Analysis of the drought effects on the physicochemical and bacteriological quality of the Inaouene River water (Taza, Morocco)

Abstract

The Inaouene basin's waters are deeply affected by pollution, which undermines their quality. Indeed, due to the increasing population and industrial development of Taza city, the Inaouene River and its tributaries Larbaa and Lahdar are currently at risk of large quantities of urban discharge, exacerbated by successive drought periods. The objective of this study was to determine the pollution levels and assess the impact of drought on the water quality of the Inaouene River, based on physicochemical, and bacteriological analyses at seven stations over two hydrological cycles (June 2020 to May 2022). The results of physicochemical analyses during the first hydrological cycle revealed averages of 15.93 °C for Temperature, 1434.43 µS cm^-1 for electrical conductivity (EC), 0.93 and 0.63 mg L^-1 respectively for total phosphorus (TP) and orthophosphate (PO₄^3-), 9 mg L^-1 for NTK, 134.23 and 278.43 mg L^-1 for BOD₅ and COD respectively, 3.99 mg L^-1 for Dissolved oxygen (DO) and 203.59 mg L^-1 for sulfate (SO₄^2-). For water bacteriological quality, the total coliforms (TC), Escherichia coli (E. coli), and intestinal enterococcus (IE) have shown averages of 3.45, 2.96, and 2.73 Log₁₀ MPN per 100 ml respectively. During the second hydrological cycle, marked by low rainfall, a pronounced degradation in water quality has been observed, affecting all parameters. Notably, water quality went from average to poor or very poor according to the Moroccan surface water quality standards (MSWQS) and from very poor to unsuitable for consumption for the Water Quality Index (WQI) during the drought period. This study confirmed the exacerbation of deterioration in the water quality of the Inaouene River during the drought period, notably evidenced by heightened concentrations of organic matter (increases of 41.53 % and 37.08 % for BOD₅ and COD, respectively), fecal contaminants (elevations of 11.48 %, 10.18 %, and 14.7 % for IE, TC, and E. coli, respectively), nutrients (increases of 38.83 % for TP, 48.67 % for PO₄^3-, and 35.82 % for NTK), and mineral content (augmentations of 28.89 % for EC, and 31.73 % for sulfate). Additionally, this degradation in quality is reflected in the elevation of water temperature and the reduction in oxygenation (of 9.39 % for Temperature, and 46,26 % for DO).