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

Abstract

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 14 C-enriched and 14 C-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 CH 4 concentration (mean error less than 1 C and 0.2 lM, respectively). The modeled CH 4 fluxes were consistent with observations in these lakes. We found that bubbling-rate-controlling nitrogen (N 2 ) stripping was the most important factor in determining CH 4 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 CH 4 m 22 d 21 ) than that at nonthermokarst zones in the same lakes and a nonyedoma, nonthermokarst lake (less than 42 mg CH 4 m 22 d 21 ).The seasonal variability of methane emissions can be explained primarily by energy input and organic carbon availability.

Modeling CO2 emissions from Arctic lakes: Model development and site‐level study

“…We upgraded the lake biogeochemistry model (bLake4Me) introduced by Tan et al . [] to improve our understanding of the carbon dynamics in pan‐Arctic lakes. Tan et al .…”

“…The above carbon load does not include any OC mobilized from thawing permafrost beneath yedoma and nonyedoma thermokarst lakes (taliks), which as described in Tan et al . [] is incorporated into the 14 C‐depleted carbon pool of sediments and can be oxidized through either aerobic or anaerobic mineralization. For yedoma lakes, due to their anoxic hypolimnion [ Walter Anthony et al ., ; Martinez‐Cruz et al ., ], usually only anaerobic oxidation occurs in sediments.…”

“…Due to the incorporation of phytoplankton metabolism and DOC mineralization, the governing equation for dissolved O 2 in Tan et al . [] is modified as where is the photosynthetic quotient (the ratio of O 2 production to CO 2 fixation). The quotient is set to 1.1 in the model [ Kirk , ; Cory et al ., ].…”

“…The quotient is set to 1.1 in the model [ Kirk , ; Cory et al ., ]. The methanotrophic consumption of O 2 , RCH 4 , is defined as a Michaelis‐Menten function of CH 4 and O 2 concentrations [ Martinez‐Cruz et al ., ; Tan et al ., ].…”

“…Recently, several studies demonstrated that the wind‐based models as used in the bLake4Me model [ Tan et al ., ] are likely to underestimate air‐water gas transfer velocity (piston velocity) during surface cooling [ MacIntyre et al ., ; Heiskanen et al ., ]. To correct this bias, several alternative approaches (e.g., the surface renewal model) were proposed to incorporate the effects of both wind speed and buoyancy flux [ Heiskanen et al ., ].…”