西藏纳木错流域冻土环境初步研究

利用在西藏纳木错流域念青唐古拉山北坡（NQN，海拔5 400 m）和西北保吉乡（BJ，海拔4 730 m）布设的两台带有四层土壤探头自动气象站(AWS)2005—2006年冬季10个月观测数据进行了统计分析。结果表明：观测期间NQN日及月平均气温均低于BJ，但变化幅度均小于BJ，土壤冻结时间比BJ长，两处的气温梯度为0.31℃/100 m。与安多月平均气温比较，推断NQN存在高山多年冻土。NQN大气—土壤及土壤内热传输速度快于BJ；冻结期内土壤中未冻水含量在0～-2.5℃时发生跃变且与土壤温度存在较好的线性关系；相同深度处NQN土未冻水含量较小。土壤温度日变化在0～40 cm深度处较明显，40cm深度以下变化很小，未冻水含量日变化在5 cm深度较明显，20 cm以下变化微弱。利用两观测点冻结深度（Df）与冻结积温（Tg）的良好相关建立模型，NQN为：Df n= 0.0016Tg+ 1.69,R2=0.9958；BJ为：Df b= 0.002 Tg+ 1.13，R2= 0.9424，并由此推断出两观测点最大季节冻结深度分别为1.69 m和1.13 m。

A Primary Study of the Environment of Frozen Ground in the Nam Co Basin, Tibet

Based on the data from two automatic weather stations (AWS) with 4-layers of soil probes located at an elevation of 5,400m at the Northern slope of Mt. Nyenquentanglha (N) and at 4,720 m at Boji (B) in the northwest of the Nam Co lake, this paper analyzed the environment of the frozen ground around the lake basin. It concludes that from September 2005 to May 2006, the daily temperature and monthly temperature at the N were both lower than those at the B, however, amplitude of daily temperature at the N was smaller than that at the BJ. The freezing period of ground at the N is longer than that at the B. From September to next May, their air temperature lapse rate is 0.31℃/100 m smaller than that in the atmosphere. Results show alpine permafrost existed at the N by comparing monthly temperature with the Ando, Tibet. Heat conduction between air and soil and within soil at the N was faster than that at the B. During freezing period, a powerful relationship was found between the soil unfrozen water content and soil temperature, the unfrozen water content abruptly declined at 0～-2℃. The Diurnal variation of soil temperature is dramatic at the 0~40 cm depth, while no trend below 40 cm; so does soil unfrozen water content at 5 cm depth, no trend below 20 cm. Based on the close correlation between a soil freezing depth (D_f) and a cumulative frost temperature (T_g), the model was proposed as the following: D_f-n= 0.0016T_g+ 1.69 at the N and D_f-b= 0.002T_g+ 1.13 at the B, using the model, the maximum freezing depth were estimated by 1.69 m and 1.13 m at the two sites, respectively.