CONTRIBUTION A L’EVALUATION DE LA QUALITE PHYSICO-CHIMIQUE DU COURS D’EAU MERZEG (PERIURBAIN DE CASABLANCA, MAROC)

Abstract

Morocco’s water resources are facing quantity and quality problems. Limited resources due largely to a semi-arid and arid climate and also to the significant deterioration in the quality grounded by different pollutants. Casablanca city (Morocco's economic capital) is one of Morocco’s parts that best illustrates these phenomena. It shows a considerable increase of the population and continuous development of industrial activities especially in the suburban area. Rivers of this area who suffer the most are the effects of these pressures, what makes compromised of their uses. Merzeg river and their tributary oued Sierni were chosen to illustrate the above impacts. These hydrosystems receive water from the waste water plant (WWTP) of the city of Berrechid as well as the release of the industrial area of Had Soualem. A companion of 14 months was conducted in order to determine the physicochemical water quality in 7 sampling stations chosen along these hydrosystems. The findings highlighted the extreme high organic load at the level of the Merzeg river and their tributary Oued Sierni as evidenced by the values of the main parameters: BOD5, COD, Ammonium, orthophosphate and total phosphorus.The waters of study stations can be described as bad to very bad. Significant mineralization was highlighted at the level of this stream. This would result from the combined effect of the degradation of the coastal chaouia groundwater and the mineral load of wastewater. The follow-up of the spatio-temporal evolution of organic pollution index “OPI” shows the polluting waters in the stations receiving releases of the STEP of Berrechid and also Had Soualem. The results of the principal component analysis (PCA) have highlighted two gradients. The first reflects the degree of pollution and eutrophication, while the second describes the mineralization of waters and seasonality. Moreover, this PCA allowed discriminating against stations according to their physicochemical data.