The impact of artificial destratification on water quality in Chaffey Reservoir

La Trobe University Faculty of Science, Technology and Engineering Murray Darling Freshwater Research Centre

MDFRC item.

Reservoir management strategies for the control of toxic cyanobacterial blooms assume that algae can be starved of light or nutrients, especially phosphorus. The failure of a bubble-plume destratification system to control blue-green algal blooms in Chaffey Reservoir, Australia, had two causes: its inability to deepen the surface mixed layer (SML) significantly despite markedly reducing the top-to-bottom temperature difference; and the high external filterable reactive phosphorus (FRP) load originating in the upstream catchment. Temperature differences as small as 0.04 degree C prevented downwards mixing of buoyant Anabaena which inhabited the SML. Artificial destratification reduced the internal phosphorus load from the sediments by over 80% compared to the internal load observed during stratified anoxic conditions. However, the annual external FRP load was at least as large as the internal load. Identification and control of the external FRP load is vital if the biomass potential of future algal blooms is to be reduced.