Ecosystem health and water quality of the Mooi River and associated impoundments using diatoms and macroinvertebrates as bioindicators

Abstract

Water is the most important element on earth for sustaining the life of all living organisms. Fresh water is needed for human life and throughout history concentrated human populations were found in close proximity to a fresh water source. Urbanization, industrialization, mining and over population have negative effects on water quality. Clean potable water has become a limiting resource worldwide and particularly in South Africa due to developing communities and informal settlements forming around rivers, mining, heavy industry, agriculture and poorly managed sanitation. These impacts are problematic for both the human population and for the aquatic organisms which are dependent on this resource as a habitat. The monitoring and management of freshwater is thus critical to this resource. In order to manage resources impacts need to be accurately identified. In the case of aquatic ecosystems constant monitoring will allow for the prevention or early detection of any threats to the integrity of the resource. The river system chosen for the present study was the Mooi River. It is the source for potable water to various communities in the area including the city of Potchefstroom. The Mooi River originates near Koster and flows south to its confluence with the Vaal River south of Potchefstroom. The water quality of the Mooi River is impacted by mining pollution from Wonderfonteinspruit (a tributary of the Mooi River), urban influences from Potchefstroom, agricultural activities and informal communities situated in the catchment area. In this study the measured water quality variables, diatom analysis and macroinvertebrate analysis were used in combination to monitor the ecosystem health of the Mooi River for the calendar year of 2014 in order to identify problem areas in the catchment and the time of year that the influence of these impacts were greatest. All of the above mentioned biomonitoring tools showed a gradual decline in ecosystem health from the origin of the Mooi River flowing downstream toward the Vaal River. This decline in ecosystem health, throughout the Mooi River, could be ascribed to the influence of the Wonderfonteinspruit and also the impact of Potchefstroom and its surrounding (sub) urban area and industries. The alteration in the physical and chemical regime in the river was clearly reflected by changes within the habitat integrity and community structure of the aquatic biota. In addition, low rainfall in the winter period had a slight impact on the ecosystem health, as pollutants become more concentrated. It can be concluded that the methods used in the study were applied successfully to identify the main detrimental influences on the water quality of the Mooi River, and that the different bioindicators used in the study were sufficient to determine the health of the Mooi River ecosystem.