Water flow pathways and the water balance within a headwater catchment containing a dambo: inferences drawn from hydrochemical investigations

Dambos, seasonally saturated wetlands, are widespread in headwater catchmen ts in sub-Saharan Africa. It is widely believed that they play an important role in regional hydrology but, despite research conducted over the last 2 5 years, their hydrological functions remain poorly understood. To improve conceptualisation of hydrological flow paths and investigate the water bala nce of a small Zimbabwean catchment containing a single dambo, measurements of alkalinity and chloride in different water types within the catchment h ave been used as chemical markers. The temporal variation in alkalinity is consistent with the premise that all stream water, including the prolonged dry season recession, is derived predominantly from shallow sources. The pr oposition that dry season recession flows are maintained by water travellin g at depth within the underlying saprolite is not substantiated. There is e vidence that a low permeability clay lens, commonly present in many dambos, acts as a barrier for vertical water exchange. However, the highly heterog eneous chemical composition of different waters precludes quantitative hydr ograph splitting using end member mixing analysis. Calculation of the chlor ide mass-balance confirms that, after rainfall, evaporation is the largest component of the catchment water budget. The study provides improved unders tanding of the hydrological functioning of dambos. Such understanding is es sential for the development and implementation of sustainable management st rategies for this landform.