Physico-chemical quality of the Medjerda River in Tunisia and suitability for irrigation during the moist and the dry seasons

Surface waters are usually exposed to industrial, urban, and agricultural wastes. This study assessed the water and the sediments quality of the important primary watercourse in Tunisia and the principal source of domestic and irrigation purposes, the Medjerda River. Water samples were analyzed for total suspended solids, calcium, magnesium, total hardness, carbonates, bicarbonates, residual sodium hazard, and magnesium hazard. They were collected from five sampling sites along the Medjerda watercourse from upstream to downstream through two campaigns, one at the end of the moist period and the other at the half of the dry one in line with irrigation. The presence of high concentrations of (i) magnesium, which varied from 25.51 to 61.65 mg l^-1 for the moist period and from 27.58 to 133.10 mg l^-1 for the dry one; (ii) carbonates that varied from 18.0 mg l^-1 for the two campaigns to respectively 49.8 and 66.0 mg l^-1 for the humid and the dry periods and (iii) total hardness that varied from 646.5 to 1043.0 mg l^-1 for the moist period and from 503.0 to 741.0 mg l^-1 for the dry one could in the future pose threats and toxicity to soil and plants when the water will be continuously used for irrigation. Sediments samples were also collected, and their contamination by heavy metals was assessed through two indicators: contamination factor (CF) and pollution load index. Results depicted severe metal contamination mainly from cadmium, of which CF varied from 3.33 to 22.66. Protection of Medjerda River and its tributaries is compulsory to prevent the apparent deterioration of its water quality.