Annual variation of methane emissions from forested bogs in West Siberia (2005–2009): a case of high CH₄ and precipitation rate in the summer of 2007

Abstract. We have been conducting continuous measurements of CH₄ and CO₂ on a network of towers (JR-STATION: Japan–Russia Siberian Tall Tower Inland Observation Network) located in taiga, steppe, and wetland biomes of Siberia. Here we describe measurements from two forested bog sites, Karasevoe (KRS; 58°15′ N, 82°25′ E) and Demyanskoe (DEM; 59°47′ N, 70°52′ E), in West Siberia from 2005 to 2009. Although both CH₄ and CO₂ accumulation (ΔCH₄ and ΔCO₂) during nighttime (duration of 7 h beginning 21:30 LST) at KRS in July 2007 showed an anomalously high concentration, the higher ratios of ΔCH₄/ΔCO₂ compared with those in other years indicate that a considerably more CH₄ flux occurred relative to the CO₂ flux in response to large precipitation recorded in 2007 (~2.7 mm d⁻¹ higher than the climatological 1979–1998 base). Estimated seasonal CH₄ fluxes based on the ratio of ΔCH₄/ΔCO₂ and the CASA 3-hourly CO₂ flux for the 2005–2009 period exhibited a seasonal variation with a maximum in July at both sites. Annual values of the CH₄ emission from the forested bogs around KRS (approx. 7.8×10⁴ km²) calculated from a process-based ecosystem model, Vegetation Integrative Simulator for Trace gases (VISIT), showed inter-annual variation of 0.54, 0.31, 0.94, 0.44, and 0.41 Tg CH₄ yr⁻¹ from 2005 to 2009, respectively, with the highest values in 2007. It was assumed in the model that the area flooded with water is proportional to the cumulative anomaly in monthly precipitation rate.