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

Salinity-induced desertification in oasis ecosystems: challenges and future directions

Salinity-induced desertification is a pressing environmental issue that poses a significant threat to the sustainability of oasis ecosystems worldwide. These ecosystems are vital to the livelihoods of millions of people living in hyper-arid, arid and semi-arid regions, providing essential resources such as food, water and other necessities. However, overexploitation of natural resources, changes in land use and climate change have led to the degradation of these ecosystems, resulting in soil salinisation, waterlogging and other adverse effects. Combating salinity-induced desertification requires a comprehensive approach that addresses both the underlying causes of ecosystem degradation and the direct consequences for local communities. The strategy may include measures for sustainable land use, reforestation and water conservation. It is also essential to involve local communities in these activities and to ensure that their perspectives are heard. The aim of this article is to examine the causes and processes of salinity-induced desertification in oasis ecosystems and the implications for their sustainability. It also examines strategies that are being used to prevent desertification and promote sustainable oasis management. This article aims to raise awareness of this critical issue and to promote action towards a more sustainable future.

Using unsupervised machine learning models to drive groundwater chemistry and associated health risks in Indo-Bangla Sundarban region

Groundwater is an essential resource in the Sundarban regions of India and Bangladesh, but its quality is deteriorating due to anthropogenic impacts. However, the integrated factors affecting groundwater chemistry, source distribution, and health risk are poorly understood along the Indo-Bangla coastal border. The goal of this study is to assess groundwater chemistry, associated driving factors, source contributions, and potential non-carcinogenic health risks (PN-CHR) using unsupervised machine learning models such as a self-organizing map (SOM), positive matrix factorization (PMF), ion ratios, and Monte Carlo simulation. For the Sundarban part of Bangladesh, the SOM clustering approach yielded six clusters, while it yielded five for the Indian Sundarbans. The SOM results showed high correlations among Ca2+, Mg2+, and K+, indicating a common origin. In the Bangladesh Sundarbans, mixed water predominated in all clusters except for cluster 3, whereas in the Indian Sundarbans, Cl--Na+ and mixed water dominated in clusters 1 and 2, and both water types dominated the remaining clusters. Coupling of SOM, PMF, and ionic ratios identified rock weathering as a driving factor for groundwater chemistry. Clusters 1 and 3 were found to be influenced by mineral dissolution and geogenic inputs (overall contribution of 47.7%), while agricultural and industrial effluents dominated clusters 4 and 5 (contribution of 52.7%) in the Bangladesh Sundarbans. Industrial effluents and agricultural activities were associated with clusters 3, 4, and 5 (contributions of 29.5% and 25.4%, respectively) and geogenic sources (contributions of 23 and 22.1% in clusters 1 and 2) in Indian Sundarbans. The probabilistic health risk assessment showed that NO3- poses a higher PN-CHR risk to human health than F- and As, and that potential risk to children is more evident in the Bangladesh Sundarban area than in the Indian Sundarbans. Local authorities must take urgent action to control NO3- emissions in the Indo-Bangla Sundarbans region.

Salinity origin in the coastal aquifer of the Southern Venice lowland

Groundwater salinization can be natural and anthropogenic in origin, although it often results from a combination of both, especially in low-lying coastal regions that are hydraulically controlled. This study proposes a method to assess the origin of salinity using environmental tracers in porewater, like Cl- and Br-, combined with depositional facies associations detected in sediment cores. Such integrated approach was tested in a target area south of the Venice Lagoon (Italy), where groundwater salinization is triggered by multiple mechanisms due to the complexity of the hydro-geomorphological environment. Batch tests were performed on sediment core samples from boreholes to quantify major anions and total inorganic N. Cl- and Br- porewater concentrations coupled with sedimentary facies association provided insights into the origin of groundwater salinity from a variety of sources, including past and present seawater intrusion, agricultural leaching, and evaporites. The strengths and limitations of the integrated approach are discussed to provide a pathway for improving water resource management and planning measures to prevent groundwater salinization in coastal areas.

Hydrogeochemical characterization and evaluation of subsurface water quality in the Proterozoic Cuddapah Basin, Andhra Pradesh, India

In the current survey, different hydrogeochemical processes governing the geochemistry of aquifers, the usefulness of groundwater for regular consumption, and agricultural purposes were evaluated around the Tummalapalle area. One hundred forty-four borehole locations were chosen to characterize the major physicochemical components of the aquifer water. The analysis results of pH inferred that the groundwater is nominally acidic to basic, and pH ranged from 6.6 to 8.4. The average concentrations of TDS, Ca²⁺, Mg²⁺, total hardness (TH), HCO₃^-, and total alkalinity (TA) are within the allowable limits of potable water quality as prescribed by the Bureau of Indian Standards (BIS) and WHO. However, the average concentrations of Na⁺, K⁺, Cl^-, and SO₄^2- were all below the permissible limit. All samples were analyzed with the help of Piper and Chadha charts to determine the dominant hydrogeochemical components of groundwater. The dominance of cations in groundwater in this region is in the sequence of Ca²⁺  > Na⁺  > Mg²⁺  > K⁺, followed by anions HCO₃^-  > Cl^-  > SO₄^2-. The Gibbs plot analysis suggested the predominance of rock aquifer interaction as the major hydrogeochemical process governing groundwater geochemistry in this region. The water quality index (WQI) of all groundwater samples in the Tummalapalle region was estimated, with 55% of the samples being potable grade. The different irrigation indices were analyzed for the groundwater samples to estimate their desirability for agriculture. The maximum number of water samples was found to be well-suited for cultivation.

Hydrogeochemical analysis of groundwater quality for drinking and irrigation with elevated arsenic and potential impact on agro-ecosystem in the upper Brahmaputra plain, India

The upper Brahmaputra floodplain is considerably enriched with geogenic contaminants, mainly Arsenic (As) exhibiting high spatial heterogeneity. With this concern, the present study was conducted in Lakhimpur district located in the upper Brahmaputra floodplain aiming to assess the groundwater (GW) suitability for drinking and irrigation. Chemical analysis of 78 GW samples revealed significantly high As (max 0.12 mgL^-1, mean 0.02 mgL^-1) followed by iron (max 62.2 mgL^-1, mean 19.94 mgL^-1) showing uneven distribution. Hydrogeochemical analysis of the GW samples revealed that majority of the water samples belong to mixed Ca²⁺- Na⁺- HCO₃^- type with weathering and forward ion exchange as the dominant processes in the aquifer system. Positive correlation among iron (Fe) and As, together with close grouping in hierarchical cluster analysis and principal components analysis, indicated the involvement of reductive hydrolysis process. Calculation of saturation indices indicated that, precipitation of Fe minerals may lead to de-coupling of Fe and As contributing to the enrichment of both the elements in the GW. Further, assessment of key parameters for irrigation water quality including water quality index indicated the GW to be suitable for irrigation purpose. Finally, toxicity implications of crops produced from As contaminated water indicated higher accumulation potential of As in the food grains implying significant impacts on the agro-ecosystem and associated health hazards.

Cl/Br mass ratio and water quality index from the Quaternary aquifer of south Bengal Basin in India

The purpose of this study is to identify suitable areas for the exploitation of groundwater for human consumption by analysing Cl/Br and other indicators of wastewater influence on groundwater quality in and around the twin megacities of Kolkata and Howrah, located on the complex deltaic system of south Bengal Basin in India. About 18%, 56.5%, 28% and 35.5% of the 287 groundwater samples comply with the Indian acceptable limits (ALs) of TDS, Cl, Fe and Mn, respectively. About 29% of the 279 samples analysed have Cl/Br < 268 where the excess Br is derived from organic degradation. About 30% samples have Cl/Br > 308 clustering mainly around a palaeo-channel indicating wastewater contamination. In addition to these, many samples have NO₃/Cl > 0.0002 and SO₄/Cl > 0.014, indicating that the groundwater is contaminated by wastewater from sewage and septic tank leakage. The concentrations of metals (Fe, Mn) and As are also higher than AL particularly on either side of the palaeo-channel, which may affect the human body functions. The localised recharge of wastewater also contains high SO₄. Sulphate reduction in the aquifer sequesters the As in groundwater into the neo-formed arsenopyrite. Based on the estimated water quality index, the groundwater samples have been classified into four types-highly suitable (28.17%), moderately suitable (23.94%), doubtful (15.85%) and unsuitable (32.04%) for drinking purpose. The first two types cover about 62% of the study area. But the highly urbanised area of Kolkata and Howrah city and the industrial areas in the southern fringe of Kolkata city have the latter two types of groundwater. The over-withdrawal of groundwater may expedite the quality deterioration of 'highly and 'moderately suitable water' of the study area into 'doubtful' and 'unsuitable for drinking' categories through mixing mechanism in the aquifer.

Chemical Quality and Hydrogeological Settings of the El-Farafra Oasis (Western Desert of Egypt) Groundwater Resources in Relation to Human Uses

In the Egyptian deserts, new land reclamation projects have been recently established to meet the increasing-population growth rate and food demand. These projects mainly depend on the different groundwater aquifers. El-Farafra Oasis is one of the “1.5-million-feddan reclamation project” areas recently established in the Western Desert of Egypt where the only available water source is the world’s largest fossil freshwater reservoir “the Nubian Sandstone Aquifer System (NSAS)”. Groundwater-dependent springs, and their artificial counterpart “drilled wells”, are reliable water systems throughout the world. In the present study, hydrochemical parameters were collected in 2015 from 16 different springs and wells of the El-Farafra Oasis, and analyzed using the different water quality indices. The calculated water quality index (WQI), its correlations with the water quality parameters Gibbs, Piper, US Salinity-Lab Staff and Wilcox diagrams, and Principal Component Analysis (PCA) were used to evaluate the groundwater suitability for human drinking and irrigation purposes. WQI values revealed good-to-excellent groundwater quality for human drinking. In addition, the spring and well water samples investigated showed good indices for irrigation activities. Gibbs and Piper’s diagrams were presented, with most samples falling into the rock-dominance category, and belonging to hydrogeochemical facies determining the following water types: Mg(HCO3)2 type water (37.5% of the samples), no dominant ions (mixed water-type category; Ca/MgCl2) (50% of the samples), and, finally, NaCl water type (the remaining 12.5%). The groundwater chemistry in the study area is mainly controlled by rock-water interactions, particularly the dissolution of carbonate rocks and silicate weathering. The elevated nutrient concentrations, in particular nitrates, are most likely due to agricultural activities, indicating substantial anthropogenic activities in the area studied.

Simulating River/Lake–Groundwater Exchanges in Arid River Basins: An Improvement Constrained by Lake Surface Area Dynamics and Evapotranspiration

Surface water–groundwater interactions in arid zones are characterized by water exchange processes in a complex system comprising intermittent streams/terminal lakes, shallow aquifers, riparian zone evapotranspiration, and groundwater withdrawal. Notable challenges arise when simulating such hydrological systems; for example, field observations are scarce, and hydrogeological parameters exhibit considerable spatial heterogeneity. To reduce the simulation uncertainties, in addition to groundwater head and river discharge measurements, we adopted remote sensing-based evapotranspiration data and lake area dynamics as known conditions to calibrate the model. We chose the Ejina Basin, located in the lower reaches of the Heihe River Basin in arid northwest China, as the study area to validate our modelling approach. The hydrological system of this basin is characterized by intensive, spatiotemporally variable surface water–groundwater interactions. The areas of the terminal lakes into which all river runoff flows vary significantly depending on the ratio between river runoff and lake evaporation. Simulation results with a monthly time step from 2000 to 2017 indicate that river leakage accounted for approximately 61% of the total river runoff. Our study shows that for areas where surface water and groundwater observations are sparse, combining remote sensing product data of surface water areas and evapotranspiration can effectively reduce the uncertainty in coupled surface water and groundwater simulations.

Impact of hydrogeochemical processes and its evolution in controlling groundwater chemistry along the east coast of Tamil Nadu and Puducherry, India

The present study area falls beside the coastal zone of Tamil Nadu, and Puducherry is characterized by varied geological formations that mostly contain groundwater resources that are primarily utilized for domestic, agricultural, industrial, and other utilities. The study aims to differentiate various hydrogeochemical processes responsible for disparities in water chemistry. Groundwater samples were collected from 66 sites during the two major seasons: pre-monsoon and post-monsoon. The analytical data were separated into terrain vice and utilized for preparing graphical plots as well as mathematical calculations to obtain the existing relationship among chemical constituents and water quality. The Ca-HCO3, Na-Cl, Ca-Na-HCO3, mixed Ca-Mg-Cl, Ca-Cl, and Na-HCO₃ are the main hydrochemical facies observed from the groundwater samples. The ionic relationship among the samples indicates the control of direct and reverse ion exchange in the concentration of Ca²⁺, Mg²⁺, Na⁺, and K⁺ in groundwater. Moreover, silicate weathering contributes more in comparison with carbonate and evaporite dissolution. Gibbs plots reveal that water-rock interaction and evaporation processes are the main mechanisms controlling the water chemistry. The saturation index of different mineral phases indicates groundwater to be oversaturated with silicate mineral phases irrespective of the terrain. Statistical methods like correlation and principal component analysis were also performed to differentiate the specific association and possible source of the dissolved constituent in the groundwater. The study concludes the influence of multiple processes such as silicate weathering, direct and reverse ion exchange, secondary dissolution, saline water intrusion, and anthropogenic sources as the main reasons responsible for variation in groundwater chemistry.

Numerical Approaches for Estimating Daily River Leakage from Arid Ephemeral Streams

Despite the significance of river leakage to riparian ecosystems in arid/semi-arid regions, a true understanding and the accurate quantification of the leakage processes of ephemeral rivers in these regions remain elusive. In this study, the patterns of river infiltration and the associated controlling factors in an approximately 150-km section of the Donghe River (lower Heihe River, China) were revealed using a combination of field investigations and modelling techniques. The results showed that from 21 April 2010 to 7 September 2012, river water leakage accounted for 33% of the total river runoff in the simulated segments. A sensitivity analysis showed that the simulated infiltration rates were most sensitive to the aquifer hydraulic conductivity and the maximum evapotranspiration (ET) rate. However, the river leakage rate, i.e., the ratio of the leakage volume to the total runoff volume, of a single runoff event relies heavily on the total runoff volume and river flow rate. In addition to the hydraulic parameters of riverbeds, the characteristics of ET parameters are equally important for quantifying the flux exchange between arid ephemeral streams and underlying aquifers. Coupled surface/groundwater models, which aim to estimate river leakage, should consider riparian zones because these areas play a dominant role in the formation of leakage from the river for recharging via ET. The results of this paper can be used as a reference for water resource planning and management in regulated river basins to help maintain riparian ecosystems in arid regions.

High levels of fluoride contamination in groundwater of the semi-arid alluvial aquifers, Pakistan: evaluating the recharge sources and geochemical identification via stable isotopes and other major elemental data

Hydrogeochemical methods were integrated to delineate the geochemical factors controlling fluoride (F^-) contamination in groundwater at four sites in the districts of Lahore (Samada) and Kasur (Sari Chimba, Kot Maiga, and Chah Fatehwala) in Panjab province of Pakistan. Hydrochemical data and stoichiometric ratios indicate Na-Cl and Na-HCO₃ as the dominant water types with silicate weathering influencing overall hydrogeochemistry of the study area. The groundwater F^- concentrations ranged between 0.54 mg/L and 17.5 mg/L, with more than 70% samples having F^- concentrations above the World Health Organization (WHO) provisional drinking water guideline (1.5 mg/L). Saturation indices determined that 100% samples were saturated with respect to calcite and 96% samples were undersaturated with respect to fluorite, indicating the influence of calcite precipitation on fluoride enrichment. A positive correlation was observed between fluoride with pH, Na⁺, and HCO₃^-, confirming that high fluoride concentrations were the result of weathering of silicate minerals and the exchange of OH^- on clay surface under the alkaline pH conditions. The isotopic values of δ¹⁸O and δ²H in groundwater ranged from 9.14 to - 5.51‰ and 56.57 to - 39.5‰, respectively. The stable isotope data indicated the meteoric origin of groundwater with some evaporative effect, which is partly influencing groundwater quality such as high pH and salinity, as a result facilitating anion exchange (OH^- for F^-) on clays surface. The research indicates that the groundwater quality of the study area is not recommendable for drinking due to its high total dissolved solids (TDS) and elevated fluoride concentrations.

Mapping of lineaments for groundwater assessment in the Desert Fringes East El-Minia, Eastern Desert, Egypt

The Eocene aquifer system in Egypt is an important source of water to meet the increasing necessities of the agricultural, drinking, and domestic purposes. This study aimed to assess the impact of the hydro-structural features identified as lineaments on the groundwater occurrence, assess the water quality status for various purposes, and provide useful information for future management. To achieve this, Landsat images have been used in conjunction with the chemical data (major, trace ions, and physicochemical parameters) and statistical analysis. The hydrochemical facies showed that the water samples belong to (1) Ca-HCO₃; (2) mixed facies CaMgHCO₃ and mixed CaNaHCO₃, and (3) Na-Cl hydrochemical facies. The water chemistry is controlled by the carbonate weathering, ion exchange, and evaporite dissolution. The groundwater analysis has indicated that the water is suitable for drinking purposes when compared with the drinking water standards. Furthermore, salinity, electric conductivity, sodium adsorption ratio (SAR), and sodium percentage (%Na) assessment show that majority of the groundwater samples are appropriate for irrigation. The satellite imagery of the area has been analyzed to determine the orientation, density, and intersection. The orientation of the lineaments is well-confirmed with regional structural setting; in addition, density maps show that the density is high throughout the study area. The results reflect a correlation between the lineaments and the hydrologic phenomena. The statistical analysis with the one-way ANOVA confirmed the importance of lineaments as explanatory variable for the observed variation in water quality. This in turn supported that the fracture is structurally controlled and mostly influences both the occurrence and quality.

Salinization of reservoirs in regions with exposed evaporites. The unique case of Upper Gotvand Dam, Iran

Construction of the great Upper Gotvand Dam in the Karun River, Iran, with an impoundment capacity of 4.5 billion cubic meters, has resulted in an environmental disaster: accumulation of 66.5 million metric tonnes of dissolved salt in the reservoir and a dramatic increase in the salinity of the reservoir water up to 200 g/L. This paper aims to identify and assess the main sources of the salinization of the reservoir water integrating multiple data: (1) geological and geomorphological evidence; (2) continuous vertical records of electrical conductivity at 11 stations along the reservoir; (3) total dissolved solids and major ion concentrations of 108 water samples at 58 sampling stations; (4) δ¹⁸O, δ²H in 35 water samples and δ³⁷Cl in 16 water samples from the reservoir and surrounding rivers and springs. Geological and geomorphological evidence, hydrogeochemical data and isotopic signature reveal that halite dissolution is the main cause of salinization in the Gotvand Reservoir. The results show that salt dissolution in the Gachsaran Formation (especially at Anbar Ridge), which was under-estimated in the study phase of the project, has provided about 86 per cent of the dissolved salt accumulated in the reservoir over a 2-year period since the impoundment of the reservoir in 2011.

Climate Change Impact on the Evolution of the Saline Lakes of the Soan-Sakaser Valley (Central Salt Range; Pakistan): Evidences from Hydrochemistry and Water (δD, δ18O) and Chlorine (δ37Cl) Stable Isotopes

The surfaces of saline lakes are shrinking at a threatening rate worldwide. Likewise, the Uchhali complex (formed by three saltwater lakes located in the Salt Range, Pakistan) that serves as a major regional source of water for humans and as a habitat for water birds must be monitored. With this objective in mind, we conducted a study coupling hydrochemistry and stable isotope compositions (δ37Cl, δ18O and δD) in order to characterize its hydrochemical properties and the main processes controlling them. Results showed that the Uchhali complex salinity has dramatically increased compared to other similar lakes in the world. While the Uchhali (UL) and Khabbeki (KL) lakes present a sodium-chloride hydrofacies, the Jahlar (JL) is of a sodium-bicarbonate type. Hydrochemistry parameters indicate that the weathering of surrounding rocks is the major vector for the increase of total dissolved solids in the water. On the other hand, the observed enrichment in heavy isotopes of the water stable isotope compositions implies that the different lakes are undergoing a long history of intense evaporation. The study of the corresponding δ37Cl isotope compositions supports the conclusion that evaporation, along with weathering, are the main driving processes. Besides climate effects that result in the decrease of annual precipitation and the increase of evaporation, water consumption for domestic purposes (household and agriculture) aggravates the rise of the lakes’ salinity.

Distribution, formation and human-induced evolution of geogenic contaminated groundwater in China: A review

The sustainability of groundwater usage faces quality problem caused by anthropogenic activity as well as geogenic contamination. With varied climate zones, geomorphology and geological background, China faces a variety of geogenic contaminated groundwater (GCG) reported known as high TDS, Fe, Mn, As, F, I, NH₄⁺, U, Cr and low I, Se, etc., may still exist some others not fully known yet. The problem of GCG is more significant in northern China due to extensive groundwater usage, arid climate and widespread Holocene strata. High salinity groundwater is mainly distributed in semi-arid/arid northwestern inland basins and coastal areas. Elevated Fe and Mn are frequently concomitant and controlled by redox potential, prevailing in the Sanjiang Plain, Yellow River Basin, and middle and lower reaches of the Yangtze River Basin. High As groundwater occurs in reducing aquifer is mainly distributed in the Yellow River, Yangtze River and Huai River Basins as well as the Songnen Plain and Xinjiang. Fluoride is characterized by its areal distribution in northern China in comparison with scatter occurrence in the south. The dissolution of F-bearing minerals as well as evaporation effect both contribute to elevated F. High iodine groundwater mainly distributed in the Yellow-Huai-Hai River Basin and low iodine prevailing in piedmont areas both pose health issues. Iodine is related to decomposition of organic matter (OC) as well as marine origin. Contributed by OC mineralization naturally-occurring NH₄⁺ was found in reducing aquifers. The GCG triggers endemic disease in addition to reduce groundwater resource. The co-occurrence like high TDS and F, As and F are frequently observed posing major challenges for mitigation. Anthropogenic influence like abstraction and pollutant infiltration would alter groundwater flow and the redox condition causing the further evolution of GCG. Identification of GCG should be made in rural areas where private wells prevail to ensure resident's health.

Hydrochemical characteristics and quality assessment of groundwater for irrigation use in central and eastern Songnen Plain, Northeast China

The hydrochemical characteristics of groundwater in Songnen Plain's agricultural area were analyzed based on aquifer types and topography classification to evaluate irrigation suitability and factors influencing groundwater quality. Samples of different groundwater types and topographical conditions within the research area were collected and chemical indices, such as sodium adsorption ratio, %Na⁺, residual sodium carbonate, and magnesium hazard values, were calculated to assess the groundwater suitability for irrigation. The results indicated that groundwater was generally neutral, with low total dissolved solids and slightly high hardness; the dominant anion in groundwater was HCO₃^-, while Ca²⁺ was the relatively stable primary cation found in water samples from the high plain and river valley plain. The nitrate in groundwater significantly exceeded WHO drinking water standards, especially in the unconfined water of the high plain, which was due to the large-scale agricultural production activities in the eastern regions. The main reactions in the groundwater system were weathering and dissolution of carbonates and sulfates and ion-exchange reactions. Horizontal zoning in water chemical characteristics was prominent; from the high plain to river valley plain and low plain, the hydrochemistry gradually transitioned from HCO₃-Ca-Na to HCO₃-Na-Ca and HCO₃-Na. Based on the chemical indices, the majority of samples were suitable for agricultural irrigation except for some in the western area with high salinity and sodium hazards. Treatment measures to groundwater and soil should be taken to reduce the possibility of soil salinization and promote crop growth in these latter regions.

Fluoride-contaminated groundwater of Birbhum district, West Bengal, India: Interpretation of drinking and irrigation suitability and major geochemical processes using principal component analysis

The present research work is confined to a rural tract located in the north-western part of Birbhum district, West Bengal, India. Chemical analysis of the groundwater shows the cations is in the order of Na⁺ > Ca²⁺ > Mg²⁺ while for anions it is HCO₃^─ > Cl^─ > SO₄^2─ > NO₃^─. The F^─ concentration was found to vary from 0.01 to 18 mg/L in the pre-monsoon and 0.023 to 19 mg/L in post-monsoon period. 86% of samples show low F^─ content (<0.60 mg/L) whereas, 8% exhibit elevated concentration of F^─ (>1.2 mg/L) mainly in the central and north-central parts of the study area at a depth of 46 to 98 m. The prime water type is CaHCO₃ succeeded by F^─-rich NaHCO₃ and NaCl waters. The suitability analysis reveals that the water at about 81% of the sampling sites is unsuitable for drinking and at 16% of sites unsuitable for irrigation. The alkaline nature of the water and/or elevated concentration of Fe, Mn and F^─ make the water unsuitable for potable purposes while the high F^─ and Na⁺ contents delimit the groundwater for irrigation uses. Multivariate statistical analysis suggests that chemical weathering along with ion exchange is the key process, responsible for mobilization of fluoride in groundwater of the study area.

Identification of the hydrogeochemical processes and assessment of groundwater quality using classic integrated geochemical methods in the Southeastern part of Ordos basin, China

Insufficient understanding of the hydrogeochemistry of aquifers makes it necessary to conduct a preliminary water quality assessment in the southern region of Ordos Basin, an arid area in the world. In this paper, the major ions of groundwater have been studied aiming at evaluating the hydrogeochemical processes that probably affect the groundwater quality using 150 samples collected in 2015. The two prevalent hydrochemical facies, HCO₃Mg·Na·Ca and HCO₃Mg·Ca·Na type water, have been identified based on the hydrochemical analysis from Piper trilinear diagram. Compositional relations have been used to assess the origin of solutes and confirm the predominant hydrogeochemical processes responsible for the various ions in the groundwater. The results show that the ions are derived from leaching effect, evaporation and condensation, cation exchange, mixing effect and human activities. Finally groundwater quality was assessed with single factor and set pair methods, the results indicate that groundwater quality in the study region is generally poor in terms of standard of national groundwater quality. The results obtained in this study will be useful to understand the groundwater quality status for effective management and utilization of the groundwater resource.

Development of a Conductivity Sensor for Monitoring Groundwater Resources to Optimize Water Management in Smart City Environments

The main aim of smart cities is to achieve the sustainable use of resources. In order to make the correct use of resources, an accurate monitoring and management is needed. In some places, like underground aquifers, access for monitoring can be difficult, therefore the use of sensors can be a good solution. Groundwater is very important as a water resource. Just in the USA, aquifers represent the water source for 50% of the population. However, aquifers are endangered due to the contamination. One of the most important parameters to monitor in groundwater is the salinity, as high salinity levels indicate groundwater salinization. In this paper, we present a specific sensor for monitoring groundwater salinization. The sensor is able to measure the electric conductivity of water, which is directly related to the water salinization. The sensor, which is composed of two copper coils, measures the magnetic field alterations due to the presence of electric charges in the water. Different salinities of the water generate different alterations. Our sensor has undergone several tests in order to obtain a conductivity sensor with enough accuracy. First, several prototypes are tested and are compared with the purpose of choosing the best combination of coils. After the best prototype was selected, it was calibrated using up to 30 different samples. Our conductivity sensor presents an operational range from 0.585 mS/cm to 73.8 mS/cm, which is wide enough to cover the typical range of water salinities. With this work, we have demonstrated that it is feasible to measure water conductivity using solenoid coils and that this is a low cost application for groundwater monitoring.

Evaluation of groundwater suitability for domestic, irrigational, and industrial purposes: a case study from Thirumanimuttar river basin, Tamilnadu, India

The Thirumanimuttar sub-basin forms an important groundwater province in south India, facing serious deficiency in both quality and quantity of groundwater due to increased demand associated with rapid population explosion, agricultural growth and industrial activities. A total of 194 groundwater samples were collected and 15 water quality parameters were analyzed using standard procedures. Na( + ), Cl( - ), Ca(2 + ), HCO(-)(3), Mg(2 + ) and SO(2-)(4) concentration ions are more dominant in both seasons. The total dissolved solids and electrical conductivity was observed good correlation with Na( + ), Cl( - ), HCO(-)(3), Ca(2 + ), Mg(2 + ), Cl( - ), PO(3-)(4) and NO(-)(3) ions indicating dominance of plagioclase feldspar weathering, anthropogenic input and over drafting of groundwater irrespective of seasons. The Hill-Piper diagram indicates alkaline earths exceed the alkalis, an increase of weak acids was noted during both the seasons. For assessing the groundwater for irrigation suitability parameters like total hardness, sodium adsorption ratio, residual sodium carbonate (RSC), permeability index, and sodium percentage are also calculated. Permanent hardness was noted in higher during both the seasons due to discharge of untreated effluents and ion exchange process. The RSC indicates 56% of the samples are not suitable for irrigation purposes in both seasons, if continuously used will affect the crop yield. From the results, nearly 72% of the samples are not suitable for irrigation.

Environmental tritium (³H) and hydrochemical investigations to evaluate groundwater in Varahi and Markandeya river basins, Karnataka, India

The present study aimed at assessing the activity of natural radionuclides ((3)H) and hydrochemical parameters (viz., pH, EC, F(-), NO(3)(-), Cl(-), Ca(2+), Mg(2+)) in the groundwater used for domestic and irrigation purposes in the Varahi and Markandeya river basins to understand the levels of hydrochemical parameters in terms of the relative age(s) of the groundwater contained within the study area. The recorded environmental (3)H content in Varahi and Markandeya river basins varied from 1.95 ± 0.25T.U. to 11.35 ± 0.44T.U. and 1.49 ± 0.75T.U. to 9.17 ± 1.13T.U. respectively. Majority of the samples in Varahi (93.34%) and Markandeya (93.75%) river basins being pre-modern water with modern recharge, significantly influenced by precipitation and river inflowing/sea water intrusion. The EC-Tritium and Tritium-Fluoride plots confirmed the existence of higher total dissolved solids (SEC > 500 μS/cm) and high fluoride (MAC > 1.5 mg/L) in groundwater of Markandeya river basin, attributed to relatively longer residence time of groundwater interacting with rock formations and vice versa in case of Varahi river basin. The tritium-EC and tritium-chloride plots indicated shallow and deep circulating groundwater types in Markandeya river basin and only shallow circulating groundwater type in Varahi river basin. Increasing Mg relative to Ca with decreasing tritium indicated the influence of incongruent dissolution of a dolomite phase. The samples with high nitrate (MAC > 45 mg/L) are waters that are actually mixtures of fresh water (containing very high nitrate, possibly from agricultural fertilizers) and older 'unpolluted' waters (containing low nitrate levels), strongly influenced by surface source.