The considerable increase in the amount of nitrogen in the surface water is a major environmental problem. It has become a great matter of worry because of the multiple environmental effects including eutrophication and health risks. The El-Kebir West watershed is a coastal plain in northeastern Algeria.This study aims to determine the physicochemical quality of waters of the western WadiEl-Kebir and its main tributariesand also to evaluate the spatiotemporal variabilityof its physicochemical quality in particular of mineral nitrogen during wet and dry periods. Four sampling campaigns were realized as follows: January 2015 and February 2016 corresponding to water high season and in March and September 2016 corresponding to the low season. The water samples were obtained from the seven stations located along western Wadi El-Kebir. Temperature, pH,conductivity,dissolved oxygen,SO42-, PO43-, NO3-, NO2-and NH4+ were measured either in situ or in the laboratory.A statistical treatment employingthe PCA method (The Principal Components Analysis) was applied for all the obtained results. It has been noticed that the S2 and S3 upstream stations are very rich in ammonium (NH4+) at the low water period with average values of 15.22 mg/L and 20.41 mg/L, respectively.This study has shown the influence of seasonal variations and anthropogenic activities on the evolution of physicochemical settings, in general, and on mineral nitrogen in particular. In conclusion,the waters of Wadi El-Kebir were of an average to poor quality.

It has been observed that water in the reservoirs has a trend towards eutrophication even under natural environment, while human activity makes the situation worse. Studies on eutrophication are mainly focused on nutritive salt control. It is an effective method to remove the nutrient substance by using attached algae | however, due to experimental limitations, the theoretical results from the lab study are commonly inapplicable to the natural environment. In this paper, based on a case study on the Hada reservoir, we have built a hydrodynamic-quality model that represents the current state of the reservoir. With the help of the model, we can verify the development of eutrophication of the reservoir and simulate the spatial-temporal evolvement, using Cladophora, to deal with eutrophication within a shallow water reservoir.