Understanding the factors contributing to groundwater salinity in the coastal region of Andhra Pradesh, India

Spatial prediction of groundwater salinity in multiple aquifers of the Mekong Delta region using explainable machine learning models

Groundwater salinization is a prevalent issue in coastal regions, yet accurately predicting and understanding its causal factors remains challenging due to the complexity of the groundwater system. Therefore, this study predicted groundwater salinity in multi-layered aquifers spanning the entire Mekong Delta (MD) region using machine learning (ML) models based on an in situ dataset and using three indicators (Cl-, pH, and HCO3-). We applied nine different decision tree-based models and evaluated their prediction performances. The models were trained using 13 input variables: weather (2), hydrogeological conditions (4), water levels (3), groundwater usage (2), and relative distance from water sources (2). Subsequently, by employing model interpretation techniques, we quantified the significance of factors within the model prediction. Performance evaluations of the ML models demonstrated that the Extra Trees model exhibited superior performance and demonstrated generalization capabilities in predicting Cl- concentration, whereas the Bagging and Random Forest models outperformed the other models in predicting pH and HCO3- concentration. The coefficients of determination were determined to be 0.94, 0.67, and 0.78 for Cl-, pH, and HCO3-, respectively Additionally, the model interpretation effectively identified significant factors that depended on the target variables and aquifers. In particular, salinity indicators and aquifers that were strongly influenced by the artificial usage of groundwater were identified. Therefore, our research, which provides accurate spatial predictions and interpretations of groundwater salinity in the MD, has the potential to establish a foundation for formulating effective groundwater management policies to control groundwater salinization.

Groundwater quality in high-sulfur coal mining region of India: Spatial distribution, source control, and health risk assessment

The groundwater quality in the vicinity of the Makum coalfield, renowned for its high-sulfur coal deposits, was investigated. The oxidation of sulfur in the coal generates acid mine drainage (AMD), a global environmental challenge that contaminates natural resources. The region's high sulfur coal content intensifies AMD formation, necessitating a comprehensive assessment of its impact on human health and the environment. This study analyzes the water quality parameters such as pH, EC, TDS, Na+, Ca+2, Mg+2, K+, HCO3-, SO4-2, F-, Cl -, and NO3- in groundwater, findings concerning low pH levels (5.8) and fluoride concentration (0.15 mg/L) compared to standards. Groundwater chemistry was analyzed to identify the sources controlling water composition through Gibbs diagrams, Piper diagrams, and saturation indices. The Gibbs diagram shows that rock weathering is the crucial factor controlling groundwater chemistry, while the Piper diagram indicates Ca-Cl as the Principal water type. Additionally, an in-depth analysis of groundwater chemistry reveals that carbonate dissolution primarily occurs due to minerals like calcite, dolomite, and gypsum, findings supported by saturation indices. The present study yielded an average water quality index of 40.19, indicating excellent to good water quality in 51 out of 52 samples analyzed. The average hazard index values for adults and children were 0.60 and 0.58, respectively, indicating that 49 of 52 samples pose negative non-carcinogenic risks associated with nitrate and fluoride contamination. The irrigation indices, graphical representations such as the Wilcox and Doneen classification, and the USSL diagram elucidate the suitability for irrigation purposes. Moreover, the Principal Component Analysis identified the sources of ions as originating from geogenic processes and mining activities. The study stresses environmental assessments, health risk management, and sustainable practices for groundwater in high-sulfur coal mining areas.

Quality and health impact of groundwater in a coastal region: a case study from west coast of southern India

Seawater intrusion seriously threatens the quality of coastal groundwater, affecting nearly 40% of the world's population in coastal areas. A study was conducted in the Kamini watershed situated in the Udupi district of Karnataka to assess the groundwater quality and extent of seawater intrusion. During the pre-monsoon period, 57 groundwater and 3 surface water samples were analyzed to understand the impact of seawater on the groundwater and surface water. The analysis revealed that the groundwater in the study area is slightly alkaline. The weighted overlay analysis map indicated that 11% of the study area is unsuitable for drinking water due to the influence of seawater. The Piper plot analysis revealed that the groundwater is predominantly CaMgCl facies. The hydrogeochemical facies evolution diagram (HFED) showed that 62% of the groundwater is affected by seawater. The HFED and Piper plots also indicate that the surface water is also affected by seawater. These results are also supported by various molar ratios such as Cl- vs. Cl⁻/HCO3⁻, Cl⁻ vs. Na⁺/Cl⁻, Cl- vs. SO42-/Cl-, and Cl⁻/HCO3- vs. Mg2+/Ca2+, suggesting that the majority of the water sample has been affected by seawater. The saturation indices indicated that mineral dissolution has significantly contributed to groundwater salinization. The correlation between sulfate concentration and calcite and dolomite dissolution suggested the influence of seawater intrusion in the coastal aquifer. The process of reverse ion exchange mainly influences the groundwater chemistry according to chloroalkali indices. The total hazard index (THI) values of nitrate and fluoride exceeded limits, posing health risks to adults and children. Studies suggest that with time and space, seawater intrusion is increasing in some pockets of the study area, especially along the west coast.

Research on the relation between hydro-chemical and geological characteristics in karst area: Case study in Zhong Liang Mountain, Southwest China

Karst groundwater, which is one of most important drinking water sources, is vulnerable to be polluted as its closed hydraulic relation with surface water. Thus, it is very important to identify the groundwater source to control groundwater pollution. The Pearson correlation coefficient among major ions (Na + K+, Ca2+, Mg2+, HCO3 -, SO4 2-, and Cl-) was employed to deduce the groundwater types in Zhong Liang Mountain, Southwest China. Then, the combined method of principal component analysis and cluster analysis were employed to identify the groundwater sources in a typical karst region of southwest China. The results shown that (1) the high positive correlation between cations and anions indicated the water-rock reaction of Ca-HCO3, Ca-SO4, (Na + K)-Cl, and Mg-SO4. (2) The major two principal components that would represent water-rock reaction of CaSO4 and Ca-HCO3 would, respectively, explain 60.41% and 31.80% of groundwater information. (3) Based on the two principal components, 33 groundwater samples were clustered into eight groups through hierarchical clustering, each group has similar water-rock reaction. The findings would be employed to forecast the surge water, that was an important work for tunnel construction and operation. PRACTITIONER POINTS: The components of groundwater was highly correlated with water-rock reaction. The principal component analysis screens the types of groundwater. The cluster analysis identifies the groundwater sources.

Characterization of groundwater salinity by hydrogeochemical and multivariate statistical analysis in the coastal aquifer of Nagapattinam district, Southern India

The impact of seawater intrusion from coast to inland terrain in the Cauvery River Basin (CRB) and Uppanar River Basin (URB) was evaluated based on major ion groundwater chemistry. TDS ranges from 229 to 2260 mg/l, and 408 to 3732 mg/l; Na+ range from 67 to 560 mg/l, and 74 to 1600 mg/l, and Cl- range from 120 to 906 mg/l, and 110 to 3260 mg/l for CRB and URB respectively. Piper Diagram, Hydrochemical Facies Evolution Diagram (HFE-D), rock-water interaction (Gibbs Plots), various bivariate plots viz., TDS vs. Cl-; Na+ vs. Cl-; Ca2+ vs. Cl-; Ca2+ vs. SO4 2-; TH vs. TDS and Principal Component Analysis (PCA) (Cluster and Factor analysis) were used to identify the seawater intrusion from coast to inland aquifers and to understand hydrogeochemical characterization and salinization processes. Piper diagram shows that most of the samples are Na+-Cl- type, HFE-D diagram also shows that most of the samples were saline intrusion type and mixing behavior, while TH vs. TDS plot shows hard fresh to hard brackish type from both the basins. PCA results clearly show the three factors, explaining 84.02 % and 76.67 % variance in URB and CRB. Factor-1 records 53.03 % alteration, with a strong confidence loading of TDS, Na+, Cl-, Ca2+, K+, SO4 2, Total Alkalinity (TA), and Total Hardness (TH) in URB indicating saline nature. A total variance of 46.23 % in CBR is more positively loaded with TH, Mg2+, Ca2+, and SO4 2- indicating rock-water interaction. Cluster analyses of these parameters illustrate the cluster distribution in CRB and URB. In URB, TDS, Na+, and Cl- ions make a cluster with a linkage distance of 5000 m, whereas in CRB, the TDS, Na+, Cl-, and TA ions make a cluster with a linkage distance of 2800 m. The factor and cluster analysis fetched out an effect of intensive use of fertilizers, aquaculture activities, and excessive groundwater exploitation. This technique gave the relationship between various chemical parameters in groundwater. Factor and cluster analysis have proven highly effective in groundwater quality studies. The study concluded that the study area has the threat of saline water intrusion in shallow aquifers with continuous influences of seawater mixing.

Hydrogeochemical characterization and assessment of factors controlling groundwater salinity in the Chamwino granitic complex, central Tanzania

Chamwino district, central Tanzania is a semi-arid granitic complex province, where groundwater is the major source of water for domestic and other uses. However, groundwater in the area is affected by salinity, thus, lowering the availability of potable water for various uses, decrease in crop production, taste less, wastage of soap, and abnormal pain. Due to this, this study sought to characterize groundwater using hydrogeochemical facies and signatures in order to identify the factors influencing the distribution of salt water in the Chamwino Granitic Complex. A total of 141 groundwater samples were collected from wells spatially distributed within the study area from January 2023 to April 2023, (a season of relatively low rainfall). All samples were subjected to in situ analyses of physicochemical parameters pH, temperature (T), total dissolved solids (TDS), electrical conductivity (EC), and salinity using a multi-parameter water analyzer and analyses of major ions (Ca2+, Mg2+, K+, Na+, Cl-, SO42-, HCO3-, and NO3-). The study revealed that the dominant cations in the groundwater are Na+ > Ca2+ > Mg2+, and the anions are Cl- > HCO3- > SO42. Five geological formations (granodiorite, tonalitic orthogenesis, migmatite, tonalite, and alluvium) were identified, and each is characterized by its unique groundwater facie. In the areas that are dominated with granodiorite, the major hydrogeochemical facies were Ca-HCO3, Na-Cl, Ca-Na-HCO3, Ca-Mg-Cl, and Ca-Cl water types; tonalitic orthogenesis was dominated by Ca-HCO3, Na-Cl, Ca-Mg-Cl, and Ca-Cl water types; migmatite was dominated by Ca-HCO3, Na-Cl, Ca-Mg-Cl, and Ca-Cl water types; tonalite was dominated by Na-Cl, Ca-Mg-Cl, and Ca-Cl water types; and alluvium was dominated by Na-Cl and Ca-Mg-Cl and Ca-Cl water types. The common hydrogeochemical facies in all five geological units are Na-Cl, Ca-Mg-Cl, and Ca-Cl water types. It is revealed that the groundwater in the study area is alkaline in nature and slightly saline with salinity level between 0.2 mg/L (fresh water) and 2.8 mg/L (brackish water) with mean 1.07 mg/L (of 141 samples). The factors controlling groundwater salinity distribution are mainly rock-water interaction and ion exchange reactions. Groundwater salinity in the study area is largely attributed to the abundance of Na+, Ca2+, Cl- and SO42-. Abundance of Na+ and Ca2+ is the results of both, weathering of feldspar minerals particularly plagioclase (Na-Ca feldspars) which are the major mineral in granites, and evaporation crystallization cycles of evaporates in semi-arid areas such as Chamwino. Also, such evaporation crystallization cycles account for the abundance of Cl- and SO42- especially in areas dominated by alluvium. However, anthropogenic activities as evidenced by elevated nitrate up to 212.6 mg/L in congested areas are also likely to contribute in area) to the elevated Cl- and SO42-. In other geological units such as tonalitic orthogneiss, migmatite and granodiorite, there was an ostensible mixing of saline water with fresh water from local recharge as indicated by the abundance of HCO3- ions. Nonetheless, the hydrogeochemical characterization of groundwater in the Chamwino granitic complex suggests that there is little possibility for groundwater to evolve to a carbonate water type (fresh water) because the groundwater salinity is mainly geogenic, unless artificial recharge through rainwater harvesting is applied.

Spatio-seasonal patterns and sources of major ions in the Longjiang River catchment, Southern China

River water quality is closely related to the major ion sources and hydrological conditions. However, there is a limited cognition about the geochemical sources and the seasonal variations of major ions. Thus, in this study, a total of 90 water samples were collected from the Longjiang River and its three tributaries in the dry and wet seasons. The samples were analyzed, including major ion concentrations and physicochemical parameters. Statistical analysis, such as correlation analysis and principal component analysis (PCA), was employed to investigate the spatial and seasonal variations in major ion composition and their respective sources. Our study revealed that the predominant major ions in the studied samples are Ca2+, Mg2+, HCO - 3, and SO2 - 4. Most of ions exhibited notable spatial disparities attributable to variations in geological settings and human activities. Regions characterized by igneous rock outcrops tend to exhibit higher levels of K+ and Na+, while areas with higher population densities in the middle and downstream segments show elevated concentrations of Cl-, NO - 3, SO2 - 4, Na+, and K+. The observed peak SO2 - 4 levels may be attributed to active mining operations. Most parameters displayed higher values in flood season than those in dry season due to dilution effects. Stoichiometric analysis indicated that carbonate weathering inputs contribute to over 85% of the mean total cation concentrations in the water, followed by contributions from silicates, atmospheric deposition, and anthropogenic inputs. On the whole, although the water quality remains non-polluted and is suitable for drinking and irrigation purposes, the enrichment of SO2 - 4 and NO - 3 may contribute to water eutrophication. Caution is warranted during the dry season due to reduced water flow resulting from dam interceptions and limited dilution capacity, potentially leading to elevated pollutant concentrations. Taken together, our results provided a scientific basis for water quality managements of monsoon rivers.

Entropy-weighted water quality index, hydrogeochemistry, and Monte Carlo simulation of source-specific health risks of groundwater in the Morava River plain (Serbia)

Population growth, urbanization, industry, floods, and agriculture globally degrade groundwater in river plains, necessitating action for its quality assessment and management. Hence, a comprehensive methodology, including hydrogeochemical facies (Piper, Gibbs), irrigation indices (SAR, Wilcox), entropy-weighted water quality index (EWQI), positive matrix factorization (PMF), and Monte Carlo simulation of source-specific health risks was used in this study to analyze groundwater in the Morava river plain (Serbia). The results revealed a prevalent Ca-Mg-HCO3 groundwater type, influenced by water-rock interactions. Although groundwater was found suitable for irrigation, only 66.7 % of the samples were considered drinkable. Agricultural activities, natural processes, and municipal wastewater were identified as primary pollution sources. The incremental lifetime cancer risk (ILCR) and hazard index (HI) threshold exceedance for adults and children ranged from 8.5 % to 39 % of the samples, with arsenic identified as the most risk-contributing contaminant. These findings provide valuable insights for researchers studying groundwater vulnerability in river plains.

Groundwater Salinity Across India: Predicting Occurrences and Controls by Field-Observations and Machine Learning Modeling

Elevated groundwater salinity is unsuitable for drinking and harmful to crop production. Thus, it is crucial to determine groundwater salinity distribution, especially where drinking and agricultural water requirements are largely supported by groundwater. This study used field observation (n = 20,994)-based machine learning models to determine the probabilistic distribution of elevated groundwater salinity (electrical conductivity as a proxy, >2000 μS/cm) at 1 km2 across parts of India for near groundwater-table conditions. The final predictions were made by using the best-performing random forest model. The validation performance also demonstrated the robustness of the model (with 77% accuracy). About 29% of the study area (including 25% of entire cropland areas) was estimated to have elevated salinity, dominantly in northwestern and peninsular India. Also, parts of the northwestern and southeastern coasts, adjoining the Arabian Sea and the Bay of Bengal, were assessed with elevated salinity. The climate was delineated as the dominant factor influencing groundwater salinity occurrence, followed by distance from the coast, geology (lithology), and depth of groundwater. Consequently, ∼330 million people, including ∼109 million coastal populations, were estimated to be potentially exposed to elevated groundwater salinity through groundwater-sourced drinking water, thus substantially limiting clean water access.

Spatio-temporal variability of public water supply characteristics and associated health hazards for children and adults in selected locations of Ambala, India

The contamination of public water supply and groundwater resources is a major concern in many parts of developing nations. Polluted water poses serious health risks to humans and the environment. This research was conducted to investigate the seasonal variations of the water quality parameters in the public water supply. To assess the supply water quality in different blocks of Ambala District, hydro-chemical analysis was conducted after a series of systematic sampling in various locations. The statistical tools for water quality indexing including water quality indexing (WQI), heavy metal pollution indexing (HMPI), pollution indexing (PI), overall pollution indexing (OPI), metal indexing (MI), and hazard indexing (HI) were used for data as well as the health hazard analysis through water pathway. Overall, 40 water samples were taken from the public water supply systems covering winter and summer seasons, and the levels of pH, total dissolved solids (TDS), EC, F- , Cl- , NO3 - , SO4 2- , HCO3 - , As, B, Cd, Co, Pb, Zn, Cr, Fe, and Mn were investigated. The weight arithmetic index method was used for WQI, and water pollution indices such as HMPI, PI, OPI, and MI were calculated using different models to check the severity of contamination. The mean hazard quotient and hazard index values calculated using the concentration levels of As, B, Cd, Co, Pb, Cr, Fe, Mn, Zn, F- , and NO3 - reveal that supply water may pose a significant health risk to both adults and children that further varies with temporal and spatial changes. During both seasons, a high carcinogenic risk for both adults and children was observed in the studied area because of high levels of As, Pb, Cd, and NO3 - . PRACTITIONER POINTS: The quality of public supply water was assessed at the selected sites of Ambala, India. High levels of NO3 - , As, Cd, and Pb were observed posing a health risk to adults and children via water pathway. 95% of the samples qualified for the excellent water quality category with respect to the levels of F- , Cl- , NO3 - , SO4 2- , HCO3 - , pH, EC, and TDS. Statistical analysis (HMPI, PI, MI, OPI, HI) using different models revealed water contamination with reference to the levels of NO3 - , As, Pb, Cr, Ni, and Cd. Immediate measures are needed to uphold the safety and health of the natives.

Seasonal variation of the quality of groundwater resources for human consumption and industrial purposes in the central plain zone of Punjab, India

Due to environmental pollution, climate change, and anthropogenic activities, the judicious use and regular assessment of the quality of groundwater for industrial, agricultural, and drinking purposes had gained a lot of attention across the globe. To assess the seasonal suitability of groundwater based on hydrochemistry and different quality indices, groundwater samples were collected and analyzed for different physicochemical parameters. Our findings indicated that the pH, electrical conductivity (EC), total dissolved solids (TDS), total hardness (TH), and calcium ion (Ca2+) content of groundwater were within acceptable limits of WHO and Bureau of Indian Standards (BIS) guidelines for drinking water. However, chloride content exceeded the acceptable levels, accounting for about 29.1% during the pre-monsoon and 15.3% during the post-monsoon period. Based on the water quality index (WQI), none of the water samples were deemed unsuitable for drinking purposes. However, when considering the synthetic pollution index (SPI), 100% of the samples were categorized as moderately polluted during both the pre-monsoon and post-monsoon periods. For industrial purpose suitability, 39.8 and 30.6% of the water samples had high corrosion tendency for pre-monsoon and post-monsoon seasons, respectively. Additionally, 77.5-93.4% of the total water samples were slightly affected by salinization on the basis of Revelle index. Generally, the groundwater quality for drinking purposes meets the WHO and BIS guidelines, with high corrosion potential for industrial use and slight salinization concerns in the area.

Spatio-temporal variation of groundwater pollution in urban wetlands and management strategies for zoning

Groundwater is an important resource to maintain the sustainable development of urban wetlands. The Jixi National Wetland Park (JNWP) was studied to realize the refined prevention and control of groundwater. The self-organizing map-K-means algorithm (SOM-KM), improved water quality index (IWQI), health risk assessment model and forward model were used comprehensively to evaluate the groundwater status and solute sources in different periods. The results showed that the groundwater chemical type in most areas was the HCO₃-Ca type. Groundwater chemistry data from different periods were clustered into five groups. Groups 1 and 5 are affected by agricultural and industrial activities, respectively. The IWQI value in the normal period was higher in most areas due to the influence of spring ploughing. The east side of the JNWP was disturbed by human activities, and the quality of drinking water continued to deteriorate from the wet period to the dry period. 64.29% of the monitoring points showed good irrigation suitability. The health risk assessment model showed that the health risk was the largest in the dry period and the smallest in the wet period. The main factors causing health risks in the wet period and other periods were NO₃^- and F^-, respectively. The overall cancer risk was within acceptable limits. The forward model and ion ratio analysis showed that the weathering of carbonate rocks was the main factor affecting the evolution of groundwater chemistry, accounting for 67.16%. The high-risk areas of pollution were mainly concentrated in the east of the JNWP. K⁺ and Cl^- were the key monitoring ions in the risk-free zone and potential risk zone, respectively. The research can be used to help decision-makers carry out fine zoning control of groundwater.

Spatial distribution and driving factors of groundwater chemistry and pollution in an oil production region in the Northwest China

Concerns have been raised on the deterioration of groundwater quality associated with anthropogenic impacts such as oil extraction and overuse of fertilizers. However, it is still difficult to identify groundwater chemistry/pollution and driving forces in regional scale since both natural and anthropogenic factors are spatially complex. This study, combining self-organizing map (SOM, combined with K-means algorithm) and principal component analysis (PCA), attempted to characterize the spatial variability and driving factors of shallow groundwater hydrochemistry in Yan'an area of Northwest China where diverse land use types (e.g., various oil production sites and agriculture lands) coexist. Based on the major and trace elements (e.g., Ba, Sr, Br, Li) and total petroleum hydrocarbons (TPH), groundwater samples were classified into four clusters with obvious geographical and hydrochemical characteristics by using SOM - K-means clustering: heavily oil-contaminated groundwater (Cluster 1), slightly oil-contaminated groundwater (Cluster 2), least-polluted groundwater (Cluster 3) and NO₃^- contaminated groundwater (Cluster 4). Noteworthily, Cluster 1, located in a river valley with long-term oil exploitation, had the highest levels of TPH and potentially toxic elements (Ba, Sr). Multivariate analysis combined with ion ratios analysis were used to determine the causes of these clusters. The results revealed that the hydrochemical compositions in Cluster 1 were mainly caused by the oil-related produced water intrusion into the upper aquifer. The elevated NO₃^- concentrations in Cluster 4 were induced by agricultural activities. Water-rock interactions (e.g., carbonate as well as silicate dissolution and precipitation) also shaped the chemical constituents of groundwater in clusters 2, 3, and 4. In addition, SO₄^2--related processes (redox, precipitation of sulfate minerals) also affected groundwater chemical compositions in Cluster 1. This work provides the insight into the driving factors of groundwater chemistry and pollution which could contribute to groundwater sustainable management and protection in this area and other oil extraction areas.

Groundwater fluoride and nitrate contamination and associated human health risk assessment in South Punjab, Pakistan

Consumption of high fluoride (F^-) and nitrate (NO₃^-) containing water may pose serious health hazards. One hundred sixty-one groundwater samples were collected from drinking wells in Khushab district, Punjab Province, Pakistan, to determine the causes of elevated F^- and NO₃^- concentrations, and to estimate the human health risks posed by groundwater contamination. The results showed pH of the groundwater samples ranged from slightly neutral to alkaline, and Na⁺ and HCO₃^- ions dominated the groundwater. Piper diagram and bivariate plots indicated that the key factors regulating groundwater hydrochemistry were weathering of silicates, dissolution of evaporates, evaporation, cation exchange, and anthropogenic activities. The F^- content of groundwater ranged from 0.06 to 7.9 mg/L, and 25.46% of groundwater samples contained high-level fluoride concentration (F^-  > 1.5 mg/L), which exceeds the (WHO Guidelines for drinking-water quality: incorporating the first and second addenda, WHO, Geneva, 2022) guidelines of drinking-water quality. Inverse geochemical modeling indicates that weathering and dissolution of fluoride-rich minerals were the primary causes of F^- in groundwater. High F^- can be attributed to low concentration of calcium-containing minerals along the flow path. The concentrations of NO₃^- in groundwater varied from 0.1 to 70 mg/L; some samples are slightly exceeding the (WHO Guidelines for drinking-water quality: incorporating the first and second addenda, WHO, Geneva, 2022) guidelines for drinking-water quality. Elevated NO₃^- content was attributed to the anthropogenic activities revealed by PCA analysis. The high levels of nitrates found in the study region are a result of various human-caused factors, including leaks from septic systems, the use of nitrogen-rich fertilizers, and waste from households, farming operations, and livestock. The hazard quotient (HQ) and total hazard index (THI) of F^- and NO₃^- showed high non-carcinogenic risk (> 1) via groundwater consumption, demonstrating a high potential risk to the local population. This study is significant because it is the most comprehensive examination of water quality, groundwater hydrogeochemistry, and health risk assessment in the Khushab district to date, and it will serve as a baseline for future studies. Some sustainable measures are urgent to reduce the F^- and NO₃^- content in the groundwater.

Groundwater quality in Zagora southeast of Morocco by using physicochemical analysis and geospatial techniques

Groundwater in Morocco is restricted because of the semiarid to arid climatic conditions; it is under threat from organic and inorganic pollution. Furthermore, it is considered the only source of potable water as well as having different usages, making its quantitative and qualitative protection an urgent priority. The present study focused mainly on the anthropogenic impact on the natural resources and groundwater quality around Zagora city. Fifteen samples were collected from wells during rainy and dry seasons in 2 years 2020-2021 and the analysis of the groundwater quality of studied stations. The suitability of the aquifer Fezouata was investigated using drinking and irrigation water quality indices. The results showed that sulfate and chloride are the dominant anions in the groundwater samples. While the mean abundance of major cations is Na +  > Mg²⁺  > Ca²⁺  > K⁺, the sodium ion is dominant and K + is the least abundant. The physicochemical parameters show that conductivity, nitrate, and sulfate exceed the limit fixed by WHO. Hydrogeochemical plots indicate that 93% of samples belong to Na-Cl facies and only 7% are mixt Cl-Mg-Ca in 2021, the results are similar except for two samples which are 13% belong Cl-Mg-Ca. The Water Quality Index suggests that 28.55% are good quality water, 23.90-47.55% are poor and very poor quality water, respectively, and 40.24% are unsuitable in 2020. Furthermore, the WQI of the 2021 campaign showed that only 17.48% were considered good quality water and 38.94% (43.58%) were poor or very poor quality water, respectively. However, 33.21% are unsuitable. Based on irrigation indices, the majority of groundwater samples can be used for agricultural purposes, notably those of the upstream part of the study area.

Hydrochemical evolution characteristics, controlling factors, and high nitrate hazards of shallow groundwater in a typical agricultural area of Nansi Lake Basin, North China

Anthropogenic nitrate contamination in groundwater could not be neglected, which has been a global issue threatening public health, especially in agricultural fields where fertilizers were used intensively. The present study focused on evaluating the groundwater evolution process, quality, and associated health risks from nitrate pollution in Nansi Lake Basin (NLB), a typical intensive agricultural region of North China. For this purpose, fifty-two shallow groundwater samples were collected and analyzed major chemical parameters in June 2022. The groundwater samples are found to be mainly dominated by HCO₃-Ca·Mg and SO₄·Cl-Ca·Mg types. Water-rock interactions like minerals dissolution/precipitation and ion exchange were found to be the important processes influencing hydrochemistry. Nitrate content in groundwater fluctuated from 1.9 to 750.0 mg/L (average:148.7 mg/L), with about 75% of samples surprisingly exceeding the permissible limit (50 mg/L) set by the World Health Organization (WHO). Anthropogenic activities can be classified as excessive nitrogen fertilizer application, livestock manure, and industrial/domestic sewage, coupled with irrigation return flow, which brought significant hazards to human health. The calculation results of entropy weighted water quality index (EWQI) showed that about half of groundwater samples are unfit for drinking purposes. Most importantly, 88.5%, 88.5%, 73.1%, and 71.2% of the water samples had considerable NO₃^- health risks (HQ > 1) for infants, children, females, and males, respectively. It is suggested that the groundwater should be chemical and biological denitrification for nitrate removal before being used for drinking purposes. The findings of this work can help policymakers to solve groundwater pollution problems and ensure healthy drinking water in such intensive agricultural basins and other similar regions worldwide.

Hydrochemical characteristics and quality assessment of groundwater in Guangxi coastal areas, China

Groundwater is a main source of water supply in Guangxi Province, China. The urbanization expansion and ocean dynamic may change the groundwater quality, which is an important issue due to its effects on human health. In this paper, the influence of seawater intrusion and anthropogenic activity on the Guangxi coastal aquatic environment was assessed by geochemical and multivariate statistical methods. The result indicated that the chemical composition of groundwater in the study area is obviously associated with seawater and the main groundwater types were Ca·Na-Cl, Ca·Na-HCO₃, and Ca-HCO₃·Cl_. The groundwater evolution path from land to sea in Guangxi is Ca-HCO3 → Na·Mg-Cl. The origin of salts in the study area is mainly controlled by mineral weathering, the hydrogen and oxygen isotopes contents point to the aqueous source of atmospheric precipitation. According to the results of PCA, seawater intrusion and pollution caused by human activities play an increasingly important role in the evolution of groundwater characteristics. Seawater intrusion is the main factor for the increase of groundwater salinity in Guangxi, while domestic sewage, industrial waste, fertilizers, and pesticides may contribute to the nitrate pollution of groundwater, especially in Beihai. The degree of groundwater nitrate pollution is as follows: Fangchenggang < Qinzhou < Beihai, which is associated with the degree of urbanization in the coastal area. Finally, the results of the water quality index (WQI) assessment show that 82.8 % of the samples were classified as excellent, while there is still a need to be vigilant about groundwater pollution caused by seawater intrusion and groundwater pollution. The results will be valuable for sustainable groundwater resource management in Guangxi coastal zone.

Delineation of seawater intrusion and groundwater quality assessment in coastal aquifers: The Korba coastal aquifer (Northeastern Tunisia)

The aim of this study is to determine the general state of the Korba aquifer (northwestern Tunisia) with respect to seawater intrusion and to assess the suitability of groundwater for drinking and irrigation purposes. A total of 60 groundwater samples were collected and analysed for physicochemical parameters (pH, EC, TDS, Na⁺, K⁺, Ca²⁺, Mg²⁺, HCO3^-, Cl^-, NO₃^-, SO₄^2- and Br^-). Major ionic ratios highlighted the dominance of the reverse ion exchange process triggered by the marine intrusion. Br^-/Cl^- ratio suggested that the irrigation with saline water and wastewater were potential additional sources of salinization. Hydrochemical Facies Evolution Diagram coupled with a GIS-based framework revealed that most of samples are located beneath the mixing line, showing dominant marine intrusion process. Based on the water quality index, most of groundwater samples were unsuitable for drinking. In addition, according to high sodium adsorption ratio, the groundwater quality was limited for irrigation purposes.

Origin and Enrichment Mechanisms of Salinity and Fluoride in Sedimentary Aquifers of Datong Basin, Northern China

The exposure of inhabitants to high fluoride and saline groundwater is the main health issue in Datong Basin, Northern China. This study aims to elucidate the spatial distribution and the mechanisms of high fluoride and salinity occurrence in the shallow sedimentary aquifers of the Datong Basin. Groundwater salinity and fluoride content, and their association with measured hydrochemical parameters, were conducted using multivariate statistical analyses. The analytical results revealed that the concentrations of fluoride and total dissolved solids (TDS) show dramatic variations within the study area. Around 41.4% of groundwater samples contained high-level fluoride concentration (F^- > 1.5 mg/L), whereas 32.8% contained elevated-level TDS (TDS > 1000 mg/L). Both fluoride and TDS concentrations had elevated trends towards the central part of the basin. Shallow groundwater was seriously affected by evaporation and evapotranspiration, which can be the critical factors responsible for rather high TDS and F^- concentrations in shallow aquifers. Water-rock reactions including silicate hydrolysis, dissolution-precipitation of carbonates and evaporates, adsorption, and ion exchange processes, as well as evapotranspiration, are the main governing factors for salinity and fluoride enrichment in groundwater. Solubility control of F-bearing and carbonate minerals is the dominant mechanism affecting F^- levels. Prevailing conditions of alkaline pH, moderate TDS and Na⁺, high HCO₃^-, and lower Ca²⁺ content facilitate the enrichment of fluoride in the study area. Excessive evapotranspiration can be also the most influencing factor responsible for high fluoride and TDS content, due to the extended residence time of groundwater and the arid climate of the central part of the Datong Basin.

Fluoride and nitrate in groundwater: a comprehensive analysis of health risk and potability of groundwater of Jhunjhunu district of Rajasthan, India

Groundwater contamination is a major concern in front of the scientific community because it is directly related to human health, especially in arid and semi-arid regions. Therefore, a comprehensive study was engaged to evaluate the water quality, potability, and human health risk assessment due to the consumption of fluoride- and nitrate-contaminated water in Jhunjhunu district of Rajasthan. In order to assess the water quality, samples were collected from 87 locations in the study region, and a total of 16 parameters were analyzed as per the standard methods. The results showed that the value of the number of quality parameters consisting of pH, EC, TDS, fluoride, chloride, nitrate, sulfate, total hardness, calcium, magnesium, and total alkalinity was higher than the recommended limit of BIS and WHO. The fluoride in 11% and nitrate in 6% of samples were observed to exceed the permissible limit of WHO. The results of risk assessment due to fluoride and nitrate revealed that hazard index values of 71% of groundwater samples for males, 78% of groundwater samples for females, and 75% of groundwater samples for children were greater than 1, indicating the significant health hazard due to consumption of groundwater. The water quality index (WQI) found that 39% of groundwater samples belong to categories that cannot be used for drinking purposes. Principal component analysis (PCA) reduced the large number of variables affecting the overall quality and chemistry of groundwater and determined four major components which account for 69.50% variance in the data. PCA concluded that both geogenic and anthropogenic sources of contamination influenced the groundwater of the study area.

Intelligent soft computational models integrated for the prediction of potentially toxic elements and groundwater quality indicators: a case study

Reports have shown that potentially toxic elements (PTEs) in air, water, and soil systems expose humans to carcinogenic and non-carcinogenic health risks. In southeastern Nigeria, works that have used data-driven algorithms in predicting PTEs in groundwater are scarce. In addition, only a few works have simulated water quality indices using machine learning modelling methods in the region. Therefore, in this study, physicochemical analyses were carried out on groundwater samples in southeastern Nigeria. The laboratory results were used to compute two water quality indices: pollution index of groundwater (PIG) and the water pollution index (WPI), to ascertain groundwater quality. In addition, the physicochemical parameters served as input variables for multiple linear regression (MLR) and artificial neural network (ANN) modelling and prediction of Cr, Fe, Ni, NO3−, Pb, Zn, WPI, and PIG. The results of WPI and PIG computation showed that about 30–35% of the groundwater samples were unsuitable for human consumption, whereas 65–70% of the samples were deemed suitable. The insights from the PIG and WPI model also revealed that lead (Pb) was the most influential PTE that degraded the quality of groundwater resources in the research area. The findings of the MLR and ANN models indicated strong positive prediction accuracies (R 2 = 0.856–1.000) with low modeling errors. The predictive MLR and ANN models of the PIG and WPI generally outperformed those of the PTEs. The models produced in this study predicted the PTEs better compared to previous studies. Thus, this work provides insights into effective water sustainability, management, and protection.