| Abstract: | Located at 1197 m in the Massif Central Français, lake Pavin has a volcanic origin. It is a dimictic and meromictic lake of 44 ha of area and 92 m depth. Samples were collected bimonthly at 8 depth (0 to 40 m) from May 1973 to April 1974. Physicochemical parameters (light energy, temperature, pH, conductivity, Oxygen, Nitrogen, Phosphorus, Silice, Carbon) and dynamics of phytoplanktonic populations (cells counts, standing crop, primary production, photosynthetic pigments) were studied.The waters of this lake are clear, with low conductivity and high concentrations of oxygen in the first 40 meters. In a water column, 0–40 meters, the means of nitrogen concentrations are between 45 and 279 µg/l and between 0 and 161 µg/l for phosphorus. Phytoplankton is caracterised by an important development of Diatoms (Melosira italica subsp. subarctica and Asterionella formosa) in winter and spring, opposed to low standing crops of Chlorophycea (Coenococcus, Sphaerocystis, Chlamydomonas) in summer. The annual mean of primary production is about 360 mg C ass./m2.J. The highes values of the activity coefficient (P/B) are found during the development of Chlorophycea, but photosynthetic efficiency is maximum in winter for Diatom populations.To summarize physico-chemical parameters and phytoplankton relationships, a synthetical mathematical model was made by Principal Components Analysis. |
