Hydrochemical and statistical studies of the groundwater salinization combined with MODPATH numerical model: case of the Sfax coastal aquifer,Southeast Tunisia

Shallow groundwater is one of the main water resources in the arid and semi-arid regions. However, it is threatened by not only the reduced rainfall and recharge capacity, but also the water table drawdown and seawater intrusion. Such factors could cause a deterioration of the water quality and consequently the loss of a valuable hydraulic resource. This study aimed to improve our knowledge on the groundwater chemical quality evolution of the Sfax shallow aquifer, one of the most vulnerable areas in Tunisia, by developing a geochemical study using statistical and numerical methods. Salinization was identified by factorial analysis, PCA, and hierarchical clustering analysis in addition to the numerical MODPATH model. These findings confirmed that the groundwater quality has deteriorated due to natural and anthropogenic processes with a different influence of mineralization factors. They also revealed the location of seawater intrusion by focusing on the most vulnerable areas which are Chaffar and Djbeniana. Methodologically, the use of MODPATH model for seawater intrusion determination might be considered as the backbone for future studies in Tunisian coastal aquifers. The numerical model supports the results obtained by the geochemical analysis. Both methods are valuable tools as they contribute to trend determinations, management, and recovery plans.     

Groundwater chemical and fecal contamination assessment of the Jerba unconfined aquifer,southeast of Tunisia

Located in the southeast of Tunisia, on the Mediterranean Sea, Jerba Island has a semiarid climate condition. The surface water scarcity has made groundwater the main source to supply the domestic, touristic, and agricultural water demand. Unconfined aquifer is a vulnerable costal aquifer system that undergoes several phenomena. This work aims at assessing the geochemical and bacteriological groundwater quality, defining groundwater pollution sources and promoting sustainable development and effective management of groundwater resources in Jerba Island. Data were collected after the wet season in 2014 from 79 wells. Electric conductivity, pH, TDS, and major and fecal tracers (total coliforms, thermotolerant coliforms, Escherichia coli, and Salmonella) were analyzed. Geochemical modeling including the relationships between geochemical tracers Na⁺ vs. Cl^?, Ca²⁺ vs. Cl^?, K⁺ vs. Cl^?, representative ionic ratios (Br^?/Cl^?, Na⁺/Cl^?, Mg²⁺/Ca²⁺), and statistical analysis were used to specify major process contributing to groundwater pollution and main factors controlling groundwater mineralization in the island. Groundwater varieties were hydrochemically classified into three types in terms of salinity values: group 1 (8.86%) to fresh water, group 2 (27.84%) to brackish water, and group 3 (63.29%) belongs to saline water. In addition, groundwater quality revealed high concentrations in chemical pollution tracers (Na⁺, Cl^?, SO₄ ^2?, and NO₃ ^?) and fecal tracers. Besides, most of the sampled wells were contaminated with nitrate (50.63%). Also, thermotolerant coliforms and E. coli were detected in all groundwater samples (96.2% of wells). Results indicated that the Jerba shallow aquifer was under serious threat from both natural and anthropogenic contamination. However, the wild discharge of domestic effluents, septic tanks, and sewage were the main origins of underground water contamination in Jerba Island. The reduction of fecal sources, through constructing normalized latrines is thus recommended.     

Isotopic behavior and self-organizing maps for identifying groundwater salinization processes in Jerba Island,Tunisia

Environmental Earth Sciences - Chott Ain Beida is an inland sabkha located in southern Algeria. Close to Ouargla city, it is surrounded by an exploited palm groove. In this study, modern climate of...     

Hydrochemical characterization of groundwater using multivariate statistical analysis: the Maritime Djeffara shallow aquifer (Southeastern Tunisia)

Worldwide, groundwater resources have been considered as the main sources of drinking, domestic uses, industrial and agriculture water demands, especially in arid and semiarid regions. Accordingly, the monitoring of the groundwater quality based on different tools and methods becomes a necessity. The aim of this study was to apply several approaches to assess the water quality and to define the main hydrochemical process which affect groundwater of the Maritime Djeffara shallow aquifer. In addition to the hydrochemical approach, two multivariate statistical analyses, hierarchical clusters analysis (HCA) and principal component analysis (PCA), were carried out to identify the natural and the anthropogenic processes affecting groundwater chemistry. Hydrochemical approach, based on 47 analyzed groundwater samples, shows that most of samples present a sulfate to mixed chloride, with sodi-potassic tendency facies. According to their chemically composition, the HCA revealed three different groups (C1, C2 and C3) according to their electrical conductivity (EC) values: C1 (average EC = 4500 µS/cm), C2 (average EC = 7040 µS/cm) and C3 (average EC = 9767 µS/cm). Furthermore, PCA results show two principal factors account 84.05% of the total variance: (1) F1 represents the natural component, and (2) F2 symbolizes the anthropic component. Moreover, the groundwater quality map of the Maritime Djeffara shows three categories: suitable, doubtful and unsuitable water for irrigation. These different results should be taken to protect water resources in arid and semiarid regions, especially at the alluvial coastal regions. Also, they help to make a suitable planning to manage and protect the groundwater resources.     

Hydrochemical analysis and evaluation of groundwater quality of a Mio-Plio-Quaternary aquifer system in an arid regions: case of El Hancha, Djebeniana and El Amra regions, Tunisia

A hydrogeochemical approach has been carried out in the Mio-Plio-Quaternary aquifer system of northern Sfax to investigate the geochemical evolution, the origin of groundwaters and their circulation patterns. The groundwater samples collected from different wells seem to be dominated by sodium chloride type to sulphate chloride type. Detail analysis of chemical data including the thermodynamic calculations was used to assess that the chemical evolution of groundwater is primarily controlled by water–rock interactions. The values of sodium absorption ratio and electrical conductivity of the groundwater were plotted in the US Salinity Laboratory diagram for irrigation water. Most of the water samples in northern Sfax fall in the fields of C4S1, C4S2 and C4S3 indicating very high salinity and medium to high sodium alkalinity hazard. Thus, groundwater quality is ranging between doubtful to unsuitable for irrigation uses under normal condition, and further action for salinity control is required in remediating such problem. Principal component analysis of geochemical data used in conjunction with bivariate diagrams of major elements indicates that groundwater mineralization is mainly controlled by (1) water–rock interaction processes, (2) anthropogenic process in relation with return flow of NO₃-rich irrigation waters and (3) domestic discharges.     

Groundwater salinization processes in shallow coastal aquifer of Djeffara plain of Medenine, Southeastern Tunisia

Urban and industrial development and the expansion of irrigated agriculture have led to a drastic increase in the exploitation of groundwater resources. The over-exploitation of coastal aquifers has caused a seawater intrusion and has seriously degraded groundwater quality. The shallow coastal aquifer of the Djeffara plain, southeastern Tunisia constitutes an example of water resource suffering an intensive and uncontrolled pumping for irrigation. Intensive exploitation of the aquifer and climate aridity caused a decrease in piezometric level and an increase in salinity. According to the hydrochemical data (Cl⁻, SO₄ ²⁻, NO₃ ⁻, HCO₃ ⁻, Br⁻, Ca²⁺, Mg²⁺, Na⁺, K⁺) and the stable isotope composition (oxygen-18 and deuterium content), groundwater salinization in the investigated system is caused by three main processes: (i) salts dissolution especially in the central part of Jerba and around Medenine plain; (ii) evaporation process; and (iii) seawater intrusion which caused the increase in salinity in the peninsula of El Jorf, in Jerba and in the North of Ben Gardane.     

GIS-based evaluation of groundwater quality and estimation of soil salinization and land degradation risks in an arid Mediterranean site (SW Tunisia)

Arabian Journal of Geosciences - The present work is concerned with the valorization of clay minerals of the Aleg formation (Coniacian-middle Campanian) in the clinker manufacturing. The studied...     

Groundwater salinization of the Sfax superficial aquifer,Tunisia

Groundwater salinization has become a crucial environmental problem worldwide and is considered the most widespread form of groundwater contamination. The origin of salinity in the coastal aquifer of the Sfax Basin, Tunisia was investigated by means of chemical analyses of groundwater samples from 65 wells. The groundwater samples present a clear gradation from calcium sulphate salinization to that of sodium chloride. The saturation indices for calcite and gypsum, and binary diagrams of different ions, together with multivariate analysis, indicate the existence of various salinization processes such as: dissolution of gypsum and calcite dispersed through the reservoir rock; ion exchange; intensive agricultural practices that produce effluents that infiltrate to the saturated zone; and sea-water intrusion, enhanced by excessive withdrawal of groundwater.     

Delineation of groundwater salinization in a coastal aquifer, Bousheher, South of Iran

The geochemical processes controlling chemical composition of groundwater are studied using hydrochemical and isotopic data in Abdan-Dayer coastal plain, south of Iran. The salinity of groundwater in the coastal plain ranges from 1,000, a fresh end-member, to more than 50,000 μS cm^?1, a saline end-member. Groundwater salinity increases from the recharge area toward areas with a shallow water table close to the Persian Gulf coast due to direct evaporation and sea water intrusion as confirmed by mixing binary diagrams, stable isotope content, and Br^?/Cl^? ratio. Groundwater flow pattern in the study area has been modified due to over-pumping of groundwater in recent years which resulted in further saline water migration toward fresh water and their mixing. The maximum mixing ratio is estimated about 15% in different parts of the study area according to chloride concentration.     

Impacts of at-site wastewater disposal systems on the groundwater aquifer in arid regions: case of Sfax City, Southern Tunisia

Groundwater in Sfax City (Tunisia) has been known since the beginning of the century for its deterioration in quality, as a result of wastewater recharge into the aquifer. An average value of 12 × 10⁶ m³ of untreated wastewater reaches the groundwater aquifer each year. This would result not only in a chemical and biological contamination of the groundwater, but also in an increase of the aquifer piezometric level. Quantitative impacts were evaluated by examining the groundwater piezometric level at 57 surface wells and piezometers. The survey showed that, during the last two decades, the groundwater level was ever increasing in the urban area with values reaching 7 m in part; and decreasing in Sidi Abid (agricultural area) with values exceeding −3 m. Groundwater samples for chemical and microbial analysis were collected from 41 wells spread throughout the study area. Results showed significantly elevated levels of sodium, chlorides, nitrates and coliform bacteria all over the urban area. High levels (NO₃: 56–254 mg/l; Na >1,500 mg/l; Coliforms >30/100 ml) can be related to more densely populated areas with a higher density of pit latrine and recharge wells. Alternatively results showed a very variable chemical composition of groundwater, e.g. electrical conductivity ranges from 4,040 to19,620 μs/cm and the dry residual varies between 1.4 and 14 g/l with concentrations increasing downstream. Furthermore a softening of groundwater in Set Ezzit (highly populated sector) was observed.     

Groundwater recharge and salinization in the arid coastal plain aquifer of the Wadi Watir delta,Sinai, Egypt

The Quaternary coastal plain aquifer down gradient of the Wadi Watir catchment is the main source of potable groundwater in the arid region of south Sinai, Egypt. The scarcity of rainfall over the last decade, combined with high groundwater pumping rates, have resulted in water-quality degradation in the main well field and in wells along the coast. Understanding the sources of groundwater salinization and amount of average annual recharge is critical for developing sustainable groundwater management strategies for the long-term prevention of groundwater quality deterioration. A combination of geochemistry, conservative ions (Cl and Br), and isotopic tracers (^87/86Sr, δ⁸¹Br, δ³⁷Cl), in conjunction with groundwater modeling, is an effective method to assess and manage groundwater resources in the Wadi Watir delta aquifers. High groundwater salinity, including high Cl and Br concentrations, is recorded inland in the deep drilled wells located in the main well field and in wells along the coast. The range of Cl/Br ratios for shallow and deep groundwaters in the delta (∼50–97) fall between the end member values of the recharge water that comes from the up gradient watershed, and evaporated seawater of marine origin, which is significantly different than the ratio in modern seawater (228). The ^87/86Sr and δ⁸¹Br isotopic values were higher in the recharge water (0.70,723 < ^87/86Sr < 0.70,894, +0.94 < δ⁸¹Br < +1.28‰), and lower in the deep groundwater (0.70,698 < ^87/86Sr < 0.70,705, +0.22‰ < δ⁸¹Br < +0.41‰). The δ³⁷Cl isotopic values were lower in the recharge water (−0.48 < δ³⁷Cl < −0.06‰) and higher in the deep groundwater (−0.01 < δ³⁷Cl < +0.22‰). The isotopic values of strontium, chloride, and bromide in groundwater from the Wadi Watir delta aquifers indicate that the main groundwater recharge source comes from the up gradient catchment along the main stream channel entering the delta. The solute-weighted mass balance mixing models show that groundwater in the main well field contains 4–10% deep saline groundwater, and groundwater in some wells along the coast contain 2–6% seawater and 18–29% deep saline groundwater.A three-dimensional, variable-density, flow-and-transport SEAWAT model was developed using groundwater isotopes (⁸⁷Sr/⁸⁶Sr, δ³⁷Cl and δ⁸¹Br) and calibrated using historical records of groundwater level and salinity. δ¹⁸O was used to normalize the evaporative effect on shallow groundwater salinity for model calibration. The model shows how groundwater salinity and hydrologic data can be used in SEAWAT to understand recharge mechanisms, estimate groundwater recharge rates, and simulate the upwelling of deep saline groundwater and seawater intrusion. The model indicates that most of the groundwater recharge occurs near the outlet of the main channel. Average annual recharge to delta alluvial aquifers for 1982 to 2009 is estimated to be 2.16 × 10⁶ m³/yr. The main factors that control groundwater salinity are overpumping and recharge availability.     

The groundwater discharge in the Mediterranean karst coastal zones and freshwater tapping: set problems and adopted solutions. Case studies

In the karstic regions of the Mediterranean coastal zones the groundwater discharge and its outcrops—the coastal and submarine springs—represent the most typical natural phenomena of littoral karst, the economic potential of which is significant. The case studies discussed in this paper concern the problems of freshwater tapping in karst coastal zones along the Mediterranean littoral. Owing to the geological and hydrogeological approach, the set problems and adopted solutions involve two most important tasks: (1) the regulation of groundwater flow in the tapping facilities and (2) the control system of saltwater encroachment in a larger protection zone, between the coast and the site of tapping facilities.     

Assessment of groundwater salinity using GIS and multivariate statistics in a coastal Mediterranean aquifer

The integration of the statistical approaches and GIS tools with the hydrogeological and geological contexts allowed the assessment of the processes that cause groundwater quality deterioration in the great important deltaic aquifer in the northeastern Tunisia (Medjerda Lower Valley Aquifer). The spatial variation of the groundwater parameters and the molar ratio (Cl^?/Br^?) were also used to determine the possible impacts from seawater intrusion and from the septic tank leachate. Sixty shallow groundwater samples were collected in 2014 and analyzed for major and trace ions over an area of about 1090 km² to determine the suitability for drinking or agricultural purposes. The total dissolved solids (TDS) content ranges from 1005 to 19,254 mgl^?1 with a mean value of 3477.18 mgl^?1. The chemistry is dominated by the sodium–chloride waters (55%). Mapping of TDS, Cl^?, Na⁺, SO₄^2? and NO₃^? using kriging method shows a clear increase in salinity toward the coastline accompanied by Na⁺ and Cl^? increase which may be related to seawater intrusion and halite dissolution. Locally, higher nitrate concentration is related to the agricultural activities inducing contribution of chemical fertilizers and irrigation with treated wastewater. The saturation indices indicate that all carbonate minerals tend to reach saturation equilibrium confirming water–rock interactions, while evaporitic minerals are still in sub-saturation state and may increase the salinity of the groundwater. The principal component analysis proves the occurrence of groundwater contamination principally by seawater intrusion in the factor I (74.15%) and secondary by an anthropogenic source in the factor II (10.35%).     

Assessing groundwater vulnerability to nitrate pollution using statistical approaches: a case study of Sidi Bouzid shallow aquifer,Central Tunisia

The study region comprises the Sidi Bouzid shallow aquifer, which is located in the western part of Central Tunisia. It is mainly occupied by agricultural land with intensive use of chemical fertilizers especially nitrates. For this reason, nitrate measurement was performed in 38 water samples to evaluate and calibrate the obtained models. Several environmental parameters were analyzed using groundwater nitrate concentrations, and different statistical approaches were applied to assess and validate the groundwater vulnerability to nitrate pollution in the Sidi Bouzid shallow aquifer. Multiple linear regression (MLR), analyses of covariance (ANCOVA), and logistic regression (LR) were carried out for studying the nitrate effects on groundwater pollution. Statistical analyses were used to identify major environmental factors that control the groundwater nitrate concentration in this region. Correlation and statistical analyses were conducted to examine the relationship between the nitrate (dependent variable) and various environmental variables (independent variables). All methods show that “groundwater depth” and “land use” parameters are statistically significant at 95% level of confidence. Groundwater vulnerability map was obtained by overlaying these two thematic layers which were obtained in the GIS environment. It shows that the high vulnerability area coincides with the likelihood that nitrate concentration exceeds 24.5 mg/l in groundwater. The relationship between the groundwater vulnerability classes and the nitrate concentrations provides satisfactory results; it showed an Eta-squared correlation coefficient of 64%. So, the groundwater vulnerability map can be used as a synthetic document for realistic management of groundwater quality.     

Application of multivariate statistical procedures on major ions and trace elements in a multilayered coastal aquifer: the case of the south Rhodope coastal aquifer

Multivariate statistical techniques including cluster analysis and principal components analysis were applied on 22 variables consisted of 3 physicochemical parameters, 8 major ions and 11 trace elements. Samples were collected from the south Rhodope multilayered coastal aquifer in north Greece which is facing saltwater intrusion and anthropogenic contamination over the last 35 years. Cluster analysis grouped the variables into five main groups while principal components analysis revealed four distinct hydrochemical processes in the aquifer system, explaining 84.5 % of the total variance between the variables. The identified processes correspond to, saltwater intrusion and subsequent reverse cation exchange, the presence of deep connate groundwater masses, application of fertilizers in shallow wells and anthropogenic contamination with heavy metals nearby an improperly constructed landfill. The wells categorized with the above techniques were grouped and five constituent ratios Na/Cl, (Mg + Ca)/Cl, Ca/(HCO₃ + SO₄), Ca/SO₄ and Ca/Mg were utilized to identify the ones which enable the more accurate distinction between the group cases. The results of stepwise discriminant analysis showed that the calculated classification function can distinguish almost 80 % of groundwater samples with the Na/Cl ratio being the most statistically significant grouping variable. All the aforementioned statistical models managed to successfully identify numerous hydrochemical processes in a complex multilayered aquifer system and to explicitly attribute them for every investigated well, allowing a deeper insight into groundwater chemical characteristics with the use of an optimized smaller number of variables.     

Understanding the origin of salinization of the Plio-quaternary eastern coastal aquifer of Cap Bon (Tunisia) using geochemical and isotope investigations

As in many other semi-arid regions, the Plio-quaternary aquifer of the eastern coast of Cap Bon peninsula (NE Tunisia) shows a parallel increase in overexploitation and mineralization of groundwater resources and so the water quality is deteriorating. Different methods using geochemistry (ions Na⁺, Cl⁻, Ca²⁺, Mg²⁺, Br⁻) and stable isotopes (¹⁸O, ²H) are compared with the hydrodynamic information for identifying the main processes involved in the increase of salinization. Along the coast, intrusion of seawater resulting from groundwater overexploitation is identified, but is not the only cause of qualitative degradation: the development of irrigation that induces soil leaching and transfer of fertilizers to groundwater over the whole aquifer extent is another major reason for the increase in salinization. A total of 48 groundwater wells were sampled to obtain additional information on the hydrochemical characteristics of the groundwater defined in previous studies.     

Geochemistry and quality assessment of groundwater using graphical and multivariate statistical methods. A case study: Grombalia phreatic aquifer (Northeastern Tunisia)

The Grombalia coastal aquifer, situated in Northeastern Tunisia, is a water source for public, agricultural, and industrial supplies in the region. The overexploitation of this aquifer, since 1959, and the agriculture activities led to the degradation, by places, of the water quality. The present study implemented graphical, modeling, and multivariate statistical tools to investigate natural and anthropogenic processes controlling Grombalia groundwater mineralization and water quality for promoting sustainable development. To attempt this goal, groundwater was collected from 33 observation wells in January 2004, and samples were analyzed for 10 physicochemical parameters (temperature, pH, salinity, Na⁺, Ca²⁺, K⁺, Mg²⁺, Cl^?, HCO^3?, and SO ₄ ^2? ). Hydrochemical facies using Piper diagram indicates a predominance of a mixed facies, of the Na-Cl-HCO₃ type, or Na-Ca-Cl-SO₄ type, and, with less expansion, Na Cl type. The main factors controlling Grombalia groundwater mineralization seem to be mineral dissolution of highly soluble salts especially, the halite dissolution existing in the surface salty deposits and, with less importance, the ion exchange and reverse ion exchange process with clay minerals existing in the aquifer. The comparison of the major ions of the Grombalia groundwater, with the World Health Organization norms of potability (WHO 2004), reveals that these waters cannot be used for human consumption without any treatment. Most waters of the Grombalia aquifer, with a relatively high salinity, are not suitable for irrigation, in ordinary conditions. Nevertheless, they can be used for permeable soils, with an adequate drainage and applying an excess of leaching water.     

唐山曹妃甸浅层地下水水化学特征及咸化成因

为了查明曹妃甸浅层地下水水化学及咸化成因,采集研究区河水、地下淡水、微咸水、咸水、卤水、雨水和海水等不同类型水样,对其水化学组成、离子比、Piper三线图、吉布斯图、氢氧同位素组成及14C测年结果进行了分析。结果表明：(1)曹妃甸浅层地下水包括全新世沉积层潜水和晚更新世沉积层微承压水,且非原始封存在地层中而是形成于全新世中晚期。(2)地下潜水向海方向分布有淡水、微咸水、咸水水质类型,微承压水以咸水和卤水为主要水质类型;近冲洪积扇前缘水化学特征主要受岩石风化作用控制,围填海区及河口处水化学特征受海水混合作用控制,滨海平原区水化学特征主要受蒸发/结晶作用控制。(3)曹妃甸浅层地下水咸化过程主要是晚更新世以来海侵海退时期形成海洋蒸发盐经大气降水和河水多期溶滤所致,其盐分来源于海水蒸发盐,河口及围填海区地下潜水盐分主要来源于现代海水入侵。