Factors controlling diurnal variation in the isotopic composition of atmospheric water vapour observed in the taiga, eastern Siberia

• Published in: Hydrological Processes
• Main Authors: Ueta, Akihiro, Sugimoto, Atsuko, Iijima, Yoshihiro, Yabuki, Hironori, Maximov, Trofim C., Velivetskaya, Tatiana A., Ignatiev, Alexander V.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2012
• Subjects: permafrost; taiga; Siberia
• Online Access: http://dx.doi.org/10.1002/hyp.9361; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fhyp.9361; https://onlinelibrary.wiley.com/doi/pdf/10.1002/hyp.9361

Abstract Deciduous forest covers vast areas of permafrost under severe dry climate in eastern Siberia. Understanding the water cycle in this forest ecosystem is quite important for climate projection. In this study, diurnal variations in isotopic compositions of atmospheric water vapour were observed in eastern Siberia with isotope analyses of precipitation, sap water of larch trees, soil water, and water in surface organic layer during the late summer periods of 2006, 2007, and 2008. In these years, the soil moisture content was considerably high due to unusually large amounts of summer rainfall and winter snowfall. The observed sap water δ 18 O ranged from −17.9‰ to −13.3‰, which was close to that of summer precipitation and soil water in the shallow layer, and represents that of transpired water vapour. On sunny days, as the air temperature and mixing ratio rose from predawn to morning, the atmospheric water vapour δ 18 O increased by 1‰ to 5‰ and then decreased by about 2‰ from morning to afternoon with the mixing ratio. On cloudy days, by contrast, the afternoon decrease in δ 18 O and the mixing ratio was not observed. These results show that water vapour that transpired from plants, with higher δ 18 O than the atmospheric water vapour, contributes to the increase in δ 18 O in the morning, whereas water vapour in the free atmosphere, with lower δ 18 O, contributes to the decrease in the afternoon on sunny days. The observed results reveal the significance of transpired water vapour, with relatively high δ 18 O, in the water cycle on a short diurnal time scale and confirm the importance of the recycling of precipitation through transpiration in continental forest environments such as the eastern Siberian taiga. Copyright © 2012 John Wiley & Sons, Ltd.