A new biomonitoring protocol to determine the ecological health of impoundments using artificial substrates

  • C Thirion Institute for Water Quality Studies, Department of Water Affairs and Forestry, Private Bag X313, Pretoria 0001, South Africa


The colonisation potential of macroinvertebrate families was measured using artificial substrates. These substrates were tested on three highveld impoundments. Bronkhorstspruit Dam was an amictic, mesotrophic impoundment, while Hartbeespoort and Roodeplaat Dams were both monomictic, eutrophic impoundments. Bronkhorstspruit Dam had the best water quality and the smallest algal population, comprising mainly diatom species. Hartbeespoort Dam had the most saline water (TDS 96–400 mg/l; NH4 <0.004–0.218mg/l; NO2+NO3 0.109–2.776mg/l; PO4 <0.04–0.06mg/l), while Roodeplaat Dam had the highest nutrient concentrations (TDS 200–373mg/l; NH4 <0.04–0.933mg/l; NO2+NO3 <0.04–2.310mg/l; PO4 0.041–0.472 mg/l). Both Hartbeespoort and Roodeplaat Dams had large algal populations that resulted in very alkaline water during summer. Microsystis dominated the phytoplankton population in these two impoundments during summer and autumn, while green algae and diatoms were dominant during winter and spring. Ecological health was determined using two different biotic indices. Two modifications of the Belgian Biotic Index and a modification of SASS4 (SASSD) were tested. Three health classes were suggested for SASSD scores and ASPT values. It is concluded that artificial substrates with SASSD (and ASPT) as a biotic index can be used to determine the biological health of impoundments, but that further refinement of the index is needed.

(Afr J Aqua Sci: 2000 25: 123-133)

Journal Identifiers

eISSN: 1727-9364
print ISSN: 1608-5914