Source Of Groundwater Recharge Research Articles

Spatiotemporally non-stationary evolution of groundwater levels in Poyang Lake Basin driven by meteorological and hydrological factors

The complex relationship between wet-dry transition in the Poyang Lake basin and groundwater storage significantly affects the lake's hydrology, downstream ecological state, and overall security along the Yangtze River in China. There is, however, a notable lack of systematic exploration into how various factors drive spatiotemporal variability in groundwater level (GWL). Using local indicators of spatial association (LISA), spatial non-stationarity models, and multi-source data, our analysis explores the spatial distribution of GWL and quantifies the influence of driving factors on its spatiotemporal non-stationarity at annual and monthly scales. We also compare driving factor contributions in hilly, plain, and local areas within the Poyang Lake basin. Our findings reveal significant local clustering of GWL, indicating substantial spatial autocorrelation and geographic heterogeneity in GWL. Influencing factors exhibit non-stationary effects on GWL at spatial and temporal scales, with precipitation (P), ground surface elevation (GSE), and soil moisture (SM) being primary contributors, generally exerting positive effects. SM contributes most during dry years and normal periods. P and the Palmer Drought Severity Index (PDSI) have greater impacts in hilly areas, while GSE shows the opposite trend. Rainfall is a source of groundwater recharge, with a lagged response observed in GWL to rainfall in this basin. The lag time is about 1–2 months. Evapotranspiration is not the dominant discharge pathway. The decrease in GWL during the dry season is mainly due to reduced precipitation recharge and increased lateral groundwater discharge from areas of high hydraulic head to areas of low hydraulic head.

Strontium Isotopic Composition as Tracers for Identifying Groundwater Recharge Sources in the Choushui River Alluvial Plain, Western Taiwan

Groundwater is a vital resource in the Chuoshui River alluvial plain (CSAP), a key agricultural area in Taiwan. Understanding groundwater recharge is crucial for sustainable water management amidst changing climatic conditions and increasing water demand. This study investigates the major ion composition, solute Sr concentrations, and 87Sr/86Sr ratios in groundwater and stream water from the Choushui River (CSR) to trace groundwater recharge sources. The Piper diagram reveals that most groundwater samples are of the freshwater Ca–HCO3 type, aligning with the total dissolved solids (TDS) classification. TDS and major ion compositions indicate that groundwater near Baguashan Terrace (BGT) and Douliu Hill (DLH) primarily derives from stream water and rainwater. Na+ and Cl− enrichment in some aquifers of BGT and DLH is attributed to the dissolution of paleo-sea salt and mixing with paleo-seawater from sedimentary porewater. Elevated dissolved Sr concentrations and lower 87Sr/86Sr ratios in these aquifers further support the intrusion of paleo-seawater. Groundwater in the proximal fan shows high TDS due to intensive weathering, complicating the use of TDS as a tracer. Sr isotopic compositions and solute Sr2+ concentrations effectively distinguish recharge sources, revealing that the CSR mainstream primarily recharges the proximal fan and BGT region, while CSR tributaries and rainwater mainly recharge the DLH region. This study concludes that Sr isotopic compositions and solute Sr2+ concentrations are more reliable than TDS and major ion compositions in identifying groundwater recharge sources, enhancing our understanding of groundwater origins and the processes affecting water quality.

Groundwater recharge sources and mechanisms in the Ethiopian central Afar rift: Insights from isotopic and hydrogeochemical tracers.

Groundwater flow and recharge mechanisms in the central Afar rift and the associated western marginal grabens and Northwestern Plateau (NWP) are poorly understood because of the complex geology and spatial heterogeneity in the aquifer systems. The major aquifers in the region include the Oligocene and Pliocene to recent volcanics and recent alluvio-lacustrine sediments. We employed hydrogeochemical, stable isotopes of water (18O and 2H), and geological structures insights to identify groundwater recharge sources and mechanisms, aiming to develop a representative conceptual groundwater flow model. Water samples from groundwater and surface water were collected based on lithological/aquifer variation and geomorphological setup for isotope and hydrochemical analysis. Findings reveal distinct isotopic differences between the deep (>350 m) and shallow groundwater systems of the Afar rift, with deep systems showing relative isotopic depletion, indicating varying recharge sources. The deep groundwater exhibited a similar isotopic signature to that of the marginal grabens and NWP. The distribution of major ion chemistry and electric conductivity (EC) of groundwaters from the western plateau to the Afar rift show significant spatial variability. However, in some corridors of western parts of the rift, there is a clear geochemical evolution along the flow paths inferring groundwater flow continuity between aquifers. The results revealed the existence of preferential deep groundwater recharge from the NWP through the highly fractured linking zones, interacting fault zones in between the marginal grabens, to the deeper volcanic aquifers of the central Afar rift. The proposed groundwater flow model of this study illustrates the deep groundwater flow from the NWP to the Afar rift is primarily directed by the orientations of the faulted marginal grabens and the highly fractured interacting zones. This model is pivotal for understanding groundwater dynamics in similar continental rift environments, offering insights for effective groundwater management.

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.

Discharge variations of qanat near an ephemeral stream

Ephemeral streams are the most important sources of groundwater recharge in arid and semi-arid regions of the world. To extract this replenishable water, most of the time, qanats are constructed parallel to the ephemeral streams. Analytical modeling of a stream-qanat system can provide an effective tool for managing such a system in a timely fashion and, thus, is commonly applied in the hydrological communities. However, the available analytical solutions of discharge variation of qanat only consider the distributed recharge from rainfall and cannot be used to investigate the effects of geometric parameters of stream and hydraulic parameters of aquifer on the discharge of qanat near an ephemeral stream. Thus, the goal of this work is to obtain a semi-analytical solution of qanat discharge due to recharge from an ephemeral stream of an arbitrary shape in a three-dimensional anisotropic homogeneous unconfined aquifer. The solution is obtained via Laplace and Fourier transformations along with the principle of superposition. The results of this study are presented in the form of qanat discharge-time curves. The influences of the qanat length, shape, and recharge distribution along the ephemeral stream are explored in great detail. The effects of the hydraulic parameters of the aquifer on the discharge of qanat are also investigated. The results of this study can be used to predict the discharge of qanat due to recharge from an ephemeral stream, to calculate the optimum length of a qanat for maximum extraction of the replenished water, to estimate the adequate recharge from the ephemeral stream and the hydraulic parameters of aquifer using the discharge data of qanat, among other applications.

Study on Hydrochemical Characteristics and Interactions between Groundwater and Surface Water in the Dongting Lake Plain

The Dongting Lake Plain is a major ecological reserve for river and lake wetlands in the Yangtze River Basin, with complex river and lake relationships and frequent water flow exchange. Studies on the hydrochemical characteristics and the mechanism of interaction between groundwater and surface water will actively promote the scientific management, utilization of water resources, and protection of the ecological environment in the Dongting Lake Plain. Based on hydrogeochemical statistics, Gibbs diagrams, ion ratios, rock weathering end-element diagrams, hydrogen–oxygen isotope relationship diagrams, and other technical methods, the chemical characteristics, ion sources, and the distribution of hydrogen–oxygen isotopes of groundwater and surface water in “the Three Inlets” and “the Four Rivers” water system areas as well as the Dongting Lake water were analyzed. Additionally, the interactions between groundwater and surface water and the proportions of these contributions were discussed. The results show that both groundwater and surface water in the Dongting Lake Plain are weakly acidic or alkaline, and the anions are mainly HCO3−, the cations are mainly Ca2+and Mg2+, with the hydrochemical types being mainly HCO3−Ca−Mg and HCO3−Ca. The chemical characteristics of groundwater and surface water are mainly affected by the interaction between water and rock; the ions in surface water mainly come from the weathered dissolution of carbonate and silicate rocks, while the ions in groundwater mainly come from the weathered dissolution of carbonate and silicate rocks, with the dissolution of evaporite rocks locally. Groundwater and surface water are mainly distributed near the local meteoric water line (LMWL), and the slope of the local evaporation line is less than that of the LMWL, which indicates that atmospheric rainfall is an important recharge source for groundwater and surface water and that at the same time, it is affected by evaporation to a certain extent. Part of the groundwater in the Dongting Lake Plain is discharged into the surface rivers in “the Three Inlets” and “the Four Rivers” water system areas, and the other part is directly discharged into Dongting Lake. According to the mass balance relationship of isotopes, the proportions of surface water in “the Three Inlets” and “the Four Rivers” water system areas contributing to Dongting Lake’s water are 18.48% and 60.38%, respectively, and the proportion of groundwater in the lake plain contributing to Dongting Lake water is 21.14%.

Spatiotemporal heterogeneity of suprapermafrost groundwater dynamic processes in the permafrost region of the Qinghai-Tibet Plateau

Suprapermafrost groundwater fulfils an important role in the hydrological cycle of the permafrost region. Under the influence of the soil freeze–thaw process in the active layer, the dynamic process of suprapermafrost groundwater is too complex to be fully quantified, which has limited our understanding of the features of groundwater dynamic processes in permafrost regions. To bridge this gap, the dynamic characteristics of the suprapermafrost groundwater level were systematically observed, and pumping tests were performed under different topographic conditions (e.g., altitude, slope orientation, and distance from the river). The results showed that the differences in the heat distribution and recharge source of groundwater at the different altitudes and slope orientations determined the phase and threshold of the variation in the suprapermafrost groundwater movement state. There was a significant Boltzmann function relationship between the groundwater level and soil temperature. The groundwater level in the downslope during melting increased earlier and that during freezing declined later than that in the upslope part during the initial thawing cycle and the initial freezing cycle, respectively. The groundwater level on the shady slope decreased twice as fast as that on the sunny slope at the initial freezing stage. There was a favourable exponential relationship between the hydraulic conductivity (K) and soil temperature in the study area. On the sunny slope, K was higher than that on the shady slope, and K was higher in the area near the river than in the area far from the river. When the melting depth of the active layer reached 2/3 of the maximum depth, K reached its maximum value. The study results also revealed that when the soil temperature was reduced to 1–0 °C, a strong linear relationship occurred between K and soil temperature.

Geochemical and Isotopic Constraints on the Recharge and Salinization Origin of Groundwater Aquifers in El Rina–Nihayaat, South Sinai, Egypt

The Sinai Peninsula is located in the arid regions of Egypt where groundwater is the sole source for drinking and irrigation and future development. Regular assessment of the geochemical processes governing the groundwater quality is important in arid regions and paleo-aquifers. This research focuses on investigating the groundwater sustainability of the Upper Cretaceous Aquifer (UCA) located at El Rina–Nihayaat area, Southwestern Sinai Peninsula. The study aims to evaluate the main source of groundwater recharge and investigate factors deteriorating groundwater quality. The study is based on the geochemical and isotopic analyses of 31 groundwater samples tapping the UCA. The groundwater flows toward the Gulf of Suez. The groundwater salinity ranges from 1078 mg/L to 13090 mg/L indicating brackish to saline water. Two main water types have been delineated: Cl-Na and Cl-Ca indicating the final stage of groundwater evolution and leaching and dissolution of aquifer matrix of marine origin. The spatial distribution of the groundwater salinity and major ions (Na+, K+, Ca2+, Mg2+, SO42-, and Cl-) increase toward the Gulf which coincides with the direction of the groundwater flow, while bicarbonate increases toward the upstream watershed. Most of the groundwater samples tapping the UCA are depleted with the isotopic content of the stable isotopes where they range from -4.43 ‰ to -6.37 ‰ for δ18O and -28.3 ‰ to -40.2 ‰ for δ2H. The groundwater samples are depleted relative to the recent rainwater and enriched to the Nubian Sandstone located underneath the UCA indicating mixing from both source(s). The mixing estimated percentages from the recent rainwater using calibrated geochemical NETPATH model range between 48.6% to 88.5% while the upward Leakes from the Nubian water ranges between the recent rain and the paleo-Nubian water ranges between 48.6 % and 88.5 % from the meteoric rainwater, while the upwelling recharge from the paleo-Nubian groundwater ranges between 11.5 % to 51.4 %. The factorial analyses indicate three main factors governing the geochemistry of groundwater in the UCA: including water-rock interactions, meteoric recharge from annual precipitation, and upward leakages from the underneath paleowater. 
 Further exploration for the UCA is recommended to determine the promising zones receiving a considerable amount of the recent rainfall.

Coupled hydrogeological modeling and nitrate transport modeling in an anthropized valley, a case study of the lower Soummam valley (Bejaïa Northeast of Algeria)

Anthropogenic activities, including wastewater discharges and fertilizer use, were identified as the primary factors influencing nitrate concentrations in the lower Soummam Valley in the North-East of Algeria. This study aimed to investigate nitrogen pollution and simulate nitrate mass transport coupled with a numerical flow model. Hydrogeochemical findings revealed significant seasonal variations between the high-water period (May 2019 and 2021) and the low-water period (September 2019 to November 2020 and 2021). During the low-water period, both temperature and electrical conductivity increased. However, pH, dissolved oxygen, and nitrate levels decreased in the high-water period. Nitrites and ammonium exhibited irregular fluctuations. The numerical flow model was developed using PMWIN and coupled with a solute transport model simulated with the Model Transport 3 Dimensions (MT3D). Calibration was conducted under steady-state conditions from 2011 to 2021 and was validated by comparing piezometric heads and nitrate concentrations measured in May 2021. Three scenarios were devised to simulate transient conditions from 2011 to 2050, considering variations in both groundwater levels and nitrate concentrations. The simulation revealed that river and dependent head boundaries are the primary sources of groundwater recharge. These boundaries contributed to approximately 87% of the total inflow. The model also depicted the water exchange between the aquifer and the river. However, the constant head boundary represented the main outflow, accounting for 85.7% of the total. The nitrate model illustrated an increase in nitrate concentrations, reaching 3.8 mg/L in 27 out of the 29 simulated wells. Both the river and groundwater head boundaries were identified as the key factors governing the hydrodynamic aquifer system and nitrate transport in the alluvial aquifer of the lower Soummam Valley.

Using multiple isotopes to determine groundwater source, age, and renewal rate in the Beishan preselected area for geological disposal of high-level radioactive waste in China

Understanding hydrogeological conditions is crucial for selecting and assessing the long-term safety performance of a high-level radioactive waste (HLW) disposal repository. Utilizing environmental isotopes as effective markers for analysing groundwater movement, this study investigates groundwater recharge sources, age, and renewal rates using multiple isotopes in China's potential HLW repository site, the Beishan area. The results indicated deep bedrock groundwater primarily derives from ancient precipitation infiltration under cold climatic conditions. A noteworthy distinction is that loose sedimentary groundwater exhibits higher tritium content (>10 TU) compared to bedrock groundwater (<3.2 TU). Groundwater within the recharge area, especially within gullies and piedmont slope deposits, is relatively youthful, with an age of less than 30 years and an annual renewal rate exceeding 5 %. In contrast, the shallow groundwater age in the intermountain basins and depressions of the discharge area generally exceeds 50 years, with an annual renewal rate often falling below 0.5 %. At the Beishan underground research laboratory site, deep groundwater at the disposal repository depth displays a corrected 14C age exceeding 8,000 years, indicating an extremely slow movement and alteration rate. As a result, the hydrogeological conditions in the Beishan area are expected to be relatively beneficial for ensuring the safety of HLW repository.

Optimized Irrigated Water Management Using Numerical Flow Modeling Coupled with Finite Element Model: A Case Study of Rechna Doab, Pakistan

The fate of agriculture in Pakistan is predominantly concerned with excessive water mining threats to the subsurface water resources. The current study integrates the Visual MODFLOW-2000 application to estimate the water balance of an aquifer bounded by the Chenab River in the West and the Ravi River in the East, which covers an area of about 2.98 million hectares. An assimilated method of groundwater flow is employed to characterize the flow dynamics of the Rechna Doab aquifer. The Digital Elevation Model (DEM) produced by the Shuttle Radar Topography Mission (SRTM) and a mesh of discretized cell size (2500 m) were incorporated into the model design. The conceptual model of the alluvial aquifer involves trifold vertical boundaries (an initial fold thickness set up to 150 m). The model input parameters are precipitation, seepage through irrigation, return flow, recharge, hydraulic conductivity and evapotranspiration. Empirical relations are established (at the basin scale) for the discharge input of irrigation canals. Model results confirm that groundwater flow follows the topographic configuration of the study area (i.e., northeast to southwest), and the seepage from irrigating canals and rainfall appeared to be the main source of groundwater recharge among various resources. The zone budget study under steady state simulation showed that the total direct recharge to the aquifer is calculated as 522,910 acre foot. The simulated water balance of the studied aquifer reflects more fluctuations in river leakage. The predictive optimized model reflects an adaptation of canal lining and installation of additional tube wells that will minimize canal seepage by 70% and lead to the reclamation of 37,000 acres of water-logged land for normal cropping.

Quantifying recharge sources to groundwater to an oasis area: Implications for strengthening water resource management under changing environmental conditions

AbstractIn order to implement sustainable management of water resources in the Desert Oasis, it is necessary to quantify the changes in the groundwater recharge process. Using the Cl−, stable hydrogen and oxygen isotope datasets extracted from 113 groundwater samples in the years of 2000 and 2020, and combining these with the MixSIAR model, changes in the groundwater recharge process and recharge source contributions in the Minqin Oasis (MO) in northwestern China area before and after ecological treatment were quantitatively analysed. Overall, confined groundwater was the greatest contributor to the recharge of shallow groundwater in the MO area in 2000. However, after 10 years of ecological rehabilitation, surface water has become the most important recharge source of shallow groundwater, with its contribution increasing by 10.6% between 2000 and 2020 ~ 2021. River water diversion projects have reversed falling groundwater levels in the MO area. Of these projects, that in the MO has seen groundwater levels rise at a rate of 0.09 m·year−1 from 2008 to 2019. This coincides with the increase in the contribution of surface water to groundwater recharge in 2020. In addition, insignificant changes were observed in the contributions made by lateral groundwater flow to groundwater recharge in the MO area in the years of 2000 and 2020 ~ 2021, indicating that groundwater in the upper and middle reaches of the MO area have contributed very little to the restoration of groundwater levels in the area's lower reaches. All these factors would appear to indicate that regional ecological management has had a lasting impact, and that the exploitation of groundwater in this desert oasis area in an inland river basin should be based upon rational planning and integrated, comprehensive management strategies.

Hydrogeochemical Characteristics and Genetic Analysis of Karst Groundwater in the Fengfeng Mining Area

The karst water resources in the Fengfeng mining area are an important water supply source in the region. In recent years, due to the influence of external environment changes, the hydrochemical environment of karst groundwater has changed. In order to scientifically understand karst groundwater and rationally develop groundwater resources, it is necessary to study the hydrochemical characteristics and evolution laws of groundwater in this area. In this study, major elements in karst groundwater of different years and hydrogen and oxygen isotopes in 2022 were analyzed. The hydrochemical types of the study area were analyzed by using the Piper trilinear diagram drawn with Aquachem10.0 software. D and 18O were used to analyze the source and elevation of groundwater recharge. Origin software was used to draw Gibbs diagrams, three-terminal diagrams, ion ratio diagrams, etc., to analyze the influencing factors of groundwater chemical components. The research results show that: (1) The groundwater in the study area is mainly HCO3-Ca(Mg) type water; (2) The main supply source of karst water in the study area is atmospheric precipitation, and the supply elevation ranges from 1166.7 to 1533.3 m; (3) Most of the karst groundwater in the study area is affected by the dissolution of carbonate and silicate rocks; (4) With the influence of human activities, mainly agricultural activities, with the passage of time, the impact of industrial activities on groundwater has been weakening.

Identification of groundwater hydrogeochemistry and the hydraulic connections of aquifers in a complex coal mine

It is important to understand the changes in the chemical composition and connectivity of each aquifer in the arid-semi-arid riverine mines under the driving force of coal mining and to establish a rapid identification of water sources in the riverine mines, which is important for the protection of groundwater resources and safe production in the study area. By analyzing the numerical characteristics of conventional elements, cluster analysis and the deuterium–oxygen and tritium isotopes of different aquifers, the groundwater chemical characteristics and hydraulic connections of each aquifer were determined. Three identification charts (Piper and Durov identification charts of conventional hydrochemical components and deuterium–tritium isotope identification charts) were established to enable the rapid identification of each aquifer water source. The results showed that the main recharge source of groundwater in the study area was atmospheric precipitation. There was a significant indigenous connection between the Quaternary aquifer and the Zhiluo Formation aquifer but a limited indigenous connection between the Zhiluo Formation aquifer and the Yan'an Formation aquifer, creating local groundwater systems that altered the local groundwater circulation patterns, driven by coal mining. Three identification charts were established to determine the water inrush sources and propose targeted solutions for water inrush from different aquifers in the Shendong mining area based on the differences in hydrochemical ion characteristics as well as deuterium–oxygen and tritium isotopes.

Groundwater recharge sources and processes in northwest India: Evidence from high frequency water isotope observations

Study regionBist-Doab, Punjab, northwest India. Study focusWater isotopes and specific electrical conductivity (SEC) are used in this paper to investigate groundwater recharge sources and processes in a catchment with a history of high groundwater abstraction for irrigation and canal irrigation. High frequency (every 10 days) samples for water stable isotope analysis (δ18O and δ2H) were sampled from a dense network of shallow (<50 m) and deep (>100 m) hand pumps and tube wells in Bist-Doab, northern Punjab between 2009 and 2014. New hydrological insights for this regionThe study indicates that groundwater recharge is dominated by meteoric sources from high intensity events. However, in a small proportion of sites located in close proximity to some canals and rivers have significant surface water inputs. Isotope observations indicate rapid changes in groundwater recharge sources linked to post-monsoon pumping and seasonal connectivity to surface water inputs, even at some deep sites. Rapid changes are likely linked to poor well integrity, highlighting the risk to groundwater sources from surface water ingress. Shallow groundwaters had significantly higher SEC compared to deeper groundwater observations (p = 0.0002). Overall groundwater SEC is still relatively low (<2000 μS/cm). However, based on previously published mean residence time of (<50 years) in shallow groundwater the high rate of change in salinity at some sites (2.5–10% per year) is of potential concern.

Irrigation‐induced evaporative water loss in a glacially derived soil site

AbstractWorldwide, significant agricultural activities take place where groundwater is used for irrigation and water losses occur due to evaporation. Water loss through evaporation is affected by the soil type, local climate and most likely crop type. Previous studies from arid regions demonstrated the utility of oxygen and hydrogen isotopes in estimating evaporative water loss during return flow back to an aquifer. This study examined the region around Kalamazoo, Michigan, United States, where the soil is formed from glacial sediments and the region experiences a temperate climate. The present study is applicable to agricultural practices in many parts of the world that are in a temperate climate zone. The study area primarily uses centre‐pivot systems supplied by wells. Water samples were taken periodically from wells close to centre‐pivot irrigation systems. Knowledge of isotope ratios in precipitation, the primary source of groundwater recharge is a prerequisite for this study. The distribution of oxygen and hydrogen in local precipitation, the so‐called Local Meteoric Water Line, is available based on several years of measurements. An evaporative model of the isotope data indicates water loss from evaporation to be in the range of 14% and 6%. This is less than what was estimated for arid region zones and is perhaps also due to the well‐drained nature of the regional soil which promotes rapid infiltration lowering evaporation. Evaporative loss was greater at wells near cornfields than at wells that supplied other crop types. Little expected correlation between the groundwater isotope data and chloride concentration is attributable to an external input of chloride from road salt used in winter months.

Groundwater chemistry and isotope for interpreting the hydrogeological conditions and hydrochemical evolution of multilayer aquifer system of Donghai island, China

Groundwater is generally important water resource for islands. Groundwater recharge source and its hydrochemical characteristics are vital issues for the sustainable development and management of island groundwater resources. In this study, taking Donghai island which is featured with multi-layer aquifer structure as an example, by comprehensive using of statistical analysis, stable isotope (2H-18O), Gibbs diagram and ion ratio graph, we conducted a comprehensive hydrochemistry investigation for the groundwater in the shallow aquifer (i.e., phreatic and feeble confined aquifers) and middle confined aquifer of this island. And the hydrochemical characteristics, recharge sources, hydrogeochemical processes and source of element components of groundwater in different aquifers of Donghai island were identified. The results show that the major ions and TDS of the shallow groundwater are higher than those of the confined groundwater, and that those aquifers have not suffered significant seawater intrusion. The main hydrochemical types of shallow groundwater and confined groundwater are Cl·SO4-Ca·Na and HCO3-Na·Mg, respectively. Different hydrochemical types and chemical component concentrations between these two aquifers indicate that the hydraulic relationship between aquifers is relatively weak. The results of 2H-18O stable isotope and deuterium excess indicate that the shallow groundwater originated from local precipitation and that the recharge period of the confined groundwater is different from the shallow groundwater. Results of ion ratio reveal that the island groundwater hydrochemistry is mainly controlled by the water-rock interaction, featuring with dissolution of silicate rocks (such as sodium feldspar, potassium feldspar, calcium feldspar and biotite). In addition, cation exchange is also an important hydrogeochemical process controlling the hydrochemical composition of the confined groundwater. The results will be helpful for understanding of the local island hydrogeology and be supportive for the groundwater resources quantitative research such as numerical modeling for Donghai island.

Environmental Isotopes of Water as Potential Tool to Distinguish the Sources of Groundwater Recharge in a Semi-arid Region: A Case Study Around Veeranam Tank, Tamil Nadu, India

Environmental Isotopes of Water as Potential Tool to Distinguish the Sources of Groundwater Recharge in a Semi-arid Region: A Case Study Around Veeranam Tank, Tamil Nadu, India

Assessment of groundwater recharge and connectivity with surface water in a mountainous watershed using natural tracers in Daejeon, Korea

The water supply from headwater streams in mountainous regions is considered an important source for sustaining both water quality and quantity in lowland areas. The Korean terrain is characterized by mountainous regions, the hydrological environment is significantly impacted by seasonal weather conditions. This study focused on investigating the hydrochemistry and isotopic composition of groundwater and surface water to identify hydrological connectivity within a mountainous watershed area in Daejeon, Korea. The estimated recharge rate using water budget methods suggests that approximately 20% of the total precipitation contributes to groundwater recharge in this site. The δ18O–δ2H values of the water samples indicate a meteoric water source for groundwater recharge, while the isotope composition of surface water reveals altitude effects, implying that groundwater recharges at a higher altitude region. Additionally, water revealed altitude effects suggesting that the groundwater was inferred to recharge at a higher altitude region. The hydrochemical conservative components (87Sr/86Sr ratio and Cl−) indicate that this watershed undergoes temporary similar water–rock interactions along its flow path, but it is also impacted by anthropogenic contaminants from the surrounding public area. The results of the three-component endmember mixing analysis demonstrate that groundwater is predominantly influenced by surface water, indicating a close interrelationship among various water bodies in mountain hydrology. These findings provide a comprehensive approach to water resource management by combining recharge rate estimation and the assessment of water body connectivity using natural tracers.

Investigating groundwater recharge using hydrogen and oxygen stable isotopes in Kabul city, a semi-arid region

There are significant concerns about the sustainability of groundwater, and the inhabitants that depend on it, due to rapid groundwater depletion from the alluvium aquifers in Kabul city. Sustainable groundwater management in Kabul requires an understanding of the sources and rates of groundwater recharge, however, both these parameters are poorly quantified. In this study, we examined the stable isotopic composition (δ18O and δ2H) of groundwater and surface water from the Upper Kabul River and Logar River. Utilizing the hydrograph separation approach, we assessed the percentage contribution of river water to groundwater, including the uncertainty analysis of its estimation. Our results, based on isotopic analysis, demonstrated that precipitation was the primary source of groundwater recharge in the Central Kabul sub-basin. Mixed recharge from the river, precipitation and irrigation return flow governed groundwater recharge in the Logar sub-basin. In Paghman and Lower Kabul, and Upper Kabul sub-basins, more rainfall input was observed besides the river contribution to groundwater recharge. We have noted substantial spatial and depth-related variation in the contribution of the river water to groundwater recharge. In the study area, the river water contribution (fraction contribution) to groundwater recharge has changed from over 60 ± 5 % (on average) in 2007 to less than 50 ± 5 % (on average) in 2020. We documented significant groundwater level depletion in the Central Kabul sub-basin and western parts of Kabul city (Paghman and Upper Kabul sub-basins). The present study provides important insights into the local water cycle in Kabul City, which is critical for developing sustainable management strategies for groundwater sources in this semi-arid region.