Abstract
Trace metal and nutrient contamination of surface water and sediments remains a global threat to biodiversity and ecosystems. Johannesburg is one of the South African cities facing challenges due to diverse industrial, commercial, and residential activities that pollute the environmental waters. With these activities, the city's soil and water have been contaminated with metals such as Pb, Cr, As, as well as nutrients such as NO3-, NO2-, SO42, PO43-, and NH3. This study assessed the seasonal variation of physicochemical parameters, nutrients, and trace elements along the Klip River. The surface water was prepared by direct analysis, using a 0.22-micropore-size PVDF syringe filter for filtration, and the major cations and trace elements were analysed by ICP-OES.
Trace elements As, Cr, Fe and Pb showed spatial variation across all the seasons, with As and Pb increasing in Spring, with concentrations ranging from 82.9 to 159 μg/L, and 53.9 to 121 μg/L. Co and Cr increasing in the Summer and Winter seasons with concentrations ranging from 5.37 to 25.1 μg/L , 1.91 to 2.78 μg/L and 5.14 to 10.74 and 3.27 to 4.52 μg/L for Co, Cr in Summer and Winter respectively. To assess the metal pollution in surface water, TMEI and TMPI were conducted. Spring exhibited the highest metal enrichment and pollution levels, particularly at Middle stream (MS2) and Down stream (DS). Both indices showed a progressive increase from US to DS, indicating an accumulation of contamination along the river. The sediment concentration was higher in all samples compared to the water samples, with the Point 1 sampling site having a higher concentration than Point 2. This indicated that Point 1 is a hotspot for pollution accumulation.
The nutrients in surface water were analysed by direct analysis using the Hanna spectrophotometer. Finally, the sediments were prepared by acid digestion using aqua regia, and the samples were analysed using ICP-OES. The sediment samples were also analysed for the LOI content to determine the organic content, which indicates elevated ionic levels likely associated with urban and industrial inputs. Furthermore, turbidity increased during the winter season, compared to other seasons suggesting possible resuspension of sediment. The nutrient analysis indicated high NH3, PO43-, and SO42- during the winter and Spring seasons. NH3 concentration ranged from 13.6 to 22.2 mg/l, and 15.6 to 17.8 mg/L; PO43- concentration ranged from 11.23 to 12.9 mg/L, and 8.67 to 18.53 mg/. While SO42- ranged from 234 to 262 mg/L and 71.3 mg/L to 146 mg/L for winter and spring respectively. In contrast, the NO3- concentrations were higher in summer, ranging between 9.13 and 29.73 ...