Abstract
The Crocodile River is situated in the north east of the Republic of South Africa. It is a large river basin with a total length of 320 km and draining a catchment of 10,450 km2. The water quality of this river is of high importance in sustaining the people and businesses relying on the sustainability of the river. The aim of the study was to use fish and water quality data to determine the present ecological state of the river and identifying the possible sources of pollution in the river. Multivariate statistical analysis was used to identify the main contaminants in the river at the various sections of the river. The results obtained indicated that species richness and diversity are high during low flow condition and the lower reaches had high species richness and diversity compared to the middle and upper reaches. The Fish Response Assessment Index indicated that the Ecological Class for the Crocodile River is mostly at C class beginning from the Kwena Dam downstream. Water quality constituents such as total dissolved solids and electrical conductivity increase with the increase in river distance in the downstream reaches. It was evident from this study that anthropogenic activities along the Crocodile River play a role in water quality deterioration and the subsequent distribution of fish during high and low flow conditions. The main sources of the pollution are believed to be agricultural activities in the upper reaches and a combination of industrial, domestic and agricultural activities in the middle and lower reaches of the Crocodile River.
Highlights
Anthropogenic activities result in a significant decrease in surface water quality of aquatic ecosystems in catchments [1]
A polynomial trend line overlaid in Figure 2 indicated that the total number of fish species caught in the Crocodile River was higher in the middle and lower reaches
The multivariate statistical methods used indicated that richness of fish species in the Crocodile River and its tributaries increase longitudinally downstream with the increase in river flow distance
Summary
Anthropogenic activities result in a significant decrease in surface water quality of aquatic ecosystems in catchments [1]. The deterioration of the water resource is due to increased pollution caused by anthropogenic activities such as industry, urbanization, afforestation, mining, agriculture, power generation and accidental water pollution [2]. River inflows contribute to main pollutants to the water resource in a catchment, thereby tending to induce serious ecological and sanitary problems [3] [4]. The pollution of rivers by human induced activity is becoming a threat to water resource and its biodiversity. In South Africa environmental pollution problems started during the first half of the 19th century, with the development of towns and industries and associated accumulation of wastes in built-up areas. The Crocodile River catchment is recognized as one of the most water-stressed catchments in South Africa, a major concern considering the increased number of people who depend on it for their livelihood, including a large demand for water by emerging farmers [6]
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