Flow management strategies to control blooms of the cyanobacterium, Anabaena circinalis, in the River Murray at Morgan, South Australia

Abstract

<jats:title>Abstract</jats:title><jats:p>The Murray–Darling river system is highly regulated and is Australia's major surface water resource. It is subject to blooms of the toxic cyanobacterium <jats:italic>Anabaena circinalis</jats:italic>, which present significant water quality problems. As a result of these blooms, an algal management strategy has been developed for the Murray–Darling basin. One of the major objectives of the strategy is the development of flow management strategies for key reaches of the river system. Intensive studies in the Murrumbidgee River, Australia, have indicated that persistent thermal stratification is a requirement for blooms of this cyanobacterium to occur. In the lower Murray, mean wind speed was found to be the major factor affecting the degree of thermal stratification under low flow conditions, which generally exist during the months of December to March. In this paper, the effect of various flow management scenarios on the likelihood of the occurrence of blooms in the River Murray at Morgan, South Australia, are assessed. A frequency analysis is carried out on 30 years of wind speed data to determine the probability of occurrence of persistent thermal stratification under a number of flow regimes. The scenarios evaluated include existing base flow conditions, altered base flow regimes, temporary releases from an upstream storage (Lake Victoria) and the temporary reduction of weir pool levels. The results obtained indicate that the dispersal of existing blooms by simultaneously reducing the weir pool levels at Locks 1–3 is the most effective and economical strategy for combating bloom formation by <jats:italic>A. circinalis</jats:italic> in the River Murray at Morgan. Copyright © 2001 John Wiley &amp; Sons, Ltd.</jats:p>