SPATIAL AND SEASONAL DISTRIBUTION OF PHYTOPLANKTON IN AN AFRICAN RIFT-VALLEY LAKE (L. ALBERT, UGANDA, ZAIRE)

An account is given of the seasonal succession and spatial distributio n of phytoplankton derived from a one-year sampling programme (1961-62 ) on Lake Albert, a large African rift lake. There is evidence of regu lation by both physical and nutrient factors. These are influenced by a marked seasonality of temperature/density stratification (temperatur e range <3 degrees C) and of water input that induces some polarizatio n along the axis of the lake. Prevailing concentrations of soluble rea ctive phosphorus are high (>100 mu g l(-1)), but those of inorganic ni trogen are low and, with large depletions of silicate-silicon, may lim it algal production. The diatom and cyanophyte components of the phyto plankton show different relationships to the seasonal cycle of limited stratification and vertical mixing. There are possible relationships, by grazing, to the described seasonal and spatial abundance of plankt onic Cladocera. Comparisons are made with other African lakes, especia lly Lake Turkana which is of similar shape and size and shows end to e nd polarization of the aquatic biota.