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The taiga ecosystem in northeastern Siberia, a nitrogen-limited ecosystem on permafrost with a dry climate, changed during the extreme wet event in 2007. We investigated the normalized difference vegetation index (NDVI) as a satellite-derived proxy of needle production and compared it with ecosystem parameters such as soil moisture water equivalent (SWE), foliar C/N ratio, δ13C and δ15N, and ring width index (RWI) at the Spasskaya Pad Experimental Forest Station in Russia for the period from 1999 to 2019. Historical variations in NDVI showed a large difference between typical larch forest (unaffected) and the sites affected by the extreme wet event in 2007 because of high tree mortality at affected sites under extremely high SWE and waterlogging, resulting in a decrease in NDVI. Before 2007, the NDVI in a typical larch forest showed a positive correlation with SWE and a negative correlation with foliar C/N. These results indicate that not only the water availability (high SWE) in the previous summer and current June but also the soil N availability increased needle production. NDVI was also positively correlated with RWI, resulting from similar factors controlling them. However, after the wet event, NDVI was negatively correlated with SWE, while NDVI showed a negative correlation with foliar C/N. These results indicate that after the wet event, high soil moisture availability decreased needle production, which may have resulted from lower N availability. Needle δ15N was positively correlated with NDVI before 2007, but after the wet event, needle δ15N decreased. This result suggests damage to roots and/or changes in soil N dynamics due to extremely high soil moisture.

Arctic terrestrial ecosystems near the treeline in river lowlands are vulnerable to the changing climate and seasonal extreme events, including flooding. We set up a simple camera monitoring system to record the timings and durations of the leafy period and the spring flush of river water at three observation sites (Boydom [B]: 70.64°N, 148.15°E; Kodac [K]:70.56°N, 148.26°E; Verkhny-Khatistakh [VK]:70.25°N,147.47°E) in the Indigirka lowland, in north-eastern Siberia. Time-lapse digital cameras were located at seven points across the three sites. The time intervals were 1–4 or 24 hours. The minimum and maximum monitoring periods were 2-years (July-2016 to August-2018) at B and 5-years (August-2013 to July-2018) at K. One camera documented the timings of river ice melt and open water periods from the riverbank of the Kryvaya River, one of the small tributaries of the Indigirka River. The other six cameras recorded several types of ground cover typical of the area, including larch trees (Larix cajanderi), shrubs (including Salix spp., and Betula nana), forbs, mosses, and graminoids in an ecosystem of sparsely forested shrublands, wetlands, and riversides. The data consists of 45,617 JPEG-format images. This dataset can be used to detect the onset and offset of the growing season and to capture the ice melt timing and water cover periods in wetlands and riversides. It may be useful in validating satellite data such as the vegetation remote sensing index for remote and little-known areas. These data may contribute to the study of the role of high-latitude ecosystems in global climate changes.

The response of CH4 emission from natural wetlands due to meteorological conditions is important because of its strong greenhouse effect. To understand the relationship between CH4 flux and wetting, we observed interannual variations in chamber CH4 flux, as well as the concentration, δ13C, and δD of dissolved CH4 during the summer from 2009 to 2013 at the taiga–tundra boundary in the vicinity of Chokurdakh (70∘37′ N, 147∘55′ E), located on the lowlands of the Indigirka River in northeastern Siberia. We also conducted soil incubation experiments to interpret δ13C and δD of dissolved CH4 and to investigate variations in CH4 production and oxidation processes. Methane flux showed large interannual variations in wet areas of sphagnum mosses and sedges (36–140 mg CH4 m−2 day−1 emitted). Increased CH4 emission was recorded in the summer of 2011 when a wetting event with extreme precipitation occurred. Although water level decreased from 2011 to 2013, CH4 emission remained relatively high in 2012, and increased further in 2013. Thaw depth became deeper from 2011 to 2013, which may partly explain the increase in CH4 emission. Moreover, dissolved CH4 concentration rose sharply by 1 order of magnitude from 2011 to 2012, and increased further from 2012 to 2013. Large variations in δ13C and δD of dissolved CH4 were observed in 2011, and smaller variations were seen in 2012 and 2013, suggesting both enhancement of CH4 production and less significance of CH4 oxidation relative to the larger pool of dissolved CH4. These multi-year effects of wetting on CH4 dynamics may have been caused by continued soil reduction across multiple years following the wetting. Delayed activation of acetoclastic methanogenesis following soil reduction could also have contributed to the enhancement of CH4 production. These processes suggest that duration of water saturation in the active layer can be important for predicting CH4 emission following a wetting event in the permafrost ecosystem.

第6回極域科学シンポジウム分野横断セッション：[IA] 急変する北極気候システム及びその全球的な影響の総合的解明―GRENE北極気候変動研究事業研究成果報告2015―11月19日（木） 国立極地研究所 2階 大会議室

第6回極域科学シンポジウム分野横断セッション：[IA] 急変する北極気候システム及びその全球的な影響の総合的解明―GRENE北極気候変動研究事業研究成果報告2015―11月19日（木） 国立極地研究所１階交流アトリウム

第6回極域科学シンポジウム特別セッション：[S] 北極温暖化とその影響 ―GRENE 北極気候変動プロジェクトと新しい方向性―11月18日（水） 国立極地研究所 2階 大会議室

第4回極域科学シンポジウム横断セッション：[IA] 「急変する北極気候システム及びその全球的な影響の総合的解明」―GRENE北極気候変動研究事業研究成果報告2013―11月12日（火） 国立極地研究所 ２階大会議室