PhD AWARDED 2014

PhD Studies at University of Bordeaux

Investigating Alluvial Aquifers with Cutting-Edge Tracers

In May 2014, I earned my PhD in Hydrogeology and Environment from the University of Bordeaux, France. My dissertation, entitled “Investigating the Behavior of Alluvial Systems, Thanks to the Classical, Isotopic and Emerging Tracers”, focused on understanding groundwater systems through a comprehensive, multidisciplinary approach. I had the privilege to be supervised by Prof. Philippe Le Coustumer and co-supervised by Dr. Hélène Celle-Jeanton, two esteemed scientists who greatly influenced my scientific path.

Research Focus and Motivation

This research was born from a fundamental question: How do shallow alluvial aquifers function and respond to both natural and anthropogenic pressures? My case study was the Allier River Aquifer in the Auvergne region of France—a major drinking water source for over 100,000 people and an area vulnerable to pollution from agriculture and urban activities.

My Methodology

To tackle this complex hydrosystem, I used an integrated methodology combining:

Hydrodynamic measurements
Hydrochemical analysis (major ions, trace elements, pharmaceuticals, and pesticides)
Stable isotope tracing (δ¹⁸O and δ²H)
Microbiological investigations (including DNA-based assessments and bacterial profiling)

Sampling spanned 19 different points—boreholes, piezometers, river water, and springs—over nearly two years of fieldwork and laboratory analysis.

Key Discoveries

I identified four main sources (end-members) contributing to aquifer recharge: rainfall, Allier River water, spring flow from adjacent hills, and the non-pumped southern section of the aquifer.
Using chemical and isotopic markers, I showed that proximity to the Allier River strongly influenced water composition, with isotopically lighter water found near the river and heavier, hill-derived water in more remote boreholes.
I documented how agricultural runoff, wastewater treatment discharge, and urban contaminants (like pharmaceuticals and pesticides) alter groundwater quality, emphasizing the system’s vulnerability.
This work helped illustrate the importance of spatial variation, residence time, and land-use practices in controlling aquifer quality.

Impact and Future Applications

My research provides a replicable framework for investigating groundwater systems, particularly in regions with high ecological and socioeconomic value. The findings support sustainable water resource management and inform strategies for protecting vulnerable aquifers.

This PhD also laid the foundation for my current and future research on groundwater vulnerability, water quality monitoring, and hydrochemical modeling, especially in the context of environmental challenges in Iraq and beyond.

Acknowledgements

I am grateful to my supervisors, Prof. Le Coustumer and Dr. Celle-Jeanton, for their guidance and mentorship. This project was supported by the ERASMUS MUNDUS framework, Agence de l’Eau Loire Bretagne, and other regional partners. I also thank my colleagues at Laboratoire Magmas et Volcans in Clermont-Ferrand for their invaluable collaboration

Click To Access This Work On The University of Bordeaux Repository

PhD Thesis Details:

TITLE: Etude du fonctionnement des hydrosystèmes alluviaux à partir des traceurs classiques, isotopiques et émergents : application à l’aquifère alluvial de l’Allier

TITLE IN ENGLISH: Study of the functioning of alluvial hydrosystems using classical, isotopic and emerging tracers: application to the Allier alluvial aquifer (Auvergne, France)

AUTHOR: Nabaz Mohammed

ISSN:

AWARDING BODY: Doctoral School of Sciences and Environments, University of Bordeaux

CURRENT INSTITUTION: University of Duhok

DATE AWARDED: May 2014

Full Text Link: [PLEASE CLICK TO VIEW THE FULL TEXT OF MY PhD]

SUPERVISOR: Philippe Le Coustumer , Hélène Celle-Jeanton

SPONSOR: University of Bordeaux, European ERASMUS MUNDUS, Agence de l’Eau Loire Bretagne, and The University of Duhok

QUALIFICATION NAME: Doctor of Philosophy of Sciences and Environments

QUALIFICATION LEVEL: PhD

LANGUAGE OF THE THESIS: English

Citation to this work:

Mohammed, Nabaz Ibraheem. 2014. Investigating the Behavior of Alluvial Systems, Thanks to the Classical, Isotopic and Emerging Tracers. PhD Thesis., University of Bordeaux. (Avilable at: https://theses.hal.science/tel-01317934)

Abstract:

Hydrodynamic, hydrochemical (major ions, traces, pharmaceuticals and pesticides), and isotopic investigations (oxygen-18 and deuterium) were carried out on 19 points, including boreholes, piezometer, surface water, and springs from February 2011 to November 2012, to assess groundwater quality in the unconfined shallow alluvial aquifer of the Allier River (one of the main tributary of the Loire River). The study area, located near the city of Clermont-Ferrand (France), plays an important socio-economic role as the alluvial aquifer is the major source of drinking water for about 100,000 inhabitants. The objective of the project aims at understanding the functioning and the vulnerability of alluvial aquifers that occupy a pre-eminent position in the hydrogeologic landscape both for their economic role - production of drinking water and agricultural development - and for their ecological role. Moreover, this study also targets at determining the factors and processes controlling shallow groundwater quality and origin. The water circulates from the south, with a natural supply from the hills in the non-pumped part of the alluvial aquifer. In the pumping zone, this general behavior is altered by the pumping that makes the water from the Allier River enter the system in a large proportion. Four end-members have been identified for the recharge of the alluvial groundwater: rainfall, Allier River, surrounding hills' aquifer and the southern non-pumped part of the alluvial system. Results indicate that, despite the global Ca-HCO3 water type of the groundwater, spatial variations of physico-chemical parameters do exist in the study area. Ionic concentrations increase from the Allier River towards east due either to the increase in the residence time or a mixing with groundwater coming from the aquifer's borders. Stable isotopes of the water molecule show the same results: boreholes close to the river bank are recharged by the Allier River (depleted values), while boreholes far from the river exhibit isotopic contents close to the values of hills' spring or to the southern part of the alluvial aquifer, both recharged by local precipitation. One borehole (B65) does not follow this scheme of functioning and presents values attesting of a probable sealing of the Allier River banks. Based on these results, the contribution of each end-member has been calculated and the functioning of the alluvial system determined. According to this general scheme of functioning, origins of pollution (agricultural, urban) have been determined and clues to the protection of such hydrosystems defined.

Keywords:

Alluvial Aquifers, Isotopic Tracers, Groundwater Vulnerability, Hydrochemical Characterization, Environmental Contaminants

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