isotopic signature
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2022 ◽  
Author(s):  
Liam Heffernan ◽  
Maria A. Cavaco ◽  
Maya P. Bhatia ◽  
Cristian Estop-Aragonés ◽  
Klaus-Holger Knorr ◽  
...  

Abstract. Permafrost thaw in northern peatlands often leads to increased methane (CH4) emissions, but gaps remain in our understanding of the underlying controls responsible for increased emissions and the duration for which they persist. We assessed how shifting ecological conditions affect microbial communities, and the magnitude and stable isotopic signature (δ13C) of CH4 emissions along a thermokarst bog transect in boreal western Canada. Thermokarst bogs develop following permafrost thaw when dry, elevated peat plateaus collapse and become saturated and dominated by Sphagnum mosses. We differentiated between a young and a mature thermokarst bog stage (~30 and years ~200 since thaw, respectively). The young bog located along the thermokarst edge, was wetter, warmer and dominated by hydrophilic vegetation compared to the mature bog. Using 16S rRNA gene high throughput sequencing, we show that microbial communities were distinct near the surface and converged with depth, but lesser differences remained down to the lowest depth (160 cm). Microbial community analysis and δ13C data from CH4 surface emissions and dissolved gas depth profiles show that hydrogenotrophic methanogenesis was the dominant pathway at both sites. However, the young bog was found to have isotopically heavier δ13C-CH4 in both dissolved gases profiles and surface CH4 emissions, suggesting that acetoclastic methanogenesis was relatively more enhanced throughout the young bog peat profile. Furthermore, young bog CH4 emissions were three times greater than the mature bog. Our study suggests that interactions between ecological conditions and methanogenic communities enhance CH4 emissions in young thermokarst bogs, but these favorable conditions only persist for the initial decades after permafrost thaw.


2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Oksana L. Rozanova ◽  
Sergey M. Tsurikov ◽  
Marina G. Krivosheina ◽  
Andrei V. Tanasevitch ◽  
Dmitry N. Fedorenko ◽  
...  

AbstractForest canopy is densely populated by phyto-, sapro-, and microbiphages, as well as predators and parasitoids. Eventually, many of crown inhabitants fall down, forming so-called ‘arthropod rain’. Although arthropod rain can be an important food source for litter-dwelling predators and saprophages, its origin and composition remains unexplored. We measured stable isotope composition of the arthropod rain in a temperate mixed forest throughout the growing season. Invertebrates forming arthropod rain were on average depleted in 13C and 15N by 1.6‰ and 2.7‰, respectively, compared to the soil-dwelling animals. This difference can be used to detect the contribution of the arthropod rain to detrital food webs. Low average δ13C and δ15N values of the arthropod rain were primarily driven by the presence of wingless microhytophages, represented mainly by Collembola and Psocoptera, and macrophytophages, mainly aphids, caterpillars, and heteropterans. Winged arthropods were enriched in heavy isotopes relative to wingless specimens, being similar in the isotopic composition to soil-dwelling invertebrates. Moreover, there was no consistent difference in δ13C and δ15N values between saprophages and predators among winged insects, suggesting that winged insects in the arthropod rain represented a random assemblage of specimens originating in different biotopes, and are tightly linked to soil food webs.


Plants ◽  
2022 ◽  
Vol 11 (2) ◽  
pp. 169
Author(s):  
Aleš Kolmanič ◽  
Lovro Sinkovič ◽  
Marijan Nečemer ◽  
Nives Ogrinc ◽  
Vladimir Meglič

The present study investigated the effects of cultivation practices on grain (oats) yield and yield components, such as straw yield, harvest index, thousand kernel weight, and plant lodging. In addition, multi-element composition and isotopic signature (δ13C, δ15N) of the oat grains were studied. The spring oat cultivar ‘Noni’ was grown in a long-term field experiment during 2015–2020, using three management practices: control without organic amendment, incorporation of manure every third year and incorporation of crop residues/cover crop in the rotation. Synthetic nitrogen (N) (0, 55, 110 and 165 kg/ha) was applied during oat development in each system. Multi-element analysis of mature grains from two consecutive years (2016 and 2017) was performed using EDXRF spectroscopy, while stable isotope ratios of carbon (C) and nitrogen (N) were obtained using an elemental analyzer coupled to an isotope ratio mass spectrometer (EA/IRMS). The results show how cultivation practices affect yield components and isotopic and elemental signatures. Increasing the N rate improved both the oat grain and straw yields and increased susceptibility to lodging. The results show how the elemental content (Si, Ca, Zn, Fe, Ti, Br and Rb) in the oat grains were influenced by intensification, and a noticeable decrease in elemental content at higher N rates was the result of a dilution effect of increased dry matter production. The mean δ15N values in oat grains ranged from 2.5‰ to 6.4‰ and decreased with increasing N rate, while δ13C values ranged from −29.9‰ to –28.9‰. Based on the δ15N values, it was possible to detect the addition of synthetic N above an N rate of 55 kg/ha, although it was impossible to differentiate between different management practices using stable isotopes.


2022 ◽  
Vol 19 (1) ◽  
pp. 1-27
Author(s):  
Roberto Velázquez-Ochoa ◽  
María Julia Ochoa-Izaguirre ◽  
Martín Federico Soto-Jiménez

Abstract. The isotopic composition of carbon in macroalgae (δ13C) is highly variable, and its prediction is complex concerning terrestrial plants. The determinants of δ13C macroalgal variations were analyzed in a large stock of specimens that vary in taxa and morphology and were collected in shallow marine habitats in the Gulf of California (GC) with distinctive environmental conditions. A large δ13C variability (−34.6 ‰ to −2.2 ‰) was observed. Life-forms (taxonomy 57 %, morphology and structural organization 34 %) explain the variability related to carbon use physiology. Environmental conditions influenced the δ13C macroalgal values but did not change the physiology, which is most likely inherently species-specific. Values of δ13C were used as indicators of the presence or absence of carbon concentrating mechanisms (CCMs) and as integrative values of the isotope discrimination during carbon assimilation in the life cycle macroalgae. Based on δ13C signals, macroalgae were classified in three strategies relative to the capacity of CCM: (1) HCO3- uptake (δ13C > −10 ‰), (2) using a mix of CO2 and HCO3- uptake (-10<δ13C > −30 ‰), and (3) CO2 diffusive entry (δ13C < −30 ‰). Most species showed a δ13C that indicates a CCM using a mix of CO2 and HCO3- uptake. HCO3- uptake is also widespread among GC macroalgae, with many Ochrophyta species. Few species belonging to Rhodophyta relied on CO2 diffusive entry exclusively, while calcifying macroalgae species using HCO3- included only Amphiroa and Jania. The isotopic signature evidenced the activity of CCM, but it was inconclusive about the preferential uptake of HCO3- and CO2 in photosynthesis and the CCM type expressed in macroalgae. In the study of carbon use strategies, diverse, species-specific, and complementary techniques to the isotopic tools are required.


Atmosphere ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1673
Author(s):  
Mao-Chang Liang ◽  
Yi-Chun Chen ◽  
Yi-Qin Gao ◽  
Xi Zhang ◽  
Yuk L. Yung

The delta values of the isotope composition of atmospheric ozone is ~100‰ (referenced to atmospheric O2). Previous photochemical models, which considered the isotope fractionation processes from both formation and photolysis of ozone, predicted δ49O3 and δ50O3 values, in δ49O3 versus δ50O3 space, that are >10‰ larger than the measurements. We propose that the difference between the model and observations could be explained either by the temperature variation, Chappuis band photolysis, or a combination of the two and examine them. The isotopic fractionation associated with ozone formation increases with temperature. Our model shows that a hypothetical reduction of ~20 K in the nominal temperature profile could reproduce the observations. However, this hypothesis is not consistent with temperatures obtained by in situ measurements and NCEP Reanalysis. Photolysis of O3 in the Chappuis band causes O3 to be isotopically depleted, which is supported by laboratory measurements for 18O18O18O but not by recent new laboratory data made at several wavelengths for 49O3 and 50O3. Cloud reflection can significantly enhance the photolysis rate and affect the spectral distribution of photons, which could influence the isotopic composition of ozone. Sensitivity studies that modify the isotopic composition of ozone by the above two mechanisms are presented. We conclude isotopic fractionation occurring in photolysis in the Chappuis band remains the most plausible solution to the model-observation discrepancy. Implications of our results for using the oxygen isotopic signature for constraining atmospheric chemical processes related to ozone, such as CO2, nitrate, and the hydroxyl radical, are discussed.


2021 ◽  
Vol 5 ◽  
Author(s):  
Micha Horacek ◽  
Wolfgang Papesch

Vegetable food stuff produced under controlled and identical conditions from one farm of identical “age” (batch) has a similar isotopic composition. This fact can be used to control the origin of vegetables. This question is of special relevance when food-contaminations have to be traced back to the producer, or certain production claims have to be controlled. However, as vegetables are harvested, brought to whole-sale merchants and to retail shops, where they remain until being bought by the consumer, one has to consider possible changes in isotopic composition during this transfer period, when comparing vegetables of questioned origin with reference samples taken directly from the field/producer. We investigated changes in the isotope composition of vegetables during storage by studying as an example cucumbers from one batch. We stored the cucumbers in a vegetable storage under controlled conditions and removed one sample every day and analyzed its isotopic composition. We found changes in the δ15N and δ18O isotope values over the investigated period of 21 days, with both parameters showing positive linear correlations, and maximum enrichments with time of more than 1.5‰ for δ15N and more than 2‰ for δ18O. However, within the interval the samples remained in a saleable condition the isotope variations remained more or less within the variability of the sample batch. Our study demonstrates that changes in the isotopic signature in vegetables might occur after harvest during storage and have to be taken into account when (commercial) samples collected in a market are investigated.


2021 ◽  
Author(s):  
Joël Thanwerdas ◽  
Marielle Saunois ◽  
Isabelle Pison ◽  
Didier Hauglustaine ◽  
Antoine Berchet ◽  
...  

Abstract. Atmospheric methane (CH4) concentrations have been rising since 2007, resulting from an imbalance between CH4 sources and sinks. The CH4 budget is generally estimated through top-down approaches using CH4 observations as constraints. The atmospheric isotopic CH4 signal, δ13C(CH4), can also provide additional constraints and helps to discriminate between emission categories. The oxidation by chlorine (Cl) likely contributes less than 5 % to the total oxidation of atmospheric CH4. However, the Cl sink is highly fractionating, and thus strongly influences δ13C(CH4). As inversion studies do not prescribe the same Cl fields to constrain CH4 budget, it can lead to discrepancies between estimates. To quantify the influence of the Cl concentrations on CH4, δ13C(CH4) and CH4 budget estimates, we perform multiple sensitivity simulations using three Cl fields with concentrations that are realistic with regard to recent literature and one Cl field with concentrations that are very likely to be overestimated. We also test removing the tropospheric and the entire Cl sink in other sensitivity simulations. We find that the realistic Cl fields tested here are responsible for between 0.3 % and 1.8 % of the total chemical CH4 sink in the troposphere and between 1.0 % and 1.2 % in the stratosphere. Prescribing these different Cl amounts in surface-based inversions can lead to differences in global CH4 source adjustments of up to 12.3 TgCH4.yr−1. We also find that the globally-averaged isotopic signature of the CH4 sources inferred by a surface-based inversion assimilating δ13C(CH4) observations would decrease by 0.53 ‰ for each additional percent of contribution from the tropospheric Cl sink to the total sink. Finally, our study shows that CH4 seasonal cycle amplitude is modified by less than 1–2 % but δ13(CH4) seasonal cycle amplitude can be modified by up to 10–20 %, depending on the latitude.


2021 ◽  
pp. geochem2021-037
Author(s):  
E.G. Potter ◽  
C.J. Kelly ◽  
W.J. Davis ◽  
G. Chi ◽  
S-Y. Jiang ◽  
...  

The Patterson Lake corridor is a new uranium district located on the southwestern margin of the Athabasca Basin. Known resources extend almost one kilometer below the unconformity in graphite- and sulfide-bearing shear zones within highly altered metamorphic rocks. Despite different host rocks and greater depths below the unconformity, alteration assemblages (chlorite, illite, kaolinite, tourmaline and hematite), ore grades and textures are typical of unconformity-related deposits. This alteration includes at least three generations of Mg-rich tourmaline (magnesio-foitite). The boron isotopic composition of magnesio-foitite varies with generation: the earliest generation only observed in shallow samples from the Triple R deposit (Tur 1) contain the heaviest isotopic signature (δ11B ≈ +26 to +19 ‰), whereas subsequent generations (Tur 2, Tur 3) yield lighter and more homogeneous isotopic signatures (δ11B ≈ +17.5 to +19.9 ‰). These results are consistent with precipitation from low temperature, NaCl- and CaCl2-rich brine(s) derived from an isotopically heavy boron source (e.g. evaporated seawater) that interacted with tourmaline and silicates in the basement rocks and/or fluids derived from depth (with low δ11B values). The lower δ11B values in paragenetically later magnesio-foitite reflect greater contributions of basement-derived boron over time whereas minor compositional variations reflect local metal sources (e.g. Cr, V, Ti) and evolving fluid chemistry (decreasing Na and Ca, increasing Mg) over time. The δ11B and chemical variation in magnesio-foitite over time reinforce the strong interactions with basement rocks in these systems while supporting incursion of basinal brines well below the unconformity contact.Thematic collection: This article is part of the Uranium Fluid Pathways collection available at: https://www.lyellcollection.org/cc/uranium-fluid-pathwaysSupplementary material:https://doi.org/10.6084/m9.figshare.c.5727555


2021 ◽  
pp. 120701
Author(s):  
Yan Ma ◽  
Dewen Zheng ◽  
Huiping Zhang ◽  
Jianzhang Pang ◽  
Yizhou Wang ◽  
...  

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Carlos A. Valdez ◽  
Roald N. Leif ◽  
Robert D. Sanner ◽  
Todd H. Corzett ◽  
Mark L. Dreyer ◽  
...  

AbstractThe one-step breakdown and derivatization of a panel of nine fentanyls to yield uniquely tagged products that can be detected by Electron Ionization Gas Chromatography-Mass Spectrometry (EI-GC-MS) is presented. The method involves the treatment of the synthetic opioids with 2,2,2-trichloroethoxycarbonyl chloride (TrocCl) at 60 °C for 3 h in dichloromethane and furnishes two products from one fentanyl molecule that can be used to retrospectively identify the original opioid. Parameters that were studied and fully optimized for the method included temperature, solvent, nature of scavenging base and reaction time. One of the two resulting products from the reaction bears the trichloroethoxycarbonyl (Troc) tag attached to the norfentanyl portion of the original opioid and greatly aids in the opioid detection and identification process. The methodology has been applied to the chemical modification of a panel of nine fentanyls and in all cases the molecular ion peak for the Troc-norfentanyl product bearing the distinctive trichloroethyl isotopic signature can be clearly observed. The method’s LLOD was determined to be 10 ng/mL while its LLOQ was found to be 20 ng/mL. This methodology represents the first application of chloroformates in the chemical modification of this class of synthetic opioids that are notoriously inert to common derivatization strategies available for GC–MS analysis.


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