Plankton Index of Biotic Integrity (P-IBI) for assessing ecosystem health within the Ouémé River basin, Republic of Benin

This study aims at assessing the impact of organic pollution on plankton communities of the Ouémé River using a Plankton Index of Biotic Integrity (P-IBI) as a tool for ecological heath assessment. Plankton and other environmental data were collected monthly from October 2014 to September 2015. An Organic Pollution Index (OPI) was calculated to classify the sampling sites, and 18 plankton candidate metrics were used to discriminate among the observed organic pollution levels. From this analysis, seven significant metrics were selected for setting up biotic integrity indices. An indicative value (IndVal) was calculated for each plankton species to identify indicator species characteristic of observed ecological statuses. The OPI shows significant organic pollution at sites, such as Kaboua, Vossa and Atchakpa-rejet, and less organic pollution at Kpassa. The plankton Index of Biotic Integrity (P-IBI) value shows significant correlation (r > 0.75) with organic pollution. Three ecological states were identified: Kaboua and Vossa were in fair condition; Kpassa, Toué, Atchérigbé and Affon in very good condition; and all other sites in good condition. Three phytoplankton and four zooplankton species were significantly associated with good conditions, whereas 108 phytoplankton species and 40 zooplankton species were significantly associated with fair conditions within the River basin.