A study of physical, chemical and biological descriptors of the water in the storage réservoir of a combined stabilization pond (Ben Slimane, Morocco), during maturation, showed an improvement of the purification output for some variables after 36 days of rétention. Such an environment, rich with a range of différent nutrients, allowed an optimal development of plankton characterized by a high species diversity that decreased with time. Zooplankton
development seemed to be limited by poor phytoplankton biomass. However, trophic factors such as nutrients and température affected the évolution of planktonic species. After 36 days of rétention, the decrease in BOD5, COD, NH4 +, N03", total Kjeldahl nitrogen (TNK), P04 3", total phosphorus (TP), and the increase in pH, dissolved oxygen and transparency, suggested that maturation had been reached at this level. Simultaneously, phyto- and zooplankton were présent in low densities. Nevertheless, beyond this stage of maturation, phytoplankton prolifération occurred, dominated by Euglena viridis whose exponential phase of growth began at the ISth day of maturation and reached a maximum density after 81 days (4.1 x 106 individus/m3). A low proportion of Chlorophyte species was observed, represented by Pediastrum boryanum and Ankyra judai. The zooplankton community was dominated by two species of Cladocera (Daphnia magna and Diaphanosoma sp). The increase in Euglena viridis density up to 81 days coincided with zooplanktonic prolifération constituted exclusively by Rotifers (Brachionus calyciflorus and Polyarthra remata). At 111 days of rétention, the zooplankton community consisted of Copepods {Acanthocyclops robustus), which reappeared at this stage, as well as Nauplii

Bibliographic information

Himmi, N. et al. (2005). Variabilités des descripteurs physiques, chimiques et biologiques d’un réservoir de stockage (lagunage mixte, Ben Slimane - Maroc) (in French) Variability of physical, chemical and biological parameters of a storage tank (mixed lagoon, Ben Slimane - Morocco) Revue des Sciences de l’Eau 18/Spécial. Pp 91-107.

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