Modeling methane emissions from arctic lakes: Model development and site-level study

To date, methane emissions from lakes in the pan-arctic region are poorly quantified. In order to investigate the response of methane emissions from this region to global warming, a process-based climate-sensitive lake biogeochemical model was developed. The processes of methane production, oxidation, and transport were modeled within a one-dimensional sediment and water column. The sizes of 14C-enriched and 14C-depleted carbon pools were explicitly parameterized. The model was validated using observational data from five lakes located in Siberia and Alaska, representing a large variety of environmental conditions in the arctic. The model simulations agreed well with the measured water temperature and dissolved CH4 concentration (mean error less than 1°C and 0.2 μM, respectively). The modeled CH4 fluxes were consistent with observations in these lakes. We found that bubbling-rate-controlling nitrogen (N2) stripping was the most important factor in determining CH4 fraction in bubbles. Lake depth and ice cover thickness in shallow waters were also controlling factors. This study demonstrated that the thawing of Pleistocene-aged organic-rich yedoma can fuel sediment methanogenesis by supplying a large quantity of labile organic carbon. Observations and modeling results both confirmed that methane emission rate at thermokarst margins of yedoma lakes was much larger (up to 538 mg CH4 m−2 d−1) than that at nonthermokarst zones in the same lakes and a nonyedoma, nonthermokarst lake (less than 42 mg CH4 m−2 d−1). The seasonal variability of methane emissions can be explained primarily by energy input and organic carbon availability.