Evaluation of groundwater quality for irrigation purpose in the south-eastern of Tunisia (Menzel Habib area)

Groundwater is considered an important water source for agricultural uses in many regions of the world including Menzel Habib area, south-eastern Tunisia. Indeed, groundwater availability and quality became crucial in agricultural activities. Thus, pH, Electrical Conductivity (EC), Total Dissolved Solids, SO4, Cl, HCO3, Na, Ca, Mg and K were determined in 39 selected groundwater samples. The obtained results indicate that sulfate is the dominant anion, while sodium is the dominant cation. The groundwater samples from Menzel Habib aquifer system are characterized by Na-Cl, Na-SO4 and mixed water types. The suitability of groundwater for irrigation was determined on the basis of various parameters such as: sodium adsorption ratio (SAR), % Na, Kelly ratio (KR), magnesium adsorption ratio (MAR) and permeability index (PI). The Kelly ratio results indicate that 61.5% of groundwater samples are unsuitable to irrigation due to surplus (> 1) sodium content. The MAR ratio demonstrates that only 8% of groundwater samples fall in bad category. However, relatively to the % Na, 18% of groundwater samples are classified as good, 49% as permissible and 33% as doubtful for irrigation purposes. Groundwater from Menzel Habib aquifer were plotted on the USSL classification based on SAR and EC and are distributed as: 8% on the area of C4S2 (high salinity and medium alkalinity), 2.5% on the C4S3 (High salinity and high alkalinity) field, 23% on the C5S2 (very high salinity and medium alkalinity) area, 10% on the C5S3 (very high salinity and high alkalinity) area and 56.5% is on the unclassified group (EC > 10000µS/cm and SAR > 32)

Groundwater quality for irrigation in an arid region-application of fuzzy logic techniques

Groundwater is the main source to answer the irrigation supply in several arid and semi-arid areas. In the present work, groundwater quality for irrigation purposes in the arid region of Menzel Habib (Tunisia) for thirty-six groundwater samples is assessed considering the application of different conventional water quality indicators, particularly, electrical conductivity (EC), sodium absorption ratio (SAR), soluble sodium percentage (SSP), magnesium adsorption ratio (MAR), Kelly ratio (KR), and permeability index (PI). The results obtained indicate a variability for EC: 3.06 to 14.98 mS.cm-1; SAR: 4.08 to 19.30; SSP: 35.78 to 71.53%; MAR: 34.19 to 56.01; PI: 38.47 to 72.74; and KR: 0.56 to 2.47. These results suggest that groundwater from Menzel Habib aquifer system is classified between excellent to unsuitable according to the applied water quality indices. Furthermore, the groundwater samples are also plotted in the Richards diagram classification system, based on the relation between SAR and EC, suggesting that almost groundwater samples present a harmful quality. Moreover, fuzzy logic model has been proposed and created to assess groundwater quality for irrigation. The membership functions are constructed for six significant parameters such as EC, SAR, SSP, MAR, KR, and PI and the rules are, then, fired to get a simple Fuzzy Irrigation Water Quality Index (FIWQI). The obtained groundwater quality results suggest that 3% of the samples from Menzel Habib region are considered as "good" for irrigation, 3% are classified as "good to permissible", 33% with a "permissible" quality, 36% "permissible to unsuitable", while 25% of groundwater present an "unsuitable" quality. Thus, the use of fuzzy logic techniques has more reliable and robust results by overcoming the uncertainties in the decision-making attributed to the conventional methods by the creation of new classes (excellent to good, good to permissible, and permissible to unsuitable) in addition to the classes proposed by Richards diagram classification (excellent, good, permissible, and unsuitable) to assess the groundwater quality suitability for irrigation purposes.This research was developed under the FCT–Fundação para a Ciência e a Tecnologia, I.P. program, through the project’s reference UIDB/04683/2020 and UIDP/04683/2020

Investigating aquifer vulnerability employing DRASTIC model and GIS techniques in Menzel Habib Shallow Aquifer, South-Eastern Tunisia

Groundwater vulnerability assessment shows an extreme sensitivity to in situ anthropogenic pollutants. A dichotomous assessment of geological and hydrological (inter alia) characteristics makes it possible to determine the vulnerability of an aquifer system. The natural vulnerability of an aquifer can be severely compromised by human activities. The physical structure and material composition of aquifers shows resistance to contaminants transport from surface to groundwater. Currently, numerous methods have been posited evaluating aquifer's vulnerability. Similarly, the DRASTIC and DRASTIC pesticides models utilize computer algorithms and hydro-geological data within a Geographical Information System (GIS) to compute spatial aquifer vulnerability. The DRASTIC and DRASTIC pesticides models are constructed using combined spatial datasets on Depth to groundwater (D), Aquifer Recharge (R), Aquifer media (A), Soil media (S), Topography (T), Impact of the Vadose Zone (I) and Hydraulic Conductivity (C) of the aquifer. The degree of vulnerability of the aquifer system can be evaluated by computing sensitivity analysis of DRASTIC index using GIS, showing the contribution of each parameter to vulnerability sensitivity. The GIS was used to develop a vulnerability map for Menzel Habib aquifer area. The obtained results indicated that moderately vulnerable areas are of 5%, while areas of no risk correspond to 95% using DRASTIC index. Otherwise, DRASTIC pesticide index indicated that 15% area of low vulnerability, 84% moderately vulnerable and 1% high vulnerability. The central area of Menzel Habib aquifer showed a low vulnerability due to dense human settlement and a deeper water level. However, agricultural areas recorded high vulnerability risk. Menzel Habib's environmental and socio-economic development is dependent on policy makers and planner's ability to use information effectively for decision making. The obtained groundwater vulnerability maps provide a basis for this aimed at protecting the aquifer from pollutants. Additionally, land use and development activities can be informed by mapping variables, showing that agriculture areas are highly vulnerable as compare to settlement areas

Sustainability and management of the Menzel Habib Aquifer System, Southeastern Tunisia

In arid and semi-arid areas, the water quantity and quality is a great problem. Salinzation is the major threat in the region of Menzel Habib (north-western Gabès, southeastern Tunisia). The region is a large basin which is essentially represented by sandy-clay formations and bordered by cretaceous reliefs. Geochemical and statistical approaches are reported in the Menzel Habib Aquifer system to examine groundwater salinization processes and factors controlling its mineralization. Geochemical studies were developed in 25 groundwater samples from the shallow aquifer to identify the origin of groundwater salinization. Groundwater geochemistry shows a high correlation between salinity and Na, Cl, Ca, Mg and SO4. These elements are mainly associated to the evaporitic Triassic by dissolution of halite, anhydrite and gypsum which occur on the area and is related to the tectonic context of the region. Additionally, bivariate diagram beween Na and Cl, and Ca and SO4 have also provided a comprehensive understanding of other salinization processes that are involving in Menzel Habib shallow aquifer such as cation exchange and reverse cation exchange

Groundwater vulnerability assessment in Menzel Habiba area, South-Eastern Tunisia

Groundwater vulnerability assessment has become a useful tool for groundwater management. Hydrogeological characteristics influence the natural (intrinsic) vulnerability of an aquifer system. However, the natural vulnerability can be severely compromised by anthropogenic influence (extrinsic vulnerability). The physical structure and material composition of aquifers show resistance to contaminants transport from surface to groundwater. Currently, numerous methods have been posited evaluating aquifer's vulnerability. Similarly, the DRASTIC and DRASTIC pesticides models utilize computer algorithms and hydro-geological data within a Geographical Information System (GIS) to compute spatial aquifer vulnerability. The DRASTIC and DRASTIC pesticides models are constructed using combined spatial datasets on: Depth to groundwater (D), Aquifer Recharge (R), Aquifer media (A), Soil media (S), Topography (T), Impact of the Vadose Zone (I) and Hydraulic Conductivity (C) of the aquifer. The degree of vulnerability of the aquifer system can be evaluated by computing sensitivity analysis of DRASTIC index using GIS, showing the contribution of each parameter to vulnerability sensitivity. The GIS was used to develop a vulnerability map for Menzel Habib aquifer area. The obtained results indicated that moderately vulnerable areas are of 5%, while areas of no risk correspond to 95% using DRASTIC index. Otherwise, DRASTIC pesticide index indicated that 15% area of low vulnerability, 84% moderately vulnerable and 1% high vulnerability. The central area of Menzel Habib aquifer showed a low vulnerability due to dense human settlement and a deeper water level. However, agricultural areas recorded high vulnerability risk. Menzel Habib's environmental and socio-economic development is dependent on policy makers and planner's ability to use information effectively for decision making. The obtained groundwater vulnerability maps provide a basis for this aimed at protecting the aquifer from pollutants. Additionally, land use and development activities can be informed by mapping variables, showing that agriculture areas are highly vulnerable as compare to settlement areas

Integration of water contamination indicators and vulnerability indices on groundwater management in Menzel Habib area, south-eastern Tunisia

Groundwater salinization is a major problem throughout arid and semi-arid areas due to different natural processes and anthropogenic activities and has caused irreparable environmental and economic effects. The objective of this study is to evaluate groundwater vulnerability of Menzel Habib which has been firstly assessed using multiple methods such as DRASTIC, DRASTIC pesticide, SINTACS and SI models. These indices are based on combination of intrinsic and specific characteristics of the aquifer. Almost the area presents a low to moderate vulnerability with the highest vulnerability on the western region, associated to lower deep of groundwater and evaporation processes, with consequent salinity increase. Total Dissolved solids, chloride, sodium, sulfate, calcium, and magnesium water contents were determined in a total of twenty-five groundwater samples from Menzel Habib aquifer. The accuracy of the best robust model was evaluated by the correlation between the different vulnerability indices and contamination water indicators. The main aim of this study is the development of a modified vulnerability index, DRASTIC_Sal, which includes the contribution of total dissolved solids from Menzel Habib groundwater. DRASTIC_Sal index is a simple approach for aquifer salinization vulnerability assessment, particularly for inland aquifers from arid and semi-arid regions with associated agricultural activities.The authors would like to acknowledge to the technical staff at the Laboratory Applied Hydrosciences Research Unit of Higher Institute of Water Sciences and Techniques of Gabe`s (Tunisia) for their help to produce this paper. This research was developed under the FCT - Fundacao para a Ciencia e a Tecnologia, I.P. program, through the projects reference UIDB/04683/2020 and UIDP/04683/2020

Geochemical processes of groundwater salinization in an arid area, southeastern Tunisia

Groundwater salinization is a major problem throughout arid and semi-arid areas due to different natural processes and anthropogenic activities and has caused irreparable environmental and economic effects. Groundwater vulnerability of Menzel Habib has been firstly assessed using multiple methods such as DRASTIC, DRASTIC pesticide, SINTACS and SI models. These indices are based on combination of intrinsic and specific characteristics of the aquifer. Almost the area presents a low to moderate vulnerability with the highest vulnerability on the western region, associated to lower deep of groundwater and evaporation processes, with consequent salinity increase. Total Dissolved solids (TDS), chloride, sodium, sulfate, calcium and magnesium water contents were determined in a total of twenty-five groundwater samples from Menzel Habib aquifer. The accuracy of the best robust model was evaluated by the correlation between the different vulnerability indices and contamination water indicators. On the Menzel Habib aquifer area, a modified vulnerability index called DRASTIC_Sal was applied including total dissolved solids water content. This index is a simple and transparent approach for salinization vulnerability assessment of aquifers, particularly inland aquifers from arid and semi-arid regions with associated agricultural activities.This work is co-funded by the national Funds provided by FCT - Fundacao para a Ciencia e a Tecnologia, I. P., with the projects UIDB/04683/2020 and UIDP/04683/2020

Management of groundwater salinization under a climate change scenario in an aridarea

Most future scenarios for water resources are predicting water scarcity, with a decrease in the amount of precipitation and limitation on groundwater recharge for the next five decades. In arid and semi- arid areas, the water quality is a great problem and groundwater salinization is one of the principal causes of degradation of water resources worldwide. Menzel Habib aquifer is located in the northwest of Gabès region (southeastern Tunisia), included in the arid Mediterranean bioclimatic area, with dry hot summers and relatively warm winters. Groundwater geochemistry from the study area shows a Na-Cl and Ca-Mg-Cl-SO 4 dominant facies. The high groundwater mineralization and its correlation between total dissolved solids and major ions suggest a contribution of SO4, Cl, Na, Ca, and Mg in groundwater salinization processes. The salinization of groundwater is mainly associated with the Triassic evaporites, with the dissolution of halite, anhydrite and gypsum, occurring in the area, and related to the tectonic context of the region. Additionally, other geochemical processes occurred, such as the cation exchange mechanisms. Changes in precipitation patterns and intensity, with water scarcity, low recharge, and excessive pumping have affected groundwater quantity and quality. Nowadays, the occurrence of climate change scenarios is a major drawback for water use for irrigation and drinking water supply in arid and semi-arid regions, such as the Menzel Habib aquifer

Hydrogeochemical processes on inland aquifer systems: A combined multivariate statistical technique and isotopic approach

Groundwater is an important resource used for multiple purposes and should be protected, especially, in semi-arid and arid regions. The aim of this study is to assess the main processes on groundwater salinization from Menzel Habib shallow and deep aquifers, southeastern Tunisia, which could be applied to further groundwater quality assessment. Indeed, there were used combined hydrogeochemical (major elements) and isotopic fingerprints (18O, 2H) data approaches using multivariate statistical methods, highlighting, Hierarchical Clustering Analysis and Principal Component Analysis. A total of 36 groundwater samples were collected from the Menzel Habib aquifer system: twenty-five from shallow aquifer and eleven from deep aquifer. The obtained results from both aquifer layers indicated three dominant hydrochemical facies: Chloride-sodic, Sulphated-sodic, and mixed water type, according to Piper classification. The determination of salinization origin of groundwater, and the understanding of its hydrological and geochemical behaviors, were assessed by a combined statistical and hydrogeochemical approach. The study of correlations established between major elements and Total Dissolved Solids is, thus, an important tool where dissolution of evaporites that can originate from the Triassic materials of Hadifa mountain, the precipitation and/or dissolution of carbonates, cationic exchange and inverse cationic exchange processes are the main processes associated to groundwater salinity increase. Moreover, the HCA has allowed to classify the groundwater samples into two clusters: the first one with low to moderate salinity and the second one with high salinity. In addition, the application of stable isotopes allowed a better understanding of the hydrodynamic functioning of this aquifer system. The isotopic data suggests a relatively high δ2H and δ18O values for groundwater samples located close to Global Meteoric Water Line (GMWL) that reflects recent recharge for the aquifer system by direct rainwater infiltration, respectively from bordered reliefs in the study area. It also showed a depletion in isotopic composition for almost groundwater samples that indicates the importance of evaporation on the hydrochemistry of the area.This work was developed under the project UIDB/04683/2020 and UIDP/04683/2020 - ICT, Fundacao para a Ciencia e Tecnologia