Microbiological Characterization of Irrigation Water and Risk Assessment for Rice Production: Application of the Biological Quality Index (IBQ6) in the M’Bahiakro Irrigated Agricultural Perimeter (Central-Eastern Côte d’I

Assessing the microbiological quality of irrigation water is essential for ensuring the proper functioning of irrigated agricultural areas and securing optimal rice production yields. This study aims to evaluate the microbiological quality of irrigation water and the potential risks it poses to rice cultivation in M’Bahiakro. The adopted methodology involved identifying microbial pollution indicators such as total coliforms, fecal coliforms, Escherichia coli, and fecal streptococci. Water samples were collected from three (03) monitoring stations during both the dry and rainy seasons. The qualitative and quantitative identification of these microorganisms was performed by filtering 100 mL of water through a cellulose membrane filter (MF) with a uniform pore diameter of 0.45 μm. The risk to rice production was assessed using the IBQ6 index method. Results revealed high contamination levels in the irrigation water, characterized by elevated loads of total and fecal coliforms, fecal streptococci, and E. coli, both upstream and downstream of the dam, thereby exposing rice farming to significant health and agronomic risks. This microbial pollution is exacerbated during the dry season, when the IBQ6 scores indicate poor water quality (34 - 35/100), threatening both crop yields and farmers’ health. A slight improvement is observed during the rainy season due to dilution effects (IBQ6: 54 - 63/100), although the water quality remains insufficient to ensure sustainable irrigation. Furthermore, high concentrations of nutrients such as phosphorus and ammonia intensify anthropogenic pressure and the risks of eutrophication. These findings underscore the need for integrated water resource management, including pollution source control, community awareness initiatives, and the implementation of ecological or physical barriers to limit the spread of pathogens.