Original Articles

OBSERVATIONS ON TEMPORAL TRENDS IN PHYTOPLANKTON DIVERSITY IN THE VAAL RIVER AT BALKFONTEIN, SOUTH AFRICA


Abstract

Phytoplankton diversity in the Vaal River at Balkfontein from March to October 1984 was investigated by employing different diversity indices. Most diversity indices showed appreciable variation during the study period indicating specific temporal trends. Greatest diversity was demonstrated for warmer months, while least diversity occurred during August and September when phytoplankton concentrations were highest. Chlorophytes were found to be the most diverse (species rich) and important (abundant) algal group. The simultaneous application of Relative Species Number and Relative Species Percentage indices in conjunction with Margalef D, Hurlbert PIE, Shannon-Wiener H and Simpson D allowed the identification of changes in community structure affected by broad categories (algal groups) comprising the community. The use of either the Hurlbert, Shannon-Wiener or Simpson's indices provides an adequate summary of phytoplankton community structure in the Vaal River.

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