Surface water pollution risk assessment of wadis, Mekerra and Saïda, in the North-Western of Algeria

Considered as the main stream of hydrographic network of Mactaa’s basin, in the west highlands of Algeria, both wadis, Mekerra and Saïda, are affected by pollution which is generated by anthropogenic activities. Makara and Saïda wadis cross the urban areas of Sidi-Bel-Abbes and Saïda respectively, in the west of Algeria, which constitute a real problem of human safety. In order to identify the pollution state on these wadis, samples have been collected during three periods of time (June 2011, July 2012 and April 2013) in the goal to characterize the physico-chemical and bacteriological quality of surface water.Results obtained describe clearly the existence of chemical and organic pollution in both wadis at high levels of calcium, magnesium, chlorides, nitrates, nitrites, phosphate, DBO5 and dissolved oxygen. The evaluation of organic pollution index (OPI) confirmed that there is a high organic pollution, upstream, which increases with high water passage towards urban areas of both cities (OPI).The bacteriological analysis results obtained show presence of high contents of faecal bacteria contamination (total coliforms (TC), faecal coliforms (TC) and faecal streptococci(FS))principally in wadi Saïda. The relationship between FC/FS justifies the predominance of human origin than of animal as source of contamination. While, the determination of microbiological quality index (MQI), for each wadi, confirms degradation of microbiological quality by the faecal pollution, mainly in Saïda urban area