Abstract
Reghaia town, located in Algiers (North of Algeria), presents a strong anthropogenic activity. The aim of this study is to assess water quality in the Reghaia Lake basin by determining current status, temporal evolution and apportionment of pollution sources. Three samplings were carried out in fourteen stations covering the lake and its principal tributaries. Sixteen physico-chemical parameters and three microbiological parameters were analyzed. The Surface Water Quality Evaluation System (SW-QES) was used to visualize the temporal evolution of available data from 1978 to 2017. The water quality index (WQI) was used to assess the global water quality for irrigation purposes and its spatial variation across the basin. The Organization for Economic Co-Operation and Development (OECD) international classification and trophic state index (TSI) were used to evaluate the trophic category of the lake. The organic pollution index (OPI) and microbiological quality index (MQI) were used to establish pollution maps of the study area. The lake has presented excessive pollution since the 1970s. The BOD5/COD ratio (0.1) recorded in 2017 indicates a very low biodegradability of Reghaia Lake waters. The value of the Canadian Council of Ministers of the Environment-water quality index (CCME-WQI) (14.31) indicates poor water quality. The values of weighted arithmetic-water quality index (WA-WQI) are extremely high (>4000), which indicates unsuitable water quality for irrigation purposes. The hypertrophic nature of the Reghaia lake was identified (TSI > 80) and confirmed by the OECD classification. Spatial distribution of pollution indicators shows that the Reghaia River and ElBiar River are the most important pollution sources. Calculations of WA-WQI with and without Coliforms indicate that the Reghaia River is the most important microbial pollution source. A slight decrease in organic pollution and remarkable improvement in microbiological quality was observed at the outlet of the lake. According to these results, sewage discharged without treatment or with insufficient treatment is the main pollution source of the Reghaia Lake, which has been a receiving environment for many years, and will continue to be polluted if we do not react effectively by stopping the pollution sources.