Data/hora: 01/06/2024 11:26:08

Provedor de dados: | 5
País: | France
Título: | Dynamique du phosphore et rôle comme facteur limitant de la production planctonique dans le panache de la Gironde sur le plateau continental Sud Gascogne
Autores: | Labry, Claire.
Data: | 2001-10-19
Ano: | 2001
Palavras-chave: | Golfe de Gascogne; Gironde; Phytoplancton; Bactéries; Phosphates; Phosphore organique; Dissous; Phosphatases; Bay of Biscay; Gironde; Phytoplankton; Bacteria; Phosphate; Dissolved organic phosphorus; Phosphatases.
Resumo: | This study was supported by the Atlantic working site of the « Programme National d’Océanographie Côtière » (PNOC, PNEC since 1999). The objectives were (1) to check the existence and to understand the mechanisms of winter phytoplankton blooms in the bay of Biscay influenced by the Gironde waters (2) to determine the limiting nutrient of the primary production associated to these blooms and to follow the seasonal evolution of the limiting nutrient, (3) to understand the consequences of this early limitation on the structuration of algal populations in spring. Since phosphorus was supposed to be the major limiting nutrient of algal growth in the Gironde plume, the different forms of the phosphorus cycle as well as the bacterial compartment, central in this cycle, were also studied in term of stocks and fluxes.  The sampling strategy consisted in three cruises in 1998, BIOMET 2 (January), BIOMET 3 (beginning of March), PEGASE (June) and six cruises in 1999, PLAGIA 1 to 6 (late February, late April, late May, late June, the middle of July and the beginning of October).  Winter algal blooms, essentially diatoms, were actually observed both in the typical waters of the plume (S &lt; 34.5) and at the limit of the plume and adjacent atlantic oceanic waters (S &gt; 34.5) in the successives years 1998 and 1999. These blooms were initiated by the occurrence of short anticyclonic windows in winter, acting on physical processes which dominate the evolution and characteristics of the Gironde plume (runoff, wind direction and speed) and, ultimately, on the evolution of the depth of the mixed layer (haline stratification) and available light (decrease of turbidity).  The algal growth was actually phosphorus limited in the typical waters of the plume at the end of the winter bloom, in spring and became nitrogen and phosphorus limited in summer until the first autumn gales restored the nutritive balance. More oceanic waters (S &gt; 34.5) were probably N+P limited from the end of the winter-the beginning of spring to autumn. Phosphorus limitation of winter blooms, associated with girondine unbalanced nutritive supplies (high NO3/PO4 ratios) favoured the development of small cells at the beginning of spring and the later presence of spring blooms (June 1998, late May 1999) composed of pico and nanophytoplankton (nanoflagellates), instead of typical diatom spring blooms for temperate waters. This size reduction of algal communities is strongthened by the competition between phytoplankton and bacteria for the phosphate uptake, bacteria being more competitives at low concentrations and being phosphorus limited sometimes in spring. The decreasing size of algal cells probably acted on the structuration of the whole food web.  The study of the different forms of phosphorus displayed the importance of the Dissolved Organic Phosphorus (DOP) pool. The potential biological lability and the capacity of algae and bacteria to use the DOP in spring when phosphate are undetectable was shown by the very high specific activities of alkaline phosphatases and the very rapid cycling of phosphate monoesters. According to the few estimations of actual phosphatasic activity and phosphate assimilation fluxes, the hydrolysis of DOP associated with the coupled assimilation of liberated phosphate would represent 91 to 99 % of the phosphorus fluxes into algal and bacterial cells when phosphate were exhausted. In such conditions DOP could satisfy most of microorganisms phosphorus needs.
Tipo: | Text
Idioma: | Francês
Identificador: | http://archimer.ifremer.fr/doc/00013/12463/9298.pdf
Editor: | Université de la Méditerranée
Relação: | http://archimer.ifremer.fr/doc/00013/12463/
Formato: | application/pdf