AN ECOLOGICAL STUDY OF A CONSTRUCTED TREATMENT WETLAND ON A COMMERCIAL CROCODILE FARM NEXT TO THE OKAVANGO DELTA, BOTSWANA By JC LE ROUX Dissertation submitted in fulfilment of the requirements for the degree Magister Scientiae in the Department of Zoology and Entomology Faculty of Natural and Agricultural Sciences University of the Free State 10 February 2020 SUPERVISOR: Prof LL Van As CO-SUPERVISOR: Dr C Jansen van Rensburg Decleration I, Tiaan le Roux, declare that the Master’s Degree research thesis that I hereby submit for the Master’s Degree qualification in Zoology at the University of the Free State is my independent work and that I have not previously submitted for a qualification at another institution of higher education. I, Tiaan le Roux, declare that I am aware that the copyright is vested in the University of the Free State. I, Tiaan le Roux, hereby declare that all royalties as regards to intellectual property that was developed during this course of and/or in connection with this study will accrue to the University of the Free State. Tiaan le Roux 10 February 2020 TABLE OF CONTENTS ACKNOWLEDGEMENTS ........................................................................................... i ABSTRACT ................................................................................................................. ii OPSOMMING ............................................................................................................ iv CHAPTER 1: INTRODUCTION .................................................................................. 1 CHAPTER 2: WETLANDS AND CONSTRUCTED TREATMENT WETLANDS (CTWs) ................................................................................................................................... 4 2.1: The history of CTWs ........................................................................................ 5 2.2: Components of CTWs ..................................................................................... 6 2.3: Wetland hydrology ........................................................................................... 6 2.4: Wetland substrates .......................................................................................... 7 2.5: Types of CTWs ................................................................................................ 8 2.5.1: Surface flow (SF) wetland ......................................................................... 8 2.5.2: Horizontal subsurface flow (HSSF) wetland .............................................. 9 2.5.3: Vertical subsurface flow (VSSF) wetland ................................................ 11 2.5.4: Hybrid systems ........................................................................................ 12 2.6: Functions and values of CTWs ...................................................................... 12 2.7: CTWs as a habitat ......................................................................................... 14 2.8: Microbial populations in CTWs ...................................................................... 14 2.9: Zooplankton in CTWs .................................................................................... 15 2.10: Wetland vegetation ...................................................................................... 15 2.11: Processes at work in CTWs ......................................................................... 16 2.12: How CTWs improve water quality ................................................................ 18 2.13: Seasonal operation of CTWs ....................................................................... 18 2.14: CTW limitations ............................................................................................ 20 CHAPTER 3: MATERIAL AND METHODS .............................................................. 21 3.1: Study area and field laboratory ...................................................................... 21 3.2: Water supply .................................................................................................. 26 3.3: Collection and identification of plankton material and other organisms ......... 26 3.4: Preparing specimens for the Scanning Electron Microscope (SEM) .............. 28 3.5: Water quality measurements ......................................................................... 29 3.6: Statistical analysis ......................................................................................... 29 CHAPTER 4: RESULTS OF KROKOVANGO CTW – TAXA COLLECTED AND WATER QUALITY .................................................................................................... 30 4.1: Phytoplankton ................................................................................................ 30 4.1.1: Phylum: Chlorophyta ............................................................................... 30 4.1.2: Phylum: Euglenophyta ............................................................................ 39 4.1.3: Phylum: Bacillariophyta ........................................................................... 42 4.1.4: Phylum: Cyanophyta ............................................................................... 48 4.2: Phytoplankton abundance .......................................................................... 53 4.2: Protozoa ........................................................................................................ 54 4.2.1: Phylum: Amoebozoa ............................................................................... 55 4.2.2: Phylum: Ciliophora .................................................................................. 57 4.3: Rotifera .......................................................................................................... 65 4.3.1: Class: Monogononta ............................................................................... 66 Order: Ploima Hudson and Gosse, 1886 ....................................................... 66 Family: Asplanchnidae Eckstein, 1883 ...................................................... 67 Family: Brachionidae Ehrenberg, 1838 ...................................................... 67 Family: Lecanidae Bartos, 1959 ................................................................. 71 Family Lepadellidae Harring, 1913 ............................................................ 73 4.3.2: Class: Digononta ..................................................................................... 75 Order: Bdelloidea Hudson, 1884 ................................................................... 76 Family Philodinidae Ehrenberg, 1838 ........................................................ 76 4.4: Cladocera ...................................................................................................... 79 4.4.1: Family Chydoridae Dybowski & Grochowski, 1894 .......................... 80 4.4.2: Family Daphniidae Strauss, 1820 .................................................... 80 4.4.3: Family Macrothricidae Norman & Brady, 1867 ................................. 85 4.5: Copepoda ...................................................................................................... 88 4.5.1: Order: Cyclopoida Burmeister, 1835 ................................................... 88 Family Cyclopidae Rafinesque, 1815 ......................................................... 89 4.6: Birds, plants and insects recorded from the Krokovango CTW ..................... 92 4.7: Results on zooplankton abundance ............................................................... 94 4.8: Physical water quality .................................................................................... 97 CHAPTER 5: DISCUSSION ..................................................................................... 98 5.1: CTWs and the Krokovango CTW ................................................................... 98 5.2: The importance of phytoplankton and microinvertebrates found in the Krokovango CTW ............................................................................................... 103 5.2.1: Phytoplankton of the Krokovango CTW ................................................ 103 5.2.2: Protozoa of the Krokovango CTW ......................................................... 106 5.2.3: Rotifera of the Krokovango CTW .......................................................... 108 5.2.4: Cladocera of the Krokovango CTW ....................................................... 111 5.2.5: Copepoda of the Krokovango CTW ...................................................... 112 5.3: Comparable studies on zooplankton composition and abundance .............. 114 5.4: Water quality of the Krokovango CTW and the Okavango Delta ................. 117 Concluding remarks ............................................................................................ 120 CHAPTER 6: REFERENCES ................................................................................. 121 APPENDIX 1: ZOOPLANKTON SPECIES COUNTS AND ABUNDANCE 2017 .... 166 APPENDIX 2: ZOOPLANKTON SPECIES COUNTS AND ABUNDANCE 2017 .... 167 ACKNOWLEDGEMENTS I would like to express my sincere appreciation to the following individuals and institutions for their contributions towards this study: My initial supervisor, Prof Jo Van As, for giving me the inspiration and opportunity to conduct this study and lending his guidance and knowledge throughout the time I was honored enough to get to know him. My current supervisor, Prof LL Van As, for her continuous support, guidance, assistance,