半干旱内陆河流域草原河流与地下水的相互作用及模拟研究

Surface water (SW)-groundwater (GW) interaction plays an important role in terrestrial ecosystem. Deeply understanding SW-GW exchange mechanisms and establishing qualified models are hot and difficult issues of the internet research..In the study, typical steppe rivers in semi-arid regions were chosen as the study object. The Xilin River of Inner Mongolia was taken as an example. Hydraulic characteristics of SW and GW, including river level, river flow velocity, groundwater head in riparian areas, water head in riverbeds at multi-level depth will be observed at different time scales (seasonal change and annual variation) and space scales (point, river reach and basin). According to the characters of frequent exchange between SW and GW and relatively high evaporation in semi-arid areas, water balance model and mechanism model of SW-GW system, which are applicable to steppe rivers-groundwater systems will be established. Water evaporation will be considered through source and sink terms in the models. The established models will be calibrated and validated by use of frequently monitored data, and further applied to forecast the response of SW-GW system under the influence of human activity in the future. Spatio-temporal variation rules of recharge and discharge relationships between SW and GW, including runoff direction, exchange amount, exchange mechanism, and their main impact factors will be tentatively revealed from experiment and simulation results. The hyporheic zone developed adjacent to the steppe rivers of Inner Mongolia will be explored for the first time. This project will provide references for the water resource utilization and ecological environmental protection in steppes and pastoral areas.

地表水-地下水相互作用对陆地生态系统具有重要作用，深入认识地表水-地下水转化机制并建立定量模型是国际研究的热点和难点问题。.本研究选取典型半干旱草原河流为研究对象，以内蒙古锡林河为例，在不同时间（年内到多年）和空间（点、河段和流域）尺度对地表水和地下水的水力特征，包括河水位、河水流速、河岸带地下水位以及河床以下不同深度的水位进行综合观测。针对半干旱地区地表水-地下水转化较频繁且蒸发较大的特点，构建适用于草原河流-地下水系统的水量平衡模型和机理模型。通过源汇项充分考虑蒸散发，利用监测频次较高的试验数据对模型进行率定和验证，进一步利用模型预报地表水-地下水系统对未来人类活动影响的响应。通过试验和模拟结果试图揭示不同时空尺度地表水和地下水的补给排泄关系，包括径流方向、转化量、转化机制及其主控因子，还将首次探索内蒙古草原河流附近的潜流带发育情况，为草原牧区水资源合理利用和生态环境保护提供参考。

了解地表水和地下水转化关系是评价和保护水资源的重要基础，草原内陆河的地表水-地下水相互作用规律尚不明确。本项目通过野外定点监测试验、理论分析和数值模拟，对典型草原内陆河的地表水-地下水转化规律进行了研究，本项目取得如下主要成果：（1）根据汛期日尺度和年内月尺度的地表水和地下水水动力学监测，锡林河地表水和浅层地下水的相互作用关系呈现明显的季节性特征，在春季融雪汛期和夏季雨季的两种水体的转化方向可能发生逆转，这两个汛期的转化量大于平水期和枯水期转化量的总和；（2）空间上，锡林河上游以地表水补给地下水为主，且上游河床潜流带对降雨响应非常快，中游锡林河水库以上河段以地下水补给地表水为主，潜流带的水流形态为上升流，受水库筑坝影响，水库下游河段以河水补给地下水为主，同时河水向河岸地下水补给，潜流带的水流形态为下降流。河道垂向交换量在1.73-25.06 m3/d，河岸与地表水的横向交换量在23.33-171.94 m3/d，土壤质地和地形差异导致左右岸的地表水-地下水补给排泄方向不同、交换量差异显著；（3）锡林河地表水和地下水水化学指标的野外监测和室内试验结果显示，研究河段地表水和下化学类型以为Ca-Cl型为主，水库上、下游水体中硝酸盐的浓度分布存在差异，结合水动力学结果，判断水库上游河段潜流带主要发生硝化作用，是河水氮素的源，而水库下游河段潜流带主要发生反硝化作用，是河水氮素的汇；（4）利用地下水模拟工具MODFLOW建立了地表水-地下水转化的汛期日尺度和年内月尺度的水流模型，利用实测数据率定和验证模型，表明模型具有一定精度，可用于进一步分析预测草原河流地表水-地下水相互作用规律，情景分析表明降雨量和渗透系数是地表水-地下水交换的敏感控制因子。研究结果为草原区水资源优化配置和防治河岸带草地退化提供理论依据。