Paleoenvironmental reconstruction of Paleolake Mababe, northwestern Botswana from sediment chemistry and biological productivity data

Abstract

Sediment samples were collected from trenches excavated in the Mababe Depression, northwestern Botswana. At present the Mababe Depression is dry Acacia parkland, but has sustained relatively large paleolakes. Sediment samples were used to determine the paleo-chemistry and paleo-productivity in Paleo-lake Mababe by determining concentrations of: soluble major cations (K, Na, Ca, Mg) and anions (Cl, SO4, NO3, HCO3), P, biogenic silica, inorganic carbon, and organic carbon. The major cations and anions provide information about past lake salinity, while P concentrations provide information about sediment erosion in source watersheds. Additionally, P is a nutrient that drives lacustrine biological productivity. Biological productivity was evaluated from variations in biogenic silica, organic carbon concentrations, carbon to nitrogen ratios and the stable isotope ratio of organic carbon.