Water chemistry and quality of the Blue Nile at Khartoum

Abstract

Measurements of physical and chemical variables were made fortnightly on the Blue Nile
near Khartoum, from May 2000 to February 2002. The variables analysed were: temperature,
pH, and concentrations of total residue, dissolved oxygen, alkalinity, phosphate-phosphorus,
nitrate-nitrogen, silica-silicon, calcium, magnesium, sodium, potassium, and oxidizable
organic matter. The seasonal variations of these factors in the Blue Nile are compared, and
the interrelationships existing between some of them are discussed. Comparisons are made
with earlier studies carried out on the same site in the Blue Nile and with some tropical
rivers. In the Blue Nile, the amounts of suspended matter and nutrients are largely dependent
upon the flood regime. Nitrate, phosphate, silicate, oxidizable organic matter and total
residue increase considerably in the Blue Nile when the river is in flood. Silicate-silicon as
silica was reduced at certain times of the year, yet the relatively high concentrations, which
were maintained throughout the year, were not expected to limit the growth of diatoms.
Drops in silicon concentrations, unlike those in nitrate and phosphate, were always followed
by a rapid restoration of a higher level. Compared with pre 1970 data, the Blue Nile at
Khartoum did not show any sign of unwelcome enrichment. The river at Khartoum is far
from being polluted by heavy metals; no cadmium, lead, or nickel was detected in the surface
waters