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Groundwater is essential for the sustainable development of the Guanzhong Basin, China, and its quality is mainly controlled by hydrogeochemical processes and anthropogenic pollution. This study used statistical and multivariate statistical analysis approaches to recognize the hydrogeochemical processes and affecting factors of groundwater in the central part of the Guanzhong Basin. Correlations among 14 hydrochemical parameters were statistically examined. Principal component analysis (PCA), factor analysis (FA), and hierarchical cluster analysis (HCA) techniques were applied to analyze the physicochemical variables to understand the affecting factors of groundwater quality in the study area. The correlation analysis results indicate that cation exchange is the dominant process affecting the concentration of Na+ and Ca2+ in the groundwater. Both the PCA and FA indicate that minerals dissolution/precipitation and human activities are the key factors that affect groundwater quality. All parameters except CO32− and pH increase from C1 to C4 obtained through the Q mode HCA. C4 has a hydrochemical type of SO4–Na·K, indicating that the sample of this cluster is primarily influenced by anthropogenic processes.

The Zhangxuan Basin serves as an ecological barrier and water conservation area for Beijing, the capital of China. Clarifying the hydrochemical evolution of groundwater in this region is essential for the effective management of groundwater resources and the protection of ecological security. In this study, based on data regarding chemistry and level of shallow groundwater from 2016 to 2022, hydrogeochemical analysis methods and geostatistical techniques were applied to investigate the hydrochemical evolution and genesis mechanisms of groundwater under the influence of human activities. The results showed that: (1) From 2016 to 2022, the groundwater remained predominantly characterized by Ca2+ and HCO3-, with the primary hydrochemical type unchanged as HCO3-Ca·Mg. (2) From 2016 to 2022, an overall decreasing trend in hydrochemical components was observed, alongside an increase in HCO3-Na type groundwater. Spatially, along the direction of groundwater flow, a general trend of increasing hydrochemical components was noted, with a significant rise in HCO3-Na type groundwater. (3) The spatiotemporal distribution and evolution of hydrochemistry were influenced by water-rock interactions, lithological characteristics, groundwater flow patterns, and human activities. Along the groundwater flow direction, lithological particles became finer, enhancing forward cation exchange and leaching, with the dissolution of silicate and carbonate minerals intensifying. In localized areas, the hydrochemical components were influenced by the extraction of groundwater source areas and the discharge of industrial waste.

Samples of groundwater were collected during a post-monsoon period (January) and a pre-monsoon period (May) in 2020 from 30 locations in the rapidly developing industrial and residential area of the Coimbatore region in southern India. These sampling periods coincided with times before and during the lockdown in industrial activity and reduced agricultural activity that occurred in the region due to the COVID-19 pandemic. This provided a unique opportunity to evaluate the effects of reduced anthropogenic activity on groundwater quality. Approximately 17% of the wells affected by high fluoride concentrations in the post-monsoon period returned to levels suitable for human consumption in samples collected in the pre-monsoon period. This was probably due to ion exchange processes, infiltration of rainwater during the seasonal monsoon that diluted concentrations of ions including geogenic fluoride, as well as a reduction in anthropogenic inputs during the lockdown. The total hazard index for fluoride in the post-monsoon samples calculated for children, adult women, and adult men indicated that 73%, 60%, and 50% of the groundwater samples, respectively, had fluoride levels higher than the permissible limit. In this study, nitrate pollution declined by 33.4% by the pre-monsoon period relative to the post-monsoon period. The chemical facies of groundwater reverted from the Na-HCO3-Cl and Na–Cl to the Ca-HCO3 type in pre-monsoon samples. Various geogenic indicators like molar ratios, inter-ionic relations along with graphical tools demonstrated that plagioclase mineral weathering, carbonate dissolution, reverse ion exchange, and anthropogenic inputs are influencing the groundwater chemistry of this region. These findings were further supported by the saturation index assessed for the post- and pre-monsoon samples. COVID-19 lockdown considerably reduced groundwater pollution by Na+, K+, Cl–, NO3¯, and F– ions due to shutdown of industries and reduced agricultural activities. Further groundwater quality improvement during lockdown period there is evidence that the COVID-19 lockdown by increased HCO3¯ ion concentration. Overall results illustrate the positive benefits to groundwater quality that could occur as a result of measures to control anthropogenic inputs of pollutants.

The main focus of the present research was to examine the appropriateness of groundwater resources for drinking purposes in the Bilate River Basin of Southern Main Ethiopian Rift, Ethiopia. The groundwater quality index (GWQI), fluoride pollution index (FPI), and human health risk were used to examine the human health risk factors associated with the intake of high fluoride groundwater. For this purpose, 29 groundwater samples were collected from the existing wells and were analyzed for various physicochemical parameters. The dominant cation was Na+, followed by Ca2+, Mg2+, and K+. The dominant anion was HCO3−, followed by Cl−, SO42−, and F−. The Gibbs plot shows that rock-water interactions are the dominant factor controlling the groundwater chemistry. By using the GWQI, the quality of groundwater samples was 31% excellent, 21% good, 31% poor, and 17% very poor. The fluoride concentration in groundwater ranges from 0.2 to 5.60 mg/L (mean, 2.10 mg/L). 59% (i.e., 17 wells) of the groundwater samples were not suitable for drinking, because they surpassed the drinking water quality limit of 1.5 mg/L. The remaining 41% (i.e., 12 wells) of the samples were suitable for drinking. The FPI indicates that 51.72% of the wells were highly polluted by fluoride. The noncarcinogenic health risk varies from 0.75 to 8.44 for children (83%), 0.34–3.84 for women (62%), and 0.27–3.01 for men (52%), which indicates that children are at higher health risk than women and men due to the physiological condition and the rates of ingestion.

Groundwater contamination in the Indo-Gangetic alluvial plain has reportedly been affected by various factors, such as mineral dissolution, overexploitation, precipitation, and ion exchange. This study was designed to interpret the hydrochemical fluctuations in the groundwater sources of a rural area in Raebareli district. Groundwater is slightly alkaline and affected by the issues of fluoride, salinity, hardness, and nitrate. The Pollution Index of Groundwater significantly categorize 57% and 79% of the samples under the “insignificant pollution” category during pre-monsoon and post-monsoon periods. The Health risk assessment indicated the high susceptibility of children toward health risks. It also indicated that fluoride had greater impact than nitrate in the study area. The multivariate statistical analysis indicates that anthropogenic activities, such as agricultural practices, including excessive fertilizer application and improper domestic and cattle waste management, are probable causes of groundwater contamination through NO3−, Cl−, Na+, and K+. Furthermore, the base exchange index classified 71.43% samples in pre-monsoon and 78.57% in post-monsoon as Na-HCO3 type. The meteoric genesis index suggested that 78.57% and 85.71% of the samples belong to shallow meteoric water percolation type during pre- and post-monsoon periods, respectively. The Piper plots revealed that HCO3–Ca·Mg and SO4·Cl–Na + K type are the prominent facies in the area, with dominance of alkalis and weak acids. According to Gibbs plot, majority of the samples fall under “rock dominance” suggesting that “rock-water” interaction was the dominant natural process controlling the groundwater chemistry.

Understanding the transport and retention of Toxoplasma gondii oocysts through soils and into ground and surface water is essential for determining the risk this parasite poses to water resources and human health worldwide. We studied here how various naturally occurring groundwater solutions containing different types of organic compounds (fulvic and humic acids) and electrolytes (NaCl, MgCl 2 , CaCl 2 ) at different concentrations can affect the transport and retention of oocysts in engineered-saturated silica sand columns subjected to continuous flow to simulate the movement of groundwater through an aquifer. Breakthrough curve results from the qPCR analysis were then compared to non-reactive tracer tests to determine parameters that govern the transport of oocysts in saturated porous media. Though breakthrough of oocysts was observed in all tested solutions, higher ionic strength and ion valency resulted in greater oocyst retention. When both organic matter and electrolyte solutions were added to the systems, the electrolyte solutions displayed a far greater influence on parasite retention when compared to the influence of the organic matter alone. Collectively, this study demonstrates the pivotal role of soil groundwater solution chemistry in both the transport and retention of this important zoonotic parasite.

Groundwater is a precious natural element which ensures global water, food, and environmental security in the twenty-first century. Systematic monitoring, sustainable utilization, preservation and remediation are critical aspects of efficient groundwater resource management. This study deals with the analysis of spatial variability and trend in groundwater chemistry as well as identification of possible contamination sources in a coastal alluvial basin of eastern India. Pre-monsoon season data of 14 groundwater-quality variables measured in ‘leaky confined’ and ‘confined’ aquifers were analyzed for ten years (2012–2021). Mann–Kendall (M–K) test with the Sen’s Slope Estimator, Spearman Rank Order Correlation (SROC) and Innovative Trend Analysis (ITA) tests were employed to assess decadal (2012–2021) trends. The analysis of the results indicated that the ‘critical’ water-quality parameters exceeding the acceptable limits for drinking are TDS, EC, TH, pH, Mg 2+ , Na + , K + , Fe 2+ , HCO 3 ˉ, Clˉ and NO 3 ˉ. Weak negative correlations between rainfall and groundwater elevation for both the aquifers reveal poor rainfall recharge into the aquifers. Therefore, a reduction in groundwater abstraction and augmentation of groundwater recharge is recommended. Trend analysis results indicated that the concentrations of TH, Mg 2+ and Fe 2+ exhibit significant increasing trends in the ‘leaky confined aquifer’. In contrast, significant rising trends in TH, Mg 2+ , Na + , Fe 2+ , HCO 3 ˉ and NO 3 ˉ concentrations are identified in the ‘confined aquifer’. Further, the SROC test could not detect the trends in groundwater quality in most blocks and for many parameters. On the other hand, the ITA test revealed significant trends in most of the parameters of the two aquifers in almost all the blocks. Trend magnitudes of the groundwater-quality parameters based on the Sen’s Slope Estimator and the ITA test vary from –63.7 to 58.65 mg/L/year for TDS, –14 to 39.07 mg/L/year for TH, –1.49 to 4.83 mg/L/year for Mg 2+ , –7.14 to 22.96 mg/L/year for Na + , –0.32 to 0.44 mg/L/year for Fe 2+ , –8.33 to 20.75 mg/L/year for HCO 3 ˉ, –26.52 to 31.01 mg/L/year for Clˉ and 1.29 to 3.76 mg/L/year for NO 3 ˉ over the study area. The results of M–K and ITA tests were found in agreement in all the blocks for both the aquifers. Groundwater contamination in both the aquifers can be attributed to weathering, geogenic processes, mineral dissolution, seawater intrusion, poor recharge pattern and injudicious anthropogenic activities. It is strongly recommended that concerned authorities urgently formulate efficient strategies for managing groundwater quality in the ‘leaky confined’ and ‘confined’ aquifers which serve as vital sources of drinking and irrigation water supplies in the study area.

Groundwater is a primary freshwater source for various domestic, industrial and agricultural purposes, especially in coastal regions where there are lacking surface water supply. However, groundwater quality in coastal regions is often threatened by seawater intrusion and contamination due to both anthropogenic activities and natural processes. Therefore, insights into groundwater geochemistry and occurrences are necessary for sustainable groundwater management in coastal regions. The main aim of this study is to investigate the hydrogeochemical characteristics and their influencing factors in a coastal area of the Mekong Delta, Vietnam (MD). A total of 286 groundwater samples were taken from shallow and deep aquifers for analyzing major ions and stable isotopes. The results show that deep groundwater is dominated by Ca–HCO3, Ca–Na–HCO3, Ca–Mg–Cl, and Na–HCO3 while shallow groundwater is dominated by the Na–Cl water type. In this region, the main geochemical processes controlling groundwater chemistry are ion exchanges, mineralization and evaporation. Groundwater salinization in coastal aquifers of the Mekong Delta is caused by (1) paleo-seawater intrusion and evaporation occurring in the Holocene and Pleistocene aquifers, (2) dissolution of salt sediment/rock and leakage of saline from upper to lower aquifers due to excessive groundwater exploitation and hydraulic connection. High nitrate concentrations in both shallow and deep aquifers are related to human activities. These results imply that groundwater extraction may exacerbate groundwater quality-related problems and suitable solutions for sustainable groundwater management in the coastal area of the Mekong Delta are needed.

This study focuses on mineral groundwater in alpine regions and its sustainable exploitation. The Tongde basin on Tibetan Plateau was investigated to reveal the hydrochemistry and formation of mineral groundwater in alpine basins and its sustainable development under anthropogenic disturbances. The results show that groundwater there is characterized by enriched strontium, with concentrations in the range of 0.29–2.03 mg/L, exceeding the mineral water threshold of 0.20 mg/L. Groundwater has large salinity variation but is predominantly fresh, with an average TDS of 456.72 mg/L and a dominant hydrochemical facies of HCO 3 -Ca. Groundwater chemistry is primarily governed by water-rock interactions, particularly silicates weathering, carbonates dissolution and cation exchange. The enriched Sr in groundwater primarily originate from the dissolution of silicate minerals and carbonate cements in arkosic sandstone and argillaceous siltstone, with albite, calcite, and strontianite being the primary minerals involved. Groundwater quality in the basin is mostly excellent to good, with EWQI values below 100. While agricultural practices have introduced nitrogen contaminants (NH 4 + , NO 2 - and NO 3 - ) into groundwater. Among them, NO 3 - would pose potential health risks to various populations and should be addressed in the development of alpine basins with the endowment of mineral water resources.