The contribution of terrestrial dissolved organic matter (DOM) to the ocean has been an enigma for decades. Tracking terrestrial DOM in the ocean has proven challenging due to factors such as the instability of terrestrial biomarkers, indistinguishable carbon isotopes from biogeochemical fractionation, and similar chemical composition between terrestrial and oceanic DOM. Here we show that the terrestrial contribution to oceanic organic carbon pools is 2 to 3 times higher than previously assumed, highlighting the need to adjust global carbon cycle models. We derive these estimates by bridging high-performance liquid chromatography with ultra-high resolution mass spectrometry to investigate the presence of terrestrial molecules that are transported from rivers to the ocean and estimate their contribution to oceanic DOM. We identified 269 molecular formulae that are likely transported from land to the ocean. These formulae exhibited resistance to biological and photochemical degradation in incubation experiments, and were widely distributed in global rivers, marginal seas and open oceans, suggesting that they are ubiquitous in inland and ocean waters and have a similar source. By relating the abundances of terrestrially derived molecular formulae to dissolved organic carbon concentrations, we estimated that a mean of 21.7 (16.7-25.0)% of oceanic DOM is likely derived from rivers.

How to cite: Yi, Y., Tanentzap, A., He, C., Merder, J., Osterholz, H., Bao, H., Hawkes, J., Cai, R., Li, S., Shi, Q., Xu, S., Zhang, C., Zhao, M., and He, D.: Underestimated input of terrestrial dissolved organic carbon to the ocean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7651, https://doi.org/10.5194/egusphere-egu25-7651, 2025.

Dissolved organic matter (DOM) represents the largest and chemically diverse reservoir of reduced carbon (~630 Gt C) in the ocean. However, the overwhelming majority is considered biologically recalcitrant (RDOC), resisting rapid biological degradation. To date, the “recalcitrance” of organic compounds in the deep sea is attributed to three main limitations: (I) Deep-sea organic matter may be inaccessible to microorganisms due to its extremely low concentrations of individual components (limitation hypothesis). (II) The molecular structure of deep-sea DOM could be inherently resistant to microbial utilization (recalcitrance hypothesis). (III) The metabolic capabilities of deep-sea microbes might be constrained, e.g., by low temperature and high hydrostatic pressure, limiting their ability to process available organic matter. In addition, the impact of global warming-induced temperature increases in the bathypelagic zone and their consequent effects on deep-sea DOM dynamics remain poorly understood. Here, we show results from a long-term incubation experiment (222 days) with Pacific deep water bacterioplankton, from the Humboldt Current System, exposed to two sources of high molecular weight dissolved organic matter (HMW-DOM, 1-30 kDa), obtained from a) the surface and b) the deep sea (1500 m), along with a detailed characterization of micro(biological) and chemical parameters, at in situ (+2.5°C) and elevated temperature (+6.5°C). The addition of the two DOM sources to deep sea bacterioplankton stimulated bacterial activity (cell abundance, biomass production, and extracellular enzyme activity). However, amendments with deep sea DOM - characterized by more similar carbohydrate and amino acid composition than the surface (Euclidean distance) - resulted in higher bacterial biomass production. This effect increased up to 4-fold under elevated temperature (+6.5°C), while DOC and TOC decreased by ~10 µM C by the end of the experiment. Biochemical characterization of DOM components (i.e., dissolved hydrolyzable carbohydrates and amino acids), collectively accounting for ~6% of DOC, showed a selective consumption of galacturonic acid and glucuronic acid, contributing ~2% of total sugars, and alanine and serine at the end of the experiment (decrease in mol% and nM). These findings suggest that i) increasing the concentration of HMW-DOM components stimulates bacterioplankton activity, ii) these organic components are generally accessible to deep-sea microbes, and iii) the bathypelagic microbiome is capable of metabolizing HMW-DOM. Furthermore, the several-fold increase in bacterial activity observed under a simulated warming scenario (+4.0°C) indicates that climate change-induced warming of the bathypelagic zone could enhance deep-sea DOM utilization. This, in turn, has the potential to alter marine biogeochemical cycles, introducing feedback loops that remain poorly understood.

How to cite: Pontiller, B., Becker, K. W., Rosmann, M., Barbot, A., Amano, C., Herndl, G. J., and Engel, A.: Dissolved organic matter composition and temperature determine organic carbon utilization in the deep ocean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13342, https://doi.org/10.5194/egusphere-egu25-13342, 2025.

Marine dissolved organic matter (DOM) has been studied for decades in understanding of its compositions and cycling. Advances in analytical techniques have revealed that marine DOM is a complex mixture of thousands of molecules. Two theories, concentration threshold and molecular composition, provide insights into DOM cycling in the global ocean, either separately or in conjunction. This study integrates four groups of incubation experiments with 1,104 DOM samples collected from across the global ocean to calculate the thermodynamics and chemical equilibrium state of each individual DOM formula, utilizing molecular composition data obtained from Fourier transform ion cyclotron resonance mass spectrometry. Our findings indicate that marine DOM transitions from a thermodynamic nonequilibrium state to an equilibrium state during the degradation process. In addition, refractory DOM was found to be a group of molecules that have approached a relative equilibrium state, leading to its bulk stability. In-house incubation experiments, observations from the open ocean water column and the global conveyor belt further consolidate this finding. We conclude that the transformation of marine DOM is influenced by both concentration and composition, which together determine its thermodynamic properties, reactivity, and refractory characteristics in the global ocean.

How to cite: Yan, Z., Xin, Y., Cai, R., Yi, Y., Li, P., and He, D.: Thermodynamic property and equilibrium state drive the spatial pattern of dissolved organic matter refractory in global ocean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4657, https://doi.org/10.5194/egusphere-egu25-4657, 2025.

Cold seeps are critical hotspots in marine ecosystems, where the biogeochemical processes of dissolved organic matter (DOM) significantly impact regional carbon reservoirs and the global ocean carbon cycle. To clarify the impact of cold seep activity on the production, transportation and transformation of DOM, we employed Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to analyze DOM from the water column and sediment overlying water collected from cold seep and non-cold seep regions in the northern South China Sea. Our results showed that the overlying water in cold seeps contained a greater diversity of unique molecules, with a larger proportion of sulfur-containing compounds compared to the non-cold seep area. Approximately half of these unique molecules, characterized by lower H/C ratios, higher molecular weights, and a predominance of highly unsaturated compounds (82.3%), were transferred to the corresponding bottom water during the bubbling process. In contrast, molecules with higher H/C ratios, lower molecular weights, and a larger proportion of aliphatics compounds (40.8%) were lost. Additionally, the bottom water of the active cold seep exhibited the formation of some labile molecules (H/C > 1.5) with lower aromaticity (AI_mod < 0.25) and the decomposition of nitrogen-containing carboxyl-rich alicyclic molecules (CRAMs) with higher aromaticity, driven by the positive priming effect. These findings highlight the profound influence of cold seep activity on DOM properties and dynamics, providing deeper insights into the complex biogeochemical processes in cold seep ecosystems and their critical implications for marine carbon cycling.

How to cite: Tang, S., Yan, Z., Yi, Y., Shen, Y., Xie, W., He, D., and Li, P.: Transportation and Transformation of Dissolved Organic Matter from Overlying to Bottom Waters of Cold Seeps in the South China Sea: Insights at the Molecular Level , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2677, https://doi.org/10.5194/egusphere-egu25-2677, 2025.

Over the last 50 years, the permanently anoxic regions in the ocean have quadrupled in size due to deoxygenation derived from global warming and climate change. Marine anoxic basins are characterized by strong vertical redox variability. In the deep, anoxic waters of these basins, bulk measurements showed an increase in concentration of some dissolved organic matter (DOM) components such as dissolved organic carbon (DOC) and dissolved organic sulfur (DOS). However, the direct abiotic effect of deoxygenation and oxygen variability into the DOM composition remains unclear. In this study, we combined state-of-art techniques in analytical chemistry, including Fourier-transform ion-cyclotron-resonance mass-spectrometry (FT-ICR-MS), inductively coupled plasma optical emission spectroscopy (ICP-OES) and high temperature catalytic oxidation (HTCO), to quantitatively and qualitatively characterize the elemental (dissolved organic C, N, S and P) and molecular composition of DOM in three anoxic basins: the Mariager Fjord (Denmark, North Sea), the Gotland Basin (Baltic Sea), and the Black Sea. Samples were grouped in function of in situ oxygen concentration into three categories: oxic (>20 µM O₂), hypoxic (1 - 20 µM O₂) and anoxic (<1 µM O₂). In addition, we abiotically incubated samples from oxic-to-anoxic transition zone of the Gotland Basin (2.5, 55, 66, and 240 m depths) for 17 and 45 days at >200 µM and <1 µM O₂ concentration in the dark, continuously monitoring oxygen concentration by optical sensors inside a closed system previously flushed with N₂ air. Our results show that elemental composition of DOM follows similar vertical patterns in all three anoxic basins as a function of the different oxygen zonation. The highest concentration of DOS and dissolved organic nitrogen (DON) was detected in deep anoxic waters. In contrast, DOC and dissolved organic phosphorus (DOP) concentration was highest in oxic waters. At a molecular level, we identified a total of 8600 molecular formulas, mostly including CHO, CHON, and CHOS compounds. Largest dissimilarities (<53% Bray Curtis) were found in the DOM signature when comparing the three sites, particularly linked to aromatic and highly unsaturated compounds, suggesting specific autochthonous processes having a key role in shaping the DOM composition in each anoxic basin. However, the proportion of DOS-related molecular formulas increased under anoxic conditions at the three sites, especially in the deep, sulfidic waters of the Black Sea, pointing towards common abiotic processes playing a key role (e.g. DOM sulfurization). Furthermore, preliminary results of the abiotic incubation experiment revealed some degree of selectivity in the molecular formulas affected by abiotic exposure to oxygen. Namely, after 45 days being exposed to oxygen, a 5 – 16% of the total DOM showed differences in their intensities, being half of them DON, DOS and DOP molecular formulas. Our study reveals novel insights into DOM composition in anoxic basins and provides a conceptual framework for future studies investigating the impact of deoxygenation in the ocean.

How to cite: Renken, M., Dittmar, T., Stock, L., Elling, F. J., Marshall, I. P. G., and Gomez-Saez, G. V.: Influence of oxygen concentration on the elemental and molecular composition of marine dissolved organic matter in anoxic basins, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10016, https://doi.org/10.5194/egusphere-egu25-10016, 2025.

The formation of recalcitrant Dissolved Organic Matter (DOM) pools in the ocean has been a longstanding challenge due to the chemical complexity of DOM. Linking nitrogen sequestration and microbial reworking via the production of recalcitrant Dissolved Organic Nitrogen (DON) molecules remains elusive. Here, we characterized intricate molecular composition of DOM using FT-ICR-MS, with a particular emphasis on DON, across  three representative regions in the tropical eastern Indian Ocean. Our findings demonstrated the microbial origin of DON in epipelagic waters, with ammonia-oxidizing archaea exerting important control on the enrichment of peptide-like compounds. Microbial respiration was identified as a key driver of DOM transformation throughout the water column. This process enhanced the recalcitrance of DOM and DON by generating molecules with high levels of unsaturation and oxidation, characterized by low bioavailability. These effects were most pronounced in the equatorial region, which demonstrated an exceptional capacity to accumulate nitrogen-rich compounds through microbial processing, thereby facilitating to long-term nitrogen sequestration. Furthermore, we provided a valuable dataset representing microbially derived recalcitrant DON. Our study highlights that a small fraction of DOM with comparatively higher bioavailability is selectively preserved, though the majority of DON persists in the deep ocean due to its recalcitrant nature. This work provides novel molecular-level insights into microbially derived recalcitrant DON molecules, and holds significant implications for the detailed interpretation of global nitrogen sequestration.

How to cite: Zhang, Y., Gan, S., Wu, Y., Zhang, J., and Ye, Q.: Efficient microbial sequestration of organic nitrogen in the eastern Indian Ocean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9137, https://doi.org/10.5194/egusphere-egu25-9137, 2025.

Lake sediments harbor substantial organic carbon (OC) reserves and exhibit remarkably high carbon fluxes, exerting a disproportionately large influence on the carbon cycle relative to their surface area. Now, the stability of lake sedimentary OC pools is increasingly threatened by ecosystem warming. Key questions remain unresolved: How does temperature influence the mineralization and turnover of OC? What mechanisms primarily drive the temperature response patterns of lake sediment OC pools? To address these gaps, we selected 13 lakes from the rapidly warming Qinghai-Tibetan Plateau (QTP) as study sites, and investigated the temperature response patterns of sedimentary OC mineralization processes by using microcosmic incubation, absorption spectroscopy, MALDI-TOF-MS, high-throughput sequencing and OC fractionation, etc. Our results reveal that in the QTP saline lake sediment environments, the stability and temperature response of OC pools are governed primarily by the chemical composition (e.g., chemical recalcitrance, molecular weight distribution) and substrate bioavailability (e.g., concentrations of dissolved and insoluble OC) rather than by mineral protection. Labile, carbon-rich organic compounds exhibit higher reactivity and temperature sensitivity during mineralization, challenging the predictions of the Carbon Quality-Temperature (CQT) hypothesis. This study discusses for the first time in lake sediments the relative importance of substrate bioavailability, OC chemical composition, and mineral protection on the temperature response patterns of mineralization processes, and provides multidimensional evidence through spectroscopic, mass spectrometric and other analytical techniques. In the context of climate warming, these findings can help us to predict more accurately the evolutionary trends of lake OC pools.

Key words: Lake sediments, organic carbon mineralization, temperature, chemical composition, substrate bioavailability, climate warming.

How to cite: Wang, B. and Sun, X.: Temperature response of organic carbon mineralization in lake sediments of the Qinghai-Tibetan Plateau is dominated by substrate chemical composition and bioavailability, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15718, https://doi.org/10.5194/egusphere-egu25-15718, 2025.

Dissolved organic matter (DOM), the largest reservoir of organic material in the ocean, plays a crucial role in the global carbon cycle and the microbial loop. While existing studies have documented significant DOM release by zooplankton, the chemodiversity and bioavailability of this DOM, along with the physiological mechanisms influencing these characteristics in heterogeneous coastal water environments, remain inadequately explored. We conducted onboard zooplankton DOM release experiments in heterogeneous estuarine-coastal water systems, followed by molecular characterization of the DOM using Fourier-transform ion cyclotron resonance mass spectrometry. Additionally, we analysed zooplankton metabolic activities through meta-transcriptomics to elucidate the relationship between the chemical properties of the released DOM and the underlying physiological processes of zooplankton. Our findings reveal substantial variations in the molecular diversity of DOM released by zooplankton across heterogeneous environment, notably between estuarine and coastal communities. We found strong correlations between the chemical reactivity of the DOM and clusters of orthologous groups (COGs) genes associated with functions such as carbohydrate metabolism, nucleotide processing, energy production, and coenzyme metabolism. Importantly, the aromaticity index (AI) of the released DOM was closely linked to metabolism-related gene functions, indicating that zooplankton metabolic processes significantly influence DOM bioavailability. This study enhances our understanding of how the organism’s metabolic processes shape the molecular characteristics of DOM they release, highlighting its implications for carbon cycling in the environment.

How to cite: Nuruddin, M. F., He, D., and Wu, L.: The metabolic mechanisms underlying zooplankton-derived dissolved organic matter’s chemical properties, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14943, https://doi.org/10.5194/egusphere-egu25-14943, 2025.

Obtaining real-time estimations of DOC concentration, reactivity and fate requires the ability to detect changes in the chemical composition of DOM. Optical sensors are increasingly used for this purpose but are typically incapable of distinguishing between variability caused by changes in the quantity versus quality of DOM.

This study developed a new fluorescence index for detecting changes in the composition of DOM. The aromaticity index (ARIX) links the fluorescence composition of aquatic dissolved organic matter to its SUVA aromaticity and predicts ratios between FT-ICR MS molecular formulae and between LC-OCD fractions. In datasets showing decoupling between DOC and absorbance due to biogeochemical processing, the correlation between DOC and absorbance measurements was significantly improved by accounting for interactions between absorbance and ARIX.

A meta-analysis spanning seven continents indicated a linear relationship tying SUVA to ARIX in bulk and extracted freshwater DOM. For DOM isolates, linearity extended into the oceans. These results provide new insights into the relationships between measurements obtained using different techniques for evaluating dissolved organic matter composition. They further have exciting implications for field studies involving water quality monitoring using optical sensors.

How to cite: Murphy, K.: Improving the estimation of DOC concentrations and aromaticity from optical measurements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4423, https://doi.org/10.5194/egusphere-egu25-4423, 2025.

Atmospheric aerosols (AAs) significantly influence the global radiative balance, air quality, biogeochemical cycles, and human health. While their climate and health impacts are well-studied, their biogeochemical role, including contributions of phosphorus (P), nitrogen (N), and organic matter (OM) to oligotrophic regions like the Mediterranean basin, is less explored. Recent studies suggest variable atmospheric deposition of trace metals and nutrients associated with both natural (i.e. recurring Saharan dust storms, biomass burning episodes) and anthropogenic origin (i.e. polluted air masses from northern and central Europe) with atmospheric OM inputs comparable to rivers. However, the detailed composition of atmospheric organic aerosols in the region remains poorly understood.

Ultrahigh-resolution mass spectrometry (UHRMS) offers unparalleled resolving power and enables detailed characterization of complex natural and anthropogenic organic matter (OM) mixtures. It also provides stoichiometric insights into organic nitrogen (N) or phosphorus (P) molecules that are often undetectable by methods like NMR spectroscopy or lower-resolution mass spectrometers. Here, we present advanced analysis of the chemical composition of aerosol particles collected in the Western Mediterranean basin. We combined atmospheric pressure photoionization (APPI) and electrospray ionization (ESI), two complementary techniques, to achieve comprehensive coverage of both polar and nonpolar molecular components through  UHRMS. Electrospray ionization (+ESI) was paired with a 21-Tesla (T) Fourier-transform ion cyclotron resonance mass spectrometer (FT-ICR MS), delivering exceptional resolving power, sensitivity, acquisition speed, mass accuracy, and dynamic range. Meanwhile, APPI (+ /-) was coupled to an Orbitrap Fusion Lumos 1M to target condensed, polyaromatic, nonpolar compounds that are challenging or impossible to detect by ESI alone.

Approximately 28,000 distinct C_cH_hN_nO_oP_pS_s molecular formulas were assigned across all 30 samples collected in the Western Mediterranean basin to ESI(+) 21-T FT-ICR MS spectra after a solid phase extraction to isolate and desalt the samples, revealing an astonishing molecular chemodiversity mainly driven by nitrogen-containing compounds (CHNO) and oxygenated compound (CHO) with minor contribution of sulphur-containing (CHOS) and phosphorus-containing (CHOP) compounds, despite their inherent poor ionisation efficiency in complex mixture. APPI(+/-) / Orbitrap Lumos 1M proved to be a powerful approach for characterizing the molecular composition of highly condensed hydrocarbons, especially the large molecular species that cannot be eluted from gas chromatography columns.

We will explore the key factors driving the molecular composition of atmospheric aerosols (AAs) and their influence on variations and potential formation pathways. Our findings aim to improve understanding of their composition and sources with a focus on biogeochemical processes in the nutrient-limited, stratified open waters of the Mediterranean Sea.

How to cite: Bridoux, M. C., Chacón-Patiño, M., Panagiotopoulous, C., Violaki, K., Meignant, I., and Nenes, A.: Enhanced molecular characterization of atmospheric organic aerosols in the Western Mediterranean basin by Fourier transform mass spectrometry , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16047, https://doi.org/10.5194/egusphere-egu25-16047, 2025.

Chemical Ionization Mass Spectrometry (CIMS) is a well-established analytical method in atmospheric research, process monitoring, forensics, breathomics and food science. Despite significant advancements in procedural techniques, several instrument configurations, especially operating at different ionization pressures, are typically needed to analyze the full range of compounds from non-functionalized parent compounds to their functionalized reaction products. For polar, functionalized compounds, very sensitive detection schemes are provided by high-pressure adduct-forming chemical ionization techniques, whereas for non-functionalized, non-polar compounds, low-pressure chemical ionization techniques have consistently demonstrated superior performance. Here, using a MION2 chemical ionization inlet and an Orbitrap Exploris^TM 120 mass spectrometer, we present multi-pressure chemical ionization mass spectrometry (MPCIMS), the combination of high- and low-pressure ionization schemes in a single instrument enabling quantification of the full distribution of precursor molecules and their oxidation reaction products from the same stream of gas without alterations. We demonstrate the performance of the new methodology in a laboratory experiment employing a-pinene, a monoterpene relevant to atmospheric particle formation, where MPCIMS allows to measure the spectrum of compounds ranging from the volatile precursor hydrocarbon to highly functionalized condensable reaction products. Furthermore, we demonstrate field applicability of the technique by measuring ambient air in automated switching sequence. MPCIMS carries the potential as an all-in-one method for the analysis of complex gas mixtures, reducing technical complexities and the need for multiple instruments without compromise of sensitivity.

How to cite: Shcherbinin, A., Finkenzeller, H., Jost, H.-J., Partovi, F., Vinkvist, N., Mikkila, J., Kontra, J., Kangasluoma, J., and Rissanen, M.: Multi-Pressure Chemical Ionization Mass Spectrometry: Comprehensive Analysis of Complex Gas Mixtures, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10553, https://doi.org/10.5194/egusphere-egu25-10553, 2025.

Polycyclic aromatic hydrocarbons (PAHs) and their derivatives, such as nitro-PAHs and oxygenated PAHs (oxy-PAHs), are persistent organic pollutants with significant environmental and health impacts. PAHs are primarily emitted through incomplete combustion processes and are well-recognized for their carcinogenic and mutagenic potential. While most studies have focused solely on the 16 parent PAHs classified by the US-EPA (US Environmental Protection Agency), PAH derivatives remain underexplored due to analytical difficulties, including low environmental concentrations and complex sampling matrices.

For these reasons, a methodology for analyzing nitro and oxy-PAHs in atmospheric matrices was developed on an HR-MS (LC-MS Orbitrap Eclipse) using an Atmospheric Pressure Chemical Ionization (APCI) in both positive and negative modes with a resolution of 60 000. This method demonstrated excellent sensitivity, achieving a detection limit of 0,03 ng m^-³ for targeted PAH derivatives with a calibration range extended from 0.3 µg L^-1 to 15 µg L^-1 equivalent to 0.03 ng m^-3 to 1.5 ng m^-3 (considering an air sample volume of 10 m³ and a sample volume of 1 mL after extraction and concentration) with excellent linearity (correlation coefficient >0.99), ensuring the accuracy and reliability of quantification across a wide concentration spectrum. The technique also incorporated rigorous validation steps, including precision, robustness, and accuracy to confirm its reliability for trace-level measurements.

Finally, the methodology was applied to emissions from different asphalt formulations using a laboratory prototype that simulates road asphalt production conditions. Filters were collected, extracted, and analyzed using LC-MS Orbitrap. This enabled the detection and analysis of specific (PAHs) and their derivatives, demonstrating its capability to simultaneously identify and quantify a wide range of these compounds.

How to cite: Bou Saad, M., Wortham, H., Doumenq, P., Temime-roussel, B., Ravier, S., Durand, A., Gaudefroy, V., Terrier, J.-P., Burban, O., and Pevere, A.: Development of a High-Sensitivity LC-MS Orbitrap Eclipse Methodology for the Detection of PAH Derivatives, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6737, https://doi.org/10.5194/egusphere-egu25-6737, 2025.

There is growing evidence that changes in the molecular composition of natural organic matter (NOM) in water drives changes in the effectiveness of water treatment processes. Hence, there is a growing interest in obtaining more detailed characterisation of natural organic matter, than traditional methods can provide. High resolution mass spectrometry is one such technique that is increasingly being used for NOM analysis. Predominately, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), has been used but Orbitrap MS is emerging as a more available, smaller, and cheaper alternative.  

Due to the high sensitivity of high-resolution mass spectrometry instrumental performance variation from day to day is a recognised problem. This means that samples measured on different days may not be directly comparable, likely due to slight variations in equipment operating conditions, laboratory ambient conditions and minor contamination left from other analysis. The aim of this study was to investigate the impact of this instrumental variation using a NOM standard mixture and ways to overcome it.

To understand the Orbitrap MS instrumental variation from day to day, a freshly prepared NOM standard mixture was analysed on several days. The data files were compiled and analysed using Compound Discoverer software. The molecular weights observed were assigned to molecular formula using the software. As part of the data processing various strategies were explored to deal with batch effects, including data-driven normalisation, removal of data with lower relative abundance and Systematic Error Removal Using Random Forest (SERRF).

For the NOM standard mixture, there were differences in the assigned molecular formulas as well as the relevant abundances. A total of 940 molecular formula were found for all the NOM mixture standard runs, with 357 found in more than one sample run. However, the compounds that were present in only one or two sample runs tended to have lower relative abundance, and hence removing compounds with lower relative abundance may reduce the influence of instrumental variation. In general, the greatest commonality across the sample runs was seen in the region where the H/C ratio was between 0.5-1.5 and the O/C ratio was <0.5, which corresponds to the condensed hydrocarbons and lignin-like compounds. The various correction strategies showed various levels of effectiveness.

How to cite: Rutlidge, H., Pickford, R., Ventura, T., and Henderson, R. K.: Strategies to deal with batch effects with high resolution Orbitrap mass spectrometry for NOM characterisation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21540, https://doi.org/10.5194/egusphere-egu25-21540, 2025.

Molecular modeling and molecular dynamics (MD) simulations are capable of improving our molecular-level understanding of natural organic matter (NOM) by providing new alternatives such as virtual experiments that may be difficult (or even impossible) to perform in real tests. The fine control of molecular structure required in molecular simulations is highly valuable and significant due to the fact that neither the structure nor (often) detailed composition of real NOM is known. The control of molecular structure and its educated variation guided by experimental data on ¹³C NMR-derived composition may be performed using Vienna Soil Organic Matter Modeller (VSOMM) [1], which allows accounting for the simultaneous presence of multiple NOM molecules of different structures. This work exploring the VSOMM is focused on examining how and whether the humic substances (HS) models representing Leonardite humic acid (LHA) can maintain stable associates in water. In this approach, the stability of HS aggregates was elucidated in the 100 ns MD simulations by varying amounts of water in a broad range, from representing "water solution in NOM" to aqueous dissolved NOM, and modifying molecular size and extent of ionization of HS models, and the type of counter-ions (Na⁺ vs Ca²⁺). Multiple properties characterizing HS-water systems have been calculated, e.g., cumulative coordination numbers, numbers of HS-HS and HS-water contacts and H-bonds at short-range distances, number and size of formed clusters as well as energies of Coulomb and Lennard-Jones interactions of HS with ions (Na⁺ or Ca²⁺), HS and water. One outcome of this modeling work is that it shows how HS dilution leads to the decomposition of HS aggregates which occurs, in particular in the presence of the Na+ counter ion, gradually. The results of this work are placed into the context of experimental data and discussion on whether the detected large HS sizes can be assigned to the presence of large aggregates and the formation of supramolecular structures [2]. Although strong interactions between HS molecules may lead to small stable aggregates (e.g., dimers) persisting during dilution, the modeling suggests that the formation and decomposition of HS associates is "a step-wise" process, and, together with experimental data on LHA dialysis proposes that large-size HS molecules (aggregated or not) may need to be taken into account while examining HS properties in aqueous solutions.

[1] Escalona, Y., Petrov, D., & Oostenbrink, C. (2021). Vienna soil organic matter modeler 2 (VSOMM2). Journal of Molecular Graphics and Modelling, 103, 107817.

[2] Borisover, M., Petrov, D., Oostenbrink, C., & Galicia-Andrés, E. (2025). Diluting humic substances in water in molecular dynamics simulations: Are aggregates stable? Colloids and Surfaces A: Physicochemical and Engineering Aspects, 704, 135507.

How to cite: Borisover, M., Petrov, D., Oostenbrink, C., and Galicia-Andrés, E.: Molecular dynamics simulations of dissolved humic substances: can small molecules maintain stable large associates? , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2312, https://doi.org/10.5194/egusphere-egu25-2312, 2025.

Dissolved organic matter (DOM) plays a crucial role in terrestrial and aquatic ecosystems through its carbon, nutrient, and contaminant transport involvement. Its transfer from soil to surface waters is influenced by soil interactions, which alter both its quantity and composition through various physical, biological, and biochemical processes before reaching surface waters.  This study aims to characterize the DOM composition across different sites and soil depths and assess how organic surface layers (peats and forest floor) affect the DOM composition in deeper mineral horizons, representing the major source of DOM in streams of mountainous catchments. We hypothesize that while organic surface layers show greater DOM compositional variability due to different primary plant sources (e.g., leaves, roots) and different stages of microbial processing, deeper mineral subsoils will contain a more uniform set of non-sorptive and persistent compounds. Despite becoming more uniform in deeper mineral horizons, we expect DOM to maintain some characteristics from the overlying organic layers.

Soil water samples were collected from four sites representing potential terrestrial sources of stream DOM within the catchment area of the Sosa drinking water reservoir located in the Ore Mountains (Germany). Each site was characterized by a different type of soil: Peat, peaty Gleysol, Cambisol, and Podzol. Soil water was sampled from three depths (D1, underneath the organic surface layer; D2, uppermost mineral horizon; and D3, deeper mineral horizon). DOM was characterized using fluorescence spectroscopy and pyrolysis gas chromatography/mass spectrometry (Py-GC-MS), with subsequent Bray-Curtis dissimilarity analysis.

The DOM characterization revealed that across sites with mineral subsoils, the number of identified compounds (i.e., variability) decreased from the organic surface layers to the deeper mineral subsoils, while for the Peat soil, the variability slightly increased. The number of common compounds and the dissimilarity analysis indicated that the organic surface layer of the peaty Gleysol influenced the DOM composition of the underlying mineral horizons more strongly than the organic surface layers of the Cambisol and the Podzol. This stronger influence likely results from the higher water content and reduced mineral interaction in the peaty Gleysol, allowing for greater vertical transport of organic compounds. Pairwise comparisons of the number of shared compounds revealed that the DOM of the Podzol was more similar to the DOM of the peaty Gleysol than to that of the Cambisol at D1, which may be explained by comparable pH conditions and comparable microbial communities adapted to acidic, organic-rich environments. The similarity of DOM composition along the depth of the sites mostly decreased, except at the Peat, where the similarity slightly increased. In contrast to our hypothesis, we found no indications of DOM becoming increasingly uniform during the passage through the mineral subsoil. In the soil with the strongest DOM adsorption in the mineral soil (i.e. the Cambisol), DOM composition showed the largest changes with increasing depth, likely because of transformative processes adding to the changes due to sorptive fractionation.

How to cite: Vieira Carlini Charamba, L., Houska, T., Kaiser, K., Knorr, K.-H., Krüger, S., Krause, T., Chen, H., Krám, P., Hruška, J., and Kalbitz, K.: Assessing compositional variability of dissolved organic matter across different soil types and depths, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15501, https://doi.org/10.5194/egusphere-egu25-15501, 2025.

Dissolved organic matter (DOM) plays a pivotal role in aquatic ecosystems, influencing water quality, microbial activity, and carbon cycling. This study investigates the composition, sources, and dynamics of DOM in Berlin’s urban groundwater, focusing on its variability across aquifer layers and the implications for water quality and ecosystem health. Groundwater samples collected over three years (2021–2023) were analyzed using fluorescence spectroscopy and excitation-emission matrices (EEMs). The primary objectives were to identify DOM sources, assess surface water infiltration risks, and explore dynamic changes in DOM composition. PARAFAC analysis, performed on fluorescence EEMs, revealed eight components (UC1–UC8). Four components were characterized as terrestrial humic (UC1, UC3, UC7, UC8), two were microbial humic (UC2, UC6), one was anthropogenic humic (UC4), and one was a protein-like component (UC5). Component distribution varied across aquifers, reflecting differences in DOM sources and transformations. Shallow aquifers contained higher dissolved organic carbon (DOC) concentrations and microbial humic components (e.g., UC2), while deeper aquifers exhibited recalcitrant terrestrial humic components (e.g., UC7, UC8), potentially stored over long time scales due to anoxic conditions and slow degradation. Protein-like DOM (UC5) was restricted to shallow aquifers, indicating recent surface water inputs.

Overall, these findings underscore the heterogeneity of DOM sources and transformations within Berlin’s groundwater system. The dominance of recalcitrant humic components in deeper aquifers suggests long-term DOM storage, whereas shallow aquifers reflect active surface-water interactions. Anthropogenic influences were most pronounced in shallow and unconfined aquifers, emphasizing the importance of protecting groundwater from urban pollution. Our findings provide valuable insights into the ecological and biogeochemical roles of groundwater DOM and its implications for water management in urban systems.

How to cite: Coulson, L. E., Cukusic, A., Hemmerle, H., Geppert, M., Karwautz, C., Wang, H., Retter, A., Schwammel, G., Bölscher, J., and Griebler, C.: Allochthonous or Autochthonous? Origins of Berlin’s Groundwater DOM, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11326, https://doi.org/10.5194/egusphere-egu25-11326, 2025.

Soil organic matter (SOM) in wetland soils, including peatlands, is crucial for maintaining ecosystem functions such as water quality, biogeochemical cycles, and regulating greenhouse gas emissions. Water-extractable organic matter (WEOM) comprises molecular compounds that dissolve in water under natural conditions. However, molecular-level studies of WEOM across wetlands in different climates and under various agricultural use intensities remain limited. We employed ultrahigh-resolution Orbitrap mass spectrometry to analyse WEOM and integrated it with data on climate types, agricultural intensities, environmental characteristics, molecular groups, microbial functional genes, and field-measured ecosystem respiration, methane and nitrous oxide fluxes. Wetland soil samples were collected from 25 regions representing four agricultural intensities: (1) no agriculture, (2) non-intensive grassland, (3) intensive grassland, and (4) arable land. Orbitrap identified 14,890 molecular formulas with masses ranging from 100 to 950 Daltons. Correlations between agricultural intensities and formula classes containing N, S, or P was visualised using Van Krevelen diagrams. We further examined the influence of climate types (tropical, temperate, continental) and agricultural intensity on WEOM molecular composition by Principal Coordinates Analysis, and linked WEOM quality changes with gas fluxes and other available environmental and microbiome characteristics. Ecosystem respiration, nitrous oxide emission, and agricultural intensity were positively correlated with the persistence of WEOM (i.e., aromaticity vs. aliphaticity) and negatively correlated with soil water content. Diversity of bacteria and archaea, as well as methane emission, were positively correlated with soil pH, but unrelated to WEOM quality. Our findings provide new insights into how WEOM chemistry changes under varying environmental and management conditions and advance our understanding of its role in global carbon and nutrient cycling.

Keywords: Wetland, WEOM, GHG emissions, Orbitrap, climate, agricultural intensity

How to cite: Teo, K. Y., Simon, C., Pärn, J., Espenberg, M., Schroeter, S. A., Gleixner, G., and Mander, Ü.: Global patterns of organic matter chemistry and biogeochemical cycling in wetland soils , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11282, https://doi.org/10.5194/egusphere-egu25-11282, 2025.

The presence of a decomposing body being victim of concealment by clandestine burial represents a localized disturbance in the complex equilibrium that characterizes the turnover of organic matter in the soil. However, although intuitively a biogeochemical analysis of the soil matrix affected by the concealment should provide clear evidence of the presence of a decomposing body, the relevant literature has shown that this is not the case, particularly with regard to the observation of TOC (Total Organic Carbon). In fact, its ubiquitous nature by definition makes the abnormal concentration of organic matter a difficult proxy to identify, but one that is urgently needed for complete crime scene profiling: the ability to distinguish the natural organic matter present in a soil from that derived from the nutrient input caused by the cadaver decomposition processes would represent the operational key to guide investigators towards a more complete and informative analysis of the case. In particular, an anomaly in the concentration and distribution of organic matter within the soil may provide information regarding the Post Burial Interval (PBI) of a concealment victim, as well as be suggestive of a possible previous burial site. For this reason, at the Forensic Taphonomy Facility of the University of Milan (Ticino-LEAFs), a simulation of clandestine burials in a natural environment was carried out using cadavers of piglets that had died of natural causes as a model for human decomposition research. At pre-determined intervals, the piglets, which had undergone various treatments prior to burial (namely being covered in quicklime, wrapped in cotton clothes, and harmed post-mortem), were exhumed and soil samples were taken at different depths to monitor changes in the concentration of the organic matter with increasing exposure of the body to the environment. For this purpose, an analysis of dissolved organic matter (DOM), both natural and affected by the presence of the body, was carried out, combined with complementary spectroscopic techniques (FT-IR). This analysis revealed anomalies in the concentration of dissolved organic matter in the soil horizons containing and immediately underlying the body, also showing the presence of organic compounds otherwise absent in the undisturbed soil. However, some variability attributable to the treatments the bodies underwent prior to burial was also observed, namely the presence of quicklime, which seems to be able to further disrupt the hypogeal environment. The rapidity of the analysis, its relative inexpensiveness, and the small amount of soil sample required could make this technique an innovative tool to be incorporated into forensic casework to help estimate the post-burial interval in the investigation of clandestine burials.

How to cite: Tagliabue, G., Masseroli, A., Golinelli, A., Tambone, F., Cattaneo, C., and Trombino, L.: Evaluating the potential of Dissolved Organic Matter (DOM) analysis and characterization for the investigation of clandestine graves, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-170, https://doi.org/10.5194/egusphere-egu25-170, 2025.