Hypersaline, alkaline (>pH 9) lakes constitute a special class of extremely saline lakes in closed basins. The major ions are typically Na+, Cl-, HCO 3 - and CO 3 2- . Sulfate is proportionately low. The high concentrations of HCO 3 - and CO 3 2- are largely responsible for buffering these lakes at such high pH. From both biological and geochemical viewpoints, hypersaline, alkaline lakes of the African Rift Valley are the best known. Unfortunately, much of the literature describing in situ biological activity in those lakes and their sediments concerns the less saline lakes of the region (Tailing et al., 1973; Hammer, 1981; Melack, 1981). However, the reports of the activity and isolation of bacteria involved in the reductive part of the sulfur cycle in the more extremely hypersaline, alkaline lakes of Africa may support the theory that these microorganisms can play a major role in the development of alkaline conditions in such closed basins.
