Diatom dynamics in a coastal ecosystem affected by upwelling: coupling between species succession, circulation and biogeochemical processes
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Notice bibliographique
Résumé
The typical phytoplankton succession scenario in coastal upwelling zones is high diatom growth during upwelling and flagellate dominance during water column stratification. Within the diatom/flagellate succession there exist short-term changes in diatom communities that are caused by physical, chemical and biological processes. In this study, we used an improved 2-D kinematic box model to assess the influence of these processes on diatom dynamics in an estuarine ecosystem affected by coastal upwelling. This model enabled us to separate hydrographic from biogeochemical processes occurring in the estuary. Hydrographic variables, nutrient concentrations and phytoplankton composition were determined over a 2 wk period in the Ra de Vigo, NW Spain. Two major hydrographic phases were identified which coincided with a clear temporal and spatial separation between 2 diatom assemblages: Thalassiosira spp./Skeletonema costatum and Chaetoceros spp./Cerataulina pelagica. During upwelling, horizontal (6.6 km d -1 ) and vertical (11.7 m d -1 ) convective fluxes were high, causing a net input of NO 3 -, HPO 4 2and SiO 4 H 4 . During this phase the Thalassiosira spp./ S. costatum standing stock was high (> 20 mol C l -1 ). Hydrographic processes, however, affected the Thalassiosira spp./S. costatum assemblage more than biogeochemical processes and this resulted in the net loss of this assemblage from the Ra and its export towards the shelf. There was a significant correlation between the biogeochemical variations in this diatom assemblage and silicate, suggesting a strong dependency of Thalassiosira spp./S. costatum on this nutrient. By comparison, due to the higher carbon-specific net growth rate of the Chaetoceros spp./C. pelagica assemblage (0.35 d -1 ) during upwelling, this assemblage maintained a high biomass in the Ra. Upwelling was followed by upwelling relaxation when horizontal (1.9 km d -1 ) and vertical fluxes (1.8 m d -1 ) were reduced and nutrient levels diminished. During upwelling relaxation there was an accumulation of Chaetoceros spp./C. pelagica biomass (>18 mol C l -1 ). Biogeochemical processes provoked a loss of Thalassiosira spp./S. costatum due to rapid sedimentation and a net increase in Chaetoceros spp./C. pelagica. It is suggested that the accumulation of Chaetoceros spp. is aided by a lower sinking rate whereas the selection of C. pelagica is more dependent on NO 3 -and HPO 4 2consumption. It is concluded that upwelling events in the Ra cause the exportation of Thalassiosira spp./S. costatum standing stock from the Ra towards the shelf, which will ultimately benefit shelf pelagic and benthic fish communities. Upwelling relaxation events favour the retention of a high standing stock of Chaetoceros spp./ C. pelagica, which is then directly available to the shellfish aquaculture of the Ra.
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Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découle