4. Electronic Theses and Dissertations (ETDs) - Faculties submissions

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    Using the South African Diatom Index (SADI) to determine the present ecological status of the Crocodile River, Kruger National Park
    (University of the Witwatersrand, Johannesburg, 2023-08) Thamae, Seeng; Snow, Gavin; Parrini, Francesca
    The Crocodile River in the Mpumalanga Province of South Africa is a river of great economic significance, while providing support to the surrounding aquatic and riparian ecosystems through ecological processes of chemical, hydrological, and geomorphological nature. This river forms part of the Inkomati River Basin, which serves as a transboundary basin shared between the Republic of South Africa, Mozambique and Eswatini. The importance of the effective management of transboundary water resources, from an African perspective, cannot be stressed enough due to the water-scarce nature of the Southern African region, particularly South Africa. Incorporating Integrated Water Resources Management (IWRM) and Strategic Adaptive Management approaches into the governance of water resources can aid in the protection of both the quality and quantity of the country’s freshwater reserve. Good governance of water resources is essential in the conservation of aquatic and riparian ecosystem biodiversity, as well as meeting the basic human needs reserve, which is essential to meet people’s daily drinking, food preparation and personal hygiene requirements. The Crocodile River is not immune to pollution of anthropogenic origin, such as urbanisation, mining, agriculture, and industrial by-products. The above mentioned constitutes some of the direct and indirect results of large-scale stresses that are exerted on a river system, mainly owing to environmental factors such as landscape, demographic, atmospheric and hydrologic changes. A few practical examples of these factors include changing population dynamics and resultant land-use requirements, accompanied by compromised riparian vegetations arising from the altered land-use. All this necessitates the regular monitoring of the quality of water in this river system. The outcome of regular river monitoring is essential to the protection of this resource through regulation and policy. The use of physico-chemical parameters to determine the health of the Crocodile River has assisted in identifying compromised aquatic and riparian ecosystems and ultimately recommending relevant mitigation strategies necessary in maintaining an acceptable standard of water quality. Incorporating biomonitoring techniques, wherein aquatic microorganisms are used to infer water quality, as a tool to assess the health of a river ecosystem has proven useful, mainly due to the sensitivity of periphyton assemblages (algae, cyanobacteria, diatoms) to changing river conditions, based on nutrients and physico-chemical parameters. The use of these organisms, in bio-assessments of aquatic ecosystems has been key to overall river health monitoring. This study highlights how diatoms, through their published ecological data, can contribute to the Resource Directed Measures method of determining the Present Ecological Status of a river, using the Crocodile (East) River as a case study. The current study was developed to assess the ecological category of the Crocodile River, along the southern boundary of the Kruger National Park. Four sampling sites were identified for the study, from which water samples were collected during September 2019, October 2019, and March 2020 sampling sessions. The basis of this was to investigate the changes in diatom communities and dominant microphytobenthos (MPB) groups (based on the tolerance to fluctuating environmental conditions amongst the various species) in response to the spatio-temporal changes in the quality and quantity of water at the four sites throughout the study period. These results were then compared to past studies to determine if there has been a change in river health over the past decade. Physico-chemical variables were measured in situ using a YSI Professional Plus (Pro Plus) multi-parameter instrument, which included temperature, pH, electrical conductivity, and dissolved oxygen. The benthic microalgal biomass of cyanobacteria, green algae and diatoms was quantified from the fluorescent signatures of the groups in situ using a bbe BenthoTorch. The bbe BenthoTorch is a hand-held apparatus that uses in situ quantification of chlorophyll-a fluorescence as an index of benthic algal biomass. The diatoms present in the samples were later prepared and isolated for microscopic identification and individual counts. The Relative Abundance (RA%) of dominant diatom species and the ecological category of each sampling site was determined using OMNIDIA software based South African Diatom Index (SADI). Ecological categories using the SADI range from A (good quality) to E (bad quality). Data analyses include the use of ordination plots (CCA and PCA) to evaluate the response of the dominant diatom species to changing environmental variables and the interspecific relationships between the diatom species in each assemblage, based on their ecological requirements. The study revealed that the ecological status of the Crocodile River when compared to previous studies had remained the same; C (moderate quality). This finding supports the use of the South African Diatom Index (SADI) in determining the Present Ecological State of the Crocodile River, in the Kruger National Park. There have been similar studies in other river systems within the Kruger National Park, wherein diatoms (specifically diatom-based index scores) were used to infer the water quality, at the time, in comparison to historic / benchmark water quality parameters. These studies were conducted in the Olifants, Letaba and the Sabie rivers of the park. The viability of these studies is motivated by benthic diatoms being particularly sensitive to changes in water quality, making them an ideal indicator of river health that is complementary to the current suite of biomonitoring tools. This method has immense potential in South Africa, provided that more focus is placed on diatoms and investment made in capacitating researchers and diatom taxonomists with the skills to perpetuate this vast field of study.
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    Modelling current and future distributions of Warburgia species at continental (Africa) and local (South Africa) scales Samista Kim
    (University of the Witwatersrand, Johannesburg, 2024) Rooplal, Samista Kim; Thompson, D.I.; Glennon, K.L.; Witkowski, E.T.F.
    Warburgia is a genus of trees and shrubs that is greatly valued in Africa for its use in traditional medicine. The genus contains four species, one of which has two subspecies: Warburgia elongata, W. salutaris, W. stuhlmannii, W. ugandensis subsp. longifolia and Wugandensis subsp. ugandensis. Individuals are harvested primarily for their bark, which contains pharmacological compounds that are used to treat various ailments. Due to the high demand, species within the genus are overharvested throughout their range and have consequently become threatened by extinction. Warburgia salutaris, the pepper-bark tree, is the only species of the genus that naturally occurs in South Africa. Like its congeners, Wasalutaris is heavily exploited for its bark and has been listed as IUCN Endangered in South Africa. This dissertation, therefore, assesses the distributions of Warburgia species in eastern and southern Africa to identify new, potentially suitable areas to increase population numbers to aid in the conservation of the genus. The aim of the first part of the study was to assess the eastern and southern African distributions of Warburgia species. Species distribution models (SDMs) were created for the four Warburgia species and two subspecies, and the geographic distributions and key environmental predictors were identified for each taxon. Environmental niche analyses were also performed to understand whether the two subspecies of W. ugandensis should be considered as a single species in accordance with the ecological species concept. The second part of the study aimed to assess how the current South African distribution of W. salutaris will be affected by future climate change. An SDM was produced to assess the current distribution of W. salutaris in South Africa and identify its key predictor climate variables. The SDM was then extrapolated into the future (2070) using two climate change scenarios, RCP 4.5 and RCP 8.5, which are greenhouse gas emission scenarios that predict future climates under a probable and extreme scenario, respectively. Ecological niche analyses were also used to assess the degree to which W. salutaris’ climatic niche will change in response to the two climate change scenarios. Results showed that the distributions of Warburgia species are restricted and primarily influenced by climatic variables that likely impact their seeds’ and seedlings’ sensitivity to water stress and desiccation. Ecological niche modelling results show that the climatic niches of W. ugandensis subsp. longifolia and W. ugandensis subsp. ugandensis are identical and should therefore be considered as a single species according to the ecological species concept. The South African distribution of W. salutaris is fragmented and restricted. The species’ current and future distribution is influenced by its sensitivity to frost and the fact that it produces seeds that are susceptible to drying out. SDMs predicted that the distribution of W. salutaris will shrink in eastern Limpopo and in parts of Mpumalanga, but increase in eastern KwaZulu-Natal by 2070 under both climate change scenarios. Overall, this species was predicted to contract from the Indian Ocean coastal belt and grassland biomes and expand into the savanna biome. This study has expanded our knowledge of the distributions and environmental drivers of Warburgia species. It was found that in general, Warburgia species have restricted ranges that are likely governed by their sensitivity to desiccation at the seed and seedling stages. Climate change is anticipated to negatively impact the populations of many plant species, especially those in Sub-Saharan Africa. While the environmental niche of W. salutaris will remain stable, its geographical distribution was predicted to expand further in the savanna biome along the eastern coast of South Africa in response to climate change. Results from this study support pursuing different conservation techniques, including propagating Warburgia populations around the Great Lakes of Africa and Mt. Kenya and in western Limpopo and eastern KwaZulu-Natal for W. salutaris only. This study therefore emphasizes the importance of using SDMs as a baseline to inform effective conservation efforts for important medicinal plant species