DIATOMS AS INDICATORS OF WATER QUALITY IN THE UPPER HENNOPS RIVER (Transvaal,South Africa)

SUMMARY

The water quality of the upper Hennops River was determined by applying the method of Lange-Bertalot (1978; 1979), which is based on groups of diatom species with similar tolerances towards pollution. A definite improvement in the water quality was indicated between the upper reaches of the river, which receives secondary treated sewage effluent discharges, and Rietvlei Dam, some 25 km downstream. According to the water quality classification of Lange-Bertalot, this represented an improvement from class III – IV (α-meso- to polysaprobic) to class II – III (α- to β-mesosaprobic). These results were in general agreement with chemical analyses, which suggests that Lange-Bertalot's method for classifying the quality of running waters can be adapted, to South African conditions. The pollution tolerances of some species not included in Lange-bertalot's classification are suggested.