Riverine biodiversity conservation in South Africa: current situation and future prospects

South Africa is richly endowed with an array of natural resources, with one exception } water. In South African water law, a river system and its associated riverine biodiversity } i.e. the entire aquatic ecosystem } is regarded as the ‘water resource’ that provides ecosystem goods and services to society (Van Wyk et al., 2006). An appreciation of riverine biodiversity in South African rivers therefore requires an understanding of the characteristics of the country’s water resources, their variability in time and space and the factors that influence their use by society. South Africa’s climate is characterized by an uneven, poorly predictable and highly seasonal distribution of rainfall, while potential evapotranspiration rates exceed rainfall over the entire country (Tyson, 1987). Droughts are common and, ironically, they are often followed by equally devastating floods. South Africa has few natural lakes and the country’s river network has flows that are highly variable between seasons and between years (Smakhtin, 2001; Hughes and Hannart, 2003). Rivers located in the wetter regions of the country tend to be perennial while those in the drier regions are characterized by more periodic (seasonal) and episodic (ephemeral) flows (Midgley et al., 1994). River systems are the primary source of water for agricultural, domestic and industrial uses and supply more than 85% of all the water that is used in South Africa, with groundwater systems providing the remainder. Large numbers of water supply reservoirs, farm dams, canals and inter-basin transfer schemes have been constructed to increase the reliability of water supplies for urban and rural users. The total capacity of South Africa’s water storage reservoirs (dams) is equivalent to 67% of the total annual runoff in all rivers (DWAF, 1996a), and most river systems have been impounded at several points along their length, thereby altering their flow regimes ‘beyond recognition’ (Davies et al., 1993; Davies and Wishart, 2000). Five of South Africa’s most important catchments and their rivers (Orange, Limpopo, Incomati, Maputo and Thukela) are shared with neighbouring countries, further complicating the problem of sustainable water resource management (Ashton and Turton, in press).