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
02:30 PM
If more UHR DOM data is the answer, what was the question? (10253)
Primary Presenter: Erika Freeman, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) (erika.freem@gmail.com)
The rapid expansion of FT-ICR-MS applications has redefined the chemical resolution at which we interrogate dissolved organic matter (DOM), yielding molecular inventories of unprecedented breadth. Yet the predictive capacity of freshwater carbon-cycling models has not scaled commensurately. This gap exposes a central methodological tension: we routinely generate exquisitely detailed molecular atlases without equivalently rigorous articulation of the ecological questions that necessitate such resolution. What we require are mechanistic roadmaps—explicit links between molecular features, microbial strategies, and biogeochemical fluxes. Within the Ecology of Molecules framework, I delineate three mechanistic pathways through which molecular information can (and must) translate to ecosystem-level prediction. (1) Molecular keystones: discrete compounds or compound classes exerting disproportionate influence on reaction kinetics, microbial community assembly, or coupled nutrient cycles—functional analogs to keystone taxa in community ecology. (2) Chemodiversity–function relationships: empirical tests of whether molecular diversity and compositional redundancy regulate process rates, stability domains, or resilience to perturbation, paralleling biodiversity–ecosystem function theory. (3) DOM–microbe interaction networks: environmentally contingent coupling between molecular composition and microbial metabolic strategies across lakes, rivers, and wetlands, revealing bidirectional feedbacks between chemical architecture and microbial trait distributions. Through comparative analyses spanning contrasting hydrologic, thermal, and land-use regimes, I show that hypothesis-driven molecular approaches—interrogating explicit mechanisms such as photochemical lability, microbial selectivity, or hydrologic sorting—consistently outperform unconstrained molecular surveys. I systematically evaluate when bulk or optical metrics achieve equivalent explanatory power, and when molecular-level resolution is indispensable for forecasting DOM reactivity, transformation pathways, and persistence under environmental change. To advance predictive freshwater C-cycle models, I propose decision criteria for strategically deploying ultra-high-resolution mass spectrometry: conditions under which molecular data resolve mechanistic uncertainty versus those in which they merely document analytical capability. Without well-posed hypotheses, comprehensive characterization becomes descriptive accumulation rather than ecological inference. I conclude with a set of actionable frameworks for designing DOM studies that operationalize molecular information into ecological prediction—and with provocation for the community: How do we shift from expanding molecular inventories to constraining carbon fate? Under what circumstances has molecular resolution genuinely reframed ecosystem understanding, and when has it obscured the mechanistic narrative we seek to explain?
02:45 PM
A GLOBAL SYNTHESIS OF ORGANIC MATTER DATA (11903)
Primary Presenter: Robert Danczak, Pacific Northwest National Laboratory (robert.danczak@pnnl.gov)
Organic matter (OM) underpins ecosystem biogeochemistry across the globe. While research has focused on OM characterization within singular ecosystems, less attention has been given to cross-ecosystem patterns. Understanding the OM patterns across ecosystems may reveal broader constraints on OM contributions to broad scale biogeochemistry. We leveraged CoreMS and custom metadata management to aggregate >5000 FTICR-MS samples collected by a variety of labs from diverse locations and ecosystems across the globe. Our analyses indicate that ecosystems represent coherent groups despite the significant spatial distances, variation in collection methodologies, and differences in instruments. We observed significant multivariate differences across ecosystems that aligned with expectations (e.g., river OM diverged from sediment OM) but some patterns were unexpected (e.g., river OM was not divergent from soil OM). To investigate differences in OM chemistry, we used a principal component analysis (PCA) to evaluate OM properties enriched in each ecosystem. The PCA captured many significant multivariate differences and revealed potential OM properties associated with ecosystem types. For example, lakes and streams were associated with increased N:C and S:C ratios indicating potential nutrient loading while sediment and ice was affiliated with H:C and P:C ratios highlighting degradation. By integrating more ecosystems, we expect that this synthesized dataset will serve as an important resource to the scientific community to contextualize local information to global patterns.
03:00 PM
Sediments act as major carbon storage and transformation in mangroves with different root structures (10987)
Primary Presenter: Ya Hsin Liu, National Pingtung University of science and technology (maxliu9134@gmail.com)
Mangroves play a vital role in carbon capturing, transforming and storage in coastalareas; however, their carbon storage and stability affected by environmental variables such as salinity, tidal change, and other biochemical factors. This study investigates how contrasting root morphologies—Avicennia marina (aerial pneumatophores), Rhizophora stylosa (supporting roots), and mixed-species stands—govern sediment carbon quantity and quality in the Haomeiliao mangrove forests in southwestern coastal areas of Taiwan. Field measurements were bi-monthly conducted across wet and dry seasons, including sediment organic carbon content, redox potential and dissolved organic matter (DOM) concentration and optical indices (fluorescence index, biological index) in porewater. Results show that, in generally, seasonal rainfall patterns induced persistent anoxia in sediments, which suppressed oxidative enzyme activity, indicating a hydrologically mediated “enzymatic latch” mechanism that declined decomposition rates of DOM and thus benefited carbon preservation and storage. Root morphology further modulated these processes: Rhizophora stands (supporting roots) showed constantly stable anoxic conditions with higher humic-like substances observed, whereas Avicennia stands (aerial roots) experienced greater redox variations, elevated enzyme activity, and higher carbon storage originated from stronger endogenous microbial and algal productions. Mixed forests displayed highest carbon concentration in the sediment , however, the humidification level of OM were lower (i.e., lower stability) of comparing to the pure Rhizophora forest. Our findings demonstrate that the interaction between root structural traits, sedimentary chemistry and seasonal rainfall patterns plays a critical role in regulating sediment carbon quality and quantity in mangrove ecosystems. Results provide critical knowledge for predicting the resilience of mangrove blue carbon under future climate-driven changes in precipitation, salinity, and species composition.
03:15 PM
Compositional and hydrological drivers of DOM degradability across land-water continua of boreal watersheds (10783)
Primary Presenter: Adrien Simonet, Université de Montréal, Groupe de Recherche Interuniversitaire en Limnologie (GRIL) (adrien.simonet@umontreal.ca)
Recent studies showed efficient depletion and transformation of the terrestrial C pool from land to water, yet the strength and shape of this pattern vary geographically and the underlying drivers remain unclear. We assessed how DOM intrinsic degradability and watershed hydrology shape broad-scale DOM patterns by measuring biological and photochemical DOM degradability in terrestrial (upland, riparian) and aquatic (stream, lake) compartments of 26 headwaters across boreal and subarctic Quebec, Canada, spanning 48.9–59.1°N; 63.2–76.2°W. We linked degradability with DOM fluorescence and water stable isotopes (d-excess) as proxies of DOM composition and cumulative exposure to degradation processes, respectively. Fulvic-like and protein-like pools showed strong and preferential losses under photochemical and biological experiment, respectively. Reactivity potential also tended to decrease from land to water and with lower d-excess (denoting longer water transit times), indicating a progressive mineralization of bio- and photodegradable substances occurred during transit. However, the loss of biodegradability potential with rising d-excess was expressed mainly in riparian zones whereas photodegradability losses were concentrated in streams and lakes. Despite regional variation, DOC losses (x̄=53%) were greatest from riparian to stream, driven by protein-like depletion (x̄=85%). Thus, DOM intrinsic degradability and watershed hydrology jointly shape broad-scale DOM patterns with implication for C budgets as both aspects will likely respond to different facets of global change.
03:30 PM
Accumulation of Ancient but Labile Dissolved Organic Matter in the Dead Sea (11332)
Primary Presenter: Danny Ionescu, Technische Universität Berlin (ionescu@tu-berlin.de)
The global reservoir of dissolved organic carbon (DOC) equals the amount of atmospheric carbon, yet the mechanisms allowing its long-term persistence in aquatic systems remain poorly resolved. The hypersaline Dead Sea offers an extreme model for testing how environmental constraints affect organic matter cycling and microbial utilization. We analyzed dissolved organic matter (DOM) from the Dead Sea, its tributary springs, and surrounding aquifers using 14C dating and Fourier-transform ion cyclotron resonance mass spectrometry. DOC concentrations in the Dead Sea were ~2000 µM, ~50-fold higher than in the deep ocean, with 14C ages of ~10,000 years. Dead Sea DOM was molecularly almost undistinguishable from submarine and coastal springs, indicating that the DOM originates mainly from groundwater and sedimentary inputs rather than in situ production. Despite its age, molecular indices revealed features typical of labile material, and in incubation experiments with a productive North Sea microbial community, Dead Sea DOM was readily consumed. DOC decreased by 15% and 800 molecular formulas were lost within 3 years, demonstrating that it remains biologically degradable under non-extreme conditions. Accordingly, the long-term accumulation of DOC in the Dead Sea is not due to intrinsic molecular recalcitrance but to environmental inhibition of microbial degradation caused by extreme salinity and ionic toxicity, redefining the concept of “refractory” DOM as a relative property, determined by local environmental and ecological constraints rather than chemical stability alone.
03:45 PM
Deciphering Labile and Refractory Organic Components in Natural Waters: Implications for Lake Carbon Cycling (11921)
Primary Presenter: Yi Ren, University of Science and Technology Beijing (2410418486@qq.com)
Photo-incubation and bio-incubation are key processes regulating the chemical composition and fate of dissolved organic matter (DOM) in inland surface waters. However, the reactivity and transformation mechanisms of different DOM components in inland natural waters remain inadequately characterized. In this study, three representative inland water bodies, an alpine lake dominated by phytoplankton, a macrophyte-dominated lake, and an urban river, were investigated using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) coupled with optical spectroscopy. Potential chemical reaction predictions were combined to elucidate the molecular transformation mechanism of DOM in photochemical and microbial incubation processes. Our results demonstrate that the critical role of intrinsic molecular properties of DOM, notably molecular weight, unsaturation, and humification degree, in regulating its reactivity and driving compositional shifts during biogeochemical processes. Molecular weight determined bio-incubation activity, while source-specific highly unsaturated and phenolic compounds modulated lacustrine DOM degradation patterns. Concurrently, complex biogeochemical processes drove compositional convergence of DOM across natural aquatic systems. Identification of refractory DOM (RDOM) revealed substantially higher RDOM content in phytoplankton-dominated lakes compared to macrophyte-dominated lakes and urban rivers. These findings elucidate the molecular drivers of DOM degradation in inland waters and provide a theoretical framework for identifying labile and refractory DOM, thereby enabling assessment of the carbon source-sink functions and cycling processes in diverse inland aquatic ecosystems.
SS050B Ecological Significance of Dissolved Organic Matter
Description
Time: 2:30 PM
Date: 15/5/2026
Room: 524B