DATE: FRIDAY, April 13, 2018 TIME: 2:30 P.M. - Room 101 (Refreshments served at 2:15 pm) PLACE: Environmental & Natural Resource Sciences Bldg. 14 College Farm Road, New Brunswick, New Jersey
THE METHANE PARADOX AND IMPORTANCE OF REDOX CYCLING IN PEAT SYSTEMS
Methane (CH4) is a potent greenhouse gas originating from both natural and anthropogenic sources. Peats and wetlands can serve as important sources and/or sinks for CH4 on a global scale, however, fundamental mechanisms of CH4 production and consumption remain poorly understood. Emerging research now recognizes that methanogenesis (CH4 production) can occur in oxygenated layers, which is not the case in classical models of CH4 cycling that only consider CH4 production under strictly bulk-anaerobic conditions. These emerging considerations of CH4 cycling lead to a methane paradox, in which methanogenesis may occur in both poorly and highly oxygenated zones. Recent studies have shown in certain cases that oxygenated peat and wetland layers may contribute more significantly to CH4 emissions compared to deeper anoxic layers. Peats that are rich in organic C and significantly contribute to global CH4 emissions often undergo dynamic redox oscillations during natural wetting and drying cycles, or during shifts in water-table depth, which allow for oxic/anoxic transition zones. Based on emerging concepts, we hypothesized that oxygenation in peats is important for promoting methanogenesis. To test this hypothesis, we incubated peat suspensions in the laboratory over a period of eight months, which included three oxygenation treatments (0%, 5%, and 10% headspace O2). Oxygenation was imposed at the start of the incubation and was then carried out over the first four months, after which anoxic conditions were maintained for another four months. Peat suspensions exposed to O2 displayed higher concentrations of headspace CH4 (by orders of magnitude) compared to strictly anoxic controls by the end of the incubation. Our findings show that prior oxygenation events have the capacity to stimulate CH4 emissions during subsequent anoxic conditions. We are currently working to identify and characterize the underlying biological and geochemical mechanisms by which O2 can stimulate CH4 emissions in peat systems. Our results have important implications for improvement of climate models and a better understanding of the global C cycle.