Nitrogen Stable Isotope Ratios Research Articles

Rapid migration of Mongolian oak into the southern Asian boreal forest.

The migration of trees induced by climatic warming has been observed at many alpine treelines and boreal-tundra ecotones, but the migration of temperate trees into southern boreal forest remains less well documented. We conducted a field investigation across an ecotone of temperate and boreal forests in northern Greater Khingan Mountains of northeast China. Our analysis demonstrates that Mongolian oak (Quercus mongolica), an important temperate tree species, has migrated rapidly into southern boreal forest in synchrony with significant climatic warming over the past century. The average rate of migration is estimated to be 12.0 ± 1.0 km decade-1 , being slightly slower than the movement of isotherms (14.7 ± 6.4 km decade-1 ). The migration rate of Mongolian oak is the highest observed among migratory temperate trees (average rate 4.0 ± 1.0 km decade-1 ) and significantly higher than the rates of tree migration at boreal-tundra ecotones (0.9 ± 0.4 km decade-1 ) and alpine treelines (0.004 ± 0.003 km decade-1 ). Compared with the coexisting dominant boreal tree species, Dahurian larch (Larix gmelinii), temperate Mongolian oak is observed to have significantly lower capacity for light acquisition, comparable water-use efficiency but stronger capacity to utilize nutrients especially the most limiting nutrient, nitrogen. In the context of climatic warming, and in addition to a high seed dispersal capacity and potential thermal niche differences, the advantage of nutrient utilization, reflected by foliar elementomes and stable nitrogen isotope ratios, is also likely a key mechanism for Mongolian oak to coexist with Dahurian larch and facilitate its migration toward boreal forest. These findings highlight a rapid deborealization of southern Asian boreal forest in response to climatic warming.

Boreal and Lusitanian species display trophic niche variation in temperate waters.

Climate change has non-linear impacts on species distributions and abundance that have cascading effects on ecosystem structure and function. Among them are shifts in trophic interactions within communities. Sites found at the interface between two or more biogeographical regions, where species with diverse thermal preferenda are assembled, are areas of strong interest to study the impact of climate change on communities' interactions. This study examined variation in trophic structure in the Celtic Sea, a temperate environment that hosts a mixture of cold-affiliated Boreal species and warm-affiliated Lusitanian species. Using carbon and nitrogen stable isotope ratios, trophic niche area, width, and position were investigated for 10 abundant and commercially important demersal fish species across space and time. In general, the niches of Boreal species appear to be contracting while those of Lusitanian species expand, although there are some fluctuations among species. These results provide evidence that trophic niches can undergo rapid modifications over short time periods (study duration: 2014-2021) and that this process may be conditioned by species thermal preferenda. Boreal species displayed spatial variation in trophic niche width and seem to be facing increased competition with Lusitanian species for food resources. These findings underscore the need to utilize indicators related to species trophic ecology to track the ecosystem alterations induced by climate change. Such indicators could reveal that the vulnerability of temperate ecosystems is currently being underestimated.

Grim up North? Exploring the diet of urban populations in post-medieval Greater Manchester, England, using stable isotope analysis

Historical evidence suggests that social status played a major role in all aspects of society in eighteenth–nineteenth century England. We present an insight into how socioeconomic status affected the dietary habits of two post-medieval urban populations from Greater Manchester, northwest England. Stable carbon (δ13C) and nitrogen (δ15N) isotope ratios were measured in humans from Cross Street Unitarian Chapel (middle class: n = 90) in Manchester city centre and Chapel Street, Hazel Grove (lower status with few middle-class individuals: n = 34). A large sample of 111 faunal remains from Cross Street (n = 37) and Norton Priory, Cheshire (n = 74), provide an animal baseline, dramatically expanding the post-medieval animal isotopic dataset for England. Sheep from Norton Priory show high δ15N isotope values indicative of saltmarsh grazing. Results for human populations revealed a mixed diet of plant and animal protein from C3 terrestrial environments with some potential contribution of aquatic protein. Significant differences revealed between the two populations indicate unequal access to food by status. Intra-population variation at Hazel Grove suggests dietary distinctions by age and sex. Non-adults consumed diets poor in high trophic level protein, whereas adult males consumed greater amounts of animal products. Conversely, the data suggests that at the wealthier Cross Street, there was greater access to high trophic level protein by all. Comparisons between the Manchester populations and those from similar socioeconomic classes from the Midlands and southern England, including London, reveal a bioarchaeological picture of dietary diversity and differential access to resources which impact significantly on well-being during this tumultuous period of industrial England.

Divergent Temporal Trends of Mercury in Arctic Char from Paired Lakes Influenced by Climate-Related Drivers.

Climate-driven changes including rising air temperatures, enhanced permafrost degradation, and altered precipitation patterns can have profound effects on contaminants, such as mercury (Hg), in High Arctic lakes. Two physically similar lakes, East Lake and West Lake at the Cape Bounty Arctic Watershed Observatory on Melville Island, Nunavut, Canada are being affected by climate change differently. Both lakes have experienced permafrost degradation in their catchments; however, West Lake has also undergone multiple underwater Mass Movement Events (MMEs; beginning in fall 2008), leading to a sustained 50-fold increase in turbidity. This provided the unique opportunity to understand the potential impacts of permafrost degradation and other climate-related effects on Hg concentrations and body condition of landlocked Arctic char (Salvelinus alpinus), an important sentinel species across the Circum-Arctic. Our objectives were to assess temporal trends in char Hg concentrations and to determine potential mechanisms driving the trends. There was a significant decrease in Hg concentrations in East Lake char, averaging 6.5%/year and 3.8%/year for length-adjusted and age-adjusted means, respectively, from 2008 to 2019. Conversely, in West Lake there was a significant increase, averaging 7.9%/year and 8.0%/year for length-adjusted and age-adjusted mean Hg concentrations, respectively, for 2009 to 2017 (the last year with sufficient sample size). The best predictors of length-adjusted Hg concentrations in West Lake were carbon and nitrogen stable isotope ratios, indicating a shift in diet including possible dietary starvation brought on by the profound increase in lake turbidity. Our study provides an example of how increasing lake turbidity, a likely consequence of climate warming in Arctic lakes, may influence fish condition and Hg concentrations. Environ Toxicol Chem 2023;42:2712-2725. © 2023 His Majesty the King in Right of Canada and The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. Reproduced with the permission of the Minister of Environment and Climate Change Canada.

High clergy feasts and suburban suppers: Diet and social status in Medieval and Early Modern Tartu, Estonia

This study explores the dietary habits of various social groups in Medieval and Early Modern Period Tartu in Estonia. Stable carbon and nitrogen isotope ratios from bone collagen were measured for 137 humans (115 adults and 22 non-adults) and 50 faunal specimens (including terrestrial mammals, birds, and fish). The results are in keeping with other comparable medieval and early modern European populations and indicate a diet largely based on terrestrial resources. Higher social status individuals from Tartu cathedral consumed significantly more marine protein than those from other burial locations. Dietary habits among commoners did not differ greatly between urban, suburban and rural locations. However, a distinct gender bias was apparent regarding access to higher trophic level protein with males having statistically significantly higher carbon and nitrogen isotope ratios compared to females.

Trophic Ecology during the Ontogenetic Development of the Pelagic Thresher Shark Alopias pelagicus in Baja California Sur, Mexico

The trophic ecology of the Pelagic Thresher shark (Alopias pelagicus) was evaluated based on chemical ecology using stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) in the vertebrae and muscles. Individuals were caught between August 2013 and October 2019 on both the coasts of Baja California Sur, Mexico. In Bahía Tortugas, the mean vertebrae (n = 35) values were 12.72 ± 1.06‰ (δ15N) and −14.79 ± 0.61‰ (δ13C), while in muscles (n = 32) these values were 16.63 ± 0.76‰ (δ15N) and −17.18 ± 0.39‰ (δ13C). In Santa Rosalía, the mean vertebrae (n = 125) isotopic values were 14.4 ± 1.59‰ (δ15N) and −14.18 ± 0.51‰ (δ13C), while in muscles (n = 43), these values were 18.08 ± 0.96‰ (δ15N) and −16.43 ± 0.34‰ (δ13C). These results show higher δ15N values in Santa Rosalía as an effect of baseline isotopic differences between the two regions, whereas the δ13C values were lower in Bahía Tortugas, suggesting offshore ecological behavior (p < 0.05). In Santa Rosalía, there were significant differences by sex for δ15N in muscle, whereas the δ13C showed ontogenetic shifts, indicating that neonates feed in coastal areas more commonly than juveniles or adults (p < 0.05). Neither sex nor ontogenetic differences were observed in Bahía Tortugas (p > 0.05), suggesting a high overlap between their isotopic niches. Therefore, Alopias pelagicus uses the same ecological niche throughout its life, and there is consistency between sexes. The mean trophic position for both tissues and regions was 4.5, which corresponds to a tertiary predator, without any differences between stages or sex. Due to their higher energetic needs, juveniles and females showed the greatest isotopic niche amplitude; thus, their ecological niche is the widest.

Stable isotopes in eye lenses reveal migration and mixing patterns of diamond squid in the western North Pacific and its marginal seas

Abstract Knowledge of the movements of marine organisms is essential for effective conservation schemes. Here, we investigated the lifetime habitat use of diamond squid, Thysanoteuthis rhombus, collected in the western North Pacific and its marginal seas (the Sea of Japan and the East China Sea) during 2021–2022, whose migratory ecology is poorly known, using bulk stable nitrogen and carbon isotope ratios in eye lenses. From the eye lens isotope profiles, the chronology of the isotopic baseline of squid habitat was estimated by removing the effect of size-dependent changes of trophic position. Then, the baseline estimates were compared to the isoscapes of particulate organic matter. The baseline chronologies showed fluctuations during the paralarval and juvenile stages, becoming stable during the adult stage, suggesting that significant movements mainly occur during the early life stages due to current transport, with adults potentially not undertaking long-distance migrations. The squids in the marginal seas mostly originated from outside the subtropical gyre, while the squids in the subtropical gyre had various sources, including outside the gyre and southern and northern parts within the gyre, revealing a complex mixing pattern of the species. These results show that isotope chronology combined with baseline isoscapes are effective tools to understand animal migrations, which can help managing various cephalopods and fish.

Effects of lipid extraction on human bone collagen: Comparing stable carbon and nitrogen isotope values with and without lipid extraction

This study analyzes 24 human bone fragments to assess how lipid extraction affects stable carbon and nitrogen isotope ratios. Eighteen samples were archaeological bone and six were modern bone. Each bone was split into two pieces, producing 48 bone samples, and half underwent lipid extraction and half did not. This was done to assess whether the two techniques yielded statistically significant differences in δ13C and δ15N. The results are an important contribution for establishing standard stable isotope preparation protocols, which affect time and cost of laboratory procedures. Further, given that many dietary stable isotope studies compare original results to published material, this study addresses whether those comparisons are suitable if some samples undergo lipid extraction while others do not.We also examine 144 articles that report stable carbon and nitrogen isotope results to evaluate the proportion of studies that conduct lipid extraction versusthose that do not. We explore those outcomes by archaeological geographic region and by stable isotope laboratories. Findings show that 15% of the published studies do lipid extraction, and they tend to be grouped by researchers and laboratories who conduct research in specific global regions. The meta-analysis of the published articles and the findings that some laboratories conduct lipid extraction, while others do not, prompted the experimental portion of this study.Results of the experimental study show no significant differences in δ13C between samples prepared with and without lipid extraction and no significant differences in δ15N between samples prepared with and without lipid extraction. These results suggest that stable carbon and nitrogen isotope analysis of human bone collagen may not require lipid extraction for certain dietary reconstruction studies, specifically for non-coastal contexts (i.e., non-marine based diets). The isotope data was analyzed overall and among subgroups (e.g., archaeological bone, modern bone, mid-valley Peruvian ecological zones, and highland Peruvian ecological zones). In all cases, stable isotope ratios from samples prepared with and without lipid extraction were not significantly different.

Multiple stable isotopes (C, N & S) provide evidence for fin whale (Balaenoptera physalus) trophic ecology and movements in the Humboldt Current System of northern Chile

Reflecting the intense coastal upwelling and high primary productivity characteristic of the Humboldt Current System (HCS), the northern coast of Chile supports a diverse and productive community of marine consumers, including worldwide important pelagic fisheries resources. Although marine mammals are relatively understudied in the region, recent studies have demonstrated that fin whale (Balaenoptera physalus) is the most frequently encountered whale species, and forages in these waters year-round. However, a current lack of information limits our understanding of whether fin whales actively feed and/or remain resident in these waters or whether whales are observed feeding as they migrate along this part of the Pacific. Here, we use stable isotope ratios of carbon, nitrogen and sulphur of fin whale skin samples collected in early summer 2020 (n = 18) and in late winter 2021 (n = 22) to examine evidence of temporal isotopic shifts that could provide information on potential migratory movements and to estimate likely consumption patterns of putative prey (i.e. zooplankton, krill, pelagic fishes and Pleuroncodes sp.). We also analysed prey items in fin whale faecal plumes (n = 8) collected during the study period. Stable isotope data showed significant differences in the isotopic values of fin whales from summer and winter. On average, summer individuals were depleted in 15N and 34S relative to those sampled during winter. Whales sampled in summer showed greater isotopic variance than winter individuals, with several showing values that were atypical for consumers from the HCS. During winter, fin whales showed far less inter-individual variation in stable isotope values, and all individuals had values indicative of prey consumption in the region. Analysis of both stable isotopes and faeces indicated that fin whales sighted off the Mejillones Peninsula fed primarily on krill (SIA median contribution = 32%; IRI = 65%) and, to a lesser extent, zooplankton (SIA zooplankton = 29%; IRI copepod = 33%). These are the first isotopic-based data regarding the trophic ecology of fin whales in the north of Chile. They provide evidence that fin whales are seasonally resident in the area, including individuals with values that likely originated outside the study area. The information presented here serves as a baseline for future work. It highlights that many aspects of the ecology of fin whales in the Humboldt Current and wider SE Pacific still need to be clarified.

Isotopic Turnover and Fractionation of δ15N and δ13C in Captive Pseudopleuronectes americanus (Walbaum)

Stable isotope ratios of nitrogen (δ15N) and carbon (δ13C) are ubiquitous ecological tracers used to elucidate an organism’s diet and habitat. However, the application of stable isotope ratios to reconstruct a consumer’s ecology relies upon accurate rates for isotopic turnover at both a tissue and species-specific level. This study estimated isotope turnover rates and trophic discrimination factors in four different tissues (liver, digestive tissue, muscle, and skin) with variable metabolic activity in winter flounder Pseudopleuronectes americanus using a controlled diet-switch experiment. Differences in half-lives were noted among the tissues and between the experimental diets for both δ15N and δ13C. The experimental diets of krill and mysis had variability in nutritional composition, resulting in similar turnovers in δ15N but slower turnovers in δ13C for fish fed krill. Turnovers in both δ15N and δ13C were strongly influenced by metabolism, with the contribution reaching up to 98%, as fish exhibited minimal overall growth. The results of this study demonstrate the importance of considering differences in the catabolic activity of tissue maintenance for fish exhibiting minimal growth, as well as differences in metabolic assimilation of dietary sources that vary in their protein and lipid contents.

Multi-isotope analysis of bone collagen of Late Pleistocene ungulates reveals niche partitioning and behavioural plasticity of reindeer during MIS 3

Here we present stable carbon, nitrogen and sulfur isotope ratios of collagen extracted from Rangifer, Equus and Bison bone (n = 128) from different stratigraphic levels at the chronologically well-constrained Middle and Upper Palaeolithic site of Les Cottés, France. Samples were taken from five phases of site use (US08, US06, US04 [upper and lower], and US02; ~ 45.8–35.3 ka cal BP) to explore the dietary and spatial palaeoecology of these ungulate species during MIS 3, and the contemporary climate. Temporal trends in δ15N values of all species broadly align with other climatic indicators at the site and the lowest values in US04 correspond to the Heinrich 4 cooling event, reflecting changes in the composition of soil/plant nitrogen at this time. Rangifer collagen is 13C-enriched compared to the other species throughout, consistent with lichen consumption. However, this isotopic niche partitioning between Rangifer and Equus/Bison is most extensive during US04, indicating plasticity in reindeer feeding behaviour, and potentially overall increased lichen biomass during this cooler/more arid phase. Rangifer δ34S values are consistently lower than Equus and Bison, which could be indicative of their more extensive spatial ranges incorporating greater inland areas. Equus and Bison demonstrate a significant decrease in δ34S values through time, which may be linked to contemporary climatic decline.

Seasonal variation in the use of food resources by sperm whales in a submarine canyon

Understanding the food and habitat requirements of apex predators relies on characterising the food web structure and carbon sources that support them. We examined the food web of sperm whales (parāoa, Physeter macrocephalus) foraging in the submarine canyon of Kaikōura (Aotearoa New Zealand) by measuring bulk stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) in sperm whale skin, potential prey and two candidate primary producers. To determine the underlying drivers of variability in bulk ratios, we measured δ13C and δ15N from individual amino acids (AAs) in a subset of whale samples. Mixing models and food web δ13C:δ15N correlations strongly suggest a food web sustained mostly by pelagic production, with a marginal contribution from coastal macroalgae. In contrast to the cephalopod-based diet recorded in most populations, the sperm whales' diet at Kaikōura appeared to be a mixture of squid and demersal fish, which may be related to the extremely high benthic productivity of the canyon. Combined with evidence from studies of habitat use, differences in the whales’ stable isotope values between summer and winter suggested seasonal variability in targeted prey, and ultimately different utilisation of organic carbon sources at the base of the food web. In summer, sperm whales appear to depend mostly on mesopelagic squid, with an increased contribution from demersal fish in winter, consistent with patterns in diving behaviour and spatial distribution. This seasonal shift in food resources suggests that submarine canyons offer a temporally dynamic range of foraging opportunities for this apex predator. Our results provide new insights into the structure of food webs supporting sperm whales, and advance our understanding of the seasonal dynamics in the use of food resources by apex predators in submarine canyons.

Striped catfish (Pangasianodon hypophthalmus) exploit food sources across anaerobic decomposition- and primary photosynthetic production-based food chains

Dietary information from aquatic organisms is instrumental in predicting biological interactions and understanding ecosystem functionality. In freshwater habitats, generalist fish species can access a diverse array of food sources from multiple food chains. These may include primary photosynthetic production and detritus derived from both oxic and anoxic decomposition. However, the exploitation of anoxic decomposition products by fish remains insufficiently explored. This study examines feeding habits of striped catfish (Pangasianodon hypophthalmus) at both adult and juvenile stages within a tropical reservoir, using stable carbon, nitrogen, and sulfur isotope ratios (δ13C, δ15N, and δ34S, respectively) and fatty acid (FA) analyses. The adult catfish exhibited higher δ15N values compared to primary consumers that feed on primary photosynthetic producers, which suggests ingestion of food sources originating from primary photosynthetic production-based food chains. On the other hand, juvenile catfish demonstrated lower δ15N values than primary consumers, correlating with low δ34S value and large proportions of bacterial FA but contained small proportions of polyunsaturated FA. This implies that juveniles utilize food sources from both anoxic decomposition and primary photosynthetic production-based food chains. Our results indicate that food chains based on anoxic decomposition can indeed contribute to the dietary sources of tropical fish species.

A dietary perspective of cat-human interactions in two medieval harbors in Iran and Oman revealed through stable isotope analysis

Cats are hypercarnivorous, opportunistic animals that have adjusted to anthropogenic environments since the Neolithic period. Through humans, either by direct feeding and/or scavenging on food scraps, the diet of cats has been enriched with animals that they cannot kill themselves (e.g., large mammals, fish). Here, we conducted carbon and nitrogen stable isotope ratio analysis to reconstruct the diet of medieval cats and investigate cat-human interactions in two medieval harbor sites (Qalhât, Oman and Siraf, Iran). The analysis included 28 cat individuals and 100 associated marine and terrestrial faunal samples pertaining to > 30 taxa. The isotopic results indicate a high marine protein-based diet for the cats from Qalhât and a mixed marine-terrestrial (C4) diet for the cats from Siraf. Cats at these sites most likely scavenged on both human food scraps and refuse related to fishing activities, with differences in the two sites most likely associated with the availability of marine resources and/or the living conditions of the cats. By shedding light on the dietary habits of cats from two medieval harbors in the Arabian Gulf and Gulf of Oman, this study illustrates the potential of stable isotope analysis in reconstructing human-cat interactions in the past.

Trophic ecology of common bottlenose dolphins in a pelagic insular environment inferred by stable isotopes

The common bottlenose dolphin (Tursiops truncatus) is a top marine predator widely dispersed in coastal and pelagic habitats and with a generalist feeding behavior. Yet, information on the trophic ecology of animals inhabiting pelagic environments is still scarce. Using carbon (δ13C: 13C/12C) and nitrogen (δ15N: 15N/14N) stable isotope ratios, we identified and quantified the main groups of prey assimilated by bottlenose dolphins inhabiting an oceanic habitat (Madeira Island, East Atlantic). Bottlenose dolphins assimilated pelagic, schooling fish (such as blue jack mackerel, Trachurus picturatus) and mesopelagic and demersal squids, which reinforces the pelagic dietary composition of insular/oceanic dolphins. Also, intra-seasonal differences were found in their stable isotope ratios, which suggest intraspecific variability in the feeding behavior among individuals living in the same area. Sex was not the main factor contributing to these differences, suggesting the lack of trophic niche segregation between adult males and females in this offshore environment. Nonetheless, further studies including different life stages and information on the ecophysiological requirements are necessary to disclose the factors responsible for the observed variability. This study showed that insular dolphins fed primarily on economically important pelagic prey, highlighting the need of developing management strategies that integrate conservation in fisheries plans.

Hydroclimatic influence on the trophic ecology of Atlantic goliath grouper juveniles (Epinephelus itajara) in a tropical estuary using non-lethal methodologies

The Atlantic goliath grouper Epinephelus itajara is the largest species of groupers in the Atlantic Ocean, reaching over 2 m total length and 400 kg. It has an ontogenetic migration, with adults using nearshore and offshore marine areas and juveniles inhabiting estuarine/mangrove areas. Despite of its high ecological relevance and classification as a threatened species for several decades in the IUCN red lists, critical phases of its life cycle, like juveniles inhabiting estuaries, are still poorly investigated. In this study, we evaluated if hydroclimatic changes may affect the trophic ecology of juveniles in a tropical estuary. We described their diet composition, isotopic niche area, food assimilation, and trophic position of juveniles across seasons using two non-lethal techniques: stomach content analysis using a stomach flushing procedure and stable isotope analysis using a dermal biopsy. A total of 87 individuals with TL ranging from 38 to 331 mm had their stomachs analyzed, of which 31 had food content. We identified 11 prey items, shrimp being the most abundant prey group (IRI% = 88.4), followed by fish (6.6), blue crab (2.8), and crab (2.2). A total of 93 specimens had their muscle's carbon (δ13C) and nitrogen (δ15N) stable isotope ratios analyzed (38–332 mm TL). Average δ13C values showed statistically significant changes across seasons, but no significant changes were observed for δ15N. As initially predicted, isotopic niche size of juveniles changed consistently along the entire hydroclimatic cycle, reaching its peak at the end of the wet season. We also observed changes in the proportion of prey assimilation by juveniles between seasons. Shrimp (92.1%) was the most assimilated prey group during the late dry season, whereas tidal crabs (36.7%), blue crab (27.8%), and shrimp (25.1%) were the most important in the late wet season. Average trophic position of juveniles remained similar across wet (3.32 ± 0.10) and dry (3.23 ± 0.11) seasons. These findings provide important information to help decision makers to promote more efficient management and conservation legislations to protect early life stages of the Atlantic goliath grouper in tropical estuaries.

Influence of Seasonal Water Level Fluctuations on Food Web Structure of a Large Floodplain Lake in China

Seasonal shifts in hydrology are known to alter the abundance and diversity of basal production resources and habitats and hence strongly influence the structure and function of river ecosystems. However, equivalent knowledge of natural lake ecosystems in floodplain regions is lacking. Here, we used stable isotope ratios of carbon and nitrogen to assess available primary production sources and consumer taxa during the dry and wet seasons in a large floodplain lake connected to the Yangtze River. Fish species showed distinct δ13C values between two hydrological periods but only small changes in δ15N values. Most of the fish species had higher estimated trophic levels in the dry season, likely indicating greater carnivory. Results of Bayesian mixing models revealed that benthic algae and benthic organic matter (BOM), combined with C3 vegetation, were the principal food sources supporting the biomass of most fish species during the low-water period, whereas benthic algae and seston were the most important carbon sources during the flood period. Overall, these findings demonstrate that seasonal hydrological changes, such as water-level fluctuations, can affect the trophic structure and ecosystem functioning of floodplain lake food webs in the subtropical zone.

Variation of δ15N in Indian coal, lignite and peat

Nitrogen (N) stable isotope ratio (δ15N) in coal organic matter (OM) provides information on the N source and dominant mechanisms affecting isotopic fractionation during coalification. However, published data on δ15N distribution in coal is rare. The present study is one of the first reports on the δ15N composition of peat, lignite, sub-bituminous and anthracite coals in India and one of the first attempts to understand the processes influencing δ15N composition at different stages of coalification from peat to anthracite. Peats were collected from the western coast of North Andaman Islands and Lake Loktak in Manipur. Plant samples were collected from the peat sampling locations. Cenozoic lignites were collected from Panandhro, Matanomadh, Umarsar and Tadkeshwar mines in Gujarat and Neyveli in Tamil Nadu. Cenozoic sub-bituminous and Permian anthracite coals were collected from Assam and Sikkim, respectively. Variation of δ15N in plants is attributed to the differences in rainfall, plant type and N sources. Lower δ15N values in peats (mean 1.19) compared to the plant samples (mean 2.77) indicate a nonlinear response of δ15N to the relative enrichment or loss of N during peat formation in Lake Loktak and decomposition of OM under anaerobic conditions leading to selective preservation of 14N in the Andaman Islands. The δ15N composition of the studied peat (−1.4–1.6), lignite (−1.4–1.8) and coals (−2.8–5.0) retains their OM source signature. Overall higher δ15N values of Cenozoic lignites compared to the Cenozoic sub-bituminous coal reflects regional differences in climate. Higher δ15N (1.3–5.0) values in Gondwana anthracites reflects the tectonic influence of Himalayan orogeny.

Prolonged baleen hormone cycles suggest atypical reproductive endocrinology of female bowhead whales.

Serial measurements of hormone concentrations along baleen plates allow for reconstructions of mysticete whale reproductive histories. We assessed gestation and calving interval in bowhead whales (Balaena mysticetus) by measuring progesterone, oestradiol, corticosterone and nitrogen stable isotope ratios (δ15N) along baleen of 10 females from the eastern Canada-west Greenland population. Three immature females (body size < 14.32 m) had uniformly low progesterone concentrations across their baleen, while seven mature females (body size ≥ 14.35 m) had repeated, sustained elevations of progesterone indicative of pregnancies. The mean duration of progesterone elevations (23.6 ± 1.50 months) was considerably longer than the approximately 14 month gestation previously estimated for this species. We consider several possible explanations for this observation, including delayed implantation or sequential ovulations prior to gestation, strategies that would allow females to maximize their fitness in variable Arctic conditions, as well as suggest modified criteria defining gestation as a shorter component of the entire progesterone peak. Calving intervals varied within and among individuals (mean = 3.7 years; range = range 2.8-5.7 years), providing population-specific reproductive estimates for growth models used in bowhead whale management and conservation.

An explainable machine learning for geographical origin traceability of mussels Mytilus edulis based on stable isotope ratio and compositions of C, N, O and H

Geographical traceability of marine bivalves has been explored continually, however the traceability results have not been recognized owing to the absence of a reasonable explanation for a certain model prediction. To address this problem, we employed an explainable machine learning to identify the origin of mussels based on stable isotope ratio and compositions of carbon (C), nitrogen (N), oxygen (O), and hydrogen (H). Our findings proved that the Extreme gradient boosting (XGBoost) model may be the best model based upon its high accuracy (93.75 %), precision (93.75 %), recall (94.51 %), F1 score (93.72 %) and AUC (0.990). The feature impact for model out of XGBoost was interpreted by SHapley Additive exPlanations (SHAP) on global and local perspective. This study demonstrated the potential of explainable machine learning to elucidate the complex relationships between desirable geographical information of mussels and the selected features.