Management strategies for cyanobacterial blooms in an impounded lowland river

The incidence of blooms of the toxic cyanobacterium Anabaena circinalis in the major rivers of the Murray–Darling Basin has been strongly related to river discharge, because they are more prevalent during times of low flows. This study into the causes of cyanobacterial blooms in Maude Weir pool on the Murrumbidgee River demonstrates that for Anabaena blooms to form, the water column needs to be persistently stratified, a condition that occurs only during times of low discharge. Based on the relationship between discharge, stratification, and bloom formation, four strategies that might be implemented to minimize the occurrence or impacts of cyanobacterial blooms in weir pools are suggested. These strategies include setting a minimum discharge, pulsing the discharge, changing the discharge height, and altering the depth of water withdrawal. These strategies are evaluated in turn using results from the field study and from the predictions of a numerical model of the weir pool system. Copyright © 2000 John Wiley & Sons, Ltd.