The assessment of diffuse pollution from acid-mine drainage using an updated and revised diatom assessment procedure as an added-value bio-monitoring tool.

Three data sources (physico-chemistry, bio-monitoring and eco-toxicology) are currently used in South Africa to establish environmental water quality conditions. Environmental water quality in turn is key information required for the "ecological reserve determination" of river reaches. Bio-monitoring in South Africa has been limited in recent times mostly to the use of the SASS procedure which relies on invertebrates only. This paper describes the re-introduction of a diatom-based water quality assessment as an added-value bio-monitoring tool. A specific example is discussed citing the response of diatom assemblages to diffuse pollution from acid mine drainage and how effective diatoms are as indicators of ecological integrity and river recovery measured downstream of the area of impact. The advantages of applying this bio-monitoring technique over other biological measures are presented in the context of technological advances in rapid image processing, species identification and software applications of diatom-based water quality indices. The valuable records of the diatom assemblages of the past, held in the South African Diatom Collection at the CSIR (KwaZulu-Natal), can now be accessed and interpreted as historical environmental water quality reference points for several rivers in South Africa.