16 Dec 2021
16 Dec 2021
Status: this preprint is currently under review for the journal BG.

Biological response to hydrodynamic factors in estuarine-coastal systems: a numerical analysis in a micro-tidal bay

Marta F.-Pedrera Balsells1, Manel Grifoll1, Margarita Fernández-Tejedor2, Manuel Espino1, Marc Mestres1, and Agustín Sánchez-Arcilla1 Marta F.-Pedrera Balsells et al.
  • 1Maritime Engineering Laboratory (LIM), Catalonia University of Technology (UPC), 08034 Barcelona, Spain
  • 2Institute of Agriculture and Food Research and Technology (IRTA), Crtra. Poble Nou, s/n Km 5,5. 43540 Sant Carles de la Rapita, Spain

Abstract. Phytoplankton primary production in coastal bays and estuaries is influenced by multiple physical variables, such as wind, tides, freshwater inputs or light availability. In a short-term perspective these factors may influence the composition of biological variables such as phytoplankton biomass, as well as the amount of nutrients within the waterbody. Observations in Fangar Bay, a small, shallow, stratified and micro-tidal bay in the Ebro Delta (NW Mediterranean Sea), have shown that during wind episodes the biological variables undergo sudden variations in terms of concentration and distribution within the bay. The Regional Ocean Model System (ROMS) coupled with a nitrogen-based nutrient, phytoplankton, zooplankton, and detritus (NPZD) model has been applied to understand this spatio-temporal variability of phytoplankton biomass in Fangar Bay. Idealised simulations prove that during weak wind events (< 6 m·s−1), the stratification is maintained and therefore there is not dynamic connection between surface and bottom layers, penalizing phytoplankton growth in the whole water column. Conversely, during intense wind events (> 10 m·s−1) water column mixing occurs, homogenising the concentration of nutrients throughout the column, and increasing phytoplankton biomass in the bottom layers. In addition, shifts in the wind direction generate different phytoplankton biomass distributions within the bay, in accordance with the dispersion of freshwater plumes from existing irrigation canals. Thus, the numerical results prove the influence of the freshwater plume evolution on the phytoplankton biomass distribution, which is consistent with remote sensing observations. The complexity of the wind-driven circulation due to the bathymetric characteristics and the modulation of the stratification implies that the phytoplankton biomass differs depending on the prevailing wind direction, leading to sharp Chl a gradients and complex patterns.

Marta F.-Pedrera Balsells et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-322', Anonymous Referee #1, 18 Jan 2022
    • AC1: 'Reply on RC1', Marta F-Pedrera Balsells, 29 Jul 2022
  • RC2: 'Comment on bg-2021-322', Anonymous Referee #2, 16 Feb 2022
    • AC2: 'Reply on RC2', Marta F-Pedrera Balsells, 29 Jul 2022
  • AC3: 'Comment on bg-2021-322', Marta F-Pedrera Balsells, 29 Jul 2022

Marta F.-Pedrera Balsells et al.

Marta F.-Pedrera Balsells et al.


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Short summary
Phytoplankton in coastal bays is influenced by physical variables (wind or freshwater inputs) that can influence the composition of phytoplankton. A numerical model has been applied to understand this variability. The simulations show that during weak wind events there is physical separation between surface and deep layers, penalising phytoplankton growth. During intense wind, mixing of the water column occurs, increasing the phytoplankton biomass in the lower layers.