# Seasonal Pollution Levels and Heavy Metal Contamination in the Jukskei River, South Africa
## 1 Introduction  
River pollution is a significant environmental issue that affects water quality, aquatic life, and human health, particularly in perennial rivers exposed to toxic substances from agricultural activities, industrial effluents, and stormwater runoff. The lack of stringent regulatory adherence exacerbates this issue, leading to the accumulation of harmful pollutants such as heavy metals, pharmaceuticals, and organic waste in river systems. These pollutants pose serious health risks to humans and aquatic organisms, necessitating urgent intervention and policy implementation to mitigate their impact [1]. Freshwater ecosystems, including streams, reservoirs, rivers, lakes, and wetlands, provide around 33% of the world's potable water; yet, humanity is facing a lack of drinkable water [2, 3, 4]. Urban rivers serve as the primary freshwater resource while also acting as major catchment sites for storm runoff and urban sewage. The impact of river pollution is extensive, affectingnot only the aquatic ecosystem and water resources, but also the health of communities, biodiversity, and economic activities [4; 5]. Cumulative effects may arise as the aquatic biotic assemblages face continuous habitat loss, degrading water quality, and intensive competition for limited resources. Depending on their life cycle and habitat needs, organisms may react differently under extreme aquatic environmental conditions, as the consequence of the changes, diversity, abundance, and community structure of aquatic inhabitants including fish and macroinvertebrate species could significantly be affected by pollution and water stress. The low quality of urban rivers and aquatic mortality prompts a pressing need to implement the proper enforcement of control measures [6; 7]. It is challenging to comprehend the physicochemical properties of river sediment, which are dependent on environmental factors including climate, geology, and human activity. Studies on the chemical and mineralogical composition of the rivers and dams showed the linkage to the spatial distribution of sediments [8; 9]. Three distinct types of sediments such as coarse, silt, and clay exhibit resistance to erosion due to their cohesive granules, which are bound together by chemical forces that promote agglomeration, hence driving the colloidal suspension and affecting water quality in river systems [8; 10]. Seasonal variations influence colloidal resuspension and sedimentation, intensifying river pollution. Sediments can be used to provide crucial insights into the source of pollution and the significance of anthropogenic impact on river contamination. Sediments can absorb contaminants, particularly heavy metals, and act as both a repository and a secondary source of toxic substances in urban rivers [11; 12]. Heavy metals constitute a category of pollutants recognized for their detrimental effects on humans and aquatic organisms, even at minimal concentrations, and are among the most prevalent contaminants detected in water [13; 14; 15]. The toxicity and environmental persistence of heavy metals is exacerbated by their tendency to bioaccumulate and biomagnify in aquatic organisms, leading to significant ecological and health risks [16; 17; 18]. The detrimental effects of river pollution are well documented; however, it is critical to consider the role of river network topology in managing pollution risks and devising effective management strategies are essential to mitigate the effect of pollution sources to ensure sustainable water resources [19; 20]. Rapid urbanization and industrialization have exposed the Jukskei River with large volumes of runoff flooding from different areas from Johannesburg City in South Africa, containing a broad range of toxic substances including heavy metals. A variety of transport channels, such as vadose zone leaching, storm water runoff, seepage atmospheric deposition, and discharge from dams and creeks have been reported to be entering the Jukskei River through the Moderfontein, Klein Jukskei, and Braamfontein Streams [21].