THE GEOMORPHOLOGY AND SOILS OF A DAMBO IN CENTRAL UGANDA

Dambos—seasonally saturated, channelless valley floors—serve as important hydrologic, fertility and carbon reservoirs throughout East and Southern Africa. Our objective in this study was to characterize the soils and saprolite material of a dambo and relate these findings to the morphology of the associated 2nd-order catchment and valley floor. We examined two cross-dambo transects in detail by augering soil profiles at regular intervals, describing soil morphology and taking samples at 10-cm depth increments for particle-size analysis, soil organic carbon (SOC), and mineralogy. Additional profiles were also described and sampled for a number of transects and spatially distributed locations (65 profiles total). For a subset of samples, we determined effective cation exchange capacity (ECEC), pH, extractable bases, acidity, and P. All samples collected were scanned with a high-resolution visible and near-infrared (VNIR) spectroradiometer, and calibration models were constructed to estimate soil properties for uncharacterized samples. Using a high-resolution Digital Elevation Model (DEM) and the soil data described, we constructed a map of dambo soil properties. The spatial patterns observed were generally consistent with qualitative descriptions of dambo margins, floors and bottoms in previous studies. Relatively unweathered saprolite at the upper transect suggests recent downcutting and incision. Sharp lithological discontinuities found in a number of soil profiles indicate that dambos in central Uganda have been shaped by variable climatic-hydrologic regimes.