Nutrient and Salinity Loading Based On The Temporal And Spatial Water Quality Data In The Upper Crocodile River Basin

Abstract

The Upper Crocodile River Basin has undergone a drastic change through anthropogenic factors such as rapid urban growth, industrial activities, agriculture and mining in the past thirty-eight years. This has led to an increase in nutrient and salinity loads with decreasing water quality. The Upper Crocodile River Basin wastewater treatment works struggle to maintain loading rates, causing partially treated wastewater to enter the river systems that increased the salinity loads. Water chemistry and discharge data from the DWS were collected, cleaned and processed; data were summated across the necessary river channels in which they are located to determine the nutrient and salinity loads in all rivers in the Upper Crocodile River Basin. The results indicated that the Hennops, Jukskei and Crocodile Rivers are responsible for the largest nutrient and salinity loading rates. Changes in land use activities and climate over the past thirty-eight years, since 1980, have drastically impacted the rate at which nutrient and salinity loads enter into the UCRB. During the early 1980s to 1990s a significant drop was observed in nutrient and salinity loading rates, spiking in the late 1990s and early 2000s, influenced by changes in water management and climatic events like the La Niña and the El Niño phenomena. The inter-basin transfer in the early 2000s and subsequent two decades have led to an overall rise in nutrient and salinity loading rates, posing serious water quality and health risks to people in the UCRB area. Mining activities, poor landfill management and leaking tailing storage facilities have resulted in increased sulphate loading rates into the UCRB. Nitrogen loading has risen due to uncontrolled waste disposal from informal settlements, industrial activities and sewage spills in the Johannesburg region. Phosphorus loading rates have risen due to agricultural fertiliser runoff, with the Jukskei River being the largest contributor to these loads in the Upper Crocodile River Basin. The loads entering the Hartbeespoort dam during summer and winter seasons in the 2016-2018 period for sulphate is 6819.24 kg/hr, 4873.62kg/hr; for nitrogen 4179.24 kg/hr, 4021.55 kg/hr and for phosphorus 40.08 kg/hr, 34.724 kg/hr, respectively. Salinity loads entering the Hartbeespoort dam during summer and winter are 42952.87 kg/hr and 27548.39 kg/hr, respectively. According to the findings, water resource management must act quickly to improve the overall quality of the water; in the upcoming ten years, as loading rates are expected to rise exponentially as a result of increased demand and stressed water use, which will lead to poor water quality. This will pose serious health and economic risks to the people of the Upper Crocodile River Basin and the populace of South Africa.