A review of cyanobacteria

Cyanobacteria (blue-green algae) are a major water quality problem in the Murray-Darling system and in other parts of the world. Cyanobacteria are photosynthetic bacteria that. under certain conditions, can multiply to large numbers and dominate otherwise healthy phytoplankton communities. Such excessive growth incidences are of major public concern because cyanobacteria are unsightly and capable of producing a variety of toxins and undesirable tastes and odours. The toxins produced by cyanobacteria can cause severe gastrointestinal illness and, in extreme cases, death in humans and animals. The presence of large numbers of cyanobacteria also significantly increases the cost of water treatment. The algae increase the suspended solids content and turbidity of the water, thereby reducing the efficiency of disinfection and blocking filters. Consequently, to prevent blooms of cyanobacteria, it is necessary to have an understanding of the complex relationship between cyanobacterial growth events and environmental conditions, such as flow, irradiance, temperature, nutrients and competitive interactions with other taxa. In this report, the many environmental factors leading to the development of cyanobacterial blooms are reviewed. Given an understanding of these factors, the discussion is then extended to include the deleterious effects caused by excessive growths of cyanobacteria, the approaches used to remedy the cyanobacterial problem and the occurrence of toxic cyanobacteria in the Murray-Darling system. Finally, the methods that have been employed to model phytoplankton populations are reviewed.