黑河流域中游盆地水文地球化学演化规律研究

黑河是我国第二大内流河,研究其水化学演化规律,对于区域水资源科学利用与管理、保障饮水安全和下游生态安全都具有重要作用。本文利用2014—2018年在黑河流域开展1∶50 000水文地质调查所获取的资料,研究了黑河干流和丰乐河两个典型剖面的水化学和同位素变化规律。结果表明,黑河中游盆地地下水主要来源于祁连山区大气降水补给,黑河干流区地下水氘氧同位素比丰乐河流域更为富集,反映了氘氧同位素的高程效应。在丰乐河流域排泄区发现了非现代气候条件下形成的古水,说明现在的盐湖盆地早期就是地下水滞留区。山前戈壁带含水层经长期淋滤作用,地下水溶解性总固体(total dissolved solids,TDS)较低,水化学类型以重碳酸型为主。溢出带以北下游地区TDS逐步增高,地下水类型以硫酸型、硫酸-氯型为主,具有两种地下水化学背景和演化模式:一种是石膏溶解-碳酸盐沉淀析出-氯化物溶解-缓慢的硅酸盐非完全溶解和阳离子交换反应模式;另一种在此基础上增加硫酸钠溶解演化模式。流域补给区和径流区地下水TDS升高的主要原因是溶滤作用。丰乐河排泄区地下水TDS升高的主要原因仍是溶滤作用,溶滤盐分的来源是表层的盐分,以石盐为主。黑河干流排泄区由于含水层较薄,水位埋深较浅,蒸发对地下水咸化的影响更大。

The hydrogeochemical evolution of groundwater in the middle reaches of the Heihe River Basin

The Heihe River is the second largest inland river in China. Studies on the hydrochemical evolution of the Heihe River Basin play an important role in utilizing and managing regional water resources as well as ensuring downstream ecological security and safety of drinking water. In this study, the hydrochemical and isotopic variation patterns of two typical profiles of the Heihe and Fengle River mainstreams were studied using data from a 1∶50000 hydrogeological survey conducted in the Heihe River Basin from 2014 to 2018. The study suggests that groundwater in the middle reaches of the Heihe River Basin mainly recharged via precipitation from the Qilian Mountain. Deuterium and oxygen-18 isotope were more enriched in the groundwater of the Heihe River than in the Fengle River mainstream, demonstrating the altitude effect for stable isotopes. Ancient water, different from modern water, was found in the Fengle River Basin drainage area, indicating the current salt lake basin was the groundwater retention area during its early stage. After an extended leaching period, groundwater TDS in the Gobi belt was low, and the hydrochemical type was mainly the bicarbonate type; downstream, TDS increased gradually and the sulfuric acid and sulfuric acid-chlorine types became dominant. Chemical evolution of groundwater in this area followed two distinctive patterns: one is gypsum dissolution-carbonate precipitation-chloride dissolution incomplete silicate dissolution followed by cation exchange, the other is sodium sulfate dissolution after the first. The primary reason for the TDS increase in the recharge/runoff area is leaching, the same reason for the TDS increase in the Fengle River discharge area, where the main source mineral, salt, primarily originated from the surface. In the discharge area of the Heihe River mainstream, owing to the thin aquifer and shallow groundwater, evaporation had a greater influence on groundwater salinization.