ABSTRACT

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."

Estuaries, connecting the freshwater and marine environment, are among the most dynamic and the productive ecosystems on Earth. However, they are under threat from anthropogenic N loading, resulting in various symptoms of eutrophication. The intensity and duration of estuarine eutrophication and the rate of estuarine recovery strongly depend on microbial N removal processes (anaerobic ammonium oxidation (ANAMMOX) and denitrification). Denitrification has been intensively studied in various estuaries, while ANAMMOX as a recently discovered N removal pathway is much less studied in estuarine ecosystems. Existing studies indicate that ANAMMOX rates and its contribution to total N2 production (ANAMMOX significance) are system specific and controlled in part by reaction-scale substrate limitations and by environmental parameters. However, community structure (abundance and composition) of ANAMMOX bacteria have not been linked to their activities along environmental gradients. In addition, ANAMMOX community interactions with aerobic ammonia oxidizers and denitrifyers have not been adequately studied in estuarine and coastal environments.

The investigators will examine the importance of ANAMMOX community structure on their activities along estuarine gradients at the CFRE. In addition, microbial interactions among ANAMMOX, denitrifying and aerobic ammonia oxidizing (AAO) communities will be examined to gain a better understanding of sedimentary N cycles in the estuary. They will address the hypothesis that the total abundance of ANAMMOX bacteria will be linearly correlated to their activities, and that members of ANAMMOX communities are influenced differently by environmental parameters present along the estuarine gradients. Depending on the community structure of ANAMMOX bacteria, temporal and spatial variations of the ANAMMOX rates and its significance to N loss will be observed along the estuary. In addition, they will explore functional linkages among ANAMMOX, denitrifying and AAO communities in estuarine sediments that will alter the pathway of N loss. In order to test the proposed hypotheses, the investigators will conduct interdisciplinary and collaborative research by integrating molecular microbial techniques, 15N isotope tracer methods and multivariate statistic analyses. Thus, this project will address key gaps in our understanding of ANAMMOX ecology by understanding how the community structure of ANAMMOX bacteria influences their activities, and lead to a more complete understanding of estuarine N loss.

Intellectual merits: This project includes interdisciplinary research in the fields of molecular microbial ecology and stable isotope geochemistry. New techniques developed by the PIs will enhance the studies of ANAMMOX ecology and understanding of global N cycle. Functional gene studies of ANAMMOX bacteria will provide a transformative tool to detect and quantify diverse ANAMMOX bacteria in the environment. The investigators will define the key factors influencing ANAMMOX communities, which will promote the understandings of ANAMMOX significances in estuarine N removal. In addition, knowledge gained from this project will be applied to a fundamental understanding of the correlation between microbial community structures and functions using ANAMMOX bacteria as a model organism, and development of a predictive framework for ecosystem response to environmental variations.

Broader impacts: This project will be manifested through diverse educational components, outreach, and improved research infrastructure at UNCW and Columbia University. Three PIs, at UNCW (microbial ecologist and geochemist) and Columbia (microbial ecologist), will provide interdisciplinary training to a postdoctoral fellow and at least one graduate student seeking M.S. or Ph.D. Additional educational impact will be accomplished both in the classrooms and through individual undergraduate research projects (DIS, honor programs, and Lamont intern program). Research experience for high school students will be achieved by including the project within the UNCW Summer Ocean Ventures program. Outreach will be facilitated by partnering with a local citizens group (NC-Coastal Ocean Federation) to recruit volunteers to participate in sampling cruises and chemical analyses, and by using the existing UNCW-CMS Planet Ocean public platform discussing estuarine nitrogen loading and attenuation.

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