Assessment of the Influence of Agriculture and Domestic Waste on Surface Water Quality A case study of Senegal River (Rosso, Mauritania)

Abstract

The physicochemical and bacteriological characteristics of the Senegal River in the Rosso region were meticulously examined across various sampling stations (Back, Djourbel, Iset, and M’Pourier) and were assessed for a total of twenty-three physicochemical and three biological parameters. These parameters encompassed Bicarbonate (HCO3-), Temperature, Turbidity, Potential of Hydrogen (pH), Electrical Conductivity (EC), Alkalinity (CaCO3), Chemical Oxygen Demand (COD), Barium (Ba), Total Suspended Solids (TSS), Total Dissolved Solids (TDS), Iron (Fe), Chromium (Cr), Copper (Cu), Potassium (K+), Manganese (Mn2+), Nitrate (NO3-), Nitrite (NO2-), Ammonia (NH4+), Phosphate (PO43-), Sodium (Na+), Sulfate (SO42-), and Zinc (Zn). The Water Quality Index (WQI), a methodological technique used to assess the effect of household and agricultural waste on the surface water quality of the Senegal River in Rosso, Mauritania, was calculated using the biological parameters, which included Escherichia coli, Total Coliforms, and Enterococcus. The findings showed that the pH level at the Djourbel Station was below the World Health Organization's (WHO) cutoff point. Additionally, all monitoring sites (Back, Djourbel, Iset, and M'Pourier) had turbidity and Chemical Oxygen Demand (COD) levels beyond allowable limits, suggesting a substantial organic load and possible human pollution. Concentrations of copper (Cu) were observed to exceed WHO recommendations at the Back and Djourbel stations, while elevated concentrations of barium (Ba) and chromium (Cr) raised concerns at the Iset and M’Pourier stations. Significantly, the M'Pourier Station had a more noticeable pollution profile, with higher concentrations of potassium (K⁺), ammonium (NH₄⁺), nitrites (NO₂⁻), bicarbonates (HCO₃⁻), electrical conductivity (EC), and total dissolved solids (TDS). Suggesting a variety of contaminant sources likely associated with domestic and agricultural runoff. Bacteriological evaluations indicated widespread contamination by Escherichia coli, Enterococcus, and total coliforms across all monitoring stations, signifying considerable fecal pollution and presenting a significant health risk. The Water Quality Index (WQI) further substantiated these findings. When the analysis included bacteriological parameters, WQI values surged to alarming levels, particularly at the Back (2660.5) and M’Pourier (2572.1) stations, indicating the water's unsuitability for any application. Even in the absence of microbiological assessments, WQI indices xii remained elevated, particularly at the Back (184.21) and Iset (108.31) stations, signifying substantial chemical contamination