Ecohydrological analysis of a South African through-flow mire: Vankervelsvlei revisited

Abstract

The Vankervelsvlei mire has one of the thickest peat deposits (more than 10 m) in South Africa, which started accumulating before 7000 BP. Two previous studies on the hydrological system that sustains the wetland reached inconsistent conclusions and disagreed strongly on the main sources of water feeding the wetland. One suggested that the wetland is fed by groundwater discharging from the underlying Table Mountain Group Aquifer, while the other proposed that the wetland is a perched system fed only by precipitation water. We tried to reconcile these discrepancies by measuring water table, hydraulic pressure and temperature in the peat profile and analysing the ionic composition of the groundwater. We also carried out radiocarbon dating (14C) of groundwater and surface water. Our results showed that both groundwater and surface water are relatively young (<50 years) and that Vankervelsvlei is hydrologically a through-flow system with (local) mineral-poor groundwater entering the mire, possibly from a catchment located in the dunes that lie to the south-east. The groundwater exits the mire at the opposite (northern) side. Our findings do not support either the hypothesis that the mire is fed by groundwater from a deep regional aquifer, or the notion that it is sustained exclusively by precipitation water.