Recent Advances in Monitoring of the Unfrozen Soil Water in the Source Area of the Yellow River, China

English Abstract:

Recent permafrost degradation in the Source Area of the Yellow River (SAYR) is obviously manifested by reduction in areal extent from continuous and discontinuous to sporadic and patchy, thinning of permafrost, and expansion of taliks. On this account, substantial transformation of surface and subsurface hydrological cycles have occurred. Therefore, the water yielding and runoff mechanism caused by ground ice-water phase change in permafrost is needed to be clarified. To investigate the trends in changes of climate, permafrost, and water resources in the SAYR, we built a monitoring network of permafrost-hydrology in the SAYR. This monitoring network includes three automatic meteorological stations, and ten active layer profiles. It is set up in consideration of elevation, landscape, and hydrology and vegetation conditions. The elevation of these sites range from 4320 m to 4720 m. The monitoring elements including the air temperature, air humidity, precipitation, radiation, and unfrozen soil moisture content, and soil temperature, and so on. Sensors with accuracy of 0.05 °C made and calibrated by the State Key Laboratory of Frozen Soil Engineering, Chinese Academy of Sciences, were set up to monitor the thermal regimes of the active layer at depths of 5 cm, 20 cm, 40 (50) cm, 80 cm, 100 cm, 120 cm, 160 cm, 200 cm, 250 cm, respectively. The CS616, with resolution of 0.1% v/v and accuracy of 3.0% v/v, were set up at comparable depths of soil temperature to monitor the unfrozen soil moisture content. All these observation elements were collected and recorded hourly or half-hourly by the CR3000 data loggers made by the Campell Scientific Inc. Additional field work including testing soil texture and measuring soil dry bulk density were carried out during the excavation of the profiles. Preliminary results demonstrate that yearly dynamics of unfrozen soil moisture content in the active layer strongly depending on the freezing and thawing processes of the soils, as well as infiltration of rainfalls and melting snow, particularly during the onset and finishing of the thawing and freezing periods. The content of soil moisture varied greatly with the diversity of ground surface condition and soil textures. These data could facilitate the research on evolutions of environments and response of permafrost to climate change in the SAYR.