Abstract
<title>Abstract</title> <p>Heavy metal contamination of aquatic ecosystems remains a major environmental concern in mining-impacted catchments due to its persistence, toxicity, and potential ecological effects. This study investigated the spatial and seasonal distribution of heavy metals in water and sediments along the Kafue River between the Mwambashi–Kafue Confluence and Kafue River Bridge, Zambia, and evaluated associated contamination levels and ecological risks. Water and sediment samples were collected from six sampling sites during the wet and dry seasons and analysed for cobalt (Co), copper (Cu), chromium (Cr), iron (Fe), zinc (Zn), and manganese (Mn) using Atomic Absorption Spectrophotometry (AAS). Physicochemical parameters were measured in situ, while contamination was assessed using the Geoaccumulation Index (Igeo), Enrichment Factor (EF), Contamination Factor (CF), Contamination Degree (CD), Ecological Risk Factor (ERI), and Potential Ecological Risk Index (RI). Pearson correlation analysis and Principal Component Analysis (PCA) were employed to identify relationships among metals and potential contamination sources. Heavy metal concentrations exhibited marked spatial and seasonal variation across the six sampling sites. Dissolved metal concentrations in water generally remained within guideline limits, whereas sediments exhibited substantial metal accumulation, confirming their role as the principal sink for contamination. Copper was identified as the dominant contaminant, recording the highest Igeo (4.079), EF (107.764), CF (25.343), and ERI (126.714) values at Pa Kapula during the wet season. Contamination Degree values indicated very high contamination at Pa Kapula (CD = 29.062–32.074) and the Mwambashi–Kafue Confluence (CD = 12.267–29.014). Potential Ecological Risk Index values revealed considerable ecological risk at Pa Kapula (RI = 137.415–145.466) with moderate to considerable ecological risk across the remaining downstream sampling sites. Correlation analysis revealed strong positive associations among Co, Cr, Fe, Zn, and Mn, whereas PCA and HCA distinguished copper from the remaining metals, indicating a different contamination pattern and supporting multiple contamination sources within the study area. The findings demonstrate that sediments are the primary reservoir of heavy metal accumulation within the investigated reach of the Mwambashi–Kafue River system, with copper representing the dominant contributor to sediment contamination and ecological risk. The combined geochemical indices and multivariate analyses indicate that mining-related activities have substantially influenced sediment quality, highlighting the importance of continued environmental monitoring and catchment management in this section of the Kafue River.</p>