Gabes Region Research Articles

Hydrochemical and statistical study of groundwaters in Gabes-south deep aquifer (south-eastern Tunisia)

Groundwater quality assessment is important to ensure sustainable safe use of water. In the region of Gabes, groundwaters represent the main source of water supply for drinking, agriculture and industry seeing the shortage in surface water. In the present paper, an attempt has been made, for the first time in this region, to study the spatial and temporal evolution of the hydrochemistry and to identify factors and phenomena governing the assessment parameters of Gabes-south groundwaters quality, based on (1) an integrated analysis of physical–chemical parameters (2) use of Geological Information System (GIS) and (3) statistical methods. To this purpose, water samples were collected during the period of 1995–2003 from nine boreholes to represent Gabes-south deep aquifer. The water samples were investigated with respect to salinity, concentrations of hydrogen (pH), calcium (Ca 2+), magnesium (Mg 2+), sodium (Na +), potassium (K +), chloride (Cl −), sulphate, SO 4 2 - , bicarbonates HCO 3 - and fluoride (F −). Spatial distribution maps of these parameters have been created using GIS contouring methods with Arcview 3.2. The analytical results obtained were interpreted using hydrochemical methods reinforced by statistical analysis (trend analysis, principal component analysis and correspondence analysis) which has been widely used to analyse large sets of variables in environmental studies. Chemical analysis show that during the considered period, salinity and major elements concentrations vary little with time, and decrease in the direction of the groundwater flow. The waters are mostly SO 4, Cl, Na and Ca type. The chemical composition of these waters is related to the lithology of the aquifer, to their origin and to the exploitation conditions. Water quality analysis indicates that Gabes-south groundwaters are mainly composed of SO 4, Cl, Na and Ca type. Results showed that fluoride concentrations exceed the World Health Organisation (WHO) maximum permissible limit of 1.5 mg/l. Therefore, the water of these boreholes must be defluorinated before use for drinking.

Comparative study of the sensitivity to cadmium of two populations of Gambusia affinis from two different sites

This study aims to demonstrate the influence of animals' origin on their sensitivity toward heavy metals. For this purpose, we compared LC(50) of cadmium in two populations of Gambusia affinis captured in two geographically isolated environments in the east of Tunisia; Oued El Gsil in the city of Monastir (S2) and Oued Chenini in the region of Gabes (S1). Although physicochemical parameters of the water (pH, dissolved oxygen and salinity) are similar in the two studied sites, cadmium concentrations in water, sediments and fish tissues from S1 are significantly higher (P < 0.01) than those from S2, 48-h and 96-h LC(50) of the (S1) population are significantly higher than those from S2. In the same way, the offspring of the polluted site (S1) population exhibit 48-h and 96-h LC(50) values much higher than those of the reference site (S2) population. These results show that the population of the Gabes region is more resistant to cadmium than that of the Monastir region and that this resistance could have a genetic basis. These results indicate the influence of the origin of animals that has to be taken into account not only in laboratory toxicity tests, but also in field ecotoxicological studies.