Natural Resources, School of


Date of this Version



A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Natural Resource Sciences, Under the Supervision of Professor Steven A. Thomas. Lincoln, Nebraska: May, 2010
Copyright 2010 Steven Walters


Invasive plant species are widely recognized as a major threat to biodiversity and ecosystem stability. Wetland ecosystems tend to be much more susceptible to invasions because of their location on the landscape where water, nutrients, and the impacts of disturbances accumulate. Invasive plants have the ability to alter ecosystem processes and community/population dynamics. The ability of invasive plants to alter these processes can have profound economic consequences. In the United States, control of invasive wetland species alone costs approximately 155 million dollars annually. The state of Nebraska spends 2 million dollars annually controlling invasive plant species in the Platte River and Republican River basins with Phragmites australis being the main focus of these efforts. P. australis can alter ecosystem processes, such as biogeochemical cycling through its aggressive growth strategy. Our objective was to quantify the effects the P. australis invasion has on biogechemical cycling, specifically the carbon cycle, within an invaded freshwater, riparian wetland in the Great Plains (Republican River Basin, NE).

This study used a dynamic closed chamber approach to measure carbon dioxide (CO2) fluxes and production, and a static chamber to quantify methane (CH4) emissions. Measurements were taken 5 times throughout the growing season of 2009 at peak gross primary production in open water, native vegetation (Scirpus sp.), and P. australis habitats. Average rates of net ecosystem exchange of carbon (NEE) were 53 ± 93, 258 ± 186, and 920 ± 752 mg C m-2 hr-1 for open water, Scirpus sp., and P. australis habitats respectively. The study found P. australis significantly increased NEE (F8,44 = 11.96; p <0.001), while methanogenesis was not significantly altered. The invasion of P. australis increased aboveground biomass to 5394 ± 1815 g m-2 from 564.2 ± 139.2 g m-2 in native habitats. The ability of P. australis to increase NEE and biomass productions compared to native species at our wetland site results in an increase in carbon sequestration and a decrease in global warming potentials.