Results from the successful EGU sessions on the ‘Application of Stable Isotopes in Biogeosciences’ that took place earlier have been published in several special issues of Organic Geochemistry and Isotopes in Environmental & Health Studies.
Steroidal compounds are crucial biomolecules in nature, governing diverse biological functions and serving as indicators of organic matter origin, depositional environmental history, and facilitating geological correlations in the petroleum geochemistry (Moldowan et al., 1985; Volkman, 2003). Nevertheless, different organisms can generate identical steroidal compounds, so confident identifications of sources can be enhanced by stable isotope analysis. Prior studies have demonstrated the utility of molecular-average d13C to improve interpretations of the phylogenetic and environmental origins of steroidal compounds (Freeman et al., 1990). However, there are challenges and limitations associated with interpretation of d13C values of steroids in geochemical contexts, including post-depositional alteration and the influence of different abiotic and biotic processes. In addition, d13C values of steroidal compounds from different sources might overlap (Piper and Thevis, 2022).
We will present results of a novel Orbitrap-based analytical method for measuring multiple stable-isotope properties of steroidal compounds, including the intramolecular distributions of single and multiple 13C and D substitutions, with the aim of providing more reliable constraints of sources, environments and alteration histories. Unlike traditional bulk carbon isotope analysis, site-specific and multiply substituted carbon isotope analysis focuses on specific carbon positions or groups of positions within organic molecules, enabling detection of variations in carbon cycling, metabolic pathways, and microbial processes that may not be evident from bulk measurements alone. A first proof of concept study focuses on forensic discrimination of isotopic structures of natural and synthetic steroids in human subjects for the purpose of sports doping applications. Preliminary results reveal differences in the measured site-specific 13C, D and clumped isotope of various isotopologues derived from natural and synthetic steroids despite the similarity in their molecular average isotope values.
References
Freeman, K.H., et al., 1990. Evidence from carbon isotope measurements for diverse origins of sedimentary hydrocarbons. Nature343, 254-256.
Moldowan, J.M., et al., 1985. Relationship Between Petroleum Composition and Depositional Environment of Petroleum Source Rocks. AAPG Bull.69, 1255-1268.
Piper, T., Thevis, M., 2022. Investigations in carbon isotope ratios of seized testosterone and boldenone preparations. Drug Test. Anal.14, 514-518.
Volkman, J., 2003. Sterols in microorganisms. Appl. Microbiol. Biotechnol.60, 495-506.
How to cite: Shawar, L., Piper, T., and Eiler, J.: Site-Specific δ13C, D and Clumped Isotope Analysis of Steroidal Compounds for Forensic and Geochemical Applications, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1492, https://doi.org/10.5194/egusphere-egu25-1492, 2025.
The stable oxygen (O) and carbon (C) isotope composition of bulk carbonate in sediments is widely used for paleoenvironmental reconstructions. This approach, however, does often not consider seasonal variability in environmental conditions. Although, this can be overcome by the consideration of the specific composition of ostracod shells which have a relatively short and variable life history, this approach has not been consequently applied in the past. Only few studies investigated the potential of ostracodes in high-resolution (e.g. seasonal) paleoenvironmental reconstructions, based on their stable isotope composition, so far.
Seasonal meteorological conditions in tropical areas such as the Caribbean region are broadly divided into dry and rainy seasons with often profound effects on hydrological and ecological conditions. How this hydrological seasonality is archived by ostracode stable isotopes (δ18O, δ13C) is largely still unclear. The present study uses variations in lake water isotopes (δ18O, δ2H) and δ13CDIC together with the hydrochemical composition (major and trace elements) of the hyperhaline Lago Enriquillo. Water samples and living ostracodes were taken during March and September (i.e. dry and rainy season) in 2022. The C and O isotopic composition of single ostracode valves of different ostracode species (Cyprideis similis, C. edentata, Perissocytheridea cribrosa, Thalassocypria cf. sarbui) were analysed. These species provide differences in their temporal-spatial distribution but are generally restricted to the upper 8 m water depth of the lake. Both types of life cycles (permanent and seasonally restricted) are shown by the ostracodes species.
Questions that are addressed in this study include: Does the water isotopic composition reflect significant differences between the dry and the rainy season? What are the sources and sinks of water for the lake? Do ostracode δ18O and δ13C values reflect the composition of water and dissolved DIC in the lake? How does ostracode ecology (i.e. habitat preferences, life cycle) affects their isotope signatures?
Our results show a low intra-annual variation in δ18O and pronounced local variability of δ13CDIC values of the lake water. Ostracode δ18O and δ13C signatures reflect the lake water composition. The individual species display differences in their isotopic composition and variation ranges. δ18O results agree with the low intra-annual variation of the lake water and display a pronounced gradient with increasing values towards areas with reduced influence of inflows. δ13C values of ostracodes, on the other hand, show strong local differences between and even heterogeneity within samples sites.
Results imply that the lake water was buffered against seasonal hydrological variations during the sampling period, but reveals large spatial variations associated with e.g. strong contrast between inflows and the lake reservoir. The deduction of paleoenvironmental conditions of Lago Enriquillo based on stable isotopes of fossil ostracodes requires therefore consideration of multiple species. The ostracode proxy information then may help to deduce past changes in the lake water cycle.
How to cite: Wrozyna, C., Berndt, C., Reuter, M., Böttcher, M. E., Schröder, B., Garcia Cocco, E., and Haberzettl, T.: Seasonal dynamics of modern ostracod stable isotope (δ18O, δ13C) compositions in a large tropical lake (Lago Enriquillo, Dominican Republic) , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6283, https://doi.org/10.5194/egusphere-egu25-6283, 2025.
Dissolved oxygen (DO) is one of the most fundamental health indicators of aqueous ecosystems. Beyond climate change and habitat modifications, excessive nutrient and pollutant inputs can significantly degrade this critical water quality parameter. Eutrophication, for instance, can drive harmful algal blooms, oxygen depletion and biodiversity loss.
In our study, we present seasonal data on DO concentrations and its oxygen stable isotope ratios (δ¹⁸ODO*) from five campaigns along the Danube River in 2023 and 2024, complemented by particulate organic carbon (POC) data as a biomass indicator. Our results highlight dynamic seasonal patterns. Photosynthesis dominated in spring and summer, while respiration and atmospheric equilibration prevailed in fall and winter. Notable hotspots were identified in the middle and lower Danube, with DO peaks of 0.35 mmol/L and 0.40 mmol/L, accompanied by δ¹⁸ODO* enrichments of +9.8 ‰* and +12.5 ‰* and POC concentrations of 0.25 mmol/L and 0.24 mmol/L. These regions, characterized by reduced river gradient und resulting lower flow velocities and turbulence, suggest enhanced primary producer activity. Notably, nutrient levels remained low, with nitrate under 0.29 mmol/L and phosphate largely undetectable, indicating minimal anthropogenic influence—likely due to environmental improvements and reduced industrial impacts in the catchment. All DO levels were within safe ecological ranges (> 0.06 mmol/L), ruling out hypoxia or harmful algal blooms.
How to cite: Maier, J., Visser, A.-N., Schubert, C. M., Wander, S. T., and Barth, J. A. C.: Seasonal Dynamics of Dissolved Oxygen in the Danube River: The Role of Primary Producers and Slope, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9857, https://doi.org/10.5194/egusphere-egu25-9857, 2025.
The Laacher See (Lake Laach), the largest volcanic lake in Germany, resulted from a massive phreatomagmatic eruption in the Eifel Region ~13,000 years ago. The enclosed lake within a small catchment is still affected by the underlying volcanic activity, providing a unique natural laboratory for investigating the sources and sinks of high dissolved carbon concentrations and associated element cycles in natural chemical gradients. The lake is continuously affected by magmatic CO2 degassing. A large number of moffettes are distributed not only along the lake shore but also at different depths of the lake, whereby gas seeps can still be found at the deepest point of the lake at 51 m. Here, seasonal investigations of the water column and porewaters from several sediment short cores and a 6 m long core at a reference site show for the first time that the sediment package is an active and special biogeochemical reactor outlining a unique type of diagenesis under the boundary conditions of high dissolved inorganic carbon. With the help of an underwater drone equipped with a temperature & depth sensor, the water column was accurately sampled at regular depth intervals. Additionally, the fingerprinting of surrounding groundwaters as potential water and elemental sources, allows for a first assessment of the cycling of dissolved carbon, water, major and trace elements. Stable H and O isotope signatures provide insight into the water sources and the seasonal water balance of the lake. The C isotopic composition of dissolved inorganic carbon (DIC) indicates its sources and fate, and explains signatures reported for authigenic sedimentary carbonates, e.g. siderite. Sulfate is consumed by microbial sulfate reduction in the upper few centimeters of the sediments, and the SO4 isotopic signature from the lake water is close to that of the moffette solution indicating similar influence of these benthic processes. The examination of porewaters from a ca. 7-meter-wide pockmark provides evidence of enhanced diagenesis under high DIC fluxes potentially affecting metal accumulation and liberation from sediments.
How to cite: Roeser, P., Jentsch, A., Albers, S., Knornschild, N., Heumann, G., de Batist, M., Brehme, M., März, C., and Böttcher, M.: Sources and sinks of water and elements in the high-CO2 volcanic Laacher See, Germany, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18841, https://doi.org/10.5194/egusphere-egu25-18841, 2025.
d26Mg values and 87Sr/86Sr ratios are used as tracers of calcite and dolomite formation in the late Miocene Lake Bira. Mg and Sr isotope ratios were analyzed in freshwaters and brines that currently feed the Sea of Galilee (the modern remnant of Lake Bira) and in limestones and dolostones comprising the Bira Formation. d26Mg and 87Sr/86Sr ratios of the Sea of Galilee waters (~0.89‰, ~0.7075) are consistent with the mixing of mainly carbonate and basaltic waters with subsurface Ca-chloride brines (e.g., Tiberias Spa). The d26Mg values in the limestones and dolostone of the Bira Formation range from ~ -1.0 to ~ -3.5‰. and -2.8 to -1.8 ‰, respectively. The d26Mg values in Lake Bira waters at that time were between ~-2 ‰ to ~1 ‰, as calculated from the fractionation factors between water and either calcite or dolomite (-2 ‰ and -0.75 ‰, respectively). Isotope mixing calculations suggest that waters with positive d26Mg values (estimated as ~1.2 ‰) were added to the lake. We suggest that these waters were Ca-chloride brines that were formed in the late Miocene Jordan Valley by interaction between evaporated seawater and the local limestones. These brines deposited the contemporaneous thick sequences of salt (halite) and gypsum in the Jordan Valley to the east of the lake. Dolomitization of the limestones increased the d26Mg of the brines during their re-circulation through the surrounding aquifers due to Rayleigh fractionation, The dolomitization process was accompanied by the production of a Ca-chloride solution.
Limestone formation required enhanced freshwater input; a process accompanied by increasing hydrological head that induced an enhanced inflow of the Ca-chloride brine with high d26Mg to the lake. Dolomite formation was associated with the weakening of the hydrological head, and diminishing flow of the brine to the lake.
The formation of dolomites in the lacustrine environment of Lake Bira and the contemporaneous deposition of gypsum in the nearby Jordan Valley provides a model for dolomitization in marginal environments (e.g., lagoons and subkhas), where the Mg is exchanging with Ca during the dolomitization process and the excess Ca taking the sulfate to form gypsum.
How to cite: Lazar, B., Halicz, L., Karasiński, J., Shaked Gelband, D., Starinsky, A., and Stein, M.: Environmental conditions for dolomite formation in the Late Miocene Lake Bira – Clues from Mg and Sr isotopes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20485, https://doi.org/10.5194/egusphere-egu25-20485, 2025.
Iron-manganese (oxy)hydroxide precipitates (Fe-Mn concretions) occur at the ocean and sea floors all over the world, typically in regions with low sedimentation rates. In shallow water environments like the Baltic Sea, Fe-Mn concretions form in areas where bottom currents prevent active sediment accumulation. The shallow brackish conditions and periodical saltwater inflows from the North Sea make the Baltic Sea a unique environment for concretion formation. Fe-Mn concretions in the Baltic Sea also grow much faster than oceanic concretions, resulting in different mineralogical, chemical, and isotopic compositions compared to deep-sea nodules. One of the areas in the Baltic Sea where Fe-Mn concretions are widespread is the Gulf of Finland, where the concretions form where Late Pleistocene glaciolacustrine varved clays, glacial till, or crystalline bedrock is exposed on the seafloor.
Due to redox-driven precipitation processes, the spherical or disc-like Fe-Mn concretions forming symmetrically around a nucleus are composed of alternating Fe- and Mn-rich layers. In addition, crust-like concretions can grow in areas with higher background sedimentation rates. During their formation, Fe-Mn concretions record the geochemical status of the sedimentary environment, making them potential archives of the geological history of sedimentary basins. Following the Last Glacial Maximum, the Baltic Sea basin has been through multiple phases of fresh and saltwater conditions before the establishment of the modern brackish Baltic Sea. The Fe-Mn concretions in the Baltic Sea have potentially recorded those changes in their chemical and stable isotopic composition, helping us to understand their formation mechanisms and growth phases through layer-by-layer sampling of the concretions from the centre outwards.
This study examines the morphological, chemical, stable isotopic and mineralogical properties of the Fe-Mn concretions in the Baltic Sea, Gulf of Finland seafloor and has an overarching aim to assess the complex geological processes controlling the formation of concretions, as well as get a closer look at the growing phases through the finer sampling of their layered structure, which could offer a new perspective on the timing of formation of these concretions relative to the development of the Baltic sea and the Gulf of Finland.
How to cite: Ojap, J. M., Liira, M., Lepland, A., Böttcher, M. E., Suuroja, S., Somelar, P., and Kirsimäe, K.: Insights into the genesis and geological significance of iron-manganese precipitates in the Baltic Sea, Gulf of Finland seafloor, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19711, https://doi.org/10.5194/egusphere-egu25-19711, 2025.
Explosive volcanic eruptions are capable of producing large amounts of ash, that affect the surrounding ecosystems. Once the ash comes in contact with seawater, the metal salts coating the ash particles quickly dissolve, releasing essential trace metals into the environment. Moderate ash exposure increases the concentrations of several essential metals in the coral host tissue and their algal endosymbionts. As a result, the photosythetic activity of algal symbionts increases, leading to healthier corals and suggesting that ash has a fertilizing effect on symbiotic corals. This study aims to investigate how the duration of ash exposure and the ash concentration affect the photophysiological state of corals and whether metal concentrations and stable isotope ratios can provide insight into the underlying biological processes.
Microcolonies of the scleractinian coral Stylophora pistillata were grown under controlled laboratory conditions, including pH, temperature and irradiance. The corals were divided into various tanks under four different conditions: a control group without ash exposure and three ash-exposure treatments (3.75 g ash/week for three weeks, 7.5 g ash/week for three weeks and 7.5 g ash/week for six weeks). These conditions were chosen to evaluate the effects of different amounts of ash and exposure durations on coral responses. Throughout the experiment, various photophysiological parameters were monitored, including photosynthesis and respiration rates, as well as the photosynthetic efficiency (measured by e.g. relative electron transfer rate and Fv/Fm). At the end of the experiment, Cu, Fe, and Zn concentrations and isotopic compositions (δ56Fe, δ65Cu and δ66Zn) were measured on the symbionts and tissues of three nubbins per tank.
Volcanic ash exposure enhanced the coral photosynthetic activity, although trace metal concentrations and isotope ratios didn’t change between the exposure conditions. The effect was also independent of the intensity or duration of exposure. However, δ65Cu levels in the coral host correlated almost perfectly with the photosynthetic parameters; corals with lighter δ65Cu demonstrated better photosynthetic performance. We propose that the δ65Cu serves as an indicator of the photochemical efficiency and may be linked to the antioxidant capacity of the coral host to mitigate oxidative stress, with stress likely increasing with long-term exposure. Understanding physiologically-induced metallomic responses following ash exposure improves the understanding of ecosystem resilience and collapse.
How to cite: Förster, F., Sauzéat, L., Ferrier-Pagès, C., Reynaud, S., and Sheldrake, T.: δ65Cu as biomarker for the photophysiological state of a symbiotic coral , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5914, https://doi.org/10.5194/egusphere-egu25-5914, 2025.
Pollution of surface and shallow groundwater by nitrate (NO3-) is a global concern resulting in deterioration of drinking water quality. Stable isotopes of NO3- (δ15N and δ18O) can be used to trace its sources which have distinct N and O isotopic signatures. The isotopic values can also be used to identify areas of natural remediation through biogeochemical processes such as denitrification. Conversion of aqueous NO3- to N2O headspace gas by Ti(III) reduction is a new method for analysis of NO3- stable isotopes. Previous literature introduces the analytical procedure but provides limited guidelines for instrument set-up and operation. Here, we present an automated purge and trap isotope ratio mass spectrometer (P&T-IRMS) combined with the Ti(III) reduction method for analysis of δ15N and δ18O in NO3-. The P&T-IRMS base analytical precision was ±0.3‰ and ±0.2‰ for δ15N and δ18O, respectively. Isotopic values were quantified down to an N2O gas concentration of 1 µl L-1 for δ15N and 2 µl L-1 for δ18O. The target NO3--N concentration needed for accurate measurements was 0.2 mg L-1. Comparison of δ15N and δ18O measured using the P&T-IRMS by Ti(III) reduction with EA-IRMS values showed high accuracy. The measurement precision (SD) and uncertainties (u) for our KNO3- internal standard were ±0.2 (±0.6) and ±0.2 (±0.9) for δ15N and δ18O, respectively. The P&T-IRMS and Ti(III) reduction method set-up showed low quantification limits and acceptable accuracy and precision in line with other well-established methods for analysis of NO3- stable isotopes. The provided guidelines will assist laboratories which utilize IRMS headspace gas instrumentation with the process of IRMS set-up and operation and establishment of an independent analytical procedure for the Ti(III) reduction method.
How to cite: Gcakasi, M. N., Stumpp, C., and Watzinger, A.: Establishment of a purge and trap continuous flow isotope ratio mass spectrometer system for analysis of stable nitrate isotopes (δ15N and δ18O) in water samples by Ti(III) reduction, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5412, https://doi.org/10.5194/egusphere-egu25-5412, 2025.
Laser spectroscopy-based gas isotope analysers (LSIA) are cheaper in acquisition and maintenance but still lack the accuracy and precision available through isotope ratio mass spectrometry (IRMS). One of the applications where LSIA are particularly advantageous are online measurements that follow gas release over time. This is even more the case in labelling experiments, where requirements regarding isotope ratio precision are lower. Yet, experiments that implement such setups remain relatively rare.
Here, we present a simple, low-cost setup that conducts automated isotope ratio measurements in gases released from various materials. The setup consists of a LSIA instrument (Picarro G2201-i or G5131-i) which is connected to up to 16 measurement chambers using a VICI selector valve actuated by a Raspberry Pi which also records the measurement data and valve position. An auxiliary pump equipped with a needle valve is placed in parallel to the LSIA to regulate the total flow rate to 500 mL min-1. Each chamber is connected to the analyser for 10 minutes, before switching to the next chamber. We therefore allow the target gas (CO2, CH4, or N2O) to accumulate over 150 minutes between measurements in each chamber. During the measurement, chamber air is pulled to the analyser and replaced by ambient air. The analyte concentration therefore decreases during the measurement time, which allows us to calculate the source isotope value through the Keeling plot method. At the end of the measurement, the analyte concentration and isotope ratio is near ambient air, such that the chamber is reset for the next cycle.
We present and compare three different experiments that used this approach. First, we studied phloem transport rates in Beech trees. For this, we pulse-labelled branches with 13CO2 and followed the release of 13CO2 from stem respiration at different heights over time. Second, we studied the conversion of 13C-acetate label injected into intact peat cores into CO2 and CH4. We quantified the fractions of label recovered as CO2 and CH4 as well as the timing of label-derived gas emissions as a function of injection depths. Finally, we adjusted this setup for measurements of natural abundance isotope ratios in soil N2O emissions to study N2O source processes from permafrost soils. Our presentation will compare these implementations and report on the experience gained during their setup.
How to cite: Kohl, L., Koskinen, M., Polvinen, T., Salmon, Y., Biasi, C., Pihlatie, M., Laurén, A., Zhuang, X., Paljakka, T., and Znamínko, M.: A simple setup for online laser spectroscopy gas isotope analysers in online chamber systems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18101, https://doi.org/10.5194/egusphere-egu25-18101, 2025.
Nitrous oxide (N2O) is a potent greenhouse gas and a significant contributor to global warming and ozone layer depletion. It is primarily emitted from soils through microbial processes such as nitrification and denitrification and shows spatial and temporal variations driven by environmental factors such as the availability of nitrogen (e.g., in the form of fertilizers), organic carbon, soil moisture, temperature and oxygen levels. However, estimates on the relative contribution of different N2O producing pathways are frequently uncertain and knowledge on how environmental factors influence N2O emissions dynamics is still limited. Therefore, closing these knowledge gaps is crucial for improving mitigation strategies.
This study aims to analyze the patterns of N₂O emissions across diverse forest and agricultural soils, taking geographic variations into account, and to determine the relative contributions of the primary N2O producing and consuming pathways specific to each soil type.
Batch experiments were conducted using four agricultural soils and four forest soils from sites of the ICOS (https://www.icos-cp.eu) and FLUXNET (https://fluxnet.org/about/) networks. Agricultural soils were obtained in France, Belgium, Italy and Switzerland, while forest soils were obtained in Finland, Sweden, Belgium and Italy. These soils exhibited a range of intrinsic characteristics, such as texture, organic matter content and type, and nitrogen sources. The incubations took place in complete darkness at a constant temperature of 22 ºC for approximately 30 hours after rewetting dry soil. Each soil type was tested with five replicates across five time points (i.e., 25 reactors for soil type). For each reactor we measured the production of N2O and its isotopic composition including the δ15N-N2Obulk, δ18O-N2Obulk, and site preference δ15N-N2OSP (i.e., the intramolecular distribution of N isotopes, since the N2O molecule has an asymmetric linear structure [N-N-O]). Additionally, the isotopic compositions of nitrate and ammonium from soil KCl extracts are being analyzed (δ15N-NO3-, δ18O-NO3-, δ15N-NH4+) and microbiological characterization is also being performed.
Preliminary results revealed significantly higher N2O production in agricultural soils compared to forest soils during the 30-hour incubation period, with rates reaching up to 130 μg N-N2O/kg/h in agricultural soils and only 0.3 μg N-N2O/kg/h in forest soils. Notable differences were also observed among the four tested soils within each category (agricultural or forest). These differences might be mainly attributed to differences in the nitrogen and organic carbon content as well as the texture. The isotopic analysis of N2O suggests that denitrification is the primary process driving N₂O emissions in the studied soils, with nitrification also contributing to varying extents depending on the soil type.
Ongoing isotopic analyses of nitrate and ammonium in soil KCl extracts alongside microbial characterization, will provide deeper insights into the dominant processes driving N2O emissions in each soil type and the key environmental factors influencing them.
How to cite: Margalef-Marti, R., Mattana, S., López-Sánchez, C., Carrey, R., Palau, J., Otero, N., Tallec, T., Heinesch, B., Feigenwinter, I., Turco, F., Rautakoski, H., Lohila, A., Peichl, M., Guerreri, R., Jansens, I., Poblador, S., Magliulio, E., Vitale, L., Lewicka-Szczebak, D., and Ribas, A.: Unraveling N2O production pathways in agricultural and forest soils using stable isotope analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20270, https://doi.org/10.5194/egusphere-egu25-20270, 2025.
Conventional isotope applications in plant ecophysiology measure isotope ratios (e.g. δ2H, δ13C) of whole molecules. However, it is well established that isotope abundance varies AMONG the CH groups of metabolites (isotopomers), because they are biochemically distinct. This variation reflects enzyme isotope fractionations and encodes metabolic information, but it is unclear how these fractionations get transferred into signals that can be recovered from archives of plant material.
Here, we will describe physical and biochemical mechanisms of hydrogen isotope fractionation in plants and compare their magnitudes. Based on observations for hydrogen isotope transfer in plants, we present a model for the extraction of H isotope signals from plant archives.
Plant responses to increasing CO2 are critical for plant productivity and as climate feedbacks. As CO2 is the substrate for photosynthesis, plants should benefit from increasing CO2, but the magnitude of this “CO2 fertilization” disagrees with biomass estimates. Photorespiration is a side reaction of photosynthesis that reduces C assimilation in most vegetation, therefore its response under climate change is critical for the future C cycle. Photorespiration should be reduced by increasing CO2 yet exacerbated by rising T, but its response is not well captured in models, adding large uncertainty to C cycle predictions.
To retrieve ecophysiological signals from plant archives, we use manipulation experiments to develop proxies for plant C fluxes, based on intramolecular abundance variation of 2H and 13C, detected by NMR. We then retrieve these proxies from archives such as tree-ring series, to derive metabolic responses over long time scales, and to improve global vegetation models.
Here we will describe progress in tracking isotopomer signals from controlled experiments to plant archives, and results on long-term trends of photorespiration in response to increasing atmospheric CO2 for two globally important ecosystems. In Sphagnum species, we link trends in photorespiration to the C sink of boreal peatlands. In the tropical tree species Toona ciliata, we describe long-term trends in photosynthetic efficiency.
As intrinsic quantities, isotope data are well suited to report on metabolic shifts, but not about fluxes in absolute numbers. Therefore we use isotopomer data as input for the LPJ-GUESS Ecosystem Model, to translate isotopomer-derived changes in photorespiration into trends in ecosystem C fluxes.
References:
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How to cite: Schleucher, J., Haddad, L., Yin, X., Zuidema, P., Zwartsenberg, S., Öquist, M., Marshall, J., and Smith, B.: Plants in changing climate: Linking isotope effects, manipulation experiments, plant archives and modelling to derive long-term ecophysiogical signals, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19505, https://doi.org/10.5194/egusphere-egu25-19505, 2025.
Intra-annual variations of oxygen isotope composition (δ18O) in tree rings offer insights into tree ecophysiology and how trees respond to climate. In this study, we focused on the interplay between the δ¹⁸O from source-water, leaf-water and photosynthates to understand how seasonal trends are integrated in tree rings. We conducted a seasonal analysis of Pinus sylvestris in Finland. Our findings reveal a significant reduction in the seasonal variability and trends of δ18O from needle-water to tree rings. This dampening effect on the seasonal trends is due to the opposing seasonal patterns: source-water δ¹⁸O increases from early spring to late summer, while the evaporative enrichment of ¹⁸O recorded in the δ¹⁸O of photosynthates at the leaf level decreases over the same period. Additionally, oxygen isotope exchange between source water and phloem sugars during wood formation contributes to the dampening of the evaporative δ¹⁸O signals in tree rings. These findings enhance our understanding of how δ¹⁸O integrates into tree rings, particularly the seasonal signals preserved along the tree growing season. This study offers new perspectives on how intra-annual δ¹⁸O proxies capture seasonal environmental variations over time, which is crucial for refining climate reconstructions and improving our knowledge of tree physiological responses to climate.
How to cite: Szejner, P., Tang, Y., Angove, C., Schiestl-Aalto, P., Sahlstedt, E., Young, G., Daniel B, N., Ansgar, K., Saurer, M., and Rinne-Garmston, K. T.: Opposing seasonal trends in source water and sugar dampen intra-annual variability in tree rings oxygen isotopes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10355, https://doi.org/10.5194/egusphere-egu25-10355, 2025.
The dual nature of tree-ring cellulose hydrogen isotope composition (δ²H) as a hydroclimatic and physiological proxy offers unique opportunities for palaeoclimatic research (Vitali et al. 2022, 2023), yet its application in long-term studies remains limited. Building on recent advances in tree-ring stable isotope research, we analyse the Alpine Holocene Tree-Ring Triple Isotope Record (AHTTRIR, Arosio et al. 2022), a comprehensive dataset spanning 9,000 years of δ²H, δ¹⁸O and δ¹³C measurements from high-altitude Alpine conifer trees. This study focuses on developing novel methodological approaches for δ²H analysis, applying species-specific values to establish the first multi-millennial δ²H chronology, and comparing it with δ¹⁸O chronology from the same dataset, which is known to contain hydroclimatic signals (Arosio et al. 2025). Despite the inherent complexity of δ²H signals and associated methodological challenges, analysis of approximately 7790 δ²H measurements from the AHTTRIR dataset shows that δ²H contains valuable information on both hydroclimatic variability and tree physiological responses. Through comparison with δ¹⁸O data, we show that δ²H provides complementary insights into plant metabolic processes, including storage mobilisation and stress adaptation mechanisms that could occur due to biotic or abiotic events affecting tree vitality, like damage to needles after insect attacks or frost. This dual-isotope approach, incorporating corrections for species- and age-specific effects, allows the separation of climatic signals from physiological responses over millennial timescales. Comparison with independent Alpine paleoclimate proxies and regional records strengthens our understanding of long-term hydroclimatic dynamics and their impact on tree metabolism throughout the Holocene. These results emphasise the importance of preserving long-term trends in isotope data, while highlighting the need for expanded tree-ring isotope research across different species and geographical regions. The establishment of this pioneering δ²H chronology advances our ability to reconstruct past climate variability while providing crucial insights into ecosystem responses to long-term environmental change.
Arosio Tito, Malin Ziehmer, Kurt Nicolussi, Christian Schluechter, Andrea Thurner, Andreas Österreicher, Peter Nyfeler, and Markus Christian Leuenberger,. 2022. “Alpine Holocene Triple Tree Ring Isotope Record.” PANGAEA, 2022. https://doi.pangaea.de/10.1594/PANGAEA.941604.
Arosio T, Leuenberger M., Nicolussi K, Esper J, Krusic P, Bebchuk T, Tegel W, Hafner A, Kirdyanov A, Schlüchter C, Reinig F, Muschitiello F and Büntgen U. 2025. “Tree-ring stable isotopes reveal a Holocene-long drying trend for central Europe”. In Revision to Science Advances
Vitali, Valentina, Elisabet Martínez-Sancho, K. Treydte, Laia Andreu-Hayles, Isabel Dorado-Liñán, Emilia Gutierrez, Gerhard Helle, Markus Leuenberger, Neil J. Loader, and Katja T. Rinne-Garmston. 2022. “The Unknown Third–Hydrogen Isotopes in Tree-Ring Cellulose across Europe.” Science of the Total Environment 813:152281.
Vitali, Valentina, Richard L. Peters, Marco M. Lehmann, Markus Leuenberger, Kerstin Treydte, Ulf Büntgen, Philipp Schuler, and Matthias Saurer. 2023. “Tree-Ring Isotopes from the Swiss Alps Reveal Non-Climatic Fingerprints of Cyclic Insect Population Outbreaks over the Past 700 Years.” Tree Physiology 43 (5): 706–21.
How to cite: Arosio, T., Leuenberger, M., Nicolussi, K., and Saurer, M.: The dual nature of the hydrogen stable isotopes in tree-rings of the Holocene, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5149, https://doi.org/10.5194/egusphere-egu25-5149, 2025.
High-resolution records of centennial climate variability are crucial considering the scarcity and overall short length of instrumental meteorological data in many regions of the world. The application of stable isotopic analysis in tree rings has emerged as a robust methodological tool for elucidating the intricate complexities of environmental history. This presentation will travel from high latitudes in North America to the Tropical Andes in South America to show how tree-ring stable isotopes can be used to reconstruct climate variability and atmospheric patterns across the Americas, as well as changes in Sea Surface Temperatures (SST). Stable oxygen isotopes (δ18O) measured in tree rings from white spruce trees from the Northwest Territories of Canada record similar large-scale climate patterns as modelled precipitation δ18O from a general circulation model (NASA GISS ModelE2 isotopically-equipped). Trees from the species Polylepis tarapacana growing at high elevation (~5,000 m a.s.l) at the South American Altiplano were used to reconstruct annual precipitation variability, which is driven by the South American Summer Monsoon, over the last 300 years. This newly developed tree-ring δ18O chronology revealed a robust hydroclimatic teleconnection showing interannual (2–5 years) and decadal (~11 years) periodicities consistent with records of Altiplano precipitation, central tropical Pacific SST, Andean ice core δ18O and tropical Pacific coral δ18O. Furthermore, new tree species of the genus Polyelpis growing in the inner tropics were discovered and found to have significant sensitivity to local and regional hydroclimate variability, showing a close link to tropical Pacific SST and El Niño–Southern Oscillation. Overall, our findings point out the importance of developing longer stable isotopes tree-ring records to overcome the inherent difficulties to reconstruct global hydroclimate variability.
How to cite: Andreu-Hayles, L., Rodríguez-Morata, C., Rodriguez-Caton, M., Boucher, E., Christie, D. A., Crispín-DelaCruz, D. B., D'Arrigo, R., Daux, V., Ferrero, E., Field, R. D., Gennaretti, F., Hermoso, I., Lavergne, A., Morales, M., Oelker, R., Requena, E. J., Ticse-Otarola, G., Varuolo-Clarke, A. M., Villalba, R., and Vuille, M.: Revealing past climate variability using tree rings and stable isotopes from tropical and boreal regions in the Americas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19720, https://doi.org/10.5194/egusphere-egu25-19720, 2025.
The C18O16O/C16O16O fractionation during photosynthesis (Δ18OA) carries rich information about plant physiology and environmental conditions, which is crucial for plant physiological, ecological, and biogeochemical studies. Δ18OA is mainly determined by the isotopic fractionation during diffusion and the CO2-leaf water oxygen exchange reaction. Therefore, Δ18OA is believed to relate to leaf physiological parameters such as the evaporative 18O enrichment of leaf water (Δe), CO2 influx and efflux. Based on current mechanistic understanding of Δ18OA, oxygen isotope composition of atmospheric CO2 (δa) can be used to estimate global gross primary productivity and to separate photosynthetic and respiratory CO2 fluxes at the ecosystem scale. However, there is uncertainty about the key physiological factors responsible for changes in Δ18OA and whether there is a difference in Δ18OA between C3 and C4 plants.
In this study, we investigated the response of Δ18OA to short-term changes in CO2 levels in three C3 species (Helianthus annuus, Vigna unguiculata and Triticum aestivum) and one C4 species (Cleistogenes squarrosa) grown under different levels of vapour pressure deficit (VPD) and nitrogen supply. Utilising a new mass-balance equation that distinguishes metabolic (mitochondrial and photo-respiratory CO2) and purely diffusive (retro-diffusive CO2) CO2 fluxes, we assessed the effect of the gross CO2 efflux from leaves.
We found a significant CO2 effect on Δ18OA for C. squarrosa, but not for the C3 species. Δ18OA was not significantly correlated with Δe of the C3 species, and Δ18OA of C4 species was not sensitive to changes in Δe driven by VPD. The gross CO2 efflux and Δ18OA were significantly correlated for both C3 and C4 species, demonstrating its role in regulating Δ18OA. We also found that the C3 species had significantly higher Δ18OA than the C4 species, due to the lower ratio of intercellular to atmospheric CO2 (Ci/Ca) in the latter. Our study reveals the distinct difference in Δ18OA between C3 and C4 species and the remarkable relationship between Δ18OA and physiological parameters, which provides new insights into how Δ18OA can be used to infer carbon cycle processes from leaf to ecosystem scales.
How to cite: Gong, X., Huang, S. M., Yu, Y. Z., and Schnyder, H.: Photosynthetic C18OO fractionation is related to within- and between-species variations in photosynthetic traits, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5413, https://doi.org/10.5194/egusphere-egu25-5413, 2025.
A quantitative understanding of 18O fractionation mechanisms in plants is highly desirable for effective utilization of the δ18O signatures of plant cellulose (δ18Ocel) in diverse climatic and ecological applications. According to the isotope theory, biochemical fractionation associated with oxygen isotopic exchange represents a critical control of δ18Ocel. Biochemical fractionation operates in both autotrophic (i.e., leaf) and heterotrophic (i.e., stem/trunk) organs, with the current δ18Ocel model assuming that its effect amounts to c. 27‰ in both types of organs. However, with respect to the autotrophic fractionation factor (εbio_A), calculations of the deviations of the δ18O enrichment of sucrose (Δ18Ols) from that of water (Δ18Olw) in a bulk leaf, -- as performed in many previous studies, -- have led to a wide range of εbio_A estimates (i.e., from 22.4 to 34‰) across different species. Such a bulk-leaf based estimation method, however, does not provide a precise quantification of εbio_A. This is because the oxygen exchange-determined intrinsic relationship between Δ18Ols and Δ18Olw, namely Δ18Ols = Δ18Olw + εbio_A, is not expected to hold at the bulk leaf level owing to complications arising from within-leaf heterogeneity that is commonly present in Δ18Olw and sucrose synthesis rate (rsuc).
Here, based on explicit consideration of potential within-leaf heterogeneity in rsuc, as well as of spatial variation characteristics of Δ18Olw as informed by the Farquhar-Gan model, we suggest that the isotopic relationship between bulk Δ18Ols and Δ18Olw should instead be expressed as the following: Δ18Ols = β*Δ18Olw + εbio_A, with β being a composite variable highly relevant to spatial variation of rsuc across the leaf. Further analysis demonstrates that β can be markedly larger or smaller than unity depending on whether rsuc progressively increases or decreases along the leaf length. With the derivation of this new equation delineating bulk leaf isotopic relationships, we propose a regression approach via which εbio_A can be robustly quantified as the intercept of a linear relationship between Δ18Ols and Δ18Olw. We subsequently applied such a regression method under highly controlled experimental settings to determine εbio_A in diverse plant species under different growth temperatures. The application of this new method allowed us to successfully constrain the estimate of εbio_A at 25°C to a narrow range of 26.4‰ ± 1.5 per mil across a range of plant species, closely aligning with the traditionally assumed value of 27‰. Additionally, a significantly inverse relationship of εbio_A with temperature was revealed from our experiment. Further comparisons will be made between our revealed temperature dependence of εbio_A with that of the heterotrophic factor εbio_H as reported in Sternberg and Ellsworth (2011). Our study represents a step forward in constraining isotope parameters in the δ18Ocel model, which has important implications for isotope-based paleoclimatic reconstruction and ecophysiological applications.
How to cite: Wen, W., Tang, X., and Song, X.: Towards a refined method for estimating 18O autotrophic fractionation during sucrose synthesis in a bulk leaf, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7605, https://doi.org/10.5194/egusphere-egu25-7605, 2025.
The so-called crucial field is an agricultural test project west of Copenhagen since 2001, where various fertilizers (such as cattle manure, mineral fertilizer and organic household waste) have been applied on different sub-plots to study their long-term effects. Moreover, some sub-plots have been 'retired' and received only minimal fertilization after 2012. To investigate the numerous effects on C and N isotopes, I am analyzing stored fertilizer, soil and grain samples. The main points of investigation are
1. how the isotopic composition of the soil and the grain changes depending on the fertilizer treatment over time (caused by the fertilizer delta values or alternated soil processes due to fertilization);
2. how the isotopic delta values of the fertilizers themselves have changed since the beginning of the experiment and
3. how long the soil isotopic delta values take to reach pre-experimental values after 'retirement'.
In addition, it is intended to do GHG-flux measurements to investigate emissions of the sub-plots and examine whether high emissions can be linked to high delta values in the soil.
How to cite: loy, B.: The isotopic timeline of an agricultural field, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3148, https://doi.org/10.5194/egusphere-egu25-3148, 2025.
An evaluation of the susceptibility of different N management systems to nitrogen (N) losses into the environment requires either the in-situ determination of the individual components of the nitrogen balance or the determination of the recovery of fertilizer N in plants and soil. For both aspects, 15N methods are essential as the 15N gas flux method (15NGF) is the only widespread in-situ method for the determination of dinitrogen (N2) emissions, and 15N labelled fertilizers can be used to assess the allocation of fertilizer N to plants and soil.
To evaluate the influence of management history on N losses, we quantified N loss pathways (NH3, N2O, N2, NO3- leaching), total N balance and 15N recovery in soil and plants of two adjacent sites over a two-year cropping sequence. One site was under integrated farming (IF) and the other under organic farming (OF) with frequent legume cultivation and occasional fertilizer input.
Though integrated farming had resulted in significantly higher pH, soil organic C and N content, the emissions of ammonia, dinitrogen and nitrous oxide after cattle slurry application as well as nitrate leaching were low and not significantly different. High 15N recovery rates in plants and soil agreed well with the low directly measured N losses. Integrating the directly measured losses into the 15N balance resulted in high overall recoveries of 84 to 100%. Conversely, unrecovered 15N was on a low level, but higher for OF (12%) than for IF (6%).
Our results confirm that 15N labelled fertilizers and their recovery can be used as an indicator for N losses, but the spatial variability is high, complicating statistically significant findings. Consideration of N2 fluxes using the 15NGF method could not close the 15N balance, indicating that unaccounted N losses have occurred. Since the directly measured N losses were not significantly different, unaccounted losses could be due to N2 emissions as their quantification was limited to two weeks after fertilizer application.
Overall, integrated farming history reduced the vulnerability towards N loss, but continuous methods for determination of N2 emissions, such as isotopomer measurements, need to be tested concomitantly, and uncertainty of 15N recovery in plants and soil needs to be reduced by more sophisticated sample mixing approaches.
How to cite: Wolf, B., Khan, F., Franco Luesma, S., Hartmann, F., Dannenmann, M., Gasche, R., Scheer, C., Gattinger, A., Niether, W., and Kiese, R.: Role of 15N methods for assessing the susceptibility of agricultural N management systems to environmental N losses, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3735, https://doi.org/10.5194/egusphere-egu25-3735, 2025.
In the last few decades, the Mediterranean area has been extensively impacted by prolonged and intense droughts and heat waves. These events, combined with heavily landscape management, ongoing for thousands of years in the region, have been affecting the ecosystems’ resources such as water availability and nutrient cycles. Mediterranean vegetation responds differently to natural and human-induced changes and within the same species, different compartments (e.g. leaves, branches and roots) may exhibit diverse responses to these stressors, providing valuable bioindicators. Stable isotopes, particularly carbon (C) and nitrogen (N), have become widely used as effective tools to study plant responses to environmental gradients such as plant water-use efficiency, nitrogen-use strategies and ecosystem functioning.
Within ITINERIS (Italian integrated environmental research infrastructures system) project, we present preliminary findings comparing d13C and d15N values in soil and vegetation samples from coastal urban and peri-urban parks along a latitudinal gradient in Italy. To evaluate the relationships between isotopic signatures and environmental changes, soil and vegetation samples were collected in three ICOS (Integrated Carbon Observation System) stations located along the coastal latitudinal transect (Pisa, Rome and Naples). Holm oak (Quercus ilex) was selected as a potential bioindicator of environmental changes and anthropogenic disturbances due to its abundant presence at all three sites. Soil and plant compartments (e.g., leaves of different ages, branches, pollen, fine roots) were collected and analysed at the start and end of the growing season to investigate the response of Mediterranean species down to organ level to a thermo-pluviometric gradient.
The main findings of this study have highlighted differences in C and N concentrations and isotope compositions across the latitudinal gradient and seasons. Capodimonte (Naples), the most southern site, reveals an enrichment in d13C and d15N in leaves compatible not only with a response to hot and dry climate, but also to a much higher degree of anthropization. Castel Porziano (Rome) exhibits a similar trend but lower d15N and N concentration. San Rossore (Pisa), the northernmost site is subject to less water stress during summer season, resulting in more diluted d13C and d15N values. The leaves in the fall showed higher d13C and N concentration compared to spring. Branches were about 1 ‰ enriched in 13C compared to leaves due to post-photosynthetic isotope fractionations. Further analyses are underway on other plant compounds, including pollen, to identify the most suitable bioindicators of Mediterranean species’ response to climate change and human impact, with potential applications in the region’s management and conservation strategies.
How to cite: Tunno, I., Scartazza, A., Micali, M., Calfapietra, C., Guidolotti, G., and Papale, D.: Carbon and Nitrogen stable isotopes comparison in urban ecosystems along a Mediterranean latitudinal transect, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8622, https://doi.org/10.5194/egusphere-egu25-8622, 2025.
Accumulation of carbon and nitrogen in freshwater wetlands is affected by climatic change. Elevated temperatures and changes in precipitation patterns may lead to degradation and thinning of peat deposits resulting from higher rates of biogenic emissions of greenhouse gases. Higher atmospheric concentrations of greenhouse gases, mainly CO2, CH4, and N2O, may then accelerate global warming. A number of recent studies have addressed the relationship between increasing deposition of reactive nitrogen (Nr, predominantly ammonium and nitrate)and stability of the N stock in peat. Under high atmospheric Nr inputs, peatlands may become a net source of N, rather than a net sink. Nitrogen inventories in ombrotrophic bogs may be influenced by biological N2-fixation (BNF), the conversion of atmospheric molecular N2 by diazotrophic microorganisms to bioavailable NH4+. Because a high energy is required to break the triple bond in the N2 molecule, microbial N2-fixation may shut off when other Nr sources are available. To verify this assumption, we studied four Sphagnum-dominated peat bogs in the Czech Republic differing in Nr deposition by a factor of two. We hypothesized that the more Nr-polluted sites in the north, Velke jerabi jezero (VJ) and Cerny potok (CP), would exhibit lower BNF rates than the less polluted sites in the south, Cervene blato (CB) and Zdarecka slat (ZS). At the end of laboratory incubations of waterlogged peat in a 15N2 atmosphere (t = 2-7 days), samples of living Sphagnum exhibited an increase in d15N values from about -3 ‰ typical of all sites to 27, 259, and 266 ‰ at VJ, CP and ZS, respectively. No significant change in d15N values was recorded at CB. At VJ, the estimated BNF rates reached 840 ng N per gram Sphagnum per day. At CP and ZS these rates were about 10 times higher. Microbial analysis revealed higher activity of diazotrophs at VJ than at CB. At VJ, autotrophic cyanobacterial diazotrophs of the Nosctocaceae family comprised 4.2 %, while at CB they were below 0.1 %. Repeated sampling at CP and ZS in spring and summer showed complex temporal trends in d15N shifts during 15N2 moss incubations. At CP, the d15N shift and BNF rates were larger in summer, whereas at ZS, a larger d15N shift and higher BNF rates were observed in spring. Vertical trends in d15N values at the end of the 15N2 incubations were also complicated. Out of four peat sampling depths (0, 10, 20 and 30 cm), the highest positive d15N shifts during incubation experiments were found 20 cm below surface at CP (561 ‰; spring) and 10 cm below surface at ZS (805 ‰; summer). Collectively, our data indicate that atmospheric Nr inputs were not the main control of BNF in the studied Central European peat bogs. Also large within-site and seasonal variability in BNF was observed. Other site characteristics, such as phosphorus availability, NH4+/NO3- ratios, and moisture conditions served as important BNF drivers.
How to cite: Novak, M., Cejkova, B., Barta, J., Santruckova, H., Jackova, I., Stepanova, M., Buzek, F., Curik, J., and Veselovsky, F.: Biological nitrogen fixation at four Sphagnum-dominated peatlands in the Bohemian Massif: Spatial and temporal variability based on 15N2 moss incubation experiments and microbial community analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20120, https://doi.org/10.5194/egusphere-egu25-20120, 2025.
The composition of heavy and light carbon isotopes in tree rings is influenced by the water supply during the time the tree ring was formed due to stomata opening and therefore the ability of the tree to favor lighter isotopes, since the absorbed carbon is used for tree ring formation. This allows calculating the Intrinsic Water Use Efficiency (iWUE) as an indicator for drought stress. With about 1400 samples (tree-rings) from 15 trees from Southwestern Germany, with three individual trees of European beech, Sessile oak, Norway spruce, Scots pine and Douglas Fir respectively, we created cross-dated time series Delta13C isotope ratio and annual growth (using ring width). Our sites included both good and bad site conditions. We linked our data with climate time series for the study area as independent variables. The variety of variables allowed us to determine, to what extent independent factors influence growth and iWUE as well as interactions between the individual factors and their cumulative effects. Statistical methods and time series analyses were used to quantify the complex relationships between water availability, competitive pressure, climatic conditions, and tree growth. This approach combines various fields of terrestrial ecosystem research on individual plant level.
First results show diverse reactions to drought depending on species and location. We found growth and iWUE to be highly dependent on the climate for all species, whereas correlations between these variables imply a tree´s strategy to cope with drought conditions. The correlations differ between individual trees of the same species meaning that location may play a greater role in its significance than previously assumed, conditional on the species. Further investigations could support hydrologically focused forest management with respect to understanding the impacts of climate change on forest ecosystems.
Therefore, an upscaling approach would allow for the depiction of iWUE on catchment level. By reconstructing past environmental conditions based on tree rings, valuable information can be obtained, contributing to the development of strategies for adapting forest stands to future climate conditions. For a deeper understanding and practical conclusions, the neighborhood relationships and competition should be quantified over the entire lifetime of an analyzed tree, since not all irregularities in isotope composition were captured.
How to cite: Keutner, P., Neumann, M., and Müller, E.-V.: Combining carbon isotopes with tree ring analysis – insights into water use efficiency and drought stress , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18733, https://doi.org/10.5194/egusphere-egu25-18733, 2025.
Predicting the physiological responses of tree species under future hydroclimate scenarios is essential for understanding and mitigating the impacts of anthropogenic climate change. Here, we present our work on reconstructing the intraseasonal physiological responses of one of the longest living tree species on Earth – Great Basin bristlecone pine (Pinus longaeva, Pinaceae). This species is infamous for its tree ring chronologies that can extend beyond 5,000 years, yet the key physiological traits that will determine its ability to tolerate warmer, drier conditions in the future remain to be characterized. Moreover, the extent to which localized changes in topoclimate and seasonal water availability will impact overall growth performance and survival is also uncertain. To address this, we collected needle samples from trees along an elevation gradient near Great Basin National Park, NV, USA. Using the unique phyllotaxy of this species, we isolated annual needle samples corresponding to five distinct growth years (2018 – 2022). We then developed a novel method for quantifying intraseasonal variation in carbon isotope discrimination and intrinsic water use efficiency by using fine-scale, sequential measurements of needle δ13C in-situ via laser ablation isotope ratio mass spectrometry. We obtained an average of 25 individual δ13C measurements along the lengths of each needle sample, which were all consistent with whole-needle δ13C values measured via traditional elemental analyzer isotope ratio mass spectrometry. However, these sequential δ13C values varied in excess of 1 ‰ (VPDB) along the lengths of each needle sample, likely reflecting intraseasonal changes in water availability through the time in which individual needles were being constructed. Paired with our previous measurements of annual ring width, stomatal density, and needle length from trees at this site, we discuss how this new method provides a more comprehensive understanding of the role of intraseasonal variation in water availability on the overall physiological performance of this species in the past as well as under future hydroclimate scenarios.
How to cite: Weitz, A., Puscas, C. M., Stremtan, C. C., Salerno, A., and Bunn, A.: High-resolution insights into the seasonal physiological responses of Great Basin bristlecone pine (Pinus longaeva) through in-situ δ13C LA-IRMS, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15848, https://doi.org/10.5194/egusphere-egu25-15848, 2025.
Temporal variability of tree-ring cellulose δ2H (δ2Hring-cel) can be a unique tool for understanding tree physiology and climate. However, we do not fully understand the drivers of temporal variability in δ2Hring-cel. Investigating seasonal δ2Hring-cel in boreal forests is particularly challenging. Previous studies on intra-annual tree-ring δ18Ohave shown that tree-ring isotope variability can result from the combined but opposing effects of source water and leaf assimilates, a dynamic likely relevant for δ2Hring-cel as well. To be able to use δ2Hring-cel as a standalone and reliable bioindicator, it is important to understand the variable hydrogen isotope fractionation between source water and tree rings. Our study aimed to provide context to this variability in a natural forest by being the first study to trace intra-annual δ2Hring-cel to the δ2H of its sources and drought indices.
The δ2H of source water, leaf water and carbohydrate pools (i.e. water-soluble carbohydrates, starch) were analysed from five pine (Pinus sylvestris) trees during 2019 at Hyytiälä forest, Finland. Their δ2H were used to model continuous δ2H of source water (δ2Hsource) and leaf sugars (δ2Hleaf-sug). Modelled and measured δ2Hleaf-sug matched moderately for 2019, and the model was applied to predict δ2Hleaf-sug during 2018. Intra-annual δ2Hring-cel were analysed in these two years at a resolution of 5-10 timepoints per year, and they were allocated to xylogenetic timepoints. They were then compared to time-integrated δ2Hsource, δ2Hleaf-sug, net assimilation rate, evapotranspiration and drought indicators.
Carbohydrate δ2H was significantly different among leaves, branches and stems. δ2Hring-cel had strong time-integrated relationships to modelled δ2Hsource, net leaf assimilation rate and evapotranspiration, but the direction of their relationships was different between years. At monthly resolution, water-soluble carbohydrate δ2H measured from one year-old needles had a strong, positive relationship to δ2Hring-cel. Similarly, the modelled δ2Hleaf-sug, had strong positive relationships to δ2Hring-cel, which were robust between years. δ2Hring-cel also had strong relationships to Standardized Soil Moisture Index (SSMI).
We show that the role of δ2Hleaf-sug superseded the role of δ2Hsource in intra-annual δ2Hring-cel, because δ2Hleaf-sug had a consistent relationship to intra-annual δ2Hring-cel in both years while δ2Hsource did not. This clearly supports the growing body of evidence that δ2Hring-cel is strongly mediated by physiological processes. Our results show promise for δ2Hring-cel functioning as a bioindicator of soil drought related physiological stress signals in long-term tree ring chronologies.
How to cite: Angove, C., Lehmann, M., Saurer, M., Tang, Y., Sahlstedt, E., Young, G., Treydte, K., Szejner, P., Leppä, K., Schiestl-Aalto, P., Wiesenberg, G., and Rinne-Garmston, K.: Intra-annual tree-ring cellulose δ2H as an indicator of drought, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9771, https://doi.org/10.5194/egusphere-egu25-9771, 2025.
The hydrogen (δ²H) and oxygen (δ¹⁸O) isotopic signatures of tree rings depend on that of the environmental water sources, such as precipitation and soil water, taken up by trees (i.e., "source water"). Analyzing δ²H and δ¹⁸O of tree rings is thus a promising approach for reconstructing the spatio-temporal origins of tree water sources. However, such reconstructions remain rare, likely due to methodological challenges, including the analysis of hydrogen isotopes in tree rings and the availability of historical source water isotope data.
In this study, we present a first attempt to reconstruct the temporal origins of water used by trees during the 20th century (1901–1995) with annually resolved tree-ring δ¹⁸O time series. The reconstruction is based on a δ¹⁸O chronology of whole wood, sampled from the latewood of spruce (Picea abies) at Bettlachstock, Switzerland. Our choice of site and species reflects a conservative approach, as a transfer function linking δ¹⁸O of tree-ring cellulose to the δ¹⁸O of source waters (e.g., stem xylem water and soil solutions) was recently established over a 17-year period (2006–2022) at the same site. After accounting for the isotopic offset between whole wood and cellulose, we estimated δ¹⁸O values of soil solution (80 cm depth) and stem xylem water during the growing season (May–September) using a linear transfer function. Further, using modeled precipitation δ¹⁸O data and the estimated δ¹⁸O of soil solution and xylem water, we deduced interannual variations in the seasonal origin index (SOI) of soil solution and xylem water during the 20th century.
Our results show that the reconstructed δ¹⁸O values and SOI of xylem water were higher than those of soil solutions, suggesting a greater contribution of summer water to xylem water than to soil solutions. Interestingly, while conditions from 1900 to 1970 remained relatively stable, we observed abrupt increases in SOI for both soil solutions and stem xylem water between 1970 and 1995. These recent changes were not due to an increase in summer precipitation amount but may be linked to shifts in seasonal precipitation patterns, causing a relative increase in the contribution of summer precipitation in tree water sources.
Despite these findings, uncertainties in precipitation isotope data and transfer functions need further investigation to draw more definitive conclusions. We hope this study will stimulate discussion on the advances and limitations of using tree-ring isotopes to reconstruct historical water sources.
How to cite: Holloway-Phillips, M., Diao, H., Bernhard, F., Wieland, A., Floriancic, M., Waldner, P., Treydte, K., Saurer, M., von Arx, G., Gessler, A., Meusburger, K., and Lehmann, M.: Tree-ring isotope-based 20th century reconstructions of the seasonal origin of water sourced by trees: Advances and limitations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12734, https://doi.org/10.5194/egusphere-egu25-12734, 2025.
Marine ecosystems play a critical role in global photosynthetic carbon fixation, with approximately 5.36 Pg C exported annually via the biological pump. Macroalgae alone sequester around 200 million tons of CO₂ annually, though these estimations are largely based on indirect calculations. Hydrogen isotope (δ²H) analyses offer a promising avenue to refine such estimates while advancing our understanding of macroalgal carbon and energy metabolism.
Stable isotope studies have been instrumental in ecological and biogeochemical research, yet the application of δ²H analyses to marine algae remains limited. Most prior studies have focused on salinity-driven δ²H variations in algae, overlooking the potential of δ²H to reveal key biochemical processes. Recent findings suggest that δ²H values of organic molecules are significantly influenced by biosynthetic fractionation (²H-εbio), governed by the interplay between photosynthetic (²H-ελ) and post-photosynthetic (²H-εΗ) processes. This metabolic signal, previously observed in terrestrial plants, is strongly modulated by the photosynthetic carbohydrate supply rate, impacting δ²H variability in organic compounds.
The giant kelp Macrocystis pyrifera provides an ideal model system to investigate these processes in marine environments. Unlike terrestrial plants, M. pyrifera offers a simplified isotopic system due to: (i) access to water with stable δ²H values, (ii) exclusion of evaporative ²H-fractionation, and (iii) a primitive vascular system that minimizes isotopic exchange across its structure. These unique features allow us to isolate and examine the variability of ²H-ελ under different light conditions, shedding light on the metabolic processes underlying δ²H variability in marine photoautotrophs.
This study highlights the potential of δ²H analyses to bridge the gap between isotopic and biochemical research in marine systems. By focusing on M. pyrifera, we aim to provide critical insights into the drivers of δ²H variability and their broader implications for understanding marine carbon dynamics and the role of macroalgae in global biogeochemical cycles. This work lays the groundwork for advancing isotopic methodologies and applying them to ecological and palaeoenvironmental studies in marine ecosystems.
How to cite: Cormier, M.-A., Steller, D., Salik, M. A., Lehmann, M., Al Sid Cheikh, M., and Gagnon, P.: Unravelling Hydrogen Isotope Fractionation in Marine Macroalgae: Insights from Macrocystis pyrifera, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18571, https://doi.org/10.5194/egusphere-egu25-18571, 2025.
Double carbonates of the norsethite-family (Ba(Mg,Mn,Fe)[CO3]2) are used as crystal chemical and geochemical analogues for the prominent rock-forming mineral dolomite (CaMg[CO3]2) and the less common kutnahorite (CaMn[CO3]2). Selected family members have been observed to occur in low- and high-temperature natural systems, like Baltic Sea sediments or different types of ore deposits. For most of the norsethite-members, neither the thermodynamic nor the reaction kinetic properties are well constrained or even known, so far.
In the present study, the dissolution behaviour of double and triple carbonate members of the norsethite family were dissolved in CO2-saturated solutions at 25°C and 1 atm total pressure. The carbonates were synthesized at high P and T and characterized as described by Liang et al. (2021, 2025) and Böttcher et al. (2022). Free-drift batch-type reactors were used. Both, the congruent and incongruent parts of the dissolution process were investigated and the partitioning of metals and stable carbon isotopes was followed. At the end of the experiment, carbonate solid-solutions were precipitated by letting CO2 to degas.
The dissolution in aqueous solutions was found to be initially congruent with respect to metal stoichiometry. The solution composition was interpreted using PHREEQC. Extrapolation of experimental congruent reaction parts give the solubility product and the free energy of formation of the respective carbonate and the time-dependent reaction path allows for the extraction of dissolution kinetic parameters. The development of 13C contents of dissolved inorganic carbon represent an experimental verification of carbonate dissolution in a system open with respect to a CO2 gas phase (sensu Garrels & Christ, 1965 and Deines et al., 1974).
These new experimental results form a base to include these phases into modelling codes for natural or underground CO2-storage systems.
How to cite: Böttcher, M. E., Haršányi, A. S., Dellwig, O., Grathoff, G., Schmiedinger, I., and Liang, W.: Thermodynamic stability and reactivity of dolomite-analogues from the norsethite-family: Carbon isotope and metal release during experimental dissolution at 25°C and 1 atm total pressure, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12689, https://doi.org/10.5194/egusphere-egu25-12689, 2025.
Biochar as an alternative filter to activated charcoal was tested for the removal of tetrachloroethene (PCE) and Naphthalene (NAP) from contaminated groundwater by means of sorption and biodegradation in batch and column experiments. Microbial communities were extracted from the aqueous and solid phases and analysed using 16S rRNA gene amplicon sequencing. Microbial biomass and its carbon isotope composition were determined using microbial phospholipid fatty acids (13C-PLFA) analysis. This approach enabled a quantitative and functional observation of the microbial community besides identifying the relevant bacteria.
Molecular biological analyses of the PCE experiments confirmed that organo-halide respiration bacteria (OHRB) established after inoculation both in the batch and throughout the columns. PLFA analysis revealed that microorganisms and also those groups that can be assigned to the PCE-degrading organisms preferentially colonize biochar, while activated charcoal is avoided possibly due to the higher PCE sorption capacity of the activated charcoal and hence lower bioavailability of PCE. The carbon isotope value of the microorganisms (13C PLFA) indicates the use of biochar as a carbon source and/or the presence of strongly isotope-fractionating biochemical processes such as methanogenesis / methane oxidation. The microbial communities were influenced by the factor char and its physical/chemical properties. It is therefore advisable to choose the filter material not only on the basis of the sorption capacity, but above all on the synergy effects that leads to a permanently active microbial community and an extension of the filter life due to the continuous and complete degradation.
The living microbial biomass in the aerobic naphthalene columns was a factor of 4 higher than in the anaerobic PCE columns. The distribution of microorganisms was similar to that in the PCE degradation experiments; i.e. greater colonization of the biochar filters compared to the activated charcoal filters. Furthermore, the microorganisms responded to naphthalene supply with increased microbial biomass and naphthalene incorporation. Once the naphthalene addition was stopped, the microorganisms were able to convert sorbed naphthalene (in the presence of ethanol). This ability is a strong indicator of the sustainability and self-cleaning potential of the colonized biochars. However, high levels of colonization and biofilm development may increase the risk of clogging negatively impacting filter system sustainability. The insights gained from this study are crucial for advancing global efforts in groundwater remediation and sustainable environmental management.
How to cite: Watzinger, A., Leitner, S., Stumpp, C., Soja, G., and Keiblinger, K.: Carbon stable isotope analysis in groundwater remediation – The role of microbial biofilm communities and biochar in PCE and NAP degradation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10869, https://doi.org/10.5194/egusphere-egu25-10869, 2025.
Mountain grasslands are currently experiencing significant changes in land use and climate, with an increased frequency of extreme droughts anticipated in the near future. Understanding the drought responses of carbon (C) allocation—a critical process in the C cycle—remains limited. In this study, we conducted an experimental summer drought on traditionally managed hay meadows and traced the fate of recent assimilates into leaf and root sucrose. We applied 13CO2 pulses at peak drought and tracked the labeled carbon into individual positions of glucose using liquid chromatography coupled with ultrahigh-resolution mass spectrometry.
Our findings revealed that drought conditions decreased total C uptake and led to a reduction in above-ground carbohydrate storage pools. The turnover of the leaf sugar pool, determined through position-specific carbon enrichment, was significantly reduced compared to the control treatment. Interestingly, below-ground C allocation to root sucrose was enhanced by drought, but the position-specific carbon enrichment was less affected, suggesting the involvement of other carbon sources.
These results demonstrate that position-specific isotope distribution provides a novel understanding of plant carbon allocation, offering new insights into the resilience and adaptation of mountain grasslands to drought stress.
How to cite: Gleixner, G.: Unveiling Carbon Allocation Dynamics in Mountain Grasslands Under Drought Stress Using Position-Specific Isotope Analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20366, https://doi.org/10.5194/egusphere-egu25-20366, 2025.
Soil acidification caused by atmospheric sulfur (S) deposition may have a significant impact on plant carbon (C) assimilation and allocation, thereby altering soil organic C (SOC) dynamics. However, it remains largely unknown for how plants allocate photosynthetic C among belowground functional sinks and whether they can leverage these limited C resources to adapt abiotic stresses. We conducted a 13CO2 pulse-labelling experiment in a grassland field to investigate the effects of simulated soil acidification by S addition on photosynthetic C allocation and analyzed the trade-offs among plant belowground functional sinks. We also elucidated the contribution of belowground C allocation to SOC formation. We found that soil acidification decreased the absolute amount of excess 13C allocated to both shoots and soils, possibly due to less photosynthetic C assimilation and aboveground biomass production. In contrast, S addition partially increased the excess 13C allocated to roots, indicating that a greater proportion of C was allocated to root biomass construction to combat acidification stress. The excess 13C in roots related negatively to soil 13C but positively to both root biomass and non-structural carbohydrates (NSC), suggesting a possible trade-off relationship in belowground 13C allocation between rhizodeposition and root growth. Our research confirms that under soil acidification stress, less photosynthetic C in roots was converted into rhizodeposition C entering the soil, while more was invested in root growth, respiration, and storage to improve their survival and ability to resist environmental stress. Although with lower excess 13C allocated to both shoots and soils, soil acidification had no effect on SOC stocks, possibly due to less SOC decomposition accompanied with suppressed microbial activity. These results provide an invaluable insight into plant C allocation strategy and its impact on belowground C dynamics under soil acidification stress.
How to cite: Shang, Y., Wang, R., and Jiang, Y.: Belowground carbon allocation response to soil acidification stress in a meadow grassland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4195, https://doi.org/10.5194/egusphere-egu25-4195, 2025.
Previous nitrogen isotope studies of bulk proteins extracted from ancient Atlantic cod (Gadus morhua) tissues document a 1-2‰ decrease in δ15N values over the last couple of centuries (Harris, 2011; Lueders-Dumont et al., 2018). Due to the nature of the nitrogen isotope signal in bulk proteins, this isotopic shift may be attributed to a decrease in trophic level and/or a change in baseline nitrogen in the Gulf of Maine over this time period. Here, we analyze the δ15N composition of individual amino acids from ancient cod bone collagen to tease out the relative importance of shifts in trophic level vs baseline nitrogen sources to cod diets through time. Preliminary data indicate that δ15N values of phenylalanine (“source” amino acid) extracted from cod bone collagen became more depleted in δ15N over the last 500 years and into the modern record. These shifts in δ15NPhe are in agreement with those found in δ15NPhe of deep-sea corals (Sherwood et al., 2011) and bivalves (Whitney et al., 2019) from the Gulf of Maine over the last 100 years. The fact that similar trends are seen in three different species occupying different ecological niches suggests the shift in source nitrogen may reflect broad changes in hydrographic conditions in the Gulf of Maine. More work is needed to corroborate these preliminary findings and is currently underway.
How to cite: Turtle, S., Johnson, B., and Dostie, P.: δ15N of Amino Acids in Ancient Cod Bone Collagen Track Shifts in Baseline Nitrogen & Cod Trophic Levels in the Gulf of Maine for the Past 4,400 years, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14238, https://doi.org/10.5194/egusphere-egu25-14238, 2025.
Nitrous oxide (N2O) is a very potent greenhouse gas, and it is also involved in stratospheric ozone destruction. It is primarily produced by microbial processes such as nitrification and denitrification. Emissions of N2O from permafrost-affected soils have only recently been discovered but are of particular concern as climate change accelerates permafrost thaw and also N2O production. Nevertheless, mechanisms underlaying N2O emissions form permafrost-affected soils remain largely unresolved. Therefore, better understanding of N2O production and consumption processes is urgently needed, and isotope tools are critical for advancing this knowledge.
Advances in isotopic laser spectroscopy, such as cavity ring-down spectroscopy (CRDS), have enabled real-time quantification of N2O isotopic ratios, offering a powerful tool to study isotope signals of N2O and microbial pathways. Here, an incubation experiment was conducted with soils collected from a permafrost peatland (bare and vegetated). Each of them was subjected to variable water holding capacities (WHC) ranging from 20% to 100%, since water availability is a primary controlling factor on N2O fluxes from soils. Incubations took place at the standard temperature of 15°C.
Additionally, the study compared three methods for determining the isotopic signature of N2O sources. In the first method, discrete gas samples were collected into glass vials over the incubation period and later analyzed offline using the Keeling plot to derive the isotopic composition. For the second method, endpoint sampling, gas samples were collected at the end of the incubation into gas bags and analyzed to directly determine the isotopic signature of the accumulated N2O. The third method involved real-time isotopic measurements, connected directly to the incubation bottles via a multiplexer. The inverse Keeling plot was then used to derive the isotopic signature. All isotope analysis of N2O were done using the Picarro G5131-i isotopic N2O analyzer.
Reliable isotopic data could only be obtained when the N2O flux flux exceeded the equivalent to 3 ppb per hour, which was rarely achieved. In the few cases, where fluxes were higher, the isotope signature of N2O indicated that denitrification was the main pathway at all moisture levels. The traditional Keeling plot approach was the most reliable method to determine the isotope source, but the inverse Keeling plot approach can be developed and offers, similar to the gas bag method, practical advantages. We discuss pros and cons of each method and ways to improve precision and reliability of the isotopic measurements in case of high and low fluxes.
How to cite: Znamínko, M., Kohl, L., Trubnikova, T., Bahn, M., and Biasi, C.: Isotopic composition of N2O emissions from a permafrost peatland: a laboratory study using three different analytical techniques , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19824, https://doi.org/10.5194/egusphere-egu25-19824, 2025.
The western Black Sea Shelf where the Danube is discharging into the Black Sea is especially sensitive to river-induced eutrophication, which peaked in the 1980s and 1990s due to human-induced nutrient input and is decreasing since the mid-1990s due to ongoing mitigation measures. The scarcity of information on Danube nutrient loads prior to the 1960s complicates the assessment of earlier nutrient input and thus to define pristine conditions to provide a reference for nutrient reduction goals. In this study, we aimed to trace modern and historical nitrogen sources to the western Black Sea Shelf during the last ~5,000 years with special focus on the past 100 years, using sedimentary records of TOC, TIC, nitrogen, and δ15N.
Our results demonstrate that the balance of riverine nitrogen discharge into the Black Sea on the one hand, and nitrogen fixation in the pelagic on the other hand is generally determined by climate effects. Specifically, this balance of riverine N input and N fixation is not only controlled by the amount of nutrients discharged by rivers, but also by the freshwater itself, which controls the intensity of thermohaline stratification and thereby the intensity of nutrient recycling from the deep basin back into the euphotic epipelagic. Our results show a gradient from the nearshore sediment directly at the Danube Delta, where riverine N is dominant to offshore sediment in 80 m water depth, where pelagic N fixation was dominant in the past. Our results based on stable isotopes also demonstrate the increased deposition of nitrogen from human activities in all stations across the shelf and the concomitant changes in deposition rates of organic matter as indication for perturbations in the epipelagic community due to the human-induced eutrophication. Finally, our stable isotope data indicate that human-induced eutrophication can be traced back to the 12th century AD, which raises the question which point in time is a feasible reference for nutrient reduction goals as the Danube was not pristine since at least 800 years.
How to cite: Neumann, A., Dähnke, K., and Sanders, T.: Reconstructing changes in nitrogen input to the Danube-influenced Black Sea Shelf during the Holocene, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19649, https://doi.org/10.5194/egusphere-egu25-19649, 2025.
Identifying and quantifying sources and cycling of nitrogen is important for understanding not only aquatic ecosystems but also planning water resource management, mitigating urban and agricultural pollution, and optimizing government policy. Stable isotopes of dissolved nitrate and nitrite (δ15N, δ18O and δ17O) have been useful in distinguishing between the diverse nitrogen sources and sinks and help understand large scale global ocean processes as well as revealing major changes in agricultural land use and urbanization.
Despite the strength of dissolved nitrate and nitrite stable isotope analysis, the strong barrier for uptake using the favored contemporary methods (bacterial denitrifier and Cd-azide reaction) due to the laborious multi-step methods, maintenance of anerobic bacterial cultures and use of highly toxic chemicals has limited the analysis to highly specialized laboratories. We evaluate the performance of the Elementar EnvirovisION using the new Titanium (III) reduction method (Altabet et al., 2019) for one step conversion of nitrate into N2O for IRMS analysis.
The EnvirovisION has been developed for high performance analysis of CO2, N2O and CH4 and dissolved nitrate. The system has the capacity to be rapidly customized for specific needs with options for dual GC columns supporting the Weigand ‘heart-cut’ N2O method (Weigand et al., 2016) and sequential N2 and N2O analysis from a single atmospheric sample.
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 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11009, https://doi.org/10.5194/egusphere-egu25-11009, 2025.
Cavity ringdown spectroscopy (CRDS) is a well-established technique used for measuring a large variety of gaseous species which are known to absorb light radiation at specific wavelengths, e.g., CO2, CH2, C2H4, water vapors, etc. In the field of environmental and geochemical research, CRDS is commonly used to determine the isotopic ratios of light isotope families, like hydrogen, carbon, oxygen, etc. Similarly, laser ablation (LA) is a solid sample introduction method which is used in conjunction with a variery of spectrometric and spectroscopic techniques and works by focusing a laser beam (of various wavelengths, pulse width and energy) onto the sample surface to convert minute amounts of the solid into fine aerosol, or gaseous phase.
Hyphenating the two techniques is a recent addition to the earth sciences tool set [1,2]. While still in its infancy, LA CRDS is a promising technique for fast, highly accurate and spatially resolved stable isotope measurements. In this contribution we look at the figures of merit of the technique when measuring δ13C, comparing different types of lasers (pulsed nanosecond solid state 213 nm wavelength, and continuously emitting infrared CO2 laser) on both organic (wood, cellulose, plastics, and plant derived material) as well as inorganic matrices (soils, CaCO3) which are critical proxies for environmental and climatic studies. We also investigate the impact of increased spatial resolution (i.e., tens of micron spot sizes) on the accuracy and precision of the analysis.
[1] Stremtan, C., Wozniak, J., Puscas, C. M., and Tamas, T.: Laser Ablation – Cavity Ring Down Spectrometry, a new method for the in-situ analysis of δ13C of organic and inorganic carbonates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17192, https://doi.org/10.5194/egusphere-egu24-17192, 2024.
[2] E. Malegiannaki, P. Bohleber, D. Zannoni, C. Stremtan, A. Petteni, B. Stenni, C. Barbante, B.M. Vinther, V. Gkinis, Towards high-resolution water isotope analysis in ice cores using laser ablation - cavity ring-down spectroscopy, Anal. (2024) 5843–5855. https://doi.org/10.1039/d4an01054j.
How to cite: Stremtan, C., Wožniak, J., Pușcaș, M., and Hofmann, M.: Spatially resolved δ13C measurements of solid samples via Laser Ablation Cavity Ringdown Spectroscopy (LA CRDS) – a new tool for environmental research, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14870, https://doi.org/10.5194/egusphere-egu25-14870, 2025.
Cavity Ring-Down Spectroscopy (CRDS) has emerged as a critical tool for measuring water isotopes in climate, environmental, and hydrological research. Key features of CRDS analyzers, such as the L2130-i and L2140-i, include high precision, minimal drift, and field deployability. However, the precision and accuracy requirements of water isotope measurements vary by application. For example, paleoclimate studies demand the highest precision (on par with IRMS), while other applications prioritize rapid analysis of large sample sets over precision.
In this study, we present updated methodological recommendations for water isotope analysis using CRDS, tailored to different precision, accuracy, and throughput requirements. We evaluated a range of analytical and data processing methods using the WICO 2024 sample set. This set, provided by the IAEA, includes six water samples with δ¹⁸O values ranging from -22‰ to +1‰ and δ²H values spanning from -163‰ to +17‰. The samples were analyzed on a Picarro L2130-i instrument in both Standard and Express mode [1]. Data were processed using the analyzer's built-in ChemCorrect software and the open-source FLIIMP software [2], which enables advanced data correction techniques such as drift and memory correction.
Our findings highlight the trade-offs between precision and throughput for different use cases and underscore the importance of selecting appropriate analysis and processing methods based on specific research needs.
References
[1] Galili, N. et al. (2025). Cavity Ring-Down Spectroscopy Performance and Procedures for High-Throughput δ¹⁸O and δ²H Measurement in Water Using “Express” Mode. Applied Spectroscopy.
[2] Sodemann, H. et al. (2023). FLIIMP - a community software for the processing, calibration, and reporting of liquid water isotope measurements on cavity ring-down spectrometers. MethodsX, 11, 102297.
How to cite: Hofmann, M., Woźniak, J., and Drori, K.: Methodological Recommendations for Water Isotope Measurements Using CRDS: Balancing Throughput and Precision, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13667, https://doi.org/10.5194/egusphere-egu25-13667, 2025.
