Stable Isotope Studies of Methane Production in Northern Wetlands

Northern peatlands are complex wetland ecosystems that are characterized as bogs, fens, or tundra. Since these systems are flooded for much of the growing season, organic matter often decomposes anaerobically. Methanogenesis is the dominant means of anaerobic metabolism occurring in these wetlands and can occur via two separate pathways. Acetoclastic methanogenesis involves the formation and subsequent degradation of acetate to form carbon dioxide and methane. Methane can also be produced by the reduction of carbon dioxide by hydrogen gas. This research uses natural abundance isotopes to discern the proportion of methane produced by each of these mechanisms in peatlands along a north-south transect across Alaska. The focus of this research was to investigate pathway shifts in methane production across latitudinal and vegetation gradients in order to discover if acetoclastice methanogenesis becomes less important at higher latitudes. Our study concluded that factors other than latitude (vegetation type and/or pH) have greater impact on methane production mechanism than does latitude. Another objective of this research was to determine if the methanogenic pathway influences the stable deuterium (äD) isotope ratios of the methane produced. This study provided further evidence that methane production mechanism influences the äD of methane causing an antipathetic relationship between the fractionation factors of D and 13C (áD and áC).