An empirical biotic index of the quality of water in South African streams and rivers

Abstract

Abstraet--A method of reducing data on stones-in-current faunal communities to a linear scale of water quality in terms of organic pollution is presented. Using data from extensive river surveys each taxon has been allotted a Quality Value (between 0 and 10) related to its occurrence in variously polluted waters. To arrive at the Biotic Index Value of a community, a faunal sample is taken and the individual animals are recorded by taxa. The number of individuals of each taxon is then multiplied by the taxon's Quality Value. The products of these multiplications are summed for the sample and this sum is then divided by the total number of individuals in the whole sample to give the Biotic Index Value. Quality Values for taxa occurring in large numbers in a wide range of water qualities vary according to the diversity and abundance of the Baetid Ephemeroptera. It is not necessary to identify all animals to the species level and sample size is not critically important. The Biotic Index is compared with indices due to other authors