Organic matter in aquatic environments includes dissolved and particulate compounds with varying lability, ranging from labile compounds that turn over rapidly, such as amino acids and carbohydrates, to refractory components that persist for thousands to millions of years. The lability of organic matter influences its fate, either incorporation into microbial biomass, respiration by heterotrophic microbes, or export to various regions. Organic matter lability is influenced by intrinsic molecular properties, as well as biotic factors, such as microbial abundance, enzymes, and community composition. In addition, abiotic factors, such as photochemical reactions, oxygen stress, sorption/desorption, and physical aggregation/disintegration, also influence the transformation and fate of organic matter. While recent advances in chemical analysis and microbial studies have significantly enhanced our understanding of these processes, several big questions remain regarding the fate of organic matter. When and where do biotic versus abiotic factors dominate organic matter transformations? Can we identify common principles that determine the fate of organic matter across all water bodies? In this session, we invite presentations on the lability and fate of organic matter in aquatic environments, including but not limited to chemical characterization, ecosystem-specific studies on organic matter source and fate, microbial production and uptake, and pathways of degradation and transformation. We welcome both field observation and lab experimental studies, aiming to synthesize research across disciplines and better understand the factors shaping organic matter lability and its role in biogeochemical processes in aquatic environments.
Lead Organizer: Shuting Liu, Kean University (liushut@kean.edu)
Co-organizers:
Yuan Shen, Xiamen University (yuanshen@xmu.edu.cn)
John Paul Balmonte, Lehigh University (jpb422@lehigh.edu)
Presentations
04:30 PM
EMERGENT LINKAGES AMONG DISSOLVED ORGANIC MATTER COMPOSITION, MICROBIAL ASSEMBLAGES AND RESPIRATION (9130)
Primary Presenter: Amy Marcarelli, Michigan Technological University (ammarcar@mtu.edu)
Dissolved organic matter (DOM) fuels microbial activity in aquatic ecosystems, and linking the supply and characteristics of DOM with dynamics of microbial assemblages is necessary to mechanistically explain variation in ecosystem respiration. Yet, the DOM pools and the microbial communities that process DOM are each complex, and understanding of their interactions is elusive. We conducted an experiment where microbial assemblages acclimated to 3 sources of DOM (fulvic acid standard, soil leachate, algal leachate) were grown on all three DOM sources in a factorial design for 14 days. We hypothesized that DOC removal and respiration would be highest when microbial assemblages were acclimated to the DOM source. Maximum CO2 accumulation rates were highest in the treatments with algal-derived DOM and algal-acclimated microbiota, and were significantly affected by DOM source, microbial enrichment and incubation time, but not the interaction among the 3. By day 10, total CO2 accumulation was 2x greater in the algal DOM than the soil DOM treatments, which in turn were an order of magnitude greater than the fulvic acid DOM treatments. Total CO2 accumulation was also affected by the interaction between DOM source and microbial enrichment, while change in DOC concentration was only affected by DOM source. We are using machine learning to determine which characteristics of DOM and microbial assemblages can accurately predict respiration rates, and whether experimentally-derived models can be applied to understanding ecosystem respiration in natural aquatic environments.
04:45 PM
Biotic and Abiotic Controls on Dissolved Organic Matter in Hydrothermal Sediments: Transformations, Mobilization, and Discharge to the Deep Ocean (9126)
Primary Presenter: Michael Seidel, University of Oldenburg (m.seidel@uni-oldenburg.de)
It is poorly understood how thermogenic transformations and advective transport shape dissolved organic matter (DOM) in deep, organic-rich hydrothermal sediments. These processes may have far-field effects on DOM biogeochemistry in the deep ocean. Here we hypothesize that in organic-rich hydrothermal systems, the DOM composition is shaped by depth- and temperature dependent processes, including microbial transformations in shallow sediments and hydrothermal alterations at deeper, high-temperature zones. Additionally, both recalcitrant and bioavailable DOM may be released into the ocean via hydrothermal fluid flow. To test this, we analyzed solid-phase extracted (SPE) DOM from porewater and sediment samples from IODP Expedition 385 from down to ~330 meters below seafloor in the Guaymas Basin (Gulf of California) and simulated DOM mobilization using hot-water Soxhlet extractions of sediments. Ultrahigh-resolution mass spectrometry (FT-ICR-MS) revealed that microbial processes enhance DOM oxygenation in shallow sediments, while sulfurization and hydrothermal alteration modify DOM in deeper layers. Our findings suggest that hydrothermal discharge introduces both labile and recalcitrant DOM into the deep ocean, influencing carbon cycling on a global scale.
05:00 PM
PHOTOCHEMICAL AND MICROBIAL PROCESSING OF DOM FROM PLANTS AND ESTUARINE WATERS IN PADILLA BAY IN THE PACIFIC NORTHWEST (8895)
Primary Presenter: Lauren Karp, Western Washington University (karpl@wwu.edu)
Biogeochemical processing of DOM in productive ecosystems like salt marshes and estuaries at the land-ocean interface plays an important role in carbon cycling. Padilla Bay is a dynamic estuary with large tidal variations and rich biodiversity, including one of the largest contiguous eelgrass meadows in North America. We are using optical techniques (absorbance, fluorescence, EEMs) and ancillary measurements (DOC, water quality parameters) to assess the sources and transformation processes of DOM in this ecosystem. Our primary goal is identifying the characteristics of DOM from different sources, with a focus on eelgrass beds, salt grass (the dominant salt marsh plant), and slough inputs to mid-bay waters at high and low tides. Our secondary goal is to assess the lability of DOM from these different sources to biotic and abiotic processing. Results from time series of photochemical degradations and biological processing using samples inoculated with bay and slough water will be reported. This work enhances the understanding of biogeochemical processes at the land-ocean interface and may inform the development of sustainable strategies for salt marsh restoration in Padilla Bay.
05:15 PM
SPATIAL AND TEMPORAL HETEROGENEITY OF ORGANIC-MATTER DECOMPOSITION IN A SMALL EUTROPHIC LAKE (8894)
Primary Presenter: Ryan Andrews, Oakland University (ryanandrews@oakland.edu)
Organic-matter decomposition (OMD) in lakes is critical to biogeochemical cycling, nutrient availability, water quality, and overall ecosystem health. OMD within and among lake habitats remains little researched compared to stream and river systems. Our study aims to identify the within- and among-habitat seasonal drivers of OMD. Briefly, we conducted a field-based experiment to assess how seasonality, within lake habitats, and nutrients influence the decomposition of litter from the emergent macrophyte Schoenoplectus acutus in a small eutrophic dimictic lake in southeast Michigan (USA). We also used the standardized cotton-strip decomposition assay that is more readily comparable to other systems. Among the inlet, outlet, littoral, intermediate (2m), and pelagic (10m) habitats, the decomposition rate of cotton strips from November 14, 2023, to August 16, 2024, has consistently been the fastest in the pelagic sites. We attribute this result to warmer bottom waters during ice-on caused by inverse stratification, and nutrient-rich cold-anoxic hypolimnetic waters during the spring and summer. The decomposition rate of the macrophyte was slower than the cotton strips, and the pelagic site had the slowest rate among habitats for the winter season (November 14, 2023, to March 18, 2024). Overall, our results highlight that nutrient availability in anoxic waters can overcome the temperature dependency of OMD in lakes.
05:30 PM
IMPACT OF LAKE BROWNING ON PHYTOPLANKTON-BACTERIAL INTERACTIONS: MEDIATED BY BACTERIAL B12 PRODUCTION (8734)
Primary Presenter: Xuan Zhou, University of Eastern Finland (xuan.zhou@uef.fi)
Lake browning, driven by elevated inputs of dissolved organic matter (DOM), is altering lake physicochemical environments and reshaping phytoplankton compositions. In this study, we investigated vitamin B12 -mediated interactions between phytoplankton and bacterial communities in lakes with low and high DOC concentration. Over 50% of phytoplankton species depend on B12, which is produced by a limited group of bacteria, and thus changes in bacterial community, due to rising DOC levels in brown lakes, may decrease the abundance of B12 auxotrophic algae. We used genetic marker of 18S V4 region for identifying eukaryotic plankton composition, rbcL for diatom, and 16S rRNA V4 region for bacteria to discover the correlations between bacterial and fungal communities in lakes with different DOC levels. We hypothesise that: (1) DOC promotes the growth of B12-consuming bacteria, reducing the abundance of B12-producing bacteria in brown lakes; and (2) the phytoplankton community may shift from diatom dominated in clear lakes to mixotrophic dominated in brown lakes that may due to competition for B12 with B12-consuming bacteria. Our findings emphasize the impact of lake browning on bacteria-alga interactions, mediated by changes of B12-producing bacteria.
05:45 PM
Impact of photodegradation on the fate of dissolved organic carbon in tropical peatland canals (9600)
Primary Presenter: Jennifer Bowen, Stanford University (bowen.jenniferc@gmail.com)
Peatland ecosystems tend to export more dissolved organic carbon (DOC) through aquatic pathways compared to other terrestrial ecosystems, contributing ~20% of all DOC export from freshwaters globally. However, the fate of DOC and its susceptibility to photodegradation versus microbial respiration in peatland-draining freshwaters remains poorly constrained. Here we quantified DOC oxidation rates and investigated when photodegradation dominated DOC oxidation in freshwater canals overlying peatlands in West Kalimantan, Indonesia. Field chemistry, hydrology, and meteorology measurements were paired with more than 100 short-term laboratory incubations to quantify and scale DOC oxidation rates throughout the day from photomineralization and microbial respiration. Our results show that photodegradation drives DOC oxidation when ultraviolet and visible photons are absorbed by DOC within a larger portion of the water column from a shallower water column depth or a higher daily photon flux. In contrast, microbial respiration drives DOC oxidation in larger canals with deeper water column depths where photodegradation is restricted to the sunlit water surface. Given that the majority of canals are small with shallow water column depths and have become unshaded from the clearing of peat swamp forests during deforestation, these findings suggest that photodegradation can substantially alter the fate of peatland-exported DOC in freshwaters draining disturbed tropical peatlands.
SS11C - Biotic and abiotic influences on the lability and fate of organic matter
Description
Time: 4:30 PM
Date: 27/3/2025
Room: W207AB