Abstract
M.Sc. (Aquatic Health)
Water is an important natural resource but undervalued. Urbanisation has resulted in an increase in water use and resulted in water being polluted. To manage water and to protect this natural resource monitoring programmes have been developed. Anthropogenic activities have resulted in a decline in water quality and ecosystem biota in the Nyl and Mogalakwena River system.
Traditionally water quality monitoring focused on physico-chemical analysis. Recently water quality has shifted towards biological monitoring which allows researchers to get a time integrated assessment of the water quality. Biomonitoring techniques are used since chemical monitoring gives a glimpse of water quality at a specific moment in time and it is time-consuming and expensive.
Nine sampling sites were selected to assess water quality of the Nyl and Mogalakwena rivers in the Limpopo Province. Physico-chemical parameters and diatom assemblages were used to assess water quality during high and low flow conditions.
The in situ results indicate that temperature, electric conductivity and chemical oxygen demand increased downstream from the source. The pH remained more or less stable with the highest peak at Glen Alpine Dam. The nutrient concentrations increased at the sewage treatment works indicating that effluents from anthropogenic activities have an influence on the water quality. Omnidia software was used to calculate the diatom indices. These index values were subsequently used to determine which ecological category the sites fell in. Diatom categories with respect to ecological classification were compared to the water quality to get a time-integrated assessment of the river system. The diatom indices indicated a decline in water quality from the source of the Klein Nyl River along its course to the confluence with the Limpopo River. There was an increase in pollution tolerant taxa (%PT) from the sewage treatment works to the Limpopo River confluence indicating a negative effect on water quality, and organic matter pollution. The diatom indices indicated poor water quality during high flow conditions which can be related with the dilution effect associated with high flow conditions, as studies indicate that high rainfall will cause an increase in nutrient loading from land to rivers.