Towards the successful application of diatom-based biomonitoring in South Africa

Abstract

Water is a scarce and precious resource in South Africa. Not only is the quality and quantity of water available limited by climatic conditions but these resources are often impacted by domestic and industrial effluents, as well as run-off from agriculture. Monitoring the aquatic environment helps to determine the impact of various pollutants. Chemical monitoring, important as it is, can only at best give a "snapshot" of water quality at a particular moment in time. Biomonitoring in particular forms a vital part of monitoring programmes as it gives a time integrated reflection of a particular pollutant or group of pollutants on the ecosystem. Although diatoms have long been studied in South Africa, as well as being used in the past to indicate water quality, the current suite of bioindicator organisms used in this country has not until recently included diatoms, or any autotrophic organisms for that matter. This body of work is presented with the aim of facilitating the use of diatoms as bioindicators of water quality in South Africa. Methods for the collection, preparation and analysis of diatoms have been collated and standardized. A number of European and other indices have been tested in diverse localities for use in indicating recent and historical water quality. The impact of diffuse mine effluent on diatom community structure has also been discussed. A new species common in impacted waters (i.e. a potential indicator species for these conditions) has been described and a guide to the common diatoms of South Africa is presented which, it is hoped, will be of use to those who wish to commence with a study of South Africa's diatom flora. The results of this study show that diatom indices are successful in reflecting both current and past water quality in South Africa. This result justifies the inclusion of diatoms with the current suite of bioindicator organisms as well as in national monitoring initiatives such as the River Health Programme. Concluding comments underline the importance of using diatoms as indicators, not only of water quality, but also as indicators of aquatic microorganism biodiversity, or loss thereof. The need for continued research in the fields of diatom ecology and taxonomy is also highlighted.