Tritium baseline concentration and the origins of water and solute in precipitation elucidated from monthly data in Osaka, Japan.

Hydrochemical evolution and salinization dynamics in Lake Chaiwopu Basin (Arid NW China): Insights from multi-tracer and geochemical modeling.

Marine deposits in western Europe provide insight into the interplay between the warm Tethys and cooler Boreal domains, offering a climatic context for the radiation of Early Jurassic species. Reconstructions of temperature for the Hettangian and Sinemurian periods are scarce, with inferred marine temperatures of 15–20 °C based on δ18O values, which are lower than those of subsequent Jurassic stages. This emphasizes the necessity for supplementary data in order to enhance our comprehension of the climatic dynamics that characterized the Early Jurassic period. This study analyses 75 invertebrate samples, including 53 specimens of Gryphaea arcuata, from Early Sinemurian marine sediments in the Fresville quarry, Normandy, France. The present study employs a multi-proxy approach, utilizing δ13C and δ18O values in conjunction with Sr and Mg contents, to assess the processes of fossil diagenesis, marine productivity, and seawater temperatures. Significant post-depositional alteration was observed in the geochemical compositions of 22 bivalve shells assigned to the genera Pseudolimea, Plagiostoma, and Chlamys, which were originally composed of aragonite, except for the outer layer, which is made of calcite. However, the low-Mg calcite shells of Gryphaea arcuata, which are renowned for their diagenetic resistance, retained the majority of their isotopic integrity. The results of the statistical analyses indicate that there was minimal late pervasive diagenesis involving meteoric waters at Fresville. This is in accordance with the typical decrease in δ13C, δ18O values, and Sr and Mg contents that such processes would otherwise cause. Published isotopic data from Sinemurian marine fossils (plesiosaur and shark teeth) were used to estimate seawater δ18O (~−1‰ VSMOW) and surface temperatures (~24 °C). The calculated benthic temperatures of Gryphaea (17 °C) correspond to habitats at depths of about 50 m. These findings suggest a positive hydrological balance and euhaline conditions in a humid tropical climate context.

This article presents a comprehensive study of the nitrogen-radon thermal mineral waters of the Jety-Oguz area, located in the southeastern part of the Issyk-Kul intermountain artesian basin (Northern Tien Shan). Based on new data from chemical and isotopic (δ18O, δD) analyses of natural waters (lake, river, and mineral) and the chemical composition of the water-bearing rocks, we identify the formation mechanisms of mineral waters with diverse composition, total dissolved solids (TDS), and temperature. Three main genetic types have been identified: (1) saline, high-TDS (up to 12.8 g/L) chloride sodium-calcium thermal waters (up to 32 °C). These waters are of meteoric origin and circulate within Middle Carboniferous carbonate rocks, acquiring their unique composition at depths of up to 3.0 km, where reservoir temperatures reach ~105 °C; (2) chloride-sulfate sodium-calcium waters (0.5 g/L, fresh, 22 °C), formed in alluvial deposits within the zone of active water exchange; and (3) low-TDS (1.8 g/L, brackish) waters of mixed composition, resulting from the mixing of a deep fluid with infiltrating meteoric waters. Isotopic data confirm a meteoric origin for all studied waters, including the high-TDS thermal types. The chemical composition diversity is attributed to several processes: mixing between the deep, high-TDS fluid and low-TDS infiltration waters, intense dissolution of evaporite rocks, and water–rock interaction. These findings are crucial for understanding the genesis of mineral waters in the Tien Shan intermountain basins and provide a scientific basis for their sustainable balneological exploitation.

The dolomite of the fourth member of Dengying Formation in Gaoshiti-Moxi area of central Sichuan Basin is rich in hydrocarbon resources. It has experienced superimposition-reformation of multistage karstification, and is the key target for studying deep ancient carbonate reservoirs. Exploration and development practices show that there are great differences in the development of karst reservoirs of the fourth member of Dengying Formation between the platform margin and intraplatform in Gaoshiti-Moxi area. However, the differences in the genetic mechanism of karst reservoirs between these two zones are unclear. Therefore, based on an integrated analysis of core, thin section, drilling, logging, and geochemical test data, this study clarifies the differences in karstification between the platform margin and intraplatform and conducts a comparative analysis of the controlling factors for the differences in karst reservoirs. Results show that the fourth member of Dengying Formation experienced superimposition-reformation of four types of paleokarstification, including eogenetic meteoric water karst, supergene karst, coastal mixed water karst, and burial karst. Large-scale dissolved fractures and caves are mainly controlled by meteoric water karstification, primarily developing three types of reservoir space: vug type, fracture-vug type, and cave type. Dolomite and quartz fillings are mainly formed in the medium-deep burial period. Four types of paleokarstification are developed in the platform margin, while the coastal mixed water karst is not developed in the intraplatform. Eogenetic meteoric water karst and supergene karst in the platform margin are stronger than those in the intraplatform, while burial karst shows no notable difference between the two zones. The thickness of soluble rock (mound-shoal complex), karst paleogeomorphology, and different types of paleokarstification are the main controlling factors for the difference in karst reservoirs between the platform margin and the intraplatform.

This study aims to compare the geothermal waters of Gümüşkent (GK), Koçpınar (KP), Dertalan (DA), Terme (TE), Kozaklı (KZ), Bayramhacı (BH), Karakaya (KK), Tuzlusu (TZ), Ziga (ZG), Narlıgöl (NG), Yeşilhisar (YH), and Kemerhisar (KH), which exhibit temperatures ranging from 17.5 °C to 86 °C. Additionally, the origins of these waters are evaluated by taking into account the cold waters of Helvadere (HD), Dokuzpınar (DP), Terme (TES), and Kozaklı (KOS), with temperatures between 10.4 °C and 13.09 °C, all located in Central Anatolia. The aquifers of these fault-controlled waters are of Paleozoic marbles and Eocene limestones; cover rocks are impermeable units. The heat production system of these waters may be due to young volcanism and granitic/syenitic intrusions as well as radiogenic sources. The types of these carbonated, sulfated, and saline waters are Ca-HCO3 in KP, GK, BH, and TE; Na-SO4 in KZ; Ca-SO4 in DA; Na-Cl in TZ, ZG, NG, KH, KK, and YH, respectively. These waters, which are of meteoric origin in terms of isotopic (δ18O and δ2H), generally have deep circulation and slow flow. The main reason for the deviation observed from the meteoric water line in some waters is evaporation. In KH, YH, and KK with low temperatures, the mineralization of these waters increased as a result of long-term gas-rock-water interaction. The causes of salinization in the Na-Cl-type waters may be the dissolution of halite minerals and the mixing of older waters trapped at depth during the closure of the Tuzgölü and salt domes in the TZ and ZG, the Central Kızılırmak basin in the YH and KK, and the Ulukışla basin in the KH. According to δ13C (‰PDB) values, the sources of CO2 gas in waters may be geogenic (marble, marine and lacustrine limestone) and/or mantle. According to δ34S‰VCDT values, the source of sulfate in waters may be evaporitic rocks in KK, ZG, KZ, TZ, KH, and volcanic and/or carbonate rocks in other waters. The 14C ages of the waters are lowest in DA (19.15 ka) and highest in KK (45.11 ka). The calculated ages are apparent because the 14C values of the waters in question are often a measure of the contribution of modern biogenic carbon to the total dissolved carbonate or bicarbonate. In this context, the waters examined may be old waters that entered the system from the late Pleistocene to the early Holocene periods.

Silver polymetallic deposits commonly produce high-grade ores, with silver contents reaching up to weight-percent levels. The reason and mechanism for the formation of such high-grade silver ores, however, remain poorly understood. Here, we demonstrate that superimposed mineralization plays a crucial role in forming high-grade silver ores in the Poshan Ag-Pb-Zn deposit in Central China. The Early Cretaceous Ag-Pb-Zn mineralization at Poshan occurs as quartz-carbonate-sulfide veins that generally contain a few hundred micrograms per gram of silver. In contrast, the high-grade silver mineralization is present as calcite−chlorite−acanthite−native silver veinlets infilling fractures of the Early Cretaceous orebodies, with silver contents ranging from thousands of micrograms per gram to weight-percent levels. Uranium-lead dating of hydrothermal calcite in the high-grade ores indicates that the enrichment of silver at Poshan occurred in the Late Miocene, specifically between 8.55 ± 0.26 Ma and 6.78 ± 0.13 Ma. Oxygen isotope analysis of individual calcite generations (Cal-1 to Cal-4), which are texturally associated with acanthite, suggests that the fluids from which silver precipitated have δ18Ofluid values of −2.5‰ to −0.4‰ (mean −1.5‰; Cal-1), −2.5‰ to +2.7‰ (mean +1.1‰; Cal-2), −3.4‰ to +1.7‰ (mean −0.2‰; Cal-3), and +4.9‰ to +6.7‰ (mean +5.8‰; Cal-4), respectively. Fluctuations in oxygen isotopes, along with the variations of the element molar ratios (Fe/Ca, Mn/Ca, and Mg/Ca) of corresponding calcite generations, suggest that fluid mixing expressed by the episodic incorporation of deep-circulating fluids into meteoric water triggered changes in fluid composition and ambient conditions, ultimately leading to metal precipitation. Acanthite and coexisting base metal sulfides show δ34S values ranging from −41.7‰ to −6.5‰, which are significantly different from the magmatic-like sulfur of the Early Cretaceous sulfides. These values suggest that an external sulfur, likely derived from bacterial sulfate reduction, was involved in the high-grade silver mineralization. This study highlights the crucial role of superimposed mineralization in the formation of bonanza silver veins in the Poshan deposit and potentially those of silver polymetallic deposits with analogous geological settings worldwide.

Sustainable water management in regions impacted by artisanal gold mining (ASGM) requires a clear understanding of hydrochemical evolution and salt transformation processes. This study examines hydrochemical changes in the Wadi Abbady through a combined approach of geochemical modeling and stable isotope analysis, with the aim of disentangling the roles of natural processes and human activities in alternating water quality. Physicochemical parameters, major ions, and isotopic signatures were analyzed to trace both natural and anthropogenic influences. Results reveal pronounced chemical evolution within the Nubian Sandstone Aquifer (NSA), primarily controlled by reverse ion exchange. Mining activities induce a hydrogeochemical transformation, converting meteoric surface water assemblages (Ca (HCO3)2-Mg (HCO3)2-NaHCO3-NaCl-Na2SO4) into slightly brackish water characterized by elevated sulfate salt concentrations (NaCl-Na2SO4-CaSO4-MgSO4-Ca (HCO3)2). Isotopic evidence indicate that the Quaternary Aquifer (QA) is not hydraulically connected to the deeper NSA, and is instead predominantly recharged by surface water through Wadi Abbady canals and irrigation return flows. End-Member Mixing Analysis (EMMA) using Cl- and δ18O indicates that irrigation canals contribute approximately 60-90% of the total recharge to the QA, while amalgamation ponds provide a smaller but consistent contribution of 10-40%. This mixing pattern highlights both the hydrogeological connection between surface and shallow groundwater systems and the increased vulnerability of the QA to contamination originating from ASGM activities. These findings advance current understanding of water quality evolution in mining-affected environments and highlight the vulnerability of local aquifer systems to unregulated mining practices. This study emphasizes the need for continuous monitoring and long-term hydrochemical assessment in comparable settings to support sustainable water management and mitigate the impacts of artisanal mining.

In this paper, the conceptual hydrogeological circulation model of natural mineral waters from Ribeirinho and Fazenda do Arco hydromineral concession (Castelo de Vide) is updated. These waters are exploited by the Super Bock Group, as bottled waters, and are commercially labeled as Água Vitalis. The physico-chemical data (2004–2024) of these waters were processed regarding their joint interpretation with recent isotopic (δ2H and δ18O) data. The study region is dominated by the Castelo de Vide syncline, which develops along the southern limit of the Central Iberian Zone. These natural mineral waters have low electrical conductivity (EC) mean values (42.80 < ECmean < 54.45 μS/cm) and a slightly acidic pH (5.14 < pHmean < 5.46), making them hyposaline waters. The recharge area of this aquifer system coincides fundamentally with the outcrops of Lower Ordovician quartzites. The updated conceptual circulation model presented in this work is essentially developed on the basis of the chloride–sodium signatures of these waters, explained by the preferential recharge of meteoric waters (δ2H and δ18O) and low water–rock interaction temperature. Such isotopic results seem to indicate the non-existence of a flow continuity between the two blocks (NW and SE) of the quartzite ridges, separated by a fault with a local orientation approximately N-S, as indicated by the most enriched isotopic values of the waters from borehole AC22 (δ18O = −5.90‰ vs. V-SMOW) located in the SE block, compared to the average isotopic value of the waters from the other boreholes (Vitalis I, II, III, IV, V and VI) located in the NW block (δ18Omean = −6.30‰ vs. V-SMOW). This study enhances the understanding of the hydrogeological and geochemical processes controlling low-mineralized (hyposaline) natural mineral waters, widely used for therapeutic and commercial purposes. Despite their global importance, detailed hydrogeological and isotopic studies of such systems are still scarce, making this conceptual model a valuable reference for their sustainable management.

Abstract Radium is a useful tracer of sediment‐derived materials, improving our understanding of the geochemical cycling of elements at ocean boundaries. We have developed an autonomous in situ sampler to collect time series samples of radium isotopes on mooring deployments. Samplers were deployed for 2 yr in the Arctic Ocean, a region particularly hard to access outside of the summer season, and collected monthly samples to create the first annual time series of radium‐228 and radium‐226 in the Arctic. Results from the Laptev Slope show increased radium‐228 and radium‐228/radium‐226 ratios in spring/summer, concomitant with increased meteoric water and brine influence. Together, these tracers indicate seasonal periods of increased influence of shelf‐ and river‐derived materials, findings which would not be possible to discern from summertime shipboard surveys alone. The development of this in situ sampler has therefore expanded our capability to use radium as a tracer to discern temporal changes in the geochemistry of remote areas of the ocean.

Abstract Stable isotope parameters (δ 2 H, δ 18 O, d exc ) of event-based and monthly composite precipitation collected between 2003 and 2009 in the south-western sector of Lake Balaton displayed the normal seasonality typical for mid-latitude continental sites. Fluctuation in δ 2 H and δ 18 O values of monthly composite precipitation in the SW Balaton Region closely followed the monthly values reported from the surroundings, especially Zagreb (Croatia) situated ∼150 km southwest-ward. The amount-weighted annual mean isotope parameters of precipitation ranged from −8.30 to −7.25‰ for δ 18 O-ann, from −58.8 to −52.2‰ for δ 2 H-ann: and from 5.7 to 7.7‰ for d exc -ann depending on which observation site and 12-month subperiod is selected in the SW Balaton region between March 2008 and November 2009. The Local Meteoric Water Line (LMWL) was determined using ordinary least squares-, reduced major axis-, and precipitation-weighted least squares regressions. A preliminary estimate for precipitation-weighted LMWL based on monthly composite data of the 2006–2009 period in the SW Balaton Region is δ 2 H = 7.35(±0.16) × δ 18 O + 2.14(±1.41) is practically identical with the LMWL determined with the same methodology for Zagreb in an overlapping period reinforcing the isotope hydrometeorological similarity between these regions. This linearized approximation of the δ 2 H–δ 18 O covariance can be used as a benchmark for modern precipitation in isotope hydro(geo)logical studies in the SW Balaton Region.

The Sepid-Sarve copper deposit is part of an Eocene volcano-sedimentary sequence located in the southern Sabzevar Zone. The copper mineralization occurs at the contact between pyroclastic and lava units with various limestone layers (including marly, Nummulitic, sandy, and clastic limestones). The ore minerals consist of malachite, azurite, chalcocite, digenite, cuprite, tenorite, covellite, and occasionally native copper. The associated hydrothermal fluids show moderate to high salinities, ranging from 3.08 to 13.38 wt.% NaCl equivalent, with homogenization temperatures between 90 and 356 °C, indicating fluid mixing during ore formation. Chalcocite is rarely accompanied by quartz, suggesting low silica content in the ore-forming fluids. The δ34S values of sulfide samples from the Sepid-Sarve deposit range from −23.9 ± 0.3‰ to −2.9 ± 0.2‰, while δ34S values of hydrothermal H2S range from −24.1 ± 0.3‰ to −21.0 ± 0.3‰. The δ18O values of hydrothermal fluids associated with mineralization fall within the range of basaltic rocks, meteoric waters, and sedimentary rocks. Geochemical variations in major and trace elements suggest the involvement of continental crustal contamination in the magmatic evolution. The studied volcanic rocks fall within the calc-alkaline to shoshonitic fields, formed in a continental arc setting, and are derived from an enriched mantle source influenced by subduction-related fluids. These rocks are characterized by HREE depletion, moderate LREE enrichment, and a weak negative Eu anomaly. Based on the results, the Sepid-Sarve deposit is classified as a stratabound (Manto-type) copper sulfide deposit, formed in a volcano-sedimentary setting associated with a subduction-related magmatic arc environment.

ABSTRACT F‐Ba‐Pb‐Zn (±Ag) deposits near the unconformity between the Armorican and Aquitaine basins formed by mixing surface waters and brines with fluid ascending from the basement. To better constrain the source of this fluid and the conditions of mixing, we analyzed the hydrogen (δD water ) and oxygen (δ 18 O water ) isotopic composition of water trapped in mineral fluid inclusions and the oxygen (δ 18 O quartz ) isotope composition. Results indicate that isotopic equilibrium was not reached during fluid mixing. The isotopic signature of basement fluid is similar/identical to Variscan meteoric water that was trapped and stored in the basement and released at the onset of the Bay of Biscay opening.

Geothermal systems are typically characterized by high-temperature and high-fluoride properties, increasing attention is focused on their environment impacts, yet understanding of fluoride enrichment mechanisms in the Qiabuqia geothermal system (Gonghe Basin, Qinghai, China) remains limited. This study collected 39 geothermal water samples from the Qiabuqia Geothermal Field. Hydrogeochemical and isotopic analyses were conducted to investigate these mechanisms, providing fundamental insights into the geochemical processes governing fluorine distribution patterns. Shallow geothermal waters (GWQ) exhibited a Cl-SO4·Na hydrochemical type, with a mean fluoride concentration of 0.9mg/L and an exceedance rate of 25.7%. In contrast, deep geothermal waters (GWN) were predominantly characterized by a Cl-HCO3·Na hydrochemical type, showing significantly elevated fluoride levels (average 4.2mg/L) with a 100% exceedance rate against the WHO drinking water standard (1.5mg/L). Hydrogen (δD) and oxygen (δ18O) isotopic compositions of GWQ cluster along the Global Meteoric Water Line (GMWL), indicating their predominant recharge sources originate from surface water and atmospheric precipitation. The GWN exhibited significant hydrogen-oxygen isotope anomalies characterized by δ18O enrichment, indicating their recharge sources originate from both vertical leakage of adjacent aquifers and long-distance groundwater migration through regional deep-seated fault systems that serve as dominant conduits for deep hydrothermal circulation. Fluoride enrichment is governed by a combination of thermal controls, mineral dissolution-precipitation equilibria, cation exchange processes, and competitive adsorption mechanisms, reflecting the coupled physicochemical interactions within the hydrothermal system. Quantitative assessment leveraging the Random Forest (RF) algorithm revealed the relative contributions to enrichment: mineral dissolution-precipitation (38%), cation exchange processes (29%), thermal regime (25%), and competitive adsorption (7%), based on feature importance analysis of the hydrogeochemical dataset. The hazard quotient (HQ) assessment for geothermal water exposure revealed distinct risk gradients across population groups: infants exhibited the highest potential health risk at 47%, followed by children (36%), adult males (32%), and adult females (24%), based on the USEPA exposure model accounting for body weight differentials and ingestion rates. Findings not only advance our understanding of this field, but also provide a scientific basis for the rational exploitation of geothermal energy and environmental protection.

Abstract. The stable isotope ratios of hydrogen (δ2H) and oxygen (δ18O) are useful for studying ecohydrological dynamics in forests. However, most isotope-based eco-hydrological studies are limited to single sites, resulting in a lack of large-scale isotope data for understanding tree water uptake. Here, we provide a first systematic isotope dataset for soil and stem xylem water collected during two pan-European sampling campaigns at 40 beech (Fagus sylvatica), spruce (Picea abies), or mixed beech-spruce forest sites in spring and summer 2023 (https://doi.org/10.16904/envidat.542, Lehmann et al., 2024). The dataset is complemented by additional site-, soil-, and tree-specific metadata. The samples and metadata were collected by different researchers across Europe following a standardized protocol. Soil samples were taken at up to 5 depths (ranging from 0 to 90 cm) and stem xylem samples from the trunks of three beech and/or spruce trees per site. All samples were sent to a single laboratory, where all analytical work was conducted. Water was extracted using cryogenic vacuum distillation and analyzed with an isotope laser spectrometer. Additionally, a subset of the samples was analyzed with an isotope ratio mass spectrometer. Data quality checks revealed a high mean total extraction efficiency, mean water amount (>1 mL), accuracy, and precision. The isotopic signature of soil and stem xylem water varied as a function of the geographic origin and changed from spring to summer across all sites. While δ2H and δ18O were strongly correlated, the soil water data plotted closer to the Global Meteoric Water Line (GMWL) than the stem xylem water. Specifically, the δ2H values of the xylem water were more enriched than those of the soil water, leading to a systematic deviation from the GMWL. Isotopic enrichment of the stem xylem water at mixed forest sites was larger for spruce trees than for beech trees. This dataset is particularly useful for large-scale studies on plant water use, ecohydrological model testing, and isotope mapping across Europe.

The Lasting Ice Area along the northern coastline of Ellesmere Island and Greenland will be the region where Arctic multiyear sea ice will persist the longest in a warming climate, making this area critical for ice-dependent species. In 2019, the Tuvaijuittuq Marine Protected Area was established for the interim protection of the waters off northern Ellesmere Island. We present the first comprehensive study of the Archer Fiord – Lady Franklin Bay system located at the northern end of Nares Strait, in the Tuvaijuittuq area. Data on the hydrography, biogeochemical cycles, pelagic and benthic productivity, and seabed sediment were collected along a nearshore-offshore transect. The region is influenced by meteoric waters as well as Pacific and Atlantic-derived waters, and likely acts as a strong seasonal CO2 sink. Despite fall-bloom conditions, low primary, secondary, and benthic productivity contrasted with the relatively high abundance of marine mammals. This productivity paradox either suggests 1) that organic matter and detritus deposited and accumulated over long periods prior to our survey sustain the benthic community on which marine mammals depend for foraging; 2) local productivity hotspots in areas outside the sampled stations; or 3) a highly efficient system with minor production surpluses. Solving this paradox will require further surveys in the area.

Spatial and temporal variations of stable isotopes in precipitation and its controlling factors across Cameroon: Local, regional and the first Cameroon meteoric water lines

Surface water origin and attenuation of meteoric water input signal in the transboundary Lake Malawi basin: Isotopic and hydrochemical evidence.

Abstract Accurate determination of the contemporaneous local meteoric water line (LMWL) is critical for isotope ecohydrological studies, as it forms the baseline for identifying water sources and assessing the degree of evaporation in water bodies. Some studies, despite requiring contemporaneous LMWLs, have used approximations from past local or nearby records, or from isotopic landscapes (isoscapes); however, the uncertainties of such approximations remain poorly understood. Using monthly Global Network of Isotopes in Precipitation data, we quantify the likelihood that LMWLs are misrepresented by past records from the same site, past or concurrent records from nearby sites, and concurrent outputs from isoscapes and isotope‐enabled atmospheric general circulation models (iGCMs). Overall, past records underestimate both slopes and intercepts of LMWLs for one to 8 years. The likelihood of obtaining significantly different LMWLs at the same site is 16.1 ± 3.1% for slopes and 30.4 ± 6.0% for intercepts. For nearby sites, these likelihoods rise to 21.6 ± 5.6% (slopes) and 52.9 ± 6.1% (intercepts) for different periods, and 20.9 ± 8.1% (slopes) and 49.3 ± 7.0% (intercepts) for the same period, both increasing with the distance between sites. Longer records increase the likelihood of obtaining significantly different LMWLs, as they may smooth out interannual variations. Under similar precipitation, temperature and vapor pressure deficit, the likelihood of obtaining significantly different LMWLs decreases marginally. Additionally, over 60% of LMWLs from isoscapes and iGCMs differ significantly from observations. Using biased LMWLs can lead to misinterpretations of, for example, ecohydrological separation between plant water and groundwater. These results underscore the importance of developing concurrent on‐site LMWLs in isotope‐based ecohydrological studies whenever feasible.

Although the number of global water stable isotope databases (δ18O and δ2H) is growing, accessible groundwater stable isotope data on developing countries (e.g., Iran), are conspicuously lacking. To fill this gap, we conducted a sampling campaign during October 2023 to measure δ18O and δ2H in 202 wells, springs, and qanats across 10 main aquifers in Iran. We also calculated the second-order water isotopic variables, namely deuterium-excess (D-excess) and line-conditioned excess (LC-excess), in the studied aquifers, which provide insight into precipitation production and dynamics. Additionally, we determined the local meteoric water line (LMWL) for each aquifer. δ2H, δ18O, D-excess, and LC-excess values in the studied aquifers varied from –79.21 to –27.81 (‰), –11.95 to –4.68 (‰), –5.99 to 24.26 (‰), and –8.18 to 4.37 (‰), respectively. Eight out of the 10 calculated LMWLs for the studied aquifers had a lower slope than the global meteoric water line. Our dataset offers new insights into hydro-meteorological and pollution pathways in the studied aquifers, which supply the water needs for over half of Iran’s population.