Nitrogen Isotopic Composition Research Articles

Forage ecology of Neotropical fish in Brazilian biomes using stable isotopes

Neotropical regions are responsible for harboring most of the global diversity of freshwater fish, providing essential ecosystem services for society. Human activities (e.g., land use changes) jeopardize aquatic ecosystems as well as species, communities, etc., impairing ecosystem services. We investigate the impact of human disturbance on the foraging ecology of Neotropical freshwater fishes across five Brazilian biomes by stable isotope analysis. We analyzed carbon (δ13C) and nitrogen (δ15N) isotopic compositions of Neotropical fishes, sourced from the SIA-BRA dataset. Fishes were categorized into herbivores, omnivores, and carnivores. We tested the correlation between human disturbances, indicated by the human disturbance index (hdi), and changes in fish diets. We expected that the assimilation of C4‑carbon from exotic forage would increase with higher disturbance levels, while δ15N levels would similarly rise due to nitrogen input from anthropogenic sources. We found increases in fish δ13C with human disturbance increases, suggesting greater assimilation of C4 carbon in places where native vegetation was replaced by C4 sources, confirmed by isotopic mixing models. In contrast, δ15N values did not show a significant relationship with human disturbance, probably due to the complex interactions and multiple sources of nitrogen in disturbed environments. Our finds suggest that stable isotope analysis provides a powerful tool for monitoring the effects of landscape changes on aquatic food webs. Particularly, the δ13C values of detritivorous fish that feed on C4 plant detritus could serve as bioindicators of environmental degradation. However, a specific isotopic characterization of each site would be valuable for more accurate niche information.

The molybdenum cycle in the oxygenated Neoproterozoic ocean was coupled to manganese carbonate mineralization

The Neoproterozoic oxygenation event is a milestone in Earth’s history, yet the redox structure and elemental cycling of the Neoproterozoic ocean remain debated. Here, we investigated iron speciation, molybdenum, and nitrogen isotopes in black shales and manganese carbonates from the upper Ediacaran Doushantuo Formation, South China, to examine the links between redox state, manganese mineralization, and molybdenum cycling. In both lithologies, high pyritic iron ratios (> 0.8) indicate a localized euxinic zone, while estimated seawater molybdenum (1.9‰) and sediment nitrogen isotopic compositions (4.19 ± 1.96‰) resemble modern values, suggesting oxygenated surface waters over euxinic depths. Negative molybdenum isotope in manganese(II) carbonates points to manganese(IV) oxide reduction, acting as a molybdenum shuttle from oxygenated surface to euxinic deep waters. Periodic euxinic contractions drove manganese(II) oxidation and mineralization, shaping molybdenum cycling. This study highlights essential manganese(II) oxidation for manganese carbonate mineralization and offers new insights into molybdenum geochemistry and ancient ocean oxygenation events.

Geographic variability of carbon and nitrogen isotope ratios of nonvolant terrestrial small mammals (Rodentia) across 3 Brazilian biomes

Abstract In this study, we investigated landscape variability of the carbon and nitrogen isotopic composition of nonvolant small mammals in the 3 main Brazilian biomes (Amazon, Atlantic Forest, and Cerrado) while also considering the differential spatial distribution of C4 plants in these biomes. We compiled a subset of data on stable carbon and nitrogen isotope ratios from nonvolant small mammals of the order Rodentia and compared the aggregated isotopic variability at the biome level using classical δ13C–δ15N biplot. The concept of isotopic niche width was used to test whether different foraging attributes drive their isotopic composition, while a Bayesian isotopic mixing model was used to estimate the proportion of 3 main food categories available to these small mammals. We also developed isoscapes in the Brazilian biomes, interpolating animals δ13C and δ15N based on the geographic coordinates of each sample and “sourcescapes” considering geographic variation of the dietary sources. The findings of this study advance our understanding of the foraging ecology of small mammals in biodiversity-rich regions of the Neotropics. Classical methodologies such as stomach content confirmed dietary choices revealed by the stable isotopic composition and also highlighted the importance of C3 and C4 plants in the diet of this group of animals, especially in biomes such as the Atlantic Forest and Cerrado, where there is a predominance of highly altered landscapes. These results confirm that replacing the original vegetation with C4 crops has altered the feeding patterns of small mammals, which could lead to critical ecological changes in the trophic structure of these areas. Vertical stratification of the dietary niche and the interaction between biome and foraging lifestyle were also observed. However, in each biome, there was significant intraspecific and interspecific variation caused by preferences for ingestion of plant and animal material, leading to different degrees of omnivory. Finally, the high local variability between individuals and species requires a larger sampling design that may also contribute to improved spatial resolution of the isoscapes.

A cross-regional examination of camelid herding practices in Peru from 900 BCE to 1450 CE: Insights from stable isotopes in camelid bone collagen and fiber.

The economic, socio-political, and cultural significance of camelids in the Andean region is well-recognized, yet an understanding of their management evolution over pre-historical periods remains limited. This study aims to fill this gap by conducting the first cross-regional assessment of camelid pastoralism in Peru from 900 BCE to 1470 CE, using stable carbon and nitrogen isotopic compositions from the bone collagen and fibers of 577archaeological camelids across 21 sites. This research investigates the spatio-temporal shifts in camelid dietary habits, focusing on how the rise of intensive agriculture may have influenced change and led to the evolution of distinct roles for camelids in coastal versus non-coastal Andean economies. Our analysis indicates an increase in δ13C values over time on the coast, suggesting a shift towards maize-based camelid diets. Conversely, δ13C values decrease over time in highland environments, suggesting camelids consumed relatively more wild C3 forage and/or cultivated crops such as tubers. The study also reveals a significant positive relationship between latitude and δ15N values, suggesting increasing environmental aridity enriches δ15N in bone collagen. After controlling for this latitudinal effect, we observe a rise in δ15N values in both coastal and non-coastal camelids, suggesting that in later periods camelids may have been foddered in agricultural fields that were enriched with guano or dung fertilizer used to intensify production. Importantly, this research uncovers a distinct dietary divergence between coastal and inland camelids. The observed divergence in diets suggests contrasting socio-economic uses of camelids, where coastal camelids were predominantly involved in ceremonial and political activities, while those in non-coastal areas were crucial to the subsistence economy.

Nitrogen in the Orgueil meteorite: Abundant ammonium among other reservoirs of variable isotopic compositions

Nitrogen, because of its abundance and variety of carrier phases, is a unique tracer of physico-chemical processes occurring throughout star and planet formations. The refractory organic matter is commonly considered as the main carrier of nitrogen in the most primitive objects of our Solar System. However, nitrogen in the form of ammonium (NH4+) was observed in the Ivuna-type carbonaceous (CI) chondrites Alais in 1834, and Orgueil just after its fall in 1864, as well as more recently on Ceres, comet 67P/Churyumov-Gerasimenko, and possibly on some asteroids. In the present study, we have measured the nitrogen content and isotopic composition in various nitrogen-bearing phases of several samples of the Orgueil meteorite, with different degrees of terrestrial weathering. Water-soluble NH4+ is present in Orgueil at a mean concentration of 0.07 ± 0.01 wt%, with a mean isotopic composition of δ15N = +72 ± 9 ‰ (14N/15N = 254 ± 2), confirming its extra-terrestrial origin. In the most terrestrially altered sample of Orgueil that we analysed, the isotopic composition is δ15N = +50 ± 12 ‰ (14N/15N = 259 ± 3). NH4+ is in species that are thermally stable up to 383 K, possibly ammonium inorganic/organic salts and ammoniated phyllosilicates. We also show that the nitrogen in Orgueil is distributed among the insoluble organic matter (IOM) (35 ± 5 %), ammonium (27 ± 5 %), and other minor water-soluble species (e.g., nitrate, amines etc.: < 6 %). The remaining nitrogen (34 ± 14 %) is mainly in an unidentified organic matter (UOM), which may be IOM lost during its extraction and/or acid hydrolysable functional groups bounded to the IOM and/or organic nitrogen trapped within minerals. The three main carriers of nitrogen in Orgueil have δ15N (and 14N/15N) values of +32 ± 1 ‰ (264 ± 0.3) for IOM, +39 ± 16 ‰ (262 ± 4) for UOM, and +72 ± 9 ‰ (254 ± 2) for NH4+.Although IOM and NH4+ have significantly different δ15N, we cannot exclude that these phases could be compositionally related because IOM is heterogeneous in 15N. Ammonium could have been produced via heating and/or aqueous alteration processes of organic matter in the CI parent body. Alternatively, or additionnally, ammonium could be a tracer of the accretion and/or later deposit of NH3 ice, NH3 hydrates, and/or NH4+ salts on the CI parent body.As shown by previous studies, Ryugu grains sampled by the Hayabusa2 mission (JAXA) have heterogeneous compositions at the millimeter scale, with nitrogen concentrations and δ15N similar or lower than Orgueil, possibly because of different parent body processing. The present study suggests that the lack or loss of 15N-rich NH4+ in some Ryugu grains may explain some of these differences with Orgueil.

Exploring the influence of atmospheric CO2 and O2 levels on the utility of nitrogen isotopes as proxy for biological N2 fixation.

Biological N2 fixation (BNF) is traced to the Archean. The nitrogen isotopic fractionation composition (δ15N) of sedimentary rocks is commonly used to reconstruct the presence of ancient diazotrophic ecosystems. While δ15N has been validated mostly using organisms grown under present-day conditions; it has not under the pre-Cambrian conditions, when atmospheric pO2 was lower and pCO2 was higher. Here, we explore δ15N signatures under three atmospheres with (i) elevated CO2 and no O2 (Archean), (ii) present-day CO2, and O2 and (iii) future elevated CO2, in marine and freshwater, heterocytous cyanobacteria. Additionally, we augment our data set from literature for more generalized dependencies of δ15N and the associated fractionation factor epsilon (ε = δ15Nbiomass - δ15NN2) during BNF in Archaea and Bacteria, including cyanobacteria, and habitats. The ε ranges between 3.70‰ and -4.96‰ with a mean ε value of -1.38 ± 0.95‰, for all bacteria, including cyanobacteria, across all tested conditions. The expanded data set revealed correlations of isotopic fractionation of BNF with CO2 concentrations, toxin production, and light, although within 1‰. Moreover, correlation showed significant dependency of ε to species type, C/N ratios and toxin production in cyanobacteria, albeit it within a small range (-1.44 ± 0.89‰). We therefore conclude that δ15N is likely robust when applied to the pre-Cambrian-like atmosphere, stressing the strong cyanobacterial bias. Interestingly, the increased fractionation (lower ε) observed in the toxin-producing Nodularia and Nostoc spp. suggests a heretofore unknown role of toxins in modulating nitrogen isotopic signals that warrants further investigation.IMPORTANCENitrogen is an essential element of life on Earth; however, despite its abundance, it is not biologically accessible. Biological nitrogen fixation is an essential process whereby microbes fix N2 into biologically usable NH3. During this process, the enzyme nitrogenase preferentially uses light 14N, resulting in 15N depleted biomass. This signature can be traced back in time in sediments on Earth, and possibly other planets. In this paper, we explore the influence of pO2 and pCO2 on this fractionation signal. We find the signal is stable, especially for the primary producers, cyanobacteria, with correlations to CO2, light, and toxin-producing status, within a small range. Unexpectedly, we identified higher fractionation signals in toxin-producing Nodularia and Nostoc species that offer insight into why some organisms produce these N-rich toxic secondary metabolites.

Neoarchaean oxygen-based nitrogen cycle en route to the Great Oxidation Event.

The nitrogen isotopic composition of sedimentary rocks (δ15N) can trace redox-dependent biological pathways and early Earth oxygenation1,2. However, there is no substantial change in the sedimentary δ15N record across the Great Oxidation Event about 2.45 billion years ago (Ga)3, a prominent redox change. This argues for a temporal decoupling between the emergence of the first oxygen-based oxidative pathways of the nitrogen cycle and the accumulation of atmospheric oxygen after 2.45 Ga (ref. 3). The transition between both states shows strongly positive δ15N values (10-50‰) in rocks deposited between 2.8 Gaand 2.6 Ga, but their origin and spatial extent remain uncertain4,5. Here we report strongly positive δ15N values (>30‰) in the 2.68-Gyr-old shallow to deep marine sedimentary deposit of the Serra Sul Formation6, Amazonian Craton, Brazil. Our findings are best explained by regionally variable extents of ammonium oxidation to N2 or N2O tied to a cryptic oxygen cycle, implying that oxygenic photosynthesis was operating at 2.7 Ga. Molecular oxygen production probably shifted the redox potential so that an intermediate N cycle based on ammonium oxidation developed before nitrate accumulation in surface waters. We propose to name this period, when strongly positive nitrogen isotopic compositions are superimposed on the usual range of Precambrian δ15N values, the Nitrogen Isotope Event. We suggest that it marks the earliest steps of the biogeochemical reorganizations that led to the Great Oxidation Event.

Measurement report: Formation of tropospheric brown carbon in a lifting air mass

Abstract. An enhanced formation of brown carbon (BrC) with a non-negligible warming effect at the tropopause has recently been found. However, its formation mechanism is unclear. Here, we report on a BrC formation process that happens during air mass upward transport by conducting simultaneous measurements on atmospheric BrC with a 4 h time resolution at the mountain foot (MF, 400 m a.s.l.) and mountainside (MS, 1120 m a.s.l.) of Mt. Hua, China, in the 2016 summer. Our results showed that the daytime light absorption (abs365 nm) of BrC on the MS is approximately 60 % lower than that at the MF due to a dilution effect caused by the planetary boundary layer expansion, but the daytime light absorption of BrC relative to black carbon on the MS is about 30 % higher than that at the MF, suggesting a significant formation of secondary BrC in the lifting process of air mass from the MF to the MS. Such a secondary formation accounted for &gt; 50 % of BrC on the MS but only 27 % of BrC at the MF. Moreover, the N:C elemental ratio of the daytime BrC was 15 % higher on the MS than that at the MF, mainly due to an aerosol aqueous-phase formation of water-soluble organic nitrogen (WSON) compounds. Stable nitrogen isotope composition further indicated that such light-absorbing WSON compounds were produced from the aerosol aqueous-phase reaction of carbonyls with NH4+. Our work revealed, for the first time, that ammonia-induced aerosol aqueous reactions can significantly promote BrC formation during the air mass lifting process, which is probably responsible for an enhanced light absorption of BrC in the upper boundary layer.

Source apportionment of organic carbon and nitrogen in sediments from river and lake in the highly urbanized Changjiang Delta

While the impact of human activities on organic matter pollution is recognized, how these impacts vary seasonally in the Changjiang Delta needs further investigation. This study addresses this gap by investigating seasonal variations in organic matter sources and ecological responses to human activities in Changjiang Delta sediments. Total organic carbon (TOC), total nitrogen (TN), and carbon (δ13C) and nitrogen (δ15N) isotopic compositions of surface sediments collected from the Taipu River and Dalian Lake wetland were analyzed. Both water bodies exhibited similar seasonal trends for TOC and TN, with the Taipu River containing an average of 0.46% and 0.03% higher concentrations of TOC and TN, respectively, compared to Dalian Lake. Additionally, the organic index (OI) and organic nitrogen (ON) index were elevated in both water bodies during the wet season. Sediments from Dalian Lake remained uncontaminated to moderately contaminated, while those from the Taipu River were generally classified as moderately to heavily contaminated. Stable isotope analysis identified terrestrial C3 plants (averaging 25.5%), C4 plants (averaging 16.0%), and municipal wastewater (averaging 16.0%) as the main contributors to organic matter in the sediments. These findings suggest that terrestrial plant material and municipal wastewater are key targets for managing organic matter contamination in the Changjiang Delta. Implementing strategic land-use planning and targeted interventions to minimize these inputs can significantly improve water quality and ecosystem health.

To eat or not to eat: novel stable isotope models reveal a shift in carnivory with nutrient availability for aquatic Utricularia spp.

Freshwater nitrogen inputs are increasing globally, altering the structure and function of wetland ecosystems adapted to low nutrient conditions. Carnivorous wetland plants of the genus Utricularia are hypothesized to reduce their reliance on carnivory and increase their assimilation of environmental nutrients when the supply of ambient nutrients increases. Despite success in using stable isotope approaches to quantify carnivory of terrestrial carnivorous plants, quantifying carnivory of aquatic Utricularia requires improvement. We developed stable isotope mixing models to quantify aquatic plant carnivory and used these models to measure dietary changes of three Utricularia species, Utricularia australis, U. gibba and U. uliginosa, in 11 wetlands across a 794-km gradient in eastern Australia. Diet was assessed using multiple models that compared variations in the natural-abundance nitrogen isotope composition (δ15N) of Utricularia spp. with that of non-carnivorous plants, and environmental and carnivorous nitrogen sources. Carnivory supplied 40-100 % of plant nitrogen. The lowest carnivory rates coincided with the highest availability of ammonium and dissolved organic carbon. Our findings suggest that Utricularia populations may adapt to high nutrient environments by shifting away from energetically costly carnivory. This has implications for species conservation as anthropogenic impacts continue to affect global wetland ecosystems.

Trophic ecology of the African riverine elephant fishes (Mormyridae).

Multiple species of the elephant fishes (Mormyridae) commonly coexist in sympatry in most African tropical rivers and lakes. In this study, we investigated the trophic ecology and potential trophic niche partitioning of eleven mormyrid fish species from the Sanaga River system in Cameroon using the stable isotope composition of carbon and nitrogen in the muscle samples. Albeit most mormyrids mainly feed on invertebrates, we found differences in isotope ratios, and we report signs of the trophic niche partitioning among species. We further found significant differences in isotopic signatures within the Mormyrus genus, suggesting ecological niche diversification among three closely related species. We have also evaluated differences in the isotopic signals between seasons in four species, which could be possibly caused by species migration and/or anthropogenic agricultural activities. To evaluate body shape, we applied geometric morphometric analyses, and we show that most of the species are clearly morphologically separated. We focused on the mormyrid ecomorphology to identify a possible interaction between shape and ecology, and we found a relationship between the δ13C (but not δ15N) isotopic signal and morphology, suggesting their interplay during mormyrid evolution. Overall, we present robust evidence of the trophic niche partitioning within the mormyrid species community, and we integrate trophic ecology with morphometrics, shedding light on the enigmatic evolutionary history of these fascinating African fishes.

Isotope and morphometrical evidence reveals the technological package associated with agriculture adoption in western Europe

This study aimed to reconstruct the environmental conditions and the crop management practices and plant characteristics when agriculture appeared in western Europe. We analyzed oak charcoal and a large number of cereal caryopsides recovered from La Draga (Girona, Spain), an early (5300 to 4800 cal. BC) agricultural site from the Iberian Peninsula. The carbon isotope discrimination (Δ13C) values of oak, the dominant forest species in the region, indicates prevalence of a wet climate at the site. Further, we reconstructed crop management conditions, achievable yield, and crop characteristics through the analysis of Δ13C, nitrogen isotope composition (δ15N), nitrogen content, and the reconstructed weight of wheat and barley caryopsides, following protocols developed by our team [Araus et al., Nat. Commun. 5, 3953 (2014)] and comparison of these parameters with present-day organic agriculture in the region. In parallel, a regional perspective was achieved through the study of wheat and barley grains of seventeen Neolithic sites from the western Mediterranean. The results suggest that rather than small-garden cultivation, a more extensive agriculture was practiced under good water availability and moderate manuring. Moreover, results from La Draga evidence that grain weight and spike morphology were comparable to contemporary cereals. Growing conditions and the prevalence of improved crop traits indicate that agriculture was fairly consolidated at the time it reached the western edge of Europe.

Lateral redox variability in ca. 1.9 Ga marine environments indicated by organic carbon and nitrogen isotope compositions.

The stepwise oxygenation of Earth's surficial environment is thought to have shaped the evolutionary history of life. Microfossil records and molecular clocks suggest eukaryotes appeared during the Paleoproterozoic, perhaps shortly after the Great Oxidation Episode at ca. 2.43 Ga. The mildly oxygenated atmosphere and surface oceans likely contributed to the early evolution of eukaryotes. However, the principal trigger for the eukaryote appearance and a potential factor for their delayed expansion (i.e., intermediate ocean redox conditions until the Neoproterozoic) remain poorly understood, largely owing to a lack of constraints on marine and terrestrial nutrient cycling. Here, we analyzed redox-sensitive element contents and organic carbon and nitrogen isotope compositions of relatively low metamorphic-grade (greenschist facies) black shales preserved in the Flin Flon Belt of central Canada to examine open-marine redox conditions and biological activity around the ca. 1.9 Ga Flin Flon oceanic island arc. The black shale samples were collected from the Reed Lake area in the eastern part of the Flin Flon Belt, and the depositional site was likely distal from the Archean cratons. The black shales have low Al/Ti ratios and are slightly depleted in light rare-earth elements relative to the post-Archean average shale, which is consistent with a limited contribution from felsic igneous rocks in Archean upper continental crust. Redox conditions have likely varied between suboxic and euxinic at the depositional site of the studied section, as suggested by variable U/Al and Mo/Al ratios. Organic carbon and nitrogen isotope compositions of the black shales are approximately -23‰ and +13.7‰, respectively, and these values are systematically higher than those of broadly coeval continental margin deposits (approximately -30‰ for δ13Corg and +5‰ for δ15Nbulk). These elevated values are indicative of high productivity that led to enhanced denitrification (i.e., a high denitrification rate relative to nitrogen influx at the depositional site). Similar geochemical patterns have also been observed in the modern Peruvian oxygen minimum zone where dissolved nitrogen compounds are actively lost from the reservoir via denitrification and anammox, but the large nitrate reservoir of the deep ocean prevents exhaustion of the surface nitrate pool. Nitrogen must have been widely bioavailable in the ca. 1.9 Ga oceans, and its supply to upwelling zones must have supported habitable environments for eukaryotes, even in the middle of oceans around island arcs.

Multi-method characterization of groundwater nitrate and sulfate contamination by karst mines in southwest China

Groundwater contamination by nitrate and sulfate in mining areas is a significant challenge. Consequently, the inputs sources of these contaminants and their evolution have received considerable attention, with the knowledge gained critical for improved management of water quality. This study integrated data on multiple stable isotopes and water chemistry data and a Bayesian isotope mixing model to investigate the relative contributions of inputs sources of sulfate and nitrate sources to bodies of water in a karst mining area in southwest China. The outcomes indicated that hydrochemical component in the water bodies of the study area is mainly derived from the dissolution of silicate rocks, carbonate rocks and sulfate minerals as well as the oxidation of sulfides. The human and agricultural wastewater, soil nitrogen, and fertilizers were the predominant inputs sources of nitrate to the mine water environment; the predominant inputs sources of sulfide were mineral oxidation, evaporite dissolution, atmospheric deposition, and sewage. Groundwater is mainly recharged from atmospheric precipitation, and surface water is closely hydraulically connected to groundwater. Nitrogen and oxygen isotope composition and water chemistry indicative of nitrification dominate the nitrogen cycle in the study area. The oxidation of pyrite and bacterial sulfate reduction (SRB) had no significant impact on the stable isotopes of groundwater. The results of this study demonstrate the inputs of different sources to nitrate and sulfate in karst mines and associated transformation processes. The results of this study can assist in the conservation of groundwater quality in mining areas and can act as a reference for future related studies.

Asteroid (101955) Bennu in the laboratory: Properties of the sample collected by OSIRIS‐REx

AbstractOn September 24, 2023, NASA's OSIRIS‐REx mission dropped a capsule to Earth containing ~120 g of pristine carbonaceous regolith from Bennu. We describe the delivery and initial allocation of this asteroid sample and introduce its bulk physical, chemical, and mineralogical properties from early analyses. The regolith is very dark overall, with higher‐reflectance inclusions and particles interspersed. Particle sizes range from submicron dust to a stone ~3.5 cm long. Millimeter‐scale and larger stones typically have hummocky or angular morphologies. Some stones appear mottled by brighter material that occurs as veins and crusts. Hummocky stones have the lowest densities and mottled stones have the highest. Remote sensing of Bennu's surface detected hydrated phyllosilicates, magnetite, organic compounds, carbonates, and scarce anhydrous silicates, all of which the sample confirms. We also find sulfides, presolar grains, and, less expectedly, Mg,Na‐rich phosphates, as well as other trace phases. The sample's composition and mineralogy indicate substantial aqueous alteration and resemble those of Ryugu and the most chemically primitive, low‐petrologic‐type carbonaceous chondrites. Nevertheless, we find distinct hydrogen, nitrogen, and oxygen isotopic compositions, and some of the material we analyzed is enriched in fluid‐mobile elements. Our findings underscore the value of sample return—especially for low‐density material that may not readily survive atmospheric entry—and lay the groundwork for more comprehensive analyses.

Precipitation mechanism of Mn ore deposits in the Datangpo Formation, Nanhua Basin, South China

During the interglacial period of the Cryogenian glaciation, the extensive “Datangpo-type” manganese ores were deposited in the Nanhua Basin. However, there has been significant controversy over the precipitation mechanism of manganese for decades. Based on iron and nitrogen isotope data from the manganese ores of the Datangpo Formation in Chongqing (South China), combined with previous research, we propose that the manganese ores of the Datangpo Formation precipitated directly in an anoxic bottom-water environment in the form of rhodochrosite. The δ56Fe values in the Bijiashan manganese ore (δ56Fe = −0.19 ± 0.13 ‰) are close to those of modern marine hydrothermal iron, and there is a strong positive correlation between the δ56Fe value and iron concentration (R2 = 0.81), indicating that the precipitation of manganese ore could be mainly affected by hydrothermal input. After comprehensively comparing the δ56Fe values of the whole rock and pyrite in the manganese ore of the Datangpo Formation, we believe that iron from hydrothermal sources directly and quantitatively combined with sulfides to form pyrite. Additionally, the bottom seawater of the basin was mainly anoxic. The nitrogen isotope composition indicates the presence of a stable nitrate reservoir in the ocean at that time, and manganese ore deposition may have been influenced by the input of high-salinity water from the open ocean. Due to the supply of NO3- from the open ocean to the graben basin, the δ15N in manganese ore is significantly higher than that in black shale. The input from the open ocean led to an increase in alkalinity in the bottom water of the basin, which favored the precipitation of rhodochrosite. Considering that the oxidation potential required for manganese oxidation precipitation is higher than that required for iron oxidation precipitation, it is most reasonable to conclude that under alkaline anoxic conditions in the bottom water layer, Mn2+ directly precipitated in the form of rhodochrosite.

Experimental assessment of elemental analyzer isotope ratio mass spectrometry normalization methodologies for environmental stable isotopes.

In stable isotope mass spectrometry, isotope delta values are normalized to internationally recognized reference scales using a combination of certified and in-house isotope reference materials. Numerous techniques exist for performing this normalization, but these methodologies need to be experimentally assessed to compare their effect on reproducibility of isotope results. We tested normalization methods by the number of reference materials used, their matrix, their isotope range, and whether normalization required extrapolating beyond the isotope range. We analyzed eight commercially available isotope reference materials on a ThermoFinnigan Delta-V isotope ratio mass spectrometer (IRMS) and an Elementar VisION IRMS for nitrogen and carbon isotope composition via solid combustion with an elemental analyzer and computed every possible isotope normalization (n = 612). Additionally, we assessed how sample matrix affected linearity effects on both instruments using five in-house reference materials. Normalizations exhibited the best performance when the reference materials spanning an isotope range of at least 20‰ were matrix matched with the samples and did not require extrapolation beyond the calibration curve. When these conditions were not met, the number of reference materials used had a significant effect on accuracy, with normalizations composed of two reference materials exhibiting particularly inconsistent performance at isotope ranges below 20‰. Linearity effects were found to exceed instrument precision by two orders of magnitude irrespective of matrix type and were not predicted by working gas diagnostics. Interlaboratory comparability of isotope results is improved when operators of elemental analyzer isotope ratio mass spectrometry (EAIRMS) systems select reference materials spanning an isotope range of at least 20‰. Additionally, using three or more isotopic reference materials, avoiding extrapolation beyond the range of the normalization curve, and matching the matrix of the reference materials to the samples improve normalizations.

Petrographic and chemical characterization and carbon and nitrogen isotopic compositions of cometary IDPs and their GEMS amorphous silicates

GEMS (glass with embedded metal and sulfides) are the dominant carrier of amorphous silicates in anhydrous interplanetary dust particles (IDPs) and one of the most suitable materials to study early solar system processes. Amorphous silicates in 105 GEMS from eight IDPs were analyzed regarding texture and chemical composition to reassess GEMS formation theories and genetic relationships to amorphous silicate material in meteorites. Petrography of bulk IDPs was investigated to understand GEMS’ relationships to other IDP components. Furthermore, carbon and nitrogen isotopic compositions were measured. Nearly all GEMS are aggregates of several subgrains with variable amount of nanophase inclusions and different Mg- and Si-contents, while single GEMS are rare. The subgrains within aggregates are typically surrounded by one or more carbon rims with high density. The chemical compositions of GEMS amorphous silicates are subsolar for all major element/Si ratios but exhibit wide heterogeneity. This is not influenced by silicon oil from the capturing process of IDPs as assumed before, as a penetration of the silicon oil is excluded by high resolution EELS (electron energy loss spectroscopy) areal density maps of silicon. Furthermore, low Fe-content in GEMS amorphous silicates shows that these are not altered by aqueous activity on the parent body as it is the case for amorphous silicate material in primitive meteorites. The subsolar element/Si ratios and the wide chemical heterogeneity point to a non-equilibrium fractional condensation origin either in the early solar nebula or in a circumstellar environment and are not in agreement with homogenization via sputtering in the ISM. The close association with carbon around GEMS subgrains and as double-rims around GEMS aggregates argue for a multi-step aggregation after formation of the smallest GEMS subgrains in the ISM or the early solar nebula. Carbon acting as matrix material connecting GEMS and other IDP components has lower areal density as seen from carbon EELS areal density maps and isotopic anomalies varying at the nanometer scale, pointing to different origins and processing of materials to varying extent or at changing temperatures.To balance GEMS’ subsolar element/Si ratios, a supersolar component in IDPs was assumed to account for the overall chondritic composition of bulk IDPs. Nevertheless, our bulk IDP analyses revealed subsolar, but variable, element/Si ratios for complete particles as well, depending on type and amount of mineral phases in each particle. Pyroxenes in the investigated particles can occur as elongated euhedral crystals, but are overall rare. The dominant crystalline fraction in the investigated IDP samples are equilibrated aggregates (EAs) that show the same chemical compositions as GEMS, indicating that the EAs are recrystallized GEMS grains and formed after GEMS formation as secondary phases.

Fertilizer Effects on the Nitrogen Isotope Composition of Soil and Different Leaf Locations of Potted Camellia sinensis over a Growing Season.

The nitrogen-stable isotopes of plants can be used to verify the source of fertilizers, but the fertilizer uptake patterns in tea (Camellia sinensis) plants are unclear. In this study, potted tea plants were treated with three types of organic fertilizers (OFs), urea, and a control. The tea leaves were sampled over seven months from the top, middle, and base of the plants and analyzed for the δ15N and nitrogen content, along with the corresponding soil samples. The top tea leaves treated with the rapeseed cake OF had the highest δ15N values (up to 6.6‱), followed by the chicken manure, the cow manure, the control, and the urea fertilizer (6.5‱, 4.1‱, 2.2‱, and 0.6‱, respectively). The soil treated with cow manure had the highest δ15N values (6.0‱), followed by the chicken manure, rapeseed cake, control, and urea fertilizer (4.8‱, 4.0‱, 2.5‱, and 1.9‱, respectively). The tea leaves fertilized with rapeseed cake showed only slight δ15N value changes in autumn but increased significantly in early spring and then decreased in late spring, consistent with the delivery of a slow-release fertilizer. Meanwhile, the δ15N values of the top, middle, and basal leaves from the tea plants treated with the rapeseed cake treatment were consistently higher in early spring and lower in autumn and late spring, respectively. The urea and control samples had lower tea leaf δ15N values than the rapeseed cake-treated tea and showed a generalized decrease in the tea leaf δ15N values over time. The results clarify the temporal nitrogen patterns and isotope compositions of tea leaves treated with different fertilizer types and ensure that the δ15N tea leaf values can be used to authenticate the organic fertilizer methods across different harvest periods and leaf locations. The present results based on a pot experiment require further exploration in open agricultural soils in terms of the various potential fertilizer effects on the different variations of nitrogen isotope ratios in tea plants.

Isotopic composition of carbon (δ13C) and nitrogen (δ15N) of petrologically different Tertiary lignites and coals

This study investigates the carbon (δ13Corg) and nitrogen (δ15N) isotopic composition of tertiary lignites and coals from six sedimentary basins: Velenje, Mura-Zala, and Zasavje in Slovenia; Sokolov in Czech Republic, Barito in Indonesia; and Istria in Croatia. The aim is to investigate the correlation between the fine detrital (fD) component and δ13C and δ15N in Velenje lignite samples. Additionally, we aim to evaluate the biogeochemical processes of organic substances during their deposition in all analyzed samples, calculate their δ13CCO2 values and compare the analyzed values of δ13C and δ15N to those reported in the literature. Thirty-two samples were analyzed, predominantly from the Velenje ortho-lignite (Pliocene), with additional lignites and coals from the Pannonian to Paleocene epochs for comparison. Carbon isotopic composition (δ13Corg) ranged from -27.9 to -23.6 ‰, and nitrogen isotopic composition (δ15N) ranged from 1.8 to 7.4 ‰. The fine-detrital lithotypes of the Velenje ortho-lignite exhibited the most negative δ13Corg values due to anaerobic bacterial activity in an intramontane alkaline lake environment influenced by the carbonate hinterland. Moreover, gelification processes affected fine-detrital organic matter more than larger wooden pieces. Terbegovci, Hrastnik meta-lignites, and Barito sub-bituminous coal also displayed low δ13Corg values, indicating limited gelification, while variations in the δ15N values suggested differences in mineralization. The Velenje xylitic lithotypes have higher δ15N values, indicating a more intense mineralization under aerobic conditions. Raša ortho-bituminous coal, deposited in a brackish environment, displayed the highest δ13Corg values and a wide range of δ15N values due to fluctuating water tables in a paralic carbonate platform environment. The lowest δ15N value was observed in the Sokolov Basin lignite coal, indicating minimal mineralization and low bacterial activity. The isotopic composition of CO2 in air (δ13Cair), which was calculated using the δ13C values in lignites and coal, ranged from -8.4 to -3.4 ‰, with Velenje lignite displaying the minimum value and Raša coal showing the maximum value. The determined δ13C and δ15N values of the coal and lignite samples in this research fall within the typical range of world coals.