THE EFFECT OF SEASON ON A BIOTIC WATER QUALITY INDEX: A CASE STUDY OF THE YELLOW JACKET AND MAZOWE RIVERS,ZIMBABWE.

Summary

The effect of season on the South African Scoring System (SASS) biotic index for rapid assessment of water quality using benthic macroinvertebrates was investigated using the Yellow Jacket and Mazowe Rivers in Zimbabwe as a case study. Several impacts in the area degraded water quality. These were habitat destruction, acid mine drainage and organic pollution. SASS score at all sites changed with season. At and downstream from polluted sites, water quality determined using SASS was best at the end of the rainy season and it deteriorated steadily into the dry season. SASS scores from sites upstream of pollution appeared to improve towards the end of the rainy season. Average Score Per Taxon indices did not have a significant pattern of seasonal variation. SASS was designed to monitor water quality in South African rivers, so when implementing any monitoring programme, selection of sampling season and the interpretation of results in areas with similar climate patterns should take seasonal effects into account, It must be appreciated that water quality at impacted sites is a dynamic variable related both to the activities of polluters and to season.