Irrigation Suitability and Ionic Toxicity of Houet River Water Used at the Dogona Market Garden Site in Bobo-Dioulasso, Burkina Faso

Abstract

Aims: To assess the irrigation suitability and ionic toxicity of Houet River water used at the Dogona market-gardening site in Bobo-Dioulasso. Study Design: This was a prospective longitudinal field study based on monthly sampling. Place and Duration of Study: The study was conducted from March 2023 to February 2024 at four georeferenced sites located upstream (P1–P2) and downstream (P3–P4) of the Dogona wastewater treatment plant (WWTP) discharge point, across the dry, rainy, and cool seasons. Methodology: Water samples were analysed for electrical conductivity (EC), total dissolved solids (TDS), and major ions, including Na⁺ and Cl⁻. Major-ion concentrations were converted to meq/L to calculate irrigation-suitability indices: SAR, %Na, PI, MAR, and Kelly’s ratio (KR). Water quality was classified using the Wilcox and USSL/Riverside diagrams. Results: EC ranged from 398.60 ± 59.55 to 1441.75 ± 458.79 µS/cm and TDS from 103.50 ± 19.53 to 392.50 ± 71.62 mg/L. SAR varied from 1.20 to 6.18, %Na from 37.40 to 85.09, PI from 7.17 to 18.50, MAR from 5.88 to 26.01, and KR from 0.43 to 3.86. Most parameters differed significantly among sampling points (p < 0.05), except Na⁺. According to the Wilcox diagram, water quality ranged from excellent to good, while the Riverside/USSL classification placed samples in classes C2S1 to C3S1, with the greatest deterioration at P3 and partial dilution at P4. Conclusion: Houet River water showed acceptable to moderate suitability for irrigation, but its use requires drainage, leaching, sodium control, and appropriate crop selection, especially immediately downstream of the WWTP discharge.