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Archaeological and palaeontological excavations frequently produce large quantities of highly fragmentary bone. These bones can help to answer questions regarding past environments and human and animal lifeways via a number of analytical techniques but this potential is limited by the inability to distinguish individual animals and generate sufficiently large samples. Using stable carbon and nitrogen isotope values of bone collagen (δ13C, δ15N), we present a metric to identify the number of isotopically distinct specimens (NIDS) from highly fragmented faunal assemblages. We quantified the amount of intra-individual isotopic variation by generating isotopic data from multiple elements from individual animals representing a wide variety of taxa as well as multiple samples from the same skeletal element. The mean intra-individual variation (inter-bone) was 0.52‰ (σ = 0.45) (Euclidean distance between two points in isotopic bivariate space), while the mean intra-bone variation was 0.63‰ (σ = 0.06). Using archaeological data consisting of large numbers of individual taxa from single sites, the mean inter-individual isotopic variation was 1.45‰ (σ = 1.15). We suggest the use of 1.50‰ in bivariate (δ13C, δ15N) space as a metric to distinguish NIDS. Blind tests of modelled archaeological datasets of different size and isotopic variability resulted in a rate of misclassification (two or more elements from the same individual being classified as coming from different individuals) of

Traditional bulk isotopic analysis is a pivotal tool for mapping consumer–resource interactions in food webs but has largely failed to adequately describe parasite–host relationships. Thus, parasite–host interactions remain undescribed in food web frameworks despite these relationships increasing linkage density, connectance and ecosystem biomass. Compound-specific stable isotopes from amino acids provides a promising novel approach that may aid in mapping parasite–host relationships in food webs. Here we apply a combination of traditional bulk stable isotope analyses and compound-specific isotopic analysis of nitrogen in amino acids to examine resource use and trophic interactions of five parasites from three hosts from a marine coastal food web (Wadden Sea, European Atlantic). By comparing isotopic compositions of bulk and amino acid nitrogen, we aimed to characterize isotopic fractionation occurring between parasites and their hosts and to clarify parasite trophic positions. Our results indicate that parasitic trophic interactions were more accurately identified using compound-specific stable isotope analysis due to removal of underlying source isotopic variation for both parasites and hosts. The compound-specific method provided clearer trophic discrimination factors in comparison to bulk isotope methods. Amino acid compound specific isotope analysis has widely been applied to examine trophic position within food webs, but our analyses suggest that the method is particularly useful for clarifying the feeding strategies for parasitic species. Baseline isotopic information provided by source amino acids allows clear identification of the fractionation from parasite metabolism by integrating underlying isotopic variations from the host tissues. However, like for bulk isotope analysis, the application of a universal trophic discrimination factor to parasite–host relationships remains inappropriate for compound-specific stable isotope analysis. Despite this limitation, compound-specific stable isotope analysis is and will continue to be a valuable tool to increase our understanding of parasitic interactions in marine food webs.

The isotopic composition of nitrogen and oxygen in nitrogen dioxide (NO2) potentially carries a wealth of information about the dynamics of the nitrogen oxides (NOx = nitric oxide (NO) + NO2) chemistry in the atmosphere. While nitrogen isotopes of NO2 are subtle indicators of NOx emissions and chemistry, oxygen isotopes are believed to reflect only the O3 / NOx / VOC chemical regime in different atmospheric environments. In order to access this potential tracer of the tropospheric chemistry, we have developed an efficient active method to trap atmospheric NO2 on denuder tubes and measured, for the first time, its multi-isotopic composition (δ15N, δ18O, and Δ17O). The Δ17O values of NO2 trapped at our site in Grenoble, France, show a large diurnal cycle peaking in late morning at (39.2 ± 0.3) ‰ and decreasing at night until (20.5 ± 0.3) ‰. On top of this diurnal cycle, Δ17O also exhibits substantial daytime variability (from 29.7 ‰ to 39.2 ‰), certainly driven by changes in the O3 to peroxyl radicals (RO2) ratio. The nighttime decay of Δ17O(NO2) appears to be driven by NO2 slow removal, mostly from conversion into N2O5, and its formation from the reaction between O3 and freshly emitted NO. As expected from a nighttime Δ17O(NO2) expression, our Δ17O(NO2) measured towards the end of the night is quantitatively consistent with typical values of Δ17O(O3). Daytime N isotope fractionation is estimated using a general expression linking it to Δ17O(NO2). An expression is also derived for the nighttime N isotope fractionation. In contrast to Δ17O(NO2), δ15N(NO2) measurements exhibit little diurnal variability (−11.8 ‰ to −4.9 ‰) with negligible isotope fractionations between NO and NO2, mainly due to high NO2 / NOx ratios, excepted during the morning rush hours. The main NOx emission sources are estimated using a Bayesian isotope mixing model, indicating the predominance of traffic emissions in this area. These preliminary results are very promising for using the combination of Δ17O and δ15N of NO2 as a probe of the NOx sources and fate and for interpreting nitrate isotopic composition records.

Sea turtles exhibit complex life histories, encompassing intermittent use of multiple spatially separated habitats throughout long lifespans. This broad scope presents challenges for collecting comprehensive biological and ecological data, yet absence of such information complicates evaluation of management strategies for populations at risk of extinction. Hawksbill sea turtles Eretmochelys imbricata are endangered worldwide, primarily due to long-term, directed harvest. However, available information regarding life stage durations, somatic growth patterns, and maturation attributes to enhance understanding of anthropogenic impacts and recovery potential remains constrained. To address these data gaps in the western North Atlantic, we conducted skeletochronological analysis for hawksbills stranded along US coastlines to generate straight-line carapace length (SCL)-at-age and somatic growth data. Generalized additive mixed models and bootstrapped von Bertalanffy growth curves were used to characterize age at maturation and covariate influence on somatic growth. For a subset of turtles, annual bone growth increment-specific stable isotope and trace element analyses were incorporated to evaluate habitat use relative to age. Integration of these data sources indicated that juveniles transitioned from oceanic to neritic habitat at 1-3 yr old and mean SCLs of 23-24 cm (range 15.7-35.0 cm). Initial ages at maturation for this population at minimum nesting female SCLs were estimated at 15-25 yr. Somatic growth varied significantly relative to size, age, and stranding location, while no association with sex or calendar year was observed. Our results demonstrate the utility of these complementary analytical approaches for generating baseline data fundamental to characterizing hawksbill sea turtle population attributes.

Nitrogen stable isotope ratios (δ15N) are routinely used to estimate consumer trophic positions (TPs). This method is very sensitive to the chosen isotopic baseline, which should incorporate all temporal isotopic variability occurring in the base of the food web sustaining the consumers. However, there is still no consensus on the different methods to represent time intervals for isotopic assimilation. It is uncertain if researchers should compute a single baseline obtained by averaging δ15N source values across all time periods, multiple baselines based on δ15N source values collected concomitantly with consumers, or consider a time lag between sources and consumers. Aiming to provide empirical evidence to help select the best option, we designed 4 methods using different temporal lags between consumers and producers based on a 9 yr time series of carbon and nitrogen stable isotopes in an estuary. The 4 tested baseline methods considered the δ15N average of producers sampled in all years (Global); the same season as consumers (Concomitantly); the season before the collection of consumers (Delayed); and the previous season as well as the same season of consumer sampling (Interpolation). Comparison of results with an expected model (based on stomach content data) showed that the Delayed method is the most appropriate. We conclude that time lags in the incorporation of stable isotope values between sources and consumers must be considered in baseline δ15N calculations to improve TP estimates and provide more reliable modeling results. Additionally, we provide other recommendations to improve sampling designs when using stable isotopes in TP estimations.

Dissimilatory nitrate reduction (DNR) to nitrite is the first step in denitrification, the main process through which bioavailable nitrogen is removed from ecosystems. DNR is catalyzed by both cytosolic (Nar) and periplasmic (Nap) nitrate reductases and fractionates the stable isotopes of nitrogen (14N, 15N) and oxygen (16O, 18O), which is reflected in residual environmental nitrate pools. Data on the relationship between the pattern in oxygen vs nitrogen isotope fractionation (18e/15e) suggests that systematic differences exist between marine and terrestrial ecosystems that are not fully understood. We examined the 18e/15e of nitrate-reducing microorganisms that encode Nar, Nap, or both enzymes, as well as gene deletion mutants of Nar and Nap to test the hypothesis that enzymatic differences alone could explain the environmental observations. We find that the distribution of 18e/15e fractionation ratios of all examined nitrate reductases forms two distinct peaks centered around an 18e/15e proportionality of 0.55 (Nap) and 0.91 (Nar), with the notable exception of the Bacillus Nar reductases, which cluster isotopically with the Nap reductases. Our findings may explain differences in 18e/15e fractionation between marine and terrestrial systems and challenge current knowledge about Nar 18e/15e signatures.

Cervids living in high latitudes have evolved to thrive in ecosystems that experience dramatic seasonal changes. Understanding these seasonal adaptations is important for reconstructing cervid life histories, ecosystem dynamics, and responses in the distant and not-so-distant past to changing seasonality caused by climate change. Cervid antlers provide a rare opportunity for insight into faunal seasonal ecology, as they are grown and shed each year. Stable isotopes of carbon and nitrogen measured directly from antlers have the potential to provide seasonal dietary data for individuals. If the isotopic signals in bone and antler are controlled by the same metabolic processes, then the stable carbon and nitrogen isotope compositions of collagen (δ13CColland δ15NColl) from incrementally grown antler tissue provide time-constrained dietary signals from the spring and summer growth season. Bone, by comparison, provides an average signal over several years. The amino acid (glutamate and phenylalanine) δ15N in antlers from modern captive caribou showed similar trophic discrimination factors to earlier results for other collagenous tissues (bone, tooth dentin, and cementum). Hence, growth rate was not the primary control on the stable isotope composition of antler collagen. We applied this knowledge to assess seasonal shifts in Quaternary fossils of three Cervidae species: elk (Cervus elaphus), moose (Alces alces), and caribou (Rangifer tarandus). Paired antler–bone δ13CColland δ15NCollfrom the same individual were used to identify differences between summer and annual diet and ecology. Intra-antler isotopic variability from serially sampled antlers was used to examine seasonal dietary shifts and specialization.

Nitrogen isotopes are a robust tool to study geological nitrogen cycle between Earth’s reservoirs. However, the application of nitrogen isotope system to understanding geological processes has been limited by the lack of constraints on equilibrium isotope fractionation factors between mineral and fluid and between mineral pairs. Here, we use first-principles methods to calculate the nitrogen isotope fractionations among aqueous ammonium, ammonium- and/or nitrate-bearing salts, and ammonium-bearing silicate minerals that commonly occur in Earth’s lithosphere. Our results show a first-order, large nitrogen isotope fractionations between the nitrate group and the ammonium group, with 15N being more enriched in the nitrate group. In detail, the nitrogen isotope fractionations among nitrate group minerals (NaNO3, KNO3, Ba(NO3)2, NH4NO3) are very small. The nitrogen isotope fractionations are also small among the ammonium group (e.g., aqueous ammonium, ammonium salts, phyllosilicate, and tectosilicate minerals) except inosilicate minerals (e.g., diopside and jadeite), which are however significantly more enriched in 15N than the other ammonium-bearing minerals. These results suggest that nitrogen isotopes may serve as a robust geothermometer only when the rock contains coexisting ammonium and nitrate minerals, or contain diopside and/or jadeite together with other ammonium-bearing silicate minerals. Given that common silicate minerals in crustal rocks (clays, micas, feldspars) do not significantly discriminate nitrogen isotopes, nitrogen isotopes can thus be used as a sensitive tool to trace material source and infer geochemical processes that may cause isotope disequilibrium, such as metamorphic devolatilization, hydrothermal alteration, crust-mantle interaction. Our results also demonstrate that authigenic clay minerals can inherit the nitrogen isotopic signature of organic matter and aqueous ammonium and thus can serve as an environmental proxy. However, it is crucial to distinguish detrital minerals from authigenic minerals in sediments when reconstruct marine and lacustrine environments in the deep time (Archean and Proterozoic).

Ammonium (NH4+), ammonia (NH3) and N2 are key nitrogen species in geological nitrogen recycling. NH3 has also been proposed to play an important role in mobilizing base metals in the form of metal-ammine complexes in hydrothermal fluids. The nitrogen isotope fractionation factors among these nitrogen species in aqueous and gaseous phases are essential parameters to trace source signatures and geochemical properties in geological processes. However, the nitrogen isotope fractionation factors for metal-ammine complexes are largely absent, and the few existing nitrogen isotope fractionation factors for the aqueous NH4+ – aqueous NH3 pair show large discrepancy between experimental results and theoretical calculations. In this study, we employed the density functional theory to systematically calculate the nitrogen isotope fractionation factors among the nitrogen species that may occur in a hydrothermal system, i.e., gaseous N2, gaseous and aqueous NH4+ and NH3, and ammine complexes of Co, Zn, Cu, Cd, Ag, Au, and Pt. Based on these new results, the large nitrogen isotope fractionations for the aqueous NH4+ – aqueous NH3 pair observed in previous experimental studies can be well explained by a combined effect of an equilibrium isotope fractionation between aqueous NH4+ and aqueous NH3 and a kinetic isotope fractionation during NH3 degassing from the solution. This suggests that the nitrogen isotopic behavior during NH3 degassing in natural hydrothermal system can be more complicated than previous thought. A numeric model is thus established here to quantify the combined isotopic effect on partial NH3 degassing. Using the new results of metal-ammine complexes, we also tested the hypothesis that nitrogen mobilization could be controlled by copper-ammine complex based on the copper concentration-δ15N relationship previously observed in meta-gabbros.

Plants acquire multiple resources from the environment and may need to adjust and/or balance their respective resource-use efficiencies to maximize grow and survival, in a locally adaptive manner. In this study, tissue and whole-plant carbon (C) isotopic composition (δ13C) and carbon/nitrogen (C/N) ratios provided long-term measures of use efficiencies for water (WUE) and nitrogen (NUE), and a nitrogen (N) isotopic composition (δ15N)-based mass balance model was used to estimate traits related to N uptake and assimilation in heart-leaved willow (Salix eriocephala Michx.). In an initial common garden experiment consisting of 34 populations, we found population-level variation in δ13C, C/N ratio and δ15N, indicating different patterns in WUE, NUE and N uptake and assimilation. Although there was no relationship between foliar δ13C and C/N ratios among populations, there was a significant negative correlation between these measures across all individuals, implying a genetic and/or plastic trade-off between WUE and NUE not associated with local adaptation. To eliminate any environmental effect, we grew a subset of 21 genotypes hydroponically with nitrate as the sole N source and detected significant variation in δ13C, δ15N and C/N ratios. Variation in δ15N was mainly due to genotypic differences in the nitrate efflux/influx ratio (E/I) at the root. Both experiments suggested clinal variation in δ15N (and thus N uptake efficiency) with latitude of origin, which may relate to water availability and could contribute to global patterns in ecosystem δ15N. There was a tendency for genotypes with higher WUE to come from more water-replete sites with shorter and cooler growing seasons. We found that δ13C, C/N ratio and E/I were not inter-correlated, suggesting that the selection of growth, WUE, NUE and N uptake efficiency can occur without trade-off.

Redox transformations of nitrogen (N) play a critical role in determining its speciation and biological availability, thus defining the magnitude and extent of productivity in many ecosystems. A range of important nitrogen transformations often co-occur in regions hosting other redox-active elements, including sulfur, iron, and manganese (Mn), especially along sharp redox gradients within aquatic sediments. This proximity in “redox real estate” produces conditions under which multi-element interactions and coupled cycling are thermodynamically favored. While previous work has reported anoxic nitrification linked to the presence of manganese (Mn) oxides in sediments, a clear connection between the cycling of Mn and N has remained elusive. Soluble Mn(III), which is stabilized via ligand-complexation, has recently been shown to represent the dominant dissolved Mn species in many environments. Here, we examined the reactivity of ligand-stabilized Mn(III) with nitrite, using natural abundance stable nitrogen and oxygen isotopes to explore reaction dynamics under a range of conditions. Oxidation of nitrite to nitrate by Mn(III)-pyrophosphate proceeded abiotically under both oxygen replete and nitrogen-purged conditions. Kinetics and isotope systematics of this reaction were measured over a range of pH (5–8), with reaction rates decreasing with increasing pH. Under all treatments, an inverse kinetic isotope effect of −19.9 ± 0.7‰ was observed for N, remarkably similar to previously documented fractionation by nitrite-oxidizing organisms. Experiments using 18O-labeled water confirmed that the source of the additional oxygen atom was from water. These findings suggest that nitrite oxidation in environments hosting abundant ligand-bound Mn(III), including porewaters, estuaries, and coastal waters, may be facilitated in part by abiotic reactions with Mn, even under functionally anoxic conditions.

During the 29th Chinese National Antarctic Research Expedition, spatial variations in nitrogen isotopic composition of particulate nitrogen (δ15NPN) and their controlling factors were examined in detail with regard to nitrate drawdown by phytoplankton and particulate nitrogen (PN) remineralization in the Prydz Bay and its adjacent areas. To better constrain the nitrogen transformations, the physical and chemical parameters, including temperature, salinity, nutrients, PN and δ15NPN in seawater column were measured from surface to bottom. In addition, the nitrogen isotopic fractionation factor of nitrate assimilation by phytoplankton in the mixed layer, and the nitrogen isotopic fractionation factor of PN remineralization below the mixed layer were estimated using Rayleigh model and Steady State model, respectively. Our results showed that suspended particles had its lowest δ15NPN in the surface layer, which was due to the preferential assimilation of 14N in nitrate by phytoplankton. The δ15NPN in the mixed layer of the Prydz Bay and its adjacent areas decreased from the inner shelf to the outer basin, ascribing to the effect of isotope fractionation during phytoplankton assimilation. In mixed layer, the spatial distribution of δ15NPN associated with particulate organic matter (POM) production can be well interpreted according to Rayleigh model and Steady State model. The nitrogen isotope fractionation factor during phytoplankton assimilating nitrate was estimated as 10.0%o by Steady State model, which was more reasonable than that calculated by Rayleigh model. These results validate the previous reports of fractionation factor during nitrate assimilation by phytoplankton. Increasing δ15NPN with depth below the euphotic zone correlated with the decreasing PN contents, and it was attributed to preferential remineralization of 14N in PN by bacteria. In subsurface and deep layer, the δ15NPN distributions also conformed to Rayleigh model and Steady State model during PN remineralization, with a fractionation factor of about 3.6% and 3.2%, respectively. It is the first time to estimate the fractionation factor during POM production and remineralization in the Prydz Bay and its adjacent areas. Such fractionation may provide a useful tool for the follow-up study of the nitrogen dynamics in the Southern Ocean.

The paper presents the first data on the nitrogen isotope composition of the associated gases of mineral waters in the North Caucasus and newly acquired data on the carbon isotope composition of the CO2 and CH4. Most of the samples were taken from the high- $${{p}_{{{\text{C}}{{{\text{O}}}_{{\text{2}}}}}}}$$ waters of the Elbrus and Kazbek volcanic areas in the Greater Caucasus. It is shown that δ15N changes in the range of –3.9 to +5.6‰ and synchronously increases in gases of the Caucasus Spa Area (CSA) with an increase in the N2 and CH4 concentrations. This correlation points to a genetic association of non-atmogenic nitrogen with sedimentary methane-generating processes. The values of δ13С in carbon dioxide in the Elbrus area vary from –11.8 to –3.0‰. The mean value of δ13С (СО2) tends to increase north of Elbrus volcano, and this trend may be a consequence of the increasing content of СО2 produced by the thermal decomposition of sedimentary carbonates in the composition of gases, as well as a result of low-temperature interaction of the high- $${{p}_{{{\text{C}}{{{\text{O}}}_{{\text{2}}}}}}}$$ waters with the Jurassic and Cretaceous carbonate rocks. It is shown that high- $${{p}_{{{\text{C}}{{{\text{O}}}_{{\text{2}}}}}}}$$ waters associated with Elbrus volcano often contain up to 12.4% CH4. This methane is characterized by high δ13С of –32.0 to –17.2‰. Analysis of the distribution of concentrations and δ13С values of СН4 around Elbrus and the presence of N2 with positive δ15N values in the gases suggest a crustal genesis of the methane. The role of magmatic activity in this situation is reduced to producing a temperature anomaly that activates carbon isotope exchange in the CO2–CH4 system.

Nitrogen isotope (δ15N) monitoring is a potentially powerful tool in tracing atmospheric nitrogen oxides (NOx); however, the isotopic fingerprint of vehicle exhaust remains poorly interpreted. This...

There is currently no reliable geochemical proxy of historical coral bleaching. Here we test the hypothesis that increases in the nitrogen isotopic signature of coral tissue, which is recorded in skeletal-bound organic material (CS-δ15N), can be used to detect coral bleaching events in the past. We measured CS-δ15N in coral colonies that showed high density thermal stress bands associated with the 1998 and 2002 mass bleaching events on the central Great Barrier Reef. Analysis of coral cores from 2 inshore and 1 mid-shelf reef found that increases in CS-δ15N occurred either side of the thermal stress events and were therefore unlikely to be a physiological response to bleaching. We then assessed whether CS-δ15N could be used to detect shelf-wide upwelling, which has been previously shown to coincide with mass bleaching events. For the inshore sites the response of CS-δ15N to upwelling was not uniform between reefs or between colonies from the same reef. However, on the mid-shelf reef, increased CS-δ15N during the known upwelling of 1998 was more consistent between cores. Analysis of a 23-year old coral core from the mid-shelf reef showed increased CS-δ15N between 1983–1985 and 1997–2000, periods where strong El Nino events were proceeded by intense wind-driven upwelling. We conclude that coral CS-δ15N is not a direct proxy for coral bleaching but can be used to detect prolonged and pervasive upwelling that coincides with mass bleaching events. Further validation with longer core records is required.

Coastal marine ecosystems are very complex and composed of myriad organisms, including offshore, coastal, and migratory fish occupying diverse trophic positions (TPs) in food webs. The illustration of trophic hierarchy based on the TP and resource utilization of individual organisms remains challenging. In this study, we applied compound-specific isotope analysis of amino acids to estimate the TP and isotopic baseline (i.e. δ15N values of primary resources at the base of food webs) for 13 fish and 1 squid species in a coastal area of Sagami Bay, Japan, where a large diversity in the isotopic baseline is caused by an admixture of ocean currents and artificial nitrogen inputs. Our results indicate that the TP of fish and squid varies between 2.9 and 3.9 (i.e. omnivorous, carnivorous, and tertiary consumers), with low variation within individual species. Moreover, the δ15N values of phenylalanine revealed the diversity of isotopic baselines between and within species. Low values (7.8-10.3‰) and high values (18.6-19.2‰), with a small variation (1σ < 1.0‰), were found in 2 offshore species and 3 coastal species, respectively. In contrast, highly variable values (9.8-19.7‰), with large variation within species (1σ > 1.0‰), were found for the remaining 9 migratory species. These results represent evidence of differential trophic exploitation of habitats between offshore and coastal species, particularly among individuals of migratory species, that were all collected in a single area of Sagami Bay.

Biochar has strong potential to improve nitrogen (N) use efficiency in both agricultural and horticultural systems. Biochar is usually co-applied with full rates of fertiliser. However, the extent to which N cycling can be affected after biochar application to meet plant N requirement remains uncertain. This study aimed to explore N cycling up to 2 years after biochar application. We applied pine woodchip biochar at 0, 10 and 30 t ha−1 (B0, B10, B30, respectively) in a macadamia orchard and evaluated the N isotope composition (δ15N) of soil, microbial biomass and macadamia leaves. Soil total N (TN) and inorganic N pools were also measured up to 2 years after biochar application. Biochar did not alter soil TN but soil NO3−-N increased at months 12 and 24 after biochar application. Soil NO3−-N concentrations were always over ideal levels of 15 μg g−1 in B30 throughout the study. Stepwise regression indicated that foliar δ15N decreases after biochar application were explained by increased NO3−-N concentrations in B30. Foliar TN and photosynthesis were not affected by biochar application. The soil in the high rate biochar plots had excess NO3−-N concentrations (over 30 μg g−1) from month 20 onwards. Therefore, N fertiliser applications could be adjusted to prevent excessive N inputs and increase farm profitability.

According to ecological theory, two species cannot occupy the same niche. Using nitrogen isotope analyses (δ15N) of amino acids, we tested the extent to which two sympatric deposit‐feeding amphipods, Monoporeia affinis and Pontoporeia femorata, partition their trophic resources. We found that trophic position (TP) and resynthesis index (∑V; a proxy for degradation status of ingested material prior to assimilation by the consumer) differ between species. The surface‐feeding M. affinis had higher TP and intermediate ∑V, both pointing to a large contribution of metazoans in its diet. P. femorata, which feeds in the subsurface layers, had lower TP and a bimodal distribution of the ∑V values, supporting previous experimental evidence of a larger feeding niche. We also evaluated whether TP and ∑V values have consequences for amphipod fecundity and embryo viability and found that embryo viability in M. affinis was negatively linked to TP. Our results indicate that the amino acid‐δ15N data paired with information about reproductive status are useful for detecting differences in the trophic ecology of sympatric amphipods., This is a field study on niche partitioning in sympatric amphipods using the amino acid nitrogen‐isotope method. Fecundity and embryo viability were measured for each individual analyzed for isotopes, meaning that ecological and physiological causes behind observed patterns could be tested and discussed in a unique way. We demonstrate that the amino acid method was useful in detecting differences in trophic ecology between two deposit‐feeding species, but that it is crucial to include measurements of physiological status when interpreting nitrogen isotope data in amino acids of consumers.

The stable isotopic composition (δ13C and δ15N) and carbon/nitrogen ratio (C/N) of particulate organic matter (POM) in the Chukchi and East Siberian shelves from July to September, 2016 were measured to evaluate the spatial variability and origin of POM. The δ13CPOC values were in the range of −29.5‰to −17.5‰ with an average of −25.9‰±2.09‰, and the δ15NPN values ranged from 3.9‰ to 13.1‰ with an average of 8.0‰±1.6‰. The C/N ratios in the East Siberian shelf were generally higher than those in the Chukchi shelf, while the δ13C and δ15N values were just the opposite. Abnormally low C/N ratios ( 10‰) values were observed in the Wrangel Island polynya, which was attributed to the early bloom of small phytoplankton. The contributions of terrestrial POM, bloom-produced POM and non-bloom marine POM were estimated using a three end-member mixing model. The spatial distribution of terrestrial POM showed a high fraction in the East Siberian shelf and decreased eastward, indicating the influence of Russian rivers. The distribution of non-bloom marine POM showed a high fraction in the Chukchi shelf with the highest fraction occurring in the Bering Strait and decreased westward, suggesting the stimulation of biological production by the Pacific inflow in the Chukchi shelf. The fractions of bloom-produced POM were highest in the winter polynya and gradually decreased toward the periphery. A negative relationship between the bloom-produced POM and the sea ice meltwater inventory was observed, indicating that the net sea ice loss promotes early bloom in the polynya. Given the high fraction of bloom-produced POM, the early bloom of phytoplankton in the polynyas may play an important role on marine production and POM export in the Arctic shelves.

Nitrogen isotope fractionations between nitrogen oxides (NO and NO2 ) play a significant role in determining the nitrogen isotopic compositions ( δ15N ) of atmospheric reactive nitrogen. Both the equilibrium isotopic exchange between NO and NO2 molecules and the isotope effects occurring during the NOx photochemical cycle are important, but both are not well constrained. The nighttime and daytime isotopic fractionations between NO and NO2 in an atmospheric simulation chamber at atmospherically relevant NOx levels were measured. Then, the impact of NOx level and NO2 photolysis rate on the combined isotopic fractionation (equilibrium isotopic exchange and photochemical cycle) between NO and NO2 was calculated. It was found that the isotope effects occurring during the NOx photochemical cycle can be described using a single fractionation factor, designated the Leighton cycle isotope effect (LCIE). The results showed that at room temperature, the fractionation factor of nitrogen isotopic exchange is 1.0289±0.0019 , and the fractionation factor of LCIE (when O3 solely controls the oxidation from NO to NO2 ) is 0.990±0.005 . The measured LCIE factor showed good agreement with previous field measurements, suggesting that it could be applied in an ambient environment, although future work is needed to assess the isotopic fractionation factors of NO + RO 2 / HO 2 → NO 2 . The results were used to model the NO– NO2 isotopic fractionations under several NOx conditions. The model suggested that isotopic exchange was the dominant factor when NOx>20 nmol mol −1 , while LCIE was more important at low NOx concentrations ( nmol mol −1 ) and high rates of NO2 photolysis. These findings provided a useful tool to quantify the isotopic fractionations between tropospheric NO and NO2 , which can be applied in future field observations and atmospheric chemistry models.

The 18O/16O (and 15N/14N) ratio of natural nitrate (NO3-) and nitrite (NO2-) can be used to extract valuable information about their source and fate as environmental contaminants, their metabolism as macronutrients in plants and animals, and their behavior in the N biogeochemical cycle. We developed an accurate, precise, sensitive (minimum sample size: 0.2 μg NO3--equivalent), and reliable (minimal oxygen exchange, loss, or gain) method to selectively isolate and purify nitrate and nitrite from natural water, soil, air, and plant materials by strong anion exchange (SAX) for low- to normal-salinity samples or strong cation exchange (SCX) for high-salinity samples, followed by quantitative conversion to their respective benzyl esters, which can be separated and individually analyzed for δ18O (and potentially δ15N) by gas chromatography (GC)/pyrolysis/GC/isotope-ratio mass spectrometry (IRMS). The method compares favorably with the currently popular bacterial denitrification and chemical reduction methods, in terms of sensitivity and reliability, and has the potential to simultaneously measure δ15N and δ18O of nitrate and nitrite from natural samples of various origins.

The potential of “biosaline agriculture” relies on easy-to-apply tools to select plant genotypes that are best adapted to saline conditions. We aimed to determine the effects of salinity-sodicity on the functional response of alfalfa varieties by evaluating instantaneous vs integrated plant-based measurements for the selection of alfalfa cultivars in biosaline agriculture. Functional responses of three alfalfa varieties were evaluated in a greenhouse study under different saline-sodic conditions. Physiological parameters included instantaneous (gas exchange and chlorophyll fluorescence) vs time-integrated (carbon isotope discrimination -∆13C- and nitrogen isotope composition -δ15N-; specific leaf weight and chlorophyll content) measurements. From all assessed physiological traits, only δ15N was able to effectively discriminate among genotypes WL656HQ, PGI908S and SW8421S, and showed the highest correlation with biomass production at all experimental stages. On average, the δ15N increased by a factor of 3.3 as salinity increased from the non-saline control treatment (ECiw ~ 0.4 dS m−1) to the highest salinity level (ECiw ~ 10.0 dS m−1) indicating that biological N fixation was significantly limited by salinity. Specific leaf weight was also significantly correlated with dry matter although to a much lesser extent than was δ15N. δ15N was found to be the best proxy for assessing alfalfa varieties for their adaptation potential in saline conditions. This parameter was able to discriminate alfalfa’s functional response within a narrow range of irrigation water salinity. δ15N was also capable of differentiating between alfalfa varieties classified as tolerant to salinity defined at a particular plant growth stage, making this an excellent tool for genotypic selection.

Organic matter in lake sediments contains information that can be used to reconstruct lake environmental histories over decades or centuries. In this study, we used organic geochemical proxies (i.e., total organic carbon [TOC], TOC/total nitrogen [TN] atomic ratios [C/N], stable carbon isotope ratios of TOC [δ13CTOC] and palmitic acid [δ13CC16:0], and nitrogen isotope ratios of bulk sediment [δ15Nbulk]) in sediments from Lake Kawaguchi, Japan, to reconstruct detailed histories of the organic matter accumulation and lake productivity over the past 130 years. Vertical profiles of the mass accumulation rate (MAR) of TOC in the eastern lake basin (core KAW14-7A) showed parallel increases with the C/N ratio from the 1960s to the 1980s, indicating an accelerated delivery of terrestrial organic matter via anthropogenic land-use change. In contrast, the C/N ratios in the western and central basins (cores KAW14-1A and KAW14-4B, respectively) were almost constant prior to the 1980s, suggesting that the increasing trends in the TOC MAR values in these cores are most likely attributable to the onset of eutrophication associated with rapid economic growth after the mid-1950s. On the other hand, the δ15Nbulk showed a gradual increase from the late 1870s, providing evidence for anthropogenic nitrogen input to the lake prior to the apparent eutrophication. After the 1960s–1970s, the δ15Nbulk values rapidly increased, demonstrating water deterioration associated with the direct nutrient discharge into the lake from domestic wastewater. The δ13CC16:0 profiles displayed similar increasing trends to δ15Nbulk from the mid-1960s, demonstrating a close relationship between lake productivity and anthropogenic nitrogen input in Lake Kawaguchi. Our geochemical records as a whole clearly show high algal productivity and enhanced deposition of organic matter in recent decades, suggesting that the amelioration of the lake water is a likely consequence of the transfer of nutrients to the sediment by enhanced productivity, rather than a decrease in the amount of nutrient inflow into the lake.

Rhyolitic rocks hosting the El Zapote epithermal Ag deposit are pervasively altered and contain ammonium ranging from 290 to 1750 ppm. High ammonium values are found in samples containing abundant fine-grained illite. This fine-grained illite shows overall low ratios of K/(Al + Fe), likely due to ammonium substituting K+. Samples containing high ammonium, greater than 1000 ppm in the proximity of Ag-bearing veins, show distinct absorption features of ammonium in short-wave infrared (SWIR) absorption spectra. Samples containing ammonium ranging from 500 to 1000 ppm show mixed absorption signatures; some show prominent absorption features related to ammonium, whereas others have no recognizable features. There is no discernible absorption feature related to ammonium for samples containing less than 500 ppm NH4. The data suggest that SWIR spectroscopy is useful in locating the proximal areas to mineralization, but the extent of ammonium alteration is much larger than that identified by SWIR spectroscopy. Nitrogen isotope compositions of ammonium are similar to those of sedimentary rocks, suggesting that the source of ammonium in altered rhyolite is sedimentary basement rocks in the area. Supplementary material: bulk rock composition is available at https://doi.org/10.6084/m9.figshare.c.5015663

A field micro-plot experiment with nitrogen isotope (15 N) labelling was performed to study the impacts of the timing of aside-dressed Napplication on urea-15 N in amaize-soil system. The treatment...

Methods in Ecology and Evolution published by John Wiley & Sons Ltd on behalf of British Ecological Society Isotopic analyses of collagen, the main protein preserved in subfossil bone and tooth, has long provided a powerful tool for the reconstruction of ancient diets and environments. Although isotopic studies of contemporary ecosystems have typically focused on more accessible tissues (e.g. muscle, hair), there is growing interest in the potential for analyses of collagen because it is often available in hard tissue archives (e.g. scales, skin, bone, tooth), allowing for enhanced long-term retrospective studies. The quality of measurements of the stable carbon and nitrogen isotopic compositions of ancient samples is subject to robust and well-established criteria for detection of contaminants and diagenesis. Among these quality control (QC) criteria, the most widely utilized is the atomic C:N ratio (C:NAtomic), which for ancient samples has an acceptable range between 2.9 and 3.6. While this QC criterion was developed for ancient materials, it has increasingly being applied to collagen from modern tissues. Here, we use a large survey of published collagen amino acid compositions (n = 436) from 193 vertebrate species as well as recent experimental isotopic evidence from 413 modern collagen extracts to demonstrate that the C:NAtomic range used for ancient samples is not suitable for assessing collagen quality of modern and archived historical samples. For modern tissues, collagen C:NAtomic falling outside 3.00–3.30 for fish and 3.00–3.28 for mammals and birds can produce systematically skewed isotopic compositions and may lead to significant interpretative errors. These findings are followed by a review of protocols for improving C:NAtomic criteria for modern collagen extracts. Given the tremendous conservation and environmental policy-informing potential that retrospective isotopic analyses of collagen from contemporary and archived vertebrate tissues have for addressing pressing questions about long-term environmental conditions and species behaviours, it is critical that QC criteria tailored to modern tissues are established.

The international trade in lion (Panthera leo) products, particularly bone, has increased substantially over the last decade. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) has established a zero-export quota for wild-origin lion bones. Whilst the trade of lion bone is permittable from captive-bred South African populations, there is no established method to differentiate between captive and wild-sourced lion derivatives in trade. This study acts as a preliminary investigation, by examining the stable carbon (δ13C) and nitrogen (δ15N) isotope composition of hair from wild and captive lion populations as well as wild prey animals in South Africa, to judge the accuracy and applicability of this method for future bone analysis. Isotopic values for δ15N are found to be significantly enriched in some wild populations, however it is not possible to discriminate between captive and wild populations using δ13C analysis alone. Using the classification algorithm k-Nearest Neighbour, the origin of simulated data was identified with 70% accuracy. When using the model to test the origin of seized samples, 63% were classified as of wild origin. Our study indicates the potential for stable isotope analysis to discriminate between captive and wild populations. Additional study of captive husbandry, and analysis of bone samples from populations of a known origin and feeding regime is recommended to improve the utility of this method for maintaining transparency in trade.

The green turtle (Chelonia mydas) is known to present an herbivorous diet as an adult; however, juveniles may have an omnivore habit, and these changes in food preference may affect the uptake and accumulation of pollutants, such as mercury (Hg). In order to better understand the influence of this ontogenetic shift on Hg accumulation, this study evaluates the concentrations of total mercury (THg), methyl mercury (MeHg), and stable isotopes of carbon and nitrogen (δ13C and δ15N) in a group of juveniles of the green turtle. Tissue samples (liver, kidney, muscle, and scutes) were sampled from 47 turtles stranded dead on the coast of Bahia, NE, Brazil, between 2009 and 2013. The turtles analyzed showed a size range of 24.9–62.0 cm and an average of 36.4 ± 7.2 cm of curved carapace length. The scutes showed to be a viable method for Hg monitoring in the green turtles. The concentrations of THg and MeHg decreased with increasing size. The isotope values of δ15N and δ13C did not show a clear relationship with the size, suggesting that the green turtles used in our work would be occupying similar trophic levels, and foraging habitat.

Approximately 700 diamond crystals were identified in volcanic (mainly pyroclastic) rocks of the Tolbachik volcano, Kamchatka, Russia. They were studied with the use of SIMS, scanning and transmission electron microscopy, and utilization of electron energy loss spectroscopy and electron diffraction. Diamonds have cube-octahedral shape and extremely homogeneous internal structure. Two groups of impurity elements are distinguished by their distribution within the diamond. First group, N and H, the most common structural impurities in diamond, are distributed homogeneously. All other elements observed (Cl, F, O, S, Si, Al, Ca, and K) form local concentrations, implying the existence of inclusions, causing high concentrations of these elements. Most elements have concentrations 3–4 orders of magnitude less than chondritic values. Besides N and H, Si, F, Cl, and Na are relatively enriched because they are concentrated in micro- and nanoinclusions in diamond. Mineral inclusions in the studied diamonds are 70–450 nm in size, round- or oval-shaped. They are represented by two mineral groups: Mn-Ni alloys and silicides, with a wide range of concentrations for each group. Alloys vary in stoichiometry from MnNi to Mn2Ni, with a minor admixture of Si from 0 to 5.20–5.60 at%. Silicides, usually coexisting with alloys, vary in composition from (Mn,Ni)4Si to (Mn,Ni)5Si2 and Mn5Si2, and further to MnSi, forming pure Mn-silicides. Mineral inclusions have nanometer-sized bubbles that contain a fluid or a gas phase (F and O). Carbon isotopic compositions in diamonds vary from –21 to –29‰ δ13CVPDB (avg. = –25.4). Nitrogen isotopic compositions in diamond from Tolbachik volcano are from –2.32 to –2.58‰ δ15NAir. Geological, geochemical, and mineralogical data confirm the natural origin of studied Tolbachik diamonds from volcanic gases during the explosive stage of the eruption.

Data on concentrations and distribution of tritium in soils of the “Atomic” Lake excavation explosion area of Semipalatinsk Nuclear Test Site (Kazakhstan, East Kazakhstan oblast) are discussed. The concentrations of tritium in surface soil horizons and in soil profiles have been determined in the bulk soil samples and in different particle-size fractions. Tritium concentration in soils reaches 240 000 Bq/kg. A correlation has been found between tritium and europium concentrations in soils. Presumably, tritium formation is controlled by two mechanisms. One of them is the neutron activation process, i.e., nuclear reactions with lithium, boron, and nitrogen isotopes present in the soil; the other mechanism is related to the capture of tritium that was initially in the charge of mineral particles formed upon condensation from the red-hot explosion zone.

Nitrogen isotopes (δ15N) can trace sources of major inorganic NOy species (here referring to nitrogen dioxide (NO2), nitric acid (HNO3), and nitrate (NO3–)) in the atmosphere. However, δ15N variati...

The influence of past variations in water column denitrification (WCD) in the eastern tropical Pacific (ETP) on the western tropical Pacific (WTP) remains ambiguous, due to the deficiency of enough down-core records of nitrogen isotope (δ15N) in the WTP. In this study, sedimentary δ15N record down a core from the northern WTP is investigated to revisit this issue. After elucidating the potential presence of multiple forms of N by analyzing bulk parameters and the potential occurrence of alteration by examining amino acids, the bulk sedimentary δ15N can be accepted as an available indicator of nitrate δ15N. Further, a comprehensive comparison of δ15N records in the North Pacific reveals largely similar variations from the last glacial maximum to early Holocene, suggesting a common feature of WCD signals associated with basin-scale processes, likely as a consequence of basin-wide ocean circulations. Our result suggests that the signals of local N2 fixation in the western Pacific marginal seas would have been constrained by a synchronous glacial-interglacial change of the source WCD signals.

The study of the carbon cycle is profound to the global ecosystem. In this paper, isotopic spectroscopy based on laser-induced breakdown spectroscopy (LIBS) was applied to the online detection of carbon isotopes and the study of atmospheric carbon cycle. The emission of carbon dioxide in the atmosphere was simulated by using a laser beam to ablate the coal, wood and paper samples. The emission spectra of smoke showed that carbon dioxide in the smoke could be detected online by the analysis of the molecular spectrum of the CN radicals. Then, taking urea as a carbon isotope sample, the isotopic shifts in the CN molecular spectra were clearly observed. The emission band of the (1,0) transition occurs red-shift of about 0.6 nm, while the emission band of the (0,1) transition appears blue-shift of about 0.8 nm. Furthermore, gaseous 13CO2 was directly detected by LIBS and the isotopic shifts in the CN bands from CO2 were also measured. Moreover, the energy differences in the isotopic shifts of the CN emission bands were calculated based on the density functional theory with the B3PW91/6-31+G(d) basis set, and the calculation results were basically consistent with the experimental values. Finally, the wavelength shifts for all the six different combinations of carbon and nitrogen isotopes were calculated. All the results indicate that the LIBS technique combined with an isotope spectrum is a promising and effective online detection method of gaseous carbon isotopes.

Nitrogen isotoperatios (δ15N) are a well-established tool for investigating the dietary and trophic behavior of animals in terrestrial and marine food webs. To date, δ15N values in fossils have primarily been measured in collagen extracted from bone or dentin, which is susceptible to degradation and rarely preserved in deep time (>100,000 years). In contrast,tooth enamelorganic matter is protected from diagenetic alteration by the mineral structure of hydroxyapatite and thus is often preserved overgeological time. However, due to the low nitrogen content (isotopic compositionhas been prevented by the analytical limitations of traditional methods. Here, we present a novel application of the oxidation-denitrification method that allows measurement of δ15N values in tooth enamel (δ15Nenamel). This method involves the oxidation of nitrogen in enamel-bound organic matter to nitrate followed by bacterial conversion of nitrate to N2O, and requires ≥100 times less nitrogen than traditional approaches. To demonstrate that δ15Nenamelvalues record diet and trophic behavior, we conducted a controlled feeding experiment with rats and guinea pigs (n=37). We determined that nitrogen concentration in tooth enamel (x̄=5.0±1.0 nmol/mg) is sufficient for δ15Nenamelanalyses with ≥5 mg untreated enamel powder. The nitrogen isotope composition of enamel reflects diet with an enrichment (Δ15Nenamel-diet) of ca. 2–4‰. δ15Nenamelvalues differ significantly between dietary groups and clearly record a shift from pre-experimental to experimental diet. The small sample size required (≤5 mg) by this method permits analyses of sample size-limited, diagenetically robust tooth enamel, and, as such it represents a promising new dietary proxy for reconstructing food webs and investigating thetrophic ecologyof extant and extinct taxa.

The open ocean nitrogen cycle is being altered by increases in anthropogenic atmospheric nitrogen deposition and climate change. How the nitrogen cycle responds will determine long-term trends in net primary production (NPP) in the nitrogen-limited low latitude ocean, but is poorly constrained by uncertainty in how the source-sink balance will evolve. Here we show that intensifying nitrogen limitation of phytoplankton, associated with near-term reductions in NPP, causes detectable declines in nitrogen isotopes (δ15N) and constitutes the primary perturbation of the 21st century nitrogen cycle. Model experiments show that ~75% of the low latitude twilight zone develops anomalously low δ15N by 2060, predominantly due to the effects of climate change that alter ocean circulation, with implications for the nitrogen source-sink balance. Our results highlight that δ15N changes in the low latitude twilight zone may provide a useful constraint on emerging changes to nitrogen limitation and NPP over the 21st century., Projected declines in marine primary production are underpinned by a slowdown in nitrogen supplied to surface waters. Here the authors detail a new means to detect this slowdown and describe major shifts in the 21st century oceanic nitrogen cycle.

17 pages, 6 figures, 1 table.-- This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY), Variations in stable carbon and nitrogen isotope compositions in incremental tissues of pelagic sharks can be used to infer aspects of their spatial and trophic ecology across life-histories. Interpretations from bulk tissue isotopic compositions are complicated, however, because multiple processes influence these values, including variations in primary producer isotope ratios and consumer diets and physiological processing of metabolites. Here we challenge inferences about shark tropho-spatial ecology drawn from bulk tissue isotope data using data for amino acids. Stable isotope compositions of individual amino acids can partition the isotopic variance in bulk tissue into components associated with primary production on the one hand, and diet and physiology on the other. The carbon framework of essential amino acids (EAAs) can be synthesised de novo only by plants, fungi and bacteria and must be acquired by consumers through the diet. Consequently, the carbon isotopic composition of EAAs in consumers reflects that of primary producers in the location of feeding, whereas that of non-essential amino acids (non-EAAs) is additionally influenced by trophic fractionation and isotope dynamics of metabolic processing. We determined isotope chronologies from vertebrae of individual blue sharks and porbeagles from the North Atlantic. We measured carbon and nitrogen isotope compositions in bulk collagen and carbon isotope compositions of amino acids. Despite variability among individuals, common ontogenetic patterns in bulk isotope compositions were seen in both species. However, while life-history movement inferences from bulk analyses for blue sharks were supported by carbon isotope data from essential amino acids, inferences for porbeagles were not, implying that the observed trends in bulk protein isotope compositions in porbeagles have a trophic or physiological explanation, or are suprious effects. We explored variations in carbon isotope compositions of non-essential amino acids, searching for systematic variations that might imply ontogenetic changes in physiological processing, but patterns were highly variable and did not explain variance in bulk protein δ13C values. Isotopic effects associated with metabolite processing may overwhelm spatial influences that are weak or inconsistently developed in bulk tissue isotope values, but interpreting mechanisms underpinning isotopic variation in patterns in non-essential amino acids remains challenging, The internship of SM at the Woods Hole Oceanographic Institution was funded by the School of Ocean and Earth Science at University of Southampton. Stable isotope analyses were paid by CT and ST research budgets and SM Ph.D. and placement funding

The co-existence of motile macroorganisms and mat-building cyanobacteria in the Paleoproterozoic FB2 Member of the Franceville sub-basin, Gabon, points to the possible emergence of multi-trophic-level biological interaction by 2.1 billion years (Ga) ago. However, it is uncertain how these shallow-marine communities acquired and cycled nitrogen, a key, biolimiting nutrient required to sustain life at all trophic levels. Here, we use carbon and nitrogen isotope data from ancient microbial mats and host sediments, in combination with bottom-water redox proxies, to constrain biogeochemical processes operating in these settings. In this shallow-marine upwelling zone, iron speciation data and redox-sensitive metal concentrations point to oxygen-deficient bottom waters, which were episodically renewed with upwelling deep anoxic waters rich in nutrients and manganese. Organic carbon and nitrogen isotopes show little difference between the mat-related structures (MRS) and host sediments, suggesting either that similar metabolisms operated in benthic and planktonic microbial communities or that benthic carbon fixation contributed organic matter to the host sediments. The isotopic fractionation between organic and inorganic carbon is as large as 44‰, implying the involvement of multiple levels of heterotrophic carbon processing, linked to phototrophy, secondary productivity, and methanotrophy. Whole-rock nitrogen isotope values in the range of −3.5 to + 1.9‰ are consistent with microbial community nitrogen fixation in a nitrate-limited ecosystem. These data suggest that nitrogen fixation, common in photosynthetic microbial mats in modern environments, operated in benthic settings in the coastal area of the mid-Paleoproterozoic Franceville sub-basin. The upwelling of deep, anoxic waters invoked for deposition of the upper part of the underlying FB1 Member suggests that basin-scale redox structure modulated nitrate availability in this otherwise oxic, shallow-marine basin shelf environment.

Isotopic measurements of plant remains from archaeological sites are now routinely used to reconstruct agricultural practices in the Old World. These studies use charred botanical remains as the analytical substrate because (1) these are the materials that are commonly preserved in the archaeological record and (2) the integrity of the isotopic compositions of archaeological plant remains that are uncharred or desiccated has been questioned, particularly for δ15N. By comparing charred and uncharred plant remains from two Late Moche (ad 600–800) sites in the Jequetepeque valley on the north coast of Peru—San Jose de Moro and Cerro Chepen—we sought to directly test the assumption that the isotopic compositions of desiccated plant remains are not representative of the isotopic compositions of the living plants. The average δ15N values of charred (+11.3 ± 4.4‰) and desiccated (+10.1 ± 5.1‰) remains from these two sites did not significantly differ from one another, suggesting that uncharred plant remains can produce reliable isotopic measurements under some circumstances. Furthermore, the relatively high δ15N values of the plant remains from these two sites are consistent with the ancient use of composted camelid manure as a fertilizer.

Resumen: Se presentan tres novedosos registros de isótopos de carbono y nitrógeno procedentes de dos contextos funerarios a cielo abierto en el interior del bosque norpatagónico. Las muestras humanas analizadas confirman la utilidad de la técnica para diferenciar las dietas terrestres de las poblaciones humanas del área andina de Patagonia. Los resultados reflejan la importancia del bosque y sus recursos en el último milenio, fortaleciendo los modelos que plantean la idea de poblaciones humanas explotando de manera regular y permanente el bosque y sus recursos en la región andina oriental de Patagonia septentrional.

Vegetation near bird and seal rookeries typically has high δ15N signatures and these high values are linked to the enriched δ15N values of rookery soils. However, Antarctic cryptogams are mostly dependent on atmospheric ammonia (NH3) and volatized NH3 from rookeries is severely depleted in δ15N-NH3. So there is an apparent discrepancy between the isotopically depleted source (NH3) and δ15N-enriched vegetation. In this article, we aim to resolve this discrepancy to better understand the mechanisms and processes involved in isotopic changes during nitrogen transfer between Antarctic marine and terrestrial ecosystems. Under laboratory conditions, we quantified whether volatized NH3 affects the isotopic signature of cryptogams. NH3 volatilizing from penguin guano and elephant seal dung was depleted (44–49‰) in δ15N when captured on acidified filters, compared to the source itself. Cryptogams exposed to the volatized NH3 were enriched (18.8–23.9‰) in δ15N. The moss Andreaea regularis gained more nitrogen (0.9%) than the lichen Usnea antarctica (0.4%) from volatilized NH3, indicating a potential difference in atmospheric NH3 acquisition that is consistent with existing field differences in nitrogen concentrations and δ15N between mosses and lichens in general. This study clarifies the δ15N enrichment of cryptogams resulting from one of the most important nitrogen pathways for Antarctic vegetation.

Nitrogen isotope (δ15N) analysis has been used to evaluate depositional redox conditions in well-preserved sedimentary systems; however, fewer N-isotope studies have been performed to reconstruct the redox conditions in lacustrine shales. In this paper, we report the δ15N data from the Upper Triassic Chang 7 Shale of the Ordos Basin, North China. Sedimentary δ15N values are significantly higher in the Chang 73 and the lower part of the Chang 72 submembers (Zone A; average = 9.4 ± 1.3‰) than in the upper part of the Chang 72 and the Chang 71 submembers (Zone B; average = 5.4 ± 1.5‰). Previous geochemical measurements (i.e., U and TOC/P) of both zones show wide redox variation, however, the average values of these redox proxies are relatively higher in Zone A than those of Zone B. Combined with lithological aspects of the Chang 7 Shale, our study suggest that Zone A was mainly deposited under suboxic bottom water conditions, whereas Zone B deposits accumulated within an oxygenated water column. Stable organic carbon isotopes (δ13Corg) and total nitrogen (TN) values of the two zones display little variation that could be attributed to changing organic matter sources and/or post-depositional alteration of δ15N. Thus, we suggest that variations in δ15N throughout the Chang 7 Shale primarily reflect differences in depositional redox conditions and δ15N values of the shale that can provide important details regarding the depositional history of unconventional resource plays.

Rationale To perform the δ15 N isotopic analysis of ammonium (NH4 + ) with an elemental analyzer (EA) coupled to an isotope-ratio mass spectrometer, it is necessary to isolate the NH4 + prior to the analysis. Existing methods are work-intensive and time-consuming. For broader applicability in the environmental sciences, it is desirable to simplify the sample preparation process. The method used here is based on the insolubility of ammonium tetraphenylborate ((C6 H5 )4 BNH4 ) in water. Its suitability for the stable isotope measurement of δ15 N values for NH4 + has already been proven (Howa et al. Rapid Commun Mass Spectrom. 2014;28:1530-1534). However, there are no studies on the usability of the method for the analysis of ammonium-containing water samples. In this study, the method was tested for its applicability to natural groundwater samples. Methods To achieve the necessary high NH4 + concentrations for complete (C6 H5 )4 BNH4 precipitation, the water samples were first freeze-dried and then prepared for the analysis. To precipitate the NH4 + , sodium tetraphenylborate ((C6 H5 )4 BNa) was added to the samples. The precipitate was then separated from the water by filtration using a membrane filter and analyzed using an EA interfaced with an isotope ratio mass spectrometer to determine the nitrogen isotope ratio. Results A consistent 15 N enrichment of +0.65‰ was found in the measured isotope ratios. No significant effect due to other ions in the water samples could be identified. There was no significant difference between the isotope ratios of the natural groundwater samples determined from the tetraphenylborate (TPB) method and those determined from the diffusion method (DM). This indicates that the TPB method can easily be used for natural groundwater samples. Conclusions The TPB method in combination with freeze-drying is an efficient technique for the precise δ15 N measurement of NH4 + in natural groundwater samples. The laboratory effort required for sample preparation is very low, and the repeatability of the measurements is very high.

Identification of nitrate sources and its transformations are important for the management of large lakes and reservoirs. The Three Gorges Reservoir (TGR) in China is one of the largest reservoirs around the world. In this study, stable isotopes of nitrogen (δ15N–NO3−) and oxygen (δ18O–NO3−) of nitrate in water were used to gain insights into nitrate sources and transformations in the tail area of the TGR. Bayesian mixing model has been conducted to estimate the proportional contribute of nitrate sources. The mixing modelling results indicated that NH4+ fertilizer (range 7–54%) and soil organic nitrogen (range 2–45%) were the dominant NO3−–N sources in the tail area of the TGR during the three season study period. Nitrification contributed a part of NO3−–N in the river water during the dry season. The nitrate from soil solution in the riparian zone with denitrified NO3− might be another major reason for the enrichment of δ15N–NO3− and δ18O–NO3− during the normal season. Reducing the use of chemical nitrogen fertilizers, especially NH4+ fertilizers, and protecting soil from erosion may be effective measures to improve water quality in the TGR.

The isotopic composition of nitrogen in soils and plants may be an indicator of transformation of its compounds and sources of N nutrition of plants. Natural 15N abundance (δ15N) was determined in soils (the total, ammonium, and nitrate nitrogen) and in plant leaves and roots of four tundra ecosystems in the Khibiny Mountains. The studied soils (Folic Leptic Entic Podzol and Leptosols) significantly differ in N availability, and plants are represented by the species, forming ectomycorrhiza, ericoid mycorrhiza, and arbuscular mycorrhiza, as well as by the species, which usually do not form a mycorrhiza. The range of δ15N in soil inorganic compounds is from –16.2 ‰ in nitrates to +6.4‰ in ammonium, which reflects the correlation between the activities of N-mineralization and nitrification and δ15N- $${\text{NH}}_{4}^{ + }$$ , as well as a potentially strong effect on the isotopic composition of nitrogen in plants. The value of δ15N in plant leaves and roots changes in a narrower range (from –7.3 to +2.4‰), which may be related to N uptake from different sources and to fractionation of N isotopes during N assimilation. Roots are 15N-enriched in comparison with leaves in most of the studied plant species, which corresponds to the concept of mycorrhiza participation in N nutrition of plants. Regardless of the type of mycorrhizal symbiosis, the difference in δ15N between roots and leaves of most plant species decreases contrary to N availability in soils.

Graphene is a one-atom-thick sheet, possessing a high electron mobility, constructed from sp2-bonded carbon atoms. Here, we hypothesize that graphene functions as a conductive material to promote anaerobic ammonium oxidation coupled with Fe(III) reduction (Feammox) in mangrove sediments slurries. In this study, graphene and 9,10-anthraquinone-2-sulfonate (AQS) were both investigated using a nitrogen isotope tracing technique. Graphene and AQS addition increased the Feammox rates by 31% and 56%. Graphene also increased the Fe(III) reduction rate by 43%, but Feammox-associated Fe(III) reduction accounted for only 1.5–4.9% of the total Fe(III) reduction. Graphene may have behaved as a conductive bridge to promote electron transfer to the Fe(III) acceptor in the Feammox process; however, the mechanisms by which graphene and AQS stimulate Feammox are different.

The goals of this study were to analyze if there is a difference in the stable isotopic ratio (δ13C and δ15N) of macrobenthic species sampled at two sandy beaches (one close to a river mouth and the other far from any freshwater input) and to identify differences in the stable isotopic ratio (δ13C and δ15N) in different body parts of three representative species of two Brazilian sandy beach macrofaunas: the polychaete Hemipodia californiensis, the mollusk bivalve Donax hanleyanus, and the crustacean decapod Emerita brasiliensis. No significant differences were detected in the δ13C stable isotopic ratio between the two sites analyzed; however, in the δ15N stable isotopic ratio, a significant difference was observed. Regarding the intraspecific response of stable isotopic ratio, D. hanleyanus showed a significant difference in carbon among different body part structures, while a trend for significance was observed for nitrogen isotopes. The differences were significant for both isotopes in E. brasiliensis, and no differences were observed among the body part structures in H. californiensis. There were significant differences in E. brasiliensis carapaces with regard to the δ15N stable isotopic ratio between the muscle and the whole body. Although the δ13C and δ15N stable isotopic ratio differs significantly in the digestive tract, muscles, and whole body of D. hanleyanus, such differences were not enough to determine changes in their trophic levels and food sources. Similar stable isotopic ratios were observed in the whole body, proboscis, and teeth of H. californiensis, highlighting this species as the top predator. In conclusion, stable isotopic analysis of benthic trophic structure can be employed as a tool in coastal management plans or environmental impact studies.

We present new data on the rates of sedimentary denitrification and its component processes (canonical denitrification, anammox and dissimilatory nitrate reduction to ammonium) for intertidal and subtidal sites in the North Sea using nitrogen isotope addition methods. We find overall average denitrification rates of 6.3 (range 0.4–10.6) µmol m−2 h−1, similar to those previously reported for this region and other temperate shelf environments. We find canonical denitrification to be the dominant (>90%) process of the three. At the subtidal sites, most of the denitrification is supported by nitrate generated within the sediments, while at the intertidal site the main source is from the water column. We go on to consider the impact of these rates on nitrogen cycling within the North Sea region and compare the sediment core incubation rate results to estimates derived from modelling approaches. Model rates are somewhat higher than those directly measured and we consider possible reasons for this.

Due to the local emissions and transportations of air pollution from the most polluted regions such as the North China Plain and Yangtze Delta metropolitan, Xuzhou is becoming one of the most polluted cities in East China. The sources and formation processes of nitrogen-containing aerosols are therefore very complex. Two continuous aerosol measurement campaigns were conducted in this industrial city during the wintertime and summertime of 2016, to investigate the chemical compositions and potential sources of total nitrogen (TN, including 89% inorganic nitrogen and 11% organic nitrogen) in PM2.5. Abrupt enhancements of nitrogen-containing aerosols (e.g., NO3− and NH4+) were found in the winter, and nitrate became as a dominant contributor in high pollution days (e.g., PM2.5 > 150 μg m−3). Nitrogen oxidation ratios (NOR) correlated significantly with aerosol liquid water content (ALWC), which was estimated by ISORPROPIA-II model. This suggested heterogeneous process might be an important pathway in nitrate formation during the high PM2.5 days. The nitrogen isotope composition (δ15N) in TN varied from −1.3 to +13.2‰ with a mean value of 6.9 ± 3.6‰ during the wintertime. An isotope-based source apportionment approach was then developed using a Bayesian isotope mixing model (SIAR) with chemical compositions as an important constrain, which improved accuracy and reduced the overall uncertainties in estimations of TN sources. From this optimized model, we identified six major sources including NH3 from combustion-related emissions (49%), NH3 derived from animal wastes (6%), NH3 from urban volatilization (3%), NOx derived from coal combustion (33%), NOx from biomass burning (5%) and NOx from vehicles (3%). Our results demonstrated that ambient NOx was dominated by coal combustion. Since NOx and NH3 are important precursors for ammonium nitrate aerosols, controlling of combustion related NOx and NH3 emissions might be an important way to reduce PM2.5 levels in this region.

The spread of millet agriculture to southeast (SE) China is critical to understanding the region's economic pattern and its potential impact on the proposed initial expansion of proto-Austronesians. In this study, we present new multidisciplinary evidence for the development of millet agriculture from three Neolithic sites in Fujian Province, China: Hulushan, Pingfengshan and Huangguashan. The carbonized seeds from Hulushan indicate the existence of millet agriculture around 3842-3649 cal. BP. Meanwhile, we tested stable carbon and nitrogen isotope ratios of faunal remains (n = 22) from Pingfengshan and Huangguashan shell midden sites in a coastal area of Fujian. The stable isotope results for pigs (δ15N values range from 4.9 to 11.2‰, and δ13C values range from −24.1 to −11.2‰) show significant variations, suggesting that these pigs were fed different foods, including C3 plants, C4 plants and marine resources. Specifically, two samples of pig collagen with strong millet signals were directly dated to about 4000-3600 cal. BP. These new findings provide substantial evidence for a new understanding of the development of millet agriculture in SE China.

24 pages; International audience; The Earth’s oxygenation represents one of the most important environmental drivers of life’s evolution, with the first rise, known as ‘the Great Oxidation Event’ (GOE), corresponding to unpreceded accumulation of atmospheric O2, changes in the flux of marine nutrients and possibly global glaciations. However, the detailed evolution of the GOE is still debated, as for instance the accumulation trends of oceanic versus atmospheric oxygen and the nature of biogeochemical responses to oxygenation. Here, we combine organic carbon and bulk nitrogen isotope compositions with major element concentrations and iron speciation data of sedimentary rocks recovered from two drill cores (T2 and T3) in the early Paleoproterozoic Turee Creek Group, Western Australia, to track the redox evolution of marine conditions during the GOE. T2 core samples of the Kungarra Formation, which consists of clastic sedimentary rocks overlaid by the glaciogenic Meteorite Bore Member, were deposited ∼2.31 Ga ago. T3 core intercepts, from bottom to top, quartzite of the Koolbye Formation, and shales and stromatolitic carbonates of the Kazput Formation, which were deposited around ∼2.25 Ga. Samples from T2 show minor variations of δ13Corg (avg. −34.5 ± 1.7‰, n = 30), with no significant difference between siliciclastic and glaciogenic sedimentary rocks. In contrast, T3 samples display an increase in δ13Corg from −32.0 to −24.8‰ (n = 54) from shales to carbonates. In both T2 and T3 cores, δ13Corg values are inversely correlated with Al2O3, suggesting a strong petrological control on δ13Corg values, inferred here as resulting from variable contributions of detrital organic matter. Bulk N contents are low, from 13.5 to 56.7 ppm and 15.7 to 53.4 ppm in T2 and T3 samples, respectively. The δ15N values show a bimodal distribution, with one mode at +2.6‰ in T2 and another at +8.8‰ in T3, independent from lithological variations. This δ15N values shift between T2 and T3 is interpreted as reflecting a change from dominating N2-fixers to NO3-assimilating organisms. This implies an increase of NO3− availability, and thus of O2 concentration, during the time interval separating the deposition of T2 and T3 sediments. Dissolved NO3− and O2 concentrations of the Turee Creek marine basin are estimated from two models using N isotope data. The dissolved NO3− concentration has an upper limit ranging from 1.91 to 3.04 µM, about one order of magnitude below the average value of modern oceans. The lower limit for dissolved oxygen concentration ranges from 1.8 to 4.4 µM, which is two orders of magnitude lower than modern oceans. Together with previous studies, the present data place quantitative constraints on the redox changes associated with the Great Oxidation Event and illustrate a stepwise increase of NO3− bioavailability between 2.31 to 2.25 Ga, in relation with increasing O2 level.