Groundwater Quality Characterization in an Overallocated Semi-Arid Coastal Area Using an Integrated Approach: Case of the Essaouira Basin, Morocco

Mohamed Ouarani,Mohammed Bahir,Driss Dhiba,David J Mulla,Salah Ouhamdouch,Driss Ouazar,Otman El Mountassir,Abdelghani Chehbouni

doi:10.3390/w12113202

Abstract

In this study, hydrogeochemical analyses were combined with geographic information system (GIS) tools to investigate salinization sources of groundwater in the downstream part of the Essaouira basin, and to analyze the spatiotemporal trends in groundwater quality. To assess groundwater suitability for drinking purposes, the quality of sampled water was compared with the World Health Organization (WHO) and the Moroccan guidelines. Wilcox and US salinity laboratory (USSL) diagrams were used to evaluate groundwater suitability for irrigation. Hydrogeochemical analyses revealed that groundwater is of Na-Cl and Ca-Mg-Cl types. The analyses of the correlation between the chemical elements showed that the water–rock interaction and the reverse ion exchange are the major processes impacting groundwater degradation in the study area. The study of groundwater suitability for drinking and irrigation purposes shows that groundwater quality in the study area is permissible, but not desirable for human consumption. Additionally, groundwater is permissible for agricultural use but with high-salinity hazards. The spatial distribution of the physicochemical elements shows a general upward gradient from the north to the south and from the east to the west. The trend in groundwater quality during the last five years shows a shifting in the quality from the mixed Ca-Mg-Cl to the Na-Cl type.

Highlights

Most of the world’s available freshwater is stored underground (96% of freshwater, excluding frozen water in glaciers) [1]
All the samples collected in 2018 and 2019 are of Na-Cl and mixed Ca-Mg-Cl detailed results of the physico-chemical analyses are given in Table S2 in the Supplementary Materials
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Summary

Introduction

Most of the world’s available freshwater is stored underground (96% of freshwater, excluding frozen water in glaciers) [1]. 43% of all consumptive agricultural use of water [1] This resource is under pressure, especially in arid and semi-arid regions where it faces many issues related to level depletion and quality degradation [2]. Water 2020, 12, 3202; doi:10.3390/w12113202 www.mdpi.com/journal/water irrigated with groundwater contributes nearly 75% of the country’s exports of high-value orchard and vegetable crops [6]. This resource is overallocated, especially in the coastal regions, as several studies have shown seawater intrusion within many Moroccan coastal aquifers [7,8,9,10,11].

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