基于稳定同位素和水化学的高寒冰川流域径流组成研究

The enhanced melting of glaciers under global warming has already resulted in the changes of hydrologic processes at the alpine glacier-fed catchment. However, there is considerable uncertainty about how the variations of runoff processes and the different water sources will respond to climate warming. Therefore, based on the stable isotopic and hydrochemical tracers, the runoff composition of the Xiaokuergan Alpine Basin at the headwaters of the Aksu River will be investigated as a case study. The objectives of this project are as follows: (1) to investigate the spatial and temporal variations of hydrochemical and stable isotopes composition in various types of waters, including the ice, snow, ice-snow meltwater, precipitation, streamflow and groundwater samples, at the whole glacierized catchment; (2) to quantify the proportions of different water sources, namely the precipitation, ice-snow meltwater and groundwater, to surface runoff using isotopic and hydrochemical tracers in conjunction with end-member mixing analysis model at different time steps such as daily, weekly, monthly, seasonal and annual etc.; (3) to evaluate the influences of variations of ice-snow meltwater on runoff processes in different time scales, including the flood period or dry period, extreme hydrological events, daily, seasonal variations. The results will provide new insights into the response of hydrological processes in the alpine glacierized basin to climate change, and the scientific basis for rational utilization of water resources in arid areas of northwest China.

气候变暖背景下，冰雪加速消融，引起高寒冰川流域径流组成改变。但冰川流域由于存在多相态水体，水文过程复杂，目前对其径流组成的研究还较薄弱。本项目选择我国天山南坡高寒冰川流域阿克苏河源小库尔干流域为研究区，旨在通过样品采集、稳定同位素和水化学示踪及模型模拟等方法，开展高寒冰川流域径流组成研究。弄清高寒冰川流域不同水体稳定同位素和水化学的时空变化特征及其水文指示意义；建立端元混合径流分割模型，对分割结果进行验证和误差评估，准确定量冰雪融水、降水和地下水对径流的贡献率；阐明不同时间尺度冰雪融水变化对流域径流过程的影响。研究结果有助于弄清全球变暖背景下冰川流域水文过程对气候变化的响应机制，为我国西北干旱区水资源合理利用提供科学依据。

气候变暖背景下，冰雪资源加速消融，导致冰雪融水在短期内大幅增加，对我国西北地区高寒冰川流域径流组成和水文过程影响显著，要深入研究这些变化过程及其影响就需要开展径流分割研究。本项目按照任务书如实进行，以高寒冰川区小库尔干流域为研究区域，应用稳定同位素和水化学示踪技术，以定量确定冰雪融水、降水等对高寒流域径流的补给比例为目标，取得了如下主要的研究成果：（1）在小库尔干流域系统采集了两个水文年的各种不同水体样品（大气降水、冰雪融水、表层冰、积雪、泉水和河水），并进行氢氧同位素和水化学离子分析，积累了具有重要科研价值的数据；（2）研究确认水汽来源对流域降水化学离子常量浓度影响显著，冰川区冰雪系统化学离子浓度变迁主要受到淋溶过程的影响，水-岩相互作用和流域水文过程是地表水和地下水化学离子浓度时空变化的主要原因。（3）研究结果表明流域沿海拔采集的河水样品中稳定同位素特征出现与降水中δ18O和δD相同的“海拔效应”，流域径流稳定同位素组成主要受各种不同补给水源充分转化混合后形成。（4）EMMA径流分割模型结果表明，青冰滩72号水文断面（海拔3 604 m）冰雪融水和降水分别占河流总流量的77.43%和22.57%；地窝子水文点（海拔2 879 m）冰雪融水、地下水和降水分别占河流流量的59.75%、19.60%和20.65%；流域出口小库尔干水文断面（海拔2 333 m）冰雪融水、地下水和降水分别占河流流量的47.36%、17.47%和35.17%。径流分割结果表明冰川区冰雪融水是小库尔干流域最重要的补给来源。本项目研究结果将为高寒山区冰川流域的水文模型提供部分参数，为进一步揭示气候变暖背景下冰雪剧烈消融引起的水文过程及其对气候变化的响应机制提供重要的理论依据。