Stable Nitrogen Isotopic Composition Research Articles

Abyssal fauna, benthic microbes, and organic matter quality across a range of trophic conditions in the western Pacific ocean

The abyssal plain covers more than half the Earth’s surface. The main food source to abyssal ecosystems is phytodetritus, which originates from phytoplankton in the surface ocean, and thus its variability to the seafloor is a major driver of abyssal ecosystem biomass and functioning. In this study, we conducted a comparative survey on organic matter (OM) quality and quantity in abyssal plain sediments and examined the distributions of megafauna, macrofauna, meiofauna, prokaryotes, and viruses in eutrophic (39°N), oligotrophic (1°N), and ultra-oligotrophic (12°N) areas of the western Pacific. We also analyzed stable carbon and nitrogen isotopic compositions of organisms at 39°N and 1°N to assess differences in benthic abyssal food-web structures with contrasting trophic states. Sediments collected at 39°N presented highest concentrations of total organic carbon (TOC) and labile OM, and high diffusive oxygen uptake rates. By contrast, the lowest values were found at 12°N. Vertical distributions of sediment macrofauna, meiofauna, and prokaryotes matched with labile OM profiles. There were prominent differences in abundances of macro- and megafauna among stations with different OM fluxes, whereas the abundance of meiofauna and prokaryotes showed smaller differences among stations. Such differences could be explained by higher turnover rates of smaller organisms. Food-web structures of abyssal plains are likely influenced by both the type and size of primary producers in surface ocean. Our results underscore the crucial importance of OM fluxes and their compositions to the abundances and vertical profiles of labile OM and benthic biota in abyssal ecosystems.

Foliar Carbon and Nitrogen Content and Stable Isotopic Composition of Selected Philippine Flora

The elemental carbon and nitrogen content, as well as the stable isotopic composition of plants, can provide information on their nutrient dynamics and physiological characteristics. With applications ranging from paleoecology to ecological modeling, this information is critical in biodiversity conservation and management especially for highly dynamic ecosystems such as the Philippines’. Here, we determined the carbon and nitrogen content and their stable isotopic ratios in selected Philippine flora across different classifications and photosynthetic pathways. Fully developed leaves from different species of grasses, succulents, shrubs, and trees were collected and analyzed using isotope ratio mass spectrometry for carbon and nitrogen concentration and stable isotopic composition. Our results showed that trees had the highest carbon and nitrogen content, while grasses that utilized the C4 photosynthetic pathway were most efficient in terms of nutrient utilization as evidenced by their high C/N ratios. Foliar stable carbon isotopic composition of the surveyed Philippine flora was an excellent measure for distinguishing among photosynthetic pathways. The stable nitrogen isotopic composition was not distinct across plant classifications and showed indications of being sensitive to environmental factors, thus limiting its use for phylogenetic tracing. Our findings thus indicate that foliar carbon and nitrogen content and stable isotopic composition provide insights that cannot be easily achieved with other measurements.

Amino acid and chlorin based degradation indicators in freshwater systems

Lakes cover a global area that is about 35 times smaller than the oceans, but carbon burial in lakes and oceans are on the same order of magnitude. Hence, understanding the processes for such high organic carbon burial in lacustrine systems is essential. We applied proxies typically used for marine environments including amino acid (AA) content and their nitrogen stable isotope composition to the water columns and sediments of three lakes that differ in their trophic states and depositions rates of sedimentary terrestrial organic matter. Additionally, we used carbon isotope fingerprinting of AAs to characterise their sources and fates. We show that this set of proxies tracks sources and degradation processes in eutrophic lakes with high sedimentary total organic carbon and nitrogen content. Those lakes also have a high total hydrolysable amino acid (THAA) content as well as higher pigment concentrations. While the Chlorin degradation Index (CI) showed increasing values with depth, the patterns were less consistent for the Degradation Index (DI). In general, all parameters failed to describe degradation in the most oligotrophic lake due to the very low organic carbon and nitrogen content in the sediment. We show that AAs are mostly of autochthonous origin and that AA contribute 5–45% to the organic material in plankton, POM, and sediment. Proxies based on AA for bacterial reworking (ΣV) or trophic level (TL) showed increasing values in the water column but relatively stable values in the sediments. Furthermore, we show that methanotrophic bacteria led to increased values for the bacterial reworking proxy (ΣV) and extraordinarily low δ13C AA values (−30 to −60‰).

δ15N-stable isotope analysis of NH x : An overview on analytical measurements, source sampling and its source apportionment.

Agricultural sources and non-agricultural emissions contribute to gaseous ammonia (NH3) that plays a vital role in severe haze formation. Qualitative and quantitative contributions of these sources to ambient PM2.5 (particulate matter with an aerodynamic equivalent diameter below 2.5 µm) concentrations remains uncertain. Stable nitrogen isotopic composition (δ15N) of NH3 and NH4+ (δ15N(NH3) and δ15N(NH4+), respectively) can yield valuable information about its sources and associated processes. This review provides an overview of the recent progress in analytical techniques for δ15N(NH3) and δ15N(NH4+) measurement, sampling of atmospheric NH3 and NH4+ in the ambient air and their sources signature (e.g., agricultural vs. fossil fuel), and isotope-based source apportionment of NH3 in urban atmosphere. This study highlights that collecting sample that are fully representative of emission sources remains a challenge in fingerprinting δ15N(NH3) values of NH3 emission sources. Furthermore, isotopic fractionation during NH3 gas-to-particle conversion under varying ambient field conditions (e.g., relative humidity, particle pH, temperature) remains unclear, which indicates more field and laboratory studies to validate theoretically predicted isotopic fractionation are required. Thus, this study concludes that lack of refined δ15N(NH3) fingerprints and full understanding of isotopic fractionation during aerosol formation in a laboratory and field conditions is a limitation for isotope-based source apportionment of NH3. More experimental work (in chamber studies) and theoretical estimations in combinations of field verification are necessary in characterizing isotopic fractionation under various environmental and atmospheric neutralization conditions, which would help to better interpret isotopic data and our understanding on NHx (NH3 + NH4+) dynamics in the atmosphere.Electronic Supplementary MaterialSupplementary material is available in the online version of this article at 10.1007/s11783-021-1414-6 and is accessible for authorized users. Supplementary material includes supplementary tables on summary of recent isotope-based source apportionment studies on ambient NH3 derived from δ15N(NH3) values (Table A1); and summary of recent isotope-based source apportionment studies on particulate NH4+ derived from δ15N(NH4+) values (Table A2).

Investigating the diet of Mesolithic groups in the Southern Alps: An attempt using stable carbon and nitrogen isotope analyses

Stable isotopic data (δ13C; δ15N) were obtained from Mesolithic human and faunal remains from north- eastern Italy in order to document the human diet and provide information on the relationship between landscape use and subsistence strategies. The bone samples were from an adult female individual (Early Mesolithic, Late Sauveterrian) buried at Vatte di Zambana (Trento), an adult male (Late Mesolithic, Castelnovian) buried at Mondeval de Sora (Belluno), and an adult female from Mezzocorona Borgonuovo (Trento). For the latter, the stratigraphic position of the burial pit and evidence of the associated ritual suggest a Mesolithic attribution. Carbon (13C/12C) and nitrogen (15N/14N) stable isotope compositions of human bone collagen were compared with those of animal remains from different taxa found in stratigraphic association with the burial. The isotopic data and the Bayesian model developed from the latter and from data in the literature indicate a very significant proportion of terrestrial resources in the protein fraction of the human diet, particularly from red deer compared to other ungulates and potentially from freshwater fish and small mammals. These results add to the information provided by zooarchaeological studies and reopen the debate on the role of secondary resources such as chamois, ibex, small mammals and fish, such as pike, in the diet of these mobile human societies. However, as this is a preliminary study based on a very small sample size, interpretations should be considered with caution.

Seasonal paleoecological records from antler collagen δ13C and δ15N

AbstractCervids 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.

Stable isotopic composition of top consumers in Arctic cryoconite holes: revealing divergent roles in a supraglacial trophic network

Abstract. Arctic cryoconite holes represent highly biologically active aquatic habitats on the glacier surface characterized by the dynamic nature of their formation and functioning. The most common cryoconite apex consumers are the cosmopolitan invertebrates – tardigrades and rotifers. Several studies have highlighted the potential relevance of tardigrades and rotifers to cryoconite holes' ecosystem functioning. However, due to the dominant occurrence of prokaryotes, these consumers are usually out of the major scope of most studies aimed at understanding biological processes on glaciers. The aim of this descriptive study is to present pioneering data on isotopic composition of tardigrades, rotifers and cryoconite from three High Arctic glaciers in Svalbard and discuss their role in a cryoconite hole trophic network. We found that tardigrades have lower δ15N values than rotifers, which indicates different food requirements or different isotopic fractionation of both consumers. The δ13C values revealed differences between consumers and organic matter in cryoconite among glaciers. However, the mechanistic explanation of these variations requires further investigation focused on the particular diet of cryoconite consumers and their isotopic ratio. Our study introduces the first observation of carbon and nitrogen stable isotopic composition of top consumers in cryoconite holes analysed by an improved method for cryoconite sample processing, paving the way for further studies of the supraglacial trophic network.

Multiple stressors shape invertebrate assemblages and reduce their trophic niche: A case study in a regulated stream

Few studies have addressed how the diversity of basal resources change with stream regulation and the potential consequences on river biota. We sampled invertebrates above and below a series of dams, over two years, at both downwelling and upwelling zones. In each zone, we recorded the daily temperature and flow variations, estimated the algal development, measured the available resources, and analysed carbon and nitrogen stable isotope compositions of the invertebrate community. The number of hydrological pulses were typically higher below the dams than above the dams especially during high-flow periods whereas the groundwater outlets had minor effects on invertebrate assemblages. Invertebrate abundance, richness and diversity tended to decrease below the dams. Co-inertia analysis showed that flow and temperature variations, and eutrophication explained most of the variance in the invertebrate assemblages, which comprised a higher number of resilient taxa below than above the dams. The proportions of pesticide-sensitive invertebrates were lower below the dams and ovoviviparous and more generalist taxa were prominent. We did not observe the expected CPOM decrease and FPOM increase downstream. Accordingly, the proportions of each functional feeding group were remarkably similar above and below the dams despite the long distance between the sectors (>100 kms). The diversity of basal resources used within assemblages progressively increased downstream above dams. In contrast, the diversity of resources used by organisms below the dams decreased from upstream to downstream suggesting a significant influence of flow regulation on aquatic food webs. Finally, the shorter trophic chains for the invertebrate assemblages below the dams suggests that the effects of stream regulation and eutrophication induced a simplification of food webs. To our knowledge, this study is the first to connect taxonomic and functional trait changes in response to multiple stressors with the associated modifications in isotopic niches within aquatic invertebrate assemblages. ContextUnderstanding how stream regulation and associated anthropogenic pressures act on aquatic assemblages and trophic niches is necessary to guide management actions. GoalWe aimed to investigate the functional responses (traits and trophic niches) of aquatic invertebrate assemblages to stream regulation and eutrophication. MethodsWe used univariate and multivariate analyses to compare the invertebrate assemblages above and below the dams and to assess the contributions of hydrology (including groundwater supplies to the river), temperature and eutrophication to the variability in the composition of invertebrate assemblages. We also considered the relative utilization of a selected set of traits describing invertebrate resilience, resistance and specialization to address the potential functional effects of stream regulation on invertebrate assemblages. Finally, carbon and nitrogen isotope analyses allowed us to characterize the length and width of invertebrate assemblage food webs as related to the availability and diversity of basal resources. ResultsInvertebrate abundance and richness generally decreased below the dams, with the highest impacts on insect taxa. Co-inertia analysis showed that stream regulation and eutrophication were main drivers of the aquatic invertebrate assemblages. The analysis separated the sites above and below the dams according to flow and temperature variation, whereas eutrophication appeared as a secondary stressor that separated the sites within each sector. Furthermore, the series of dams resulted in (i) a higher proportion of resilient (e.g., multivoltine) and resistant (ovoviviparous) taxa and a majority of generalists in assemblages below dams, (ii) an impact on the classical dynamics of CPOM (decrease) and FPOM (increase) sources from upstream to downstream, and (iii) a reduction in the diversity of resource use and in the trophic chain length of invertebrate assemblages below dams. The cooler and less oxygenated upwelling zones had lower invertebrate abundance; however, contrary to our expectation, the variation in the groundwater supply did not affect the composition of epigean invertebrate assemblages. ConclusionThis study provides insights about the impacts of flow regime alteration and eutrophication on food webs that may have been caused by regulation of permanent streams. To our knowledge, this is the first to connect taxonomic and functional trait changes in response to multiple stressors with the associated modifications in energy fluxes in aquatic invertebrate assemblages. This study suggests that bed stability, which is associated with a reduction in channel mobility below the dams and with moderate eutrophication, may provide the shelter and resources that can locally favour invertebrate assemblage dynamics and lessen the effects of flow regulation. In addition, the study suggests that the biological trait-based approach and isotope analysis are complementary approaches for addressing ecosystem functioning. The relative utilization of traits indicates the functional potential of aquatic invertebrate assemblages to face multiple stressors whereas isotope analysis is an expression of the actual effect of the stressors on the trophic structure of aquatic invertebrate assemblages.

Diet of spiny lobsters from Mahé Island reefs, Seychelles inferred by trophic tracers

Spiny lobsters (Panulirus longipes, P. penicillatus and P. versicolor) are an important resource in Seychelles, where they inhabit coastal carbonate and granite reefs that have been impacted by multiple coral bleaching events over the past two decades. Little is known about their biology and ecology in this region. Interspecific competition for food resources was previously suggested, but no quantitative data on the diet of spiny lobsters were available. Using carbon and nitrogen stable isotope compositions and fatty acid profiles of three spiny lobster species and their potential prey, a Bayesian mixing model for diet estimation was applied to compare the diet proportions of spiny lobsters among species and between reef types (carbonate and granite reefs). Model outputs suggested the three lobster species consume mainly crustaceans (Anomoura hermit crabs; half of the diet), then Echinoidea (sea urchins), algae and molluscs. P. versicolor was found to consume slightly more molluscs and algae than the two other studied species, which was consistent with its lower trophic level (2.4 vs 2.8 for the two other species). Trophic level did not increase with carapace length of spiny lobsters, but large individuals had higher carbon isotopic values suggesting that they might feed closer to the coast or more on detritus feeders than their smaller congeners. Diets of spiny lobsters were fairly similar between carbonate and granite reefs, except that lobster inhabiting granite reefs consumed more sea urchins. While our overall findings were consistent with gut contents of Panulirus spp. from other world regions, they should be confirmed, as the discrimination of several prey based on trophic tracers was low, which increased mixing model uncertainty.

Effect of irrigation salinity and ecotype on the growth, physiological indicators and seed yield and quality of Salicornia europaea

The euhalophyte species Salicornia europaea is cultivated for oilseed and as a fodder crop in various parts of the world. In saline coastal environments it possesses great potential for the subsistence of the most disadvantaged farmers. We investigated the effect of salinity levels in irrigation water on the germination capacity, shoot biomass and seed productivity as well as diverse quality traits (nitrogen content in shoots and seeds and fatty acids, in seeds) and physiological traits (stable carbon and nitrogen isotopes and ion content) of two accessions collected in the United Arab Emirates (UAE). The three salinity levels tested were irrigation with fresh water (0.3 dS m−1), brackish water (25 dS m−1) and sea water (40 dS m−1). In addition, a hypersaline condition (80 dS m−1) was also tested for germination. The best germination rates were achieved with seeds exposed to fresh and brackish water, while imbibition with sea water decreased germination by half and hypersaline water inhibited it almost totally. However, the best irrigation regime in terms of biomass and seed yield involved brackish water. Moreover, rising salinity in the irrigation increased the stable isotope composition of carbon (δ13C) and nitrogen (δ15N), together with the Na+ and K+ of shoots and seeds, and the lipid levels of seeds, while the total nitrogen content and the profile of major fatty acids of seeds did not change. Differences between the two ecotypes existed for growth and seed yield with the best ecotype exhibiting lower δ13C and higher K+ in both shoots and seeds, lower Na+ and higher δ15N in shoots, and lower N in seeds, together with differences in major fatty acids. Physiological mechanisms behind the response to irrigation salinity and the ecotypic differences are discussed in terms of photosynthetic carbon and nitrogen metabolism.

Seasonal variation and driving factors of carbon and nitrogen stable isotope values of plankton in four lakes of Yunnan Province

浮游生物是湖泊食物网的重要组成，其碳、氮稳定同位素能够反映元素地球化学循环和食物来源的波动，是了解水域生态系统结构变化的重要手段之一.本文选取云南4个不同类型湖泊，开展浮游生物碳、氮稳定同位素组成（δ¹³C、δ¹⁵N）的季节变化与湖泊对比研究.大型深水湖泊（抚仙湖和阳宗海）中，浮游植物δ¹³C值在夏、秋季（-20.34‰±1.98‰）显著高于冬、春季（-28.00‰±2.51‰），反映夏秋季藻类生长速率较高、HCO₃^-无机碳源利用增多等的影响.而小型浅水湖泊（长桥海和大屯海）中浮游植物δ¹³C值在夏季最高（-21.24‰±0.88‰），可能与雨季流域输入增强、陆源有机质占比增加有关.4个湖泊浮游生物δ¹⁵N值具有一致的变化特征，春季显著高于其他季节.分析表明，云南地区雨季以面源污染为主向旱季以点源污染为主的转变，导致氮素营养盐季节性来源差异，并通过生物吸收作用影响了浮游生物δ¹⁵N值的季节变化.在浮游动物与浮游植物的稳定同位素差值（即富集度）方面，营养水平高的小型浅水湖泊中δ¹³C富集度为1.61‰±0.90‰、δ¹⁵N富集度为2.71‰±1.22‰，显著小于营养水平低的大型深水湖泊（分别为2.60‰±0.98‰和4.19‰±1.25‰），表明随着湖泊营养水平的增加，浮游动物更多地以浮游植物为食，导致有机碳在不同营养级之间的传输过程中具有更强的耦合作用，且相邻营养级之间具有更低的δ¹⁵N富集度特征.;Plankton is an important component of lake food webs. Their carbon and nitrogen stable isotope values can reflect the fluctuation of biogeochemical cycling and food sources and can be applied to track the changes of aquatic ecosystem structure. In this paper, four lakes with distinct typology from Yunnan Province were selected to uncover the seasonal changes in carbon and nitrogen stable isotopic compositions of plankton. The carbon stable isotope values of phytoplankton in large deep lakes (Lake Fuxian and Lake Yangzong) are enriched in summer and autumn (mean ±SD: -20.34‰±1.98‰), but relatively depleted in winter and spring (-28.00‰±2.51‰), which may reflect a higher growth rate of plankton and greater assimilation of bicarbonate (HCO₃^-) during the growing season. In small shallow lakes (Lake Changqiao and Lake Datun), carbon stable isotopic values of phytoplankton are mostly enriched in summer (-21.24‰±0.88‰) among the four sampling seasons. This may be related to the increased input of terrigenous organic matter during the rainy season, and a decreased lower water level due to overuse of agricultural irrigation in summer. In contrast to the carbon stable isotope values, the nitrogen stable isotope composition of plankton displayed a similar trend of seasonal variations across lakes where a significantly more positive value was found in spring than in other seasons. Further analyses revealed that that seasonal variation in the nitrogen stable isotope of plankton is related to the seasonal difference of nitrogen sources and their distinct isotopic compositions. Specifically, non-point source pollution, mainly related to agricultural fertilizers with depleted nitrogen stable isotopic value, is often dominant in the rainy season, while point source pollution predominantly derived from sewage input with enriched nitrogen stable isotopic composition is commonly observed in the dry season. In terms of stable isotope fractionation between zooplankton and phytoplankton (i.e. trophic enrichment), small shallow lakes were characterized by smaller carbon (1.61‰±0.90‰) and nitrogen (2.71‰±1.22‰) stable isotopic enrichment than those in large deep lakes (2.60‰±0.98‰ and 4.19‰±1.25‰, respectively) in this study. Zooplankton often displays a higher degree of dependence on autochthonous organic carbon (such as phytoplankton) with increasing nutrient status, reflecting a stronger coupling of organic carbon transfer between trophic levels. Similarly, a smaller degree of nitrogen stable isotope enrichment is evidenced in more eutrophic lakes in this study.

Radium and nitrogen isotopes tracing fluxes and sources of submarine groundwater discharge driven nitrate in an urbanized coastal area

The quantitative evaluations of nutrients delivered by submarine groundwater discharge (SGD) have been widely conducted worldwide, but sources of nutrients in the discharged submarine groundwater remain unclear. Identifying these sources of nutrients is essential to the protection and management of marine ecological environments. This study aims to evaluate the magnitudes of SGD and the associated nitrate in the Guangdong-Hongkong-Macao Greater Bay Area (GHM Greater Bay Area), China, and identify the sources of SGD-driven nitrate in this region using radioactive radium (Ra) isotopes (223Ra, 224Ra, and 228Ra) and stable nitrogen (N) and oxygen (O) isotope composition of nitrate (δ15N-NO3− and δ18O-NO3−). The results of the Ra mixing model show that the estimated SGD and the associated nitrate fluxes into the Greater Bay Area are (9.15 ± 1.26) × 108 m3/d and (3.77 ± 0.52) × 107 mol/d, respectively, both of which are comparable to the contributions from the Pearl River. Combing NO3− dual isotopic signatures of sampled coastal groundwater and five kinds of potential nitrate sources, we found that ammonium (NH4+) fertilizer and natural soil N are the two main sources of nitrate in discharged submarine groundwater and rivers. No anthropogenic inputs from manure or sewage waste were identified. This study provides significant insights into the establishment of effective management strategies for controlling SGD-nutrients into the bay and protecting the marine ecological environment.

Biomass burning related ammonia emissions promoted a self-amplifying loop in the urban environment in Kunming (SW China)

Particulate ammonium (NH4+) is one of the most important inorganic components in aerosol. The concentrations of NH4+ in PM2.5 significantly increased when PM2.5 levels elevated. Increased understanding of the atmospheric processes and sources of ambient ammonia is an effective way to control atmospheric ammonia and tackle air pollution problems. This study focused on the concentration and nitrogen stable isotopic composition of particulate NH4+ in PM2.5 in a southwest typical plateau city, Kunming. The trend in NH4+concentrations was parallel to the trend in PM2.5 levels, with obviously increased concentrations observed in November. Aerosol pH and liquid water content (ALWC) were synchronously simulated by the ISORROPIA-II model. And the ammonia gas-particle conversion ratio (f) was calculated for each day. Then, we proposed that a self-amplifying feedback mechanism of NH4+ formation was associated with the variations of ALWC, pH, and the ammonia gas-particle conversion ratio. Based on the inverse analysis of the nitrogen isotopic composition of particulate NH4+, the corresponding δ15N values of initial ambient NH3 were estimated to be −27.4‰–15.3‰, with an average of −8.1 ± 8.3‰. Results from Back trajectory analysis, PSCF analysis, and isotope-based source apportionment of NH3 shed light on source compositions and potential source regions, indicating that, in the study area, ambient NH3 during slightly polluted days were dominated by biomass burning emissions, which might have been originated from local emissions and regional transport process in late autumn.

First overview on trophic relationships of the invasive ctenophore Mnemiopsis leidyi in a Mediterranean coastal lagoon (Berre Lagoon, France): benthic–pelagic coupling evidenced by carbon and nitrogen stable isotope composition

The ctenophore Mnemiopsis leidyi, ranking among the 100 most damaging bioinvaders in the world, is a major predator of zooplankton, known to alter the biodiversity and functioning of the ecosystems in which it has been introduced. This first survey on the trophic relationships of M. leidyi in a Mediterranean lagoon (Berre, South of France) was performed through stable isotope analyses. Carbon and nitrogen isotope composition was used (1) to determine the types of prey ingested by this ctenophore and (2) the influence of individual size on its isotope composition, and (3) to make assumptions to explore its trophic relationships with the native jellyfish Aurelia sp.. The two gelatinous species ingested mainly (79% to 97% of the diet) planktonic prey (copepods, cirriped nauplii, gastropod larvae and cladocerans), but also preyed upon benthic organisms (mainly harpacticoid copepods and the amphipod Monocorophium insidiosum) in lower proportions (2.5% to 21%). Size-related changes in M. leidyi diet were evidenced with an increase in trophic level and benthic prey consumption in the larger individuals. These two gelatinous organisms probably play an important and underestimated role in the benthic–pelagic​ coupling in coastal lagoons by transferring benthic organic matter to the pelagic food webs.

Intraindividual and interpopulation variability in carbon and nitrogen stable isotope ratios of bone collagen in the modern red deer (Cervus elaphus)

Stable isotope analyses of bone collagen are increasingly used in ecological studies. They are especially valuable in palaeoecological research due to the time of bone collagen preservation. However, such studies are usually subjected to some limitations, such as small size of the dataset and unknown sex or age of analysed individuals, which could potentially influence the results. We investigated variability of stable carbon and nitrogen isotope composition (δ13C and δ15N) within different parts of the skeleton of modern red deer (Cervus elaphus) from Poland, Scotland (UK) and Slovenia. We also tested weather there were differences in isotopic composition of bone collagen between males and females and individuals of different ages representing various populations. The mean differences between samples taken from the same mandibles and between various bones of the same individuals amounted to not more than 0.88‰ (SE ± 0.24) for δ15N and 0.46‰ (SE ± 0.07) for δ13C. Values of δ15N and δ13C in bone collagen did not differ significantly between males and females. Furthermore, we did not find any relationship between isotopic composition of bone collagen and age of the studied individuals. We conclude that carbon and nitrogen isotope ratios in the distal appendicular elements or fragments of mandible bones of the same individuals are comparable and can be alternately used in ecological studies of modern and ancient red deer specimens.

Carbon and Nitrogen Stable Isotopes Evidence for the Environmental Impact of the Cage Fish Farm in Poyang Lake, China.

The carbon and nitrogen stable isotope compositions of the sediment organic matter, fish feed and fish feces were measured to assess the impact of the aquaculture waste from the cage fish farm in Poyang Lake. The results provide evidence of the non-negligible effect of aquaculture waste on the sediment organic matter. The δ13C and δ15N of sediments varied from - 27.62 to - 25.66‰ and 4.83 to 6.92‰, respectively. The sediment organic matter had a mixed source of waste feed, fish feces and plankton. The average contribution ratio of waste feed and fish feces was 53.1% and 24.6%, respectively. The aquaculture derived organic matter ratio was high with ranging from 57.6 to 95.6%. The aquaculture waste seemed to disperse widely enough to influence the study site about 2.5km distance from the cage. The dispersion and resuspension were the main two factors which can explain the great effect area found in this study.

Chemical characterization and stable nitrogen isotope composition of nitrogenous component of ambient aerosols from Kanpur in the Indo-Gangetic Plains

Measurements of water-soluble total nitrogen (WSTN), water-soluble inorganic nitrogen (WSIN), water-soluble organic nitrogen (WSON) and ẟ15NTN (total N) was carried out on PM2.5 aerosol samples during wintertime to understand the major sources of ambient nitrogenous species at a heavily polluted location of Kanpur in north India. During the nighttime sampling campaign, WSON and NH4+_N contributed dominantly to the WSTN. Ammonium-rich condition persisted during sampling (NH4+/SO42− average equivalent mass ratio = 3.1 ± 0.7), suggesting complete neutralization of SO42− and formation of NH4NO3, which is stable in winter due to low temperature and high relative humidity (RH). Stagnant atmospheric conditions during wintertime enhanced concentrations of ionic species (SO42−, NH4+, and NO3−) at this location. Good correlations between NO3−_N, NH4+_N and biomass burning tracer K+BB (and also between NO3−_N, NH4+_N and SO42−) suggests a strong impact of biomass burning activities. Multi-linear regression (MLR) analysis shows a strong dependence of ẟ15N on NO3−_N, SO42− and WSON in night-1 (10:00 pm to 2:00 am) and on NO3−_N and SO42− in night-2 (2:00 am to 6:00 am) depicting different formation and removal mechanism of aerosols during both the time-periods. ẟ15NTN in PM2.5 varied from +8.8 to +15.5‰ (10.8 ± 1.3), similar to the variability observed for many urban locations in India and elsewhere. NH4+_N and WSON control the final ẟ15N value of nitrogenous aerosols. High relative humidity during nighttime enhanced the secondary organic aerosols formation due to aqueous-phase formation and gas to particle-phase partitioning. Isotopic fractionations associated with multi-phase reactions during gas to particle conversion of NH3 would result in an increase in ẟ15N by ~48‰ to 51‰ (at T of 5.4 °C to 15.4 °C) than that of the emission source(s), which indicates the most likely N-emission sources at Kanpur to be from agriculture activities and waste generation.

Sulfur isotopes (δ34S) in Arctic marine mammals: indicators of benthic vs. pelagic foraging

Consumer tissue stable carbon isotope compositions (δ13C) are well established indicators of benthic and pelagic foraging in marine ecosystems. Stable sulfur isotope compositions (δ34S) are also potentially useful in this regard but have not been widely utilized outside of estuaries and salt marsh ecosystems. To test the ability of δ13C and δ34S to reflect benthic and pelagic foraging, we analyzed the stable carbon, nitrogen (δ15N), and sulfur isotope compositions of bone collagen from walrus (an obligate benthic feeder) and ringed seal (a mixed benthic/pelagic feeder) sampled from across the North American Arctic. Both had relatively low δ34S values compared to those typically observed in marine consumers. These data suggest an important role for benthic microalgae in coastal marine food webs in the Arctic. At all of the 10 locations where both taxa could be sampled, walrus had lower δ34S values than ringed seal, suggesting that this measurement is a useful indicator of benthic and pelagic foraging in nearshore Arctic environments. Contrary to expectations, there were no consistent differences in δ13C between walrus and ringed seal at any of these sites, suggesting that this measurement may not always be best interpreted in light of benthic vs. pelagic foraging, particularly when comparisons are made across trophic levels. When the foraging ecology of a consumer is unknown, our data suggest that δ34S may be a more sensitive indicator of the relative importance of benthic and pelagic prey in the diet than δ13C.

Characterizing the spatiotemporal nitrogen stable isotopic composition of ammonia in vehicle plumes

Abstract. Vehicle emissions have been identified as an important urban source of ammonia (NH3). However, there are large uncertainties regarding the contribution of vehicle emissions to urban NH3 budgets, as well as the role of NH3 in spatiotemporal fine particulate matter (PM2.5) formation and nitrogen (N) deposition patterns. The N stable isotopic composition (δ15N) may be a useful observational constraint to track NH3 emission sources and chemical processing, but previously reported vehicle δ15N(NH3) emission signatures have reported a wide range of values, indicating the need for further refinement. Here we have characterized δ15N(NH3) spatiotemporal variabilities from vehicle plumes in stationary and on-road measurements in the USA and China using an active NH3 collection technique demonstrated to accurately characterize δ15N(NH3) on the order of hourly time resolution. Significant spatial and temporal δ15N(NH3) variabilities were observed and suggested to be driven by vehicle fleet composition and influences from NH3 dry deposition on tunnel surfaces. Overall, a consistent δ15N(NH3) signature of 6.6±2.1 ‰ (x‾±1σ; n=80) was found in fresh vehicle plumes with fleet compositions typical of urban regions. Our recommended vehicle δ15N(NH3) signature is significantly different from previous reports. This difference is due to a large and consistent δ15N(NH3) bias of approximately −15.5 ‰ between commonly employed passive NH3 collection techniques and the laboratory-tested active NH3 collection technique. This work constrains the δ15N(NH3) urban traffic plume signature, which has important implications for tracking vehicle NH3 in urban-affected areas and highlights the importance of utilizing verified collection methods for accurately characterizing δ15N(NH3) values.

Carbon and nitrogen isotopes to distinguish sources of sedimentary organic matter in a Caribbean estuary

ABSTRACT Carbon and nitrogen stable isotope compositions (δ13C and δ15N) of organic matter (OM) and total organic carbon to total nitrogen ratio (Corg/TN) in a sediment core collected in Sagua estuary (Cuba), were investigated to elucidate the origin of the Sedimentary OM (SOM) and changes in its main sources, over the last 100 years. Results showed almost constant values in the elemental and isotope composition of SOM from 1908 to 1970 with an abrupt change after 1970. From 1970 to 2005, δ13C increased from -21.2 up to -19.3 ‰, while δ15N declined from 1.5 to values close to 0 ‰. The output of the mass-balance model for the identification of OM sources indicated that δ13C and Corg/TN values are generally influenced by marine Particulate OM (POM) sources. Between 1900 and 1970, the main OM source in sediments was marine POM (>85 %), with freshwater POM contributing ca. 15%. Since 1970, the establishment of the Alacranes Dam determined drastic environmental changes influencing the OM sources in the area. Mixing models pointed to seagrasses (79 %) as the main contributors to SOM in the first period, while since 1973 onward, the contribution of human-derived sources such as fertilizers and urban discharges became greater. This information can provide baseline data for the environmental management of the Sagua watershed.