[en] Water resource issues constitute a major concern in arid and semiarid areas in Tunisia. To meet rising demand for different human activities considerable importance is being given to improving the natural groundwater recharge by the installation of hydraulic catchments. In central Tunisia, numerous retention sites and dams have been built since 1990, for example, the el Ogla dam in the Nadhour-Saouaf basin. In order to determine the implication of these hill reservoirs on the hydrodynamic functioning and water quality of the aquifer system, hydrochemical (major elements) and isotopic methods have been employed. The interpretation of these results showed that the shallow aquifer is recharged mainly by surface water and water dam infiltration from the el Ogla and Sahel catchments. A tentative isotopic mass balance based on stable isotope contents leads to the quantification of the artificial recharge rate, which ranges between 42% and 86% of precipitation in the humid period. (author)

[en] Southern Tunisia is characterized by the presence of several hydrogeological basins, which extend over Tunisian borders. The Continental Intercalaire aquifer is one of the most important aquifer systems in this area and contains several interconnected aquifer levels. This investigation, based on the study of stable isotope (1^8O, 2^H) contents, aims to determine the location and the altitude of recharge basin of this aquifer system. A campaign of water sampling was conducted to know the origin of waters, the conditions of old and recent recharge and the isotopic gradient. (author)

[en] The Djeffara plain located south-eastern Tunisia, is characterized by the presence of important aquifer systems. The aquifer system of Djeffara of Gabes is one of the most significant and it is formed by a shallow and deep aquifers. However, urban and industrial developments have led to a sharp increase in the exploitation of groundwater resources especially in shallow aquifer. The intensive exploitation caused a decrease in piezometric level and the deterioration of groundwater quality with the increase in salinity. This study shows that groundwater flows from El Hamma region and Matmata relief to the Mediterranean Sea in the East. The hydrochemical analyses prove that the shallow aquifer groundwater is homogeneous and characterized by a Cl-(S_O4)-Na-(Ca-Mg) water type. The water salinity increases near El Hamma sabkhas and in the coastal region. Isotopic approach using stable isotopes ( (1^8O, 2^H) ) shows that the shallow aquifer is recharged by vertical leakage from the Continental Intercalaire aquifer in El Hamma region where groundwaters are depleted in stables isotopes, and by rain water infiltration in Matmata Mountains. These isotopic values confirm also the connection between the various aquifer levels through the existing faults and prove the influence of evaporation process in shallow groundwater. (author)

[en] The Continental Intercalate and the Djeffara aquifers are the most important groundwater resources in Southern Tunisia. Previous hydrogeologic and isotopic studies (¹⁸0, ²H, ³H, ¹⁴C) allow to define the main hydrodynamic and hydrochemical characteristics for each aquifer. The Continental Intercalaire aquifer, which has important water reserves contains very old groundwater with low ¹⁴C activities and very depleted values of stable isotopes (¹⁸O, ²H). This is why this aquifer is considered as fossil and contains non renewable resources. Compared to the Continental Intercalate aquifer, Djeffara aquifer has more scattered stable isotopes values which confirms that there are different, water origins. Near to the El Hamma faults, isotopic contents of Djeffara aquifer are very similar to the isotopic signature of the Continental Intercalate, indicating mixing flows between the two systems and showing that the recharge of Djeffara of Gabes is partially ensured by the discharge of the old water of the Continental Intercalate through faults. (author)

[en] The Continental Intercalaire and the Djeffara aquifers are the most important groundwater resources in Southern Tunisia. Previous hydrogeologic and isotopic studies (¹⁸O, ²H, ³H, ¹⁴C) allow to define main hydrodynamic and hydrochemical characteristics for each aquifer. Continental Intercalaire aquifer which has important reserves is very old with low ¹⁴C activities and very depleted values of stable isotopes (¹⁸O, ²H). That is why this aquifer is considered as fossil and non renewable resources. Compared to the Continental Intercalaire aquifer, Djeffara aquifer has more scattered stable isotopes values which confirms that there are different water origins. Near to the El Hamma faults, isotopic contents of Djeffara aquifer are very similar to the isotopic signature of the Continental Intercalaire indicating mixing flows between the two systems and showing that the recharge of Djeffara of Gabes is partially ensured by the discharge of the old water of the Continental Intercalaire through faults of the region. (author)

[en] The Grombalia‘s groundwater is of a high interest because it is a major source of drinking water and irrigation in the north east of Tunisia. However, several factors indicate that the quality of its water is very poor, most notably due to high concentrations of nitrates.Water analysis showed that nitrates exceeded the WHO drinking water standard (50 mg/L)in 68% of the total samples. Such high concentrations of nitrates suggest an important leaching of substantial quantities of nitrogen-rich products into the subsoil water.The main objective of this study is to evaluate groundwater resource level, to determine groundwater quality using hydrogeochemical and isotopic tools. A total of twenty seven groundwater samples were collected from wells during February and March 2014 and analyzed for chemical and physical parameters In the present work the use of chemical and isotopic tools show a significant deterioration of groundwater quality in the whole area.The isotopic studies showed heterogeneity values of stable isotopes and show the contribution of modern rainwater in the recharge of groundwater and prove the presence of the evaporation process which increases the concentration of salts in groundwater. The values of Tritium in the groundwater samples suggest the existence of two recharge periods, pre 1950 and post 1960.

[en] The study area constitutes the major part of the plain of Jeffara, located at the south-east of Tunisia. This plain is characterized by an arid climate with rare and irregular pluviometry. The hydrochemical approach is used to define the chemical characteristics of the water in these aquifer systems. Indeed, the water salinity varies between 0.6g/? and 9g/?, and increases from the Daher mountains in the west to the Mediterranean Sea. The groundwaters are homogeneous and characterized by a Cl-(SO₄) and Na-(Ca-Mg) water type. The isotopic approach shows that the carbone-14 activities, measured in groundwater, evolve in the same direction of groundwater flow. These activities suggest a recent recharge area in eastern piedmont of the Dahar mountains, as well as the zone of the Sahel Abebsa and Zeuss-Koutine. The isotopic values confirm, also, the communication between the various major levels through the existing faults and discontinuities in this area

[en] Niger is the largest nation in West Africa (with 1.26 million km2), located between the Sahara and sub- Saharan regions without coast line. The majority of the country is covered by desert. Low precipitation (151 mm per year in 2009, World Bank 2010) and recurring droughts have made groundwater an essential water source. In the Diffa region (ca. 150 000 km2), located in south-eastern Niger and in the north-west of Lake Chad, groundwater is an important water source for the local population, together with surface water from Lake Chad and less importantly from the Komadougou Yobe River. A decreasing trend in rainfall, and hence shrinking of the area around Lake Chad, and irrigation development proposed by Nigerian authorities to meet growing food demand have led to actual and potential increases in groundwater exploitation. Moreover, water from Lake Chad has high salt content, limiting its usage. Groundwater resources in the region are found in several aquifer systems: (a) the Manga Quaternary aquifer covering nearly the entire Diffa region at 20 m to more than 50 m depth, except in a central part of the region (less than 10 m depth); (b) the alluvial aquifer located in the Komadougou valley and in topographic depressions of the region at a shallow depth (less than 10 m); (c) the Pliocene aquifer in the Pliocene sands and silts, covering the entire region at about 300 m depth in most of the region or at about 200 m in the central part; (d) the Continental Intercalary/Hamadien aquifer, covering the entire region at 40 to 60 m depth with a very low or zero recharge rate. To improve groundwater resource use and management of the potable water supply in the Diffa region, Technical Cooperation project NER8011 was conducted from 2009- 2012 to characterize the Manga Quaternary aquifer system. The project was entitled Studying the Recharge Process and the Status of Mineral Deposits Within the Manga Aquifer (Diffa region). The project was implemented by le Ministere de L'Hydraulique et de l'Environnement, Direction des Ressources en Eau of Niger

[en] Nitrate contamination still remains one of the main groundwater quality issues in several aquifers worldwide, despite the perduring efforts of the international scientific community to effectively tackle this problem. The classical hydrogeological and isotopic investigations are obviously of paramount importance for the characterization of contaminant sources, but are clearly not sufficient for the correct and long-term protection of groundwater resources. This paper aims at demonstrating the effectiveness of the socio-hydrogeological approach as the best tool to tackle groundwater quality issues, while contributing bridging the gap between science and society. An integrated survey, including land use, hydrochemical (physicochemical parameters and major ions) and isotopic (δ¹⁵N_NO3 and δ¹⁸O_NO3) analyses, coupled to capacity building and participatory activities was carried out to correctly attribute the nitrate origin in groundwater from the Grombalia Basin (North Tunisia), a region where only synthetic fertilizers have been generally identified as the main source of such pollution. Results demonstrates that the basin is characterized by high nitrate concentrations, often exceeding the statutory limits for drinking water, in both the shallow and deep aquifers, whereas sources are associated to both agricultural and urban activities. The public participation of local actors proved to be a fundamental element for the development of the hydrogeological investigation, as it permitted to obtain relevant information to support data interpretation, and eventually guaranteed the correct assessment of contaminant sources in the studied area. In addition, such activity, if adequately transferred to regulators, will ensure the effective adoption of management practices based on the research outcomes and tailored on the real needs of the local population, proving the added value to include it in any integrated investigation. - Highlights: • Effectiveness of socio-hydrogeology in groundwater quality assessment is proven. • Dual origin of nitrate contamination: fertilizers and anthropogenic organic matter. • High nitrates in the deep aquifer suggest hydraulic connections with the shallow. • Dissolution of evaporites is triggered by nitrate contamination. • Public participation provides essential information for correct data interpretation.

[en] Highlights: • Current knowledge of nitrate pollution origin in (semi)arid regions is still scarce. • New frontiers for nitrate source apportionment in (semi)arid regions are discussed. • δ¹⁵N/δ¹¹B systematics: not effective for groundwater with high B natural background. • SIAR outcomes are highly dependent on the values attributed to the sources. • Unbiased source apportionment is fundamental to support groundwater management. The assessment of nitrate pollution origin using stable isotope techniques is a fundamental prerequisite for the application of sustainable groundwater management plans. Although nitrate pollution is a worldwide groundwater quality problem, existing knowledge on the origin of nitrate pollution in arid and semi-arid regions is still scarce. Using the example of the Grombalia aquifer (NE Tunisia), this work summarizes the main strengths and constraints of multi-isotope techniques targeting at nitrate source identification and apportionment The results highlighted that, even in the case of well-established methodologies, like those of isotope hydrogeochemistry (δ¹⁵N_NO3, δ ¹⁸O_NO3 and δ ¹¹B) and mixing modelling for source apportionment, it is fundamental to take into account regional and local end-members to avoid biased data interpretation and to fully exploit the potential of such accurate tools.