Short-term impacts of Phragmites management on nutrient budgets and plant communities in Great Lakes coastal freshwater marshes
Invasive plant management is a key focus of wetland managers, and considerable resources have been devoted to control of non-native Phragmites australis in many Great Lakes coastal wetlands. This study examined short-term (1-year) impacts of herbicide management by comparing wetland plant productivity, nutrient availability, and plant communities before and after herbicide treatment in two coastal wetlands. We also monitored a third wetland in years 3–5 following herbicide treatment. After herbicide treatment, annual aboveground net primary production and plant nitrogen and phosphorus uptake decreased dramatically (by an average of 88%, 80% and 89% respectively; p < 0.05); porewater soluble reactive phosphorus (SRP) and surface water ammonium increased at one site (p < 0.05), while porewater ammonium increased at the other site (p < 0.05); porewater dissolved organic carbon concentrations increased at both sites (p < 0.05); and porewater nitrate did not change at either site. Despite large reductions in Phragmites biomass following herbicide treatment, floristic quality did not improve. When scaled to the area surrounding Lake Erie’s Western Basin treated with herbicide in 2012, the reduction in plant nutrient uptake accounted for 24 × 103 kg of phosphorus and 159 × 103 kg of nitrogen, nutrients potentially available for export to coastal waters. This amount was small relative to average annual (2009–2014) loading from the Maumee River, but similar in magnitude to summer loading in 2012 (57% of total nitrogen and 478% of SRP riverine loading), a year of low discharge and loading. Our results highlight the trade-offs inherent in managing invasive plants.
KeywordsGlyphosate Herbicide Invasive species management Nutrient retention Phragmites australis Wetland ecosystem services
We thank the Detroit River-Lake Erie Cooperative Weed Management Area for access to herbicide treatment data, the United States Fish and Wildlife Service and the Michigan Department of Natural Resources for access to study sites within the Detroit River International Wildlife Refuge, and John Hartig, Greg Norwood, Steven Dushane, Joseph Robison, Zachary Cooley, and Eugene Jaworski for logistical support. We thank Audrey Johnson, Jennifer Kirk, Shawn Duke, Pennelope Richardson-Bristol, Jay Krystynak, Lisa Denys, Jerry Tyrrell, and Joshua Goldberger for assitance in the field and the lab.
This project was funded by a Grant from the National Oceanic and Atmospheric Administration (Award # NA09OAR4170172).
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