Ecological Research on South African rivers - a preliminary synthesis

Abstract

Ecological research on South African rivers has progressed in a number of phases. Until 1950 work was mainly taxonomic and descriptive, an essential prerequisite for more detailed studies. The realisation that South African rivers, a vital national resource, were deteriorating in the face of overexploitation, led to a coordinated research programme by the NIWR in the 1950's and 1960s, which included in-depth studies on representative rivers such as the Great Berg, the Tugela, the Jukskei/Crocodile and the Vaal. Major advances resulted from this programme, including the description of physical zonation along rivers, and the associated changes in the biotic community; the identification of the main factors limiting species distributions in rivers, such as temperature, silt, food availability and flow rate. Comparisons with conditions in temperate Northern Hemisphere Rivers indicated that South African Rivers are prone to more violent events such as flooding and drying out, that most are geologically young, and therefore steeper, faster flowing, and with poorly developed floodplains. Considerable effort was devoted to understanding the consequences and effects of pollution in rivers, particularly through changes in the invertebrate fauna. In the last thirty years a large number of South African rivers have been impounded to improve their water storage and supply capacity, and since the river research programme of the 1950's and 1960's there has been a corresponding switch to research on the lentic water bodies created by these dams. As a result, research on flowing water ecology has largely been confined to the enthusiasm and efforts of a few individual workers. A number of new conceptual ideas have been developed in other parts of the world, notably in the USA, and South African researchers have yet to have the opportunity of testing and using these ideas for the understanding and maintenance of river systems here. This report reviews the literature on South African river ecology, summarizes the level of knowledge available at present, and suggests research directions and specific projects which will contribute most to our ability to maintain the essential functions of our rivers in the future