How to cite: Barker, S., Preece, C., Berstan, R., and Seed, M.: Analysis of dissolved nitrate stable isotopes using the one-step Ti (III) reduction method and Elementar EnvirovisION System  , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8338, https://doi.org/10.5194/egusphere-egu23-8338, 2023.

For decades, the search for terrestrial abiotic CH₄ has been a central quest in geology and astrobiology. Most of this research has focused on crustal fluid samples collected at surface seeps, hydrothermal vents, and wells. Nonetheless, in such open systems processes like mixing with shallow biotic CH₄, oxidation, and diffusion can lead to large uncertainties in the initial composition of deeply originated CH₄¹. Extracting natural CH₄ from fluid inclusions entrapped in minerals could overcome the effects of shallow contamination occurring in natural open systems and shed light on the origin of deep CH₄ in a wide variety of geodynamic settings^2,3.  

In this abstract, we present a novel approach for bulk off-line fluid inclusion extraction for the analysis of δ¹³C-CH₄ using a Cavity Ring-Down Spectroscopy (CRDS) analyzer (Picarro G2201-i). Two fluid extraction techniques were compared: ball milling in ZrO₂ jars and sample crushing in a stainless-steel sealed tube under a piston. The accuracy and precision of the different protocols was evaluated with blanks, CH₄ isotopic labelling and interlaboratory comparisons.   

Blanks and isotopically labelled tests with the ball milling technique suggested that milling speed, and duration, and sample mass and type may strongly affect the CH₄ concentrations and isotopic compositions measured by the CRDS analyser. These effects are mainly ruled by the blank production of CH₄ –demonstrated by gas chromatography analyses– and potentially other molecules induced by frictional heating. The blank gases may cause interference effects on the absorption bands detected by the CRDS analyser. This effect was marked by a large offset in the δ¹³C-CH₄ measured in the high-range analytical modes of the Picarro G2201-i. The magnitude of the interference was inversely correlated to the CH₄ concentration.Other processes such as CH₄ diffusion and adsorption may play a role in the observed changes in CH₄ concentrations and isotopic compositions. Experimental conditions involving high CH₄ concentrations and sample mass could well reproduce CH₄ isotopic composition. 

Crushing in a sealed stainless-steel tube produces lower blank levels compared to ball milling, nevertheless the crushing efficiency and CH₄ release is lower due to smaller rock sample size.   

The presented ball milling protocol provides a simple and fast way to extract and accurately analyse CH₄ hosted in fluid inclusions even if great care should be considered for samples with low CH₄ concentrations where contamination and interferences can potentially alter the CH₄ isotopic signature of natural samples.   

References 

• 1 - Young et al. (2017). 10.1016/j.gca.2016.12.041 
• 2 - Klein et al. (2019). 10.1073/pnas.1907871116 
• 3 - Grozeva et al. (2020). 10.1098/rsta.2018.0431 

This work is part of project that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 864045).    

How to cite: Olivieri, O. S., Brovarone, A. V., Fiebig, J., Ressico, F., Marassi, V., Casolari, S., and Sissmann, O.: Exploring new protocols for bulk off-line fluid inclusion extraction for the analysis of δ13C-CH4 using a Cavity Ring-Down Spectroscopy (CRDS) analyzer., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12808, https://doi.org/10.5194/egusphere-egu23-12808, 2023.

Measuring soil dinitrogen (N₂) emissions is notoriously challenging under field conditions. Hence, N₂ emissions represent a significant uncertainty in the nitrogen mass balance of terrestrial ecosystems. The ¹⁵N gas flux (¹⁵NGF) method is the only method currently available for directly quantifying N₂ emissions in situ. However, this method has rarely undergone independent validation under field conditions. In this study, our objectives were to: (1) Quantify N₂ emissions and their role in the fertilizer N mass balance of a wheat rotation using the ¹⁵NGF method (2) Verify the obtained quantities of N₂ emissions using a mass balance approach and (3) Verify the temporal N₂ emission dynamics at the soil-atmosphere interface using vertical soil profiles of ¹⁵N₂ enrichment.

To achieve these objectives, we grew winter wheat in lysimeters and applied ¹⁵N enriched mineral fertilizers via fertigation in three doses (sum 170 kg N ha^-1). We then analyzed gaseous (NH₃, N₂O, N₂) and hydrological N losses, as well as fertilizer N fates in plant and soil, and ¹⁵N₂ enrichment in soil air.

Our results showed that N₂ emissions directly measured using the ¹⁵NGF method amounted to 30 ± 4 kg N ha^-1, which was equivalent to 18 ± 3 % of the applied fertilizer N. These measurements agreed with unrecovered fertilizer N obtained from the ¹⁵N fertilizer mass balance, although the latter had large inherent uncertainty (21 ± 21 kg N ha^-1). N₂O emissions, however, were negligible (0.14 ± 0.02 kg N ha^-1). The temporal variability of measured N₂ emissions after fertilizer additions was generally well explained by ¹⁵N₂ enrichment in soil gas.

Overall, we provide independent validation of the ¹⁵NGF method in measuring N₂ emissions in the field and highlight the significant role of these emissions in the nitrogen balance of crop systems. Our data also suggest that soil gas measurements in combination with diffusion modeling could serve as an alternative method for quantifying N₂ emissions. These results should encourage a wider application of the ¹⁵NGF method in order to improve our understanding of N₂ emissions and reduce the current uncertainties in estimates of these emissions.

How to cite: Yankelzon, I., Schilling, L., Wrage-Moennig, N., Tenspolde, A., Ostler, U., Butterbach-Bahl, K., Hartl, L., Gasche, R., Matson, A., Well, R., Scheer, C., and Dannenmann, M.: Lysimeter-based full N balance as a tool to test field N2 flux measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8103, https://doi.org/10.5194/egusphere-egu23-8103, 2023.

Plants in semi-arid environments have adapted to scarce nitrogen (N) resources by becoming more efficient at using and taking it up, or by relying on symbiotic organisms. Common mycelial/mycorrhizal networks (CMNs) may help plants access and assist to a spatio-temporal redistribution of resources in soil. While CMNs have been extensively investigated in temperate forests and grasslands, their importance in semi-arid environments is still uncertain. This study evaluates the existence and importance of CMNs in N translocation in semiarid environments, using Helianthemmum almeriense as the host plant mycorrhized with Terfezia claveryi. We hypothesize that the presence of CMNs is a response mechanism to N scarcity due to soil heterogeneity. Through this mechanism, host plants and mycorrhizal fungi provide redistribution of N, playing a determinant role at all spatial scales, from the facilitation of seedling establishment to the persistence and coexistence of different plant communities. To test our hypothesis, we designed a mesocosm that allowed only hyphae to cross into an adjacent compartment. Three different tests were used to assess the existence and directionality of CMN. In the first test (T1), an adult plant was labeled with ¹⁵N and on the other side, only unlabeled soil was present. In this way, we could check if the mycorrhizal fungus tends to homogenously distribute the ¹⁵N to places where there is no other plant. In the second test (T2) we had an adult plant and in the adjacent compartment, four-week-old seedlings that were already mycorrhized with mycelium coming from the compartment with the adult plant. In this case, the ¹⁵N marker was applied where the adult plant was located, and we checked whether there was a transfer of ¹⁵N to the seedlings. In T3, we used a set of mesocosms equal to T2, but this time ¹⁵N was applied on the side where the seedlings were located. The idea was to determine whether the distribution of the ¹⁵N was proportional to the size of the plant that could receive it. The three types of mesocosms were sampled before labeling (day 0), 7 and 14 days after labeling. Our results reveal that ¹⁵N translocation to adjacent compartments occurred in all three tests, but in significantly different amounts. The translocation of ¹⁵N was significantly higher in those tests where there was a plant in the adjacent compartment (Tests 2 and 3) compared to T1. We also found that the contribution (%) of ¹⁵N to the total plant N pool was significantly higher for one-month-old seedlings in both T2 and T3, compared to adult plants. Under controlled greenhouse conditions, we have shown that the mycelium seems to act as an effective hub for N translocation, but we have not found the amounts transferred under our experimental conditions to be nutritionally remarkable. Our results should be further evaluated under natural conditions, to verify whether this N transfer has a greater nutritional significance than that found under controlled conditions, and also whether this CMN may play a more important role in signaling between plants adapted to semi-arid regions.

How to cite: Andrino, A., Morte, A., Arenas, F., Figueiredo, A., Sauheitl, L., Navarro, A., Guarnizo, Á. L., Guggenberger, G., and Boy, J.: Determining the relevance of common mycelial networks in the nitrogen nutrition of plants adapted to semi-arid ecosystems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15191, https://doi.org/10.5194/egusphere-egu23-15191, 2023.

Anammox plays a pivotal role in both natural and engineered systems as a process that simultaneously converts fixed nitrogen to N₂ and regenerates NO₃^–. In aquatic and terrestrial ecosystems, isotopic measurements, especially of the NO₃^– pool, provide an essential constraint on the processes that regulate the supply and elimination of fixed nitrogen, but the isotope effects of anammox remain poorly constrained.

We present measurements of the δ¹⁵N and δ¹⁸O of NO₃^–, NO₂^–, and NH₄⁺ as processed by anammox in a mixed microbial community enriched for N removal from wastewater. We find that oxygen isotope effects expressed in NO₂^– include a substantial contribution from equilibration reactions with water superimposed on kinetic isotope effects. Equilibrium between water and NO₂^– during processing by anammoxis greatly accelerated above rates observed under abiotic conditions even during growth phases when NO₂^– is rapidly being consumed. In turn, δ¹⁸O of NO₃^– nearly completely reflects the incorporation of O atoms derived from water with little additional isotopic fractionation. The δ¹⁵N values of NO₃^– and NO₂^– also show evidence for an equilibrium isotope exchange reaction between these molecules, which raises the possibility that nitrite oxidation is partially reversible, while introducing a high degree of variability into the δ¹⁵N of NO₃^– generated by anammox. Finally, variation observed in the δ¹⁵N of NH₄⁺ consumed by anammox can be connected to physiological limitations within the anammox cell.

Despite this complexity, we were able to use NO₂^– and NO₃^– isotope measurements to diagnose changes in the activity of anammox and related processes within the wastewater treatment system during a low-temperature perturbation experiment. These results provide new constraints for interpreting the variability in δ¹⁵N and δ¹⁸O of NO₃^–in natural systems, with implications for estimating relative rates of fixed N turnover processes.

How to cite: Magyar, P., Hausherr, D., Niederdorfer, R., Huang, K., Mohn, J., Bürgmann, H., Joss, A., and Lehmann, M.: Equilibrium and kinetic controls contribute to nitrogen and oxygen isotope effects during anammox in a wastewater treatment system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4677, https://doi.org/10.5194/egusphere-egu23-4677, 2023.

The sulfur (S) cycle is directly linked to the global carbon and iron cycles. Sulfur plays an important role in the preservation of organic matter (OM) over geological time scales. Assimilatory and dissimilatory sulfate reductions (ASR and DSR, respectively) are the main processes shaping the sulfur cycle and carry different sulfur isotopic fractionation (-1 to -3 ‰, and -20 to -75 ‰, respectively). The reduced S species produced by DSR react during early diagenesis with OM (sulfurization) to form organic-S, and/or with iron (Fe) to form pyrite. Although in most cases organic- and pyritic-S have a common origin (i.e., DSR), organic-S in marine sediments is typically ³⁴S enriched relative to its co-existing pyrite by up to 40 ‰ (global average is ~10‰). This isotopic difference is assumed to depend on specific paleo-environmental conditions and different sulfurization pathways (open-closed system for sulfate, Fe availability, redox state, OM type, etc.). Different sulfurization pathways may affect the type and distribution of S-bonds in sedimentary OM and thus can strongly affect the structure and character of sedimentary OM.

Recently, new instrumentations and methods were developed for the rapid determination of organic- and pyritic-S concentrations and δ³⁴S values using a Rock-Eval analyzer (RE) coupled to a MC-ICPMS. A new parameter, Tmax-S (the temperature at maximum peak of organic-S generation), was suggested to represent the organic-S thermal stability in pyrolysis conditions. Applying this parameter to thirteen organically rich and thermally immature samples of various geological settings and paleo-environmental origins revealed several interesting empirical correlations. The Tmax-S value was found to differ among the rocks and to linearly correlate (R²=0.98) with the percentage of pyrolyzed organic-S out of the total organic-S in the rock. Moreover, Tmax-S was strongly correlated with the distribution of sulfidic and thiophene compounds in the rock (R²=0.87). This suggests that Tmax-S may be used as a tool to evaluate the distribution of different S-bonds in the organic molecule, and, as a proxy, their sulfurization and paleoenvironmental conditions.

The rock samples' Tmax-S values also correlate with their isotopic difference between organic- and pyritic-S (Δ³⁴S_{organic-pyrite}; R²=0.76). The Δ³⁴S_{organic-pyrite} values of the rocks extended between 1 to 40‰ where marine samples characterized by low Tmax-S values (~400-450 °C) and large Δ³⁴S_{organic-pyrite} values (~20-40‰) and lacustrine samples by high Tmax-S values (~450-480 °C) and small Δ³⁴S_{organic-pyrite} values (~1-5‰). This correlation further supports the link between paleo-environmental conditions, specific sulfurization pathways, and the organic-S structures (represented by Tmax-S). It may shed light on some fundamental questions regarding the role of S isotopic distribution between pyrite and OM during deposition and diagenesis.

How to cite: Cohen-Sadon, H., Rosenberg, Y. O., Feinstein, S., and Amrani, A.: Development of new proxies for sulfurization and paleo-environmental conditions using a Rock-Eval coupled to MC-ICPMS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11001, https://doi.org/10.5194/egusphere-egu23-11001, 2023.

Soils from a coastal peatland (Drammendorf,  southern Baltic Sea) were investigated for the biogeochemical impact of flooding with brackish seawater. The peatland was rewetted in late 2019 through the partial removal of a dyke and brackish water with high sulfate concentration from a lagoon (Kubitzer Bodden) allowed to intrude into the peatland. Soil cores were retrieved about 2 and 3 years after the initial rewetting event. Pore waters were extracted from soil cores using rhizons and samples were analyzed besides physical parameters for major ions, nutrients, water stable isotopes, dissolved inorganic carbon (DIC) concentrations, and stable isotopes in C and S species. Solid phase samples were analyzed for contents of CNS and acid-extractable metal and nutrient species, and the stable isotope composition of acid-volatile sulfide (AVS), chromium-reducible sulfide (CRS, pyrite).Results from the post-event campaigns are compared with pre-flooding conditions. Poree water generally showed a trend towards freshening with depth as remains from the pre-flooding conditions. . Different sites are furthermore characterized by different amounts of diagenetically released dissolved inorganic carbon (DIC). A mixing evaluation of ẟ¹³C-DIC signatures together with major ion concentrations reveals potential DIC sources, like organic matter/methane oxidation, carbonate dissolution and mixing with seawater-derived DIC. DIC from the dissolution of minor soil carbonates may lead to a relative enrichment of ¹³C in DIC. Brackish water intrusion and cation exchange are reflected by the downward gradients in pore water compositions, with Na and Mg decreasing and Ca increasing with depth. Soil organic carbon is dominating with inorganic carbon being a minor fraction in most parts. Dissolved pore water sulfate and high total sulfur in the top soils with decrease downward trends further reflect the importance of post-event enhanced sulfur cycling leading to characteristic sulfur isotope signatures. AVS is depleted in the top soils with highest contents at about 5 cmbsf. Pyrite sulfur dominates and show different enrichment zones with the sediment columns. Contents in CRS contents covary with TOC, indicating that the benthic diagenetic system is controlled by organic matter availability, as in normal marine sediments.  The study demonstrates the role of electron acceptor availability for benthic carbon cycling, and the kinetics of biogeochemical interactions upon oxidation of reduced carbon, mineral authigenesis/dissolution, and ion exchange processes. The results of implications for coastal processes in the humid climate zone during times of increasing seawater level rise.

How to cite: Saban, R., Boettcher, M. E., Jenner, A. K., Anthony, S. E., Juransinski, G., Ehlert von Ahn, C., Roeser, P., and Schmiedinger, I.: Isotope biogeochemistry of the carbon-iron-sulfur cycle in a temperate coastal peatland after flooding by brackish seawater, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16235, https://doi.org/10.5194/egusphere-egu23-16235, 2023.

Microbially mediated iron (Fe) reduction is suggested to be one of the earliest metabolic pathways on Earth and Fe(III)-reducing microorganisms might be key inhabitants of the deep and hot biosphere [1, 2]. Since microbial Fe cycling is typically accompanied by Fe isotope fractionation, stable Fe isotopes (δ⁵⁶Fe) are used as tracer for microbial processes in modern and ancient marine sediments [3, 4]. Here we present Fe isotope data for dissolved and sequentially extracted sedimentary Fe pools from subseafloor sediments that were recovered during International Ocean Discovery Program Expedition 370 from a 1,180 m deep hole drilled in the Nankai Trough off Japan where temperatures of up to 120°C are reached at the sediment-basement interface. The expedition aimed at exploring the temperature limit of microbial life and identifying geochemical and microbial signatures that differentiate the biotic and abiotic realms [5, 6]. Dissolved Fe (Fe(II)_aq) is isotopically light throughout the ferruginous sediment interval but some samples have exceptionally light δ⁵⁶Fe values. Such light δ⁵⁶Fe values have never been reported in natural marine environments and cannot be solely attributed to microbially mediated Fe(III) reduction. We show that the light δ⁵⁶Fe values are best explained by a Rayleigh distillation model where Fe(II)_aq is continuously removed from the pore water by diffusion and adsorption onto Fe (oxyhydr)oxide surfaces. While the microbially mediated Fe(II)_aq release has ceased due to an increase in temperature beyond the threshold of mesophilic microorganisms, the abiotic diffusional and adsorptive Fe(II)_aq removal continued, leading to uniquely light δ⁵⁶Fe values. These findings have important implications for the interpretation of Fe isotope records especially in deep subseafloor sediments.

References:

[1] Vargas, M. et al., 1998. Nature 395: 65-67.

[2] Kashefi, K. and Lovley, D.R., 2003. Science 301: 934-934.

[3] Beard, B.L. et al., 1999. Science 285: 1889-1892.

[4] Anbar, A.D. and Rouxel, O., 2007. Annu. Rev. Earth Planet. Sci. 35: 717-746.

[5] Heuer, V.B. et al., 2017. In Proc. IODP Volume 370.

[6] Heuer, V.B. et al., 2020. Science 370: 1230-1234.

How to cite: Köster, M., Staubwasser, M., Meixner, A., Kasemann, S. A., Manners, H. R., Morono, Y., Inagaki, F., Heuer, V. B., Kasten, S., and Henkel, S.: Uniquely low stable iron isotopic signatures in deep marine sediments caused by Rayleigh distillation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6603, https://doi.org/10.5194/egusphere-egu23-6603, 2023.

Migratory insects serve an important role to ecosystems and economies as they participate in the long-distance transfer of nutrients, pollen, and biomass. However, migratory insects are understudied, especially compared to birds and mammals, partially because traditional tracking techniques (e.g. mark-recapture, biologgers) are often ineffective for insects because insects are small, short-lived, and numerous. Thus, isotope geolocation has become an effective tool for studying dispersing insects. The painted lady butterfly (Vanessa cardui (L.)) is a virtually cosmopolitan species that was recently found to make regular, annual multi-generational migrations across the Sahara Desert. Previous work geolocating painted ladies with hydrogen isotopes has shown early spring migratory movements of painted ladies from sub-Saharan Africa to Mediterranean Europe and autumn movements to the sub-Sahara from Europe. However, these previous works using hydrogen isotopes were unable to offer refined estimates of natal origin due to the inherent limitations of the technique. Here, we update previous hydrogen isotope-based geographic assignment by (1) using an updated model of hydrogen isotope variations across the landscape (i.e., isoscape), (2) combining with strontium isotope-based geographic assignment, and (3) expanding the number of geolocated butterflies to include capture locations on both sides of the Sahara Desert across different years. Using this method, we spatially refine previous estimates of the natal origins of successful trans-Saharan migrants and estimate the distances that successful migrants travelled. Overall, this study demonstrates the advantages of combining hydrogen and strontium isotopes for the geographic assignment of migratory butterflies and further advances our understanding of long-distance insect migration.

How to cite: Reich, M., Ghouri, S., Zabudsky, S., Talavera, G., and Bataille, C.: There and back again: Combining hydrogen and strontium isotopes refines the trans-Saharan migratory patterns of the butterfly Vanessa cardui, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13891, https://doi.org/10.5194/egusphere-egu23-13891, 2023.

Life evolution has been shaped by marine and continental environmental dichotomy. Particularly, the ecological history of vertebrates is divided into several aquatic and terrestrial phases. Even today, some species spend time in both marine and continental environments during their lifetime. Nevertheless, the timing and location of past ecological transitions, as well as the monitoring of current migration, are still challenging to trace.

To reconstruct the aquatic environments of vertebrates (i.e. seawater vs freshwater), stable (δ¹³C, δ¹⁸O, δ³⁴S) and radiogenic (⁸⁷Sr/⁸⁶Sr) isotope systems applied to mineralized tissues have been commonly used in the past decades^1–6. Nevertheless, these methods hold some limitations as they cannot be applied universally.

Here, we measured the lithium stable isotope composition of mineralized tissues (δ⁷Li) from extant vertebrates living in various aquatic environments (seawater, freshwater/terrestrial, and "transitional environments”). We highlight the potential of δ⁷Li to decipher vertebrates that live in these different environments, in contrast to δ³⁴S and δ¹⁸O that cannot distinguish – in some cases – species living in intermediate waters from those living in seawater. Furthermore, we measured the δ⁷Li values of fossil apatites from extinct vertebrates and obtained values that fall within the range of aquatic environment of their extant relatives⁷. This new proxy may therefore profit studies in ecology, archaeology and palaeontology.

¹ M. T. Clementz, A. Goswami, P. D. Gingerich and P. L. Koch, Journal of Vertebrate Paleontology, 2006, 26, 355–370.

²  J. Fischer, S. Voigt, M. Franz, J. W. Schneider, M. M. Joachimski, M. Tichomirowa, J. Götze and H. Furrer, Palaeogeography, Palaeoclimatology, Palaeoecology, 2012, 353–355, 60–72.

³ J. Goedert, C. Lécuyer, R. Amiot, F. Arnaud-Godet, X. Wang, L. Cui, G. Cuny, G. Douay, F. Fourel, G. Panczer, L. Simon, J.-S. Steyer and M. Zhu, Nature, 2018, 558, 68–72.

⁴ J. Goedert, R. Amiot, D. Berthet, F. Fourel, L. Simon and C. Lécuyer, Sci Nat, 2020, 107, 10.

⁵ L. Kocsis, A. Ősi, T. Vennemann, C. N. Trueman and M. R. Palmer, Palaeogeography, Palaeoclimatology, Palaeoecology, 2009, 280, 532–542.

⁶ B. Schmitz, S. L. Ingram, D. T. Dockery and G. Åberg, Chemical Geology, 1997, 140, 275–287.

⁷ F. Thibon, J. Goedert, N. Séon, L. Weppe, J. E. Martin, R. Amiot, S. Adnet, O. Lambert, P. Bustamante, C. Lécuyer and N. Vigier, Earth and Planetary Science Letters, 2022, 599, 117840.

How to cite: Thibon, F., Goedert, J., Séon, N., Weppe, L., Martin, J. E., Amiot, R., Adnet, S., Lambert, O., Bustamante, P., Telouk, P., Lécuyer, C., and Vigier, N.: Lithium isotopes potential in (paleo)ecology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1093, https://doi.org/10.5194/egusphere-egu23-1093, 2023.