Water quality of the Blue Nile at Khartoum, Sudan, before complete filling of the Grand Ethiopian Renaissance Dam

Abstract

Physico-chemical variables were monitored biweekly for the Blue Nile at Khartoum between July 2017–June 2019. The aim was to document the present status of water quality at Khartoum before complete filling of the Grand Ethiopian Renaissance Dam (GERD). Physico-chemical parameters within acceptable limits recommended by WHO for drinking water included pH (7.2–10.8), temperature (13.7–30.4 °C), conductivity (137–281 μS cm⁻¹), total dissolved solids (75–141 mg l⁻¹), total residue (5–3194 mg l⁻¹), alkalinity (93–176 mg CaCO₃ l⁻¹), dissolved oxygen (3.5–10.9 mg l⁻¹), nitrite–nitrogen (<detection limit (DL)−43 µg l⁻¹), ammonium–nitrogen (<DL−940 µg l⁻¹), nitrate– nitrogen (<DL−1468 µg l⁻¹), phosphate–phosphorus (<DL−63 µg l⁻¹), silica (4.0–23.6 mg l⁻¹), iron (<DL−250 µg l⁻¹) sodium (3.2–15.7 mg l⁻¹), potassium (0.7–5.6 mg l⁻¹), calcium (6.2–30.3 mg l⁻¹), and magnesium (1.5–11.5 mg l⁻¹). Total residue and pH were amongst the measured variables that were outside of the WHO recommendations. This study revealed that the Blue Nile remains generally unpolluted, and has not been significantly negatively affected by runoff from urbanisation or sewage contamination. This study presents further evidence that industrial wastes discharged upstream of Khartoum have not accumulated downstream as they are carried into the Main Nile by the annual floodwater pulses. The water is therefore currently suitable for drinking and all other uses. However, accumulation of pollutants in the Blue Nile may be problematic once filling of the GERD is complete as the discharge during flooding events necessary to flush the river will be reduced.