Signatures Of Groundwater Research Articles

Regional Isotopic Signatures of Groundwater in Croatia

Tracer methods are useful for investigating groundwater travel times and recharge rates and analysing impacts on groundwater quality. The most frequently used tracers are stable isotopes and tritium. Stable isotopes of oxygen (δ18O) and hydrogen (δ2H) are mainly used as indicators of the recharge condition. Tritium (3H) is used to estimate an approximate mean groundwater age. This paper presents the results of an analysis of stable isotope data and tritium activity in Croatian groundwater samples that were collected between 1997 and 2014 at approximately 100 sites. The composition of the stable isotopes of groundwater in Croatia originates from recent precipitation and is described using two regional groundwater lines. One of them is applied to groundwater accumulated in the aquifers in the Pannonian part of Croatia and the other is for groundwater accumulated in the Dinaric karst of Croatia. The isotope content shows that the studied groundwater is mainly modern water. A mix of sub-modern and modern water is mostly accumulated in semi-confined porous aquifers in northern Croatia, deep carbonate aquifers, and (sub)thermal springs.

Multi-tracer approach for assessing complex aquifer systems under arid climate: Case study of the River Tata catchment in the Moroccan Anti-Atlas Mountains

Within the arid Tata River catchment of the Moroccan Anti-Atlas Mountains groundwater is the only source for drinking and irrigation water supply. Nevertheless, the hydrogeological and hydrogeochemical setting of the area is understudied. In order to develop sustainable groundwater management strategies a profound understanding of the region's groundwater system is essential. In terms of comprehensive field surveys, aquifer structure and properties as well as water composition were evaluated. The Lower Cambrian Limestone and Dolomite Series as well as the Quaternary sediments were identified to be the major aquifer systems. Isotopic signatures of groundwater indicate direct groundwater recharge trough fractures and a major flow direction similar to the drainage system of the Tata River. Hydrochemical composition mainly reflects the mineralogy. The primary processes are calcite and bassanite dissolution as well as dedolomitization and feldspar weathering. Water of irrigation return flow drains downstream and is pumped repeatedly, with each cycle contributing to contamination and water loss through evaporation, while the water is used for irrigation and daily needs. In turn, groundwater quality decreases along its flow path from N to S. The hydrogeological conceptual model, visualizing all results, can be used by stakeholders to integrate groundwater related aspects into site-specific agricultural practices as well as to set up numerical flow and transport models.

Geochemical characterization of groundwater evolution south of Grand Canyon, Arizona (USA)

Better characterization of the geochemical evolution of groundwater south of Grand Canyon, Arizona (USA), is needed to understand natural conditions and assess potential effects from breccia-pipe uranium mining in the region. Geochemical signatures of groundwater at 28 sampling locations were evaluated; baseline concentrations for select trace elements (As, B, Ba, Cr, Li, Mo, Rb, Se, Sr, Th, Tl, U, V) were established, and anomalous chemistry characteristics were identified. Concentrations at some groundwater sites exceeded the USEPA drinking water standard for As of 10 μg/L (Red Canyon, Miners, JT, Havasu, and Warm Springs) and U of 30 μg/L (Salt Creek Spring). Four springs from the study area (Blue, Havasu, Fern, and Warm Springs) had unique chemistry, which may indicate a deep flow path or potential contribution of fluids from lower in the crust. Other springs in the study area were distinguished by major anion water type: sulfate, bicarbonate, and a mixture of the two. Water type distinctions were somewhat spatially segregated, with sulfate type present on the western side of the study area, bicarbonate type on the eastern side, and a mixture of the two interspersed between the endmember sites. Sulfate-type water from this study area had low strontium isotopic ratio (87Sr/86Sr) values. The location of spring discharge within single drainages of the Grand Canyon may influence chemistry, as groundwater discharging from bedrock was altered after flowing through alluvial material. Geochemical analysis of groundwater in Grand Canyon indicates the importance of continued monitoring and better understanding of short-term chemical fluctuations.

Seasonally Variant Stable Isotope Baseline Characterisation of Malawi’s Shire River Basin to Support Integrated Water Resources Management

Integrated Water Resources Management (IWRM) is vital to the future of Malawi and motivates this study’s provision of the first stable isotope baseline characterization of the Shire River Basin (SRB). The SRB drains much of Southern Malawi and receives the sole outflow of Lake Malawi whose catchment extends over much of Central and Northern Malawi (and Tanzania and Mozambique). Stable isotope (283) and hydrochemical (150) samples were collected in 2017–2018 and analysed at Malawi’s recently commissioned National Isotopes Laboratory. Distinct surface water dry-season isotope enrichment and wet-season depletion are shown with minor retention of enriched signatures ascribed to Lake Malawi influences. Isotopic signatures corroborate that wet-season river flows mostly arise from local precipitation, with dry-season flows supported by increased groundwater contributions. Groundwater signatures follow a local meteoric water line of limited spread suggesting recharge by local precipitation predominantly during the peak months of the wet-season. Relatively few dry-season groundwater samples displayed evaporative enrichment, although isotopic seasonality was more pronounced in the lowlands compared to uplands ascribed to amplified climatic effects. These signatures serve as isotopic diagnostic tools that valuably informed a basin conceptual model build and, going forward, may inform key identified Malawian IWRM concerns. The isotopic baseline establishes a benchmark against which future influences from land use, climate change and water mixing often inherent to IWRM schemes may be forensically assessed. It thereby enables both source-water protection and achievement of Sustainable Development Goal 6.

The role of loess weathering in the groundwater chemistry of the Chaco-Pampean Plain (Argentina)

The Chaco-Pampean Plain (CPP), Argentina, is one of the most extensive loess areas in the world, higlhly productive in terms of agriculture and livestock and with a generalized groundwater signature of Na-HCO3 water type. High As concentrations have been often reported in aquifers throughout the entire CPP related to higher pH and alkalinity values. The processes leading to the groundwater from the humid Matanza-Riachuelo Aquifer System (MRAS) to acquire its alkalinity and pH have been investigated by means of detailed sampling of water and solid phases and geochemical modeling (Phreeqc code). The model has also been applied to two extra areas of the CPP with different climates: the semi-arid Río Dulce Alluvial Aquifer (RDA), and the arid Northern area of the La Pampa province (NLP). The analyses of groundwater from the three different regions (from humid to arid) confirm the positive correlation between arsenic and the high pH and HCO3 concentrations. The model has offered insights into key soil-rock interaction parameters that determine the groundwater chemistry of the CPP. Thus, in addition to the already known calcite precipitation, Ca retention by the volcanic glass exchange complex has appeared as crucial for groundwater to acquire the characteristic Na-HCO3 signature. Moreover, the model has also highlighted the role of low CO2 pressures in attaining the high pH values measured in poorly vegetated soils. Of particular significance is the unexpected role played by the formation of secondary alumino-silicates in increasing (rather than decreasing) pH. Further investigations on the role of volcanic glass in the soil exchange properties and the chemical composition of the exchange complex together with the accurate determination of the clay mineralogy are needed to understand the high pH and alkalinity values of groundwater of this vast region.

Using geochemical and isotopic tracers to characterize groundwater dynamics and salinity sources in the Wadi Guenniche coastal plain in northern Tunisia

Northeastern Tunisia is a sub-humid region with annual rainfall ranging from 600 to 650 mm. Unconfined groundwater in this area is easily accessible and represents an important perennial water source for agricultural activities. The present study deals with a multi-parameter investigation of one of the most important basins in northeastern Tunisia: the Wadi Guenniche plain (130 km2). Hydrochemical (major elements and Br−) and isotopic (18O, 2H and 3H) investigations were carried out on 32 shallow wells to gain insights into groundwater recharge and salinity. The dominant water types were Ca–Mg/Cl–SO4 and Na/Cl with electric conductivity values varying between 0.86 and 6.6 mS/cm. Based on ion ratios and saturation indexes, groundwater salinity originated from weathering of carbonate and evaporite minerals and cation-exchange with clays. Additional influence of anthropogenic activities shown by high NO3− concentrations exceeding 100 mg/L was identified in different parts of the plain resulting from irrigation return flow. A six-year record of 18O and 2H signatures of daily rainwater (n = 293) enabled to define a Local Meteoric Water Line for the Bizerte area (δ2H = 7.02 δ18O + 8.27). The isotopic signature of groundwater was very similar to that of the mean annual rainfall in Bizerte suggesting direct recharge of the aquifer. Tritium levels in sampled wells were relatively high and indicated recent recharge and short residence time. Annual recharge of 100 mm was estimated using a mixing model based on 3H contents in precipitation and groundwater.

Long-term meteorological data and isotopic composition in precipitation, surface water and groundwater revealed hydrologic sensitivity to climate change in East Ukraine

ABSTRACTOur study focused on the incorporation of stable isotope ratios in water in climatic and hydrological observations to understand local hydroclimatic processes and determine basic hydrological sensitivity to climate change in East Ukraine. Long-term meteorological data from two stations at Kharkiv and Izyum showed that air temperature was significantly increased only for the cold period (November–April), while precipitation amount increased during all seasons. Applying two-component mixing model with stable isotope ratios in water, we determined that surface water in both regions was dominantly recharged by the cold precipitation. The highest share of cold precipitation contribution (∼79 %) was found in the river with the shortest water transit time. The isotopic signature of groundwater also indicated that water resources were mainly recharged during the cold period. Our findings reveal that basic hydrological sensitivity of the transboundary (Ukraine/Russian Federation) Seversky Donets River basin relates to hydroclimate changes mainly observed in November–April. We suggest that climate changes can influence surface water and groundwater but also the overall regional water availability that is highly dependent on the cold precipitation in these regions.

Rapid groundwater recharge dynamics determined from hydrogeochemical and isotope data in a small permafrost watershed near Umiujaq (Nunavik, Canada)

Hydrogeochemical data are used to better understand recharge dynamics and to support a hydrogeological conceptual model in a 2-km2 watershed in a discontinuous permafrost zone in Nunavik, Canada. The watershed contains an upper (surficial) and lower aquifer within Quaternary deposits, above and below a marine silt layer containing ice-rich permafrost mounds. The analysis is based on water samples from precipitation, groundwater monitoring wells, ground ice in permafrost mounds, thermokarst lakes and a perennial stream. Groundwater geochemistry in both aquifers reflects young, poorly evolved waters, with mainly Ca-HCO3 water types and low mineralisation ranging from 11 to 158 mg/L total dissolved solids (TDS), implying short pathways and rapid travel times of a year or less. While relatively low, TDS signatures in groundwater and surface water show increasing values downgradient. Groundwater isotope values (δ18OH2O and δ2HH2O) are often strongly influenced by snowmelt, while those of thermokarst lakes show evidence of evaporation. Recharge along the cuesta contributes to a transverse component of groundwater flow within the valley with higher TDS and δ13CDIC values influenced by open-system weathering. Even where permafrost-free, the marine silt unit has a strong confining effect and plays a more important role on recharge dynamics than the discontinuous permafrost. Nevertheless, the vulnerability of these types of hydrogeological aquifer systems is expected to increase due to rapid recharge dynamics associated with the gradual loss of the confining effect of permafrost. This hydrogeochemical data set will be useful as a baseline to document impacts of permafrost degradation on the hydrogeological system.

Multivariate analysis and geochemical signatures of groundwater in the agricultural dominated taluks of Jalandhar district, Punjab, India

The present study is focused on the agriculturally dominated taluks of Nakodar, Shahkot and Phillaur in Jalandhar district, Punjab. Integrated multivariate technique along with geochemical signatures and vertical depth profiles of major ions were studied to assess the hydrogeochemical characteristics, processes influencing the aquifer chemistry and suitability appraisal for different uses. The analytical results revealed that the groundwater is hard to very hard in nature and their relative abundance of major ions are Na+ > Mg2+ > Ca2+ > K+ and HCO3– > SO42− > CO32– > Cl− > NO3− > F− > PO42− respectively. Elevated levels of NO3− (2 samples) in Phillaur taluk and F− (1 sample in every three taluks) were observed in shallow aquifer of the study area. The overall results of the water quality index show that a major part of the study area possesses good water quality. The taluk wise WQI results depict that certain pockets fall in poor (3 samples in Phillaur, 1 in Shahkot) to very poor (1 sample of Nakodar) water classes. The chemical compositions of the study area were predominantly Ca2+–Mg2+–HCO3– followed by Ca2+–Mg2+–Cl−–SO42−facies. Both Nakodar and Shahkot taluk shows Na+-Mg2+–HCO3– water type, while Phillaur taluk shows Mg2+–HCO3– water type. The water type of the shallow aquifer is complex in nature showing Na+-Mg2+–HCO3– type, further it changed to Na+–HCO3– in the intermediate zone. Interpretation of the geochemical signatures of the groundwater suggested that natural weathering and dissolution of silicate and carbonate minerals and ion exchange process are largely controlling the aquifer chemistry. Principal component analysis (PCA) extracts five principal components (PC's), where PC1, PC2 and PC4 are influenced by mixed factors i.e., lithogenic and anthropogenic inputs. PC3 is exclusively affected by anthropogenic factors like domestic sewage, fertilizer and irrigation return flow respectively and PC5 is mainly controlled by natural factors.

Chemical and isotopic signature of groundwater in the Santa Ninfa karst system and possible inferences on neotectonics

The Santa Ninfa karst system is an area strongly controlled by tectonics, whose intense fracturing gave rise to the formation of a large number of cavities that foster the drainage of water. The hydrogeochemical characters of groundwater circulating in this aquifer, together with its isotopic signature, were investigated in detail. The chemistry of groundwater reflects the nature of the rocks hosting the aquifers, constituted by primary and diagenetic selenitic gypsum, salts, and gypsum- arenite, whose dissolution is responsible of the geochemical fingerprint of the quasi-totality of the samples. A single site (CAM) is characterised by a different chemical composition, indicating a mixing between Ca-sulphate, Ca-bicarbonate and a NaCl-rich water. From the chemical point of view, no evidence of interaction between shallow groundwater and deep fluids has been detected. Conversely, isotopic fluctuations highlight mixing processes between surficial (evaporated) runoff and groundwater. Different mixing proportion among these endmembers can be reflected in variations of the chemical character of the sampled springs. Changes in mixing proportions can be the effect of differential permeability variations, in turn produced by local stress field changes during seismogenic processes. In this scenario the geochemical monitoring of the Santa Ninfa karst aquifer could be of relevant interest in the study of seismogenic processes in this area, with particular reference to the relationship between seismic and geochemical transients.

Hydrogeochemical and isotopic signatures of groundwater in the Andasa watershed, Upper Blue Nile basin, Northwestern Ethiopia

This study aims to evaluate the hydrogeochemical and isotopic signatures of water (surface and groundwater) of the Andasa watershed in the upper Blue Nile Basin, northwest Ethiopia using integrated hydrogeochemical and isotopic methods with the help of Hierarchical Cluster Analysis (HCA) and Principal Component Analysis (PCA) techniques. To achieve this, major cation and anion (n = 61) and stable isotope (δ2H and δ18O; n = 36) analyses have been done. The result revealed that geogenic (rock-water interaction) and anthropogenic (waste disposal landfill site, agricultural practices, diverted river via open canal) effects are the major water quality controlling factors. Rock-water interaction is more dominant factor that produced alkaline earths bicarbonate hydrogeochemical facies. Moreover, the Cl and δ18O relationship shows a shift towards the right from vertical axis (δ18O) which signifies anthropogenic effects. Using HCA and PCA techniques, EC, TDS, Ca, Na, Mg, HCO3, SO4, Cl and NO3 were identified as the leading hydrogeochemical parameters in determining the area. Accordingly, Mg-Ca-HCO3, Ca-Mg-HCO3 and Ca-Na-HCO3 found to be the main water types. Silicate minerals are responsible for controlling the hydrogeochemical property of the waters in the area through hydrolysis and cation exchange processes. Most of the samples signify evaporation prior to recharge in the wet seasons and irrigation return flow in the dry seasons. Most river samples show depleted δ18O and δ2H reflecting that their source is highland area of the watershed. From hydrogeochemical and isotopic signatures, the north and northeast parts of the area are the discharging zones and southern and central parts are the recharging zones.

Insights from stable isotopes of water and hydrochemistry to the evolutionary processes of groundwater in the Subei lake basin, Ordos energy base, Northwestern China

ABSTRACTChanges in groundwater evolutionary processes due to aquifer overexploitation show a world-wide increase and have been of growing concern in recent years. The study aimed to improve the knowledge of groundwater evolutionary processes by means of stable water isotopes and hydrochemistry in a representative lake basin, Ordos energy base. Groundwater, precipitation, and lake water collected during four campaigns were analysed by stable isotopes and chemical compositions. Results showed that temperature effect predominated the isotope fractionation in precipitation, while evaporation and inadequate groundwater recharge were the key factors explaining high salinity and isotopic enrichment in lake water. Additionally, the Kuisheng Lake was a preferential area of groundwater recharge, while the Subei Lake received less sources from underlying aquifer due to the combined effects of low permeable zone and upstream groundwater captured by the production wells. The homogeneous isotope signatures of groundwater may be ascribed to the closely vertical hydraulic connectivity between the unconfined and the confined aquifers. Isotopically enriched groundwater pumping from well field probably promoted isotopic depletion in groundwater depression cone. These findings not only provide the conceptual framework for the inland basin, but also have important implications for sustainable groundwater management in other groundwater discharge basins with arid climate.

Mantle fluids associated with crustal-scale faulting in a continental subduction setting, Taiwan

We report noble gas signatures of groundwater, hot springs, and bedrock samples from a major fault system that separates regional-scale blocks of accreted, continental materials in southern Taiwan. Despite the continental setting, the isotopic signatures argue for the presence of mantle derived fluids, suggesting that the active fault system is deep-seated. This is consistent with deep, non-volcanic tremors identified in the same area. We speculate that the mantle fluids are escaping along a crustal-scale fault marked by clusters of non-volcanic tremors directly beneath the southern Central Range. The evidence of these tremors and electrical conductivity anomalies along the strike of the fault recognized previously correlated up dip with the surface trace of a major active fault support the hypothesis.

Evolution of the chemical and isotopic composition of groundwater under a semi-arid climate; the case of the Cenomano-Turonian aquifer within the Essaouira basin (Morocco)

This study evaluated how the chemical and isotopic composition of the groundwater in the Cenomano-Turonian aquifer of the Essaouira basin from Morocco has changed in response to low annual rainfall associated with climate change during the period 1995–2018. The study of the chemical composition of groundwater shows a Cl–Ca–Mg type facies which was maintained during the observation period (1995–2018). The electrical conductivity (EC) and the Cl− content of groundwater increased during the study period in response to low rainfall with a mean values range from 1214 (1995) to 2482 µs/cm (2018) for EC and from 11.36 (1995) to 14 meq/L (2018) for Cl−. Stable isotope measurements indicate that the Cenomano-Turonian aquifer is recharged by rainfall of Atlantic origin. Levels of 18O during the period 2007 and 2016 were generally stable with slight fluctuations (≈ 1‰) that may be due to analytical errors, suggesting that climate change has no effect on the isotopic signature of groundwater in the study area. Tritium levels in groundwater decreased between 2007 and 2016, possibly due to low recharge rates associated with low annual rainfall during this period.

Impacts of sediment compaction on iodine enrichment in deep aquifers of the North China Plain

To understand the effects of large-scale sediment compaction on iodine enrichment in the groundwater system of the North China Plain (NCP), hydrogeochemical and isotope (2H, 18O and 87Sr/86Sr) geochemical features of groundwater, seawater and pore water of the deep aquifer sediments were characterized. Groundwater iodine concentration ranged from 5.8 to 1110 μg/L and approximately 80% of groundwater samples have iodine concentration more than 100 μg/L. High iodine groundwater (>100 μg/L) is mainly distributed in the Bohai bay area where serious land subsidence occurs. The sediments deposited during several events of marine transgression are considered as the main source of groundwater iodine. The pore solution compacted from the clayey sediments has a iodine concentration up to 830 μg/L, indicating that marine source iodine was stored in the clayey layers. The hydrogen and oxygen isotope signatures of groundwater show that the groundwater from NCP is mainly recharged by precipitation and the pore water from sediment compaction due to intense land subsidence. The Cl/Br molar ratio and 87Sr/86Sr signatures of groundwater and sediment pore water further suggest the effects of mixing with compaction-released pore solution on the hydrochemical evolution of high iodine groundwater. Based on groundwater δ2H, Cl concentration and 87Sr/86Sr, the results of two end-members mixing model calculation indicate that the compaction-released pore solution contributes approximately 49.1–68.9% iodine to high iodine groundwater, and the iodine from compaction-released pore solution ranges between 407 and 572 μg/L. The results of this study therefore suggest that the compaction of clayey sediments can be a major hydrogeological process controlling the genesis of high iodine groundwater in deep aquifers at NCP.

Tracing natural groundwater recharge to the Thiaroye aquifer of Dakar, Senegal

Urban groundwater in Sub-Saharan Africa provides vital freshwater to rapidly growing cities. In the Thiaroye aquifer of Dakar (Senegal), groundwater within Quaternary unconsolidated sands provided nearly half of the city’s water supply into the 1980s. Rising nitrate concentrations traced to faecal contamination sharply curtailed groundwater withdrawals, which now contribute just 5% to Dakar’s water supply. To understand the attenuation capacity of this urban aquifer under a monsoonal semi-arid climate, stable-isotope ratios of O and H and radioactive tritium (3H), compiled over several studies, are used together with piezometric data to trace the origin of groundwater recharge and groundwater flowpaths. Shallow groundwaters derive predominantly from modern rainfall (tritium >2 TU in 85% of sampled wells). δ18O and δ2H values in groundwater vary by >4 and 20‰, respectively, reflecting substantial variability in evaporative enrichment prior to recharge. These signatures in groundwater regress to a value on the local meteoric water line that is depleted in heavy isotopes relative to the weighted-mean average composition of local rainfall, a bias that suggests recharge derives preferentially from isotopically depleted rainfall observed during the latter part of the monsoon (September). The distribution of tritium in groundwater is consistent with groundwater flowpaths to seasonal lakes and wetlands, defined by piezometric records. Piezometric data further confirm the diffuse nature and seasonality of rain-fed recharge. The conceptual understanding of groundwater recharge and flow provides a context to evaluate attenuation of anthropogenic recharge that is effectively diffuse and constant from the vast network of sanitation facilities that drain to this aquifer.

Salinization and Deterioration of Groundwater Quality by Nitrate and Fluoride in the Chittur Block, Palakkad, Kerala

Chittur block represents a mid-land region of Palakkad district, Kerala and the block differs from the rest of the blocks in its climate and availability of groundwater. About 75% of the people depend on agriculture for their livelihood. Results showed that groundwater salinity levels (up to 1,963 mg/L TDS),fluoride (up to 6.3 mg/L) and nitrate (up to 141 mg/L) contents have increased significantly in tandem with the increase in groundwater abstraction. Before human intervention the chemical weathering of gneisses and granites was the main process impinging on the chemical signature of groundwater. The initial chemical equilibrium conditions change with increasing groundwater withdrawal rates and fertilizer input, in a milieu of lower natural groundwater recharge. The appearance of higher levels of bicarbonate, linked to denitrification processes, and the decrease in calcium, due to calcite precipitation, can lead to increased content of sodium and fluoride in groundwater. In this scenario the use of groundwater resources for human consumption and agriculture represents a public health risk if water management actions do not change the trend in water use in the near future. The potential loss of fertile soil by groundwater salinization must also be considered when planning sustainable policies in a region with over dependence on groundwater resources.

Assessments of seasonal groundwater recharge and discharge using environmental stable isotopes at Lower Muda River Basin, Malaysia

An accurate estimation of groundwater recharge is required to properly manage aquifers, especially for riverbank filtration method (RBF) purposes. The isotopes correlations and differences in different water bodies were studied to assess the sources of groundwater recharge and preliminary tools in understanding of the surface water and groundwater interactions in the Lower Muda River Basin. The environmental isotope and hydrochemical sampling results had emphasised that the area near Lower Muda River Basin had a connection with the river and was actively recharging the near-river shallow alluvial aquifer, via RBF method. Furthermore, the shallow groundwater that was close to Muda River from groundwater signatures had indicated the recharge of the shallow aquifer system by Muda River based on the plots along LMWL on a δ2H versus δ18O. The comparisons between like δ2H and δ18O isotopes in the rainwater revealed the variations in the rainfall amount and the 18O-depleted water of those isotopes for wet season precipitation as compared to dry seasons. Furthermore, the groundwater δ2H and δ18O isotopes exhibited a slight deviation from the δ2H and δ18O isotopic meteoric water line in Lower Muda River. Therefore, in this basin, the groundwater could be a combination of river water and precipitation, which had led to the recharge of river water being more than the recharge of rainfall infiltration.

Assessment of groundwater facies in Wates Coastal Area, Kulon Progo, Yogyakarta, Indonesia

The groundwater quality in Wates coastal area is generally a good category but there are high salinity values at some locations. The chemical quality of groundwater from place to place is different. The difference of water quality is a major problem in the study area. A total of 27 groundwater samples were collected in August, 2017. Geochemical signatures of groundwater were used to analyze the major ionic concentrations in the groundwater, to identify the dominant hydrogeochemical processes, and to determine the relationship between groundwater flow and spatial distribution of water types. Hierarchical Cluster analysis and Schoeller diagram, Gibbs plots, Scatter diagrams, and Piper Trilinear diagram were employed to evaluate the hydrogeochemical evolution of groundwater. In Schoeller diagrams, the relative tendency of ions in meq/L shows Na + > Mg 2+ > Ca 2+ > K + and HCO 3 - >Cl - > SO 4 2- trends, typically in saline water. Gibbs diagram reveals that the groundwater chemistry is mainly controlled by rock weathering with secondary contribution from evaporation source. Based on the results of Hierarchical Cluster analysis and Piper diagram, dominant hydrogeochemical facies in the study area are Ca-HCO 3 , Na-Cl, and Ca-Na-HCO 3 types. Ca-HCO 3 facies are almost throughout the study area and the evolution of groundwater was mainly controlled by the silicate weathering process. Na-Cl water types are grouping in the study area influenced by cation exchange and evaporation processes, while Ca-Na-HCO 3 types are locally grouping with silicate weathering and cation exchange processes. The geology implies that common silicate minerals are found everywhere in the study area. In fact, the distributions of groundwater facies are related to the local geology, which may result in different hydrochemical processes. In addition, lithology is very influential on the existence of groundwater in the study area

Tracing groundwater recharge sources in the northwestern Indian alluvial aquifer using water isotopes (δ18O, δ2H and 3H)

Rapid groundwater depletion from the northwestern Indian aquifer system in the western Indo-Gangetic basin has raised serious concerns over the sustainability of groundwater and the livelihoods that depend on it. Sustainable management of this aquifer system requires that we understand the sources and rates of groundwater recharge, however, both these parameters are poorly constrained in this region. Here we analyse the isotopic (δ18O, δ2H and tritium) compositions of groundwater, precipitation, river and canal water to identify the recharge sources, zones of recharge, and groundwater flow in the Ghaggar River basin, which lies between the Himalayan-fed Yamuna and Sutlej River systems in northwestern India. Our results reveal that local precipitation is the main source of groundwater recharge. However, depleted δ18O and δ2H signatures at some sites indicate recharge from canal seepage and irrigation return flow. The spatial variability of δ18O, δ2H, d-excess, and tritium reflects limited lateral connectivity due to the heterogeneous and anisotropic nature of the aquifer system in the study area. The variation of tritium concentration with depth suggests that groundwater above c. 80 mbgl is generally modern water. In contrast, water from below c. 80 mbgl is a mixture of modern and old waters, and indicates longer residence time in comparison to groundwater above c. 80 mbgl. Isotopic signatures of δ18O, δ2H and tritium suggest significant vertical recharge down to a depth of 320 mbgl. The spatial and vertical variations of isotopic signature of groundwater reveal two distinct flow patterns in the aquifer system: (i) local flow (above c. 80 mbgl) throughout the study area, and (ii) intermediate and regional flow (below c. 80 mbgl), where water recharges aquifers through large-scale lateral flow as well as vertical infiltration. The understanding of spatial and vertical recharge processes of groundwater in the study area provides important base-line knowledge for developing a sustainable groundwater management plan for the northwestern Indian aquifer system.