Rivers transport large amounts of organic carbon, trace metals, and nutrients from land to coastal oceans. At the land-sea interface, elemental fluxes and transformations are influenced by processes occurring in rivers, wetlands, and estuaries. Increasing anthropogenic pressure, such as land-use change and increasing frequency of extreme events (e.g., hurricanes, fires), are altering the sources and quality of organic carbon and nutrients exported to coastal ecosystems. Maintaining the integrity of coastal aquatic systems is critical because they provide essential ecosystem services. Effectively adapting to meet these challenges requires us to understand the biogeochemical linkages of carbon and nutrient cycles to ecosystem processes and microbial activity, and how they are altered by human activities. This session aims to bring together scientists from all fields of biogeochemistry, covering ecosystems at different latitudes and spatio-temporal scales. We welcome contributions that address carbon and nutrient fluxes across the land-ocean continuum, biogeochemical transformations in rivers, coastal wetlands and estuaries, as well as the fate of terrestrial carbon in marine environments. We also encourage submissions that explain mechanisms underlying observed patterns in the distribution or transformation of sedimentary, particulate, and dissolved organic matter, their relationship to CO2 outgassing or uptake, and microbial community composition across aquatic gradients. In addition, we are interested in approaches to quantify the response of coastal aquatic systems to environmental stressors to guide conservation and restoration efforts.
Lead Organizer: Michael Seidel, University of Oldenburg (m.seidel@uni-oldenburg.de)
Co-organizers:
Sairah Malkin, University of Maryland (smalkin@umces.edu)
Patricia M. Medeiros, University of Georgia (medeiros@uga.edu)
Sasha Wagner, Rensselaer Polytechnic Institute (wagnes3@rpi.edu)
Nicholas D. Ward, Pacific Northwest National Laboratory (nicholas.ward@pnnl.gov)
Presentations
04:30 PM
Reducing uncertainties of organic matter transport in the land-ocean continuum of tropical systems (9115)
Primary Presenter: Ryan Pereira, Heriot-Watt University (r.pereira@hw.ac.uk)
Aquatic environments integrate multiple sources and processes over space and time that influence ecosystem functionality. The complexity of these systems and their multiple interactions with the surrounding environment are conceptualised, but often lack empirical scrutiny that allows further understanding of how inland waters mobilise, and utilise carbon and nutrients during transportation to the ocean. This is particularly evident in tropical waters. To advance or understanding we apply advanced geochemical analyses (liquid chromatography with organic carbon and nitrogen detection and high-resolution mass spectrometry) to investigate the flux and composition of dissolved organic matter (DOM) in conjunction with measurements of surfactant activity and organic biomarkers to explore differences between the main water column and the water’s surface film, known as the surface microlayer. We show that the transition from the dry to the wet season is a likely critical factor in DOM mobilisation and transport, while the enrichment of DOM in the microlayer is dominated by surface-active organics likely of biogenic origin from land to ocean of in tropical ecosystems. We further explore the impacts of organic matter enriched in the surface microlayer on the exchange of climate active gases in natural and perturbed fresh and marine waters.
04:45 PM
UNCOVERING SEASONAL PATTERNS IN HIGH-FREQUENCY DATA FOR KEY ENVIRONMENTAL PARAMETERS IN A TEMPERATE ESTUARY (9589)
Primary Presenter: Wilton Burns, University of New Hampshire (wiltonburns@gmail.com)
The health, quality, and ecological resilience of estuarine and riverine environments are impacted synergistically by a variety of environmental parameters. Changes in abiotic parameters can influence aquatic ecosystems from the bottom up. In this study, we assessed how eight abiotic environmental parameters (water temperature, dissolved oxygen (DO), pH, salinity, turbidity, wind speed, photosynthetically active radiation (PAR), and precipitation) have changed over two decades at four sampling stations in the Great Bay Estuary (GBE). These sites are managed under the National Estuarine Research Reserve System (NERRS) System-Wide Monitoring Program (SWMP). We evaluated long-term trends in daily means and upper 95th and lower 5th percentile data, with a focus on shoulder season dynamics. Our goal was to determine what, if any, significant changes have occurred in GBE that could impact the ecology of the system. We found similar patterns in the rates of change in daily means, upper 95th, and lower 5th percentile data; however, there were different rates of change throughout the year for all parameters. We observed significant increasing trends in water temperature, salinity, pH, and PAR. Conversely, DO, turbidity, and wind speed exhibited decreasing trends. These changes varied by month, highlighting the distinct rates of change among parameters and the importance of breaking down long-term analyses by season.
05:00 PM
EFFECTS OF MODEL ROOT EXUDATES ON SOIL RESPIRATION IN CONTRASTING SALT MARSHES (9002)
Primary Presenter: Britany Guo, University of Georgia (bg06386@uga.edu)
Salt marshes play a crucial role in the global carbon (C) cycle through efficient sequestration in soils. Yet, the mechanisms that lead to marsh organic C preservation versus microbial degradation remain unclear. Root exudates can help to build new soil organic matter but may also catalyze decomposition of previously buried C through biotic and abiotic priming mechanisms. We hypothesized that priming mechanisms differ between organic and mineral soils, with biotic co-metabolism dominating in the former and abiotic mechanisms in the latter. To test this, we continuously supplied mineral and organic marsh soils with 13C-glucose (biotic priming), 13C-oxalic acid (abiotic priming), or unamended seawater (control) under oxic or anoxic conditions for 7 days in flow-through reactors, which simulate porewater percolation. Glucose stimulated respiration, as net dissolved inorganic C (DIC) production, more than oxalic acid in both marsh soils. However, after normalizing DIC production to the amount of substrate added, we found proportionally higher respiratory response to oxalic acid than to glucose, particularly in the mineral soils. This was supported by 13C-DIC mixing models which estimated greater contributions from existing soil C to net C respiration in oxalic acid treatments. These findings suggest that abiotic priming may more effectively mobilize native soil C than biotic priming (co-metabolism), particularly in mineral salt marshes.
05:15 PM
Phytoplankton group classification by integrating trait information and observed environmental thresholds (9037)
Primary Presenter: Hoang Vuong Dang, The University of Western Australia (hoangvuong.dang@research.uwa.edu.au)
Assigning phytoplankton taxa to functional groups is essential for aquatic ecology models but challenging in systems with high taxonomic diversity. Without a clear framework, many models subjectively group phytoplankton at the phyla or class level, aggregating the substantial functional and trait diversity that occurs within these groups. However, this creates challenges for model parameterization and evaluation. To address this, we developed a data-driven approach to define phytoplankton functional groups, considering species trait information and occurrence data from a 12-year dataset of the Hawkesbury-Nepean River (Australia). Our framework reduces subjectivity by using multi-correlation and principal component analysis to identify key environmental factors. K-prototype was used to classify phytoplankton based on a priori species-level trait and observed threshold ranges across the factor gradients defined by threshold indicator taxa analysis. Five trait-threshold classified groups had statistically distinct environmental preferences and morphological and physiological characteristics and were more homogeneous than taxonomic-based groups. These groups were integrated into a 3D hydrodynamic-biogeochemical model (2017 – 2018), parameterized using their unique traits and ecological thresholds. The model successfully simulated historical conditions and captured group-level dynamics in chlorophyll-a and biomass, including bloom events. The insights gained from this study can be extended to other urban rivers, offering a practical approach to managing phytoplankton blooms.
05:30 PM
Effect of dissolved organic carbon from a point- and non-point-source of nutrients on oxygen demand of a subtropical estuary (9159)
Primary Presenter: Jing Lu, Griffith University (jing.lu1124@gmail.com)
Nutrient and organic matter inputs can drive hypoxia in estuarine waters. However, the relative effect of point- and non-point sources has not been directly compared, which can be crucial for developing targeted management strategies to address the specific impacts of each source. This study compared the effect of three nutrient sources, i.e., simulated soil erosion runoff (soil slurries), sewage treatment plant (STP) and aquaculture effluent, on dissolved oxygen (DO) demand in a subtropical estuary. We also chemically characterized the organic compounds in these sources. Using three-day incubations in the dark as a measure of the potential demand, we found that nutrient source-specific factors drove DO demand. For soil slurry treatments, dissolved organic carbon (DOC) concentration was most highly correlated with DO demand (R2 = 0.52). For STP treatments, a combination of concentrations of total nitrogen (TN), phosphate (PO4-P), and ratios of TN: total phosphorus (TN:TP) and DOC: ammonium (DOC:NH4) were most correlated with DO demand (R2 = 0.5). The combination of chlorophyll-a concentrations and DOC: TDN (total dissolved nitrogen) explained most of the DO demand for aquaculture treatments (R2 = 0.80). Chemical characterization revealed that soil slurries contained organic compounds that were more bioavailable than STP and aquaculture effluents, with glucose and fatty acids being the dominant forms. Conversely, STP effluent comprised small organic acids that were likely derived from the breakdown of organic compounds in sewage, whilst aquaculture effluent had more lipophilic compounds. DOC bioreactivity, measured as mg DO mg-1 DOC d-1, of the three sources correlated with C:N ratios and N:P ratios. These results suggest that microbes in the estuarine water were organic carbon and nutrient limited, depending on the source and concentrations. Our findings highlight the importance of considering organic carbon concentration, form, and source in monitoring and managing nutrient and organic matter inputs to waterways.
05:45 PM
THE MOBILITY AND RETENTION OF DISSOLVED ORGANIC MATTER IN PERMEABLE SEDIMENTS OF A HIGH-ENERGY SUBTERRANEAN ESTUARY (9701)
Primary Presenter: Kojo Amoako, Carl von Ossietzky Universität Oldenburg (kojo.amoako@uol.de)
Permeable sandy aquifers beneath high-energy beaches are potent biogeochemical reactors with high respiration rates. Besides contributing to nutrient and trace metal fluxes, little is known about their role as sinks or sources of dissolved organic matter (DOM). We explored DOM-solid phase interactions by analyzing the molecular composition of water- and acid-leachable sedimentary DOM down to 24m in a subterranean estuary (STE) on Spiekeroog Island, German North Sea, using fluorescence spectroscopy and FT-ICR-MS. We also examined the coprecipitation of DOM and Fe3+ (oxy)hydroxides in STE porewaters containing reduced Fe2+ after exposure to air. For both sediment treatments, ~10% of total organic carbon was leachable as dissolved organic carbon (DOC). Water leachates contained aliphatic, nitrogen-rich compounds indicative of marine origin, while acid leachates were more variable, including oxidized aromatic and labile compounds, likely from both terrestrial and marine sources. Fe-DOM coprecipitation induced molecular composition changes, but DOC removal was within analytical uncertainties, and molecular fractionation varied across sampling periods. Thus, DOM-Fe coagulation at redox zones of deep beach STEs may be low and influenced by transport-driven changes in porewater chemistry. Overall, terrigenous DOM is preferentially retained in sediments, while the labile fraction is more mobile. We suggest that in deep beach STEs, organo-mineral interactions are more important in governing DOM dynamics than infiltrating sea- and groundwater.
SS14C - Biogeochemical Connections and Ecosystem Adaptation Across the Land-Ocean Continuum
Description
Time: 4:30 PM
Date: 30/3/2025
Room: W207CD