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BG2.1

EDI
Application of Stable Isotopes in Biogeosciences

This session is open to all contributions in biogeochemistry and ecology where stable isotope techniques are used as analytical tools, with foci both on stable isotopes of light elements (CHONS …) and new systems (clumped and metal isotopes). We welcome studies from both terrestrial and aquatic (including marine) environments as well as methodological, experimental and theoretical studies that introduce new approaches or techniques (including natural abundance work, labelling studies, multi-isotope approaches).

Co-organized by GMPV1/SSS5, co-sponsored by EAG
Convener: Michael E. Böttcher | Co-conveners: Kirstin Dähnke, Gerd Gleixner, Anne-Désirée Schmitt
Presentations
| Tue, 24 May, 13:20–15:45 (CEST)
 
Room 2.15

Tue, 24 May, 13:20–14:50

Chairpersons: Michael E. Böttcher, Gerd Gleixner, Kirstin Dähnke

13:20–13:27
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EGU22-555
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ECS
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Fulmati Ram et al.

The large difference in the degree of discrimination of stable carbon isotopes (δ13C) between C3 and C4 plants has been widely used to retrieve the palaeoenvironmental condition by analysing δ13C of bulk sedimentary organic matter (SOM). Underlying in these studies was the assumption that carbon retains the pristine signature of its photosynthetic pathway during later stages of decomposition in soil and sediments. However, there remains considerable uncertainty associated with studies of SOM, especially those from marginal marine environments. The probable presence of organic matter derived from varied sources, e.g., marine sources, terrestrial C3, and C4 plants make reconstruction of the paleo-environment difficult using δ13CSOM as a stand-alone tool. The sediments also undergo different stages of microbial decomposition, which can also alter the original organic carbon source signatures. Hence a robust method needs to be developed for identifying the specific phase that can withstand the alteration of the original δ13C of SOM. In the present study, we attempted to develop a simple means for identifying a robust oxidation-resistant organic carbon (OROC) phase for bulk isotopic analysis. The data along with the straight-chain n-alkane lipid compound were used to retrieve the Holocene (last 10 Kyr) paleo-environment from a sediment core raised from the Rann of Kachchh, western India. One purpose was to see if the climate had any role in the growth and collapse of an Indus Valley Civilisation (IVC) metropolis Dholavira, a UNESCO heritage site in the vicinity of the core location.

The sediment samples were chemically treated over different oxidation times (24 to 240 hours) following the commonly used dichromate oxidation method (0.1M K2Cr2O7/ 2M H2SO4, 60 ⁰C). No more oxidation loss was observed between pre-and post-treatment of SOM after 72 hours suggesting that the remaining organic carbon represents the most resistant phase. The isotopic composition (δ13COROC)would thus represent the original isotopic signature of the refractory organic carbon. In the specific sediment core, the δ13COROC values showed no significant difference from the δ13CSOM exhibiting a good down-depth correlation (R2 >0.8). The δ13C data of the core top sediment along with the modern plants in the Rann suggest that local vegetation dominantly controlled the organic matter composition. The efficacy of the method was also tested by analysing δ13COROC and δ13CSOM (δ13CSOM ranged from -18.2 ‰ to -20.6 ‰) in ten marine sediment samples from the northern Indian Ocean indicating preservation of marine organic matters after the oxidation experiment. The sediment core data suggest a mixture of terrestrial C3, C4, and marine organic matter throughout the Holocene period. A significant increase in the concentration of C4 photosynthesizing plant groups around 4.2 Kyr is observed and most likely is an expression of enhanced aridity due to the Meghalayan age drought that pervaded the Indian subcontinent and beyond. This is fascinating as the drought has earlier been linked to the collapse of the IVC based on other proxies.

How to cite: Ram, F., Thakkar, M., Chauhan, G., Bhusan, R., Juyal, N., and Sarkar, A.: Carbon isotope and organic geochemistry of the Holocene sediments from Rann of Kachchh: implications to the preservation of organic matter and climate during the Indus Valley Civilisation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-555, https://doi.org/10.5194/egusphere-egu22-555, 2022.

13:27–13:34
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EGU22-1056
Ales Vanek et al.

Vertical profiles of Tl, Pb and Zn concentrations and Tl and Pb isotopic ratios in a contaminated peatland/fen (Wolbrom, Poland) were studied to address questions regarding (i) potential long-term immobility of Tl in a peat profile, and (ii) a possible link in Tl isotopic signatures between a Tl source and a peat sample. Both prerequisites are required for using peatlands as archives of atmospheric Tl deposition and Tl isotopic ratios as a source proxy. We demonstrate that Tl is an immobile element in peat with a conservative pattern synonymous to that of Pb, and in contrast to Zn. However, the peat Tl record was more affected by geogenic source(s), as inferred from the calculated element enrichments. The finding further implies that Tl was largely absent from the pre-industrial emissions (>~250 years BP). The measured variations in Tl isotopic ratios in respective peat samples suggest a consistency with anthropogenic Tl (ε205Tl between ~ -3 and −4), as well as with background Tl isotopic values in the study area (ε205Tl between ~0 and −1), in line with detected 206Pb/207Pb ratios (1.16–1.19). Therefore, we propose that peatlands can be used for monitoring trends in Tl deposition and that Tl isotopic ratios can serve to distinguish its origin(s). However, given that the studied fen has a particularly complicated geochemistry (attributed to significant environmental changes in its history), it seems that ombrotrophic peatlands could be better suited for this type of Tl research.

How to cite: Vanek, A., Vejvodova, K., Mihaljevic, M., Ettler, V., Penizek, V., Trubac, J., Sutkowska, K., Teper, L., Golias, V., and Vankova, M.: Thallium and lead variations in a contaminated peatland: An isotopic study from a mining/smelting area, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1056, https://doi.org/10.5194/egusphere-egu22-1056, 2022.

13:41–13:48
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EGU22-2352
Joachim Mohn et al.

Nitrous oxide (N2O) dominates greenhouse gas emissions in wastewater treatment plants (WWTPs). Formation of N2O occurs during biological nitrogen removal, involves multiple microbial pathways, and is typically very dynamic. Consequently, N2O mitigation strategies require an improved understanding of nitrogen transformation pathways and their modulating controls. Analyses of the nitrogen (N) and oxygen (O) isotopic composition of N2O and its substrates at natural abundance have been shown to provide valuable information on formation and reduction pathways in laboratory settings, but have never been applied to full-scale WWTPs.

Here we show that N-species isotope ratio measurements at natural abundance level, combined with long-term N2O monitoring, allow identification of the N2O production pathways in a full-scale plug-flow WWTP (Hofen, Switzerland). The proposed approach can also be applied to other activated sludge systems. Heterotrophic denitrification appears as the main N2O production pathway under all tested process conditions, while nitrifier denitrification was less important, and more variable. N2O production by hydroxylamine oxidation was not observed. Fractional N2O elimination by reduction to dinitrogen (N2) during anoxic conditions was clearly indicated by a concomitant increase in SP, δ18O(N2O) and δ15N(N2O). The extent of N2O reduction correlated with the availability of dissolved inorganic N and organic substrates, which explains the link between diurnal N2O emission dynamics and organic substrate fluctuations. Consequently, dosing ammonium-rich reject water under low-organic-substrate conditions is unfavourable, as it is very likely to cause high net N2O emissions.

Our results demonstrate that monitoring of the N2O isotopic composition holds a high potential to disentangle N2O formation mechanisms in engineered systems, such as full-scale WWTP. Our study serves as a starting point for advanced campaigns in the future combining isotopic technologies in WWTP with complementary approaches, such as mathematical modelling of N2O formation or microbial assays to develop efficient N2O mitigation strategies.

How to cite: Mohn, J., Gruber, W., Magyar, P., Zeyer, K., von Känel, L., Morgenroth, E., Lehmann, M. F., Braun, D., and Joss, A.: Tracing N2O formation in full-scale wastewater treatment with natural abundance isotopes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2352, https://doi.org/10.5194/egusphere-egu22-2352, 2022.

13:48–13:55
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EGU22-2569
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ECS
Chirantan Pramanik and Itay Halevy

Impurities in CaCO3 minerals, present as ion substitutions (e.g., Mg2+ for Ca2+, SO42- for CO32-), are common and known to affect the fractionation of isotopes between the mineral and its parent fluid (e.g., the carbonate–water O isotope fractionation, the CAS–SO42- S isotope fractionation). The difficulty in achieving isotopic equilibrium during experimental precipitation of carbonate minerals motivates the calculation of such effects by ab initio DFT methods. However, even a single substitution in a model lattice composed of as many atoms as computationally possible results in impurity concentrations that are much higher than those typical of most natural and experimental samples. For example, calculations of the CAS–SO42- S isotope fractionation were performed at CAS concentrations of 59,000 and 30,000 ppm in calcite and aragonite, respectively, ∼threefold higher than the highest natural concentrations. The calculations yielded a CAS–SO42- S isotope fractionation of 3.6 and 4.5‰ in calcite and aragonite (at 25°C), respectively, at odds with experimental values of ∼1‰ at the highest CAS concentrations in both calcite and aragonite. It is unknown whether the disagreement arises from the much higher CAS concentration in the calculations than in the experiments.

To overcome these computational limitations, we developed an approach in which the fractionation in the computationally largest possible “doped” model lattice is combined with the fractionation in a “pure” lattice. Using this approach, we determined the dependence of mineral–solution isotopic fractionation on the concentration of SO42- and Mg2+ impurities in CaCO3. The doped and pure lattices were modeled using ab initio methods implemented in the PWscf code of the Quantum ESPRESSO package, using periodic boundary conditions and the PBE exchange-correlation functional. Trigonal calcite and orthorhombic aragonite unit cells were used to form supercells of various dimensions containing 10 to 540 atoms. The ionic cores were described by ultrasoft pseudopotential and the Brillouin zone sampling was restricted to a single k-point for large supercells. Doped supercells contained a single SO42- or Mg2+, and pure cells contained none. We calculated the defect formation energies and observed that the spurious effect from the impurities in imaginary supercells is minimized for a supercell size of ∼40 atoms or more. Phonon frequencies were calculated for various isotopic combinations using the PHonon code, and the frequencies were used to calculate the isotopic fractionation using the reduced partition function theory. The dependence of the bulk mineral–solution isotopic fractionation on the impurity concentration was then calculated as a weighted average of a single doped supercell and an arbitrary number of pure supercells. We will present the impurity dependence of the mineral–solution fractionation of O, C, Ca, Mg, and S isotopes and the carbonate clumped isotope composition of the CaCO3, and compare to observations, where available. We suggest that a similar approach can be used to study the effect of any impurity, at an arbitrary concentration, on any isotopic system, in any mineral.

How to cite: Pramanik, C. and Halevy, I.: Ab initio calculations of the isotopic effects of sulfate and Mg impurities in carbonate minerals, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2569, https://doi.org/10.5194/egusphere-egu22-2569, 2022.

13:55–14:02
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EGU22-3715
Catia Milene Ehlert von Ahn et al.

The impact of submarine groundwater discharge (SGD) on coastal biogeochemistry is currently under intense investigation. SGD can impact diagenesis and in general act as a potential source of elements, especially dissolved carbon, to coastal surface waters. However, qualitative and quantitative assessments of SGD are challenging since it requires the identification of suitable geochemical tracers for the complex hydrological and biogeochemical processes in the subterranean estuary. In this communication, we report on combined investigations carried out in Königshafen Bay (North Frisian island Sylt, Germany), a tidal area in the eastern North Sea. Sampling encompassed vertical porewater gradients, and surface waters collected through transects in the bay, and in tidal cycles at the outlet of the bay. Potential surface and subterrestrial freshwater endmembers are used to assess the results. Besides major and minor elements, this study focuses on the stable carbon isotope composition of dissolved inorganic carbon (DIC) and the activity of radium (Ra) isotopes. Our main aim is to characterize the interaction between diagenesis and the composition of SGD, as well as the resulting impact on the carbon system of the water column, and, via tidal exchange extended to the coastal North Sea. Porewaters showed usually an increase of isotopically light DIC with depth and a freshening already in the top 50 cmbsf at some sites. This indicates that both, carbon diagenesis and mixing of seawater with fresh groundwaters at depth impact the distribution of DIC. The activities of the short-living Ra isotope (224Raex) were higher in the bay compared to the open North Sea. Porewater activities were up to 30 times higher than in the bay’s surface waters with a maximum development at intermediate salinities. In the water column at the outlet of the bay, 224Raex and 223Ra showed maximum activities during low tide as a consequence of the highest contribution of waters in contact with the sediments of the bay. Moreover, due to the high hydraulic gradient developed during low tide more contribution from potential endmembers enriched in Ra can be expected. Further work is on the way to quantify the impact of SGD on the tidal basin and the indirect role for the North Sea carbon system on different temporal and spatial scales.

 The investigations are supported by the DFG-project KiSNet, the BMBF project COOLSTYLE (CARBOSTORE), the DAAD, the DFG RTG Baltic TRANSCOAST, and the Leibniz IOW.

How to cite: Ehlert von Ahn, C. M., Jenner, A.-K., Scholten, J., Schell, A., Schmiedinger, I., Hoffmann, J., Roeser, P., Nantke, C., and Böttcher, M.: Isotope hydrogeochemistry investigations (223,224Ra, DI13C) on submarine groundwater discharge in a tidal bay (eastern North Sea), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3715, https://doi.org/10.5194/egusphere-egu22-3715, 2022.

14:02–14:09
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EGU22-4462
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ECS
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Kateřina Vejvodová et al.

The purpose of this study was to investigate the key geochemical and mineralogical factors that could affect the fractionation of stable thallium (Tl) isotopes in soil. A set of grassland soil samples enriched in geogenic Tl in combination with selected Tl-containing mineral materials from the Czech Republic (Kluky) were investigated for this purpose. A combination of X-ray diffraction analysis (XRD), chemical extractions and stable isotope analysis were used to understand the behaviour of Tl and its isotope systematics within the soil profile. The results demonstrate significant incorporation of Tl in pedogenic Mn-oxide, which led to a large accumulation of the heavy 205Tl isotope (~+14 ε205Tl units), presumably resulting from continuous redox reactions with Mn-oxides and systematic accumulation of heavy isotope fraction onto the oxide surface(s). Consequently, we concluded that the Mn-oxide-controlled Tl uptake is the primary cause of the observed 205Tl enrichment in the middle profile zone, at the A/B soil horizon interface, with up to +4 of ε205Tl. Furthermore, our results displayed a clear relationship between the Tl isotopic fractionation degree and the Mn-oxide soil concentration (R2 = 0.6), as derived from the oxalate-extractable data. A combination of soil and mineralogical considerations suggests that 205Tl enrichment in the soil samples is also partly due to the Tl present in micaceous clay minerals, mainly illite, which is the predominant pedogenic Tl host phase. Supported by our previous results, this Tl behaviour can be inferred from systematic Mn-oxide degradation and the associated Tl (enriched in 205Tl) cycling in the studied soils and therefore, presumably in the redoximorphic soils in general.

How to cite: Vejvodová, K., Vaněk, A., Mihaljevič, M., Ettler, V., Trubač, J., Vaňková, M., Drahota, P., Vokurková, P., Penížek, V., Zádorová, T., Tejnecký, V., Pavlů, L., and Drábek, O.: The key controls of thallium isotopic fractionation in soil, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4462, https://doi.org/10.5194/egusphere-egu22-4462, 2022.

14:09–14:16
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EGU22-4830
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ECS
Eugeniusz Pronin et al.

The soft-water lake vegetation is sensitive to changes in water quality, especially pH and nutrient concentration. Furthermore, little is known about the biogeochemistry of those types of water bodies. Therefore, to recognize the relationship between the aquatic plants and the co-created sediments, we applied in our study the analysis of stable carbon and nitrogen isotopic composition (δ13C and δ15N) of organic matter of ten characteristic plants for soft-water lakes and sediments on which they have grown. We investigated physicochemical parameters of two types of water: one from the immediate surroundings of plants and the second type collected just above or directly from sediment (if they were more organic and looser). In the middle of the vegetation season (June 2020), the studies were performed on 14 soft-water lakes along a pH gradient (from 4.78 to 9.21). We found a high positive relationship between δ13C values of plants and sediments (Spearman rank correlations r= 0.69; N=85) and moderate positive relationships between δ15N values of plants and sediments (r= 0.31; N=85). Both for δ13C and δ15N, the variability of plants isotopic values was higher in plants organic matter than in sediments (for plants; δ13C from -33.76‰ to -9.93‰ and δ15N from -5.49‰ to 5.95‰; for sediments δ13C from -30.13‰ to -13.60‰ and δ15N from -2.92‰ to 4.82‰). In the case of Lobelia dortmanna, Fontinalis antipyretica, Luronium natans and Isoëtes lacustris δ13C values were higher in organic matter of the sediments than in investigated aquatic plants. On the other hand, especially samples for Elodea canadensis and Myriophyllum alterniflorum had opposite patterns, where values of δ13C were much higher in plants. The δ15N values of plants were lower than those reported for the deposits, and this pattern was more constant, with two exceptions recorded for Luronium natans and Chara globularis. Comparing the physicochemical parameters of surrounding and sediments waters, we found only high differences in total nitrogen concentration (TN) where higher concentration was reported in sediment water. In addition, the distribution of environmental variables for both water from anong plants and sedimentary water (Principal Components Analyzes - PCA's) indicates a higher relationship between the values of δ13C and δ15N of plant and sediments organic matter and the TN concentration in the sediment water. Moreover, the results of PCA for both waters types showed some relationship of δ13C of plants and sediments with pH, conductivity and Ca2+ concentration, which were more evident for sediment water. Founded here, strong relationships between plants and sediments δ13C values might confirm that in the cases of most investigated plants, they highly participate in sediment creation in those low-productive soft-water lakes. However, this assumption is less established when we focus on δ15N results. Moreover, both δ13C and δ15N of plants organic matter varied more than sediments, suggesting that allochthonous materials are also engaged in sediments creations. The further species-specific analysis is needed to better explain the present trends and relationships.

The studies were financed by Polish National Science Centre, under project No 2019/32/C/NZ8/00147.

How to cite: Pronin, E., Banaś, K., Chmara, R., Ronowski, R., Merdalski, M., Szmeja, J., Santoni, A.-L., and Mathieu, O.: Variation of stable carbon and nitrogen isotopes composition of plants and sediments along pH gradient of soft-water lakes in Poland , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4830, https://doi.org/10.5194/egusphere-egu22-4830, 2022.

14:16–14:23
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EGU22-5359
Michael E. Böttcher et al.

The role that of fresh surface and ground water sources play on the coastal water balance, element balances, and the associated biogeochemical processes is currently a matter of intense debate and investigation. The measures of fresh and saline water mixing in coastal areas have been found to be challenging, however stable water isotopes (O-16, O-17, O-18), in combination with further hydrochemical tracers, provide a valuable tool to identify different sources, that are furthermore linked to different biogeochemical processes, e.g. impacting the benthic and pelagic carbon cycle.

In the present communication, we report on combined investigations in pore and surface waters of Königshafen Bay (North Frisian island Sylt, Germany), a tidal area in the eastern North Sea. In addition, tidal cycles at the outlet of the bay were sampled. Results are compared to potential surface and subterrestrial fresh water endmembers, open North Sea, submarine groundwater discharge in the backbarrier tidal area of Spiekeroog, as well as the Elbe river estuary. Besides dissolved major and minor elements, the stable water isotope composition is used to characterize the temporal and spatial distribution of different water sources to the bay and the seasonal dynamics in the water column. Porewater gradients indicate different degrees of freshening, locally already in the top 50 cm below the seafloor with spatial heterogeneity. Different fresh water endmembers are indicated both by the water isotope and hydrochemical signatures. It turns that at least two fresh water sources can be identified for sediments under SGD impact, that differ in composition from surface water sources draining into the southern North Sea. Further work is on the way to investigate the dynamics in the (sub)surface fresh water sources for the tidal basin and the link to other geochemical tracers, as well as the coupling to the dissolved carbon system on different temporal and spatial scales.

  

The investigations are supported by the DFG-project KiSNet, the BMBF project COOLSTYLE (CARBOSTORE), the DAAD, the DFG project Baltic Transcoast, and Leibniz IOW.

How to cite: Böttcher, M. E., Jenner, A.-K., Nantke, C., von Ahn, C. M. E., Schmiedinger, I., Schell, A., Patricia, R., Riedel, R., Janßen, S., Gilfedder, B. S., and Moosdorf, N.: Hydrology and -chemistry of a tidal basin (Königshafen, North Sea): A water isotope perspective, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5359, https://doi.org/10.5194/egusphere-egu22-5359, 2022.

14:23–14:30
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EGU22-5442
Marco M. Lehmann et al.

Recent studies suggest that isotope ratios of the carbon-bound non-exchangeable hydrogen (δ2H) in plant cellulose and lipids can indicate changes in the primary carbon and energy metabolism; however, systematic investigations are scarce.

Here, we studied δ2H patterns in two different tobacco (N. sylvestris) model systems, where severe changes in the plant primary metabolism were known: 1) along a nitrogen (N) supply gradient and 2) in a starch-less knockout mutant (pgm). Specifically, we measured δ2H of water, bulk soluble sugars, transitory starch, and cellulose in leaves and roots, using a novel hot water vapor equilibration method and TC/EA-IRMS. Besides, we measured δ2H values of leaf n-alkanes with GC-IRMS.

We observed clear δ2H differences in sugars and starch along the N gradient and a 2H-enrichment of both assimilates in pgm compared to a wild type control. The photosynthetic 2H-fractionation between leaf water and sugars/starch reached a maximum of ca. 100‰ in both model systems and was related to changes in concentrations of primary metabolites (e.g. sugars, starch, organic and amino acids), enzymatic activities, gas-exchange, and growth. The signal of the primary carbon metabolism was also visible in δ2H of leaf and root cellulose in both system, but dampened compared to those of sugars and starch. In contrast, the signal was absent in leaf n-alkanes in both systems.

Our results provide the first direct evidence that changes in the primary leaf carbon metabolism are imprinted on δ2H of plant carbohydrates in leaf and roots. The metabolic signal might therefore be reconstructed from plant material of important paleo archives (e.g. tree-ring cellulose, lake sediments) and help to better understand plant-climate interactions. The absence of the signal in δ2H of leaf n-alkanes is surprising and suggests a strong difference in metabolic fluxes between carbohydrates and lipids. Yet, this observation may help to further disentangle the processes shaping hydrogen isotopes in plants.

How to cite: Lehmann, M. M., Schuler, P., Cormier, M.-A., Ghiasi, S., Werner, R. A., Saurer, M., and Wiesenberg, G.: Hydrogen isotopes in assimilates and cellulose, but not in n-alkanes, integrate signals of the plant primary carbon metabolism, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5442, https://doi.org/10.5194/egusphere-egu22-5442, 2022.

14:30–14:37
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EGU22-6485
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ECS
Tassiane Junqueira et al.

The Great Lakes basin is one of the world’s most important freshwater resources, critical not only to public water supply but also for agriculture, transportation, hydroelectric power, and as an ecosystem. Anthropogenic contamination in all Great Lakes has been causally linked to ecosystem deterioration since the start of the industrial revolution, and it has been pervasive and cumulative. A major anthropogenic contaminant in the Great Lakes is copper [(Cu): a trace metal that has been a concern for decades. Point-sources for Cu include industrial activities such as metal mining, smelting, and chemical industries. However, Cu is also introduced to surface waters from diffuse sources, such as fertilizer application or urban runoff, as well as by atmospheric deposition and natural weathering processes. The importance of these geogenic versus anthropogenic sources is spatiotemporally variable and there are a multitude of sources and processes controlling the environmental fate of Cu in the Great Lakes region that remain poorly quantified (Bentley et al., 2022). Nontraditional stable isotopes have proven useful as environmental tracers for metal contaminants in human-impacted areas and served as an excellent tool to quantify a variety of biogeochemical processes (i.e., adsorption to mineral and organic surfaces, biological uptake). To understand the impacts of anthropogenic activities on Cu concentrations in the environment, background Cu isotope compositions of relatively pristine environments must first be determined. However, Cu isotopic analyses of baseline conditions in the Great Lakes are extremely scarce. In this work, we explore the use of Cu isotope analyses to quantify the baselines and sources of Cu in two tributaries in the Great Lakes. Surface water samples were collected from 44 locations along the Spanish River (Lake Huron) and Trent River (Lake Ontario) in August 2021, together with samples of probable endmember phases that include (agricultural) soils, municipal wastewater effluents and mine waste materials in the respective catchments. Water quality in the studied catchments was variable (6.6 < pH < 9.1; 58.7 mg/L < alkalinity < 216.7 mg/L), with recorded Cu concentrations in the river water samples ranging between 0.79 to 4.88 ng/ml, tending towards higher concentrations upstream compared to downstream, and presenting peaks in specific locations, suggesting anomalous Cu input in these areas. δ65Cu in the rivers analyzed (−1.02 to 0.09‰) present values above the natural average of upper continental crust (0.07 ± 0.10‰) and uncontaminated sedimentary materials from estuaries (−0.04 ± 0.18‰), revealing distinct mixing of two or more sources (including geogenic, mine waste and agriculture fertilizers). We contextualize the Cu compositions observed in surface water samples to those in endmember materials with mixing models and geospatial analysis of the catchments to quantify possible sources. Our results may help distinguish historic versus new contaminant sources and geogenic versus anthropogenic contributions, as well as major pathways by which metals are loaded into the Great Lakes, besides facilitating the protection of this critical freshwater resource from legacy and emerging metal pollution.

How to cite: Junqueira, T., Sullivan, K., Harrison, A., and Vriens, B.: Source-tracking metal contamination using Cu isotopes in two tributaries in the Great Lakes region, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6485, https://doi.org/10.5194/egusphere-egu22-6485, 2022.

14:37–14:44
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EGU22-7528
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ECS
Swea Klipsch et al.

Calcium sulfates are the dominating salts but the respective sulfate sources are debated. In order to quantify the relative contribution and spatial distribution of sulfate sources and to identify biological sulfate recycling processes, we analyzed δ18OSO4, Δ17OSO4, 87Sr/86Sr, and δ34SSO4 of sulfate from Atacama Desert soils (Chile). Surface samples were taken along four W-E transects from the Pacific coast to the Pre-Andean Cordillera between 19.5°S and 25°S. Additionally, lacustrine gypsum and sulfate extracted from groundwater feeding the Salar de Llamará and sodium sulfates from the Salar del Huasco were analyzed.

Sulfur from the ocean comprise high δ34SSO4 values compared with low δ34SSO4 volcanic sulfate allowing to estimate the marine sulfur contribution to the total sulfate sample. δ34SSO4 decreases with distance from the coast principally confirming previously published results [1]. Because Sr substitutes for Ca in Ca-Sulfates, 87Sr/86Sr follows similar systematics, at least for samples taken within the coastal fog zone (<1200 m).  However, δ34SSO4 and 87Sr/86Sr of samples taken above 1200 m are decoupled indicating sulfate dissolution and re-precipitation or deposition of supra-regional Ca-rich aerosols with high 87Sr/86Sr values.

Positive ∆17OSO4 values observed in all analyzed samples (0.1‰ to 1.1‰) suggest a significant contribution from secondary atmospheric sulfate (SAS) to Atacama Desert soils. Distinct mass-independent 17O anomalies of SAS originate from atmospheric oxidation of reduced sulfur species from volcanic or anthropogenic emissions, or biogenic sulfur gases such as dimethyl sulfide (DMS) by O3 or H2O2. Within our dataset we can distinguish between a SAS(DMS) endmember, comprising high ∆17OSO4 and δ34SSO4 and a SASAtacama endmember comprising moderate Δ17OSO4 and low δ34SSO4. Highest Δ17OSO4 values, interpreted to represent a pure SASAtacama endmember, are observed in samples from the Coastal Cordillera of the southernmost transect which is generally higher than the present maximum level of fog advection (1200 m). Lowering of Δ17OSO4 values results from 1) dilution of the positive Δ17OSO4 fromSAS by marine and/or terrestrial sulfate with Δ17OSO4 ≈ 0‰, and 2) resetting of Δ17OSO4 due to biological sulfate reduction and reoxidation. Lowest Δ17OSO4 values are observed in sulfates from salars and soils from alluvial fans.

In general, Δ17OSO4 andδ18OSO4 of our data show an inverse relationship reflecting not only the source contributions but also biological sulfate cycling. Thus, large Δ17OSO4 anomalies (≈1‰) that suggest a dominant contribution from SASAtacama, also indicate the relative absence of biologically processed sulfate and thus, low water availability.

[1] Rech et al. (2003), Geochim. Cosmochim. Acta 67, 575-586

How to cite: Klipsch, S., Herwartz, D., Voigt, C., Münker, C., Chong, G., Böttcher, M. E., and Staubwasser, M.: Insights into sulfate sources and water availability in the Atacama Desert through triple oxygen, strontium, and sulfur isotopes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7528, https://doi.org/10.5194/egusphere-egu22-7528, 2022.

Tue, 24 May, 15:10–16:40

15:10–15:17
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EGU22-8197
Cristian Gudasz et al.

The measurement of δ2H of non-exchangeable-H (δ2Hn) in organic matter (OM) by isotope-ratio mass spectrometry is often hampered by the difficulties in controlling H isotope exchange of the exchangeable H fraction (fex) and removal of residual moisture. The determination of δ2Hin organic matter requires control of the isotopic composition of fex. This can be achieved through dual water H isotope exchange experiments. However, these experiments are laborious, sensitive to the method used (e.g. prior sample treatment, temperature, time) and are costly. This has resulted in a wide range of reported fex for known isotopic references. Moreover, it is not always clear that samples are completely dry following the H exchange experiments, leading to even larger variations. The δ2Hdata is typically used in ecological studies for source attribution due to the large observed separation between contributing end members. However, it is not clear to what degree the analytical errors in δ2H determined by incomplete H isotope exchange of fex and the residual moisture impact the source attribution. Here we developed a simple offline sample preparation system, the Isobox, and a protocol for the measurement of δ2Hin natural OM as well as pure organic compounds. We performed dual water H isotopic exchange experiments with both liquid and vapor water at near 0 and 105°C respectively. We analyzed three keratin reference materials (KHS, CBS and USGS42), two amino acids (Isoleucine and Threonine), along with caffeine (USGS62) and polyethylene (IAEA-CH-7) as drying references. We have also used natural samples of demineralized soil and green algae to create known mixtures to test these methods and their analytical uncertainty impact on the source attribution. We show that the liquid water exchange experiments led to fex close to the theoretical expectations for both keratin and pure compounds. Depending on the research question careful determination with controlled dual water procedure for the determination of δ2Hmay be required. However, simple sample treatment with exposure to a single isotopically known water can be used to derive δ2H for source attribution. The offline sample preparation system and equilibration method we developed is simple, accurate and cost effective and can be implemented in virtually any laboratory for the analysis of a wider range of OM types.

How to cite: Gudasz, C., Lundholm, J., Geibrink, E., Öquist, M., and Karlsson, J.: An offline sample preparation system and water exchange reaction method for the measurement of δ2H of non-exchangeable hydrogen in organic matter , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8197, https://doi.org/10.5194/egusphere-egu22-8197, 2022.

15:17–15:24
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EGU22-8563
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ECS
Kaj Sullivan et al.

The Nova-Bollinger Ni-Cu sulfide ore deposit is hosted in layered mafic and ultramafic intrusive rocks of the Mesoproterozoic Albany-Fraser zone, located about 160 km east-northeast of Norseman, Western Australia. Nova and Bollinger are two adjacent but spatially distinct orebodies with a combined pre-mining resource estimate of 13.1 million tonnes (Mt) with about 2 % Ni, 0.8 % Cu, and 0.1 % Co (IGO Ltd., unpublished data, 2018) 1. Significant challenges are posed in exploring for magmatic Ni-Cu deposits that are buried under post-mineral cover. For example, electromagnetic and gravity surveys identify numerous targets but are unable to distinguish economic mineralization. Previously, it was suggested that the regular pattern of S isotope compositions (δ34SCDT) of surficial sulfate in lakes and groundwaters in southern Australia provides an ideal baseline against which to search for anomalous δ34SCDT values associated with base-metal or gold mineralization 2. In the absence of lakes and readily accessible groundwaters in prospective areas, soils and rocks make a convenient sampling medium. Here, we investigated the exploration potential of δ34SCDT of the trace sulfur content of unconsolidated surface sediments, saprolite, and bedrock samples above Nova and two nearby sub-economic prospects, Griffin and Chimera. The δ34SCDT values likely reflect a two end-member system, with values ranging from -5.8 at depth to 21.4 ‰ near the surface, showing little dependence on lithology. Values in samples closer to the surface are similar to modern seawater sulfate that has a globally homogenous δ34SCDT value of 21.0 ± 0.2 ‰ 3, whereas at depth, values approach typical mantle S isotopic compositions of 0 ± 2 ‰ 4. In support of this, rocks at Nova have a δ34SCDT of around 0 ‰ and regional metagabbro are between -2 and 4 ‰ 5. On a regional scale, in both Western Australia (Yilgarn Block) and South Australia, the δ34SCDT values of surficial gypsum have a regular pattern over distances of up to 1000 km, with the highest values (~ 21 ‰) near coastlines decreasing to δ34SCDT values of ~ 14 ‰ further inland 2. This is suggested to be predominantly the result of the delivery of salts to the Australian landscape as aerosols, with volatile biogenic S compounds of mostly marine origin (δ34SCDT of ~ 1 ‰) that proportionately increase in importance further inland resulting in decreasing  δ34SCDT values 2. Located approximately 200 km inland, δ34SCDT results in samples within 10 metres of the surface at Nova, Griffin, and Chimera are in agreement with this and range from 12.6 to 20.4 ‰. Given that near-surface δ34SCDT values above Nova, Griffin, and Chimera appear to be mostly related to seawater-derived sulfate with minimal magmatic influence, δ34SCDT shows little potential as a field sampling technique to vector for deposits buried under post-mineral cover. However, at depth, δ34SCDT shows a clear relationship between the mixing of seawater sulfate and magmatic S weathering into the environment, indicating that analysis of S isotopes of otherwise apparently barren cores has utility in mineral exploration.

How to cite: Sullivan, K., Drummond, J., Polito, P., Stoltze, A., and Leybourne, M. I.: Sulfur isotope compositions in the weathering profile of magmatic Ni-Cu deposits in SW Australia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8563, https://doi.org/10.5194/egusphere-egu22-8563, 2022.

15:24–15:31
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EGU22-12211
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ECS
Wenhao Wang et al.

Rhenium (Re) is a redox-sensitive element. Recent advances in the precision of measurement of the stable isotopic composition of Re (δ187Re) allow exploration of its potential as a proxy for paleoredox and/or chemical weathering [1]. However, as yet, there have been few studies reporting the geochemical cycling of Re and stable Re isotopes in the modern environments [2] [3], and processes that regulate the Re isotope behavior in hydrothermal systems remain unexplored.

Here we present results of the analysis of Re concentration and δ187Re (relative to NIST3143) for water samples collected from hydrothermal and groundwater systems in Iceland. We show that Re in basalt-hosted boiled hydrothermal fluids from Hellisheidi, Nesjavellir, Reykjanes and Svartsengi sites is isotopically heavier (δ187Re = –0.01 to +0.32‰) than Re in Icelandic basalts (δ187Re = ~–0.32‰). The direction of fractionation holds regardless of types of fluid reservoir (meteoric vs. seawater), and is consistent with precipitation of isotopically light sulfides in the hydrothermal system and/or kinetic fractionation of Re during degassing. By contrast, Re in cold (< 10°C) groundwaters collected from the Mývatn area is isotopically indistinguishable from host basalt. Natural hot spring waters exhibit variable δ187Re values (–0.28 to +0.26‰), likely reflecting mixing between hydrothermal and groundwater endmembers. The relatively isotopically heavy δ187Re from hydrothermal sources has the potential to modify the oceanic budget, which has implications for the isotope mass balance of Re.

[1] Dellinger et al. (2020) JAAS, 35, 377. [2] Dickson et al. (2020) GCA, 287, 221-228. [3] Dellinger et al. (2021) EPSL, 573, 117131.

How to cite: Wang, W., Dickson, A., Dellinger, M., Burton, K., Clark, D., Eggertsson, G. H., Einarsdóttir, Í. E., Hilton, R., Ingimarsson, H., Mesfin, K. G., and Prytulak, J.: Fractionation of stable rhenium isotopes in terrestial hydrothermal systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12211, https://doi.org/10.5194/egusphere-egu22-12211, 2022.

15:31–15:38
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EGU22-12236
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ECS
Anna-Kathrina Jenner et al.

Land-ocean interactions in the coastal zone are of particular interest regarding the exchange of substances, like nutrients, carbon, sulfur, metals, and water. The rising sea level is and will enhance the pressure of salty solutions on previously fresh water ecosystems. We present here new results on the isotope biogeochemistry of a rewetted peatland, at the southern Baltic Sea, that is impacted by event-type flooding with brackish seawater. Sediment cores on transects through the wetland were investigated for their pore water and solid phase (mineral and organic matter) composition. Different fractions of the soils and solutions were analyzed for the elemental composition, mineral micro-textures, and the stable isotope composition (H, C, O, S) to understand the changes in water and biogeochemical carbon-sulfur-metal cycles due to flooding and the consequence for the development of sulfur isotope signatures in authigenic mineral phases and organic matter.

Flooding events with brackish water increased the availability of sulfate as an electron acceptor for microbial carbon transformations. This added sulfur impacted the remineralization capacity of organic substrates and created space for mineral authigenesis, with related iron sulfide textures. It yields isotope signals that are indicative for non-steady state biogeochemistry of coastal ecosystems and allow for a transfer of proxy information to other modern and past coastal organic-rich peatlands.

The soil cores from the peatland reflects the intense activity of sulfate-reducing bacteria and the associated formation of iron sulfides (essentially pyrite) and provided the isotope evidence for site-dependent sulfurization of organic matter. Sedimentary sulfur fractions and their stable isotope signatures are controlled by the availability of dissolved organic matter and/or methane, reactive iron, and in particular dissolved sulfate and, thereby, from the relative position with respect to the coast line, and depend on the surface topography and soil characteristics. Further mechanistic investigations consider the role of DOS upon changing sulfur substrate availability.

 

Acknowledgement for support by DFG-Baltic TRANSCOAST, ERASMUS, DAAD, Leibniz-IOW

How to cite: Jenner, A.-K., Böttcher, M. E., Fernández-Fernández, L. E., Otto, D., Zeller, M. A., Koebsch, F., Jurasinski, G., Kreuzburg, M., Rach, B., Winski, L., Westphal, J., Ehlert von Ahn, C. M., and Schmiedinger, I.: After the flood: Sulfur authigenesis and isotope discrimination in a rewetting coastal fen, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12236, https://doi.org/10.5194/egusphere-egu22-12236, 2022.

15:38–15:45
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EGU22-12261
Gwenaël Imfeld et al.

Contamination of soils by organic pollutants such as pesticides, hydrocarbons or chlorinated solvents in agricultural, urban and industrial soils is a widespread issue. Knowledge on the occurrence, extent and pathways of (bio)degradation of persistent pollutants in soil is crucial to improve the monitoring of their persistence and predict ecotoxicological risks. One of the latest important analytical developments is the coupling of gas/liquid-chromatography to continuous-flow isotope ratio mass spectrometry allowing to measure various stable isotopes ratios specific to each pollutant molecule. Starting from about the year 2000, compound-specific isotope analysis (CSIA), based on natural abundance, has successfully been applied to evaluate the occurrence and transformation pathways of industrial pollutants in groundwaters. However, the need of a sufficient mass of analyte for CSIA combined with low pesticide concentrations (sub-ug g-1) and the co-enrichment of non-volatile soil components, leading to the so-called ‘matrix effect’ during chromatographic separation, currently challenge CSIA application to pesticide residues in soil. Here, we examined preparation procedures of soil samples to maximize the analytical performance for precise and sensitive CSIA without altering the isotope ratio of the target pesticides. Overall, our results emphasize the versatility of QuEChERS approaches as a standard preparation method for pesticide CSIA from soil samples and possible adaptations for specific matrix-analyte combinations to reach more selective extraction. Different families of pesticides with contrasted physico-chemical properties were extracted from various types of soil for CSIA from microcosms, mesocosms and field studies. No significant isotope fractionation for carbon (Δδ13C ≤ 1‰) and nitrogen (Δδ15N ≤ 0.5‰) was observed, despite variable extraction efficiencies. CSIA coupled to enantioselective analysis (ESIA) enabled to evaluate the degradation extent and mechanisms in soil of the chiral fungicide metalaxyl (i.e., S-MTY and R-MTY enantiomers). Significant enantioselective degradation (kS-MTY= 0.007 – 0.011 day−1 < kR-MTY=0.03 – 0.07 day−1) was associated with significant carbon stable isotope fractionation (Δδ13CS-MTY from 2 to 6‰). Column mesocosm experiments showed that biodegradation of anilide herbicides and fungicides (i.e. acetochlor, alachlor, S-metolachlor, butachlor and metalaxyl) was favored in the soil solution of soil-plant systems, independently of the soil type, whereas degradation in soil remained limited. CSIA of terbutryn, an urban biocide commonly added in facade paints and renders, highlighted its persistence in outdoor soil lysimeters and its potential transport into groundwater. In a field study, we demonstrated the applicability of CSIA to track at the catchment scale the degradation and export of the pre-emergence herbicide S-metolachlor from soil to water and identify the contributing source areas. Based on maximum shifts in carbon stable isotope signatures (Δδ13C = 4.6 ± 0.5‰) of S-metolachlor we estimated maximum degradation in soil to have reached 96 ± 3% two months after first application. Altogether, this study emphasizes the variability degradation of different pesticides in soils and proposes a framework using CSIA to examine the contribution of pesticide dissipation processes in polluted urban and agricultural soils.

How to cite: Imfeld, G., Masbou, J., and Payraudeau, S.: Compound-specific isotope analysis (CSIA) of pesticide residues in soil to evaluate in situ degradation over space and time, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12261, https://doi.org/10.5194/egusphere-egu22-12261, 2022.