Temporal evaluation of surface water quality in semiarid regions: a case study of the Ouled Mellouk dam in north-western Algeria

The present work aimed at evaluating the impact of human activity and geology formations on the surface water quality of the Ouled Mellouk dam (Algeria). Methodology aims to assess the seasonal variations of the physicochemical parameters (electrical conductivity (EC), total dis-solved solids (TDS), pH, SO2- (4), Cl-, Ca2+, Na+, HCO3-, NO3- , PO- 43 , and Mg-2(+)) and pollution parameters (organic matter (OM), suspended solids, 5-day biochemical oxygen demand (BOD5), and chemical oxygen demand (COD)) during the period from 2007 to 2013. The results of phys-icochemical parameters show a high salinization recorded essentially during the periods of heavy precipitation or flooding, due to the leaching of dolomitic limestones and evaporitic deposits from the saliferous formations of the Ouarsenis and Doui mountains. The high con-centrations of nitrate, nitrite, ammonium, and OM observed can be attributed to the influence of anthropogenic factors and the use of fertilizers in agriculture. Principal component analysis (PCA) application shows that salinization (49.92%), anthropogenic pollution (19.38%), and agricultural pollution (12%) are the most significant degradation factors, respectively. Saturation index of carbonates and gyp-siferous minerals shows the carbonates tend to precipitate before the gypsiferous minerals, which allowed the chemical elements coming from the dissolution of gypsum and halite to acquire significant contents. The evolution of biological oxygen demand and organic pollution showed slight pollution of the dam water.