Determination of the ecological quality of Oued Nfifikh and Oued El Maleh (Morocco) using the generic diatomic index and the global normalized biological index

The quality of rivers and water reserves has now become a major concern due to the combined effects of climate change and human activities, which contribute to their degradation. This study assesses the water quality of four sites in Greater Casablanca, located upstream and downstream of two wadis: the Oued El Maleh dam (M1), its downstream in Mohammedia (M2), the Oued Nfifikh discharge area (N1), and its downstream (N2). The samples targeted diatoms and macroinvertebrates to calculate two biotic indices: the Generic Diatomic Index (GDI) and the Global Normalized Biological Index (GNBI), which were then compared to the Organic Pollution Index (OPI) determined by physicochemical analyses. The results revealed that the M1 site has a high diversity of diatoms (H' = 2.63), bio-indicators of good ecological quality (Achnanthidium, Cymbella, etc.), confirmed by a GDI of 13.01 (moderately eutrophic state) and an OPI of 4.3. On the other hand, the M2, N1, and N2 sites show low diatom diversity (H' = 1.46; 1.77; 0.94) and the presence of pollution-tolerant species (Bacillaria paradoxa, Nitzschia palea, etc.), with low GDIs (4.74; 7.59; 2.21) indicating pollution. The dominance of resistant taxa (gastropods at M2, hirudinae at N1, chironomidae at N2) and weak GNBI (4, 3, 2) confirm this degradation, as do OPIs (1.5; 2; 1.75). These results revealed that only M1 maintains a good ecological status, while M2, N1, and N2 are polluted, reflecting the impact of urban and industrial discharges. This deterioration highlights the need for effective management measures to protect these aquatic ecosystems, particularly in areas downstream of urban centers where anthropogenic pressures are increasing.