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
09:00 AM
Temporal changes in terrestrial organic matter loading to coastal sediments of the Baltic Sea (8906)
Primary Presenter: Tom Jilbert, University of Helsinki (tom.jilbert@helsinki.fi)
Early diagenesis in coastal marine sediments is primarily controlled by inputs of organic matter. These inputs may be derived from a range of autochthonous and allochthonous sources, which display variable reactivity in the sediment column and thus affect the balance between carbon burial and regeneration. In the low-salinity Baltic Sea, eutrophication and associated loading of autochthonous carbon have led to marked shoaling of sedimentary redox zones, promoting methane release and compromising the function of marine sediments as a carbon sink. However, up to 30% of organic matter in sediments of the Baltic Sea is estimated to be of allochthonous origin (Miltner & Emeis, GCA 65, 2001). Human activities in catchment areas, including forest clearance and ditching, may have significantly impacted fluxes of terrestrial organic matter across the land-sea interface, yet the scale of these impacts on carbon loading to marine sediments remains unknown. Here I will discuss new data from CuO extractions of dated sediment cores in the northern Baltic Sea, showing coherent temporal changes in the magnitude and composition of lignin inputs to sediments over the past five decades. These changes reflect the evolution of land use and forest industry activities during this period, suggesting a direct signal of changes in terrestrial organic matter inputs to marine sediments. Furthermore, porewater data from key locations show that this material has contributed to overall carbon loading and stimulation of methanogenesis in the upper sediment column.
09:15 AM
Influence of terrestrial inputs on Arctic planktonic community structure at eroding permafrost coasts (9411)
Primary Presenter: Gabriel Juma, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (gabriel.juma@awi.de)
The Arctic is currently warming about four times faster than the global average. This increases permafrost thaw, and the supply of carbon, nutrients and sediment into the nearshore zones. However, it remains understudied how these changes influence planktonic community structure, that form the basis of the Arctic food web. Here, we investigated the interplay between seawater physical and chemical parameters and planktonic composition and abundance at Herschel Island (Canadian Arctic). In July 2022 and 2023, we sampled up to 2000 m along a retrogressive thawing slump-affected transect area, and along a non-slump-affected area. We found significantly higher turbidity and concentrations of particulate carbon and nitrogen, near the shore, and in the slump-affected transect, confirming increased input of terrestrial material in degrading permafrost coasts. Phytoplankton and microzooplankton abundances were higher in the non-slump affected transect than in slump affected transect. However, bacterial biomass did not differ significantly between the transects. Although diatoms groups of Pseudo-nitzchia delicatissima and Skeletonema costatum dominated the phytoplankton community in both transects, Dinobryon were only observed in slump-affected transect. Shannon-Weiner diversity index also confirmed a higher diversity in the non-slump affected transect. Our results show that permafrost thaw affects planktonic community composition and abundance. Higher slumping activity enhances input of carbon and nutrients, but light attenuation due to sediment input might be negatively affecting phytoplankton productivity.
09:30 AM
DIFFERENT DISSOLVED ORGANIC MATTER SOURCES SUSTAIN MICROBIAL LIFE IN THE SUBTERRANEAN ESTUARY OF A HIGH-ENERGY BEACH (9683)
Primary Presenter: Grace Abarike, Carl von Ossietzky Universität Oldenburg (grace.abarike@uol.de)
In subterranean estuaries (STEs), microbial life is fueled by dissolved organic matter (DOM) introduced with meteoric groundwater and seawater. In high-energy beaches with dynamic porewater advection, microbes face frequent changes in groundwater composition, even at several meters depth. However, the distribution of DOM in the deep STE and its processing by microbes is poorly understood. We incubated sediment with deep (6 m) STE groundwater of low (1.6) and high (29.1) salinity from a high-energy beach on Spiekeroog Island, Germany. We quantified dissolved organic carbon (DOC) and analyzed DOM,and microbial community composition. Ultra-high resolution mass spectrometry revealed that both groundwater types contained mainly reworked DOM; however, meteoric groundwater had a more terrestrial DOM signature. During incubation, DOC concentrations increased primarily due to leaching of sedimentary organic matter, providing an additional carbon source. The DOM composition changed significantly from start to end and similarly for both groundwater types. Some molecular formulas (MF) were lost during incubation, indicating continuous degradation of recalcitrant DOM in the deep STE. Characteristics of newly detected MF in both groundwater types were indicative of labile DOM and some of them were also identified in sediment-leachates. The contribution of sediment-derived DOM as a potential substrate for deep STE microbial communities was confirmed in a study of a continuous 24 m long core at the same site.
09:45 AM
Ecological and biogeochemical impacts of tidal impoundment on coastal salt marshes: establishing baselines for assessing post-restoration ecosystem responses (9129)
Primary Presenter: Shao-Min Chen, University of Georgia (shaomin.chen@uga.edu)
Structures restricting tidal flow to coastal marshes are common and often have negative consequences for ecosystem functioning. Restoration of tidal connectivity between impounded wetlands and saltwater bodies has the potential to restore reduced or lost ecosystem functions. Here we investigated ecological and biogeochemical processes in an impounded coastal wetland and a nearby brackish marsh with natural hydrology in Gulf Shores, AL. Surface water levels, plant communities, soil porewater chemistry, nitrogen cycling, and greenhouse gas emissions were measured seasonally over two years in each wetland. Freshwater retention was evident by higher surface water levels and lower salinities in the impounded marsh. The lower salinities and sulfate levels in the impounded site resulted in lower porewater sulfides but much higher dissolved methane and methane gas fluxes to the atmosphere. Taller plants that are typical of fresh-to-brackish wetlands were observed in the impounded marsh, which may explain the more oxidizing soil conditions and near-complete denitrification inhibition. The impounded wetland had lower denitrification rates likely reflecting competition for nitrate and dissolved organic carbon with plants and DNRA microbes, respectively, and inhibition from more oxidizing conditions. In the nearby brackish marsh, the soil carbon accumulation rates were 43% higher compared to the impounded wetland. Together, our data demonstrates that tidal impoundment reduces wetland ecosystem functioning by decreasing N removal efficiency by 21% and C accumulation rates by 30%.
10:00 AM
Dynamics of dissolved organic matter in seawaters and sediment pore waters from river-impacted coastal sea (9718)
Primary Presenter: Meilian Chen, University of Tennessee, Knoxville (mchen51@utk.edu)
As one of the world’s largest marginal seas, the South China Sea (SCS) plays an important role in regional and even global carbon budgets. Yet, understanding regarding DOM dynamics in coastal seawaters and sediment pore waters is still limited. Here, optical and molecular methods are utilized to investigate spatiotemporal dynamics of seawater dissolved organic matter (DOM) and composition of sediment pore water DOM in northern SCS. Generally, higher chromophoric and fluorescent DOM (CDOM and FDOM), coincident with higher CDOM molecular weight and humification index, are observed in summer monsoon than in the winter monsoon due to the seasonality of riverine runoffs. Nearshore surface seawaters were plume-affected whereas CDOM and FDOM of bottom waters were enhanced by inputs from sediment resuspension, leading to higher levels in bottom waters offshore. Furthermore, high abundance of condensed aromatics (~12.6±3.2%) and S-containing formulas (20±2%) were found in sediment pore waters, implying coastal sediment pollution caused by presumably anthropogenic activities. Common formulas shared by all pore water samples at different sites and depths are predominated by CHO-only molecular formulas (97%) which largely fall in the lignin-like/CRAMs(i.e., carboxyl-rich alicyclic molecules) category of the van Krevelen diagram. The study provides insights into the DOM dynamics in a river-impacted subtropical/tropical sea.
10:15 AM
Interspecific differences in coralline algae calcification and internal pH regulation response to ocean acidification (9746)
Primary Presenter: Blanca Alvarez Caraveo, University of California, Los Angeles (alvarezblanca@g.ucla.edu)
Coralline algae are foundational species that act as important reef builders in many marine ecosystems. Coralline algae primarily produce high-Mg calcite, a more soluble calcium carbonate polymorph which renders these organisms more susceptible to ocean acidification (OA). In the study we evaluate the interspecific impact that OA has on the calcification and δ11B, a proxy for the internal pH of their calcification space (pHcf), of different species of coralline algae. We examine four species from two distinct morphological groups: geniculate (Corallina spp. and Corallina berteroi) and non-geniculate coralline algae (Phymatolithopsis repanda and Pneophyllum spp.). We exposed specimens to four pH treatments that represented ambient seawater pH (8.03) and three end-of-century seawater pH scenarios (7.93, 7.83, and 7.63) following IPCC relative concentration pathways. We found that OA resulted in a decrease in calcification for all species. Additionally, all species maintained an internal pHcf well above seawater pH, consistent with previous studies. Three species maintained a constant pHcf across all pH treatments, indicating a marked resilience to ocean acidification. This study provides insight into the ability of different geniculate and non-geniculate coralline algae species to potentially regulate the internal pH of their calcification space (pHcf) to buffer against the impacts of OA.
SS14A - Biogeochemical Connections and Ecosystem Adaptation Across the Land-Ocean Continuum
Description
Time: 9:00 AM
Date: 30/3/2025
Room: W207CD