The use of multivariate analysis as a tool to illustrate the influence of environmental variables on phytoplankton composition in the Vaal River, South Africa
The highly eutrophic Vaal River system is subjected to algal blooms that cause problems ranging from aesthetically unacceptable conditions to the release of toxins. In order to understand how environmental variables influence one another and to determine the key environmental variables that affect phytoplankton composition, multivariate analyses were applied. Results showed that the most important environmental variables influencing one another, as well as phytoplankton composition, were turbidity, temperature, conductivity and nutrients, such as SiO2-Si. Turbidity influenced phytoplankton biomass through its effect on light availability in the water column. In general, Cyanobacteria, Euglenophyceae and the filamentous centric diatom Aulacoseira granulata were favoured by high temperatures, low inorganic N:P ratios and low conductivity levels, while the unicellular centric diatoms were favoured by the opposite conditions. Green algae were capable of tolerating wider environmental variability than other algal groups.