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Potential for Suboxic Ammonium Oxidation in Louisiana Continental Shelf Sediments
Citation:
Devereux, R., D. Beddick, J. Lehrter, AND B. Jarvis. Potential for Suboxic Ammonium Oxidation in Louisiana Continental Shelf Sediments. Gulf Estuarine Research Society (GERS) Fall 2016 Meeting, Pensacola Beach, FL, November 03 - 05, 2016.
Impact/Purpose:
Sediment studies for C,N,S in the Gulf of Mexico
Description:
Sediments deposited onto the Louisiana continental shelf (LCS) west of the Mississippi River Delta form mobile muds varying in thickness from meters near the outfall to centimeters on the western portion of the shelf. The muds have high concentrations of iron which promote rapid carbon, nitrogen, and sulfur cycling through the terminal mineralization of organic matter and oxidation-reduction reactions coupled to sulfur cycling. In addition to anaerobic ammonium oxidation with nitrite (anammox), anoxic ammonium oxidation via manganese oxide reduction has been proposed to occur in marine sediments. Several recent studies have also pointed to the potential for ammonium oxidation coupled to ferric iron oxidation (Feammox) as a quantitatively import process in upland and wetland soils, but this process has not been widely investigated in marine sediments. The potential for anoxic ammonium oxidation was investigated in sediment cores collected at twelve stations across the LCS. Over the course of our studies, we have consistently observed higher than expected concentrations of NOx five or more cm beneath the sediment-water interface. Comparisons of sediment concentration profiles indicated that high NOX concentration at times co-occurred in sediment horizons where both ammonium and ferric iron concentrations decreased from what would otherwise have been typical concentration profiles. These profiles were evaluated using a 1D diffusion model to gain rate estimates for the apparent ammonium consumption. Although the results are less than definitive, they demonstrate the potential for both manganese- and iron-dependent ammonium oxidation to occur in coastal marine sediments.