Effects of land use changes on water quality in Eerste River, South Africa

Abstract

Landuse/land cover change is the key factor causing water quality changes worldwide. Stellenbosch town in the Western Cape, South Africa depends on Eerste River water for drinking and irrigation. The water quality of Eerste River downstream of Stellenbosch has been reported to be deteriorating. The main objective of this study wasto assess the spatial and temporal variation of water quality due to land use changes in Eerste River. Water samples were collected from 8 selected sampling points on the river during the period 12 February to 1 April 2016. To assess the variation of water quality, temperature, DO, EC, TDS, total phosphorus, nitrogen ammonia, turbidity, salinity, oxidation reduction potential, and chemical oxygen demand were analysed using standard methods. The Principal Component Analysis (PCA) was used toextract the most important factors and physico-chemical parameters affecting water quality while Cluster Analysis (CA) was used to group similar sampling sites.PCA results for historical data,Factor 1 describes 31.4 % total variance with a strong significant loading of ammonia, orthophosphate and total phosphorusCA identified 3 classes from 8 sampling points. Site 1, 2, 3 and 4 formed Group 1; at these sample sites the water is relatively clean and Site 1 and 2 fall within in a protected area. Site 5 and 6 are classified in the same group situated after industries and wineries and site 7 and 8 form group 3 located before and after the wastewater treatment plant.The status of water quality indicates that turbidity, nitrates and nitrogen, ammonia exceed the South African Water Targets from sampling sites. It can be concluded that water quality variation is mainly driven by and nitrates. As such the City of Cape Town which monitors water quality downstream of Stellenbosch should decrease the number of monitoring sites from four to three sampling points. For the year 1985to 2015, the forest cover has been decreasing from about 15 % to about 10% and from 2010 to 2015 decline was about 8% to about 2% while there is an increase of settlements from 1985 to 2015 about 38% to 55%. Bareland has been decreasing from 8% to 3%. There is a strong significant correlation (p<0.05) between water quality and land use changes.