cover the landscape year-round, protecting soils and soaking up nitrogen. 

Trevor Russell of Friends of the Mississippi River, who co-authored the report, said Minnesota is growing too many annual crops, a practice that leaves the land bare and vulnerable part of the year. But he said he doesn't expect farmers to make the switch on their own. 

"It's all well and good to say we need more perennial crops on the landscape, but unless those things are profitable, that's not going to happen," he said. "We don't have the tools to compel that kind of widespread landscape change."

He says there's hope in a couple state-funded programs looking at new crops for biofuels and other products. 

"If we get those things in place, we have an economic incentive to put more perennial crops on the landscape, and that's going to get us to prosperous farms and clean water," Russell said.