Cation exchange in a temporally fluctuating thin freshwater lens on top of saline groundwater

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• 作者：S. Eeman ; P. G. B. De Louw ; S. E. A. T. M. Van der Zee
• 关键词：Oscillating flow ; Drained fields ; Hydrochemical modeling ; Salt ; water/fresh ; water relations
• 刊名：Hydrogeology Journal
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：25
• 期：1
• 页码：223-241
• 全文大小：3473KB
• 刊物类别：Earth and Environmental Science
• 刊物主题：Hydrogeology; Hydrology/Water Resources; Geology; Water Quality/Water Pollution; Geophysics/Geodesy; Waste Water Technology / Water Pollution Control / Water Management / Aquatic Pollution;
• 出版者：Springer Berlin Heidelberg
• ISSN：1435-0157
• 卷排序：25

文摘

In coastal-zone fields with a high groundwater level and sufficient rainfall, freshwater lenses are formed on top of saline or brackish groundwater. The fresh and the saline water meet at shallow depth, where a transition zone is found. This study investigates the mixing zone that is characterized by this salinity change, as well as by cation exchange processes, and which is forced by seepage and by rainfall which varies as a function of time. The processes are first investigated for a one-dimensional (1D) stream tube perpendicular to the interface concerning salt and major cation composition changes. The complex sequence of changes is explained with basic cation exchange theory. It is also possible to show that the sequence of changes is maintained when a two-dimensional field is considered where the upward saline seepage flows to drains. This illustrates that for cation exchange, the horizontal component (dominant for flow of water) has a small impact on the chemical changes in the vertical direction. The flow’s horizontal orientation, parallel to the interface, leads to changes in concentration that are insignificant compared with those that are found perpendicular to the interface, and are accounted for in the 1D flow tube. Near the drains, differences with the 1D considerations are visible, especially in the longer term, exceeding 100 years. The simulations are compared with field data from the Netherlands which reveal similar patterns.