Browsing by Author "Sepono, Sephooko"

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    Assessment of heavy metals and their impacts on aquatic ecosystems and river health in the Mohokare river using SASS-5
    (National University of Lesotho, 2025) Sepono, Sephooko; George, Mosotho J
    To improve freshwater monitoring in Southern Africa, this study recommends integrating chemical analysis with biological biomonitoring frameworks like SASS-5 to detect ecological degradation early. This investigation assessed heavy metal contamination and its ecological impacts on the Mohokare River, a transboundary river flowing between Lesotho and South Africa. Sampling was conducted at six strategically selected sites: Matsoaing (control site in Butha-Buthe), Matlakeng, Mohloka-qala, Ha Fusi, Ha Setho, and Bolikela (in Mafeteng). These sites represent gradients of pollution from upstream pristine conditions to downstream urban and agricultural zones. Water and sediment samples were analyzed for Fe, Zn, Cu, Mn, and Pb using Atomic Absorption Spectroscopy (AAS). Sediment extraction involved Van Veen grab sampling and aqua regia digestion (HNO₃ and HCl) under controlled heating. Biological assessments were conducted using the South African Scoring System version 5 (SASS-5) and Average Score Per Taxon (ASPT) metrics, with macroinvertebrates sampled via standardized kick sampling. Results showed that Pb concentrations in water exceeded the South African aquatic ecosystem standard (0.01 mg/L) at all sites, reaching up to 0.065 mg/L at Bolikela. Fe concentrations also surpassed acceptable levels (0.3 mg/L) at four sites, peaking at 2.45 mg/L. In contrast, sediment-bound metal concentrations remained within Canadian Sediment Quality Guidelines. The cleanest site, Matsoaing, recorded the highest SASS-5 (104) and ASPT (7.43) scores, indicating excellent ecological condition, while Ha Setho and Bolikela, located downstream of Maseru, had the lowest scores (SASS-5: 38 and 46; ASPT: 4.22 and 4.60 respectively). Multivariate analyses including Spearman’s correlation and Principal Component Analysis (PCA) revealed strong negative correlations between Pb, Fe, and biological indices. These statistical insights helped pinpoint pollution sources and demonstrated a spatial pattern aligning with land-use impacts, especially urban effluents near Maseru and agricultural runoff downstream. This study demonstrates that elevated heavy metal concentrations, particularly Pb, are linked to macroinvertebrate diversity loss and deteriorating river health. It emphasizes the value of combined chemical-biological assessments in identifying pollution hotspots and guiding catchment management in data-scarce, Transboundary Rivers.