The Bottom Fauna and Sediments in a Drying Phase of a Saline African Lake (L. Chilwa, Malawi)

Abstract

A study of the bottom fauna and sediments of Lake Chilwa, Malawi, was carried out in late 1967 when the lake appeared to be drying out. The mud fauna at low lake level was poor, while skeletal remains suggested a more diverse and richer fauna, including a large mollusc community, when the level was higher earlier in the year. Sediments were characterised by high values for pH, conductivity, CaCO3 and exchangeable Na +. As the soils had been inundated at some stage, the results of analyses indicated the changes undergone by muds on exposure, namely loss of organic matter, phosphorus and exchangeable Na +. The physical nature of the substrate at low lake level rather than increased salinity is thought to have been largely responsible for the low benthic values. Potential problems of faunal re-colonisation are considered.