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The role of surface vertical mixing in phytoplankton distribution in a stratified reservoir

We investigated convection caused by surface cooling and mixing attributable to wind shear stress and their roles as agents for the transport of phytoplankton cells in the water column by carrying out two daily surveys during the stratified period of the Sau reservoir. Green algae, diatoms, and cryptophyceae were the dominant phytoplankton communities during the surveys carried out in the middle (July) and end (September) of the stratified period. We show that a system with a linear stratification and that is subject to weak surface forcing, with weak winds , < 4 m S (-1) and low energy dissipation rate values of the order of 1028 m2 s23 or lower, enables the formation of thin phytoplankton layers. These layers quickly disappear when water parcels mix because there is a medium external forcing (convection) induced by the night surface cooling, which is characterized by energy dissipation rates on the order of , 5x10(-8)m2s(-3). During both surveys the wind generated internal waves during the entire diurnal cycle. During the day, and because of the weak winds, phytoplankton layers rise in the water column up to a depth determined by both solar heating and internal waves. In contrast, during the night phytoplankton mixes down to a depth determined by both convection and internal waves. These internal waves, together with the wind-driven current generated at the surface, seem to be the agents responsible for the horizontal transport of phytoplankton across the reservoir.

© Limnology and Oceanography, 2007, vol. 52, núm. 2, p. 620-634

Association for the Sciences of Limnology and Oceanography (ASLO)

Author: Serra Putellas, Teresa
Vidal Hurtado, Jordi
Casamitjana, Xavier
Soler i Ortega, Marianna
Colomer, Jordi
Date: 2007
Abstract: We investigated convection caused by surface cooling and mixing attributable to wind shear stress and their roles as agents for the transport of phytoplankton cells in the water column by carrying out two daily surveys during the stratified period of the Sau reservoir. Green algae, diatoms, and cryptophyceae were the dominant phytoplankton communities during the surveys carried out in the middle (July) and end (September) of the stratified period. We show that a system with a linear stratification and that is subject to weak surface forcing, with weak winds , < 4 m S (-1) and low energy dissipation rate values of the order of 1028 m2 s23 or lower, enables the formation of thin phytoplankton layers. These layers quickly disappear when water parcels mix because there is a medium external forcing (convection) induced by the night surface cooling, which is characterized by energy dissipation rates on the order of , 5x10(-8)m2s(-3). During both surveys the wind generated internal waves during the entire diurnal cycle. During the day, and because of the weak winds, phytoplankton layers rise in the water column up to a depth determined by both solar heating and internal waves. In contrast, during the night phytoplankton mixes down to a depth determined by both convection and internal waves. These internal waves, together with the wind-driven current generated at the surface, seem to be the agents responsible for the horizontal transport of phytoplankton across the reservoir.
Format: application/pdf
ISSN: 0024-3590 (versió paper)
1939-5590 (versió electrònica)
Document access: http://hdl.handle.net/10256/9717
Language: eng
Publisher: Association for the Sciences of Limnology and Oceanography (ASLO)
Collection: Reproducció digital del document publicat a: http://dx.doi.org/10.4319/lo.2007.52.2.0620
Articles publicats (D-F)
Is part of: © Limnology and Oceanography, 2007, vol. 52, núm. 2, p. 620-634
Rights: Tots els drets reservats
Subject: Fitoplàncton -- Sau, Pantà de (Catalunya)
Phytoplankton -- Sau, Pantà de (Catalonia)
Title: The role of surface vertical mixing in phytoplankton distribution in a stratified reservoir
Type: info:eu-repo/semantics/article
Repository: DUGiDocs

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