Collaborative Research: RUI -- Response of Nitrifying Bacteria to Fluctuating Hypoxia in Estuarine and Marine Sediments

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ABSTRACTOCE- 0352221 / OCE- 0352216 Nitrification contributes to removing fixed nitrogen from ecosystems; it is a centrally important process modulating ecosystem productivity and the global nitrogen budget. In anoxic estuaries, nitrification is compromised, reducing the removal of fixed nitrogen. Bottom water anoxia leads to increased HS- concentrations in pore waters that can lead to extended inhibition of aerobic nitrifying bacteria. A researcher at the University of West Florida believes that the loss of nitrification activity during weeklong hypoxic events will reduce denitrification rates, although N2 production by anaerobic NH4+ oxidation (anammox) may be enhanced. In this study, the scientist from the University of West Florida will investigate how the community composition of aerobic nitrifiers differs under varying oxygen tensions. How the nitrifiers respond to short-term hypoxic events will also be considered, as well as how the degree of hypoxia and bottom water NO3- concentrations (either through denitrification or anammox) will affect N2 levels. And, finally, because adaptation by the nitrifying community to periodic hypoxia and HS- exposure has important ecological implications, the researcher will investigate the degree to which nitrifiers can adapt to intermittent hypoxia lasting hours to days, specifically when intermitted with exposure to HS-. If communities adapt to and become HS- tolerant, then they can nitrify when conditions are favorable without extended lag periods. Thus, nitrogen removal through denitrification would be more efficient in these systems. In addition, the role of anammox in estuarine environments is not well studied, particularly its contribution to estuarine nitrogen budgets. If anammox rates are significant, it will suggest a major revision of the fixed nitrogen removal processes in estuaries.