Silicate Weathering Processes Research Articles

Hydrogeochemical characteristics of groundwater contamination in Guwahati city, Assam, India: Tracing the elemental Threads

Groundwater serves as an important resource for drinking and agriculture in many countries, including India. Assessing the quality of groundwater is essential for understanding its chemical characteristics and suitability for consumption. This study aims to explore the factors affecting the hydrogeochemical changes in groundwater within Guwahati City, Assam, India. Groundwater samples were collected and analyzed for major and trace elements, as well as anion concentrations. Concentrations of As, Al, Ba, Cu, F−, Fe, Mn, and Pb exceeded the permissible limits set by both World Health Organization (WHO) and Bureau of Indian Standards (BIS), indicating serious health concerns for the local inhabitants. The distribution pattern of trace elements exceeding the guideline values is intricate, suggesting widespread contamination of groundwater throughout the study area. The Heavy Metal Pollution Index (HPI) and Water Quality Index (WQI) revealed that, except for the central zone, groundwater across the entire study area requires intervention. Piper plot illustrated that the groundwater is predominantly of Ca–HCO3 type, indicating the dominance of alkaline earth and weak acids. Groundwater hydrogeochemistry is mainly controlled by rock-water interaction and evolves through silicate weathering, carbonate weathering, and cation exchange processes. Multivariate statistical analysis identified distinct groups of groundwater based on chemical characteristics, emphasizing the role of both natural processes and anthropogenic activities in influencing groundwater quality. Regular monitoring, management, and intervention of groundwater sources throughout the study area are crucial for long-term use. The findings of this study will assist stakeholders, regulators, and policymakers in formulating strategies for the sustainable use of groundwater.

Glacier‐Fed Lakes Are Significant Sinks of Carbon Dioxide in the Southeastern Tibetan Plateau

AbstractDissolved inorganic carbon (DIC) sources, transportation, and transition in inland water bodies have been intensively studied due to their important role in the global carbon cycle. While glacier‐fed lakes play a crucial role in global carbon cycling, related studies are limited. In this study, we investigated the spatiotemporal variability of DIC in the maritime glacier‐fed lakes of the southeastern Tibetan Plateau, identifying the carbon sources and potential controlling factors of DIC pathways The results revealed significant temporal variations in DIC and δ13C‐DIC, with averages of 7.29 ± 0.45 mg C L−1 and –8.6 ± 0.2‰ in summer, and 3.40 ± 0.54 mg C L−1 and –7.4 ± 0.6‰ in winter, respectively. Temporal variations in DIC and δ13C‐DIC were mainly controlled by carbonates weathering and silicate weathering processes. The chemical weathering reactions facilitate the consumption of dissolved CO2. Undersaturated pCO2 (120.02 ± 29.18 μatm) relative to atmospheric equilibrium suggests considerable capacity for CO2 uptake within glacier‐fed lakes system. We estimated that the maritime glacier‐fed lakes in the southeastern Tibetan Plateau absorb a total of 9.6 ± 2.7 × 10−3 Tg C‐CO2 yr−1, highlighting their significant contribution to the global carbon budget. The distinctive landscape of the glacier‐fed system and the vulnerable weathering environment result in seasonal and spatial variations of DIC concentration and δ13C‐DIC values, as well as the chemical weathering‐induced CO2 sink in glacier regions. Given the accelerated glacier retreat observed in this area, further studies on the temporal variability of DIC in the water column are urgently needed to identify the mechanisms driving the biogeochemical reactions inside glacier‐fed lake. Our study highlights the unrecognized role of maritime glacier‐fed lakes as CO2 sinks and emphasizes their significance in regional carbon budgets.

Global Cooling‐Driven Summer Monsoon Weakening in South China Across the Eocene‐Oligocene Transition

AbstractRecent research has suggested that East Asia has experienced a prevailing monsoon climate since the Eocene. However, there is little knowledge about the development of the East Asian monsoon system before the Miocene, particularly in southern China, due to a lack of well‐dated continuous sediment records. Here, we present new magnetic proxy records from International Ocean Discovery Program Site U1501 in the northern South China Sea. We conducted rock magnetic experiments, made scanning electron microscopy observations and performed diffuse reflectance spectrum analysis on the late Eocene‐early Oligocene core sediments. The magnetic signal of the sediments is dominated by detrital magnetite and titanomagnetite formed during the silicate weathering and erosion processes, which were used to infer the evolution of summer monsoon precipitation in southern China. Our results along with geochemical and clay mineral data from Site U1501 strongly indicate that the East Asian summer monsoon generally weakened across the Eocene‐Oligocene transition. This change was linked to coeval global cooling rather than tectonic processes. Prior to the Eocene‐Oligocene transition, the summer monsoon intensified, likely due to the latest Eocene warming event caused by the enhancement of the Atlantic Meridional Overturning Circulation, which may have preconditioned the Earth system for the greenhouse‐to‐icehouse transition.

Strontium isotopes as tracers for water-rocks interactions of groundwater to delineate iodine enrichment in aquifer of Datong Basin, northern China

Groundwater iodine has direct importance for human dietary iodine intake in areas where drinking water is of groundwater origin. Iodine affected aquifer system in Datong Basin of North China was studied with a focus on strontium isotopes and major ion chemistry, in order to estimate the controlling hydrological and geochemical processes. The data revealed a rather complicated mixing pattern of various groundwater source end-members that were subject to different water-rock interactions, such as silicate weathering, evaporite and carbonate dissolution. Groundwater from the recharge area of east margin was characteristic by 87Sr/86Sr ratios higher than 0.71643, which implied the silicate weathering process. Groundwater from the discharge area and west margin might be originated from evaporite and carbonate dissolution processes with low 87Sr/86Sr ratios. Mixing models of three end-members based on Sr isotope and contents reflected that the type of water-rock interactions shifted from silicate weathering towards evaporite dissolution along the groundwater flow path from east margin to basin center. Abundant iodine and natural organic matters (NOMs) were discovered in groundwater located at the discharge area with Sr isotopic values between 0.710 and 0.717, implying evaporite dissolution governing iodine and NOMs enrichment in groundwater. Silicate weathering process had negligible influence on iodine and NOMs enrichment in groundwater. While carbonate dissolution made negative contribution for iodine releasing to aqueous phases. The PHREEQC inverse modeling results illustrated that dissolution of halite, calcite, gypsum and kaolinite and cation exchange significantly changed chemical composition of groundwater along the groundwater paths from the two basin margins to central area.

Extricating hydrogeochemical evolution of geothermal fluids of an unexplored section in North-Eastern Himalayas, Arunachal geothermal province, India

The thermal springs of the study area are situated in North-eastern Arunachal Himalayas, India along Subansiri and Siang River valleys with surface temperature ranging between 20 and 57 °C. The pH of thermal springs varies from 7.69 to 9.31, indicating near neutral to alkaline nature of thermal and non-thermal waters. The major geochemical processes influencing hydrochemistry are demonstrated using conventional graphical plots, geochemical modelling by PHREEQC and multivariate statistical analysis. The thermal waters of Chetu and Taksing in Subansiri valley are primarily Na–Cl and Na–HCO3 type, while, thermal water of Yangte in Siang valley is also mixed water-type and others of Ca–Mg–HCO3 type. The geochemically distinct type of waters is obvious from dendrogram derived from hierarchical cluster analysis. Quartz geothermometer predicts reservoir temperatures of thermal springs of 88 ± 13 °C; while, Na–K Giggenbach geothermometer predicts 182 °C and 176 °C for Chetu and Taksing hot springs. Thermal waters are immature and highly prone to mixing with meteoric waters as evident from enthalpy-chloride modelling. Evaporite dissolution, silicate weathering and ion exchange processes are found to contribute to total ion budget in geothermal waters. The saturation indices studies depict oversaturation of all thermal waters with calcite and dolomite. Considering all geochemical features, a conceptual hydrological model resembling geomorphology and origin of thermal springs of North-Eastern Arunachal Himalaya has been proposed. The thermal waters of Subansiri valley display very high Sr and F− content which prohibit them from drinking and utilization purposes. High concentration of toxic elements is addressed to geogenic causes over anthropogenic contributions due to lesser accessibilities at hot spring spots.

Geo-Appraisal of groundwater resource for sustainable exploitation and management in Ibulesoro, Southwestern Nigeria

Groundwater exploitation requires better understanding of the resource availability and quality/vulnerability. Geophysical techniques, pumping test, hydraulic measurement, borehole logging and quality test analysis have been used in Ibulesoro, southwestern Nigeria, to understanding the hydrogeological system in terms of groundwater availability, aquifer delineation, and evaluate the groundwater physico-chemical and biological contents. The study utilized multi-criteria evaluation techniques (GWPIV) to assess the overall aquifer potential/vulnerability. The geology of the area comprises granite, migmatite, migmatite gneiss, biotitic granite, and gneiss. The main water-bearing unit was the weathered layer and fractured basement, which are usually unconfined aquifer. The hydraulic conductivity and formation factor is related by y = 0.239e0.0519x with correlation coefficient of 0.0961. The average hydraulic conductivity and transmissivity are 0.52 m/d and 5.78 m2/d respectively. The hydrogeological parameters viability increases southwardly, just as groundwater movement/flow is due south. The average thickness of the weathered layer and overburden are 8.6 m and 16.1 m respectively, with dominant resistivity in the range of 80 – 200 ohm-m. The best drilling points (migmatite/gneiss geologic units) are where the fractured basement underlies the weathered layer which most not necessarily exceed 30 - 35 m. The average depth to basement rock is 16.1 m. The obtained GWPIV varied from 1.12 to 1.71, with an average of 1.30 suggesting low potential but good for drinking and irrigation uses in its present state, however highly vulnerability to contamination, as the vadose zone thickness (5.68 m avg.), AVI (0.57 avg.), and LC (0.0818 mhos avg.) all point to the low protective capability. The water types is mixed Ca-Mg-Cl. The mechanism controlling the groundwater quality falls in the mixed zone, which indicates contribution from soil/rock-water interaction, precipitation, and evaporation; while carbonic weathering is more active than the silicate weathering process.

Hydrogeochemical Characteristics and Suitability of Groundwater for Drinking and Irrigation from Shallow Aquifers of PG1 Watershed in Chandrapur District of Maharashtra

An endeavor has been made to understand the hydrogeochemical characteristics of groundwater from shallow aquifers of the PG1 watershed (latitudes 19°38’30” to 19°50’30” N and longitudes 79°04’00” to 79°11’00” E). The appropriateness of groundwater has also been checked for various purposes. The groundwater from the study area is alkaline and slightly saline. The Ca2+ ˃ Mg2+ ˃ Na+ ˃ K+ and HCO3- ˃ SO42- ˃ Cl- ˃ NO3- was the ascendancy of cations and anions. The earth metals (Ca + Mg) exceeded the alkali metals (Na + K). The positive correlation interpreted from the interrelationship of Na+ vs Cl- exhibited a silicate weathering process for the liberation of ions in groundwater at the rock-water interface. In addition to the non-lithological source, anthropogenic inputs were inferred, indicating the agricultural fertilizers and domestic wastewater. All the groundwater samples from the study area are suitable for drinking and domestic use. The groundwater from the study area is also suitable for irrigation with negligible exceptions.

Hydrogeochemical processes and groundwater evolution of the São Sebastião-Marizal aquifer system in the Tucano Central Basin, Bahia, Brazil

• New hydrogeochemical and physicochemical data for 35 samples of the São Sebastião-Marizal Aquifer System. • Ca–Na–Mg–HCO 3 –Cl facies of recharge zones evolves to Mg–Ca–Cl and Na–Cl facies along groundwater flow in the Marizal and São Sebastião aquifers, respectively. • Silicate weathering exerts a dominant control on groundwater composition. • Water-rock interaction is the main hydrogeochemical process. • Physicochemical parameters are more variable within the unconfined Marizal aquifer. • Alkaline to alkaline earth ratios indicate that reverse ion exchange predominates in the Marizal aquifer. • The hydrogeochemical signature indicates that silicate weathering and ion exchange processes contribute equally in the São Sebastião aquifer.

Nitrate health risk and geochemical characteristics of water in a semi-urban: implications from graphical plots and statistical computing

ABSTRACT The aim of this study was to assess the nitrate health risks due to water consumption via oral and dermal contact routes and to evaluate the geochemical characteristics of waters in the Umunya area, Nigeria, as implied from ionic ratios, graphical plots, and multivariate statistics. This study is the first to assess the human health risks associated with nitrate contamination in the semi-urban. Standard methods were used to achieve the aim of the study. Water from commercial and household sources were sampled. Measured physicochemical properties showed that the water resources are slightly contaminated. Health hazard quotient (oral) ranged from 0–0.5072 for men, 0–0.5994 for women, and 0–0.6858 for children. On the other hand, the maximum hazard quotient (dermal) for men, women, and children were 0.0013, 0.0016, and 0.0042, respectively. The total hazard index for men, women, and children respectively varied from 0–0.509, 0–0.601 and 0–0.690. Overall, it was indicated that 46.67%, 53.33%, and 53.33% of the water samples expose men, women, and children to low chronic health risk of nitrate. However, the risk for water ingestion was higher than that for dermal absorption. Hydrogeochemical plots revealed that Ca2+-Mg2+-HCO3 − and Na+-HCO3 − water types, representing recharge and base ion exchange processes, respectively, are predominant. Principal component analysis and R-type hierarchical clustering revealed that the hydrogeochemical characteristics are mostly controlled by geogenic factors than human-related factors. The geology of the area and silicate weathering processes were implicated as the major influencers of the hydrogeochemistry. For sustainable development and improved water monitoring in the area, the insights provided in this paper are considered very beneficial.

Anthropogenic processes drive heterogeneous distributions of toxic elements in shallow groundwater around a smelting site

Smelting activities have a far-reaching influence on the quality of soil and groundwater, while most studies have neglected the information on the pollution characteristics of groundwater. The hydrochemical parameters of shallow groundwater and the spatial distributions of toxic elements were investigated in this study. Correlations analysis and groundwater evolution revealed that the major ions were primarily determined by silicate weathering and calcite dissolution process, and anthropogenic processes had a significant effect on groundwater hydrochemistry. Almost 79%, 71%, 57%, 89%, 100%, and 78.6% of samples exceeded the standards of Cd, Zn, Pb, As, SO42-, and NO3-, and their distribution is closely related to the production process. Analysis of soil geochemistry indicated that the relatively mobile forms of toxic elements strongly influence the origin and concentration in shallow groundwater. Besides, rainfall with high magnitude would lead to a decrease of toxic elements in shallow groundwater, whereas the area once stacked waste residue was the opposite. It is recommended to strengthen risk management of the limited mobility fraction while devising a plan for waste residue treatment in accordance with the local pollution conditions. The research on controlling the mechanism of toxic elements in shallow groundwater, along with sustainable development in the study area and other smelting zones may benefit from this study.

Potential arsenic–chromium–lead Co-contamination in the hilly terrain of Arunachal Pradesh, north-eastern India: Genesis and health perspective

In the recent times, multi-metal co-contamination in the groundwater of various parts of the globe has emerged as a challenging environmental health problems. While arsenic (As) has been reported with high fluoride and at times with uranium; and Cr & Pb are also found in aquifers under high anthropogenic impacts. The present work probably for the first time traces the As–Cr–Pb co-contamination in the pristine aquifers of a hilly terrain that are under relatively less stress from the anthropogenic activities. Based on the analyses of twenty-two (n = 22) groundwater (GW) samples and six (n = 6) sediment samples, it was found that Cr being leached from the natural sources as evident from 100% of samples with dissolve Cr exceeding the prescribed drinking water limit. Generic plots suggests rock-water interaction as the major hydrogeological processes with mixed Ca2+-Na+-HCO3- type water. Wide range of pH suggests localized human interferences, as well as indicative of both calcite and silicate weathering processes. In general water samples were found high only with Cr and Fe, however all sediment samples were found to contain As–Cr–Pb. This implies that the groundwater is under-risk of co-contamination of highly toxic trio of As–Cr–Pb. Multivariate analyses indicate that the changing pH as the causative factor for Cr leaching into the groundwater. This is a new finding for a pristine hilly aquifers, and we suspect such condition may also be present in other parts of globe, and thus precautionary investigations are needed to prevent this catastrophic situation to arise, and to alert the community in advance.

Hydrochemical characterization, mechanism of mobilization, and natural background level evaluation of arsenic in the aquifers of upper Gangetic plain, India

Although arsenic (As) contamination has been extensively investigated in the aquifers of the lower and middle Gangetic plains, less attention has been given to the distribution and fate of As in the groundwater of the upper Gangetic plain, India. In the current study, groundwater samples (n = 40) were collected from Moradabad district in the upper Gangetic plain and analyzed for several physicochemical parameters to characterize the groundwater chemistry and evaluate various geogenic and anthropogenic factors controlling the occurrence, mobilization, and fate of As in the plain. Arsenic concentrations in groundwater ranged from 0.17 μg/L to 139 μg/L, with the majority of high-As groundwater associated with high Fe, Mn, and HCO3− and low NO3−, SO42−, and negative Eh values, implying that As was released via reductive dissolution of Fe and Mn oxyhydroxides in reducing conditions under the influence of organic matter degradation. Interrelationships between various geochemical variables and the natural background level (NBL) quantification of As suggested the influence of anthropogenic processes on the mobility of As in groundwater. Piper and Gibbs diagrams and various bivariate plots revealed that the majority of groundwater was of the Ca2+ − Mg2+ − HCO3− type and that the major ions in groundwater were derived from carbonate and silicate weathering, cation exchange and reverse ion exchange processes, and anthropogenic activities. Moreover, the results of principal component analysis (PCA), and hierarchical cluster analysis (HCA) also suggested geogenic and anthropogenic sources for the ion concentration in groundwater. The health risk assessment showed a higher non-carcinogenic risk for children and a higher carcinogenic risk for adults, respectively, due to the daily intake of As contaminated groundwater. Overall, this study represents the first systematic investigation of the distribution, geochemical behavior, and release process of As in groundwater in the study area and provides a strong base for future research in the alluvial aquifers of the upper Gangetic plain.

HYDROGEOCHEMICAL BEHAVIOUR AND GROUNDWATER SUITABILITY OF VISLON AREA, PART OF WRD WATERSHED, CHANDRAPUR DISTRICT, MAHARASHTRA, INDIA

An attempt has been done to understand the hydrogeochemical characteristics of groundwater from shallow aquifers of Vislon village, a part of WRD watershed (Lat. 20º06’30"N and Long. 79º 07' 00"E). The appropriateness of groundwater has also been checked for various purposes. The groundwater from study area is alkaline and slightly saline in nature. The Ca2+ > Mg2+ > Na+ > K+ and HCO3 - > SO4 2- > Cl- > NO3 - was the ascendancy of cations and anions. The earth metals (Ca + Mg) found to exceed the alkali metals (Na + K). The positive correlation interpreted from interrelationship of Na+ vs Cl- exhibited, silicate weathering process for liberation of ions in groundwater at rock-water interface. In addition the non-lithological source, anthropogenic inputs were also inferred indicating the agricultural fertilizers and domestic wastewaters. All the groundwater samples from the study area are suitable for drinking as well as domestic use. The groundwater from study area is also suitable for irrigation purpose with negligible exceptions

Spatio-temporal variation of groundwater chemistry in the Upper Oti Basin of Ghana

The Oti Basin is located at northeastern part of Ghana. Two major geological formations of Voltaian sedimentary supergroup exist: Kwahu-Morago and Oti-Pendjari groups. A total of 133 groundwater samples and 7 surface water samples were collected for two major seasons, viz. dry season (February, 2020) and wet season (November, 2020), and analysed for cations and anions. This is to determine the sources of ions, including pollutants and the reactions that promote them for sustainable groundwater management. Results of major ions revealed groundwater is potable base on the WHO permissible limits. Wet season nitrate and sulphate were higher than that of dry season, suggesting anthropogenic influence. Pearson's correlation shows major contributors of total dissolved solids were Mg, Na and HCO3 with a correlation (r = 0.439, 0.874 and 0. 945) respectively. In the wet season, major contributors were TH, Mg, Na, SO4 and HCO3 with correlation (r = 0.548, 0.537, 0.856, 0.530 and 0.936) respectively. Gibbs plot suggests chemical weathering and precipitation to be the main contributors to the water chemistry. The dominant hydrochemical facies within the basin for both seasons was Na-K-HCO3 water type. The plot of Ca2+ + Mg2+ vs. HCO3- + SO42- suggests both silicate weathering and ion exchange processes are taking place within the basin. Mineral stability diagrams signify kaolinite as the most stable mineral phase in the groundwater. Chloro-alkaline indices were negative for both seasons leading to base-exchanged softened water production. Consequently, majority of ions evolved from natural geochemical processes whilst nitrate and sulphate presence might be due to anthropogenic sources.

Hydrogeochemical processes, mobilization controls, soil-water-plant-rock fractionation and origin of fluoride around a hot spring affected tropical monsoonal belt of eastern Odisha, India

Fluorosis, poor crop yield, and degraded soil fertility due to excess fluoride are mostly associated with igneous exposures and fertilizer use. Geochemical, petrographic, microprobe and mineralogical examinations revealed thermal spring origin of fluoride (up to 15.8 mg L−1) affecting agriculture and public health in eastern India. No fluoride was detected in plant leaves and exposed charnockite, but nearby soils and siderite precipitates are enriched in fluoride up to 3.4 g kg−1. Both geogenic hot spring and fertilizer origin are proposed with fluorosis severity found to be closer to the hot spring where the stream, pond, and well enrichments might have resulted upon mixing with high F− hot spring water. The pond, stream, bore well, hand pump, well and hot spring water in the region are mostly fresh water (dissolved solids <1000 mg L−1) and hard to very hard in nature with a pH of 5.7–9.7 and a temperature of 23–55 °C. Major water is of NaCl type with minor components of mixed CaMgCl, CaHCO3 and CaCl types enriched in the order Na+>Ca2+≈Mg2+>K+>Si4+>FeT > Al3+ and Cl−> HCO3− > NO3− > SO42−> PO43−. Stream, pond, and bore well waters exhibit better suitability for irrigation use compared to hot spring and well waters, while all the studied water resources are of poor to unsuitable quality for human consumption. Carbonate weathering dominated silicate weathering processes for the stream, pond, and bore well water, while the latter was for hot spring and well water. Reverse ion exchange is the major process that prevailed in the region where rock-water interaction and evaporation governed the regional hydrochemistry. Fluoride mobilization is favored under alkaline conditions and enhanced by competitive anions in the order NO3− > SO42−> PO43−. Acidic rainwater does not favor fluoride release from soil, and F-containing siderite is prone to release fluoride under ambient conditions.

Geochemical evolution and the processes controlling groundwater chemistry using ionic ratios, geochemical modelling and chemometric analysis in uMhlathuze catchment, KwaZulu-Natal, South Africa

The sources of chemical constituents of groundwater and its associated hydrogeochemical processes in the part of Mhlathuze catchment was identified. Groundwater of the area is classified into soft to very hard and the nature is identified as acidic to alkaline. The overall electrical conductivity is < 3000 μS/cm except in three wells. The predominant water type is NaCl (69% of samples) and CaMgCl facies. Gibbs plots, mCa/Mg ratio, mNa/Cl ratio, Ca + Mg vs HCO3+SO4 plot, Na + K vs HCO3 plot, Ca/Na vs HCO3/Na, Chloroalkaline indices (CAI 1, CAI 2) and Ca + Mg–HCO3–SO4 vs Na + K–Cl plots confirm the impact of silicate, carbonate mineral weathering and ion exchange reaction in this aquifer. However, few wells are influenced by the evaporation process. Groundwater is highly undersaturated with sulphate, chloride minerals and saturated with carbonate minerals. CA revealed that Cl and SO4 are derived from anthropogenic sources and a significant positive correlation between HCO3 and Cl reveals that wastewater recharge has most likely simulated the mineral weathering in the vadose zone, which could have further enhanced HCO3 and Cl in the aquifer. PCA resulted in three factors. Factor 1 defines the influence of geogenic and anthropogenic processes while Factors 2 and 3 imply the mineral weathering and nitrification processes. Hierarchical cluster analysis defines that evaporation, anthropogenic input, silicate and carbonate weathering and nitrification process are the sources of chemical constituents of groundwater in this aquifer.

Hydrogeochemistry and quality evaluation of groundwater and its impact on human health in North Tripura, India.

Groundwater contamination becomes an alarming threat to the provision of ecosystem services and natural resources. A very high level of groundwater contamination has been observed in the northeastern states particularly in North Tripura district. Therefore, the present study considered the region as a case study to evaluate the hydrogeochemical facies, heavy metal pollution and irrigation indices, and their impact on human health. For the investigation, we have collected a total of 35 groundwater samples from North Tripura district. Hydrogeochemical facies through Piper plot reflect Ca2+-Mg2+-HCO3- and Na+-HCO3- as dominant water types. Gibbs plot identifies the dominance of rock-water interaction process in groundwater hydrochemistry. Geochemical plots indicate the dominance of silicate weathering, ion exchange and carbonate dissolution processes in groundwater mineralisation. The order of trace metal contaminations follows Fe > As > Zn > Mn > Cu > Pb. Results of heavy metal indices suggest above 80% samples are at high risk due to high Fe contamination. The risk of the heavy metal indices is associated with rising elevation in southern part of North Tripura. Findings of health risk assessment study imply that children face much carcinogenic and non-carcinogenic risks than adults because of unsafe levels of Fe and As. Multivariate statistical tools are applied to unravel interrelationships among all ions and trace metals as well as probable hydrogeochemical processes in groundwater. Results of Wilcox and USSL plots suggest 77% samples meet irrigation suitability criteria. Besides, the analysis suggests a better insight to identify hydrogeochemical processes controlling groundwater chemistry and the suitability of groundwater for irrigation and drinking purposes. The study also suggests treatment and sustainable management of groundwater resources is compulsory to reduce trace metal contaminations before public use.

Groundwater quality and its suitability for drinking and irrigational purpose in Bhojpur district: middle Gangetic plain of Bihar, India

Abstract A total of 138, samples have been collected in both pre and post monsoon season to understand the seasonal variability in groundwater quality and its suitability for drinking and domestic water supply. The samples were analysed for physical parameters, major ions along with fluoride and uranium. The results were integrated with GIS to represent both seasonal and spatial variations of groundwater quality parameters, drinking groundwater quality index (DGQI) and irrigation groundwater quality index (IGQI). Results show that groundwater is alkaline in nature and largely controlled by the silicate weathering, ion exchange and reverse ion exchange processes. However high nitrate concentration exceeding the WHO guideline suggests the influence of anthropogenic activities on groundwater quality. The average values of the major ions concentrations was found higher in pre monsoon season due to change in the recharge. The DGQI values of 6 samples in pre monsoon and 2 samples in post monsoon season falls under poor water quality. However, individual irrigation indices along with the combine IGQI indicate groundwater is suitable for irrigation in both the seasons. These results along with the seasonal and spatial variability map may help the decision makers in planning for better domestic and irrigation water supply.

Genesis, evolution, speciation and fluid-mineral equilibrium study of an unexplored geothermal area in Northeast Himalaya, India

Arunachal Pradesh geothermal area, located in the Northeast Himalayan geothermal province is an unexplored geothermal area in India due to its rugged terrain and inaccessibility. In this study, a detailed geochemical characterization of the thermal waters is carried out to elucidate the source of the dissolved constituents and also to determine the subsurface reservoir temperature. The thermal waters are found to be nearly neutral to slightly alkaline (pH = 7.15 to 8.40) having highly variable EC values (EC ranges from 204 to 3600 µS/cm). Most of the thermal waters are mixed cation (Na, Ca)-HCO3-SO4 type whereas a few of them are of Na-HCO3 type. Silicate weathering and ion-exchange processes are found to be the two important mechanisms controlling the concentrations of the dissolved solutes in the thermal waters. The temperature dependant (20 to 198 °C) speciation analysis of the major ions (Na, K, Ca and Mg) shows that the composition of the reservoir fluid is dominated by free Na+ ions followed by K+, Ca2+ and Mg2+. The sulphate complex is found to be majorly dominated by both CaSO4 and MgSO4 whereas carbonate is mainly controlled by CaCO3 and CaHCO3+ species. Environmental stable isotope (δ18O, δ2H) data confirms the meteoric origin of these thermal waters. The isotope composition of the thermal waters in this region is found to be depleted compared to the non-thermal water samples indicating a high altitude precipitational recharge for these thermal waters. The altitude of the recharge estimated from the δ18O-altitude plot reveals that the precipitation occurring at the Gorichen Peak (altitude of 6858 m), the highest peak of the Arunachal Pradesh, is the main source of recharge for these thermal waters. Of different silica geothermometers, the quartz geothermometer gives the most conservative estimate (71 to 133 °C) of subsurface reservoir temperature. The quartz geothermometer gives a lower estimate of reservoir temperature due to mixing with non-thermal water. However multicomponent geothermometrical modelling results give a tightly constrained subsurface temperature i.e. 160±2 °C which may be taken as the probable reservoir temperature in this unexplored geothermal region. The study highlights the potential of integrated isotope-geochemical studies in expanding the geothermal energy utilization in India.

Impact of Flooding on Shallow Groundwater Chemistry in the Taklamakan Desert Hinterland: Remote Sensing Inversion and Geochemical Methods

Understanding the effect of flooding on groundwater quality is imperative for oasis vegetation protection and local ecological environment development. We used geochemical and remote sensing inversion methods to evaluate the effects of flood recharge on the groundwater hydrochemical and geochemical processes in the Daliyaboy Oasis. Groundwater samples were collected from 30 ecological observation wells in the study area before (PRF) and after (POF) the flood. Except for small changes in HCO3− and K+ and a decrease in pH, ion levels were higher POF than PRF, and the water chemistry was essentially unchanged. In the POF groundwater, HCO3− was correlated with Cl−, Na+, Mg2+, total soluble solids (TDS), and electrical conductivity (EC), but not with SO42−, Ca2+, K+, or pH, and was positively correlated with all other variables, while the remaining variables, except for pH, were strongly positively correlated with each other. PRF water chemistry was controlled by silicate and evaporite mineral weathering and evaporation processes, resulting in high groundwater TDS, EC, and a major ion content, while POF major groundwater ions were regulated by mineral weathering and flood recharge. We demonstrated the high accuracy of remote sensing inversion, confirming this as a reliable method for evaluating groundwater chemistry. The results of the study help to reshape and predict the history of the regional hydrogeological environment and hydrogeochemical development, and provide a theoretical basis for assessing the rational use of local water resources and protecting the ecological environment.