基于土壤水文过程示踪的高寒山区植被用水与径流来源研究--以我国祁连山北麓上游流域为例

How does the soil water replenish and partition in the vadose zone is the key problem to understand the complex interactions between hydrological processes and ecological processes. The soil water partitioning into water pools can imply such interactions, which is separated for plant transpiration and streamflow after the soil water replenishment by precipitation. The part consumed by plants also reflects their water use strategies and adaptation of different vegetation to different climate types. Due to the very different climate types in our country, it is highly needed to understand the replenishment and partitioning of the soil water, the relationship between plant water sources and the streamflow water sources, and the mechanisms behind the partitioning. The study area named Tianlaochi for this project is located at an upper catchment of Heihe River Basin, the northern part of Qilian Mountains in alpine cold regions. In this catchment, a systematic ecohydrological-monitoring site has been founded. Suction cup lysimeters, centrifugation and cryogenic distillation will be applied to obtain the soil water samples of different water pools in soil water partitioning. By analyzing the stable isotopes of the soil water samples, plant water use and streamflow water sources will be studied on seasonal and rain-event time scale. The relationship will be discussed between the plant water sources and the streamflow water sources in this alpine cold region. The mechanism will be revealed in the soil water replenishment and the partitioning. The conceptual model will be constructed, which is significant to study the catchment soil hydrological processes and the adaptation of the typical native vegetation in the study area.

非饱和带中土壤水分的更新及分配问题是理解非饱和带水文过程和生态过程之间复杂相互作用的关键。降水更新后的土壤水分在植被用水和径流中的分配是不同类型植被为适应不同气候特征的水分利用策略和与水文过程相互作用的反映。我国不同气候类型区域土壤水分更新分配过程中植被用水及径流补给特征及二者之间相互关系还不清楚，分配机制有待进一步研究。本项目拟选择位于我国西北高寒山区的祁连山北麓黑河上游天涝池流域，依托该流域已有生态水文观测站，组合使用吸杯式采样器法、离心法和低温真空抽提法获得不同分配去向土壤水分，使用稳定同位素示踪研究流域季节和降水事件尺度天然林植被用水和径流来源时空变化特征，探讨我国高寒山区流域植被用水和径流来源的相互关系，理解土壤水分更新和分配过程机制，构建祁连山高寒山区流域生态水文过程的概念模型，为高寒山区流域土壤水文过程和典型天然林生态适应性研究提供可靠依据。

理解非饱和带水文过程和生态过程之间复杂相互作用的关键在于厘清非饱和带中土壤水分的更新及分配问题。降水更新后的土壤水分在植被用水和径流中的分配，决定了不同类型植被为适应不同气候特征的水分利用策略和与水文过程的相互作用。本课题选择我国西北高寒山区的祁连山北麓黑河上游天涝池流域，依托该流域的生态水文观测站系统布设采样点，2019年7月至9月，连续采集降水事件样品，日径流样品，8次野外采集树枝样品、不同深度土壤样品、土壤水样品及径流样品，实验室分析测试水分中的氢氧稳定同位素值。通过对比圆柏林穿透水和云杉林的穿透水中的δ18O，圆柏林穿透水的δ18O略高于云杉林穿透水中的δ18O，但若以林外降水δ18O为起点计算穿透水的稳定同位素特征值的改变量，表明云杉林的降雨截留效应要大于圆柏林的降雨截留效应。通过利用吸杯式采样器法、离心法和低温真空抽方法获取的土壤水分同位素特征结果差异显著，这种显著差异表明土壤水分确实可以理解为是由不同的滞留时间组成的土壤水分库。依据各土层在实验条件下土壤水的稳定同位素完全混合的时间结果，要达到100 %的完全混合状态需要相当长的时间（以月计），但在95 %的置信区间内，以圆柏样地为例，自土壤表层向下对应0-15、15-30、30-45、45-60 cm深度，各土层的混合平衡时间分别为4.04 d、4.75 d、5.71 d、6.46 d，为使用稳定水同位素示踪研究流域季节和降水事件尺度天然林植被用水和径流来源时空变化特征提供了土壤水分库中水分充分混合的时间依据，也为高寒山区流域土壤水文过程和典型天然林生态适应性研究提供了可靠依据。