Signatures Of Groundwater Research Articles

Assessment of groundwater fluoride and human health effects in a hard rock province of south India: Implications from Pollution Index Model (PIM) and GeographicalInformationSystem (GIS) techniques.

This research examines whetherthe groundwater in the Sivakasi Region of South India is suitable for consumption, and assesses the possible health hazards for various age demographics including infants, children, teenagers, and adults. A totalof 77 groundwater samples were gathered, covering a total area of 580km2 and analyzed for major and minor ions. The hydrogen ion concentration (pH) of the samples indicates neutral to marginally alkaline. The total dissolved solids (TDS) fluctuate from 255 to 2701mg/l and electrical conductivity varies from 364 to 3540µS/cm. A wide range of fluoride concentration was detected (0.1 to 3.2mg/l) with nearly 38% groundwater samples surpassing the proposed limit (1.5 mg/l) suggestedby the World Health Organization in 2017. Gibbs plot analysis suggested that most of thesamples were influenced by geogenic factors, primarily rock weathering in this region. Correlation analysis showed that most of the samples were impacted by both natural and human sources. The pollution index of groundwater (PIG) fluctuated from 0.67 to 2.60 with approximately 30% and 53% of samples falling into insignificant and low pollution categories, respectively. Furthermore, 10% and 5% of total samples were characterized as moderate and high pollution levels, and 2% asvery high pollution category. Spatial analysis using GIS revealed that 440.63km2 were within safe fluoride levels according to theWHO standards, while 139.32km2 were identified as risk zone. The principal component analysis (PCA1) showedstrong positive loadings on EC (0.994), TDS (0.905), Mg2+ (0.910), Cl- (0.903) and HCO3- (0.923) indicating rock water interaction. PCA2 accounts the high positive factor loading on HCO3- (0.864) indicating ion exchange and mineral leaching. The PCA1 and PCA2 indicated that variables such as mineral leaching and rock water interaction are themajor mechanisms contributing to the chemical signatures in groundwater, which may support for theelevated fluoride levels in certain areas. Risk assessments, including Hazard Quotient results showed that 71%, 61% 38%, and 34% of groundwater samples exceededthe permissible THI limit (THI > 1) for infants, children, teenagers, and adults, respectively. The study recommends implementing measures such as denitrification, defluorination, rainwater harvesting, and improved sanitation infrastructure to enhance the health conditions in the study region. Additionally, it suggests introducing educational programs in rural areas to create awarenessabout the health dangers due to consumptionof water with high fluoride levels.

Identification of hydrochemical processes of groundwater in Nekor-Ghiss plain (Morocco): using the application of multivariate statistics and Geographic Information Systems (GIS) to map groundwater

In arid and semiarid zones, groundwater is a vital and indispensable natural resource. Indeed, these water resources have become extremely limited due to several factors, including climate change, salinization, and overexploitation. This study covers the hydrochemical characterization of groundwater in the Nekor-Ghiss plain which is located in northern Morocco. To achieve this objective, a set of 79 water samples was analyzed, for various physical and chemical parameters of the samples, including E.C, pH, TDS, HCO3−, SO42−, Ca2+, Mg2+, Na+, K+, PO43−, NO3−, NO2− and NH4+. Several methods were used to interpret the hydrochemical data, namely graphical methods, principal component analysis (PCA), hierarchical ascending classification, and ion exchange indices. A detailed geochemical study of groundwater is described to identify the origin of the chemical composition of groundwater. The results show that the samples studied are characterized by very high mineralization (> 1500 mg/l), with the predominance of Na+, Cl− and SO42− ions. The interpretation of geochemical signatures of groundwater in the Nekor-Ghiss plain shows sulfate-sodium (Na–SO4) and chloride-sodium (Na–Cl) facies. Natural geochemical processes are responsible for water regulation, while human activities exert a limited influence on this control. Marine intrusion, evaporation, and the ion exchange process largely control the chemistry of the aquifer. Using PCA to confirm controlled water chemistry processes revealed three homogeneous groups. The study contributes to a better understanding of the quality and mineralization of groundwater in the Nekor-Ghiss plain, and it will serve as a reference for other plains with similar characteristics.

Comprehending hydrochemical fingerprint, spatial patterns, and driving forces of groundwater in a topical coastal plain of Northern China based on hydrochemical and isotopic evaluations

To comprehensively comprehend the hydrochemical features, spatial patterns, and controlling mechanisms of groundwater in the Longkou coastal plain (LCP), a prime coastal plain in northern China, a detailed study utilizing statistical analyses, Piper diagram, Gibbs model diagram, ion ratio methods, and reverse hydrogeochemical simulation was performed on 76 groundwater samples collected in 2021. The findings of this study reveal that the groundwater in the LCP has an average pH value of 7.6, indicating weak alkalinity. The groundwater types are predominantly mixed, followed by Cl–Ca. The NO3− concentration in groundwater is relatively high, with a mean value of 326 mg/L, originating mainly from agricultural production activities. In addition to NO3−, the spatial distribution analysis of the principal chemical constituents in the groundwater demonstrated a subtle north-south gradient. The chemical signatures of groundwater are primarily influenced by the process of rock weathering, resulting from the dissolution of silicates and carbonates minerals as well as gypsum. Indeed, cation exchange represents a pivotal hydrogeochemical reaction within the groundwater system of the region. The intrusion of seawater into groundwater primarily exhibits a mild nature, mostly in the form of mixing intrusion in the initial stage, affecting the western and northern regions of the LCP to a greater extent. The primary source of groundwater recharge is attributed to atmospheric precipitation; however, it is partially affected by evaporation. In addition, LCP groundwater is also being recharged by seawater intrusion, mainly in the western and northern parts of the study area. Overall, the findings of this research hold significant implications for the strategic management of groundwater resources and the implementation of measures to prevent and mitigate seawater intrusion not only in the LCP but also in analogous coastal regions across the globe.

Wildfire-induced shifts in groundwater discharge to streams identified with paired air and stream water temperature analyses

Within the western United States, increasingly severe and frequent wildfires may alter the magnitude, timing, and quality of water exported from burned areas by streams. Post-fire hydrologic studies often focus on peak stream flow responses to shifts in runoff generation or on annual streamflow yield response to changes in evapotranspiration following fire. However, the magnitude and duration of wildfire effects on groundwater recharge, changes in subsurface routing, and consequences for stream low flows sourced predominately by baseflow are poorly understood. Here, we demonstrate an approach using the amplitude and phase of paired annual air and stream water temperature signals to broadly identify changes in watershed subsurface flow contributions after fire. Watersheds were classified using pre-fire temperature data, as having air-coupled (i.e., reduced apparent groundwater signature), deep groundwater, or shallow groundwater stream temperature signals. Changes in pre- and post-fire paired air and stream water temperature metrics were compared for locations (n = 17) spanning a large range of physiographic and climatic conditions across the western United States. Pre- and post-fire comparisons were computed by quantile using bootstrapped confidence intervals (ci = 95), as well as in aggregate using Kruskal-Wallis and post-hoc Dunn tests. Statistical comparisons of pre- and post-fire temperature metrics suggest that overall, watersheds classified as having minimal groundwater influence are the most likely to experience fire-induced subsurface hydrologic change. More specifically, watersheds classified as having air-coupled or shallow groundwater signals experienced increases in the magnitude of groundwater discharge, with more stable annual thermal regimes post-fire that are less-coupled to ambient air temperature. These findings form the basis of a conceptual framework for watershed resistance to subsurface hydrologic change following fire that can be broadly applied as a first approximation for water management, impacts on aquatic habitat, and post-wildfire response planning.

Geochemistry, stable isotopes and statistic tools to estimate threshold and source of nitrate in groundwater (Sardinia, Italy)

In the European Union, nitrate vulnerable zone (NVZ) should be designed for the mitigation of nitrate (NO3−) contamination caused by agricultural practices. Before establishing new NVZ, the sources of NO3− must be recognized. A geochemical and multiple stable isotopes approach (hydrogen, oxygen, nitrogen, sulfur and boron) and statistical tools were applied to define the geochemical characteristics of groundwater (60 samples), calculate the local NO3− threshold and assess potential sources of NO3− contamination in two study areas (hereafter Northern and Southern), located in a Mediterranean environment (Sardinia, Italy). Results of the integrated approach applied to two case study, permits to highlight the strengths of integrating geochemical and statistical methods to provide nitrate source identification as a reference by decision makers to remediate and mitigate nitrate contamination in groundwater.Hydrogeochemical features in the two study areas were similar: near neutral to slightly alkaline pH, electrical conductivity in the range of 0.3 to 3.9 mS/cm, and chemical composition ranging from Ca-HCO3− at low salinity to Na-Cl− at high salinity. Concentrations of NO3− in groundwater were in the range of 1 to 165 mg/L, whereas the nitrogen reduced species were negligible, except few samples having NH4+ up to 2 mg/L. Threshold values in the studied groundwater samples were between 4.3 and 6.6 mg/L NO3−, which was in agreement with previous estimates in Sardinian groundwater.Values of δ34S and δ18OSO4 of SO42− in groundwater samples indicated different sources of SO42−. Sulfur isotopic features attributed to marine SO42− were consistent with groundwater circulation in marine-derived sediments. Other source of SO42− were recognize due to the oxidation of sulfide minerals, to fertilizers, manure, sewage fields, and SO42− derived from a mix of different sources.Values of δ15N and δ18ONO3 of NO3− in groundwater samples indicated different biogeochemical processes and NO3− sources. Nitrification and volatilization processes might have occurred at very few sites, and denitrification was likely to occur at specific sites. Mixing among various NO3− sources in different proportions might account for the observed NO3− concentrations and the nitrogen isotopic compositions. The SIAR modeling results showed a prevalent NO3− source from sewage/manure. The δ11B signatures in groundwater indicated the manure to be the predominant NO3− source, whereas NO3− from sewage was recognized at few sites. Geographic areas showing either a predominant process or a defined NO3− source where not recognize in the studied groundwater. Results indicate widespread contamination of NO3− in the cultivated plain of both areas. Point sources of contamination, due to agricultural practices and/or inadequate management of livestock and urban wastes, were likely to occur at specific sites.

Mechanisms of iodine enrichment in the pore-water of fluvial/lacustrine aquifer systems: Insight from stable carbon isotopes and batch experiments

• High iodine groundwater occurs in discharge area of fluvial/lacustrine aquifer systems. • Local transformation of sediment Fe minerals explains the enrichment of pore-water iodine in the deep sediments. • Iodine-rich pore-water in the shallow sediments near the coastal area is related to the marine transgressions. The wide occurrence of high iodine groundwater is posing negative effects on human health. The land subsidence due to groundwater over-exploitation causes the release of iodine-rich pore-water trapped in clayey sediment into groundwater, however, the mechanisms of iodine enrichment in pore-water were still unclear. In this study, we selected the Datong Basin (DB) and North China Plain (NCP) with few and severe land subsidence, respectively, to understand the contributions of complex hydro-biogeochemical processes on the enrichment of iodine in groundwater and pore-water by using the inorganic/organic carbon isotope and batch experiments. The results showed that at the DB, the range of groundwater iodine was 4–2175 µg/L, and the enrichment of groundwater iodine is mainly related to the transformation of iron oxyhydroxides triggered by microbial degradation of organic matter, which was reflected by the more depleted δ 13 C DIC signatures of groundwater and gradual increasing trend of ratio of HCl-extractable Fe(II)/sediment Fe total and sediment δ 13 C DOC signatures with depth. In comparison, groundwater iodine at the NCP had the range of 2–1106 µg/L, and pore-water rich in iodine preserved in the clayey sediment serves as the main source. The depth profiles of sediment iron mineral fractions and δ 13 C DOC signatures suggested that the NCP sediments experienced lower degree of reductive transformation of iron minerals and microbial degradation of natural organic matter. At some specific depths higher than 300 m, the evident higher ratios of HCl-extractable Fe(II)/sediment Fe total indicate that the local transformation of iron minerals can explain the pore-water rich in iodine at deep sediments, which was supported by the results of microbial batch experiments. The pore-water with high iodine concentration preserved in the shallow sediment is more likely related to the marine transgressions. This study helps to improve our understanding of the mechanisms of high iodine groundwater, which may provide some new insights on further groundwater management.

Geochemical ratios mediated understanding of estuarine dynamics in submarine groundwater discharge prevalent basaltic aquifer

Submarine groundwater discharge (SGD) has been recognized as an integral pathway of hydrological cycle. The role of SGD as a mechanism for material transport from terrestrial to marine ecosystems has also been investigated, considering the large hydrological flux and a massive load of solutes is found to be carried as SGD to the coastal oceans. However, there are challenges in recognizing the process and delineating specific areas which are susceptible to SGD. Considering the unique geochemical signature of groundwaters found in varied lithology, this paper investigates the possibility of using geochemical ratios and their variability in coastal areas as a tracer for the identification of SGD. The Br−/Cl− ratio, prevalently used for identification of seawater-groundwater mixing is investigated. The study raises questions over the viability of Br−/Cl− as a tracer as Br− rich groundwater in the SGD prevalent area may be a cause of elevated Br−/Cl− ratio in the coastal oceans. Furthermore, the peculiar observation of Fe+2 enrichment in coastal seawater also indicated the influence of differential weathering on the subterranean estuarine (STE) sediments releasing Fe+2 as the groundwater in the area is not enriched in groundwater. This observation is very important in the context of rising sea levels as a larger STE due to rising sea levels can cause higher mobilization of Fe+2 in coastal oceans causing a direct influence on the coastal ecosystem.

18O, 2H, and ³H isotopic data for understanding groundwater recharge and circulation systems in crystalline rocks terrain of Southeastern Brazil

The 18O, 2H and ³H isotopes have been used to identify recharge and circulation patterns in aquifer systems by determining the relationships between isotopic signatures of meteoric, ground, and surface waters. This research investigates a Crystalline Aquifer System in Southeastern Brazil, where the isotopic fractionation results from the effects of precipitation, altitude, and continentality, while the Local Meteoric Water Line (LMWL) is expressed as δ2H = 8.49 δ18O + 18.97. The isotopic signature of groundwater follows that of rain, varying according to the climate conditions of each sector of the basin. The groundwater in the upper sector of the basin have a renewal time of up to 25.75 years and low mineralization, being an important recharge zone for the Crystalline Aquifer System. However, in the lower and hotter sector of the basin, the evaporative processes influence the recharge and, therefore, the groundwater is more mineralized with a renewal time of up to 85 years, indicating an infiltrated water source upstream. Surface water is enriched with heavy isotopes resulting from evaporation due to sun exposure, with isotopic data plotting above the LMWL during the rainy season and similar to groundwater during the dry season, showing the effluent character of the main drainage channels. We propose a conceptual model where the isotopic signature and mineralization of groundwater are influenced by the relief, climate conditions, and lithological diversity.

Comparison of groundwater composition from the Monturaqui and Punta Negra Basins, northern Chile: implications for porphyry copper exploration

Groundwaters recovered from the Salar de Punta Negra and Monturaqui basins in the Atacama Desert of northern Chile exhibit distinctly different isotopic, major, trace, and porphyry copper elemental compositions related to contrasting morphostructural, geochemical, and hydrodynamic settings. Comparison of these distinct groundwater signatures with groundwaters from known porphyry copper deposits (Salar de Hamburgo and Spence Deposit), can be used to determine if either basin might be prospective for porphyry copper mineralization. Groundwaters within the Punta Negra Basin exhibit geochemical characteristics consistent with other closed basin settings throughout the arid Andes. Elemental and isotopic compositions within the Punta Negra Basin reflect closed basin evaporitic processes consistent with the hyperarid, volcanic setting of the central Andes. Pathfinder metals and isotopic compositions are not consistent with porphyry copper type mineralization as described for groundwaters within the Salar de Hamburgo Basin, and the Spence Deposit. Within the Monturaqui Basin the geochemical composition of groundwaters are characteristic of diffuse hydrothermal activity. Sulfur isotopic composition within the waters of the northern Monturaqui Basin exhibit δ 34 S CDT isotopic signatures that fall within the range for sulfide mineralization as reported for groundwaters in and around the Spence Deposit and the Salar de Hamburgo. However, porphyry copper related elements within the Monturaqui Basin are impoverished relative to groundwaters of the Spence and Escondida Deposit. Such impoverishment in porphyry related elements, taken in conjunction with enriched δ 13 C PDB compositions, elevated groundwater temperatures, groundwater compositions dominated by HCO 3 , SO 4 , and Si, and the proximity of the Monturaqui Basin to the current magmatic arc are consistent with a volcanic hydrothermal origin. In summary, the groundwater geochemistry of the Monturaqui and Punta Negra Basins are not indicative of porphyry copper-type mineralization. Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues

Regional-scale hydrogeochemical evolution across the arsenic-enriched transboundary aquifers of the Ganges River Delta system, India and Bangladesh

Arsenic (As) dynamics within the extensively contaminated aquifers of the Ganges River delta have been widely studied over the past few decades, but the hydrogeochemical signatures across the delta aquifers remain to be characterized. Here, we characterize the varied geochemical and isotopic (δ18O, δ2H) signatures of groundwater across the delta and interpret the hydrogeochemical evolution pathways and the driving processes on a regional-scale as a function of the delta hydrostratigraphy. Our hydrostratigraphic model identifies three major aquifer sub-systems across the delta from north-west to south-east: a single continuous unconfined aquifer (Type I); a semiconfined vertically-segregated aquifer sub-system (Type II); and a nearly confined multilayered aquifer sub-system (Type III). The Type I aquifer is dominated by Ca-Mg-HCO3-rich waters, while the aquifers to the south (Type II and Type III) exhibits increasing dominance of Na-Cl hydrogeochemical facies at shallow and intermediate depths and Na-HCO3 hydrogeochemical facies in the deep aquifers. The spatial distribution of As is also found to be heavily dictated by hydrostratigraphy, wherein the Type I aquifer sub-system yields similar concentrations across depths, while the Type II and Type III aquifer sub-systems exhibit a sharp increase in As-safe aquifers with depth. Although dominant reducing conditions occur within the delta groundwater, co-occurrence of redox-sensitive solutes from varying redox stability fields indicates to the development of overlapping redox zones. Stable isotopic signatures of groundwater exhibit a progressive depletion away from the Bay of Bengal. The Type I aquifer exhibits relatively homogenous hydrogeochemical signatures, possibly suggesting deeper infiltration of recharge under higher vertical hydraulic gradients, while the Type II and Type III aquifers exhibit variability across depth, which is possibly a reflection of horizontally stratified groundwater flows, dictated by the spatial geometry of the intervening aquitard layers.

Isotopic signature of groundwater and climate change within a semi-arid environment

The negative effects of climate change on water resources from arid and semi-arid environments are of great interest to academics and policymakers. In this regard, this paper aims to assess the climate change impact on water resources within semi-arid environments, with a focus on the Essaouira Basin. To assess these effects we based on the isotopic signature of groundwater. This approach shows that (a) the recharge of groundwater is ensured by the precipitation of Atlantic origin without significant evaporation. (b) low recharge rate following the decrease in the precipitation rate (16% for the period 1978–2015) experienced by the study area in recent years, (c) The presence of old or fossil water in the study area suggests a low rate of renewal and the overexploitation of the groundwater in this basin, (d) The temporal evolution of the 18O contents generally shows an enrichment character of 1–1.5‰, which can probably be due to the evaporation phenomenon following the increase in the air temperature caused by climate change. However, it can be concluded that the isotopic signature of the groundwater within the Essaouira basin has not been spared from the effects of climate change.

Unveiling the extent of salinization to delineate the potential submarine groundwater discharge zones along the North-western coast of India

The North-West coast of India was notable for the urbanization and semiarid climate, particularly the Gujarat coastal region which was facing water crises and aquifer salinization issue. Under the light of these critical issues, the present study investigates the sources of aquifer salinization and probable location of submarine groundwater discharge (SGD) using an integrated approach of major ion chemistry, statistical techniques, and isotopic signature of groundwater (GW). The evolution of GW reveals that water facies changes from Ca2+-Mg2+-Cl− to Na+-Cl type from the south Gujarat towards the Gulf of Khambhat. Log-normal distribution of Cl− and NO3− divulges that different pollution sources influence the GW quality. Statistical findings supplemented with Isotopic signatures, ionic ratios and cross plots identified four classes of GW, which varies with degree of anthropogenic and seawater influences. Results suggested that seawater intrusion heavily influences 42% of the total GW samples, whereas 58% samples showed the probability of SGD. The study recommends the feasible locations of check dams as a remedial measure for controlling the salinization of coastal aquifer.

Hydrological, physicochemical and metabolic signatures in groundwater and snowmelt streams in the Japanese Alps

The unique hydrology and physicochemistry of alpine streams provide an important influence on the structure and function of inhabiting biological communities. A substantial body of research exists on alpine streams across many regions of the globe (e.g. Europe, North and South America and Greenland). To date, however, there have been few studies investigating the environmental conditions present in alpine streams across the Japanese archipelago. The lack of information on alpine streams in Japan is problematic as unique regional climates, e.g. some of the highest levels of snowfall globally, are likely to have repercussions for morphological, hydrological, physicochemical and metabolic signatures, causing them to differ from those observed in other regions. In this study we compare the morphology, hydrology, physicochemistry and metabolic activity of snowmelt and groundwater fed streams in the Kamikochi region of the Japanese Alps. Stream discharge, water chemistry (major ions, silica, dissolved oxygen), water temperature and channel stability were measured over a period of 16 months in 2017–2018. Metabolic activity was determined using Resazurin-Resorufin (Raz-Rru) Smart Tracer and variation in the Raz transformation rate was assessed to understand the effects of hydrology and physicochemistry on ecosystem functioning. Snowmelt streams were characterised by higher variability of water temperature, water chemistry and stream discharge, both, within and between sites. Indeed, two of the snowmelt streams experienced no flow conditions for several periods and also floods. In comparison, water chemistry, water temperature and stream discharge in groundwater fed streams were more temporally stable. Metabolic activity was higher in one groundwater fed stream, attributed to significant growth of macrophytes. These findings indicate that the patterns of morphology, hydrology, physicochemistry and metabolic activity across streams in the Japanese Alps largely resemble those identified elsewhere, although there were higher levels of inter-stream variation. The diversity and inter-site variation of hydrological and physicochemical conditions are likely responsible for the unique flora and fauna in the streams. This study therefore indicates the potential importance of habitat templates for the aquatic biodiversity hotspot in this region.

Groundwater recharge from heavy rainfall in the southwestern Lake Chad Basin: evidence from isotopic observations

ABSTRACT We examine groundwater recharge processes and their relationship to rainfall intensity in the semi-arid, southwestern Lake Chad Basin of Nigeria using a newly compiled database of stable isotope data (δ2H, δ18O) from groundwater and rainfall. δ18O signatures in groundwater proximate to surface waters are enriched in 18O relative to regional rainfall and trace focused groundwater recharge from evaporated waters via ephemeral river discharge and Lake Chad; groundwater remote from river channels is comparatively depleted and associated with diffuse recharge, often via sand dunes. Stable isotope ratios of O and H (δ2H, δ18O) in groundwater samples regress to a value along the local meteoric waterline that is depleted relative to weighted mean composition of rainfall, consistent with rainfall exceeding the 60th percentile of monthly precipitation intensity. The observed bias in groundwater recharge to heavy monthly rainfall suggests that the intensification of tropical rainfall under global warming favours groundwater recharge in this basin.

Groundwater geochemical signatures and implication for sustainable development in a typical endorheic watershed on Tibetan plateau.

Groundwater resource is significantly important for sustainable development of the world, especially for arid endorheic watersheds. A total of 28 groundwaters were collected for hydrogeochemical analysis from the arid Chaka watershed on Tibetan plateau to illustrate the hydrochemical evolution, formation mechanisms and feasibility of groundwater in small arid endorheic watersheds where groundwater is much scarcer. The results showed groundwater has a slightly alkaline nature, and varies from soft fresh HCO3-Ca type to hard brackish/saline Cl-Na type along the groundwater flow path in the watershed with the total hardness in the range of 270-2,127 mg/L and the total dissolved solids in the range of 282-41,770 mg/L. Nitrogen and fluoride in phreatic water are found sporadically exceeding the permissible limits with the maximum value of 118 mg/L for nitrate, 1.2 mg/L for ammonia and 1.2 mg/L for fluoride. Hydrochemistry of phreatic and confined groundwater is naturally governed by water-rock interactions including minerals (halite, gypsum and anhydrite) dissolution, silicate weathering and cation-exchange reaction. The salinity of phreatic water is also dominantly controlled by the strong evaporation. Human activity is one of the important mechanisms influencing the hydrochemical signature of groundwater regardless ofthe depth. Groundwater has a great hydrogeochemical discrepancy spatially across the watershed and varies from excellent to extremely poor quality in phreatic aquifers. A better water quality that under the good to medium categories was observed in the confined aquifers with 80% of samples having the EWQI value less than 100 and others in the range of 100-150. Phreatic groundwater away from the river and in the downstream area has a relatively poor quality for domestic and agricultural purposes, and should be avoided to direct utilization. This research can improve the understanding of groundwater hydrogeochemical feature, genesis, and its constraints on the availability and feasibility of groundwater resources in small arid watersheds worldwide.

Spatiotemporal Variation of Groundwater Recharge in the Lower Reaches of the Poyang Lake Basin, China: Insights From Stable Hydrogen and Oxygen Isotopes

AbstractUnderstanding of groundwater recharge and associated hydrological processes is important for sustainable management and utilization of water resources, especially in the monsoon regions. However, few systematic studies have been conducted on the spatiotemporal variation of groundwater recharge. In this study, stable isotopes of precipitation and groundwater were used to explore the spatiotemporal variation of groundwater recharge in the lower reaches of the Poyang Lake Basin of China, a region affected by the interplay of different monsoons. The results indicated that isotopic values (δ2H and δ18O) of precipitation exhibited obvious seasonal variations, higher in winter and lower in summer, controlled by different monsoons. The stable isotopes of groundwater also presented distinct seasonal variations, revealing the dominant influence of seasonal precipitation, but they had different characteristics in space. In the northern study area and Rao and Xin Basins, the isotopic signatures of groundwater showed the shift to lower values in summer and higher values in winter, consistent with those of precipitation, while in the Ganfu Plain, which is characterized by poorly permeable strata, isotopic signatures of groundwater presented opposite temporal variations than those of precipitation (lagged behind precipitation). The characteristics of groundwater isotopes might be linked with the spatial heterogeneity of groundwater recharge rate, which was affected by recharge mechanisms, lithology of aquifer materials, and interaction between groundwater and lake water. This study provides insights into the groundwater recharge of the Poyang Lake Basin and other similar areas.

Continental-scale analysis of shallow and deep groundwater contributions to streams

Groundwater discharge generates streamflow and influences stream thermal regimes. However, the water quality and thermal buffering capacity of groundwater depends on the aquifer source-depth. Here, we pair multi-year air and stream temperature signals to categorize 1729 sites across the continental United States as having major dam influence, shallow or deep groundwater signatures, or lack of pronounced groundwater (atmospheric) signatures. Approximately 40% of non-dam stream sites have substantial groundwater contributions as indicated by characteristic paired air and stream temperature signal metrics. Streams with shallow groundwater signatures account for half of all groundwater signature sites and show reduced baseflow and a higher proportion of warming trends compared to sites with deep groundwater signatures. These findings align with theory that shallow groundwater is more vulnerable to temperature increase and depletion. Streams with atmospheric signatures tend to drain watersheds with low slope and greater human disturbance, indicating reduced stream-groundwater connectivity in populated valley settings.

U-series and Sr isotopes as tracers of mineral weathering and water routing from the deep Critical Zone to streamflow in a high-elevation volcanic catchment

Tracing water routing and groundwater contribution to streamflow is a key tool for better understanding limited water resources. Measurements of U-series activity ratios and radiogenic Sr isotope ratios in drill cores, streams, and groundwater samples were employed to investigate weathering controls and better understand hydrologic flow paths and evolution through the heterogenous subsurface of a montane catchment. Situated within the semi-arid geologically complex volcanic setting of the Valles Caldera National Preserve in northern NM, this study focuses on streams draining the tallest (3432 masl) resurgent dome (Redondo Peak). Recent drilling of groundwater monitoring wells allowed for the collection and isotopic analysis of intact continuous cores and groundwater collected from similar depths, a unique and valuable contribution to U-series studies, within a high elevation headwater catchment focusing on two hillslopes with contrasting Critical Zone (CZ) structure and several distinct groundwater stores.U-series composition of core samples identified UTh fractionation from recent (< 1.25 Ma) disturbance in both hillslopes; however, (234U/238U) and (230Th/238U) disequilibria and 87Sr/86Sr values indicated more intense weathering and lithologic complexity in the hillslope underlain by volcanic breccia over vesicular tuff compared to the hillslope underlain by fractured tuff. The weathering profile of the site composed of breccia overlying vesicular tuff was influenced by the presence of shallow groundwater situated above deeper groundwater stores, which have distinctively higher (234U/238U) activity ratios and 87Sr/86Sr signatures than those of the deep groundwater stores in the fractured tuff site. The combination of U-series and Sr isotopes across time and in isotope mixing analysis highlights the utility of pairing these two isotope tracers that pinpoint distinct groundwater stores and help to isolate controls on U-series isotopes. Time series of U and Sr isotope signatures of groundwater and surface water suggest small seasonal changes in composition of streamflow while USr isotope mixing analysis suggests that deep groundwater from the fractured tuff aquifer system generates more than 90% of streamflow to the greater catchment whereas shallow groundwater and soil water contribute less than 10% to streamflow, primarily following spring snowmelt. Importantly, constraining streamflow sources using isotope mixing analysis highlights that deep groundwater from fractured bedrock within the CZ sustains streamflow here and emphasizes the need to consider deep groundwater in future studies of fractured bedrock systems.

Hydrochemical and Isotopic Study of Water Resources in Khan Al-Baghdadi Area, Al- Anbar Province / West of Iraq

This hydrochemical study of the surface and groundwater in Khan AL-Baghdadi area, western Iraq, included the interpretation of physical, chemical, and biological properties. Water samples were collected from wells (14 samples) and surface water of Euphrates River (6 samples) for the dry and wet periods of October 2018 and April 2019, respectively. The stable isotopes analysis was performed for the dry period only. The surface water samples were characterized by slightly alkaline, fresh, excessively mineralized, Ca-chloride type, and hard to very hard water class. While the groundwater samples were characterized by slightly alkaline, brackish, excessively mineralized, Ca-chloride and Na-Chloride type, and hard to very hard water class. The stable isotopic analysis was used in studying the interaction between water resources of Euphrates River and groundwater. Stable isotopes (δD and δ18O) were used to study the hydrological aspects of water resources in the study area. The results showed that surface and groundwater samples have similar source with a correlation relationship between them, in addition to the clear effect of river recharge on groundwater. The variation in δ2H and δ18O signature of groundwater in the study area is caused mainly by variation in isotopic composition of recharge water zone and mixing water. Using the δ 2H and δ 18O diagram, all surface and groundwater samples were plotted below the global meteoric water line (GMWL) and Local Meteoric Water line (LMWL), indicating the influences of the evaporation processes and seasonal variation.

Helium Isotopic Signature of a Plate Boundary Suture in an Active Arc–Continent Collision

We report new noble gas signatures of groundwaters, hot springs, and bedrock samples from two major fault systems that form the plate boundary suture between the Eurasian Plate and the Philippines Sea Plate. In the south, the Eurasian Plate dips east beneath the Philippine Sea Plate, and the boundary between the arc and accretionary prism is marked by the Chihshang Fault, which also dips east beneath the arc. The fault is well-defined by seismicity and extends to at least 25 km, close to the crust–mantle boundary. This fault could be an important conduit for the passage of mantle helium along the suture. In the north, as the subduction direction flips from the east-dipping Eurasian Plate to the north-dipping Philippine Sea Plate, the plate boundary fault is represented by a more complex system of east- and west-dipping structures. Low helium isotopes in this area evidence the weaker mantle signal, both before and after a Mw 6.4 earthquake. It is possible that as the subduction direction flips from south to north along strike, the tortuosity of the fault-related conduits increases, reducing the flow and limiting the release of mantle-derived gases.