wcm.02.2025.402.413

Biomonitoring tools are constantly evolving, with South Africa being no exception. This study aims to improve the knowledge of ecological preferences and tolerances of diatom species in the Karoo and to expand upon the diatom baseline for this semi-arid area. The natural water of the Karoo has wide ranges within its chemistry – often with extremely high concentrations of dissolved salts. The diatom community composition of natural Karoo waters was sampled (n = 510). A total of 543 diatom species were recorded, but the 322 species with abundance over 1% were used in the analyses. The significant environmental drivers that potentially influence these communities included electrical conductivity, calcium, chloride, oxidised nitrogen and strontium. Multivariate analysis (CCA) revealed the three main measured variables influencing diatom community composition to be lithium, chloride and oxidized nitrogen. These were followed by sulphate, selenium, silica and scandium. Several diatom taxa (as yet unidentified) have tolerances to the extremely saline conditions of the natural springs and ground water of the Karoo.