Adaptations of salt marsh to semi-arid environments and management implications for the Orange River mouth

Abstract

The desertified floodplain of the Orange River Mouth (ORM) is characterised by large areas completely devoid of vegetation. Although barren areas are a natural feature of salt marshes on the west coast of southern Africa, more than 70 ha of salt marsh have been lost through bad management practices. Salt marsh plants have adapted to the low rainfall, high evaporative demand and hypersaline topsoil by accessing the uppermost layer of groundwater (i.e. that below the water table), which can be saline rather than hypersaline. This study demonstrated that although the water table was shallow enough to be accessible to the dominant salt marsh species, Sarcocornia pillansii, it was too saline and had too low a water potential to be of use to the plant. The hypersaline groundwater in turn controls the edaphic salinity and this effect—combined with the low rainfall and a lack of backflooding—prevents seedling recruitment. Rehabilitation of the desertified marsh can succeed only if the groundwater salinity is reduced. Then the establishment of favourable physico-chemical conditions is expected to result in the natural recolonisation of the bare areas by S. pillansii.