Assessing Groundwater Mineralization Process, Quality, and Isotopic Recharge Origin in the Sahel Region in Africa

Aboubacar Modibo Sidibé,Xueyu Lin,Sidi Koné

doi:10.3390/w11040789

Abstract

In the Sahel region in Africa, and in most arid regions, groundwater is the crucial source for water supply since surface water is scarce. This study aimed to understand a complex geochemical mechanism controlling the mineralization process in the Taoudeni Basin. A thousand randomly distributed groundwater samples acquired from different aquifers were used for this research. The results show that the majority of the samples observed are of the Ca2+-Mg2+-HCO3− and Na+-HCO3− types depending on the different aquifers. Mg2+ and Ca2+ may react with HCO3− precipitating as calcite and dolomite. The Na+-HCO3− groundwater type is mainly derived from the ion exchange process. This type indicates a paleo-marine depositional environment or that it passes through paleo-marine channels. Calcium of the standard Ca2+-HCO3− groundwater type exchanges with the sodium. Groundwater is characterized by the water-rock interactions that indicate the chemical alteration of the rock-forming minerals influencing its quality by a dissolution. The δ2H and δ18O stable isotopes designate the evaporation importance in the basin and recharge with recent rain. The bicarbonate-type presence in groundwater suggests that it is young and fresh water. Multivariate statistical methods, notably Principal Component Analysis and Hierarchical Cluster Analysis, confirm affinities among the aquifers and identify three main clusters grouped into two water types. Cluster 1 consists of Infra-Cambrian and Quaternary aquifers, whereas cluster2 includes the Precambrian basement and Permian-Triassic aquifers.

Highlights

Groundwater is a vital livelihood resource for economic and social development
Multivariate statistical methods, notably Principal Component Analysis and Hierarchical Cluster Analysis, confirm affinities among the aquifers and identify three main clusters grouped into two water types
The methodology implemented in this paper allows a better evaluation of the different sources of groundwater and of the hydrochemical and anthropogenic processes impacting on the groundwater’s chemistry

Summary

Introduction

Groundwater is a vital livelihood resource for economic and social development. These waters are generally the primary source of drinking water for the population living in the Sahel-Sudanian region. The degradation of groundwater quality is due to human activities and the lack of environmental protection policies. The groundwater reserves are significant, but the current climatic conditions at the study area, with annual rainfall between 600 and 1000 mm, do not allow a complete reconstitution of the water extracted by human activities. The present research considers the mineralization process, the origins of groundwater quality, and the anthropogenic factors, in addition to the climate variability impact. Climate variability affects groundwater fluctuations, and the rebound in

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