Physicochemical Characterization of Surface Waters in the Ono Lagoon Watershed Under Multiple Anthropogenic Pressures, Bonoua (Southeastern Ivory Coast)

Domestic, industrial, and agricultural pressures are increasingly impacting the Ono Lagoon watershed (Bonoua, Ivory Coast). This study aimed to identify the main sources of pollution and assess the physicochemical quality of surface waters. Twenty-five (25) sites were sampled, and ten (10) parameters were analyzed: pH, temperature, electrical conductivity, nitrate, nitrite, ammonium, orthophosphate, sulfate, potassium, and sodium. Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA), two multivariate statistical methods, revealed moderate mineralization (mean electrical conductivity: 34.8 µS/cm) and significant acidity (mean pH: 5.43), both below World Health Organization (WHO) standards. Orthophosphate concentrations exceeded WHO guidelines at 88% of the sites, indicating substantial agricultural pressure. PCA identified three main gradients: seasonal nitrate leaching, agro-industrial inputs (sulfate, ammonium), and domestic pollution (nitrite, orthophosphate, potassium, sodium). HCA grouped the sites into three distinct clusters, with site S25 showing particularly degraded water quality. These results highlight the complex interactions among different pollution sources and emphasize the importance of regular monitoring of surface waters. They also underscore the need for integrated and targeted management strategies to mitigate the impacts of domestic and agricultural activities on the watershed’s surface waters. In summary, this study provides essential information to guide the protection and sustainable management of water resources in the Ono Lagoon watershed.