Assessment of phytobenthos in the lower Phongolo River catchment in relation to changing environmental conditions A Kock orcid.org / 0000-0002-2408-6932 Thesis accepted for the degree Doctor of Philosophy in Science with Environmental Sciences at the North-West University Promoter: Prof V Wepener Co-promoter: Prof JC Taylor Co-promoter: Prof NJ Smit Graduation: May 2020 22711066 Diatoms matter! They produce approximately 30% of the world’s oxygen, and they are useful tools in detecting and forecasting the pace of environmental change. If we succeed in relating to this remarkably different organism, we might even hope to relate to one another for the good of all creation. Evelyn E. Gaiser Think like a Diatom i Table of Content Table of contents Table of contents ...................................................................................................................ii Acknowledgements .............................................................................................................. vii Summary .............................................................................................................................. ix List of Figures ...................................................................................................................... xii List of Tables .................................................................................................................... xviii List of Abbreviations ............................................................................................................ xix Chapter 1: General introduction ............................................................................................ 1 1.1 Introduction ..................................................................................................................... 1 1.2 Study hypotheses and aims ............................................................................................ 4 1.3 Thesis layout ................................................................................................................... 5 1.4 References...................................................................................................................... 7 Chapter 2: Spatial and temporal variation of the diatom community composition and the influence of environmental variables on the community distribution within the lower Phongolo River floodplain. .................................................................................................................. 11 2.1 Introduction ................................................................................................................... 11 2.2 Materials and methods .................................................................................................. 13 2.2.1 Site description ................................................................................................... 13 2.2.2 Physico-chemical water quality ........................................................................... 27 2.2.3 Diatom sampling, preparation and analysis ......................................................... 28 2.2.4 Statistical analysis ............................................................................................... 29 2.3 Results .......................................................................................................................... 29 2.3.1 Monthly flow of the Phongolo River ..................................................................... 29 2.3.2 Flood release (2013) versus the absence of a flood release (2017/18) ............... 30 2.3.3 Spatial and temporal connectivity between aquatic ecosystem types for 2017/18 34 2.4 Discussion..................................................................................................................... 43 2.4.1 Physico-chemical water quality ........................................................................... 43 2.4.2 Effect of a flood release on diatom diversity (2013 vs 2017/18) ........................... 44 2.4.3 Spatial and temporal variations ........................................................................... 45 ii Table of Content 2.5 Conclusions .................................................................................................................. 48 2.6 References.................................................................................................................... 49 Chapter 3: River and wetland diatom community structures and stable isotope signatures in the lower Phongolo floodplain. ............................................................................................ 53 3.1 Introduction ................................................................................................................... 53 3.2 Materials and methods .................................................................................................. 55 3.2.1 Study area........................................................................................................... 55 3.2.2 Physico-chemical water quality ........................................................................... 55 3.2.3 Phytobenthos sampling and preparation ............................................................. 55 3.2.3.1 Diversity analysis ............................................................................................. 55 3.2.3.2 Stable isotope sampling and preparation.......................................................... 55 3.2.4 Stable isotope analysis........................................................................................ 56 3.2.5 Data analysis ...................................................................................................... 57 3.3 Results .......................................................................................................................... 57 3.3.1 Physico-chemical water quality ........................................................................... 57 3.3.2 Diatom community .............................................................................................. 60 3.3.3 Periphyton stable isotopes .................................................................................. 63 3.4 Discussion..................................................................................................................... 65 3.4.1 Connectivity of rivers and floodplain pans and structuring of diatom communities65 3.4.2 Stable isotope signatures .................................................................................... 66 3.5 Conclusion .................................................................................................................... 67 3.6 References.................................................................................................................... 69 Chapter 4: Reconstruction of historical diatom community structures in Nyamithi Pan sediment cores. .................................................................................................................................. 73 4.1 Introduction ................................................................................................................... 73 4.2 Materials and methods .................................................................................................. 75 4.2.1 Study area........................................................................................................... 75 4.2.2 Core sample collection and age analysis ............................................................ 75 4.2.3 Carbon dating ..................................................................................................... 76 4.2.4 Diatom analysis ................................................................................................... 77 iii Table of Content 4.2.5 Statistical analysis ............................................................................................... 77 4.3 Results .......................................................................................................................... 77 4.3.1 Age-depth ........................................................................................................... 77 4.3.2 Diatom community .............................................................................................. 79 4.4 Discussion..................................................................................................................... 82 4.5 Conclusion .................................................................................................................... 84 4.6 References.................................................................................................................... 85 Chapter 5: A lentic microcosm approach to determine the toxicity of DDT and Deltamethrin on diatom communities. ........................................................................................................... 89 5.1 Introduction ................................................................................................................... 89 5.2 Material and methods .................................................................................................... 91 5.2.1 Experimental framework ...................................................................................... 91 5.2.2 Physico-chemical variables ................................................................................. 92 5.2.3 Diatom sampling and analysis ............................................................................