Spatio-seasonal variability of surface water mineralization in the Bonoua region, Southeastern Côte d’Ivoire

Introduction Surface waters in tropical coastal regions are essential for domestic, agricultural, and industrial uses, yet they are increasingly threatened by anthropogenic pressures and seasonal variability. Methods This study evaluates the spatio-seasonal variability of surface water mineralization in the Bonoua region (Southeastern Côte d’Ivoire) based on two sampling campaigns conducted during the rainy and dry seasons across rivers and lagoons. A total of 28 samples (14 rainy season; 14 dry season) were analyzed for physicochemical parameters, major ions, nutrients, and trace metals. Hydrochemical facies were determined using Piper diagrams, mineralization processes were interpreted using Gibbs diagrams and ionic ratios, and multivariate relationships were examined through Principal Component Analysis (PCA). Water quality was further assessed using the Modified NSF-WQI. The results reveal pronounced seasonal contrasts. Results Electrical conductivity increased by +107.8%, reaching 1,240 μS cm −1 at site L3 during the dry season, while total dissolved solids increased by +118.1%. In contrast, Fe (−46.9%) and PO 4 3− (−52.5%) concentrations decreased during the dry season. Hydrochemical facies shifted from Cl-NO₃–Ca dominance (93% during the rainy season) toward increased HCO₃–Ca waters during the dry season (21%). Gibbs diagrams indicate a predominance of atmospheric precipitation control (86% rainy season, 79% dry season), with evapoconcentration observed at site L3. PCA highlights a dominant mineralization factor (PC1 explaining 54.76% of the variance, associated with EC, TDS, and major ions), while nutrients and redox-sensitive elements are represented by secondary components. Modified NSF-WQI results identify poor water quality at site L3 during the dry season (Modified NSF-WQI = 43.2), mainly related to elevated EC, NH₄ + , and PO 4 3− concentrations. Discussion These findings demonstrate that seasonal hydrological dynamics combined with anthropogenic inputs, including fertilizers and domestic effluents, significantly influence surface water chemistry in the Bonoua region. This study provides a valuable baseline for monitoring and managing freshwater resources in tropical coastal environments facing increasing environmental pressures.