[A-CG38] 北極域の科学

[ACG38-P08] Intra-seasonal variations in CH₄ emissions observed by automatic and manual chambers, and in dissolved CH₄ concentration at taiga-tundra boundary in northeastern Siberia

*新宮原 諒^1,2、両角 友喜¹、鄭 峻介²、村瀬 潤³、鷹野 真也¹、樊 荣¹、Trofim Maximov^4,5 (1.北海道大学大学院環境科学院、2.北海道大学北極域研究センター、3.名古屋大学大学院生命農学研究科、4.ロシア科学アカデミーシベリア支部寒冷圏生物学研究所、5.北東連邦大学自然科学研究所)

キーワード：メタンフラックス、自動開閉チャンバー、溶存メタン、水位、安定同位体比、ロシア北極域

Methane emission from northern wetlands contributes significantly to the global CH₄ emission, and may be affected by changes in Arctic climate and ecosystems. Controls on CH₄ emission such as soil temperature, thaw depth, plant productivity and water level have been reported for northern wetlands (Nakano et al., 2000, Atmos. Environ.; Parmentier et al., 2011, J. Geophys. Res. Biogeosci.; Ström et al., 2015, Biogeochem.). Water level is important partly because water saturation in soil layer makes reductive conditions, which is essential for the CH₄ production by methanogenic archaea. However, formation of soil reductive conditions can lag water level rise as reported in subtropical pasture (Chamberlain et al., 2016, J. Geophys. Res. Biogeosci.), which complicates relationship between water level and CH₄ flux. Our previous study (Shingubara et al., 2016, JpGU meeting) reported that a wet event concurrent with heavy precipitation increased CH₄ flux for three years despite of decreasing water level at taiga-tundra boundary in northeastern Siberia, likely through soil reduction over multiple years.

To investigate intra-seasonal variation in CH₄ emission in detail, we observed CH₄ flux by automatic chambers at taiga-tundra boundary in the vicinity of Chokurdakh (70° 37′ N, 147° 55′ E) on the lowland of the Indigirka River in summers from 2013 to 2016. A transect was set across a sedge wet area, a sphagnum wet area and a shrub mound, and automatic chambers were installed at these areas. These chambers were connected to a photoacoustic field gas monitor (INNOVA 1412, LumaSense Technologies) to monitor CH₄ flux. To assess variations in CH₄ production, oxidation and transport processes, dissolved CH₄ concentration, δ¹³C and δD were observed at observation points of manual chambers in 2011, 2012, 2013 and 2016, and at observation points of both manual and automatic chambers in 2016. Relationship of summer-season variations in CH₄ flux against water level changes (precipitation events and drainage) and thawing process of active layer will be discussed in this presentation.