Isotope Analysis Research Articles

Isotopic niches reveal the trophic structure of the cetacean community in the oceanic waters around the Azores

IntroductionThe oceanic waters around the Azores host a high diversity of cetaceans, with 28 species of toothed and baleen whales present year-round or seasonally. This high cetacean biodiversity likely plays an important role in the structure, functioning and productivity of the ecosystem, and may increase trophic redundancy, thus contributing to food web resilience to disturbances.MethodsHere we used stable isotope (δ13C and δ15N) analysis to characterize trophic niches, assess niche overlap, describe the trophic structure and discuss potential redundancy in the cetacean community. Using 407 samples from 12 species, we estimated Standard Ellipse Areas and overlaps between species and used a hierarchical clustering analysis to identify trophic guilds.Results and discussionδ13C and δ15N values ranged from -20.53 to -15.46‰ and from 7.78 to 14.41‰ respectively, suggesting the use of diverse habitats and resources among cetacean species. Clustering analysis revealed that species were grouped into four trophic guilds, segregated mainly by trophic position (TP): a low-TP guild with three zooplanktivore baleen whales, a mid-TP guild with micronektivores, a high-TP guild with micronekton and nekton consumers, and a cluster with only Pseudorca crassidens. There was significant isotopic niche overlap between one pair of species within each guild, indicating some potential for trophic redundancy in the community. Yet, these pairs also showed some form of spatial or temporal partitioning, suggesting that mechanisms promoting species coexistence could play a key role in structuring the cetacean community in the region and in its ecological role.

Ecological impact of a generalist invader in the aquatic food web is mediated by environmental context

Abstract Freshwater ecosystems are threatened by the introduction of invasive species. Generalist invaders often compete with native species for shared resources, resulting in possible native species niche displacement. However, environmental heterogeneity may modulate the level of individual specialisation in invasive species, altering the outcome of interspecific competition between invasive and native species. The objectives of our study were to (1) evaluate the environmental context of dietary specialisation and trophic position of an invasive species according to the Environmental Matching Hypothesis (EMH), and (2) consider how the environmental context of invasive species dietary resource use may influence the dietary niche of native species competing for similar resources. Resource use, trophic position and dietary niche were determined using gut content and stable isotope analyses for the invasive round goby (Negobius melanostomus) and the native yellow perch (Perca flavescens), along environmental gradients in an invaded fluvial ecosystem. Our results were in support of EMH for the invader diet and resource specialisation, but not trophic position. Under environmental conditions of high water‐conductivity, round gobies were generalists feeding mostly on pelagic prey. Under more challenging environmental conditions of low water‐conductivity, the invader specialised on preferred high‐quality benthic prey. The ecological impact of the round goby was greatest at low water‐conductivity sites where the invader was a benthic specialist; there was a greater relative dietary niche overlap between the invader and the native species. Our study uniquely illustrates how invasive species’ resource specialisation can be modulated by spatial environmental heterogeneity within ecosystems, and how this can subsequently alter the ecological impact of the invader on native species in aquatic food webs.

Determining sugar and molasses origin by non‐exchangeable hydrogen stable isotope of ethanol and carbon isotope ratio mass spectrometry

AbstractThis study explores the differentiation of sugar and molasses produced from sugar beet and cane, which are susceptible to fraudulent labeling due to differing production costs. The research aimed to authenticate these products by botanical origin using novel analytical techniques. Utilizing ethanol isotopic measurement–isotope ratio mass spectrometry (IRMS) for non‐exchangeable hydrogen stable isotopes alongside carbon stable isotopes analysis through elemental analyzer–IRMS, the study accurately identified the origin of various sugar and molasses samples, pinpointed mislabeled goods, and determined the source of products with previously unknown provenance. These methods were also effective in revealing sugar and molasses adulteration and quantifying the extent of such fraud. The combined isotope analyses demonstrated their potential as robust tools for combating misrepresentation and adulteration in the sugar industry.

Liquid Chromatography Coupled to Isotope Ratio Mass Spectrometry Expanded to Include Organic Mobile Phases.

Current commercially available liquid chromatography coupled to isotope ratio mass spectrometry systems (LC-IRMS) oxidize all eluent and thus can only operate with all-aqueous mobile phases, limiting their application to a small subset of analytes and mixtures that can be separated without organic solvents. We report a novel rotating-catalytic disc desolvation device with subsequent laser-activated photocatalytic analyte combustion to create CO2 for high precision carbon isotope ratio measurements compatible with both aqueous and organic liquid mobile phases. Sucrose, glucose, androsterone, or androsterone acetate in 20% and 50% H2O-CH3OH solutions were introduced by flow injection to the interface to IRMS for sugars and steroids, respectively. Sucrose δ13CVPDB linearity was excellent over 1-10 μg (33-655 nmol C) injections, using IRMS compatible He/1%O2 oxidation gas. The limit of precise isotope analysis (LOIA) of δ13CVPDB was 1 μg (35 nmol C) for sucrose and 10 μg (655 nmol C) for androsterone with average precisions of SD(δ13C) ± 0.8‰. Calibration was performed with and bracketed the δ13CVPDB isotope ratio range using androsterone-acetate and glucose. With further development to improve sensitivity and application to chromatography, the prototype proof-of-principle LC-IRMS shows promise to resolve a major drawback in current LC-IRMS systems and may open LC-IRMS to many more compounds than currently possible.

Seasonal dynamic of the benthic food web in subtidal sandbanks

Submarine sandbanks are prevalent worldwide but, paradoxically, these ecosystems and their dynamics remain largely unknown. As submarine sandbanks are targeted by a large variety of human activities, there is an urgent need for sound scientific knowledge for environmental impact assessments (EIAs) and the appropriate management of biodiversity in these areas. To our knowledge, the present study is the first to investigate the seasonal dynamics of the benthic food web in sandbank areas. We performed a stable isotope analysis in the French part of the southern North Sea. This area is typified by numerous sandbanks and by massive phytoplankton blooms in spring. We found a very simple food web structure that is heavily dependent on organic matter particles in seawater. Primary consumers, i.e. deposit feeders and, to a lesser extent, suspension feeders, dominate the benthic biomass. Small predator-scavengers such as annelids, shrimps and crabs prey upon them. Fish predators such as Echiichthys vipera represent a very restricted proportion of the biomass. We observed that the general structure of the food web is relatively well preserved over seasons. We thus propose that the functioning of the ecosystem is resilient to natural disruptions—such as dune migrations—and, probably, to anthropogenic disturbances.

Drought Stress Might Induce Sexual Spatial Segregation in Dioecious Populus euphratica—Insights from Long-Term Water Use Efficiency and Growth Rates

P. euphratica stands as the pioneering and dominant tree within desert riparian forests in arid and semi-arid regions. The aim of our work was to reveal why dioecious P. euphratica in natural desert riparian forests in the lower Tarim River exhibits sexual spatial distribution differences combined with field investigation, tree ring techniques, isotope analysis techniques, and statistical analyses. The results showed that P. euphratica was a male-biased population, with the operational sex ratio (OSR) exhibiting spatial distribution differences to variations in drought stress resulting from groundwater depth change. The highest OSR was observed under mild drought stress (groundwater depth of 6–7 m), and it was reduced under non-drought stress (groundwater depth below 6 m) or severe drought stress (groundwater depth exceeding 7 m). As drought stress escalated, the degradation and aging of the P. euphratica forest became more pronounced. Males exhibited significantly higher growth rates and WUEi than females under mild drought stress. However, under severe drought stress, males’ growth rates significantly slowed down, accompanied by significantly lower WUEi than in females. This divergence determined the sexual spatial segregation of P. euphratica in the natural desert riparian forests of the lower Tarim River. Furthermore, the current ecological water conveyance project (EWCP) in the lower Tarim River was hard to fundamentally reverse the degradation and aging of the P. euphratica forest due to inadequate population regeneration. Consequently, we advocated for an optimized ecological water conveyance mode to restore, conserve, and rejuvenate natural P. euphratica forests.

Hydrochemistry and isotope hydrology of groundwater and surface water in the Sor and Gebba watershed, southwestern Ethiopia

The Sor and Gebba watershed plays a crucial role in the water resources of the Baro-Akobo River Basin. However, various factors have had a detrimental effect on the watershed. Unplanned groundwater extraction, wetland drainage, surface water pollution, and land use changes have all intensified due to population growth, urbanization, commercial farms, industrial development, poor water resources management, and improvements in living standards. This research utilized major hydrochemical ions and environmentally stable isotopes to elucidate the interaction between groundwater and surface water in the watershed, which are reliable tracers in various hydrologic processes. During the 2020 wet season and 2022 dry season, over 25 meteoric water samples were collected from different locations for hydrochemical and isotopic analysis. The hydrochemical analysis revealed that the dominant water type is Ca–Mg–HCO3−. Among the anions, HCO3− was the most dominant, followed by NO3−, Cl−, and SO42−, and those of cations Ca2+, followed by Na+, Mg2+, and K+. The spatial analysis of environmentally stable isotopes confirmed the interaction between groundwater and surface water in the watershed. The quality of groundwater is primarily influenced by rock-water interaction (Gibb's diagram) and, to some extent, by evaporation (Isotope study). A graph of the water samples closely aligned with the Addis Ababa-local meteoric water line indicates their meteoric origin. However, there was a slight deviation to the left due to the effects of distance and altitude. The isotopic correlation further supported the interaction between different water sources.

Unveiling Hunnic legacy: Decoding elite presence in Poland through a unique child’s burial with modified cranium

This article presents a double burial from Czulice indicating elements of the Hunnic culture. Individual I, aged 7–9, and Individual II, aged 8–9 with a skull deformation, were both genetically identified as boys. Individual II, who exhibited genetic affinity to present day Asian populations, was equipped with gold and silver items. In contrast, Individual I displayed European ancestry. The application of strontium isotope analysis shed light on the origins of the individuals. Individual I was non-local, while Individual II was identified as a local, but also falling within the range commonly associated with the Pannonian Plain. Stable isotope analysis suggested a diet consisting of inland resources. Through radiocarbon dating, this burial was determined to date back to the years 395–418 CE, making it the earliest grave of its kind discovered in Poland. The analyses have provided new insights into the nature of the relationship between the Huns and the local inhabitants.

Ungulate niche partitioning and behavioural plasticity of aurochs in Early Holocene southern Scandinavia revealed by stable isotope analysis of bone collagen

This study examines the impact of the extensive climatic and environmental changes associated with the Early Holocene on the feeding ecology of aurochs, European bison, red deer, and Eurasian elk in southern Scandinavia from radiocarbon dates and analysis of stable carbon and nitrogen isotopes. Molecular sex information is utilised in the study of aurochs to understand the underlying reasons behind observed intraspecific differences. Asynchronous diachronic changes in dietary palaeoecology were observed between the included taxa. The observed trends in foraging and habitat use among herbivores in our dataset can be attributed to the directional vegetation change from open landscape to forest. Our findings imply that environmental changes and/or interspecific competition contributed to the local extinction of European bison and impacted the niches of remaining species through niche overlap (cervids) and partitioning (between cervids and aurochs). Thus, our observations are consistent with the influence of multiple mechanisms that acted concurrently.

Hydrological variability of middle European peatland during the Holocene, inferred from subfossil bog pine and bog oak dendrochronology and high-resolution peat multiproxy analysis of the Budwity peatland (northern Poland)

Subfossil pine and oak tree trunks were excavated during exploitation of the Budwity peatland in Northern Poland. Based on dendrochronological analysis, the woodland successions in peatland were reconstructed and correlated with moisture dynamics of the peatland ecosystem inferred from the high-resolution multi-proxy analysis of the peatland deposits. From the results of dendrochronological analysis and the 14C wiggle matching methods, four floating pine chronologies (5882–5595; 5250–5089; 3702–3546; and 2222–1979 mod. cal BP) and two oak chronologies (4932–4599 and 4042–3726 mod. cal BP) were developed. The organic sediments of the peatland (6 m thick) were deposited over approximately nine thousand years. The lower complex (525–315 cm) comprises minerogenic peat, while the upper complex (315.0–0.0 cm) is composed of ombrogenic peat. Subfossil tree trunks are distributed across various peat horizons, which suggests multiple stages of tree colonisation followed by subsequent dying-off phases. Multiproxy sediment analyses (lithological, geochemical and δ13C stable isotope, pollen, plant macrofossils, Cladocera, diatom, and Diptera analyses) indicate that the two earliest phases of pine colonisation (5882–5595 and 5250–5089 mod. cal BP) and the two stages of oak colonisation (4932–4599 and 4042–3726 mod. cal BP) were associated with periodic drying of the peatland. Conversely, tree dying-off phases occurred during periods of increased water levels in the peatland, coinciding with stages of increasing climate humidity during the Holocene. The two most recent phases of pine colonisation occurred during the ombrogenic stage of mire development. Remnants of the dead forest from these phases, marked by subfossil trunks still rooted in the ground, were preserved and exposed presently during peat exploitation, approximately 2.5 m below ground level. The identified phases of tree colonisation and subsequent dying-off phases show correlation with analogical phenomena observed in the other investigated European peatlands.

Screening Disinfection Byproducts in Arid-Coastal Wastewater: A Workflow Using GC×GC-TOFMS, Passive Sampling, and NMF Deconvolution Algorithm

Disinfection during tertiary municipal wastewater treatment is a necessary step to control the spread of pathogens; unfortunately, it also gives rise to numerous disinfection byproducts (DBPs), only a few of which are regulated because of the analytical challenges associated with the vast number of potential DBPs. This study utilized polydimethylsiloxane (PDMS) passive samplers, comprehensive two-dimensional gas chromatography (GC×GC) coupled with time-of-flight mass spectrometry (TOFMS), and non-negative matrix factorization (NMF) spectral deconvolution for suspect screening of DBPs in treated wastewater. PDMS samplers were deployed upstream and downstream of the chlorination unit in a municipal wastewater treatment plant located in Abu Dhabi, and their extracts were analyzed using GC×GC-TOFMS. A workflow incorporating a multi-tiered, eight-filter screening process was developed, which successfully enabled the reliable isolation of 22 candidate DBPs from thousands of peaks. The NMF spectral deconvolution improved the match factor score of unknown mass spectra to the reference mass spectra available in the NIST library by 17% and facilitated the identification of seven additional DBPs. The close match of the first-dimension retention index data and the GC×GC elution patterns of DBPs, both predicted using the Abraham solvation model, with their respective experimental counterparts—with the measured data available in the NIST WebBook and the GC×GC elution patterns being those observed for the candidate peaks—significantly enhanced the accuracy of peak assignment. Isotopic pattern analysis revealed a close correspondence for 11 DBPs with clearly visible isotopologues in reference spectra, thereby further strengthening the confidence in the peak assignment of these DBPs. Brominated analogues were prevalent among the detected DBPs, possibly due to seawater intrusion. The fate, behavior, persistence, and toxicity of tentatively identified DBPs were assessed using EPI Suite™ and the CompTox Chemicals Dashboard. This revealed their significant toxicity to aquatic organisms, including developmental, mutagenic, and endocrine-disrupting effects in certain DBPs. Some DBPs also showed activity in various CompTox bioassays, implicating them in adverse molecular pathways. Additionally, 11 DBPs demonstrated high environmental persistence and resistance to biodegradation. This combined approach offers a powerful tool for future research and environmental monitoring, enabling accurate identification and assessment of DBPs and their potential risks.

Isotopic, mycotoxin, and pesticide analysis for organic authentication along the production chain of wheat-derived products

Wheat-based products are staples in diets worldwide. Organic food frauds continuously threaten consumer trust in the agri-food system. A multi-method approach was conducted for the organic authentication and safety assessment of pasta and bakery products along their production chain. Bulk and Compound-Specific (CS) Isotope Ratio Mass Spectrometry (IRMS) suggested the δ15Nbulk, δ15Nleucine and δ15Nproline as promising organic markers, with CS able to distinguish between pairs which bulk analysis could not. Processing significantly affected the values of δ15Nleucine, δ13Cproline and δ13Cleucine. Multi-mycotoxin analysis (HT-2, T-2, DON, ZEN, OTA, AFB1) revealed higher contamination in conventional than organic samples, while both milling and baking significantly reduced mycotoxin content. Lastly, from the evaluation of 400 residues, isopyrazam was present at the highest concentration (0.12 mg/kg) in conventional wheat, exhibiting a 0.12 Processing Factor (PF), while tebuconazole levels remained unchanged in pasta production (90 °C) and reduced below LOQ in biscuits and crackers (180–250 °C).

Linking anatomical and histological traits of the digestive tract to resource consumption and assimilation of omnivorous tetra fishes.

This study explores the interplay between digestive tract traits, food intake, and assimilation in omnivorous tetra fishes (Psalidodon bifasciatus, P. aff. gymnodontus, and Bryconamericus ikaa) from the Iguaçu River basin, an ecologically significant region known for high endemism. We hypothesize that variations in digestive tracts across species would be associated with differences in diet, isotopic composition in fish tissues, and overall diet assimilation. To test this, we employed stereoscopic and light microscopy to characterize the gross anatomy, histomorphology, and histochemistry of fish digestive tracts. Additionally, we used stomach content and stable isotope analyses to trace fish diets. While these tetra fishes shared histological structures, disparities were noted in anatomical digestive traits and diet preferences. The smallest species, B. ikaa, with a shorter intestine, had fewer pyloric caeca and primarily consumed animal-based diets. Conversely, P. bifasciatus and P. aff. gymnodontus, with longer intestines, displayed numerous pyloric caeca and consumed a balanced mix of animal and plant items. Despite anatomical and dietary differences, all three species predominantly assimilated animal-origin food. The tetra fishes had histological variations among digestive tract segments, with the esophagus having the thickest muscular layer, gradually thinning towards the posterior intestine. The final portion of the intestine exhibited a significant expansion in the lumen perimeter, while the esophagus had the smallest lumen area. Goblet cells were most concentrated in the posterior intestine for all species. The gross anatomy of these tetra fishes aligns with their omnivorous habit, while diet assimilation was dominated by animal-origin food. These findings provide crucial insights into the structural and tissue characteristics of their digestive systems, laying the groundwork for deeper exploration into the physiological aspects of their digestive tracts and enhancing our understanding of their feeding strategies.

Effect of Water‐Rock Ratio on the Stable Isotope Record of Fluid‐Rock‐Deformation Interactions in Detachment Shear Zone

AbstractOxygen and hydrogen stable isotope analyses of quartz and muscovite veins from the footwall of the Raft River detachment shear zone (Utah) provide insight into the hydrology and fluid‐rock interactions during ductile deformation. Samples were collected from veins containing 90%–100% quartz with orientations either at a high angle or sub‐parallel to the surrounding quartzite mylonite foliation. Stable isotope analysis was performed on 10 samples and compared with previous quartzite mylonite isotope data sets. The results indicate that the fluid present during deformation of the shear zone was meteoric in origin, with a δ2H value of approximately −100‰ and a δ18O value of approximately −13.7‰. Oxygen stable isotope O18O depletion correlates with the muscovite content of the analyzed rocks. Many of the analyzed samples in this and other studies show an apparent lack of equilibrium between the oxygen and hydrogen isotope systems, which can be explained by hydrogen and oxygen isotope exchange at varying fluid‐rock ratios. Our results suggest that the Raft River detachment shear zone had a low static fluid‐rock ratio (<0.1), yet experienced episodic influxes of fluids through semi‐brittle structures. This fluid was then expelled out into the surrounding mylonite following progressive shearing, causing further 18O‐depletion and fluid‐related embrittlement.

Granite weathering profiles accumulate vegetation-derived mercury

Weathering of silicate rocks, particularly granitic rocks, generates the pedosphere that is of crucial importance in functioning terrestrial ecosystems. The pedosphere hosts large amounts of mercury (Hg). The source of Hg in granite weathering products is currently poorly constrained, however. Here we conducted Hg isotopic analyses on two weathering profiles developed on granitic plutons in Central and South China. Soils from both profiles show a downward decrease in Hg concentration but consistently negative ∆199Hg values. Mercury in precipitation, granites, and vegetation display positive, near-zero, and negative ∆199Hg values, respectively. The negative ∆199Hg values in the two weathering profiles are consistent with estimates of vegetation-derived Hg, supporting that Hg in weathering profiles are dominantly sourced from vegetation. Hg in vegetation is transported into surface soil firmly bonded to organic matter and migrates downwards weathering profiles. This study provides insights into the biogeochemical cycle of Hg in the granite-weathering crust and helps to explain the negative ∆199Hg values observed in terrestrial-derived sedimentary rocks.

Distinguishing the contributions of different smelting emissions to the spatial risk footprints of toxic elements in soil using PMF, Bayesian isotope mixing models, and distance-based regression

Toxic element pollution of soils emanating from smelting operations is an escalating global concern due to its severe impact on ecosystems and human health. In this study, soil samples were collected and analyzed to quantify the risk contributions and delineate the spatial risk footprints from smelting emissions for 8 toxic elements. A comprehensive health risk contribution and delineation framework was utilized, consisting of Positive matrix factorization (PMF), spatial interpolation, an advanced Bayesian isotope mixing model via Mixing Stable Isotope Analysis in R (MixSIAR), and distance-based regression. The results showed that the mean concentrations of As, Cd, Cu, Hg, Pb, and Zn exceeded the background levels, indicating substantial contamination. Three sources were identified using the PMF model and confirmed by spatial interpolation and MixSIAR, with contributions ranked as follows: industrial wastewater discharge and slag runoff from the smelter site (48.9 %) > natural geogenic inputs from soil parent materials (26.7 %) > atmospheric deposition of dust particles from smelting operations (24.5 %). Among the identified sources, smelter runoff posed the most significant risk, accounting for 97.9 % of the non-carcinogenic risk (NCR) and 59.9 % of the carcinogenic risk (CR). Runoff also drove NCR and CR exceedances at 7.8 % and 4.7 % of sites near the smelter, respectively. However, atmospheric deposition from smelting emissions affected soils across a larger 0.8 km radius. Although it posed lower risks, contributing just 1.1 % to NCR and 22.6 % to CR due to the limited elevation of toxic elements, deposition reached more distant soils. Spatial interpolation and distance-based regression delineated high NCR and CR exposure hotspots within 1.4 km for runoff and 0.8 km for deposition, with exponentially diminishing risks at further distances. These findings highlight the need for pathway-specific interventions that prioritize localized wastewater containment and drainage controls near the smelter while implementing broader regional air pollution mitigation measures.

Acid mine drainage from coal mines in the eastern Himalayan sub-region: Hydrogeochemical processes, seasonal variations and insights from hydrogen and oxygen stable isotopes

Uncontrolled coal mining using non-scientific methods has presented a major threat to the quality of environment, particularly the water resources in eastern himalayan sub-region of India. Water bodies in the vicinity of mining areas are contaminated by acid mine drainage (AMD) that is released into streams and rivers. This study attempted to assess the impact of AMD, deciphering hydrogeochemical processes, seasonal fluctuations, and stable isotope features of water bodies flowing through and around coal mining areas. Self-organising maps (SOMs) used to separate and categorize AMD, AMD-impacted and non-AMD impacted water from the different study locations for two sampling seasons revealed four clusters (C), with C1 and C2 impacted by AMD, C3 and C4 showing negligible to no impact of AMD. AMD impacted water was SO42- - Mg2+- Ca2+ hydrochemical type with sulphide oxidation and evaporation dominating water chemistry, followed by silicate weathering during both the sampling seasons. Water with negligible-to-no AMD-impact was Mg2+- Ca2+- SO42- to Ca2+ - HCO3- to mixed hydrochemical type with rock weathering and dissolution, followed by ion exchange as major factors controlling water chemistry during both the sampling seasons. Most of physicochemical parameters of C1 and C2 exceeded the prescribed limits, whereas in C3 and C4 water samples, parameters were found within the prescribed limits. Stable isotopes of hydrogen (δ2H) and oxygen (δ18O) during post-monsoon (PoM) varied between -29.98 ‰ to -41.04 ‰ and -6.60 ‰ to -3.94 ‰; and during pre-monsoon (PrM) varied between -58.18 ‰ to - 33.76 ‰ and -8.60 ‰ to -5.46 ‰. Deuterium excess (d-excess) ranged between 12.47 ‰ to 1.57 ‰ during PoM and 15.17 ‰ to 5.70 ‰ during PrM season. The stable isotopes analysis revealed that evaporation, mineral dissolution and mixing with rainwater are the key factors in study area.

Co-occurrence of elevated arsenic and fluoride concentrations in Wuliangsu Lake: implications for the genesis of poor-quality groundwater in the (paleo-)Huanghe (Yellow River) catchment, China

The co-occurrence of high As and F concentrations in saline groundwater in arid and semi-arid regions has attracted considerable attention. However, the factors determining the elevated concentrations of the two elements in surface water in these regions have not been sufficiently studied, and their implications for the poor-quality of local groundwater (high levels of As, F, and salinity) are unknown. A total of 18 water samples were collected from Wuliangsu Lake, irrigation/drainage channels, and the Huanghe (i.e., Yellow River) in the Hetao Basin, China. The pH, concentrations of As and F as well as those of other major elements, and stable isotope (H and O) compositions were analyzed. The water samples had a high pH (7.85–9.01, mean 8.25) and high TDS (402–9778 mg/L, mean 1920 mg/L) values. In six of the 10 lake samples, As concentration was above 10 μg/L (maximum 69.1 μg/L) and, in one of them, F concentration was above 1.5 mg/L. Interestingly, the high As, F, and TDS values simultaneously detected in the lake water were similar to those previously reported in local groundwater, and all water samples showed a significant positive correlation between As and F concentrations (R2 = 0.96, p < 0.01), except for two samples with abnormally high Ca2+ levels. The results of stable isotope analysis and Cl/Br ratios suggested that the lake experienced strong evaporation, which is consistent with the high TDS values. Evaporative concentration is suggested as the main factor contributing to the elevated As and F concentrations in the lake water. In addition, the major ions (e.g., Na+, Cl−, HCO3−, and OH−) and pH in the lake water increased during evaporation, leading to desorption of As and F. Thus, the evaporation process, including evaporative concentration and desorption, was considered primarily responsible for the elevated As and F in the lake water. Based on the results of this study, we presume that the paleolakes in the study area have experienced intense evaporation process. As a result, As, F, and major elements accumulated in sediments (or residual lake water) and were buried in the fluvial basins; then, they were released into the groundwater through multiple (bio)hydrogeochemical processes. By combining the results of this study with those obtained from previous groundwater analyses, we propose a new hypothesis explaining the origin of elevated As and F concentrations in saline groundwater in arid and semi-arid regions.

Vermilion monazite: A new Archean reference material for U-Pb and Sm-Nd microanalysis

Monazite (Vermilion) from the ∼2.7 Ga Vermilion Granitic Complex (Minnesota, USA) was investigated as a potential reference material for U-Pb geochronology, using electron microprobe, high-precision ID-TIMS and high-spatial resolution techniques (LA-(Q/SF/MC)-ICP-MS and SHRIMP). Vermilion monazite is relatively homogeneous in BSE images. It is characterised as a monazite-(Ce) with uniform, relatively LREE-enriched chondrite-normalised REE patterns (Eu/Eu* = 0.074–0.085). ID-TIMS U-Pb analyses yielded concordant to slightly (−0.6% to 1.8%) discordant isotope data with weighted mean 207Pb*/206Pb* dates of 2668.6 ± 1.8 Ma (2σ, MSWD = 1.3, n = 3) and 2666.8 ± 1.8 Ma (2σ, MSWD = 4.0, n = 4). High-spatial resolution data from SHRIMP and LA-(Q/SF/MC)-ICP-MS agree with the ID-TIMS age. Using Vermilion monazite as primary reference material, LA-SF-ICP-MS analyses reproduced the age of several other reference monazites within −1.13% to +1.64% accuracy. Nd isotopes obtained via ID-TIMS and solution MC-ICP-MS returned consistent 143Nd/144Nd ratios of 0.510694 ± 0.000040 (2σ) and 0.510726 ± 0.000014 (2σ), respectively. The LA-MC-ICP-MS 143Nd/144Nd ratios of 0.51071 ± 0.00001 (2σ) and 0.51065 ± 0.00001 (2σ) are also in agreement within uncertainties. Results of Sm-Nd isotope analyses by LA-MC-ICP-MS from two laboratories yielded mean 147Sm/144Nd ratios of 0.0869 ± 0.0002 (2.5% RSD, 2σ, n = 58) and 0.0835 ± 0.0001 (2.2% RSD, 2σ, n = 50), reflecting small variations in individual fragments. The initial epsilon Nd (εNdi) varies from −0.8 ± 0.5 to 0.6 ± 0.4 (2σ). The reproducibility of our results shows that Vermilion monazite can be used as a primary reference material for U-Pb geochronology and is suitable as a secondary reference material for Sm-Nd isotopic tracing. The Archean age of Vermilion monazite, the oldest available as a reference material, will facilitate the investigation of Archean crustal evolution processes and broaden the prospect of studying ancient metamorphic events by combining matrix-matched U-Pb geochronology and Sm-Nd isotopic tracing.

Detrital zircon and rutile of southern Mexico Cambrian–Ordovician sandstone: Their significance for sediment provenance and Rheic Ocean evolution

The Cambrian–Ordovician Tiñú Formation of southern Mexico is key for identifying sediment sources along the northern margin of Gondwana, enhancing our understanding of early Paleozoic paleogeography and linking it with age-equivalent units in terranes with Gondwanan affinity. This study integrates detrital zircon U–Pb ages, Hf isotope signatures, and heavy mineral chemical data. U–Pb detrital zircon ages indicate sources from Stenian–Tonian (900–1200 Ma) to Calymmian (1400–1600 Ma) ages. The Stenian to Tonian zircon population, with peak ages around 1.0 Ga and model ages ranging from 1.68 to 1.90 Ga, suggests a provenance from the metaigneous rocks of the Oaxacan and Guichicovi complexes. The presence of the Calymmian zircon population, tourmaline crystals, and rutile grains displaying lower crystallization temperatures compared to the high-temperature rutile from the Oaxacan Complex suggests additional sources. Hf isotope signatures from Calymmian-aged zircon grains, with model ages between 1.95 and 2.30 Ga, match well with the Paleo-Mesoproterozoic Catarina Unit in the southern Chiapas Massif Complex. Further potential sources may include the basement of the Putumayo Province in Colombia and igneous rocks from the western Guiana Shield and the Rio Negro-Juruena Province. The Tiñú Formation provenance is comparable to coeval metasedimentary units across the northwestern margin of Gondwana found in Belize, the southern Chiapas Massif Complex, and Guatemala. The Tiñú Formation was likely deposited adjacent to the rifted margin of the Rheic Ocean. The results also emphasize combining U–Pb–Hf isotope analysis and trace elements in detrital zircon and rutile as effective provenance tracers.