B41C-0441
Using Optical Oxygen Sensors and Injection Experiments to Determine in situ Microbial Rate Constants for Methane Oxidation and Heterotrophic Respiration in a Boreal Bog and Fen

Thursday, 17 December 2015
Poster Hall (Moscone South)
Nicholas Waldo1, Andrea Wong1, Colby Moorberg2,3, Mark P Waldrop4, Merritt R Turetsky5 and Rebecca Bergquist Neumann2, (1)University of Washington Seattle Campus, Civil and Environmental Engineering, Seattle, WA, United States, (2)University of Washington Seattle Campus, Civil & Environmental Engineering, Seattle, WA, United States, (3)Kansas State University, Department of Agronomy, Manhattan, KS, United States, (4)USGS California Water Science Center Menlo Park, Menlo Park, CA, United States, (5)University of Guelph, Guelph, ON, Canada
Abstract:
Wetlands are the largest natural source of methane to the atmosphere, and play a key role in feedback cycles to climate change. In recognition of this, many researchers are developing process-based models of wetland methane emissions at various scales. In these models, the three key biogeochemical reactions are methane production, methane oxidation, and heterotrophic respiration, and they are modeled using Michaelis–Menten kinetics. The majority of Michaelis-Menten rate constants used in models are based on experiments involving slurries of peat incubated in vials. While these slurries provide a highly controlled setting, they are different from in situ conditions in multiple ways; notably they lack live plants and the centimeter-scale heterogeneities that exist in the field.

To determine rate constants in a system more representative of in situ conditions, we extracted peat cores intact from a bog and fen located in the Bonanza Creek Experimental Forest near Fairbanks, Alaska and part of the Alaska Peatland Experiment (APEX) research program. Into those cores we injected water with varying concentrations of methane and oxygen at multiple depths. We used planar oxygen sensors installed on the peat cores to collect high resolution, two dimensional oxygen concentration data during the injections and used oxygen consumption rates under various conditions to calculate rate constants. Results were compared to a similar but smaller set of injection experiments conducted against planar oxygen sensors installed in the bog. Results will inform parametrization of microbial processes in wetland models, improving estimates of methane emissions both under current climate conditions and in the future.