WATER TRANSPARENCY CHARACTERISTICS OF SOUTH AFRICAN IMPOUNDMENTS

Abstract

Some water transparency characteristics (Secchi disc transparency, mean diffuse light attenuation coefficient and turbidity) of a number of South African impoundments are compared. In general most impoundments may be considered to be highly turbid; for 92 impoundments considered in this paper the modal mean Secchi disc transparency was in the class 0 to 0,5 m. The geographical distribution of water transparency within South Africa shows good agreement with the geographical distribution of sediment production, indicating that suspended inorganic material is the dominant factor governing water transparency in most impoundments. There is evidence that eutrophication and mineralization are processes which lead to increased water transparency. High turbidity and its role in influencing the limnology and management of impoundments is discussed. More in-depth investigations are needed to evaluate the contributions by coloured substances, suspended silt and phytoplankton to light attenuation within individual impoundments.