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

Methane is a powerful
greenhouse gas that is produced
in large
quantities in marine sediments. Microbially mediated oxidation of
methane in sediments, when in balance with methane production, prevents
the release of methane to the overlying water. Here, we present a
gene-based reactive transport model that includes both microbial and
geochemical dynamics and use it to investigate whether the rate of
growth of methane oxidizers in sediments impacts the efficiency of
the microbial methane filter. We focus on iron- and methane-rich coastal
sediments and, with the model, show that at our site, up to 10% of
all methane removed is oxidized by iron and manganese oxides, with
the remainder accounted for by oxygen and sulfate. We demonstrate
that the slow growth rate of anaerobic methane-oxidizing microbes
limits their ability to respond to transient perturbations, resulting
in periodic benthic release of methane. Eutrophication and deoxygenation
decrease the efficiency of the microbial methane filter further, thereby
enhancing the role of coastal environments as a source of methane
to the atmosphere.