Cultural eutrophication is the leading cause of water quality degradation worldwide. The traditional monitoring of eutrophication is time-consuming and not integrative in space and time. Here, we ...examined the use of carbon (δ13C) and nitrogen (δ15N) isotopic composition to track the degree of eutrophication in a bay of Lake Titicaca impacted by anthropogenic (urban, industrial and agricultural wastewater) discharges. Our results show increasing δ13C and decreasing δ15N signatures in macrophytes and suspended particulate matter with distance to the wastewater source. In contrast to δ15N and δ13C signatures, in-between aquatic plants distributed along the slope were not only affected by anthropogenic discharges but also by the pathway of carbon uptake, i.e., atmospheric (emerged) vs aquatic (submerged). A binary mixing model elaborated from pristine and anthropogenic isotope end-members allowed the assessment of anthropogenically derived C and N incorporation in macrophytes with distance to the source. Higher anthropogenic contribution was observed during the wet season, attributed to enhanced wastewater discharges and leaching of agricultural areas. For both seasons, eutrophication was however found naturally attenuated within 6 to 8 km from the wastewater source. Here, we confirm that carbon and nitrogen stable isotopes are simple, integrative and time-saving tools to evaluate the degree of eutrophication (seasonally or annually) in anthropogenically impacted aquatic ecosystems.
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•C and N stable isotopes were measured in four compartments of Lake Titicaca.•Anthropogenic discharge affects baseline C and N isotope signatures.•C recycling from soil, anthropogenic and lacustrine sources affect the δ13C signature.•δ15N signatures track anthropogenic contamination independently of plant type.•Decreased anthropogenic contribution in the bay assessed by isotope mixing model.
The development of the isotopic niche, an n-dimensional hypervolume (with n being the number of isotopes) occupied by a population in delta space, has revolutionized the study of animal interactions ...in wild populations. While the isotopic niche offers a useful means to understand interactions at many ecological resolutions (e.g., individual, population, community, ecosystem), a variety of intrinsic and extrinsic factors drive isotopic variability and influence the ultimate geometry of observed niche dimensions. Here, we provide an updated synthesis to guide the application of bulk stable isotope ratios to study ecological niches. We summarize progress in the application of bulk stable isotope ratios for evaluating niches to synthesize a formal definition of the isotopic niche. We identify six broad categories to describe drivers of isotopic variance introduced by the animal, its environment, and the researcher, and provide recommendations to account for such variations before, during, and after sample collection and data analyses. Our synthesis illustrates the considerations that should be made before employing the isotopic niche to broader ecological contexts, and offers guidance for the use and interpretation of isotopic niche dynamics in future studies.
We report the first Ni and Cr stable isotope data for ureilite meteorites that are the mantle residue of a carbon‐rich differentiated planet. Ureilites have similar Ni stable isotope compositions as ...chondrites, suggesting that the core‐mantle differentiation of ureilite parent body (UPB) did not fractionate Ni isotopes. Since the size of Earth is potentially larger than that of UPB; with diameter >690 km), resulting in higher temperatures at the core‐mantle boundary of Earth, it can be predicted that the terrestrial core formation may not directly cause Ni stable isotope fractionation. On the other hand, we also report high‐precision Cr stable isotope composition of ureilites, including one ureilitic trachyandesite (ALM‐A) that is enriched in lighter Cr stable isotopes relative to the main‐group ureilites, which suggests that the partial melting occurred on UPB. The globally heavy Cr in the UPB compared to chondrites can be caused by sulfur‐rich core formation processes.
Plain Language Summary
The stable isotope fractionation of siderophile elements is robust to trace the planetary core formation processes. However, whether nickel (Ni) isotopes fractionate during the core formation is highly debated, since the origin of Ni stable isotope difference between bulk silicate Earth and chondrites is not clear. Here, we report high‐precision Ni stable isotope data (expressed as δ60/58Ni, the per mil deviation of Ni60/Ni58 ratios relative to NIST SRM 986) for ureilite meteorites that come from the mantle of a carbon‐rich differentiated body. Ureilites have an average δ60/58Ni value of 0.26 ± 0.13‰ (2SD, N = 22) that is highly consistent with that of chondrites with δ60/58Ni = 0.23 ± 0.14‰ (2SD, N = 37), which suggests that planetary core formation does not effectively fractionate Ni stable isotopes. There is a ureilite trachyandesite that enriches lighter Cr stable isotopes (δ53Cr = −0.11 ± 0.02‰; δ53Cr as the per‐mil deviation of Cr53/52Cr ratios relative to NIST SRM 979) relative to the main‐group ureilites (δ53Cr = −0.05 ± 0.04‰; 2SD, N = 10), which suggests that the partial melting occurred on ureilite parent body (UPB). The globally heavy Cr in the UPB compared to chondrites can be caused by sulfur‐rich core formation processes.
Key Points
Planetary magmatic processes do not fractionate Ni stable isotopes
Ureilite parent body (UPB) has similar δ60/58Ni values as chondrites, and Earth's core formation does not fractionate Ni stable isotopes
Cr stable isotopes recorded partial melting and sulfur‐rich core formation on UPB
Variability in C and N stable isotopes has been acknowledged to hinder their use as tracers of food sources in the study of trophic interactions in ecosystems. This is particularly so whenever ...benthic primary production is substantial (variability in δ13C) and the ecosystem under study is affected by human impacts (variability in δ15N) in aquatic ecosystems.
In this study, we aim to better understand the large and often unexplained variability in the natural abundance of δ13C and δ15N signatures of aquatic plants by analyzing the isotopic composition of plants from 81 lentic systems from NE Spain in relation to extrinsic (alkalinity, pH, nutrient concentrations, water body typology and basin land use) and intrinsic (functional group, carbon assimilation metabolism, elemental composition) predictors.
We have encountered significant plasticity in isotopic signatures of aquatic plants associated with the variation in local conditions at the regional scale. The δ13C signature varied from −43.1‰ to −7.5‰ (35.7‰ range) and drivers were both intrinsic and extrinsic. The functional group was the most important factor as it is influenced by different carbon sources. Aquatic plants with leaves in contact with the atmosphere (helophytes, free floating and floating attached; −34.8‰ to −14.6‰) responded in a similar way as terrestrial plants. This contrasted with the enriched mean values of rooted submerged plants (−16.7‰ to −10.5‰) that were more enriched than the described terrestrial C3 range (−34‰ to −22‰) and completely overlapped the terrestrial C4 range (−20‰ to −8‰). Concentration of DIC and pH also emerged as important extrinsic factors driving δ13C variability.
The δ15N signature ranged from −5.2‰ to 20.1‰ (25.2‰ range) and the variability was mostly associated with extrinsic factors such as water body type and basin land use, as they influence both the δ15N signature and concentration of the dissolved inorganic nitrogen in the aquatic ecosystems.
Only one multifactorial model including the functional group (with the largest contribution), DIC and pH was selected as the best model explaining the variability in δ13C signatures of aquatic plants. The final model had a relatively large explained deviance and was consistent with the previous unifactorial results. Two different models were selected as the best models explaining variability in δ15N signatures of aquatic plants. The models included the geomorphological type of water body as the variable with the largest contribution, and the percentage of either natural or agricultural coverage in the basin. These results are summarized in a conceptual model showing the predictors and their range and direction of variation.
This study shows that extrinsic factors are of greater importance in influencing the stable‐isotope signatures of aquatic plants compared to terrestrial plants, because of varied sources and an often limited isotopic discrimination.
The investigation of leachate leakage at numerous landfill sites is urgently needed. This study presents an exploration of environmental tracing methods using δ2H and δ13C-difference in dissolved ...carbon (δ13CDIC-DOC) to localize leachate leak points at landfill sites. δ2H, δ13CDIC, δ13CDOC, δ18O, and an array of physicochemical indices (e.g., total dissolved solids, temperature, and oxidation reduction potential) were monitored in both leachate and groundwater from different zones of a landfill site in China during the year of 2021–2023. Moreover, data for these parameters (i.e., the isotopic composition and physicochemical indices) from twelve published landfill cases were also collected, and these groundwater/leachate data points were located within 1 km away from the landfill boundary. Then statistical analyses, such as Pearson correlation analysis and redundancy analysis (RDA), were performed using both the detected and collected parameters at landfill sites. Consequently, the intensity of interaction between leachate and background groundwater was found to significantly control the isotopic fractionation features of hydrogen and carbon, and both the content of major contamination indicators (total dissolved solids, chemical oxygen demand, and ammoniacal nitrogen) and the oxidation reduction potential were the key impact factors. Accordingly, the water type used to indicate leachate leakage points was determined to be leachate that significantly interacted with the background groundwater or precipitation (LBGP). δ2H showed a perfect linear correlation (0.81 ≤ r2 < 1.0) with δ13CDIC-DOC in leachate under highly anaerobic landfill conditions, and the δ2H &δ13CDIC-DOC combinations in the LBGP were significantly different from those in the other water types. For groundwater with total dissolved solids lower than 1400 mg/L at landfill sites, a strong positive linear correlation (r = 0.83) was revealed between δ13CDIC and δ13CDOC. Based on these insights, δ2H versus δ13CDIC-DOC plots and RDA using δ2H and δ13CDIC-DOC as response variables were proposed to localize leak points at both lined landfills and leachate facilities. These findings further understanding of the isotopic fractionation features of hydrogen, carbon, and oxygen and provide novel environmental tracer methods for investigating leachate leak points at MSW landfill sites.
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•δ2H &δ13CDIC-DOC plot was proposed to trace leachate leaks at landfill sites.•RDA based on δ2H &δ13CDIC-DOC was used to trace leachate leaks at landfill sites.•Isotopic fractionation features of H, CDIC, CDOC, and O at landfill sites were revealed.•Waters around leachate leak points showed specific isotopic composition.•Controlling factors on isotopic fractionation of H and C at landfills were explored.
Debates persist about the interpretations of stable isotope based proxies for the surface uplift of the central–northern Tibetan Plateau. These disputes arise from the uncertain relationship between ...elevation and the δ18O values of meteoric waters, based on modern patterns of isotopes in precipitation and surface waters. We present a large river water data set (1,340 samples) covering most parts of the Tibetan Plateau to characterize the spatial variability and controlling factors of their isotopic compositions. Compared with the amount-weighted mean annual oxygen isotopic values of precipitation, we conclude that river water is a good substitute for isotopic studies of precipitation in the high flat (e.g., elevation >3,300 m) interior of the Tibetan Plateau in the mean annual timescale. We construct, for the first time based on field data, contour maps of isotopic variations of meteoric waters (δ18O, δD and d-excess) on the Tibetan Plateau. In the marginal mountainous regions of the Plateau, especially the southern through eastern margins, the δ18O and δD values of river waters decrease with increasing mean catchment elevation, which can be modeled as a Rayleigh distillation process. However, in the interior of the Plateau, northward increasing trends in δ18O and δD values are pronounced and present robust linear relations; d-excess values are lower than the marginal regions and exhibit distinct contrasts between the eastern (8‰–12‰) and western (<8‰) Plateau. We suggest that these isotopic features of river waters in the interior of the Tibetan Plateau result from the combined effects of: 1) mixing of different moisture sources transported by the South Asian monsoon and Westerly winds; 2) contribution of moisture from recycled surface water; and 3) sub-cloud evaporation. We further provide a sub-cloud evaporation modified Rayleigh distillation and mixing model to simulate the isotopic variations in the western Plateau. Results of this work suggest that stable isotope-based paleoaltimetry studies are reliable in the southern through eastern Plateau margins; towards the central–northern Plateau, this method cannot be applied without additional constraints and/or large uncertainties.
•1340 river water samples (458 new) across the Tibetan Plateau are compiled.•Contour maps of river water δ18O/δD and d-excess values are constructed.•River water δ18O is good substitute of annual mean precipitation in Tibet interior.•Controlling factors for isotopic variations of meteoric water are discussed.•Implications for stable isotope-based paleoaltimetry studies in the Tibetan Plateau.
Fractionation of soil organic carbon (SOC) is crucial for mechanistic understanding and modeling of soil organic matter decomposition and stabilization processes. It is often aimed at separating the ...bulk SOC into fractions with varying turnover rates, but a comprehensive comparison of methods to achieve this is lacking. In this study, a total of 20 different SOC fractionation methods were tested by participating laboratories for their suitability to isolate fractions with varying turnover rates, using agricultural soils from three experimental sites with vegetation change from C3 to C4 22–36 years ago. Enrichment of C4-derived carbon was traced and used as a proxy for turnover rates in the fractions. Methods that apply a combination of physical (density, size) and chemical (oxidation, extraction) fractionation were identified as most effective in separating SOC into fractions with distinct turnover rates. Coarse light SOC separated by density fractionation was the most C4-carbon enriched fraction, while oxidation-resistant SOC left after extraction with NaOCl was the least C4-carbon enriched fraction. Surprisingly, even after 36 years of C4 crop cultivation in a temperate climate, no method was able to isolate a fraction with more than 76% turnover, which challenges the link to the most active plant-derived carbon pools in models. Particles with density >2.8 g cm−3 showed similar C4-carbon enrichment as oxidation-resistant SOC, highlighting the importance of sesquioxides for SOC stabilization. The importance of clay and silt-sized particles (<50 μm) for SOC stabilization was also confirmed. Particle size fractionation significantly outperformed aggregate size fractionation, due to the fact that larger aggregates contain smaller aggregates and organic matter particles of various sizes with different turnover rates. An evaluation scheme comprising different criteria was used to identify the most suitable methods for isolating fractions with distinct turnover rates, and potential benefits and trade-offs associated with a specific choice. Our findings can be of great help to select the appropriate method(s) for fractionation of agricultural soils.
•Combined physical and chemical fractionation was most successful.•Dispersion and size separation is advisable to increase the range of turnover rates.•Isolating more than five fractions inherits the risk of redundancy in turnover rates.•Non-oxidizible and high density (>2.8 g cm-3) fractions contained fewest young C.•None of the methods isolated a fraction which entirely consisted of young C.
This study investigates mercury (Hg) dynamics in Pacific Saury (Cololabis saira) across the North Pacific Ocean, specifically off East Japan in 2018. Saury traits vary with total mercury (THg) ...concentrations in muscle tissues ranging from 0.017 to 0.082 μg g-1 w.w., averaging of 0.042 (n=46). A positive correlation between THg and saury length (Knob length , 270 to 319 mm) indicates increased Hg concentration with size. Stable isotopic tracers suggest Pacific Euphausiids (Krill) are significant contributors to the saury diet (>70% of total). Significant correlations between logarithm THg concentration (Log THg) and δ15N (‰) (R2 = 0.70) demonstrate Hg trophic biomagnification, with slight regional variations. Comparative analysis between the eastern (ENPO) and western North Pacific Ocean (WNPO) indicates differences, with WNPO saury exhibiting lower δ15N values and higher THg levels than ENPO saury. This suggests that the WNPO, located near East Asia, the world's largest Hg emitter, experiences elevated Hg levels in seawater due to anthropogenic release. Overall, this study advances understanding of Pacific Saury's ecological interactions and Hg bioaccumulations, emphasizing the importance of species-specific behaviors and regional influences in ecological studies.
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•The study reveals an increase in Hg concentration with size in Pacific saury.•Stable isotopic tracers reveal Pacific Euphausiids (Krill) as a major part of saury diet.•Positive correlations between Hg concentration and δ15N (‰) reveal trophic magnification with slight regional variations.•Elevated saury Hg levels in the WNPO could result from East Asian anthropogenic influence.
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