Variations in potential CH4 flux and CO2 respiration from freshwater wetland sediments that differ by microsite location, depth and temperature

Wetlands are a valued ecosystem because of their ability to improve water quality through pollutant removal, their high biodiversity, their carbon sequestration capabilities, and their ability to dampen storm hydrographs through water storage. However, wetlands also contribute to global warming, most obviously through microbial methane production. Driving the biochemical processes that enable methanogenesis is a diverse community of microorganisms under the influence of multiple environmental factors that are poorly constrained in greenhouse gas flux models. Sediments were collected from several distinct microsites across a fresh-water, constructed temperate wetland in Columbus, Ohio, U.S.A. Depth and temperature were tested for their influence on methane emission rates under two controlled temperatures. Pyrosequencing analysis of the 16S rRNA gene was used to investigate microbial communities associated with microsites and depths. Unvegetated, open-water and vegetated microsite sediments had similar potential methane flux rates when cores were separated into shallow and deeper depths. Deeper sediments lacked the ability to produce detectable methane without substrate addition. A 10 °C increase in temperature accelerated the rate of methane production and carbon dioxide respiration by 2–3 fold across all microsites. Methanogens were initially most prevalent in sediments collected from open-water microsite sediments, although had little effect on potential methane flux rates during incubations. These results suggest that upper limit methane emissions are similar across microsites in the absence of other field scale effects, such as redox boundaries, vegetation, or hydrologic fluctuations.