青藏高原湿地土壤冻结、融化期间的陆面过程特征

Features of land surface process over wetland at Tibetan Plateau during soil freezing and thawing periods

利用青藏高原中部玉树隆宝湿地2015年7月—2016年7月的观测资料,分析了土壤冻结、融化前后土壤温、湿度和地表能量收支特征,结果表明:冻土持续时期为12月至次年4月,深层土壤的冻结较浅层土壤滞后,融化过程快于冻结过程,5—40 cm土壤全部冻结历时51 d,全部融化历时19 d。土壤体积含水量年变化幅度达0.6 m^3/m^3。冻结过程5—40 cm土壤体积含水量下降,融化过程5—10 cm土壤体积含水量升高。土壤冻结之后,感热通量白天的值升高,潜热通量白天的值降低,净辐射和土壤热通量均降低,土壤热通量日变化幅度增大。土壤融化之后,潜热通量、净辐射和土壤热通量白天的值升高。地表反照率、鲍恩比、土壤热导率和土壤热扩散率冻结后增大融化后减小,土壤热容量冻结后减小融化后增大。

Using observed data at Longbao wetland, Yushu from July 2015 to July 2016, features of soil temperature, soil moisture and surface energy budget were analyzed. The results show that the frozen period of soils lasts from preceding Decem- ber to subsequent April. The soils at deeper depths freeze later than that near the surface. The thawing process is faster than the freezing process. The soil at 5 - 40 cm depth：completely freezes within 51 d and thaws within 19 d. The magnitude of annu- al variability of soil water content is up to 0.6 m3/m3. 5 - 40 cm soil moisture decreases during the freezing period and 5 - 10 cm soil moisture increases during the thawing.period. When the soil is frozen, sensible heat flux increases while latent heat flux decreases during the daytime, net radiation and soil heat flux both decrease, and the diurnal variation of soil heat flux becomes larger. After thawing, latent heat flux, net radiation and soil heat flux all increase during the daytime. Surface albedo, the Bowen ratio, and the thermal conductivity and diffusivity of soil increase after freezing and decrease after thawing. The soil thermal capacity decreases after freezing and increases after thawing.