Hydrogeochemistry of groundwaters in a semi-arid region. El Ma El Abiod aquifer, Eastern Algeria

In this work, we present results of the hydrogeochemical and isotopic studies on groundwater samples from the El Ma El Abiod Sandstone aquifer, in Tébessa, Algeria. Chemical and environmental isotope data are presented and discussed in order to identify the geochemical processes and their relation with groundwater quality as well as to get an insight into the hydrochemical evaluation, in space and time, of groundwater and of the origin of dissolved species. A combined hydrogeologic and isotopic investigation have been carried out using chemical and isotopic data to deduce a hydrochemical evaluation of the aquifer system based on the ionic constituents, water types, hydrochemical facies, and factors controlling groundwater quality. All of the investigated groundwaters are categorized into two chemical types: low mineralized water type and relatively high mineralized water type. Interpretation of chemical data, based on thermodynamic calculations and geochemical reaction models of selected water groups constructed using PHREEQC, suggest that the chemical evolution of groundwater is primarily controlled by water–rock interactions, involving (1) acidic weathering of aluminosilicates, (2) dissolution of secondary carbonate minerals, and (3) cation exchange of Na⁺ for Ca²⁺. However, the original composition of groundwater may have been modified by further secondary processes such as mixing of chemically different water masses. The combined use of SI and mass-balance modeling has shown to be a useful approach in interpreting groundwater hydrochemistry in an area where large uncertainties exist in the understanding of the groundwater flow system. Interpretation of ¹⁸O and ²H, suggest that the recharge of the investigated groundwaters may result from different mechanisms.     

Hydrogeochemistry and isotope techniques to determine water interactions in groundwater-dependent shallow lakes,Wet Pampa Plain,Argentina

This paper gives an account of the implementation of hydrochemical and isotopic techniques to identify and explain the processes that govern solute exchange in two groundwater-dependent shallow lakes in the Southeastern Pampa Plain of Argentina. Water samples (lakes, streams, spring water and groundwater) for hydrochemical and stable isotopic determination were collected and the main physical–chemical parameters were measured. The combination of stable isotope data with hydrogeochemical techniques was used for the identification of sources and preferential recharge areas to these aquatic ecosystems which allowed the explanation of the lake water origin. The hydrochemical processes which explain Los Padres Lake water chemistry are evaporation from groundwater, CO₂ input, calcite dissolution, Na⁺ release by Ca²⁺ and Mg²⁺ exchange, and sulfate reduction. The model that best aligns with La Brava Lake hydrochemical constraints includes: mixing, CO₂ and calcite dissolution, cationic exchange with Na⁺ release and Mg²⁺ adsorption, and to a lesser extent, Ca/Na exchange. This model suggests that the fractured aquifer contribution to this water body is greater than 50 %. An isotopic-specific fingerprint for each lake was identified, finding a higher evaporation rate for La Brava Lake compared to Los Padres Lake. Isotopic data demonstrate the importance of these shallow lakes as recharge areas to the regional aquifer, becoming areas of high groundwater vulnerability. The Tandilia Range System, considered in many hydrogeological studies as the impermeable bedrock of the Pampean aquifer, acts as a fissured aquifer in this area, contributing to low salinity waters and with a fingerprint similar to groundwater isotopic composition.     

Multivariate statistical analysis of chemical and stable isotopic data as indicative of groundwater evolution with reduced exploitation

Groundwater resources in the North China Plain (NCP) are undergoing tremendous changes in response to the operation of groundwater exploitation reduction (GWER) project. To identify groundwater evolution in this complex context, hierarchical cluster analysis (HCA) and principal component analysis (PCA) were combined to interpret an integrated dataset of stable isotopes and chemical data from four sampling campaigns in a pilot area of groundwater control. We proposed a novel HCA approach integrating stable isotopes and chemical signals, which successfully partitioned the groundwater samples into the unconfined and the confined water samples. Stable isotopic evidence showed that the lateral inflow and the surface water may contribute more to groundwater recharge in this region than local modern precipitation. The unconfined water’s main hydrochemical types were Na type with mixed anions, and Na–Cl–SO₄ type, while the confined water was mainly Na–Cl and Na–SO₄ types. Geochemical processes mainly involved the dissolution/precipitation of halite, gypsum, Glauber's salt, feldspar, calcite and dolomite, as well as the cation exchange. PCA results showed that water–rock interaction (i.e., salinity-based and alkalinity-based processes) predominated the hydrochemical evolution, along with local nitrate contamination resulting from fertilizers and domestic sewage. The GWER project regulated the natural evolution of unconfined water chemistry, and significantly reduced the unconfined water’s salinity (mainly Na⁺, Mg²⁺, SO₄^2?). This may be attributed to upward leakage from low-salinity confined water at some parts of the aquifer. Additionally, insignificant changes in the confined water’s salinity reflected that the impact of GWER on the confined aquifer was negligible. This study facilitates the groundwater classification effectively in the areas lack of geological data, and enhances the knowledge of groundwater chemical evolution in such a region where groundwater restoration is in progress, with important implications for groundwater sustainable management in similar basins worldwide.     

河套灌区西部浅层地下水咸化机制

浅层地下水水位埋深浅、含盐量高,是导致河套灌区土壤次生盐渍化的重要原因.以河套灌区西部地区为研究区,通过对浅层地下水的水化学和氢氧同位素特征分析以及水文地球化学模拟,探讨了灌区浅层地下水的补给来源和主控水-岩作用过程,并定量估算了蒸发作用对浅层地下水含盐量的影响.研究区内浅层地下水为弱碱性咸水,pH为7.23~8.45,总溶解性固体（total dissolved solids,TDS）变化范围为371~7 599 mg/L;随着地下水咸化程度增大,水化学类型由HCO₃-Na·Mg·Ca型向Cl-Na型过渡.引黄灌溉和大气降水是浅层地下水的主要补给来源,径流过程中浅层地下水受蒸发作用和植物蒸腾作用影响,地下水化学组分主要来源于蒸发盐溶解和硅酸盐风化水解,并受强烈的蒸发作用和离子交换作用影响.水文地球化学模拟和主成分分析结果显示,蒸发作用和岩盐溶解作用对区内浅层地下水咸化贡献最大,石膏和白云石等矿物的溶解、硅酸盐的水解、Na-Ca离子交换以及局部地形起伏对地下水咸化过程也有较大贡献.      

贵阳市岩溶地下水水化学演化机制:水化学和锶同位素证据

岩溶地下水的水化学特征及其水岩作用过程研究对岩溶地下水合理开发利用和污染防治具有重要意义.综合利用水化学分析、主要离子比值、锶含量和87Sr/86Sr比值分析和反向水文地球化学模拟,深入分析了贵阳市地下水和地表水不同季节的水化学特征变化和水文地球化学演化过程.水化学特征分析表明,贵阳市地下水以HCO₃·SO₄-Ca型和HCO₃-Ca·Mg型为主,水化学组成在季节和空间分布上存在一定的规律性变化,地表水与地下水的直接混合对地下水化学组成有一定的影响.锶同位素比值和水文地球化学反向模拟表明,地下水水化学组分主要受岩石风化作用的控制,以方解石和白云石为主的碳酸盐的溶解－沉淀作用以及硫酸盐和岩盐的溶解是控制研究区地下水水化学特征的重要过程,并受上覆孔隙含水层硅酸盐矿物水解的影响.      

Origin of groundwater salinity in the Fasa Plain,southern Iran,hydrogeochemical and isotopic approaches

The study area, the Fasa Plain, is situated in the semiarid region of Fars Province in the south of Iran. The Salloo diapir is a salt dome that crops out in the northwest of the study area. Isotopic and hydrochemical analyses were used to examine the water and how the origin of salinity and the diapir affect the quality of the groundwater quality in the study area. Groundwater was sampled from 31 representative pumping wells in alluvial aquifer and five springs in order to measure their stable isotope compositions, bromide ion concentration, and physical and chemical parameters. The alluvial aquifer was organized into two main groups based on the chemistry, with Group 1 consisting of low-salinity well samples (544–1744 µS/cm) with water type Ca–Mg–HCO₃–SO₄ which were taken in the center and north of the area, and Group 2 consisting of high-salinity samples (2550–4620 µS/cm) with water type Ca–Mg–Cl–SO₄ which were taken from the wells in the south and southwest of the area. A saline spring near the salt dome with an EC of 10,280 µS/cm has water type Na–Cl, while the compositions of the water in the other karstic springs is comparable to the fresh groundwater samples. All groundwater samples are undersaturated with respect to gypsum, anhydrite, and halite and are supersaturated with respect to calcite and dolomite. Stable isotopes (δ¹⁸O and δ²H) differentiated four water types: saline springs, freshwater spring, fresh groundwater, and saline groundwater. The results indicate that meteoric water is the main origin of these water resources. Halite dissolution from the salt dome was identified as the origin of salinity. The Na/Cl and Cl/Br ratios confirmed the results. Groundwater compositions in the southwestern part of the area are affected by the intrusion of saltwater from the salt dome. The average saltwater fraction in the some water wells is about 0.2%. In the south and southwestern part of the area, the saltwater fraction is positive in mixed freshwater/saltwater (Group 2). Different processes interact together to change the hydrochemical properties of Fasa’s alluvial aquifer. The main processes that occur in the aquifer are mixing, gypsum dissolution, and calcite precipitation.     

Hydrogeological characterization of a carbonate aquifer using geophysical and geochemical approach: case of the Krachoua Formation in Tataouine area,Southern Tunisia

An integrated hydrogeological investigation involving geological surface data, well data (lithostratigraphical and piezometric data) and the vertical electrical sounding (VES) method was carried out in Tataouine area, Southern Tunisia to characterize the hydrogeology and the geochemistry of the Krachoua Formation aquifer. The electrical data were used to differentiate lithostratigraphic units and characterize their hydrogeological potentialities. Major elements contents within groundwater samples were assessed and some plots and diagrams have been established in order to investigate the hydrochemical properties of this aquifer and the origin of its mineralization. The Krachoua aquifer exhibits a general drawdown of the piezometric level from 2004 to 2015 reflecting a dramatic decrease in groundwater resources due to increased groundwater abstraction during the last decades. Flow directions shows that the recharge of this aquifer considered as a free aquifer is directly ensured by rainfalls over the outcropping fractured limestones. The geometry of the Krachoua Formation aquifer is tectonically controlled and structured in horst and graben features that impacted greatly the hydrogeology and the hydrodynamics of the area. Subsequent thickness and facies variations within this aquifer influenced the reservoir quality and the groundwater flows. The increased values of salinity to the northwest of the study area seems to be mainly related to the dissolution of the Upper Liassic gypsum of Mestaoua Formation which outcrops widely and can be dissolute easily by meteoric water and contaminate the Krachoua aquifer. This fact is also supported by the sulfated and calci-magnesian chloride facies of this aquifer related to the dissolution of evaporitic rocks (gypsum, anhydrite, and halite). However low salinity values are recorded within the zone where these evaporitic rocks are relatively deep.     

Integrated hydrochemical assessment of the Quaternary alluvial aquifer of the Guadalquivir River, southern Spain

The alluvial aquifer of the Guadalquivir River comprises shallow Quaternary deposits located in the central-eastern part of the Province of Jaén in southern Spain, where groundwater resources are used mainly for crop irrigation in an important agricultural area. In order to establish the baseline hydrochemical conditions and processes determining the groundwater quality, groundwater and river water samples were collected as part of an integrated investigation that coupled multivariate statistical analysis with hydrochemical methods to identify and interpret the groundwater chemistry of the aquifer system. Three main hydrochemical types (Mg–Ca–HCO₃, Ca–Mg–SO₄–HCO₃–Cl and Na–Ca–Mg–Cl–SO₄) were identified. Further interpretation, using R-mode principal components analysis (PCA) conducted with 13 hydrochemical variables, identified two principal components which explain ⅔ of the variance in the original data. In combination with the hydrochemical interpretation, mineralogical analyses of the aquifer sediment together with inverse geochemical modelling using NETPATH showed that dedolomitization (calcite precipitation and dolomite dissolution driven by gypsum dissolution) is the principal hydrochemical process controlling the regional groundwater chemistry. Other processes such as silicate weathering, ion exchange, mixing between river water and groundwater, and agricultural practices also affect the groundwater chemistry.     

Salinity problem of groundwater in the Wadi Tharad Basin, Saudi Arabia

In Wadi Tharad the groundwater has been subjected to hydrochemical study to identify the process (s) that led to the formation of relatively highly saline water in shallow alluvial aquifer. The chemical analyses results show that the groundwater salinity was highly variable and randomly distributed along the wadi course. This variation could be attributed to intensive evaporation on effluent prone surface irrigation water that led to precipitation of evaporates (e.g., calcite, dolomite, gypsum and probably halite). The intensive irrigation practice through mineral dissolution recharged the groundwater with a marked increase in the salinity. The local hydrogeological condition is also involved in determining the risk of the groundwater salinity as a consequence of irrigation practice. This revised version was published online in July 2006 with corrections to the Cover Date.     

Chemical and physical parameters as trace markers of anthropogenic-induced salinity in the Agua Amarga coastal aquifer (southern Spain)

Agua Amarga coastal aquifer in southern Spain has been the subject of chemical and physical measurements since May 2008 in order to monitor the potential effects of water withdrawal for the Alicante desalination plants on the salt marsh linked to the aquifer. Electrical conductivity contour maps and depth profiles, piezometric-head contour maps, hydrochemical analyses, isotopic characterizations and temperature depth profiles show not only the saltwater intrusion caused by water abstraction, but also the presence of a pronounced convective density-driven flow below the salt marsh; this flow was a consequence of saltwork activity in the early 1900s which generated saline groundwater contamination. The influence of a seawater recharge programme, carried out over the salt marsh in 2009–2010, on the diminishing groundwater salinity and the recovery of groundwater levels is also studied. Based on collected field data, the project provides a deeper understanding of how these successive anthropogenic interventions have modified flow and mixing processes in Agua Amarga aquifer.     

Hydrochemical characteristics and salinity of groundwater in the Ejina Basin, Northwestern China

A hydrochemical investigation was conducted in the Ejina Basin to identify the hydrochemical characteristics and the salinity of groundwater. The results indicate that groundwater in the area is brackish and are significantly zonation in salinity and water types from the recharge area to the discharge area. The ionic ration plot and saturation index (SI) calculation suggest that the silicate rock weathering and evaporation deposition are the dominant processes that determine the major ionic composition in the study area. Most of the stable isotope δ¹⁸O and δD compositions in the groundwater is a meteoric water feature, indicating that the groundwater mainly sources from meteoric water and most groundwater undergoes a long history of evaporation. Based on radioactive isotope tritium (³H) analysis, the groundwater ages were approximately estimated in different aquifers. The groundwater age ranges from less than 5 years, between 5 years and 50 years, and more than 50 years. Within 1 km of the river water influence zone, the groundwater recharges from recent Heihe river water and the groundwater age is about less than 5 years in shallow aquifer. From 1 km to 10 km of the river water influence zone, the groundwater sources from the mixture waters and the groundwater age is between 5 years and 50 years in shallow aquifer. The groundwater age is more than 50 years in deep confined aquifer.     

Hydrochemical changes in a small tropical island’s aquifer: Manukan Island, Sabah, Malaysia

Small islands groundwater are often exposed to heavy pumpings as a result of high demand for freshwater consumption. Intensive exploitation of groundwater from Manukan Island’s aquifer has disturbed the natural equilibrium between fresh and saline water, and has resulted increase the groundwater salinity and leap to the hydrochemical complexities of freshwater–seawater contact. An attempt was made to identify the hydrochemical processes that accompany current intrusion of seawater using ionic changes and saturation indices. It was observed that the mixing between freshwater–seawater created diversity in geochemical processes of the Manukan Island’s aquifer and altered the freshwater and seawater mixture away from the theoretical composition line. This explained the most visible processes taking place during the displacement.     

Groundwater hydrochemistry and origin in the south-eastern part of Wadi El Natrun,Egypt

The demand for water is rapidly increasing in Egypt, because of high population and agriculture production growth rate, which makes research of water resources necessary. The regional multi-aquifer system of the Miocene–Pleistocene age is discharged in Wadi El Natrun area. Intensive aquifer overexploitation and agricultural development in the area are related to groundwater quality deterioration. Hydrochemical and hydrogeological data was evaluated to determine the groundwater origin and quality in the south-eastern part of wadi, which appears to be more significant for water supply owing to lower groundwater salinity. The dominance of the high mineralised Cl groundwater type was found; however, also less mineralised SO₄ and HCO₃ types were identified there. Based on the ion relations, halite and gypsum dissolution and ion exchange are the most important hydrochemical processes forming the groundwater chemical composition. The Cl dominated groundwater matches the discharge part of the regional hydrogeological system. Contrary, the presence of HCO₃ and SO₄ hydrochemical types corresponds to the infiltration and transferring parts of the hydrogeological system indicating the presence of zones conducting low mineralised groundwater. The discharge area of the over-pumped aquifer in Wadi El-Natrun lies 23 m beneath the sea level with the shoreline being at the distance of 100 km, thus there is a real risk of seawater intrusion. Using the hydrochemical facies evolution diagram, four samples in the centre of the discharge area indicate advanced seawater intrusion. The zones of the highest demand for groundwater quality protection were indicated based on a spatial pattern of hydrogeochemical composition.     

Magnetostratigraphy and environmental magnetism in a Pleistocene sedimentary sequence, Marcos Paz, Argentina

The deterioration of groundwater quality, particularly due to salinization, because of the overexploitation of groundwater in the Lower Central Plain of Thailand remains a major concern. With increasing demand for water there is a growing need for sustainable management of the resource, which would benefit from an improved understanding of the sources of chloride contamination. Thus, a hydrochemical and isotopic study was carried out to chemically characterize groundwater and to investigate possible sources of salinization, and in particular of chloride contamination, in the multi-layered Bangkok aquifer system. Groundwater samples were taken from four topmost aquifers (Bangkok, Phra Pradaeng, Nakhon Luang, and Nonthaburi). Additionally, short-term rainwater sampling, as well as river and seawater sampling was performed and later analyzed for ionic composition and stable water isotopes. Ionic and isotopic data indicate at least three different recharge sources for groundwater. The major recharge source is rainwater. The influence of seawater is limited to the coastal region and tidally influenced areas of the two main rivers (Chao Phraya and Tha Chin). Bromide data also suggest the influence of saline water in deeper aquifers due to trapped water. Most importantly, although the influence of seawater on groundwater is recognizable, the surrounding geology contributes a significant number of dissolved ions detected in the groundwater.     

Groundwater flow and residence time in a karst aquifer using ion and isotope characterization

In order to identify the origin of the main processes that affect the composition of groundwater in a karstic aquifer, a hydrogeochemical and isotopic study was carried out of water from numerous observation wells located in Sierra de Gador, a semiarid region in SE Spain. Several natural and anthropogenic tracers were used to calculate groundwater residence time within this complex aquifer system. Analysis of major ions enabled the principal geochemical processes occurring in the aquifer to be established, and the samples were classified into four distinctive solute groups according to this criterion. Dissolution of carbonate rocks determines the chemical composition of less mineralized water. In another group, the concurrent dissolution of dolomite and precipitation of calcite in gypsum-bearing carbonate aquifer, where the dissolution of relatively soluble gypsum controls the reaction, are the dominant processes. Marine intrusion results in highly mineralized waters and leads to base exchange reactions. The groundwater enrichment of minor and trace elements allowed classification of the samples into two classes that are linked to different flow patterns. One of these classes is influenced by a slow and/or deep regional flow, where the temperature is generally elevated. The influence of sulphate reduces by up to 40 % the barium concentration due to the barite precipitation. Isotope data (T, ¹⁴C) confirm the existence of recent local flows, and regional flow system, and ages of ground water may reach 8000 years. The importance of gypsum dissolution in this aquifer is proved by the δ³⁴S content.     

Spatio-temporal characterization of the Pliocene aquifer conditions in Wadi El-Natrun area,Egypt

Wadi El-Natrun area has recently undergone extensive urban and agricultural expansion. Due to the absence of natural surface irrigation supplies, the only source of water in the area is the Pliocene groundwater aquifer. As a result, secondary salinization from increased abstractions is the major threat to the groundwater aquifer. There is a dire need for efficient strategies to ensure long-term sustainability of the area’s productive agriculture. These strategies should be based on scientific spatio-temporal monitoring and analysis of the groundwater conditions that is also lacking. To capture the spatio-temporal variability in groundwater conditions, field measurements of total dissolved solids, electrical conductivity, pH, temperature, and water level as well as lab-based ionic composition were performed on 47 groundwater samples collected during 2006 and 2007. Determinations of the hydrochemical characteristics, water types, salt assemblages, and the sodium adsorption ratio were carried out on the samples. Reference data sets recorded in 1973 and 1997 were available for the area and were used to monitor the changes occurred in these periods. Geographic information system (GIS) was appraised for mapping and for integrated analysis of the different layers. Remotely sensed change detection techniques were applied to the Landsat TM and the ETM + imageries and used to highlight the extensive reclamation and urbanization and to find key trends for the alterations in the groundwater conditions and their spatial association with land covers. Results revealed a topographic depression-induced flow pattern, predominance of leaching and dissolution processes, the presence of saline lakes, over-pumping from the Pliocene aquifer, and temporal changes in land uses are the main factors combined to control the spatio-temporal variability in the groundwater. Results also clarified the presence of two: northwestern and southeastern zones that varied distinctively in their hydrodynamic and hydrochemical characteristics. The northwestern zone showed an average water level decline of 15 m, the water of which is brackish (av. 2,037 mg/l) with dominant Na⁺, Cl⁻ and SO₄ ²⁻ ions. The groundwater of this zone is characterized by high to very high salinity hazard and high to very high alkali hazard and is not recommended for irrigation on soils with poor drainage and without proper management for salinity control. The southeastern zone showed water level decline less than 2 m, the water of which is fresh (av. 424 mg/l) with major Na⁺, HCO₃ ⁻, Cl⁻, and SO₄ ²⁻ ions, and quality suitable for irrigation with medium to high salinity and low to medium alkali hazards. The article represents the first step towards an integrated management of Wadi El-Natrun groundwater resources within a GIS framework.     

Hydrochemical and isotopic study of groundwater in Wadi El Hechim–Garaa Hamra basin, Central Tunisia

Hydrochemical and isotopic study of Miocene and Mio-Plio-Quaternary (M-P-Q) aquifers in Wadi El Hechim?CGaraa Hamra basin, Central Tunisia was undertaken in order to investigate recharge mode and processes leading to mineralization of groundwater as well as interaction between both systems. The results revealed striking differences between the two aquifer systems. While the Miocene aquifer contains recently recharged waters with generally low mineralization (around 0.5?g?L^?1), stemming mainly from dissolution of carbonate minerals, the M-P-Q aquifer reveals TDS values reaching 3?g?L^?1, controlled mainly by dissolution of evaporitic minerals. Isotopic data indicate that the Miocene aquifer contains water recharged in past several decades (bomb tritium and bomb radiocarbon detected). The M-P-Q system appears to be much slower, with time scales of groundwater flow possibly reaching some thousands of years. Sharp discontinuity of hydrochemical and isotope characteristic of groundwater observed across the major tectonic fault separating the Miocene and M-P-Q aquifers supports the idea of very limited (if any) hydraulic interconnection between both studied systems. This in turn calls for revision of existing conceptual models of groundwater flow in the region postulating significant groundwater fluxes crossing the fault in the direction of M-P-Q aquifer and adjacent aquifers in the Wadi al Fakka plain.     

贺兰山西麓典型干旱区绿洲地下水水化学特征与演变规律

针对地下水资源过量开采而出现的绿洲水文生态问题,以贺兰山西麓具有典型特征的内蒙古腰坝绿洲为研究对象,分开采期、非开采期对地下水进行系统取样分析,综合运用描述性统计、相关性分析、离子比例系数和Piper三线图示法,全面系统地研究了地下水水化学的时空变异特征与演变规律。研究结果表明：①季节变化对潜水和承压水水化学类型空间变异性影响较小,潜水水文化学性质受外界因素干扰较大,承压水受外界因素干扰较少;②蒸发浓缩、阳离子交换和人为混合是控制研究区潜水水质演变的主要水文化学过程;③潜水子系统总溶解固体较高,水化学类型变化也较复杂,主要从HCO3·SO4.Cl-Na·Mg·Ca型向Cl·SO4·HCO3-Mg·Na、Cl·SO4-Na·Mg型演化。承压水水化学类型比较单一,主要以低矿化度的HCO3-Na·Mg·Ca型为主。