有无积雪覆盖下浅层土壤水热过程是青藏高原多年冻土区水能循环中的一个重要不确定因素。为了研究积雪覆盖对高寒沼泽、草甸浅层土壤水热过程的影响,在青藏高原多年冻土区选择了典型的有无积雪覆盖的沼泽、草甸建立观测场,观测浅层土壤的温度和水分状况。通过分别研究积雪对高寒沼泽、草甸浅层土壤温度和水分的影响,结果表明:高寒沼泽、草甸在有积雪覆盖下浅层土壤开始冻结和消融的时间都有所滞后,且冻结持续时间相应有所增加。由于积雪覆盖,浅层土壤温度变化速率略有减小而水分变化速率略有增加,积雪起到了抑制土壤温度变化速率和促进土壤水分变化速率的作用。积雪覆盖对秋季冻结过程和夏季融化过程浅层土壤的温度和水分的影响明显大于冬季冻结降温过程和春季升温过程,且对融化过程的影响较冻结过程明显。通过对比分析有无雪盖沼泽和草甸土壤,说明积雪的覆盖对沼泽土壤温度的影响要大于草甸土壤,对土壤水分融升过程的影响大于冻降过程,且对沼泽浅层土壤的影响大于草甸浅层土壤。

The average altitude of Tibetan Plateau is over 4000 m above sea level with vast areas of permafrost. The interaction between permafrost and the atmosphere is realized by the dynamic water-heat process within the active layer. The snowy condition on the earth surface directly impacts on the variations of the thickness of the active layer and the annual mean soil temperature in the permafrost area. Thus, the shallow soil water-heat process with or without snow cover is a very important uncertain factor in the water and energy circulation processes of the permafrost areas in Tibetan Plateau. In typical alpine meadow and swamp, the active soil moisture and temperature at different depth of layer were observed to reveal the influences of the snow cover changes on the soil water-heat processes. The results show that the thawing and freezing started-time of active soil were later and the duration of freezing were longer with snow cover than that without snow both in alpine meadow and swamp areas. With the snow cover, the active soil temperature variation rate decreased while the soil moisture variation rate increased. The snow cover plays important roles in restraining the soil temperature change and b accelerating the moisture change in active soil layer. The impacts of snow cover on soil temperature and moisture are greater in autumn and summer than that in winter and spring, and the influence is more dominant in melting process than in freezing process. Snow cover results in reducing the annual maximum soil temperature and rising the annual minimum soil temperature in alpine swamp. On the contrary, both the annual maximum and minimum soil temperature increase under snow cover in alpine meadow. By comparing the temperature differences between the annual maximum and minimum temperature of swamp and meadow soil with or without snow cover, it shows that the snow cover has greater influence on swamp soil temperature than on meadow soil. Some parameters, such as time of melting (T_s), duration of melting and increasing (T_r), the range of soil moisture content increasing (ΔW_s), time of freezing (T_d) , duration of freezing (T_z) and the range of soil moisture content falling (ΔW_d), were selected to objectively reflect the influence of snow cover on soil moisture during the freezing process. The results show that the snow cover has more influence on soil moisture in melting and rising process than that in freezing and falling process, and has a more influence on swamp soil moisture than on meadow soil.