Origin and stability of pit lake water in Baiyinhua, Inner Mongolia, based on hydrochemistry and stable isotopes

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.

The stable isotope hydrology of Sable Island, Nova Scotia, Canada with implications for evaluating the water budget of wild horses

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.

A protocol for distilling animal body water from biological samples and measuring oxygen and hydrogen stable isotopes via cavity ring-down spectroscopy

The application of stable isotope analysis (SIA) to the fields of ecology and animal biology has rapidly expanded over the past three decades, particularly with regards to water analysis. SIA now provides the opportunity to monitor migration patterns, examine food webs, and assess habitat changes in current and past study systems. While carbon and nitrogen SIA of biological samples have become common, analyses of oxygen or hydrogen are used more sparingly despite their promising utility for tracing water sources and animal metabolism. Common ecological applications of oxygen or hydrogen SIA require injecting enriched isotope tracers. As such, methods for processing and analyzing biological samples are tailored for enriched tracer techniques, which require lower precision than other techniques given the large signal-to-noise ratio of the data. However, instrumentation advancements are creating new opportunities to expand the applications of high-throughput oxygen and hydrogen SIA. To support these applications, we update methods to distill and measure water derived from biological samples with consistent precision equal to, or better than, ± 0.1 ‰ for δ17O, ± 0.3 ‰ for δ18O, ± 1 ‰ for δ2H, ± 2 ‰ for d-excess, and ± 15 per meg for Δ17O.

Topographic influence on ecohydrology in volcanic watersheds of the western Pacific monsoon area: evidence from water stable isotope composition of meteoric water, thermal water, and plants

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.

Stable isotope hydrology of surface and ground waters in King George Island, Antarctica

The region around the tip of the Antarctic Peninsula is warming fast, a situation that will lead to widespread changes in local hydrological cycles. King George Island (KGI) hosts a complex network of lakes and rivers, fed by glaciers, snow and rain, and underlain by thick permafrost. We present here the first study of the stable isotope composition of the surface waters in the ice-free southern peninsulas of KGI. Permafrost samples had the highest δ18O and δ2H values (-6.7 and -50 ‰, respectively), and river waters the lowest (-9.1 and -70 ‰, respectively), with groundwater (-8.2 and -62.7 ‰, respectively), lakes (-8.6 and -66.8 ‰, respectively) and (summer) meltwater (-9 and -69.5 ‰, respectively) having intermediary values. Our results suggest that a clear separation of the various water bodies (permafrost, snow, meltwater, lakes) based on the δ18Owater and δ2Hwater is possible. Further, water in lakes on a W-E transect (i.e. with increased distance from the Bellingshausen Sea) have a general tendency towards lower δ18O (and δ2H) values. The results allow for the establishment of a baseline against which ongoing and future changes of the hydrological cycle could be analysed, and past climate changes be reconstructed.

Spatial and meteorological controls of stable water isotope dynamics of precipitation in Kashmir Valley, Western Himalaya, India

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.

Preventing drift of oxygen isotopes of CO2-in-air stored in glass sample flasks: new insights and recommendations

It is known that the oxygen isotope composition of CO2-in-air, when stored over longer time periods in glass sample flasks, tends to drift to more negative values while the carbon isotope composition remains stable. The exact mechanisms behind this drift were still unclear. New experimental results reveal that water already inside the flasks during sampling plays a major role in the drift of the oxygen isotopes. A drying method to remove any water sticking to the inner walls by evacuating the flasks for more than 72 h while heating to 60 °C significantly decreases drift of the oxygen isotopes. Moreover, flasks not dried with this method showed higher differences among drift rates of individual flasks. This is explained through the buildup of H2O molecules sticking to the inner walls. Humidity of the air samples in the flasks as well as surface characteristics will lead to differences among flasks. Results also show that permeability of water is higher through Viton O-ring flask seals than through polychlorotrifluoroethylene (PCTFE) shaft seals, and that the stability of flasks sealed with the latter is significantly better over time.

Automated rapid triple-isotope (δ15N, δ18O, δ17O) analyses of nitrate by Ti(III) reduction and N2O laser spectrometry

The nitrogen and oxygen (δ15N, δ18O, δ17O) stable isotopic compositions of nitrate (N O 3 - ) are crucial tracers of nutrient N sources and dynamics in aquatic and atmospheric systems. Methods to reduce aqueous N O 3 - to N2O gas (microbial or Cd method) before 15N and 18O isotope analyses require multi-step conversion or toxic chemicals, and 17O in N2O cannot be disentangled by IRMS due to isobaric interferences. This technical note describes the automation of the stable-isotope analyses of nitrate by coupling the new Ti method with a headspace autosampler and an N2O triple-isotope laser analyzer based on off-axis integrated cavity output spectroscopy. The automation yielded accurate and precise results for routine determinations of δ15N, δ18O, and δ17O values for aqueous nitrate in environmental waters. Systematic corrections were required for cavity pressure, N2O concentration and water vapour content to obtain the highest precision for all three isotopic ratios. For the first time, an automated laser-based system facilitates routine low-cost triple isotope analyses in studies where high-temporal resolution isotope analyses of NO3- are required but have been, until now, cost-prohibitive and time-consuming (e.g. atmospheric N pollution).

Regional groundwater flow system characterization of volcanic aquifers in upper Awash using multiple approaches, central Ethiopia

ABSTRACTCharacterization 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.

Carbon, nitrogen, and oxygen stable isotope ratios of striped dolphins and short-finned pilot whales stranded in Hokkaido, northern Japan, compared with those of other cetaceans stranded and hunted in Japan

Strandings of striped dolphins (SD) and short-finned pilot whales (PW) in Hokkaido, northern Japan, are rare but have recently increased, probably due to global warming. We quantified δ13C, δ15N, and δ18O in muscles of SD (n = 7) and PW (n = 3) stranded in Hokkaido and compared these values with those in muscles (red meat products) of hunted SD and PW in three areas of central and southern Japan. δ18O in stranded SD, except for the calf, decreased with increasing body length (BL), whereas δ13C increased, with no BL-related changes in δ15N. The variability of δ18O (range of maximum and minimum) was larger in the stranded SD (7.5 ‰) than of the hunted SD in three areas (0.9, 1.9, and 1.4 ‰), whereas that of δ15N was smaller in the stranded SD than in the hunted SD. Similarly, the variability of δ18O was larger in the stranded PW in Hokkaido (3.3 ‰) than in the hunted PW in central Japan (1.4 ‰). The larger variability of δ18O and smaller variability of δ15N in stranded SD imply long-term sojourning in coastal waters and feeding on small amounts of limited prey species at low trophic levels before death.

Nitrate isotopes (δ15N, δ18O) in precipitation: best practices from an international coordinated research project

Stable isotope ratios of nitrogen and oxygen (¹⁵N/¹⁴N and ¹⁸O/¹⁶O) of nitrate (NO₃^-) are excellent tracers for developing systematic understanding of sources, conversions, and deposition of reactive atmospheric nitrogen (N_r) in the environment. Despite recent analytical advances, standardized sampling of NO₃^-) isotopes in precipitation is still lacking. To advance atmospheric studies on N_r species, we propose best-practice guidelines for accurate and precise sampling and analysis of NO₃^- isotopes in precipitation based on the experience obtained from an international research project coordinated by the International Atomic Energy Agency (IAEA). The precipitation sampling and preservation strategies yielded a good agreement between the NO₃^- concentrations measured at the laboratories of 16 countries and at the IAEA. Compared to conventional methods (e.g., bacterial denitrification), we confirmed the accurate performance of the lower cost Ti(III) reduction method for isotope analyses (¹⁵N and ¹⁸O) of NO₃^- in precipitation samples. These isotopic data depict different origins and oxidation pathways of inorganic nitrogen. This work emphasized the capability of NO₃^- isotopes to assess the origin and atmospheric oxidation of N_r and outlined a pathway to improve laboratory capability and expertise at a global scale. The incorporation of other isotopes like ¹⁷O in N_r is recommended in future studies.

Determination of nitrate sources in a karst plateau reservoir based on nitrogen and oxygen isotopes

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.

New insights into diffusive kinetic fractionation during liquid condensation under supersaturated environment: an alternative approach for isotope tagging of ground-level water vapour

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 (S_i). This study revealed: (1) S_i, 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 (δ ²H) 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.

Hydrochemistry and stable isotopes revealed focused and diffuse recharge processes in the Sonora River basin, Mexico

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.

Nitrate isotopes reveal N-cycled waters in a spring-fed agricultural catchment

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.

Stable isotope patterns of German rivers with aspects on scales, continuity and network status

In Germany, river monitoring for tritium started in the early 1970s. Today this monitoring network consists of 50 stations and includes stable isotopes. The stable isotope time series to the end of 2021 are at least four years and for some stations up to 30 years long. Daily river water samples were collected during an extraordinary dry season from October 2018 until end of January 2019 from six selected stations of the Rhine and five stations of the Elbe basin. The most dominating stable isotope effects in river water are the seasonal and altitude effects, but also a continental effect is visible. The isotopes indicate snow and ice melt contributions in the Rhine and Danube during the summer months and a consecutive dilution of these signals by mixing with tributary rivers. Close to the coasts in northern Germany, stable isotope patterns reflect influence of seawater and tides. Daily patterns during the dry season 2018/2019 surprisingly do not exhibit extreme changes but rather trends of enhanced groundwater contribution. Long-term continual data across scales are important for comparing and identifying hydrological processes in German river basins of different size and mean catchment altitudes, and highlight the benefits of a co-organized national network.

Use of isotopes in examining precipitation patterns in north-central Ukraine

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.

Assessing land use influences on isotopic variability and stream water ages in urbanising rural catchments

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.

Quantifying the contribution of evaporation from Lake Taihu to precipitation with an isotope-based method

Moisture recycling plays a crucial role in regional hydrological budgets. The isotopic composition of precipitation has long been considered as a good tracer to investigate moisture recycling. This study quantifies the moisture recycling fractions (f_r) in the Lake Taihu region using spatial variations of deuterium excess in precipitation (d_P) and surface water vapour flux (d_E). Results show that d_P at a site downwind of the lake was higher than that at an upwind site, indicating the influence of lake moisture recycling. Spatial variations in d_P after sub-cloud evaporation corrections were 2.3, 1.4 and 3.2 ‰, and d_E values were 27.4, 32.3 and 31.4 ‰ for the first winter monsoon, the summer monsoon and the second winter monsoon, respectively. Moisture recycling fractions were 0.48 ± 0.13, 0.07 ± 0.03 and 0.38 ± 0.05 for the three monsoon periods, respectively. Both using the lake parameterization kinetic fractionation factors or neglecting sub-cloud evaporation would decrease f_r, and the former has a larger influence on the f_r calculation. The larger f_r in the winter monsoon periods was mainly caused by lower specific humidity of airmasses but comparable moisture uptake along their trajectories compared to the summer monsoon period.

How do precipitation events modify the stable isotope ratios in leaf water at Lhasa on the southern Tibetan Plateau?

Serving as a medium between source water and cellulose, leaf water contributes to the isotope ratios (δ¹⁸O, δ²H) of plant organic matter, which can be used for paleoclimate reconstruction. This study is the first to examine the diurnal variations in the δ¹⁸O and δ²H of leaf water on the southern Tibetan Plateau. The δ¹⁸O and δ²H of leaf water were relatively low when precipitation events occurred. In particular, ¹⁸O and ²H of leaf water became extremely depleted 5 h after the precipitation event. Our findings demonstrate that precipitation can modify the isotope ratios of leaf water from external and internal causes. First, precipitation events affect meteorological elements, lead to decreases in leaf transpiration, and immediately weaken the isotope enrichment of leaf water ('rapid effect' of precipitation). Second, precipitation events affect the internal plant-soil water cycle process, causing the plant to preferentially use deeper soil water, and the corresponding isotope ratios of leaf water exhibit extremely low values 5 h after precipitation events ('delay effect' of precipitation). This study suggests that researchers need to be cautious in separating the signals of precipitation and hydrological processes when interpreting isotope records preserved in tree-ring cellulose archives from the Tibetan Plateau.

Stable hydrogen and oxygen isotope abundance of major bottled water brands sold in the United Kingdom

Bottled water in the UK has a ∼20 % share of the soft drinks market with a sales value of >£1.5 billion. Bottled water is susceptible to fraud and it is important to characterise the chemical signature of aquifers used by the bottled water industry. Measuring ¹⁸O/¹⁶O and ²H/¹H ratios in bottled water is one important step in fraud prevention and aquifer characterisation as these ratios in groundwater tend to be stable or change very slowly through time. Here we characterise the isotopic signature of 30 brands of bottled water sold in the UK. The average δ¹⁸O of bottled waters is -7.4 and -48.4 for δ²H. This isotopic composition is closely related to that of the annual rainfall and follows latitudinal and longitudinal gradients which combine to explain 77 % of the δ¹⁸O variance.

Museum-archived and recent acquisition nitrates from the Atacama Desert, Chile, South America: refinement of the dual isotopic compositions (δ15N vs. δ18O)

Sodium nitrate ores from the Atacama Desert in South America were economically important as they represented huge natural resources for the fertilizer and explosives industries during the early nineteenth to early twentieth centuries. Nitrogen and oxygen isotope ratios (δ¹⁵N and δ¹⁸O) of these desert nitrates generally show unique compositions (from close to 0 and up to ca. +50 ‰, respectively). The nitrates indicate the provenance as atmospheric in origin due to the mass-independent photochemical reaction of nitric oxide (NO) with ozone (O₃) in the atmosphere to produce nitrate (NO₃^-). This paper examines the previously existing isotope data for specimens acquired from the Atacama Desert. It then reports new data from dual isotope analysis of historic nitrate specimens archived in museums in the UK. In the stable isotope signatures for nitrates from two areas of the Atacama Desert, Tarapacá in the north and Antofagasta in the south, were examined, and this analysis enabled a more detailed definition of their isotopic compositional ranges. This improved database is useful for tracing the provenance of the historic nitrates used in gunpowder and saltpetre, and also the cause of nitrate pollution in natural environments for which routine chemistry alone cannot provide the definite evidence for the origin.

Effects of phenotypic variability on the oxygen and hydrogen isotope compositions of grains in different winter wheat varieties

Stable isotope analyses are the leading method for geographic origin determination, especially of plant-based agricultural products. Origin analysis is typically done by comparing a suspicious sample to reference materials with known geographic origin. Reference materials are usually collected at the species level, assuming different varieties of a species to have comparable isotope compositions within a given location. We evaluated whether different phenotypes that are expressed in different varieties of winter wheat (Triticum aestivum L.) influence the oxygen (δ¹⁸O) and hydrogen (δ²H) isotope composition of plant tissue water and organic compounds. We found that mean δ¹⁸O and δ²H values among winter wheat varieties did not differ significantly in leaf water, however, differed significantly in bulk dried grain tissue. The differences in bulk dried grain δ¹⁸O and δ²H values among varieties can be related to differences in phenotypic trait expression among varieties. Despite this substantial phenotypic variability, the overall variability of bulk dried grain δ¹⁸O and δ²H values among varieties was small (SD 0.54 ‰ for oxygen, 3.60 ‰ for hydrogen). We thus conclude that reference materials collected at the species level should be sufficient for geographic origin analysis of winter wheat and possibly other cereals using δ¹⁸O and δ²H values.

Impact of Indian summer monsoon in westerly dominated water resources of western Himalayas

We used stable water isotopes of oxygen and hydrogen to identify and estimate the seasonal contribution of precipitation to the regional hydrology of Sindh and Rambiara catchments of western Himalayas. The different source waters exhibit significant spatio-temporal variations that correspond to the change in seasonal meteorology, precipitation form and moisture sources. The two-component hydrograph separation based on d-excess suggests that the western disturbances (WD) contribute dominantly (76 ± 4 %) to the regional hydrology, compared to Indian summer monsoon (ISM) rainfall (24 ± 4 %). A comparison of d-excess values of WD and ISM indicates the groundwater consists of 90 ± 3 % WD sources and 10 ± 2 % ISM sources, signifying distinct seasonal variations in groundwater recharge sources. The sine wave model results showed that the annual mean residence time (MRT) of groundwater for the Sindh catchment (5.8 ± 0.6 months) is greater than the Rambiara groundwater (3.6 ± 0.5 months). The lower isotope values observed in the river water than in the precipitation suggest its origin from the snowmelt. This study provides valuable insights into the hydrological processes operating in the high altitude Himalayan catchments to facilitate the improved understanding of runoff generation mechanisms and water resource management in future climate change scenarios.

A density functional theory (DFT) study on reduced partition function ratios of oxygen species adsorbed on a Pt19 cluster and oxygen isotope effects

A density functional theory (DFT) computation on oxygen species adsorbed on platinum (Pt) catalyst surfaces has been carried out to elucidate oxygen isotope fractionation observed at the cathode of a polymer electrolyte membrane fuel cell (PEMFC). The Pt(111) catalyst surface was modelled by a Pt₁₉ cluster, and O, OH, OHH, OO, OOH, OHOH and HOHOH were assumed to be the oxygen species adsorbed on the Pt(111) surface. The oxygen isotope reduced partition function ratios (RPFRs) of the adsorbed species were calculated using the vibrational frequencies obtained by normal mode analyses performed on the optimized structures. Various oxygen isotope exchange equilibria among the adsorbed oxygen species and oxygen and water molecules in the gas phase were examined using their RPFRs. Experimental observation that the lighter ¹⁶O is enriched in water molecules exhausted from the cathode is explainable in a satisfactory manner by assuming oxygen isotope exchange equilibria of O₂ molecule with O, OH, OO and OOH adsorbed on the Pt(111) surface that appear in the first half of the conversion reaction from O₂ to H₂O and those of H₂O molecule with the adsorbed oxygen species, OHH, OHOH and HOHOH, formed in the latter half of the conversion reaction.

The evolution of hydrochemical and isotopic signatures from precipitation, surface water to groundwater in a typical karst watershed, Central Texas, USA

The Upper Cibolo Creek (UCC) karst watershed in Central Texas, USA, represents a portion of the drainage area that supplies water to the recharge zone for the Edwards Aquifer. However, the surface water-groundwater interactions along the UCC are not well quantified, and the hydraulic interactions are important for water budget and water quality of the aquifer. In this study, we investigated the evolution of hydrochemical and isotopic signatures (δ¹⁸O, δ²H and d-excess) from precipitation, surface water to groundwater in the UCC watershed from 2017 to 2019, and investigated surface water-groundwater interactions using samples from 14 creeks/spring sites. Factor analysis for the observed parameters demonstrates that changes in water hydrochemistry are primarily controlled by human activity, precipitation input, and water-rock interaction. Hierarchical clustering analysis of temporal isotope variations confirms that significant surface water-groundwater interactions occur in the UCC watershed. We identified relationships between nitrate concentrations at creek/spring sites and land-use conditions, and nitrate input sources were determined utilizing the dual-isotope analyses (δ¹⁵N and δ¹⁸O) of nitrate. This study provides capacity for a more precise assessment of water resources and water quality in Central Texas.

Preparation of high-precision CO2 with known triple oxygen isotope for oxygen isotope analysis

The objective of this work is to propose a more effective way to prepare an in-house CO₂ with known triple oxygen isotope compositions. The major experimental steps include: (1) the O₂ is combusted to CO₂ on a graphite rod at 750 °C with Pt-catalyst for 3-4 min; and (2) converted CO₂ is subsequently purified by two cryogenic traps. The results show high reproducibility of δ¹³C and δ¹⁸O values of the converted CO₂ within 0.010-0.020 ‰ and 0.006-0.010 ‰ (1σ, SD), and the identical δ¹⁸O value within error with that of the original O₂. Additionally, we have measured the triple oxygen isotope compositions of converted CO₂ using an O₂-CO₂ Pt-catalyzed oxygen-isotope equilibration method. The measured δ¹⁷O values of CO₂ show high reproducibility within 0.006 ‰ (1σ, SD), and are identical within error with the original O₂ as well. Notably, our experiments also found that the O₂ with heavier oxygen isotope ratios (δ¹⁸O > 40 ‰, VSMOW) might have a lesser conversion efficiency, and this effect, combined with the lighter isotope preferential fractionations during the reaction processes of O₂ to CO and CO to CO₂, may explain the observed lower ¹⁷O/¹⁶O and ¹⁸O/¹⁶O ratios of the converted CO₂ relative to the original O₂.

Spatial distribution of stable isotopes (18O and 2H) in precipitation and groundwater in Iran

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.

First conceptual hydrogeological model of two intermountain Andean basins based on isotopes and hydrochemistry

Mountains arid environments are vulnerable under climate change scenarios. Variations in the recharge sources and the rising temperature can affect the water availability, threaten the socio-productive systems on local and regional scales. In this sense, two hydrological systems were studied in the Andes Range, Argentina, by hydrochemical and isotope techniques, with the purpose to understand the origin of water, the groundwater recharge, and to conceptualize the groundwater flow system. In the two sampling periods (winter and summer seasons) most of the waters were characterized by low mineralization and a HCO₃-Ca type. The isotopic composition showed wide ranges of variation consistent with the altitudinal differences existing in the study systems. However, no significant isotope changes were observed between the samples collected in winter and summer periods. Therefore, little influence of liquid precipitation is inferred in the recharge source of both hydrological systems. This means that the western sector of the valley, where the ice bodies and permafrost are located, is the main recharge area for groundwater of both basins. This confirms the former hypothesis used for the hydrogeochemical conceptual model proposed, and highlights the importance of protecting these environments to ensure the provision of water in arid lands.

Spectroscopic investigation of hydrogen and triple-oxygen isotopes in atmospheric water vapor and precipitation during Indian monsoon season

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.

Quantifying nitrate pollution sources of the drinking water source area using a Bayesian isotope mixing model in the northeastern suburbs of Beijing, China

Nitrate pollution has become an environmental problem of global concern. One effective way for controlling the nitrate pollution of water is to identify the pollution source and reduce the input of nitrate. This study traces and quantifies the sources of nitrate contamination to groundwater and surface water in the northeastern suburbs of Beijing, where an emergency groundwater source zone is located. Nitrogen and oxygen stable isotope analysis, geospatial analysis techniques, principal component analysis, correlation analysis, and a Bayesian isotope mixing model were used to achieve our goals. The results show that the main sources of nitrate pollution in groundwater were manure and sewage (M&S) (42.6 %) > soil nitrogen (SN) (26.6 %) > NH4+ in fertilizer and rain (NHF&R) (24.5 %) > NO3- fertilizer (NOF) (5.0 %) > NO3- in atmospheric deposition (NAD) (1.3 %), and main sources of nitrate in surface water were M&S (28.8 %) > SN (20.4 %) > NAD (19.8%) > NOF (16.5%) > NHF&R (14.5 %). Due to the high permeability of the aquifer in the study area, there was a strong hydraulic connection between groundwater and surface water. The discharge of treated wastewater (reclaimed water) into the mostly dried river channel in the study area might aggravate nitrate pollution in the groundwater.

The stable isotope composition of hoarfrost

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.

Stable isotopes reveal groundwater to river connectivity in a mesoscale subtropical watershed

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.

Assessment of multiple stable isotopes for tracking regional and organic authenticity of plant products in Hesse, Germany

As demand for regional and organically produced foodstuff has increased in Europe, the need has arisen to verify the products' origin and production method. For food authenticity tracking (production method and origin), we examined 286 samples of wheat (Triticum aestivum), potatoes (Solanum tuberosum), and apples (Malus domestica) from different regions in Germany for their stable isotope compositions of oxygen, hydrogen, carbon, nitrogen and sulphur. Single-variate authentication methods were used. Suitable isotope tracers to determine wheat's regional origin were δ¹⁸O and δ³⁴S. δ¹³C helped to distinguish between organic and conventional wheat samples. For the separation of the production regions of potatoes, several isotope tracers were suitable (e.g. δ¹⁸O, δ²H, δ¹⁵N, δ¹³C and δ³⁴S isotopes in potato protein), but only protein δ¹⁵N was suitable to differentiate between organic and conventional potato samples. For the apple samples, ²H and ¹⁸O isotopes helped to identify production regions, but no significant statistical differences could be found between organically and conventionally farmed apples. For food authenticity tracking, our study showed the need to take the various isotopes into account. There is an urgent need for a broad reference database if isotope measurements are to become a main tool for determining product's origin.

The Continental Intercalaire groundwaters of the Tidikelt (In-Salah region, Algeria). Hydrochemical and isotopic features

The Continental Intercalaire (CI) groundwaters of the Tidikelt (In-Salah region) are characterized by a high salinity and ion concentrations higher than the maximum standards for drinkability. The total dissolved solids range from 850 to 3390 mg L^-1 for conductivities ranging from 1470 to 6780 μS cm^-1. Their chemical facies is dominated by Cl^-, SO₄^2- and Na⁺, respectively. Alkali ions, Cl^- and SO₄^2- are acquired through the dissolution of Halite (NaCl) and Gypsum (CaSO₄, 2H₂O). CI waters have depleted δ values for ¹⁸O and ²H, corresponding to a cold end-member. This is an indication of a very homogeneous aquifer which is similar to what was observed for the CI in the eastern sub-basin (Great Oriental Erg) and for palaeowaters elsewhere in the Middle-East and Libya. Tritium analyses show that these waters are all very weakly tritiated, which is a testimony of the non-renewed character for these waters. Both δ¹³C and ¹⁴C measured on more than a dozen of samples also show that CI groundwaters are old, with ages comprised between 19,000 and 35,000 years with an average δ¹³C of -10 ‰. This means that these waters are derived from old precipitation whose features were totally different from the very scarce prevailing ones.

Organic contamination in online laser-based plant stem and leaf water isotope measurements for pre-extracted samples

Water stable isotopes have been widely used as natural tracers to investigate soil-plant-atmosphere interactions. Recent developments in induction module cavity ring-down spectroscopy (IM-CRDS) have made it possible to rapidly complete isotope analyses, and to combust co-extracted organic compounds at the same time. However, the agreement between IM-CRDS and isotope ratio mass spectrometry (IRMS) analyses has generally been poor and was primarily attributable to spectral interference of IM-CRDS. Here we evaluated the impacts of organic contamination on the isotope ratios using IM-CRDS with two different methods. No spectral interference was observed for solid samples measured directly by IM-CRDS, whereas clear organic contamination occurred in isotope analyses for pre-extracted plant stem and leaf samples. Our results demonstrate that IM-CRDS can fully combust co-extracted organic compounds by in-line oxidation in the direct measurement of solid samples, although this may not guarantee that the IM-CRDS can obtain better isotopic data than IRMS. It may be risky to evaluate the performance of IM-CRDS by measuring pre-extracted water samples because cryogenic vacuum distillation is likely to introduce extra organic compounds, which may not be fully removed during subsequent IM-CRDS measurement. In addition, spectral variables are useful for post-processing corrections.

Triple-isotope calibration of in-house water standards supplemented by determination of 17O content of USGS49-50 reference materials using cavity ring-down laser spectrometry

The procedure of calibrating in-house water standards suitable for routine analyses of triple-isotope composition of water samples using Picarro L2140-i CRDS analyser is presented and discussed. Such standards are indispensable for achieving and maintaining high quality of isotope analyses of water in terms of their precision and accuracy. A set of seven different water standards consisting of three in-house standards and four secondary standards commercially available was calibrated against VSMOW2/SLAP2 primary reference materials. The calibrated standards cover a wide range of isotopic composition, with δ values ranging from close to zero to the values comparable with SLAP2. The apparent consistency of the calibrated values of δ²H, δ¹⁸O and d-excess with corresponding certified values for commercially available USGS47-50 standards and the consistency of the calibrated values of δ¹⁷O and Δ¹⁷O with its literature values for USGS47-48 standards confirm the high quality of the performed calibration. Moreover, the calibration exercise allowed to obtain δ¹⁷O and Δ¹⁷O values for USGS49 and USGS50 standards, not reported so far.

The impact of temperature on the water isotope (2H/1H, 17O/16O, 18O/16O) fractionation upon transport through a low-density polyethylene membrane

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.

18Oxygen Substituted Nucleosides Combined with Proton Beam Therapy: Therapeutic Transmutation In Vitro

Purpose

Proton therapy precisely delivers radiation to cancers to cause damaging strand breaks to cellular DNA, kill malignant cells, and stop tumor growth. Therapeutic protons also generate short-lived activated nuclei of carbon, oxygen, and nitrogen atoms in patients as a result of atomic transmutations that are imaged by positron emission tomography (PET). We hypothesized that the transition of ¹⁸O to ¹⁸F in an ¹⁸O-substituted nucleoside irradiated with therapeutic protons may result in the potential for combined diagnosis and treatment for cancer with proton therapy.

Materials and Methods

Reported here is a feasibility study with a therapeutic proton beam used to irradiate H₂¹⁸O to a dose of 10 Gy produced by an 85 MeV pristine Bragg peak. PET imaging initiated >45 minutes later showed an ¹⁸F decay signal with T_1/2 of ∼111 minutes.

Results

The ¹⁸O to ¹⁸F transmutation effect on cell survival was tested by exposing SQ20B squamous carcinoma cells to physiologic ¹⁸O-thymidine concentrations of 5 μM for 48 hours followed by 1- to 9-Gy graded doses of proton radiation given 24 hours later. Survival analyses show radiation sensitization with a dose modification factor (DMF) of 1.2.

Conclusions

These data support the idea of therapeutic transmutation in vitro as a biochemical consequence of proton activation of ¹⁸O to ¹⁸F in substituted thymidine enabling proton radiation enhancement in a cancer cell. ¹⁸O-substituted molecules that incorporate into cancer targets may hold promise for improving the therapeutic window of protons and can be evaluated further for postproton therapy PET imaging.

Stable isotopic composition of precipitation in a tropical rainforest region of the Niger Delta, Nigeria

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.

Effect of the El Niño-Southern Oscillation on hydrogen and oxygen isotope ratios of precipitation in Guilin, SW China

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.

Evaporation loss along the Calueque-Oshakati Canal in the Cuvelai-Etosha Basin (Northern Namibia): evidence from stable isotopes and hydrochemistry

Since 1973, Kunene River water has been carried from the Calueque reservoir in Angola along a 160 km open concrete canal to the town of Oshakati in the central part of the Cuvelai-Etosha Basin and has been supplying drinking water to the most densely populated rural area of Namibia. Despite its importance for the region, intra-seasonal water quality and the technical condition of the canal are not routinely checked. Water samples were collected during four field campaigns right before the onset of the rainy season (November 2013 and 2014), and after the rainy season (June 2014 and May 2015), at 16 sites along the canal for stable water isotopes (deuterium, oxygen-17 and oxygen-18) and hydrochemical analyses. The isotope patterns and chemical composition of the canal water is discussed in comparison to local rain, Kunene source water, surface water and groundwater. Clear isotope enrichment indicates evaporative loss of water. A Craig-Gordon model was used to estimate water loss. The loss increases with distance from the source with a maximum of up to 10 %, depending on the season. The results are discussed in context of water availability, vulnerability and water resources management in this water-scarce area.

Environmental isotope characteristics of water sources in the Sokoto Basin - an evaluation of the role of meteoric recharge and residence time

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.

Oxygen-18 and Carbon-13 isotopes in eCO2and erythrocytes carbonic anhydrase activity of Finnish prediabetic population

Complex human physiological processes create the stable isotopic composition of exhaled carbon dioxide (eCO2), measurable with noninvasive breath tests. Recently, isotope-selective breath tests utilizing natural fluctuation in 18O/16O isotope ratio in eCO2 have been proposed for screening prediabetic (PD) individuals. It has been suggested that 18O/16O fractionation patterns reflect shifts in the activity of carbonic anhydrase (CA), an enzyme involved in the metabolic changes in the PD state. To evaluate the applicability of the breath sampling method in Finnish PD individuals, breath delta values (BDVs, ‰) of 18O/16O (δ18O) were monitored for 120 min in real-time with a high-precision optical isotope ratio spectrometer, both in the fasting state and during a 2-hour oral glucose tolerance test (2h OGTT) with non-labelled glucose. In addition, the BDV of 13C/12C (δ13C) was measured, and total erythrocyte CA activity was determined. δ18O and CA did not demonstrate any statistically significant differences between PD and non-diabetic control (NDC) participants. Instead, δ13C was significantly lower in PD patients in comparison to NDCs in the fasting state and at time points 90 and 120 min of the 2h OGTT, thus indicating slightly better potential in identifying Finnish PD individuals. However, overlapping values were measured in PD participants and NDCs, and therefore, δ13C cannot be applied as a sole measure in screening prediabetes at an individual level. Thus, because the combination of environmental and lifestyle factors and anthropometric parameters has a greater effect on glucose metabolism and CA activity in comparison to the PD state, 18O/16O and 13C/12C fractionations or CA activity did not prove to be reliable biomarkers for impaired glucose tolerance in Finnish subjects. This study was conducted under the clinicaltrials.gov ID NCT03156478.

Application of isotope techniques to enhance the conceptual hydrogeological model and to assess groundwater sustainability in the Pampean plain in Córdoba, Argentina

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.

Geochemical evolution, residence times and recharge conditions of the multilayered Tubarão aquifer system (State of São Paulo - Brazil) as indicated by hydrochemical, stable isotope and 14C data

The Tubarão aquifer system constitutes a very complex, multilayered aquifer enclosed in the Paraná basin (central-southern part of Brazil). Despite the relatively low productivity of wells, groundwater represents an important source of water for the very populated and industrialized zones of the State of São Paulo. An extensive water sampling campaign was carried out followed by hydrochemical and isotopic (δ ²H, δ ¹⁸O, δ ¹³C and ¹⁴C) studies, aiming at a better understanding of the aquifer's geochemical evolution, recharge processes, and its groundwater residence times. Two main hydrochemical facies were recognized and divide the aquifer in two portions. The shallow portion - the active hydrological zone of the aquifer - is characterized by the Ca-HCO₃ water type, evolving as a system open to atmospheric CO₂. Mean residence times are typically lower than 5000 years. The lower portion is mostly characterized by the stagnant, Na-HCO₃ water type, evolving under closed system conditions. Residence times average up to 15,000 years, but can reach 44,000 years, which indicates the exploitation of (possibly non-renewable) fossil waters. This study contributes to the establishment of proper policies regarding the sustainable groundwater exploitation of the Tubarão aquifer system.

Water isotopes and chemical tools for understanding pesticide transfer in a watershed of the volcanic island of Martinique (French West Indies)

Monitoring of water quality over several years has revealed a persistent pesticide contamination of surface and groundwater in several Caribbean Islands, with pesticide concentrations locally over the drinking-water limit set in Europe, i.e. 0.1 µg L^-1 per substance. For Martinique, mainly one pesticide, chlordecone (CLD), remains of major concern despite its withdrawal from the market in 1993. Since the first sampling campaign in 1999-2000, time and space variations of CLD concentrations in surface water and groundwater are still not well understood and difficult to correlate with climate, geological or hydrogeological contexts. We carried out a study in the Chalvet catchment (northeast Martinique) in order to understand more precisely how water movements may explain pesticide transfer. Various tools such as δ²H - δ¹⁸O and chemical parameters were used. Deuterium excess d was proven relevant for determining how CLD is transported in groundwater; it highlighted the role of the groundwater/surface water interaction in spatial and temporal variability of surface water quality. The resulting conceptual hydrogeological model also helps understanding why CLD still has high concentrations in surface water. The approach proposed here can be used in other Caribbean islands that are poorly equipped for explaining pesticide occurrences in surface waters.

Water exchange processes estimation in a temperate shallow lake based on water stable isotope analysis

The estimation of lake hydrological characteristics such as evaporation/inflow ratios and water residence time becomes necessary for understanding cycling and potential retention of natural and anthropogenic substances into the lake. The aim of this work was to estimate the evaporation loss and the water residence time of a temperate shallow lake based on the water isotope mass balance approach. One representative freshwater temperate shallow lake from the Argentinian Pampa Plain was selected. Groundwater, lake and stream samples (N = 56) were collected for δ ²H-H₂O and δ ¹⁸O-H2O determinations. Moreover, water level fluctuations of the lake and its inflow stream were recorded with data loggers. Both the δ ²H and δ ¹⁸O relationship and d-excess of lake water indicated evaporation. Water isotopes and daily stream flow data recorded in the inflow stream evidenced groundwater contribution to Los Padres Stream. Monthly evaporation as a fraction of inflow estimations of the lake water indicated that about 20-25 ± 12% lake water was lost through lake surface evaporation and revealed that hydrologic balances were regulated mainly by changes in water inflow rather than evaporation. A mean residence time of 1.11 ± 0.65 year was also calculated. This lake hydrological information is relevant for the region and crucial to improve water management plans.

Use of environmental isotopes to assess groundwater pollution caused by agricultural activities

This work applied environmental isotope techniques to validate the results of previous studies on recharge sources in a rural area in central Chile (34.3° S and 71.3° W) and discern the origin of nitrate contamination in wells. Stream water and groundwater samples were taken during three surveys, two during spring snowmelt and one in low-water conditions. Chemical analyses included major cations and anions, isotope analyses included ¹⁸O-H₂O; ²H-H₂0; ³H-H₂0; ¹⁸O-NO₃ ^- and ¹⁵N-NO₃ ^-. The stable isotope data show that surface water and deep groundwater present depleted isotope values associated with recharge from the Andes Mountains and that shallow groundwater has more enriched isotope values that reflect the contribution of local recharge from rainwater infiltration. Depleted isotope values observed in shallow groundwater show the effect of recirculated river water used for irrigation. These results are consistent with the conceptual groundwater model developed in previous studies. Some wells have nitrate concentrations above the allowable limit for drinking water. The stable nitrogen isotopes indicate that nitrate is associated mainly with urea and ammoniacal fertilizers, and nitrate is attenuated by denitrification. The results of this study are relevant to improving management of groundwater resources used for drinking water.

Isotopic composition and hydrogeochemistry of a periglacial Andean catchment and its relevance in the knowledge of water resources in mountainous areas

Glacial and periglacial basins contain the largest reserves of fresh water in the world. These areas are extremely sensitive to global warming and climate change. The dry Andes of South America are characterized by large periglacial areas. This study focuses on the water isotopic composition and hydrochemistry of a typical periglacial environment of the Andes, in the Vallecitos catchment (2400-5500 m a.s.l.), Cordillera Frontal, Argentina. Detailed fieldwork was conducted between 2013 and 2017 with 240 samples collected for major ions and physicochemical parameters, and 67 samples analysed for ²H and ¹⁸O. The chemical composition of precipitation is typical Ca-HCO₃, while streams and groundwaters are Ca-MgSO₄ type. The isotope content of precipitation shows a wide dispersion. The snow samples are in general more depleted than the rainfall. Some springs vary their composition seasonally, associated to the melting of perennial snow patches. In general, all samples from the upper basin present depleted isotope contents related to recharge at higher altitudes, whereas samples from the lower basin show more enriched values. Intermediate compositions reflect the melting of snow and degrading ice-rich permafrost. These results will give a better understanding of the dynamics of water to manage water resources.