Distribution spatio-temporelle du phytoplancton et du zooplancton dans le lac Saint-Jean (Québec), un réservoir hydroélectrique

• Published in: Revue des sciences de l'eau
• Main Authors: D. Bussières, R. Côté, P. Desgagnés
• Format: Article in Journal/Newspaper
• Language: French
• Published: Université du Québec - INRS-Eau, Terre et Environnement (INRS-ETE) 2005
• Subjects: Sciences Humaines et Sociales; Social Sciences and Humanities; Lac Saint-Jean; Réservoir hydroélectrique; Phytoplancton; Zooplancton; Lake Saint-Jean; Hydroelectric reservoir; Phytoplankton; Zooplankton; envir; geo; Salmo salar
• Online Access: http://www.erudit.org/fr/revues/rseau/2002-v15-n3-rseau3309/705471ar.pdf; https://www.erudit.org/fr/revues/rseau/2002-v15-n3-rseau3309/705471ar.pdf; https://id.erudit.org/iderudit/705471ar; https://doi.org/10.7202/705471ar; https://constellation.uqac.ca/2003/; https://www.erudit.org/fr/revues/rseau/2002-v15-n3-rseau3309/705471ar/; https://academic.microsoft.com/#/detail/2162073394

The lake Saint-Jean is well known to fishermen and renowed for its freshwater salmon (Salmo salar). Of its 21 tributaries, three provide about 75% of its water; they are the Peribonka, the Mistassini and the Ashuapmushuan rivers. Although it is the fifth largest lake in the province of Quebec, its water is renewed four to five times a year; about a quarter of its 1 053 km2 area is only 3 m deep, with a maximum depth of 63 m in the middle. This kind of shallow lake is very sensitive to winds.The present study looked at the spatial and temporal variability of phytoplankton and zooplankton; ten stations were distributed over the whole lake (Figure 1 and Table 1) and water samples were taken at different depths (1, 2, 5, 10, 15 and 20 m when possible) from June to October 1997. Several physicochemical parameters were measured; phytoplankton and zooplankton samples were collected as well and the main species were identified and counted. The mean surface water temperature was 16° C compared to the average of the 1, 2 and 5 m data of 15°C and the deep layer (10, 15 and 20 m) of 13°C; from mid-August to mid-October, the water temperature is the same at all depths because of very good mixing due to the strong winds. Referring to the same layers, the mean values of chlorophyll a for the study period were 1.6, 1.3 and 0.6 mg m-3. For the early June sampling, values of chlorophyll a varied from 0.6 to 1.9 mg m?3. As for July and August, values between 3 and 4 mg m-3 were recorded; the overall mean of chlorophyll a was 1.3 mg m-3. The correlation coefficient between chlorophyll a and the temperature, for all data, was 0.56 (p<0.01). As stated before, a very good mixing of the upper water layer is encountered, bringing the phytoplankton to depths below the photic layer evaluated at about 4 m; such conditions of light limitation do not foster a good photosynthetic activity.Nitrates and orthophosphates were always low during the study, respectively lower than 0.8 mg L-1 and between 0.1 and 0.2 mg L-1. Linear or exponential ...