Assessing how invasive cattail treatment affects methane emissions in Lake Ontario meadow marshes

Abstract

Wetlands sequester carbon and buffer extreme weather events; however, they are also the largest natural source of methane, a potent greenhouse gas (GHG). We assessed the effects of invasive cattail (Typha spp.) removal on methane emissions and carbon storage at the Braddock Bay Wildlife Management Area on the southern coast of Lake Ontario. We measured methane fluxes in two restored marshes and an uninvaded meadow marsh using a backpack cavity ring-down analyzer, logged belowground environmental conditions to model methane fluxes over time, and estimated carbon storage of the different sites. In 2019, data were collected during a record high flood event in Lake Ontario, and we did not find a significant difference in methane fluxes among the control, treatment, and uninvaded areas. However, under lower water conditions in 2020, the cattail monoculture (control) emitted more methane than areas with cattail removal with replanting, and the uninvaded wet meadow had the lowest average flux during the growing season. Soil moisture (and water levels) decreased over the growing season, while temperatures and biomass increased. Areas where cattail had invaded (whether removed or not) had greater percent soil organic carbon than the uninvaded meadow marsh. The control sites had greater carbon stored aboveground than replanted sites. Our results indicate that methane emissions may be mitigated through plant community restoration; however, ensuring that the native plant community establishes will be important to long-term carbon sequestration. In addition, a mesocosm experiment was conducted to investigate methane emissions when substrate and plant community were manipulated. The experiment included six treatments with two different substrate types and three plant community types. The two substrate types were the top five cm from cattail monocultures, “cattail substrate”, and the next layer below the layer of organic matter, “topsoil removed substrate”. There were three levels of planting treatments: no plants, cattail (Typha x glauca), and native grass, Calamagrostis canadensis. The findings indicated that mesocosms with the topsoil removed had significantly lower methane emissions than those with topsoil. Moreover, no significant differences in emissions were observed between Canada bluejoint (Calamagrostis canadensis) and Typha x glauca. However, it is important to note that this was a limited experiment, and more data is required for comprehensive analysis. Our results show that substrate type appears to be a more important factor contributing to methane emissions than plant identity.