Assessing diatom community composition and structure in palaeosediments of a southern Cape coastal wetland

Palaeoenvironmental studies are important as they aid in reconstructing histories of past landscapes and provide key long-term information for the conservation and management of ecosystems. The southern Cape coast is a focus area for palaeoenvironmental research due to its high botanical and climatic importance. A three-metre sediment core was retrieved from Whale Rock wetland (Plettenberg Bay, southern Cape Coast) and spanned ~8000 years – a large proportion of the Holocene epoch. Diatom data preserved in palaeosediments of the Whale Rock wetland are presented within this study. A total of 48 diatom species was identified. Based on the multivariate statistical analysis, the diatom assemblages were divided into three zones: Zone WR-1-A (~7200 – 6450 cal yr BP); Zone WR-1- B (~6450 – 6250 cal yr BP) and Zone WR-1-C (~250 cal yr BP – to present). Two diatom preservation hiatus periods were observed at ~8000 – 7200 cal yr BP and ~6400 – 230 cal yr BP. The results indicated that benthic diatom species were significantly dominant throughout the Whale Rock record. The diatom evidence revealed that the Whale Rock wetland system freshened over time as diatom species identified in Zone WR-1-A and Zone WR-1- B indicated marine influences whereas Zone WR-1-C displayed a dominance of species that thrive in freshwater conditions. A transitional phase occurred at ~6400 cal yr BP where abrupt changes began prior to the significant ~6400 – 230 cal yr BP diatom preservation hiatus period. Principal Component Analysis showed that salinity was the main environmental driver of change impacting the species abundance and diversity of diatom communities within the wetland system throughout the Holocene. When compared with regional palaeoenvironmental and palaeolimnological data, it is evident that several other wetland systems moved from a marine/brackish favoured system to a freshwater system with the transitional phase occurring at different periods within the Holocene. This study indicated that diatoms are powerful biological proxies of environmental change. It is recommended that the site be revisited to investigate further the hiatus phases to further explore the lack of diatom preservation for these periods and to also contribute more palaeoenvironmental proxy evidence as well as modern hydrological information.Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 202