The Phytoplankton and Water Quality of Sennar and Roseires Reservoirs, Sudan

Abstract

The aim of the study was to evaluate the effect of heightening of Roseires Dam on the phytoplankton and physico-chemical characteristics of Sennar reservoir (13°32' 55" and 13°24'59" N and 33°38'05" and 33°39'53" E) and Roseires reservoir (11°48' 26" and 11°32'45" N and 34°26'46" and 34°28'33"E) on the Blue Nile, Sudan. The heightening project that was completed in 2013 increased the storage capacity of Roseires reservoir from 3.0×10 9 m 3 to 7.4×10 9 m 3 . The study provides baseline data before the completion of the Grand Ethiopian Renaissance Dam (GERD) on the Blue Nile. No studies on the phytoplankton of Sennar or Roseires reservoir have been undertaken since late 1960s because of accumulating deficit of trained research personnel and the very low level of scientific research funding. Present water analyses include Secchi transparency, electrical conductivity, pH, alkalinity, nitrate–nitrogen, phosphate–phosphorus, calcium, potassium, sodium, cadmium, cobalt, chromium, copper, iron, lead, magnesium, manganese, and zinc. Statistical analysis shows that there were no significant differences between the samples taken from Sennar and Roseires reservoirs. The quality of the water of the two reservoirs has not changed since 1960s, still being within allowable limits set by the Sudanese Standards and Metrology Organization and WHO for drinking. Strikingly, algal biomass remained extremely low in the two reservoirs during the present study. Visual observations and analysis of water samples collected from the two reservoirs and from the Blue Nile at Khartoum showed that the recurrent peaks reported by previous workers did not appear, while turbidity and concentrations of nutrients remained unexpectedly high with no signs of any algal growth during December 2015 December 2017. Environmentalists are alarmed that pollution in the Blue Nile within Sudan will become a problem after the completion of GERD when regulation of water flow downstream will result in only a fraction of the Blue Nile water reaches Sudan throughout the year allowing for the accumulation of pollutants.