Xia Qiwen, He Jiangtao, Li Binghua, He Baonan, Huang Junxiong, Guo Minli, Luo Dan
Key Laboratory of Groundwater Conservation of Ministry of Water Resources, China University of Geosciences, Beijing 100083, China; Beijing Water Science and Technology Institute, Beijing Engineering Technique Research Center for Exploration and Utilization of Non-Conventional Water Resources and Water Use Efficiency, Beijing 100048, China.
Key Laboratory of Groundwater Conservation of Ministry of Water Resources, China University of Geosciences, Beijing 100083, China.
Water Res. 2022 Nov 1;226:119222. doi: 10.1016/j.watres.2022.119222. Epub 2022 Oct 7.
The reuse of reclaimed water (RW) for river ecological restoration in global water-shortage regions has inevitably brought some potential risks for groundwater. However, little is known about the effects of reclaimed water on the hydrochemical evolution of groundwater especially under long-term infiltration conditions. Herein, 11-years monitoring data (2007-2018) of reclaimed water and groundwater were adopted to analyze the characteristics and genesis of groundwater hydrochemical evolution under long-term infiltration of reclaimed water from Jian River to Chaobai River in Beijing. The results showed that the hydrochemical components in groundwater totally performed a significant increase in Na, Cl, and Kand decrease in Ca, Mg, and HCO concentration after long-term infiltration of reclaimed water. Meanwhile, a significant hydrochemical evolution difference between the groundwater of Jian River and Chaobai River was observed. In Jian River, the hydrochemical type in groundwater shifted gradually from HCO-Ca·Mg to the type of HCO·Cl-Na·Ca approaching reclaimed water. In contrast, the hydrochemical evolution in the Chaobai River shows an obvious opposite trend from HCO-Ca·Mg to HCO·Cl-Na·Mg and finally deviating reclaimed water type of Cl·HCO·SO-Na. PHREEQC simulation indicated that the differences in hydrochemical evolution were mediated synergically by sediment thickness and geochemical processes (e.g. mixing and sulfate reduction). In such mediators, thinner sediment and strong mixing in the Jian River were confirmed to be the genesis of groundwater hydrochemical evolution progressively approaching reclaimed water. Different from the Jian River, multiple regression analyses revealed that the genesis of groundwater hydrochemical evolution in the Chaobai River was divided into two stages according to the increase of sediment thickness. Reclaimed water quality and infiltration amount are the leading proposed cause in the initial stage (2007-2008) due to thinner sediment formation, contributing 53.5% and 29.8% within the 95% confidence interval, respectively. Subsequently, the rise in sediment thickness is proved to play a crucial role in groundwater hydrochemical evolution trend away from reclaimed water (2009-2018), with a contribution of 41.6% within the 95% confidence interval. It is mainly attributed to the reduced reclaimed water infiltration rate and favorable sulfate reduction conditions. These findings advance our understanding on groundwater hydrochemical evolution under long-term infiltration of reclaimed water and also guide future prediction of evolution trends.
在全球水资源短缺地区，将再生水用于河流生态修复不可避免地给地下水带来了一些潜在风险。然而，人们对再生水对地下水水化学演化的影响知之甚少，尤其是在长期入渗条件下。在此，采用了11年（2007 - 2018年）的再生水和地下水监测数据，来分析北京从箭河到潮白河再生水长期入渗条件下地下水水化学演化的特征及成因。结果表明，再生水长期入渗后，地下水中的水化学成分总体上表现为钠、氯和钾显著增加，钙、镁和碳酸氢根浓度降低。同时，观察到箭河和潮白河地下水之间存在显著的水化学演化差异。在箭河，地下水中的水化学类型逐渐从碳酸氢根 - 钙·镁型转变为接近再生水的碳酸氢根·氯 - 钠·钙型。相比之下，潮白河的水化学演化呈现出明显相反的趋势，从碳酸氢根 - 钙·镁型转变为碳酸氢根·氯 - 钠·镁型，最终偏离再生水的氯·碳酸氢根·硫酸根 - 钠型。PHREEQC模拟表明，水化学演化的差异是由沉积物厚度和地球化学过程（如混合和硫酸盐还原）协同介导的。在这些介导因素中，箭河较薄的沉积物和强烈的混合作用被证实是地下水水化学演化逐渐接近再生水的成因。与箭河不同，多元回归分析表明，根据沉积物厚度的增加，潮白河地下水水化学演化的成因分为两个阶段。在初始阶段（2007 - 2008年），由于沉积物形成较薄，再生水水质和入渗量是主要原因，在95%置信区间内分别贡献了53.5%和29.8%。随后，沉积物厚度的增加被证明在地下水水化学演化趋势远离再生水（2009 - 2018年）中起关键作用，在95%置信区间内贡献为41.6%。这主要归因于再生水入渗率降低和有利的硫酸盐还原条件。这些发现增进了我们对再生水长期入渗条件下地下水水化学演化的理解，也为未来演化趋势的预测提供了指导。
