青藏高原不同高寒生态系统类型下多年冻土活动层水热过程差异研究

Study on the differences of thermal-moisture dynamics in the active layer of permafrost in different alpine ecosystems on the Tibetan Plateau

基于青藏高原北麓河地区高寒草原、高寒沼泽草甸和高寒草甸生态系统下多年冻土活动层水热过程的监测数据,对活动层水热过程特征开展了相关研究。研究结果显示,在活动层厚度、冻融时间、持续时间以及活动层土壤水分含水量分布方面,不同的高寒生态系统下活动层的上述属性特征差异明显。高寒草原下多年冻土活动层厚度最大,土体开始融化的时间最早,每年持续融化的日数也最长;高寒草甸最小,高寒沼泽草甸居中。高寒草原下活动层土壤含水率从上到下逐渐增加,水分基本集中在活动层的中下部分;高寒沼泽草甸下活动层土壤水分的分布情况相对比较均衡;高寒草甸下活动层土壤含水率分布呈现从上到下逐步减少的模式,越靠近地表土壤含水率越大。对监测数据的进一步分析发现,不同的高寒生态系统下,近地表地温与气温温差累计值、近地表土壤有机质含量、n因子特征以及近地表地温标准差统计特征都具有明显的区别。研究分析表明,多年冻土活动层水热过程特征与高寒生态系统类型具有明显的关联性,高寒生态系统会影响近地表能量通量,从而使地-气热量交换产生差异,这一差异又将改变活动层土壤温度、水分分布特征及其动力学过程。

Based on the observation within the active layer beneath different alpine ecosystems,including alpine grassland,alpine swamp meadow and alpine meadow,in Beiluhe area on the Tibetan Plateau,the thermal-moisture dynamics were studied. The results show that the differences are evident about the aspects such as active layer depth,initial times and duration of freeze and thaw,and spatial moisture distribution. Beneath alpine grassland,the active layer has deepest depth,earliest initial thawing and the longest duration of thawing among the all three types of ecosystems,following by that beneath alpine swamp meadow and then by alpine grassland. Beneath the alpine grassland water content within the active layer increases from the top to the bottom,most of the water concentrates in the middle lower part. Beneath alpine swamp meadow water content is relatively even. Beneath alpine swamp meadow water content gradually reduces from top to bottom,and the closer to surface the larger the soil moisture content is. Further analysis of the monitoring data finds that there are obvious differences in ground surface temperature and air temperature,organic material content,n-factor and the statistical characteristics of standard deviation on near surface temperature among various alpine ecosystems. The study indicates that the thermal-moisture dynamics are closely related to the alpine ecosystem which affects the near surface energy fluxes and makes difference in the earth-atmosphere heat exchange and then changes the temperature and moisture characteristics of the active layer.