南水北调水回补对北京密怀顺河道回补区地下水水质影响

南水北调水源密云-怀柔-顺义(密怀顺)潮白河地下水回补工程，是密怀顺地下水源地可持续利用和河道生态恢复的重要保障. 基于密怀顺回补河道区长期地下水水质监测数据，综合运用水质评价、统计学方法，分析了不同回补时期的地下水水化学变化特征；同时，采用水文地球化学模拟软件(PHREEQC)分析核心回补路线——小中河调水路线回补影响下的潮白河段地下水水文地球化学变化，结合聚类分析方法探究了地下水水化学变化成因. 结果表明:①回补区地表水、地下水整体水质良好，南水北调水源及本地地下水水化学类型主要为HCO₃-Ca-Mg型. 补水以来，地下水水质整体得到改善，补水区域地下水中的Na+、Cl?明显降低. ②根据水化学模拟，2017年底，小中河调水回补河道附近的地下水中南水与本地地下水混合比例变为1∶10，但经过2018—2019年的回补，河道附近地下水中南水占主导地位，回补后所采集的地下水样中水化学成分基本与南水趋于一致. ③根据水岩作用模拟，影响回补区地下水水质的主要因素为南水-当地地下水混合作用、矿物溶解及阳离子交换作用. 研究显示，南水回补改善了地下水水质，并通过混合与水岩相互作用影响地下水水化学演化. 

Influence of South-to-North Transfer Water Recharge by River Infiltration on Groundwater Quality in Mi-Huai-Shun Area,Beijing

The groundwater recharge by the South-to-North Water Transfer Project in Chaobai River is a strong guarantee for the sustainable supply of groundwater sources and the ecological restoration of the rivers in the Miyun-Huairou-Shunyi (Mi-Huai-Shun). Based on the long-term water quality monitoring data in the recharge area, water quality evaluation, hydrogeochemical simulation, and statistical methods were used to analyze the characteristics of the groundwater hydrochemical changes. Meanwhile, the hydrogeochemical simulation software (PHREEQC) was used to simulate the hydrogeochemical changes near the rivers affected by the core water transfer route, the Xiaozhong River. Combined with the cluster analysis method, the influencing factors of hydrogeochemical changes were elucidated. The results showed that both the surface water quality and groundwater quality in the recharge area were good, the main chemical types of the water of South-to-North water diversion and local groundwater were HCO₃-Ca-Mg. It also showed that the groundwater quality had been improved because of the recharge. The concentrations of Na+ and Cl? in the groundwater of the recharge area decreased significantly. The hydrogeochemical simulation indicated that after receiving the South-to-North water recharge, the proportion of the South-to-North water in the groundwater near the main recharge river was about 10% by the end of 2017. Furthermore, the groundwater near the river was dominated by South-to-North water after the recharge in 2018 and 2019, and the chemical compositions of groundwater were basically the same as those of South-to-North water. According to the simulation of water-rock interaction, the main factors affecting the groundwater quality in the recharge area included mixing of the south water and with local groundwater, mineral dissolution, and cation exchange. These findings can provide a scientific basis for site selection, planning, and water source selection for the safe natural infiltration of rivers to replenish groundwater.