Dissolution Of Evaporite Minerals Research Articles

Hydrochemical and geoelectrical investigation to determine the origin and spatial distribution of the salinization of the unconfined Plio-Quaternary aquifer of Tabeditt, Southern Tunisia

The expansion of irrigated agriculture and the overexploitation of groundwater in the Tabeditt region lead to a serious deterioration of the chemical quality of water. The compilation of hydrogeological and geophysical studies is essential in order to assess the quality of the Plio-Quaternary waters and to determine the origin of the salinization of these waters. In this study, hydrochemical analyses were carried out on groundwater samples in the Tabeditt region. Hydrochemical data have shown that the salinity in this area could exceed 6 g/L. The interpretation of major ion analyses demonstrates that mineralization is controlled by natural processes. The mineralization process consists of the dissolu-tion of evaporite minerals, namely gypsum, anhydrite, and halite. The geoelectrical study is carried out to obtain information about the distribution and quality of water in the Plio-Quaternary. Interpreta-tion of the resistivity models show the presence of two main zones: the first, near Tabeditt Wadi, is characterized by low values, indicating the influence of salt water in the groundwater and the second, located on the right bank of Wadi Jmal, is characterized by variable resistivity values, generally high, indicating the lateral changes in lithological facies, and the presence of fresh water. In such an arid region suffering from scarcity and degradation (or depletion) of water resources, it is important to implement a master plan that keeps under control the number of wells both known and unknown ones taping these aquifers.

Simulation of Rock-Water Interaction in the Southwestern Part of El Minya Governorate of Egypt

Abstract Twenty-one groundwater samples were picked up from the southwest of El Minya Governorate, Egypt. These samples’ physicochemical characteristics were analyzed. Using a water quality index software (WQI) and the United States Salinity Laboratory (USSL) staff chart, water samples were assessed for drinking and irrigation applications. The interaction between water and rock was assessed using the saturation index (SI), chloro-alkaline indices (CAI), Gibbs ratios (GC and GA), end-member diagram (END), corrosion ratio (CR), factor analysis, and dendrogram. Datasets elucidated that water samples were distinguished by SO42-, Na+, and Cl- dominance, excessive mineralization, hardness, and fresh to slightly saline water. The examined water is divided into two types: SO4. Ca-Cl. Mg (30%) and SO4. Na-Cl (70%). All samples were over-saturated with anhydrite, aragonite, calcite, dolomite, and gypsum minerals except for halite and sylvite minerals dissolution, according to SI. The existence of reversible ion exchange between alkaline earth’s (Ca2++Mg2+) ions in water and alkalis’ ions (Na++ K+) in solids; this is explained by the negative values of the chloro-alkaline indices, which point to recharging from rainfall. The Gibbs diagram showed that the dominant interaction is rock weathering. The silicate weathering and evaporite mineral dissolution control the water composition and salinity, which led to an excess of the dominant ions, as demonstrated by the END. Three wells in the research area are potentially unhealthy and unfit for irrigation and drinking.

Hydrogeochemical processes and nitrate contamination of shallow groundwater in the Gareb-Bouareg region, northeastern Morocco

In semiarid regions, groundwater faces considerable challenges due to both natural and human-induced contaminants, including nitrate contamination. These issues impact the availability of groundwater, a vital resource. Therefore, it is crucial to identify the sources and mechanisms contributing to salinization and nitrate contamination. In this study, we examined the hydrogeochemical characteristics of shallow groundwater in the Gareb-Bouareg region, northeast Morocco. The aim was to determine and understand the key processes that govern its chemical composition and assess nitrate contamination. A total of 50 groundwater samples were collected from existing wells and analysed for major cation and anion concentrations. The results showed that the dissolution of evaporite minerals, cation exchange and evaporation are the predominant processes of groundwater mineralization. In 72% of the samples, nitrate concentrations surpassed the anthropogenic origin threshold value of 10 mg/L, while 16% of the samples exceeded the drinking water standard of 50 mg/L. The highest values were found in the rural and urban areas, at 122 mg/L and 84.24 mg/L, respectively. Nitrate levels and the depth to the water table reveal the impacts of surface contamination sources. The spatial distribution and interrelationship between nitrate and other parameters suggest possible distinct origins of dissolved nitrates associated with various anthropogenic activities.

Geochemical Characteristics and Formation Mechanisms of the Geothermal Waters from the Reshui Area, Dulan of Qinghai, China

The Reshui area, located to the northeast of the Qinghai–Tibet Plateau, exhibits complex geological conditions, well-developed structures, and strong hydrothermal activities. The distribution of hot springs within this area is mainly controlled by faults. In this paper, five hot springs from the area were taken as the research object. We comprehensively studied the geochemical characteristics and genetic mechanism of the geothermal water by conducting a field investigation, hydrogeochemistry and environmental isotopic analysis (87Sr/86Sr, δ2H, δ18O, 3H). The surface temperature of the geothermal water ranges from 84 to 91 °C. The geothermal water in the area exhibits a pH value ranging between 8.26 and 8.45, with a total dissolved solids’ (TDS) concentration falling between 2924 and 3140 mg/L, indicating a weakly alkaline saline nature. It falls into the hydrochemical type CI-Na and contains a relatively high content of trace components such as Li, Sr, B, Br, etc., which are of certain developmental value. Ion ratio analysis and strontium isotope characteristics show that the dissolution of evaporite minerals and carbonate minerals serves as a hot spring for the main source of solutes. Hydrogen and oxygen stable isotope characteristics findings indicate that the geothermal water is primarily recharged via atmospheric precipitation. Moreover, the tritium isotopic data suggest that the geothermal water is a mixture of both recent water and ancient water. Moreover, the recharge elevation is estimated to be between 6151 and 6255 m. and the recharge area is located in the Kunlun Mountains around the study area. The mixing ratio of cold water, calculated using the silicon enthalpy equation, is approximately 65% to 70%. Based on the heat storage temperature calculated using the silicon enthalpy equation and the corrected quartz geothermal temperature scale, we infer that the heat storage temperature of geothermal water in the area ranges from 234.4 to 247.8 °C, with a circulation depth between 7385 and 7816 m. The research results are highly valuable in improving the research level concerning the genesis of high-temperature geothermal water in Reshui areas and provide essential theoretical support for the rational development and protection of geothermal resources in the area.

Salinisation of soils in semi‐arid endorheic zone: Case of Chott El Beida (Algeria)

AbstractChott El Beida, North of Algeria (Setif, 585 km2), is an endorheic zone located in a semi‐arid climate. It is among the first chotts listed under the Ramsar Convention on the Wetlands of International Importance. Numerous studies on wetlands in the Setif region have focused on hydrogeology, avifauna, and vegetation. However, only one study has been devoted to soil studies. This study focused on the pedological and geochemical aspects of salinity in this area. This study was conducted on a toposequence of 200 m comprising eight soil profiles. A set of 24 samples were collected from the top to a depth (0–200 cm) and were subjected to a series of physical and chemical analyses. The concentrations of the major elements were used to determine the chemical facies and calculate the saturation indices for each mineral and residual alkalinity using geochemical modelling with PHREEQC. This study shows that the salinity in Chott El Beida is very variable, varying from less saline to extremely saline, moving from the outside to the centre of the chott, with two types of saline profiles: the descending type towards the outside of the chott and the ascending type in the highly saline depression. Geochemical investigations demonstrated that the dominant facies is (Na‐Cl) which is in accordance with the neutral saline pathway. The phenomenon of salinisation in Chott El Beida is controlled mainly by the precipitation of minerals, namely, calcite, aragonite, dolomite, gypsum, and anhydrite, and the dissolution of evaporite minerals. The study of calcite residual alkalinity and generalised residual alkalinity showed that salinisation evolves in the neutral saline path without the risk of alkalinization.

Appraisal of rock–water interaction and frailty of groundwater to corrosion and salinization, northwestern Gulf of Suez, Egypt

AbstractFrom 12 groundwater samples taken in Egypt's northwestern Suez Gulf, it can be concluded that the water is not suitable for drinking or irrigation purposes. The water is highly mineralized, has extreme hardness, and is very saline, with salinity levels above 3000 ppm. The dominant ions in the water samples are Cl, Na, SO4, and HCO3, and there are two distinct water types: SO4. Ca–Cl (90%), and SO4. Na-Cl (10%). The research also revealed that three wells had become salinized due to dominant ions from sewage water recharge and seawater invasion. The water samples were found to be oversaturated with carbonate, silicate, iron oxide, and evaporite mineral dissolution, which could be harmful to human health. The water was found to exhibit ion exchange, where alkaline earth's (Ca + Mg) ions associated with solids and alkalis' ions (Na + K) in water samples exchange ions. The water was also found to have a high propensity for corrosion, making it unsafe to move groundwater over long distances. The excessive salinity of the water in the research area also makes it undesirable for drinking and irrigation purposes. Overall, the research findings suggest that measures need to be taken to ensure the safety of the groundwater in the area and prevent further contamination. The findings also highlight the importance of regular monitoring and testing of groundwater to ensure that it meets safe levels for human consumption and agricultural use.

Geochemical evaluation of mud volcanic sediment and water in Northern Borneo: A baseline study

A comprehensive geochemical investigation was carried out to characterise the sediment and water seeping out from mud volcano, in Kampung Meritam, Limbang, northern Borneo. Chemical analysis included major oxides, trace metals, rare earth elements, and major ions. Interpretation of results reveals that the geochemical composition of sediment samples is originated from sedimentary provenance particularly Setap Shale, which is the dominant Formation present in this region. The concentration of trace elements and major oxides were used to identify the origin and weathering nature of sediment. SiO2 is the dominant major oxide present in the sediment samples with an average concentration of 58.24%. Whereas for trace metals, Ba is dominating with an average concentration of 263ppm. Environmental pollution indices such as contamination factor, geoaccumulation index, and enrichment factor were used to assess the contamination level of mud volcanic sediments. Hydrochemistry of mud volcano suggests that the water is derived from ionic enriched solute, indicated by Na-Cl water type. The average concentration of Na+ and Cl- is 987 mg/L and 10457.50 mg/L. The ionic ratios suggest that water-rock interaction including carbonate mineral dissolution is the predominant process that controls the water chemistry. Gibbs diagram shows that the water is influenced by the dissolution of evaporite minerals. Thermodynamic stability and saturation index were used to evaluate the mineral stability and saturation condition during weathering. Ca2+ and Mg2+ were released into the water due to the reverse ion exchange process, which was supported by XRD results. Higher ionic strength and Log pCO2 values suggest longer residence time of water in the aquifer matrix and therefore significant dissolution of enriched solute due to the intensive water-rock interaction. The outcome of this study would provide the basis for a better understanding on the geochemical characteristics of Meritam mud volcano in Northern Borneo.

Chemical and isotopic evidences on evaporite dissolution as the origin of high sulfate water in a karst geothermal reservoir

Using multiple isotopes including 87Sr/86Sr in water, δ34SSO4, δ18OSO4, δ18OH2O and δ2HH2O, δ13CDIC and 14CDIC in water, we have investigated the origin and evolution of sulfate concentration (1472 mg/L) in the Tangquan Karst geothermal system in Nanjing, China. The sulfate has been found to be mainly derived from dissolution of gypsum and other evaporite minerals occurring in the carbonate reservoir. The dissolution of evaporite minerals is relatively easier than carbonate at elevated temperatures. We confirmed this differentiated dissolution process by reverse hydrogeochemical simulation using the PHREEQC code. The origin of sulfate is supported by 87Sr/86Sr isotope ratio (0.7088–0.709) with a typical marine signature. We further constrained the origin of sulfate with δ34S in aqueous SO4 (27.6‰–34.2‰) and δ18O in aqueous SO4 (14.3‰–18.4‰). Such sulfate-rich geothermal water usually occurs in open karst geothermal systems, favorable for Spa therapy in many places of the world.

Hydro-Geochemical Applications and Multivariate Analysis to Assess the Water–Rock Interaction in Arid Environments

Thirty groundwater samples were taken from Assiut’s northern outskirts. The physicochemical properties of these samples were investigated. For the evaluation of water–rock interaction, the saturation index (SI), chloro-alkaline indices (CAI1 and CAI2), Gibbs ratios for cations and anions (GC and GA), principal component analysis (PCA), and hierarchical cluster analysis (HCA) were used. (1) With the exception of five samples that were supersaturated, the rest of the groundwater samples were under-saturated with carbonate mineral dissolution (calcite, dolomite, and aragonite) and evaporite mineral dissolution (anhydrite, gypsum, halite, and sylvite). (2) The presence of ion exchange between alkali elements (Na+ + K+) and earth alkaline elements (Ca2+ + Mg2+) is explained by the positive values of the chloro-alkaline indices. (3) In four groundwater samples, negative chloro-alkaline indices suggest reverse ion exchange and an increasing alkali element content. (4) The Gibbs diagram demonstrates that, with the exception of four samples that reflect saline groundwater, the majority of the groundwater samples are freshwater recharging from the fresh surface water in the research area. (5) Groundwater types include Ca-HCO3 (11%), Mg-HCO3 (48%), Na-HCO3 (23%), Mg-Cl (13%), and Na-Cl (3%). (6) The alkali, earth alkaline elements, and sulphate are the key controls on groundwater salinity, according to PCA and HCA. (7) The somewhat saline groundwater in the research area’s western desert margins should not be used since it poses a health danger to people.

Hydrogeochemistry of the groundwater system of the transboundary basement and volcanic aquifers of the Bulal catchment, Southern Ethiopia

The evaluation of groundwater geochemistry of transboundary aquifers has an important role in the management and sustainable use of groundwater resources in arid and semi-arid regions. This study presents the results of an integrated hydrogeochemical study of the Bulal transboundary aquifers located in the Borena zone, along the Ethiopia-Kenya border. The main aquifers are basic volcanic rocks, subordinate felsic pyroclastic deposits, and metamorphic basement rocks. These aquifers are overlain by alluvio-lacustrine sediments, eluvial soil and regolith. The groundwaters are dominated by Na+ and HCO3− and mixed water types. Silicate weathering and evaporation are the dominant hydrogeochemical processes controlling the chemistry of the groundwaters in most parts of the catchment. However, dissolution of evaporitic minerals might have also played a significant role in adding major ions into the groundwater system. Groundwater in the volcanic aquifers are Na–HCO3, Ca–Mg–HCO3, Na–Ca–HCO3 and Na–Cl–SO4 water types while Ca–Mg–HCO3, Na–Ca–Cl–SO4 and Ca–Mg–SO4 water types are dominant in the metamorphic basement aquifers. The groundwater in the catchment mainly evolved from Na–HCO3 in the west, Ca–Mg–HCO3 in the north, and Na–Ca–Cl–SO4 in the central east and southeast to Na–Ca–HCO3 type in the southern low-lying areas along the groundwater flow direction. The study has significant implications for the management of groundwater quality in the region.

Hydrochemical and geothermometry characterization for a geothermal system in semiarid dry climate: The case study of Hamma spring (Northeast Algeria)

Climate change has increased the odds of worsening drought in arid and semiarid dry regions of North Africa. Although the thermal waters have a minimal influence on the yield of aquifers systems, these resources have a great socio-economic value, being widely used for various rheumatologic, dermatologic and psychiatric treatments. Our study aims to characterize the physicochemical parameters and geothermal properties of El Hamma hydrothermal systemin northeastern Algeria. We collected twelve water samples during April 2019 to identify the origin of the thermal groundwater and to evaluate the reservoir temperature in the geothermal system; based on major chemical constituents concentrations, saturation indices, and chemical geothermometer temperatures. We measured temperature, pH, and electric conductivity (EC) conventionalparameters. The temperature of the thermal water sample reaches 52.8 °C, the pH is slightly alkaline, with EC up to 3100 μS/cm.We applied the diagram program to determine the hydrochemical facies, and the equilibrium state of the solid/liquid phase. We used Geothermometers to determine the origin, and temperature at depth of thermal waters. The facies are chlorinated and sodium sulphates; which is mainly related to the dissolution of evaporitic minerals and the weathering of silicates. The geothermometers have given temperatures ranging from 80.73 °C to 126.63 °C for the thermal reservoir. The results have identified the Jurassic limestone at more than 2300 m depths as the main thermal reservoir. Moreover, the application of the International Institute for Geothermal Research (IIRG) diagrams to the hot waters has shown a "γ" diagram type, leading to confirm that the hot solutions are of deep origin, with waters circulating in the basement and carbonate formations.

Origin of sulphate in the unsaturated zone and groundwater of a loess aquifer

AbstractThe use of the sulphate mass balance (SMB) between precipitation and soil water as a supplementary method to estimate the diffuse recharge rate assumes that the sulphate in soil water originated entirely from atmospheric deposition; however, the origin of sulphate in soil and groundwater is often unclear, especially in loess aquifers. This study analysed the sulphur (δ34S‐SO4) and oxygen (δ18O‐SO4) isotopes of sulphate in precipitation, water‐extractable soil water, and shallow groundwater samples and used these data along with hydrochemical data to determine the sources of sulphate in the thick unsaturated zone and groundwater of a loess aquifer. The results suggest that sulphate in groundwater mainly originated from old precipitation. When precipitation percolates through the unsaturated zone to recharge groundwater, sulphates were rarely dissolved due to the formation of CaCO3 film on the surface of sulphate minerals. The water‐extractable sulphate in the deep unsaturated zone (>10 m) was mainly derived from the dissolution of evaporite minerals and there was no oxidation of sulphide minerals during the extraction of soil water by elutriating soil samples with deionized water. The water‐extractable concentration of SO4 was not representative of the actual SO4 concentration in mobile soil water. Therefore, the recharge rate cannot be estimated by the SMB method using the water‐extractable concentration of SO4 in the loess areas. This study is important for identifying sulphate sources and clarifying the proper method for estimating the recharge rate in loess aquifers.

Hydrogeochemical characteristics and groundwater quality assessment in the plain area of Yarkant River Basin in Xinjiang, P.R. China.

The deteriorating groundwater quality due to natural genesis and anthropogenic activities has prevented the sustainable use of groundwater. The characteristics and factors affecting groundwater quality for drinking in shallow aquifers (depth ≤ 100 m) in the plain area of Yarkant River Basin in Xinjiang were analyzed using water quality index (WQI), geostatistics, and geochemical methods. Results showed that the groundwater was weak-alkaline with neutral pH, with dominant water types being SO4•HCO3-Ca•Mg, SO4•Cl•HCO3-Na•Ca, SO4•HCO3•Cl-Ca•Na, Cl•SO4-Na•Ca, and HCO3•SO4-Mg•Ca. WQI ranged between 31.79 and 549.37, and about 14.43%, 31.96%, 18.56%, 22.68%, and 12.37% of the all samples were excellent, good, medium, poor, and extremely poor quality, respectively. The proportion of excellent quality was the highest in single structure phreatic aquifer (SSPA, 50.00%) and good quality were the highest in multilayered structure phreatic aquifer (MSPA, 34.21%) and multilayered structure confined aquifer (MSCA, 28.89%). With the extension of the river, the groundwater quality gradually degenerated from south to north in phreatic aquifer (PA, including SSPA and MSPA). The further away from the Yarkant river, the worse the groundwater quality of PA. Furthermore, the WQI showed excellent, good, and an alternation of medium and poor quality (including extremely poor quality) from south to north in the MSCA. The groundwater quality deterioration might have been affected by the dissolution of evaporite minerals, such as halite, gypsum, and anhydrite and ion exchange process. In addition, local effects of anthropogenic activities and land usage patterns on the groundwater quality should be reckoned as well.

An experimental and numerical study of evaporite mineral dissolution and density-driven flow in porous media

Subsurface mineral dissolution problems exhibit complex behaviors, which are difficult to model and validate numerically. Controlled, physically-validated experimental problems can be used to better understand mineral dissolution and subsequent numerical representation, bridging the gap between numerical models and field observations. The objective of this work was to collect the first controlled, physical measurements in a porous aquifer overlying an evaporite mineral, and to create a numerical model of the system. The problem studied was modified from the classic HYDROCOIN Level 1 Case 5 problem. Three flow gradients in a porous aquifer were investigated in duplicate in a 2-D box-problem. The duplicate measurements had high variability, shown by numerical modeling to be a result of initial conditions, variable flux representing dissolution, sharp gradients, and variable dispersivity. The physical measurements of parameters and fields were important for calibration success. The numerical models, including sensitivity analyses, were capable of simulating flow patterns, observed concentrations, and peaks resulting from observed initial conditions. The numerical models were a key tool in understanding factors influencing the flow and spread of salt within the system. The models were limited by the ability to detail physical observations, difficult in both the laboratory and for potential field applications. The results provided insight in the HYDROCOIN Level 1 Case 5 numerical simulations, with flow appearing to be swept-forward; however, observed concentrations were lower than commonly modeled.

On the common occurrence of sulphate with elevated δ34S in European mine waters: Sulphides, evaporites or seawater?

The stable isotopic (δ34S, δ18O, δ2H) composition of mine waters has been examined from coal and metal mines, of varying depth, in Spain (Asturias), the UK (north Derbyshire/Yorkshire) and Poland (Bytom, Upper Silesia). δ18O and δ2H data confirm a meteoric origin for all waters. The mine waters have elevated sulphate concentrations relative to recent meteorically-derived groundwaters and have elevated SO42−/Cl− ratios relative to marine water. In the shallower mines and Markham No. 3, the dissolved sulphate δ34S is low, suggesting the sulphate is derived from the oxidation of sulphide minerals. In most of the deeper mines, the dissolved sulphate δ34S is too high (>15‰), to be derived from simple pyrite oxidation. In the deep Polish and Spanish mine waters, the source of sulphate may be evaporite mineral dissolution, but such a mechanism is problematic in the case of the Caphouse (UK) mine. Fractionation associated with sulphate reduction may have contributed to elevated dissolved sulphate δ34S. Elevated sulphate in deep coal mine waters may not always be simply derived from pyrite oxidation. The consistent observation of elevated dissolved sulphate δ34S in deep coal mines suggests a distinct genetic pathway, the origin of which as yet remains equivocal.

Mobilization of co-occurring trace elements (CTEs) in arsenic contaminated aquifers in the Bengal basin

The mobilization of co-occurring trace elements (CTEs) in aquifers with known metal(loid) contamination may exacerbate potential human health threats where release mechanisms are not geochemically limited. This study investigates the co-mobilization of the potentially toxic CTEs antimony (Sb), molybdenum (Mo), vanadium (V), uranium (U), and selenium (Se) with arsenic (As) and iron (Fe) in contrasting high and low As aquifers surrounding the river Bhagirathi in Murshidabad, West Bengal, India. We sought to determine the dominant release mechanisms and fate of each CTEs as they relate to redox conditions, major element dissolution pathways, and characteristics of dissolved organic matter (DOM). Groundwater samples collected in 2013 and 2015 field campaigns across six villages in the Murshidabad district were analyzed for major and trace elements, as well as the quantity and optical properties of DOM. East of the river Bhagirathi, the Holocene aquifer contained groundwater with compositions reflective of carbonate mineral dissolution and silicate mineral weathering, along with clear signs of Fe reduction and associated mobilization of As, Sb, Mo, V, and U. Relatively oxic groundwater in the Pleistocene aquifer underlying the study sites on the west side of the river showed minimal Fe reduction and signatures of carbonate mineral dissolution and silicate mineral weathering (i.e., Nabagram), or evaporite mineral dissolution (i.e., Kandi). In groundwater samples from the more oxic Pleistocene aquifer, concentrations of As, Sb, Mo, and V were substantially lower than in the Holocene aquifer, however, U concentrations were relatively higher where carbonate mineral dissolution predominated (i.e., Nabagram). Compelling positive correlations between Fe and CTEs in the Holocene but not in the Pleistocene aquifer implicated Fe reductive processes as the probable pathway for CTEs release. The presence of humic-like DOM ligands and inorganic ions (i.e., Ca2+, CO32−) may also enhance CTEs mobility via aqueous complexation reactions, or possibly by inhibiting CTEs adsorption. We further hypothesize that carbonate mineral dissolution mobilizes U in the absence of Fe reduction, and that U solubility in the reducing Holocene aquifer may be facilitated by carbonate mineral dissolution products (e.g., Ca2+, HCO3−, CO32−) that promote U complexation and the inhibition of (bio)immobilization pathways. Conclusively, potentially toxic CTEs are being mobilized concomitantly with As in the Murshidabad district of West Bengal, probably by microbial Fe reduction. Because these aquifers still contain requisite organic matter and bulk sediment Fe required for Fe reductive processes, it follows that concentrations of CTEs may increase in the future. We therefore argue that despite moderately low concentrations of CTEs in the current study, mechanistic modeling efforts and more extensive monitoring of trace metal(loid)s should be performed to ensure that drinking water supplies do not pose additional health threats in the coming years.

Hydrogeochemistry and evaluation of groundwater suitability for irrigation purpose in the Mornag region, northeastern Tunisia

In semiarid regions, salinization and anthropogenic contaminants are considered as the principal threat to groundwater resource availability. Consequently, the origin and processes of salinization should be identified, to take a sustainable measurement to mitigate these problems. In the present study, groundwater samples from 18 dug wells were collected during the sampling campaign carried out in May 2016 in order to identify the main natural and anthropogenic processes that control the quality of groundwater in the Mornag shallow aquifer (northeastern Tunisia) and to evaluate its suitability for agricultural irrigation purpose. This may create a clear database for decision maker to take suitable actions to sustainably manage the groundwater resources. The hydrogeochemical parameters (major ions concentration, pH, TDS, EC) were examined to assess the quality of groundwater and to identify the main mineralization processes. Permeability index (PI), percentage of sodium (%Na) and the ratio of sodium adsorption (SAR) were investigated to evaluate the groundwater suitability for irrigation. It has been demonstrated that the major ions abundance follows the order of sodium > calcium > magnesium > potassium and chloride > sulfate > bicarbonate > nitrate. Dissolution of evaporite minerals, such as halite, gypsum and anhydrite, and reverse ion exchange are the predominant processes of groundwater mineralization, generating the Cl–SO4–Ca and Na–Cl major water types. The calculated irrigation water quality index displayed that 55% of the Mornag groundwater samples are distinguished by elevated SAR and PI, suggesting their unsuitability for irrigation. So, the present study has provided a precious insight into the major geochemical processes occurring in the Mornag shallow groundwater and their suitability for irrigation which will support future management of these resources.

Geochemical and isotopic characterization of groundwater in the alluvial aquifer of Guelma (north-eastern Algeria)

This study aims at determining the factors and the processes controlling groundwater quality, origin, and chemistry in the alluvial aquifer of Guelma northeastern of Algeria. Hydrochemical and isotopic investigations were carried out on 21 points, including boreholes, wells, springs, and surface waters in June 2016. A thorough hydrogeological investigation has revealed that groundwater is Ca–Mg/SO4–Cl facies. The combined use of geochemical tools and multivariate statistical analysis indicates that groundwater composition is largely governed by water-rock interactions, particularly the dissolution of evaporitic minerals as well as ion exchange processes. This study reports for the first time the isotopic contents (δ18O, δ2H) of the alluvial aquifer and the surface water. The stable isotope composition for the ground- and surfacewater samples has shown a homogeneous isotopic signature and reveals non-evaporated waters in the northern and central parts of the aquifer. This is the indication of the presence of a significant recharge by modern rainfall. Evaporated waters that are characterized by relatively enriched δ18O and δ2H contents are located in the western part of the plain. This suggests the occurrence of partial evaporation at the surface prior to, during, or after infiltration through the unsaturated zone.

Geochemical evolution of groundwater in hard-rock aquifers of South India using statistical and modelling techniques

ABSTRACTMultivariate statistical analysis and inverse geochemical modelling techniques were employed to deduce the mechanism of groundwater evolution in the hard-rock terrain of Telangana, South India. Q-mode hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used to extract the hydrogeochemical characteristics and classify the groundwater samples into three principal groups. Use of thermodynamic stability diagrams and inverse geochemical modelling in PHREEQC identified the chemical reactions controlling hydrogeochemistry of each of the groups obtained from statistical analysis. The model output showed that a few phases are governing the water chemistry in this area and the geochemical reactions responsible for evolution of groundwater chemistry along the flow path are (i) dissolution of evaporite minerals (dolomite, halite); (ii) dissolution of primary silicate minerals (albite, anorthite, K-feldspar, biotite); (iii) precipitation of secondary silicate minerals (kaolinite, quartz, gibbsite, Ca-montmorillonite) along with anhydrite and calcite; and (iv) reverse ion exchange processes.

Integrating hydrogeological, geophysical, and remote-sensing data to identify fresh groundwater resources in arid regions: a case study from Western Iraq

There is a limited availability of fresh groundwater in the western part of Iraq due to the aridity of the region, and new water supplies are required to meet the demands of potential industrial, mining, and agricultural projects. Consequently, the factors that influence the quality, availability, and distribution of fresh groundwater in the region were assessed by combining hydrogeological, geophysical, and remote-sensing data within a GIS environment. For this purpose, the Shuttle Radar Topography Mission elevation data, geophysical data (gravity and magnetic), and hydrogeological database were used in an integrated approach. It was concluded that both a regionally extensive, deep intergranular aquifer and shallow-fractured and karstified carbonate aquifers have the potential to contain fresh groundwater in the region. It was inferred from the hydrochemical statistics that the main factors controlling groundwater chemistry are the dissolution of evaporite minerals and the weathering of carbonate rocks. Gravity (measured and satellite) data and magnetic data were processed and interpreted to identify the locations and characteristics of subsurface structures. Source Parameter Imaging was applied to calculate depth to the magnetic basement map from gridded magnetic data. The decompensative anomaly maps showed that zones with fresh groundwater are distributed on gravity lows which coincide with areas with a large depth to basement. Most of the fresh groundwater zones in the region are distributed between the pre-Tertiary and Tertiary axes of the Ha’il Arch due to increased recharge along this structure caused by intense fracturing. The extension of the gravity high outside the Iraq territory may suggest similar freshwater zones of groundwater occur in Syria, Jordan, and Saudi Arabia.