Stable Isotopes δ13C Research Articles

Trace Element Geochemistry and Stable Isotopic (δ13C and δ15N) Characterisation of Nevşehir Coals, Türkiye

The Nevşehir coals are located in the Central Anatolian Crystalline Complex (CACC), Türkiye, and no reports exist on trace element, nitrogen, and carbon isotope composition data of the Nevşehir coals. The present study aims to geochemically characterise the Nevşehir coals to determine their trace elemental enrichment patterns and possible sources. Nevşehir coals are found within Late Miocene Kızılöz Formation (Arafa Member) rocks. These coals are part of the huminite maceral group; the dominant maceral group is ulminites. The minerals in coals are inorganic, such as oxidised framboidal pyrite, iron oxide minerals, quartz, clay, and carbonate minerals. Coals have great potential regarding trace elements. Benefits might arise from mining and using some of the critical elements derived from coal. Compared with the world coal average, the coal samples in this study are enriched in As (149.25 μg/g), V (245 μg/g), Cr (159 μg/g), Ga (18 μg/g), Ni (216 μg/g), Th (17 μg/g), Zn (143 μg/g), and U (54 μg/g). The arsenic content in this study is associated with inorganic components such as oxidised framboidal pyrite. Vanadium in coal is mainly associated with aluminosilicates and organic matter. Chromium originates from the clay minerals within coals. Uranium in coal is mainly associated with organic matter. Nickel and zinc in coal are predominantly associated with sulphides. The δ15N contents of the samples are comparable to those of several references, including plants, terrestrial creatures, and organic nitrogen. The δ13C–δ15N isotopic range and average values for four coal samples ranged from −25.66‰ to −25.91‰ (−25.80‰) and 3.6‰ to 4.3‰ (3.9‰), respectively, demonstrating that C3 type modern terrestrial vegetation was common in the palaeomires of the studied coal seams.

Carnivore community reassembly provides a test of Eltonian niche conservatism

The repatriation of species is common, especially in conservation efforts aimed at restoring trophic interactions. Whether the Eltonian niches of restored species are conserved in reassembled ecological communities is largely unknown. Within mammalian carnivores, we hypothesized that the Eltonian niches of sympatric competitors would be structured by trophic facilitation from subsidies provided by large carnivores (i.e. carrion) and humans (i.e. food subsidies). Using stable isotopes (δ13C, δ15N), we quantified the Eltonian niches of an apex predator, the grey wolf Canis lupus and two subordinate guild members, coyotes Canis latrans and red foxes Vulpes vulpes, from Michigan, USA across three periods that differed in community composition: a ‘historical' carnivore community (1910–1930), a ‘reduced' community which lacked wolves (1950–1970), and a ‘reassembled' carnivore community featuring wolves as well as human food subsidies (2000–2020). In historical and reassembled communities, wolves constrained the niche space of coyotes via resource facilitation, regardless of human presence, such that the consumption of deer by coyotes increased by an average of 1.4–1.8‐fold in the presence of wolves. Without wolves, coyotes exhibited an isotopic (dietary) niche breadth ~ 2–5× greater (3.33 ± 0.74‰2) than in the historical (0.64 ± 0.11‰2) and reassembled (1.66 ± 0.63‰2) communities. Conversely, we found that the niche breadth of foxes was conserved across the historical (1.91 ± 0.41‰2) and reduced (1.98 ± 0.75‰2) communities but increased ~ 4‐fold in the presence of human resource subsidies (7.52 ± 1.95‰2). Notably, we found that trophic facilitation by wolves and resource subsidies from humans altered the foraging strategies of individuals, resulting in disparate foraging strategies for foxes in the reassembled community. Our results highlight that Eltonian niche conservatism in carnivore communities is driven by resource subsidies, both from the provisioning of carrion by large carnivores to meso‐carnivores and from human foods subsidizing small carnivores. More broadly, our work suggests that large carnivore repatriation can restore some species interactions, while human resource subsidies can decouple others.

Seabird biomonitoring indicates similar plastic pollution throughout the Canary Current.

Marine plastic pollution is an emerging global threat for biodiversity. Plastic ingestion is one of the most typical and studied consequences with petrels being a particularly vulnerable group. We studied the plastic ingestion by Cory's shearwater (Calonectris borealis) fledglings in three islands of the Canarian Archipelago (Tenerife, Gran Canaria and Lanzarote). Breeders from different islands show substantial spatial segregation in their foraging areas across the Canary Current Large Marine Ecosystem (CCLME), a critical marine biodiversity hotspot and an important fishing ground in the North Atlantic Ocean. Here, we used a combination of plastic ingestion parameters (number, maximum length, type and colour of plastics) and stable isotopes (δ13C and δ15N) to study potential differences in plastic ingestion loads and trophic niche between three colonies. Our findings reveal a high incidence of plastic ingestion (>90%) among birds from the three islands. However, although adult birds show foraging and trophic niche segregation across the CCLME, no substantial differences were found in plastic ingestion. White and transparent threadlike fragments were predominantly ingested, likely originating from fishing activities in the CCLME. We provide a baseline for monitoring of plastic pollution in the CCLME and highlight Cory's shearwater as an effective bioindicator of pelagic ecosystems. Our findings emphasize the need for more standardized plastic monitoring programs covering other islands, and for management measures in the fishing activities conducted in the CCLME.

Long-term trends in summer hypoxia and associated driving factors in the Pearl River Estuary, China.

In this study, we collected in situ water quality data during the summer months from 1985 to 2021 and surface sediment organic carbon and stable carbon isotope (δ13C) data from 2002 and 2020 in the Pearl River Estuary (PRE), to analyze long-term trends in hypoxia and explore changes in deoxygenation processes and their potential drivers. Our results showed that hypoxic events in the PRE transitioned from episodic in Lingdingyang Bay in the 2000s to periodic in the lower estuary by the late 2010s. During this transition, the dominant deoxygenation processes shifted from being caused by terrestrial and wastewater emissions to eutrophication. Increased wastewater discharge, reduced sediment load, weakened wind mixing and strengthened coastal upwelling are potential factors contributing to the changes in deoxygenation processes and the deterioration of hypoxic conditions. This study provides a scientific basis for formulating policies to mitigate hypoxia in large estuaries deeply affected by human activities.

Deep‐sea food‐web structure at South Sandwich Islands (Southern Ocean): net primary production as a main driver for interannual changes

Food‐webs are a major component of ecosystems and determinant for their functioning and structure. The food chain length (FCL) is a key feature of food‐webs and it is crucial for the resistance of the community to external stressors. The Southern Ocean (SO) food‐web is known for being short and dominated by an Antarctic krill Euphausia superba surplus, though recent studies proved the existence of different pathways. However, previous studies focused on the pelagic realm, with the deep‐sea and benthopelagic coupling remaining poorly understood. Using stable isotopes of δ13C and δ15N in muscle from individuals collected during toothfish fishing seasons 2020, 2021 and 2022, we 1) studied the bathyal food‐web structure at South Sandwich Islands; 2) evaluated the interannual variability of FCL; and 3) tested which FCL hypothesis better explains the variability at the SO deep‐sea. Our results show that this food‐web is composed of five trophic levels with both Patagonian Dissostichus eleginoides and Antarctic Dissostichus mawsoni toothfish as top predators. The 4th and 5th trophic levels are mostly composed of fish, while in the 3rd trophic level we mainly found cephalopods and crustaceans. The benthopelagic coupling occurs at different trophic levels, though mostly between the 3rd and 4th trophic level. The FCL varied between years, being in 2022 0.30 trophic levels shorter than in 2020. Our results suggest that food‐webs including a benthic component are longer than pelagic and coastal SO food‐webs. The FCL is positively related with net primary productivity, supporting that the productivity hypothesis explains the variability in FCL in SO bathyal food‐webs in slope and seamount areas. With climate change, the productivity in the SO is expected to increase which will increase the length of the food‐web. This change will affect the structure of the ecosystem, increasing assimilation losses, exposure to biomagnifying contaminants and changing nutrient cycles.

Comparison of cadmium pathways in a high Cd accumulating cultivar versus a low Cd accumulating cultivar of Theobroma cacao L.

Understanding cadmium (Cd) pathways in cacao trees is critical for developing Cd mitigation strategies. This study investigates whether Cd uptake and translocation mechanisms differ between a low and a high Cd-accumulating cacao cultivar. We sampled three replicate trees of each cultivar, and a grafted cultivar that shared the same scion as the low Cd accumulator but had a different rootstock. All cultivars grew in the same field with similar bioavailable soil Cd. We utilized Cd stable isotope analyses to trace Cd pathways within the trees, complemented by micro-scale imaging of Cd distribution in leaves and branches, and nutrient and Cd quantification across tree organs. The high Cd accumulator exhibited 2.9-fold higher Cd uptake than the low Cd accumulator, while the grafted cultivar showed 1.7-fold higher uptake. These differences matched Mn uptake. The δ114/110Cd values of organs increased in the order: roots≤nibs, young leaves≤branches≤pod husks<mature leaves for the high and grafted cultivar, and nibs≤roots≤branches≤pod husks<mature leaves for the low cultivar. The enrichment in heavy isotopes correlated with a progressive retention of Cd compared to Mn along the xylem pathway from roots to branches to leaves. The differences in Cd isotope compositions between cultivars indicate that there are differences in translocation processes, yet they did not affect the relative Cd internal distribution. Cd mass balances and internal translocation factors (ITF) corroborated that differences in nib Cd concentrations among cultivars were primarily due to uptake rather than translocation.

Feeding Habits and Individual Specialization in Adult Female South American Sea Lions (Otaria flavescens) in Patagonia

Studying trophic feeding habits and their variation over time is crucial for understanding individual and population success. Although many generalist feeders’ populations appear to use diverse trophic resources, they are often composed of individuals that specialize in only a subset of these resources, a phenomenon known as individual trophic specialization (ITS). The South American sea lion (SASL) (Otaria flavescens), widely distributed along the South American coast, is an opportunistic and generalist predator with a diverse diet, making it a good model for studying ITS. We aimed to estimate the diet composition and the degree of ITS among SASL females on Isla Arce, Argentina, over a period of three years (2012 to 2014). For that, we analysed stable isotopes (δ15N and δ13C) in vibrissae from 12 females. Over the three years studied, females from this colony primarily fed on pelagic prey. At the population level, the most commonly consumed prey varied between the Argentine anchovy (Engraulis anchoita) in 2012 and 2014 and the Patagonian squid (Doryteuthis gahi) in 2013. Consuming mostly pelagic resources throughout the year, unlike previous studies in nearby colonies, suggests the existence of different foraging strategies in lactating females. Although the prey contribution varied between years, the analysis indicated that SASL females breeding on Isla Arce show some degree of ITS, which could be a mechanism adopted by individuals to mitigate the potential competition given by sustained population increases.

A new model for radiocarbon dating of marine shells from the Netherlands

Abstract A new model for the interpretation of radiocarbon (14C) dates of Holocene marine shells is presented. For the Netherlands, the size of reservoir effect is difficult to assess, as these shells often lived in an environment of mixed marine- and river waters. Both stable isotopes 13C and 18O of the shell carbonate give insight in the environmental conditions the shells lived in. River water occurs in two main categories, distinguished by 18O: the Rhine which is dominant, and other rivers. This leads to two estuary mixing lines between the North Sea and rivers. The stable isotopes of the shell carbonate are also indicative for additional processes, such as uptake of secondary carbonate from the soil by shells, and exchange of C isotopes between atmosphere and water. Extensions of the main model deal with special cases such as pools of stagnant water and lakes. The model leads to an assessment of the recent 14C activities of the system the shells lived in, called 14aSYS. The measured 14C activities relative to these 14aSYS values determine the 14C age of the shells and include the reservoir effect. This way we circumvent normalizing to δ13C = –25‰, i.e. the terrestrial timescale and the subsequent correction for reservoir effects. The model is applied to a large legacy dataset of marine shells from the Netherlands, obtained during the last 7 decades. It contains 1116 14C dated shells; for the majority of these, the 3 isotopes 13C, 14C and 18O are measured.

Isotopic variability of the invasive blue crab Callinectes sapidus in the Gulf of Cadiz: Impacts and implications for coastal ecosystem management.

The variability in trophic position and carbon isotopic signatures can provide information about their dietary flexibility and its ability to adapt to changing environmental conditions. The impact of the invasive blue crab Callinectes sapidus was assessed by estimating its trophic position and isotopic niche using stable isotopes (δ1³C, δ1⁵N, δ³⁴S) across different invaded Atlantic coastal areas. This study, the first of its kind in the eastern Atlantic range, reveals the crab's omnivorous behavior with a wide trophic position (TP=2-4), consistent with findings from its native range. Significant spatial variability in trophic roles was observed between habitats, with salt marshes showing enriched δ1³C and lower TP due to differences in primary producers like Spartina detritus and phytoplankton. Estuaries exhibited higher and broader δ1⁵N and TP ranges, influenced by prey availability and anthropogenic nitrogen inputs, that implies a significant impact on marine benthic and pelagic animal communities. Seasonal changes in the Guadalquivir estuary, linked to overwintering and brooding migrations, showed sexual differences in isotopic signatures, with males more enriched in δ1⁵N than females, indicating varied prey availability or metabolic differences. Overall, the Atlantic invaded range displayed broader and lower TP compared to the Mediterranean, underlining the blue crab's flexible and diverse trophic role across different habitats and trophic levels. The variability in trophic position and carbon isotopic signatures reflects the dietary flexibility of this invasive species and its potential effects on native fauna. These findings emphasize the need to consider trophic interactions in ecosystem management and conservation efforts.

Trophic diversity of the bloom-forming jellyfish community in the coastal waters of China assessed by stable isotope analysis

A growing realization indicates that the trophic ecology of jellyfish is more diverse than once thought, yet a holistic view reflecting the trophic structure and trophodynamics in bloom-forming jellyfish community remains rare. Based on stable isotope δ13C and δ15N analysis, we estimated the trophic characteristics of common blooms jellyfish Nemopilema nomurai, Cyanea spp., Aurelia coerulea and Aequorea spp. in the coastal waters of China (CWC). Our data indicated that most of the isotopic niche space in the overall planktonic food web was occupied by the bloom-forming jellyfish community. The large spectrum of isotopic niche highlights the diverse ecological roles and potentially broad trophic relevance of these jellyfish in the food web. The substantial trophic diversity of these jellyfish resulted from the various trophic positions occupied by different taxa, complicated niche differentiation and overlap patterns, inconsistent size-based trophic variation, and spatial and temporal variation patterns. Isotopic niche comparisons indicated the presence of niche differentiation, reflecting the difference and individual-specific characteristic in resource exploitation and feeding preference among different jellyfish. Additionally, the inconsistent size-based trophic variation among groups derived from an increase in trophic level with size for Cyanea spp., A. coerulea and Aequorea spp. medusae to no change for N. nomurai medusae, which suggests the complexity in size-related trophic shift patterns within the jellyfish group. Additional diversity also arose from variation in the spatiotemporal structuring of jellyfish trophic ecology, which might be caused by the occurrence of trophic heterogeneity at the base of the planktonic food web. In conclusion, our study characterized the trophic structures of the bloom-forming jellyfish community in the CWC, and revealed their trophic diversity resulting from interspecific, intraspecific (ontogenetic), and spatiotemporal variation. These results hold strong potential to further improve the understanding of the trophic ecology and functional roles of the jellyfish community. Furthermore, this study provides a systematic and valuable isotopic data set, spanning from the food web baseline to zooplanktonic organisms and jellyfish community, against which compare with trophic investigations in future in planktonic food web of the CWC.

Inter-island variability in trace elements and trophic ecology of Brown Booby (Sula leucogaster) in the South Atlantic.

This study investigates essential (Mg, Ca, Fe, Mn, Cu, Zn, Se, Ni) and non-essential (Li, Be, Cr, Rb, Sr, Cs, Cd, Sn, Ba, and Pb) element concentrations and stable isotope (δ13C, δ15N, δ34S) compositions in feathers of Brown Boobies (Sula leucogaster) from three distinct Atlantic islands: the Archipelagos of Saint Peter and Saint Paul (SPSP), Abrolhos, and Cagarras. We aimed to investigate the ecological and environmental factors influencing these seabird populations and assess potential variations in contaminant exposure and dietary habits based on location, sex, and maturity stages. Our finding revealed significant geographical differences in trace element concentrations. The Brown Boobies from Cagarras had higher concentrations (mean±SD, μg g-1) of Fe (29±20) and Mn (0.82±0.82) than those from Abrolhos (Fe: 21±20; Mn: 0.24±0.09) and SPSP (Fe: 15±16; Mn: 0.21±0.06). Tin concentrations were also higher in Cagarras (Sn: 0.02±0.01) than in SPSP (Sn: 0.01±0.01). Our analyses revealed significant differences in Li, Mg, Rb, and Zn concentrations between adults and juveniles. However, there were no sex-related differences in element concentrations within each locality. SIBER analyses revealed distinct dietary differences among the three Brown Boobies populations, with the Cagarras seabirds occupying a higher trophic position compared to the SPSP population. This study highlights the importance of considering different populations to understand contaminant exposure and ecological dynamics in Brown Boobies along the South Atlantic. The Cagarras population shows significantly higher contaminant levels, likely due to proximity to anthropogenic activities. These results highlight the necessity for ongoing monitoring to evaluate long-term effects on the more impacted population and to ensure seabird health and sustainability in the Atlantic Ocean.

Climatic variability as a principal driver of primary production in the southernmost subalpine Rocky Mountain lake

ABSTRACT Mountain lakes are sensitive indicators of anthropogenically driven global change, with lake sediment records documenting increased primary production during the twentieth century. Atmospheric nutrient deposition and warming have been attributed to changes in other Western mountain lakes, however, the intensity of these drivers varies. We analyzed a sediment core representing a 270-year record from Santa Fe Lake, New Mexico, to constrain the southern margin of Rocky Mountain lakes and quantify patterns of change in lake biogeochemistry, production, and diatoms since 1750. Lake sediments were dated using 210Pb and analyzed for carbon (C), nitrogen (N), stable isotopes (δ13C, δ15N), diatoms, and phototrophic pigments. The abundance of cyanobacteria, purple sulfur-reducing bacteria, and diatom pigments were elevated during the stable conditions of the Little Ice Age; these phototrophic groups declined in the late 1800s and reached a minimum by 1950. From 1950 to 2020, sediments recorded an increased abundance of cryptophyte, diatom, and chlorophyte groups. The C and N (percentage dry mass) increased after 1950, whereas δ15N and δ13C values declined. Changes since the mid-twentieth century are contemporaneous with warming trends in the Southwest and modest deposition of atmospheric N. Our findings highlight the geographic variability of mountain lake responses to changing environmental conditions.

Wetland Ecosystem Service Preservation? Geochemical Changes in Systems with Mangroves and Shrimp Farms in the Northern Ecuadorean Coast

Mangrove sediments serve as paleoenvironmental records of organic matter and nutrient accumulation. Ecuador, the world’s largest producer of whiteleg shrimp Penaeus vannamei in brackish waters, lost 43% of its continental mangroves between 1969 and 1999. Currently, more than 70,000 hectares of shrimp farms operate in estuaries with mangroves and within mangrove reserves. Variations in mangrove coverage and the extent of shrimp farms are described for the period 1996–2020 for two mangrove reserves, REMACAM and RVSMERM, with an observed increase in the extent of shrimp farms in both reserves. Four sediment cores obtained from mangrove drains and drains transformed into shrimp farm infrastructures were analyzed to observe the impact of this activity on the cumulative changes in total organic carbon (TOC) content and total nitrogen (TN) content, the fractionation of stable isotopes δ13C and δ15N, as well as the TOC/TN ratio. The mangrove drains in REMACAM had 3.8 times more TOC and 2.3 times more TN than drains transformed into shrimp farms in RVSMERM, with lower TOC/TN ratios. The organic matter in sediments from sectors with a higher proportion of shrimp farms mainly came from particulate organic matter of freshwater and freshwater algae compared to mangrove drains. Increases in TOC and TN content were recorded in all analyzed sectors, which could be attributed to the cumulative impact of population growth, the development of other agricultural crops, and continental deforestation, despite the fact that proportionally, the highest increases occurred in the sector with a greater influence of shrimp farms.

Metabolic Characterization of Deceased Donor Kidneys Undergoing Hypothermic Machine Perfusion Before Transplantation Using 13C-enriched Glucose.

The provision of a metabolic substrate is one mechanism by which hypothermic machine perfusion (HMP) of kidneys provides clinical benefit. This study aimed to describe de novo metabolism in ex vivo human kidneys undergoing HMP before transplantation using 13C-labeled glucose as a metabolic tracer. Cadaveric human kidneys were perfused with modified clinical-grade perfusion fluid (kidney perfusion solution [KPS-1], Organ Recovery Systems), in which glucose was uniformly enriched with the stable isotope 13C ([U-13C] glucose). The sampled perfusion fluid was analyzed using a blood gas analyzer, and metabolic profiling was performed using 1-dimensional and 2-dimensional nuclear magnetic resonance spectroscopy and mass spectrometry. Functional outcome measures included serum creatinine levels and the development of delayed graft function. Fourteen kidneys were perfused with the modified KPS-1 and successfully transplanted. The mean duration of HMP was 8.7 h. There was a sustained increase in the conversion of glucose into de novo glycolytic end products, such as lactate, in donor kidneys during HMP. There was no significant association between functional outcomes and metabolism during the HMP. De novo anaerobic metabolism was indicated by continuing lactate production, as indicated by increasing concentrations of universally 13C-labeled lactate ([U-13C] lactate) in perfusion fluid from all kidneys. This was more evident in donation after circulatory death donor kidneys. Our study is the first to use [U-13C] glucose to describe the metabolism during HMP. The consequences of an initial warm ischemic insult on circulatory death in donor kidneys continue during the preservation period.

New evidence on the Late Bronze – Early Iron Age human nutrition in the Crimea (northern Pontic Region) based on the stable isotope analysis and radiocarbon dating

The application of geochemical methods (stable isotope δ13C, δ15N analysis, chemical elemental analysis and radiocarbon dating) for studying human and animal bones from burials and cultural layers of archaeological sites of Crimea made it possible to highlight the issues of the development of agriculture and cattle-bгeeding during the Late Bronze – Early Iron Ages. One of the controversial questions is the problem of transition from sedentary forms of agriculture and cattle-breeding to mobile cattle-breeding among ancient communities in the Eurasian steppe and forest-steppe. On the base of data obtained various groups of people were identified, which are characterized by different nutritional systems, primarily related to the specifics of their economic activities. The inhabitants of the settlements are characterized by the predominance of fish, seafood, milk and meat. Coastal individuals had access to marine food and C4 plants that they consumed. The presence of various indirect evidence related to land cultivation such as tools for agriculture, suggests the presence of agriculture and the cultivation of millet at the Bai-Kiyat I settlement of the Late Bronze Age by the bearers of the Late Sabatinovka and Early Belozerka cultures. Another group of people from this settlement is associated with pastoral activities. Their diet includes more meat and dairy products, as well as plant foods with photosynthesis of C3. Our research suggests the presence of seminomadic cattle-breeding among the communities of the Sabatinovka and Belozerka cultures of the Late Bronze Age and transhumance pastoralism among the bearers of the Kizil-Koba culture of the Early Iron Age.

Climate, soil, and viticultural factors differentially affect the sub-regional variations in biochemical compositions of grape berries

Terroir leaves its influence on the flavor build-up in grape berries by triggering biochemical reactions that ultimately shape the typicality of the produced wines. However, the complex relationship between terroir, carbon stable isotopic composition, and the biochemical composition of grapes remains poorly understood. To fill these gaps, grape berries were harvested at maturity from two grape cultivars, Cabernet Sauvignon and Merlot (Vitis vinifera L.), across 32 sites within the Eastern Foothills of the Helan Mountains region over two vintages. The climate and soil data for these sites were collected, and cultivation practices were surveyed. In parallel, the grape quality indicators were measured at maturity to explore their variations among sub-regions and the correlations between terroir factors and grape quality. Moreover, the carbon stable isotopes (δ¹³C) were measured to evaluate the water status of vines at different sites. Results indicated that organic acids and anthocyanins exhibited a strong vintage effect, with the cooler vintage exhibiting higher levels of these compounds relative to the warmer vintage. Specifically, the Hongsipu sub-region, with a cooler climate, consistently demonstrated higher anthocyanin concentrations than other sub-regions in both vintages of the study. Further analysis revealed that the cultivar Cabernet Sauvignon displayed a higher ratio of di-hydroxylated to tri-hydroxylated anthocyanins in the cooler year, whereas Merlot exhibited the opposite trend. The Mantel test identified several critical factors influencing anthocyanin concentration, including total soil phosphorus (Tp), total soil potassium (Tk), soil thickness (Thickness), precipitation (April-September precipitation, Pre4–9), April-September average temperature (4–9 Tave), April-September active accumulated temperature (4–9 Aa), April-June active accumulated temperature (4–6 Aa), July-September active accumulated temperature (7–9 Aa), temperature diurnal range (May, July, August, September, DR-5 and DR 7–9), trellis system, vine density, and δ13C. Finally, structural equation modeling (SEM) was used to analyze and summarize the relationships between terroir factors, anthocyanin concentration, and δ¹³C. The results indicated that June and September precipitation had a positive impact on anthocyanin concentrations, while soil total potassium content had a negative impact. On the other hand, the July to September temperature diurnal range, trellis system, vine perimeter, and canopy height were the main drivers of δ¹³C, which further influenced grape anthocyanin concentrations. This research contributes to a scientific foundation for grape cultivation in the Eastern Foothills of the Helan Mountains and provides valuable insights for practices in other regions.

Damming of streams due to the construction of a highway in the Amazon rainforest favors individual trophic specialization in the fish (Bryconops giacopinii).

In Amazonian streams, damming caused by road construction changes the system's hydrological dynamics and biological communities. We tested whether the degree of specialization in fish (Bryconops giacopinii) individuals is higher in pristine stream environments with intact ecological conditions than in streams dammed due to the construction of a highway in the Amazon rainforest. To achieve this, stomach content data and stable isotopes (δ13C and δ15N) in tissues with varying isotopic incorporation rates (liver, muscle, and caudal fin) were used to assess the variation in consumption of different prey over time. The indices within-individual component (WIC)/total niche width (TNW) and individual specialization were employed to compare the degree of individual specialization between pristine and dammed streams. The condition factor and stomach repletion of sampled individuals were used to infer the intensity of intraspecific competition in the investigated streams. The species B. giacopinii, typically considered a trophic generalist, has been shown to be, in fact, a heterogeneous collection of specialist and generalist individuals. Contrary to our expectations, a higher degree of individual specialization was detected in streams dammed by the highway. In dammed streams, where intraspecific competition was more intense, individuals with narrower niches exhibited poorer body conditions than those with broader niches. This suggests that individuals adopting more restricted diets may have lower fitness, indicating that individual specialization may not necessarily be beneficial for individuals. Our results support the notion that intraspecific competition is an important mechanism underlying individual specialization in natural populations. Our results suggest that environmental characteristics (e.g., resource breadth and predictability) and competition for food resources interact in complex ways to determine the degree of individual specialization in natural populations.

13C-enrichment NMR spectroscopy: a tool to identify trophic markers and linkages

Current climate change, particularly ocean warming, will induce shifts in marine species distribution and composition, affecting the marine food web and, thus, trophic interactions. Analyses of the stable isotopes 13C and 15N are commonly used to detect trophic markers for food web analyses. With the current standard methods used in food web ecology, it is still challenging to identify potential changes in the uptake and utilization of trophic markers. In this work, we present a 13C-enrichment analysis by NMR spectroscopy to track the uptake and utilization of dietary carbon in a simple laboratory experiment of a primary producer and its consumer (algae and bivalve). In particular, we tested the hypothesis of a temperature-dependent use of dietary carbon by tracing the incorporation of 13C-atoms. Unicellular phytoplankton, Phaeodactilum tricornutum, was reared in a medium containing 13C-labeled bicarbonate. The accompanying 13C-NMR spectra of labeled P. tricornutum showed a specific profile of 13C-labeled compounds, including typical trophic markers such as the polyunsaturated omega-3 fatty acid eicosapentaenoic acid (EPA). Afterwards, 13C-labeled P. tricornutum was fed to King scallops, Pecten maximus, kept at two different temperatures (15°C and 20°C). Tissue-specific NMR spectra of P. maximus revealed elevated 13C-NMR signals, particularly of the fatty acid EPA in the digestive gland, which was not evident in muscle tissue. The comparison between the two temperatures indicated a change in trophic markers. At the higher temperature, less unsaturated fatty acids were detected in the digested gland, but increased 13C-labels in sugars were detected in the adductor muscle. This might indicate a change in the uptake and utilization of the trophic marker EPA in P. maximus due to a shift in energy conversion from favored beta-oxidation at colder temperatures to conversion from carbohydrates in the warmth. Our approach indicates that besides the accumulation of trophic markers, their incorporation and conversion are additional important factors for the reliable interpretation of trophic linkages under climate change.

Comparison of zooplankton assimilation of different carbon sources and fatty acids in a eutrophic lake and its restored basins

The ecological restoration of eutrophic lakes significantly influences the food composition of zooplankton. Zooplankton serve as the principal trophic link, transferring energy from phytoplankton to fish. Understanding the alterations in zooplankton carbon source compositions following ecological restoration and the seasonal variations in this relationship is crucial. This study employs stable carbon isotope (δ13C) and fatty acid (FA) analyses to investigate the seasonal changes in carbon source contributions to zooplankton between the restored and unrestored segments of Lake Xuanwu. Results from FA analysis reveal higher proportions of algal dietary markers in zooplankton FAs in both segments during spring and autumn. Summer exhibits a shift with zooplankton utilizing more bacterial FAs in the restored part and more algal FAs in the unrestored part. While approaching winter, zooplankton in the restored part consume more algal FAs but less in the unrestored part. Zooplankton FAs enriched in δ13C are associated with assimilation of more terrestrial carbon, contrasting with depleted δ13C when zooplankton relies more on phytoplankton. Isotope mixing models indicate a substantial contribution of terrestrial carbon to zooplankton carbon sources, especially in autumn (42.3% unrestored, 51.2% restored) and winter (41.4% unrestored, 36.8% restored), while phytoplankton has a higher contribution in summer (34.5% restored, 46.9% unrestored). These findings contribute to a comprehensive understanding of carbon cycling variations in food webs between eutrophic lakes and ecologically restored lakes.

Enantiomer-Specific Stable Carbon and Nitrogen Isotopic Analyses of Underivatized Individual l- and d-Amino Acids by HPLC + HPLC Separation and Nano-EA/IRMS.

We developed a new method for stable carbon and nitrogen isotopic (δ13C and δ15N) analysis of underivatized amino acid (AA) enantiomers simultaneously, based on high-performance liquid chromatography (HPLC) separation and off-line isotopic measurement. l- and d-Enantiomers of each AA were isolated using a ReproSil Chiral-AA column, purified by wet chemical procedure, and analyzed for δ13C and δ15N values with a nanomol-scale elemental analyzer/isotope-ratio mass spectrometry (nano-EA/IRMS) system. We successfully achieved the separation of l- and d-enantiomers of 15 proteinogenous AAs, with all l-enantiomers eluting before respective d-enantiomers. The δ13C and δ15N values of AA enantiomers were consistent before and after HPLC separation, demonstrating that this analytical method conserves isotopic information. By coupling this column with a multidimensional HPLC system for isolating individual AAs, we analyzed l- and d-AAs in a natural sample, peptidoglycan isolated from Gram-positive bacterium Bacillus subtilis. Results show a surprisingly large 15N-depletion, up to 20‰, in d-glutamic acid relative to its l-counterpart. The first example, to our knowledge, of δ13C and δ15N analyses of underivatized AA enantiomers is expected to contribute to various research areas in the future.