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
06:30 PM
NITRATE CYCLING IN A LARGE, EUTROPHIC COASTAL LAGOON: SEASONAL VARIABILITY AND DRIVING FACTORS OF THE FILTER FUNCTION (6355)
Primary Presenter: Mindaugas Zilius, Klaipeda University (mindaugas.zilius@jmtc.ku.lt)
Lagoons, being situated at the interface between land and marine environments, are potentially important sites for nitrate (NO3–) retention due to massive nutrient loads, long retention time and high biogeochemical transformation rates. Although nitrogen (N) cycling is of considerable importance for eutrophication, only a few studies have quantified the multiple processes responsible for NO3– turnover (i.e. denitrification, DNRA, and NO3– assimilation) in lagoons. Simultaneous measurements of pelagic assimilatory and benthic dissimilatory processes in combination with quantifying riverine loads allowed us to depict a complete budget of seasonal NO3– cycling in the largest European lagoon (Curonian Lagoon, SE Baltic Sea). The specific NO3– transformation pathway was driven by the seasonal availability of NO3– in the water column. In spring, NO3– was in excess and the dominant N form in the water column fueling both pelagic and benthic processes. Deep light penetration illuminated half of the lagoon water column and sediment, and sustained photosynthetic activity, thus affecting benthic processes. In summer, a decrease in riverine loads resulted in lower NO3– concentrations, which affected only benthic processes. Whereas pelagic assimilation rates were maintained by active organic mineralization coupled with nitrification. Together, NO3– processes can retain up to ~70 % of the total N load. Our results show that under present climate conditions eutrophic lagoons are effective NO3– filters, but with ongoing changes and extreme events, their filter capacity may decrease.
06:30 PM
Linkages among biogeochemical processes, habitat loss, and nutrient exchange with the coastal ocean in a lagoonal estuary impacted by high nitrogen loading (5195)
Primary Presenter: Roxanne Marino, Cornell University (rmm3@cornell.edu)
Estuaries exist at the land-sea margin, so are both directly impacted by N pollution and important in the processing of terrestrial nutrients. West Falmouth Harbor (WFH) is a shallow estuary in Massachusetts (USA) that intercepts high-N groundwater discharge from a local aquifer impacted by a wastewater treatment facility. Our early work (2005-09) showed a net import of total N (TN), total P (TP), and inorganic P (DIP) from the coastal ocean during the summer. Import of P from coastal waters was sufficient to maintain N-limiting conditions, and the estuary on average retained the entire, large terrestrial N load plus additional N from the adjacent coastal waters (Buzzards Bay). This N retention was presumably a combination of seasonal storage and biogeochemical processes. Since 2010, there has been a significant loss of eelgrass habitat in the harbor. Between 2014 and 2019 we again measured summer season nutrient fluxes and found a continued net import of DIP, but a change to a small export of TP and a significant export of TN from WFH. Examining the incoming and outgoing tide data revealed that the concentrations of N and P in coastal waters that daily enter WFH have decreased, perhaps related to changes in N. Atlantic circulation patterns and warming coastal waters. Hence we are seeing changes in WFH seasonal net nutrient fluxes due to processes acting at both regional (climatic) and ecosystem scales. Inorganic N:P ratios still indicate strong N limitation of primary production, suggesting control of N inputs remains critical to ecosystem health and habitat recovery.
06:30 PM
Nitrogen removal in stormwater control measures along a vegetation gradient in coastal South Carolina (5562)
Primary Presenter: Darcy Perin, University of South Carolina (dperin@email.sc.edu)
Stormwater runoff is the major contributor to non-point source pollution and can contaminate many aquatic environments. Stormwater Control Measures (SCMs) are structural devices, such as retention ponds and constructed wetlands, used to control stormwater runoff from developed landscapes. One of the main pollutants found in stormwater runoff is nitrogen. Nitrogen is a macronutrient that limits primary productivity. In excess quantities, introduced nitrogen can lead to coastal eutrophication, harmful algal blooms, and coastal hypoxia. Although SCMs tend to be highly effective at removing particulate-associated pollutants, such as phosphorus, they are often much less effective at removing nitrogen. In this research, we aim to provide an estimate of nitrogen removal rates (denitrification) across a series of SCMs along a vegetation gradient. It is hypothesized that SCMs with more vegetation remove greater amounts of nitrogen compared to unvegetated SCMs (e.g., conventional stormwater retention ponds) because organic material provided by vegetation is a substrate for denitrification. We used whole sediment core 15N-labeled incubations and the isotope pairing method to measure denitrification rates at the center and the edge of several different types of SCMs in Georgetown and Horry Counties, in coastal SC (e.g., conventional unvegetated stormwater ponds, ponds with littoral shelves, constructed wetland). Thus far, we measured higher nitrogen removal rates (up to two orders of magnitude) in the more vegetated SCMs, which supports our main hypothesis. We anticipate results of this research will provide recommendations for improved use of vegetation in SCMs to maximize nitrogen removal and improve the water quality of stormwater runoff associated with coastal development.
06:30 PM
WARMING AND EUTROPHICATION PROMOTE NITROGEN REMOVAL AND N2O EMISSIONS IN COASTAL WETLANDS (5745)
Primary Presenter: Fenfang Wang, Xiamen University (ffwang@stu.xmu.edu.cn)
Global warming and eutrophication are fundamental threats to coastal wetlands, but their impacts on nitrogen (N) removal and N2O emissions remained unresolved. Here, we conducted sediment incubation experiments in coastal mangroves and salt marshes across different climatic zones in China. Denitrification was the major N removal process with potential rates of 0.3-51.4 mg N kg-1 d-1, while anammox played a minor role (0-22%). Denitrification increased by 0.2-0.8 and 0.3-4.5 mg N kg-1 d-1 for 1℃ warming and 1 mg L-1 NO3-N increase, respectively. Subtropical wetlands had the largest rate increase followed by tropical and temperate zones. Changes in climate and eutrophication in the past three decades drove N removal and N2O release at rates of 108-164 and 12-17 Gg N yr-1. The N removal is equivalent to carbon loss of 115-176 Gg C yr-1 based on the stoichiometry of organic matter consumption. Predicted scenarios of warming and nitrate enrichment would increase denitrification and N2O emissions by 4.4-24.8% in China’ coastal wetlands by 2050s. Overall, coastal wetlands have been and will continue to be effective filters of nitrogen pollution.
06:30 PM
Effects of Heavy Rainfall on Nutrients in Coastal Environments: Result from the Geum River Estuary, Korea (5725)
Primary Presenter: MINYOUNG LEE, Chonnam university (dlalsdud2005@naver.com)
In order to evaluate the effect of heavy rainfall on nutrients in the coastal environment, we measured the concentrations of organic and inorganic nutrients in seawater at the Geum River Estuary in August 2021 (weak rainfall) and August 2022 (heavy rainfall). The correlations between dissolved organic carbon (DOC), particulate organic carbon (POC), dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), dissolved silicate (DSi) and salinity showed the significant negative correlations (r2>0.8) in August 2022. The concentrations of DOC, POC, DIN, and DSi were higher up to 10 times in August 2022 than in August 2021. In order to determine the origin of DOC, we measured fluorescent dissolved organic matter (FDOM) and identified components (C, M, and T peak) using PARAFAC modeling. The correlations between peak M, peak C, peak T and DOC showed the significant positive correlations (r2>0.9) in August 2022. This study cannot exactly discriminate origin of DOC due to inputting various sources through heavy rainfall. Therefore, in order to determine the origin of organic matter, studies on 13C, 18O, and molecular structure are necessary.
06:30 PM
CARBON AND NUTRIENT EXPORT ACROSS SALTMARSH TO ESTUARINE CHANNEL: DO RHIZOSPHERE PROCESSES PLAY A CRITICAL ROLE? (4811)
Primary Presenter: Panunporn Tutiyasarn, University of Hamburg (panunporn.tutiyasarn@uni-hamburg.de)
Rhizosphere processes such as rhizosphere and microbial respiration produce belowground CO2 representing approximately 35 to 350 fold of atmospheric condition. High dissolved CO2 in soil water promotes soil acidification enhancing soil-mineral (carbonate or silicate) weathering process and controlling dissolved organic carbon (DOC) adsorption on soil-mineral surface. However, surprisingly little is known about the contribution of soil CO2 to carbon and dissolved silica (DSi) generation in the saltmarsh. This study pinpoint the feedback of soil CO2 gradients coupling with various rainfall regimes on carbon and nutrient export from the saltmarsh soil to the leachate water. Using the soil columns approach by manipulating three different soil CO2 conditions and precipitation gradients coupled with water chemistry analysis, we found that the effect of elevated CO2 on inorganic carbon (as total alkalinity or TA) showed logarithmic behavior and the magnitude increased up to 2.9 fold. While, the precipitation gradients showed a linear relationship with TA and the magnitude was highly pronounced with 3.3 fold. Furthermore, both elevated CO2 and precipitation posed a significant increase of the DSi production with the same observable behavior as TA. However, elevated soil CO2 did not significantly affect DOC mobilization. Together, our findings help explain that soil containing high CO2 plays a role in the generation of TA and DSi. It also provides the direct link between the role of rhizosphere processes and enrichment of carbon and nutrient export in saltmarsh soil.
06:30 PM
Intensified Mussel Farming; Impacts on Nutrient Budgets and Ecology in a Eutrophic Semi-enclosed Fjord System (6592)
Primary Presenter: Marie Maar, Aarhus university (mam@ecos.au.dk)
Mussel aquaculture provides food products with a high-quality protein content. At the same time, mussels store nutrients in their tissue that are removed from the system through harvesting. However, increasingly development of suspended bivalve aquaculture in the coastal zone also comes with a price as the ecological carrying capacity of the ecosystem may be exceeded. The aim of the present study is to support future fjord-management by estimating the nutrient budgets and ecological impacts of intensified mussel aquaculture in a shallow semi-enclosed system, the Limfjorden, using 3D ecosystem modelling. Model results showed a net removal of nutrients by suspended mussel cultures at basin scale, whereas at farm scale the efficiency was lower due to increased sediment fluxes. An increase in mussel farming from the current 4 kt-fresh weight to a future projection of 104 kt- fresh weight did not exceed the ecological carrying capacity with respect to impacts on sediment chemistry but could cause local declines in benthic bivalve populations. Intense mussel farming provided ecosystem services such as better oxygen conditions and higher Secchi depth together with lower nutrient- and chlorophyll a concentrations on basin-scale. There was a redistribution of nutrients, chlorophyll a concentrations, and Secchi depth between sub-basins in the fjord depending on farming location and intensity. Overall, intensified mussel farming could contribute to the mitigation of eutrophication effects by removing nutrients from land sources and by reducing the local sediment loading.
06:30 PM
DISTRIBUTION OF TRACE ELEMENTS AND MACRONUTRIENTS IN A GLACIAL RIVER PLUME: COPPER RIVER, ALASKA (7255)
Primary Presenter: Emily Ortega, University of Alaska Fairbanks (elortega@alaska.edu)
The Northern Gulf of Alaska (NGA) shelf is a subpolar ecosystem, which is impacted by seasonal freshwater input from rivers fed by glacial and snow melt in addition to precipitation. This input contributes to the temporal and spatial patterns of micro- and macronutrients observed in the vicinity of, and along the Alaska Coastal Current (ACC), a defining feature of the NGA shelf that acts as an alongshore transport mechanism and a barrier between the inner shelf and further offshore waters. The sediment-laden Copper River is the largest source of freshwater to the ACC (and the NGA) providing large input of dissolved and particulate trace elements and silicic acid, but little nitrate and phosphate to the shelf region. A survey of the Copper River plume at peak flow in July of 2019, highlighted its impact on the biogeochemstry of the shelf. Differences in nutrient ratios (N:P) delineated “fresh” and “aged” plume waters and reflected a combination of particle scavenging of P and inhibition of primary production in turbid waters. Concentrations of H₄SiO₄ were approximately double (20.0±5.46 µM) in the “fresh” plume compared to “aged” plume waters (10.26±2.81 µM). Trace metal concentrations declined rapidly as plume waters aged and mixed with surrounding coastal water. For example, labile particulate Fe decreased by several orders of magnitude, and dissolved Fe ranged from 6.09 to 0.05 nM across the study region.
06:30 PM
DAM REMOVAL AND THE FATE OF SEDIMENT: CAN MACROPHYTES MINIMIZE SEDIMENT LEAKAGE OF GREENHOUSE GASES AND NUTRIENTS? (6915)
Primary Presenter: Anna Bottone, Uppsala University (anna.bottone@ebc.uu.se)
Reservoirs act as a barrier to sediment flow along the water-ocean continuum and host processes of organic matter (OM) sedimentation and mineralization through which nutrients are retained from downstream water bodies, leading to decreased river functioning. Moreover, OM mineralization in sediment is enhanced during reservoir operation by sediment exposure to oxygen or by littoral vegetation influencing reservoirs GHG footprint. Hence, dam removals are becoming more common once they are no longer functional, but the fate of the accumulated sediment is still not well understood. Here we investigate the effect of changes in sediment water content on GHG emission, nutrient leaking, and macrophytes-sediment interaction by means of sediment mesocosms collected from a reservoir in southern Sweden. Mesocosms were divided into treatments simulating pre and after dam removal conditions with and without vegetation. We hypothesize that the presence of macrophytes increases the degradation of sediment organic carbon to carbon dioxide (CO2) under drying condition, while under water-logged condition they facilitate methane release. We further hypothesize that macrophytes will reduce nutrients leakage to the water. Preliminary results show that vegetated sediments act as CO2 sinks while methane emission shows dependence on plant species but both independently of hydrological conditions. Macrophytes also hamper nutrient release in sediment pore water. Results from this experiment is expected to inform strategies for minimizing environmental impacts from sediments at dam removal.
06:30 PM
Biogeochemical Drivers of Methane Cycling in a Rewetted Coastal Peatland (5352)
Primary Presenter: Sara Anthony, University of Rostock (sara.anthony@uni-rostock.de)
Peatlands are an integral part of the natural carbon cycle, but have often been drained and used for agricultural purposes. Rewetting of drained peatlands can help mitigate anthropogenic climate change, and their health and function as a carbon sink is integral to achieving a sustainable future. Rewetting reduces the output of carbon dioxide (CO2) and nitrous oxide (N2O) but comes with increased methane (CH4) emissions. For coastal peatlands, the magnitude of CH4 release may be reduced through rewetting with brackish water which is thought to simultaneously promote methanotrophy and inhibit methanogenesis. To investigate this assumption and elucidate the influence of biogeochemistry on CH4 cycling, a 1-year intensive monitoring campaign of a recently rewetted coastal peatland was initiated in July 2022, with biweekly surface water and porewater sampling. The first results of this monitoring will be presented, including pH measurements, CH4 and CO2 concentrations, δ13C-CH4, δ13C-CO2, iron speciation, acetate, methylamines, major cations, anions, nutrients, and dissolved organic carbon as well as organic carbon fractions to characterize the biogeochemistry and the intricacies of methane production, consumption, and release at the site.
06:30 PM
Lability of land- and sediment-derived dissolved organic carbon in high Arctic fjords (Spitsbergen) (5648)
Primary Presenter: Katarzyna Koziorowska-Makuch, Institute of Oceanology Polish Academy of Sciences (kkozio@iopan.gda.pl)
Dissolved organic carbon (DOC) is the largest organic carbon pool in the ocean. While in the open waters this pool is relatively constant, it continuously evolves in the coastal zone with the most prominent changes occurring in the Arctic. Although there are some quantitative estimations of different DOC loads to the Arctic fjords, their fate remains highly unknown. It is still unclear to what extent the DOC entering the fjords is bioavailable and how fast can it be remineralised. Therefore, the following research objectives have been formulated: to assess the lability of the terrigenous and sediment-derived DOC, and to estimate remineralization rate constants and half-life times for bioavailable DOC fractions. This has been done through the 180-days-lasting incubation experiments of soil leachates mixed with surface seawater and sediment interstitial waters mixed with bottom water. For the study site, Spitsbergen fjords have been selected. The results indicate that both the soil leachates and interstitial waters contain a lot of DOC (420-2730 μmol L-1 and 220-470 μmol L-1, respectively), which is highly bioavailable – the DOC decay observed during the experiments was 61-66% and 40-60%, respectively. This high lability of DOC indicates that its supply to the water column has the potential to play an essential role in sustaining the bacterial loop in the fjord and, through CO2 release, in amplifying ocean acidification in the coastal zone. This knowledge is extremely desired as it allows for a better understanding of the processes shaping carbon cycling in the Arctic fjords.
06:30 PM
ACID-BASE PROPERTIES OF DISSOLVED ORGANIC MATTER EXTRACTED FROM THE EBRO RIVER (5108)
Primary Presenter: Joao Alves Macedo, University of Lleida (joaocarlosalvesmacedo@hotmail.com)
Dissolved organic matter (DOM) is a complex and heterogeneous mixture of chemical compounds ubiquitous in aquatic ecosystems. The DOM has acid-base properties (i.e., proton binding) that are essential in controlling the biogeochemical cycles of carbon and nutrients. For example, interactions between metals and DOM are conditioned by environmental factors such as pH, ionic strength, and temperature, and the competition with other cations, including protons, for the binding sites of the DOM. Here we investigate the proton binding properties of DOM extracted from two distinct points along the Ebro River (NNE of Spain), the second longest and fastest flowing of the Iberian Peninsula. The first sample was collected at the source of the river, and the second one after an area under great demographic and agricultural pressure. We used the non-ideal competitive adsorption (NICA) model to describe heterogeneity and biding at equilibrium and account for the impact of ionic strength via the Donnan electrostatic interaction model. We identify potential changes in DOM composition according to variations in 1) the number of chemical groups available for cation binding; 2) the intrinsic proton affinity constants; 3) the chemical heterogeneity. The obtained intrinsic binding parameters can provide insight into DOM reactivity, source, fate, and bioavailability, and better predict potential changes under future environmental stressors in terms of temperature and pH.
06:30 PM
Dissolved organic matter composition influences metabolic activity and ammonium uptake across biomes (6376)
Primary Presenter: Anna Lupon, CEAB-CSIC (anna.lupon@gmail.com)
Carbon (C) and nitrogen (N) cycles in streams are highly coupled because many N processes are mediated by dissolved organic matter (DOM) availability. Yet, our knowledge on how DOM stoichiometry influences in-stream C and N processing is far from complete. To assess the role of DOM stoichiometry (i.e. C:N ratio) as a driver of stream aerobic metabolism and N uptake, we performed constant-rate additions of resazurin and ammonium, with and without a co-release of acetate, in 17 headwater streams of five biomes. The streams showed contrasting concentrations of dissolved organic C (DOC; 0.5⎼30 mg C/L) and dissolved inorganic N (DON; 0.008⎼0.5 mg N/L), resulting in a wide range of DOC:DON ratios (from 5 to 201). For each release, we calculated in-stream ammonium and acetate uptake, and analyzed heterotrophic activity based on resazurin transformation. Under ambient DOC conditions, DOC:DON ratio was not related to global patterns of heterotrophic activity. However, DOM stoichiometry explained 32% of the variability in in-stream ammonium uptake velocity, with higher values observed in Arctic streams holding high DOC:DON ratios. When acetate was co-released, both heterotrophic activity and ammonium uptake generally augmented, with larger increases occurring in streams with higher acetate uptake rates. In this case, DOC:DON ratio explained 15% and 50% of the variability in heterotrophic activity and ammonium uptake, respectively. Overall, our results highlight that DOM stoichiometry is critical for understanding the coupling between C and N cycling in headwater streams.
06:30 PM
Impacts of physical disturbance on sediment organic matter reactivity: an experimental approach (5470)
Primary Presenter: Christian Lønborg, Aarhus University (c.lonborg@ecos.au.dk)
A wide range of physical anthropogenic processes (e.g. bottom trawling, dredging) frequently disturb many coastal sediments, which cause resuspension of sediment derived organic matter into the overlaying water column. However, the potential impacts of this resuspension on the standing stocks and degradation pathways of organic matter remains to be determined. In this presentation, we will discuss results from an experiment designed to test whether reoccurring physical disturbance of sediments affect the organic matter pool in coastal waters. Our results demonstrate that reoccurring disturbance indeed affect not only the standing stocks, but also the degradation pathways of the sediment derived organic matter. These results are therefore not only of importance for understanding carbon and nutrient cycles, but also for guiding potential conservation efforts aiming at reducing human impacts on coastal waters.
06:30 PM
2H/1H RATIOS OF THE NON-EXCHANGEABLE HYDROGEN OF PARTICULATE ORGANIC MATTER: A NEW TOOL FOR QUANTIFYING POM SOURCES AT THE LAND-OCEAN INTERFACE (5799)
Primary Presenter: Nicolas Savoye, Univ.Bordeaux (nicolas.savoye@u-bordeaux.fr)
Particulate organic matter (POM) is a key component of aquatic system functioning. It mainly comprises i) autochthonous macro and microphytes and ii) more refractory allochthonous terrestrial organic material. Each differs by origin and role in aquatic biogeochemical and ecological processes and is challenging to differentiate. POM origin and composition are usually quantified with C and N elemental and isotopic ratios and by applying Bayesian mixing models. However, these tools may suffer of a lack of source discrimination in rivers; hence new tracers of POM origin are needed. Terrestrial organic matter 2H:1H ratios are controlled by meteoric water but differ significantly between land and aquatic-based primary production. We hypothesized that this ratio of the non-exchangeable H of POM could independently quantify POM composition over three years in the Loire River, France, at the river-estuary interface. Previous work using C and N elemental and isotopic data suggested that POM comprises terrestrial matter and phytoplankton. The POM non-exchangeable 2H:1H values revealed distinctive signatures: the terrestrial POM component had higher values but was constant over time (-110 ± 3‰ VSMOW), whereas phytoplankton was more 2H depleted (-147 ‰ to -120 ‰) and controlled by river water temperature. These signatures allowed us to quantify POM composition over the study period using a two-component H isotope mixing model. The H isotope results highly compared with the previous C- and N-based mixing models, indicating new potential for H isotopes in studies of POM flux dynamics
06:30 PM
DISSOLVED ORGANIC MATTER AND MICROBIAL COMMUNITY DYNAMICS IN SUBTERRANEAN ESTUARIES UNDER SALINIZATION AND CHANGING GROUNDWATER FLOW (6244)
Primary Presenter: Dini Adyasari, University of Alabama (dadyasari@ua.edu)
The subterranean estuary (STE) has been recognized as a reactive biogeochemical zone at the groundwater–seawater interface in coastal areas. In this study, we conducted controlled laboratory experiments to elucidate dissolved organic matter (DOM) processing and microbial community dynamics in STEs under various particle size distributions, salinity regimes, and incubation times. Incubations with silt-dominated sediments generated pore water characterized by high dissolved organic carbon (DOC)-to-dissolved organic nitrogen (DON) ratio, while the addition of high-ionic-strength treatments to the incubations led to reduced DOC solubility, selective removal of aromatic compounds, and altered ammonium (NH4+) generation pathway from predominantly biological (mineralization) to abiotic (ion exchange) pathways. Our experiments further indicated that the long incubation time caused the enrichment of DOC, DON, and bulk DOM consisting of degraded DOM compounds. Regarding the microbial community, Firmicutes, Proteobacteria, and Desulfobacterota were the most abundant phyla in incubated sediments. Although some phyla’s relative proportions were affected by different treatments, the taxonomic assemblages at the phylum level were similar across all samples. We observed a strong correlation between Bacillus and Verrucomicrobiae with highly refractory DOM, suggesting their role in the degradation process. Our results illustrate the sensitivity of DOM cycling in STEs to climate change variables, consequently affecting the quantity and quality of DOM transported to coastal waters worldwide.
06:30 PM
IMPACT OF LAND USE ON ORGANIC MATTER IN THE QUINNIPIAC RIVER AND ESTUARY (7258)
Primary Presenter: Joanna Kinsey, Quinnipiac University (joanna.kinsey@quinnipiac.edu)
Estuaries are highly productive, semi-enclosed aquatic ecosystems that are hotspots for biogeochemical transformation and exchange. Allochthonous and autochthonous inputs impact nutrient remineralization, microbial consumption, and particulate and dissolved organic matter flux to the coastal ocean. To investigate how the Quinnipiac River and its estuary were impacted by land use and precipitation over several years, ten locations between Wallingford and New Haven, Connecticut, USA were sampled. At each location abiotic measurements (temperature, pH, and salinity) and water samples were collected. Filtered water samples were analyzed for absorbance, fluorescence, and dissolved organic carbon concentrations. Particulate samples were analyzed for particulate organic carbon concentrations and base-extracted filters were measured for absorbance and fluorescence. Additionally select dissolved and particulate samples were analyzed for stable carbon isotopes (δ13C) and nitrate and nitrite concentrations. Preliminary results suggest enhanced primary production and carbon in the estuary that was reduced prior to the waters reaching Long Island Sound. Additionally, localized changes in pH and chemical composition were measured due to nearby construction and road work.
06:30 PM
EXPLORING RELATIONSHIPS BETWEEN BIOGEOCHEMICAL VARIABLES AND THE CHARACTERISTICS OF AGGREGATED FINE PARTICLES (‘FLOCS’) IN A MUDDY TIDAL RIVER (4939)
Primary Presenter: Christopher Eager, Waikato Regional Council (chris.eager@waikatoregion.govt.nz)
Dispersal and settling of fine sediments within aquatic environments is often a primary control on water quality, visibility, and ecosystem health. However, our current understanding of the fate of fine cohesive sediments is incomplete due to complexities associated with the process of flocculation (i.e. the aggregation of particles), which alters the size, composition and thus settling rate of particles. In particular, within tidal rivers, both hydrodynamic and biogeochemical conditions can vary substantially over a tidal cycle. Here, we report field observations from the heavily sediment-laden tidal Kaipara River in New Zealand. Measurements throughout several tidal cycles included floc particle size distributions obtained from floc cameras, suspended sediment concentrations from optical backscatter sensors calibrated against in-situ water samples. High-frequency physico-chemical measurements were also captured by in-situ EXOsondes (temperature, salinity, dissolved oxygen, pH, turbidity, FDOM, and Chl-a), alongside select wet-chemical analyses (DOC, POC, N, P, Chl-a concentration, DOM) on discrete water samples. We explore the temporal variability of, and relationships between, the biogeochemical variables and the characteristics of the aggregated particles (‘flocs’).
06:30 PM
ESTUARINE FLOCCULATION DYNAMICS OF ORGANIC CARBON AND METALS FROM BOREAL ACID SULPHATE SOILS (6314)
Primary Presenter: Eero Asmala, Geological Survey of Finland (eero.asmala@gtk.fi)
Transformation of terrestrial dissolved and colloidal material into suspended particles in estuaries is a critical process that impacts the global biogeochemical cycles of carbon and trace metals. These flocculation and aggregation processes occur due to the increasing salinity and pH towards the open sea. The role of pH is particularly relevant in the context of acid sulphate soils that can generate extremely low pH conditions and high soluble trace metal concentrations in river waters. We examined the flocculation dynamics with a series of experiments where natural river water draining acid sulphate soils was mixed with artificial seawater to simulate freshwater-seawater gradient in estuaries. The study focused on the changes in particle size distribution, optical properties of dissolved organic matter and behavior major metal elements. The humic-like DOM fluorescence showed inverse relationships with concentrations of organic-bound particulate Al and Fe, and particulate organic carbon, indicating co-precipitation of humic-like organic matter and dissolved metals. We also identified two major, distinct particle pools pertinent to the flocculation process: the finer classes (9-11 µm) showed low initial volume concentrations until salinity 1, while the coarsest classes (>150 µm) showed a strong initial increase that leveled off and turned to decrease at salinity 2. Our findings underline the importance of low-salinity flocculation and aggregation processes as crucial part of the coastal filter, regulating the transport of organic matter and metal elements from land to sea.
06:30 PM
RARE EARTH ELEMENTS AND YTTRIUM ALONG EASTERN ATLANTIC ESTUARIES (5251)
Primary Presenter: Franciele Novais, Universidade Federal da Bahia (novais1992@hotmail.com)
This is the first extensive study of REE in sediments from 12 estuaries along the Eastern Atlantic Coast in Brazil (i.e., Bahia: Jaguaripe, Paraguaçu, São Paulo, Mataripe, Subaé, Serinhaem, and Maraú; Pernambuco: Capibaribe and Santa Cruz Channel; and Espírito Santo: Doce, Piraquê Açú, and Vitória Bay). Here we quantified the abundances and determined the sources and fractionation of REE and Y. Concentrations of Al, Fe, and Mn were also evaluated to comprehend the influence of diagenetic remobilization. The ƩREEY varied from 6 mg kg-1 (Santa Cruz Channel; >90% sand) to 336 mg kg-1 (Piraquê-Açú; 50% silte+clay). Abundances of REE normalized by post-Archean Australian shale (PAAS) tended to be enriched in light REE (LREE; La to Nd) over heavy REE (HREE; Er to Lu). The estuaries Capibaribe, Jaguaripe, Paraguaçu, São Paulo, Mataripe, Subaé, and Doce River showed MREE enrichment. Five estuaries showed a significant positive correlation between ƩREEY and Al, Fe, and Mn. LREE showed a significant correlation with Al (r2>0.7) and Fe (r2>0.8) for most studied areas. REE were significantly correlated to Mn (r2>0.8) only for 5 estuaries. The bottom types and positions along the estuarine zones influence REEY, Al, Mn, and Fe concentrations. Anthropogenic activities are not impacting REE distribution and fractionation. The REE abundances observed here corroborate the characterization of the estuaries of Brazil’s east coast and can be used as a background for the region.
06:30 PM
IS THE IRON (FE) CONTAINED IN GLACIAL NANOPARTICLES BIOAVAILABLE TO MARINE MICROBIAL COMMUNITIES? A KERGUELEN ISLAND CASE STUDY (6296)
Primary Presenter: Rhea Thoppil, Sorbonne University (rhea.thoppil@obs-banyuls.fr)
Biogeochemical processes in the Southern Ocean (SO) are crucial for global ocean balance. Being the largest high-nutrient-low-chlorophyll region, surface waters in the SO hold a large potential for biological activity, in particular carbon dioxide drawdown and the “greening” of the SO. But these biological processes are limited by the essential nutrient iron (Fe). The accelerated melting of glaciers in the SO could be a significant source of Fe but whether this glacial Fe is bioavailable to microorganisms is inadequately understood. Answering such questions is vital for a better understanding of the influence of glacial Fe on marine microbes and their contribution to the carbon cycle. One pathway of interest is siderophores, low molecular weight compounds that can strongly bind to Fe in seawater and thereby render Fe bioavailable. In this study, we provided colloids obtained from lakes that were influenced or not by glacial melt to SO coastal marine microbial communities. Taxonomic profiling displayed significant differences in microbial community compositions between treatments, with known siderophore synthesizers contributing for about half of the relative abundance in incubations amended with glacial-lake colloids. Furthermore, Fe-related gene annotation analyses showed a higher relative abundance of siderophore synthesis and transport genes in these incubations. This indicates that natural bacterial communities can utilize siderophores to access Fe from glacial nanoparticles hence exhibiting different metabolic responses to a novel resource of Fe in the SO.
06:30 PM
THE IMPORTANCE OF LAND COVER IN CARBON AND IRON EXPORT IN NEWFOUNDLAND, CANADA. (6904)
Primary Presenter: Kavi Heerah, Memorial University of Newfoundland and Labrador (kmheerah@mun.ca)
The effects of land cover on the export of dissolved organic matter (DOM) and iron has been widely studied in the literature. While broad differences in land cover type are well understood the importance of small-scale differences has not been as well explored. Newfoundland, Canada is dominated by boreal and peat environments that are capable of transporting large amounts of ecologically relevant carbon and iron from land into the open ocean. The landscapes present are not completely homogonous with small lakes, shrubs, barrens, forest, and in peat environments small, stunted stands of trees can be found. These small breaks in the homogeneity of the landscape, in addition to other geological features, act to create distinct ecozones across the island of Newfoundland. In June 2022, we sampled rivers directly draining into the coast from 7 different ecozones. Two rivers were sampled for each ecozone, and samples were subjected to an artificial salinity gradient mimicking the conditions of an estuary. Changes in carbon and iron concentrations, DOM properties, and iron carrying capacities were assessed for each ecozone. Statistical analysis of the results show the importance of small differences in the landscape and have implications for carbon and iron burial in the coastal environment
06:30 PM
Tracking freshwater browning and coastal water darkening from the Baltic Sea forests to the Barents Sea (5279)
Primary Presenter: Anders Frugaard Opdal, University of Bergen (anders.opdal@uib.no)
The forest cover of Northern Europe has been steadily expanding during the last 120 years. More terrestrial vegetation and carbon fixation leads to more export to surface waters. This may cause freshwater browning, as more degraded plant-litter end up as chromophoric (coloured) dissolved organic matter. Although most freshwater ultimately drains to coastal waters, the link between freshwater browning and coastal water darkening is poorly understood. Here, we explore this relationship through a combination of centennial records of forest and coastal water clarity, contemporary optical measurements in lakes and coastal waters, as well as an ocean drift model. We suggest a link between forest cover in Northern Europe and coastal water clarity in the Baltic, Kattegat and Skagerrak Sea and suggest that brown coloured freshwater from Northern European catchments dictates coastal water clarity across thousands of kilometres, from the Baltic lakes to the Barents Sea
06:30 PM
IN-SITU RADON-IN-WATER DETECTION BENEFITS HIGH RESOLUTION SUBMARINE GROUNDWATER DISCHARGE ASSESSMENT (5952)
Primary Presenter: Shibin Zhao, Ocean University of China (ouc_zshib@163.com)
Submarine groundwater discharge (SGD) has been considered as a potential contributor to harmful algal bloom, coastal eutrophication, acidification and hypoxia. Natural radon (222Rn) is an excellent tracer for studying SGD and other oceanographic processes. In the past decades, radon measurement approaches for aquatic research have been fully developed but still suffer limitations. Here, based on our self-developed PIC radon detector, we not only refined the continuous integrated spatial survey measurement but also developed an automatic submersible radon determination approach to produce in-situ high data throughput at any water depth of interest. We demonstrate radon measurement efficiency of the PIC is 2-fold higher than a traditional RAD7 detector and is far less influenced by moisture. The radon degassing efficiency of the membrane contactor is comparable to the shower-head type air-water exchanger but is independent of operating position. We successfully deployed the submersible system in 3-meter water depth over a 100-hours period in an anthropogenic influenced bay. Based on high temporal resolution observations, the SGD flux was estimated to be 25.4±14.5 cm/d. Groundwater derived DIN and DIP occupied 74% of total DIN and 82% of total DIP input of this regions, respectively. The SGD fluxes pattern plotted together with the tidal variations revealed that tidal pumping may be the main driving force that affects nutrient, carbon and other dissolved matters dynamics in coastal aquifers.
06:30 PM
Permafrost and Groundwater Interaction: current state and future perspective (5703)
Primary Presenter: Magdalena Diak, Institute of Oceanology of Polish Academy of Sciences (diakmagdalena@gmail.com)
Groundwater circulation in the polar regions is controlled by the presence of permafrost, which acts as an aquitard and inhibits groundwater recharge and discharge. Climate change significantly contributes to permafrost thaw, which causes the formation of new paths for groundwater seepage accompanied by previously immobile chemical substances. The primary objectives of this work are the systematisation of existing knowledge on the effects of permafrost thaw on the aquatic system, identification of knowledge gaps and future research needs. The research area is focused on the permafrost regions of the Northern Hemisphere. The obtained findings reveal our poor understanding of the influence of permafrost thaw on the solute fluxes, especially via groundwater discharge, to aquatic systems and the consequences of the delivered fluxes on the biogeochemistry of surface waters. The investigation of aquatic ecosystem structure, functioning, and stability affected by permafrost thawing and associated delivery of solutes to surface waters remains understudied. As the long-term measurements are lacking and studied areas are differentiated, thus we can only speculate about future ecological changes. Investigation and a better understanding of the effects of permafrost thaw on constituent fluxes to surface waters are still research priorities. Funding: Project No. 2019/34/H/ST10/00645 "Submarine Groundwater Discharge in a Changing Arctic Region: Scale and Biogeochemical impact", which is supported by the Norwegian Financial Mechanism and Polish national Basic Research Program
06:30 PM
Preliminary investigation of submarine groundwater discharge into the Gulf of Varna, NW Black Sea (6831)
Primary Presenter: Stanislaw Kurowski, University of Alabama (smkurowski@crimson.ua.edu)
The Gulf of Varna is located on the western coast of the Black Sea and includes the Port and city of Varna. With a population of 340 thousand, the city is the third-largest city in Bulgaria, and it has been a significant economic, social and cultural center for almost three millennia. Evidence shows that the Ancient Greeks settled this site because of the nearshore freshwater resources. Nevertheless, the sources and magnitude of submarine groundwater discharge (SGD) at this and similar sites along the coastline of the Black Sea were hardly investigated. Using radon (222Rn) as a tracer during the research done in the fall of 2019 (wet season), hotspots of SGD were identified on the southern shore of the gulf. Results indicate that these are primarily saline seepages. We also found that SGD hot spots were associated with high dissolved P and N, which were found in the eastern part of Varna Lake and Varna Beach (next to the city’s historic center). Correlations were observed between groundwater discharge and the Monstrilla sp. and Lamellibranchia veliger populations. The preliminary data indicate that the magnitude of SGD is affected by hydraulic gradients, and the effect of tidal pumping is negligible. Further, we hypothesize that the local gulf circulation might regulate SGD. Observed high nutrient concentration might be related to leakages from artificial channels connecting the gulf with the Lake of Varna. Several toxic wastewater leaks have been reported, affecting water quality in the gulf.
06:30 PM
INFLUENCE OF IONIC STRENGTH ON THE CHARACTERIZATION OF THE INORGANIC CARBON SYSTEM IN RIVERINE WATERS (5906)
Primary Presenter: Katelyn Schockman, NOAA Atlantic Oceanographic and Meteorological Laboratory (katelyn.schockman@noaa.gov)
Rivers are important contributors of carbon, nutrients, and other chemical species, providing the link between biogeochemical cycling on land and the coastal oceans. Appropriate physico-chemical characterizations of rivers are important for accurately studying these biogeochemical processes. In specific, river carbon chemistry has an important spatiotemporal variability, which has not been well constrained due to data limitations. The sparseness of data results in larger uncertainties when estimating changes in carbon cycling within these river regions, including estimates of pH, CO2, and calcium carbonate saturation states. A relevant aspect to properly characterizing rivers, and thus accurately modelling the inorganic carbon system, is ionic strength (i.e., specific conductance). Here we present a novel method to measure ionic strength based on spectrophotometric pH methods, which improves both the accuracy and precision of ionic strength measurements compared to more traditional conductometric instruments. The impacts of these measurement improvements on inorganic carbon system parameter estimations was investigated near the Mississippi River Delta and Tampa Bay, two regions within the Gulf of Mexico that are strongly influenced by river runoff. Our findings suggest that ionic strength errors can cause significant biases in calculations of pH, CO2 fluxes, and calcium carbonate saturation. Thus, accurate measurements of ionic strength are a critical component to obtaining an accurate picture of the inorganic carbon system variability in river influenced coastal margins.
06:30 PM
CAN COMPREHENSIVE 14C AND 13C INVENTORIES OF SWISS RIVER AND LAKE CATCHMENTS EFFECTIVELY CONSTRAIN LATERAL CARBON FLUXES? (6073)
Primary Presenter: Alexander Brunmayr, Imperial College London (asb219@ic.ac.uk)
As the critical importance of the land-ocean continuum's role in the global carbon balance is becoming ever more apparent, terrestrial carbon cycle models are now increasingly including an explicit representation of lateral carbon transport. However, the fluxes and mechanisms associated with lateral carbon transport through inland waters remain highly uncertain and poorly constrained. In this study, we investigate how burgeoning 13C and 14C datasets covering river and lake catchments in Switzerland help constrain a novel land-river-lake carbon cycle model. The measured samples comprise representative carbon phases and fractions in all major carbon reservoirs, and isotopic analysis allows us to effectively disentangle the different carbon sources in the receiving basins. Our datasets include 13C and 14C measurements of particulate and dissolved organic carbon, and dissolved inorganic carbon in river and lake water, dissolved phases of carbon in groundwater, and particulate, dissolved, and mineral-associated organic carbon in soils. These snapshots in time are supplemented with long-term isotopic records from lake sediments. The assimilation of these comprehensive and diverse datasets by our model exposes both the capabilities and limitations of high-density 13C and 14C data for the study of lateral carbon transport. We seek to further explore the potential of synergetic land-water sampling strategies for more effective model calibration, and ultimately to constrain the magnitude and sensitivity of lateral carbon fluxes as a component of the terrestrial carbon cycle.
06:30 PM
Understanding the biogeochemical interactions of the Scheldt-North Sea River-Ocean continuum through multiscale modelling (6562)
Primary Presenter: Ny Riana Randresihaja, UCLouvain (ny.randresihaja@uclouvain.be)
Predicting and understanding the river-estuary-ocean continuum over short and long-time scales are pressing demands for the next decade and beyond. Growth of computing resources had already greatly helped the discipline of coupled land-ocean-atmosphere regional models to evolve over recent years. But many challenges remain to be tackled and land-ocean continuum modelling is one of them. Indeed, the kilometre-scale regional coupled prediction approach, especially when coupled with biogeochemistry, has a lot of progresses to achieve in terms of solving coupled physical- biogeochemical processes in the different components and interactions between them. This project aims to quantify the multi-scale interactions along the river-estuary-ocean-atmosphere continuum from hourly to multi-annual time scales over the Scheldt-North Sea region. In particular, we will assess how the physical and biogeochemical dynamics of the North Western Continental Shelf (NWCS) (i.e. limited by the 200m isobath) and Southern Bight of the North Sea (SBNS) are influenced by the small-scale variability of the Scheldt river-estuary and the atmosphere. For solving the multiscale interactions along the land sea continuum, we propose to develop a modelling framework, coupling unstructured (finite-elements) and structured (finite-differences) grid models for fully resolving in three dimensions the continuum of scales and processes from a few hundreds of meters up to several tens of kilometers. For the atmosphere, we will assess the impact of atmospheric forcing resolution provided by the regional climate model MAR on the quality of ocean prediction over the NWCS. Simulations coupling in 1-way will be done to assess the impact of weather events (e.g. storms, heat wave) on the ocean physics. From a biogeochemical point of view, the modelling system developed will offer an optimal way to quantify the transfer of organic and inorganic materials (e.g. suspended particulate materials, SPM) from the land to the sea and to track pollution events.
SS009P Biogeochemical Cycling Across the Land-Ocean-Continuum
Description
Time: 6:30 PM
Date: 6/6/2023
Room: Mezzanine