Highly Dynamic Methane Emission from the West Siberian Boreal Floodplains

The West Siberia Lowland (WSL) is one of the biggest wetland areas in high latitudes; however, measurements of gas fluxes from WSL floodplain wetlands were absent. During 2015–2016, we made first effort to estimate methane emission from floodplain using chamber method. Obtained fluxes varied greatly with medians from zero to 17.5 mgC·m−2·h−1. We found that observed heterogeneity could be addressed for further upscaling by grouping the flux observations using a set of environmental parameters: i) floodplain width (wide/narrow), ii) microtopography (elevated/depressed), iii) inundation during the measurements («wet»/«dry»). We found that several classes could be easily merged basing on CH4 emission rates: i) flux median from both «wet» and «dry» depressions of wide floodplains reached 4.21 mgC·m−2·h−1, ii) «wet» elevations within wide floodplains and all small «wet» floodplains had lower flux of 1.47 mgC·m−2·h−1, iii) «dry» elevations within wide floodplains and all small «dry» floodplains had the lowest median of 0.07 mgC·m−2·h−1. Besides the common factors which influence the methane fluxes, we also found extreme methane emission during ten days after main water subsiding in Ob’ floodplain with further gradual decreasing of fluxes and dispersions. We suggested that methane release could be triggered by abrupt hydrostatic pressure decrease induced by water drawdown.