Changes in density and composition of algal assemblages over time in two water purification plants
Oosthuizen, Marthinus Gerrit Johannes
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In recent years, due to a change in the water situation in South–Africa and the effect of eutrophication in our water systems, there has been a significant increase in algal abundance and changes in species composition. The aim of this study was to investigate algal assemblages at two water purification plants with the main focus on dominant species that may pose a problem in the water purification process. Both water purification plants, especially the one at Virginia, experience problems with blue–green bacteria that are toxic and detrimental to water purification. There was also a need to determine the time of year that blooms of problematic algae occur in the system, in order to develop sufficient measures to remediate the situation. Chemical data helped with the explanation of algal tendencies. To achieve the principal aims of the study, algal species were identified and the concentrations were determined. It was possible to relate algal assemblages, dominance and succession to the prevailing environmental variables. Sixty three phytoplankton species, belonging to seven major algal groups, were identified. Aside from these, thirty four species were only identified up to genus level. The blue–green bacteria, diatoms and green algae were the main phytoplankton groups and constantly succeeded each other. Blooms of blue–green bacteria occurred in the raw water due to high temperatures and dissolved inorganic nitrogen concentrations in the late summer periods. These organisms did not penetrate far into the purification process, indicating that the purification procedures were sufficient for effective removal of blue–green bacteria.