Dissertation Research: Effects of Oxic-Anoxic Dynamics on Methanogenesis and Methane Oxidation in Humid Tropical Forests-Evidence from Stable Isotope Distributions

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The dynamics and the stable isotope geochemistry of methane in wet, tropical forest soils are poorly understood, compromising our ability to predict rates of methane flux and 13 C exchange with the atmosphere. Quantifying the source/sink strength and * 13 C signature of methane flux is crucial if we hope to evaluate the role of the tropics in the global methane budget. In systems where redox fluctuates, such as wet tropical forest soils, variations in oxygen influence methane emissions by altering the balance between methanogenesis and methane oxidation. This study explores the effects of oxygen variations on methanogenesis, methane oxidation and 13 C exchange with the atmosphere. Patterns of methane flux and 13 C exchange will be documented across natural gradients of oxygen in the field. Sources and sinks of methane will be identified, both in soil and across the landscape, through gas concentrations and stable isotope analysis. A series of mechanistic laboratory experiments will be performed to explore the effects of oxygen variation on gross methanogenesis, methane oxidation and stable isotope fractionation. This study will advance our knowledge of the factors that regulate methane and 13 C flux from wet tropical forests to the atmosphere.