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The Complex Terminal (CT) and Plio-Quaternary (P-Q) aquifers in the Chott Gharsa plain in southwestern Tunisia have been investigated with the aid of chemical and isotopic tools. It has been demonstrated that groundwater from the CT is mainly of palaeo-origin, especially in the western and central parts of the plain where the most negative values of δ18O and δ2H were observed (between -8.1 and -7.6‰ for δ18O, and -60 to -57‰ for δ2H), combined with low concentrations of radiocarbon (6.8-7.5 pmc) and absence of tritium. Modern recharge of the aquifer occurs only in the eastern part of the system where younger waters were observed, as indicated by their stable isotope composition, relatively high radiocarbon content and presence of tritium. Groundwater from the P-Q multi-layer aquifer represents mixtures of ascending deep CT waters and modern water recharging the P-Q aquifer system. Isotope mass balance was used to quantify mixing proportions. The calculations showed that the contribution of deep CT groundwater to the P-Q aquifer system reaches about 75% in the western and central parts of the plain where the CT aquifer remains strongly artesian. This contribution decreases to about 15% towards the eastern part of the plain, as a consequence of significant reduction of artesian pressure in this area of the CT aquifer. Chemical data suggest that mineralization of the studied groundwater systems is controlled mainly by dissolution of evaporative minerals (halite, anhydrite and gypsum) and cation exchange reactions with the matrix, possibly enhanced by recent anthropogenic disturbance of the system caused by lowering of the water table due to heavy exploitation and return flow of saline irrigation water into the P-Q aquifer. © 2012 Copyright 2012 IAHS Press. Source


Aggoune A.,Arrondissement des Ressources en Eau
Journal of Hydro-Environment Research | Year: 2014

The Rejim Maatoug aquifer, which located in south-western Tunisia, constitutes a good example of overexploited resources. Hydrogeological and geochemical data were examined to determine the main factors and mechanisms controlling the groundwater chemistry and the hydrodynamic functioning of this aquifer based on a multi-tracer approach. Thirty-one groundwater samples from the CT Miocene aquifer of Rejim Maatoug and Djerid regions were collected in 2010 for major chemical element analysis. Physical parameters such as temperature, pH and electrical conductivity (EC) were measured in the field. Three groundwater samples were selected for 14C measurements. Four groundwater samples were chosen for 3H measurements. The chemical data indicates that dissolution of evaporate minerals, evaporation and cation exchange processes seem to be the main factors controlling groundwater mineralization. The geological and hydrogeological studies show the important role of the deep existing faults in controlling the hydrodynamic functioning of the aquifer systems in southern Tunisia. The isotopic data shows that groundwater in this area is a mixture of recent shallow waters located in the Mio-Plio-Quaternary sands and paleo-deep waters of the carbonate Senonian aquifer. Low 3H and 14C contents, observed in some sampled wells (3H=0.15 TU in C1N1, 14C=8.8 pmc in Matr2), indicates that the recharge of the Miocene aquifer occurs mainly through upflow leakage of Senonian deep aquifer while there is no evidence of significant recharge in major part of the plain and mountains piedmonts that can be observed. © 2013. Source


Abid K.,University of Sfax | Zouari K.,University of Sfax | Abidi B.,Arrondissement des Ressources en Eau
Carbonates and Evaporites | Year: 2010

In southern Tunisia, the major aquifer system is characterised by the superposition of two principal levels; the "complex terminal" (CT) which forms the surface aquifer and the "continental intercalaire" (CI) which constitutes the deep aquifer. The hydrodynamic functioning of this aquifer system is largely influenced by tectonics, lithologic variation and recharge conditions. The tectonics has contributed to the discontinuity of the aquifer levels by creating some barriers which play the role of hydraulic sills. A study of the CI potentiometric map shows three principal flow directions. These flow directions converge at the Sill Zone. The total mineralisation evolution shows an increase from the periphery of the basin to the discharge area. Dissolution of halite, gypsum and/or anhydrite-bearing rocks is the principal source of the salinity of the groundwater. The dissolution of these evaporitic rocks is confirmed by mineral saturation indices, which show an under-saturation of water samples with respect to the mentioned minerals. Moreover, the insulation of certain compartments of the reservoir and intercommunications between the aquifer levels seem to play a principal role in the deterioration of chemical quality of water. In this study, the isotopic tools have been applied to understand the hydrodynamic functioning in the region. These techniques have confirmed the results of the hydrogeologic and hydrochemical studies concerning the interconnection between the different aquifers. They indicate also the recent local recharge of the CI reservoir throughout Cretaceous outcrops, and the older origin of all groundwater in the aquifer system. © 2010 Springer-Verlag. Source


Ben Cheikh N.,University of Sfax | Zouari K.,University of Sfax | Abidi B.,Arrondissement des Ressources en Eau
Quaternary International | Year: 2012

Salinization is a common environmental problem of groundwater contamination, particularly in developed coastal aquifers. The Sfax basin is located on the Mediterranean coast, southeastern Tunisia, and is dominated by industrial activities. The problem of groundwater mineralization in the south part of this aquifer has long been attributed to the marine influence. In this study, a combined hydrogeological and isotopic survey using chemical tracers was conducted in addition to discharge and groundwater level measurements. The results preclude seawater intrusion as an origin of groundwater mineralization. It seems that the main source of groundwater mineralization is due to the mixture with salty water lodged in the C/T (Cenomanian-Turonian) aquifer. This mixture process is carried out by the simultaneous effect of (1) a lateral flow of saline water coming from C/T aquifer in the southwest (Menzel Habib) and (2) a local vertical leakage from the same C/T formation which forms the basement of the studied aquifer. The depleted isotope signature of the majority of groundwater is characteristic of old recharge occurring during the late Pleistocene-Holocene, with the exception of some local recent refill areas. © 2011 Elsevier Ltd and INQUA. Source


The study of the coastal basins of Sfax and Djeffara in northern Gabes, based on the interpretation of hydrochemical (major elements) and isotopic (18O, 2H and 14C) data, has allowed us to understand the hydrodynamic functioning of the Miocene aquifer. Indeed, the geochemical data highlight the presence of two different groundwater types: (Na-Cl) in the Sfax basin and (Cl/SO4-Ca/Na) to (Na-Cl) in the northern Gabes basin. This difference between groundwater types underlines the variability of the origins of groundwater mineralization. The use of isotopic tools showed a relatively old water, with the exception of some local recent recharge inferred by the rainwater infiltration through Zemlet Beida Mountain in the upstream part of the northern Gabes basin. This is also confirmed by the high 14C contents of groundwater in this region. Consequently, it is noted that the transition from south to north along the coast is marked by a big lateral variation of lithology and thickness of the waterbearing formation, underlining the independence of the coastal aquifers of Sfax and Djeffara in the absence of any significant flow exchange between the two basins. © 2012 Copyright 2012 IAHS Press. Source

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