The major ion chemistry of some southern African saline systems

Abstract

Africa south of about 23° S has few natural athalassic lakes, saline 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 have not previously been reported in the literature, and compares them with 66 South African waters, five of which have not previously been reported, and with saline lakes in East Africa.

The highest value for total 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 pan at Oranjemund at the mouth of the Orange River). The dominant ions in fresh waters in the region are Ca²⁺ and HCO ⁻_inf3 /CO ²⁻_inf3 in the interior and in Namibia, and Na²⁺ and Cl⁺ on the south and east coasts. Regardless 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 concentration at high salinities, appears to be the determinant of the proportions of the major ions in these systems.

The permanent springs on gypsous crusts along the coast of Namibia, although dominated by Na⁺ and Cl⁻ ions, contain considerable quantities of both Ca²⁺ and SO ²⁻₄ ions.