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This study characterized groundwater resources for the Nakivale sub-catchment of the transboundary Victoria Basin in Uganda using classical hydrochemical and stable isotopic approaches. Groundwater in the study area is essential for domestic, agricultural, and industrial uses. As a sub-domain of the larger Victoria Basin, it also plays a crucial role in shaping the hydrological characteristics of this vital transboundary basin, both in terms of quality and quantity fronts. This makes its sustainable management and development vital. The predominant groundwater type is Ca-SO4, with other types including Ca-HCO3, Na-Cl, Na-HCO3, and Ca-Mg-SO4-Cl. Hydrochemical facies analysis highlights the importance of rock–water interactions in controlling groundwater chemistry, mainly through incongruent chemical weathering of Ca-rich plagioclase feldspars and the oxidation of sulfide minerals, such as pyrite, which are prevalent in the study area. Groundwater recharge is primarily influenced by the area's topography, with recharge zones characterized by lineament networks, located in elevated areas. Stable isotope analyses indicate that groundwater mainly originates from local precipitation, while tritium data suggest the presence of both recent and older groundwater (likely over 20 years old). The study's comprehensive approach and findings contribute significantly to the understanding of groundwater systems in the region, thus providing valuable insights for policymakers and stakeholders involved in water resource management and development strategies. [ABSTRACT FROM AUTHOR]

Isotopic evidence of groundwater and stream water is frequently used to investigate water exchanges with groundwater. Monthly sampling of rain, stream water, and groundwater was conducted at Tims Branch watershed in South Carolina for the oxygen and hydrogen stable isotope (δ2H and δ18O) measurement, as well as pH and oxidation–reduction potential (ORP). Together with a mass balance perspective, it was determined that it takes a few weeks to one month for groundwater in the hyporheic zone to fully exchange with stream water. From hydrodynamic modelling, we show that substantial (up to 70 %) groundwater exchange occurs at gaining and losing sites. Groundwater exfiltration, i.e. inflow into stream water, contributes up to 4 % to stream water, with the remainder from upstream exfiltration. A 2–4 % per day renewal rate of adjacent groundwater would indirectly indicate a groundwater residence time in the order of half a month to a full month (assuming either a well-mixed case or large dispersion rate in pulse flow case), in agreement with a greatly reduced variability of δ2H and δ18O of groundwater compared to stream water and rain. This reduced variability of stable isotope signal from groundwater confirms our hypothesis that riparian groundwater mixing at Tims Branch is more of a mixed type rather than a pulse flow type. A monthly time scale is sufficient for groundwater to become anoxic at exit points into stream water resulting in the episodic production of natural organic matter- and iron-rich flocs upon oxidation. [ABSTRACT FROM AUTHOR]

This study aimed to synthesise and interpret stable isotopic data (δ2H and δ18O) from various sources to understand the isotope hydrology around coal mine operations in Elk Valley, B.C., Canada. The data, including precipitation, groundwaters, seeps, and mine rock drains, were used to construct a local meteoric water line (LMWL) for the Elk Valley, evaluate the spatiotemporal isotopic composition of its groundwater, and assess mine seepage and mine rock drain discharge. The study revealed a robust LMWL relation (δ2H = 7.4 ± 0.2 · δ18O – 4.3 ± 4.1). The groundwater and seep data indicated a winter season bias and a north–south latitudinal gradient, suggesting rapid near-surface groundwater flow without significant post-precipitation evaporation. Porewater isotope samples from unsaturated mine rock piles (MRPs) showed site-specific evaporation patterns, potentially due to convective air flows or exothermic sulphide oxidation. This research revealed the influence of groundwater and meltwater on rock drain discharge. Based on evaporative mass balance calculations, MRPs seasonally contributed ca. 5 %(December base flow) and 22 % (snowmelt) to drain discharge. The findings underscore the value of stable isotope data collections in the Elk Valley to help better define and quantify the hydrology–hydrogeology, including a better understanding of evaporative conditions in MRPs. [ABSTRACT FROM AUTHOR]

Groundwater is a critical resource in the Upper Chao Phraya basin, providing consistent water supplies for agricultural, domestic, and industrial activities, especially during the dry season. This study utilized tritium and carbon-14 dating techniques to investigate groundwater age, analyzing 273 samples collected in 2021 from various wells and depths across the basin. Tritium and carbon-14 were measured using liquid scintillation counting (LSC). The results revealed a wide range of groundwater ages, including recently recharged water with tritium concentrations up to 2.4 TU, corresponding to groundwater ages ranging from a few months to 44.17 years BP (Before Present), with an average of 18.26 years BP. Older groundwater was identified with carbon-14 concentrations as low as 3.22 pMC, indicating ages of up to 22,899 years, with a mean age of 6687 years BP. Correlation analysis showed a positive relationship between tritium and carbon-14 concentrations (r = 0.52). Spatial distribution patterns indicated that tritium concentrations were higher in northern and mountainous areas, identifying these as critical recharge zones. In contrast, lower carbon-14 concentrations in the central and southern areas suggested the presence of older groundwater, emphasizing the need for careful management of these ancient water reserves. The spatial variation in tritium and carbon-14 concentrations highlights differences in groundwater circulation and recharge patterns, enabling the identification of key recharge zones in the northern and highland regions. This highlights the importance of conserving these areas from pollution and over-extraction. The presence of old groundwater in the central and southern areas further emphasizes the need for ongoing monitoring to sustainably manage these long-term water resources. This study enhances the understanding of groundwater dynamics in the Upper Chao Phraya basin and provides valuable insights for improving water resource management strategies. [ABSTRACT FROM AUTHOR]

Stable isotope techniques are precise methods for studying various aspects of hydrology, such as precipitation characteristics. However, understanding the variations in the stable isotope content in precipitation is challenging in Iran due to numerous climatic and geographic factors. To address this, forty-two precipitation sampling stations were selected across Iran to assess the fractional importance of these climatic and geographic parameters influencing stable isotopes. Additionally, deep learning models were employed to simulate the stable isotope content, with missing data initially addressed using the predictive mean matching (PMM) method. Subsequently, the recursive feature elimination (RFE) technique was applied to identify influential parameters impacting Iran's precipitation stable isotope content. Following this, long short-term memory (LSTM) and deep neural network (DNN) models were utilized to predict stable isotope values in precipitation. Interpolated maps of these values across Iran were developed using inverse distance weighting (IDW), while an interpolated reconstruction error (RE) map was generated to quantify deviations between observed and predicted values at study stations, offering insights into model precision. Validation using evaluation metrics demonstrated that the model based on DNN exhibited higher accuracy. Furthermore, RE maps confirmed acceptable accuracy in simulating the stable isotope content, albeit with minor weaknesses observed in simulation maps. The methodology outlined in this study holds promise for application in regions worldwide characterized by diverse climatic conditions. [ABSTRACT FROM AUTHOR]

In the context of expected future melt reductions in the high‐Andes, the buffering capacity of non‐glacial stores, and especially of high‐altitude bofedal wetlands, is of increasing importance. Isotope signatures potentially indicative of water undergoing evaporation on transit through bofedales have been found in the tropics, but end‐member uncertainty has so far prevented streamflow separation using this signal. We undertook a stable isotope sampling campaign over the 2022 wet‐dry season transition in a 53.6 km2, 16% glacierized catchment in southern Peru with a bofedal coverage of 11%. Diurnal proglacial hydrographs and remote sensing were used to interpret seasonal snowmelt dynamics and identify the dry periods when glacial melt and bofedal contributions are assessed to be the two principal components of streamflow. Following the final wet season precipitation event, a rapid ~3 week transition occurs in the main river from a stable isotope signature consistent with dynamic rainfall/snowmelt contributions to one of ice‐melt. In both wet and dry seasons, the main river and tributary streams show evaporative enrichment suggesting ongoing supply from water transiting bofedales. A two‐component mixing model using lc‐excess during the dry season shows the bofedal source contribution varies from 9% to 20% [±9–10%], indicating that streamflow is greatly augmented by the presence of glaciers at these headwater scales. However, applying these proportions to river discharge shows a sustained bofedal contribution of around 0.09 m3/s during the dry season study window whereas the flux of glacial water halves from 0.73 to 0.36 m3/s over this timeframe. The results highlight the important role of bofedales and the connected groundwater system in buffering seasonal declines in streamflow months into the dry season, and suggests the hydrological functioning of bofedales as part of this wider system should be considered when exploring the effectiveness of potential options to sustain baseflows in a post‐glacial future. [ABSTRACT FROM AUTHOR]

Study region: Apuan Alps (NW-Tuscany, Central Italy). Study focus: Definition of the hydrogeological conceptual model of carbonate aquifer systems in order to define their recharge areas, using a multidisciplinary and integrated approach that involves geochemistry and isotopic tools. The proposed approach was tested on the Apuan Alps carbonate aquifers that contain precious groundwater resources to be protected, but their management is difficult to carry out without a detailed knowledge. The study of the groundwater hydrodynamics in terms of pathways and extension is often difficult to perform using conventional hydrogeological surveys. Geochemistry and isotopic tool can therefore provide an important contribution. However, to use such tools it is necessary to provide a characterization of the infiltration waters through which the isotopic data of the main springs can be interpreted. The paper proposes a hydrogeological approach combined with geochemical methodologies and 13C data of water and rock samples for selecting springs representative of local infiltration. New hydrological insights for the region: An isotopic characterization of infiltration water was performed, and the definition of the vertical isotope gradient specific for the area of interest was defined. By crossing this gradient with the geological structures, morphology and hydrology features of the territory, the feeding areas of two of the most important karst springs in the Apuan Alps region were delimited, thus testing the proposed methodology.

The Taoudéni Basin, spanning 20% of Burkina Faso, holds vital aquifers for the Sahel's water security and development. However, limited understanding of these aquifers' hydrodynamics, including the flow patterns, mineralization processes, and renewal rates, hinders sustainable management practices in this arid region. Therefore, this study aims to investigate the aquifer hydrodynamics, mineralization processes and groundwater renewal in the transboundary Taoudéni Basin. Through a combination of hydrogeochemical and isotopic analyses, alongside existing data, this study examines 347 physicochemical samples, 149 stable isotope samples, and 71 tritium samples collected from 2013 to 2022. The findings reveal mineralization and stable isotopes (δ18O, δ2H) spatially aligned with the groundwater flow direction, validating this and indicating potentially multiple independent aquifers. The predominant mineralization mechanisms involve silicate hydrolysis and carbonate dissolution, supplemented by minor processes like evaporitic dissolution and cation exchange. The anthropogenic influence suggests potential groundwater recharge with potential pollution in the "SAC1", "SAC2", "GFR", "GGQ", and "GKS" geological formations. The stable isotopes (δ18O, δ2H) indicate recharge occurred over 4.5 kyr B.P., while tritium (3H) analysis confirms the presence of old, mixed waters, indicating slow renewal. Overall, this study highlights the minimal recent recharge and limited renewal rates, questions tritium's efficacy for old water detection, and emphasizes the need for sustainable management. [ABSTRACT FROM AUTHOR]

The aim of this paper is to describe the surveys performed in order to update the interpretive conceptual circulation model of the Ladeira de Envendos hyposaline hydromineral system (Central Portugal). The geology of the Ladeira de Envendos region is strongly controlled by the Amêndoa-Carvoeiro synform, of Ordovician-Silurian age, presenting continuous and aligned quartzite ridges on the NE flank, that form the basic structure of a set of inselbergs. The physico-chemical analysis of the Ladeira de Envendos natural mineral spring and borehole waters was provided by the Super Bock Group Enterprise (Concessionaire of the Ladeira de Envendos). Furthermore, two sampling campaigns took place to increase knowledge on the isotopic composition of the studied natural mineral waters. The stable (δ2H, δ18O) isotopic data indicate that local meteoric waters infiltrate around 400 m altitude and evolve to the natural mineral waters (of Cl-Na facies) through a NW–SE underground flow path ascribed to the highly fractured and permeable quartzite rocks. From recharge to discharge, the infiltrated meteoric waters acquire silica (±9 mg/L) due to water–quartzite rock interaction. These natural mineral waters emerge at temperatures around 21 °C, being the up flow of these waters controlled by the rock fractures and local faults. The natural mineral waters mean residence time range between 25 and 40 years, as indicated by the 3H content of these waters, enhancing an active recharge of this hydromineral system. The results obtained indicate existence of three hydrogeological subsystems, ascribed to three inselbergs, with similar groundwater circulation paths. These multi and interdisciplinary studies should be seen as an important contribution to the sustainable management of this type of natural mineral water resources. [ABSTRACT FROM AUTHOR]

Isotope technology is widely used in geochemical mechanisms analysis; however, studies on the origin of pit lake water by isotopes in coal concentration areas in grassland are rare. In this study, 20 groups of water samples were collected, which were subjected to chemical analysis to determine the hydrogeochemical characteristics of pit lake water. The mechanisms of pit lake water formation and recharge–evaporation were ascertained through principal component analysis and the Rayleigh fractionation model. The results indicate that the phreatic water is least affected by evaporation, followed by confined water, surface water and pit lake water. The ionic composition of surface water, phreatic water and most of the confined water is mainly affected by leaching, some confined water can be recharged by surface or phreatic water; while the ionic composition of pit lake water is dominantly affected by evaporation (69.4 %) and is less affected by groundwater recharge (17.1 %) and human activities (11.5 %). The pit lake water is recharged by precipitation, phreatic water and the lateral runoff of confined water; however, the proportion of phreatic and confined water recharge is small. The evaporative loss of the pit lake water is 40–61 % of the initial water body. [ABSTRACT FROM AUTHOR]

We investigated the stable isotope hydrology of Sable Island, Nova Scotia, Canada over a five year period from September, 2017 to August, 2022. The δ2H and δ18O values of integrated monthly precipitation were weakly seasonal and ranged from –66 to –15 ‰ and from –9.7 to –1.9 ‰, respectively. Fitting these monthly precipitation data resulted in a local meteoric water line (LMWL) defined by: δ2H = 7.22 ± 0.21 · δ18O + 7.50 ± 1.22 ‰. Amount-weighted annual precipitation had δ2H and δ18O values of –36 ± 11 ‰ and –6.1 ± 1.4 ‰, respectively. Deep groundwater had more negative δ2H and δ18O values than mean annual precipitation, suggesting recharge occurs mainly in the winter, while shallow groundwater had δ2H and δ18O values more consistent with mean annual precipitation or mixing of freshwater with local seawater. Surface waters had more positive values and showed evidence of isolation from the groundwater system. The stable isotopic compositions of plant (leaf) water, on the other hand, indicate plants use groundwater as their source. Fog had δ2H and δ18O values that were significantly more positive than those of local precipitation, yet had similar 17O-excess values. δ2H values of horsehair from 4 individuals lacked seasonality, but had variations typical to those of precipitation on the island. Differences in mean δ2H values of horsehair were statistically significant and suggest variations in water use may exist between spatially disparate horse communities. Our results establish an important initial framework for ongoing isotope studies of feral horses and other wildlife on Sable Island. [ABSTRACT FROM AUTHOR]

Today, the importance of modern science and technology, especially the use of environmental isotopes in various studies, including hydrology and geohydrology, is obvious for anyone. Given the quantitative and qualitative crisis status of groundwater resources in Iran, having accurate isotopic data on the quantitative and qualitative status of water resources can lead to good planning and, consequently, proper management of water resources. Due to the lack of sufficient studies on the environmental isotopes in Iran, which, of course, is due to the lack of technologies, high costs of sample transfer to overseas and sanctions, while reviewing the sampling of Groundwater resources, sample preparation methods for stable isotopes of ²H, 18O, 34S, and 13C, and the standards for each isotope; related devices such as Gasbench+ DeltaPlusXP, Elemental Analyzer-Isotope Ratio Mass Spectrometer (EA-IRMS), and Total Inorganic Carbon-Total Organic Carbon (TIC-TOC), as well as measurement methods are presented. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The transit time of precipitation entering a catchment and leaving it as streamflow spatiotemporally varies according to the flow paths that precipitation takes. However, investigating influences of hydrometeorological variables and catchment characteristics on time‐variable transit times is challenging due to the complex water flow through heterogeneous landscapes. Recent studies investigated the fraction of streamflow younger than approximately 3 months (Fyw) using multi‐year data (long‐term Fyw) or one‐year calculation windows to investigate its time‐variability (time‐variable Fyw). Nonetheless, it is still unclear if the inter‐annual variability of one‐year Fyw is due to hydrological influences or its uncertainty, and no minimum time series length for the long‐term Fyw was defined yet. Here, we investigated the impact of catchment characteristics and hydrometeorological variables on the long‐term Fyw, the time‐variable Fyw, and the Fyw depending on discharge of nine river basins in Central Europe. All methods of estimating Fyw led to similar results, with Fyw depending on discharge deemed unreliable due to the monthly sampling interval of streamflow isotopes. Danube and Rhine had the lowest Fyw (0.06), medium Fyw (0.20) were found in eastern basins (e.g., Oder), and the western ones (e.g., Mosel) had the highest Fyw (0.33). Spatial analysis indicated a negative relationship between Fyw and altitude. Contradicting or lacking spatiotemporal relationships to other variables pointed to unknown influential factors controlling the runoff process. Using flow duration curves, it was found that basins with a low flow variability had low Fyw, indicating that the old water of their runoff stems from large subsurface storage. With increasing calculation window size, the within‐basin variability of time‐variable Fyw decreased. Long‐term Fyw depended on the method used to define 'long‐term' and the time series length and start and end date. We thus recommend future studies to calculate long‐term and time‐variable Fyw to facilitate comparability between different catchments, and to account for this source of uncertainty. Further, more studies are needed in diverse catchments to investigate the hydrometeorological impacts on Fyw and thus on runoff generation processes. [ABSTRACT FROM AUTHOR]

Study region: The Peace-Athabasca Delta, northeastern Alberta, a Ramsar Wetland of International Importance. Study focus: To explore the cause of change in water isotope composition at an ‘index lake’ (δSSL; ‘PAD 18’), a terminal basin where inflow equals evaporation, and the consequences for characterizing lake water balance across a region subject to the same atmospheric conditions. For two decades, water isotope composition at PAD 18 provided a relatively constant, reliable estimate of δSSL, but experienced a pronounced shift in 2020–2021 when average flux-weighted ice-free season relative humidity increased by 4.6% from 66.2% (2015–2019) to 70.8% (2020–2021). Using flux-weighted air temperature and relative humidity data from 2020–2021, an independent calculation of δSSL was determined to be equivalent to the average isotope composition of PAD 18 during 2020–2021. New hydrological insights: Results reveal re-equilibration of the lake water with the atmosphere following the rise of relative humidity readily provides an explanation for the change in isotope composition of PAD 18. We demonstrate the importance of accurate characterization of δSSL, via the index lake method, for isotope-mass balance calculations using evaporation-to-inflow ratios from measurement of water isotope compositions of 61 lakes across the PAD in July 2021. Findings highlight the value of an index lake and appropriate parameterization of isotope-mass balance models for assessment and ongoing monitoring of water balances of nearby lakes, especially amidst future climatic variability.

This work presents the dataset of stable water isotopes of oxygen and hydrogen measured in water samples from different sources (precipitation, surface water, groundwater, tap water) across Kazakhstan from 2017 to 2018 and from 2020 to 2023. The dataset includes results on isotopic composition of 399 water samples, namely precipitation: event-based (n = 108), cumulative monthly (n = 22); surface water: lakes, reservoirs, brooks, rivers, channels (n = 175), groundwater: shallow and artesian groundwater, spring (n = 85), tapwater (n = 9). For each sample name of the source, location, latitude, longitude and date of sampling, measurement uncertainty (one standard deviation) are available. The samples were assessed by plotting the data in dual δ18O vs. δ2H isotope space with reference to values found in the published literature and fitting a linear regression equation for Astana (event) precipitation. Overall, this is the first dataset covering wide range of sources across Kazakhstan, which could be used by global and regional water resource assessments and studies such as tracing water sources, hydrograph separation and end-member analyses, isotope mass balance, evapotranspiration partitioning, residence time analysis and groundwater recharge.

Understanding the partitioning of snow and rain contributing to either catchment streamflow or evapotranspiration (ET) is of critical relevance for water management in response to climate change. To investigate this partitioning, we use endmember splitting and mixing analyses based on stable isotope (18O) data from nine headwater catchments in the East River, Colorado. Our results show that one third of the snow partitions to ET and 13% of the snowmelt sustains summer streamflow. Only 8% of the rainfall contributes to the summer streamflow, because most of the rain (67%) partitions to ET. The spatial variability of precipitation partitioning is mainly driven by aspect and tree cover across the sub-catchments. Catchments with higher tree cover have a higher share of snow becoming ET, resulting in less snow in summer streamflow. Summer streamflow did not contain more rain with higher rainfall sums, but more rain was taken up in ET.

Isotopic and nuclear techniques are indispensable in many fields, including health, industry, food, and agriculture. The techniques discussed, collectively known as fallout radionuclide, fingerprint, and isotope hydrology, are currently being employed to characterize and assess phenomena that could potentially degrade soil and water resources. Given the intricate nature of erosion and sedimentation processes in landscapes and water reservoirs, conducting a comprehensive characterization and evaluation of these phenomena is imperative. A traditional literature review was conducted to obtain the most thorough understanding of both the current state of the art and the subject matter regarding the conception of these techniques’ application and the manner of their use (use combined/integrated or use isolated in search of particular results on a single type of degradation, whether soil or water). There is no evidence that an integrative methodology employing these isotopic and nuclear techniques has previously been utilized (as evidenced by 109 current publications), thereby impeding the analysis of the potential sequential occurrence of soil and water degradation. The findings substantiate the hypothesis that isotopic and nuclear techniques can be integrated sequentially through a synergistic convergence. This represents an emerging methodology for addressing the complex needs of the landscape’s soil and water degradation process.

Groundwater is a critical resource in the Upper Chao Phraya basin, providing consistent water supplies for agricultural, domestic, and industrial activities, especially during the dry season. This study utilized tritium and carbon-14 dating techniques to investigate groundwater age, analyzing 273 samples collected in 2021 from various wells and depths across the basin. Tritium and carbon-14 were measured using liquid scintillation counting (LSC). The results revealed a wide range of groundwater ages, including recently recharged water with tritium concentrations up to 2.4 TU, corresponding to groundwater ages ranging from a few months to 44.17 years BP (Before Present), with an average of 18.26 years BP. Older groundwater was identified with carbon-14 concentrations as low as 3.22 pMC, indicating ages of up to 22,899 years, with a mean age of 6687 years BP. Correlation analysis showed a positive relationship between tritium and carbon-14 concentrations (r = 0.52). Spatial distribution patterns indicated that tritium concentrations were higher in northern and mountainous areas, identifying these as critical recharge zones. In contrast, lower carbon-14 concentrations in the central and southern areas suggested the presence of older groundwater, emphasizing the need for careful management of these ancient water reserves. The spatial variation in tritium and carbon-14 concentrations highlights differences in groundwater circulation and recharge patterns, enabling the identification of key recharge zones in the northern and highland regions. This highlights the importance of conserving these areas from pollution and over-extraction. The presence of old groundwater in the central and southern areas further emphasizes the need for ongoing monitoring to sustainably manage these long-term water resources. This study enhances the understanding of groundwater dynamics in the Upper Chao Phraya basin and provides valuable insights for improving water resource management strategies.

Region: New Zealand Focus: Application of a seasonal precipitation isoscape for New Zealand, to incorporate influences of regional scale atmospheric circulation, and local topography. New hydrological insights: Our regionally calibrated sinusoidal model demonstrated substantial variation in the strength (amplitude and fit) of seasonal cycles of precipitation isotope values across New Zealand. Amplitudes of sine models fitted to monthly precipitation δ18O records from 51 sites ranged from 0.38 to 3.14‰ and were lowest in coastal and windward areas. Offsets (central tendencies) of seasonal cycles predictably decreased at higher elevations and latitudes, but the best interpolation models appear to capture some of the orographic effects present across New Zealand’s South Island. Phase (lag) of seasonal cycles was generally lower in the south and east of the country. We suggest that seasonal cycles of precipitation stable isotope values in some areas of New Zealand (but not others) are conducive to calculation of catchment transit times and may require consideration for interpreting sources of recharge to groundwater and river water. Uncorrected δ18O isoscapes produced by interpolation of sine parameters offered better fits to monthly precipitation δ18O values than previous model predictions available for New Zealand, and subsequent residual correction further improved isoscape performance. These results have wider implications for the application of stable isotopes as environmental tracers in regions with mixed marine- and continental-type climates.

The Rio Loa is a perennial river that crosses the Atacama Desert. A basin-wide survey enables for the first time, the hydrologic regime origin, persistence and processes to be identified. Perennial baseflow in the Rios Loa and Salado largely originates from intra-arc aquifers which are poorly known. However, the data indicate that despite flood flow being largely confined to the summer (DJF) season, sufficient storage exists in these aquifers to maintain year-round stream flow from high-altitude, across the Atacama Desert to the coast. The intra-arc aquifers of the Western Cordillera receive recharge from time-variable precipitation infiltration and time-invariant lithospheric inputs. Lithospheric inputs potentially include slab/mantle dehydration, upper crustal melt devolatilization and/or thermally induced upflow of deeply penetrating meteoric water through buried evaporites or carbonates. Downstream, aquifers in the Pre-Andean basins variably interact with surface water, depending on location, river stage and time of year, but they do not supply significant additional sources of baseflow. Hydrochemical processes include those related to volcanic activity, soil carbonate generation, silicate weathering, CO2 degassing and calcite precipitation. Solutes undergo concentration by evaporation, gypsum dissolution, and are further affected by localized NO3, and SO4 inputs and mixing with saline waters. Stable isotopes reveal subcatchment specific precipitation and evaporation, whilst carbon and tritium isotopes are used to analyze recharge sources and processes in the intra-arc aquifers and downstream mixing. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Water Resources Journal / Revue Canadienne des Ressources Hydriques is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Río Loa is a perennial river that crosses the Atacama Desert. A basin-wide survey enables for the first time, the hydrologic regime origin, persistence and processes to be identified. Perennial baseflow in the Ríos Loa and Salado largely originates from intra-arc aquifers which are poorly known. However, the data indicate that despite flood flow being largely confined to the summer (DJF) season, sufficient storage exists in these aquifers to maintain year-round stream flow from high-altitude, across the Atacama Desert to the coast. The intra-arc aquifers of the Western Cordillera receive recharge from time-variable precipitation infiltration and time-invariant lithospheric inputs. Lithospheric inputs potentially include slab/mantle dehydration, upper crustal melt devolatilization and/or thermally induced upflow of deeply penetrating meteoric water through buried evaporites or carbonates. Downstream, aquifers in the Pre-Andean basins variably interact with surface water, depending on location, river stage and time of year, but they do not supply significant additional sources of baseflow. Hydrochemical processes include those related to volcanic activity, soil carbonate generation, silicate weathering, CO2 degassing and calcite precipitation. Solutes undergo concentration by evaporation, gypsum dissolution, and are further affected by localized NO3, and SO4 inputs and mixing with saline waters. Stable isotopes reveal subcatchment specific precipitation and evaporation, whilst carbon and tritium isotopes are used to analyze recharge sources and processes in the intra-arc aquifers and downstream mixing.

Key message: Little vertical or circumferential variation in within-tree xylem water δ2H and δ18O within three tree species. Vertical and circumferential patterns of xylem water isotope signatures in large trees are rarely characterized but may influence interpretation of water source investigations and soil/xylem water isotope offsets. To examine vertical and circumferential variation in xylem water δ2H and δ18O, we collected xylem tissue at 5 heights (0, 1, 4, 7 and 10 m) from three replicate trees of three species with contrasting xylem anatomy, two angiosperms (Liquidambar styraciflua and Quercus nigra) and one gymnosperm (Pinus taeda). Concurrently, we also determined δ2H and δ18O of groundwater, soil water, and recent precipitation. On a different day, we collected circumferential samples at 1 m from the same trees to test for sectorality effects. Water from stem and soil samples were cryogenically extracted and analyzed for δ2H and δ18O. Mean xylem water δ2H and δ18O were significantly different between species, both vertically and circumferentially. We did not find significant (p = 0.05) systematic variation in δ2H or δ18O with height. We found no significant evidence for sectorality effects on δ2H, δ18O. Variances of vertical synoptic xylem water δ2H or δ18O were similar between species, 7.2–10.4‰ for δ2H and 0.58–0.81‰ for δ18O. Circumferential variances were also similar between species, 4.0–6.0 for δ2H and 0.37–0.44 for δ18O. A mixing model showed that sweetgum, water oak and loblolly pine, were drawing most of their water from deep soil from 45 to 190 cm (84.7, 68.4 and 53.2%, respectively) however, soil water-excess values indicate δ2H fractionation effects on these estimates. Dual isotope mixing model evaluation with single and multiple sample configurations showed that source water estimates were not affected by within tree variability of xylem water signatures. Xylem water δ2H and δ18O variability with height or circumference, was 3.2 and 2.7 times less than between tree variation because of transient temporal and spatial processes and is, therefore, not likely to affect interpretations of water sourcing in these three species. [ABSTRACT FROM AUTHOR]

In the Himalayas, the lives and livelihoods of millions of people are sustained by water resources primarily depending on the moisture brought by Western Disturbances and Indian Summer Monsoon. In the present study, a network of 12 precipitation stations was established across the Kashmir Valley to understand the spatial and meteorological factors controlling precipitation isotopes. Temperature and relative humidity are dominant meteorological factors, whereas altitude, proximity to forest canopy, land use/land cover, windward and leeward sides of the mountains are the main physical factors influencing precipitation isotopes. The study suggests that the Mediterranean Sea and nearby water bodies along with continental recycling are the dominant sources of moisture from October to May, while the Arabian Sea, Bay of Bengal and continental recycling are the main sources of moisture from June to September. However, some precipitation events from October to May collect moisture from the Arabian Sea and some precipitation events from June to September collect moisture from the Mediterranean Sea. The occasional passage of Western Disturbances in summer merging with the Indian Summer Monsoon yields heavy to very heavy precipitation. The study provides a better understanding of complex spatial and meteorological phenomena controlling precipitation isotopes across the Western Himalayas. [ABSTRACT FROM AUTHOR]

Characterization of the groundwater flow systems is important for sustainable water resource management decision-making. We have used vertical profiles of electrical conductivity (EC) and water temperature taken at 2 m intervals during drilling of 109 boreholes, and samples for stable isotope analysis (δ18O, δ2H) taken from 47 boreholes to characterize groundwater recharge, flow and discharge. 222Rn measurements and piezometric evidence were used to complement results from the EC and stable isotopes. The converging evidence shows that groundwater in the study area is characterized by a mix of two different groundwater flow systems: i) the deep groundwater systems are connected to the regional groundwater flow originating from the highlands, outside the surface water basin, ii) the shallow groundwater systems get recharge from local rains. The local recharge zones are located in highly urbanized and industrialized zones posing risk to recharge reduction and pollution. Therefore, attention should be given to protect groundwater resources from contamination and increase groundwater resilience to climate change. [ABSTRACT FROM AUTHOR]

Rainforests play an important role in hydrological and carbon cycles, both at regional and global scales. They pump large quantities of moisture from the soil to the atmosphere and are major rainfall hotspots of the world. Satellite-observed stable water isotope ratios have played an essential role in determining sources of moisture in the atmosphere. Satellites provide information about the processes involving vapour transport in different zones of the world, identifying sources of rainfall and distinguishing moisture transport in monsoonal systems. This paper focuses on major rainforests of the world (Southern Amazon, Congo and Northeast India) to understand the role of continental evapotranspiration in influencing tropospheric water vapour. We have used satellite measurements of 1H2H16O/1H216O from Atmospheric InfraRed Sounder (AIRS), evapotranspiration (ET), solar-induced fluorescence (SIF), precipitation (P), atmospheric reanalysis-derived moisture flux convergence (MFC) and wind to discern the role of ET in influencing water vapour isotopes. A global map of the correlation between δ2Hv and ET-P flux indicates that densely vegetated regions in the tropics show the highest positive correlation (r > 0.5). Using mixing models and observations of specific humidity and isotopic ratio over these forested regions, we discern the source of moisture in pre-wet and wet seasons. [ABSTRACT FROM AUTHOR]

Investigating the sources, migration and proportional contribution of nitrate is essential to effectively protect water quality. δ15N-NO3–, δ18O-NO3– and Stable Isotope Analysis in R (SIAR) were used to qualitatively and quantitatively analyse nitrate sources in the Pingzhai Reservoir water body. The values of δ15N-NO3– and δ18O-NO3– in water vary with season. Soil organic nitrogen and chemical fertilisers are the main sources of nitrate in autumn, while domestic sewage and livestock manure are the primary sources of nitrate in winter and spring. The SIAR results showed that chemical fertilisers, livestock manure, sewage, and soil organic nitrogen had the highest proportional contribution. In autumn, the proportional contribution of chemical fertilisers to river and reservoir were 47 and 51 %. During winter, the proportional contributions of livestock manure and sewage to river and reservoir were 53 and 68 %, respectively, and in spring 49 and 68 %, respectively. Considering the fragility of karst ecosystems, strict measures should be formulated for the use of chemical fertilisers and standards for sewage discharge should be raised. Control nitrogen input from agricultural activities and prevent water quality deterioration. [ABSTRACT FROM AUTHOR]

The study of the isotope hydrogeology of bogs in the Northwestern Russia included the analysis of the potential of the integrated use of changes in the major hydrogeochemical characteristics of bog water and radon-222, an alternative marker of groundwater flow, in the hydrological continuum of the Ilasskii Bog Massif (IBM), which is a typical bog of the southern White-Sea type, common in the region. It was found that the hydrogeochemical runoff from the IBM forms mostly by internal bog water rather than by surface water bodies. [ABSTRACT FROM AUTHOR]

Climate warming accelerates the global water cycle. However, the relationships between climate warming and hydrological processes in the alpine arid regions remain unclear. Herein, high spatiotemporal resolution sampling of surface water and groundwater was performed at the Qaidam Basin, an extremely arid area in the northeastern Tibetan Plateau. Stable H-O isotopes and radioactive 3H isotopes were combined with atmospheric simulations to examine climate change and hydrogeological characteristics. The surface water heavy isotopes enrich during the wet season and deplete during the dry season. The contribution of precipitation to river discharge was considerably higher in the eastern region of the basin (approximately 45 %) than in the central and western regions (10 %–15 %). The H-O isotopic compositions showed a gradually negative spatial pattern from the west to the east in the Eastern Kunlun Mountains water system; a reverse pattern occurred in the Qilian Mountains water system. This distribution pattern was jointly regulated by the westerly water vapor transport intensity and local hydrothermal conditions. Increased precipitation and cryosphere shrinkage caused by climate warming mainly accelerated basin groundwater cycle. In the eastern and southwestern Qaidam Basin, precipitation and ice/snow meltwater infiltrate structural channels that favor water flow, such as fractures and fissures, facilitating rapid seasonal groundwater recharge and increased terrestrial water storage. However, under future increases in precipitation in the southwestern Qaidam Basin, compensating for water loss from long-term melting of ice and snow will be challenging, and the total water resources may show an initially increasing and then decreasing trend. [ABSTRACT FROM AUTHOR]

A hydro-geochemical characterization was conducted in the northern part of the Sonora River basin, covering an area of 9400 km2. Equipotential lines indicated that groundwater circulation coincided with the surface water flow direction. Based on the groundwater temperature measured (on average ∼21 °C), only one spring exhibited thermalism (51 °C). Electrical conductivity (160–1750 μS/cm), chloride and nitrate concentrations (>10 and >45 mg/L) imply highly ionized water and anthropogenic pollution. In the river network, δ18O values revealed a clear modern meteoric origin. Focused recharge occurred mainly from the riverbeds during the rainy season. During the dry season, diffuse recharge was characterized by complex return flows from irrigation, urban, agricultural, mining, and livestock. Drilled wells (>50 m) exhibited a strong meteoric origin from higher elevations during the rainy season with minimal hydrochemical anomalies. Our results contribute to the knowledge of mountain-front and mountain-block recharge processes in a semi-arid and human-altered landscape in northern Mexico, historically characterized by limited hydrogeological data. [ABSTRACT FROM AUTHOR]

Nitrate stable isotopes provide information about nitrate contamination and cycling by microbial processes. The Fischa-Dagnitz (Austria) spring and river system in the agricultural catchment of the Vienna basin shows minor annual variance in nitrate concentrations. We measured nitrate isotopes (δ15N, δ18O) in the source spring and river up to the confluence with the Danube River (2019–2020) with chemical and water isotopes to assess mixing and nitrate transformation processes. The Fischa-Dagnitz spring showed almost stable nitrate concentration (3.3 ± 1.0 mg/l as NO3–-N) year-round but surprisingly variable δ15N, δ18O-NO3– values ranging from +5.5 to +11.1‰ and from +0.5 to +8.1‰, respectively. The higher nitrate isotope values in summer were attributed to release of older denitrified water from the spring whose isotope signal was dampened downstream by mixing. A mixing model suggested denitrified groundwater contributed > 50 % of spring discharge at baseflow conditions. The isotopic composition of NO3– in the gaining streams was partly controlled by nitrification during autumn and winter months and assimilation during the growing season resulting in low and high δ15N-NO3– values, respectively. NO3– isotope variation helped disentangle denitrified groundwater inputs and biochemical cycling processes despite minor variation of NO3– concentration. [ABSTRACT FROM AUTHOR]

Stable water isotopes in ground-level vapour are key to estimating water exchange between geospheres. Their sampling, however, is limited to laser-absorption spectrometers and satellite observations, having inherent shortcomings. This study investigates diffusive kinetic fractionation during liquid condensation under supersaturated environment, providing a cost-effective, reliable way of sampling ground-level vapour isotopes (18O, 2H). Experiments were undertaken at three locations in India with 'liquid' samples collected from condensation of ambient air at 0°C. Simultaneously, pristine 'vapour' was sampled via cryogenic-trapping using liquid nitrogen–alcohol slush at –78°C. The 'liquid' condensed under supersaturation was progressively more depleted in 18O, and less enriched in 2H than expected under equilibrium fractionation, with an increasing degree of supersaturation expressed as saturation index (Si). This study revealed: (1) Si, molecular density, Rh, T together control the extent of isotopic kinetic fractionation. (2) The presence of diffusive concentration gradient inhibits the flow of heavier isotopes during liquid condensation. (3) The stochastic nature of the process cannot be explained using a physics-based model alone. The artificial neural network model is hence deployed to sample δ18O (δ2H) within –0.24 ± 1.79‰ (0.53 ± 11.23 ‰) of true value. (4) The approach can be extended to ground-validate isotope-enabled general circulation models and satellite observations. [ABSTRACT FROM AUTHOR]

• Ambient and urban groundwater expressed in streamflow for a Precambrian Shield basin. • Elevated Chloride in cold region basin helps identify urban groundwater in streamflow. • Summer urban groundwater can rival ambient groundwater contributions to streamflow. • Fall tracer-based models show less groundwater compared to graphical separation. Groundwater-surface water (GW-SW) interactions are complex phenomena that vary naturally over space and time and are being influenced by environmental change. The Whitson River watershed is a mixed land-use Precambrian shield watershed located in Northeastern Ontario, Canada in which groundwater is a source of municipal water supply and in which groundwater and surface waters are at risk of potential impacts from urban runoff, ongoing municipal drainage projects, periodic flooding, and climate change. This study used watershed-scale synoptic surveys of stable isotopes (δ18O and δ2H) and geochemistry, and corresponding mixing-model approaches (two-component and three-component) to quantify the seasonal and spatial variation in surface water, ambient, and urban groundwater contributions to streamflow. Multiple mixing models were generated based on isotope and geochemical source water identification, and the performance of these models was compared. Mixing-model analyses showed that groundwater contributes a critical, sustaining source to streamflow (> 50 % or more) during summer baseflow conditions, dropping to ∼ 15 % in fall when connection to shield lakes and wetlands dominate. Three-component mixing models showed similar results to the two-component models, refining groundwater contributions into ambient and urban groundwater sources. Estimated urban groundwater contributed 30 % or more to summer baseflow, dropping to ∼ 4 % in the fall. Baseflow estimates derived from graphical hydrograph separation were similar to mixing model groundwater estimates in the summer but suggest this approach overestimates groundwater contributions during the fall. These results demonstrate the complexity of source water contributions to streamflow and the challenges in their determination in mixed-land-use Precambrian Shield landscapes where communities are largely located. Assessment of source water contributions to streamflow across the Whitson River sub-watershed has generated a region-specific conceptualization (e.g. urban versus ambient groundwater) of a basin that is experiencing increased urban development, providing information that will be of value for long term management. [ABSTRACT FROM AUTHOR]

• Grassland hydrodynamics are responding in unexpected ways to concurrent climate change and woody encroachment. • Discharge has declined in recent decades despite > 100 years of climate wetting, suggesting a shift in hydrological connectivity. • Isotope trends indicate that changes in woody cover and climate led to increased contribution of winter precipitation to recharge. In grasslands around the world, climate change is occurring in tandem with woody encroachment (the spread of woody vegetation in grass-dominated ecosystems). State transitions from grassland to shrub/woodland have been identified aboveground via changes in species cover and composition, but the hydrological impact of these transitions is not well understood. Shifts from grass- to woody-dominance have the potential to impact evapotranspiration, soil moisture dynamics, and groundwater recharge. Therefore, it is possible that the consequences of aboveground vegetation change may be observable in the hydrological system. We leveraged long-term hydrological records from a tallgrass prairie site in northeastern Kansas, USA, to examine how concurrent changes in climate and land-cover have altered hydrological dynamics over the last century. Stream discharge has declined in recent decades despite > 100 years of climate wetting. The relationship between incoming precipitation and streamflow has weakened over the last 40 years, suggesting that shifts in the physical landscape are altering patterns of hydrological connectivity. Long-term isotope records show a divergence in the isotopic composition of precipitation (no change in δ18O) and stream/groundwater (decreasing δ18O) over the last decade. These results suggest that woody encroachment is accelerating the hydrological cycle, potentially by decreasing groundwater recharge (via increased evapotranspiration) and/or increasing infiltration rates (via creation of macropores). Holistically, these changes illustrate the interdependence of above- and below-ground processes in the local hydrological cycle, and the cascading long-term consequences (decades to centuries) for critical zone function once woody encroachment has occurred. [ABSTRACT FROM AUTHOR]

Study region: Vltava River basin, South Bohemian Region of the Czech Republic, Central Europe Study focus: To understand the dynamics of nutrients (nitrogen, phosphorus, and organic carbon) in streams, we combined hydrometeorological, hydrochemical and isotopic data (stable water and nitrate isotopes) from three catchments with different predominant land-use effects (forest, agricultural and settlement). New hydrological insights for the study region: Our study underlines that current climate change and associated hydrological changes, such as decrease in flow, play an important role in the transport and dynamics of nutrients in the catchment. We have found that due to the different origins and pathways, individual nutrients had diverse behaviour patterns in streams and responded differently to changing climate. Hydrological patterns in streams became clear when systematic and continuous monitoring under a changing climate was applied, highlighting the need for such data to better understand the impact of hydrological drivers, particularly for long-term dynamics. In three studied catchments, streamflow showed a decreasing trend in line with rising air temperature, declining snow cover and increasing evapotranspiration. Time series analyses of nitrate concentrations revealed decreasing trends, whereas dissolved organic carbon increased in all catchments regardless of land use. Long-term trends of total phosphorus concentrations were positive in anthropogenically impacted streams. Stable nitrate isotopes indicated distinct nitrate sources and processes, but also their seasonality in relation to hydrological patterns and land use.

Improved understanding of catchment‐scale hydrology and nutrient transport in agricultural catchments is needed. Here, the annual young water fraction is determined for three southern Ontario headwater catchments using the stable water isotope δ18O; the dominant event contributions for three streams were also determined using a two‐component isotopic hydrograph separation. On an annual average, Nissouri Creek (loamy soils, high tile drainage) sees the lowest amount of event water, followed by Big Creek (clay soils, high tile drainage) and then North Creek (clay soils, low tile drainage). Event hydrograph separations show Nissouri Creek has significantly higher median amounts of pre‐event water than Big and North Creek during events. These results in indicate soil type may be more influential than tile drainage presence with respect to the contribution of event contributions to total stream flow; specifically, higher contributions of event water occurred in the two clay soil catchments, despite differing tile presence. Antecedent moisture and event characteristics did not uniformly explain the observed pre‐event water contributions for events across all sites, with pre‐event contributions only weakly and positively correlated with discharge at event commencement and negatively with isotopic variability in stream water. The total contribution of pre‐event water during events was significantly correlated with mean event turbidity and the flow‐weighted mean concentrations of dissolved organic carbon, total phosphorus and total dissolved phosphorus, but not total nitrogen or nitrate. The correlations we observed between pre‐event water and water chemistry were stronger than between event size and water chemistry, suggesting isotopic information adds insight that simple hydrometrics are unable to provide. Our results show that event water is responsible for phosphorus loss at the watershed scale, indicating actions targeting fast pathways or targeting pools of phosphorus available to those fast pathways can aid in reducing phosphorus transported by event water. [ABSTRACT FROM AUTHOR]

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This study assessed the chemical composition of major elements and stable isotopes (H and O) in precipitation, groundwater, and surface water in São Francisco 1 (SF1) sub-basin (approximately 14,000 km 2 ), located at the São Francisco River headwater region, fractured aquifer system region with a complex geologic framework. Both groundwater and surface water exhibited low mineral content, with average electrical conductivity of 147.2 ± 99.4 μS.cm -1 and 65.7 ± 78.7 μS.cm -1 , respectively. The ionic abundance (mEq.L -1 ) followed Ca 2+  > Na +  > Mg 2+  > K + for cations and HCO₃ -  > SO₄ 2-  > Cl -  > NO₃ -  > F -  > PO₄ 3- for anions, with most samples being calcic and/or magnesian bicarbonates. Chemical composition was primarily influenced by rock-water interactions and wet-season precipitation in surface water. The isotopic composition of precipitation showed a seasonal pattern, with lower values in the wet season (-63.87 ‰ for δ 2 H and - 9.86 ‰ for δ 18 O) and higher values in the dry season (-5.12 ‰ for δ 2 H and - 2.12 ‰ for δ 18 O). Groundwater remained constant (-43.71 ‰ for δ 2 H and - 6.70 ‰ for δ 18 O), while surface water varied seasonally (-44.95 ‰ for δ 2 H and - 7.07 ‰ for δ 18 O in the wet season, and - 38.12 ‰ for δ 2 H and - 6.14 ‰ for δ 18 O in the dry season), reflecting wet-season precipitation inputs. Consistent groundwater Evaporation Line (EL) slopes across seasons suggest that the recharge was gradual and slow. The Mann-Whitney test for chemical and isotopes tracers pointed out that surface water-groundwater connectivity was present in both seasons, although enhanced in the wet season. In Lower SF1, identical distributions (p = 1) of NO₃ - , δ 2 H and δ 18 O underscore the stronger connectivity and mixing within this compartment. Groundwater was the primary source of streamflow, contributing from 60 % to 85 %, and wet-season precipitation was another source of surface water., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Site-focused hydrogeological studies are often touted as a fundamental requirement for the effective conservation of groundwater-dependent ecosystems (GDEs) as they unveil important detail about processes that threaten groundwater and connected ecosystems. We used a hydrogeochemical and isotopic approach to characterise groundwater source, movement and recharge in a highly complex coastal dune system, the Cooloola Sand Mass, in south-east Queensland, Australia. For a relatively small area (620 km 2 ), Cooloola contains a variety of GDEs including wetlands, fens, lakes, and streams. GDEs within Cooloola are exposed to a myriad of threats including over-abstraction, saltwater intrusion and climatic drying. Conservation approaches are broadly applied to these valuable habitats, where greater hydrological understanding could inform management actions. Major ions, trace elements, stable water isotopes (δ 18 O and δ 2 H) from 83 sites, as well as isotope tracers ( 3 H and 14 C) from 12 sites were used to characterise groundwater sources, movement, recharge processes and estimate mean residence time (MRT). Estimated MRTs ranged from 12 to 100 years, with recharge of the regional aquifer reliant on high monthly rainfall totals (>150-200 mm) associated with La Niña phases across eastern Australia. Results highlight the complex nature of the groundwater system with GDEs depending solely on the regional aquifer, shallow perched aquifers, or a mix of both sources. Each of these sources are exposed to different threats depending on recharge mechanisms, coastal proximity and surrounding land-use., Competing Interests: Declaration of competing interest The authors declare no competing financial interests., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

The insufficient taking into account of groundwater as a basis for implementing protection measures for coastal wetlands can be related to the damage they are increasingly exposed to. The aim of this study is to demonstrate the pertinence of combining hydrogeological tools with assessment of pollutant fluxes and stable isotopes of O, H and N, as well as groundwater time-tracers to identify past and present pollution sources resulting from human activities and threatening shallow groundwater-dependent ecosystems. A survey combining physico-chemical parameters, major ions, environmental isotopes ( 18 O, 2 H, 15 N and 3 H), with emerging organic contaminants including pesticides and trace elements, associated with a land use analysis, was carried out in southern Italy, including groundwater, surface water and lagoon water samples. Results show pollution of the shallow groundwater and the connected lagoon from both agricultural and domestic sources. The N-isotopes highlight nitrate sources as coming from the soil and associated with the use of manure-type fertilizers related to the historical agricultural context of the area involving high-productivity olive groves. Analysis of EOCs has revealed the presence of 8 pesticides, half of which have been banned for two decades and two considered as pollutant legacies (atrazine and simazine), as well as 15 molecules, including pharmaceuticals and stimulants, identified in areas with human regular presence, including rapidly degradable compounds (caffeine and ibuprofen). Results show that agricultural pollution in the area is associated with the legacy of intensive olive growing in the past, highlighting the storage capacity of the aquifer, while domestic pollution is sporadic and associated with regular human presence without efficient modern sanitation systems. Moreover, results demonstrate the urgent need to consider groundwater as a vector of pollution to coastal ecosystems and the impact of pollutant legacies in planning management measures and policies, with the aim of achieving 'good ecological status' for waterbodies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

The objective of this work is to present a long-term dataset of water stable isotopes in rainfall samples from northwestern Mexico. These data is useful to generate a local meteoric water line as a reference tool for atmospheric and ecohydrological studies within the North American Monsoon region and to compare across the globe. This work shows the isotopic variation of the rainfall collected at a permanent location in Ciudad Obregon, Sonora, Mexico (27.511850, -109.956316), between 2014 and 2021. The isotopic composition of 138 rain samples was analyzed for both oxygen (δ18O) and deuterium (δ2H) with laser spectroscopy. The slope of the resulting local meteoric water line was m = 6.59 with an intercept of -1.15 (R² = 0. 91). During the monitored period at the studied region the presence of hurricanes, cold fronts and the hegemony of rainfall attributed to the North American Monsoon is recorded in the dataset.

North-central Ukraine is vulnerable to temperature increases and precipitation pattern changes associated with climate change. With water management becoming increasingly important, information on current water sources and moisture recycling is critically needed. Isotope ratios of oxygen (δ18O) and hydrogen (δ2H) in precipitation are sensitive to these variables and allow comparisons across the region. The δ2H and δ18O values from collected precipitation in Kyiv and Cherkasy in 2020 and published 3H data for Kyiv from the year 2000 show an influence of the North Atlantic Oscillation (NAO) and provide information about processes affecting precipitation along the storm trajectory. The δ18O values also show a correlation with temperature, indicating that precipitation patterns may be affected by the rising temperatures in the region, as predicted by recent regional studies using Representative Concentration Pathway scenarios and the global climate model GFDL-ESM2M. When compared to backtracked storm trajectory and NAO data, clear relationships emerged between water isotope ratios, storm paths, and likely moisture recycling. Overall, δ2H, δ18O, 3H, and backtracked storm trajectory data provide more regional and local information on water vapour processes, improving climate-change-driven precipitation forecasts in Ukraine. [ABSTRACT FROM AUTHOR]

Vegetation plays a significant role in the isotopic fractionation of rainwater during rainfall partitioning through the canopy into throughfall and stemflow. Most studies focus on the isotopic composition of throughfall, whereas that of stemflow has been studied much less frequently. Moreover, only three studies to date have investigated stemflow isotopic composition at the intra‐storm scale. Therefore, knowledge of the isotopic shift between rainfall and throughfall/stemflow at fine resolutions is sorely needed in order to better understand water input to forest soils. In this study, intra‐event rainfall, throughfall and stemflow in a Scots pine forest under Mediterranean conditions were monitored (5‐min time step) over a 20‐month period (May 2018 to December 2019) and water samples of each component were collected sequentially by means of automatic samplers for isotopic analysis (18O and 2H). Results obtained for 21 rainfall events show that throughfall was usually more enriched than rainfall and stemflow was more enriched than throughfall. Isotopic differences between rainfall and throughfall/stemflow indicated that throughfall was more depleted during the higher air temperature season whereas stemflow was more enriched. The isotopic shift did not show any direct relationship with either meteorological variables or the amount effect. At the intra‐storm scale, stemflow was more enriched than rainfall and throughfall at the start of the rainfall event and tended to decrease towards the end. Our results suggest that evaporation led to stemflow enrichment due to stemflow residing longer on the vegetative surfaces than throughfall. However, most fractionation factors can occur during the same event. Our study will improve understanding of the physical processes that control stemflow isotopic composition in coniferous trees before reaching the ground, as a step towards improving isotope‐based models for forest‐water interactions. [ABSTRACT FROM AUTHOR]

Stable water isotopes are invaluable in helping understand catchment functioning and are widely used in experimental catchments, with higher frequency data becoming increasingly common. Such datasets incur substantial logistical costs, reducing their feasibility for use by decision makers needing to understand multi-catchment, landscape-scale functioning over a relatively short period to assess the impact of proposed land use change. Instead, reconnaissance style surveys (high spatial resolution across the landscape at a lower temporal frequency, over a relatively short period) offer an alternative, complementary approach. To test if such sampling could identify heterogeneities in hydrological functioning, and associated landscape controls, we sampled 27 stream sites fortnightly for one year within a peri-urban landscape undergoing land use change. Visual examination of raw data and application of mean transit time and young water fraction models indicated urbanisation, agriculture and responsive soils caused more rapid cycling of precipitation to stream water, whereas mature forestry provided attenuation. We were also able to identify contiguous catchments which functioned fundamentally differently, meaning their response to land use alteration would also be different. This study demonstrated how stable water isotopes can be a valuable, low-cost addition to tools available for environmental decision makers by providing local, process-based information. [ABSTRACT FROM AUTHOR]

Carbonate aquifers are characterised by strong heterogeneities and their modelling is often a challenging aspect in hydrological studies. Understanding carbonate aquifers can be more complicated in the case of strong seismic events which have been widely demonstrated to influence groundwater flow over wide areas or on a local scale. The 2016–2017 seismic sequence of Central Italy is a paradigmatic example of how earthquakes play an important role in groundwater and surface water modifications. The Campiano catchment, which experienced significant discharge modifications immediately after the mainshocks of the 2016–2017 seismic sequence (Mmax = 6.5) has been analysed in this study. The study area is within an Italian national park (Sibillini Mts.) and thus has importance from a naturalistic and socio-economic standpoint. The research strategy coupled long-period artificial tracer tests (conducted both before and after the main earthquakes), geochemical and discharge analyses and isotope hydrology with hydrogeological cross-sections. This study highlights how the seismic sequence temporarily changed the behaviour of the normal faults which act predominantly as barriers to flow in the inter-seismic period, with water flow being normally favoured along the fault strikes. On the contrary, during earthquakes, groundwater flow can be significantly diverted perpendicularly to fault-strikes due to co-seismic fracturing and a consequent permeability increase. The interaction between groundwater and surface water is not only important from the point of view of scientific research but also has significant implications at an economic and social level. [ABSTRACT FROM AUTHOR]