Typha x glauca invasion in wetlands of the Great Lakes region: Are impacts time-dependent?

Typha x glauca (hybrid cattail) invasions can greatly alter wetland characteristics and processes. Invasion effects are likely to vary depending on how long a site has been invaded but these time-dependent effects have not been thoroughly explored. Early effects following Typha invasion include an accumulation of litter and a decrease in plant species diversity. As the invasion proceeds, wetland biogeochemistry can be affected as well. We examined paired Typha-invaded and uninvaded wetland plots to assess differences in vegetation, soil characteristics, and denitrification potential. We used historical aerial photographs to approximate the age of invaded sites; younger sites were estimated to have been invaded <20 years ago and older sites, >21 years ago. Older Typha sites had lower Shannon-Weiner diversity (old =0.43, young =0.61 (p =0.28), uninvaded =0.99 (p <0.01)), more litter mass (old =535, young =344 (p =0.127), uninvaded = 59 (p <0.01) g/m²), higher redox potential (old = -170, young = -370 (p=0.04), uninvaded = -279 (p =0.09) mV), and lower denitrification rates than both uninvaded and younger Typha sites. Our results suggest that Typha litter may provide organic carbon for denitrifiers, but over time, litter accumulation may increase redox potential, eventually limiting rates of denitrification in older sites.