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Rationale: The analysis of nitrogen isotopes in aqueous dissolved nitrate is an effective method for identifying pollution sources and offers the potential to study the nitrogen cycle. However, the measurement of nitrogen isotope ratios of nitrate still requires extensive sample preparation or derivatization. Methods: In this study, a modified commercially available liquid chromatography–isotope ratio mass spectrometer (LC‐IRMS) interface is presented that enables automated measurement of δ15N signatures from nitrate by online reduction of nitrate in two consecutive steps. First, vanadium(III) chloride is used as a reducing agent to convert NO3− to NxOy under acidic conditions. The mix of nitrogen oxides is then transferred into a stream of helium and reduced to nitrogen (N2) analysis gas via a hot copper reactor. Prior to the online conversion of aqueous nitrate into elemental nitrogen, the sample was chromatographically separated from potential matrix effects on a PGC column. Results: Precision was achieved at a level below 1.4‰ by injecting 10 μL of 50 mg L−1 N, using five different nitrate standards and reference materials. These materials spanned a range of more than 180‰ in δ15N. To demonstrate the applicability of the method, we measured water samples from an enrichment experiment, where isotopically enriched ammonium chloride was administered into a small river over the course of 2 weeks. In contrary to our expectation, the δ15N values of river nitrate showed values between +0.4 ± 0.4‰ and +4.1 ± 0.3‰, varying over a small range of 3.7‰. Conclusions: Our study showed that the measurement of nitrate nitrogen isotope ratios with a modified LC‐IRMS system is possible but that further modifications and improvements would be necessary for a robust and user‐friendly instrument. [ABSTRACT FROM AUTHOR]

The mercury content in the hair of residents in the industrial city of Cherepovets (0.297 mg/kg) is three times lower than that of residents in the specially protected natural area of Kirillovsky district (0.877 mg/kg), which is approximately 110 km away from Cherepovets. In both the residents of the industrial city and in the protected area, the mercury content in hair increases with the age of the individuals. In the population of the city, there is no difference between the mercury content in the hair and the frequency of fish consumption. The mercury content in the hair of the population from the protected area depends on the frequency of fish consumed in their diet. The average value of the ratio of stable nitrogen isotopes (δ15N) in the hair of the participants is 10.11‰. No differences have been established between the ratio of stable nitrogen isotopes (δ15N) in the hair of residents of the industrial city (10.00‰) and the protected area (10.19‰). People with a mercury content in their hair above the median value had statistically significantly higher δ15N values in both residents of industrial city and protected area. A correlation was established between the isotopic signature of nitrogen and the amount of mercury in the hair both in the whole sample (Rs = 0.515, at p = 0.000), and in the industrial city (Rs = 0.425, at p = 0.002) and in the protected area residents (Rs = 0.706, at p = 0.000). That may be due to the differences in diet, as rural population has a traditionally high level of consumption of wild freshwater fish from local reservoirs while people from industrial city mainly purchase fish (seafood, marine fish, freshwater fish) from supermarkets. [ABSTRACT FROM AUTHOR]

The steadily growing demand for fertilizers and increasing interest for organic inputs result in rapid expansion and diversification of the solid nitrogen (N) fertilizer market. Fertilizer legislations distinct different fertilizers classes (i.e. organic, organo-mineral, inorganic), but standards and norms related to nutrient- and carbon origin remain dynamic and lag behind. This, together with poor analytical understanding of commercially available N sources leaves many open questions to industries and farmers, fostering increased prevalence of fertilizer adulteration and false claims on the organic fertilizer market. This work presents a thorough, science-based multivariate assessment on a wide sample set (n = 52) of the solid N fertilizer market, including multiple state-of-the-art analytical attributes, such as stable isotopes of nitrogen and carbon. Results present the possibility to correctly (94%) classify N fertilizers using multivariate fingerprinting with linear discriminant analysis. We extract analytical cut-off values for discriminants indicative for ingredient origin and conclude that, when a fertilizer has (i) a bulk δ15N below 2‰; and (ii) a relatively high total N content (> 15%), from which (iii) a high share (> 50%) is water soluble (i.e. in ammonium or nitrate form), it is extremely unlikely to be of pure biologic origin. We also present additional analyses (e.g. amino acids, peptide sequences, δ13C of specific compounds, and stable isotopes of boron) that can then be used to further trace down the N sources in novel fertilizer products. This work contributes to future debates, regulations, and further development of analytical standards for solid N fertilizers, possibly to be used in fraud detection. [ABSTRACT FROM AUTHOR]

Stream and floodplain restoration is a popular billion‐dollar industry in the United States, with many restorations being conducted to satisfy water pollution regulations and nutrient reduction goals. The long‐term efficacy of these restorations is, however, not well studied, and key soil metrics that can be used for performance assessments have not been developed. We evaluated a chronosequence of 12 restoration sites spanning an age range of 0–22 years to assess changes in denitrification rates and associated soil parameters. Restored versus unrestored reaches were compared for denitrification rate and functional gene nosZ, bulk soil δ15N, soil organic carbon (SOC), soil organic matter (SOM), bulk density, and soil moisture. Denitrification, SOM, SOC, and soil moisture were all found to increase with site age at restored sites, with the largest increase for the 10–22 age category. Bulk density decreased with time, with a significant decrease in restored floodplain soils. Bulk soil δ15N was highest immediately after restoration, decreased with restoration age, and was not positively correlated with denitrification. This may reduce its potential as a proxy for denitrification. Overall, this study reveals that selected soil metrics (SOC, SOM, soil moisture, and bulk density) could serve as a valuable proxy for denitrification and could help assess the denitrification effectiveness of floodplain restorations at the decadal time scales. Ideally, the soil metrics should be combined with other short‐term assessment measures, such as those for stream and groundwaters, for a robust performance assessment of restored floodplains. [ABSTRACT FROM AUTHOR]

Eutrophication in coastal waters has been increasing remarkably, severely impacting the water quality in mariculture bays. In this study, we conducted multiple isotopic measurements on suspended particulate nitrogen (δ15N-PN) and dissolved nitrate (δ15N-NO3− and δ18O-NO3−) in Zhanjiang Bay, a typical mariculture bay with a high level of eutrophication in South China, to investigate the changes in nitrogen sources and their cycling between the rainy and dry seasons. During the rainy season, the study found no significant relation between δ15N-PN and δ15N-NO3− due to the impact of heavy rainfall and terrestrial erosion. In the upper bay, a slight nitrate loss and slightly higher δ15N-NO3− and δ18O-NO3− values were observed, attributed to intense physical sediment-water interactions. Despite some fluctuations, nitrate concentrations in the lower bay mainly aligned with the theoretical mixing line during the rainy season, suggesting that nitrate was primarily influenced by terrestrial erosion and that nitrate isotopes resembled the source. Consequently, the isotopic values of nitrate can be used for source apportionment in the rainy season. The results indicated that soil nitrogen (36%) and manure and sewage (33%) were the predominant nitrogen sources contributing to nitrogen loads during this period. In contrast, the dry season saw a deficient ammonium concentration (<0.2 µmol/L) in the bay, due to nearly complete consumption by phytoplankton during the red tide period. Additionally, the significant loss of nitrate and simultaneous increase in the stable isotopes of dissolved and particulate nitrogen suggest a strong coupling of assimilation and mineralization during the dry season. More active biogeochemical processes during the dry season may be related to decreased runoff and increased water retention time. Overall, our study illustrated the major seasonal nitrogen sources and their dynamics in Zhanjiang Bay, providing valuable insights for formulating effective policies to mitigate eutrophication in mariculture bays. [ABSTRACT FROM AUTHOR]

Summary: Rising atmospheric carbon dioxide concentrations (CO2) and atmospheric nitrogen (N) deposition have contrasting effects on ectomycorrhizal (EM) and arbuscular mycorrhizal (AM) symbioses, potentially mediating forest responses to environmental change.In this study, we evaluated the cumulative effects of historical environmental change on N concentrations and δ15N values in AM plants, EM plants, EM fungi, and saprotrophic fungi using herbarium specimens collected in Minnesota, USA from 1871 to 2016. To better understand mycorrhizal mediation of foliar δ15N, we also analyzed a subset of previously published foliar δ15N values from across the United States to parse the effects of N deposition and CO2 rise.Over the last century in Minnesota, N concentrations declined among all groups except saprotrophic fungi. δ15N also declined among all groups of plants and fungi; however, foliar δ15N declined less in EM plants than in AM plants. In the analysis of previously published foliar δ15N values, this slope difference between EM and AM plants was better explained by nitrogen deposition than by CO2 rise.Mycorrhizal type did not explain trajectories of plant N concentrations. Instead, plants and EM fungi exhibited similar declines in N concentrations, consistent with declining forest N status despite moderate levels of N deposition. [ABSTRACT FROM AUTHOR]

The stable nitrogen isotope ratio δ15N is used as a marker of dietary protein sources in blood. Crop fertilization strategies affect δ15N in plant foods. In a double-blinded randomized cross-over dietary intervention trial with 33 participants, we quantified the effect of fertilizer type (conventional: synthetic fertilizer and organic: animal or green manure) on δ15N in blood plasma. At study baseline, plasma δ15N was +9.34 ± 0.29‰ (mean ± standard deviation). After 12 days intervention with a diet based on crops fertilized with animal manure, plasma δ15N was shifted by +0.27 ± 0.04‰ (mean ± standard error) compared to synthetic fertilization and by +0.22 ± 0.04‰ compared to fertilization with green manure (both p < 0.0001). Accordingly, differences in the δ15N values between fertilizers are propagated to the blood plasma of human consumers. The results indicate a need to consider agricultural practices when using δ15N as a dietary biomarker.

Arctic food webs are being impacted by borealisation and environmental change. To quantify the impact of these multiple forcings, it is crucial to accurately determine the temporal change in key ecosystem metrics, such as trophic position of top predators. Here, we measured stable nitrogen isotopes (δ15N) in amino acids in harp seal teeth from across the North Atlantic spanning a period of 60 years to robustly assess multi‐decadal trends in harp seal trophic position, accounting for changes in δ15N at the base of the food web. We reveal long‐term variations in trophic position of harp seals which are likely to reflect fluctuations in prey availability, specifically fish‐ or invertebrate‐dominated diets. We show that the temporal trends in harp seal trophic position differ between the Northwest Atlantic, Greenland Sea and Barents Sea, suggesting divergent changes in each local ecosystem. Our results provide invaluable data for population dynamic and ecotoxicology studies. [ABSTRACT FROM AUTHOR]

Predicted increases in extreme droughts will likely cause major shifts in carbon sequestration and forest composition. Although growth declines during drought are widely documented, an increasing number of studies have reported both positive and negative responses to the same drought. These divergent growth patterns may reflect thresholds (i.e., nonlinear responses) promoted by changes in the dominant climatic constraints on tree growth. Here we tested whether stemwood growth exhibited linear or nonlinear responses to temperature and precipitation and whether stemwood growth thresholds co‐occurred with multiple thresholds in source and sink processes that limit tree growth. We extracted 772 tree cores, 1398 needle length records, and 1075 stable isotope samples from 27 sites across whitebark pine's (Pinus albicaulis Engelm.) climatic niche in the Sierra Nevada. Our results indicated that a temperature threshold in stemwood growth occurred at 8.4°C (7.12–9.51°C; estimated using fall‐spring maximum temperature). This threshold was significantly correlated with thresholds in foliar growth, as well as carbon (δ13C) and nitrogen (δ15N) stable isotope ratios, that emerged during drought. These co‐occurring thresholds reflected the transition between energy‐ and water‐limited tree growth (i.e., the E–W limitation threshold). This transition likely mediated carbon and nutrient cycling, as well as important differences in growth‐defense trade‐offs and drought adaptations. Furthermore, whitebark pine growing in energy‐limited regions may continue to experience elevated growth in response to climate change. The positive effect of warming, however, may be offset by growth declines in water‐limited regions, threatening the long‐term sustainability of the recently listed whitebark pine species in the Sierra Nevada. [ABSTRACT FROM AUTHOR]

Recently, new spatiotemporal-scale particle observations by autonomous profiling floats equipped with bio-optical sensors have revealed that, in addition to gravitational particle sinking, the downward transport of surface particles by physical mixing events, which has been overlooked, contributes to particulate organic carbon export. However, the subsequent behavior of these exported particles in the mesopelagic zone (e.g., particle fragmentation and degradation) remains unclear, although it may influence the efficiency of carbon transport to further depths. This study successfully depicted the new annual mean mesopelagic particulate nitrogen (PN) dynamics with multi-layer, steady-state suspended PN pools by reanalyzing seasonal data on the stable nitrogen isotopic compositions of both suspended and sinking particles, each with different profiles, from subarctic station K2 and subtropical station S1 in the North Pacific, which are both CO2 sinks but in different oceanic settings. As analytical conditions, we assumed that the net loss of sinking PN was entirely due to abiotic fragmentation of particle aggregates to non-sinking particles and that the apparent 15N enrichment associated with heterotrophic degradation in the suspended PN pools was vertically constant. The 15N mass balance for the PN supply to the uppermost mesopelagic pool, derived from such constraints, allowed estimating the PN export by the mixed-layer pump, which was 1.6 times greater at K2 than at S1. However, its contribution to the total export (including gravitational PN sinking) from the surface layer was approximately 20% at both stations. Moreover, the ratio of PN supplied to the uppermost pool by the mixed-layer pump and by the fragmentation of particle aggregates was also similar at both stations, approximately 1:1. Using these ratios, together with separate observations of the mixed-layer pump-driven flux, it may be possible to estimate the efficiency of the particulate organic carbon transport due to the biological gravitational pump responsible for carbon sequestration in the deep sea.

Using skeletal remains from the eighteenth-century Fortress of Louisbourg, this study aimed to explore whether the adolescent (< 25 years) and adult (> 25 years) male experiences were synonymous in this New France colony. Additionally, this study also considered the geographic origins of these adolescent males to better understand their lived experience at Louisbourg. For this study, skeletal remains from 13 adolescent male individuals (16-25 years) were compared to 24 adult male individuals (27-47 years). Osteological analysis involved the assessment of macroscopic indicators of stress, including cribra orbitalia, porotic hyperostosis, linear enamel hypoplasia, fractures, Schmorl's nodes, periosteal new bone formation, dental caries, and dental abscesses. When statistically compared, there were no differences between these age cohorts and the prevalence of these indicators. Mortuary data were also assessed, including burial depth, coffin use, and the prevalence of grave goods, again with no differences observed between these age cohorts. We explored dietary patterns and their relationship to geographic origin by measuring stable carbon (d13C) and nitrogen (d15N) isotope ratios in bone collagen and d13C values of tooth enamel carbonate. All but one of the adolescent individuals consumed a mixed C3 and C4 diet during childhood, suggesting possible origins in an area consistent with what is now the eastern United States. Based on this multi-proxy approach, it is likely that the male adolescents in this group were soldiers from New England stationed at Louisbourg after the first siege in 1745 and had a similar lived experience to that of adult males. [ABSTRACT FROM AUTHOR]

The natural abundance of plant and bulk soil 15N isotopic signatures provides valuable insights into the magnitude of nitrogen cycling and loss processes within terrestrial ecosystems. However, 15N isotopic signatures are highly variable in space due to natural and anthropogenic factors affecting N cycling processes and losses. To date, most studies on foliar and bulk soil 15N isotopic signatures have focused on N-limited forest ecosystems at relatively large spatial scales, while similar studies in N-enriched ecosystems at finer spatial scales are lacking. To address this gap and evaluate links between soil 15N isotopic signatures and ecosystem N cycling and loss processes (plant N uptake, N leaching, and gaseous loss), this study quantified foliar and bulk soil 15N isotopic signatures, soil physicochemical parameters, gaseous (N 2 O), and hydrological (NO 3) N losses at 80 sites distributed across a heterogeneous landscape (∼5.8 km2). To account for the spatial-temporal heterogeneity, the measurements were performed in four campaigns (March, June, September 2022, and March 2023) at sites that considered different land uses, soil types, and topography. Results indicated that foliar and bulk soil 15N isotopic signatures were significantly (P < 0.05) more enriched in arable and grassland ecosystems than forests, suggesting a more open N cycle with significant N cycling and losses due to higher N inputs from fertilizers. Similar to soil inorganic N, N 2 O fluxes, and NO 3 leaching rates, landscape-scale foliar and soil 15N isotopic signatures varied widely spatially, particularly at grassland and arable land (−3 to 9.0‰), with bivariate and multivariate analyses also showing significant relationships between landscape-scale soil 15N isotopic signatures and the aforementioned parameters (r2: 0.29 to 0.82). Based on these relationships, our findings suggested that foliar and bulk 15N isotopic signatures may capture fine-scale areas with persistently high and low environmental N losses (N 2 O fluxes and NO 3 leaching) within a heterogeneous landscape. • Land use controls soil and foliar 15N isotopic signatures within a landscape. • Arable soils outdid forest soils in 15N-enrichment indicating an open arable N cycle. • Soil and foliar δ15N were positively related, showing plant uptake of cycled soil N. • Enriched soil 15N indicated persistent hotspots of N 2 O fluxes and NO 3 leaching. [ABSTRACT FROM AUTHOR]

Introduction: Contemporary dietary and nutritional transitions are commonplace, but difficult to study directly. In Brazil, and Latin America, this generalized process, leading to current obesity and malnutrition problems, started more than four decades ago. Although body weight and food availability are used to measure changes, not much information on food consumption and nutrition exist. Stable isotope analysis allows for the study of modern individual diets because it reflects the proportional contribution of different foods, general dietary patterns, and the effect of metabolism. Furthermore, when samples from tissues reflecting different time points are used, it allows for the assessment of individual transitions., Objectives: To explore intra-person isotopic variation for the first time in the Southern Hemisphere for modern humans, and examine the nutritional transition reported for Brazil in the past four decades., Materials: Stable carbon and nitrogen isotope values from 68 14 C-dated bone samples (vertebra, occipital, parietal, femur) from 17 individuals born in 1963, from three cemeteries., Results: Data reflect chronologically ordered high intra-individual δ 15 N variation tracking the dietary and nutrition transition over the last few decades, while no relationship between δ 13 C values and time was found. Vertebrae, reflecting diets from the mid 2000s, showed lower δ 15 N values than other bones reflecting the mid 1980s and early 1990s., Discussion: We show how different bones capture nutritional transitions over the lifespan of modern individuals. Nitrogen isotope values were lower in recent tissues as a consequence of the changes in the agri-food industry and worldwide consumption patterns that have intensified in Latin America in the last decades., (© 2025 Wiley Periodicals LLC.)

Omnivores are generally opportunistic foragers and have a flexible dietary response to resource abundance and availability. Their populations may consist of individuals that differ from each other in terms of their trophic positions, which implies that the dietary response to resource fluctuations differs within a population. We investigated how changes in the abundance of sika deer (Cervus nippon) affected dietary variation and body condition in the Asian black bear (Ursus thibetanus). We used fecal analysis, nitrogen stable isotopes (δ15N), and body measurements to determine whether the variation in dietary meat content of Asian black bears is positively related to variations in the density of the sika deer population, whether male bears have a higher trophic position compared to females, and whether dietary meat content is positively related with body mass or body condition of bears. We found a positive correlation between the occurrence of deer remains in bear feces and deer density, suggesting that bears change their diet in response to temporal changes in deer density. Male bears had higher δ15N values than females, and neither values varied when deer density decreased. Males selectively consumed deer after a reduction in deer density, whereas females consistently consumed more plant‐based diet. The δ15N values were positively related with body mass of adult (>4 yr) bears but had no relationship with body condition of bears of either sex or any age class. Deer seem to be an important food source for large adult males, which have an advantage in mating. Thus, increasing herbivore abundance and availability altered the foraging strategy of Asian black bears, but the importance of herbivore on bear diet differs within a population. [ABSTRACT FROM AUTHOR]

Multiple environmental forcings, such as warming and changes in ocean circulation and nutrient supply, are affecting the base of Arctic marine ecosystems, with cascading effects on the entire food web through bottom‐up control. Stable nitrogen isotopes (δ15N) can be used to detect and unravel the impact of these forcings on this unique ecosystem, if the many processes that affect the δ15N values are constrained. Combining unique 60‐year records from compound specific δ15N biomarkers on harp seal teeth alongside state‐of‐the‐art ocean modelling, we observed a significant decline in the δ15N values at the base of the Barents Sea food web from 1951 to 2012. This strong and persistent decadal trend emerges due to the combination of anthropogenic atmospheric nitrogen deposition in the Atlantic, increased northward transport of Atlantic water through Arctic gateways and local feedbacks from increasing Arctic primary production. Our results suggest that the Arctic ecosystem has been responding to anthropogenically induced local and remote drivers, linked to changing ocean biology, chemistry and physics, for at least 60 years. Accounting for these trends in δ15N values at the base of the food web is essential to accurately detect ecosystem restructuring in this rapidly changing environment. [ABSTRACT FROM AUTHOR]

Pollen records and macrobotanical remains indicate maize was grown minimally during the Middle Woodland (200 BCE - CE 500) in eastern North America. However, previous isotopic studies have found limited evidence of its consumption by people in archaeobotanical assemblages. Hypothetically, if deer (Odocoileus virginianus Zimmermann) were feeding on maize (Zea mays L.) in gardens prior to its adoption as a human dietary staple, this may indicate a niche construction process which would later lead to shifts in hunting strategies. This construction of garden spaces or niches has implications for decreased mobility and greater investment in garden crops. To evaluate this hypothesis in the Ohio River Valley, we measured stable nitrogen (δ15N) and carbon (δ13C) isotope compositions of bulk collagen in deer bones (N = 25) from archaeological sites spanning the Middle Woodland (200 BCE - CE 400/500) to Late Precontact (CE 1400-1630). Our hypothesis was not confirmed: little (one deer of 19) evidence for maize consumption occurred in the analyzed deer remains. Five deer of 19 did indicate the possibility of feeding in deeply wooded areas, reflecting canopy effect. Dog (Canis lupus familiaris L.) bone samples (N = 2) were also analyzed for these isotopes and one indicates some consumption of maize. [ABSTRACT FROM AUTHOR]

Aquatic plants are the dominant biota in retaining nitrogen (N) pollutants discharged into river ecosystems, but the sensitivity of plant N pools and N assimilation to riverine N loadings, which is essential for evaluating river biogeochemistry and functions, remains poorly understood. Here, concentrations and stable isotopes of N in river water and aquatic plants were measured along the Nanming River in Guiyang of southwestern China. Total N (TN) contents of aquatic plants increased, but the increments decreased with river N concentrations. The δ15N of plant TN decreased with sewage N loadings along the river, which revealed a distinct shift of plant N preference from ammonium to nitrate. Higher levels of nitrate reductase activity in plants at the downstream river section supported the elevated nitrate preference and assimilation, which might explain the decreased nitrate concentrations observed in the river water of the downstream section. These findings contributed to understanding riverine N biogeochemical processes and their response to N loadings, which can help trace sewage N pollution and its ecological effects on river ecosystems. Plain Language Summary: Aquatic plants are important primary producers and play a key role in sustaining the structure and function of river ecosystems. Nitrogen (N) is an essential nutrient and aquatic plants can acquire N from river water. Because sewage N pollutants are often more 15N‐enriched than unpolluted N sources, N contents and isotopes of aquatic plants have been widely used to evaluate sewage N pollution. However, plant N‐use strategies and their responses to N pollution are largely uncertain in river systems, which hinders an accurate evaluation of riverine N pollution. Along a city river, we found that plant N contents increased but their responsiveness to river N pollution decreased. Moreover, plant δ15N did not increase but decreased with elevated N loadings, which revealed an altered plant N preference from ammonium to nitrate and was supported by higher nitrate reductase activities in plants under N pollution. Clearly, disproportional increases in plant N‐uptake ability and between ammonium and nitrate assimilation should be considered when using plant N contents and δ15N to trace sewage N pollution. These findings can help understand river N biogeochemistry and the effects of sewage N pollution on river ecosystems. Key Points: Plant total nitrogen (N) contents increased, but δ15N decreased with increasing N loadingsPlant nitrate preference over ammonium increased in N‐polluted river sectionsSewage N pollution would not always cause high δ15N in river plants [ABSTRACT FROM AUTHOR]

The eutrophication degree in the coastal bay has been increasing significantly for the past years, due to the increasing nutrient discharge. However, the factors controlling sources and nitrogen (N) cycling in the different types of bays are still poorly understood. In this comparative study, nitrate dual isotopes (δ15N−NO3− and δ18O−NO3−) and ammonium nitrogen isotope (δ15N−NH4+), were used to determine the origin of nitrate in Qinzhou Bay (with riverine input) and Tieshangang Bay (without riverine input) in Beibu Gulf and to study biogeochemical processes associated with nitrogen cycling. The nutrient concentrations generally showed a decreased trend from the upper bay to the outer bay. The isotopic values in Tieshangang Bay were generally higher than that in the Qinzhou Bay, suggesting that there are differences in nitrate sources and transformation processes between the two bays. The dominant sources from manure and sewage (41%) and soil N (30%) from runoff input were responsible for the high nitrate observed in the upper Qinzhou Bay. Though manure and sewage (59%) were also dominant nitrate sources in the upper Tieshangang Bay, a decrease in source from soil N (20%) occurred due to less runoff input. Nutrients were retained in the upper Tieshangang Bay due to weak hydrodynamic conditions, which caused higher NH4+ concentrations in the upper bay. Significant nitrate loss occurred in the outer Qinzhou Bay, which was related to the intense hydrodynamic condition. Moreover, phytoplankton assimilation mainly utilized NH4+ due to sufficient NH4+ in the outer Qinzhou Bay. In contrast, nitrate loss was also found in the outer Tieshangang Bay, which is mainly related to the phytoplankton assimilation due to the weak hydrodynamic condition. In addition, the greater enrichment of δ18O−NO3− than δ15N−NO3− during both bays suggests that atmospheric deposition also contributes to the nitrate pool in the water and the impact of atmospheric deposition on the whole Beibu Gulf is relatively consistent. By this comparative study, we found that different nitrate biogeochemical processes occurred in these two types of bays, which were mainly determined by the difference of human activities and hydrodynamic conditions.

Marine transitional environments play an important role in human sustainability. Around these ecosystems, coastal lagoons are subject to high anthropogenic pressure from population growth. The increased demand for goods and services is associated with the elevated discharge of untreated and treated wastewater into lagoon systems. The absence of benthic organisms in lagoon environments has been linked to extreme natural conditions and severe anthropogenic impact at both spatial and temporal scales. However, the mechanisms that lead to the presence of azoic sediments in lagoon environments have yet to be studied. This study aimed to determine the vertical variability of textural groups, geochemistry, and benthic foraminiferal fauna to understand how natural and anthropogenic components generate a vertical sediment sequence with low or absent benthic foraminifera in a subtropical coastal lagoon in the southwestern end of the Gulf of California. A 41 cm-long sediment core was collected from La Paz Lagoon at a 1-m depth. The core was sectioned every centimeter, and sediment subsamples were dried and homogenized for grain size, calcium carbonate, elemental and isotopic carbon and nitrogen analyses, and benthic foraminifera quantification. Muds with fine sands towards the core's base characterized the sedimentary sequence. Organic carbon and total nitrogen increased from the base (1.4% and 0.06%, respectively) to the core-top (CT, 3.0% and 0.14%, respectively), significant from the 27 cm interval. Calcium carbonate content was very low (<0.8%). The relationship of δ13C vs. C:N ratio indicated that sedimentary organic carbon was derived from the marine and sewage source mixture. The δ15N of organic matter increased by 3.7‰, starting from the 27 cm interval towards the CT. The nitrogen sewage input source was relatively more significant than nitrogen fixation. The few individuals (<18 ind. in 10 g) and genera (Ammonia and Elphidium), as well as the absence of foraminifera in 19 of 41 intervals in the core, indicated that environmental conditions were unfavorable, even for colonization of environmentally stress-tolerant genera. The frequency of azoic sediments was higher from the 25 cm interval to the CT vs. from the base to the 25 cm interval. Moreover, the AEI revealed severe to moderate hypoxia in the study area. The limited presence of benthic foraminifera and calcium carbonate preservation corroborated that the quality of the lagoon's environment has deteriorated along with population growth, which requires strategic programs to sustain this transitional ecosystem. • Muds with high organic carbon content and very low calcium carbonate. • Few individuals and only two genera: Ammonia and Elphidium in sediment core. • Absence of foraminifera in 19 of 41 intervals in the sediment core. • AEI revealed severe to moderate hypoxia in the lagoon. • Nitrogen sewage input source was more significant than nitrogen fixation. [ABSTRACT FROM AUTHOR]

Intra-tooth or sequential stable isotope analyses are nowadays widely implemented in zooarchaeological research. Sequential isotopic analyses have been mainly restricted to the mineral fraction of the enamel, while a wider implementation in dentine collagen has been generally eluded, despite conforming an essential organic compound for paleodietary studies. In high-crowned teeth, dentine grows oblique to the vertical axis of growth and some challenges arise when trying to isolate dentine increments during a sequential sampling. Previous sampling strategies slice the whole dentine thickness and provide sequences where isotopic variation is largely attenuated. In this study, we show a new proposal for performing carbon and nitrogen isotope analyses of dentine collagen which better fits dentine's growth. We implemented it in mandibular second molars of an experimental modern sheep flock. Our sampling largely reduces the isotopic "damping" of previous approaches and provides short time-span samples. Sequential δ13C values obtained in dentine tissue yielded similar resolution to those obtained in enamel tissue of the same individuals. This proposal, especially suitable for caprine and other bovid species, broadens the implementation of dentine collagen signatures in the field of stable isotope analyses in zooarchaeology. • New proposal for intra-tooth isotopic analyses of dentine in hypsodont species. • Stable carbon and nitrogen isotopes of dentine collagen are sequentially analyzed. • The method is tested in experimental sheep specimens raised under controlled diet. • The new sampling protocol yields high time resolution in high-crowned teeth. [ABSTRACT FROM AUTHOR]

In this study, published and unpublished data on bulk organic matter from surficial sediments along the Southwestern Atlantic Margin (SAM) were gathered to identify sources and understand carbon transport over this large and complex area under the regime of strongly coupled climatic-hydrological-oceanographic interactions. To achieve this goal, total organic carbon (TOC), total nitrogen (TN), stable carbon (δ13C), and nitrogen (δ15N) isotopes, as well as calcium carbonate data from 242 sedimentary samples over the SAM were analyzed. Cluster analysis defined three geochemically distinct groups, closely related to sedimentary and hydrodynamic controls. Our results show that the latitude of 28°S marks a transition region in terms of the sedimentary bulk organic matter. To the south, organic material is strongly influenced by the continental contribution from the La Plata River and by the action of the Brazilian Coastal Current, whereas to the north, the contribution of La Plata River gradually decreases. Oceanographic fronts, currents, and river supply are the main mechanisms that drive organic matter distribution over the SAM. • Sedimentary organic matter is associated with mud content and areas of intense primary productivity. • Sedimentary organic matter exhibits distinct characteristics both south and north of Cape Santa Marta, as well on the continental shelf compared to the slope. • Sedimentary δ15N provides insights into the nitrogen sources absorbed during primary production, revealing nuances in nutrient availability and algal utilization in different SAM regions. • Despite the La Plata River's role as a significant terrigenous source, marine organic matter signals dominate the SAM, potentially overshadowing terrigenous contributions. [ABSTRACT FROM AUTHOR]

• The pristine plant populations were replaced by more minerotrophic species since the Middle Age. • Self-regenerating processes takes place in bogs of the Harz Mts. • Fire episodes intensified during hydrological disturbances. • Long-term carbon accumulation rates may be linked to changes in plant composition. • δ13C and δ15N related to the degree of decomposition and the vegetation composition. Mountain peatland ecosystems are unique islands of biodiversity, hosting endangered, vulnerable, and protected plants and animals. In addition, these ecosystems constitute important natural carbon stores. Their stratigraphy can be used to reconstruct the development of these ecosystems as well as the impact of various human activity over millennia. To examine the dynamics of an ombrotrophic peatland (Odersprungmoor) ecosystem in the Harz Mts. (Germany) in relation to environmental changes, fire, pollution and human activity, we have undertaken high-resolution analyses of plant macrofossils, testate amoebae, macrocharcoal morphologies, non-destructive X-Ray fluorescence and carbon (δ13C) and nitrogen (δ15N) stable isotopes, and bulk density, combined with radiocarbon dating (AMS). Our study revealed that: i) the pristine plant populations composed mainly by Sphagnum fuscum and Sphagnum rubellum were replaced by Sphagnum medium/divinum since the Middle Age (ca. 600 cal yr BP) presumably due to pollution deposition. Hence we suggest that i) bogs in the Harz Mts. might have lost their natural character, and that oligotrophic Sphagnum species populations have either diminished or were replaced by vascular plant populations, ii) long-term carbon accumulation rates were similar to those from northern hemisphere lowland peatlands, and changing rates over time may be linked to changes in plant composition and water table depth, iii) fire episodes, which intensified during hydrological disturbances, partly impacted plant succession, iv) Eriophorum vaginatum is a good indicator of local hydrological disturbances in mountain bogs, v) despite lowering of the water table depth during the last decades, Sphagnum rubellum re-appeared at the sampling site, vi) decomposition coincided with higher N:P ratios while phosphorus got enriched at the peatland surface, vii) δ13C and δ15N were not related to average reconstructed water levels, but to the degree of decomposition and the vegetation composition, viii) we see strong indications of a self-regeneration process leading to expansion of oligotrophic Sphagnum species in the bogs of the in bogs of the Harz Mts. [ABSTRACT FROM AUTHOR]

Forest management can alter the mobilization of mercury (Hg) into headwater streams and its conversion to methylmercury (MeHg), the form that bioaccumulates in aquatic biota and biomagnifies through food webs. As headwater streams are important sources of organic materials and nutrients to larger systems, this connectivity may also increase MeHg in downstream biota through direct or indirect effects of forestry on water quality or food web structure. In this study, we collected water, seston, food sources (biofilm, leaves, organic matter), five macroinvertebrate taxa and fish (slimy sculpin; Cottus cognata) at 6 sites representing different stream orders (1–5) within three river basins with different total disturbances from forestry (both harvesting and silviculture). Methylmercury levels were highest in water and some food sources from the basin with moderate disturbance (greater clearcutting but less silviculture). Water, leaves, stoneflies and fish increased in MeHg or total Hg along the river continuum in the least disturbed basin, and there were some dissipative effects of forest management on these spatial patterns. Trophic level (δ15N) was a significant predictor of MeHg (and total Hg in fish) within food webs across all 18 sites, and biomagnification slopes were significantly lower in the basin with moderate total disturbance but not different in the other two basins. The elevated MeHg in lower trophic levels but its reduced trophic transfer in the basin with moderate disturbance was likely due to greater inputs of sediments and of dissolved organic carbon that is more humic, as these factors are known to both increase transport of Hg to streams and its uptake in primary producers but to also decrease MeHg bioaccumulation in consumers. Overall, these results suggest that the type of disturbance from forestry affects MeHg bioaccumulation and trophic transfer in stream food webs and some longitudinal patterns along a river continuum. [Display omitted] • Forestry increases methylmercury (MeHg) in small streams but impacts along the river continuum are unclear. • Elevated MeHg in basal compartments at upstream through downstream sites linked to greater % clearcutting in one basin. • This elevated basal MeHg did not increase fish Hg due to lower trophic transfer in this basin. • MeHg in some compartments increased longitudinally in the basin with low forestry disturbance. • Little evidence of forestry impacts on biomagnification efficiency along river continuum. [ABSTRACT FROM AUTHOR]

The resident and tourist population in the Mexican Caribbean has grown exponentially, increasing the availability of dissolved inorganic nutrients in coastal waters through submarine groundwater discharge (SGD). Recently, a new massive drift of Sargassum spp. has occurred that can provide new organic matter and enrich coastal water with nutrients. In different sites in the Mexican Caribbean, the chemical composition of the water was analyzed, and the δ 15 N of Thalassia testudinum was determined between 2016 and 2019. Evidence of SGD was observed in Akumal Bay due to high silicate concentrations and its negative correlation with salinity. Seasonal and interannual variation in NH 4 + concentration was observed at these sites. In October 2018, SGD contributed ∼70 times more nitrogen and ∼194 times more phosphorus than the decomposition of the pelagic macroalgae Sargassum spp. The δ 15 N data showed that Akumal Bay received nitrogen of anthropogenic origin and that nitrogen fixation processes or probably assimilation of nitrogen of the leachates of pelagic Sargassum spp were dominant at Mahahual and Xahuayxol., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The Gulf of California is a highly biodiverse marine basin located in the northeast Mexican Pacific Ocean. In the past three decades, this basin has experienced increased hypoxia in shallow waters, which threatens its coastal ecosystems. The aim of this study is to analyze δ15N and δ13C isotopes of organic matter in coastal sediments to characterize sources of primary production and shifts in biogeochemical processes that reflect increasing oxygen deficiency in the shallow coast of the eastern Gulf of California. Surface sediments samples were collected from 8 to 47 m deep along the coastal margin of Sinaloa and Sonora. This region is characterized by the development of anthropogenic activities, which could be the main source of organic matter evidenced in the marine environment. The C:N ratio and δ13C of sedimentary organic matter suggest that the dominant source is of marine origin. Values of δ15N measured in organic matter of surface sediments below 15 m are larger than >8‰. This enrichment suggests denitrification and hypoxic conditions in the water column, which could be associated with an increase in the frequency, periodicity, and intensity of shallow hypoxic events in the Gulf of California. • Shallow hypoxia in the continental coast of the Gulf of California. • 15N enrichment of organic matter suggests denitrification conditions. • Sedimentary organic matter was predominantly of marine origin. • Low nitrate concentrations in surface water indicate its complete utilization. [ABSTRACT FROM AUTHOR]