Effects of sewage disposal into the White Nile on the plankton community

Abstract

wenty water samples and 30 plankton samples were taken from the sewage disposal site (El Lamab, south of Khartoum), from 250 m upstream and 250 m downstream during January–March, 1987 and Februar–April, 1988. The water samples were examined for physical and chemical characteristics. Plankton samples were examined for species composition and relative abundance of phytoplankton and zooplankton. At the disposal site, the sewage effluent increased conductivity, nutrients and suspended solids, elevated BOD, and depleted oxygen. The pattern of abundance in the phytoplankton was almost reversed, due to the disappearance of many diatoms, replaced by blue-green algae, and the appearance of Euglenophyceae, found only at the disposal site. Copepods dominated over cladocerans, which are usually dominant under natural conditions. Rotifers, normally less abundant, also flourished at the disposal site. However, these effects were localized: physical, chemical and biological conditions returned to normal 250 m downstream.