隔档式构造区岩溶地下水流系统多级次嵌套结构的水化学识别

川东隔档式构造区岩溶地下水流系统表现出多级次嵌套结构的特征, 之前主要是定性的水文地质条件分析, 缺乏来自水化学方面的量化依据。利用41个浅层和19个深层岩溶水样的水化学资料开展分析, 发现浅层岩溶水为HCO₃-Ca·Mg型,ρ(Mg2+)较低, 深层岩溶水为SO₄-Ca·Mg型且ρ(Mg2+)明显偏高, 说明地下水在岩溶含水层中的滞留时间与ρ(Mg2+)具有正变关系。对典型剖面地下水流系统的分析表明, 优先采用ρ(Mg2+)来评价地下水滞留时间, 将地下水排泄点ρ(Mg2+)小于20, 50 mg/L分别作为划分局部-中间、中间-区域水流系统的依据。浅层岩溶水受地貌作用控制明显, 其中浅切沟谷泉点为局部地下水流系统的排泄点, 深切沟谷泉点一般属于中间或区域流动系统的排泄点。ρ(Mg2+)反映了泉水循环的滞留时间, 也能够反映钻孔所揭露的深循环特征。这种水化学识别方法可为相似岩溶区识别地下水流系统的多级次嵌套结构提供参考。 

Hydrogeochemical indicators of hierarchically nested structure of karst groundwater flow systems in the ejective folds area

The karst groundwater flow system in the ejective folds area in the eastern Sichuan Basin shows the characteristics of a hierarchically nested structure. However, previous studies were mainly focused on hydrogeological conditions analysis, lacking qualitative evidence directly from hydrochemistry. In this study, the authors collected and sorted the chemistry data of representative karst springs and boreholes in the study area, namely, 41 shallow karst waters and 19 deep ones. The Pipper chart shows that the shallow karst water is HCO₃-Ca·Mg and low Mg2+ concentration, while the deep karst water is SO₄-Ca·Mg and high Mg2+ concentration. For both shallow and deep karst groundwater, the analysis of the groundwater flow system of a typical profile shows that the Mg2+ concentration value can be used to evaluate the groundwater residence time. The shallow karst groundwater system is highly controlled by geomorphology, among which the shallow incised valley springs are the discharge points of the local groundwater flow system. However, springs in deep gullies correspond to intermediate or even regional flow systems. This pattern is verified by the groundwater residence time evaluation from the Mg2+ concentration, which also reflects the movement characteristics of deep-circulation groundwater flow revealed by hot springs and boreholes.The hydrochemical characteristics can effectively indicate the pattern of groundwater flow systems. This paper provides a reference for identifying the hierarchically nested structure of groundwater flow systems in similar karst areas.