Setting flow levels for controlling cyanobacterial blooms in tropical weir pools

Abstract

Toxic cyanobacterial blooms occur frequently in water supply weir pools and storages in tropical Australia and elsewhere. They flourish under warm stratified conditions and their amelioration and management is an ongoing problem. We investigated bloom occurrence and growth in 3 separate water storages on the Fitzroy River in Queensland, Australia. We show that there is an opportunity to reduce its prevalence by manipulation of the riverine flow to remove the stratification, and to raise the turbidity through the resuspension of the finely divided bottom sediments. These effects are not due solely to flushing the weirs but to “resetting” the optical and mixing depths so that conditions are inimical to buoyant cyanobacteria. The persistence of the sediment particles in the water column, and the size of the discharge are the two most important factors in determining the effectiveness of the procedure. © 2002 Taylor & Francis Group, LLC.