Browsing by Author "Du Plessis, D."

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    Impacts of cage aquaculture on the farm dam ecosystem and its use as a multipurpose resource : implications for irrigation
    (Stellenbosch : University of Stellenbosch, 2007-12) Du Plessis, D.; Leslie, Alison J.; Salie, Khalid; University of Stellenbosch. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
    Small farm dams (< 20 ha) in the Western Cape Province provide adequate water conditions for intensive cage production of rainbow trout (Oncorhynchus mykiss). A major environmental concern of cage aquaculture, however, is the high inputs of nutrients via commercial diets and the subsequent eutrophication of the water source. Eutrophication can result in the degradation of the general water quality (increasing pH levels, oxygen depletion, increased hydrogen sulphide and free ammonia) and shifts in the phytoplankton structure (increased biomass, single species dominance). Deterioration of water quality will affect the success of the fish farming enterprise as well as the performance of irrigation equipment by increasing the risk of clogging and corrosion. Water quality, phytoplankton and zooplankton compositions were monitored at four sites from June 2005 to November 2006 to determine the effects of cage culture on the farm dam environment, its associated biota as well as irrigation water quality. The distribution of nutrients, nitrogen and phosphorus, was mainly influenced by the stratification and mixing regime of the water bodies. Nutrient concentrations increased during the winter mixing period while in the summer months, they seem to settle to the lower part of the water column. Nutrient concentrations of production sites and reference sites were comparable except for the ammonia levels that were significantly higher at the production sites. Phytoplankton corresponded with nutrient availability resulting in high biomass during winter. In terms of biomass, phytoplankton was approximately two times more abundant in production sites compared to reference sites. Assemblage dominance by cyanophytes (Anabaena circinalis, Microcystis spp.) was found more often in production sites, while reference sites were dominated by dinophytes (Ceratium hirundinella, Peridinium spp.). Zooplankton biomass concurred with high phytoplankton biomass in winter. Zooplankton assemblages in production sites sustained much higher biomass. Effects of cage culture on irrigation water quality are evident from increased algal biomass and shifts in species composition. These results indicated that at its present production level, cage culture had impacts on the farm dam environment and irrigation water quality. The most significant evidence was given by increased plankton biomass and single species dominance in production sites. However, these findings can not solely be ascribed to the introduction of aquaculture as various other factors may also contribute to the water quality of these ecosystems.
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    Smart home : energy management system for demand side management
    (2014-12) Du Plessis, D.; Randewijk, P. J.
    With South Africa’s energy grid currently under severe pressure due to a lack of planning, electricity prices have escalated. This has forced consumers to look toward finding innovative ways to reduce their consumption. The aim of this research project was to create a system that assists in the reduction of household power consumption by simplifying the process of power saving. This is done by enabling consumers to remotely monitor and control their household devices. To achieve this goal, a power management system was designed that consists of a Beaglebone black, the main electronic controller, and a circuit for measurement and control. The measurement circuit measures the power consumption, it is then sent to Trintel’s SMART Platform enables users to remotely monitor and control the devices by using a web-based interactive graphical user interface.