Rivers transport large amounts of organic carbon, trace metals and nutrients from land to coastal oceans. At the interface between land and sea, elemental fluxes and transformations are strongly influenced by processes occurring across the continuum of rivers, wetlands, and estuaries. Increasing anthropogenic pressure (e.g., land use changes) and frequency of extreme events (e.g., hurricane landfalls, fires) are increasingly altering the sources and quality of organic carbon and nutrients exported to coastal ecosystems. Preserving the integrity of coastal aquatic systems is key as these systems provide critical ecosystem services to support societal development. It is therefore crucial to understand the biogeochemical connections of the carbon and nutrient cycles to ecosystem processes and microbial processing and how they are affected by humans. In our session we seek to bring together scientists from all areas of biogeochemistry that cut across boundaries, covering ecosystems from a wide range of latitudinal settings and spatiotemporal scales. Contributions that examine carbon and nutrient fluxes across the land-ocean-continuum, biogeochemical transformations in rivers, coastal wetlands, (subterranean) estuaries, and the fate of terrestrial carbon in the marine environment are particularly welcome. We also encourage submissions that seek to explain mechanisms underlying observed patterns in the distribution or rates of sedimentary, particulate, and dissolved organic matter transformation, their linkage to CO2 outgassing or uptake and microbial community composition across aquatic gradients, as well as approaches to quantify the response of coastal aquatic systems to environmental stressors in order to guide possible conservation and rehabilitation efforts.
Lead Organizer: Michael Seidel, University of Oldenburg (m.seidel@uni-oldenburg.de)
Co-organizers:
Patricia M. Medeiros, University of Georgia, USA (medeiros@uga.edu)
Sasha Wagner, Rensselaer Polytechnic Institute, USA (wagnes3@rpi.edu)
Nicholas D. Ward, Pacific Northwest National Laboratory, USA (nickdward@gmail.com)
Presentations
08:30 AM
Advancing an integrated understanding of land-ocean connections in shaping the marine ecosystems of Coastal Temperate Rainforest ecoregions (7428)
Primary Presenter: Brian Hunt, University of British Columbia (b.hunt@oceans.ubc.ca)
Land and ocean ecosystems are strongly connected and mutually interactive. As climate changes and other anthropogenic stressors intensify, the complex pathways that link these systems will strengthen or weaken in ways that are currently beyond reliable prediction. In this review we offer a framework of land-ocean couplings and their role in shaping marine ecosystems in Coastal Temperate Rainforest (CTR) ecoregions, where high freshwater and materials flux result in particularly strong land-ocean connections. Using the largest contiguous expanse of CTR on Earth, the Northeast Pacific CTR (NPCTR), as a case study we integrate current understanding of the spatial and temporal scales of interacting physical, geochemical, and biological processes across the land-ocean continuum, and examine how these processes structure marine ecosystems from nearshore to offshore domains. We look ahead to the potential effects of climate and other anthropogenic changes on the coupled land-ocean meta-ecosystem. Finally, we review key data gaps and provide research recommendations for an integrated, transdisciplinary approach that we hope will guide future evaluation of ongoing impacts in marine ecosystems of the NPCTR and other CTRs globally. In the light of extreme events, including heatwaves, fire and flooding that are occurring almost annually, this agenda is not only necessary but urgent.
08:45 AM
COMPOSITION OF PARTICULATE ORGANIC MATTER AT THE RIVER-ESTUARY INTERFACE: A COMPREHENSIVE STUDY AT A MULTI-ECOSYSTEMS SCALE (5958)
Primary Presenter: FERCHICHE Florian, Univ.Bordeaux (florian.ferchiche@u-bordeaux.fr)
Particulate organic matter (POM) is a key component of biogeochemical cycles and constitutes the baseline of the food webs. In riverine systems, POM is a mixture of sources (e.g. terrestrial POM, phytoplankton, microphytobenthos) originating from different reservoirs. POM elemental and isotopic ratios are widely used in aquatic biogeochemistry and ecology to estimate and even quantify the origin and composition of POM. However, POM elemental and isotopic values are usually highly variable in space and time making their use restricted to snapshot studies or requiring a dense temporal sampling strategy. In this study, POM was sampled for C and N elemental and isotopic ratios along with miscellaneous environmental parameters with the aim of quantifying the composition of POM and identifying the drivers of its spatial and temporal variability at the river-estuary interface. This study has been performed in 28 temperate rivers of France with monthly to bimonthly sampling over one to four annual hydrological cycles. The diversity of studied rivers translates into a large diversity of environmental drivers, resulting in a complete comprehension of the dynamics of POM composition. After the determination of the elemental and isotopic signatures of the POM sources, the results of the mixing models will be presented. Then, the drivers of both the temporal and spatial dynamics of POM position will be determined. Finally, a typology of river-estuarine interfaces based on POM composition and drivers will be put forward.
09:00 AM
Fate of riverine terrestrial dissolved organic carbon on the North West European Shelf (5842)
Primary Presenter: Helen Powley, Plymouth Marine Laboratory (hpo@pml.ac.uk)
Terrigenous carbon in aquatic systems is increasingly recognised as an important part of the global carbon cycle. Despite this, the fate and distribution of terrigenous dissolved organic carbon (tDOC) in oceanic systems is poorly understood. We have implemented a theoretical framework for the degradation of tDOC across the land to ocean continuum in a 3D hydrodynamical-biogeochemical model on the North West European Shelf. A key feature of this model is that both photochemical and bacterial tDOC degradation rates are age dependant constituting an advance in our ability to describe carbon cycling in the marine environment. Over the time period 1986-2015, 183 Gmol yr-1 of riverine tDOC is input to the shelf. Results indicate that bacterial degradation is by far the most important process in removing tDOC on the shelf, contributing to 73% (133 G mol yr-1) of the total removal flux, while 21 % (38G mol yr-1) of riverine tDOC was advected away from the shelf. Explicitly including tDOC in the model increased the air-sea carbon dioxide (CO2) flux by 111 Gmol yr-1 (4%), an amount approximately equivalent to the CO2 released by the UK chemical industry in 2020. Overall, 61% of riverine tDOC input to the shelf is outgassed as CO2 while approximately 19% is incorporated into the foodweb. This work can improve the assumptions of fate of tDOC by Earth System Models and demonstrates that the inclusion of tDOC in models can impact ecosystem dynamics and change predicted global carbon budgets for the ocean.
09:15 AM
TRACING RIVERINE IRON THROUGH DYNAMIC ESTUARINE SYSTEMS TO THE WEST FLORIDA SHELF (5073)
Primary Presenter: Hannah Hunt, University of South Florida (hannahhunt@usf.edu)
Iron (Fe) is an essential micronutrient for primary production but is often present at low concentrations (<0.1 nM), limiting primary production and nitrogen fixation over vast regions of the surface ocean. Dissolved Fe (dFe) is routinely elevated (up to 10 nM) in waters overlying the West Florida shelf, yet the relative importance of key dFe sources remains unclear. Dissolved Fe isotopic compositions (δ56Fe) are a valuable oceanographic tool for identifying sources and internal cycling of dFe in the global ocean. The δ56Fe endmembers of key Fe sources to the surface ocean are well established, but limitations on spatial and temporal data leaves a high degree of uncertainty in the global riverine δ56Fe endmember (-1.34 to +1.78‰). Across the estuarine transition, removal processes such as flocculation, scavenging and precipitation facilitate significant loss of riverine Fe from the dissolved phase and are associated with a high degree of Fe isotopic fractionation. Here we present dFe and δ56Fe data from five key rivers (Hillsborough, Alafia, Manatee, Peace, Caloosahatchee) three estuaries (Tampa Bay, Charlotte Harbor and Caloosahatchee Estuary) and eleven submarine groundwater wells on the West Florida Shelf to investigate the relative importance of such Fe sources to the shelf environment. We aim to further constrain mechanisms of modification, addition, or removal of dFe through the riverine-estuarine-open ocean transition in this region, with implications for understanding the role of riverine derived Fe on primary production, nitrogen fixation, and red tide.
09:30 AM
A PEATY SEA: FATE OF TERRESTRIAL DOC IN COASTAL SOUTHEAST ASIA (5078)
Primary Presenter: Patrick Martin, Nanyang Technological University (pmartin@ntu.edu.sg)
The tropical peatlands of Southeast Asia deliver roughly 10% of the global land–ocean flux of terrestrial DOC (tDOC). The land boundaries and seasonally reversing ocean circulation of Southeast Asia’s shelf sea ensure that this tDOC has a relatively long residence time on the shelf, creating ideal conditions to track tDOC biogeochemical processing. We will present results from our recent work to better understand the flux and fate of this tDOC in the shelf sea. Using satellite remote sensing, we have detected a significant increase in coastal tDOC concentrations by about 0.3 micro-mol l-1 year-1over the last two decades that is likely linked to large-scale peatland deforestation and drainage. Moreover, a mass balance analysis of carbon stable isotopes between the dissolved organic and inorganic carbon pools indicates that at least 60–70% of the peatland tDOC is remineralized within the shelf sea, creating significant acidification in the shelf waters. Degradation experiments with peatland tDOC and model simulations indicate that the rates of purely microbial and purely photochemical remineralization are slow, but that partial photodegradation greatly enhances the rate of subsequent microbial remineralization. We will also discuss efforts to incorporate tDOC transport and degradation into a regional shelf sea biogeochemical model for Southeast Asia.
09:45 AM
Regional drivers of organic carbon age in lotic systems of the conterminous United States (7369)
Primary Presenter: S. Leigh McCallister, Virginia Commonwealth University (slmccalliste@vcu.edu)
Radiocarbon data show that a fraction of riverine organic carbon (OC) has been pre-aged in the terrestrial environment. Relatively little is known, however, about the regional climatic, anthropogenic, and landscape factors that promote the mobilization of aged OC to rivers. This study examines associations between riverine OC and river basin characteristics. It leverages data from three sources: 1) a spatially extensive compliation of literature-reported radiocarbon measurements from the conterminous United States, 2) the U.S. Environmental Protection Agency’s Stream-Catchment (StreamCat) database and 3) fire regime data from the U.S. Department of Agriculture Forest Service Landscape Fire and Resource Management Planning Tools (LANDFIRE, 2021). The compiled radiocarbon data include 99 dissolved organic carbon (DOC) and 57 particulate organic carbon (POC) ages, respectively after averaging by location. We used the random forest (RF) machine learning algorithm to build independent models with StreamCat data as predictor variables. Each model used 3,000 trees and a random 75:25 data split for model validation, and results were averaged across 1,000 iterations (mean 14C-DOC-MSE = 5,186.1, r = 0.54; mean 14C-POC-MSE = 12,299.8, r = 0.68). Our results suggest that the controls on radiocarbon age vary between the OC pools. Anthropogenic drivers were associated with the presence of old POC while land cover and related processes were the primary variables affecting DOC age.
SS009A Biogeochemical Cycling Across the Land-Ocean-Continuum
Description
Time: 8:30 AM
Date: 6/6/2023
Room: Auditorium Illes Balears