多泥沙河流湿地水循环过程同位素溯源模拟研究

The periodic change of reservoir water level and the fluvial processes of the alternate deposition and erosion may change wetland hydrological cycle in the upper basin of reservoir, and may affect the health and stability of wetland ecosystem. In order to solve the disadvantages of the water cycle model used to simulate wetland water cycle, this study take the wetland of the Sanmenxia reservoir located in the middle reaches of the Yellow River as the example, the stable isotope technique is used to study the sediment-laden river wetland water cycle within different operation mode of reservoir. The methods of field investigation, sample acquisition, isotope characterization and model simulation are used in the study. The dynamic changes of deuterium and oxygen isotope （2H and 18O）values in precipitation, surface water, groundwater and soil water and their inter-relationships are analyzed to identify the potential water sources of wetland to reveal wetland water compensation mechanism. The isotope mixing model is established to quantify the relative contribution of rainfall, runoff and groundwater to wetland. By analyzing the relationship between 2H and 18O and precipitation, runoff, evaporation and wate level in wetland, and considering their contribution to wetland water as the weight, the isotope-water circulation model is established to simulate the wetland water cycle process, and revealed the water circulation law of wetland under the change of reservoir water level. The study aims to provide decision support for the management of reservoirs and wetlands.

水库水位的周期性变化和泥沙冲淤交替会改变库区湿地的水循环过程，影响湿地生态系统的健康和稳定。本项目以黄河中游三门峡库区湿地为研究对象，针对模型模拟方法描述湿地水循环过程的不足，利用稳定同位素技术，探究水利工程不同运行方式下多泥沙河流湿地水循环变化机理。本研究基于野外调查-样品采集-同位素特征分析-模型模拟的研究方法，系统分析水库不同水位条件下湿地降水、地表水、土壤水以及地下水的氘氧同位素（2H和18O）的动态变化和相互联系，定性识别湿地水分补给来源，揭示水库不同水位下湿地的补水机制；建立同位素质量混合模型，量化降水、地表水、土壤水以及地下水对湿地水分的贡献；建立湿地2H和18O与降水量、径流量、蒸发量以及水位的耦合关系，以各水体的贡献量为权重，构建同位素水循环模型，模拟湿地水循环过程，揭示水库调控下湿地的水循环变化机理，旨在为水库和湿地的管理提供决策支持。

三门峡水库的特殊运行方式，形成了独具特色的多泥沙河流湿地生态系统—三门峡库区湿地。受气候变化和人类活动的影响，三门峡库区湿地面临着面积萎缩、生态系统退化、水体重金属污染和生物多样性丧失等多重威胁，严重影响湿地生态系统的健康。本文在实地查勘和野外采样分析基础上，系统分析三门峡库区湿地主要水循环要素变化特性和不同水体稳定氢氧同位素组成特征，确立降水、河流水、地下水和土壤水在水库不同运行条件下的相互补给关系，基于稳定同位素溯源方法，构建同位素质量混合模型模拟三门峡库区湿地在水库不同运行方式下的水循环过程。湿地内土壤水中稳定氢氧同位素含量最为富集，河水次之，地下水最为贫化。地下水和土壤水在水库泄水期时的同位素含量高于水库蓄水期。河流水在水库蓄水期时的稳定氢氧同位素含量呈总体增加的趋势，水库泄水期呈总体减小；地下水在水库蓄水期总体减小，泄水期总体增加；土壤水在水库蓄水期和泄水期均呈沿程减小的变化趋势。三门峡库区湿地不同水体中稳定氢氧同位素的组成变化均由不同程度的降水蒸发作用和人类活动取用水造成的。水库蓄水期，库水位高于地下水位，湿地河流水补充地下水；水库泄水期，水库水位下降低于地下水位，此时地下水侧向渗漏补给河流水。SIAR模型运算结果较其他两种模型结果的不确定性小。水库蓄水期，河流水、土壤水和降水补充地下水，河流水对地下水的贡献最大，约占40~60%；土壤水次之，约占30~40%，降水的贡献最小，仅占10~20%。水库泄水期，地下水、土壤水和降水补充河流水，地下水对河流水的贡献约占30~70%，土壤水对河流水的贡献约占10~50%，降水对河流水的贡献较小，仅占10~20%。