δ15N Values Research Articles

Effect of starvation on physiological and survival traits of Mimachlamys varia (Linneaus, 1758)

In order to better understand Mimachlamys varia (Linneaus, 1758) response to nutritional stress, a controlled-condition experiment was conducted. Two scallop batches (i.e. juveniles and adults) were completely food-deprived for 3 months. Changes in mass and energy content of tissues (adductor muscle, digestive gland, rest of the soft tissues), as well as stable carbon and nitrogen isotope ratios of the adductor muscle were monitored weekly. Both batches exhibited a 3-phase response to starvation. For adults, phase 1, was characterized by a fast loss in mass, an δ15N-enrichment, a stable calorific power, and a low mortality, corresponding to a transitional stage associated with protein-storage consumption. Phase 2 (day 28–42) exhibited a stabilization of mass and δ15N values, coinciding with a digestive gland calorific power drop and an acceleration in mortality. This corresponds to a “protein sparing” stage where highly energetic fuel such as lipids, which are stored especially in the digestive gland in pectinids, are consumed in priority. Juveniles exhibited a distinct response characterized by a significant mass loss and an increase in calorific power during the first phase (day 0–28). This body weight decrease may involve the remobilization of low-caloric biochemical compounds (e.g. proteins) using the structure as internal fuel, thus limiting somatic maintenance costs. During the second month, body mass and calorific power stabilized, indicating a “protein sparing” stage. In a third phase for both age classes, mass decreased again together with a sharp increase in mortality: essential structure was ultimately remobilized. The survival rate of juveniles was higher than that of adults during the first two months of the experiment (97% and 64%, respectively). Although the time required for starvation to deplete of half the cohort is higher for juveniles than for mature individuals, increase in mortality rate after reaching the “Point of No Return”, (e.g. the beginning of the last phase) was higher in juveniles than in adults. These results highlight the potential impacts of starvation at the population level, beyond the direct impact on individual survival. For instance, individuals may not effectively contribute to reproduction during the spawning period if exposed to a prolonged winter starvation episode. In particular, since highly energetic compounds stored in the digestive gland are often used as fuel to initiate gametogenesis in pectinids. Similarly, decrease in somatic weight in juveniles may delay their sexual maturity and hence their ability to contribute to population reproductive potential.

Bryophytes enhance nitrogen content in decaying wood via biological interactions

AbstractAn increase in the nitrogen (N) content in coarse woody debris (CWD) facilitates its decomposition, affecting the cycling of N and other nutrients in forest ecosystems. Bryophytes may increase the N content by transferring the N in bryophyte tissues to the underlying CWD. This study examined whether and how bryophytes increase N content in the underlying CWD using N‐stable isotope ratios (δ15N) as tracers for N sources. The N content and δ15N values in CWD with bryophytes were significantly higher than those in CWD without bryophytes. However, the δ15N values in CWD with bryophytes differed significantly from those in bryophytes on CWD, demonstrating that the N in bryophytes did not cause the increase in N content in CWD. The analyses using δ15N further indicated that the high N content in CWD with bryophytes may be attributed to increased N supply from wood‐decomposing fungi and N‐fixing bacteria. This increase in N content may result from the enhanced moisture content in CWD beneath bryophytes, which facilitates the activity of wood‐decomposing fungi and N‐fixing bacteria. Notably, the influence of bryophytes on the N content in CWD differed between bryophyte life forms: bryophytes that form dense mats increased the N content in CWD, whereas those with loose mats decreased the N content. This difference can be explained by the greater humidity experienced by CWD with bryophytes forming dense mats than that experienced by CWD with bryophytes forming loose mats. Given that the N content in CWD affects the decay processes, the results highlight the importance of biological interactions associated with bryophytes in forest ecosystems.

Inter- and intrapopulation resource use variation of marine subsidized western fence lizards

Marine resource subsidies alter consumer dynamics of recipient populations in coastal systems. The response to these subsidies by generalist consumers is often not uniform, creating inter- and intrapopulation diet variation and niche diversification that may be intensified across heterogeneous landscapes. We sampled western fence lizards, Sceloporus occidentalis, from Puget Sound beaches and coastal and inland forest habitats, in addition to the lizards’ marine and terrestrial prey items to quantify marine and terrestrial resource use with stable isotope analysis and mixing models. Beach lizards had higher average δ13C and δ15N values compared to coastal and inland forest lizards, exhibiting a strong mixing line between marine and terrestrial prey items. Across five beach sites, lizard populations received 20–51% of their diet from marine resources, on average, with individual lizards ranging between 7 and 86% marine diet. The hillslope of the transition zone between marine and terrestrial environments at beach sites was positively associated with marine-based diets, as the steepest sloped beach sites had the highest percent marine diets. Within-beach variation in transition zone slope was positively correlated with the isotopic niche space of beach lizard populations. These results demonstrate that physiography of transitional landscapes can mediate resource flow between environments, and variable habitat topography promotes niche diversification within lizard populations. Marine resource subsidization of Puget Sound beach S. occidentalis populations may facilitate occupation of the northwesternmost edge of the species range. Shoreline restoration and driftwood beach habitat conservation are important to support the unique ecology of Puget Sound S. occidentalis.

Integrative approaches to the study of animal management practices during the Neolithic of South Iberian Peninsula: the case of El Toro cave (Antequera, Málaga, Spain)

The introduction and adoption of livestock played a pivotal role in shaping subsistence strategies of populations in the southern Iberian Peninsula during the Neolithic. However, there is lack of information regarding animal management strategies, such as grazing areas and changes in foddering strategies, and their correlation with the environmental characteristics, type of site and use of the settlement. The study of feeding strategies of domesticates provides a crucial information about the interaction between the management of the environment, husbandry systems and the exploitation of animal products. In this study, we use the archaeozoological data and the δ13C and δ15N stable isotope composition of the faunal bone collagen to understand herding systems and management strategies during the Neolithic in Phases IV and IIIB at El Toro cave (Antequera, Málaga). Archaeozoological and isotopic results revealed diverse husbandry practices and feeding strategies in El Toro cave during the Neolithic. The variability in δ13C and δ15N values suggests the access of domesticates to different grazing areas and foddering strategies. This study contributes new insights into husbandry practices during the Neolithic and opens new perspectives for analysing animal management in mountain areas.

Nitrogen isotopes in herbaria document historical nitrogen sewage pollution in the Mersey Estuary, England

A schematic figure illustrating how nitrogen isotopes (δ15N) from treated–raw sewage enters an estuary, is taken up by macroalgae (seaweed). Treated sewage produces more elevated δ15N values compared to raw sewage.

Urban living can rescue Darwin's finches from the lethal effects of invasive vampire flies.

Human activity changes multiple factors in the environment, which can have positive or negative synergistic effects on organisms. However, few studies have explored the causal effects of multiple anthropogenic factors, such as urbanization and invasive species, on animals and the mechanisms that mediate these interactions. This study examines the influence of urbanization on the detrimental effect of invasive avian vampire flies (Philornis downsi) on endemic Darwin's finches in the Galápagos Islands. We experimentally manipulated nest fly abundance in urban and non-urban locations and then characterized nestling health, fledging success, diet, and gene expression patterns related to host defense. Fledging success of non-parasitized nestlings from urban (79%) and non-urban (75%) nests did not differ significantly. However, parasitized, non-urban nestlings lost more blood, and fewer nestlings survived (8%) compared to urban nestlings (50%). Stable isotopic values (δ15 N) from urban nestling feces were higher than those from non-urban nestlings, suggesting that urban nestlings are consuming more protein. δ15 N values correlated negatively with parasite abundance, which suggests that diet might influence host defenses (e.g., tolerance and resistance). Parasitized,urban nestlings differentially expressed genes within pathways associated with red blood cell production (tolerance) and pro-inflammatory response (innate immunological resistance), compared to parasitized,non-urban nestlings. In contrast, parasitized non-urban nestlings differentially expressed genes within pathways associated with immunoglobulin production (adaptive immunological resistance). Our results suggest that urban nestlings are investing more in pro-inflammatory responses to resist parasites but also recovering more blood cells to tolerate blood loss. Although non-urban nestlings are mounting an adaptive immune response, it is likely a last effort by the immune system rather than an effective defense against avian vampire flies since few nestlings survived.

Human diet in Lithuania during the Late Roman and Migration periods ( ca. 200–700 AD) based on stable carbon and nitrogen isotope data

In this study, 71 human individuals were subjected to stable carbon (δ13C) and nitrogen (δ15N) isotope analysis of bone collagen samples for the purpose of determining human dietary patterns in Lithuania during the Late Roman and Migration periods. More specifically, based on the isotopic data, the aim was to determine and evaluate any potential dietary differences between individuals on the basis of their sex, age, social status and place of residence during the periods in question. The results of this study suggest that there were isotopically clearly distinguishable dietary differences between individuals from different parts/regions of Lithuania. Also, statistically significant dietary differences (on the basis of δ15N values) between males and females were observed (although, when making the same sex-based isotopic comparisons at an individual site level, the same result was observed only among those from Marvelė cemetery). However, no statistically significant isotopic differences were detected between different social or age groups. Overall, these results give us one of the first glimpses into the types of dietary habits practiced by people in various parts of Lithuania during the Roman and Migration periods, which could also serve as a good starting point for future investigations into other dietary aspects in the territories and periods in question that still remain unknown.

Trophic characteristics of pelagic and bottom nekton in certain water masses in the western Chukchi Sea, by δ15N and δ13C data

To compare the trophic characteristics of pelagic- and bottom-dwelling fish in the western Chukchi Sea, isotopic composition of carbon and nitrogen (δ13С and δ15N) is considered separately for the Subarctic water mass (invaded from the Bering Sea) and local Arctic water mass. In summer of 2018 and 2019, the proper water mass occupied mostly the area southward from 71оN and the latter one – northward from this latitude. The isotopic composition of both pelagic and bottom nekton in the southern area was characterized by higher values of δ13C (up to 2 % higher) and low values of δ15N (up to 1 % lower) in comparison with those in the northern area. That was interpreted that in the southern area, within the water from the Bering Sea, more than 90 % of the sampled bottom fish species were linked with prey from the bottom community. In the northern area, within the Arctic water, all samples of bottom fish were characterized by minimal content of heavy carbon δ13C isotope, comparable with the values in samples of pelagic fish that indicated a significant role of pelagic prey in nutrition of the bottom nekton.

Amino acid‐specific nitrogen stable isotope analysis reveals the trophic behavior of Icelandic fin whales in winter and suggests variable feeding strategies

AbstractFin whales (Balaenoptera physalus) aggregate west of Iceland during summer, where they feed mostly on krill, but their winter distribution is poorly known. This study investigates the winter behavior of fin whales that summer off Iceland by analyzing amino acid‐specific nitrogen isotope ratios in the baleen plates. This technique is increasingly used in large marine vertebrates to discriminate between changes in trophic position and changes in isotopic baseline levels, while ruling out the effect of fasting on these patterns. Analyses were conducted on samples extracted from two baleen plate segments: one corresponding to winter, another to summer. The trophic position was higher and slightly more variable in winter (3.6 ± 0.7) than in summer (3.0 ± 0.4), which indicates that during winter fin whales tend to feed on fish and are more generalist in feeding habits. Interestingly, the δ15NPhe values were not lower in winter than in summer (winter: 5.2‰ ± 2.4‰; summer: 4.0‰ ± 2.1‰). This was unexpected because baseline δ15N values (e.g., zooplankton) tend to be lower at low latitudes, where fin whales are believed to spend the winter. Fin whales may remain in relatively high latitudes during winter or visit low‐latitude areas with locally higher than average δ15N values, such as upwelling areas.

Nitrogen isotopes and geochemistry of the basal Datangpo Formation: Contrasting redox conditions in the upper and lower water columns during the Cryogenian interglaciation period

The late Neoproterozoic witnessed series of remarkable geological evolutions, including the Sturtian and Marinoan glaciation events during the Cryogenian. A stratified oceanic redox structure has been proposed for this period, and the dynamics of the deep water redox conditions have been well illustrated by trace metals and their isotopes. However, variations in the redox conditions of the upper water column have received much less attention. Sedimentary nitrogen isotopes (δ15N) are critical for reconstructing the redox conditions in the upper water columns of ancient oceans. Existing research on the N cycle during the Cryogenian period is scarce, and the majority of studied samples were collected from shallow and medium water depth facies. To address this paucity of studies, we conducted a high-resolution N isotope study in combination with Fe speciation and Mo concentration data from two deep-water sections of black shales in the basal Datangpo Formation in the Nanhua Basin, a typical organic-rich stratum deposited during the Cryogenian interglaciation period. While the trace metal proxies suggest a fluctuating euxinic–ferruginous bottom water column for the lower interval and a stable euxinic bottom water column for the upper interval, the redox conditions of the upper water column were relatively stable, as indicated by minimal changes in the recorded δ15N values. Furthermore, the δ15N values of black shales in the basal Datangpo Formation of the Nanhua Basin have a limited range (3.1‰ − 5.8‰, average of 4.3‰, standard deviation (SD) = 0.5‰, n = 104) and show no water-depth gradient, indicating the presence of a relatively large and stable nitrate reservoir and a deep redox chemocline in the Nanhua Basin. The characteristic of the nitrate reservoir reflected by these δ15N signals can be roughly analogized to the global interglacial ocean, although only the counterpart northeast Svalbard can be used for comparison. Therefore, the nitrate availability in the marine water column may have had little effect on animal radiation during the Cryogenian interglacial period. These findings help to clarify the N cycle in the Cryogenian Nanhua Basin and shed light on its significance on bioevolution.

The association between haemosporidian infection and non-breeding moult location in great reed warblers revisited by combining feather stable isotope profiles and geolocator data

Stable isotope analysis provides valuable insights into the ecology of long-distance migratory birds during periods spent away from a specific study site. In a previous study, Swedish great reed warblers (Acrocephalus arundinaceus) infected with haemosporidian parasites differed in feather isotope ratios compared to non-infected birds, suggesting that infected and non-infected birds spent the non-breeding season in different locations or habitats. Here, we use a novel dataset comprising geolocator data, isotopes, and haemosporidian infection status of 92 individuals from four Eurasian populations to investigate whether parasite transmission varies with geography or habitats. We found that the probability of harbouring Plasmodium and Leucocytozoon parasites was higher in birds moulting in the eastern region of the non-breeding grounds. However, no geographic pattern occurred for Haemoproteus infections or overall infection status. In contrast to the previous study, we did not find any relationship between feather isotope ratios and overall haemosporidian infection for the entire current dataset. Plasmodium-infected birds had lower feather δ15N values indicating that they occupied more mesic habitats. Leucocytozoon-infected birds had higher feather δ34S values suggesting more coastal sites or wetlands with anoxic sulphate reduction. As the composition and prevalence of haemosporidian parasites differed between the old and the current dataset, we suggest that the differences might be a consequence of temporal dynamics of haemosporidian parasites. Our results emphasize the importance of replicating studies conducted on a single population over a restricted time period, as the patterns can become more complex for data from wider geographical areas and different time periods.

Contrasting potential for biological N2 fixation at three polluted central European Sphagnum peat bogs: combining the 15N2-tracer and natural-abundance isotope approaches

Abstract. Availability of reactive nitrogen (Nr) is a key control on carbon (C) sequestration in wetlands. To complement the metabolic demands of Sphagnum in pristine rain-fed bogs, diazotrophs supply additional Nr via biological nitrogen fixation (BNF). As breaking the triple bond of atmospheric N2 is energy-intensive, it is reasonable to assume that increasing inputs of pollutant Nr will lead to BNF downregulation. However, recent studies have also documented measurable BNF rates in Sphagnum-dominated bogs in polluted regions, indicating the adaptation of N2 fixers to changing N deposition. Our aim was to quantify BNF in high-elevation peatlands located in industrialized central Europe. A 15N2-tracer experiment was combined with a natural-abundance N-isotope study at three Sphagnum-dominated peat bogs in the northern Czech Republic in an attempt to assess the roles of individual BNF drivers. High short-term BNF rates (8.2 ± 4.6 g N m2 d−1) were observed at Malé mechové jezírko, which receives ∼ 17 kg Nr ha−1 yr−1. The remaining two peat bogs, whose recent atmospheric Nr inputs differed from Malé mechové jezírko by only 1–2 kg ha−1 yr−1 (Uhlír̆ská and Brumiště), showed zero BNF. The following parameters were investigated to elucidate the BNF difference: the NH4+-N / NO3--N ratio, temperature, wetness, Sphagnum species, organic-N availability, possible P limitation, possible molybdenum (Mo) limitation, SO42- deposition, and pH. At Malé mechové jezírko and Uhlír̆ská, the same moss species (S. girgensohnii) was used for the 15N2 experiment; therefore, the host identity could not explain the difference in BNF at these sites. Temperature and moisture were also identical in all incubations and could not explain the between-site differences in BNF. The N : P stoichiometry in peat and bog water indicated that Brumiště may have lacked BNF due to P limitation, whereas non-detectable BNF at Uhlír̆ská may have been related to the 70-fold higher SO42- concentration in bog water. Across the sites, the mean natural-abundance δ15N values increased in the following order: atmospheric deposition (−5.3 ± 0.3 ‰) < Sphagnum (−4.3 ± 0.1 ‰) < bog water (−3.9 ± 0.4 ‰) < atmospheric N2 (0.0 ‰). Only at Brumiště was N in Sphagnum significantly isotopically heavier than in atmospheric deposition, possibly indicating a longer-term BNF effect. Collectively, our data highlight spatial heterogeneity in BNF rates under high Nr inputs as well as the importance of environmental parameters other than atmospheric Nr pollution in regulating BNF.

Preliminary Results of Stable Isotope Analysis on Bone Collagen Samples from the Avar-Age Cemetery Privlaka-Gole Njive

The material culture of the Avar era is considered to be one of the best documented Early Medieval material cultures of central Europe. The nomadic Avar community settled in the Carpathian basin at the end of the 6th century and remained as rulers until the Frankish wars at the end of the 8th century. Unlike the neighbouring communities, there is no evidence of the Avars being Christianised, and their relatively conservative burial customs, in which great importance is attached to the costumes of the deceased, have enabled archaeologists not only to create a precise typological-chronological framework but also to analyse the different ways of life of the Khaganate population. Among other things, stable carbon and nitrogen isotope analyses have recently been undertaken to establish and better understand the dietary practices of certain communities. This represents an important factor in social organisation. The authors of this paper conducted a stable isotope analysis of 22 selected bone samples from the Privlaka-Gole njive site, to this date the largest Avar-age inhumation cemetery in Croatia with 231 excavated graves. Overall, it seems that there are no major differences in diet regarding sex, age and social stratification, although females do exhibit slightly lower δ15N values than males, while non-adults and older adults exhibit slightly higher δ15N values than younger adults.

Stable isotopes reveal intrapopulation heterogeneity of porbeagle shark (Lamna nasus)

Porbeagle (Lamna nasus) is an ubiquist, highly mobile and long-living shark species with spatial and temporal sex and size segregation observed in catches. Porbeagle sharks were targeted by commercial fisheries in the European waters until the closure of the fishery in 2010. Most of the French fleet catches were located in Bay of Biscay, Celtic Sea and the English Channel. The aim of the study was to find out occurrences of spatial segregation within the shark population in the Northeast Atlantic Ocean based on the stable isotope method. Carbon and nitrogen stable isotopes (δ13C, δ15N) were measured in muscle of porbeagle sharks fished in the Bay of Biscay and the Celtic Sea between April and September 2008, and April and June 2009. Neither influence of sex nor ontogenic isotopic shift was detected in the sampled sharks, but muscle δ13C and δ15N values increased significantly from offshore towards coastal area, which reflected inter-areas variability. Realized isotopic niches were similar amongst offshore areas whilst in St Georges’ Channel muscle isotopic composition exhibited higher inter-individual variability. This underpins the lack of information on life history of porbeagle sharks and underlines the need of more information on the species movements to support population management in European waters.

Palaeodiet during the pre-dormancy period of MIS 3 Romanian cave bears as inferred from dental microwear analysis

Cave bears (Ursus spelaeus) have been recognized as being predominantly herbivorous. However, Romanian Carpathian cave bears have displayed a flexible diet based on a wide range of δ15N values. In this work, we analyse 97 lower first molars of Ursus spelaeus and contemporaneous Ursus arctos from different sites in this region, using dental microwear analysis to reconstruct their pre-dormancy diets during MIS 3. Newly obtained radiocarbon dates of the individuals are also reported. The short-term diet of all populations studied is identified as omnivorous, with a preference for the consumption of hard objects. For the first time, the widespread presence of puncture pits on U. spelaeus populations has been observed, which could be linked to the intake of seeded and hard-shelled fruits from temperate broadleaf trees. Hence, the dietary patterns of Carpathian cave bears exhibit similarities to those of present-day brown bears inhabiting the same region and suggests that the Carpathians served as an ecological refuge for cave bear specimens. This is reinforced by an early 27.1 cal kyr B.P. date from an individual from Urşilor Cave, which sheds light on the potential dietary continuity of Romanian Carpathian cave bear populations even during the final phases leading up to their extinction.

Isotopes prove advanced, integral crop production, and stockbreeding strategies nourished Trypillia mega-populations

After 500 y of colonizing the forest-steppe area northwest of the Black Sea, on the territories of what is today Moldova and Ukraine, Trypillia societies founded large, aggregated settlements from ca. 4150 BCE and mega-sites (>100 ha) from ca. 3950 BCE. Covering up to 320 ha and housing up to 15,000 inhabitants, the latter were the world's largest settlements to date. Some 480 δ13C and δ15N measurements on bones of humans, animals, and charred crops allow the detection of spatio-temporal patterns and the calculation of complete agricultural Bayesian food webs for Trypillia societies. The isotope data come from settlements of the entire Trypillia area between the Prut and the Dnieper rivers. The datasets cover the development of the Trypillia societies from the early phase (4800-4200/4100 BCE), over the agglomeration of mega-sites (4200/4100-3650 BCE), to the dispersal phase (3650-3000 BCE). High δ15N values mostly come from the mega-sites. Our analyses show that the subsistence of Trypillia mega-sites depended on pulses cultivated on strongly manured (dung-)soils and on cattle that were kept fenced on intensive pastures to easy collect the manure for pulse cultivation. The food web models indicate a low proportion of meat in human diet (approximately 10%). The largely crop-based diet, consisting of cereals plus up to 46% pulses, was balanced in calories and indispensable amino acids. The flourishing of Europe's first mega-populations depended on an advanced, integral mega-economy that included sophisticated dung management. Their demise was therefore not economically, but socially, conditioned [Hofmann et al., PLoS One. 14, e0222243 (2019)].

Will the experimental population control of an invasive crayfish influence the diet and trophic position of a native crayfish? An assessment using stable isotopes

Context Trophic overlap between invasive and native species can cause a competitive displacement of the native. In Australian freshwaters, the invasive crayfish Cherax destructor has proliferated into the ranges of native Euastacus species. Aims To examine trophic overlap between C. destructor and the critically endangered Euastacus dharawalus and determine whether C. destructor population control causes shifts in the diet and trophic position of E. dharawalus. Methods We compared δ13C and δ15N values of tissue from both species collected from two sites. Population control of C. destructor was then conducted at one site, whereas the C. destructor population remained uncontrolled at the second site. The δ13C and δ15N values of E. dharawalus were then once again assessed. Key results Both species occupied similar trophic positions and consumed similar proportions of each food resource prior to control efforts. However, we found increases in the contribution of detritus to the diet of E. dharawalus following the removal of C. destructor, whereas no dietary shifts occurred at the uncontrolled site. Conclusions and implications The increase in detrital consumption suggests that control of C. destructor increased the availability of a preferred resource. Further, dietary competition between C. destructor and E. dharawalus is likely and reinforces C. destructor representing a substantial threat to Euastacus crayfish.

Assessing spatial impacts of historical pulp mill effluent on trophic dynamics in a coastal marine ecosystem using stable isotope (δ13C and δ15N) analysis

Boat Harbour, Nova Scotia was a tidal estuary that was converted into a wastewater treatment facility for pulp mill effluent in 1967. Treated effluent from Boat Harbour was discharged into the coastal Northumberland Strait, contributing significant nutrient and freshwater inputs into the coastal environment, potentially impacting local biogeochemistry and ecosystem structure. This study used stable isotope analysis of carbon (δ13C) and nitrogen (δ15N) of representative taxa to assess spatial variability in nutrient sources and trophic dynamics. Results identified stable isotope variation with depleted δ13C and δ15N values in taxa near Boat Harbour. Blue mussel (Mytilus edulis) and mummichog (Fundulus heteroclitus) were the most suitable bioindicators for identifying variation in nutrient sources. Stable isotope signatures in this study may be reflective of residual pulp mill effluent-derived nutrients, differences in marine versus terrestrial nutrient sources, and a pronounced coastal salinity gradient. The present study defined the baseline nutrient conditions of the Northumberland Strait and will be useful in assessing the effectiveness of remediation activities.

Use of the nitrogen/ oxygen isotope fractionation technique for tracing nitrogen removal from activated sludge in municipal wastewater treatment plants

The dual isotope fractionation technique of nitrogen and oxygen has been successfully applied to analyze microbially-driven nitrogen transformations and partitioning in aquatic ecosystems, but not in municipal water treatment facilities. Nitrogen removal efficiency in wastewater treatment plants using activated sludge is critical and difficult to monitor. Here, we tested the nitrogen and oxygen isotope fractionation technique for capacity to trace nitrogen removal from municipal wastewater. Long-term monitoring of Anaerobic/anoxic/aerobic (A2/O) process municipal wastewater treatment plants revealed that nitrogen removal performance gradually improved with increasing seasonal temperatures. The δ15N value of activated sludge increased from 5.18‰ (January) to 6.37‰ (June). An increase in temperature promoted the increase in NO3--N from 1.23 mg/L (January) to 6.06–7.02 mg/L (June to August) in the aerobic reaction. The δ15NNO3 decreased from 17.82‰ to 37.37‰ to 4.09–17.68‰, and variability in utilization of light and heavy isotopes gradually decreased. The slope of the ratio δ15NNO3:δ18ONO3 gradually decreased from 21.58 ± 12.15 (January) to 0.57 ± 0.51 (August). The dynamic response of δ15N values in sludge and isotopes in water revealed the migration transformation of nitrogen and realized the differential analysis to denitrification performance with seasonality. It also provided a technical basis for long-term stable nitrogen removal system.

An Assessment of Mangrove Ecosystem Condition by Foliar Stable Nitrogen Isotope Ratio Index in Okinawa, Japan

Despite providing valuable ecosystem services, mangroves are endangered under the recent global natural as well as anthropogenic changes. Conservation of mangroves is now one of the pillars of Sustainable Development Goals (SDG) 2030. An assessment of mangrove is essential before initializing any conservation strategy. This paper aimed to assess the ecosystem conditions of mangroves and the relative changes in ecosystem conditions from the natural background under different scales of anthropogenic interruption in Okinawa Prefecture, Japan. To assess mangrove’s ecosystem condition, foliar stable nitrogen isotope ratio (δ15N) of mangroves is used as ecosystem monitoring indicator. Whereas, a difference index (DI) of mangrove foliar δ15N is established to compare the relative deviation in ecosystem conditions of anthropogenically impacted mangroves from reference mangroves. Results showed that the mean foliar δ15N values of Bruguiera gymnorrhiza, Kandelia obovata, and Rhizophora stylosa on Okinawa Island (Is.) are 5.12 ± 2.32‰, 7.54 ± 2.85‰ and 7.09 ± 3.29‰, respectively, on Iriomote Is., 1.83 ± 1.93‰, 2.01 ± 0.31‰ and 1.04 ± 2.38‰, respectively, and on Ishigaki Is., foliar δ15N values of Bruguiera gymnorrhiza and Rhizophora stylosa are 5.23 ± 3.33‰ and 6.00 ± 3.63‰, respectively. A range of negative to positive values from -0.54 to 3.66 of DI indicates different level of changes in ecosystem conditions of the mangroves compared to the reference sites, which is set at zero. A significant negative correlation between DI values and the forest area ratio of the watersheds has been observed. It indicates that the forest cover is the driver of maintaining pristine condition of an ecosystem. Findings of the study recommended that Todoroki and Manko mangrove watersheds in Okinawa, Japan should be taken into consideration for necessary conservation on priority basis.