Assessing salinization of coastal groundwater by tidal action: The tropical Wouri Estuary, Douala, Cameroon
Assessing salinization of coastal groundwater by tidal action: The tropical Wouri Estuary, Douala, Cameroon
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DOI：
10.1016/j.ejrh.2021.100842
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发表时间：
2021-08
期刊：
影响因子：
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通讯作者：
Goabaone J. Ramatlapeng;E. Atekwana;Hendratta N. Ali;I. Njilah;G. R. Ndondo
中科院分区：
文献类型：
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作者：
Goabaone J. Ramatlapeng;E. Atekwana;Hendratta N. Ali;I. Njilah;G. R. Ndondo
研究区域：西非喀麦隆杜阿拉。研究重点：喀麦隆杜阿拉沿海浅层地下水的含盐量影响了其饮用和工业用途。以前的研究表明，盐渍化是由武里河口的潮汐洪水引起的。通过水位和盐度的时间序列调查，探讨了地下水盐渍化的潮汐成因，并评估了地下水和邻近河口潮溪中稳定水同位素（δ¹⁸O和δ d）和主要阳离子（Ca²+和Mg²+）。在时间序列测量期间，我们抽取地下水超过5个潮汐循环，以诱导水流进入测试井。时间序列的地下水位模拟了河口的水位变化。但是，地下水的时间盐度与河口水的潮汐盐度变化并不对应，说明河口水没有侵入地下水。地下水和河口样品的δ¹⁸O和δ d沿杜阿拉当地大气水线共线下降，且d值超过bb10，表明地下水未蒸发雨水补给或蒸发浓缩缺乏盐碱化。盐度-δ¹⁸O关系表明，沿海地下水含水层盐度的来源并非海水入侵。地下水Mg²+/Ca²+比值<1，而河口水Mg²+/Ca²+比值为6 ~ 8，说明地下水盐分来源非海水。本文认为，杜阿拉沿海地下水的盐度不受邻近武里河口潮汐盐渍化的影响，而是受含水层中地质源的影响。
Study regionDouala, Cameroon, West Africa.Study focusSalinity of shallow coastal groundwater in Douala, Cameroon impairs its use for drinking and industrial purposes. Previous studies suggest that salinization is from tidal flooding from the Wouri Estuary. We aimed to test the tidal origin of groundwater salinization by conducting a time series investigation of water level and salinity, and assessed the stable water isotopes (δ¹⁸O andδD) and major cations (Ca²+and Mg²+) in groundwater and adjacent estuarine tidal creek. During the time series measurements, we pumped groundwater for over 5 tidal cycles to induce flow into a test well.New hydrologic insights for the regionThe time-series groundwater level mimicked water level changes in the estuary. However, the temporal salinity in groundwater did not correspond to tidal salinity changes of estuarine water, indicating that estuarine water did not intrude groundwater. Theδ¹⁸O andδD of the groundwater and estuarine samples are collinear and fall along the local meteoric water line of Douala and had d-excesses of >10, indicating a non-evaporated rain recharge of groundwater or lack of salinization by evapoconcentration. The salinity-δ¹⁸O relationship showed that the origin of salinity in the coastal groundwater aquifer is not from seawater intrusion. The Mg²+/Ca²+ratios of <1 in groundwater compared to 6–8 in estuarine water support the non-seawater origin of groundwater salinity. We conclude that the salinity of coastal groundwater in Douala is not affected by tide-induced salinization from the adjacent Wouri Estuary but by geogenic sources in the aquifer.