Évolution nycthémérale des composantes biochimiques du phytoplancton de la retenue du barrage Idriss premier (Fès, Maroc)

The diel changes of the biochemical composition of the phytoplankton were studied in the Idriss first reservoir (located on the Inaouen river at thirty Km from the city of Fes, Morrocco) during September 1994. Several biomass and metabolic indicators (proteins, carbohydrates, lipids, chlorophyll a and primary production) were assessed every fourth hour over tow days (7, 8 and 9 September). Since the Protein/Carbohydrates ratio (P/C) is largely recognised as a good integrator of the metabolic functions of the cells, we examined its distribution pattern concomitantly with aforementioned parameters. The results demonstrated enhanced P/C ratios clearly indicating that nutrients were sufficiently available for growth. In addition, this index showed a diel significant variation with levels higher in the night than in the day. Moreover, these results suggest that phytoplankton species during the night used the day-synthesised carbohydrates to insure the cell metabolic functioning. The P/C presents relatively high values in proposition to the ones that have been recorded in temperate regions, and seems to be related to azotic inputs of the Inaouen river.