THE MAJOR ION CHEMISTRY OF SOME SOUTHERN AFRICAN SALINE SYSTEMS

Africa south of about 23-degrees-S has few natural athalassic lakes, s aline or freshwater. South Africa, however, is rich in temporary pans, many of which are saline, while permanent saline springs occur along the coastal strip of the Namib Desert in Namibia. This paper examines the chemistry of the major ions in 67 Namibian waters, 47 of which hav e not previously been reported in the literature, and compares them wi th 66 South African waters, five of which have not previously been rep orted, and with saline lakes in East Africa. The highest value for tot al dissolved solids in South African waters was 276 g l-1 (Koekiespan, south-western Cape) and the highest for Namibian waters were 160 g l- 1 (Hosabes, a small spring on a gypsous crust) and 302 g l-1 (a salt p an at Oranjemund at the mouth of the Orange River). The dominant ions in fresh waters in the region are Ca2+ and HCO3-/CO32- in the interior and in Namibia, and Na2+ and Cl+ on the south and east coasts. Regard less of the geochemistry of their substrata, the dominant ions in the saline waters throughout the region are Na+ and Cl-. Thus differential precipitation of CaCO3 and CaSO4, as a result of evaporative concentr ation at high salinities, appears to be the determinant of the proport ions of the major ions in these systems. The permanent springs on gyps ous crusts along the coast of Namibia, although dominated by Na+ and C l- ions, contain considerable quantities of both Ca2+ and SO42- ions.