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

[MIS03-05] Lake and drained lake basin system in central Yakutia of Eastern Siberia

*Yoshihiro Iijima¹, Takahiro Abe², Hitoshi SAITO³, Hotaek Park⁴, Tetsuya Hiyama³ (1.Department of Geography, Tokyo Metropolitan University, 2.Mie Univ., 3.Nagoya Univ., 4.JAMSTEC)

Keywords:permafrost, thermokarst, hydrological change, channeling

In the permafrost region of the Arctic, thermokarst, a phenomenon of ground subsidence due to the thawing of the near-surface permafrost layer associated with climate change, is becoming increasingly prominent. In recent years, it has been pointed out that this topographical change may significantly alter hydrological processes by developing a network of water channels along the valleys of polygonal microtopography of thermokarst in permafrost regions. In addition, wetlands and small lakes are formed in the depressions where subsidence has progressed (thermokarst lakes). As these water bodies grow horizontally, they close to each other, then collapse and merge due to lateral erosion, eventually becoming valleys and draining. These processes of lake formation, channelization, and drainage have drawn attention in recent years as the "Lake and drained lake basin system" as they bring about significant changes in the water resources and ecosystems of the permafrost region. In this study, we conducted a geomorphological analysis in the central basin of the Lena River (Central Yakutia) in Eastern Siberia as a case study of a permafrost region where this channelization process is about to occur.
In an area where thermokarst lakes are densely distributed, small water bodies with a diameter of 100 m or less are formed in the visible images from satellites, but the connection of lakes by lateral erosion remains small-scale at present. On the other hand, from the geomorphological analysis using a fine-resolution digital elevation model (AW3D), it was confirmed that the depressions were lined up in rows, and the valleys were developed in a state where they could be connected in a channel shape. Since it is not possible to determine the direction in which the water bodies are connected or the future channel direction only from the visible image, it is suggested that the direction of the future channel can be estimated by combining geomorphological analysis.
Since 2000, the effects of climate change have become significant in Eastern Siberia, and wetlands due to thermokarst have grown and expanded in many places. In other words, it appears that the current phase is the phase in which water bodies are developing on the ground surface. In the future, if the thawing progresses, thermokarst lakes further expand, and the connection and channelization progress, it is expected that runoff and drying will occur in this area as well. This hydrological consequence is highly likely to be related to the irreversible evolution of ecological processes, so it is necessary to evaluate the spatiotemporal variation.