积雪与植被覆盖变化对冻土活动层土壤水热动态的协同影响研究

The water and thermal flux and exchange among snow, vegetation and active soil in permafrost region, which is sensitive to climate change, is one of the key hydrological cycle processes in Qinghai-Tibet Plateau. However, we have no knowledge on a few issues rising from the global climate change in permafrost region, such as how the seasonal snow cover change influences on the water and thermal dynamic processes in alpine grassland soil, what the collaborative relationship between snow and vegetation cover change was within effecting on active layer soil water thermal process. The aim of this study was to research the impacts of the seasonal snow and vegetation cover change on active soil water and thermal flux and their dynamics in alpine meadow and alpine swamp (two typical grasslands in Qinghai-Tibet Plateau) during the freeze-thaw periods, and to understand the water and thermal coupling processes, dynamic features under the change of snow and vegetation cover. The alternation experimental sites were setup by using snow fence and differed vegetation coverage in alpine meadow and alpine swamp selected in typical permafrost region of Qinghai-Tibet Plateau. The present study will be expounded the synergy effects of the seasonal snow and vegetation cover change on active soil water and heat processes, and to reveal the mechanism of synergy effects of the interaction about snow and vegetation cover change with permafrost on land surface processes in permafrost region. Meanwhile, this study will helpful to understand the special ecological hydrology in permafrost region and the change trend of the regional soil water cycle under the influence of global climate change. Moreover, the obtained results will also provide the theoretical base and scientific basis for improving the research of cold land surface processes and ecological hydrology model development in the Qinghai-Tibet Plateau, China.

多年冻土区积雪-植被-活动层土壤水热交换是青藏高原关键的水循环过程，且对全球气候变化十分敏感。然而在全球气候变化下季节性积雪覆盖变化在多大程度上及如何影响多年冻土区高寒草地土壤水热动态过程，以及季节性积雪覆盖变化与高寒草地植被覆盖变化对活动层土壤水热过程的影响存在何种协同关系目前尚不明确。本项目拟通过野外设置不同积雪厚度和植被覆盖情景的交互观测试验，研究青藏高原多年冻土区季节性积雪覆盖变化下不同植被覆盖程度对高寒草甸、高寒沼泽活动层土壤冻融过程中水、热通量的影响及其动态过程；了解基于积雪和植被协同影响的高寒草地生态系统冻土活动层土壤水热过程；揭示积雪-植被-冻土变化对高寒草地陆面过程（能水循环）的协同作用机制；阐明全球气候变化下青藏高原特殊的高寒草地冻土活动层土壤水分循环过程。研究结果有利于深入理解特殊的冻土生态水文学规律，并为推动寒区陆面过程研究和生态水文模型的发展提供理论支持。

积雪对气候变化十分敏感，尤其是季节性积雪，在干旱和寒冷地区既是最活跃的气候因素，也是最敏感的环境变化影响因子。在青藏高原，季节性积雪还是影响多年冻土分布及土壤水热过程的一个非常重要的因素。本项目选择了青藏高原多年冻土区最具典型性和代表性的植被类型—高寒草甸和高寒沼泽草地，通过设置野外积雪、植被覆盖变化的交互观测试验，发现积雪覆盖变化很大程度上影响了多年冻土区草地活动层土壤的水热动态过程。当积雪厚度大于15cm，将延迟较低植被覆盖度土壤温度和含水量的冻降时间和融升时间以及较高植被覆盖度土壤含水量的冻降、融升时间；较高植被覆盖度的土壤温度在积雪的影响下，其融升时间提前而冻降时间推后。同时，积雪覆盖降低了活动层土壤温度的变化幅度和频率，改变了不同深度土壤含水量的变化幅度和频率。研究结果证实了在多年冻土区积雪和植被覆盖变化协同影响活动层土壤的水热动态过程。项目研究结果初步揭示了积雪-植被-冻土变化对高寒草地陆面过程（能水循环）的协同作用机制，对认知高寒多年冻土区冻土水文过程及发展基于水循环机理的寒区水文模型和陆面过程模型等具有重要意义，为深入理解全球气候变化下青藏高原脆弱的生态系统未来的变化趋势和驱动因素提供科学依据和理论支持。