DISSERTATION RESEARCH: The influence of invasive plants on nitrogen removal, via denitrification, in constructed wetlands

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This dissertation research will compare soil microbial denitrification rates among plots with native vegetation, invasive vegetation, and plots without vegetation in multiple constructed wetlands in Australia in order to determine the optimal conditions for N removal. Human activities have resulted in nitrogen (N) pollution, and this N is affecting water bodies across the globe. Excess N can contaminate drinking water, produce toxic algae, and decrease freshwater biodiversity. In addition, excess N can stimulate algal blooms; subsequently, the death and decomposition of these algae can rob the water column of oxygen. One approach to mitigating these problems is to enhance the biological removal of N via the construction of wetlands. In general, wetland soils are hotspots for denitrification, which is the microbial conversion of dissolved nitrate (NO3-) to N gases. Denitrification, therefore, removes N from wetlands and downstream aquatic systems. Although wetland soils are generally ideal for denitrification, it is unknown how wetland plant community structure influences denitrification rates, and whether denitrification rates can be optimized via management of wetland plant communities. Constructed wetlands often have more invasive species than natural wetlands, and it is also unclear whether removing the invasive species influences N removal via denitrification. Plant community structure can influence a wetland's value for wildlife and biodiversity, and may influence its efficacy for denitrification, as well. The proposed research will directly inform the planning and implementation of constructed wetlands and ultimately can be used to help land managers to create and restore wetlands that better meet N mitigation goals.