Phytoplankton Dynamics in the Bafing River under Artisanal Gold Mining Pressure, Côte d’Ivoire

The Bafing River, the main right-bank tributary of the Sassandra River, was investigated to characterize its physicochemical parameters and phytoplankton community. Located in northwestern Côte d’Ivoire, this study aimed to assess the diversity, composition, and spatial distribution of phytoplankton in the Sassandra River basin. Physicochemical parameters (pH, temperature, conductivity, and dissolved oxygen) were measured in situ using a HANNA portable multiparameter device (model HI9828), while phytoplankton samples were collected with a 20 µm mesh plankton net from April to December 2022. Qualitative analysis identified 82 taxa distributed across 35 genera, 17 families, 12 orders, 9 classes, and 5 phyla. Chlorophyta (56.09%) and Euglenophyta (17.07%) were the most diverse groups, followed by Heterokontophyta (14.63%), Cyanoprokaryota (9.75%), and Dinophyta (3.65%). Spatially, the highest algal densities were observed at the Gorlo station and Lac Ranch (downstream), while the lowest densities were recorded upstream, notably at the Min, Bafing, and Godigui stations. Physicochemical analysis indicated relatively cool, acidic, and relatively oxygenated waters. These results provide an essential reference for ecological monitoring and water quality assessment of the Bafing River, particularly under anthropogenic pressures such as artisanal gold mining.