This study aimed to investigate the seasonal variation of zooplankton diversity and abundance in the Nokoué Lagoon in southern Benin. Through extensive sampling, a total of 109 zooplanktonic taxa were identified and quantified. The average zooplankton abundance was found to be 60 individuals per liter, with copepods and rotifers being the most dominant groups, comprising 68.1% and 29.1% of the total abundance, respectively. The key factor identified as driving the structure of the zooplanktonic assemblages was salinity, which showed significant seasonal variation. The results revealed that during the high water period, when the lagoon was filled with fresh water, rotifers were dominant, zooplanktonic diversity was highest, and abundances were quite high. Conversely, during the low water period, when the lagoon was characterized by brackish water, diversity was minimal, and abundance decreased slightly. The study also found that some areas of the lagoon showed high abundances independent of salinity levels, suggesting that other factors such as riverine inputs or the presence of acadjas (home-made brush parks used as fish traps) may also have notable effects on the zooplankton community. Overall, the findings of this study provide valuable insights into the functioning of one of the most biologically productive lagoons in West Africa.

Le présent travail vise à apprécier la qualité physico-chimique des eaux de l’Ouémé supérieur au Bénin. L’étude concerne Quatre (04) communes. Les données ont été collectées en Octobre 2021 et en Mars 2022. Les paramètres physiques in-situ et les paramètres chimiques au laboratoire ont été étudiés. La description par les box plots (Boîtes à moustaches), le test de Shapiro-Wilk et celui de Kruskall Wallis au seuil α = 5% ont été utilisés. Les paramètres tels la salinité, °C, , , , , Ca2+, Mg2+, Fe2+ et le Cl- sont significativement différents des autres paramètres et ne respectent pas les normes des eaux de surface. Les résultats de la Classification Hiérarchique Ascendante (CAH) ont permis d’identifier trois groupes. Le groupe 1, constitué de : pH, OD, Salinité, , , , , Ca2+, Mg2+, Fe2+ et le Cl- ; proviennent principalement des activités agricoles et des eaux usées. Le groupe 2, constitué de : °C, STD et la DCO ; proviennent des différents éléments chimiques solubles dans l’eau. Le groupe 3, constitué de : CE, provient de la minéralisation globale de l’eau. L'eau est alors contaminée à travers les constituants physico-chimiques évalués. This work aims to assess the physico-chemical quality of the waters of the upper Ouémé in Benin. The study covered four (04) communes. The data was collected in October 2021 and March 2022. The in-situ physical parameters and the chemical parameters in the laboratory were studied. The description by the box plots, the Shapiro-Wilk test and the Kruskall Wallis test at the threshold α = 5% were used. The parameters such as salinity, , , , , Ca2+, Mg2+, Fe2+ and the Cl- are significantly different from the other parameters and do not respect the standards of the surface water. The results of the Hierarchical Ascending Classification (HAC) have helped us to identify three groups. The group 1, made up of: pH, DO, Salinity, , , , , Ca2+, Mg2+, Fe2+ and the Cl-; come mainly from agricultural activities and wastewater. The group 2, made up of: °C, STD and COD; come from the different chemical elements that are soluble in water. The group 3, made up of: CE, comes from the global mineralization of water. The water is then contaminated through the physico-chemical constituents which have been evaluated.

Le présent travail vise à apprécier la qualité physico-chimique des eaux de l’Ouémé supérieur au Bénin. L’étude concerne quatre (04) communes. Les données ont été collectées en octobre 2021 et en mars 2022. Les paramètres physiques in-situ et les paramètres chimiques au laboratoire ont été étudiés. La description par les box plots (Boîtes à moustaches), le test de Shapiro-Wilk et celui de Kruskall Wallis au seuil α = 5% ont été utilisés. Les paramètres tels la salinité, T°C,〖 NO〗_2^-,  NO_3^-, NH_4^+, PO_4^(3-), Ca2+, Mg2+, Fe2+ et le Cl- sont significativement différents des autres paramètres et ne respectent pas les normes des eaux de surface. Les résultats de la Classification Hiérarchique Ascendante (CAH) ont permis d’identifier trois groupes. Le groupe 1, constitué de : pH, OD, Salinité,〖 NO〗_2^-,  NO_3^-,〖 NH〗_4^+,〖 PO〗_4^(3-), Ca2+, Mg2+, Fe2+ et le Cl- ; proviennent principalement des activités agricoles et des eaux usées. Le groupe 2, constitué de : T°C, STD et la DCO ; proviennent des différents éléments chimiques solubles dans l’eau. Le groupe 3, constitué de : CE, provient de la minéralisation globale de l’eau. L'eau est alors contaminée à travers les constituants physico-chimiques évalués.   This work aims to assess the physico-chemical quality of the waters of the upper Ouémé in Benin. The study covered four (04) communes. The data was collected in october 2021 and march 2022. The in-situ physical parameters and the chemical parameters in the laboratory were studied. The description by the box plots, the Shapiro-Wilk test and the Kruskall Wallis test at the threshold α = 5% were used. The parameters such as salinity, NO_2^-,  NO_3^-, NH_4^+, PO_4^(3-), Ca2+, Mg2+, Fe2+ and the Cl- are significantly different from the other parameters and do not respect the standards of the surface water. The results of the Hierarchical Ascending Classification (HAC) have helped us to identify three groups. The group 1, made up of: pH, DO, Salinity, 〖 NO〗_2^-,  NO_3^-,〖 NH〗_4^+,〖 PO〗_4^(3-), Ca2+, Mg2+, Fe2+ and the Cl-; come mainly from agricultural activities and wastewater. The group 2, made up of: T°C, STD and COD; come from the different chemical elements that are soluble in water. The group 3, made up of: CE, comes from the global mineralization of water. The water is then contaminated through the physico-chemical constituents which have been evaluated.