Claims are invalid

The news article on the closure by the Department of Water Affairs of the Hartbeespoort Dam metsi a me project (5 April, pg 20) refers.

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Firstly, we have gone on record to express our concerns regarding the continued persuance of food web manipulation at Hartbeespoort Dam. In this regard we have challenged the notion that the selective harvesting of fish will result in larger populations of zooplankton (tiny aquatic invertebrates) which, in turn will graze on and reduce the algal biomass in the dam.

Our independent and joint published research has shown this theory to be invalid for South African dams on several counts. We are of the opinion that the fishery component of the project should not have commenced without its likelihood of success having first been validated. A project designed by us to explicitly test the validity of the approach at the dam was regrettably and inexplicably blocked, and the fish removal proceeded in the absence thereof.

Secondly, with respect to the claims made about improvements to the Hartbeespoort Dam ecosystem, we are of the opinion that these have been made in the absence of any rigorously-controlled scientific substantiation. There are many factors that can bring about an apparent increase or decrease in, for example, the level of algae in a particular water body, inter alia simple meteorological variations over time.

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The role of any or all such interactive factors has to be quantified and excluded before any claims of improvement can be made, especially in a highly polluted environment such as Hartbeespoort Dam. We do not believe that this process has been applied to the aforementioned claims, rendering them scientifically invalid and misleading.

Department of Water Affairs cancels Harties clean-up project.