| Summary: | In this dissertation I focused on some of the least-understood aspects of the carbon cycle in northern peatlands _ the biological controls on production, the presence and importance of the anaerobic CH_ consumption pathway, and the physical controls on emission. A more clear understanding of the controls on CH_ emissions from critical northern peatland systems will help constraint predictive models of carbon-climate feedbacks. In chapter 1, I evaluated the linkages between porewater CH_, CO_, and iron concentrations within the upper active layer of a chronosequence of wetland basins in Barrow, Alaska. Iron concentrations varied amongst basin ages, with younger basins containing more iron in the upper soil profiles. Basin age also correlated with the thickness of the organic layer. Basinspecific seasonal mean porewater CH_ concentrations had a negative relationship with total Fe and Fe(III) concentrations; CH_ concentrations were positively related to organic layer thickness. Thus, the highest seasonal mean concentrations of CH_ were found in older basins with thick organic layers and low Fe loads. A manipulated experiment confirmed a direct suppression effect on net CH_ fluxes following Fe(III) and humic acids soil amendments, thus connecting in situ CH_ production and release with soil electron acceptor availability. Chapters 2 and 3 present the findings of a pair of anoxic soil incubations that use stable isotope tracers to simultaneously determine methanogenesis and anaerobic oxidation of methane (AOM) rates. In both experiments, I used treatments to determine the effect of different electron acceptors on CH_ cycling rates. The in vitro incubations of Alaskan soil showed a significant positive correlation between methanogenesis and AOM rates, and an increase in methanogenesis rates with increasing depth within the active layer. There was also an interaction between soil depth and the kinetic rate constant for AOM, suggesting that AOM increased with Fe(III) presence in shallow soil depths. Genetic surveys of ...
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