Factors Controlling Nitrogen Removal and Retention in Marine Sediments

Rachel Presley, University of Maine, School of Marine Sciences, Orono, United States, Anne E Giblin, Marine Biological Laboratory, Ecosystems Center, Woods Hole, MA, United States, Christopher K Algar, Dalhousie University, Department of Oceanography, Halifax, NS, Canada, Sean O'Neill, University of Maine, School of Marine Sciences, Darling Marine Center, Walpole, United States and Jeremy Joel Rich, University of Maine, School of Marine Sciences, Orono, ME, United States
Disruption of the global nitrogen (N) cycle has led to environmental problems and increased interest in the fate of N. Denitrification and anammox remove N from systems as dinitrogen, while dissimilatory nitrate reduction to ammonium (DNRA) retains N as ammonium. Controlling factors on the partitioning between these pathways need to be identified to determine the fate of N in the marine environment. Previous research indicates that availability of organic carbon (C) and nitrate (NO3-) impact partitioning, but other factors such as hydrogen sulfide (H2S) may also play an important role.

Using marine sediments from coastal Maine (5-6 m water depth), we are altering substrate fluxes to sediments using anaerobic sediment thin disc reactors in experiments to determine how these fluxes may influence which N cycling processes dominate. The thin layer of sediment allows for rapid exchange with the overlying water in a flow-through reactor with constant flux of NO3- to the sediment thin discs. Stable isotope techniques, using 13C and 15N additions, are being used to determine C utilization and denitrification, anammox, and DNRA rates. This experimental design allows us to quantify a wide range of substrate ratios for C:NO3- and H2S:NO3-, and their effect on partitioning between NO3- reduction processes. Results of this study will be compared to a maximum entropy production (MEP) model and provide insights on controlling factors of denitrification, anammox, and DNRA.