Applying Multivariate Analysis and Organic Pollution Index to Evaluate Mexa and Cheffia Dams, Algeria

This study provides a comprehensive assessment of surface water quality in the Mexa and Cheffia dams located in the El Tarf region, northeastern Algeria. The work focuses on evaluating pollution levels, organic contamination, and nutrient status using several indices. Sampling was carried out at two different sites over a 12-month period (May 2024 to April 2025). The Water Pollution Index (WPI) classified all seasons in both reservoirs as “very highly polluted”, reflecting strong mineralisation and ionic enrichment. The Organic Pollution Index (OPI) indicated predominantly high to very high organic pollution, with Cheffia showing 91.7 % high organic pollution and 8.3 % very high organic pollution, and Mexa presenting 100 % high organic pollution. The Nutrient Pollution Index (NPI) revealed strong seasonal contrasts, ranging from moderate pollution (0.66-2.47) in summer-autumn to extremely high nutrient enrichment (up to 7.44) in winter and spring. Trophic evaluation based on the TN : TP ratio showed seasonal variability, with 50 % of the observations corresponding to oligotrophic conditions, while the remaining observations exhibited eutrophic to hypertrophic states, especially in Mexa. Overall, the integrated index assessment highlights that both reservoirs are subjected to substantial mineral, organic, and nutrient pressures, with Mexa displaying greater variability and Cheffia showing relatively more stability across indices.