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 distributionof phytoplankton derived from a one-year sampling programme (1961–62)on Lake Albert, a large African rift lake. There is evidence of regulationby both physical and nutrient factors. These are influenced by a markedseasonality of temperature/density stratification (temperature range <3°C) and of water input that induces some polarizationalong the axis of the lake. Prevailing concentrations of soluble reactivephosphorus are high (>100 µg l^-1), but those ofinorganic nitrogen are low and, with large depletions of silicate-silicon,may limit algal production. The diatom and cyanophyte components of thephytoplankton show different relationships to the seasonal cycle of limitedstratification and vertical mixing. There are possible relationships, bygrazing, to the described seasonal and spatial abundance of planktonicCladocera. Comparisons are made with other African lakes, especially LakeTurkana which is of similar shape and size and shows end to end polarizationof the aquatic biota.