Airborne dust deposition in the Okavango Delta, Botswana, and its impact on landforms

Abstract

AbstractThis study investigated the local‐scale generation and movement of dust in the seasonal swamps of the Okavango Delta, Botswana, with a view to examining possible transfer of material between flood plains and islands. It was found that most of the dust load was carried in the lowest 3 m of the air column, and consisted mainly of amorphous silica, indicating that dust was generated largely on the flood plains. Dust loads were found to be highest above the flood plains and lowest over the interiors of islands, probably due to the baffling effect of the island trees on wind velocity. The contrast in dust loads between islands and flood plains suggests that there is a net transfer of dust from flood plains to islands, but it was not possible to quantify this transfer. It is evident, however, that flood plains experience net erosion and islands net aggradation. A strong seasonality in dust loads was observed, with the maximum dust loads coinciding with maximum wind velocity in October. This also coincides with peak seasonal flooding in the delta, and only non‐inundated flood plains are capable of generating dust. Years of low flood therefore appear to be more dusty. There may also be transfer of material from higher‐lying to lower‐lying flood plains, which may reduce the topographic contrast on the flood plains. Copyright © 2004 John Wiley & Sons, Ltd.