Microalgal diversity changes as a bioindicator of aquatic metal pollution on the Central African Copperbelt

Intensification of mining has increased the vulnerability of stream ecosystems on the Central African Copperbelt (CACB) to metal pollution. This study assessed the response of microalgae to mining pollution as bioindicators of aquatic ecosystem health in the Upper Kafue River (UKR) on the CACB. Seasonal sampling was conducted at three sites along the UKR: Kafue River Farm (KRF), Hippo Pool (HP), and Mufuchani Bridge (MB). Stream sediment and microalgae samples were analysed for metals. Microalgae were identified morphotaxonomically for relative abundance (p_i), Shannon-Wiener diversity (H'), Margalef's richness (M), and Simpson's dominance (D). There were significantly high concentrations in sediment and microalgae, respectively, of Cu (7.04 g/kg; 3.1 mg/kg), Co (214 mg/kg; 0.8 mg/kg), and Pb (68 mg/kg; 0.3 mg/kg) at HP, which also had the highest sediment contamination by Cu (CF = 176) and metal pollution load (PLI = 2.4). However, KRF had the lowest metal concentrations in sediment and microalgae but showed the highest microalgae diversity (H' = 4.0) and taxa richness (M = 5.6). Microalgae genera such as Fragilaria sp. and Closterium sp. were dominant at KRF, while pollution-tolerant species including Microcystis sp. and Volvox sp. were prevalent at HP and MB. Metal bioaccumulation in microalgae was generally higher during the dry season (Cr 0.044-Ni 0.92 mg/kg DW). Principal components analysis confirmed strong correlations between environmental factors and microalgae metrics (p < 0.05). The findings demonstrate the sensitivity of microalgae to site-specific variability in mining pollution, supporting their potential as bioindicators of aquatic ecological health in the CACB and similarly impacted landscapes.