Molecular composition and characteristics of Sediment-adsorbed Dissolved Organic Matter (SDOM) along the coast of China.

Sediment-adsorbed Dissolved Organic Matter (SDOM) in coast plays a crucial role in the terrestrial and marine carbon cycle processes of the global environment. However, understanding the transport dynamics of SDOM along the coast of China, particularly its interactions with sediments, remains elusive. In this study, we analyzed the δ13C and δ15N stable isotopic compositions, as well as the molecular characteristics of SDOM collected from coastal areas spanning the Bohai Sea (BS), Yellow Sea (YS), East China Sea (ECS), and South China Sea (SCS), by using isotope ratio mass spectrometry and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS). We identified the predominant sources of carbon and nitrogen in coastal sediments, revealing terrigenous origins for most C and N, while anthropogenic sources dominated in the SCS. Spatial variations in SDOM chemodiversity were observed, with diverse molecular components influenced by distinct environmental factors and sediment sources. Notably, lignins and saturated compounds (such as proteins/amino sugars) were the predominant molecular compounds detected in coastal SDOM. Through Mantel tests and Spearman's correlation analysis, we elucidated the significant influence of spatial environmental factors (temperature, DO, salinity, and depth) and sediment sources on SDOM molecular chemodiversity. These findings contribute to a more comprehensive understanding of the carbon cycle dynamics along the Chinese coast.

Carbon budget at the individual-tree scale: dominant Eucalyptus trees partition less carbon belowground.

Large trees in plantations generally produce more wood per unit of resource use than small trees. Two processes may account for this pattern: greater photosynthetic resource use efficiency or greater partitioning of carbon to wood production. We estimated gross primary production (GPP) at the individual scale by combining transpiration with photosynthetic water-use efficiency of Eucalyptus trees. Aboveground production fluxes were estimated using allometric equations and modeled respiration; total belowground carbon fluxes (TBCF) were estimated by subtracting aboveground fluxes from GPP. Partitioning was estimated by dividing component fluxes by GPP. Dominant trees produced almost three times as much wood as suppressed trees. They used 25 ± 10% (mean ± SD) of their photosynthates for wood production, whereas suppressed trees only used 12 ± 2%. By contrast, dominant trees used 27 ± 19% of their photosynthate belowground, whereas suppressed trees used 58 ± 5%. Intermediate trees lay between these extremes. Photosynthetic water-use efficiency of dominant trees was c. 13% greater than the efficiency of suppressed trees. Suppressed trees used more than twice as much of their photosynthate belowground and less than half as much aboveground compared with dominant trees. Differences in carbon partitioning were much greater than differences in GPP or photosynthetic water-use efficiency.

Body size mediates trophic interaction strength of novel fish assemblages under climate change.

Ecological similarity plays an important role in biotic interactions. Increased body size similarity of competing species, for example, increases the strength of their biotic interactions. Body sizes of many exothermic species are forecast to be altered under global warming, mediating shifts in existing trophic interactions among species, in particular for species with different thermal niches. Temperate rocky reefs along the southeast coast of Australia are located in a climate warming hotspot and now house a mixture of temperate native fish species and poleward range-extending tropical fishes (vagrants), creating novel species assemblages. Here, we studied the relationship between body size similarity and trophic overlap between individual temperate native and tropical vagrant fishes. Dietary niche overlap between vagrant and native fish species increased as their body sizes converged, based on both stomach content composition (short-term diet), stable isotope analyses (integrated long-term diet) and similarity in consumed prey sizes. We conclude that the warming-induced faster growth rates of tropical range-extending fish species at their cool water ranges will continue to converge their body size towards and strengthen their degree of trophic interactions and dietary overlap with co-occurring native temperate species under increasing ocean warming. The strengthening of these novel competitive interactions is likely to drive changes to temperate food web structures and reshuffle existing species community structures.

A bout of aerobic exercise in the heat increases carbohydrate use but does not enhance the disposal of an oral glucose load, in healthy active individuals.

We investigated if a bout of exercise in a hot environment (HEAT) would reduce the postprandial hyperglycemia induced by glucose ingestion. The hypothesis was that HEAT stimulating glycogen use would increase the disposal of the ingested glucose (i.e., OGTT; 75 g of glucose). Separated by at least 1 week, nine young-healthy individuals underwent three trials after an overnight fast in a randomized order. Two trials included 50 min of pedaling at 58±5% VO2MAX either in a thermoneutral (21±1ºC; NEUTRAL) or in a hot environment (33±1ºC; HEAT) eliciting similar energy expenditure (503±101 kcals). These two trials were compared to a no-exercise trial (NO EXER). Twenty min after exercise (or rest), subjects underwent an OGTT, while carbohydrate oxidation (CHOxid, using indirect calorimetry) plasma blood glucose, insulin concentrations (i.e., [glucose], [insulin]), and double tracer glucose kinetics ([U- 13C] glucose ingestion and [6,6-2H2] glucose infusion) were monitored for 120 min. At rest, [glucose], [insulin], and rates of appearance/disappearance of glucose in plasma (glucose Ra/Rd) were similar among trials. During exercise, heart rate, tympanic temperature, [glucose], glycogen oxidation, and total CHOxid were higher during HEAT than NEUTRAL (i.e., 149±35 vs 124±31 µmol·kg-1·min-1, p=0.010). However, during the following OGTT glucose Rd was similar in HEAT and NEUTRAL (i.e., 25.1±3.6 vs 25.2±5.3 µmol·kg-1·min-1, p=0.981). Insulin sensitivity (i.e., ISIMATSUDA) only improved in NEUTRAL compared to NO EXER (10.1±4.6 vs 8.8±3.7 a.u.; p=0.044). In summary, stimulating carbohydrate use with exercise in a hot environment does not improve postprandial plasma glucose disposal or insulin sensitivity in a subsequent OGTT.

Niche partitioning and individual specialisation in resources and space use of sympatric fur seals at their range margin.

Ecological theory predicts niche partitioning between high-level predators living in sympatry as a mechanism to minimise the selective pressure of competition. Accordingly, male Australian fur seals Arctocephalus pusillus doriferus and New Zealand fur seals A. forsteri that live in sympatry should exhibit partitioning in their broad niches (in habitat and trophic dimensions) in order to coexist. However, at the northern end of their distributions in Australia, both are recolonising their historic range after a long absence due to over-exploitation, and their small population sizes suggest competition should be weak and may allow overlap in niche space. We found some niche overlap, yet clear partitioning in diet trophic level (δ15N values from vibrissae), spatial niche space (horizontal and vertical telemetry data) and circadian activity patterns (timing of dives) between males of each species, suggesting competition may remain an active driver of niche partitioning amongst individuals even in small, peripheral populations. Consistent with individual specialisation theory, broad niches of populations were associated with high levels of individual specialisation for both species, despite putative low competition. Specialists in isotopic space were not necessarily specialists in spatial niche space, further emphasising their diverse individual strategies for niche partitioning. Males of each species displayed distinct foraging modes, with Australian fur seals primarily benthic and New Zealand fur seals primarily epipelagic, though unexpectedly high individual specialisation for New Zealand fur seals might suggest marginal populations provide exceptions to the pattern generally observed amongst other fur seals.

Effects of Water Isotope Composition on Stable Isotope Distribution and Fractionation of Rice and Plant Tissues.

Rice origin authenticity is important for food safety and consumer confidence. The stable isotope composition of rice is believed to be closely related to its water source, which affects its origin characteristics. However, the influence of water availability on the distribution of rice stable isotopes (δ2H and δ18O) is not clear. In this study, three irrigation waters with different isotopic values were used to investigate isotopic water use effects of Indica and Japonica rice, using pot experiments. Under three different water isotope treatments, the δ2H values of Indica polished rice showed significant differences (-65.0 ± 2.3, -60.5 ± 0.8 and -55.8 ± 1.7‰, respectively, p < 0.05) compared to δ13C and δ15N, as did Japonica polished rice. The values of δ2H and δ18O of rice became more positive when applying more enriched (in 2H and 18O) water, and the enrichment effect was higher in rice than in the corresponding plant tissue. In addition, the δ2H and δ18O values of Indica rice leaves decreased at the heading stage, increased at the filling stage, and then decreased at the harvest stage. Japonica rice showed a similar trend. δ2H changes from stem to leaf were more negative, but δ18O changes were more positive, and δ2H and δ18O values from leaf to rice were more positive for both brown and polished rice. The results from this study will clarify different water isotopic composition effects on rice and provide useful information to improve rice origin authenticity using stable isotope-based methods.

Investigating isotopic markers for hazelnut geographical authentication: Promising variables and potential applications.

Hazelnuts' features and price are influenced by their geographical origin, making them susceptible to fraud, especially counterfeit claims regarding their provenance. Stable isotope analysis is a recognised approach to establish the geographical origin of foods, yet its potential in hazelnut authentication remains unexplored. In this prospective study, we assessed multiple isotopic markers in hazelnuts from different origins and evaluated the most promising variables for geographical authentication by chemometric tools. Our findings indicate that bulk δ18O, along with δ2H and δ13C in the main fatty acid methyl esters, exhibit significant potential in discriminating geographical origins, and 87Sr/86Sr analysis could serve as a proficient confirmatory tool. Though no single marker alone can differentiate between all the studied origins, employing a multi-isotopic approach based on PLS-DA models achieved up to 92.5 % accuracy in leave-10 %-out cross-validation. These findings will probably lay the groundwork for developing robust models for hazelnut geographical authentication based on larger datasets.

Seeing further into the early steps of the endangered atlantic goliath grouper (Epinephelus itajara): Eye lenses high resolution isotopic profiles reveal ontogenetic trophic and habitat shifts.

Estuarine mangroves are often considered nurseries for the Atlantic Goliath grouper juveniles. Yet, the contributions of different estuarine primary producers and habitats as sources of organic matter during early ontogenetic development remain unclear. Given the species' critically endangered status and protection in Brazil, obtaining biological samples from recently settled recruits in estuaries is challenging. In this study, we leveraged a local partnership with fishers and used stable isotope (C and N) profiles from the eye lenses of stranded individuals or incidentally caught by fishery to reconstruct the trophic and habitat changes of small juveniles. The eye lens grows by the apposition of protein-rich layers. Once these layers are formed, they become inert, allowing to make inferences on the trophic ecology and habitat use along the development of the individual until its capture. We used correlations between fish size and the entire eye lens size, along with estuarine baselines, to reconstruct the fish size and trophic positions for each of the lens layers obtained. We then used dominant primary producers and basal sources from mangrove sheltered, exposed estuarine and marine habitats to construct an ontogenetic model of trophic and habitat support changes since maternal origins. Our model revealed marine support before the juveniles reached 25 mm (standard length), followed by a rapid increase in reliance on mangrove sheltered sources, coinciding with the expected size at settlement. After reaching 60 mm, individuals began to show variability. Some remained primarily supported by the mangrove sheltered area, while others shifted to rely more on the exposed estuarine area around 150 mm. Our findings indicate that while mangroves are critical for settlement, as Goliath grouper juveniles grow, they can utilize organic matter produced throughout the estuary. This underscores the need for conservation strategies that focus on seascape connectivity, as protecting just one discrete habitat may not be sufficient to preserve this endangered species and safeguard its ecosystem functions.

Measurement of O2 Uptake and Evolution in Leaves In Vivo Using Stable Isotopes and Membrane Inlet Mass Spectrometry.

Oxygen is both product and substrate of photosynthesis and metabolism in plants, by oxygen evolution through water splitting and uptake by photorespiration and respiration. It is important to investigate these processes simultaneously in leaves, especially in response to environmental variables, such as light and temperature. To distinguish between processes that evolve or take up O2 in leaves in the light, in vivo gas exchange of stable isotopes of oxygen and membrane inlet mass spectrometry is used. A closed-cuvette system for gas exchange of leaf discs is described, using the stable isotopes 16O2 and 18O2, with a semi-permeable membrane gas inlet and isotope mass separation and detection by mass spectrometry. Measurement of evolution and uptake, as well as CO2 uptake, at a range of light levels allows composition of a light response curve, here described for French bean (Phaseolus vulgaris) and maize (Zea mays) leaf discs.

Metabolic activity of Planktothrix rubescens and its consequences on oxygen dynamics in laboratory experiment: A stable isotope study.

Fluctuations in dissolved oxygen (DO) contents in natural waters can become intense during cyanobacteria blooms. In a reconnaissance study, we investigated DO concentrations and stable isotope dynamics during a laboratory experiment with the cyanobacterium Planktothrix rubescens in order to obtain insights into primary production under specific conditions. This observation was extended to sub-daily timescales with alternating light and dark phases. Dissolved oxygen concentrations and its isotopes (δ18ODO) ranged from 0.02 to 0.06 mmol · L-1 and from +9.6‰ to +23.4‰. The δ18ODO proved to be more sensitive than concentration measurements in response to metabolic variation and registered earlier shifts to dominance by respiration. Oxygen (O2) contents in the headspace and its isotopes (δ18OO2) ranged from 2.62 to 3.20 mmol · L-1 and from +9.8‰ to +21.9‰. Headspace samples showed less fluctuations in concentration and isotope trends because aquatic processes were hardly able to alter signals once the gas had reached the headspace. Headspace δ18OO2 values were corrected for gas-water equilibration and were determined to be higher than the mean δ18OH2O of -8.7‰. This finding suggests that counteracting respiration was important even during the highest photosynthetic activity. Additionally, headspace analyses led to the definition of a fractionation factor for respiration (αR) of this cyanobacterium with a value of 0.980. This value confirms the one commonly used for cyanobacteria. Our findings may become important for the management of water bodies where decreases in DO are caused by cyanobacteria.

Isotopic evidence of autochthonous organic matter acting as a major sink of anthropogenic heavy metals in modern lacustrine sediments.

The knowledge of major sources, sinks, and the burial fate of various pollutants added to modern aquatic ecosystems under changing environmental conditions is limited but crucial for our sustainability. In this context, the spatial distributions and causative factors of organic matter (OM) and heavy metal accumulations have been explored in modern lacustrine sediments of a large urbanized and protected wetland (ULB: Upper Lake Bhopal) in Central India. For this purpose, geochemical properties, in particular, stable isotopes (δ13C and δ15N) were measured in the ULB surficial sediments (core depth ∼0-1 cm; n = 19), and additionally collected riverbed sediments (n = 2) and atmospheric free-fall dust samples (n = 3) from the lake periphery. The major and trace element data indicate widespread mafic sediment provenance and nearly dysoxic lacustrine conditions. The riverine supply of soil OM from cropped lands and the lake productivity (algae, largely sustained by nutrients from sewage and agricultural runoff) are the major OM sources to the western and eastern lake portions, respectively. The fractional contribution from autochthonous TOC (∼0.19-0.95, mean ∼0.62) predominates that of allochthonous TOC (∼0.05-0.81, mean ∼0.38). Whereas, atmospheric dust deposition is a primary anthropogenic source of heavy metals (Pb and Zn). The lake productivity rather than soil OM or any mineral sorbent is found responsible for the anthropogenic enrichments of Pb and Zn in the ULB surficial sediments, especially on the eastern ULB portion under high anthropogenic pressure. Therefore, the settled OM (primarily autochthonous) being oxidizable acts as a temporary but major sink of anthropogenic heavy metals in modern lacustrine sediments, which are vulnerable to heavy metal efflux to the water column by sediment diagenesis.

Triple isotopes (δD, δ18O, δ17O) characteristic of river water and groundwater in an arid watershed from Qaidam Basin, Northwestern China: implications for hydrological cycle.

Combining traditional stable isotopes (δD and δ18O) and triple oxygen isotope (δ17O) is conducive to tracing hydrological cycle processes. The application of triple oxygen isotopes primarily focuses on precipitation, which is lacking in river water and groundwater. In this study, the spatial variations of δD, δ18O, δ17O, d-excess and 17O-excess of river water and groundwater in the Golmud River basin as well as the correlation between them were investigated to elucidate water origin and assess the evaporation influence on water bodies during flood season. Spatial changes in δD, δ18O and δ17O of river water exhibit a decrease-increase-stability pattern contrary to that observed for d-excess, 17O-excess has no distinct trend but is higher at both the source and downstream regions. The results show that river water and groundwater originate from precipitation in the mountainous area, and the meltwater in the source region also contribute to the river water with high d-excess and 17O-excess during flood season. The combination of d-excess and 17O-excess reveal that river water is also affected by evaporation and mixing of river water in tributaries. It was found that the river water is recharged in the mountains, undergoes evaporation in the upstream region and leaks into groundwater in the midstream region, which is recharged by the groundwater and evaporated again in the downstream region. This study could provide a more comprehensive understanding of the potential and value of triple oxygen isotopes in the hydrological cycle.

How and when glacial runoff is important: Tracing dynamics of meltwater and rainfall contribution to river runoff from headwaters to lowland in the Caucasus Mountains.

As glacier degradation is intensifying worldwide, understanding how and when glacial runoff is important becomes imperative for economic planning and societal adaptation in response to climate change. This research highlights a probable emergence of new low-flow periods, ranging from one to several weeks, with an anticipated 50-90 % reduction in runoff even in major rivers originating in glacierized mountains by the mid to late 21th century. While the predicted decline in annual and monthly runoff appears moderate for most glaciated regions globally, the emergence of new deglaciation-induced summer low flow periods could create critical "bottle necks" constraining effective water resources management. In this study, a nested catchment approach (7.6-2259 km2) in conjunction with an isotopic tracer method (D, 18O), was employed to quantify the seasonal dynamics of snow and glacial meltwater and rainfall contribution to runoff across various scales of river catchments for the underreported Caucasus Mountains. Although the contribution of meltwater was predictably dominant in the headwaters (75-100 %), it still constituted a substantial 50-60 % of river runoff in the lower reaches most of the time from June to September. While the relative capacity for rainwater storage was found to significantly increase with watershed scale, during weeks devoid of noteworthy rainfall, the runoff in river basins with a mere 7 % glaciation basically entirely consists of what is formed in the glacierized headwaters. The glacial runoff was prevalent in the melt component from late July/early August to mid-September: not less than 30-60 % to the total runoff in the headwaters and 30-40 % in the lower reaches. An approach is proposed to account for the spatial heterogeneity of stable water isotopic content within snow cover and glacier ice. Sources of uncertainties and soundness of assumptions typically used for isotopic hydrograph separation are discussed with particular consideration given to the study objectives.

Surface and groundwater flow exchanges and lateral hydrological connectivity in environments of the Matusagaratí Wetland, Panama.

The Matusagaratí wetland in the Panamanian Darien is one of the largest wetlands in Central America. These types of riverine wetlands, associated with large drainage basins, are complex hydrological environments where variations in water flows and exchanges condition the existence of different wetland habitats. The work aimed to establish the hydrological functioning of the Matusagaratí wetland in different sectors of the Balsas River, emphasizing the exchanges of surface and groundwater flows and the hydrological connectivity that exists between the different laterally linked wetland environments. For this purpose, a monitoring network for surface water and groundwater was established along transects intersecting various wetland environments in the middle and lower basin of the Balsas River. This network is complemented by measurement points for surface water located in streams and in the upper basin of the river. Data collected in sensors installed in boreholes were compared to river level and precipitation data. Continuous water level recording sensors were installed at the monitoring points, and samples were collected for the determination of major ions and stable isotopes. The results indicate that in the mangroves of the lower basin and in the cativo forests of the middle basin levee there is a strong exchange of water between the river and the shallow groundwater. This water exchange is strongly influenced by the tide which spreads from the estuary to the continent through the river. Meanwhile, in the middle basin, mixed forests and orey forests developed on the alluvial plain exhibit a hydrological functioning that depends primarily on precipitation inputs. This study provides data that could serve as a basis for the management of this large tropical wetland that, despite having protection initiatives, could be hydrologically impacted by unsustainable socio-economic practices.

The exploratory dataset of isotopic composition of different water sources across Kazakhstan.

This work presents the dataset of stable water isotopes of oxygen and hydrogen measured in water samples from different sources (precipitation, surface water, groundwater, tap water) across Kazakhstan from 2017 to 2018 and from 2020 to 2023. The dataset includes results on isotopic composition of 399 water samples, namely precipitation: event-based (n = 108), cumulative monthly (n = 22); surface water: lakes, reservoirs, brooks, rivers, channels (n = 175), groundwater: shallow and artesian groundwater, spring (n = 85), tapwater (n = 9). For each sample name of the source, location, latitude, longitude and date of sampling, measurement uncertainty (one standard deviation) are available. The samples were assessed by plotting the data in dual δ18O vs. δ2H isotope space with reference to values found in the published literature and fitting a linear regression equation for Astana (event) precipitation. Overall, this is the first dataset covering wide range of sources across Kazakhstan, which could be used by global and regional water resource assessments and studies such as tracing water sources, hydrograph separation and end-member analyses, isotope mass balance, evapotranspiration partitioning, residence time analysis and groundwater recharge.

Different responses of oxygen and hydrogen isotopes in leaf and tree-ring organic matter to lethal soil drought.

The oxygen and hydrogen isotopic composition (δ18O, δ2H) of plant tissues are key tools for the reconstruction of hydrological and plant physiological processes and may therefore be used for disentangling reasons of tree mortality. However, how both elements respond to soil drought conditions before death have rarely been investigated. To test this, we performed a greenhouse study and determined predisposing fertilization and lethal soil drought effects on δ18O and δ2H values of organic matter (OM) in leaves and tree rings of living and dead saplings of five European tree species. For mechanistic insights, we additionally measured isotopic (i.e., δ18O and δ2H values of leaf and twig water), physiological (i.e., leaf water potential and gas-exchange) and metabolic traits (i.e., leaf and stem non-structural carbohydrate concentration, C:N ratios). Across all species, lethal soil drought generally caused a homogenous 2H-enrichment in leaf and tree-ring OM, but a low and heterogenous δ18O response in the same tissues. Unlike δ18O values, δ2H values of tree-ring OM were correlated with those of leaf and twig water and with plant physiological traits across treatments and species. The 2H-enrichment in plant OM also went along with a decrease in stem starch concentrations under soil drought compared to well-watered conditions. In contrast, the predisposing fertilization had generally no significant effect on any tested isotopic, physiological, and metabolic traits. We propose that the 2H-enrichment in the dead trees is related to (i) the plant water isotopic composition, (ii) metabolic processes shaping leaf non-structural carbohydrates, (iii) the use of carbon reserves for growth, and (iv) species-specific physiological adjustments. The homogenous stress imprint on δ2H but not on δ18O suggests that the former could be used as a proxy to reconstruct soil droughts and underlying processes of tree mortality.

Effects of particle size, storage conditions, and chemical pretreatments on carbon and oxygen isotopic measurements of modern tooth enamel.

Isotopic analysis of human tooth enamel can provide life history information useful in forensic identification. These applications depend on the availability of reference data documenting isotopic values for individuals with known life history and on the comparability of data from reference and case work samples. Here we build on previous methodological research, which has largely focused on paleontological and archaeological samples, and conduct experiments using enamel from modern human teeth targeting three sample preparation variables (sample particle size, storage conditions, and chemical pretreatments). Our results suggest that differences in particle size affect the efficiency of sample reactions during pretreatment and analysis, with coarse particles giving reduced loss of enamel carbonate during acid pretreatments but producing slightly higher oxygen isotope values than fine particles during analysis. Data for samples stored in dry and ambient environments following pretreatment were indistinguishable, suggesting no exchange of oxygen between samples and ambient water vapor. Finally, chemical pretreatments with a range of commonly used reactants and conditions showed a pervasive, moderate oxygen isotope shift associated with acetic acid treatment, which may be caused by exchange of enamel hydroxyl groups with reagents or rinse waters. Collectively, the results emphasize the importance of methodological standardization to improve comparability and reduce potential for bias in the forensic application of tooth enamel isotope data.

Preserved particulate organic carbon is likely derived from the subsurface sulfidic photic zone of the Proterozoic Ocean: evidence from a modern, oxygen-deficient lake.

Biological processes in the Proterozoic Ocean are often inferred from modern oxygen-deficient environments (MODEs) or from stable isotopes in preserved sediment. To date, few MODE studies have simultaneously quantified carbon fixation genes and attendant stable isotopic signatures. Consequently, how carbon isotope patterns reflect these pathways has not been thoroughly vetted. Addressing this, we profiled planktonic productivity and quantified carbon fixation pathway genes and associated organic carbon isotope values (δ13 CPOC ) of size-fractionated (0.2-2.7 and >2.7 µm) particulate matter from meromictic Fayetteville Green Lake, NY, USA. The high-O2 Calvin-Benson-Bassham (CBB) gene (cbbL) was most abundant in the <2.7 µm size fraction in shallow oxic and deep hypoxic waters, corresponding with cyanobacterial and eukaryote algal populations. The low-O2 CBB gene (cbbM) was most abundant near the lower oxycline boundary in the larger size fraction, coincident with purple sulfur bacteria populations. The reverse citric acid cycle gene (aclB) was equally abundant in both size fractions in the deepest photic zone, coinciding with green sulfur bacteria populations. Methane coenzyme reductase A (mcrA), of anaerobic methane cyclers, was most abundant at the lower oxycline boundary in both size fractions, coinciding with Methanoregula populations. δ13 CPOC values overlapped with the high-O2 CBB fixation range except for two negative excursions near the lower oxycline boundary, likely reflecting assimilation of isotopically-depleted groundwater-derived carbon by autotrophs and sulfate-reducers. Throughout aphotic waters, δ13 CPOC values of the large size fraction became 13 C-enriched, likely reflecting abundant purple sulfur bacterial aggregates. Eukaryote algae- or cyanobacteria-like isotopic signatures corresponded with increases in cbbL, cbbM, and aclB, and enrichment of exopolymer-rich prokaryotic photoautotrophs aggregates. Results suggest that δ13 CPOC values of preserved sediments from areas of the Proterozoic Ocean with sulfidic photic zones may reflect a mixture of alternate carbon-fixing populations exported from the deep photic zone, challenging the paradigm that sedimentary stable carbon isotope values predominantly reflect oxygenic photosynthesis from surface waters.

Early prey intake of a short-finned pilot whale (Globicephala macrorhynchus Gray, 1846, Cetacea: Delphinidae) in the Canary Islands.

This study reveals early prey eating by a short-finned pilot whale (Globicephala macrorhynchus Gray, 1846, Cetacea: Delphinidae) in the Canary Islands. Stomach contents, trophic markers, skin isotopic ratios of nitrogen (δ15N:15N/14N) and carbon (δ13C:13C/12C), and fatty acid profiles of the blubber of a short-finned pilot whale of 213 cm size euthanized in free-ranging conditions were analyzed. A total of 15 species of oegopsid squids, mostly diel vertical mesopelagic migrant species of the families Enoploteuthidae, Ommastrephidae, and Histioteuthidae, as well as mother's milk, were identified in the stomach contents. Asperoteuthis acanthoderma (Lu, 1977, Cephalopoda: Chiroteuthidae) was found as first time in this area, suggesting the possibility of its presence on both sides of the subtropical Atlantic, extending its current known distribution. The δ15N value (11.55‰) was higher than expected based on the size range of squid ingested, but lower than that of adult pilot whales, suggesting that mother's milk intake has a significant effect on these values in calves. Similarly, the δ13C values (-17.99‰) were shifted to those of adult pilot whales rather than the ingested squids, also due to the ingestion of high-fat breast milk. The fatty acid (FA) composition of blubber showed a clear stratification. Long-chain polyunsaturated fatty acids (LC-PUFA) were mainly present in the inner layer, while most relevant ≤C20 monounsaturated fatty acids (MUFA) were more abundant in the outer layer.

[Hydrochemical Characteristics and Its Origin of Surface Water and Groundwater in Dianbu River Basin].

Chaohu lake is a key water body for water pollution prevention and treatment in our country. However， it has been at a higher eutrophication level recently. Here， the surface water and groundwater in the Dianbu River Basin， a secondary tributary of Chaohu Lake， were taken as the research object. In order to test the hydrochemical composition and hydrogen and oxygen isotope values of different water bodies， 30 groups of surface water samples， 36 groups of groundwater samples， 16 groups of hydrogen and oxygen stable isotope samples， and 18 groups of groundwater hydrogen and oxygen stable isotope samples were collected in August 2021 （wet season）， November 2021 （normal season）， and February 2022 （dry season）. The seasonal and spatial variation characteristics were analyzed to explore the hydrochemical characteristics and formation mechanism of water bodies by means of mathematical statistics， Piper triangular diagram， Gibbs figures， and ion ratios. The following results were obtained： ① precipitation was the main source of surface water and groundwater in Dianbu River Basin， and the evaporation fractionation effect of surface water was more significant than that of groundwater. At different periods， the surface water was more enriched with stable isotopes of hydrogen and oxygen than groundwater. The stable isotopes of hydrogen and oxygen in water showed seasonal variation， relative enrichment in the wet season， and depletion in the dry season. ② Both surface water and groundwater in the Dianbu River Basin were weakly alkaline， and the concentration of ions in surface water was significantly lower than that in groundwater. Ca2+ and Na+ were the main cations in surface water， Ca2+ was the main cation in groundwater， and the dominant anion in all water was HCO3-. The hydrochemical typology of surface water was mainly HCO3·Cl-Na·Ca， and that of groundwater was mainly HCO3-Na·Ca. ③ The concentrations of the main hydrochemical indexes of surface water and groundwater showed certain seasonal and spatial differences. From the wet season to the dry season， the concentrations of TDS， K+， Na+， Ca2+， Mg2+， Cl-， and SO42- in surface water showed an increasing trend on the whole. The concentrations of Na+， Ca2+， and Mg2+ in groundwater showed little change but increased slightly， whereas the concentrations of Cl-， SO42-， and NO3- showed an increasing trend on the whole. The concentrations of Cl-， SO42-， and NO3- in the water showed relatively large seasonal fluctuations. From upstream to downstream， the concentrations of the main hydrochemical indexes in surface water first decreased and then increased， among which the concentration of NO3- increased the most. The concentrations of the main hydrochemical indexes of groundwater in the direction of runoff changed little overall， but the concentration in the discharge area was higher than that in the recharge area. ④ The formation of hydrochemical characteristics of the water was mainly controlled by water-rock interaction but was also influenced by human factors. The water-rock action was mainly the weathering dissolution of silicate rock， salt rock， and carbonate rock. Man-made pollutants such as sewage from a sewage treatment plant， domestic sewage， and feces had obviously changed the hydrochemical characteristics of the local water. ⑤ Compared with that in 2016， the concentration of NO3- in surface water showed a certain degree of reduction. The nitrogen pollution control work carried out by the local government had achieved certain results， but it was still necessary to strengthen the pollution prevention and control of sewage and feces in the downstream of the Dianbu River， some tributaries （such as the Dingguang River and Maqiao River）， and some residential areas.