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
09:00 AM
Chemogeography of dissolved organic matter across freshwater and marine ecosystems (10208)
Primary Presenter: Jianjun WANG, Nanjing Institute of Geography and Limnology Chinese Academy of Sciences (jjwang@niglas.ac.cn)
Dissolved organic matter (DOM) consists of thousands of molecules whose spatial variation reflects the ecological and biogeochemical processes shaping carbon cycling. We introduce a framework for the chemogeography of DOM and demonstrate its utility across major aquatic domains. In rivers, molecular richness and composition show clear geographic structure driven by watershed characteristics, hydrology, and climatic factors. Moving to the global ocean, chemogeographic turnover reveals systematic horizontal and vertical gradients, with decreasing rates toward deep and high-latitude waters where DOM composition becomes increasingly homogenized. For lakes, we highlight how functional chemogeography, integrating intrinsic molecular traits with extrinsic traits such as environmental responses and transformation pathways, provides explanatory power for DOM persistence, ecosystem processes, and predictive modeling. Together, these examples show that chemogeography and its functional extension offer a scalable framework for linking molecular complexity with environmental drivers across ecosystems such as rivers, lakes, and oceans. This approach advances our ability to interpret and predict DOM dynamics under global environmental change.
09:15 AM
Chemodiversity of dissolved organic matter in boreal inland waters and links to water history (10648)
Primary Presenter: Michaela de Melo, Université du Québec à Montréal (michaelaldemelo@gmail.com)
Recent studies of DOM in inland waters have increasingly highlighted the importance of terrestrial-aquatic links and of hydrological connectivity in shaping both DOM concentration and composition. Here we present a study of large-scale patterns in DOM composition in boreal inland waters where we establish links to hydrologic, watershed and environmental factors. For this we used ultrahigh-resolution mass spectrometry to analyze the molecular composition of DOM from over 400 sites including lakes, reservoirs, and fluvial systems, encompassing broad geographic, climatic and environmental gradients in Eastern Canada. Rarefaction curves of DOM molecular richness, both overall and by system type, approach asymptotes, indicating good coverage of DOM diversity in our dataset. Lakes had the highest molecular richness and the most distinct DOM composition relative to that of reservoirs and fluvial systems. Redundancy analysis identified deuterium excess (d-excess), an index of water evaporation and an integrator of previous water history, as the strongest driver of DOM variation, with land cover features further contributing to these differences. The low molecular novelty and uniqueness that we observed across system types, combined with the prevalence of ubiquitous molecules, suggests that degradation processes dominate over the production of new DOM along the aquatic continuum. This is further supported by patterns in putative biochemical transformations, quantified by matching mass differences between peaks to known reactions. Transformation rates were highest in lakes and declined with increasing d-excess, suggesting that individual molecules undergo more transformations in evaporatively enriched systems than in other environments. Overall, these results offer new insights on how water history and landscape context shape DOM diversity and transformations across boreal inland waters.
09:30 AM
09:45 AM
The molecular characterization, source identification and biogeochemical processes of DOM derived from diverse sources in aquatic ecosystems (11625)
Primary Presenter: Shasha Liu, University of Science and Technology Beijing (liushashajida@163.com)
Dissolved organic matter (DOM) plays an essential role due to its high activities in freshwater systems, which exert significant influence on carbon cycling, nutrient dynamics, and migration of pollutants. However, due to the complexity of chemical composition, sources and biogeochemical processes of DOM, the understanding of their migration, transformation and fate within freshwater ecosystem remains limited. Specially in the context of global warming and eutrophication, the sources and fate of DOM will also undergo significant dynamic changes. Therefore, in this study the extraction and characterization strategy, source identification method and biogeochemical processes of DOM were systematically explored. Firstly, we optimized the extraction methods of organic matter from diverse sources, and thus identified their specific molecular fingerprint of organic matter in multiple medium. For example, the results showed that the optimized PPL solid-phase extraction at a 1:500 PPL/DOC ratio with dual ESI mode coupled with FT-ICR-MS enabled effective full-component molecular characterization of algae-derived DOM. And then based on this, we established a quantitative source apportionment model for aquatic DOM by integrating spectroscopic, molecular (FT-ICR-MS), and isotopic fingerprints. Refractory molecules were identified as the stable, source-diagnostic fraction of DOM, and then applied random forest importance ranking to quantify how optical and molecular parameters explain the variability of these signatures, allowing us to select the key tracers for model input and develop a new multi-proxy method for DOM source apportionment. This model has successfully applied in several lakes such as Lake Erhai and Caohai. Moreover, the biogeochemical processes including degradation, precipitation and environmental effect were also explored. Mineral adsorption exhibited distinct fractionation: terrestrial DOM (rich in aromatic compounds) was strongly adsorbed, while algal DOM (aliphatic-rich) showed weaker, reversible adsorption, thus eutrophication might potentially weaken carbon sink potential in lakes. Degradation experiments indicated that aliphatic compounds were readily bio-degraded, whereas aromatic, highly unsaturated compounds persisted, forming a refractory carbon sink. Furthermore, the molecular fingerprint and potential risk of anthropogenic microplastic-derived DOM (MP-DOM) were also explored. The results showed that MP-DOM was more aliphatic, oxygenated and lower aromaticity and they also showed higher potential for generating toxic disinfection by-products compared to natural organic matter with protein-like substances identified as key precursors. This research provides critical methodological advances for the characterization and source identification of DOM, and also provide theoretical insights for the precise management of lake organic pollution and proactive risk assessment and control of microplastics.
10:00 AM
Depth-dependent DOM dynamics in the Saguenay Fjord (Quebec, Canada) (11560)
Primary Presenter: Celine Gueguen, Universite de Sherbrooke (celine.gueguen@usherbrooke.ca)
Dissolved organic matter (DOM) is central to carbon cycling in coastal and estuarine systems, yet its dynamics in strongly stratified fjords remain poorly understood. We examined depth-dependent DOM composition in the Saguenay Fjord, a sill-bounded system influenced by freshwater from the Saguenay River and saline intrusions from the St. Lawrence Estuary. Using optical measurements and high-resolution mass spectrometry in both positive and negative ionization modes, we identified distinct molecular and optical signatures across depths and basins. DOM was largely allochthonous, with humic-like fluorescence dominating surface waters (80 ± 7%) and decreasing at depth (50 ± 8%). Molecular profiles revealed highly unsaturated carbon (31–33%), carboxyl-rich alicyclic molecules (19–20%), and condensed aromatics (18–19%), with CRAM enriched upstream and condensed aromatics near the fjord bottom. Nitrogenous compounds and increasing apparent oxygen utilization at depth indicated microbial and sediment-driven transformations. Strong stratification isolates deep waters, while surface mixing promotes transport. These findings highlight how terrestrial inputs, microbial activity, and water mass structure shape DOM composition, influencing carbon cycling and export to the St. Lawrence Estuary.
10:15 AM
Thermal Rearrangement of Dissolved Organic Matter-Microbe Interactions Magnifies the Climate Forcing Potential of Northern Lakes (10354)
Primary Presenter: Sommer Starr, Trent University (sommerfaithstarr@gmail.com)
Dissolved organic matter (DOM) represents one of Earth’s largest and most reactive carbon pools, with its molecular composition influencing its environmental persistence and ecosystem function. Anthropogenic warming, which is most pronounced in northern ecosystems, is rapidly altering the dynamics of DOM production, export, and processing in aquatic systems. Here, we present a large scale (1600 km) space-for-time substitution across a boreal-to-temperate gradient to test the hypothesis that warming fundamentally reworks the relationships between DOM composition, microbial community function, and carbon emissions. We sampled 40 lakes over all seasons, integrating molecular-level DOM characterization, shotgun metagenomics sequencing of microbial communities, in situ measurements of GHG fluxes, and assessments of lake metabolism. We found that warming moves lakes along a continuum from CO2-dominated systems to potent CH4 emitters, driven by a thermal reorganization of both DOM composition and microbial community structure. By linking high-resolution chemodiversity data with microbial taxonomy and ecosystem function, this research provides a mechanistic framework to predict how climate-driven shifts in ecosystem function and structure will alter the role of northern lakes in the global carbon cycle. These findings are critical for informing models of future atmospheric carbon loading and guiding climate mitigation and freshwater resource protection policy.
SS050A Ecological Significance of Dissolved Organic Matter
Description
Time: 9:00 AM
Date: 15/5/2026
Room: 524B