Gene-Based Modeling of Methane Oxidation in Coastal Sediments: Constraints on the Efficiency of the Microbial Methane Filter

Methane is a powerfulgreenhouse gas that is producedin largequantities in marine sediments. Microbially mediated oxidation ofmethane in sediments, when in balance with methane production, preventsthe release of methane to the overlying water. Here, we present agene-based reactive transport model that includes both microbial andgeochemical dynamics and use it to investigate whether the rate ofgrowth of methane oxidizers in sediments impacts the efficiency ofthe microbial methane filter. We focus on iron- and methane-rich coastalsediments and, with the model, show that at our site, up to 10% ofall methane removed is oxidized by iron and manganese oxides, withthe remainder accounted for by oxygen and sulfate. We demonstratethat the slow growth rate of anaerobic methane-oxidizing microbeslimits their ability to respond to transient perturbations, resultingin periodic benthic release of methane. Eutrophication and deoxygenationdecrease the efficiency of the microbial methane filter further, therebyenhancing the role of coastal environments as a source of methaneto the atmosphere. Witha novel gene-based reactive transport model, we showthat the slow growth of anaerobic methane oxidizers limits methaneoxidation during transient perturbations, thereby allowing the releaseof methane to the overlying water.