Seawater intrusion into coastal aquifers from semi-arid environments, Case of the alluvial aquifer of Essaouira basin (M
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ORIGINAL ARTICLE
Seawater intrusion into coastal aquifers from semi‑arid environments, Case of the alluvial aquifer of Essaouira basin (Morocco) Salah Ouhamdouch1 · Mohammed Bahir1,2 · Driss Ouazar2 Accepted: 1 November 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Marine intrusion phenomenon is the main phenomenon threatening the groundwater quality in coastal aquifers around the world. This phenomenon is generally caused by the overexploitation of aquifers, decline in the piezometric level and the rise in sea level under the climate change effect. There are several approaches to study and assess the marine intrusion phenomenon. For this study, the crossing of piezometric, hydrochemical and isotopic approaches was adopted to highlight the state of this phenomenon within the Plio-quaternary aquifer of the Essaouira basin. The couples (Na, Cl), (Ca, Mg), (Br, Cl), (δ2H, δ18O), (δ18O, Cl) were determined for 24 samples capturing the shallow aquifer of the Essaouira basin. The piezometric approach shows that negative piezometric levels are registered. The ionic ratios Br/Cl close to 1.5 and 1.7‰, Na/Cl close to 0.86, Mg/Ca and S O4/Cl weak showed that the seawater begins to invade the freshwater of the Plio-quaternary aquifer of Essaouira basin. This intrusion demonstrated by ionic ratios and corroborated by isotopic approach and the combined use of oxygen-18 contents and chlorides has a mixing rate of 15.9% at the well 11/51, 14.5% at the sample 45/51, 13.2% at the well 149/51, 13.3% at point O114 and 12.8% at the well O94. However, the results of the hydrogeochemical and isotopic approach suggest intrusion up to 2 km from the sea; this reflects a warning sign about the groundwater deterioration of the study area. Keywords Hydrochemistry · Isotopy · Morocco · Seawater intrusion · Semi-arid environment
Introduction The populations density in coastal zones, almost 70% of the world population lives in coastal zone (Bear et al. 1999). The groundwater overexploitation, the proximity to seawater and climate change cause qualitative and quantitative degradation of groundwater in these areas (Bahir et al. 2016, 2018; Carreira et al. 2018; Hamed et al. 2018; Ouhamdouch et al. 2018, 2020; Farid et al. 2013). The marine intrusion phenomenon is a phenomenon closely linked to the geographical context (i.e. proximity to the sea). It remains one of the major problems impacting groundwater in several coastal aquifers around the world (Custodio 1997). It is defined as the temporary or permanent migration of saltwater into the * Mohammed Bahir [email protected] 1
High Energy and Astrophysics Laboratory, Faculty of Sciences Semlalia, Cadi Ayyad University, PO Box. 2390, 40000 Marrakesh, Morocco
IWRI, Mohammed VI Polytechnic University, Hay My Rachid, 43150 Ben Guerir, Morocco
2
freshwater of the aquifer following a decline in the piezometric level and/or a rise in sea level. Generally, two main factors can cause a seawater advance in coastal aquifers; a natural factor and an anthropog
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