多年冻土区活动层冻融状况及土壤水分运移特征

利用位于典型多年冻土区的唐古拉综合观测场2007年9月1日—2008年9月1日实测活动层剖面土壤温度和水分数据，对多年冻土区活动层的冻结融化规律进行研究；同时，对冻融过程中的活动层土壤液态水含量的变化特征进行分析，探讨了活动层内部土壤水分分布特征及其运移特点对活动层冻结融化过程的影响. 结果表明：活动层融化过程从表层开始向下层土壤发展，冻结过程则会出现双向冻结现象. 一个完整的年冻融循环中活动层冻结过程耗时要远远小于融化过程. 活动层土壤经过一个冻融循环，土壤水分整体呈现下移的趋势，土壤水分逐步运移至多年冻土上限附近积累. 同时，土壤水分含量和运移特征会对活动层冻融过程产生显著的影响.

Processes of soil thawing-freezing and features of soil moisture migration in the permafrost active layer

The freezing-thawing process and the dynamics of soil moisture were analyzed with the measured data of temperature and moisture within the active layer at the Cryosphere Research Station on Qinghai-Xizang Plateau from September 1, 2007 to September 1, 2008. Both freezing and thawing processes within the active layer developed from the surface to permafrost table. The freezing duration of soil within entire active layer was 25 days, while the thawing duration was nearly 4 months, The freezing process took much less time than the thawing process. The duration of the diurnal freezing-thawing cycles of topsoil decreased with depth. Frequent diurnal freezing-thawing cycles brought a daily cycle of soil water phase changing, which made the topsoil releasing and absorbing latent heat of phase change, changing the soil hydraulic and thermal properties. The migration of soil moisture had different characteristics at different stages of the freezing-thawing cycle. In general, during a freezing-thawing cycle, the soil water molecules will migrate downwards, i.e., soil moisture will transport from the entire active layer to the upper limit of permafrost. In the meantime, the content and migration of soil water have a significant impact on the seasonally freezing and thawing process within the active layer.