Water Resources and Environmental Geology, Department of Biology & Geology, University of Almería, Almería 04120, Spain.
Water Resources and Environmental Geology, Department of Biology & Geology, University of Almería, Almería 04120, Spain.
Sci Total Environ. 2022 May 1;819:152013. doi: 10.1016/j.scitotenv.2021.152013. Epub 2021 Nov 28.
Saltwater extraction in coastal aquifers generates a negative hydraulic barrier that prevents marine intrusion and produces a general freshening landward from this barrier. In the Andarax delta aquifer, SE Spain, two instances of saltwater extraction were performed and their effect on the aquifer hydrochemistry was studied. C groundwater dating, together with chemical analysis, reflects the presence of waters with different infiltration ages. Old marine groundwater (~10 ky) must be the remains of marine intrusion generated during the Holocene transgression at the same time the delta was formed. The freshening induced by the saltwater extraction triggers cation exchange between the aquifer substratum and groundwater. Unlike what is described in other examples of cation exchange in coastal aquifers, in the Andarax delta the freshening causes an exchange between Mg, which is released into the groundwater, and Na, which is held in the clay mineral structural unit. This process is reverted the moment the hydraulic barrier stops acting. Short saltwater pumping-stopping cycles generate fast inversions in this exchange chemical reaction. At the same time, a clear excess of Ca ion can be seen in all the groundwater samples. This excess is attributed to the release of this ion resulting from the overall marine intrusion in this area during the Holocene transgression. Contrasting what occurs with the Na-Mg exchange, the Na-Ca exchange process is more long-lasting in time.
在沿海含水层中进行的咸水抽取会产生一个负水压屏障，阻止海水入侵，并在这个屏障的内陆方向产生普遍的淡水化现象。在西班牙东南部的安达卢斯三角洲含水层中，进行了两次咸水抽取实验，研究了其对含水层水化学的影响。地下水 C 年代测定法与化学分析相结合，反映了具有不同入渗年龄的水的存在。古老的海水地下水（~10 千年）必须是在同一时期三角洲形成时全新世海侵期间生成的海水入侵的残余物。咸水抽取引起的淡水化触发了含水层基质与地下水之间的阳离子交换。与沿海含水层中描述的其他阳离子交换实例不同，在安达卢斯三角洲，淡水化导致 Mg 在含水层中释放并与 Na 发生交换，而 Na 则被保存在粘土矿物结构单元中。一旦水压屏障停止作用，这个过程就会被逆转。短时间的咸水抽停周期会使这种交换化学反应迅速反转。同时，所有地下水样本中都可以看到明显过量的 Ca 离子。这种过剩归因于该地区在全新世海侵期间发生的整体海水入侵导致的该离子的释放。与 Na-Mg 交换相反，Na-Ca 交换过程在时间上更为持久。
