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The aquifers in the M'léta Plain are crucial for supplying drinking water and supporting industrial and agricultural water needs. However, they are facing a pollution risk and environmental degradation. The present study aims to assess the groundwater quality in the M'léta Plain, focusing on its physicochemical properties, statistics of the aquifer, pollution risks, and factors influencing the water mineralisation process. The analysis of 16 samples reveals that the water contains high levels of sulphates and chlorides, often accompanied by sodium, calcium, or magnesium. This suggests two distinct water types or facies: one characterised by sodium chloride or calcium chloride, and the other with calcic or sodic sulphate waters, sometimes including magnesium sulphate. These facies may be attributed to the influence of different formations at the outcrop. Statistical analyses reveal a strong correlation between electrical conductivity and the majority of chemical elements, indicating the impact of freshwater interacting with the underlying rock formations on mineralisation. Some results also show undersaturation of certain minerals. Furthermore, the study evaluates the water's suitability for irrigation in the M'léta Plain in accordance with Richards' classification. [ABSTRACT FROM AUTHOR]

This study investigates the hydrogeochemical processes of groundwater in the Naama watershed in southwestern Algeria, aiming to determine the relationship between geochemical processes and groundwater quality. Multivariate statistical and thermodynamic techniques were applied to 22 groundwater samples to understand the hydrochemical evolution of the watershed. The results indicate that the water is predominantly characterized by a calcium-bicarbonate water type in the center of the study area (23% of samples) and a sodium chloride sulfate water type mainly located in the north due to Triassic dissolution and proximity to Sabkha (50% of samples), and the remaining 27% of samples are represented by the sulfate-sodium facies. Cluster analysis and principal component analysis revealed three major hydrochemical types reflecting different hydrochemical processes occurring along groundwater flow as electrical conductivity increased. The findings of this study could inform strategies for the sustainable management of groundwater resources in the Naama region and similar regions. [ABSTRACT FROM AUTHOR]

The Bellezma Mounts, located in the northeast of Algeria, present cases of hydrothermalism with temperatures ranging between 30° C and 63° C. For the evaluation of the thermal potential of this dissymmetrical mountains chains (often rectified in the South, where Cretaceous and Jurassic limestones emerge), we used a multidisciplinary approach, notably geology, geophysics, hydrogeology, hydrochemistry and the isotopic tool. Hydrogeological investigations have shown that these carbonate formations can offer an important aquifer potential. From the hydrochemical point of view, the warm waters of the Bellezma mounts are characterized by the presence of three different chemical facies: the sulfated-sodium, the bicarbonate-calcium and the chloride-calcium. Evaporite terrigenous origin is attributed to sodium, chlorides and sulphates of these waters. The thermal waters circulation in this region, at great depths in the crystallophyllian formations and the carbonate ones, in contact with terrigenous salt formations, could be responsible of the salinity characterizing these waters, in some places. Geothermometry has shown that these thermal waters acquire a high temperature in their original tanks coming from a depth ranging from 1100 to 2600 m through a fault system that affects the basement. The use of the isotopic tool has shown that the thermal waters of this region are ancient and that their recharge is weak or non-existent. [ABSTRACT FROM AUTHOR]

The present study aims to investigate the hydrogeochemical characteristics of the Terminal Complex (TC) groundwater in the Biskra region (north-east Algeria) to understand the hydrogeochemical processes that control their chemical composition using multivariate statistical techniques, bivariate and thermodynamic plots. A total of forty-five (45) water samples were collected from wells exploiting the TC aquifer and analyzed for electrical conductivity, pH, temperature, and major ions (April 2019). The results obtained indicate that the quality of the water does not meet WHO standards for drinking water, with contents of major elements exceeding the standard for most of the wells, except for the wells in the northern part, which are of good quality. Four types of hydrochemical facies were identified, revealing the diversity of processes that control water chemistry in the study area: (i) a sulfate sodium facies (47%), (ii) a sulfate calcium facies (37%), (iii) a bicarbonate magnesium facies (9%) and (iv) a sulfate magnesium facies (7%). Facies (i), (ii) and (iv), highlighted in the southern and south-western parts, are linked to the dissolution of salts and gypsum from evaporite formations. Facies (iii), identified in the northern part, reflects the dissolution of carbonate formations located in the aquifer recharge limits (recharge zone). The application of principal component analysis indicates that Na+, Cl−, Ca2+, Mg2+, SO42− and TDS represent the axis of mineralization. The dissolution of halite, gypsum, and anhydrite-bearing rocks is the primary mechanism for conducting groundwater salinization. These processes are confirmed by the PHREEQC model which reveal that calcite and dolomite precipitation favors the dissolution of evaporites where almost all water samples are undersaturated with respect to gypsum, anhydrite and halite (evaporite minerals). In addition, bivariate plots of the different ions show that cation exchange reactions leading to the adsorption of Ca2+ on clay minerals and simultaneous release of Na+ ions and silicate weathering are also processes that influence the groundwater chemistry of the Terminal Complex aquifer. [ABSTRACT FROM AUTHOR]

North-eastern Algeria is characterised by several thermal springs. The aim of this work is to study the Tamersite spring, which has not received any study and to compare to those relating to the Djaarir spring. For this purpose, four samples were collected from these thermal springs in 2017, having a temperature ranging between 26 and 35°C, anal most neutral pH and high values of electrical conductivity. In order to evaluate the thermal water potential of these springs, we adopted an interdisciplinary approach. The hydrochemical tool shows that hot water is characterised by the presence of two different chemical facies: the first of bicarbonate–sodium type, the second of chloride-sodium type. This analysis allowed also attributing a terriferous, evaporitic origin to sodium, chlorides and bicarbonates. The salinity characterizing these thermal waters is mainly due to deep runoff in cristallophyllian formations and carbonates formations being in contact with the terriferous, saliferous formations. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the hydro-chemical characteristics of Ouargla, Algeria basin groundwaters harvested from the Mio Pliocene aquifer. The study covered 70 samples; the physical parameters, potential of hydrogen (pH), and electrical conductivity EC μS.cm−1 were determined in situ, using a multiparameter; the laboratory analysis included dry residuals DR (mg/L), calcium Ca2+ (mg/L), magnesium Mg2+ (mg/L), sodium Na+ (mg/L), potassium K+ (mg/L), bicarbonates HCO3− (mg/L), sulfates SO42− (mg/L), and chloride Cl− (mg/L). The piper diagram shows that the Ouargla basin ground waters divided into two facies, sodic chlorinated in 93% and sodic sulphated in 7% of samples. The United States Salinity Laboratory Staff (USSL) diagram was used to detect the suitability of groundwater in irrigation where the results show that the groundwater was classed into two classes, poor water (C4 S4) and bad water (C4 S4). Furthermore, indices such as the Kelly index (KI), sodium adsorption ratio (SAR), sodium solubility percentage (Na%), and magnesium hazards (MH) confirm the negative effect of groundwater on soil permeability in 96%, 80%, 89%, and 53% of samples. The permeability index (PI) shows that the analyzed samples were considered as doubtful (71%) and safe (29%), otherwise there is no risk related to residual sodium carbonate (RSC). The geo-spatial distribution of deferent indices shows that all the study area has poor groundwater for irrigation, except the south-west part, where the groundwaters of this sub-area do not form a problem related to RSC. [ABSTRACT FROM AUTHOR]

Groundwater quality degradation is a significant environmental issue worldwide, with potentially severe economic consequences and harm to ecosystems and biodiversity. This can directly affect human health, particularly in developing countries where rapid and uncontrolled urbanization is on the rise. Groundwater is the primary resource for meeting the water needs of the Eloued region, located in southeastern Algeria. Water is considered unfit for human consumption if its physico-chemical elements exceed national or international standards or guidelines. We used the GPI and SPI indices to evaluate the quality of groundwater suited for drinking. Groundwater samples were obtained from 22 wells at depths of more than 250 m. Standard analytical procedures were used to determine the physicochemical characteristics of the collected samples, which included pH, EC, TDS, Na + , Ca +2 , Mg +2 , K + , Cl - , HCO 3 - , SO 4 -2 , NO 3 - , NO 2 - , NH 4 + and PO 4 -3 . Multivariate statistical analysis and GIS techniques were used to process the results. The results of the selected physicochemical parameters were compared with World Health Organization (WHO) guidelines to determine the quality of drinking water. The findings indicate that the waters of the terminal complex aquifer are salty and contain medium to high quantities of main ions that surpass the established drinking water limits. The primary ions' relative abundance is Cl -  > SO 4 -2  > HCO 3 -  > NO3 for anions and Na +  > Ca +2  > Mg +2  > K + for cations. Groundwater chemical types were dominated by Na + , Ca +2 , Cl - , and SO 4 -2 . Principal Component Analysis (PCA) showed that alteration and dissolution of carbonates, evaporates, salts, partly silicates, and evaporation, are the main reasons affecting the chemical composition of water in Eloued. The GPI results show that 18.18%, 54.54%, and 27.27% of the water samples were classed as lightly polluted, moderately polluted, or substantially polluted for drinking purposes, respectively. According to the SPI study, 9.09%, 36.36%, 36.36%, and 18.18% were considered drinkable, mildly contaminated, moderately polluted, and seriously polluted for drinking purposes, respectively. According to the GPI and SPI models' geographical distribution maps, potable water is generally scarce and concentrated in the northeastern section of the research area, near the town of Ourmes., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

This study focuses on the hydrodynamic and hydrochemical functioning of the karst system in Sidi Kada Mountains. These later extend between the Ghriss plain in the North and the Saida Mountains in the South. The hydrochemical approach was used to understand the hydrodynamic behaviour of the karst system which is represented by dolomitic limestone formation of Upper Jurassic. The geological data were used to delimit an impluvium with an area of 535.1 km² and a perimeter of 220.7 km. The functioning of this karst system was studied using several physic-chemical parameters, namely pH, temperature, electrical conductivity, TDS, Ca2+, Mg2+, Na+, HCO3-, Cl-, NO3-, SO42-. Frequency distributions of the water electrical conductivity (CFD) indicate that the system is characterized by two hydrodynamic sub-regimes, in which fracture networks control the base flow and conduit networks control the quick flow. The results of the hydrochemical analysis show that the waters facies are bicarbonated and magnesian. During periods of high water, the contents of chemical elements decreased, except for calcium and nitrates. During periods of low water, the participation of the saturated zone generates an increase in Mg2+ contents. The waters are typically characterised by an average conductivity of 848 μS/cm in deep waters. The shallow waters, influenced by anthropogenic actions, have an average conductivity of 1344 μS/cm and waters where exists the evaporite lenticular mass have relatively high values of conductivity, ranging from 1886 to 2644 μS/cm with an average of 2102 μS/cm. The good correlation between the chlorides and sulphates indicates the leaching of the soil layer. The correlation between Ca2+ and SO42- is negative but weak (r = -0.176), implied that Ca2+ was no derived from gypsum in the majority of samples. In contrast the water points whose chemistry is marked by the dissolution of gypsum or anhydrites have a good correlation between Ca2+ and SO42- (r = 0.93). The supersaturating regarding calcite and dolomite indices indicates mainly a flow in the saturated zone and through the unsaturated zone with a relatively high pCO2 (from 1.5 × 10-2 to 4 × 10-2). Biogenic CO2 initiates the mineralisation process in the unsaturated zone within an open system. The relationship between the saturation indices regarding calcite and dolomite shows that 87% of water varied from equilibrium and oversaturated. This is indicative of a slightly aggressive water with relatively slow circulation. [ABSTRACT FROM AUTHOR]

Knowledge of the quantity and quality of groundwater is a prerequisite to encourage investment in the development of a region and to consider the sedentarisation of populations. This work synthesises and analyses data concerning the chemical quality of the available water acquired in the Foum el Gueiss catchment area in the Aures massif. Two families of waters are observed, on the one hand, calcium and magnesian chlorated-sulphate waters and on the other hand, calcium and magnesium bicarbonate waters. Multivariate statistical treatments (Principal Component Analysis - PCA and Discriminant Analysis - DA) highlight a gradient of minerality of the waters from upstream to downstream, mainly attributed to the impact of climate, and pollution of agricultural origin rather localised in the lower zones. These differences in chemical composition make it possible to differentiate spring, well and borehole waters. The main confusion is between wells and boreholes, which is understandable because they are adjacent groundwater, rather in the lower part of the catchment area. The confusion matrix on the dataset shows a complete discrimination with a 100% success rate. There is a real difference between spring water and other samples, while the difference between wells and boreholes is smaller. The confusion matrix for the cross-validation (50%). [ABSTRACT FROM AUTHOR]

The present study aims to evaluate the groundwater quality in an area characterized by significant human anthropic activities within the upper Seybouse. In order to assess the quality, a total of 20 samples were analyzed to identify the chemical and bacteriological composition of the water, its variations, and their potential impacts on the environment and human health. The results revealed concentrations of the chemical and bacteriological elements exceeding the WHO standards, with high levels of electrical conductivity (EC) (peak = 4210 μS/cm), Ca 2+ (peak = 340.68 mg/L), Na + (peak = 360 mg/L), HCO 3 - (peak = 287 mg/L), Cl - (peak = 542 mg/L), SO 4 2- (peak = 687 mg/L), NO 3 - (pek = 65.91 mg/L), fecal coliforms (FC) (peak = 160 UFC/mL), fecal Streptococcus (FS) (peak = 43 UFC/mL), and Clostridium perfringens (CP) (peak = 29 UFC/mL). Within the basin, two different facies have been identified: Cl-SO 4 -Na type and Cl-SO 4 -Ca type. The calculated Water Quality Index (WQI) indicates that none of the groundwater samples are suitable for drinking or human consumption. The detection of pathogenic microorganisms through diverse molecular methods has revealed the existence of eight distinct species, encompassing pathogenic strains that can affect human health. Moreover, the dissolution of geologic formations can influence the water's chemistry. In this region, groundwater pollution seems to be influenced by anthropogenic and agricultural factors such as fertilizer application, irrigation practices, and the release of domestic sewage., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The current paper sheds light on geochemical methods used to characterize water-rocks interaction. The concern is to assess the vulnerability of groundwater resources to contamination in Aflou, an area in central Saharan Atlas of Algeria. This study of hydrochemistry reveals lithological impact on hydrochemistry in Aflou syncline. Our study region is like a basin meaning that the important groundwater resources are located in the sandstones of the Intercalary Continental Aquifer (Barremian-Albian). This study marks a noticeable influence of evaporated minerals and ascents of Triassic materials, which are widely propagated along with different levels for several wells of Djebel Amour. Lithology influence on the hydrochemistry of this aquifer is very visible by evaporation contained essentially in the Triassic and in the marly intercalations of the Portlandian, the Barremian-Aptian-Albian and those of the Mio-Pliocene. For Aflou region, the lower Cretaceous (Portlandian) and Upper Jurassic (limestone) formations, the calcium sulfated facies, have very high levels of SO4–, Cl–, Ca2+, and Na+. Integration of both graphical and Piper diagram, saturation index values (estimated by Phreeq-C method) and geographic information system tool was helpful not only to create the database for analysis of spatial variation in respective water quality parameters but also to decipher the hydrogeochemical process occurring in our study area. This study utilized the inverse distance weighted (IDW) interpolation method to interpolate and estimate cell values in Aflou syncline by averaging the values of sample data points in the neighborhood of each processing cell. IDW method has been used in establishing maps. The examination of iso-contents maps and the principal component analysis results show that the water composition was very closely related to the lithological nature of the different formations. [ABSTRACT FROM AUTHOR]

This study aims to determine the physicochemical and bacteriological parameters of surface and groundwater of Bouhamdane basin, located in the North-eastern part of Algeria. Water resources in this area constitute the main source for public drinking, agricultural and industrial supplies in the region. For this purpose, a total of 20 water samples were collected from the Zenati and Bouhamdane rivers, wells and springs and have been analysed for 19 physicochemical elements. Total Coliforms, faecal Coliforms, faecal Streptococci and sulphite-reducing Clostridium were also investigated. The results showed that the water samples have pH values ranging between 6.48 and 8.11, electrical conductivity ranges between 348 and 2150 μS/cm and Nitrate amounts range between 6.16 and 65.2 mg/L. High concentrations of fluoride were noted in the North-eastern part of the study area and the phosphates were relatively high in surface water samples (up to 6.45 mg/L). Hydrochemical facies using Piper diagram indicates that waters are mainly of Cl-Na-K and HCO3-Na-K types. According to thermodynamic calculations and stability diagrams, the chemical evolution of waters is mainly controlled by water–rock interactions. The bacteriological analysis showed that 35% of 20 samples are contaminated, which can represent an important threat for the riparians. [ABSTRACT FROM AUTHOR]

With a flow estimated at 1200 m3∙s−1 and a height of 8 m downstream, the flood that occurred on October 10, 2008 spread along the M'zab River over a length of more than 180 km. Material and human damage is visible, but its effects on the quality of the waters of the alluvial layer remain unknown: this is the purpose of this paper. Samples of groundwater were taken during the period 2005–2012 in 4 oases of the valley. Physicochemical analyses were performed using molecular and flame spectroscopic methods and also volumetric methods on water samples. The results obtained were interpreted using histograms and hydrochemical diagrams, such as the Avignon software (L.H.A) (version 4, 2008). Low effect of flood on the water quality of the alluvial aquifer was manifested by concentrations of magnesium sulphate and calcium chloride. On the other hand, there is an accumulation of salts infiltrated by sewage except for the zone of Bouchen. The diagrams show that there is an improvement in water quality in this area. [ABSTRACT FROM AUTHOR]

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The Hammamet Plain, situated in the northwest of the Tezbent mountain range, northeast of Algeria, drains carbonate aquifers through some important karst springs. The physical and chemical characteristics of spring and well water samples were studied for 2 years to assess the origin of groundwater and determine the factors driving the geochemical composition. The ionic speciation and mineral dissolution/precipitation was calculated. Water wells, characterizing groundwater circulation at shallow depths, are moderate to high mineralized waters of Na-HCO type. In contrast to the shallow environment, the CO-rich, deeper waters are of the Ca-HCO-SO type and undergo significant changes in the baseline chemistry along flow lines with increasing residence time. The main factors controlling the groundwater composition and its seasonal variations are the geology, because of the presence of carbonate formations, the elevation and the rate of karst development. In both groups, the carbonate chemistry is diagnostic of the effect of karst development. The supersaturation with respect to calcite indicates CO degassing, occurring either inside the aquifer in open conduits, or at the outlet in reservoirs. The undersaturation with respect to calcite shows the existence of fast flow and short residence time conditions inside the aquifer. Interaction between groundwater and surrounding host rocks is believed to be the main process responsible for the observed chemical characteristics of groundwater in the study area. [ABSTRACT FROM AUTHOR]

The intensive exploitation of groundwater resources in the region of Hodna (Southeastern Algeria) has greatly influenced the hydrochemical functioning of the shallow aquifer. This resulted in a significant decline in the piezometric level of the aquifer. In terms of hydrochemical facies, water is Ca-HCO3 type in the Northern part of the plain due to limestone formations and SO4 -Cl-Na type in the South, because of the closeness of a salt lake. Eighteen groundwater samples were sampled and analyzed, in order to highlight the groundwater hydrochemical processes. Multivariate statistical techniques were applied to the obtained analyses on groundwater quality, with the purpose of defining the main controlling factors affecting the Hodna plain hydrochemistry. The statistical analysis reveals the presence of three groups, presenting an increased potential of salt proportionally to groundwater flow direction. Initially, in the aquifer boundaries and in the infiltration areas the facies result as bicarbonate. In the southern part of the plain, groundwater becomes SO4 -Cl rich, because of the dissolution of salt formations and the presence of the Hodna salt lake. Nitrate concentrations could be related to agricultural activities in the plain. Isotopic analyzes showed that the aquifer recharge is very quick and its groundwater have undergone high evaporation at the salt lake. [ABSTRACT FROM AUTHOR]

This study presents the results of the first investigation on natural occurrence of radium and radon in Algerian thermal water systems. Activity concentrations of Rn and Ra isotopes were measured in sixteen hydrothermal springs of northwestern Algeria. Samples displayed high activities, especially for 222Rn, 224Ra and 226Ra (up to 377 × 103 Bq/m3, 730 Bq/m3 and 4470 Bq/m3, respectively). Approximately, 50% of the investigated springs displayed activities of combined long-lived Ra (226Ra + 228Ra) in excess of the maximum contaminant level (MCL) of the WHO and EPA for drinking water. Factors controlling the distribution of radionuclides in the aquifer system are investigated. The observed correlation between Ra isotope and TDS suggests that adsorption/desorption is not the dominant process controlling the distribution of Ra in waters. Our results indicate that the excess SO 4 2− limits the concentration of dissolved Ba2+ and thereby, the elevated Ra activities in these hydrothermal systems are not simply limited by co-precipitation with BaSO 4 (barite). The data shows that Ra activities are likely dominated by the recoil process of parent isotopes in the aquifer solids. The minimal abundance of clay minerals and oxides in the aquifer, in addition to thermal activities in northwestern Algeria, significantly enhances the mobilization of Ra into waters. [Display omitted] • Radionuclides of short and long-lived radium along with radon were investigated in hydrothermal systems from northwestern Algeria. • Activity levels of radium in 50% of the investigated springs exceeds the (MCL) of radium in drinking water. • Geochemical and hydrogeochemical mechanisms controlling radionuclides mobilization in hydrothermal systems are provided. • Findings show that these waters should be used with caution, especially, where radionuclides exceed the permissible limits. [ABSTRACT FROM AUTHOR]

This work aims to evaluate the hydrochemical characteristics of a shallow aquifer located between carbonated formations and salt lake in the Chemora region in northeastern Algeria. Hydrochemical, multivariate statistical, and the thermodynamics techniques were used to investigate the hydrochemical evolution within the aquifer. Twenty-five water samples were collected during May 2013 in this the aquifer wells. The results indicate that this shallow water is characterized by sulfate-dominant facies representing about 64% of cases, followed by the chloride with 24%, and the remaining (12%) is represented by the bicarbonate facies. The sulfate facies is acquired mainly by the alteration of pyrite. The saturation index showed that all carbonate minerals are supersaturated and all evaporate minerals are undersaturated which suggest that their soluble component Na+, Cl−, Ca2+, andconcentrations are not limited by mineral equilibrium. The application of the cluster analysis and the principal components analysis based on major ion contents defined 3 main chemical water types reflecting different hydrochemical processes with salinity increases along the groundwater flow. [ABSTRACT FROM PUBLISHER]

The studied area is in the south of Algeria. Chemical data are used to determine the status of water quality in the Albian sandstone aquifer of Ain oussera, as well as to clarify the hydrological regime in the study area, to identify spatial and temporal variations of water quality and sources of contamination (natural and anthropogenic). Waters in sandstone are dominated by a magnesium chloride type and sodium chloride type. Interpretation of chemical data with thermodynamic calculation suggests that the chemical evolution of groundwater is primarily controlled by water–rock interactions. Piezometric map suggests that water is moving from the south toward north. The agricultural irrigation effluent and domestic effluents have largely contributed to contamination of groundwater. [ABSTRACT FROM AUTHOR]

Chemical data are used to clarify the hydrogeological regime in the Merdja area in Tébessa, as well as to determine the status of water quality in this area. Groundwater from the aquifer in the Merdja area can be divided into two major groups according to geographical locations and chemical compositions. Water in the center part of the area of study is characterized by the dominance of chloride, sulfate, sodium, and potassium; whereas waters in the limestone aquifers in the west are dominated by the same cations but have higher concentrations of bicarbonate. Stable isotopes show that the Tébessa aquifers contain a single water type, which originated in a distinct climatic regime. This water type deviates from the Global Meteoric Water Line (MWL), as well as from the Mediterranean meteoric water line. The water is poor in tritium, and thus can be considered generally older than 50 years. Piezometric map suggests that water is moving from the west towards the center of the studied area, and from east towards center. Degradation of water quality can be attributed to agricultural fertilizers in most cases, although the wadi El Kebir River is a contributor to pollution in the middle part of the studied area. [ABSTRACT FROM AUTHOR]

In the Cheffia Mounts, in the NE of Algeria, the water of many springs are thermo-mineral. The most used by patient are the springs as Sidi Trad, Zatout et Beni Salah. Others are not to known by want of equipping and physical planning for access and use. Here, we present preliminary results of the study of water of these springs. The oldest analyses date from the 1968 year. During the 2001 yr, we obtained new data which permit us the hydrochemical characterization of waters, and their representation on Piper diagram and statistic analysis (Principal Component Analysis, PCA). Numerous chemical facies are identified and permit the distinction of two groups of springs: ∙ one group is characterized by unsalted waters but with a smell of rotten eggs (H2S), as Sidi Trad spring; ∙ another group contains salted waters with abundant bicarbonate mineralization and carbonated by CO2, as the others. [ABSTRACT FROM AUTHOR]

Salt pan brines in desert areas are globally known to be rich sources of lithium. This study reports the results of a regional survey of brine chemistry in chotts (salt pans) conducted along a 550 km long valley in the northeast Algerian Sahara, one of the major desert areas on Earth. A dataset composed of 50 samples, including brine, river, and aquifer, is integrated and discussed in order to study the characteristics of Sahara brines. Brines contain up to 66 mg L−1 of lithium, salinities up to ~400 g L−1, and magnesium concentrations ~690 times greater than that of lithium. The primary source of major ions would occurr by dissolution of ancient evaporites of the substrate by aquifer waters. Near surface lithium concentration of brines in chotts across the study area and in the aquifer Complexe Terminal defines a pattern of increasing values to the north, where maximum values coincide with chotts (Melghir and Merouane) having the largest sizes (up to 1,840 km2) and placed at the lowest altitudes (36 m below sea level). This pattern coincides with the northwards plunging structured substrate. Lithium grades increase consistently with salinity during the concentration through evaporation. However, lithium continues to concentrate beyond evolved brines whether due to the precipitation of lithium-free salts leading to lithium increases in residual brine, and/or by unknown processes supplying additional lithium. Discussed aspects are expected to drive an increasing interest on chotts, which would reveal in the future, as a stimulating opportunity for Algeria and the Saharan region. • Algerian Sahara chott brines are Cl–SO 4 /Na–Mg, with Li up to 66 mg L−1. • Major ions derive from the dissolution of ancient evaporites by aquifer waters. • The location, size, and altitude of chotts follow the N-plunging structured substrate. • Li grades in brines increase northwards similar to that of the aquifer waters. • Li sources are unknown and brine grades are ruled by evaporative concentration. [ABSTRACT FROM AUTHOR]