Analysis of freshwater diatom deformities in the Karoo, South Africa

Abstract

Several studies regarding the effects of excess nutrients and metals as possible causes of deformities found in diatom cells have been conducted in Europe, North America and Australia. This is the first study in South Africa which catalogued and analysed diatom deformities in detail. We assessed diatom deformities in response to a large water chemistry dataset, including pH, electrical conductivity, alkalinity, hardness, nutrients, heavy metals and radioactive elements. The freshwaters of the Karoo exhibited wide ranges in many of their environmental variables. Diatom deformities were categorised into four types (outline, raphe, striation and mixed/other), and each cell measured and photographed. Correlations and multivariate analyses between environmental variables and deformity type, as well as diatom species, were performed. A cumulative criterion unit (CCU) ratio, using South African aquatic ecosystem limits, was calculated for Al, Cd, Cu, Mn, Pb, Se and Zn to determine if the combined effect of these metals exerted any influence on the cause of deformities. No single stressor could be linked to the deformities. Instead, variables showing to be most probable to exert an influence are electrical conductivity, oxidised nitrogen, sulphate and lithium, with selenium and strontium having a lesser influence. The CCU application did not yield expected results. This could be due to the naturally highly mineralised water found in the Karoo.