Elsevier

Applied Geochemistry

Volume 26, Issue 8, August 2011, Pages 1386-1398
Applied Geochemistry

Investigation by multivariate analysis of groundwater composition in a multilayer aquifer system from North Africa: A multi-tracer approach

https://doi.org/10.1016/j.apgeochem.2011.05.012Get rights and content

Abstract

A multi-tracer approach has been carried out in the Sbeïtla multilayer aquifer system, central Tunisia, to investigate the geochemical evolution, the origin of groundwaters and their circulation patterns. It involves statistical data analysis coupled with the definition of the hydrochemical and isotopic features of the different groundwaters. Principal Components Analysis (PCA) of geochemical data used in conjunction with bivariate diagrams of major and trace elements indicate that groundwater mineralization is mainly controlled by water–rock interaction and anthropogenic processes in relation to return flow of irrigation waters. The PCA of isotopic data and bivariate conventional diagrams of stable and radiogenic isotopes i.e. δ18O vs. δ2H and δ18O vs. 14C provide valuable information about the origin and the circulation patterns of the different groundwater groups. They permit classifying groundwaters into three groups. The first group is characterized by low 3H concentrations, low 14C activities and depleted stable isotope contents. It corresponds to an old end-member in relation with palaeoclimatic recharge which occurred during the Late Pleistocene and the Early Holocene humid periods. The second group is distinguished by high to moderate 3H concentrations, high 14C activities and enriched heavy isotope signatures. It corresponds to a modern end-member originating from a mixture of post-nuclear and present-day recharge in relation to return flow of irrigation waters. The third group is characterized by an average composition of stable and radiogenic isotope signatures. It provides evidence for the mixing between the upward moving palaeoclimatic end-member and the downward moving present-day end-member.

Highlights

► We investigate the hydrodynamics and hydrochemistry of a multilayer aquifer system. ► We examine the geochemical evolution, the origins and the circulation patterns of groundwater. ► The mineralization is controlled by water-rock interaction and return flow process. ► Groundwater derives from palaeoclimatic and modern end-members. ► Mixing by upward and downward leakage occurs between these two end-members.

Introduction

In most North African regions, the hydrogeology is largely controlled by tectonics, which created several multilayer aquifer systems. In these systems, faulting activity, which has been most active, has played a significant role in the lateral compartmentalization of the superposed aquifers. This compartmentalization, enhanced by high hydraulic heads and anthropogenic processes such as overexploitation and irrigation practices, has disturbed and complicated the hydrodynamic functioning of water tables, originally obeying a “Piston flow” circulation model, especially through the mixing of different groundwaters. Indeed, the potentiometric conditions and flow patterns of most exploited multilayer aquifer systems in North African regions at the present-day differs significantly from those found prior to the onset of drilling and the considerable borehole exploitation. Large-scale drilling generally disrupts the initial condition so that water tables are no longer in a steady state with hydraulic gradients largely reflecting topography. In contrast, water pumping has caused steadily declining water-levels and reduced potentiometric pressure over time, which has disturbed the stratification of groundwater bodies. Consequently, mixed groundwaters are always obtained during the sampling of pumped groundwaters creating problems for groundwater resource management.

In this study, hydrogeologic, hydrochemical and isotopic information from the aquifer system will be integrated and used to determine the main factors and mechanisms controlling the chemistry of groundwaters in the study area and to identify the origins of water bodies and their migration pathways. The main issues that will be addressed by this study include: (1) the relative importance of geologic and hydrogeologic factors in controlling the groundwater circulation within the aquifer system; (2) the validity of statistical clustering techniques to characterize the geochemical features and the isotopic signatures of groundwaters; (3) the geochemical effects and age of leakage influencing groundwaters and (4) the appraisal of the value of chemical and isotopic approaches to delineate flowpaths and evaluate evolutionary processes.

Section snippets

Physiographic setting

Tunisia is located in the Western Mediterranean, which represents a climatic transition zone open to the influence of the cool North Atlantic air masses and the warm Mediterranean air masses (Rindsberger et al., 1990). Moreover, specific geomorphologic characteristics of Tunisia i.e. the absence of high mountains and the relatively limited geographic extension allow the integration of Saharan air masses into the atmospheric circulation (Celle-Jeanton et al., 2001a). However, hydrometeorological

Geology and hydrology

As shown in the geological map (ONM, 1985) (Fig. 1) and the lithostratigraphic column (Dassi, 2004) (Fig. 2), the lithologic units in the study area extend from the Cretaceous to the Quaternary. The Cretaceous series, which outcrops in the surrounding Mountains of Semmaama, Douleb, Mrhila and Rheradok are constituted mainly of clay, marl, limestone, marly limestone and sandstone marine deposits. These series belong to the Sidi Khralif, Melloussi, Bou Hedma, Fahdène, Annaba, Biréno, Alèg and

Analytical procedure

The sampling campaign was undertaken in the study area during June 2000. A total of 40 groundwater samples (Fig. 1) were collected from springs and selected private and public wells for chemical and isotopic analyses (Table 1).

Samples destined for major and minor element analyses were filtered through 0.45-μm filters and collected in acid-rinsed 100-mL polyethylene bottles. Chemical analyses were undertaken using ion chromatography and ICP MC where calibrations were performed using appropriate

Hydrochemical study

A preliminary characterization, carried out using the Piper triangular diagram (Piper, 1944), is shown in Fig. 4. This diagram is used to obtain a preliminary geochemical characterization through the identification of different types of groundwaters. It shows that most groundwater samples are characterized by mixed water type with a slight tendency to Cl, SO4 and/or Ca water-types.

To accurately identify the main processes governing the hydrochemistry of groundwaters in the system a factor

Summary and conclusions

The hydrochemical and isotopic features of the multilayer aquifer system of the Sbeïtla basin, central Tunisia, have been investigated using multivariate statistical analysis and bivariate conventional diagrams to determine the main hydrochemical processes of salinization and to identify the origin and circulation patterns of groundwaters.

The deep confined aquifer is characterized by artesian heads, which maintain a higher potentiometric level than the semi-confined and unconfined aquifers.

Acknowledgments

Acknowledgement is hereby given to the German Academic Exchange Service (DAAD) for financial support of this work. I greatly appreciate constructive comments of two anonymous reviewers and editorial handling by Dr. Asa Danielsson. I am also grateful to Prof. Ron Fuge for his helpful and constructive comments.

References (94)

  • W.B. Mann et al.

    Comments of the NBS tritiated-water standards and their use

    Int. J. Appl. Radioact. Isot.

    (1982)
  • A. Mencio et al.

    Assessment by multivariate analysis of groundwater–surface water interactions in urbanized Mediterranean streams

    J. Hydrol.

    (2008)
  • J.P. Montoroi et al.

    Groundwater geochemistry of a small reservoir catchment in Central Tunisia

    Appl. Geochem.

    (2002)
  • B. Ouda et al.

    New paleoenvironmental data for the late Quaternary of Maknassy (central Tunisia)

    Compt. Rende. Acad. Sci.

    (1998)
  • K.J. Stetzenbach et al.

    Geochemical and statistical evidence of deep carbonate groundwater within overlying volcanic rock aquifers/aquitards of southern Nevada, USA

    J. Hydrol.

    (2001)
  • T.Y. Stigter et al.

    A impact of the shift from groundwater to surface water irrigation on aquifer dynamics and hydrochemistry in a semi-arid region in the south of Portugal

    Agric. Water Manage.

    (2006)
  • M.M. Uliana et al.

    Tracing regional flow paths to major springs in Trans-Pecos Texas using geochemical data and geochemical models

    Chem. Geol.

    (2001)
  • M.M. Uliana et al.

    Regional groundwater flow paths in Trans-Pecos, Texas inferred from oxygen, hydrogen, and strontium isotopes

    J. Hydrol.

    (2007)
  • S. Wold et al.

    Principal component analysis

    Chemometr. Intell. Lab. Syst.

    (1987)
  • G.M. Zuppi et al.

    Hydrogeology as a climate recorder: Sahara (North Africa) and the Po Plain (Northern Italy)

    Global Planet. Change

    (2004)
  • S.G. Abd El Samie et al.

    Groundwater recharge and flow in the Lower Cretaceous Nubian Sandstone aquifer in the Sinai Peninsula, using isotopic techniques and hydrochemistry

    Hydrogeol. J.

    (2001)
  • G.B. Allison

    The relationship between 18O and deuterium in water and in sand columns undergoing evaporation

    J. Hydrol.

    (1982)
  • Begemann, F., 1959. Neubestimmung der natürlichen irdischen Tritiumzerfallsrate und die Frage der Herkunft des...
  • Ben Youssef, M., 1980. Etude stratigraphique et microbiologique du Crétacé des Jebel Koumine et Kharoub (Tunisie...
  • Bismuth, H., Boltenhagen, C., Donze, P., Le Ferve, J., Saint-Marc, P., 1981. Le Crétacé moyen et supérieur de Jebel...
  • Blavoux, B., 1978. Étude du cycle de l’eau au moyen de l’oxygène 18 et du deutérium. Thesis, Paris-6 Univ.,...
  • Blondel, J.A.T., 1991. Les séries à tendance transgressive marine du Miocène inférieur à moyen de la Tunisie centrale....
  • J.K. Böhlke et al.

    Combined use of groundwater dating, chemical and isotopic analyses to resolve the history and fate of nitrate contamination in two agricultural watersheds, Atlantic coastal plain, Maryland

    Water Resour. Res.

    (1995)
  • Bousnina, L., 1997. Le climat de Sfax,...
  • Burollet, P.F., 1956. Contribution à l’étude stratigraphique de la Tunisie centrale. Annale des mines et de la...
  • H. Celle-Jeanton et al.

    Isotopic typology of the precipitation in the Western Mediterranean region at three different time scales

    Geophys. Res. Lett.

    (2001)
  • Chaieb, M., Boukhriss, M., 1998. Flore suscinte et illustrée des zones arides et sahariennes de Tunisie. APNES,...
  • I. Clark et al.

    Environmental Isotopes in Hydrogeology

    (1997)
  • M.L. Coleman et al.

    Reduction of water with zinc for hydrogen isotope analysis

    Anal. Chem.

    (1982)
  • Conrad, G., Fontes, J.Ch., 1970. Hydrologie isotopique du Sahara nord-occidental. Isotope Hydrology 1970. IAEA, Vienne,...
  • H. Craig

    Isotopic variation in meteoric waters

    Science

    (1961)
  • W. Dansgaard

    Stable isotopes in precipitations

    Tellus

    (1964)
  • Daoud, A., 1995. Caractérisation géochimique et isotopique des eaux souterraines et estimation du taux d’évaporation...
  • Dassi, L., 2004. Etude hydrogéologique, géochimique et isotopique du système aquifère du bassin de Sbeïtla (Tunisie...
  • L. Dassi

    Use of chloride mass balance and tritium data for estimation of groundwater recharge and renewal rate in an unconfined aquifer from North Africa: a case study from Tunisia

    Environ. Earth Sci.

    (2010)
  • L. Dassi et al.

    Identifying sources of groundwater recharge in the Merguellil basin (Tunisia) using isotopic methods: implication of dam reservoir water accounting

    Environ. Geol.

    (2005)
  • W.M. Edmunds

    Contribution of isotopic and nuclear tracers to study of groundwater

  • Edmunds, W.M., Shand, P., Guendouz, A., Moulla, A.S., Mamou, A., Zouari, K., 1997. Recharge Characteristics and...
  • Etcheverry, D., 2002. Valorisation des méthodes isotopiques pour les questions pratiques liées aux eaux souterraines –...
  • G. Faure

    Principles of Isotope Geology

    (1986)
  • Fontes, J.C., 1985. Some considerations on ground water dating using environmental isotopes. Hydrogeology in the...
  • J.C. Fontes et al.

    Paléohydrologie isotopique de l’Oued el Akarit (sud tunisien) au Pleistocene superieur et a l’Holocene

    Palaeogeog. Palaeolclim. Palaeoecol.

    (1983)
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