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Evolutionary process of saline groundwater influenced by palaeo-seawater trapped in coastal deltas: A case study in Luanhe River Delta, China
Estuarine, Coastal and Shelf Science ( IF 2.8 ) Pub Date : 2020-07-27 , DOI: 10.1016/j.ecss.2020.106894
Xianzhang Dang , Maosheng Gao , Zhang Wen , Hamza Jakada , Guohua Hou , Sen Liu

Coastal aquifers provide fresh drinking water to over 20% of the world's population. In recent times, they have come under immense pressure due to salinization. This study aims to investigate the origin of groundwater salinity and elucidate the major processes controlling shallow groundwater (depth of 0–50 m) evolution in the Luanhe River Delta since the Holocene. Rapid increase in Electric Conductivity (EC) profile was observed in the area, as such, based on the vertical distribution of EC and sedimentary history, shallow groundwater was generalized into two zones for analysis: the groundwater in Holocene stratum (HSG) and groundwater in Late Pleistocene stratum (PSG). The isotopic (δ 18O, δ 2H and 14C) analyses showed that the HSG is recharged by modern surface water, while the PSG having enriched isotopic values could have been recharged during a warmer Holocene transgression period. The hydrochemistry analyses demonstrated that seawater is the major source of salinity in groundwater and over time a series of geochemical processes (mineral weathering and/or cation exchange) modified the chemistry of the groundwater. The combined use of Cl and δ 18O yielded four classes of groundwater (fresh water, brackish water, saline water and brine), while the mixing phenomena between fresh water and seawater was identified to be the main evolutionary process of the shallow groundwater. To improve understanding of evolution of multiple groundwater types in a spatial context, a conceptual model was developed integrating the results derived from the presented study in a vertical cross-section. The conceptual model shows that the residual seawater mixes with freshwater from surface recharge at the shallow aquifer of the delta plain where the lagoon environment provides salinity concentration conditions for the formation of hyper-saline water. Due to the precipitation and accumulation of the salinity from hyper-saline water, some brine might form formed in late Pleistocene continental stratum. In addition, the submarine groundwater discharge may be mainly from deeper inland fresh groundwater, but it is not significantly affected by the hyper-saline water from the shallow aquifer in Luanhe River delta.



中文翻译:

滞留在沿海三角洲的古海水影响下的盐分地下水演化过程-以in河三角洲为例

沿海含水层为世界20%以上的人口提供新鲜的饮用水。近年来,由于盐碱化,它们承受着巨大的压力。本研究旨在调查全新世以来since河三角洲地下水盐分的成因,并阐明控制浅层地下水(0-50 m深度)的主要过程。在该地区观察到电导率(EC)曲线迅速增加,因此,基于EC的垂直分布和沉积历史,浅层地下水可分为两个区域进行分析:全新世地层(HSG)的地下水和新世地层的地下水。晚更新世地层(PSG)。同位素(δ 18 O,δ 2 H和14C)分析表明,HSG由现代地表水补给,而富含同位素值的PSG可能在全新世越暖期间补给了。水化学分析表明,海水是地下水中盐分的主要来源,随着时间的推移,一系列地球化学过程(矿物风化和/或阳离子交换)改变了地下水的化学性质。结合使用的Cl -和δ 18O产生了四类地下水(淡水,微咸水,盐水和盐水),而淡水和海水之间的混合现象被认为是浅层地下水的主要演化过程。为了增进对空间背景下多种地下水类型演变的理解,开发了一个概念模型,该模型在垂直截面中整合了本研究的结果。概念模型表明,残留的海水与三角洲平原浅层含水层中地表补给产生的淡水混合,那里的泻湖环境为形成高盐度水提供了盐分浓度条件。由于高盐度水的盐分沉淀和积累,在晚更新世陆相地层中可能会形成一些盐水。此外,

更新日期:2020-08-15
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