There is a myriad of organic matter molecules in aquatic ecosystems that continuously undergo microbial and abiotic transformation, processes that critically influence carbon storage and climate feedback. Studies in the past two decades have made substantial progress in characterizing dissolved organic matter (DOM) across aquatic environments due to the advancements in ultrahigh‐resolution mass spectrometry and statistical approaches. For instance, the number of studies characterizing DOM using Fourier-transform ion cyclotron resonance mass spectrometry has increased by more than 500% since 2014 and now accounts for almost 10% of all DOM studies. Yet, a systematic understanding of what determines the microbial transformation and persistence of DOM across spatiotemporal scales remains elusive. Outstanding questions include: how does DOM composition change across large-scale geographical gradients such as latitude, elevation and water depth? How do these patterns vary under environmental change? What is the relative importance of abiotic and biotic processes in determining DOM composition? The growing amount of molecular chemistry and biology data now provide opportunities to answer these questions. This session will bridge chemical complexity with ecosystem biogeochemistry and advance our ability to predict the fate of organic carbon under environmental change. Diverse speakers from a mix of career stages and backgrounds will share talks and posters spanning the full range of freshwater to marine ecosystems and methodological approaches, including observational, experimental, and modelling studies.
Lead Organizer: Jianjun WANG, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences (jjwang@niglas.ac.cn)
Co-organizers:
Andrew Tanentzap, Trent University (atanentzap@trentu.ca)
Núria Catalán, Centre for Advanced Studies of Blanes, CSIC (ncatalangarcia@gmail.com)
Presentations
04:30 PM
The NOSC-ΔG relationship in DOM: why it works, why it fails (10573)
Primary Presenter: Thomas Sibille, Technische Universität Bergakademie Freiberg (thomas-peter.sibille@mineral.tu-freiberg.de)
Dissolved organic matter (DOM) regulates carbon storage and microbial activity across aquatic ecosystems, yet we still lack a clear mechanistic link between its molecular composition and thermodynamic favourability and persistence. We combine quantum chemistry with a structure informed Random Forest model to predict the Gibbs free energy of oxidation per mole of carbon for more than 4000 environmentally relevant molecules, and apply these predictions to ultra high resolution mass spectrometry data from standard DOM reference materials. By revisiting the relationship between the nominal oxidation state of carbon (NOSC) and Gibbs free energy, we show that NOSC captures first order trends across broad DOM quality gradients but fails within individual molecular formulae and NOSC classes, where structurally similar molecules can differ by more than 100 kJ molC⁻¹ in predicted gibbs free energy. These results link DOM chemodiversity to thermodynamic constraints on microbial use and help to explain why DOM fractions with similar elemental composition can follow divergent degradation pathways across aquatic redox gradients due to underlying structural and thermodynamic diversity.
04:45 PM
Environmental and Microbial Controls on Dissolved Organic Matter Across Aquatic Ecosystems (10978)
Primary Presenter: Yongqin Liu, Institute of Tibetan Plateau Research, Chinese Academy of Sciences (yqliu@itpcas.ac.cn)
Dissolved organic matter (DOM) is a key component of the global carbon cycle, yet its molecular evolution across major aquatic ecosystems remains unclear. We analyzed 141 samples from glaciers, mountain rivers, coastal waters, and the open ocean using FT-ICR MS, microbial 16S rRNA sequencing, and environmental measurements. DOM composition exhibited increasing homogenization and recalcitrance along the land-to-ocean continuum. The universal DOM pool, dominated by lignin-like molecules, increased from 65% in glaciers to 97% in the open ocean and was primarily regulated by environmental factors. In contrast, the non-universal DOM pool declined sharply and was strongly influenced by microbial communities, especially in glacier and open-ocean systems. These findings reveal distinct environmental and biological controls on DOM transformation and provide new insights into carbon cycling processes across connected aquatic ecosystems.
05:00 PM
Longitudinal change of riverine dissolved organic matter from source to sea and its photochemical and microbial transformation (10326)
Primary Presenter: Norbert Kamjunke, Helmholtz Centre for Environmantal Research (norbert.kamjunke@ufz.de)
Transformations of organic matter along large rivers from their headwaters to the estuaries are ecologically important, yet field studies combining full river transect sampling with degradation experiments remain scarce. We investigated the Elbe River from headwaters in the Czech Republic to the North Sea and combined longitudinal sampling with degradation experiments to (1) track longitudinal changes in dissolved organic matter (DOM) composition, (2) test photochemical and microbial degradation of terrestrial DOM from deadwood leachate in headwaters, (3) assess bacterial DOM consumption in downstream river stretches, and (4) evaluate photodegradation of organic micropollutants along the entire river. DOM composition shifted longitudinally from allochthonous-dominated, aromatic, oxygen-rich, high-molecular-weight compounds in headwaters to more saturated, nitrogen-enriched, low-molecular-weight components in the estuary. We found that bacterial degradation of terrestrial DOM was higher than photochemical loss in headwaters. Further downstream, bacteria then preferentially consumed younger, autochthonous, oxygen-rich DOM. Additional flume experiments showed substantial photodegradation of organic micropollutants over the river stretch. This unique dataset clarifies the dynamic transformations and pronounced variability of DOM across the land–ocean continuum.
05:15 PM
Hydrology and trophic status control lake dissolved organic matter concentration and composition at a continental scale (10477)
Primary Presenter: Amir Reza Shahabinia, Université du Québec à Montréal (amir.shahabi66@gmail.com)
Dissolved organic matter (DOM) is a key component of the lake biogeochemistry. Hydrology links variables influencing lake DOM at local and watershed scales, but its role at macroscales remains poorly understood. We studied the DOM concentration and composition from 548 lakes across the five major Canadian continental basins, using absorption spectroscopy and parallel factor analysis, and ultra‐high resolution mass spectroscopy, and linked these to deuterium excess, derived from stable water isotopes as a proxy for evaporation and regional hydrology. DOM concentration and composition varied greatly within and across basins, with strong correlations between molecular and optical properties. At a continental scale, d-excess and TP concentration were the main drivers of DOM concentration and composition. TP positively influenced DOM concentration, and specific DOM components, likely mediated by nutrient-driven effects on lake metabolism. DOM concentration declined with d-excess, but the relationships between individual DOM molecular classes and d-excess differed among DOM components and basins, resulting in regional differences in DOM composition along hydrologic gradients. The inferred source composition of DOM based on these patterns had subtle regional differences, with Aliphatics linked to average regional altitude, and Aromatics linked to average regional soil organic content. We conclude that differences in DOM processing along the hydrologic continuum is the main factor driving differences in DOM composition in lakes at a continental scale.
05:30 PM
Urban infrastructure and seasonal hydrology alter dissolved organic matter along coastal ecosystem gradients (11964)
Primary Presenter: Liz Ortiz Munoz, Florida International University (lortizmu@fiu.edu)
Dissolved organic carbon (DOC) concentrations and dissolved organic matter (DOM) composition are shaped by multiple factors in urban waters. In coastal cities, interactions among tidal flooding, stormwater infrastructure, and freshwater inputs can create variable DOM pools, but the timing and seasonal dynamics of these hydrological and biogeochemical interactions remain unclear. We investigated how subtropical wet and dry seasonal variability and marine tidal flooding (high tide events) affect DOC concentrations and DOM composition across n = 100 canal sites in Miami (Florida, USA), and assessed how DOM varied with impervious ground, stormwater infrastructure, and septic density. Sites were sampled in wet and dry seasons during five synoptic events in 2021 and 2022 and analyzed for DOC concentrations and DOM characteristics using absorbance and fluorescence spectroscopy. DOC concentrations and DOM composition remained stable between the wet and dry seasons, which may be related to consistent hydrological conditions maintained through management strategies that reduce flooding. In contrast, marine tidal flooding events led to distinct shifts in DOM composition, characterized by increases in protein-like, tryptophan-like, and fresh lignin-like DOM and decreases in microbial- and terrestrial humic-like DOM. Marine intrusions can promote the transformation toward more labile DOM, overriding typical seasonal dynamics. Higher stormwater influence was associated with elevated dissolved oxygen and a shift in DOM composition toward fresher, microbial-like material. Results highlight the importance of considering hydrological water management and episodic marine intrusions when evaluating DOM dynamics in urban coastal ecosystems.
05:45 PM
INFLUENCE OF ENVIRONMENTAL FACTORS ON THE COMPOSITION AND FATE OF CUPRIC OXIDE (CuO) DERIVED OXYDATION PRODUCTS OF DISSOLVED ORGANIC MATTER (DOM) (11281)
Primary Presenter: Magali Pucet, Université de Sherbrooke (magali.pucet@usherbrooke.ca)
Thawing permafrost and increased river discharge are releasing carbon, including lignins into Arctic rivers and coastal waters. Hudson and James Bays, at the southern edge of the Canadian Arctic, rank among the fastest-warming regions globally, making it critical to examine how environmental changes affect the composition and fate of dissolved organic matter (DOM). Lignin phenols, derived from the breakdown of terrestrial vascular plants, are molecularly diverse compounds used as biomarkers to trace DOM transformation and watershed vegetation. They are extracted via alkaline CuO oxidation and quantified using liquid chromatography coupled with high-resolution mass spectrometry. This study investigates the bio- and photo resistance of lignin phenols and CuO-derived oxidation products in surface DOM from the Moose and Winisk River outflows into Hudson and James Bays. Short-term in situ incubations (3 days) revealed that lignin phenol concentrations decreased under light (0.3%) but increased with microorganisms (0.7%). Conversely, fatty acid-like products rose under light (+3.8%), indicating photoresistence, while lignin phenols were photosensitive. Microorganisms caused fatty acid-like products to vary by +4.1% and -3.5%, suggesting production or consumption. Overall, lignin phenols were biorefractory, while fatty acid-like compounds responded to microorganisms depending on their DOM source. These findings highlight that the chemical properties of lignin phenols and CuO-derived oxidation products can be altered by environmental factor such as light and microbial activities.
SS050C Ecological Significance of Dissolved Organic Matter
Description
Time: 4:30 PM
Date: 15/5/2026
Room: 524B