DISSERTATION RESEARCH: Effects of urbanization and climate change on denitrifier community structure and function

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Human welfare depends heavily on ecosystem services like water purification and nutrient cycling. Many of these natural services, in turn, rely on reactions performed by the most abundant and diverse group of organisms on Earth ? microbes. Remarkably little is known about how human drivers affect the structure and function of microbial communities. To help address this research gap, this project will involve a series of experiments to explore how urbanization and climate change may affect denitrifying bacteria (denitrifier) communities in streams. Denitrifiers are the only organisms that can permanently remove reactive nitrogen (N) from ecosystems. Too much reactive N in water bodies leads to serious water quality problems like harmful algal blooms and regional hypoxia. Denitrifiers in streams, therefore, provide an important ecosystem service. The project?s objective is to experimentally determine if and how multiple stressors commonly associated with watershed urbanization and climate change affect stream denitrifier community structure and function. These stressors include increased pollutant and nutrient concentrations, as well as higher temperatures. To meet this objective, microbial communities from eight different study streams will be subjected to combinations of chemical treatments (heavy metals, salt, and nutrients), and incubated at one of three temperatures (28, 38, and 48ºC). The amount of N removed will be measured over the incubation period and denitrifier community composition before and after incubation will be characterized by using molecular fingerprinting methods. Project results will be used to address whether 1) urbanization and climate change are likely to change denitrifier community structure, 2) changes to denitrifier community structure are likely to increase or decrease denitrification rates, and 3) interactions among stressors are additive or synergistic. Furthermore, by taking communities from study streams with various degrees of watershed urbanization, experiment results will be used to draw inferences on whether denitrifier communities and denitrification rates in urban versus forested streams are more or less sensitive to further environmental degradation. Most knowledge of streams comes from studying undisturbed streams, but the majority of U.S. streams are heavily impacted by human activity. Recently, there has been an explosion of research targeting N cycling in urban streams, but this work has largely ignored the microbial communities mediating N transformations. Findings from the proposed project will lead to new insights on denitrification, an important component of the N cycle, by exploring effects of urbanization and climate change on stream denitrifier communities. The project may provide information relevant to stream management and restoration efforts. Broader impacts will also include mentoring students. The doctoral student's dissertation research is being incorporated into the high school environmental science curriculum on human impacts on aquatic ecosystems being developed with a local high school teacher. Project findings will also be disseminated to the broader scientific community by written publications in peer reviewed journals and oral presentations at national conferences.