Assessment of surface water quality in a semi-arid Mediterranean region. Case study of Sikkak dam (north-western Algeria)

Abstract

As far as industry, agriculture, urbanization, lithology and climate are concerned, surface-water vulnerability to pollution has not ceased to amplify especially in semi-arid to arid areas. In the countries of the southern shore of the Mediterranean and most particularly in Algeria, surface-water quality is highly impacted by anthropogenic activities and climate change. It thus requires a complete diagnosis of the evolution of these impacts through a survey. The present study aims at characterizing and assessing the temporal evolution of surface-water quality in Sikkak wadi watershed (north-western Algeria), particularly at the Sikkak dam. The methodology that was applied to assess and interpret monthly surface-water quality results gathered throughout an 11-year period of time survey (2005 2015) included the following: a quality-grading method, a trend-following approach, a seasonal analysis as well as a principal components analysis (PCA). The results analyzed according to the classification of the Algerian National Agency for Water Resources (ANRH) revealed that the Sikkak dam water is characterized by a natural mineralization that is good (61.37%) to medium (38.63%) taking into account electrical conductivity (EC), chloride, sodium, calcium, magnesium and sulfate contents. However, it is found to be highly contaminated by organic pollution ranging from bad grade (46.37%) to fairly medium quality (34.98%). COD, BOD, nitrate, nitrite, ammonium and orthophosphate were used as the evaluation parameters. In general and taking into account all the parameters of pollution, the ‘medium’ and ‘good’ classes dominate the quality of the surface water of the Sikkak dam with a percentage of 40.37% and 37.28% successively, followed by the ‘poor’ (20.72%) and ‘very poor’ (1.63%) classes. The trend-following method shows that the surveyed waters moderately tend towards more alkaline and exhibit increasing COD and chloride. Further, the waters show a decreasing EC, BOD5, organic matter, nitrogen and phosphate as well as most of the salinizing and carbonating compounds. This is mainly due to the contribution of wastewater treatment plant in improving the water quality. The PCA confirmed that the different forms of pollution (domestic, industrial, agricultural) and salinization (for 56.77%) are the main factors for the degradation of the quality of the dam water.