Application of biotic indices to determine the ecological status of Oued El Abid Basin, Azilal, Morocco

Morocco is one of the countries the most affected by water shortages, and the Beni Mellal-Khenifra region is not an exception, specifically The Oued El Abid basin. The study was carried out over an annual cycle at 7 stations. Biotic indices including the Normalized Global Biological Index (IBGN), the River Habitat Quality Index (HQI), and the Riparian Quality Index (RQI) were used for the ecological diagnosis. The surface water quality was assessed by analyzing 15 physicochemical parameters (temperature, pH, DO, EC, COD, NO 3– , Cl - , SO 4 2- , PO 4 3- , TH, Fe 2+ , Cu 2+ , Pb, Cr, Cd). Current results indicate a notable degradation in water quality downstream of Oued El Abid, at S7, with high values for COD (42.01 mg L -1 ), EC (1538 µS cm −1 ), and Cl - reaching 205.9 mg L -1 , and upstream of Oued Ahansal (S2) with DO (3.02 mg L -1 ) and COD (36 mg L -1 ) values, which classify this stream as poor to average, linked to domestic and agricultural pollution. Metals analyzed reveal a total or partial absence in places. The values of the three biotic indices classify the water at the various stations studied as being of critical quality for stations S2 and S7, of average quality for S3, S4, and S6, and of average to good quality for S1 and S5. PCA revealed that the three biotic indices shows a high negative correlation with EC and a strong positive correlation with DO. This suggests that less conductive and better-oxygenated waters are associated with better biological quality. Distance-based linear models (DistLM) show that several environmental variables significantly influence the variation of biological or ecological parameters of Oued El Abid aquatic ecosystem.