Collaborative Research: Environmental Controls on Anammox and Denitrification Rates in Estuarine and Marine Sediments

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The newly discovered process of anaerobic ammonium oxidation (anammox) is an important process in marine environments. The contribution of anammox to global N budgets remains highly uncertain, however. To develop a predictive understanding of nitrogen sinks, comprehensive knowledge on the dynamics of environmental controls that trigger a switch from heterotrophic denitrification to anammox is necessary.In this project, researchers from Brown University and the Ecosystems Center at the Marine Biological Laboratory will test the hypothesis that coupled variation in organic matter and nitrate delivery to the zone of anoxic nitrate respiration drives the switch from heterotrophic denitrification to anammox. They will assess this hypothesis by integrating modeling, laboratory experiments, and field measurements, with the following three objectives: (1) to develop and empirically test bioreaction network models to predict the relative flux of nitrogen sink pathways under varying organic carbon and nitrate; (2) to test the interactive effects of varying organic matter and nitrate delivery rates in sediment microcosm experiments; and (3) to conduct field measurements along natural environmental gradients in Massachusetts Bay and Plum Island Sound Estuary.The microcosm experiment should provide a direct test of the hypothesis that anammox is favored under conditions when nitrate delivery rates are high relative to organic matter loading. The field measurements will test the predictive power of models under in situ conditions. In addition to nutrient flux measurements and sediment porewater profiles, anammox and denitrification rates will be measured using two methods, based on the isotope pairing technique: conventional slurries and intact cores under in situ conditions.Broader impacts: Theoretical and methodological advances from this research will be distributed to the community through the Denitrification Research Coordination Network. The proposed research will support a graduate student and a postdoctoral researcher in the Brown-MBL program, strengthening institutional partnerships to the mutual benefit of the graduate student, postdoctoral researcher and PIs. Undergraduate students will be involved in summer research projects, as well as educational outreach activities through Brown University's ARISE program in local high schools that serve racially diverse students.