Pollutant load discharge from a Southwestern Mediterranean river (Mazafran River, Algeria) and its impact on the coastal environment

This work aimed to assess the water quality of Mazafran River, the most important wadi in Bou-Ismail Bay, and to study the impact of its pollutant discharges into the adjacent coastal waters. To this end, a sampling campaign (August 2016) was conducted at various locations in the lower Mazafran River and the adjacent coastal waters. Collected river water samples were analysed for different pollutants and water quality parameters (chemical oxygen demand COD, biochemical oxygen demand BOD5, total Kjeldahl nitrogen TKN, total phosphorus TP, chlorophyll Chl a and dissolved oxygen DO). The coastal receiving waters were monitored for nutrients (NO3, NO2, PO4, SiO2) and nutrient stoichiometry (N/P/Si), suspended particulate matter (SPM) and Chl a. Based on these results, the extent of the pollution plume was assessed. Principal component analysis (PCA) was performed using the field data to evaluate the influence of the studied parameters on the sampling station characteristics. Mazafran surface water monitoring indicates poor water quality conditions for all sampling stations, primarily because of upstream wastewater discharges. The upstream station received the highest biodegradable organic load (COD/BOD5 ratio of 1.23) and TP level (9.7 mg/l). The midstream and downstream stations were characterised by an increase in COD/BOD5 ratio (1.59 and 2.36, respectively) and high concentrations of TKN (85 and 54 mg/l, respectively), probably resulting from the inputs of nearby industrial effluents and nutrients runoffs. The pollutant load carried by the Mazafran River entering the coastal waters contributed to an extra enrichment of nutrients, an imbalance in N/P/Si ratio leading to a case of Si limitation, an increase of SPM concentrations and a shift in chlorophyll content. The dynamic of the pollution plume was mainly limited by the low flow discharge of the river and current circulation, which resulted in a decreasing gradient from the mouth to the open sea and from east to west. Overall, our results highlighted the heavy pollution of the Mazafran River and its negative impact on the coastal water characteristics of the surrounding area