Located between land and oceans, coastal aquatic ecosystems such as estuaries and coastal wetlands are dynamic ecosystems that connect the terrestrial, riverine, marine, and atmospheric biogeochemical cycles. They receive large inputs of terrestrial organic matter, and carbon and nitrogen inputs from upstream rivers, groundwater flows, and the ocean. Along the land-to-ocean aquatic continuum, carbon and nitrogen in coastal ecosystems are biogeochemically processed, sequestered in sediments, exported to the ocean, or exchanged with the atmosphere in form of the greenhouse gases carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Therefore, coastal aquatic ecosystems play an important role in regional and global greenhouse gas budgets. Anthropogenic impacts such as land-use changes and global warming can significantly alter these processes and enhance coastal greenhouse gas fluxes. This session aims to bring together the many different disciplines (e.g., biogeochemists, hydrologists, limnologists, oceanographers) to advance our understanding of greenhouse gas fluxes in coastal aquatic and coastal vegetated ecosystems, and how these fluxes may change in the future. We welcome observational, experimental, and modelling studies, especially those exploring the following themes: 1) spatial and temporal variability of coastal greenhouse gas fluxes, 2) drivers that control coastal sediment-water-air gas exchange, 3) advances in existing, and new techniques to determine coastal greenhouse gas fluxes, and 4) anthropogenic impact on coastal greenhouse gas fluxes and future projections under different climate change scenarios, including the impact of extreme events such as floods and fire.
Lead Organizer: Judith Rosentreter, Center for Coastal Biogeochemistry, Faculty of Science and Engineering, Southern Cross University, Lismore, Australia (judith.rosentreter@scu.edu.au)
Co-organizers:
Bradley Eyre, Center for Coastal Biogeochemistry, Faculty of Science and Engineering, Southern Cross University, Lismore, Australia (Bradley.Eyre@scu.edu.au)
Bryce Van Dam, Institute of Carbon Cycles, Helmholtz-Zentrum Hereon, Geesthacht, Germany (bryce.dam@hereon.de)
Florian Roth, Baltic Sea Centre, Stockholm University, Stockholm, Sweden; Tvärminne Zoological Station, University of Helsinki, Hanko, Finland (florian.roth@helsinki.fi)
Presentations
06:30 PM
A “SUPER” BLUE CARBON FACTORY IN SEAGRASS MEADOWS OF DONGSHA ISLAND (4716)
Primary Presenter: Wen-Chen Chou, National Taiwan Ocean University (wcchou@mail.ntou.edu.tw)
We found a unique diel pattern with extremely high pH and low pCO2 levels across a diel cycle occurred repeatedly in four different seasons within the seagrass meadows of the inner lagoon (IL) on Dongsha Island. We proposed that this distinct diel pattern in pH and pCO2 could be associated with the enhancement of total alkalinity (TA) production coupled to carbonate sediment dissolution in a semienclosed lagoon. The confinement of the IL may hamper water exchange and seagrass detritus export to the adjacent open ocean, which may result in higher organic matter loading to the sediments, and longer residence time of the water in the IL, accompanied by microbial respiration (both aerobic and anaerobic) that may reduce carbonate saturation level to drive carbonate dissolution and thus TA elevation, thereby forming such a unique diel pattern in carbonate chemistry (i.e. a “super” blue carbon factory). These findings highlight the importance of considering TA production through metabolic carbonate dissolution when evaluating the potential of coastal blue carbon ecosystems to buffer ocean acidification and to absorb atmospheric CO2, which provide a very valuable theoretical proposition for conserving and restoring seagrass meadows as a promising strategy for climate change mitigation.
06:30 PM
DIVERSE SOURCES AND FACTORS CONTRIBUTE TO METHANE EMISSIONS FROM SOUTHERN TEXAS COASTAL ESTUARIES (5063)
Primary Presenter: Hao Yu, Texas A&M University-Corpus Christi (hao.yu@tamucc.edu)
Methane emissions from three lagoonal estuaries in southern Texas, northwest Gulf of Mexico, were investigated from May 2008 to May 2021 to evaluate the contributions from different sources and factors influencing CH4 transport. Although the estuaries were connected, there were high spatial variations in CH4 emissions due to diverse vegetation, hydrological processes, and influences of extreme weather and human activities. More CH4 was released from the seagrass-dominated lagoon than from the tidally controlled mangrove estuary and the bay with open water. Seagrass meadows unexpectedly emitted more CH4 (221.1±190.7 µmol/m2·d) than mangrove creeks (94.7±81.3 µmol/m2·d), at least partly due to tidal processes. Tides could reduce CH4 emissions by decreasing dissolved CH4 concentrations by exporting CH4 from mangrove creeks to the outer bay during ebbs and diluting CH4 concentrations using floods. The highest daily CH4 flux appeared in the channel of the lagoon dominated by seagrass, suggesting that the disturbance of vegetated sediment could severely enhance CH4 emissions. In addition, gas leakages from a petroleum platform were observed to be a direct anthropogenic CH4 input to the atmosphere. Moreover, mangrove dieback caused by extreme cold events and riverine transport of CH4 due to heavy rains significantly enhanced local CH4 emissions. This study indicated diverse sources and complicated factors that impacted CH4 emissions in coastal areas, which needs thorough consideration.
06:30 PM
INCREASING NITROUS OXIDE EMISSIONS ON WARMING REEFS WHERE KELP HAS DECLINED. (5070)
Primary Presenter: Zuhairah Dindar, University of New South Wales (zuhairah.dindar@unsw.edu.au)
Nitrous oxide (N2O) is an ozone-depleting greenhouse gas that has 300 times higher global warming potential than carbon dioxide. Although the oceans contribute about 21% of atmospheric global N2O emissions, we know little about N2O dynamics in nearshore systems. Here, we document the four-fold increase in the abundance of a large N2O-producing invertebrate (Herdmania grandis) over two decades in warming reefs that were previously dominated by carbon-capturing kelp but have since become tropicalised. Temperature manipulation experiments revealed that N2O production by Herdmania also increased significantly with temperature. By upscaling our results to a coastal region of Australia impacted by warming, we estimate that under future warming scenarios, subtropical reefs will produce more N2O than adjacent estuaries. Our findings suggest that we are severely underestimating N2O production from coastal systems, and further tropicalisation of subtropical and temperate reefs in the future may increase greenhouse gas emissions on a global scale.
06:30 PM
Spatiotemporal variability of nitrous oxide concentrations along the Elbe estuary (Germany) (5149)
Primary Presenter: Gesa Schulz, Helmholtz Centre Hereon (gesa.schulz@hereon.de)
Nitrous oxide is a powerful greenhouse gas. Estuaries are potential sources of nitrous oxide, but their emission estimates are associated with significant uncertainties due to limited data availability and high spatiotemporal variability. In this study, we present nitrous oxide measurements from nine research cruises done from 2017 to 2022 along the Elbe estuary (Germany), a known source of nitrous oxide. We calculated nitrous oxide saturation, flux densities and emissions. Further, we analyzed nutrient and oxygen concentrations to identify nitrous oxide production pathways and drivers. We found that the estuary was a year-round source of N2O, with highest emissions in winter when dissolved inorganic nitrogen loads and wind speeds are high. However, in spring and summer, nitrous oxide saturation and emission do not decrease in scale with dissolved inorganic nitrogen loads indicating that in-situ production. Two hot-spots of nitrous oxide production existed: the Hamburg Port and the mesohaline estuary downstream of the estuarine turbidity maximum zone (MTZ). Nitrous oxide production was fueled either by riverine organic matter in the Hamburg Port or by marine organic matter in the MTZ. Previous measurements in the Elbe Estuary revealed that nitrous oxide saturation was decoupled from DIN loads after an improvement of water quality in the 1990s that allowed for phytoplankton growth to reestablish, highlighting the overarching control of organic matter on nitrous oxide production in the well-mixed temperate Elbe Estuary.
06:30 PM
Nitrous oxide fluxes in a coastal Mediterranean area: the Balearic Sea case study (5304)
Primary Presenter: Susana Flecha, Instituto Mediterráneo de Estudios Avanzados, IMEDEA (CSIC-UIB) (susana.flecha@csic.es)
Nitrous oxide gas is the third most important GHG after carbon dioxide, with a global warming potential 300 times larger compared to carbon dioxide on a century timescale. Nitrous oxide production shows large spatial and temporal variability and emission estimates for aquatic systems are uncertain. Specifically, coastal areas are poorly represented in global estimates of marine nitrous oxide emissions. Here, we report nitrous oxide concentrations and air-sea fluxes from the coastal area of the Balearic Islands (Western Mediterranean Basin). Nitrous oxide levels and related biogeochemical variables were measured in three coastal sampling sites between 2018 and 2022, with two located close to the densely populated island of Mallorca and one in a pristine area in the Cabrera Archipelago National Park. Nitrous oxide concentrations in seawater during the study period ranged from 6.5 to 9.5 nM, without significant differences between the sampling sites. Averaged estimated nitrous oxide fluxes oscillated between -1.6 and 1.7 µmol m-2 d-1. All sites generally behaved as weak nitrous oxide sources following a strong seasonal pattern throughout the sampling period.
06:30 PM
Impact of water salinity on microbial processes in a rewetted Baltic coastal peatland: An incubation study (5711)
Primary Presenter: Nina Schulze, University of Rostock (nina.schulze@uni-rostock.de)
Coastal Peatlands are important carbon sinks and can have a significant impact on mitigating climate change. In recent years, efforts to rewet previously drained peatlands have therefore increased. However, the impact of salinity on the success of rewetting measures is to date not well known. The aim of this study was thus to investigate changes in biogeochemistry and carbon release under two different salinity regimes over 3 months. Samples for this study were taken from a coastal peatland at the German Baltic Sea coast near Drammendorf. The area is situated in the south-west of the island of Rügen, Germany. It was drained for grassland use in the 1970s and was rewetted three years ago, in late 2019, by removing the former dike and flooding it with brackish water from the nearby bay, Kubitzer Bodden. Peat samples representative of 3 depths from the coastal peatland were incubated as slurries under anoxic conditions at 15 °C. First results of this study, including production of CH4 and CO2 over time, pH values, values of δ13C-CH4 and δ13C-CO2, iron speciation, acetate, SO4, nutrients, and DOC, will be presented.
06:30 PM
Crabs and microbial feeding shifts due to Sargassum beaching on mangrove sediments enhance blue carbon storage (5943)
Primary Presenter: Tarik Meziane, Muséum National d'Histoire Naturelle (tarik.meziane@mnhn.fr)
Net carbon accumulation in mangroves forests strongly depends on the quantity and quality of organic matter (OM) supplied to sediments, including also OM transported by coastal waters such as the macroalgae Sargassum. Mesocosms that simulate the tides were used during 60 days to assess the effect of eutrophication by Sargassum thallus spp. of mangrove sediments. The concentration and d13C signature of fatty acids (FAs) and organic carbon as well as the sediments-air CO2 fluxes were used to follow the evolution of the quantity and the quality of sedimentary OM (SOM) in the top 10 cm layer. Sargassum beaching led to a preferential degradation of the labile fraction of OM from both Sargassum (d13C = -17,7‰ and high concentration of essential FAs) and mangrove leaves (d13C: -28,9‰ and high concentrations of 18:2w6 and 18:3w3), better preserving the refractory OM from leaves (Long chain FAs). Inputs of macroalgae induced a negative priming effect and enhanced the preservation of blue carbon in the sediments. This effect led to a 2 to 3 times higher OM accumulation in subsurface sediments, compared to when no thallus were added. The FAs composition of crabs hepatopancreas reared in some of the mesocosms revealed they preferentially fed on OM from Sargassum, and that their activity enhanced the negative priming effect by 30%.
06:30 PM
A NOVEL METHOD FOR RADIOCARBON DATING GREENHOUSE GAS EMISSIONS FROM SALTMARSH SOILS TO ADDRESS KEY BLUE CARBON CHALLENGES (5961)
Primary Presenter: Alex Houston, University of St Andrews (ah383@st-andrews.ac.uk)
Saltmarshes gain organic carbon (OC) through in-situ (autochthonous) production by vegetation and benthic microalgae, and the accumulation of marine and terrestrial material during tidal inundation (allochthonous). Scotland’s saltmarshes are estimated to accumulate 16 kt CO2 equivalent annually, approximately 0.04 percent of Scotland’s national greenhouse gas emissions in 2020. A key blue carbon challenge is to empirically understand, under current and predicted warmer conditions, the sources of OC accreted into and respired from saltmarshes. This can help determine the proportion of the total OC pool which could represent carbon savings under management intervention scenarios. Alongside 13C and 15N isotopes, radiocarbon (14C) analysis/dating can be used to determine the sources of saltmarsh surficial soil OC. We collected soil cores and surficial sediment samples from three contrasting Scottish saltmarshes and analysed them for 14C to gain an understanding of the age and sources of the autochthonous and allochthonous organic matter (OM) accumulating. We also aerobically incubated sub-samples of the soil in temperature-controlled experiments at 11 degrees C and 20 degrees C. The evolved CO2 was collected on molecular sieve traps and analysed for 14C content/age. Our results will facilitate comparison of the age of the bulk OM and the respired CO2 to the thermogravimetrically measured reactivity of the OM, contributing to a growing evidence base for emissions from saltmarshes, and the sources of OC accreting in their soils, which is vital for understanding how they cycle carbon.
06:30 PM
CARBON IN THE “AMAZÔNIA AZUL”: AUTONOMOUS MEASUREMENTS OF CO2 FROM THE AMAZON RIVER TO THE COASTAL OCEAN OF BRAZIL (6043)
Primary Presenter: Carlos Musetti de Assis, GEOMAR (cmusetti@geomar.de)
The ocean’s role in the greenhouse gas dynamics has been on the radar of scientists for the last decades for better understanding and thus forecasting the future conditions, due to increasing, mainly, carbon dioxide (CO2) atmospheric concentrations. Compared to open ocean regions, coastal waters show more variability, and these complex systems are harder to predict, mainly due to its interactions with land, human activity and coastal ecosystems. The Brazilian “Amazônia Azul” (combination of Brazil’s Exclusive Economic Zone and Continental Shelf) still has limited amount of carbon data available, mostly due to the lack of sufficient studies with spatial and temporal coverage with a common standardized methodology. Besides that, the Amazon river plays an important role as source of CO2 in the flooded areas of the river and as a sink of CO2 in the river plume, with influence in the western tropical Atlantic. To improve the understanding of the dynamics in “Amazonia Azul” and to increase data coverage, we implemented in 2022 an autonomous measuring system in the first Brazilian ship of opportunity (SOOP) line. The line is operating between Santos and Manaus (1300 km up in the Amazon river), measuring continuously temperature, salinity, dissolved oxygen, CO2 in the surface water. Here we present the first data set spanning from the inland Amazon river to the offshore coastal waters of Brazil. The data show the sharp gradient between riverine and coastal waters and the resulting over- and undersaturation for CO2.
06:30 PM
DEVELOPMENT AND VALIDATION OF A METHODOLOGY FOR THE DIRECT ANALYSIS OF DISSOLVED CO2 IN COASTAL WATERS (6114)
Primary Presenter: MARTIN RANGEL-GARCIA, Universidad Nacional Autónoma de México (martin.r.gq31@hotmail.com)
The atmospheric concentration of carbon dioxide (CO2) has continuously increased over the last decades due to rapid population growth and increasing emissions from burning fossil fuels. The absorption of atmospheric CO2 in the oceans affects the balance of the carbonate system, in which the availability of carbonate ions decreases while the amount of hydrogen ions increases, leading to acidification. The partial pressure of CO2 (pCO2) dissolved in seawater is often indirectly determined through a mathematical calculation involving two variables of the carbonate system, commonly pH, total alkalinity (TA), or dissolved inorganic carbon (DIC). This requires the availability of expensive equipment, materials, and reagents necessary for analyzing each variable, and these techniques are usually demanding in terms of human resources. In this study, a new methodology for the direct analysis of pCO2 in discrete seawater samples was implemented with a small gas balancer and direct measurement with a CO2 detector (LICOR-850). It was compared to the indirect measurement through DIC and pH as reference methodology. We found a good analytical quality in the proposed methodology, with an accuracy of 106%, a limit of quantification 20 times lower than the average surface seawater value, a linearity of 0.9991, and robustness to variations of typical seawater salinities. Hence, the proposed method is a simple and cheap technique for analyzing pCO2 in marine-coastal seawater, which can be used in other regions where budgetary constraints limit its long-term monitoring.
06:30 PM
N2O FLUXES ACROSS SEDIMENT-WATER-AIR INTERFACES IN ANTROPOGENICALLY IMPACTED COASTAL REGIONS: THE CASE OF LAKE GREVELINGEN (THE NETHERLANDS) (6542)
Primary Presenter: Damian Arévalo-Martínez, Radboud University Nijmegen (d.arevalomartinez@science.ru.nl)
Coastal regions play a crucial role for greenhouse gases (GHG) budgets since biological cycling and sediment-water-air exchanges are more intense than in open ocean settings. Since coastal ecosystems already experience seasonal hypoxia, ongoing deoxygenation is of concern as it could exacerbate GHG-driven global warming, negatively affecting several biological communities. Lake Grevelingen is a saline coastal reservoir with seasonally hypoxic conditions resulting from limited water exchange after two dams were built in the 60s–70s. As such, it offers an excellent opportunity to elucidate the role of oxygen temporal-spatial variability on GHG dynamics. N2O stands out among other GHG because of its contribution to stratospheric ozone depletion and its effectiveness in enhancing Earth’s warming. Given the tight coupling of N2O production and low oxygen concentrations, coastal margins are expected to be high sources to the atmosphere. However, emission estimates in these areas are highly uncertain and mechanistic understanding on the benthic-pelagic coupling of N2O fluxes and its potential changes with deoxygenation is still rudimentary. In this presentation, we show the first results of an extensive campaign which combines novel benthic profiling, high-resolution water column and surface water measurements, and floating chamber experiments. We discuss the spatial and temporal variability of N2O fluxes across the sediment-water-air interfaces in the lake and present a budget which could be used to improve the representation of coastal fluxes in ocean models.
06:30 PM
Eddy covariance measurements of carbon dioxide fluxes over the coastal Baltic Sea (6693)
Primary Presenter: Aki Vähä, University of Helsinki (aki.vaha@helsinki.fi)
The fate of carbon in the coastal sea is emerging as a vital component in the global carbon cycle. In a healthy state, the coastal sea acts a carbon sink, but a degraded state could potentially turn the coastal sea to a source of carbon in the form of emitted carbon dioxide (CO2) and methane (CH4). However, the carbon budget in the coastal sea is often poorly constrained due to an inadequate amount of available data. A new eddy covariance (EC) flux tower for measuring sea–atmosphere gas fluxes was installed in a semi-enclosed bay in the coastal Baltic Sea in early 2022. The quasi-continuous EC measurements enable for a better-restrained carbon budget. Although the amount of data is limited due to the small magnitude of fluxes and especially the interference of fluxes from land, we are able to obtain flux estimates in three unobstructed sectors around the tower. We report here the preliminary results for CO2 fluxes between April 2022 and January 2023. The measured mean monthly CO2 fluxes varied between −0.3 ± 0.4 µmol m−2 s−1 (± STD, net sink) and 0.4 ± 0.4 µmol m−2 s−1 (net source). The measured CO2 fluxes were relatively small, but all monthly mean fluxes differed significantly (p < 0.05) from 0 except in September. There was a significant (p < 0.05) difference in the day- and night-time CO2 fluxes from April to October, likely reflecting the diurnal changes in the environmental drivers. More analysis is needed in order to distinguish the fluxes from the land interference and to determine which environmental parameters are driving the fluxes.
06:30 PM
Filling gaps by seamlessly modelling and observing carbon fluxes in the eastern Brazilian coast and the Amazon River plume (6731)
Primary Presenter: Karel Castro-Morales, Friedrich Schiller University Jena (karel.castro.morales@uni-jena.de)
Compared to the ocean carbon sink found in most parts of the global ocean, the tropical Atlantic Ocean represents a significant source of carbon to the atmosphere. Furthermore, the Amazon River plume is a strong sink of atmospheric carbon dioxide (CO2 atm) in the western tropical Atlantic Ocean, which largely influences the biogeochemical dynamics of the land-aquatic continuum in this region. Anthropogenic activities have a significant influence on the Amazon River and its coastal shelf system, thus a better understanding of the impact on carbon emissions and sinks is required. However, large observational gaps in both time and space restrict process understanding and quantification of this region’s carbon fluxes and budgets. To better constrain the carbon cycle components of the Amazonas shelf system, we combine highly-resolved continuous measurements of partial pressure of CO2 (pCO2) with an ocean biogeochemistry simulation of the tropical Atlantic using the MITgcm-Darwin model. Model output shows that the carbon absorbed by the Amazon River plume in the form of pCO2 increased by 10 µatm from 2016 to 2022. As a response of higher CO2 uptake, surface-ocean total alkalinity and dissolved inorganic carbon also increase over time. The model also depicts a spatial gradient in the river-to-ocean transition. Model evaluation of these results is presented, but it is challenging due to lack of biogeochemical observations in Amazon River plume region. To overcome this, high-resolution pCO2 measurements are carried out with a ship-of-opportunity line along the coast of Brazil (Brazilian-SOOP line). These data will ultimately provide an updated perspective of air-sea carbon fluxes in this important region and will support further evaluation and optimization of the ocean biogeochemistry model.
06:30 PM
INFLUENCE OF REACTIVITY ON GHG FLUXES TO THE ATMOSPHERE IN A MACROTIDAL ESTUARY (GUADALQUIVIR ESTUARY, SW SPAIN) (6829)
Primary Presenter: Jairo Sánchez Rodríguez, University of Cadiz (jairo.sanchez@uca.es)
Estuaries are systems characterized by high fluxes of greenhouse gases (GHG) to the atmosphere and play a major role in the biogeochemical cycles in the coastal zones. The distribution and water-atmosphere fluxes of the three most important GHG (CO2, CH4 and N2O) have been studied over 3 samplings between 2021 and 2022 in the Guadalquivir Estuary. These samplings consist of tidal cycles at different stations along the estuary. Samplings have been carried out under different climatic and hydrodynamic conditions. There is an important longitudinal gradient in the estuary, with low mean fluxes at the mouth of the estuary (CO2: 4.9 ± 3.4 mmol m-2 d-1; CH4: 8.6 ± 2.9 micromol m-2 d-1; N2O: -0.9 ± 1.9 micromol m-2 d-1) and high mean fluxes and variability in the inner zone (CO2: 95.8 ± 66.6 mmol m-2 d-1; CH4: 54.0 ± 65.9 micromol m-2 d-1; N2O: 42.4 ± 32.8 micromol m-2 d-1). These fluxes suggest that the estuary would act as a source of the three gases to the atmosphere. Fluxes variability are affected by several factors: temperature, salinity, water-atmosphere degassing, biogeochemical processes, benthic fluxes, and lateral inputs. Thus, the last three factors are the predominant processes influencing gas dynamics, affected by changes in temperature and rainfall regime.
06:30 PM
Isotopic Analysis of Greenhouse Gas Outgassing in the Coastal High Arctic (6987)
Primary Presenter: Shawnee Traylor, MIT-WHOI Joint Program (straylor@whoi.edu)
The steady uptick in global temperature may bring significant perturbations to the cycling and transfer of carbon (C) in the coastal Arctic. Given the high C content of Arctic soils, the region may become an increasingly important source of methane (CH4) and carbon dioxide (CO2) in coming decades. We present targeted observations along a lake to bay system during the spring thaw in the coastal Canadian high Arctic, which has been shown to deliver a pulse of greenhouse gases from the freshwater system to the bay, where they are rapidly ventilated to the atmosphere. As warming impacts the timing and dynamics of the ice retreat, C sources may shift and the magnitude of outgassing may change. We investigate the sources and pathways of the dissolved CO2 and CH4 via stable carbon isotope analyses, and augment our spatial survey by employing a profiling autonomous kayak (ChemYak) outfitted with a suite of biogeochemical sensors. Observed CH4 ranged from 1-5900 ppm, with δ13C values ranging from -70 to -47‰ (mean: -61.1±10.5‰); CO2 ranged from 100-3350 ppm, with δ13C values of -12 to 38‰ (mean: 6.1±13.1‰). Isotopic depletion was correlated with lower CH4, and enrichment consistent with a primary productivity signal was seen in lower concentrations of CO2. Isotopic signatures clustered with habitat type, revealing spatial variability in the processes controlling the production and transformation of CH4. Through this work, we aim to improve our understanding of the interannual variability present at this site and evaluate the system’s response to a changing climate.
06:30 PM
Nitrous oxide consumption in sediments of a tropical coastal lagoon (7021)
Primary Presenter: Tanisha Nag, National Centre for Coastal Research (tanisha.nag@gmail.com)
<p>N2O production and consumption processes in coastal sediments contribute significantly to the global N2O budget. Rate measurements, however, have largely remained restricted to high latitude ecosystems. To bridge this gap, N2O fluxes at the sediment-water interface were measured along the inlet regions of a tropical, shallow coastal lagoon (Pulicat lagoon) on the East coast of India. Pulicat is connected to the coastal waters of the Bay of Bengal through three such inlets. Intact core incubation experiments were conducted using sediment cores sampled during the wet season (December) of the years 2020 and 2022.</p> <p>Negative N2O fluxes at the sediment-water interface were observed in both years, indicating sediment uptake of N2O during the wet season. Water column salinity and temperature conditions prevalent during the wet season played an influential role in sediment N2O uptake. Furthermore, the sediment-water incubators were treated with inhibitors in a parallel experimental set-up to understand the role of nitrification and denitrification in driving N2O uptake at the sediment-water interface. Allylthiourea was used as a nitrification inhibitor, and acetylene was used as a denitrification inhibitor. A framework of benthic N2O cycling in the ecosystem has been illustrated based on an understanding of the controls and pathways of N2O consumption in Pulicat sediments revealed by the experiments.</p> <p>N2O consumption in Pulicat sediments is an important finding in terms of the global N2O budget and climate change.</p>
06:30 PM
HIGHLY RESOLVED SPATIOTEMPORAL MONITORING OF GAS TRANSFER VELOCITIES IN SURFACE WATERS BY INFRARED REMOTE SENSING WITH EXTENSIONS TO METHANE FLUX MEASUREMENT (7151)
Primary Presenter: Edwin Cowen, Cornell University (eac20@cornell.edu)
Water transports, stirs, mixes, and disperses mass. It exchanges gasses with the atmosphere, primary among them for life and a better understanding of climate change, are carbon dioxide and oxygen. There is a critical need for detailed spatiotemporal monitoring of water’s full transport ability, its mean and turbulent transport capacities, and in particular, the gas transfer velocities at the air-water interface. We present an open-source infrared-based quantitative imaging remote sensing tool that uniquely addresses this critical need. Here we focus on using remotely mounted infrared cameras deployed from fixed platforms, but these tools can be mounted on aerial vehicles, such as drones. While we elect to work with infrared imaging due to its unique ability to sample surface waters absent the requirement for artificial seeding or illumination and its ability to quantify the transport of methane, such as ebullition and aerenchymous transport, the developed tools are equally well suited to visible light images that are adequately illuminated and seeded. We leverage fundamental gas transfer and turbulence theory and the ability of quantitative image velocimetry techniques to extract the instantaneous highly resolved water surface turbulence to calculate the spatiotemporally resolved gas transfer velocity field in surface waters. We present an overview of our developed infrared quantitative imaging technique, our approach to calculating the gas transfer velocity, recent field measurements of gas transfer velocities and initial efforts at quantifying methane fluxes.
06:30 PM
SEASONAL VENTILATION CONTROLS THE EMISSION OF NITROUS OXIDE IN THE NW IBERIAN UPWELLING (7328)
Primary Presenter: Mercedes de la Paz Arándiga, Instituto de Investigaciones Marinas- CSIC (mercedes.delapaz@iim.csic.es)
Nitrous oxide (N2O) represents a double threat to the Earth’s climate as a powerful greenhouse gas and first ozone-depletion gas, and is subject to increasing unprecedented concentrations due to human activities. Hence, demand for the scientific community to include global greenhouse budgets other than just carbon dioxide is growing. The N2O intense outgassing in coastal upwelling systems represents over 20% of the global N2O flux, despite covering only 3% of the world´s ocean. Hot-spots of N2O emission are geographically constrained to Eastern Boundary Upwelling Systems (EBUS) in tropical and subtropical latitudes, but besides these low oxygen systems, the knowledge about the dynamics of the upwelling systems is relatively scarce. In this study we present novel data-base of the nitrous oxide monthly time series measurements in the Galicia Upwelling System, to assess the spatial and seasonal variability of N2O concentrations and sea-air fluxes in this region and to investigate how it relates to the occurrence of upwelling. The results show that the upwelling area of Galicia behave as a net source of N2O to the atmosphere, showing the increase from the shelf to the inshore of 50% in the northern rías, and up to 130% higher in the Ria de Vigo, where the upwelling have a notable impact on the N2O emissions.
SS003P Coastal Aquatic Greenhouse Gas Fluxes Under Global Change
Description
Time: 6:30 PM
Date: 7/6/2023
Room: Mezzanine