大兴安岭湿地多年冻土区活动层水热特征分析

大兴安岭北部是我国唯一的中高纬度多年冻土区，其水热特征分析对陆气能量交换、生态系统和气候变化等研究有重要意义。基于2011—2020年期间对大兴安岭森林生态站附近的湿地多年冻土开展的气温和0~2 m地温和土壤含水量数据，对大兴安岭湿地多年冻土活动层的水热特征进行了分析。结果表明：湿地多年冻土活动层内地温的变幅随深度减小，且具有滞后性。融化期地表温度高于深层地温，冻结期相反。2012年、2013年、2019年和2020年的平均融化速率分别为0.49、0.61、0.47和0.56 cm·d^-1，向上平均冻结速率分别为1.34、2.12、2.58和1.65 cm·d^-1。向下平均冻结速率分别为1.69、1.02、3.32和1.00 cm·d^-1，最大融化深度分别为78.73、85.65、66.22和74.94 cm。2012年5月—2013年5月期间，土壤未冻水含量随地温变化的拟合关系较好，相关系数大于0.90，且深层拟合效果优于表层。融化期土壤水分变化幅度大，与地温的相关性差，随深度增加相关性减弱。湿地充足的水分为多年冻土的双向冻结提供了条件。研究成果可为大兴安岭湿地多年冻土区的冻融循环、水热耦合机理和模拟研究提供数据基础和理论依据。

Analysis of heat and water transferring characteristics in the active layer of permafrost in the wetland of the Greater Khingan Mountains

Besides being an important part of cryosphere， the permafrost in the northern Greater Khingan Mountains is the only permafrost region at the mid-to-high latitudes in China. Analysis on the hydrothermal characteristics in this region is of great significance to the research of land-atmosphere energy exchange， terrestrial ecosystems， and climate change. Based on the air temperature， ground temperature and moisture content at the depths between 0-2 m collected in a wetland permafrost near the Greater Khingan Mountains Forest Ecological Station from 2011 to 2020， the heat and water transferring characteristics of the permafrost active layer in the Greater Khingan Mountains wetland were analyzed. Results show that the varying range of ground temperature in the active layer of the wetland permafrost decreases with depth and has a significant hysteresis. The ground surface temperature is higher than that at deep depths during the ground thawing period， and it is opposite during the ground freezing period. The average ground thawing velocities were 0.49， 0.61， 0.47， and 0.56 cm·d^-1 in 2012， 2013， 2019， and 2020. The corresponding average upward ground freezing velocities were 1.34， 2.12， 2.58， and 1.65 cm·d^-1， respectively. The average downward ground freezing velocities were 1.69， 1.02， 3.32， and 1.00 cm·d^-1， and the maximum thawing depths of the active layer were 78.73， 85.65， 66.22， and 74.94 cm， respectively. From May 2012 to May 2013， the soil moisture content remained much correlated with the ground temperature. During the freezing period， the unfrozen soil water content was related with the ground temperature in a good power function， and the correlation coefficient is greater than 0.90， and the fitting result for deep soil is better than that at surface soil. During the thawed period， the correlation between the soil moisture content and ground temperature is not good and the correlation coefficient is less than 0.50. In addition， the correlation coefficient decreases with depth. Sufficient soil moisture in the wetland is in favor of the bidirectional freezing in the permafrost active layer. In the depth less than or equal 1.4 m， the ground temperature is strongly correlated with the air temperature. As a strong thermal insulation material， the snow dampens the ground temperature variation with air temperature in winter and somehow keeps the ground ‘warm’. The process of snow melting delays the ground from thawing. Besides， the vegetation layer will impede the solar radiation arriving the ground surface and decrease the ground surface temperature， which will weaken the correlativity between air and ground temperatures and preserve the permafrost. This study will provide a good data basis and theoretical advanced investigation for modelling the ground freezing and thawing with consideration of both heat and water transferring in a coupled way the permafrost regions of the Greater Khingan Mountains wetland.