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Understanding the critical thresholds of dissolved oxygen (O2) that trigger adaptive physiological responses in aquatic organisms is long hampered by a lack of robust, non-lethal or non-invasive methodologies. The isotope fractionation of triple O2 isotopes (18O/17O/16O) during respiration is linked to the amount of oxygen utilised, offering a potential avenue for new insights. Our experimental research involved measuring the oxygen isotope fractionation of dissolved O2 in closed-system aquatic respirometry experiments with wild sticklebacks (Gasterosteus aculeatus). These fish were either naturally adapted or experimentally acclimated to hypoxic and normoxic conditions. The aim was to observe their oxygen usage and isotope fractionation in response to increasingly severe hypoxia. Initial observations revealed a progressive 18O enrichment from the preferential uptake of 16O to a dissolved oxygen threshold of 3–5 mg O2 L–1, followed by an apparent reversal in oxygen isotope fractionation, which is mixing of 16O and 17O with the remaining O2 pool across all populations and indicative of a systematic change in oxygen metabolism among the fish. Unexpectedly, sticklebacks adapted to hypoxia but acclimated to normoxia exhibited stronger oxygen isotope fractionation compared to those adapted to normoxia and acclimated to hypoxia, contradicting the hypothesis that hypoxia adaptation would lead to reduced isotope discrimination due to more efficient oxygen uptake. These preliminary experimental results highlight the novel potential of using dissolved O2 isotopes as a non-invasive, non-lethal method to quantitatively assess metabolic thresholds in aquatic organisms. This approach could significantly improve our understanding of the critical oxygen responses and adaptation mechanisms in fish and other aquatic organisms across different oxygen environments, marking a significant step forward in aquatic ecological and physiological research. [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]

Various approaches based on the natural variations of carbon isotopes (14C and 13C) in dissolved inorganic carbon (DIC) are routinely used to study groundwater dynamics and to estimate recharge rates by deriving groundwater ages. However, differences in 14C activities in groundwater samples collected repeatedly from the same wells and discordantly young 14C groundwater ages compared to noble gases led some authors to question the validity of radiocarbon dating. Poor sampling protocols and storage effects (14C contamination) for radiocarbon analysis are a critical factor in explaining age determination discrepancies. We evaluated the impact of storage protocols on carbon isotope exchange with atmospheric carbon dioxide by comparing glass versus standard plastic field sampling bottles for various storage times before radiocarbon and 13C analyses. The 14C bias after 12 months in pre-evacuated glass vials was minimal and within analytical precision. However, storage of DIC samples in plastic sampling bottles led to marked changes in 14C and 13C contents (up to ∼15 pmC and ∼ 5 ‰, respectively, after 12 months), meaning contamination led to younger groundwater age estimations than it should have been. Protocols for sampling and storing DIC samples for radiocarbon using pre-evacuated glass bottles help avoid atmospheric 14CO2 contamination and microbial activity. [ABSTRACT FROM AUTHOR]

Rationale: Stable‐isotope analyses of nitrate (NO3−) in various water sources are crucial for understanding nitrogen pollution and its impact on aquatic ecosystems. We evaluated the accuracy and precision of stable‐isotope analyses of nitrate conducted by international laboratories. Methods: Six samples with nitrate (2 mg L−1 NO3−‐N) were sent to 47 laboratories. The NO3− had a 30–50 ‰ range of δ values for δ15N, δ18O and δ17O. One blind duplicate evaluated reproducibility and the effect of water δ18O. Laboratories used diverse methods to convert nitrate to N2O, N2, CO or O2 for stable‐isotopic measurements (microbial, cadmium, titanium and elemental analysis) and isotope‐ratio mass spectrometry or laser‐based technologies. Results: Thirty‐six international laboratories (83 %) reported results; however, 23 % did not analyze the test samples due to technical difficulties. Of the reporting laboratories, 79 % and 84 % produced accurate δ15N and δ18O results falling within ±0.8 ‰ and ±1.1 ‰ of the benchmark values, respectively. Three laboratories produced only outliers. The duplicate revealed most laboratories gave internally reproducible results at appropriate analytical precision. For δ17O, six laboratories reported results, but 67 % could not reproduce results within their claimed analytical measurement precision. One complication is a lack of nitrate reference materials for δ17O. Conclusions: Analyst experience contributed to better performance, and underperformance was from compromised standards or inappropriate δ range of working reference materials. The stable isotope community must develop new nitrate reference materials for δ15N spanning −20 ‰ to +80 ‰ and new materials for δ17O. [ABSTRACT FROM AUTHOR]

Recently, δ17O and its excess (Δ′17O) have become increasingly significant "triple-oxygen-isotope" indicators of distinctive hydrological processes in hydrology and climatology. This situation mirrors the research regarding δ18O and δ2H in the 1960s towards a solid theoretical base and a surge in application examples and field studies worldwide. Currently, systematic global measurements for δ17O in precipitation are still lacking. As a result, attempts have been made to define a Global δ17O/δ18O Meteoric Water Line (GMWL), often by using regional or local datasets of varying systematicity. Different definitions of the global reference slope (λref) for determining Δ′17O values have been proposed, by ongoing debate around a proposed consensus value of 0.528. This study used worldwide samples archived in the IAEA Global Network of Isotopes in Precipitation (GNIP) to (a) derive a δ17O/δ18O GMWL based on four-year monthly records from 66 GNIP stations, (b) formulate local δ17O/δ18O meteoric water lines (LMWL) for these stations' areas, and (c) evaluate regional and seasonal variations of Δ′17O in precipitation. The GMWL for δ17O/δ18O was determined to be δ′17O = 0.5280 ± 0.0002 δ′18O + 0.0153 ± 0.0013, in keeping with the consensus value. Furthermore, our results suggested that using a line-conditioned 17O-excess is a viable alternative over the global λref in the context of regional hydrology and paleoclimatology interpretations; however, without challenging the global λref as such. [ABSTRACT FROM AUTHOR]