oa Civil Engineering = Siviele Ingenieurswese - Biomass removal and management : Hartbeespoort Dam remediation



The effect of eutrophication in the Hartbeespoort Dam manifests itself through vast and excessive algae blooms, as well as prolific growth of water hyacinths in all areas of the dam, although concentrations occur along the shoreline and in funnelled areas because of wind action. Furthermore, the seeds of the hyacinths also germinate from mid-July along the shallow areas. Calculated from the total incoming (external PO load >420 tons/annum) and available nutrients from the dam (internal PO load >2 000 tons), the growth potential of the photosynthesising biomass is much more than the estimated 10 000 to 20 000 tons of biomass which are produced over one year from the 2 000 hectare full-level surface area of the dam that is exposed to the sun. Variably the blue-green algae and the exotic hyacinths (category 1 aquatic weed) make up most of the biomass. Biomass is managed by harvesting and removing both algae and hyacinths from the surface of the dam. This does not only curb the immediate growth, but also removes nutrients already trapped in the biomass. This approach results in an immediate improvement of the visible and noxious conditions in the dam.


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