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
11:00 AM
The relative importance of DOM source and mineral characteristics for adsorption (10436)
Primary Presenter: Mona Abbasi, Uppsala University (mona.abbasi@ebc.uu.se)
Adsorption of dissolved organic matter (DOM) onto minerals plays a critical role in carbon sequestration in terrestrial and aquatic ecosystems. It remains unclear if mineral properties or DOM composition are more relevant for predicting adsorption. We tested this by quantifying the maximum adsorption capacity (Qmax) of five minerals (podzol Bs horizon, agricultural subsoil, glacial stream sediment, kaolinite-dominated clay, synthetic goethite) and five DOM sources (humic lake, peat, leaf litter, algae, and pyrogenic organic matter) using a modified Langmuir model. Three minerals were also treated with sodium hypochlorite to remove pre-existing organic matter, enabling assessment of adsorption onto bare mineral surfaces. Qmax values spanned 31–28,630 mg C kg-1, exceeding previously reported ranges, and showing that both DOM composition and mineral properties variably control adsorption capacity. Even strongly adsorbing minerals such as goethite and clay showed a large variation across DOM sources, with highest adsorption for peat and lowest for algae. Likewise, DOM sources differed in their affinities for the mineral surfaces. Sodium hypochlorite treatment increased DOM adsorption, depending on material type and mineral characteristics, such as hydrous aluminum and iron phases. Overall, carbon adsorption onto minerals depends on both mineral and organic matter characteristics, suggesting that soil models that do not consider organic matter characteristics are limited in describing adsorption and predicting carbon sequestration potential in soils and aquatic ecosystems.
11:00 AM
Greenhouse gases emissions via DOM photodegradation in tropical peatlands and eutrophic lakes, Indonesia (10534)
Primary Presenter: KENSUKE WATANABE, Toho University (6125028w@st.toho-u.ac.jp)
Dissolved organic matter (DOM) photodegradation is one of the major sources for greenhouse gases (GHGs; CO₂, CH₄, CO) from the aquatic ecosystems to the atmosphere. However, little is known about estimations of GHGs emissions via DOM photodegradation. Studies, especially in the tropical regions, remain limited despite the more intense solar radiation than other regions. In this study, to estimate rates and potentials of GHGs emissions via DOM photodegradation in the tropical aquatic ecosystems, we conducted the photodegradation experiments using Indonesian bog (River Sabanga) and eutrophic lake (Lake Rawa Besar) waters under an artificial sunlight simulator. In bog and lake waters, three GHGs emissions were observed under light. In bog water, CO2 rate and potential were the highest, followed by CO, with very low CH4. CH4 rate and potential in lake water were very low but CO2 and CO were high and not significantly different between them. CO₂ rate in bog water was significantly higher than in lake water, while no significant difference was observed for the CH4 and CO between the two waters. CH4 potential in lake water was significantly higher than bog water. Meanwhile, under dark, all GHGs emission rates were negligible except for CO2 in lake water. In Lake Rawa Besar, cyanobacterial blooms have been observed, suggesting CO2 release via DOM biodecomposition due to abundant bioavailable and low-molecular weight DOM. This study demonstrated that eutrophication is very important not only for water quality deterioration but also for GHGs emissions.
11:00 AM
A Multi-Omics Approach to Quantifying Eddy-driven Dissolved Organic Carbon Export in an Oligotrophic Ocean (11165)
Primary Presenter: Emily Hu, Center for Chemical Currencies of a Microbial Planet (emily.hu.899@gmail.com)
The dissolved organic carbon (DOC) pool, which is released and recycled by marine microbes, constitutes a major reservoir for carbon in the ocean. In the western subtropical North Atlantic, time-series data has shown the accumulation of DOC in the surface ocean in the summertime, which is then introduced to the ocean interior through deep convective mixing in the wintertime. However, ocean eddies have been shown to contribute to particulate organic carbon export and likely also transport dissolved organic carbon to the mesopelagic on sub-seasonal timescales throughout the year. Here, we use a multi-omics approach to observationally demonstrate how microbial community structure and DOC cycling vary across an ocean eddy and to estimate the contribution of eddy subduction to DOC export in the oligotrophic North Atlantic. Taxonomic information from metabarcoding data is complemented by metaproteomics, metatranscriptomics, and metabolomics to interrogate how the metabolic function of these communities varies across an eddy. We compare and interpret our findings with a coupled physical-biogeochemical model for the Bermuda Atlantic Time Series (BATS) region to evaluate whether observed patterns align with mechanistic predictions.
11:00 AM
Interactive effects of nutrients, oxygen, and composition on estuarine DOM biodegradation (11326)
Primary Presenter: Lily Karg, Michigan Technological University (lilynoelkarg@gmail.com)
Biodegradation of dissolved organic matter (DOM) fuels aquatic biogeochemistry and is controlled by interacting environmental and chemical factors. We investigated how nutrients, oxygen, and DOM composition alter rates of biodegradation in the Chesapeake Bay, USA, an estuary impacted by nutrient pollution and hypoxia that receives considerable terrestrial and freshwater DOM. Building on previous work, we predicted that nutrient and dissolved organic carbon (DOC) additions would stimulate biodegradation under aerobic and anaerobic conditions, and DOM composition would strongly influence rates of biodegradation and humification. 4-day respirometry experiments using Chesapeake Bay water were conducted to monitor changes in DOC concentration, carbon dioxide (CO2) production, and DOM composition measured by optical properties. While nutrient additions did not alter total CO2 accumulation, nitrogen and phosphorus additions reduced the time to peak CO2 accumulation rates by ~2 hours, and algal-derived DOM led to ~50% more CO2 accumulation than soil-derived DOM. Total CO₂ accumulation was approximately 10% higher under aerobic than anaerobic conditions. This suggests DOM biodegradation can be supported by alternative electron acceptors supplied by nutrient additions. These results demonstrate that interactions between controlling factors may lead to unanticipated changes in DOM biodegradation under shifting environmental conditions.
11:00 AM
DOM concentration and reactivity along the boreal aquatic network of La Romaine River, Québec, Canada (11586)
Primary Presenter: Camille St-Arneault, Université du Québec à Montréal (st-arneault_sergerie.camille@courrier.uqam.ca)
Dissolved organic matter (DOM) exported from terrestrial ecosystems to freshwaters plays a central role in the global carbon cycle, undergoing biological and photochemical degradation to CO₂ along the aquatic continuum. Hydrology, and in particular water residence time, is a major control on biological and photochemical reactivity at the watershed scale. Here, we investigate DOM dynamics throughout the aquatic network of a large boreal watershed by tracking DOM concentration and biological and photochemical reactivity. We sampled groundwater, lakes, streams and rivers from orders 1 to 8 (La Romaine River) within the watershed to assess how concentration and reactivity evolve along the continuum. Preliminary results show a net loss of ~40 % of DOC between order-1 and order-6 rivers, as well as a decrease in photochemical reactivity along the continuum, indicating progressive DOM removal, particularly in lakes. However, biological reactivity shows little change and localized increases in DOC concentration and reactivity also occur, pointing to DOM replenishment. Overall, our findings highlight water residence time as a major control on DOM concentration and reactivity in freshwaters, while demonstrating that lateral inputs can substantially modulate its influence at the watershed scale.
11:00 AM
Quantitative and qualitative characterization of DOM excreted by <i>Ephemera</i> mayflies in stream ecosystems (11684)
Primary Presenter: YUKO SUGIYAMA, Okayama University of Science (yuko-sugiyama@ous.ac.jp)
Aquatic insects play an important role in the biogeochemical cycling of freshwater ecosystems, particularly through their release of dissolved organic carbon (DOC) and related compounds. Among them, Ephemera mayflies are one of the key collector-gatherers that process fine particulate organic matter (FPOM). Recent studies have shown that Ephemera larvae convert ingested FPOM into dissolved organic matter (DOM), thereby contributing directly to stream DOC pools. We characterized the DOM excreted by Ephemera larvae using DOC analysis and excitation–emission matrix (EEM) fluorescence spectroscopy. Rearing experiments were conducted on E. orientalis and E. japonica in ultrapure and natural stream water under controlled laboratory conditions. Water samples collected over 10 days were analyzed for DOC and fluorescent DOM. Both species showed increases in DOC concentration and in the intensities of protein-like fluorescence peaks (Ex/Em ≈ 275/330 nm) and humic-like peaks (Ex/Em ≈ 350/425–440 nm; 275/450 nm), confirming that Ephemera larvae excrete DOM containing both labile and humified components. Moreover, E. japonica, which inhabits steep upstream reaches, excreted higher DOC concentrations and stronger fluorescent DOM signals than E. orientalis, a downstream species. These results indicate species-specific differences in DOM production and suggest that E. japonica may contribute disproportionately to DOM cycling in headwater ecosystems.
SS050P Ecological Significance of Dissolved Organic Matter
Description
Time: 11:00 AM
Date: 14/5/2026
Room: 517C