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Precipitation in the plum rain period accounts for 40%-50% of annual precipitation in the monsoon region. To clarify the temporal variability of the isotopic composition of precipitation during the plum rain period from event to interannual time scale and identify the influencing factors, we analyzed the isotopic composition of precipitation and its influencing factors in Nanjing from 2015 to 2022. By using the Hybrid Single-particle Lagran-gian Integrated Trajectory (HYSPLIT) model with specific humidity analysis, we investigated the water vapor source and influencing factors. The results showed that 1) the isotopic abundance of atmospheric precipitation was depleted in the summer and enriched in winter. dx was lower in summer and higher in winter. The isotopic abundance of precipitation from the plum rain was depleted compared to mean value of the whole-year. 2) There was no significant correlation between δ2H and δ18O of the plum rain (precipitation) with local meteorological factors. However, dx was lower in light rain, reflecting the effect of sub-cloud evaporation. The average dx was higher during plum rain period in years with more total plum rain precipitation. 3) The low-latitude South China Sea and the western Pacific Ocean source area provided water vapor for the plum rain. The shift of moisture source region led to abrupt changes in precipitation isotopes. Our results could provide data support for studies on precipitation isotopes in the monsoon region, as well as a reference point for further understanding the precipitation mechanism of the plum rain and stu-dying the seasonal variability of atmospheric circulation in the East Asian monsoon region.

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Groundwater, the world's largest freshwater resource, faces significant challenges due to the overexploitation and depletion of aquifers in the 21st century. Small island groundwater aquifers are particularly valuable, and a scientific understanding of the behavior of subsurface water systems is vital. A comprehensive study using radiocarbon, stable oxygen isotopes, stable hydrogen isotopes, and hardness analysis (Δ14C, δ18O, δD, Ca, Mg) of groundwater was conducted in Kikai Island, a southern island in the Amami archipelago, Japan. The geological features and small size of the island make it an ideal location for assessing groundwater recharge and discharge relationships. Groundwater dynamics were investigated using samples collected seasonally from 15 points around the island (wells, springs, and an underground dam). Δ14C results indicated that despite considerable differences in precipitation, spatial variations were more prominent than seasonal variations, suggesting the presence of a large groundwater reservoir. The stable isotopes and hardness values, commonly used to detect groundwater dynamics, did not provide clear evidence to support this trend for the study site, a low-lying small island. However, the combination of deuterium excess (d-excess) values with radiocarbon analysis has the potential to provide a better understanding of groundwater flow. This study further illustrates that a combined approach utilizing Δ14C, δ18O, δD, and hardness levels can yield invaluable insights into groundwater dynamics. Considering geomorphic and geological features, groundwater in Kikai Island was categorized into five groups, providing insights into spatial groundwater flow. Results of this study indicate that the use of 14C allows the detection of groundwater movement with a high dynamic range and increased sensitivity, deepening our understanding of the diverse carbon sources that influence the groundwater system. Insights from this study are especially important for the efficient water management in comparable small carbonate islands and for tackling issues associated to overexploitation, pollution, and water scarcity.

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In Taiwanese volcanic watersheds, we investigated stable water isotopes in meteoric water, plants, and thermal water. Meteoric water exhibited a seasonal cycle, with heavier isotopes in winter and lighter ones in summer, especially in the southern region. The northern monsoon signal lagged the south by two weeks. In the Tatun mountains, young water fractions indicated prevalent old water sources. In the northern watershed, streamwater mainly came from the winter monsoon, while the southern one was influenced by alternating monsoons. Both indices indicated that winter plants depended on summer rainfall. Streamwater and plants had distinct sources in winter, supporting ecohydrological separation. Thermal spring water's d-excess helped identify water-rock interactions, with low d value signaling such interactions. The topographic wetness index showed a higher summer monsoon contribution to southern streamwater but a lower one to plants. The mean linear channel direction significantly affected the monsoon contribution fraction, with northeast-oriented channels vulnerable to northeastward winter monsoons. Finally, we developed a model illustrating hydrological processes on short and long timescales. Our findings enhance our understanding of hydrological disturbances' impact on water resources and ecosystems.

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Climate models for the 21st century project further reduction in the warm season precipitation and more frequent droughts across Mexico. In the possible scenario of enhanced aridity from global warming, the δ18O (-10.6 to -6.3 ‰) and δ2H (-71.1 to -57.1 ‰) compositions and deuterium-excess (0.2-14.6‰) of shallow groundwater from two different basins (Sandia and El Potosi) with similar geological and geomorphological settings were considered to evaluate the influences of early summer rainfall and later summer tropical storms on aquifers at water-scarce southeast margin of the Chihuahuan Desert. Groundwater of the Sandia Basin was recharged mainly from tropical storms. Higher CO2 partial pressure (log pCO2: -2.70 to -1.61) caused more gypsum dissolution (Ca-Mg-SO4 facies) and the effect of irrigation return flow (Ca-Mg-Cl facies) was minor. Even though the El Potosi Basin is in proximity, its groundwater was recharged from both the early and late summer precipitations. The multivariate factor analysis helped to separate the process of rock-water interactions from the recharge seasonality. Gypsum dissolution was less as the partial pressure of CO2 was comparatively lower (log pCO2: -3.01 to -2.15), and the ion exchange along with carbonate mineral dissolutions led to Ca-Mg-HCO3 facies. Over-exploitation under the condition of reduced warm season rainfall would continue to enhance the salinity of groundwater in this region. Hence, the drought mitigation policies should prioritize sustainability of the depleted aquifers and cultivation of salinity resistant crops.

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Water vapor, the most important greenhouse gas in the atmosphere, has four natural stable isotopologues (H216O, H217O, H218O and HD16O), and their isotopic compositions can be used as hydrological tracers. But the underlying processes and pattern-dynamics of the isotopic compositions of atmospheric water vapor and precipitation in response to various meteorological conditions during monsoon season in a tropical hot and humid region is poorly understood. Here, we present results of H and triple-O-isotopes of water in precipitation and atmospheric water vapor during monsoon season exploiting high-resolution integrated cavity output spectroscopy technique. We observed a distinct temporal variation of the isotopic compositions of water at different phases of the monsoon. The diurnal patterns of the isotopic variations were influenced by the local meteorological factors such as temperature, relative humidity and amount of precipitation. We also investigated the monsoonal dynamics of the second-order isotopic parameters, so-called d-excess and 17O-excess along with the influence of local meteorological factors on isotopic variations to improve our understanding of the underlying isotopic fractionation processes. Consequently, our results provide a unique isotopic-fingerprint dataset of rainwater and atmospheric water vapor for a tropical region and thus shed a new light on hydrological and meteorological processes in the atmosphere.

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Iran is a semi-arid and arid country which always faces a water shortage crisis. Thus, the water resources in Iran should be studied by accurate methods such as stable isotope techniques. In precipitation sampling stations across Iran, the δ18O (ranges from -16.3 to -0.3 ‰, -4.9 ‰ average), δ2H (-114 to -13 ‰, -24.2 ‰ average) and d-excess (-2.1 to -22.7, 16.5 ‰ average) values are higher compared to δ18O (ranges from -10.9 to -3.1 ‰, -6.7 ‰ average), δ2H (-71 to -6 ‰, -37.4 ‰ average) and d-excess (1.0 to -21.6 ‰, 14.9 ‰ average) values in groundwater stations. Stable isotope distribution maps in precipitation and groundwater were also developed for Iran. The stepwise technique was used to study the role of parameters influencing stable isotopes in Iran precipitation. Results show the dominant role of temperature, elevation and latitude as well as 'cP and MedT' air masses mixture on stable isotope values in precipitation. Furthermore, the contribution percentage of each air mass which influences Iran in groundwater resources recharge was studied using 'Simmr' package in R programming language. Finally, the accuracy of the developed stable isotope distribution maps was validated.

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Atmospherically deposited hoarfrost is probably the least important quantitative component of the hydrosphere, yet in places acts as an important source of water. Although countless studies have investigated the stable isotope composition of virtually all other components of the global hydrosphere, little is known on its stable isotope composition. We addressed this gap in knowledge by investigating the stable isotope composition of hoarfrost and precipitation in the Southern Carpathian Mountains (East-Central Europe) in relation with the local and regional meteorological parameters and hoarfrost characteristics. Hoarfrost and precipitation were collected at the Țarcu Peak Weather Station (2180 m a.s.l.) between December 2018 and February 2019. The main sources of moisture (as indicated by high deuterium excess values) were the Black (and possibly Caspian) Sea as well as the terrestrial sources in Eastern Europe and Western Asia. Hoarfrost was deposited during periods of intense wind, with δ18O and δ2H being strongly correlated with air temperature. No correlation has been found between the intensity of hoarfrost deposition and its stable isotope characteristics. Our data indicates that the δ18O values of hoarfrost deposits faithfully record air temperature variability during deposition, while the d-excess parameter records conditions at the moisture sources.

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Fluoride contamination in groundwaters of a rural region in semi-arid Western India has been studied using combination of geochemical-and-isotopic techniques, in conjunction with Health Quotient assessment approach. The objective of this study is to determine the sources and controls on fluoride content and to evaluate probabilistic non-carcinogenic risk associated with its long-term consumption. F- ranges from 0.3 to 12 mg L-1, shows high spatial variability, and ~ 35% of the samples have F- > 1.5 mg L-1 (WHO maximum limit for drinking). Two sources are identified: high F- results from water-rock interaction of F-bearing minerals in granites and gneisses, while phosphate fertilizers can contribute up to ~ 0.46 mg L-1 of groundwater F- that can be significant for low F- samples. High F- samples are characterized by high pH, Na and alkalinity, and low Ca. Calcite precipitation drives the solubility of F-bearing minerals. Kinetic fractionation of water isotopes (18O and 2H) demonstrates that evaporation plays role in enriching groundwater F-. Non-carcinogenic risk, estimated by Hazard Quotient ([Formula: see text]), ranges from 0.13-5.72 to 0.26-11.86 for adult and children, respectively. Conservative estimate shows that ~ 0.467 million of adults and~0.073 million of children in four sub-districts are under the risk of fluorosis-while the residents of other five sub-districts remain safe from it. Finally, we suggest stakeholders to install F- treatment plants to ensure the health safety of local residents in the high-risk zones, create awareness in farmers for optimum use of fertilizers, and promote rainwater harvesting, for better management of groundwater resources and quality in the region.

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The Corumbataí River basin (São Paulo, Brazil) has a critical situation regarding water availability due to the intensive use to support agriculture and urbanization, requiring scientific information to face water demand. The aim of this study is to present a hydrological characterization based on the analysis of seasonal isotope variations (rainfall, groundwater, and surface water) and hydrometric data. Results indicate that baseflow contribution varies from 50 % to 70 % of the total flow, and water isotopic composition denotes a seasonal regime marked by the mixing of surface and groundwater in the wet period and groundwater discharge during the dry season. The results presented indicated the strong seasonal connection between atmospheric inputs and water movement across the basin, which poses an urgent need to diversify monitoring methods and create feasible regional and political regulations to control the effects on basin water resilience in the face of climate change and growing demand.

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The isotopic compositions of oxygen (δ 18O) and hydrogen (δ 2H) of precipitation were determined from three different locations in the western Niger Delta (Warri, Ughelli and Abraka) between 2014 and 2015. 18O and 2H in wet season precipitation were more depleted compared to the dry season. Similarly, d-excess computed for wet season precipitation is lower than that for the dry season. The δ 18O and δ 2H variations in precipitation suggest the effect of the convective system and north-easterly and south-westerly trade winds. The decrease in δ 18O and δ 2H was also observed in precipitation data of a continuous rain event of two successive days. The local meteoric water lines estimated for Warri, Ughelli and Abraka were δ 2H = 8.8 δ 18O + 9.1 ‰ (R 2 = 0.93), δ 2H = 6.9 δ 18O + 10.7 ‰ (R 2 = 0.98) and δ 2H = 7.9 δ 18O + 11.3 ‰ (R 2 = 0.87), respectively. The Niger Delta regional meteoric water line of δ 2H = 7.7 δ 18O + 10.2 ‰ (R 2 = 0.91) was derived from the monthly average from the three locations. The provided local meteoric water line for the Niger Delta from unweighted stable isotopic data represents a baseline for regional water resources studies.

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The water sources of the Sokoto Basin are mainly of interrelated origin. The groundwater is composed of old water recharged in different climate regimes and of recent meteoric water. The recharge source is influenced by both local and regional moisture circulation given the lower slope and intercept of the local meteoric water line (LMWL) relative to those of the global meteoric water line (GMWL) and distribution of the deuterium excess d from -20 to +14 ‰. The identified interrelated water sources were confirmed by variations in tritium measured between 4.9 and <0.4 TU. The groundwater and surface water were identified to be of mixed origin, consisting of interrelated and recent types. This depicts active recharge taking place across the basin. The groundwater recharge was established to be renewable; however, rational water exploitation should be exercised considering growing water demand with the corresponding population rise.

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This study monitored the isotopic compositions of precipitation in Guilin as well as the influence of El Niño-Southern Oscillation (ENSO) on the isotope ratios and water vapour sources from 2015 to 2016. The results indicate that the lower isotope values of precipitation from ocean water vapour source are affected by long transport distance and fractionation during summer and autumn. In contrast, the isotope values of winter and spring precipitation are affected by continental air masses and their evaporation sources yielding higher values. The intercepts of the local meteoric water line in Guilin are larger than those of the global meteoric water line, which is typical for subtropical monsoon climate. During the El Niño event, development of anomalous anticyclonic circulation enhances the northbound transport over the western Pacific and brings abundant water vapour to the southern part of China. During El Niño event prevailing period, precipitations exhibit a lower δ 18O value and low d (deuterium excess) value, indicating that the 2015/2016 ENSO event had a significant effect on the precipitation distribution, precipitation amount, and isotope ratios in regional precipitation.

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In the present study we investigated the isotope effects associated with water loss from closed low-density polyethylene (LDPE) bottles via diffusion at temperatures between 4 and 60 °C. While at low temperatures (4 and 10 °C) no substantial diffusional loss of water was observed within storage time, a pronounced loss was found for the experiments at room temperature and 60 °C. The latter was associated with a substantial increase in δ 18O, δ 17O, and δ 2Η values, and a decrease in the deuterium excess. The magnitude of the isotope effects essentially depended on the extent of water evaporation from the closed bottles through the LDPE membrane.

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Increasingly, modern hydrological technologies are dynamically altering river water flow and drastically affecting river hydrogeochemical cycle regimes globally. The present study focused on the reservoir discharges of artificial floodwaters that influence spatiotemporal variations in the physicochemical and stable isotope compositions in the lower Yellow River (LYR) of China. The surface water samples were collected at the nine sites along the LYR during the pre-, inter-and post-flood periods. Then, the collected samples were analysed with the following standard method. The δD and δ18O slopes of the waterline clearly indicated that the prolonged reservoir water and different water flows impacted the hydrological cycle in the LYR regions compared to GMWL (global meteoric water line) and LMWL (local meteoric water line). The thermal stratification processes of the water in the largest reservoir slightly enriched the heavy isotopes, and physicochemical alteration was neglected. Statistical analysis of two-way ANOVA revealed that the p-values (p < 0.01, p < 0.05) were very strong for most of the variables between the periods, and the linear regression exhibited weak values (R2 = 0.253, R2 = 0.150) at the surface water temperature variations and suggested no significant influence of isotope composition. Overall, the Xiaolangdi reservoir water prolonged time rates, and artificial floodwater flow had a very small effect on the isotope composition; in particular, a large high turbidity concentration in the discharged artificial floodwaters was the only considerable ecological risk condition in the LYR. This kind of proper monitoring work is immensely important and prevents reservoirs from causing hydrological cycle impacts in the LYR and the adjacent coastal ecosystems.

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The objective of this work is to enhance the conceptual hydrogeological model in the Río Cuarto River basin by using isotope and hydrochemical techniques. The precipitation pattern, as reflected in the average values of δ 2H and δ 18O in stations located in the plains and in the mountains, showed an isotope depletion from the East to the West, attributed to continental and altitude effects. Groundwater quality is mainly the result of two controlling factors: lithology and flow distances from recharge. The aquifers show fresh calcium/sodium bicarbonate water in the upper and medium basin (coarse fluvial sediments) which evolve to sodium sulphate and chloride waters in the low basin (mainly loess and fine alluvial sediments). The confined aquifer systems in the lower basin (C and D systems) averaged more negative stable isotope values, indicating that groundwater recharged during colder climatic conditions (Pleistocene period). Groundwater dating with 14C confirmed that groundwater ages range from modern to 45,000 years BP showing that as the water flows towards deeper layers and farther from the mountainous recharge area, groundwater age increases. The confined aquifers can potentially be exploited in order to partly cover different water needs but they should be managed in a sustainable way.

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In 2015 and 2016, groundwater samples were collected in Hanoi to analyse the isotopic composition (δ2H, δ18O and 3H) and elucidate the relationship between groundwater and surface water, as well as the origin of the groundwater. The values for δ18O and δ2H indicate that the groundwater originated from evaporated meteoric water and the isotope enrichment is due to the evaporation of shallow groundwater. Evaporation is the primary process affecting stable isotope signatures. Water samples collected from both Holocene and Pleistocene aquifers are more depleted in the heavy isotopes 18O and 2H than the rainfall in the area. This indicates that part of the groundwater is paleo-groundwater or may be caused by the altitude effect due to recharge at a higher elevation. The results also show the close interaction between two granular aquifers and the Red River. Furthermore, the contribution of modern groundwater could be observed by the appearance of tritium in both aquifers. The presence of tritium indicates that originally tritium-free groundwater from the margins of the basin has been diluted by young water. The results of this study might help managers to evaluate the origin and reserves of groundwater more accurately.

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The study investigates the factors that control the isotopic composition of tropical precipitation in Bangladesh. Daily and monthly rainfall samples were collected from three stations from 2013 to 2015: (1) northern and moderately high altitude: Sylhet, (2) middle part of the country (close to Tropic of Cancer): Savar, and (3) southern coastal region: Barisal. To escape from the post-evaporation effect, proper care was adopted. This is supported by the fact that the local meteoric water lines (LMWLs) derived for the daily precipitations of all stations mostly follow the global meteoric water line (GMWL). The results exhibit a clear seasonal and spatial variation in both δ 18O and δ 2H of precipitation. 18O is more depleted in samples collected during rainy (monsoon) seasons, while 18O enrichment is associated to winter and summer (pre-monsoon) seasons. During rainy season, intra-seasonal variability of δ18O rainfall is clearly seen and remarkable depletion of 18O is observed during the period of intense convective activity over the Bay of Bengal. This feature indicates that isotope variability in Bangladesh is controlled by large-scale convective activity rather than local rainfall amount.

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Our 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.

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The stable isotopes of oxygen and hydrogen can provide useful insights into water origin and hydrological processes. The present study aims to investigate the characteristics of stable H/O isotopes of groundwater and surface water in a coastal area of the Vietnamese Mekong Delta. Isotopes and chloride concentrations of surface water show a highly seasonal and linearly spatial variability, depending on the distance to the sea. The seasonal variation of upstream discharge and rainfall plays an important role in changes of the isotopic compositions and chloride concentrations. Tide also influences on chloride concentrations of surface water while it does not change the isotopic compositions. Evaporation plays a crucial role in changes of isotopic compositions, while the influence of freshwater/seawater mixing on isotopic variabilities is negligible. Groundwater has a spatial heterogeneity in isotopic compositions and chloride concentrations, reflecting different recharge sources and seawater intrusion processes. Groundwater in shallow aquifers originates from rainfall and surface water with small evaporative losses, and it experienced different magnitudes of mixing with seawater. Groundwater in deep aquifers might be recharged by open-surface water evaporation in the last glacial age with minor impacts of seawater intrusion on these aquifers.

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Water scarcity is a leading concern in both developing and developed nations. Coping with water scarcity requires an understanding of various hydrological processes that act upon precipitation, surface and groundwater at a local scale. We measured isotopic signatures of several water samples from two distinct ecosystems, i.e. tropical savanna in the West and the warm semi-arid region in the East lying across the Western Ghats mountain range, India, to understand the hydrological processes. The results show that the hydrogeological conditions strongly influence the isotopic characteristics of water of different resources, governed by different hydrological processes, even at close spatial scales. Based on the local evaporation lines of different water resources within a particular ecosystem, it is inferred that the water resources are well linked at one site, but have diverse connectivity at the other site. Further, the isotopic signatures of all the water resources are systematically affected by the monsoon precipitation. In addition, anomalously depleted isotopic signatures are observed during known hailstorm events. This may provide a means to trace their signature in the existing water resources.

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