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Illinois Ag News Headlines
Plants As a Tool for Roadside Contaminant Removal
Illinois Ag Connection - 09/22/2023

Tall, densely growing Phragmites and cattail (Typha) are familiar plants alongside highways and byways in the northern United States, flourishing in salty roadsides and degraded wetland environments created by chemicals applied to roads in the colder months known as deicers. Recently, a team of researchers from UConn’s College of Agriculture, Health, and Natural Resources and Loyola University Chicago decided to investigate whether these invasive species can help remove some of the salt and metal contaminants along those same roads. Their findings are published in Ecological Engineering.

Department of Natural Resources and the Environment Associate Professor Beth Lawrence has been working with researchers at Loyola interested in the management and restoration of wetlands in the Great Lakes region, focusing primarily on invasive plant species. After wetlands are invaded by tall, nutrient-loving, and salt-tolerant species like Phragmites and cattail, conditions become too shady and crowded for native species to thrive, eventually resulting in a homogenized environment that reduces wildlife habitat viability, changes nutrient cycling, and alters greenhouse gas emissions, says Lawrence:

“When these invasive species come in, they change the nature of the ecosystem. We are interested in promoting biodiversity and oftentimes managers want to get rid of those invasive species.”

Typically, herbicides are used to kill invasive plants, but this approach is limited in effectiveness, says Lawrence, so the researchers were interested to see if mechanical harvesting methods could be a sustainable option for restoring the ecosystem.

Lawrence says that after World War II, the quantity of road salt application has grown exponentially, and there are growing concerns about their impact on the environment. Roadside ecosystems are increasingly saline and contain high loads of heavy metals like zinc and lead from cars and their emissions. The chemistry of salt ions mobilizes heavy metals in soil, making it easier for them to move around the environment and cause problems.

“There is pressure from the public and environmental groups to mitigate road salt impacts. As a society, we demand drivable roads after storms, but there are clear environmental costs. Once road salts get out into the environment they can contaminate our aquifers, groundwater or surface waters,” says Lawrence.

Once the salt is in the environment, it is very difficult to remove; however, some plants that grow in brackish conditions take up and store salt in their tissues. The researchers wondered if cattail and Phragmites are taking up salts and metals along busy roads, and if so, whether harvesting the plant material would reduce the contaminants in the environment.

The team worked with the Illinois Tollway to identify 10 wetland detention basins that were all between half a hectare to one-and-a-half hectares in size. Lawrence says what’s unique about this study is the scale: much of this kind of work has been done experimentally in the greenhouse in small pots, but the researchers here got to work with hectares of land.

The locations were all dominated by either cattail or Phragmites, and the team estimated the percentages of each. Half of the locations were randomly designated as controls and the team harvested biomass from the other half for two growing seasons. They also measured a variety of conditions before they started the experiment, such as biomass, soil chemistry, and the chemistry of the plant tissues.

After harvest, the researchers analyzed the plant materials for salts and metals and they found that cattail was more effective at taking up salts, with the highest amounts stored in green tissue.


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