SPATIO-TEMPORAL OF WATER QUALITY AND NUTRIENTS IN THE TROPICAL EBRIÉ LAGOON, CÔTE D’IVOIRE

This study assessed the spatial and seasonal variability of physicochemical parameters and nutrient concentrations in sectors IV and V of the Ebrié lagoon, following reports of massive fish mortality. Monthly water sampling was conducted at 11 stations from February 2014 to January 2015. Temperature, pH, salinity, conductivity, dissolved oxygen, transparency, suspended matter, nitrate, nitrite, ammonium and orthophosphate were measured. Seasonal differences were evaluated using analysis of variance, and principal component analysis (PCA) was used to identify station groups and relationships among variables. Water temperature ranged from 28.0 to 31.4 °C, and dissolved oxygen concentrations ranged from 4.4 to 8.7 mg/L. Salinity and conductivity were generally higher during the dry season, whereas ammonium and orthophosphate concentrations tended to increase during the rainy season. Nitrate concentrations were higher during the dry season at several stations, reaching 5.29 mg/L. Nitrite concentrations reached 0.71 mg/L and were generally higher during the rainy season. These elevated nitrite concentrations may pose a risk to aquatic organisms. PCA distinguished three station groups associated with differing nutrient levels and physicochemical conditions. Salinity was strongly correlated with conductivity, while orthophosphate was negatively correlated with water transparency (r = −0.96). Overall, the results indicate seasonal variation in water quality, with rainy-season nitrite elevation warranting continued monitoring of the lagoon’s aquatic environment.