Inventory and classification of open-water tarns and large rock pools in the uKhahlamba-Drakensberg National Park of South Africa

The Maloti-Drakensberg World Heritage Site spanning the mountainous border between South Africa and Lesotho is home to numerous small, natural open water bodies known locally as “tarns,” which occur from the foothills at around 1300 m up to at least 3000 m in altitude. These range from small rock pools lying directly on bedrock to large grassy pans exceeding 200 m in diameter, with many intermediate types and morphologies. The few studies to date on these water bodies have revealed endemic flora and fauna, including aquatic macrophytes, branchiopod crustaceans and other macroinvertebrates. The hydrogeomorphology of these systems and their diversity in terms of persistence and hydroperiod is very poorly understood. Using Google Earth imagery, 358 seasonal water bodies were identified within the uKhahlamba-Drakensberg National Park of South Africa and classified according to landscape position, habitat type, maximum extent of inundation and surface hydrology. Persistent open water bodies are extremely scarce in the Northern Drakensberg, widely dispersed in the Central Drakensberg and most common in the Southern Drakensberg where they are concentrated in two major clusters. They are most common in the 1900–2200 m altitude range in shelf landscape positions on Elliot Formation geology. The great majority are conventional “tarns”: < 30 m in extent, seasonal, littoral systems (<2 m deep) and endorheic. This classification provides a starting point for application of the International Union for Conservation of Nature (IUCN) Red List for Ecosystems approach to previously under-represented and poorly studied open-water ecosystems in the Afromontane regions of southern Africa and elsewhere.