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Major ions hydrochemistry and isotopic data ( 18 O, 2 H, 3 H, 14 C) have been used to improve the understanding of mineralisation processes, origins, and circulation patterns of groundwaters of the Bou Hafna and Haffouz region in Central Tunisia. Hydrochemical investigation indicates that the salinity in groundwater, which varies greatly from 0.2 to 1.3 g/l, results mainly from the dissolution of evaporates (halite, gypsum and anhydrite), cation exchange and dedolomitization processes. The use of stable isotopes tracers (d 18 O, d 2 H) has classified groundwaters samples into two groups. The non-evaporated groundwaters are distinguished by relatively depleted isotope contents, highlighting significant recharge at higher altitudes. The evaporated groundwaters are characterized by enriched d 18 O and d 2 H contents, reflecting the contribution of return flow of irrigation waters to the recharge of the studied aquifer system. Tritium contents, varying from 0.03 to 1.23 UT, provide evidence of the presence of two sources of recharge that correspond to pre-nuclear recharge, and to a mixture between pre-nuclear water and the contemporaneous recharge. The 14 C activities, ranging between 7.4 and 78.6 pmc, identify two groundwater groups. The first group is dominated by the direct infiltration of present day meteoric water at higher altitude. The second group is formed by a mixture of recent and palaeoclimatic groundwaters. [ABSTRACT FROM AUTHOR]

Groundwaters from the intermediate aquifer of Sfax basin have been investigated using chemical tracers and environmental isotopes to reveal the hydrogeological features of this system and characterize the dynamics of groundwater salinization in this sector. The origin of salinity in the studied aquifer was investigated based on the chemical analyses of 30 groundwater samples. Groundwater is characterized by Na-Cl and Na-SO water types. The saturation indices for calcite and gypsum, and binary diagrams of different ions showed that the main hydrogeochemical processes were the dissolution of carbonates (mainly calcite scattered through the reservoir rocks), the dissolution of evaporites (halite, gypsum and anhydrite) and the cation exchange processes. The isotopic composition investigation allowed the definition of two groups. The first group is represented by groundwater with the highest oxygen-18 content (δO ranges between −5.36 and −4.22 ‰, and δH ranges between −39.2 and −36 ‰). The high δO values in this group can be attributed to the evaporation effect. The second group includes the most depleted waters (δO varies between −6.84 and −5.79 ‰, and δH varies between −42.4 and −36.5 ‰). The combined analyses of stable isotopes and major ions (Cl) showed that mixing between old and recent water and evaporation were the main processes explaining the variation of salinity of the intermediate aquifer of the Sfax basin. [ABSTRACT FROM AUTHOR]

The groundwater of the Korba plain represents major water resources in Tunisia. The Plio-Quaternary unconfined aquifer of the Cap-Bon (north-east Tunisia) is subject to the intensive agricultural activities and high groundwater pumping rates due to the increasing of the groundwater extraction. The degradation of the groundwater quality is characterized by the salinization phenomena. Groundwater were sampled and analysed for physic-chemical parameters: Ca2+, Mg2+, Na+, K+, Cl-, SO42-, HCO3-, NO3-, pH, electrical conductivity (EC), and the temperature (T°). The hydrochemical analysis is coupled with the calculation of the saturation indexes (SI gypsum, SI halite, SI calcite and SI dolomite), ionic derivation and with the ion correlations compared to chloride concentrations: Na+/ Cl-, Ca2+/ Cl- and Mg2+/ Cl- ratios. Seawater fractions in the groundwater were calculated using the chloride concentration. Those processes can be used as indicators of seawater intrusion progression. EC methods were also conducted to obtain new informations on the spatial scales and dynamics of the fresh water-seawater interface of coastal groundwater exchange. The mixing zone between freshwater and saltwater was clearly observed from the EC profile in the investigated area where a strong increase in EC with depth was observed, corresponding to the freshwater and saltwater interface. Results of hydrochemical study revealed the presence of direct cation exchange linked to seawater intrusion and dissolution processes associated with cations exchange. These results, together with EC investigation, indicated that the groundwater is affected by seawater intrusion and is still major actor as a source of salinization of the groundwater in Korba coastal plain. Further isotopic and hydrological investigations will be necessary to identify and more understood the underlying mechanisms. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The determination of the origin of the salinity in the Zeroud aquifer (central of Tunisia) and the understanding of its hydrogeological and geochemical behaviors related to severe natural and anthropogenic constraints were approached by the combined survey of major element concentrations and stable isotopes (O, H). The hydrogeochemical investigations of the Zeroud aquifer show that groundwaters can be classified into two major water facies: Ca-SO-Cl and Na-Cl. The main hydrogeochemical processes that typically control the groundwater mineralization are dissolution of evaporates (halite, gypsum and anhydrite), dedolomitization, cation exchange and mixing processes related to the return flow of irrigation waters and the artificial recharge operations. The stable isotope signatures reveal that the first significant recharge origin is related to the direct infiltration of actual meteoric water particularly observed in the foot of hills bordering the basin and in the vicinity of the Zeroud Wady. A main part of groundwater is significantly affected by evaporation, giving evidence of a recharge mostly from the dam water during the artificial recharge operations. Moderated evaporation of waters was observed in the southern part of the basin, especially in the agricultural areas. [ABSTRACT FROM AUTHOR]

Detailed hydrogeochemical and isotopic data of groundwaters from the Hammamet-Nabeul unconfined aquifer are used to provide a better understanding of the natural and anthropogenic processes that control the groundwater mineralization as well as the sources of different groundwater bodies. It has been demonstrated that groundwaters, which show Na-Cl and Ca-SO-Cl water facies, are mainly influenced by the dissolution of evaporates, the dedolomitization and the cation-exchange process; and supplementary by anthropogenic process in relation with return flow of irrigation waters. The isotopic signatures permit to classify the studied groundwaters into two different groups. Non-evaporated groundwaters that are characterized by depleted δO and δH contents highlighting the importance of modern recharge at higher altitude. Evaporated groundwaters with enriched contents reflecting the significance infiltration of return flow irrigation waters. Tritium data in the studied groundwaters lend support to the existence of pre-1950 and post-1960 recharge. Carbon-14 activities in shallow wells that provide evidence to the large contamination by organic C corroborate the recent origin of the groundwaters in the study area. [ABSTRACT FROM AUTHOR]

In the Grombalia region, Cap Bon Peninsula, northeastern Tunisia, increasing population and development of agricultural activity during the last few decades have engendered large expansion of groundwater pumping from the shallow, unconfined aquifer. Recently, the water table has displayed some signs of overexploitation such as decline in the water level in boreholes and considerable deterioration of water quality. Hydrochemical and isotopic data were used in conjunction with hydrogeological characteristics to investigate the groundwater composition in this aquifer. It has been demonstrated that groundwaters, recharged mainly in the surrounding foothills, acquire their mineralization principally by water–rock interaction, i.e., dissolution of evaporites and reverse cation exchange, and secondarily by return flow of irrigation waters. The isotopic signature of groundwaters permits identification of two different types. Water with depleted δO and δH contents is interpreted as recharge by non-evaporated rainfall, originating from a mixture of Atlantic and Mediterranean air masses. However, water with relatively enriched δO and δH contents is thought to reflect contamination by return flow of irrigation waters. Tritium contents, ranging between 1.2 and 4.5 TU indicate that groundwaters in an unconfined aquifer derive from post-nuclear recharge or contain a significant component of post-1950s water. The recent origin of these groundwaters is confirmed by the high carbon-14 activities, exceeding sometimes 100%, indicating the existence of a significant fraction of organic C. This younger source of radiocarbon is, however, highlighted by the depleted δC contents, corresponding to a system where CO of C4 plants predominates. [ABSTRACT FROM AUTHOR]

Hydrochemistry of groundwater is largely determined by both natural processes, such as dissolution, cation exchange, mixing, evaporation; and anthropogenic activities, which can affect the aquifer systems by contaminating them or by modifying their hydrological cycle. Both natural and anthropogenic processes vary in time and space; which is reflected in groundwater hydrochemistry variation. The objective of this study is the determination of the main hydrogeochemical processes that affect the quality of shallow groundwaters in the Grombalia basin, located in the Cap Bon Peninsula, north-eastern Tunisia. In this area, the chemical composition of groundwater is mostly characterized by Na–Cl–NO3–Ca water type which reveals the implication of natural and anthropogenic major factors. Natural factors are dissolution of evaporatic minerals, i.e. halite and gypsum and cation exchange with clays, while anthropogenic factors are pollution with industrial Sr-rich waste water and return flow of irrigation water, highly contaminated by MgSO4 and methyl-bromide fertilizers. [ABSTRACT FROM AUTHOR]