The impact of freshwater sources like surface river and submarine groundwater discharge (SGD) on the coastal water, the element balance therein, and the associated biogeochemical transformations within the subterranean estuary is currently a matter of intense debate and investigation. A quantification of freshwater mixing in coastal areas has been found to be challenging. In this sense the combination of stable water isotopes with further (isotope) hydro(bio)geochemical tracers provides a fundamental valuable tool to identify different freshwater sources found in the mixing zone with seawater.

Here, we report the geochemical and isotopic composition of porewaters of permeable sediments in front of a coastal peatland, the Huetelmoor (southern Baltic Sea). Gradients in pore water measurements from 5 m long stationary porewater lances are used to calculate the zero-salinity (ZS) component. The application of binary mixing approaches on water isotopes and conservative elements on the compositional gradients yields temporarily relatively stable ZS compositions but with substantial isotope differences for spatially distant lances. This indicates a subterranean estuary under steady-state conditions with different fresh waters entering the coastal area. At least two freshwater sources can be identified for sediments impacted by SGD without substantial impact of short-term hydrological or meteorologic processes. These results are compared to the composition of potential endmembers, such as the local surface and groundwaters, the local meteoric water line, and the open brackish Baltic Sea.

Besides stable isotopes, also dissolved major and minor elements were used to characterize the biogeochemical processes leading to the non-conservative behavior of nutrients, the carbon system, and trace elements. In addition, tritium-noble gas dating of the pore waters allows for an estimate of the fresh water residence time before mixing with the brackish Baltic Sea water.

Results will be discussed in the context of other SGD sites along the northern German coast.

Acknowledgement for support by DFG RTG Baltic TRANSCOAST, DFG-KiSNet, BMBF COOLSTYLE/CARBOSTORE, DAAD, and Leibniz IOW

How to cite: Jenner, A.-K., Saban, R., Ehlert von Ahn, C. M., Westphal, J., Roeser, P., Schmiedinger, I., Sültenfuss, J., and Böttcher, M. E.: Fresh water sources for submarine groundwater discharge to the southern Baltic Sea , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18347, https://doi.org/10.5194/egusphere-egu24-18347, 2024.

The interface between the terrestrial and marine environments regulates the interactions between the adjoining domains. Natural and anthropogenic alterations influence the processes and exchanges of materials. This study aims to determine the biogeochemical processes before and after anthropogenic changes in the coastal protection at the southern Baltic Sea coast proximal to a peatland (Hütelmoor, Rostock, Germany). Spatial and temporal investigations, with the use of stationary porewater lances, characterize the dynamics of biogeochemical transformation processes. Porewaters were measured for in-situ physico-chemical parameters and analyzed for dissolved organic and inorganic carbon (DOC and DIC), major ions, redox-sensitive elements and nutrients concentrations. Stable isotopes (ẟ¹³C-DIC and -DOC, ẟ²H- and ẟ¹⁸O-H₂O, and ẟ³⁴S- and ẟ¹⁸O-SO₄, and ẟ³⁴S-H₂S) and non-stable isotopes (²²³Ra, ²²⁴Ra) were also measured. Results indicate high concentrations of DOC which may have originated from peat degradation and high concentrations of DIC, which may have been derived from organic matter mineralization, terrestrial and marine carbonate dissolution, and Baltic Sea-derived DIC. Minor contributions from CH₄ oxidation cannot be ruled out. Diagenetic transformations are also reflected in the vertical profiles of redox-sensitive ions (such as Fe, Mn, SO₄ and H₂S). Sulfate, dominantly from Baltic Sea water and microbial reduction-oxidation, influences diagenesis. Water is a mixture of different brackish and freshwater sources.  Moreover, submarine groundwater discharge (SGD) was observed from 150 cmbsf and also evident in ²²⁴Ra activities. With the changes in the coastal protection status, internal transport processes of porewaters in the sediment are evidently influenced by the hydrogeodynamics along the coastline on a local to regional scale.

How to cite: Saban, R., Jenner, A.-K., Ehlert von Ahn, C. M., Schmiedinger, I., and Böttcher, M.: Temporal and spatial investigations of the isotope biogeochemistry of a coastal peatland area under sporadic flooding , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3580, https://doi.org/10.5194/egusphere-egu24-3580, 2024.

Dual-clumped isotope thermometry relies on the joint measurement of ∆₄₇ and ∆₄₈ in CO₂ evolved from phosphoric acid digestion of carbonates (Fiebig et al., 2019). The benefit over ∆₄₇-only measurements is its capability to identify if ∆₄₇was affected by rate-limiting kinetics in addition to temperature, and to reconstruct accurate carbonate formation temperatures devoid of this kinetic bias (Bajnai et al., 2020).

Direct measurements of ∆₆₃ and ∆₆₄ in carbonates are technically not feasible. During acid digestion of carbonates, fractionations of clumped isotopes (∆₆₃ → ∆₄₇ and ∆₆₄ → ∆₄₈) occur, but the exact magnitudes of acid fractionation factors (AFFs) are not consistently established and vary across different published sources.

Theoretical models by Guo et al. (2009) indicate cation-dependent differences in AFFs for different carbonate mineralogies. Follow-up empirical studies yielded somewhat inconsistent results for ∆₄₇ – some did not observe any differences in AFFs (e.g., Defliese et al., 2015 for calcite, aragonite, and dolomite; Bonifacie et al., 2017 for calcite and dolomite), whereas others did report differences (e.g., Murray et al., 2016 for calcite and dolomite; Müller et al., 2017 for calcite, aragonite, dolomite, and magnesite).

Advancements in gas source mass spectrometry have led to significant improvements in the long-term external repeatability of clumped isotope measurements, e.g., from > 20 ppm to 7-9 ppm for ∆₄₇ (Bernecker et al., 2023). With this improved analytical set-up, we analyzed an assorted collection of scrambled aragonite, calcite, dolomite, siderite and witherite samples for their ∆₄₇ and ∆₄₈ values. We show that cation substitution and mineralogy have no effect on AFFsfor aragonite , calcite, dolomite and witherite. Moreover, the dual clumped isotope compositions of additionally investigated low-temperature aragonite and dolomite samples plot indistinguishable from the calcite equilibrium line. Altogether these findings strongly imply that the ∆₄₇-∆₄₈ -T framework established for calcite (Fiebig et al., 2021) is extendable to aragonite and dolomite.

Defliese, W.F. et al. Chem. Geol. 396, 51–60 (2015).

Murray, S.T. et al. Geochim. Cosmochim. Acta 174, 42–53 (2016).

Müller, I.A. et al. Chem. Geol. 449, 1–14 (2017).

Bonifacie M. et al. Geochim. Cosmochim. Acta 200, 255-279 (2017).

Fiebig, J. et al. Chem. Geol. 522, 186–191 (2019).

Bajnai, D. et al. Nat. Commun. 11, 4005 (2020).

Fiebig, J. et al. Geochim. Cosmochim. Acta 312, 235–256 (2021).

Bernecker, M. et al. Chem. Geol. 642, 121803 (2023).

How to cite: Bernecker, M., Bonifacie, M., Staudigel, P., Petrash, D., Haussühl, E., Dietzel, M., Davies, A., Tagliavento, M., Siebert, J., Wehr, N., and Fiebig, J.: Investigating the effect of cation substitution and mineralogy on the dual clumped isotope composition of carbonates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11056, https://doi.org/10.5194/egusphere-egu24-11056, 2024.

Quantitative reconstruction of temperature remains the major focus and challenge of paleoclimate research, especially in the terrestrial realm. This study is aimed at testing the usefulness of Δ₄₇ of earthworm’s biospheroids (EBS) as a temperature proxy by comparing the EBS-derived T₄₇ values to those obtained from previously studied land snails. For this purpose, the Dunaszekcső loess record in southern Hungary has been selected, which is an extensively studied section with a high resolution ¹⁴C chronology [1,2,3], revealing stadial-interstadial variations in sedimentation rates.

Sixteen samples were collected in 10 cm resolution from the loess layers between 850-770 cm and 695-615 cm representing the GI-5.1 (30.6-30.8 ka) and GI-3.1 (27.5-27.8 ka) periods and surrounding stadials [4]. The associated temperature was calculated previously between 8-15 °C [4] based on the clumped isotope compositions of mollusc shells of these layers.

The impact of sample preparation methods on Δ₄₇ values of secondary carbonates is unknown and is a potential concern. To test this, two different sample preparation methods were applied on Trochulus hispidus shells recovered from the mentioned loess layers: 1) treatment in 1 m/m% HCl solution and 2) treatment with 3 m/m% H₂O₂ solution under vacuum and in ultrasonic bath in ultrapure water. The reconstructed temperatures based on the Δ₄₇ values of the snail shells typically fell between 7-15 °C (HCl pretreatment) and 9-14 °C (H₂O₂ pretreatment), in very good agreement with previous published land snail T₄₇ data [4]. The average temperatures obtained from biospheroids reveal the same stadial-interstadial temperature pattern previously reconstructed by molluscs. The mean T₄₇ values of the two pretreatment methods are within the expected temperature range derived from the snail shells.

Clumped isotope analysis was also performed on biospheroid samples from the same layers, and the calculated temperatures were compared with those obtained from snail shells by Újvári et al. [4]. To demonstrate that the biospheroid carbonates from the same layers are of the same age as the examined molluscs, we performed radiocarbon dating on the biospheroids. Our primary goal is to investigate whether the Δ₄₇ compositions are affected by the so-called vital effect and to what extent the formation of biospheroid carbonates is influenced by these kinetic effects. To achieve this goal, a long-term experiment is going on. We perform climate chamber experiments [5,6,7] at temperatures of 8, 11 and 15 °C. Other variables, including relative humidity, CO₂ concentrations and the stable isotope compositions of diet and spray liquid are also controlled. The first results will be presented.

References:

[1] Újvári, G. et al. 2014, Quaternary Science Review Vol. 106, 140-154

[2] Újvári, G. et al. 2016, Quaternary Geochronology Vol. 35, 43-53

[3] Újvári, G. et al. 2019, Palaeogeography, Palaeoclimatology, Palaeoecology Vol. 518, 72–81

[4] Újvári, G. et al. 2021, AGU, Advancing Earth and Space Science, Paleoceanography and Paleoclimatology, Volume 36, Issue 8

[5] Canti, M.G. 2009, Soil Biology & Biochemistry Vol. 41, 2588-2592

[6] Lambkin, D.C. et al. 2011, Applied Geochemistry Vol. 26, S64-S66

[7] Versteegh, E.A.A et al. 2014, Soil Biology and Biochemistry Vol. 70, 159-161

How to cite: Czébely, A., Túri, M., Kiss, D., Újvári, G., Kertész, T., and Rinyu, L.: Clumped isotope temperatures from secondary carbonates in loess: comparability of different preparation methods of snail shells and earthworm biospheroids, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16279, https://doi.org/10.5194/egusphere-egu24-16279, 2024.

Carbonate clumped isotope analysis, a relatively new methodology, is still developing rapidly, that is well described by the frequency of changes in the applied methodological conventions. The extent of development is also characterized by the growing, sometimes special, nature of the application areas. Innovations, while promising, can present unforeseen challenges and sometimes brings unexpected difficulties, such as the integration of 10¹³ Ohm resistance in the amplification circuits of Thermo Scientific 253 Plus 10 kV Isotope Ratio Mass Spectrometer (IRMS).

The goal of this improvement was that even very small ion beams can be analyzed with the factor of 3 better signal to noise ratio, which is an important aspect from the point of view of clumped isotope analysis. Unfortunately, 10¹³ Ohm resistance has a significant temperature dependency, which highly influences the magnitude of the detected intensities as well as on the overall long-term stability of the measurement. The daily temperature fluctuation in summer is very significant in Hungary. Under extreme conditions, when the lab's air conditioning could not maintain the desired temperature range, the long-term Δ₄₇ reproducibility of the system achieved an SD = 60 ppm value.

In order to reduce this effect a prototype Peltier cooling device has been installed on the surface of the detector house of our IRMS. To demonstrate the achieved accuracy, precision, and long-term stability (SD <= 30 ppm) of the modified measurement system, we present results of clumped isotope analyses of international carbonate standard samples and naturally formed travertine samples (known formation temperatures are in the range of 5-95°C) and compare them with formerly published data of two reputable laboratories from the clumped community, which use different measurement equipment:

• ETHZ: Thermo Scientific MAT253 IRMS and Kiel IV automatic carbonate device [1]
• MIT: Nu Perspective IRMS and NuCarb automated sample preparation unit [2]

Additionally, we offer insight into the infrastructure and analytical methodology of the clumped isotope laboratory established at ICER (ATOMKI, Debrecen, Hungary). The modification implemented and the attained long-term stability may serve as a valuable reference for other laboratories encountering similar challenges.

Keywords: carbonate clumped isotope, Peltier cooling, long-term reproducibility

References

[1] Bernasconi, S. M., I. A. Müller, K. D. Bergmann, et al. (2018) Reducing uncertainties in carbonate clumped isotope analysis through consistent carbonate-based standardization. Geochemistry, Geophysics, Geosystems, v. 19, 2895-2914.

[2] Anderson, N. T., J. R. Kelson, S. Kele et al. (2021) A Unified Clumped Isotope Thermometer Calibration (0.5–1,100°C) Using Carbonate-Based Standardization. Geophysical Research Letters, v. 48, e2020GL092069.

How to cite: Rinyu, L., Czébely, A., Kiss, D., Kele, S., and Túri, M.: Improving the long-term Δ47 reproducibility of the Thermo Scientific 253 Plus 10 kV IRMS using a prototype Peltier cooling device, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10068, https://doi.org/10.5194/egusphere-egu24-10068, 2024.

The oxygen isotope composition of cellulose (δ¹⁸O values) has been suggested to contain information on stomatal conductance (g_s) responses to rising pCO₂. The extent by which pCO₂ affects leaf water and cellulose δ¹⁸O values (δ¹⁸O_LW and δ¹⁸O_C) and the isotope processes that determine pCO₂ responses of g_s in δ¹⁸O_LW and δ¹⁸O_C are, however, unknown. We tested the effects of pCO₂ on g_s, δ¹⁸O_LW and δ¹⁸O_Cin a greenhouse experiment, where six herbaceous plant species were grown under pCO₂ levels ranging from 200 to 500 ppm. An increase in pCO₂ caused a decline in g_s. The effects of g_s on δ¹⁸O_LW were caused by direct and indirect mechanisms but were generally small. The model parameter effective path length (L_m) was unaffected by changes in pCO₂. pCO₂ effects on δ¹⁸O_LW were not directly transferred to plant δ¹⁸O_C but were attenuated in grasses and amplified in dicotyledonous herbs and legumes. This is likely because of functional group specific pCO₂ effects on the model parameter p_xp_ex. Our study removes critical uncertainties for using δ¹⁸O_C as a proxy for g_s. At the same time, our study shows that g_s effects on δ¹⁸O_LW and δ¹⁸O_C are rather small, possibly too small to be detected in natural settings.

How to cite: Kahmen, A., Holloway-Phillips, M., Morgener, E., Basler, D., and Nelson, D. B.: Is the sensitivity of leaf water and cellulose δ18O values sufficient for detecting effects of increasing atmospheric CO2 on stomatal conductance in plants? , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14826, https://doi.org/10.5194/egusphere-egu24-14826, 2024.

Triple oxygen isotopes of lacustrine gypsum and carbonate deposits are used to quantitatively assess past hydroclimate conditions. An accurate interpretation of these paleo-archives requires a fundamental understanding of processes driving the variability of ¹⁷O-excess in hydrologically different lake systems and their dynamics. Here, we present results of an ongoing monitoring study of triple oxygen and hydrogen isotopes and lake hydrology of two adjacent lakes in southern Spain, which differ in morphology, hydrogeological functioning, and water chemistry. Laguna Grande is a permanent, ∼8 m deep water body that receives groundwater discharge from the aquifer. In contrast, Laguna Chica is a temporal lake with a maximum depth of 1.5 m, which is only fed by precipitation and basin discharge and desiccates during exceptionally long periods of drought. The region is characterized by semi-arid climate and strong seasonality of precipitation. The dataset comprises three hydroperiods between 2020 and 2023. This period has been extremely dry in the South of Spain. We compare non-steady-state isotope and hydrological mass balance model results to monthly observations of lake levels and lake water isotope data to assess the mechanisms that control lake hydrology from daily to annual scale.

Laguna Grande showed significantly less isotope variability (δ¹⁸O ranged from 5.7 to 9.6‰, ¹⁷O-excess from -34 to -86 per meg, d-excess from -28 to -43‰) than Laguna Chica (δ¹⁸O ranged from -1.5 to 20.8‰, ¹⁷O-excess from -7 to -153 per meg, d-excess from -2 to -89‰). In general, ¹⁷O‑excess and d‑excess decreased with increasing δ¹⁸O, indicating the impact of evaporation. The highest δ¹⁸O and lowest ¹⁷O-excess and d-excess values occurred at the end of summer before the start of the next rainy season. Annual average δ¹⁸O of Laguna Grande increased by ∼0.7‰ per year, while ¹⁷O-excess (∼10 per meg per year) and d-excess (∼2 ‰ per year) decreased slightly. This indicates that evaporation exceeded water inflows, which is consistent with the 2 m water level drop observed over the study period. Laguna Chica showed high interannual isotope variability. In particular, the timing of desiccation determines its maximum evaporative isotope enrichment. The highest δ¹⁸O and lowest ¹⁷O-excess and d-excess were observed in October 2022, just before complete desiccation. The lake was refilled in the subsequent rainy season but dried up in May 2023 preventing it from reaching the high level of evaporation observed in the preceding hydroperiods. Changes in the length of the hydroperiod and the timing of desiccation need to be considered when interpreting isotope data of paleo-lake water obtained from lake sediment archives. The non-steady-state isotope-hydrological mass balance model agrees reasonably well with observations, showing that lake’s isotope variability can be predicted even in highly dynamic systems. However, uncertainty in the lake volume-to-surface area ratio at low water level stages challenge accurate prediction of the lake isotope composition. 

How to cite: Voigt, C., Gázquez, F., Sánchez-Villanueva, A. I., Martegani, L., Ruíz-Caballero, E., Cañada, J., and Rodríguez-Rodríguez, M.: How hydroclimate variability drives triple oxygen isotope dynamics in permanent and temporal lakes in Southern Spain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6261, https://doi.org/10.5194/egusphere-egu24-6261, 2024.

Bound amino acids constitute a significant portion of soil organic nitrogen, which represents an essential source of nitrogen for plant and microbial nutrition. The analysis of the content and isotope enrichment of bound amino acids still represents a significant challenge due to the degradation of certain amino acids following the conventional acid hydrolysis method, due to the low isotope enrichment levels reached under near-native soil conditions and due to the lack of isotopically labelled standards for some key amino acids. In this study, we used both a ¹³C-labeled and unlabeled 16 algal amino acid mixture to establish standard calibration curves for various amino acids, using the 6-Aminoquinolyl-N-hydroxysccinimidyl carbamate (AQC) derivatization method and the ultra-high-performance liquid chromatography with high-resolution Orbitrap mass spectrometry (UPLC-Orbitrap MS) platform. Molecular ions of AQC-derivatives for all amino acids were identified at the expected m/z values of the respective isotopologues, and the isotope calibration curves exhibited excellent linearity for those amino acids where we had isotope standards at hand (polynomial R² > 0.9896). However, the polynomial fitting terms differed between single amino acids. Subsequently, we developed equations to relate the calibrated regression terms to physicochemical properties of the respective amino acids. First, we conducted a linear regression using the Orbitrap-derived ¹³C atom % of unlabeled standards against the carbon atom number of the specific amino acid-AQC derivative molecules, demonstrating great linearity (R² = 0.9728). This linear regression curve allowed us to predict the natural ¹³C abundance of amino acids unavailable as isotopically labelled standards (e.g. hydroxyproline, meso-diaminopimelic acid). Consequently, based on further regressions, we could ultimately develop isotope calibration curves for those amino acids unavailable as ¹³C labelled standards based on the integrated isotope calibration functions. This general predictive model can be applied to comprehensively and highly sensitively (¹³C enrichment ~0.01 at %) quantify isotope enrichments of the whole soil amino acids profile, providing valuable insights for a better understanding of the overall fate of different amino acids in soils.

How to cite: Li, T., Li, Y., Tian, Y., Salas, E., Liu, X., and Wanek, W.: Development of a comprehensive and ultrasensitive isotope calibration method for soil amino acid profiles using Orbitrap mass spectrometry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7124, https://doi.org/10.5194/egusphere-egu24-7124, 2024.

Exploring invasive plant species, in this case the infamous Fallopia japonica, has become pivotal in understanding their impact on biogeochemical processes within ecosystems. Building upon the work of Girardi et al., who investigated how F. japonica uses polyphenols to inhibit nitrification, our study employs stable isotope analysis to delve into the biogeochemical niche-building mechanisms of this invasive species. Following Girardi et al.’s findings, which highlighted the inhibitory effects of resveratrol on potential nitrification rates in F. japonica invaded riparian ecosystems, our research takes a step further to investigate the broader implications of the success of F. japonica. We employed stable isotopes, ¹³C-CO2 and ¹⁵N-NO3 and -NH4, to shed light upon the biogeochemical dynamics associated with the invasive prowess of F. japonica and find whether Fallopia japonica exhibits a higher affinity for ammonium than nitrate when compared to the native species Urtica dioica, and whether it allocates resources predominantly to root growth.

Contrary to previous hypotheses, our results challenge the belief that F. japonica exhibits a higher affinity for ammonium than nitrate compared to native species. Through our labelling experiments on young F. japonica and Urtica dioica (native) plants, we discovered that F. japonica displays a lower affinity for ammonium than U. dioica. Additionally, F. japonica demonstrated higher nitrogen-use efficiency and a pronounced preference for allocating resources to root biomass, underlining its ability to efficiently utilize nitrogen resources. These findings shed light on the intricate mechanisms behind the ability of F. japonica to disrupt ecosystems, emphasizing the importance of stable isotopes in unraveling such complexities. Through the integration of stable isotope probing techniques and a comprehensive understanding of rhizosphere processes, our work contributes to the ongoing efforts to foster sustainable and efficient agricultural systems in the face of global change. Moving forward, our research trajectory aims to explore the impact of phenols on nitrification in soils. Specifically, we plan to apply phenols to soil and investigate their effects on nitrification, with potential implications for denitrification processes. This endeavor aligns with the broader goal of understanding the multifaceted interactions between invasive plant species and biogeochemical processes, contributing to the development of effective strategies for invasive species management.

Keywords:                      Fallopia japonica, Urtica dioica, invasive species, native species, nitrogen cycle, nitrogen use efficiency, ammonium, ¹⁵N labelling, ¹³C labelling, biogeochemical niche, stable isotopes

How to cite: Grange, S., Girardi, J., Mendoza-Lera, C., Dyckmanns, J., Muñoz, K., Brunn, M., and Jungkunst, H.: Biogeochemical Niche building of Invasive Fallopia japonica: Insights from Stable Isotope Probing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22257, https://doi.org/10.5194/egusphere-egu24-22257, 2024.

The Laurentian Great Lakes are a globally unique freshwater resource, playing a pivotal role in public water supply and agriculture, transportation, hydroelectric power, and ecosystem functioning. However, the Great Lakes also have a long history of metal contamination, especially in so-called Areas-of-Concern near urban areas and industrial sites. One major anthropogenic contaminant in the Great Lakes is Zn, derived from point-sources such as metal mining, smelting, and chemical industries, as well as diffuse sources such as fertilizer application or urban runoff, in addition to natural inputs from atmospheric deposition and natural weathering. Disentangling the importance of these geogenic versus anthropogenic sources and processes is critical to improving our understanding of the cycling and environmental fate of Zn in the Great Lakes region.

We examined spatiotemporal variations in Zn concentrations and isotopic compositions, as well as bulk physicochemical and mineralogical properties, of a total of 72 surface sediments and sediment core samples across nearshore-to-offshore gradients and depositional environments with distinct limnological conditions spanning >50 years.

Our results reveal spatial variations in both Zn concentrations (18 to 580 mg/kg) and isotopic compositions across oligotrophic (Lake Huron) to mesotrophic (Lake Erie) environments. Interestingly, the intra-lake heterogeneity is comparable to or higher than the variability observed at the inter-lake (basin-scale) level, with no upstream-to-downstream accumulation being evident. The isotopic signatures of surface sediment, measured as δ⁶⁶Zn and ranging from -0.09‰ to +0.41‰, suggest a predominantly geogenic source for Zn. Furthermore, an examination of temporal trends in sediment cores from Lake Huron and Lake Erie indicates consistent metal concentrations and Zn isotopic signatures, implying minimal biogeochemical fractionation within the lakes themselves. Across all sediments and both lakes, metal concentrations and isotopes are positively but not very strongly (R²<0.49 overall) correlated to TOC, TN, and TP, but not to chlorophyll a.

In summary, our findings indicate that sedimentation plays a crucial role as a repository for metals in the Great Lakes, exerting significant influence on the distribution patterns of metals throughout the basin. Furthermore, the higher levels of metals at locations with historical contamination remain spatially constrained and do not seem to disrupt the interconnected system of the Great Lakes.

How to cite: Junqueira, T., Ferreira-Araújo, D., and Vriens, B.: Zinc Isotope Study of Baseline Occurrence Patterns and Potential Contamination of Sediments from the Great Lakes Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1377, https://doi.org/10.5194/egusphere-egu24-1377, 2024.

During the last decades great attention was paid to Particulate Matter (PM) due to the correlation between fine PM exposure and adverse health effects.

  Among the airborne pollutants, Lead (Pb) is one of the most widespread and toxicologically important. Metallic Pb and inorganic Pb compounds are classified as possible carcinogenic for humans. Pb can bioaccumulate in the human body system, causing damage to human nervous system, cardiovascular diseases, reproductive impairments, and catalyzing cells oxidative stress.

  In Italy, Legislative Decree no. 155 of 13/08/2010 (implementation of European Directive 2008/50/EC) defines the atmospheric PM10, PM2.5 and airborne pollutants threshold concentration values. These threshold values are applied for anthropogenic particulates, so, the Pb source apportioning in PM can offer the key to manage the problem.

   Pb has four stable isotopes, i.e. ²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb, and ²⁰⁸Pb. The isotopic ratios of Pb act as “fingerprint” that allows to identify the PM emission sources in the environment (crustal, vehicular traffic, municipal solid waste incinerator, etc …).

  The PM 2.5 and PM10 sampling will be carried out by ARPAC monitoring network, using high-volume samplers placed in Campania (Italy) environmental interest points (urban centers, busy roads…). The sampling flow is 2.36 m³/h, single sampling time is 24 hours and the use of quartz fiber filters Ø = 47mm is provided (according to the technical standard UNI EN 12341:2014).

  Precise and accurate measurement of Pb and relative isotope ratios requires a multi-step process for analysis of solid samples:

• Microwave-assisted treatment of filters with strong acid to solubilize all the metallic species (EPA 3051 A 2007);
• A First qualitative and quantitative measurement by Inducted Coupled Plasma Optical Emission Spectroscopy (ICP-OES) to estimate the total Pb concentration (moreover, the quali-quantitative determination of other metals is an important information for environmental purposes);
• Lead Extraction and purification from matrix and interfering elements by ionic resins in ISO 4 clean room;
• Mass spectrometry measurement for lead isotope analysis by High Resolution Multi-Collector Inducted Coupled Plasma Mass Spectrometry (HR-MC-ICPMS).
• Improvement of data interpretation accuracy comparing experimental data to isotopic lead ratio values in research databases (i.e. IBERLID: lead isotope database and tool for metal provenance and ore deposits research).

  However, the identification of anthropogenic Pb sources enables to establish the origin of a portion of collected PM. So, when an overcoming of PM threshold concentration is observed, thanks to the isotopic analysis information, competent authorities can act in an efficient and successful way.

How to cite: Caso, G., Di Rosa, M., Di Rosa, S., Rubino, M., and Marzaioli, F.: Lead in particulate matter source apportioning by HR-MC-ICPMS stable isotope ratio measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6355, https://doi.org/10.5194/egusphere-egu24-6355, 2024.

Chromium (Cr) is a redox sensitive element and Cr isotope composition (δ⁵³Cr) has been widely utilised to reflect the extent of Cr(VI) reduction during Cr pollution mitigation, as well as changes in past atmospheric/oceanic oxygenation. Whilst redox transformations are thought to primarily drive the Cr isotopic variability in modern aquatic environments, other processes, such as ligand promoted dissolution, can occur, potentially overprinting the intrinsic δ⁵³Cr signal.

In this study, laboratory-controlled batch and flow-through column experiments on two distinct soil materials were conducted to understand the leaching behaviour of Cr and Cr isotopes, under both oxygenated and O₂-free conditions. Significant dissolution of Cr(III), together with Fe and Mn, from the solid phase in the presence of low-molecular-weight organic acids was observed over the time course of all experiments. Initial isotope analyses on Cr(III)-citrate complexes show that δ⁵³Cr values are ~ −0.60 to −0.09‰, reflecting the pristine Cr isotopic signature of the two soil materials. In addition, whilst formation of authigenic Fe particles means that a fraction of dissolved Cr is scavenged, such that solid phase Cr may be associated with Fe, Cr does not seem to be remobilised during reductive dissolution of Fe (and Mn) oxides in these experiments.

Results from this study have several implications. Firstly, as Cr is a known carcinogen, increased levels of organic ligands, e.g., in paddy field systems, can cause increased environmental and health risks. Secondly, organic ligands may play an overlooked role in modulating the input and removal processes of dissolved Cr to/from various environments. Finally, ligand-bound Cr(III) likely has a ‘stabilised’ isotopic signature that is distinct from Cr(VI), making it possible to trace this ‘additional’ Cr in aquatic systems; it is difficult to characterise or quantify these Cr-organic complexes using conventional analytical methods.

This work is part of the CHROMA project funded by H2020-MSCA-IF (101031974).

How to cite: Wang, W., Chrastný, V., Hettler, J., Kumar, N., and Kraemer, S.: Isotope fingerprinting of organically complexed chromium – the natural story of a pollutant, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18111, https://doi.org/10.5194/egusphere-egu24-18111, 2024.