[M-IS03] Wetland ecosystems under pressure, impacts on the environment and social activities

[MIS03-03] Thermal characteristics of the active layer in Khurkh wetland, northeastern Mongolia

*Gansukh Yadamsuren¹、Jambaljav Yamkhin^2,3,4、Masayuki Kawahigashi¹、Nyambayar Batbayar⁵、Munkhdavaa Munkhjargal²、Vandandorj Sumiya⁵、Tsogt-Erdene Gansukh⁴、Ulambayar Ganbold⁴、Ochirkhuyag Jargalsaikhan⁵、Nandintsetseg Nyam-Osor⁵ (1.Department of Geography, Graduate School of Urban and Environmental Sciences, Tokyo Metropolitan University, Tokyo, Japan、2.Research Institute of Cold and Arid Region, Ulaanbaatar, Mongolia、3.Geocryo LLC, Ulaanbaatar, Mongolia、4.Permafrost Department, Institute of Geography and Geoecology, Mongolian Academy of Sciences, Ulaanbaatar, Mongolia、5.Wildlife Science and Conservation Center, Ulaanbaatar, Mongolia)

キーワード：Isolated permafrost, Peat, Thermal offset, Zero-curtain, Semi-arid region

Isolated patches of permafrost, where ground thermal changes are affected by ecosystem factors such as vegetation cover rather than climate, may be vulnerable to environmental disturbances in semiarid regions. However, the impacts of ecosystem factors on the isolated permafrost remain underestimated in Mongolia. This study monitored changes in the ground temperature with respect to peat distribution, leading to resolve the ground temperature dynamics at five boreholes in a wetland. At the borehole underlain by permafrost, the range of negative thermal offset was greater than that at the permafrost-free sites because of the latent heat flux in the water-saturated soil beneath the peat layer. The permafrost-free sites had shorter zero curtains with mineral soils compared with wetter soils underlain by isolated permafrost. Vegetation shading and relatively moist conditions cooled the ground surface in the permafrost distributed area, thereby increasing soil moisture accompanied by peat soil development due to the lower decomposition rate of organic matter. Decrease in ground temperature, and development of permafrost have impeded subsurface water percolation, which, in turn, accelerated the reduction of decomposition of plant debris and ground temperature. These processes were associated with vegetation–soil negative feedback for establishing suitable conditions for the existence of isolated permafrost in semiarid regions. In seasonally water-saturated soil, ground temperatures slightly decreased with depth because of sensible heat flux, leading to warmer ground conditions. An ecosystem-driven permafrost in the Khurkh River valley was formed, and vegetation–soil negative feedback enhanced the resilience of isolated patches of permafrost to climate change.