Wetland ecosystems maintain and improve water quality through the process of denitrification, an increasingly important ecosystem service due to global N pollution. Invasive plants have the potential to disrupt denitrification by altering the environmental conditions that facilitate this process. Great Lakes coastal wetlands are experiencing widespread invasion by highly productive hybrid cattail with largely uncertain biogeochemical effects. Through field and controlled mesocosm studies, we sought to determine the effects of cattail invasion through time on denitrification rates and associated environmental factors in a Great Lakes coastal wetland. In the field, we found that cattail density correlated with increased denitrification and a suite of environmental and plant community characteristics and denitrification rates were positively correlated with NH4 +, sediment organic matter, reduced water levels, and cattail stand age. Through our controlled mesocosm study, we documented conditions 1- and 5-year following invasion and found that denitrification rates and soil organic matter increased in year 5, and cattail and year-since-invasion altered plant communities and soil NH4 +. Only a weak correlation between denitrification rates and cattail treatments was noted, however, owing to high replicate variability. Our results indicate that with increasing cattail residence time, one ecosystem service, biodiversity, was negatively impacted, while two other services, denitrification and sediment carbon accumulation, were enhanced. Thus, this highly invaded wetland still provides valuable services to aquatic ecosystems and to society. A holistic perspective is therefore critical when evaluating invasive species impacts in which negative impacts are weighed against other ecosystem services, which may be stimulated.
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Acknowledgments We thank Michael Grant for assistance in chemical analysis, Steve Bertman and Jennifer Tank for analytical assistance and method development, and Chester Elliot, Emily Kay, Erica Mynarich, Brian Schuetz, and Sharon Shattuck for many hours of work in the lab and field. This research was supported by National Science Foundation grant DGE-0343372 to N. Tuchman and M. Freyman, National Science Foundation REU Site: Biosphere–Atmosphere Interactions in a Changing Global Environment, Award 0851421 to K. Nadelhoffer, D. Karowe, and M.A. Carroll, and by an award from the Loyola University Chicago Office of the Provost to N. Tuchman.
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- Aquatic macrophyte
- Ecosystem service
- Invasive species
- Typha × glauca