Diatom associations and succession in Lake Kariba, South Central Africa

Abstract

Diatom Associations formed by 1% or more of species, found by the Thomasson analysis method are discussed in relation to the morphology and limnology of the four basins of Lake Kariba. A brief comparison is made with associations in two stretches of the Zambesi river. A dominant association formed by certain species of Melosira demonstrated a pattern of succession, in relation to the thermal cycle in the lower, middle and upper lake by variations of the percentage occurrence of species forming it: Melosira granulata dominated during homothermy and remained so throughout stratification in the lacustrine conditions at the barrier or wall; M. granulata v. angustissima dominated during overturn and became the dominant species in the riverine conditions of the two uppermost basins. Results from the Central basin illustrated the intermediate position of this area of the lake. The pattern was disrupted in the far N.E sub-basin of the Sanyati basin, which in general showed individuality and where accidental and ambivalent plankters became co-dominant with the Melosira association during homothermy.

A second association, formed by species of Cyclotella, Fragilaria and Synedra was a regular feature of the diatom population, it was sub-dominant to the melosira association at the barrier but gradually decreased up-lake and was superseded by accidental and ambivalent planktonic species. Except for the N/E Sanyati sub-basin, the diatom associations showed a gradual change from upper to lower lake, thus basin individuality was not seen.