Department of Earth and Environmental Sciences, Indian Institute of Science Education and Research Bhopal, Bhopal By-pass Road, Bhauri, Bhopal 462066, Madhya Pradesh, India.
Department of Earth and Environmental Sciences, Indian Institute of Science Education and Research Bhopal, Bhopal By-pass Road, Bhauri, Bhopal 462066, Madhya Pradesh, India.
J Contam Hydrol. 2022 Jun;248:104000. doi: 10.1016/j.jconhyd.2022.104000. Epub 2022 Mar 19.
This study attempts to learn the groundwater salinization mechanism in the large and well-populated coastal Gujarat alluvial plain under growing anthropogenic pressures. For this purpose, geochemical compositions and Sr/Sr were analyzed in 53 groundwater samples collected in the three different seasons during 2016-2017. Additionally, surface water samples collected in each season from two nearby large rivers (Narmada and Tapi) and urban sewage discharge of Surat city were also analyzed. Excluding a few salinity hotspots (EC >8-18 mS/cm), the seasonal average of EC (~2.3-2.5 mS/cm) in groundwater shows little fluctuations negating evaporation as the major salinization process. Localized anthropogenic inputs as traced using NO also fail to explain the widespread groundwater salinity. A strong marine influence on the groundwater salinity is revealed by an average Cl/Br of ~655 ± 104 mol/mol in groundwater (except a few outliers) falling close to the seawater composition. The lateral seawater intrusion at shallow depths is generally not supported by the freshening of coastal groundwater samples and generally seaward movements of shallow groundwater as indicated by regional piezometric heads. However, few (Ca)-Mg-Cl type groundwaters collected from north of the Narmada River fall in the piezometric depressions and hint at seawater intrusion and/or upconing of deep saline aquifers. The Sr isotope budget in most of the alluvial groundwater samples is controlled by the seepage groundwater-seawater mixing. Exceptional Sr/Sr values owing to Sr inputs from different age terrains are found in the northeastern groundwater and a few groundwater samples collected downslope of ancient deposits in the central alluvium. The upconing of salty waters having marine signatures partly altered by aquifer-water interactions primarily governs the regional groundwater salinity, which makes the study area vulnerable to continued salinization by excessive groundwater extraction.
本研究旨在探讨在人为压力不断增加的情况下，大型且人口稠密的古吉拉特沿海冲积平原地下水盐化的机制。为此，在 2016-2017 年的三个不同季节采集了 53 个地下水样本，并对其地球化学成分和 Sr/Sr 进行了分析。此外，还分析了来自两条附近大河（讷尔默达河和塔皮河）和苏拉特市城市污水排放口的地表水样本。除了少数几个盐分热点（EC>8-18 mS/cm）外，地下水的季节平均电导率（EC2.3-2.5 mS/cm）波动不大，否定了蒸发是主要盐化过程的观点。使用硝酸盐追踪的局部人为输入也未能解释广泛的地下水盐分。地下水盐分受海水影响较大，平均 Cl/Br 为655±104 mol/mol（除了少数异常值），接近海水成分。浅部侧向海水入侵一般不支持海岸地下水的淡化，区域测压头也表明浅部地下水一般向海移动。然而，从讷尔默达河以北采集的少数（Ca）-Mg-Cl 型地下水样本位于测压凹陷区，暗示了海水入侵和/或深部咸含水层上涌。大多数冲积地下水样本的锶同位素收支受渗流地下水-海水混合控制。东北部地下水和中部冲积层中古老沉积物下游采集的少数地下水样本由于来自不同时代地形的锶输入，出现了异常的 Sr/Sr 值。具有海水特征的咸水的上涌部分受含水层-水相互作用的影响，主要控制着区域地下水的盐分，这使得研究区容易受到过度地下水开采引起的持续盐化的影响。
