Landscape sensitivity and ecological change in western Zambia: The long-term perspective from dambo cut-and-fill sediments

A series of small, shallow seasonally, or interannually, waterlogged depressions (dambos) in the upper Zambezi Valley in western Zambia hold shallow peat deposits and are bounded on their western margin by sandy lunette dunes. Using luminescence dating of sands, fossil pollen analyses and the macrocharcoal record from cored peat, the long-term stability of these landforms and the vegetation they now support is investigated at a site east of the upper Zambezi. Although the upper lunette dune sediments accumulated between 14 +/- 2 and 6 +/- 1 ka, the onset of peat accumulation and preservation within the dambo did not occur until 2800cal a BP, suggesting that only from this point onwards were conditions stable and wet enough year-round to allow the formation and preservation of peat during this time. Results from this study indicate that the long-term behaviour of the dambo conforms to a cut-and-fill dynamic, where under more arid conditions the dambo becomes a dry pan, providing a sediment source for the adjacent lunette dune. In contrast, during wetter times, when the dambo holds surface water year-round, it becomes an organic-rich sediment repository preserving a fossil pollen record of long-term vegetation change.