永定河生态补水下渗对地下水质量的影响

以永定河北京段2019~2020年的生态补水为例,通过室内混合实验和淋滤实验研究河水下渗对地下水质量的影响.结果表明,水化学指标的种类与下渗前相比无变化,水-岩相互作用对指标浓度的改变作用也比较有限,指标的浓度水平总体上介于河水和地下水之间.下渗水对地下水质量的改变作用从根本上取决于河水与地下水的质量差异和河水的补给量,两者的质量差异越大且河水的下渗量越大,改变作用就越明显,反之则越微弱.由于补水水源的质量较好,永定河生态补水下渗对地下水质量的影响总体上可接受,而且对影响地下水质量的“瓶颈”指标(如硝酸盐氮)有一定改善作用.

Impact of infiltration of ecology water replenishment of the Yongding River on groundwater quality and the mechanism

The problems of river flow reduction, water ecological degradation and so on affected by the climate changes and human activities have attracted extensive attention. It’s considered to be the quickest and the most effective means to alleviate or solve these problems by means of artificial recharge such as water diversion. After the water is recharged into the river, some of it will infiltrate through the riverbed to recharge the underlying groundwater. Affected by the quality of the water source and the water-rock interaction in the infiltration, the leakage recharge of the water into the groundwater may change the groundwater quality, which has become a problem worthy of attention. Taking the ecology water replenishment of the Beijing section of the Yongding River in 2019~2020 as an example, this study studied the impacts of the river water infiltration on the groundwater quality through the indoor mixing test and the leaching test. The results show that, the species of the hydrochemical indicators of the water do not change compared with those before the infiltration, the impact of the water-rock interaction on the concentrations of these indicators is also relatively limited, and the content levels of the indicators are generally between those of the river water and the groundwater. The impact of the infiltration on the groundwater quality is fundamentally determined by the quality difference between the river water and the groundwater and the infiltration volume of the river water. That is, the greater the quality difference and the greater the infiltration volume, the more obvious the impact will be; otherwise, the weaker the impact will be. Due to the good quality of the recharge water source of the Yongding River, the impact of the ecology water replenishment of the river on the groundwater quality is generally acceptable, and it can improve the “bottleneck” indicators (such as nitrated nitrogen) affecting the groundwater quality to a certain extent.