Researcher finds harvesting invasive species promotes biodiversity but increases methane release

Lawrence and her field crew quantify wetland vegetation and collect soil and biomass samples in twenty Connecticut wetlands to investigate how tidal restoration and vegetation zones affect carbon storage and nitrogen removal from coastal wetlands.
Lawrence and her field crew quantify wetland vegetation and collect soil and biomass samples in twenty Connecticut wetlands to investigate how tidal restoration and vegetation zones affect carbon storage and nitrogen removal from coastal wetlands.

As an assistant professor in the Department of Natural Resources and the Environment (NRE), Beth Lawrence focuses much of her research on the consequences of managing invasive plants. One such project is a three-year $650,000 EPA-funded collaboration in Northern Michigan with Oregon State University, Loyola University, Michigan Technological University, Dartmouth College and the Sault Ste. Marie Tribe of Chippewa Indians, seeking alternative ways to combat a vigorous invasive hybrid cattail species.

The project focused on the St. Marys River and Les Cheneaux Island region of the Great Lakes, where invasive cattails have encroached and diminished native-dominated wetlands, reducing the biodiversity of plants, fish and wildlife. To study how to promote biodiversity in marshes where the cattail dominates, the group uses an amphibious harvester, cutting and shredding large swarths of cattails at the base and collecting the cut biomass that may prove useful for other applications.

“We’ve been doing this at a variety of sites, scales and durations over the last couple years to investigate how cattail harvest affects plant, fish, bird and animal diversity, as well as nutrient and carbon cycling in these wetlands,” explains Lawrence, who has a joint appoint in UConn’s Center for Environmental Science and Engineering. “We have found that harvesting cattails increases light penetration to the surface, and over time, we see that the cattails are not able to grow back, which provides an opportunity for native species to return. That’s pretty exciting.”

But there is a caveat: Wetlands are the world’s largest natural source of methane, a potent greenhouse gas, and disturbing invasive cattails may increase methane release to the atmosphere.

“What’s interesting in this project is how the carbon cycle is affected by harvesting this invasive species,” Lawrence says. “While harvesting increases biodiversity, it also increases methane emissions as the stored carbon is released after harvest. It’s complicated but it’s important to understand the tradeoffs, whether we want to manage a wetland for biodiversity or carbon sequestration.”

In a new project, funded with $298,000, from the Illinois Tollway, Lawrence is working with some of the same collaborators to assess the retention of road salt in wetland detention basins in the Chicago area.

NRE master's degree studentSean Ooi conducts denitrification enzyme assays in the laboratory to estimate nitrogen removal from coastal wetlands.
NRE master’s degree student Sean Ooi conducts denitrification enzyme assays in the laboratory to estimate nitrogen removal from coastal wetlands.

Road salt contributes to the salination of freshwater areas throughout North America, reducing drinking water quality and affecting freshwater environments. The salt compounds leach into groundwater and subsequently infiltrate lakes and streams.

Cattails and common reed are two large invasive species that thrive in salty roadside ditches and detention basins and are capable of taking up and storing chlorides and heavy metals found in these roadside environments. The group is harvesting these basins and examining the chemistry and retention properties of these invasive plants. They are working with the Metropolitan Water Reclamation District of Greater Chicago with the idea of combining the invasive plant biomass with the water district’s biosolids to create compost available for use by local municipalities.

“However,” says Lawrence, “While we’re interested in turning invasive species into something useful for society, such as soil amendments or biomass fuels, we need to know the chemical composition of its biomass,” Lawrence says.

In a project focusing on Long Island Sound, Lawrence is working with Associate Professor Ashley Helton (NRE) and Associate Professor Chris Elphick (UConn’s Department of Ecology and Evolutionary Biology) on a three-year $317,000 EPA-funded project. The group is examining how shifts in wetland vegetation associated with sea level rise and tidal restoration may affect carbon and nitrogen cycling.

Coastal wetlands on the Eastern Seaboard have salinity zones, becoming less salty and drier further inland, and plants sort themselves out along those gradients. Native Spartina marsh grasses live nearer the ocean, while the invasive grass Phragmites is not particularly flood or salt tolerant, so it grows at higher and drier elevations. This tall invasive plant outcompetes native grasses, reducing biodiversity, but, as with other invasive species, it is capable of sequestering carbon and removing nitrogen at higher rates than native grasses.

“While invasive Phragmites has negative consequences for biodiversity, there are some benefits,” Lawrence says. “Our work suggests that soils dominated by Phragmites have greater nitrogen removal rates and hold on to carbon more effectively. It’s critical to investigate and quantify these tradeoffs in ecosystem services so we can make more informed decisions on how we manage our remaining natural areas.”

Lawrence is also involved in several other projects including:

  • A study of the effects of road salt on forested wetland plant communities and biogeochemistry in eastern Connecticut.
  • A collaborative project involving cranberry bog restoration in Massachusetts. The state is restoring these agricultural wetlands to native-dominated wetlands that remove nitrogen and provide habitat for wildlife.
  • A project with educators in the Long Island Sound region to create an interactive climate change module for high school teachers highlighting local examples of how climate change affects us in our backyard.

“These issues are important because in an era of global human domination, we need to wisely allocate limited conservation funding,” Lawrence notes. “Do we spend our limited restoration dollars on combating invasive wetland plants that provide important carbon sequestration and nitrogen removal services? Or should we focus our conservation efforts on areas that harbor unique assemblages of species?  These are questions that keep me up at night.”

The research related to Long Island Sound is funded by EPA Award LI 96172701. The Illinois Tollway work is funded by AG190307 from the Illinois Tollway. The research related to the effects of road salt in Eastern Connecticut is funded by USDA NIFA McIntire-Stennis Project CONS00968. The Massachusetts cranberry bog project is funded by USDA NIFA Hatch Project 1020626.

By Kim Colavito Markesich