A University of Kentucky study shows that small-scale wetlands - one planted in soil, the other floating on mats - can help clean up a mix of farm runoff, personal care products and other harmful chemicals. Researchers at UK's Martin-Gatton College of Agriculture, Food and Environment found that these wetlands can reduce not only "forever chemicals" but also nutrients that fuel algal blooms in Kentucky rivers.
This work on mesocosms, published in the Science of Total Environment, forms the centerpiece of an ongoing project led by water resources engineer Tiffany Messer, The Bill Gatton Foundation Endowed Chair and associate professor in the Department of Biosystems and Agricultural Engineering.
A mesocosm is an experimental system that examines the natural environment under controlled conditions.
"Mesocosms are a powerful tool because they let us isolate key variables while still mimicking field conditions," Messer said. "It's an essential step when trying to understand how these systems perform outside the lab."
Messer's team built 40 waist-high tanks that mimic treatment wetlands, a nature-based alternative to concrete wastewater facilities now serving several Kentucky towns. Emily Nottingham Byers, lead author and postdoctoral scholar at the Kentucky Water Research Institute at the University of Kentucky, stocked half the tanks with marshy soil and bulrush. The remaining tanks held identical vegetation on polyethylene rafts, so the roots dangled freely in the water. Each tank received measured doses of four widely encountered contaminants - glyphosate, atrazine, caffeine and perfluorooctanesulfonate (PFOS) - along with nitrate to simulate the runoff that flows toward rivers often used as drinking-water intakes.
"Those four contaminants turn up again and again in our stream surveys," said Messer, referring to a 2024 paper that first mapped 77 pollutants across Kentucky watersheds. "We wanted to know whether they would hamper nitrogen removal through microbial processes in a controlled setting, and whether the plants could lock any of the pollutants away in their tissue."
In the first month, soil-based cells had a slight advantage: their submerged root zones and resident microbes effectively eliminated nearly half the nitrate load while also removing PFOS and atrazine by approximately one-third from the water.
As summer heat spurred growth, the floating treatment wetlands overtook their grounded counterparts, cutting nitrate to background levels and trimming 70% of each herbicide.
"The mat systems become living filters," said Messer. "Once the root curtains reach full length, every liter of water that flows through its microbial habitat has an opportunity to be removed from the water."
Plant tissue analysis shed light on where the chemicals ended up. Most of the glyphosate and PFOS built up in stems and leaves above the water, suggesting that simple mowing or pruning each year could help keep those pollutants from reentering the water. Atrazine lodged deeper in the root mass, calling for removal of the entire plant if targets for that herbicide tighten. Caffeine and its metabolite paraxanthine followed a split pattern: half in foliage, half in roots.
Charting the future
Wetlands take up more space than concrete basins, so adoption depends on local priorities and state clean-water funding. Some Kentucky communities already use wetlands to treat wastewater, and Messer hopes to work with county engineers to test pilot cells below existing lagoon systems.
The study offers tips for designing wetlands based on local needs. The soil-filled basins act quickly early in the growing season, making them a fit for communities that see heavy inflows in spring. However, floating mats were shown to deliver stronger late-summer performance when rivers shrink and contaminant concentrations rise. Managers can also time harvests based on the main chemical they want to remove - trimming leaves for PFOS or removing full plants for atrazine.
Messer stresses that these are treatment systems, not wildlife preserves.
"They're pretty, but they aren't fishing ponds," said Messer. "The goal is to protect aquatic life in the receiving stream by polishing what leaves wastewater outfalls and land use practices."
The team plans on longer trials to pinpoint when wetlands reach saturation and to test whether periodic plant harvest resets their capacity. They also intend to explore low-cost options such as biochar or iron filings placed beneath mats to target sulfate, the lone contaminant that eluded removal in the greenhouse.
BAE is a partnership between Martin-Gatton CAFE and the Stanley and Karen Pigman College of Engineering. To learn more, visit https://bae.ca.uky.edu/.
Research reported in this publication was supported by the National Institute of Environmental Health Sciences of the National Institutes of Health under Award Number P30ES026529. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
Research reported in this publication was supported by the U.S. National Science Foundation under Award Nos. 2042761 and 1922695. The opinions, findings, and conclusions or recommendations expressed are those of the author(s) and do not necessarily reflect the views of the U.S. National Science Foundation.
This material is based upon work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, Hatch Project under award number W-4045. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the Department of Agriculture.
