BG2.1

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.

Impurities in CaCO₃ minerals, present as ion substitutions (e.g., Mg²⁺ for Ca²⁺, SO₄^2- for CO₃^2-), 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–SO₄^2- 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–SO₄^2- 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–SO₄^2- 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 SO₄^2- 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 SO₄^2- 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.

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 (²²⁴Ra_ex) 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, ²²⁴Ra_ex 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.

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.

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.

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.

The measurement of δ²H of non-exchangeable-H (δ²H_n) 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 (f_ex) and removal of residual moisture. The determination of δ²H_n in organic matter requires control of the isotopic composition of f_ex. 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 f_ex 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 δ²H_n data 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 f_ex 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 δ²H_n in 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 f_ex 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 δ²H_n may 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.

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.

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.

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 (k_S-MTY= 0.007 – 0.011 day⁻¹ < k_R-MTY=0.03 – 0.07 day⁻¹) was associated with significant carbon stable isotope fractionation (Δδ¹³C_S-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.