Temporal dynamics of intra-and extra-cellular microcystins concentrations in Koka reservoir (Ethiopia): Implications for public health risk

Abstract

This study was carried out with a view of understanding the temporal dynamics of microcystin concentrations in both algal seston and water samples and the associated public health risk. All the major MC variants, namely MC-LR, MC-YR, and MC-RR, were detected in both the algal seston and water samples. In the majority of the samples, the most potent variant, MC-LR, constituted the greatest proportion of the total MC concentration suggesting extremely high potential public health risk. The exceptionally high concentrations (μg L⁻¹) of all the variants, MC-LR (815), MC-YR (466.6) and MC-RR (265.68), were observed in May. Although the extracellular MCs were relatively less concentrated and less frequently detected, concentrations (μg L⁻¹) of up to 20 of MC-LR, 6.13 of MC-YR, and 1.27 MC-RR were encountered. The strong and significant association between <i>Microcystis</i> abundance and concentration of nitrate (Spearman Rank Order Correlation r = 0.793, p < 0.001) may suggest that nitrate is the key dictating factor in the dynamics of <i>Microcystis</i>, and may have consequently influenced the MC levels in the reservoir.