The spatial distribution patterns of freshwater diatom species in the southern Karoo related to their associated environmental conditions

Abstract

The aim of this study was to investigate the distribution of diatom species and their relationship to measured environmental factors within the Karoo. TWINSPAN was used to identify groups of indicator species and samples. Five groupings, that would best describe the species and their habitats, emerged. Two of the five groups (Group 000 and 001) were restricted to the Southern Karoo of which Group 000 was indicated by Nitzschia elegantula while Group 001 did not have any specific indicator species. Group 01 was indicated by Achnanthidium minutissimum which does not reflect the water chemistry but rather could be an indicator of habitat disturbance (e.g. desiccation during drawdown within the reservoir). Halamphora veneta and Achnanthidium minutissimum were indicators for Group 10 even though the latter was grouped in 01. Water bodies reflecting low flow water with anthropogenic influences (Group 11) are indicated by Planothidium frequentissimum, Amphora pediculus, Amphora sp1, Sellaphora nigri and Gomphonema parvulum. While an overlap of certain groups of species occurred (shown through Detrended Correspondence Analysis), there is a differentiation of species and the habitats in which they occur. The multivariate analysis and TWINSPAN indicator groups reveal that the diatom species identified in this study serve as effective indicators of varying water chemistry types within the Karoo. Key environmental factors influencing habitat groupings include electrical conductivity, chloride, calcium, sulphate, and several micronutrients, notably lithium. This extensive dataset marks an important advancement in establishing indicator groups for South African diatoms, providing a foundational framework for future ecological assessments.