Year-round simulated methane emissions from a permafrost ecosystem in Northeast Siberia

Abstract

Abstract. Wetlands of northern high latitudes are ecosystems highly vulnerable to climate change. Some degradation effects include soil hydrologic changes due to permafrost thaw, formation of deeper active layers, and rising topsoil temperatures that accelerate the degradation of permafrost carbon and increase in CO2 and CH4 emissions. In this work we present 2 years of modeled year-round CH4 emissions into the atmosphere from a Northeast Siberian region in the Russian Far East. We use a revisited version of the process-based JSBACH-methane model that includes four CH4 transport pathways: plant-mediated transport, ebullition and molecular diffusion in the presence or absence of snow. The gas is emitted through wetlands represented by grid cell inundated areas simulated with a TOPMODEL approach. The magnitude of the summertime modeled CH4 emissions is comparable to ground-based CH4 fluxes measured with the eddy covariance technique and flux chambers in the same area of study, whereas wintertime modeled values are underestimated by 1 order of magnitude. In an annual balance, the most important mechanism for transport of methane into the atmosphere is through plants (61 %). This is followed by ebullition ( ∼ 35 %), while summertime molecular diffusion is negligible (0.02 %) compared to the diffusion through the snow during winter ( ∼ 4 %). We investigate the relationship between temporal changes in the CH4 fluxes, soil temperature, and soil moisture content. Our results highlight the heterogeneity in CH4 emissions at landscape scale and suggest that further improvements to the representation of large-scale hydrological conditions in the model will facilitate a more process-oriented land surface scheme and better simulate CH4 emissions under climate change. This is especially necessary at regional scales in Arctic ecosystems influenced by permafrost thaw.

FLUXNET-CH4 Synthesis Activity: Objectives, Observations, and Future Directions

“…During transport, CH 4 can pass through unsaturated soil layers and be consumed or oxidized by aerobic bacteria (Wahlen 1993). Process-based biogeochemical models developed and applied at site, regional, and global scales simulate these individual processes with varying degrees of complexity (Bridgham et al 2013;Melton et al 2013;Poulter et al 2017;Castro-Morales et al 2018;Grant and Roulet 2002). The large range in predicted wetland CH 4 emissions rates suggests that there is both substantial parameter and structural uncertainty in large-scale CH 4 flux models, even after accounting for uncertainties in wetland areas Saunois et al 2016a;Melton et al 2013;Riley et al 2011).…”

Interpreting eddy covariance data from heterogeneous Siberian tundra: land-cover-specific methane fluxes and spatial representativeness

“…Budishchev et al, 2014), remotely sensed fluxes (e.g. Chen et al, 2009) and vegetation data for model input (e.g. Stoy et al, 2013).…”

Evaluating two soil carbon models within the global land surface model JSBACH using surface and spaceborne observations of atmospheric CO<sub>2</sub>

“…The observations show that litterfall has strong influences on heterotrophic respiration (Chemidlin Prévost-Bouré et al, 2010). At seasonal timescales in the different latitudinal zones, there is no clear influence of litterfall driving the heterotrophic respiration seen in the models, which primarily results from the pre-defined turnover times of the fast litter pools smoothing out individual litter fall events.…”

“…One way to evaluate soil carbon models has been to use observations of soil carbon stocks . At small scales, rates of gas exchange measured in chambers have also been used (Ťupek et al, 2019), but the separation of heterotrophic and autotrophic respiration is laborious (Chemidlin Prévost-Bouré et al, 2010). It is anyhow challenging to find reasons for differences in heterotrophic respiration between large-scale models as the litter input to the soil influences heterotrophic respiration, and this litter input varies between the models.…”