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Software for calculation of 6 diatom indices and diversity indices has been created for both Macintosh and IBM compatible computers. This software runs with the data base Omnis 5 under Windows 3.0. It includes three taxonomic files: families, genera and species, and an inventories file. Four types of data inputs are possible. It is always possible to operate simulations and to carry out investigations with simple or combined characters. All files and results of investigations can be listed in different ways. This data base is compatible with both word processing and spreadsheet systems.

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The inclusion of diatoms into the current suite of biomonitoring tools in use in South Africa, as well as the use of European and other diatom indices in South Africa, and in particular the Crocodile and West Marico water management area, is discussed. The indices, when compared to chemical analyses, proved useful in providing an indication of the quality of the investigated waters. Several widely distributed diatom species were shown to have similar ecological tolerances in South Africa when compared to Europe. Although most of the diatoms encountered in the study were cosmopolitan, several possibly endemic species were recorded. The occurrence of endemic species, not included in existing diatom indices may lead to miscalculations of diatom indices. It is concluded that although diatom indices developed in Europe and elsewhere are useful at the present to indicate water quality, a diatom index unique to South Africa including endemic species will have to be formulated.

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