Environ Earth Sci (2012) 66:1359–1370 DOI 10.1007/s12665-011-1346-8

ORIGINAL ARTICLE

Hydrochemical and isotopic study of groundwater in Wadi El Hechim–Garaa Hamra basin, Central

Hichem Yangui • Kamel Zouari • Kazimierz Rozanski

Received: 30 November 2010 / Accepted: 2 September 2011 / Published online: 24 September 2011 Ó Springer-Verlag 2011

Abstract Hydrochemical and isotopic study of Miocene region postulating significant groundwater fluxes crossing and Mio-Plio-Quaternary (M-P-Q) aquifers in Wadi El the fault in the direction of M-P-Q aquifer and adjacent Hechim–Garaa Hamra basin, Central Tunisia was under- aquifers in the Wadi al Fakka plain. taken in order to investigate recharge mode and processes leading to mineralization of groundwater as well as inter- Keywords Groundwater recharge Hydrochemistry action between both systems. The results revealed striking Stable and radioactive isotopes Wadi El Hechim–Garaa differences between the two aquifer systems. While the Hamra basin Central Tunisia Miocene aquifer contains recently recharged waters with generally low mineralization (around 0.5 g L-1), stem- ming mainly from dissolution of carbonate minerals, the Introduction M-P-Q aquifer reveals TDS values reaching 3 g L-1, controlled mainly by dissolution of evaporitic minerals. Groundwater resources are of great importance for agri- Isotopic data indicate that the Miocene aquifer contains cultural development in arid and semi-arid areas around water recharged in past several decades (bomb tritium and Mediterranean basin where surface waters are scarce or bomb radiocarbon detected). The M-P-Q system appears to absent. In most cases, aquifers are intensively exploited to be much slower, with time scales of groundwater flow satisfy ever growing agricultural and domestic needs. possibly reaching some thousands of years. Sharp discon- Adequate assessment, management and protection of the tinuity of hydrochemical and isotope characteristic of available groundwater resources require good understand- groundwater observed across the major tectonic fault sep- ing of their hydrodynamic and hydrochemical characteris- arating the Miocene and M-P-Q aquifers supports the idea tics. Hydrochemical and isotopic methodologies are of very limited (if any) hydraulic interconnection between nowadays well established in hydrological studies of both studied systems. This in turn calls for revision of groundwater systems (Gonfiantini et al. 1974; Fontes et al. existing conceptual models of groundwater flow in the 1983; Edmunds et al. 2003; Guendouz et al. 2003;Edm- unds 2005). Among others, they can provide quantitative insight in the dynamics of groundwater flow as well as may H. Yangui (&) BP 197, Sakiet Eddaier 3011, , Tunisia serve as indicators of interaction between water bearing e-mail: [email protected] layers within a single multilayer aquifer or between sepa- rate aquifers. Such information is of particular importance K. Zouari for aquifers located in dry areas and characterized by Laboratoire de Radio-Analyses et Environnement, Ecole Nationale d’Inge´nieurs de Sfax, complex lithology influenced by tectonic activities. This is BP 1173, 3038 Sfax, Tunisia the case of Wadi El Hechim–Garaa Hamra basin in Central Tunisia which was the subject of this study. K. Rozanski The Wadi El Hechim–Garaa Hamra basin is located in a Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, semi-arid climate. Groundwater exploited from Miocene al. Mickiewicza 30, 30059 Krakow, Poland and Mio-Plio-Quaternary (M-P-Q) aquifers is the main 123 1360 Environ Earth Sci (2012) 66:1359–1370 water resource for the region. The central aim of this work southwestern part of the study area at Wadi El Hechim was to define groundwater origin and to characterize its synclinal and by Wadi Al Htab located to the north at mineralization and recharge schemes, as well as to check Garaa Hamra synclinal. Except the baseflow of Wadi El the existing conceptual model of groundwater flow. Such Htab, estimated to be around 8.8 mm3 year-1 (Lafforgue information will further facilitate better use of precious 1981), water flows are not perennial and occur only by groundwater resources in the study area and will assist flash floods in rainy seasons. management strategies being developed for the investi- gated groundwater system. Geological setting

The Wadi El Hechim–Garaa Hamra basin belongs to cen- Study area tral Atlas of Tunisia. The later is marked by E–W, NE–SW and SW–NE fold belts verging to the south and limited by The Wadi El Hechim–Garaa Hamra basin which extends strike-slip fault corridor systems (Zargouni 1985; Boukadi over an area of approximately 280 km2, is located in the 1994;Be´dir 1995; Boutib and Zargouni 1998;Be´dir et al. central part of Tunisia. It is bordered by mountains (Dj) of 2001; Zouaghi et al. 2008). The strike-slip fault systems are Kharroub–Koumine to the west, Rakhmat to the east and ancient deep faults which are occasionally associated with Ezzitoun–Al Hfay to the south (Fig. 1). The area is char- salt Triassic tectonic activities as of Koumine and Hamra acterised by a semi-arid climate. Mean annual evaporation anticlines (Fig. 1). In southern and central Tunisia the later of about 1,200 mm year-1 exceeds considerably annual rejuvenation of these old tectonic events [e.g. precipitation estimated to approximately 280 mm year-1 Fault; Sidi Ali Ben Oun Fault (S.A.B.O)] during the time of (CRDA of Kasserine 2004). Surface water resources are upper Cretaceous and Tertiary had largely guided deposit represented by Wadi El Hechim located in the distribution following major tectonic directions (Burollet

Fig. 1 Geographic location of the study area and simplified geology of Wadi El Hechim– Garaa Hamra basin, central Tunisia. AA0 cross-section as shown in Fig. 3

123 Environ Earth Sci (2012) 66:1359–1370 1361

1956; Chihi 1984; Zargouni 1985; Ben Ayed 1986; as a single sequence and attributed to M-P-Q age. In south Boukadi 1994;Be´dir 1995). and central Tunisia, M-P-Q series enclose multi-layer In the Wadi El Hechim–Garaa Hamra basin, the sedi- aquifers with important groundwater reserves as is the case ments date from Triassic to Quaternary (Fig. 2). The sed- of Miocene and M-P-Q aquifers on Wadi El Hechim–Garaa imentary series are characterized by several hiatuses and Hamra basin. unconformities due to erosion and/or non-depositional intervals. Indeed, since the later upper Cretaceous (Middle Hydrogeological setting Turonian) to lower Miocene time (Langhian), the central part of Tunisia (including the study area), was an emerged As shown in the cross-section (Fig. 3), two distinct aquifers zone known as ‘‘Kasserine islet’’ and it was as consequence are identified in the study area: the Miocene and the M-P-Q devoid of deposits characteristic for this period (Fig. 2) units which are separated by major, north–south fault (Burollet 1956; Marie et al. 1984). Since middle Miocene (S.A.B.O). The Miocene aquifer is located at the southern central Tunisia was affected by extension–compression part of the study area, upstream of S.A.B.O. fault, along the regimes (Atlas phase) which led to the formation of folded western part of Wadi El Hechim synclinal. Deposits are ranges oriented NE–SW (known as Atlasic fold ranges) and composed of sand and sandstone dated to middle Miocene separated by Mio-Plio-Quaternary microbasins (Chekhma age (Serravallian–Tortonian) known as Saouaf formation. 1996; Mannaı¨-Tayech 2006; Zouaghi et al. 2008). Around Aquifer deposits are characterized by good permeability south and central Atlas of Tunisia, depressions located and range of thickness between 200 and 400 m, from the within fold belts were filled-in by continental deposits border to central part of Wadi El Hechim synclinal, dated from Serravallian–Tortonian to Pleistocene age respectively. Average transmissivity, obtained by pumping (Saouaf and Segui formations, respectively) as a result of tests reaches approximately 5.8 9 10-3 m2 s-1 (El Amri an active erosion affecting uplifts (Figs. 1, 2). Deposit 1992). Groundwater is exploited for agriculture, domestic sequences are of regressive character; they are character- and drinking water needs mainly by dug wells concentrated ized by significant variations in thickness and patterns with around Wadi El Hechim bed and also by few boreholes. several unconformities. All regressive series are assigned Miocene groundwater is only marginally exploited due to

Fig. 2 Synthetic lithostratigraphic column of the study area

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Fig. 3 Hydrogeological cross- section of Miocene and Mio- Plio-Quaternary aquifers located in Wadi El Hechim– Garaa Hamra basin. For the position of the cross-section see Fig. 1

low demographic and economic development in the Wadi December 2007 (Fig. 4). Measurements of temperature and El Hechim synclinal. Nevertheless, several hydrogeologi- pH of groundwater were carried out in the field. The chem- cal studies underlined the role of this aquifer in the ical and isotopic analyses were conducted in the laboratory recharge of plain system located to the east of of Radio-Analysis and Environment ‘‘LRAE’’ at the the study area (Fig. 1) (El Amri 1992; Amouri 1994; National School of Engineering in Sfax (Tunisia). Major Simonot 1996; Yangui et al. 2010). Based on piezometric element concentrations were determined by liquid-ion map, water flow of about 2 mm3 year-1 was estimated chromatography (HPLC) using a Dionex DX 100 ion chro- from the Miocene to M-P-Q aquifer (El Amri 1992). matograph equipped with a CS12 and an AS14A-SC Ion Pac The M-P-Q aquifer system is located in the northern part columns and an AS-40 auto-sampler. The total alkalinity of the study area, downstream of the S.A.B.O. fault, along (HCO3) was determined by titration with 0.1 HCl against the Garaa Hamra synclinal. It consists of a thick (up of methyl orange and bromcresol green indicators. Strontium 500 m) Mio-Plio-Quaternary filled basin. Aquifer is com- ion was analysed using an inductively coupled plasma- posed mainly of clayey sands (with varying grain sizes), atomic emission spectrometer (ICP-AES), Liberty 200AX- inter-bedded with layers of clay and sandy clay as well as Varian on samples that had been filtered through 0.45-lm conglomerates of gravels and gypsum. As it was stated filters and acidified to pH = 2 using 16 N pure HNO3. above, the M-P-Q deposits are characterized by high ver- Stable isotope composition of water samples (d18O, tical and lateral heterogeneity and thus the system is d2H) was measured by isotope ratio mass spectrometry assigned as a single multi-layer aquifer. Groundwater is after standard CO2 equilibration (Epstein and Meyada exploited from relatively permeable levels composed 1953) and zinc reduction (Coleman et al. 1982) sample essentially of gravels, sands and clayey sands. Average preparation techniques. The 13C/12C ratios in the total transmissivity, obtained from pumping tests, is about dissolved inorganic carbon pool (TDIC) were measured at 2.2 9 10-3 m2 s-1 (El Amri 1992). the isotope hydrology laboratory of the IAEA, by con-

Piezometric map of the study area suggest that general verting the TDIC to CO2 with 100% H3PO4 followed by direction of groundwater flow is from SW to the NE of the cryogenic separation and isotope analysis by mass spec- basin (Fig. 4), with some discharge occurring into the M-P- trometry (Boaretto et al. 1998). The results are reported as Q aquifer through S.A.B.O. fault and possibly towards the relative differences (d values) with respect to V-SMOW Sidi Bouzid plain. In the northern part of the basin, over the and V-PDB standards, for d18O(d2H) and d13C, respec- Garaa Hamra synclinal, the M-P-Q groundwater discharges tively, expressed in per mille. Analytical precision of stable into evaporation area of Barhmiyya. As shown in Fig. 4, isotope analyses was in the order of 0.1% for d18O and groundwater may also flow towards Hajeb Layoun basin, d13C and 1% for d2H. Tritium content was measured in the downstream of Kasserine Fault. IAEA isotope hydrology laboratory in Vienna using elec- trolytic enrichment followed by liquid scintillation spec- trometry (Taylor, 1977). The results are reported in Tritium Sampling and analytical procedure Units (TU) (one TU is equivalent to one 3H atom per 1018 atoms of hydrogen 1H) (Clark and Fritz 1997) with ana- Water samples were collected from nine dug wells (W) and lytical uncertainty in the order of 0.3 TU. The radiocarbon seven boreholes (B) during one sampling company in content in TDIC pool was measured at the LRAE Laboratory 123 Environ Earth Sci (2012) 66:1359–1370 1363

Fig. 4 Distribution of sampling sites. Arrows indicate postulated general directions of groundwater flow

through benzene synthesis and liquid scintillation spec- along the general direction of groundwater flow is supported trometry (Fontes 1971). The measured 14C/12C ratios were by intermediate TDS values observed in the central part of compared with 14C activity of the modern radiocarbon Garaa Hamra (B1, B2, B3, and W6). Groundwater sampled standard of Oxalic Acid I and expressed as percent of modern from the boreholes tapping M-P-Q aquifer at the eastern part carbon (pmc) (Taylor 1987). Analytical results obtained in of Wadi El Hechim synclinal, close to S.A.B.O. fault (B4, the framework of this study are summarized in Table 1. B5) reveal the TDS values up of 2.5 g L-1. Substantial, abrupt deterioration of groundwater quality across the S.A.B.O. fault points to weak interconnection between Results and discussion Miocene and M-P-Q aquifers, apparently stemming from largely impermeable nature of the fault. Hydrochemistry Origin of groundwater mineralization Total dissolved solids (TDS) As seen in the Piper diagram (Fig. 5), groundwater in Mio-

The analysed Miocene water samples (W7; W8, W9, B7, B8) cene aquifer evolves from HCO3–Ca–Mg type for shallow reveal relatively homogenous TDS content of less than 1 g aquifer levels (W7, W8, W9) to HCO3–Ca–Na type for deep L-1. These low values are clearly related to the aquifer aquifer level (B6, B7). Groundwater sampled from M-P-Q matrix composed mainly of washed sand and sandstone aquifer is of homogenous SO4–Ca–Mg type. Figure 6 deposits. In the northern part of the basin (Garaa Hamra depicts the relationship between concentrations of major synclinal), the samples collected in the M-P-Q aquifer are ions and TDS values for both studied aquifers. The most characterized by significantly higher TDS values, ranging striking feature of the correlation diagrams shown in Fig. 6 is from 2 to 3 g L-1. Highest TDS values (ca. 3 g L-1) are a distinct separation of the data points representing Miocene observed downstream of the basin, towards the discharge and M-P-Q aquifers. In general, SO4, Ca, Mg, Na and Cl are area of the M-P-Q aquifer (W1, W2, W3, W4, and W5). This positively correlated with TDS (Fig. 6a, b, c, e, f). The can be linked to partial evaporation of water during discharge contribution of K and HCO3 to the total mineralization, and/or in the dug wells itself, as well as to prolonged inter- particularly in Miocene aquifer, is less significant action with aquifer matrix. Gradual increase of TDS values (Fig. 6d, g).

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Table 1 Hydrochemical and isotopic data of sampled groundwater in the Wadi El Hechim - Garaa Hamra basin (Central Tunisia)

18 2 3 14 13 Water Aquifer Depth pH T TDS Ca Mg Na K HCO3 Cl S04 NO3 Ion d O d H H C C point (m) (°C) (mg L-1) (meq L-1) (meq L-1) (meq L-1) (meq L-1) (meq L-1) (meq L-1) (meq L-1) (meq L-1) balance % VS TU pmc % versus (%) VSMOW VPDB

W1 M-P-Q 25 7.0 20.6 2570 12.13 13.33 10.66 n.d 3.87 3.95 29.55 0.52 -2 -5.50 -32.3 W2 52 8.8 20.5 2500 12.62 14.01 10.16 0.41 3.90a 2.73 25.74 3.53 2 -5.37 -30.2 0.5 66.0 -8.0 W3 50 7.3 21.1 2474 10.89 16.62 9.16 0.65 3.17 4.10 29.45 n.d - -5.31 -33.6 0.5 W4 60 7.3 19.3 2591 9.65 13.77 13.05 0.60 4.50 10.77 25.37 n.d -6 -5.16 -35.2 W5 62 7.3 19.1 2531 9.64 13.67 13.01 0.77 6.56 13.91 18.59 n.d -3 -5.95 -35.9 \0.3 W6 93 7.4 20.5 2116 7.77 12.11 10.76 0.55 3.33 8.15 21.13 n.d -2 -5.02 -36.2 \0.3 Bl 120 7.8 21.8 2440 9.23 8.81 13.71 0.26 3.40 8.93 17.16 4.72 -3 -5.51 -34.5 1.0 29.4 -8.4 B2 150 7.8 21.4 2430 10.06 8.81 19.58 0.36 4.60 9.44 19.82 3.87 ‘ -4.65 -28.5 \0.3 65.5 -9.0 B3 200 8.1 27.3 2030 8.98 10.06 15.34 0.00 4.40 6.02 18.24 4.27 2 -5.26 -34.7 \0.3 55.0 -8.0 B4 200 7.5 23.5 2798 9.11 13.18 21.75 0.61 5.00 16.25 25.36 n.d -2 -5.52 -37.6 \0.3 B5 105 7.7 28.8 2910 11.01 12.67 23.37 n.d 3.40 13.68 27.96 0.22 2 -3.62 -21.5 0.7 55.6 -8.9 W7 Miocene 30 7.6 21.4 281 2.58 1.80 0.83 0.12 3.33 0.65 1.53 n.d -2 5.58 -35.2 6.6 W8 45 7.9 21.5 340 1.89 2.95 0.59 0.10 2.85 0.61 2.15 026 -3 -5.67 -31.1 2.3 107.0 -11.3 W9 42 8.0 21.0 337 2.82 2.88 1.07 0.11 3.67 0.97 2.09 n.d -6.32 -38.5 2.0 B6 120 7.9 22.2 590 151 2.41 5.80 0.18 4.00 1.83 3.17 0.77 -5.38 -30.9 2.3 71.0 -9.4 B7 220 7.8 22.9 390 0.93 0.88 4.63 0.15 4.40 0.52 1.69 0.20 -2 -5.81 -35.4 3.2 86.6 -10.0 nio at c 21)66:1359–1370 (2012) Sci Earth Environ B boreholes, W dug wells, n.d not detected, TDS total dissolved solids, VSMOW Vienna Standard Mean Ocean Water, TU Tntium units, pmc percent of modern carbon, VPDB Vienna Pee Dee Belemnite a 2- -1 2- -1 The CO3 content in this sample is equal 0.25 meq L . In the remaining samples the amounts of CO3 are \ 0.2 meq L Environ Earth Sci (2012) 66:1359–1370 1365

and HCO3 ions present in this system. Indeed, carbonate deposits such as limestone and dolomite dated to Albian— Lower Turonian age (Zebbag Formation) represent the main deposits at mountain outcrops around Wadi El Hechim synclinal (Figs. 1, 2; Dj. Kharroub, Dj. Ezzitoun). In addition, carbonates of Zebbag Formation are the sub- stratum of Miocene aquifer at Wadi El Hechim synclinal. Numerous studies of M-P-Q aquifer systems in central Tunisia revealed that groundwater originating from shal-

low layers is enriched in SO4 and Cl when compared to groundwater sampled from deeper layers (El Amri 1992; Jribi 2004; Yangui et al. 2010). This effect can be explained by evaporation coupled with salts leaching dur- ing recharge. Salts concentrated in the soil by evaporation after each rainfall are dissolved by next rainfall event and transported deeper into the system. Positive correlation between Na and Cl contents (Fig. 7d) indicates that these elements most probably derive from the same source i.e. the dissolution of halite. Apparent excess of Na versus Cl, especially for deep M-P- Q groundwater (B1, B2, B3, B4, B5), can be explained by Fig. 5 Piper diagram of the analyzed groundwater samples repre- ion exchange reactions with clay minerals abundant within senting Miocene and Mio-Plio-Quaternary aquifers located in Wadi M-P-Q strata. During these reactions Na ions, previously El Hechim–Garaa Hamra basin adsorbed on the surface of clay minerals in the aquifer matrix are exchanged with Ca and/or Mg. In order to better understand the processes leading to Apparent impact of ion exchange reactions can be linked the observed mineralization, bivariate diagrams of to relatively long residence time of groundwater, induced chemical constituents in the analysed groundwater sam- in part by low permeability of M-P-Q aquifer system. ples were established. Samples representing M-P-Q aquifer reveal a strong positive correlation of the sum of Isotopic indicators

Ca and Mg ions with the SO4 content, and at the same 18 2 time lack of any correlation with HCO3 content (Fig. 7a, Stable isotopes ( O, H) b). In addition, Ca ? Mg content reveals high excess with respect to carbonate dissolution line (Fig. 7b). This Stable isotope composition of the analyzed groundwater points to dissolution of evaporitic minerals (e.g. gypsum, samples is plotted in Fig. 8 in the d2H–d18O space, on the or epsomite) as a major source of these ions in background of global and regional meteoric water lines. groundwater of M-P-Q aquifer. Several previous studies Oxygen-18 and deuterium content in the Miocene aquifer of other M-P-Q aquifers located in central and southern varies from -5.38 to -6.32% and from -30.9 to -38.5%, Tunisia linked elevated mineralization and deterioration respectively. Groundwater samples representing M-P-Q of water quality to dissolution of gypsum layers which aquifer reveal similar range of d values, with one exception are relatively abundant within M-P-Q sequences (Maliki of sample B5 which is isotopically enriched when com- 2000; Ouda 2000; Zouari et al. 2003; Jribi 2004; Yangui pared to the remaining samples from this group. The et al. 2010). This hypothesis is strongly supported by average d18O value for Miocene samples (-5.75 ± 0.16 positive correlation of the measured strontium concen- %) is ca. 0.4 % lower than the corresponding values for 2 tration with SO4 content in M-P-Q samples, as shown in M-P-Q samples (-5.32 ± 0.10 %) while the mean d H Fig. 7c. Indeed, the presence of Sr ions in groundwater values are statistically indistinguishable (-34.2 ± 1.2% is often linked to Sr-bearing minerals such as celestite and -33.9 ± 0.8%, respectively). This slightly lower 18 (SrSO4) associated to gypsum and with strontianite mean d O for Miocene groundwater might be an indica- (SrCO3) (Gosselin et al 2004; Faye et al 2005). tion of higher elevation of the recharge area(s) of this In contrast to M-P-Q aquifer, the data points repre- aquifer when compared to M-P-Q aquifer (mountains Dj. senting Miocene aquifer (Ca ? Mg versus HCO3, Fig. 7b) Kharroub and Dj. Ezzitoun). On the other hand, this dif- fall on the 1:1 dissolution line strongly suggesting disso- ference may also stem from the fact that M-P-Q samples lution of carbonate minerals as a major source of Ca, Mg reveal lower deuterium excess (d = d2H - 8 9 d18O) 123 1366 Environ Earth Sci (2012) 66:1359–1370

Fig. 6 a–g Hydrochemical correlations of Ca, Mg, Na, K, HCO3, Cl, SO4 and HCO3 contents versus TDS

when compared to Miocene samples (8.7 and 11.8%, Miocene water samples are located in Fig. 8 between respectively), pointing to some evaporation history of these the Global Meteoric Water Line GMWL waters. (d2H = 8 9 d18O ? 10) (Craig 1961); and Regional

123 Environ Earth Sci (2012) 66:1359–1370 1367

Fig. 7 Hydrochemical relationships a (Ca ? Mg/SO4); b (Ca ? Mg/HCO3); c (Sr/ SO4); d (Na/Cl)

Meteoric Water Line RMWL (d 2H = 8 9 d 18O ? 13.5) (Maliki et al. 2000) established for Sfax city (Fig. 1). Mean isotopic composition of rainfall at Sfax (amount-weighted) is equal -4.6% (d18O) and -23.3% (d2H). It is apparent that Miocene waters are depleted in 18O and 2Hby approximately -1.1 and -10.9%, respectively, when compared to Sfax precipitation. This difference most likely is the result of coupled altitude and continental effect on isotopic composition of rainfall. The study area is located ca.120 km west of the Mediterranean coast, some 200–500 m higher than Sfax city. Two groups of samples representing M-P-Q aquifer can be identified. The first one consists of samples originating from shallow aquifer levels located close to piedmonts of Rakhamt and Koumine mountains (B1, W1; W2; W5). Samples from this group are located between RMWL and GMWL, in a position similar to Miocene samples. The second group represents mostly deep aquifer levels. The data points plot to the right-hand side of the GMWL indicating partial evaporation of the analyzed groundwater Fig. 8 d2H–d18O diagram of the analyzed groundwater samples representing Miocene and Mio-Plio-Quaternary aquifers located in samples. This evaporative isotope signature is most prob- Wadi El Hechim–Garaa Hamra basin ably a reminiscence of partial evaporation of water during 123 1368 Environ Earth Sci (2012) 66:1359–1370

Fig. 9 Spatial distribution of tritium (3H) and radiocarbon (14 C) contents in Miocene and M-P-Q aquifer systems

slow infiltration process controlled by low permeability of Tritium contents of M-P-Q groundwater samples are M-P-Q deposits. As indicated above, this partial evapora- significantly lower; detectable tritium was found in two tion may also contribute to generally higher mineralization dug wells (W2, W3) and two boreholes (B1, B5). However, of M-P-Q groundwater when compared to Miocene these values are not conclusive as they are accompanied by aquifer. relatively low 14C content of TDIC reservoir. The tritium concentration of ca. 0.5 TU detected in W2 and W3 may Radioactive isotopes: (3H, 14C) stem from atmospheric contamination if those dug wells were not frequently used before sampling. Alternatively, it Tritium content of Miocene and M-P-Q groundwater was may also indicate small admixture of recent, vertical analyzed in 14 samples. The results are presented in recharge at the aquifer level tapped by these two dug wells Table 1 and their spatial distribution is shown in Fig. 9 (ca. 50 m depth). In addition, 1.0 TU detected in B1 may together with 14C data. be the result of leakage of recent water in case the borehole Groundwater samples collected in the Miocene aquifer is not properly constructed. This is very likely in the light reveal generally high tritium contents (between 2.0 and 6.6 of low 14C content in this borehole (cf. discussion below). TU). These values have to be compared with recent tritium Traces of tritium found in B5 (0.7 TU) may have the same levels in rainfall in Tunisia which fluctuate around 5 TU origin. (Maliki 2000; Celle et al. 2001; Jribi 2004; Ben Ammar The 14C/12 and 13C/12C ratios were analyzed in five et al. 2006; Kamel et al. 2006; Yangui et al. 2010). Tritium M-P-Q samples (one dug well and four boreholes—cf. is present both in shallow dug wells and in boreholes. This Table 1 and Fig. 9). The radiocarbon content in TDIC pool is a strong indication of the presence of modern recharge appears to be significantly lower when compared to Mio- waters dominating the system. Post-bomb age of ground- cene aquifer, with the lowest value (29.4 pmc) detected in water in the Miocene aquifer is confirmed also by high 14C B1 borehole located in the northern, most distant part of the contents in the TDIC pool. The dug well W8 even reveals M-P-Q aquifer. Significantly higher radiocarbon content traces of bomb 14C signal. Apparently, fast recharge of the detected in W2 dug well located in the same area (cf. Miocene system is facilitated by its lithology dominated by Fig. 9) may reflect true vertical age structure of ground- sands. water. Further upstream (boreholes B2 and B3),

123 Environ Earth Sci (2012) 66:1359–1370 1369 significantly higher 14C contents when compared to B1 analyses.Contribution of K.R. was partly supported by statutory funds were observed (65.5 and 55.0 pmc, respectively). This of the AGH University of Science and Technology (project No.11.11.220.01). difference may indicate some aging effect, possibly aug- mented by exchange of carbon with the matrix along the general direction of groundwater flow. Interaction of TDIC References pool with the aquifer matrix is also suggested by relatively 13 high d C values, ranging from -8.0 to -9.0%. Amouri M (1994) Etude hydroge´ologique du syste`me aquife`re de Sidi Bouzid. DGRE, Tunisia Be´dir M (1995) Me´canismes ge´odynamiques des bassins associe´s aux couloirs de coulissement de la marge atlasique de la Tunisie, Conclusions sismostratigraphie, sismo-tectonique et implications petrolie`res. The`se Es Sciences, Universite´ de II, p 315 The results of the presented study provide a striking Be´dir M, Boukadi N, Tlig S, Ben Timzal F et al (2001) Subsurface example of the role of tectonic faults in controlling Mesozoic Basins in the Central Atlas of Tunisia, tectonics, sequence deposit distribution and hydrocarbon potential. AAPG regional groundwater flow. Hydrochemical and isotopic Bull 85:885–907 characteristics of Miocene and M-P-Q aquifers in the Wadi Ben Ammar S, Zouari K, Leduc C et al (2006) Caracte´risation El Hechim–Garaa Hamra basin, separated by major fault isotopique de la relation barrage-nappe dans le bassin de (S.A.B.O. fault), revealed striking differences between Merguellil (Plaine de , Tunisie centrale). Hydrol Sci J 51(2):272–284 both systems. The Miocene aquifer contains recently Ben Ayed N (1986) Evolution tectonique de l’Avant—pays de la recharged waters with generally low mineralization chaıˆne alpine de Tunisie du Me´sozoı¨que a’ l’Actuel. The`se de (around 0.5 g L-1), stemming mainly from dissolution of Doctorat Sciences. Universite´ Paris Sud Orsay, p 327 carbonate minerals. In contrast, the M-P-Q aquifer reveals Ben Youssef M (1999) Stratigraphie ge´ne´tique du Cre´tace´ de Tunisie, -1 Micropale´ontologie, stratigraphie se´quentielle et ge´odynamique TDS values reaching 3 g L . Its chemistry is controlled des bassins de la marge sud et pe´ri-te´thysienne. The`se de mainly by dissolution of evaporitic minerals. Doctorat Sciences. Universite´ Tunis II, p 420 Although available isotope data do not allow quantita- Boaretto E, Thorling L, Sveinbjornsdottir AE, Yechieli Y, Heineme- 14 tive interpretation of tritium and carbon isotope data in ier J (1998) Study of the effect of fossil organic carbon on Cin groundwater from Hvinningdal, Denmark. Radiocarbon terms of groundwater age, there is a clear indication that 40:915–920 both studied systems greatly differ in terms of dynamics of Boukadi N (1994) Structuration de l’Atlas de Tunisie: signification groundwater flow. While the Miocene aquifer contains des noeuds et des zones d’interfe´rences structurales au contact water recharged during the past several decades (bomb des grands couloirs tectoniques. The`se de Doctorat Sciences. Universite´ Tunis II, p 249 tritium and bomb radiocarbon detected), the M-P-Q system Boutib L, Zargouni F (1998) Disposition et ge´ome´trie des plis de appears to be much slower, with the time scales of l’Atlas centrome´ridional de Tunisie. De´coupage et cisaillement groundwater flow possibly reaching some thousands of en lanie´res tectnoiques. CR Acad Sci Paris, France 362:261–265 years. A more detailed isotope study would be required to Burollet PF (1956) Contribution dans l’e´tude stratigraphique de la Tunisie centrale. Ann Min Geo 18, Tunisia quantify groundwater ages in both systems. Celle H, Zouari K, Travi Y et al (2001) Caracte´risation isotopique des Sharp discontinuity of hydrochemical and isotope pluies en Tunisie. Essaie de typologie dans la re´gion de Sfax. GR characteristic of groundwater observed across the major Acad Sci Paris 6:625–631 tectonic fault separating the Miocene and M-P-Q aquifers Chekhma H (1996) Etudes stratigraphiques, se´dimentologiques et tectoniques de la re´gion de — provides a strong argument in favour of very limited (if (Tunisie centrale). The`se de Doctorat Sciences. Universite´ Tunis any) hydraulic interconnection between both studied sys- II, p 247 tems. This in turn calls for revision of existing conceptual Chihi L (1984) E´ tude tectonique et microtectonique du graben de models of groundwater flow in the region, postulating Kasserine (Tunisie centrale) et des structures voisines (Jebel Selloum Jebel Maargaba), D.Sc Thesis, University of Paris-Sud, significant groundwater fluxes crossing the fault in the Orsay, France direction of M-P-Q aquifer and adjacent aquifers in the Coleman ML, Shepherd TJ, Durham JJ, Rouse JE, Moore GR (1982) Wadi Al Fakka plain. Reduction of water with zinc for hydrogen isotope analysis. Anal On the management side, the presented study provides Chem 54:993–995 Clark ID, Fritz P (1997) Environmental isotopes in hydrogeology. an important hint that the Miocene aquifer currently Lewis Publishers, New York, p 328 exploited only to a very limited extent, can in future play a Craig H (1961) Isotopic variation in meteoric waters. Sciences crucial role as a groundwater resource needed for expan- 133:1702–1703 sion of agricultural activities in the area, with no risk to DGRE (2004) Annuaire d’exploitation des nappes phre´atiques. Tunis, Tunisia affect the capacities of the M-P-Q aquifer. Edmunds W, Guendouz A, Mamou A, Moulla A, Shand P, Zouari K (2003) Groundwater evolution in the Continental Intercalaire Acknowledgments The authors would like to thank IAEA and aquifer of southern Algeria and Tunisia: trace element isotopic LRAE teams for their help in performing of chemical and isotopic indicators. Appl Geochem 18:805–822

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