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L'étude des variations des descripteurs physiques, chimiques et biologiques des eauxd'un réservoir de maturation du lagunage mixte (Ben Slimane, Maroc), a montré uneaugmentation des valeurs de certaines variables (oxygène dissous, transparence) après le36ème jour de rétention en raison d'une remise en solution.A 36 jours de rétention, la chute des teneurs de la DBO5, de la DCO,des composés azotés (NH4+,NO3-, NTK) et phosphorés(PO43-, PT), et l'augmentation du pH, de l'oxygènedissous et de la transparence laissent présager une maturation à cette date de mesure. Lesdensités planctoniques enregistrées à ce niveau sont les plus basses.Au-delà de ce stade de maturation, le phytoplancton prolifère avec dominance d'Euglenaviridis qui montre un pic de densité (4,1.106Individus/m3) le 81ème jour. Le début de sa phaseexponentielle de croissance est observé à partir du 18ème jour dematuration. La densité cellulaire est ensuite atténuée vraisemblablement en raison de ladiminution de la charge organique (DBO5 et DCO) après le81ème jour et de l'intensité de broutage par le zooplancton herbivoresurtout Acanthocyclops robustus qui montre son maximum de croissance le138ème jour.Après le 81ème jour de maturation, Euglena viridis est remplacéepar deux espèces de Chlorophycées (Pediastrum boryanum et Ankyra judai) dont le maximum dedensité (91% de la densité algale totale) est atteint le 138ème jour.La prolifération de ces espèces coïncide avec des valeurs en nitrates dépassant 10,6 mgN/L.A la fin de cette période d'étude (le 138ème jour), lezooplancton est à sa prolifération maximale (106 individus/m3). Il estdominé par Acanthocyclops robustus avec présence de Nauplii et de Daphnia magna. LesRotifères présents depuis le début de la maturation disparaissent à 138 jours de rétention.L'étude bactériologique a révélé un rendement épuratoire remarquable atteignant 100% pourles coliformes fécaux et les streptocoques fécaux.A study of physical, chemical and biological descriptors of the water in the storagereservoir of a combined stabilization pond (Ben Slimane, Morocco), during maturation, showedan improvement of the purification output for some variables after 36 days of retention.Such an environment, rich with a range of different nutrients, allowed an optimaldevelopment of plankton characterized by a high species diversity that decreased with time.Zooplankton development seemed to be limited by poor phytoplankton biomass. However, trophicfactors such as nutrients and temperature affected the evolution of planktonicspecies.After 36 days of retention, the decrease in BOD5, COD,NH4+, NO3-, total Kjeldahlnitrogen (TNK), PO43-, total phosphorus (TP), and theincrease in pH, dissolved oxygen and transparency, suggested that maturation had beenreached at this level. Simultaneously, phyto- and zooplankton were present in low densities.Nevertheless, beyond this stage of maturation, phytoplankton proliferation occurred,dominated by Euglena viridis whose exponential phase of growth began at the 18th day ofmaturation and reached a maximum density after 81 days (4.1x106individus/m3). A low proportion of Chlorophyte species was observed,represented by Pediastrum boryanum and Ankyra judai. The zooplankton community was dominatedby two species of Cladocera (Daphnia magna and Diaphanosoma sp).The increase in Euglena viridis density up to 81 days coincided with zooplanktonicproliferation constituted exclusively by Rotifers (Brachionus calyciflorus and Polyarthraremata). At 111 days of retention, the zooplankton community consisted of Copepods(Acanthocyclops robustus), which reappeared at this stage, as well as Nauplii Cladocera(Daphnia magna) and residual Rotifers (Brachionus calyciflorus and Polyarthra remata). Theremarkable decrease in Euglena density on day 111 and their complete disappearance on day138 was probably linked to grazing by herbivorous zooplankton and to low organic matterconcentrations. Euglena viridis was replaced by two Chlorophytes (Pediastrum boryanum andAnkyra judai) reaching their maximum density (91% of total algal density) on day 138. Theproliferation of these species coincided with values exceeding 10.6 mg N/L. Zooplankton weredominated by Acanthocyclops robustus with the presence of Nauplii and Daphnia magna(106individuals/m3). Rotifers were present since the beginning of the maturation, but wereabsent by 138 days of retention.The qualitative and quantitative changes in phyto- and zooplankton result from factorsthat control the growth and the loss of these populations. A low growth rate can lead tobiomass accumulation if the growth exceeds loss. On the other hand, a low and stable biomasscan result from a high growth rate that is compensated by important losses. Zooplanktongrazing and algal sedimentation, which are the two main mechanisms related to phytoplanktondecline, are two selective processes (POURRIOT et al., 1982). In stabilization ponds, foodchains are established that allow water clarity and minimize algal proliferation. Thebacteriological study showed a remarkable purification, with reductions reaching 100% forfaecal coliforms and faecal Streptococcus

Variabilités des descripteurs physiques, chimiques et biologiques d'un réservoir de stokage (lagunage mixte, en Slimane - Maroc)