Benthic metabolism is critically important to evaluate the trophic status and thus, the environmental health of shallow coastal ecosystems. Global warming and coastal eutrophication are altering the benthic metabolism and carbon cycling, which can lead to disturbances of the ecosystem services in coastal areas. However, there are major uncertainties in the benthic metabolism estimates due to the high heterogeneity of coastal regions, and the large variability of metabolic rates at different time scales. This session invites contributions that present new ecological results on benthic metabolism and fluxes, and their controls and responses to environmental changes and stressors in near-shore aquatic systems. This session also welcomes presentations on methodological advances for in situ metabolic and flux measurements and inverse modeling approaches that advance data interpretation.
Lead Organizer: Carmen Castro, Instituto de Investigaciones Marinas (CSIC) (cgcastro@iim.csic.es)
Co-organizers:
Mariña Amo-Seco, Instituto de Investigaciones Marinas (CSIC) (amoseco@iim.csic.es)
Peter Berg, University of Virginia (USA) (pb8n@virginia.edu)
Presentations
08:30 AM
BENTHIC STUDIES IN THE RAPIDLY CHANGING COASTAL OCEAN (4718)
Primary Presenter: Markus Huettel, Florida State University (mhuettel@fsu.edu)
Estuarine, coastal and shelf sediments cover only a small fraction of the global seafloor yet their proximity to land and decreasing water depth amplify physical, chemical, and biological processes affecting their biogeochemistry and cycling of matter. In the Anthropocene, sedimentary environments are increasingly impacted by human activities, and in the shelf, the effects are amplified as the shallow water depths limits dilution of anthropogenic nutrient input resulting in more frequent algal blooms and expanding hypoxia. Technological challenges and high costs associated with investigations at the seafloor and in high-energy shallow water environments make it difficult for investigators to keep up with the relatively rapid changes in the global shelf environment, which now is increasingly influenced by effects of sea level rise, warming, acidification and storms. This presentation addresses some recent technological developments and new insights gained through them with emphasis on benthic studies in the shelf environment.
08:45 AM
Importance of sediment resuspension for benthic biogeochemical function in coastal settings: A case study from a temperate estuary (5427)
Primary Presenter: Lisbeth Sørensen, University of Southern Denmark (lisbethf@biology.sdu.dk)
Sediment resuspension is rarely considered when assessing benthic carbon mineralization in coastal environments. Using a hydrodynamically calibrated sediment erosion device (EROMES), we quantified the impact of erosion events on benthic biogeochemistry across 4 seasons. Enhanced sediment erosion increased the benthic O2 uptake rate and the release of dissolved inorganic carbon (DIC). This was mainly associated with the reoxidation of FeSx and enhanced mineralization of organic carbon, and for the latter due to a porewater washout of DIC. Sediment resuspension changes the redox conditions and increases the oxygen penetrations depth, with implications for the benthic N and P dynamics. Sediment resuspension is thus an important player in stimulating local primary production and maintaining the sulfide buffer capacity in coastal environments. The impact of sediment resuspension on the benthic environment varied across the season and was mainly driven by the size of the FeSx pools within the sediment. The effect of sediment resuspension on the near bed O2 consumption rate as compared to pre suspension rates was highest in August and lowest in January with 4- and 2-fold increases, respectively. Repeated subsequent resuspension events gradually reduced the impact of a given resuspension event. This study shows that sediment resuspension is an important but overlooked factor for the biogeochemical function of coastal environments that needs more attention in future studies to access responses towards anthropogenic and climatic impacts.
09:00 AM
In situ time series measurements of pore water nitrate in sediments (6804)
Primary Presenter: Allison Schaap, National Oceanography Centre UK (allison.schaap@noc.ac.uk)
Aquatic sediments play an important role in the cycling of biogeochemical compounds (e.g. nutrients). However, our understanding of these processes is limited by the need to collect intact sediment cores and extract the porewater for chemical analysis in order to measure the concentrations and gradients of the compounds involved, precluding observations in dynamic areas. Here we demonstrate a new approach for performing in situ time series measurements of nitrate concentrations in sediment pore water. An autonomous lab-on-chip sensor which performs spectrophotometric nitrate measurements was deployed in an estuarine river on the UK’s south coast. Rhizon filters were attached to the sensor’s sample intakes and inserted horizontally into the sediment to extract pore water for analysis, with one measuring the nitrate in the overlying water. Repeat measurements at 2.5-3 cm depth (n=124 over 5 days in winter; n=124 over 3 days in summer) revealed tidal and seasonal influences on pore water nitrate concentration. In winter, the pore water nitrate ranged from 0-30 µM with a tidal cycle out of phase with that of the water above. In summer the pore water nitrate ranged 0-8 µM with a tidal cycle in phase with the overlying water. This powerful technique can reveal temporal variability in porewater biogeochemistry, which is hard to capture by traditional methods. It could be expanded to examine any compound which can be measured with lab-on-chip sensors (e.g. phosphate, silicate, pH, total alkalinity) to enable new understandings of human impacts and natural biogeochemical processes.
09:15 AM
Sediment-water fluxes and benthic metabolism in two Brazilian estuaries under different anthropogenic influence (6191)
Primary Presenter: Paula Moraes, Oceanographyc Institute, Universidade de São Paulo (pamoraes@usp.br)
Castal areas are subject to a wide variety of anthropogenic impacts, among the most common are the impact of domestic sewage and uses for aquiculture. These human actions affect the estuarine environment in different ways, influencing the benthic community and consequently its metabolism patterns. There is a general scarcity of studies targeting nutrient fluxes and benthic metabolism measurements in different contrasting human impacted area, in particular in low latitude coastal zones. In this study, the impact on nutrient fluxes and benthic metabolism was observed in an oyster farming at Cananéia-Iguape Estuarine-Lagoon Complex (pristine estuary) and in a sewage discharge area in São Vicente-Santos Estuarine Complex (impacted estuary), in southeastern Brazilian coast. Intact sediment corers were sampled on both estuaries in two seasons (summer and winter) and processed in laboratory. Laboratorial dark incubations were performed to measured flux of dissolved gases and inorganic nutrients. A second incubation was performed with stable isotope paring techniques, to observe the effects on the benthic denitrification rates. Results showed a higher metabolism in sediment of São Vicente in both seasons. These results coincide with a bigger macrofauna and higher organic matter and chlorophyll content in this location. In general, São Vicente station showed the highest values of organic matter, higher regeneration from sediments of ammonium and nitrate and dinitrogen consumption, and higher rates of denitrification. In summer, nutrient fluxes, sediment metabolism, and denitrification rates increased in both sites.
09:30 AM
Impact of suspended mussel aquaculture on benthic oxygen fluxes and metabolism (5336)
Primary Presenter: Mariña Amo-Seco, Instituto de Investigacións Mariñas (IIM-CSIC) (amoseco@iim.csic.es)
Suspension cultures of mussels generate large amount of highly labile faeces that alters the benthic-pelagic coupling. This study quantifies the impact of an extensive mussel aquaculture located in the NW Iberian coastal upwelling system on benthic oxygen fluxes and metabolism. Two aquatic eddy covariance (AEC) systems were deployed concurrently, one below a mussel raft and one at a reference site during the summer upwelling season. The sites were 3 km apart, located in the aphotic zone, and exposed to comparable bottom currents. The intense oxygen consumption found below the mussel raft (48 mmol m-2 d-1) was 2.4 times larger than at a reference site. These results were consistent with the higher biodeposition below the mussel raft observed in previous studies, and emphasize the impact mussel aquaculture can have on the benthic-pelagic coupling.
09:45 AM
MICROBES IN DIFFERENT ARCTIC SEDIMENT FRACTIONS SHOW DISTINCT SEASONAL PATTERNS AND SUBSTRATE HYDROLYSIS RATES (5897)
Primary Presenter: Chyrene Moncada, Max Planck Institute for Marine Microbiology (cmoncada@mpi-bremen.de)
In marine sediments, heterotrophic microbes are central to organic matter exchange and transformation processes, ultimately affecting how much organic matter is sequestered. To date, little is known about how these communities change in composition and substrate utilisation across seasons. Here, we sampled surface sediments from Isfjorden, Svalbard, in winter, spring, and summer 2021 to 2022. We fractionated the sediment into the pore water (PW), cells which are loosely attached to grains (LA), and those firmly attached to grains (FA). We then assessed seasonal shifts in the community composition of the fractions through 16S rRNA gene sequencing, and quantified hydrolysis rates of fluorescently-labelled laminarin and mucin, a common polysaccharide and glycoprotein in the marine environment. Across seasons, cell numbers in the bulk sediment were 2-4x108 cells/mL; up to 90% were in the FA fraction. Cell counts in PW and LA fluctuated more, with an increase in spring for PW (4% +/- 2%) and in spring and summer for LA (9% +/- 3%) In PW and LA, there were more Colwellia, Polaribacter, Yoonia-Loktanella in spring and summer, while there were more Lutimonas in winter. In FA, Woeseia and Maribacter stayed abundant across seasons. In winter, mucin was hydrolysed and consumed between 1 and 2 days in PW and LA, while in FA, hydrolysis only peaked after 7 days. Summer hydrolysis rates for laminarin were higher in PW and LA compared to winter. This study demonstrates that bacterial fractions within surface sediments respond differently to seasonal changes and substrate input.
SS019A Benthic Metabolism and Fluxes in Shallow Coastal Ecosystems – Controls and Responses to Environmental Stressors
Description
Time: 8:30 AM
Date: 8/6/2023
Room: Sala Portixol 2