Distinct groundwater recharge sources and geochemical evolution of two adjacent sub-basins in the lower Shule River Basin,northwest China

Based on analysis of groundwater hydrogeochemical and isotopic data, this study aims to identify the recharge sources and understand geochemical evolution of groundwater along the downstream section of the Shule River, northwest China, including two sub-basins. Groundwater samples from the Tashi sub-basin show markedly depleted stable isotopes compared to those in the Guazhou sub-basin. This difference suggests that groundwater in the Tashi sub-basin mainly originates from meltwater in the Qilian Mountains, while the groundwater in the Guazhou sub-basin may be recharged by seepage of the Shule River water. During the groundwater flow process in the Tashi sub-basin, minerals within the aquifer material (e.g., halite, calcite, dolomite, gypsum) dissolve in groundwater. Mineral dissolution leads to strongly linear relationships between Na⁺ and Cl^? and between Mg²⁺+ Ca²⁺ and SO₄ ^2??+?HCO₃ ^?, with stoichiometry ratios of approximately 1:1 in both cases. The ion-exchange reaction plays a dominant role in hydrogeochemical evolution of groundwater in the Guazhou sub-basin and causes a good linear relationship between (Mg²⁺+ Ca²⁺)–(SO₄ ^2??+?HCO₃ ^?) and (Na⁺+ K⁺)–Cl^? with a slope of ?0.89 and also results in positive chloroalkaline indices CAI 1 and CAI 2. The scientific results have implications for groundwater management in the downstream section of Shule River. As an important irrigation district in Hexi Corridor, groundwater in the Guazhou sub-basin should be used sustainably and rationally because its recharge source is not as abundant as expected. It is recommended that the surface water should be used efficiently and routinely, while groundwater exploitation should be limited as much as possible.     

Hydrogeochemical characterization of major factors affecting the quality of shallow groundwater in the coastal area at Kimje in South Korea

This study has evaluated the main hydrogeochemical characteristics that affect the quality of shallow groundwater in the coastal area at Kimje in South Korea. In this area, the chemical composition of groundwater is mostly classified into Na⁺?Cl^? and Ca²⁺+Mg²⁺?NO₃^-+Cl^? types. These types are affected by three major factors: seawater intrusion, fertilizers and redox processes. The Na⁺?Cl^? type, which is generally localized in the coastal area, shows typical characteristics of groundwater affected not only by modern seawater but also by old seawater residing in the reclaimed land. In contrast, the Ca²⁺+Mg²⁺?NO₃^-+Cl^? type, which is usually found inland, is very contaminated by fertilizers. As groundwater flows from the inland area to the coast, the redox condition changes from an oxic condition to a suboxic/anoxic condition. In addition, the reclamation has caused a large amount of underlying organic matter. These effects provide optimum conditions for the occurrence of redox processes in the coastal area.     

Origin and distribution of saline groundwaters in the upper Miocene aquifer system, coastal Rhodope area, northeastern Greece

 This paper describes the origins and distribution of saline groundwaters in the coastal area of Rhodope, Greece. The aquifer system includes two aquifers within coarse-grained alluvial sediments in the coastal part of the study area. Two major water-quality groups occur in the study area, namely Ca²⁺-rich saline groundwater and Ca²⁺-poor, almost fresh groundwater. The main process controlling the groundwater chemistry is the exchange of calcium and sodium between the aquifer matrix and intruding seawater. The natural salt water in the study area is probably residual water that infiltrated the aquifer system during repeated marine transgressions in late Pleistocene time. Seawater intrusion into the coastal aquifer system occurs as a result of overpumping in two seawater wedges separated vertically by a low-permeability layer. The rate of intrusion averages 0.8 m/d and is less than expected due to a decline of the aquifer's permeability at the interface with the seawater. The application of several hydrochemical techniques (Piper and Durov diagrams; Na⁺/Cl^–, Ca²⁺/Cl^–, Mg²⁺/Cl^–, and Br^–/Cl^– molar ratios; Ca²⁺/Mg²⁺ weight ratio; and chloride concentrations), combined with field observations, may lead to a better explanation of the origin of the saline groundwater. Received, May 1997 / Revised, May 1998, December 1998 / Accepted, February 1999     

Seasonal variation in major ion chemistry of a tropical mountain river,the southern Western Ghats,Kerala, India

A comprehensive and systematic study to understand various geochemical processes as well as process drivers controlling the water quality and patterns of the hydrochemical composition of river water in Muthirapuzha River Basin, MRB (a major tributary of Periyar, the longest river in Kerala, India), was carried out during various seasons, such as monsoon, post-monsoon and pre-monsoon of 2007–2008, based on the data collected at 15 monitoring stations (i.e., 15 × 3 = 45 samples). Ca²⁺ and Mg²⁺ dominate the cations, while Cl^? followed by HCO₃ ^? dominates the anions. In general, major ion chemistry of MRB is jointly controlled by weathering of silicate and carbonate rocks, which is confirmed by relatively larger Ca²⁺ + Mg²⁺/Na⁺ + K⁺ ratios as well as Ca²⁺/Na⁺ vs. Mg²⁺/Na⁺ and Ca²⁺/Na⁺ vs. HCO₃ ^?/Na⁺ scatter plots. The relationship between Cl^? and Na⁺ implies stronger contributions of anthropogenic activities modifying the hydrochemical composition, irrespective of seasons. The water types emerged from this study are transitional waters or waters that changed their chemical character by mixing with waters of geochemically different ionic signatures. However, various ionic ratios, hydrochemical plots and graphical diagrams suggest seasonality over the hydrochemical composition, which is solely controlled by the rainfall pattern. Relatively higher pCO₂ indicates the disequilibrium existing in natural waterbodies vis-à-vis the atmosphere, which is an outcome of both the contribution of groundwater to stream discharge and anthropogenic activities. Hence, continuous monitoring of hydrochemical composition of mountain rivers is essential in the context of climate change, which has serious implications on tropical mountain fluvial-hydro systems.     

Evaluation of hydrogeochemistry and water quality in Bist-Doab region,Punjab, India

Agricultural activities act as dominant polluter of groundwater due to increased fertilizers and pesticides usage. Bist-Doab region, Punjab, India, is one such region facing deterioration of groundwater quality due to usage of fertilizers. This study aims in delineating and evaluating the groundwater quality in the region. Water samples are collected from canals, reservoir, and shallow and deep groundwater. Water types in canal and reservoir in Kandi region are Mg²⁺HCO₃ ^? and Mg²⁺Ca²⁺Na⁺HCO₃ ^?, respectively. While water types of shallow and deep groundwaters are found to be of two types: Na⁺Mg²⁺Ca²⁺HCO₃ ^? and Ca²⁺Mg²⁺Na⁺HCO₃ ^?. Presence of Mg²⁺ in groundwater at locations adjoining canals indicates recharge due to canal. The major ion (Na⁺, Mg²⁺, Ca²⁺, HCO₃ ^?) chemistry of the region is due to weathering of rocks that are rich in sodic minerals and kankar. Deep groundwater quality in the region meets BIS and WHO standards for drinking purpose, unlike shallow groundwater which is of poor quality at many locations. Both shallow and deep groundwater with high sodium concentration (>1.5 meq/l) affect cropping yield and permeability of soil matrix. High concentration of SO₄ ^2? and NO₃ ^2? (>1 meq/l) in shallow groundwater at few locations indicates influence of anthropogenic (fertilizer) activity. Factor analysis indicates that the major cations, bicarbonate and chloride are derived from weathering/dissolution of source rocks. Higher concentration of nitrate and presence of sulphate in shallow groundwater at few locations is due to usage of fertilizers and pesticides.     

Cation-exchange characteristics of Amazon River suspended sediment and its reaction with seawater

The cation-exchange characteristics of Amazon River suspended sediment have been studied in order to determine the contribution of exchangeable cations to the geochemical fluxes from the river. Sediment samples were obtained throughout most of the Amazon Basin. The range of exchangeable cation compositions is very narrow in the river and in seawater as well. In river water, the exchangeable cation complement (equivalent basis, exclusive of H⁺) is 80% Ca²⁺, 17% Mg²⁺, 3% Na⁺ plus K⁺. In seawater Na⁺ and Mg²⁺ are about equal (38%) while Ca²⁺ ~ 15% and K⁺ ~ 9%.On reaction with seawater, river suspended sediment took up an amount of Na⁺ equal to nearly one-third of the dissolved river load, as well as amounts corresponding to 15–20% of the dissolved fluvial K⁺ and Mg²⁺. These estimates reflect an unusually high suspended-sediment:dissolved-solids ratio of 6.4 at the time of sampling. At a more representative world average ratio of four, the uptake of Na⁺ would be 20% of the dissolved fluvial load, and that for K⁺ and Mg²⁺ about 10%. Over the annual cycle of the Amazon, it is estimated that ion exchange has a still smaller effect, as a consequence of the low average suspended-solids:dissolved-solids ratio of 1.7.Variations in the ratio $\text{X}{}_{\mathrm{Ca}}\text{X}{}_{\mathrm{Mg}}$, the equivalent fraction of exchangeable Ca²⁺ and Mg²⁺, throughout the river, can be described by a single isotherm. This same isotherm accurately describes the distribution of exchangeable Ca²⁺ and Mg²⁺ on sediment equilibrated with seawater, despite that a high proportion of exchange sites is occupied by Na⁺ and K⁺.     

Hydrochemical and isotopic characteristics of groundwater in the Yanqi Basin of Xinjiang province, northwest China

In this study, hydrochemical and isotope investigations were conducted in the Yanqi Basin to determine the chemical composition, and to gain insight into the groundwater recharge process in the Yanqi Basin. It mainly used hydrochemistry, environmental isotopes, and a series of comprehensive data interpretation, e.g., statistics, ionic ratios, and Piper diagram to obtain a better understanding of the functioning of the system. The following hydrochemical processes were identified as the main factors controlling the water quality of the groundwater system: weathering of silicate minerals, dissolution, ion exchange, and to a lesser extent, evaporation, which seemed to be more pronounced down gradient of the flow system. As groundwater flows from the recharge to discharge areas, chemical patterns evolve in the order of Ca²⁺–HCO₃ ^?, Ca²⁺/Mg²⁺–HCO₃ ^? to Ca²⁺–Mg²⁺–Cl^?–SO₄ ^2?, Na⁺–K⁺–Cl^?–SO₄ ^2? and Na⁺–Cl^? according to lithology. The environmental isotope (δ ¹⁸O, δ ²H, ³H) measurements further revealed that precipitation was the main recharge source for the groundwater system; some local values indicated high levels of evaporation. Tritium and CFC analysis were used to estimate the ages of the different groundwater; the tritium values of the groundwater samples varied from 2.82 to 29.7 TU. The age of the groundwater at depths of <120 m is about 30–50 years. CFC values obtained for six samples to determine groundwater age; the age of the groundwater is about 20–50 years.     

Secular variation in the major-ion chemistry of seawater: Evidence from fluid inclusions in Cretaceous halites

The major-ion (Mg²⁺, Ca²⁺, Na⁺, K⁺, , and Cl⁻) chemistry of Cretaceous seawater was determined from analyses of seawater-derived brines preserved as fluid inclusions in marine halites. Fluid inclusions in primary halite from three evaporite deposits were analyzed by the environmental scanning electron microscopy (ESEM) X-ray energy dispersive spectrometry (EDS) technique: the Early Cretaceous (Aptian, 121.0-112.2 Ma) of the Sergipe basin, Brazil and the Congo basin, Republic of the Congo, and the Early to Late Cretaceous (Albian to Cenomanian, 112.2-93.5 Ma) of the Khorat Plateau, Laos, and Thailand. The fluid inclusions in halite indicate that Cretaceous seawater was enriched several fold in Ca²⁺, depleted in , Na⁺, and Mg²⁺, and had lower Na⁺/Cl⁻, Mg²⁺/Ca²⁺, and Mg²⁺/K⁺ ratios compared to modern seawater. Elevated Ca²⁺ concentrations, with Ca²⁺ >  at the point of gypsum saturation, allowed Cretaceous seawater to evolve into Mg²⁺-Ca²⁺-Na⁺-K⁺-Cl⁻ brines lacking measurable .The major-ion composition of Cretaceous seawater was modeled from fluid inclusion chemistries for the Aptian and the Albian-Cenomanian. Aptian seawater was extreme in its Ca²⁺ enrichment, more than three times higher than present day seawater, with a Mg²⁺/Ca²⁺ ratio of 1.1-1.3. Younger, Albian-Cenomanian seawater had lower Ca²⁺ concentrations, and a higher Mg²⁺/Ca²⁺ ratio of 1.2-1.7. Cretaceous (Aptian) seawater has the lowest Mg²⁺/Ca²⁺ ratios so far documented in Phanerozoic seawater from fluid inclusions in halite, and within the range chemically favorable for precipitation of low-Mg calcite ooids and cements. Results from halite fluid inclusions, together with Mg²⁺/Ca²⁺ ratios measured from echinoderm and rudist calcite, all indicate that Early Cretaceous seawater (Hauterivian, Barremian, Aptian, and Albian) had lower Mg²⁺/Ca²⁺ ratios than Late Cretaceous seawater (Coniacian, Santonian, and Campanian). Low Aptian-Albian Mg²⁺/Ca²⁺ seawater ratios coincide with negative excursions of ⁸⁷Sr/⁸⁶Sr ratios and δ³⁴S_SO4, and peak Cretaceous ocean crust production rates, all of which suggests a link between seawater chemistry and midocean ridge hydrothermal brine flux.     

Impact of anthropogenic activities on the chemistry and quality of groundwater: a case study from a terrain near Zarand City, Kerman Province, SE Iran

Groundwater of an aquifer located in the vicinity of a large coal washery near Zarand City, Iran consists of two hydrochemically differing facies, which have been informally designated as groundwater (A) and groundwater (B). Groundwater (A) is native, brackish in composition and is characterized by Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ and SO₄ ^2? > HCO₃ ^? > Cl^? > NO₃ ^?. Spearman’s rank correlation coefficient matrices, factor analysis data, and values of chloro-alkaline indices, C ratio and Na⁺/Cl^? molar ratio indicate that in the groundwater (A), the ionic load of Ca²⁺, Mg²⁺, Na⁺, K⁺, SO₄ ^2? and HCO₃ ^? is derived essentially from weathering of both carbonates and aluminosilicates and direct cation and reverse cation–anion exchange reactions. Groundwater (B) is the polluted variant of the groundwater (A), brackish to saline in composition, and unlike the groundwater (A), consists of HCO₃ ^? as the dominant anion. In comparison with the groundwater (A), the groundwater (B) contains higher concentrations of all ions, and its average ionic load (av. = 59.74 me/L) is 1.43 times higher than that of the groundwater (A) (av. = 41.54 me/L). Additional concentrations of Ca²⁺, Mg²⁺, K⁺, SO₄ ^2?, Cl^? and HCO₃ ^? in the groundwater (B) are provided mainly by downward infiltrating water from the coal washery tailings pond and reverse cation–anion exchange reaction between tailings pond water and exchanger of the aquifer matrix during non-conservative mixing process of groundwater (A) and tailings pond water. Certain additional concentrations of Na⁺, K⁺ and NO₃ ^? in the groundwater (B) are provided by other anthropogenic sources. Quality wise, both groundwaters are marginally suitable for cultivation of salt-tolerant crops only.     

Groundwater recharge and evolution in the Dunhuang Basin,northwestern China

Groundwater recharge and evolution in the Quaternary aquifer beneath the Dunhuang Basin was investigated using chemical indicators, stable isotopes, and radiocarbon data to provide guidance for regional water management. The quality of groundwater and surface water is generally good with low salinity and it is unpolluted. The dissolution of halite and sylvite from fine-grained sediments controls concentrations of Na⁺ and K⁺ in the groundwater, but Na⁺/Cl⁻ molar ratios >1 in all samples are also indicative of weathering of feldspar contributing to excess Na⁺. The dissolution of carbonate minerals yields Ca²⁺ to the groundwater, thereby exerting a strong influence on groundwater salinity. The δ¹⁸O and δ²H values in unconfined groundwater are enriched along the groundwater flow path from SW to NE. In contrast, confined groundwater was depleted in heavy isotopes, with mean values of −10.4‰ δ¹⁸O and −74.4‰ δ²H. Compared with the precipitation values, all of the groundwater samples were strongly depleted in heavy isotopes, indicating that modern direct recharge to the groundwater aquifers in the plains area is quite limited. The unconfined water is generally young with radiocarbon values of 64.9–79.6 pmc. In the northern basin, radiocarbon content in the confined groundwater is less than 15 pmc and an uncorrected age of ∼15 ka, indicates that this groundwater was recharged during a humid climatic phases of the late Pleistocence or early Holocene. The results have important implications for inter-basin water allocation programmes and groundwater management in the Dunhuang Basin.     

A geochemical and stable isotope investigation of groundwater/surface-water interactions in the Velenje Basin,Slovenia

The geochemical and isotopic composition of surface waters and groundwater in the Velenje Basin, Slovenia, was investigated seasonally to determine the relationship between major aquifers and surface waters, water–rock reactions, relative ages of groundwater, and biogeochemical processes. Groundwater in the Triassic aquifer is dominated by HCO₃ ^–, Ca²⁺, Mg²⁺ and δ¹³C_DIC indicating degradation of soil organic matter and dissolution of carbonate minerals, similar to surface waters. In addition, groundwater in the Triassic aquifer has δ¹⁸O and δD values that plot near surface waters on the local and global meteoric water lines, and detectable tritium, likely reflecting recent (<50 years) recharge. In contrast, groundwater in the Pliocene aquifers is enriched in Mg²⁺, Na⁺, Ca²⁺, K⁺, and Si, and has high alkalinity and δ¹³C_DIC values, with low SO₄ ^2– and NO₃ ^– concentrations. These waters have likely been influenced by sulfate reduction and microbial methanogenesis associated with coal seams and dissolution of feldspars and Mg-rich clay minerals. Pliocene aquifer waters are also depleted in ¹⁸O and ²H, and have ³H concentrations near the detection limit, suggesting these waters are older, had a different recharge source, and have not mixed extensively with groundwater in the Triassic aquifer.     

Water geochemical characteristic variations in and around a karst-dominated natural reserve area,southwestern China

This paper reports original data on the physical and chemical parameters of precipitation, river water and groundwater in and around the Longhushan Nature Reserve Area, located in southwestern China karst region, and provides a preliminary characterization of the hydrogeochemical process governing the natural water evolution in this area. The rainfall and river water mainly pertain to the HCO₃ ⁻–Ca²⁺ type and groundwater mainly pertain to the HCO₃ ⁻–Ca²⁺ + Mg²⁺ type. The HCO₃ ⁻ was the predominant anion and Ca²⁺ was the predominant cation in all waters, respectively. The Gibbs Boomerang Envelop model, the 1:1 relationship of Na⁺ plus K⁺ versus Cl⁻ as well as the 1:1 relationship of Ca²⁺ plus Mg²⁺ versus HCO₃ ⁻ all suggested geochemical weathering is the main controlling factor for the geochemical compositions of this natural water. In surface water, the Mg²⁺/Ca²⁺ ratios ranged from 0.32 to 0.42 and the Na⁺/Ca²⁺ varied between 0.04 and 0.05. In the groundwater, the Mg²⁺/Ca²⁺ ratios varied from 0.37 to 0.62 and were below the ideal ratio of 0.8. These ratios showed the presence of a dolomite source. Analysis of trace elements showed that As, B, Pb, Se, Sr, V and Zn elements were abundant in the natural water during summer in this region.     

Effects of poor quality irrigation waters on the nutrient leaching and groundwater quality from sandy soil

Sodium (Na⁺) in poor quality irrigation water participate in ion-exchange processes results in the displacement of base cations into solution and a raised concentration in groundwater. Knowledge of the rate of decrease of nutrients from soils resulting from poor water quality application is essential for long-term planning of crop production while minimizing the impact on groundwater quality. In this study, we examined the effect of sodium adsorption ratio (SAR) of irrigation water on nutrients leaching and groundwater quality in columns of sandy soil. Three types of irrigation waters at three NaCl–CaCl₂ solutions with the following levels of SAR (5, 15, and 30) were synthesized in laboratory. With the application of solutions, exchange occurred between solution Na⁺ and exchangeable cations (Ca²⁺, Mg²⁺, and K⁺), resulting in the displacement of these cations and anions into solution. Increasing the level of SAR from 5 to 15 and 30 resulted in increase in the average exchangeable sodium percentage (ESP) of the soil from 10.4 to 20.3, and 32.5, respectively. Adverse effect of high Na⁺ concentration in the solutions on raising ESP was less pronounced in solution having low SAR. Leaching of Ca²⁺, Mg²⁺, K⁺, and P from soil with the application of solutions represents a significant loss of valuable nutrients. This sandy soil showed the high risk for nutrients transfer into groundwater in concentrations exceeding the groundwater quality standard. Irrigation with poor quality water, which is generally more sodic and saline than regional groundwater, increases the rate of sodification and salinization of shallow groundwater.     

Isotopic and geochemical characteristics of groundwater in the Senegal River delta aquifer: implication of recharge and flow regime

Groundwater and surface water samples were collected to improve understanding of the Senegal River Lower Valley and Delta system, which is prone to salinization. Inorganic ion concentrations and environmental isotopes (¹⁸O, ²H and ³H) in groundwater, river, lake and precipitation were investigated to gain insight into the functioning of the system with regard to recharge sources and process, groundwater renewability, hydraulic interconnection and geochemical evolution. The geochemical characteristics of the system display mainly cation (Ca²⁺ and/or Na⁺) bicarbonated waters, which evolve to chloride water type; this occurs during groundwater flow in the less mineralized part of the aquifer. In contrast, saline intrusion and secondary brines together with halite dissolution are likely to contaminate the groundwater to Na–Cl type. Halite, gypsum and calcite dissolution determine the major ion (Na⁺, Cl⁻, Ca²⁺, Mg²⁺, SO₄ ²⁻ and HCO₃ ⁻) chemistry, but other processes such as evaporation, salt deposition, ion exchange and reverse exchange reactions also control the groundwater chemistry. Both surface water and groundwater in the system show an evaporation effect, but high evaporated signatures in the groundwater may be due to direct evaporation from the ground, infiltration of evaporated water or enriched rainwater in this region. The stable isotopes also reveal two types of groundwater in this system, which geomorphologically are distributed in the sand dunes (depleted isotopes) and in the flood plain (enriched isotopes). Consideration of the ³H content reinforces this grouping and suggests two mechanisms of recharge: contribution of enriched surface water in recharging the flood plain groundwater and, in the sand dunes area where water table is at depth between 8 and 13 m, slow recharge process characterized the submodern to mixed water.     

Preliminary study on strontium-rich characteristics of shallow groundwater in Dingtao Area,China

Based on the analysis of element correlation, the Gibbs diagram, hydro-geochemical ion ratios, isoline maps of groundwater and soil, and change patterns of strontium content after normalization, the study examines water-rock interaction of shallow groundwater in Dingtao area. The results suggest that strontium in the study area mainly comes from water-rock interactions, and the strata interacting with groundwater are the top of Quaternary and Neogene. The element correlation analysis shows that the formation of strontium-rich groundwater is sufficiently affected by sulfate and carbonate. The Gibbs diagram suggests that the chemical composition of groundwater is mainly influenced by water-rock interactions, accompanied by evaporation crystallization. c(Ca²⁺+Mg²⁺)/c(HCO₃^-+SO₄^2-) reflects that the main reactions in the groundwater system is weathering dissolution of carbonate and sulfate, and ion exchange takes place. c(Na⁺)/c(Cl^-) indicates that Na⁺ in groundwater may have water-rock interactions with rocks it flows through. c(Cl^-)/c(Ca²⁺) indicates that the hydrodynamic condition in the pumping well is poor and the water circulation is slow. The study examines the macro isoline map change patterns, correlation curves of change of strontium content in groundwater and shallow soil, and correlation curves of change of strontium content in groundwater, shallow soil, and deep soil. The results suggest that the strontium content in the study area has the same change pattern in groundwater and in soil, which further indicates that strontium in the study area comes from water-rock interactions.     

Geochemistry and quality of groundwater of Gummanampadu sub-basin, Guntur District, Andhra Pradesh, India

Groundwater survey has been carried out in the area of Gummanampadu sub-basin located in Guntur District, Andhra Pradesh, India for assessing the factors that are responsible for changing of groundwater chemistry and consequent deterioration of groundwater quality, where the groundwater is a prime source for drinking and irrigation due to non-availability of surface water in time. The area is underlain by the Archaean Gneissic Complex, over which the Proterozoic Cumbhum rocks occur. The results of the plotting of Ca²⁺ + Mg²⁺ versus HCO₃ ^? + CO₃ ^2?, Ca²⁺ + Mg²⁺ versus total cations, Na⁺ + K⁺ versus total cations, Cl^? + SO₄ ^2? versus Na⁺ + K⁺, Na⁺ versus Cl^?, Na⁺ versus HCO₃ ^? + CO₃ ^2?, Na⁺ versus Ca²⁺ and Na⁺: Cl^? versus EC indicate that the rock–water interaction under alkaline condition is the main mechanism in activating mineral dissociation and dissolution, causing the release of Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃ ^?, CO₃ ^2?, SO₄ ^2? and F^? ions into the groundwater. The ionic relations also suggest that the higher concentrations of Na⁺ and Cl^? ions are the results of ion exchange and evaporation. The influences of anthropogenic sources are the other cause for increasing of Mg²⁺, Na⁺, Cl^?, SO₄ ^2? and NO₃ ^? ions. Further, the excess alkaline condition in water accelerates more effective dissolution of F^?-bearing minerals. Moreover, the chemical data plotted in the Piper’s, Gibbs’s and Langelier–Ludwig’s diagrams, computed for the chloro-alkaline and saturation indices, and analyzed in the principal component analysis, support the above hypothesis. The groundwater quality is, thus, characterized by Na⁺ > Ca²⁺ > Mg²⁺ > K⁺: HCO₃ ^? + CO₃ ^2? > Cl^? > SO₄ ^2? > NO₃ ^? > F^? facies. On the other hand, majority of groundwater samples are not suitable for drinking with reference to the concentrations of TDS, TH, Mg²⁺ and F^?, while those are not good for irrigation with respect to USSL’s and Wilcox’s diagrams, residual sodium carbonate, and magnesium hazard, but they are safe for irrigation with respect to permeability index. Thus, the study recommends suitable management measures to improve health conditions as well as to increase agricultural output.     

Major ions chemistry of groundwater in the arid region of Zhangye Basin, northwestern China

As one of the most arid regions in the world, the study area, Zhangye Basin is located in the middle reaches of the Heihe River, northwest China. Besides aridity, rapid social and economic development also stimulates greater demand for water, which is gradually fulfilled by groundwater extraction. In this study, the conventional hydrochemical techniques and statistical analyses were applied to examine the major ions chemistry and hydrochemical processes of groundwater in the Zhangye Basin. The results of chemical analysis indicate that no one pair of cations and anions proportions is more than 50% in the groundwater samples of the study area. High-positive correlations were obtained among the following ions: HCO₃ ^?–Mg²⁺, SO₄ ^2?–Mg²⁺, SO₄ ^2?–Na⁺ and Cl^?–Na⁺. TDS depends mainly on the concentration of major ions such as HCO₃ ^?, SO₄ ^2?, Cl^?, Mg²⁺ and Na⁺. The hydrochemical types in the area can be divided into two major groups: the first group includes Mg²⁺–Na⁺–HCO₃ ^?, Mg²⁺–Na⁺–Ca²⁺–HCO₃ ^?–SO₄ ^2? and Mg²⁺–Ca²⁺–Na⁺–SO₄ ^2?–HCO₃ ^? types. The second group comprises Mg²⁺–Ca²⁺–SO₄ ^2? type, Mg²⁺–Ca²⁺–SO₄ ^2?–Cl^? type and Mg²⁺–Na⁺–SO₄ ^2?–Cl^? type. The ionic ratio plot and saturation index calculation suggests that the silicate weathering, to some extent, and evaporation are dominant factors that determine the major ionic composition in the study area.     

National scale evaluation of groundwater chemistry in Korea coastal aquifers: evidences of seawater intrusion

Pollution of groundwater by seawater intrusion poses a threat to sustainable agriculture in the coastal areas of Korea. Therefore, seawater intrusion monitoring stations were installed in eastern, western, and southern coastal areas and have been operated since 1998. In this study, groundwater chemistry data obtained from the seawater intrusion monitoring stations during the period from 2007 to 2009 were analyzed and evaluated. Groundwater was classified into fresh (<1,500 μS/cm), brackish (1,500–3,000 μS/cm), and saline (>3,000 μS/cm) according to EC levels. Among groundwater samples (n = 233), 56, 7, and 37% were classified as the fresh, brackish, and saline, respectively. The major dissolved components of the brackish and saline groundwaters were enriched compared with those of the fresh groundwater. The enrichment of Na⁺ and Cl⁻ was especially noticeable due to seawater intrusion. Thus, the brackish and saline groundwaters were classified as Ca–Cl and Na–Cl types, while the fresh groundwater was classified as Na–HCO₃ and Ca–HCO₃ types. The groundwater included in the Na–Cl types indicated the effects of seawater mixing. Ca²⁺, Mg²⁺, Na⁺, K⁺, SO₄ ²⁻, and Br⁻ showed good correlations with Cl⁻ of over r = 0.624. Of these components, the strong correlations of Mg²⁺, SO₄ ²⁻, and Br⁻ with Cl⁻ (r ≥ 0.823) indicated a distinct mixing between fresh groundwater and seawater. The Ca/Cl and HCO₃/Cl ratios of the groundwaters gradually decreased and approached those of seawater. The Mg/Cl, Na/Cl, K/Cl, SO₄/Cl, and Br/Cl ratios of the groundwaters gradually decreased, and were similar to or lower than those of seawater, indicating that Mg²⁺, Na⁺, K⁺, SO₄ ²⁻, and Br⁻, as well as Cl⁻ in the saline groundwater can be enriched by seawater mixing, while Ca²⁺ and HCO₃ ⁻ are mainly released by weathering processes. The influence of seawater intrusion was evaluated using threshold values of Cl⁻ and Br⁻, which were estimated as 80.5 and 0.54 mg/L, respectively. According to these criteria, 41–50% of the groundwaters were affected by seawater mixing.     

Hydrogeochemical investigation and groundwater quality assessment of Pratapgarh district,Uttar Pradesh

Hydogrochemical investigation of groundwater resources of Paragraph district has been carried out to assess the solute acquisition processes and water quality for domestic and irrigation uses. Fifty-five groundwater samples were collected and analyzed for pH, electrical conductivity, total dissolved solids, hardness, major anions (F^?, Cl^?, NO₃, HCO₃ ^?, SO₄ ^2?) and cations (Ca²⁺, Mg²⁺, Na⁺, K⁺). Study results reveal that groundwater of the area is alkaline in nature and HCO₃ ^?, Cl^?, Mg²⁺, Na⁺ and Ca²⁺ are the major contributing ions to the dissolved solids. The hydrogeochemical data suggest that weathering of rock forming minerals along with secondary contributions from agricultural and anthropogenic sources are mainly controlling the groundwater composition of Pratapgarh district. Alkaline earth metals (Ca²⁺+Mg²⁺) exceed alkalis (Na⁺+K⁺) and weak acid (HCO₃ ^?) dominate over strong acids (Cl^?+SO₄ ^2?) in majority of the groundwater samples. Ca-Mg-HCO₃ and Ca-Mg-Cl-HCO₃ are the dominant hydrogeochemical facies in the groundwater of the area. The computed saturation indices demonstrate oversaturated condition with respect to dolomite and calcite and undersaturated with gypsum and fluorite. A comparison of groundwater quality parameters in relation to specified limits for drinking water shows that concentrations of TDS, F^?, NO₃ ^? and total hardness exceed the desirable limits in many water samples. Quality assessment for irrigation uses reveal that the groundwater is good for irrigation. However, values of salinity, sodium adsorption ratio (SAR), residual sodium carbonate (RSC), %Na and Kelley index are exceeding the prescribed limit at some sites, demanding adequate drainage and water management plan for the area.     

Geochemical evaluation of nitrate and fluoride contamination in varied hydrogeological environs of Prakasam district,southern India

Hydrogeochemical controlling factors for high rate of groundwater contamination in stressed aquifer of fractured, consolidated rocks belonging to semi-arid watershed are examined. The groundwater in mid-eastern part of Prakasam district confining to Musi-Gundlakamma sub-basins is heavily contaminated with nitrate and fluoride. Distinct water chemistry is noticed among each group of samples segregated based on concentration of these contaminants. The nitrate is as high as 594 mg/l and 57 % of the samples have it in toxic level as per BIS drinking water standards, so also the fluoride which has reached a maximum of 8.96 mq/l and 43 % of samples are not fit for human consumption. Nitrate contamination is high in shallow aquifers and granitic terrains, whereas fluoride is in excess concentration in deeper zones and meta-sediments among the tested wells, and 25 % of samples suffer from both NO₃ ^? and F^? contamination. Na⁺ among cations and HCO₃ ^? among anions are the dominant species followed by Mg²⁺ and Cl^?. The NO₃ ^?-rich groundwater is of Ca²⁺–Mg²⁺–HCO₃ ^?, Ca²⁺–Mg²⁺–Cl^? and Na⁺–HCO₃ ^? type. The F^?-rich groundwater is dominantly of Na⁺–HCO₃ ^? type and few are of Na⁺–SO₄ ^2? type, whereas the safe waters (without any contaminants) are of Ca²⁺–Mg²⁺–HCO₃ ^?– and Na⁺–HCO₃ ^? types. High molecular percentage of Na⁺, Cl^?, SO₄ ^2? and K^? in NO₃ ^? rich groundwater indicates simultaneous contribution of many elements through domestic sewerage and agriculture activity. It is further confirmed by analogous ratios of commonly associated ions viz NO₃ ^?:Cl^?:SO₄ ^2? and NO₃ ^?:K⁺:Cl^? which are 22:56:22 and 42:10:48, respectively. The F^? rich groundwater is unique by having higher content of Na⁺ (183 %) and HCO₃ ^? (28 %) than safe waters. The K⁺:F^?:Ca²⁺ ratio of 10:5:85 and K⁺:F^?: SO₄ ^2? of 16:7:77 support lithological origin of F^? facilitated by precipitation of CaCO₃ which removes Ca²⁺ from solution. The high concentrations of Na⁺, CO₃ ^? and HCO₃ ^? in these waters act as catalyst allowing more fluorite to dissolve into the groundwater. The indices, ratios and scatter plots indicate that the NO₃ ^? rich groundwater has evolved through silicate weathering-anthropogenic activity-evapotranspiration processes, whereas F^? rich groundwater attained its unique chemistry from mineral dissolution-water–rock interaction-ion exchange. Both the waters are subjected to external infusion of certain elements such as Na⁺, Cl^?, NO₃ ^? which are further aggravated by evaporation processes leading to heavy accumulation of contaminants by raising the water density. Presence of NO₃ ^? rich samples within F^? rich groundwater Group and vice versa authenticates the proposed evolution processes.