Seasonal plankton development in the White and Blue Nile near Khartoum

Summary

Little is known about the biology of the Nile system, of which over 4000 km lie within the Sudan. As part of a long term programme of investigation, now in progress, the plankton of the two main rivers, the White and Blue Nile was examined from 1951 to 1953 at Khartoum shortly before their junction. The regular annual fluctuations of plankton density in both rivers do not coincide completely, but show dependance upon their specific hydrological regimes, which are briefly summarised. The dams erected on both rivers upstream of Khartoum store up water and create favourable conditions for the development of a pure plankton formation. Free flow and flood conditions coincide with a decrease of plankton while storage and low river levels on the whole favour an increase, or at least the persistance of pure plankton.