青藏高原地表蒸散发过程与稳定同位素内陆水循环研究

Water stable isotopes have wide application in the hydrological cycles and paleo climate changes on the Tibetan Plateau. Observations showed that there is an apparent increasing trend in water isotopes from the semi-arid region in the middle of plateau to the arid region in the northern plateau, and it is also assumed that the local land surface water cycle is much involved. However, the processes that can contribute the increasing of local vapor water isotopes in the local hydrological cycle is not adequately addressed yet. In this proposal, we focus on the field in-situ observation of water isotopes fractionation during the soil evaporation and vegetation transpiration processes, together with simultaneous observation of surface vapor isotopes in the semi-arid middle plateau and arid region in northwestern plateau. Our first purpose is to reveal how the evapotranspiration processes affect the evaporated vapor isotopes in different climate conditions. We will also measure the large spatial scale atmospheric vapor isotope variations across the plateau scale, together with surface soil water isotope observation, aiming for establishing a relationship between soil water isotopes with near surface atmospheric vapor isotopes. In the proposal, we will also make effects on the evapotranspiration partitioning by observing the simultaneous soil water, plant water and vapor water isotopes. The results from this project will help to unveil the processes and mechanisms on how the spatial water isotope pattern was formed. The work will also promise for an improved understanding the hydrological cycle and paleoclimatic isotope record research work, as well as on plateau eco-hydrology.

青藏高原地水体同位素在现代水循环与过去气候环境变化记录研究中起着重要的作用。水体从高原中部的半旱区到北部的干旱区稳定同位素值显著上升，而其中内陆的水循环过程起着重要的作用。但内陆水循环过程如何影响水体同位素的空间变化仍不清楚。本申请项目计划开展青藏高原中部半干旱区与西北部干旱区地表蒸散发过程中水体同位素分馏过程野外实验，结合同步的大气水汽同位素监测以及气象观测，揭示不同气候条件下土壤与植被的蒸散发如何对水汽同位素产生影响；通过大空间尺度大气水汽与地表土壤水同位素同步监测，揭示地表蒸发过程与水汽同位素变化的关系；同时，通过土壤、植被、大气同位素观测结果，揭示不同气候区地表蒸腾与蒸散发的比率。本项目的研究成果将阐明青藏高原水体同位素空间变化形成的关键过程与机制，对于青藏高原内陆的水循环过程研究、稳定同位素古气候记录研究以及生态水文学研究都有意义。

青藏高原地水体同位素在现代水循环与过去气候环境变化记录研究中起着重要的作用。水体从高原中部的半旱区到北部的干旱区稳定同位素值显著上升，而其中内陆的水循环过程起着重要的作用。但内陆水循环过程如何影响水体同位素的空间变化仍不清楚。本项目系统开展了高原中南部降水、大气水汽、陆地土壤蒸发与植被蒸腾过程稳定同位素观测实验，研究了不同空间尺度水循环过程中的稳定同位素变化及影响机制，揭示了内陆水循环与大空间尺度水汽输送对水体稳定同位素的影响。本研究利用同位素方法测量的藏北高原地区T/ET比率平均值为0.43，发现土壤含水量是决定T/ET比率的主导因子，而叶面积指数只起次要作用，这项研究成果填充了高原面上地表蒸散发研究的空缺。通过大气水汽同位素的连续监测研究，明确了高原南部大气水汽氢氧双同位素的季节变化特征及控制因子，冬季大气水汽瑞利分馏机制控制水汽同位素变化，而在夏季季风期，水汽同位素与热带印度洋及青藏高原上的强降水呈现负相关。在更大空间尺度的水循环研究中，发现季风区降水同位素受控于大尺度的大气环流过程，与ENSO循环有直接的相关性，取得了一系列系统性研究成果，揭示了大气环流如何通过强对流降水的年际变化影响降水同位素，纠正了以前认为的降水同位素受当地气温或降水量变化控制的普遍认识。.这些研究成果为季风区稳定同位素气候记录研究、陆地稳定同位素水循环、生态系统水分利用研究提供了新的解释或结果。