Abstract
The deterioration of water quality in our freshwater sources is on the increase worldwide and, in South Africa, mostly due to the discharge of municipal sewage effluent. Here we report on the use of principal component analysis, coupled with factor and cluster analysis, to study the similarities and differences between upstream and downstream sampling sites that are downstream of municipal sewage plants. The contribution of climatic variables, air temperature, humidity, and rainfall were also evaluated with respect to variations in water quality at the sampling sites. The physicochemical and microbial values were higher than the Department of Water Affairs and Forestry (DWAF) and World Health Organization (WHO) guidelines. The cluster analysis showed the presence of two clusters for each of the Mvudi, Dzindi, and Luvuvhu Rivers and Nandoni reservoir sampling sites. The principal component analysis (PCA) accounted for 40% of the water quality variation and was associated strongly with pH, electrical conductivity, calcium, magnesium, chloride, bromide, nitrate, and total coliform, and negatively with rainfall, which represented Mvudi downstream and was attributed to the Thohoyandou sewage plant. The PCA accounted for 54% of the variation and was associated strongly with electrical conductivity, sulfate; total dissolved solids, fluoride, turbidity, nitrate, manganese, alkalinity, magnesium, and total coliform represented Dzindi downstream, with inflows from the Vuwani sewage plant and agriculture. The PCA accounted for 30% of the variation and was associated strongly with total dissolved solids, electrical conductivity, magnesium, fluoride, nitrate, sulfate, total coliform average air temperature, and total rainfall, and negatively associated with manganese and bromide represented Luvuvhu upstream and was associated with commercial agriculture. The PCA accounted for 21% of the variation and was associated strongly with turbidity, alkalinity, magnesium, chloride, fluoride, nitrate, and strongly negatively associated with rainfall, which represented Luvuvhu downstream, associated with inflows from Vuwani oxidation ponds, Elim and Waterval sewage plants, and agriculture. The PCA accounted for 14% of the variation and was moderately associated with rainfall and weakly associated with chloride and bromide and negatively associated with nitrate, which represented the natural Nandoni reservoir system. The continued discharge of effluent may render the raw water supply unsuitable for human consumption and lead to eutrophication due to nitrate enrichment and proliferation of harmful algal blooms and schistomiasis infections in the long term.
Highlights
Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs [1]
Cluster 1 was composed of Mvudi upstream activities, which involved subsistence and vegetable cultivation and the washing of motor cars using the waters of the Mvudi River
Cluster 2 was composed of Dzindi upstream activities which involved subsistence and vegetable cultivation at the Dzindi irrigation scheme and the washing of motor cars using the waters of the Dzindi River, and this was more pronounced during the dry and wet periods of October to December
Summary
Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs [1]. One of the most severe environmental problems is the discharge of partially-treated sewage to freshwater bodies, reducing the quality of drinking water [2]. Hirji et al [5] indicated that existing sewage plants were overloaded as a result of ever-increasing volumes of wastewater generated by the increasing urban population. The results of a study conducted along Fez and Sebou rivers in the region of Fez in Morocco indicate that severe pollution occurred in most urbanized and industrial areas [6]. In South Africa, water quality management is essential since it is predicted that, by the year 2025, the demand for water will outstrip its supply [7]. The deterioration of water quality, coupled with semi-arid conditions, may jeopardize the economic growth and development of South Africa
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