Carbon fixation by primary producers is the key rate-limiting process that shapes the functioning of aquatic ecosystems and defines their role as source or sink of atmospheric carbon dioxide. Many physical and biogeochemical factors determine the rates of primary production, however, their relative contribution is far from being resolved. Most of these controls have double-edge effects and interact with each other, complicating our understanding of the dynamics of primary production across spatial and temporal scales. This understanding is crucial to better predict and manage the consequences of the wide range of anthropogenic pressures acting on aquatic ecosystems. In order to improve our knowledge in this field, we first need to understand how hydro-thermodynamics set favourable or harmful conditions for the growth of primary producers, by e.g., sustaining the supply of nutrients, affecting mixing and stratification, and regulating horizontal and vertical water fluxes. Second, we must improve our understanding of the biogeochemical cycling of key chemical elements (C, N, P, Si, O 2 , Fe) in the water column and the sediment, including phytoplankton ecophysiology, grazing, organic matter remineralization, and inorganic carbon processes. Third, we need to advance our approaches to reliably quantify air-water gas-exchange to better determine the role of surface waters as a net sink or source of carbon dioxide to the atmosphere. The analysis of long-term public or research data, the growing availability of high-resolution physical/biogeochemical data collected with autonomous vehicles/profilers and high frequency sensors, and innovative modelling approaches have all the potential to increase our mechanistic understanding of primary production. We welcome data-driven, conceptual or model-based research on the interaction between physical and biogeochemical processes in natural or anthropogenically disturbed freshwater and marine ecosystems.
Lead Organizer: Camille Minaudo, University of Barcelona, Spain (camille.minaudo@ub.edu)
Co-organizers:
Sebastiano Piccolroaz, Università degli Studi di Trento, Italy (s.piccolroaz@unitn.it)
Bieito Fernández-Castro, University of Southampton, United Kingdom (B.Fernandez-Castro@soton.ac.uk)
Shubham Krishna, Helmholtz-Zentrum Hereon, Germany (Shubham.Krishna@hereon.de)
Hannah Chmiel, Limnology Center, EPFL, Switzerland (hannah.elisa.chmiel@gmail.com)
Presentations
06:30 PM
HYDRODYNAMIC AND WATER QUALITY MODELLING OF A SUBTROPICAL EUTROPHIC RESERVOIR (6573)
Primary Presenter: Agustin Rios, Universidad de la Republica (arios@fing.edu.uy)
Introduction The major hydropower reservoir of Uruguay, Rincón del Bonete, has shown cyanobacterial blooms almost every year during the last decades. Although reservoir’s water quality is monitored since the begging of 2000s, little is known about how hydro-thermodynamics influence transport of substances and set conditions for the growth of primary producers. Objectives This work aims to contribute to a better management of the water quality in Rincón del Bonete reservoir by developing numerical tools that helps to understand the system dynamics and predict its future behaviour. A particular interest is to explore the conditions that explained the absence of blooms in a recent summer (2020-2021). Methods A numerical model was calibrated and validated based on a combination of continuous measurements, remote sensing estimations, and historical periodic monitoring data. Delft3D-FLOW was used to characterize hydrodynamics, thermal structure, and vertical mixing in the reservoir, while Delft3D-ECO was used to represent water quality and primary production using FLOW results as an input. Results and conclusions The model can simulate spatial and temporal variability of hydrodynamics, temperature, nutrients, sediments, dissolved oxygen, and phytoplankton. It contributed to the identification and quantification of the processes that determine the phytoplankton dynamics in the reservoir. The light climate and vertical mixing showed to play a key role in the non-formation of blooms in the summer of 2020-2021.
06:30 PM
THE EFFECT OF NUTRIENT RATIOS ON PRODUCTION OF TASTE AND ODOUR COMPOUNDS IN DRINKING WATER RESERVOIRS (6698)
Primary Presenter: Inge Elfferich, Cardiff University (elfferichi@cardiff.ac.uk)
Predicting when a drinking water source will be affected by taste and odour (T&O) metabolites, produced by cyanobacteria, is challenging yet critical for supply management. A low ratio total nitrogen to total phosphorus (TN:TP) can select for cyanobacteria growth, and high ammonium to nitrate ratios (NH4+:NO3-) can trigger T&O formation. Water from a drinking water reservoir in the UK, with a realistic phytoplankton community, was incubated for 23 days at 20°C with 12-hour day-night cycles. Oxygen was measured continuously as a proxy for primary productivity. Six nutrient treatments were added, three NH4+:NO3- ratios (high = 1:1, medium = 1:10 and low = 1:100) combined with two TN:TP ratios (high = 100:1 and low = 10:1), representing observed conditions whilst targeting the extremes. Productivity at high NH4+:NO3- and low TN:TP increased after 7 days, peaked at 2 weeks, and then declined. Both treatments with low NH4+:NO3- took 2 to 3 weeks to become productive, but productivity was maintained for longer and reached higher levels. Elevated T&O concentrations occurred in four treatments; low NH4+:NO3- with high or low TN:TP ratios as well as medium or high NH4+:NO3- with low TN:TP. To predict T&O events, nutrient ratios, concentrations, and a proxy for in situ primary productivity must be measured. The difference in lag-time between NH4+ and NO3- addition and subsequent primary productivity, indicate that direct relationships might disguise the real process. Therefore, laboratory and in situ studies should be undertaken to understand the site-specific drivers of T&O events.
06:30 PM
RESPONSE OF THE UNICELLULAR UCYN-C CROCOSPHAERA SUBTROPICA TO PHOSPHORUS LIMITATION (5920)
Primary Presenter: Saverio Rana, Mikrobiologický ústav AV ČR, v. v. i. (rana@alga.cz)
Nitrogen fixing organisms - diazotrophs are a key ecological group of the ocean since they provide the food web with biologically fixed ammonium. As the nitrogen fixation requires a high amount of energy, and since the concentration of inorganic phosphorus is subject to fluctuations in the ocean, P may be a limiting inorganic nutrient for this process. Here, we investigated how phosphorus limitation affected the model single-celled diazotrophic cyanobacterial species, Crocosphaera subtropica (formerly Cyanothece) ATCC 51142. We evaluated growth, nitrogen and carbon fixation, photosynthetic efficiency and quantified the energy cost of carbon and nitrogen metabolisms, under P- limited and replete conditions. Overall, growth rates, nitrogen and carbon fixation of C. subtropica decreased under P-limitation. Interestingly, nitrogen fixation showed a shift towards the latest hours of the dark period compared to the early peak displayed by the P- replete culture. Moreover, P usage efficiency for nitrogen and carbon fixation were, respectively, three- and two-times lower in the P- limited than in the replete condition. Despite the reduction in growth rates and nitrogen and carbon fixation, our data suggest that C. subtropica is still able to grow under P- limiting condition. While improving our understanding of P limitation in relation to the physiological process of nitrogen fixation, the results help to model nitrogen fixation on a global scale.
06:30 PM
TEP PRODUCTION, AGGREGATION, AND SINKING POTENTIAL OF THE SMALLEST MARINE PHYTOPLANKTON (6030)
Primary Presenter: Catrina Shurtleff, Arizona State University (cshurtle@asu.edu)
Despite their high abundance in oligotrophic ocean regions, small-celled phytoplankton (<5 µm) have traditionally been viewed as contributing little to export production due to their small size. However, recent studies have shown that the picocyanobacterium Synechococcus forms abundant microaggregates (5-60 µm) and produces transparent exopolymer particles (TEP), the sticky matrix of marine aggregates. TEP and aggregation were also shown to be enhanced under nutrient limited growth conditions. In this study we carried out experiments to test whether other small phytoplankton species exude TEP and form microaggregates, and if these are enhanced under growth-limiting conditions. The picocyanobacterium Prochlorococcus marinus (0.8 µm), the nanodiatom Minutocellus polymorphus (4 µm), and the picoprasinophyte Ostreococcus lucimarinus (0.6 µm) were grown in axenic batch culture experiments under nutrient replete and limited conditions. We found that nutrient limitation increased TEP concentration in all three species, and formation of microaggregates was significantly enhanced in Minutocellus and Ostreococcus in distinct size ranges. Surprisingly, Ostreococcus, the smallest eukaryote known, produced more TEP than Prochlorococcus and Minutocellus per unit cell volume. These findings show how nutrient limited conditions enhance TEP production and microaggregation of phytoplankton with some of the smallest cells, providing a mechanism for their incorporation into larger, sinking particles and contribution to export production in oligotrophic oceans.
06:30 PM
Primary productivity in surface waters of the Irish EEZ (6372)
Primary Presenter: Ankit Swaraj, University of Galway (a.swaraj1@nuigalway.ie)
There currently exists a critical knowledge gap in Irish/European marine science, in that there is almost no in situ data on primary productivity in Irish waters. While satellite data for net primary productivity has been available for over a decade now, there have been no systematic studies validating/ground truthing remote sensing estimates. This poster will introduce new work being conducted at the University of Galway that combines and compare different approaches to the measurement of primary productivity in surface seawaters around Ireland to provide improved regional estimates of phytoplankton production from within the Irish EEZ and the European coastal shelf. Through cooperation with the Marine Institute, we will utilize obtain new data on bio-optical, macronutrient, carbon system and O2/Ar for gross primary productivity estimates across the Irish continental shelf. Shipboard incubations using H218O will be performed to obtain estimates of gross oxygen productivity (GOP) via measurement using a MIMS. In the Celtic Sea, gliders with oxygen sensors will be used to infer regional scale GOP. The data gathered in this work will also help to inform baselines for carbon cycling budgets in Irish waters and help determine key parameters with regard to Ireland’s Blue carbon footprint and inform policy for the Irish government’s achieving it’s UN SDG targets.
06:30 PM
Modelling feedbacks between a deposit-feeding bivalve (Macomona lilliana) and micophytobenthic production (5266)
Primary Presenter: Conrad Pilditch, University of Waikato (karin.bryan@waikato.ac.nz)
Globally, estuarine ecosystems stressed by anthropogenic activities such as increased nutrient and sediment loading. The ecological processes that drive the uptake of nutrients and responses to increased turbidity are inherently non-linear, and so minor changes to loading can drive rapid and unpredictable changes in ecosystem dynamics. Here we explore one of the processes that mediates benthic productivity in a key intertidal species, the deposit-feeding bivalve, Macomona lilliana, using a simple non-linear model. M. lilliana feed on microphytobenthos (MPB) at the sediment surface, and through the exhalent siphon excrete nutrients into porewaters at depth. This behaviour pressurises the sediment, and effectively pumps limiting porewater nutrients back to the surface making them available to MPB. We modelled this system where MPB are controlled by the activities of M. lilliana (i.e. grazing rates and pumping capacity which supplies limited nutrients) and light (controlled by water column turbidity) using published field and lab measurements. Pressurisation caused by the pumping activity is superimposed on a background pressure generated by the tide and waves, which are used to generate upward flow using Darcy’s law. The model shows that slow variations in forcing parameters like light can cause a rapid biomass response, associated with a shift between a MPB-dominated system to a M. Lilliana-dominated system. The model is critically dependent on assumed mortality rate, which was used as a tuning parameter, to bring the MPB and M. lilliana biomass into observed ranges.
06:30 PM
Contrasting responses of two diazotroph communities to warming, Fe and P addition in the tropical Western Pacific (7492)
Primary Presenter: Yuanyuan Feng, Shanghai Jiao Tong University (yuanyuan.feng@sjtu.edu.cn)
The nitrogen (N2) fixation of marine diazotrophs is critical for providing bioavailable nitrogen to support the carbon export in the broad expanse of N-limited ocean. The availability of iron (Fe) and phosphorus (P) is considered as the limiting factors on the growth of diazotrophs. However, how the future warming will interact with the resource limitation of the N2 fixation and C export is still largely unknown for the natural diazotroph communities. Here we conducted ship-board incubation experiments to investigate the effects of iron (Fe) and P amendments on the biological N2 and carbon fixation under future warming conditions on two different diazotroph communities collected from the oligotrophic Western Pacific region. Our results reveal that the effects of both Fe addition and warming are size-dependent. Trace level (0.5 nM) Fe amendments stimulated both N2 and C fixation, and this effect was magnified with phosphate (0.1 μM) amendments. Although warming in general alleviated the extend of Fe limitation and thus promoted C fixation of both communities, contrast responses of N2 fixation to warming were determined by the diazotroph community structure. The N2 fixation rate of diazotroph community dominated by unicellular diazotroph UCYN-B increased with 5ºC of warming; while warming weakened the N2 fixation of Trichodesium dominated community in spite of nutrient amendments. The size-dependent response of N2 fixation to Fe availability and warming further suggests the needs of considering size-fractions for the future biogeochemical projection models.
06:30 PM
REGIONAL PATTERNS IN ECOSYSTEM METABOLISM IN LAKES ACROSS CANADA (5489)
Primary Presenter: Amir Reza Shahabinia, Université du Québec à Montréal (amir.shahabi66@gmail.com)
Lake metabolism provides fundamental information on how C and energy cycle within these systems, and lakes interact with surrounding environments. Assessments of lake gross primary production (GPP) and respiration (R) and their net balance (NEP and P/R) have been limited to communities or to a limited number of lakes and narrow environmental and geographic gradients, because conventional approaches require either long incubations, intensive sampling or deployment of monitoring equipment, none of which are amenable to implementation in large scale studies. Here, we present the preliminary results of a large-scale comparative study of lake metabolism, where we explore the patterns and drivers of GPP, R, NEP and P/R of lakes across Canada, part of the Canadian LakePulse Network. We measured summer mixed-layer metabolic rates in these lakes using an oxygen isotopic (δ18O2) approach that combines ambient O2 concentration and isotopic signature, which provides an integrative snapshot of mixed-layer metabolism in the case of stratified lakes in summer or whole lake metabolism in the case of shallow lakes. The sampled lakes were distributed across major Canadian ecoregions, covering a wide range of in-lake, watershed, and climatic features. GPP and R varied across lakes and regions, as a function of trophic status, dissolved organic carbon (DOC), and chlorophyll a. Preliminary results suggest that there are systematic regional differences in lake metabolism, likely driven by a combination of region-specific landscape properties as well as average regional lakes specific properties.
06:30 PM
Massive blooms of Noctiluca scintillans (Dinophyceae) as a response to monsoon anomaly in Pingtan, Fujian in 2022: A process-oriented 3-D modeling study (5258)
Primary Presenter: Zhonghao Lin, Nanjing University of Information Science and Technology (linzhonghao761@163.com)
The dinoflagellate Noctiluca scintillans blooms from April to June in the northwest Taiwan Strait (TWS), but its scales vary interannually. A massive Noctiluca scintillans bloom broke out nearby Pintan Island in April 2022, as confirmed by light microscopy analysis, which affected the local fishery to a certain extent. Chlorophyll data from the MODIS Aqua satellite showed a marked increase in the TWS in April 2022 compared to April 2021. The Zhe-Min Coastal Current (ZMCC), driven by the northeast monsoon in winter, can transport nutrient-rich water into the TWS and promote phytoplankton blooms. The massive phytoplankton bloom provided sufficient food source for Noctiluca scintillans, but the mechanism of the massive Noctiluca scintillans bloom nearby Pingtan Island is not well understood. In this study, we developed a three-dimensional biological-physical model for the TWS: the Finite Volume Coastal Ocean Model (FVCOM) and a Nutrient-Phytoplankton-Zooplankton (NPZ) model were coupled to investigate the influence of external physical forcing on the nutrient, phytoplankton, and zooplankton dynamics in the TWS. This high-resolution coupled model presents the year-round continuous model simulation results from April 2021 to April 2022 and provides a diagnostic analysis of different wind-forcing influences on nutrients and phytoplankton fluxes. The simulation experiments showed that the intensification of the northeast monsoon strengthened the ZMCC, and increased its impact area. The northeast monsoon induced the westward and southward Ekman transport, leading to the onshore/offshore accumulation of phytoplankton and zooplankton. The headland topography of Pingtan Island promoted the accumulation of nutrients and phytoplankton, providing favorable conditions for the bloom of Noctiluca scintillant. The enhancement of the northeast monsoon could be associated with the 3-year lasting La Nina extreme climate event. This study highlights the importance of climate change on Noctiluca scintillans blooms in the TWS and provides the scientific basis for predicting the occurrence of Noctiluca scintillans blooms in the Pingtan sea area. Keywords: Noctiluca scintillans blooms, Modeling, Biological-physical coupling, Taiwan Strait
SS035P Physical and Biogeochemical Controls of Primary Production Dynamics in Aquatic Ecosystems
Description
Time: 6:30 PM
Date: 7/6/2023
Room: Mezzanine