Modelling the effects of artificial mixing and copper sulphate dosing on phytoplankton in an Australian reservior

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An artificially destratified reservoir was simulated with the freshwater phytoplankton model PROTECH (Phytoplankton Responses To Environmental Change). The chosen site for validation was a highly managed drinking water supply reservoir (Myponga Reservoir, South Australia). Chemical dosing using copper sulphate (CuSO4) and artificial mixing via an aerator and two raft-mounted mechanical surface mixers (hereafter referred to as surface mixers) are used at Myponga to manage water quality, in particular the threat of cyanobacteria growth. The phytoplankton community was adequately modelled and showed that the community was dominated by species tolerant of low light doses (R-type strategists). The light limitation in the water body was found to be the controlling factor on phytoplankton succession. Subsequently, small fast-growing species and larger motile phytoplankton (C and CS-type, respectively) do not have the opportunity to dominate under all simulated conditions, diminishing the need for CuSO4 dosing. These simulations demonstrated that the individual and combined impact of the management strategies reduces the total algal biomass, but have minimal effect upon phytoplankton functional-type succession, and R-type species continued to dominate under all simulated scenarios. It was concluded that, due to the light-limitation and current nutrient availability in Myponga Reservoir, the probability of persistent populations of undesirable scum-forming cyanobacteria is minimal, even in the absence of artificial control.

David M. Lewis, J. Alex Elliott, Justin D. Brookes, Anthony E. Irish, Martin F. Lambert and Colin S. Reynolds