Effect of Landscape Position On Potential Methane Oxidation and Methanotrophs in Pulsing Wetlands.

Methane (CH₄) is a critical greenhouse gas and wetlands contribute approximately 25% of the global emissions of CH₄. Methanotrophic microorganisms offset CH₄ emissions by oxidizing CH₄. Although work in pure cultures and laboratory incubations have shown the potential importance of methanotrophs in regulating net CH₄ flux, few field based studies have been done on the microbial ecology of these CH₄ oxidizing communities and how they respond to differing land management systems. In particular hydrologic pulsing of wetlands would be expected to alter methanotroph communities and their ability to oxidize CH_4, but this is entirely uninvestigated. The objective of this study was to determine rates of potential CH₄ oxidation and shifts in community structure of the methanotrophs over seasonal gradients in flow-through, pulsing wetlands. Three landscape treatments (upland, intermediately flooded, and permanently flooded sites) were studied in two replicate freshwater pulsing experimental wetlands at the Olentangy River Wetland Research Park, The Ohio State University, Columbus. Potential CH₄ oxidation was highest in the winter and greater in the permanently flooded sites than in the intermittently flooded sites (p<0.05). Phospholipid fatty acid (PLFAs) profiling of methanotrophs showed that Type I (low CH₄ affinity) and type II (high CH₄ affinity) methanotrophs were more pronounced in winter which corresponded to seasonal high rates of potential CH₄ oxidation. Concentrations of the type II methanotroph PLFA biomarker (18:ω9c) was significantly higher (p<0.05) than the Type I PLFA biomarkers in all seasons and landscape positions.