Assessment of water quality in the Groenwater Spruit, Postmasburg, Northern Cape

Abstract

The Northern Cape province is known for its harsh climate with minimal rain and continued droughts, coupled with high evaporation. The province has two perennial rivers; the Orange river and the Vaal river systems supplying water for both economic and domestic needs of the province. The Lower Orange Water Management Area (WMA) is located in a way that the majority of its surface water is found in the main stem of the Orange river. Postmasburg connects both the Lower Orange WMA and the Lower Vaal WMA. The Groenwater Spruit is a south west flowing river that discharges into the Lower Orange WMA and directly intersects with the Orange river. The catchment area of the Lower Orange WMA is predominantly used for large-scale mining activities and agriculture with extensive irrigation schemes, producing large volumes of return flows. With all these anthropogenic stressors taking place within the catchment area, there is minimal water quality data available for the catchment area hence, the study was conducted to assess the water quality of the Groenwater Spruit. To determine the water quality, this study collected seasonal measurements of 14 parameters (pH, temp, EC, TDS, DO, SO4, NO3, PO4, Mn, Fe, As, Cr, E. coli and total coliform) from six sampling sites along the Groenwater Spruit during a one-year period. Physical parameters were measured in-situ using a hand-held instrument, chemical and microbiological parameters were analysed ex-situ using various laboratory methods. The obtained water quality results were assessed against the WHO, SANS (241) and DWAF for domestic water use standards and agricultural water use guidelines to give indication for the fitness for use. Furthermore, PCA was used to comprehensively evaluate all the selected water quality parameters across the Groenwater Spruit, to identify and analyse the sources of water pollution while ANOVA was used to compare seasonal variations at 95% confidence level. Results for the physical parameters revealed that pH measured an average of 11 and 9.6 for the dry and wet periods, respectively. The measured pH values from both seasons were non-compliant to the set WHO (6.5 - 8.8) and DWAF (6.5 - 8.4) standards. The average TDS values for the dry and wet seasons (256.5 mg/L and 268.3 mg/L) were within the acceptable SANS set standard at ≤ 1200 mg/L but above the set DWAF guidelines of 0 - 0.02 mg/L. EC was only complaint to the DWAF guidelines of ≤ 540 mg/L, with an average measurement of 254 mg/L during the dry season and

517.1 mg/L for the wet season. Among all the selected chemical parameters for this study, DO, PO4, Fe and Mn each measured values were above their specific set WHO, SANS and DWAF standards and guidelines. As and Cr were only compliant to their specific set SANS standards. SO4 was compliant to SANS (≤ 500 mg/L) and DWAF (≤ 500 mg/L) standards with a mean of < 90 mg/L for both seasons. NO3 recorded a mean of 27.1 mg/L and 18.4 mg/L for the dry and wet seasons, respectively. These measured values were only within the acceptable WHO set standard (≤ 50 mg/L) and the DWAF guidelines (≤ 30 mg/L) but above the SANS standards. Total Coliform obtained from the study, for both seasons (67 cfu/100 mL and ≥ 685 cfu/100 mL for the dry and wet season) were higher than the WHO, SANS and DWAF set standard at ≤ 10 cfu/100 mL. The expected E. coli detection from WHO and SANS is 0 cfu/100 mL and so, the samples from the study area (39 cfu/100 mL and ≥ 837 cfu/100 mL for the dry and wet seasons) were non-compliant to this standard. For the wet season sampling, PCA extracted three principal components that accounted for 91.9 % of the total variance. The strong positive loadings of F1 (temperature, Fe, As and Cr ) were mainly influenced by variables related to natural and anthropogenic factors such as, rock weathering, dissolution, geomorphic variations, agriculture return flows, mining and industrial effluents. F2 with positive loadings of NO3, PO4, TDS and Mn signifies runoffs from chemical fertilizers, sewage and the disposal of manures and industrial activities prevalent in the catchment area. F3 had positive DO, which may be explained by the increased water volume in the Goenwater Spruit. Three components were retained for the dry season at 84.13% cumulative of the variance. The high positive loadings of F1 (temperature, EC, TDS, Fe, As, and Cr) were also influenced by natural factors and anthropogenic factors in the study area. The positive loadings of PO4 and total coliform from F2 is mainly influenced by the direct pollution from manure, sewage and fertilizer, and from F3 (SO4 and NO3) is influenced by anthropogenic activities such as the discharge of untreated domestic, municipal waste waters. The findings from this study has highlighted the sources and types of pollution within the Groenwater Spruit. Therefore, it is recommended that long-term monitoring programmes be implemented focusing on the areas where increased anthropogenic activities have been observed.