Initiating biological control for Nymphaea mexicana zuccarini (Nymphaeaceae) in South Africa
- Authors: Reid, Megan Kim
- Date: 2020
- Subjects: Nymphaea mexicana zuccarini -- Biological control -- South Africa , Nymphaeaceae -- Biological control -- South Africa , Invasive plants -- Biological control -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144510 , vital:38352
- Description: Nymphaea mexicana Zuccarini (Nymphaeaceae) is an aquatic plant originating from south-eastern USA that is becoming increasingly invasive in South Africa as other invasive aquatic plants are being managed successfully through biological control. Mechanical and chemical control of aquatic weeds is expensive, damaging to the environment, and only effective in the short term, so biological control is more desirable as a management strategy for N. mexicana. The biological control of invasive alien plants requires that agents are host specific so that non-target risks are mitigated. For success to be achieved, it is important to ensure that the genetic structure of invasive populations is clarified so that agents can be collected from populations in the native range that match genetically to populations in the invasive range. This is especially important in cases where the morphology of invasive alien plants does not reflect genetic differences between populations. A previous study of the genetic structure of the invasive populations of N. mexicana in South Africa suggests the presence of hybrid forms of the plant in South Africa, with only one of these populations matching with samples from the native range. However, the study only used samples from two sites in the native range using amplified fragment length polymorphisms (AFLPs), so it was necessary to conduct further genetic analyses using samples from more sites in the native range. Hence, the first aim of this study was to develop a better understanding of the genetic structure of N. mexicana populations in the native and invaded range. Genetic samples were collected from sites in the native range during field surveys for potential biological control agents, and inter-simple sequence repeats (ISSRs) were used to compare the genetic structure of invasive and native populations of N. mexicana in South Africa. The results from these analyses suggest that seven of the 14 investigated invasive populations of N. mexicana in South Africa are genetically similar to populations in the native range, while the remaining seven populations are likely to be hybrid forms of the plant. This knowledge will be useful to target populations for biological control and highlights the need for further genetic analyses to determine the parentage of these hybrids so that biological control efforts are more likely to be successful. The initiation of a biological control programme requires that a series of steps are taken in order to maximise the likelihood that this form of intervention will be successful. The first few steps include: identification of the target weed and its genetic structure; exploration in the native range for potential biological control agents; and prioritisation of these agents based on factors such as climatic and genetic compatibility, feeding damage, abundance, and likely host range. Hence, the second aim of this study was to conduct surveys for potential biological control agents in the native range of N. mexicana, and to prioritise these agents. Field surveys were conducted between August and October in 2018 at 17 sites in Florida, Louisiana, and Texas, USA. Sites were selected based on climatic similarity of native sites compared to invasive sites by use of MaxEnt modelling. Native N. mexicana plants were searched for natural enemies, and these were prioritised based on feeding damage, abundance, incidence, and observations of field host range. Two species were prioritised: Bagous americanus LeConte (Coleoptera: Curculionidae) and Megamelus toddi Beamer (Hemiptera: Delphacidae). These species will be imported into quarantine facilities at Rhodes University for host specificity tests to be conducted. Understanding the factors that contribute to the successful establishment of biological control agents is important to improve the efficiency and reduce the costs incurred during the initiation of biological control programmes. Acquiring knowledge of the factors that predict the efficacy of biological control agents is similarly important, and these factors are discussed in the last chapter of this study. The challenges of the biological control of hybrids are also considered, and recommendations are made for the control of N. mexicana and other plants in South Africa.
- Full Text:
- Date Issued: 2020
- Authors: Reid, Megan Kim
- Date: 2020
- Subjects: Nymphaea mexicana zuccarini -- Biological control -- South Africa , Nymphaeaceae -- Biological control -- South Africa , Invasive plants -- Biological control -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144510 , vital:38352
- Description: Nymphaea mexicana Zuccarini (Nymphaeaceae) is an aquatic plant originating from south-eastern USA that is becoming increasingly invasive in South Africa as other invasive aquatic plants are being managed successfully through biological control. Mechanical and chemical control of aquatic weeds is expensive, damaging to the environment, and only effective in the short term, so biological control is more desirable as a management strategy for N. mexicana. The biological control of invasive alien plants requires that agents are host specific so that non-target risks are mitigated. For success to be achieved, it is important to ensure that the genetic structure of invasive populations is clarified so that agents can be collected from populations in the native range that match genetically to populations in the invasive range. This is especially important in cases where the morphology of invasive alien plants does not reflect genetic differences between populations. A previous study of the genetic structure of the invasive populations of N. mexicana in South Africa suggests the presence of hybrid forms of the plant in South Africa, with only one of these populations matching with samples from the native range. However, the study only used samples from two sites in the native range using amplified fragment length polymorphisms (AFLPs), so it was necessary to conduct further genetic analyses using samples from more sites in the native range. Hence, the first aim of this study was to develop a better understanding of the genetic structure of N. mexicana populations in the native and invaded range. Genetic samples were collected from sites in the native range during field surveys for potential biological control agents, and inter-simple sequence repeats (ISSRs) were used to compare the genetic structure of invasive and native populations of N. mexicana in South Africa. The results from these analyses suggest that seven of the 14 investigated invasive populations of N. mexicana in South Africa are genetically similar to populations in the native range, while the remaining seven populations are likely to be hybrid forms of the plant. This knowledge will be useful to target populations for biological control and highlights the need for further genetic analyses to determine the parentage of these hybrids so that biological control efforts are more likely to be successful. The initiation of a biological control programme requires that a series of steps are taken in order to maximise the likelihood that this form of intervention will be successful. The first few steps include: identification of the target weed and its genetic structure; exploration in the native range for potential biological control agents; and prioritisation of these agents based on factors such as climatic and genetic compatibility, feeding damage, abundance, and likely host range. Hence, the second aim of this study was to conduct surveys for potential biological control agents in the native range of N. mexicana, and to prioritise these agents. Field surveys were conducted between August and October in 2018 at 17 sites in Florida, Louisiana, and Texas, USA. Sites were selected based on climatic similarity of native sites compared to invasive sites by use of MaxEnt modelling. Native N. mexicana plants were searched for natural enemies, and these were prioritised based on feeding damage, abundance, incidence, and observations of field host range. Two species were prioritised: Bagous americanus LeConte (Coleoptera: Curculionidae) and Megamelus toddi Beamer (Hemiptera: Delphacidae). These species will be imported into quarantine facilities at Rhodes University for host specificity tests to be conducted. Understanding the factors that contribute to the successful establishment of biological control agents is important to improve the efficiency and reduce the costs incurred during the initiation of biological control programmes. Acquiring knowledge of the factors that predict the efficacy of biological control agents is similarly important, and these factors are discussed in the last chapter of this study. The challenges of the biological control of hybrids are also considered, and recommendations are made for the control of N. mexicana and other plants in South Africa.
- Full Text:
- Date Issued: 2020
Investigating cell culture models for improved understanding of adipose tissue and co-morbidities in vitro
- Authors: Stoffels, Mihlali
- Date: 2020
- Subjects: Uncatalogued
- Language: English
- Type: thesis , text , Masters , MSc
- Identifier: http://hdl.handle.net/10962/164674 , vital:41154
- Description: Thesis (MSc)--Rhodes University, Faculty of Science, Biotechnology Innovation Centre, 2020
- Full Text:
- Date Issued: 2020
- Authors: Stoffels, Mihlali
- Date: 2020
- Subjects: Uncatalogued
- Language: English
- Type: thesis , text , Masters , MSc
- Identifier: http://hdl.handle.net/10962/164674 , vital:41154
- Description: Thesis (MSc)--Rhodes University, Faculty of Science, Biotechnology Innovation Centre, 2020
- Full Text:
- Date Issued: 2020
Investigating the relationship between Heat Shock Proteins and HIV Transactivator of Transcription
- Authors: Flax, Lili Marie
- Date: 2020
- Subjects: Uncatalogued
- Language: English
- Type: thesis , text , Masters , MSc
- Identifier: http://hdl.handle.net/10962/163307 , vital:41027
- Description: Thesis (MSc)--Rhodes University, Faculty of Science, Biochemistry and Microbiology, 2020.
- Full Text:
- Date Issued: 2020
- Authors: Flax, Lili Marie
- Date: 2020
- Subjects: Uncatalogued
- Language: English
- Type: thesis , text , Masters , MSc
- Identifier: http://hdl.handle.net/10962/163307 , vital:41027
- Description: Thesis (MSc)--Rhodes University, Faculty of Science, Biochemistry and Microbiology, 2020.
- Full Text:
- Date Issued: 2020
Investigation into the influence of an alien plant species on the soil microbiota of the sub-Antarctic, Marion Island
- Authors: Pienaar, Robert Daniel
- Date: 2020
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/124039 , vital:35531
- Description: Embargo applied. Embargo period to expire in April of 2021.
- Full Text:
- Date Issued: 2020
- Authors: Pienaar, Robert Daniel
- Date: 2020
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/124039 , vital:35531
- Description: Embargo applied. Embargo period to expire in April of 2021.
- Full Text:
- Date Issued: 2020
Livelihood implications of a possible Ramsar declaration of the Swartkops estuary, Eastern Cape, South Africa
- Authors: Vembo, Glen Muchengeti
- Date: 2020
- Subjects: Uncatalogued
- Language: English
- Type: thesis , text , Masters , MSc
- Identifier: http://hdl.handle.net/10962/164715 , vital:41157
- Description: Thesis (MSc)--Rhodes University, Faculty of Science, Environmental Science, 2020
- Full Text:
- Date Issued: 2020
- Authors: Vembo, Glen Muchengeti
- Date: 2020
- Subjects: Uncatalogued
- Language: English
- Type: thesis , text , Masters , MSc
- Identifier: http://hdl.handle.net/10962/164715 , vital:41157
- Description: Thesis (MSc)--Rhodes University, Faculty of Science, Environmental Science, 2020
- Full Text:
- Date Issued: 2020
Managing the invasive aquatic plant Sagittaria platyphylla (Engelm.) J.G. Sm(Alismataceae): problems and prospects
- Ndlovu, Mpilonhle Sinothando
- Authors: Ndlovu, Mpilonhle Sinothando
- Date: 2020
- Subjects: Aquatic weeds -- Biological control -- South Africa , Sagittaria latifolia -- Biological control -- South Africa , Noxious weeds -- Biological control -- South Africa , Invasive plants -- Biological control -- South Africa , Listronotus , Insects as biological pest control agents
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167121 , vital:41439
- Description: Sagittaria platyphylla (Engelm.) J.G.Sm. (Alismataceae), commonly known as Delta arrowhead, is an invasive aquatic macrophyte native to southern United States of America (USA) that has become a serious weed in freshwater systems in South Africa, New Zealand, Australia, and recently China. In South Africa, the plant was first detected in Krantzkloof Nature Reserve, KwaZulu-Natal Province in 2008, and due to its known impact in other countries, it was listed as a Category 1a invader species under the National Environmental Management: Biodiversity Act 2004 (NEM: BA). This listing required mechanical and chemical control methods to be implemented by the South African National Biodiversity Institute’s (SANBI), Invasive Species Programme (ISP), with the aim of eradicating the weed. Despite the eradication efforts, by 2016, the weed was recognized as one of the country’s top 10 worst and fastest spreading invasive alien plants. Since its introduction in 2008, the plant has spread both within and between sites in South Africa, increasing from one site in 2008 to 72 sites by 2019. Once introduced into lotic systems, the plant spread rapidly downstream, in some cases up to 120km within six years, with an average of 10 km per year. Extirpation over the last ten years was only possible at a limited number of sites. Under the current management approach, the invasion is foreseen to spread to new sites within a 5 km radius of the current populations. Due to the failure of conventional control mechanisms, biological control is currently being considered as a potential control option. Four potential biological control agents are under investigation, but none have been released. Amongst them is the fruit and flower feeding weevil Listronotus appendiculatus Bohm. (Coleoptera: Curculionidae) which showed most potential as a suitable biological control agent. This study demonstrated that L. appendiculatus herbivory negatively influenced the overall fitness of S. platyphylla by reducing the plant’s growth rate and above ground biomass. Listronotus appendiculatus herbivory also reduced the plant’s size and the potential to kill adult plants. Most importantly, L. appendiculatus larval feeding damage significantly reduce viable-germinating seeds, the weed’s primary dispersal mechanism. Therefore, a biological control programme is advised to be integrated within the current management plan.
- Full Text:
- Date Issued: 2020
- Authors: Ndlovu, Mpilonhle Sinothando
- Date: 2020
- Subjects: Aquatic weeds -- Biological control -- South Africa , Sagittaria latifolia -- Biological control -- South Africa , Noxious weeds -- Biological control -- South Africa , Invasive plants -- Biological control -- South Africa , Listronotus , Insects as biological pest control agents
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167121 , vital:41439
- Description: Sagittaria platyphylla (Engelm.) J.G.Sm. (Alismataceae), commonly known as Delta arrowhead, is an invasive aquatic macrophyte native to southern United States of America (USA) that has become a serious weed in freshwater systems in South Africa, New Zealand, Australia, and recently China. In South Africa, the plant was first detected in Krantzkloof Nature Reserve, KwaZulu-Natal Province in 2008, and due to its known impact in other countries, it was listed as a Category 1a invader species under the National Environmental Management: Biodiversity Act 2004 (NEM: BA). This listing required mechanical and chemical control methods to be implemented by the South African National Biodiversity Institute’s (SANBI), Invasive Species Programme (ISP), with the aim of eradicating the weed. Despite the eradication efforts, by 2016, the weed was recognized as one of the country’s top 10 worst and fastest spreading invasive alien plants. Since its introduction in 2008, the plant has spread both within and between sites in South Africa, increasing from one site in 2008 to 72 sites by 2019. Once introduced into lotic systems, the plant spread rapidly downstream, in some cases up to 120km within six years, with an average of 10 km per year. Extirpation over the last ten years was only possible at a limited number of sites. Under the current management approach, the invasion is foreseen to spread to new sites within a 5 km radius of the current populations. Due to the failure of conventional control mechanisms, biological control is currently being considered as a potential control option. Four potential biological control agents are under investigation, but none have been released. Amongst them is the fruit and flower feeding weevil Listronotus appendiculatus Bohm. (Coleoptera: Curculionidae) which showed most potential as a suitable biological control agent. This study demonstrated that L. appendiculatus herbivory negatively influenced the overall fitness of S. platyphylla by reducing the plant’s growth rate and above ground biomass. Listronotus appendiculatus herbivory also reduced the plant’s size and the potential to kill adult plants. Most importantly, L. appendiculatus larval feeding damage significantly reduce viable-germinating seeds, the weed’s primary dispersal mechanism. Therefore, a biological control programme is advised to be integrated within the current management plan.
- Full Text:
- Date Issued: 2020
Metallophthalocyanines linked to metal nanoparticles and folic acid for use in photodynamic therapy of cancer and photoinactivation of bacterial microorganisms.
- Authors: Matlou, Gauta Gold
- Date: 2020
- Subjects: Cancer -- Photochemotherapy , Nanoparticles , Phthalocyanines , Anti-infective agents -- Therapeutic use , Photochemotherapy , Photochemistry
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/166540 , vital:41377
- Description: This thesis presents on the synthesis and characterization of novel asymmetric and symmetrical metallophthalocyanines (MPcs) substituted with carboxylic acid functional groups and centrally metallated with zinc and indium. The MPcs are further covalently linked to cysteine capped silver nanoparticles (cys-AgNPs), amino functionalized magnetic nanoparticles (AMNPs) and folic acid (FA) through an amide bond between the carboxylic group of MPcs and the amino group of FA, cys-AgNPs or AMNPs. The covalent linkage of MPcs to FA improved the water solubility of MPcs and allowed for singlet oxygen quantum yield determination in water. Asymmetric MPcs and their conjugates were found to have improved photochemical and photophysical properties compared to symmetrical MPcs and their conjugates. The heavy atom effect of AMNPs and AgNPs improved the triplet and singlet oxygen quantum yields of MPcs. MPcs and their conjugates (MPc-FA, MPc-AMNPs, MPc-AgNPs) were found to have lower in vitro dark cytotoxicity and higher photodynamic therapy (PDT) activity on MCF-7 breast cancer cells. The water soluble MPc-FA had better PDT activity when compared to MPc-AMNPs due to the active targeting of folic acid-folate binding on cancer cell surface. MPcs and MPc-AgNPs conjugates also showed excellent in vitro cytotoxicity on S. aureus under light irradiation compared to dark cytotoxicity. The photosensitizing properties of MPcs and their conjugates are demonstrated for the first time in this thesis, both on breast cancer cells (MCF-7) through photodynamic therapy and on microorganisms (S. aureus) through photodynamic antimicrobial chemotherapy.
- Full Text:
- Date Issued: 2020
- Authors: Matlou, Gauta Gold
- Date: 2020
- Subjects: Cancer -- Photochemotherapy , Nanoparticles , Phthalocyanines , Anti-infective agents -- Therapeutic use , Photochemotherapy , Photochemistry
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/166540 , vital:41377
- Description: This thesis presents on the synthesis and characterization of novel asymmetric and symmetrical metallophthalocyanines (MPcs) substituted with carboxylic acid functional groups and centrally metallated with zinc and indium. The MPcs are further covalently linked to cysteine capped silver nanoparticles (cys-AgNPs), amino functionalized magnetic nanoparticles (AMNPs) and folic acid (FA) through an amide bond between the carboxylic group of MPcs and the amino group of FA, cys-AgNPs or AMNPs. The covalent linkage of MPcs to FA improved the water solubility of MPcs and allowed for singlet oxygen quantum yield determination in water. Asymmetric MPcs and their conjugates were found to have improved photochemical and photophysical properties compared to symmetrical MPcs and their conjugates. The heavy atom effect of AMNPs and AgNPs improved the triplet and singlet oxygen quantum yields of MPcs. MPcs and their conjugates (MPc-FA, MPc-AMNPs, MPc-AgNPs) were found to have lower in vitro dark cytotoxicity and higher photodynamic therapy (PDT) activity on MCF-7 breast cancer cells. The water soluble MPc-FA had better PDT activity when compared to MPc-AMNPs due to the active targeting of folic acid-folate binding on cancer cell surface. MPcs and MPc-AgNPs conjugates also showed excellent in vitro cytotoxicity on S. aureus under light irradiation compared to dark cytotoxicity. The photosensitizing properties of MPcs and their conjugates are demonstrated for the first time in this thesis, both on breast cancer cells (MCF-7) through photodynamic therapy and on microorganisms (S. aureus) through photodynamic antimicrobial chemotherapy.
- Full Text:
- Date Issued: 2020
Mineralogy, geochemistry and origin of the Neoproterozoic Xaudum iron-formation in Botswana
- Authors: Ntantiso, Mawande
- Date: 2020
- Subjects: Xaudum iron-formation , Iron ores -- Botswana , Formations (Geology) -- Botswana , Mineralogy -- Botswana , Paleoclimatology -- Proterozoic
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167211 , vital:41447
- Description: Banded iron-formations (BIF) formed in three different geological periods in the Earth’s history, namely the Archean, Paleoproterozoic and Neoproterozoic. Each of these periods has a corresponding index BIF type attributed to them. The oldest is the Archean Algoma-type BIF which is typically dominated by smaller-volume BIF deposits associated with volcanic rocks and greenstone belts. The next is the volumetrically far more abundant Superior-type BIF of the Paleoproterozoic lacking any obvious volcanic relation. The youngest BIFs were deposited after a hiatus of a billion years in the Neoproterozoic and are believed to be genetically linked to Marinoan ice-age. The global re-introduction and distribution of BIF in the Neoproterozoic highlights a shift in the Earth’s tectonics, climate, biosphere and ocean chemistry from the older Archean and Paleoproterozoic counterparts. Various models have been postulated by researchers in attempts to explain how Neoproterozoic iron-formations formed. In all the available models, the Snowball Earth Hypothesis initially proposed by Kirshvink (1992) is an overarching concept. In this study, four cores from the Neoproterozoic Xaudum iron-formation (XIF) in Ngamiland, northwest of Botswana, were sampled and analysed following a partnership between Postgraduate Research in Iron and Manganese Ore Resources (PRIMOR) and Tsodilo Resources Ltd. The study sets out to explore the mineralogy and chemistry of XIF in order to determine its origin, constrain the redox conditions in the paleo-basin, assess it in the context of other Neoproterozoic iron-formations and older Archean and Paleoproterozoic iron-formations, and inform metallurgical processing. The mineralogy of XIF consists of magnetite, quartz, amphibole, garnet, biotite and chlorite in decreasing abundance. This mineral assemblage is characteristic of medium grade metamorphosed iron-formations. Algoma and Superior-type BIFs which experienced late-diagenetic and very low-grade metamorphism have a complex mineral assemblage consisting of hematite, magnetite, quartz, and several carbonate (dolomite-ankerite series and siderite) and silicate phases (greenalite, riebeckite and stilpnomelane). The geochemical results show that XIF has higher Mn3O4 and Al2O3 average contents when compared to Algoma and Superior type BIF. The detrital components in XIF correlate with High Field Strength Elements (HFSE) suggesting increased delivery of siliciclastic material during deposition. This trend is comparable to other NIF deposits suggesting a global high input of siliciclastic material into Neoproterozoic paleodepositional environments. This trend is different from Archean and Paleoproterozoic BIF deposits which are close to pure chemical sediments lacking measurable detrital contributions. In the XIF, bulk-rock Mn3O4 and Al2O3 in drillcore SW have higher averages of 2.4 and 2.6 wt. % respectively, compared to the other three cores. The Mn3O4 shows a positive statistical relationship with Co, suggesting that Neoproterozoic oceans and atmosphere were possibly more oxic than in the Archean and Paleoproterozoic. The Mn3O4 shows an antithetic relationship with Fe2O3 suggesting that the paleobasin was chemically heterogeneous in terms of redox conditions, with Fe2O3 depositing presumably in deeper parts removed from a detrital source, and Mn3O4 depositing possibly more proximal to a paleo-shoreline in a shallower setting where there was higher delivery of siliciclastic material from the continent due to correspondingly higher Al2O3 and TiO2 contents. The REE patterns of XIF show positive-sloping trends of depletion in LREE and enrichment in HREE which resemble those of seawater. However, the REE slope becomes a lot flatter and resembles closer the signature of PAAS and adjacent diamictite facies, which agrees with the idea of high siliciclastic input in the paleobasin comparable to other NIF. XIF also appears to lack clear Ce or Eu anomalies. The lack of the former points to the oceans possibly not being oxic enough to drive the fractionation of Ce into Mn oxides like in the modern oceans, or that the Ce behaviour is obscured by the high siliciclastic input in XIF. Similarly, the lack of positive Eu anomaly shows a weak to absent hydrothermal signal into to modern shallow seawater where Fe and Si were sourced, or detritally derived REE contamination. Extensive weathering under hot and humid climate during glacial retreat is shown by the low K2O/Al2O3 ratios and high CIA values ranging from 80-99. Re-glaciation signifies the return of cold and arid and it is represented by high K2O/Al2O3 ratios and low CIA values ranging from 64-78. The previous genetic models of NIF by Klein (1993), Baldwin et al. (2012) and Lechte and Wallace (2015) provide an essential foundation for the development of a XIF genetic model. The genetic model of XIF proposes deposition on an open continental shelf characterized by a steady influx of detrital material. The seawater has been anoxic since the Paleoproterozoic and further induced by basin stagnation due to the ice covering the basin. Two overlapping oxidative stages are assumed for the precipitation of Fe and Mn across lateral redox gradients in the paleobasin. The exact oxidative pathways and mechanisms for the above processes remains unconstrained.
- Full Text:
- Date Issued: 2020
- Authors: Ntantiso, Mawande
- Date: 2020
- Subjects: Xaudum iron-formation , Iron ores -- Botswana , Formations (Geology) -- Botswana , Mineralogy -- Botswana , Paleoclimatology -- Proterozoic
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167211 , vital:41447
- Description: Banded iron-formations (BIF) formed in three different geological periods in the Earth’s history, namely the Archean, Paleoproterozoic and Neoproterozoic. Each of these periods has a corresponding index BIF type attributed to them. The oldest is the Archean Algoma-type BIF which is typically dominated by smaller-volume BIF deposits associated with volcanic rocks and greenstone belts. The next is the volumetrically far more abundant Superior-type BIF of the Paleoproterozoic lacking any obvious volcanic relation. The youngest BIFs were deposited after a hiatus of a billion years in the Neoproterozoic and are believed to be genetically linked to Marinoan ice-age. The global re-introduction and distribution of BIF in the Neoproterozoic highlights a shift in the Earth’s tectonics, climate, biosphere and ocean chemistry from the older Archean and Paleoproterozoic counterparts. Various models have been postulated by researchers in attempts to explain how Neoproterozoic iron-formations formed. In all the available models, the Snowball Earth Hypothesis initially proposed by Kirshvink (1992) is an overarching concept. In this study, four cores from the Neoproterozoic Xaudum iron-formation (XIF) in Ngamiland, northwest of Botswana, were sampled and analysed following a partnership between Postgraduate Research in Iron and Manganese Ore Resources (PRIMOR) and Tsodilo Resources Ltd. The study sets out to explore the mineralogy and chemistry of XIF in order to determine its origin, constrain the redox conditions in the paleo-basin, assess it in the context of other Neoproterozoic iron-formations and older Archean and Paleoproterozoic iron-formations, and inform metallurgical processing. The mineralogy of XIF consists of magnetite, quartz, amphibole, garnet, biotite and chlorite in decreasing abundance. This mineral assemblage is characteristic of medium grade metamorphosed iron-formations. Algoma and Superior-type BIFs which experienced late-diagenetic and very low-grade metamorphism have a complex mineral assemblage consisting of hematite, magnetite, quartz, and several carbonate (dolomite-ankerite series and siderite) and silicate phases (greenalite, riebeckite and stilpnomelane). The geochemical results show that XIF has higher Mn3O4 and Al2O3 average contents when compared to Algoma and Superior type BIF. The detrital components in XIF correlate with High Field Strength Elements (HFSE) suggesting increased delivery of siliciclastic material during deposition. This trend is comparable to other NIF deposits suggesting a global high input of siliciclastic material into Neoproterozoic paleodepositional environments. This trend is different from Archean and Paleoproterozoic BIF deposits which are close to pure chemical sediments lacking measurable detrital contributions. In the XIF, bulk-rock Mn3O4 and Al2O3 in drillcore SW have higher averages of 2.4 and 2.6 wt. % respectively, compared to the other three cores. The Mn3O4 shows a positive statistical relationship with Co, suggesting that Neoproterozoic oceans and atmosphere were possibly more oxic than in the Archean and Paleoproterozoic. The Mn3O4 shows an antithetic relationship with Fe2O3 suggesting that the paleobasin was chemically heterogeneous in terms of redox conditions, with Fe2O3 depositing presumably in deeper parts removed from a detrital source, and Mn3O4 depositing possibly more proximal to a paleo-shoreline in a shallower setting where there was higher delivery of siliciclastic material from the continent due to correspondingly higher Al2O3 and TiO2 contents. The REE patterns of XIF show positive-sloping trends of depletion in LREE and enrichment in HREE which resemble those of seawater. However, the REE slope becomes a lot flatter and resembles closer the signature of PAAS and adjacent diamictite facies, which agrees with the idea of high siliciclastic input in the paleobasin comparable to other NIF. XIF also appears to lack clear Ce or Eu anomalies. The lack of the former points to the oceans possibly not being oxic enough to drive the fractionation of Ce into Mn oxides like in the modern oceans, or that the Ce behaviour is obscured by the high siliciclastic input in XIF. Similarly, the lack of positive Eu anomaly shows a weak to absent hydrothermal signal into to modern shallow seawater where Fe and Si were sourced, or detritally derived REE contamination. Extensive weathering under hot and humid climate during glacial retreat is shown by the low K2O/Al2O3 ratios and high CIA values ranging from 80-99. Re-glaciation signifies the return of cold and arid and it is represented by high K2O/Al2O3 ratios and low CIA values ranging from 64-78. The previous genetic models of NIF by Klein (1993), Baldwin et al. (2012) and Lechte and Wallace (2015) provide an essential foundation for the development of a XIF genetic model. The genetic model of XIF proposes deposition on an open continental shelf characterized by a steady influx of detrital material. The seawater has been anoxic since the Paleoproterozoic and further induced by basin stagnation due to the ice covering the basin. Two overlapping oxidative stages are assumed for the precipitation of Fe and Mn across lateral redox gradients in the paleobasin. The exact oxidative pathways and mechanisms for the above processes remains unconstrained.
- Full Text:
- Date Issued: 2020
Molecular and morphological approaches reveal hidden diversity in the genus hippopotamyrus pappenheim, 1906 (teleostei: mormyridae) in southern Africa
- Authors: Mutizwa, Tadiwa, Isaac
- Date: 2020
- Subjects: Uncatalogued
- Language: English
- Type: thesis , text , Masters , MSc
- Identifier: http://hdl.handle.net/10962/164546 , vital:41128
- Description: Thesis (MSc)--Rhodes University, Faculty of Science, Department of Icthyology and Fisheries Science, 2020
- Full Text:
- Date Issued: 2020
- Authors: Mutizwa, Tadiwa, Isaac
- Date: 2020
- Subjects: Uncatalogued
- Language: English
- Type: thesis , text , Masters , MSc
- Identifier: http://hdl.handle.net/10962/164546 , vital:41128
- Description: Thesis (MSc)--Rhodes University, Faculty of Science, Department of Icthyology and Fisheries Science, 2020
- Full Text:
- Date Issued: 2020
Molecular simulations of potential agents and targets of Alzheimer’s disease
- Authors: Carlisle, Tanya
- Date: 2020
- Subjects: Alzheimer's disease -- Treatment , Alzheimer's disease -- Molecular aspects , Amyloid beta-protein precurs , Amyloid beta-protein
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/140025 , vital:37825
- Description: The World Alzheimer Report statedin 2016 that approximately 46.8 million people were living with dementia and this figure is expected to triple by 2050. Alzheimer’s Disease was discovered to be a precursor to dementia in 1976 and since then efforts to understand Alzheimer’s have been prioritized. To date, there are very few effective forms of treatment for Alzheimer’s, many are known to offer only mild calming of the symptoms and have side effects such as diarrhea, nausea, loss of appetite and sleep disturbances. This has been due to lack of understanding on how Alzheimer’s is caused. With the two main hallmarks of the disease now being more understood it has opened the doorway into the discovery of new treatments for this disease. This study focuses on the hallmark involving the aggregation of the β-amyloid protein to form plaques surrounding the neurons of the brain. Copper, Zinc and Iron have also been found in high concentrations in and surrounding these plaques. This study focused on the screening of the South African Natural Compound database (SANCDB) to discover hits that have potential destabilizing action against the Beta-amyloid aggregate. If one of these compounds could prove to have destabilizing action on the aggregate it could open the doorway to new potential forms of treatment. Over 700 SANCDB compounds were docked, and the top hits were taken to molecular dynamics to further study the interactions of the compounds and the aggregate. However, the hits identified had strong binding to the aggregate causing it to become stable instead of the desired effect of destabilizing the structure. This information, however, does not rule out the possibility of these compounds preventing the formation of the aggregates. Further, interactions of copper with β-amyloid and copper were determined by solubilizing the aggregate and introducing copper ions in a dynamics simulation. Possible interactions between copper and the methionine residues were visualised.
- Full Text:
- Date Issued: 2020
- Authors: Carlisle, Tanya
- Date: 2020
- Subjects: Alzheimer's disease -- Treatment , Alzheimer's disease -- Molecular aspects , Amyloid beta-protein precurs , Amyloid beta-protein
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/140025 , vital:37825
- Description: The World Alzheimer Report statedin 2016 that approximately 46.8 million people were living with dementia and this figure is expected to triple by 2050. Alzheimer’s Disease was discovered to be a precursor to dementia in 1976 and since then efforts to understand Alzheimer’s have been prioritized. To date, there are very few effective forms of treatment for Alzheimer’s, many are known to offer only mild calming of the symptoms and have side effects such as diarrhea, nausea, loss of appetite and sleep disturbances. This has been due to lack of understanding on how Alzheimer’s is caused. With the two main hallmarks of the disease now being more understood it has opened the doorway into the discovery of new treatments for this disease. This study focuses on the hallmark involving the aggregation of the β-amyloid protein to form plaques surrounding the neurons of the brain. Copper, Zinc and Iron have also been found in high concentrations in and surrounding these plaques. This study focused on the screening of the South African Natural Compound database (SANCDB) to discover hits that have potential destabilizing action against the Beta-amyloid aggregate. If one of these compounds could prove to have destabilizing action on the aggregate it could open the doorway to new potential forms of treatment. Over 700 SANCDB compounds were docked, and the top hits were taken to molecular dynamics to further study the interactions of the compounds and the aggregate. However, the hits identified had strong binding to the aggregate causing it to become stable instead of the desired effect of destabilizing the structure. This information, however, does not rule out the possibility of these compounds preventing the formation of the aggregates. Further, interactions of copper with β-amyloid and copper were determined by solubilizing the aggregate and introducing copper ions in a dynamics simulation. Possible interactions between copper and the methionine residues were visualised.
- Full Text:
- Date Issued: 2020
Molecular simulations of potential agents and targets of Alzheimer’s disease
- Authors: Joli, Luxolo
- Date: 2020
- Subjects: Alzheimer's disease -- Chemotherapy , Alzheimer's disease -- Treatment , Ligands (Biochemistry) , Proteins -- Chemistry , Molecular dynamics -- Simulation methods
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/146411 , vital:38523
- Description: Alzheimer's Disease (AD) is a neurodegenerative brain disorder that was first discovered in 1901 by Dr Aloïs Alzheimer and was later reported publicly in 1906. The German doctor had a 51-yearold woman patient called Auguste Deter, who was suffering from a rare brain disorder with early signs of memory loss and cognition. Alzheimer's Disease is the most common type of dementia that affects people with the age of 65 years and older. There is no single known cause of Alzheimer’s disease however, amyloid β-peptide (Aβ1–40/42) was found to be at the centre of AD pathogenesis and this connection was referred as “amyloid hypothesis”. It is suspected that an accumulation of amyloid β-peptide is a major contributor to neuronal dysfunction and degeneration. Alzheimer’s disease is complex and therefore, currently there is no medication available that treats the disease. However, there are approaches that focus on helping people maintain mental function, manage behavioral symptoms, and slow down the symptoms of disease. According to South Africa’s 2011 census, there are approximately 2.2 million people in South Africa with some form of dementia and therefore there is a need to find a treatment for the disease. This study aims to find agents and targets of Alzheimer’s Disease by using different computational techniques such as molecular modelling. The study will use compounds from the South African Compounds Database (SANCDB) and the following therapeutic targets α-, β- and γ-secretase, acetylcholinesterase, tau protein and neprilysin. A successful High-throughput Virtual Screening (HTVS) study to determine lead compounds was performed using a computational program called KNIME. Molecular docking was achieved with GLIDE as it allows for exhaustive ligand flexibility. The docking calculations were carried out using the high level of precision XP (extra precision) for enhanced docking accuracy. The binding affinities (docking scores) for the best bound ligands obtained from docking were in the order of -5 kcal/mol or less. The ligandSANC00370 was the best binding ligand against the protein 1J1C_B and had the best binding energy of -13.94 kcal/mol compared to others. The receptor-ligand complexes were analyzed using the interaction diagrams obtained from the Discovery Studio Visualizer and Maestro programs. Molecular Dynamics simulations were performed on the complexes obtained from docking to help in optimizing their interactions. The simulations were performed using the Desmond tool with the OPLS3 force field. 100 ns simulations were performed for six systems with the best docking score results epresenting each of the therapeutic targets and for the other complex systems, 50 ns simulations were performed. The Desmond simulations were analyzed using the Simulations Interaction Diagrams such as PL-RMSD, L-RMSF, P-RMSF, L-Torsions, P-SSE, LP-Contacts and L-Properties. Maestro was used to visualize the stability of the ligands in the active site during the simulation. All 13 Desmond simulations were successful however, there were 9 simulations which produced satisfactory results while the others were nsatisfactory. Based on the molecular docking and Molecular Dynamics results of this study, 9 potential targets and 6 potential agents were obtained successfully and can be studied further as therapeutics for Alzheimer’s Disease.
- Full Text:
- Date Issued: 2020
- Authors: Joli, Luxolo
- Date: 2020
- Subjects: Alzheimer's disease -- Chemotherapy , Alzheimer's disease -- Treatment , Ligands (Biochemistry) , Proteins -- Chemistry , Molecular dynamics -- Simulation methods
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/146411 , vital:38523
- Description: Alzheimer's Disease (AD) is a neurodegenerative brain disorder that was first discovered in 1901 by Dr Aloïs Alzheimer and was later reported publicly in 1906. The German doctor had a 51-yearold woman patient called Auguste Deter, who was suffering from a rare brain disorder with early signs of memory loss and cognition. Alzheimer's Disease is the most common type of dementia that affects people with the age of 65 years and older. There is no single known cause of Alzheimer’s disease however, amyloid β-peptide (Aβ1–40/42) was found to be at the centre of AD pathogenesis and this connection was referred as “amyloid hypothesis”. It is suspected that an accumulation of amyloid β-peptide is a major contributor to neuronal dysfunction and degeneration. Alzheimer’s disease is complex and therefore, currently there is no medication available that treats the disease. However, there are approaches that focus on helping people maintain mental function, manage behavioral symptoms, and slow down the symptoms of disease. According to South Africa’s 2011 census, there are approximately 2.2 million people in South Africa with some form of dementia and therefore there is a need to find a treatment for the disease. This study aims to find agents and targets of Alzheimer’s Disease by using different computational techniques such as molecular modelling. The study will use compounds from the South African Compounds Database (SANCDB) and the following therapeutic targets α-, β- and γ-secretase, acetylcholinesterase, tau protein and neprilysin. A successful High-throughput Virtual Screening (HTVS) study to determine lead compounds was performed using a computational program called KNIME. Molecular docking was achieved with GLIDE as it allows for exhaustive ligand flexibility. The docking calculations were carried out using the high level of precision XP (extra precision) for enhanced docking accuracy. The binding affinities (docking scores) for the best bound ligands obtained from docking were in the order of -5 kcal/mol or less. The ligandSANC00370 was the best binding ligand against the protein 1J1C_B and had the best binding energy of -13.94 kcal/mol compared to others. The receptor-ligand complexes were analyzed using the interaction diagrams obtained from the Discovery Studio Visualizer and Maestro programs. Molecular Dynamics simulations were performed on the complexes obtained from docking to help in optimizing their interactions. The simulations were performed using the Desmond tool with the OPLS3 force field. 100 ns simulations were performed for six systems with the best docking score results epresenting each of the therapeutic targets and for the other complex systems, 50 ns simulations were performed. The Desmond simulations were analyzed using the Simulations Interaction Diagrams such as PL-RMSD, L-RMSF, P-RMSF, L-Torsions, P-SSE, LP-Contacts and L-Properties. Maestro was used to visualize the stability of the ligands in the active site during the simulation. All 13 Desmond simulations were successful however, there were 9 simulations which produced satisfactory results while the others were nsatisfactory. Based on the molecular docking and Molecular Dynamics results of this study, 9 potential targets and 6 potential agents were obtained successfully and can be studied further as therapeutics for Alzheimer’s Disease.
- Full Text:
- Date Issued: 2020
Nutrient removal and biofuel potential of MaB-floc biomass from an integrated algal pond system treating domestic sewage
- Authors: Sibelo, Linda
- Date: 2020
- Subjects: Biomass energy , Waste products as fuel , Algal biofuels , Sewage -- Purification -- Nutrient removal
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144955 , vital:38395
- Description: Integrated algal pond systems (IAPS) are a passive water treatment technology derived from the Oswald designed advanced integrated wastewater pond systems (AIWPS®) and effect wastewater treatment based on biological activity of microorganisms within the system, solar energy and gravity. The technology consists of an advanced facultative pond (AFP), a series of interconnected high rate algal oxidation ponds (HRAOP) and algal settling ponds. The symbiotic relationship between microalgae and bacteria facilitated by paddlewheel mixing of HRAOP results in the formation of biomass aggregates known as MaB-flocs. MaB-floc formation enhances nutrient abstraction, gravitational sedimentation and separation from water hence forming two product streams; recyclable water and biomass, both with valorisation potential. This work aimed to determine the suitability of MaB-floc biomass generated in the HRAOP of an IAPS treating domestic sewage as feedstock for biofuel production based on the content of carbohydrate and lipid. Nutrient removal efficiency, biomass productivity and bulk lipid and carbohydrate concentration were monitored for two consecutive three-month periods in the winter and summer seasons of 2018/19. Maximum removal efficiencies of nitrogen and phosphorus were determined as 71% and 75% respectively, demonstrating the efficiency of IAPS as a wastewater treatment technology. MaB-floc biomass productivity in winter and summer was 9.4 g/m2/d and 16.5 g/m2/d respectively indicating the heavy influence of seasonal temperature, possibly day length, and solar irradiation on biomass productivity in the HRAOP. Summer productivity was lower than the maximum theoretical productivity of 25 g/m2/d possibly due to photoinhibition of photosynthesis as well as grazing pressures caused by the proliferation of rotifers mainly of the Brachionus genus. MaB-floc biomass consistently contained higher amounts of carbohydrate than lipid despite the changes in species dominance from Scenedesmus sp. and Desmodesmus sp. in winter to Pediastrum sp. in summer. Variations in MaB-floc biomass carbohydrate content were linked to changes in nitrogen concentration, mainly in the form of nitrates. Lower nitrogen concentration significantly increased the carbohydrate content of MaB-floc biomass from 17.5 ± 0.15% to 33.5 ± 0.3 % recorded in summer. In winter, biomass carbohydrate increased from 18.3 ± 1.2% to 35.8 ± 0.3%.To induce accumulation of carbohydrates through nitrogen starvation, isolated microalgal species native to the HRAOPs of the IAPS at Institute for Environmental Biotechnology Rhodes University(EBRU) were used. The outcome from the laboratory studies showed that carbon partitioning within isolated strains could be altered from carbohydrate to lipid which is more energy-rich. Hence, exploring the biodiesel production option using HRAOP MaB-floc biomass, which had a lipid content ranging between 12.1 ± 0.64 % and 13.9 ± 0.5 %, would require a preconditioning step in the form of nitrogen starvation to enhance its lipid content. Overall, the outcome of outdoor monitoring studies on biomass biochemical composition indicated that HRAOPs operating under natural environmental conditions preferentially generated a biomass rich in carbohydrate. Therefore, anaerobic digestion may be a more viable option for HRAOP MaB-floc biomass because of the high carbohydrate levels ranging between 24.9 ± 0.6 % and 25.6 ± 1.3 % of the dry MaB-floc biomass weight. Despite the low biomass C/N ratio (7.1 to 7.8), the MaB-floc biomass can be anaerobically co-digested with a higher C/N ratio (24) substrate such as in-pond digester sludge, to improve methane yields calculated to be between 0.31 m3 CH4/ kg MaB-floc biomass and 0.33 m3 CH4/ kg MaB-floc biomass. Anaerobic digestion of biomass also produces CO2 which can be recovered and added to HRAOPs to enhance MaB-floc biomass productivity while lowering greenhouse gas emissions from a wastewater treatment plant. The digestate from the anaerobic process, which is rich in nitrogen and phosphorus can be used as a biofertiliser. Thus, a potential MaB-floc biomass biorefinery consisting of biogas and bio-fertiliser pathways can be established using IAPS treating sewage as the platform technology. IAPS is a system designed to operate in a way that is passive and without substantial environmental impact but technological innovations and a reduction in the size of the system are required to make the technology more acceptable.
- Full Text:
- Date Issued: 2020
- Authors: Sibelo, Linda
- Date: 2020
- Subjects: Biomass energy , Waste products as fuel , Algal biofuels , Sewage -- Purification -- Nutrient removal
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144955 , vital:38395
- Description: Integrated algal pond systems (IAPS) are a passive water treatment technology derived from the Oswald designed advanced integrated wastewater pond systems (AIWPS®) and effect wastewater treatment based on biological activity of microorganisms within the system, solar energy and gravity. The technology consists of an advanced facultative pond (AFP), a series of interconnected high rate algal oxidation ponds (HRAOP) and algal settling ponds. The symbiotic relationship between microalgae and bacteria facilitated by paddlewheel mixing of HRAOP results in the formation of biomass aggregates known as MaB-flocs. MaB-floc formation enhances nutrient abstraction, gravitational sedimentation and separation from water hence forming two product streams; recyclable water and biomass, both with valorisation potential. This work aimed to determine the suitability of MaB-floc biomass generated in the HRAOP of an IAPS treating domestic sewage as feedstock for biofuel production based on the content of carbohydrate and lipid. Nutrient removal efficiency, biomass productivity and bulk lipid and carbohydrate concentration were monitored for two consecutive three-month periods in the winter and summer seasons of 2018/19. Maximum removal efficiencies of nitrogen and phosphorus were determined as 71% and 75% respectively, demonstrating the efficiency of IAPS as a wastewater treatment technology. MaB-floc biomass productivity in winter and summer was 9.4 g/m2/d and 16.5 g/m2/d respectively indicating the heavy influence of seasonal temperature, possibly day length, and solar irradiation on biomass productivity in the HRAOP. Summer productivity was lower than the maximum theoretical productivity of 25 g/m2/d possibly due to photoinhibition of photosynthesis as well as grazing pressures caused by the proliferation of rotifers mainly of the Brachionus genus. MaB-floc biomass consistently contained higher amounts of carbohydrate than lipid despite the changes in species dominance from Scenedesmus sp. and Desmodesmus sp. in winter to Pediastrum sp. in summer. Variations in MaB-floc biomass carbohydrate content were linked to changes in nitrogen concentration, mainly in the form of nitrates. Lower nitrogen concentration significantly increased the carbohydrate content of MaB-floc biomass from 17.5 ± 0.15% to 33.5 ± 0.3 % recorded in summer. In winter, biomass carbohydrate increased from 18.3 ± 1.2% to 35.8 ± 0.3%.To induce accumulation of carbohydrates through nitrogen starvation, isolated microalgal species native to the HRAOPs of the IAPS at Institute for Environmental Biotechnology Rhodes University(EBRU) were used. The outcome from the laboratory studies showed that carbon partitioning within isolated strains could be altered from carbohydrate to lipid which is more energy-rich. Hence, exploring the biodiesel production option using HRAOP MaB-floc biomass, which had a lipid content ranging between 12.1 ± 0.64 % and 13.9 ± 0.5 %, would require a preconditioning step in the form of nitrogen starvation to enhance its lipid content. Overall, the outcome of outdoor monitoring studies on biomass biochemical composition indicated that HRAOPs operating under natural environmental conditions preferentially generated a biomass rich in carbohydrate. Therefore, anaerobic digestion may be a more viable option for HRAOP MaB-floc biomass because of the high carbohydrate levels ranging between 24.9 ± 0.6 % and 25.6 ± 1.3 % of the dry MaB-floc biomass weight. Despite the low biomass C/N ratio (7.1 to 7.8), the MaB-floc biomass can be anaerobically co-digested with a higher C/N ratio (24) substrate such as in-pond digester sludge, to improve methane yields calculated to be between 0.31 m3 CH4/ kg MaB-floc biomass and 0.33 m3 CH4/ kg MaB-floc biomass. Anaerobic digestion of biomass also produces CO2 which can be recovered and added to HRAOPs to enhance MaB-floc biomass productivity while lowering greenhouse gas emissions from a wastewater treatment plant. The digestate from the anaerobic process, which is rich in nitrogen and phosphorus can be used as a biofertiliser. Thus, a potential MaB-floc biomass biorefinery consisting of biogas and bio-fertiliser pathways can be established using IAPS treating sewage as the platform technology. IAPS is a system designed to operate in a way that is passive and without substantial environmental impact but technological innovations and a reduction in the size of the system are required to make the technology more acceptable.
- Full Text:
- Date Issued: 2020
Observations of diffuse radio emission in the Abell 773 galaxy cluster
- Authors: Sichone, Gift L
- Date: 2020
- Subjects: Galaxies -- Clusters -- Observations , Radio astronomy -- Observations , Astrophysics -- South Africa , Westerbork Radio Telescope , A773 galaxy cluster , Astronomy -- Observations , Radio sources (Astronomy
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144945 , vital:38394
- Description: In this thesis, we present 18 and 21 cm observations of the A773 galaxy cluster observed with the Westerbork radio telescope. The final 18 and 21 cm images achieve a noise level of 0.018 mJy beam‾ 1 and 0.025 mJy beam-1 respectively. After subtracting the compact sources, the low resolution images show evidence of a radio halo at 18 cm, whereas its presence is more uncertain in the low resolution 21 cm images due the presence of residual sidelobes from bright sources. In the joint analysis of both frequencies, the radio halo has a 5.37 arcmin2 area with a 6.76 mJy flux density. Further observations and analysis are, however, required to fully characterize its properties.
- Full Text:
- Date Issued: 2020
- Authors: Sichone, Gift L
- Date: 2020
- Subjects: Galaxies -- Clusters -- Observations , Radio astronomy -- Observations , Astrophysics -- South Africa , Westerbork Radio Telescope , A773 galaxy cluster , Astronomy -- Observations , Radio sources (Astronomy
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144945 , vital:38394
- Description: In this thesis, we present 18 and 21 cm observations of the A773 galaxy cluster observed with the Westerbork radio telescope. The final 18 and 21 cm images achieve a noise level of 0.018 mJy beam‾ 1 and 0.025 mJy beam-1 respectively. After subtracting the compact sources, the low resolution images show evidence of a radio halo at 18 cm, whereas its presence is more uncertain in the low resolution 21 cm images due the presence of residual sidelobes from bright sources. In the joint analysis of both frequencies, the radio halo has a 5.37 arcmin2 area with a 6.76 mJy flux density. Further observations and analysis are, however, required to fully characterize its properties.
- Full Text:
- Date Issued: 2020
Performance of an integrated algal pond for treatment of domestic sewage: a process audit
- Authors: Dube, Anele
- Date: 2020
- Subjects: Water -- Purification , Sewage -- Purification -- Anaerobic treatment , Algae -- Biotechnology , Waste disposal -- South Africa , Integrated algae pond systems (IAPS)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167043 , vital:41432
- Description: Integrated algae pond systems (IAPS) are energy efficient, robust, passive systems that use the principles of fermentation, photosynthesis and microbial metabolism to remediate wastewater, producing a good quality effluent with reuse potential. In addition to the treatment of wastewater, IAPS have the ability to generate two additional product streams viz. biogas and biomass. The latter adds to the attractiveness of the system. However, the implementation of this technology, like many passive systems, has remained limited at a commercial scale, and the inclination is still towards grey technologies. The aim of this research was to investigate the capabilities and potential of a demonstration-scale IAPS and use results obtained to establish a process audit framework. The aspects considered for the audit included performance efficiency, effluent water quality, biomass composition, quantity and productivity within the ponds, and cost analysis of operation and maintenance over a 9-year period. Plant performance was closely monitored during the course of the study and this led to a review of previously adopted plant management strategies. Troubleshooting exercises were also carried out when plant performance declined. Results showed that IAPS efficiently reduced standard water parameters with the exception of pH, dissolved oxygen, and nitrate whose values increased from raw influent to final effluent. The following water quality parameters were established for the final effluent: total suspended solids 55 ± 7.1 mg. L-1 (n = 28); chemical oxygen demand 94.1 ± 10.6 mg. L-1 (n = 28) (after removal of algae); pH 9.9 ± 0.01 (n = 26); ammonium nitrogen 1.7 ± 0.3 mg. L-1 (n = 25); nitrate 3.3 ± 0.6 mg. L-1 (n = 25); ortho-phosphate 1.6 ± 0.2 mg. L-1 (n = 25); electrical conductivity 98.7 ± 2.0 mS m-1 (n = 26) and faecal coliforms (per 100 mL) 1482.6 ± 636.0 (n = 24). The final effluent measured consistently high chemical oxygen demand and total suspended solids, however close analysis showed that total suspended solids could be controlled by increasing the frequency of removal of settled biomass within the settling ponds. Biomass produced contained microalgae, bacteria, metazoa, and protozoa. The biomass productivity achieved was as high as 130.6 kg ha-1 d-1; however, about 33% was lost to the final effluent due to inadequate settling. Results obtained during the course of this study and outcomes of earlier work on IAPS are taken as the baseline to determine parameters needed for the development of the process audit framework. Techniques utilised to derive the blue print process audit protocol for IAPS included a turtle diagram, a flow diagram and a checklist. Attention to plant management proved vital in determining overall performance. Cost, including operating and maintenance, of treating water using the demonstration scale system on a per person equivalent per year basis was determined as ZAR 123.87 (where, ZAR to USD = 0.07).
- Full Text:
- Date Issued: 2020
- Authors: Dube, Anele
- Date: 2020
- Subjects: Water -- Purification , Sewage -- Purification -- Anaerobic treatment , Algae -- Biotechnology , Waste disposal -- South Africa , Integrated algae pond systems (IAPS)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167043 , vital:41432
- Description: Integrated algae pond systems (IAPS) are energy efficient, robust, passive systems that use the principles of fermentation, photosynthesis and microbial metabolism to remediate wastewater, producing a good quality effluent with reuse potential. In addition to the treatment of wastewater, IAPS have the ability to generate two additional product streams viz. biogas and biomass. The latter adds to the attractiveness of the system. However, the implementation of this technology, like many passive systems, has remained limited at a commercial scale, and the inclination is still towards grey technologies. The aim of this research was to investigate the capabilities and potential of a demonstration-scale IAPS and use results obtained to establish a process audit framework. The aspects considered for the audit included performance efficiency, effluent water quality, biomass composition, quantity and productivity within the ponds, and cost analysis of operation and maintenance over a 9-year period. Plant performance was closely monitored during the course of the study and this led to a review of previously adopted plant management strategies. Troubleshooting exercises were also carried out when plant performance declined. Results showed that IAPS efficiently reduced standard water parameters with the exception of pH, dissolved oxygen, and nitrate whose values increased from raw influent to final effluent. The following water quality parameters were established for the final effluent: total suspended solids 55 ± 7.1 mg. L-1 (n = 28); chemical oxygen demand 94.1 ± 10.6 mg. L-1 (n = 28) (after removal of algae); pH 9.9 ± 0.01 (n = 26); ammonium nitrogen 1.7 ± 0.3 mg. L-1 (n = 25); nitrate 3.3 ± 0.6 mg. L-1 (n = 25); ortho-phosphate 1.6 ± 0.2 mg. L-1 (n = 25); electrical conductivity 98.7 ± 2.0 mS m-1 (n = 26) and faecal coliforms (per 100 mL) 1482.6 ± 636.0 (n = 24). The final effluent measured consistently high chemical oxygen demand and total suspended solids, however close analysis showed that total suspended solids could be controlled by increasing the frequency of removal of settled biomass within the settling ponds. Biomass produced contained microalgae, bacteria, metazoa, and protozoa. The biomass productivity achieved was as high as 130.6 kg ha-1 d-1; however, about 33% was lost to the final effluent due to inadequate settling. Results obtained during the course of this study and outcomes of earlier work on IAPS are taken as the baseline to determine parameters needed for the development of the process audit framework. Techniques utilised to derive the blue print process audit protocol for IAPS included a turtle diagram, a flow diagram and a checklist. Attention to plant management proved vital in determining overall performance. Cost, including operating and maintenance, of treating water using the demonstration scale system on a per person equivalent per year basis was determined as ZAR 123.87 (where, ZAR to USD = 0.07).
- Full Text:
- Date Issued: 2020
Photo-physicochemical characterization and in vitro Photodynamic Therapy Activity of Phthalocyanine-Graphene Quantum Dots Conjugates
- Authors: Nene, Lindokuhle Cindy
- Date: 2020
- Subjects: Photochemotherapy , Cancer -- Chemotherapy , Quantum dots , Graphene , Nanomedicine
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/140463 , vital:37891
- Description: This thesis reports on the preparation of several differently substituted Zn(II) phthalocyanine (Pc) complexes and their respective graphene quantum dots (GQDs) conjugates. In addition, Pc complexes substituted with biologically active molecules used in cancer therapeutics, namely: benzothiazole and morpholine, were also prepared and conjugated to GQDs. The photo-physicochemical properties were determined for both the complexes and their respective conjugates including the fluorescence/ triplet quantum yields and lifetimes as well as the singlet oxygen generating abilities. Upon conjugation to GQDs, the fluorescence of the Pc complexes decreased (insignificant decrease in some cases), with an increase in the triplet quantum yields. However, the singlet quantum yields of the Pcs in the conjugates did not show an increase with the increase in the triplet quantum yields. This is suspected to be due to the screening effect. The cytotoxicity of the complexes in vitro decreased upon conjugation, as a result of reduced actual number of Pc units provided in the conjugate for therapy. An increase in the efficacy upon quaternization was observed, and a relatively better performance was also observed for the cationic complex in combination with the biotin- functionalized GQDs, 7-GQDs-Biotin. Moreover, the cellular uptake of 7-GQDs-Biotin over 24 h was relatively high compared to complexes alone and other Pcs-GQDs conjugates.
- Full Text:
- Date Issued: 2020
- Authors: Nene, Lindokuhle Cindy
- Date: 2020
- Subjects: Photochemotherapy , Cancer -- Chemotherapy , Quantum dots , Graphene , Nanomedicine
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/140463 , vital:37891
- Description: This thesis reports on the preparation of several differently substituted Zn(II) phthalocyanine (Pc) complexes and their respective graphene quantum dots (GQDs) conjugates. In addition, Pc complexes substituted with biologically active molecules used in cancer therapeutics, namely: benzothiazole and morpholine, were also prepared and conjugated to GQDs. The photo-physicochemical properties were determined for both the complexes and their respective conjugates including the fluorescence/ triplet quantum yields and lifetimes as well as the singlet oxygen generating abilities. Upon conjugation to GQDs, the fluorescence of the Pc complexes decreased (insignificant decrease in some cases), with an increase in the triplet quantum yields. However, the singlet quantum yields of the Pcs in the conjugates did not show an increase with the increase in the triplet quantum yields. This is suspected to be due to the screening effect. The cytotoxicity of the complexes in vitro decreased upon conjugation, as a result of reduced actual number of Pc units provided in the conjugate for therapy. An increase in the efficacy upon quaternization was observed, and a relatively better performance was also observed for the cationic complex in combination with the biotin- functionalized GQDs, 7-GQDs-Biotin. Moreover, the cellular uptake of 7-GQDs-Biotin over 24 h was relatively high compared to complexes alone and other Pcs-GQDs conjugates.
- Full Text:
- Date Issued: 2020
Photocatalysis of 4-chloro and 4-nonylphenols using novel symmetric phthalocyanines and asymmetric porphyrin supported on polyacrylonitrite nanofibres
- Authors: Jones, Benjamin Martin
- Date: 2020
- Subjects: Nanoparticles , Phthalocyanines , Electrospinning , Porphyrins , Nanofibers , Photocatalysis , Photocatalysis -- Environmental aspects
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/164770 , vital:41163
- Description: This work explores the synthesis and characterisation of novel symmetrical phthalocyanines and novel asymmetric porphyrins that have been embedded or linked respectively,and electrospun into fibres for application in the photocatalysis of environmental pollutants. The phthalocyanines contain pyrrole moieties without hetero atom linkers to maintain a rigid structure. The porphyrin contains a carboxy moiety utilized to construct an amide bond between the complex and the polymer prior to the spinning process. The new compounds were characterized by elemental analyses, proton nuclear magnetic resonance (HNMR)Fourier-transform infrared spectroscopy (FTIR), MALDI-TOF and UV-vis spectroscopy. The general trends of fluorescence, triplet and singlet oxygen quantum yields are described as well as their appropriate lifetimes. The photocatalytic activity of phthalocyanine embedded fibres were compared against those that had been dyed. Unfortunately, during the degradation process, the dyed fibres leeched compound and the studies could not be continued. It was seen that the porphyrin fibres linked to the polymer showed the most efficient photocatalytic activity against 4-cholorphenol and 4-nonylphenol due to irradiation at lower wavelengths consequently having higher frequencies and transferring more energy.
- Full Text:
- Date Issued: 2020
- Authors: Jones, Benjamin Martin
- Date: 2020
- Subjects: Nanoparticles , Phthalocyanines , Electrospinning , Porphyrins , Nanofibers , Photocatalysis , Photocatalysis -- Environmental aspects
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/164770 , vital:41163
- Description: This work explores the synthesis and characterisation of novel symmetrical phthalocyanines and novel asymmetric porphyrins that have been embedded or linked respectively,and electrospun into fibres for application in the photocatalysis of environmental pollutants. The phthalocyanines contain pyrrole moieties without hetero atom linkers to maintain a rigid structure. The porphyrin contains a carboxy moiety utilized to construct an amide bond between the complex and the polymer prior to the spinning process. The new compounds were characterized by elemental analyses, proton nuclear magnetic resonance (HNMR)Fourier-transform infrared spectroscopy (FTIR), MALDI-TOF and UV-vis spectroscopy. The general trends of fluorescence, triplet and singlet oxygen quantum yields are described as well as their appropriate lifetimes. The photocatalytic activity of phthalocyanine embedded fibres were compared against those that had been dyed. Unfortunately, during the degradation process, the dyed fibres leeched compound and the studies could not be continued. It was seen that the porphyrin fibres linked to the polymer showed the most efficient photocatalytic activity against 4-cholorphenol and 4-nonylphenol due to irradiation at lower wavelengths consequently having higher frequencies and transferring more energy.
- Full Text:
- Date Issued: 2020
Prediction of mass spectra for natural products using an ab initio approach
- Authors: Novokoza, Yolanda
- Date: 2020
- Subjects: Molecular dynamics , Molecular dynamics -- Computer simulation , Mass spectroscopy , Electron impact ionization
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167166 , vital:41443
- Description: Mass spectrometry (MS) is a technique that measures the fragmentation of molecules, dependent on the molecule’s chemical composition and structure, by first introducing a charge on the molecules. The instrument records the mass to charge ratio, but the energy from the ionization process causes the molecule to fragment. The resultant mass spectrum is highly indicative of not only the molecule analyzed, but also its chemical composition. MS is used in research and industry for both routine and research purposes. One such way to ionize molecules for MS is by bombarding the molecule with electrons which is the basis of electron impact mass spectrometry (EIMS). Although EIMS is widely used, prediction of electron impact mass spectra from first principles is a challenging problem due to a need to accurately determine the probability of different fragmentation pathways of a molecule. Ab initio molecular dynamics based methods are able to explore in an automatic fashion the energetically available fragmentation paths thus give reaction mechanisms in an unbiased way. The mass spectra of five molecules have been explored in work-flows leading to the prediction of mass spectra. These molecules include three natural products alpha-hispanolol, PFB oxime derivative and boronolide (for which experimental mass spectra were not available) and two compounds from the NIST database (for which experimental mass spectra were available). For each of these systems many random conformations were generated using the RDKit library. To all conformations random velocities were applied to each atom. Ab initio molecular dynamics was performed on each conformer, using these initial random velocities using CP2K software, at DFTB+ level at a variety of highly raised temperatures (to accelerate the formation of fragments) Fragmentation was monitored by iterating through all bonds, and identifying bond breakages during dynamics. Graph theoretical packages were used then to track distinct fragments generated. For each of these fragments, charges were determined from Mulliken analysis for all atoms on the fragment from the QM calculations and sum of atomic spin densities per fragment was also plotted. The fragment with the greatest charge (corresponding to the formation of a cation fragment) was taken for plotting on the mass spectrum. Finally, from the mass of the fragment and its elemental composition, the isotopic distribution for the fragment was determined, and this distribution was included by addition in to the mass spectrum. For all trajectories, the sum of all isotopic distributions determined the final mass spectrum.
- Full Text:
- Date Issued: 2020
- Authors: Novokoza, Yolanda
- Date: 2020
- Subjects: Molecular dynamics , Molecular dynamics -- Computer simulation , Mass spectroscopy , Electron impact ionization
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167166 , vital:41443
- Description: Mass spectrometry (MS) is a technique that measures the fragmentation of molecules, dependent on the molecule’s chemical composition and structure, by first introducing a charge on the molecules. The instrument records the mass to charge ratio, but the energy from the ionization process causes the molecule to fragment. The resultant mass spectrum is highly indicative of not only the molecule analyzed, but also its chemical composition. MS is used in research and industry for both routine and research purposes. One such way to ionize molecules for MS is by bombarding the molecule with electrons which is the basis of electron impact mass spectrometry (EIMS). Although EIMS is widely used, prediction of electron impact mass spectra from first principles is a challenging problem due to a need to accurately determine the probability of different fragmentation pathways of a molecule. Ab initio molecular dynamics based methods are able to explore in an automatic fashion the energetically available fragmentation paths thus give reaction mechanisms in an unbiased way. The mass spectra of five molecules have been explored in work-flows leading to the prediction of mass spectra. These molecules include three natural products alpha-hispanolol, PFB oxime derivative and boronolide (for which experimental mass spectra were not available) and two compounds from the NIST database (for which experimental mass spectra were available). For each of these systems many random conformations were generated using the RDKit library. To all conformations random velocities were applied to each atom. Ab initio molecular dynamics was performed on each conformer, using these initial random velocities using CP2K software, at DFTB+ level at a variety of highly raised temperatures (to accelerate the formation of fragments) Fragmentation was monitored by iterating through all bonds, and identifying bond breakages during dynamics. Graph theoretical packages were used then to track distinct fragments generated. For each of these fragments, charges were determined from Mulliken analysis for all atoms on the fragment from the QM calculations and sum of atomic spin densities per fragment was also plotted. The fragment with the greatest charge (corresponding to the formation of a cation fragment) was taken for plotting on the mass spectrum. Finally, from the mass of the fragment and its elemental composition, the isotopic distribution for the fragment was determined, and this distribution was included by addition in to the mass spectrum. For all trajectories, the sum of all isotopic distributions determined the final mass spectrum.
- Full Text:
- Date Issued: 2020
Production, purification and characterization of a multifunctional, thermostable and acido/alkaline stable putative xylanase from the psychrotrophic bacterium, Sphingomonas aerolata
- Authors: Mathibe, Brian Nkanyiso
- Date: 2020
- Subjects: Uncatalogued
- Language: English
- Type: thesis , text , Masters , MSc
- Identifier: http://hdl.handle.net/10962/164478 , vital:41122
- Description: Thesis (MSc)--Rhodes University, Faculty of Science, Biochemistry and Microbiology, 2020
- Full Text:
- Date Issued: 2020
- Authors: Mathibe, Brian Nkanyiso
- Date: 2020
- Subjects: Uncatalogued
- Language: English
- Type: thesis , text , Masters , MSc
- Identifier: http://hdl.handle.net/10962/164478 , vital:41122
- Description: Thesis (MSc)--Rhodes University, Faculty of Science, Biochemistry and Microbiology, 2020
- Full Text:
- Date Issued: 2020
Seasonal trends of rainfall intensity, ground cover and sediment dynamics in the Little Pot River and Gqukunqa River catchments, South Africa
- Authors: Herd-Hoare, Sean
- Date: 2020
- Subjects: Land degradation -- Control -- South Africa -- Eastern Cape , Vegetation mapping -- South Africa -- Eastern Cape , Rain and rainfall -- South Africa -- Eastern Cape , Gqukunqa River catchment (South Africa) , Little Pot River catchment (South Africa) , Tsitsa River catchment (South Africa)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/146288 , vital:38512
- Description: Natural rangelands provide a variety of ecosystem services including livestock production which occurs on land under freehold land tenure and on land under communal tenure. There is an ongoing debate around the extent to which land degradation is occurring on these rangelands under different land management and land tenure systems and what the main degradation drivers are. Over-grazing, rainfall and soil type are key drivers of rangeland dynamics and the resultant sediment yield in the river systems, however, over-grazing is an outcome of land management while rainfall and soil type are natural drivers. This study explores the relationship between rainfall and daily sediment flux as well as the seasonal trends of vegetation cover and the study is part of a greater research effort called the Tsitsa Project which is based in the Tsitsa River catchment (near Maclear, Eastern Cape, South Africa). The Tsitsa Project aims at developing and managing both land and water in a sustainable way by improving the land, water and lives of people living in the Tsitsa River catchment. The restoration efforts of the Tstisa Project will aid in extending the lifespan of both the proposed dams on the Tsitsa River. The Tsitsa River catchment is characterised by grasslands, steep topography, highly erodible soils with many large gullies present and a very high sediment yield in the Tsitsa River which allowed for the exploration of some of the system drivers of sediment yield in this catchment. The study involved two sub-catchments of the Upper Tsitsa River catchment of different land management strategies: one dominated by commercial livestock farms (Little Pot River catchment) and one dominated by communal rangelands (Gqukunqa River catchment). The aim of this study was to determine the seasonal trends of rainfall intensity, ground cover and sediment dynamics in the Little Pot River and Gqukunqa River catchments. The purpose of the findings was to improve management strategies in degraded areas and catchments. In order to achieve this aim a variety of field and desktop methods were used. Field methods involved measuring variables including: vegetation biomass, vegetation cover, soil surface hardness, biocrust cover and slope angle for a range of Normalized Difference Vegetation Index (NDVI) values from the Sentinel-2A sensor. The study assessed the system response of the field variables in both catchments over one rainfall season (2018-2019). Desktop methods included various NDVI analyses as well as analyses of trends and relationships between vegetation dynamics, rainfall and sediment. The relationship between erosive rainfall events, daily rainfall, antecedent rainfall and daily sediment flux was explored over the time period of January 2016 to January 2019 and October 2015 to January 2019 for the Little Pot River catchment and the Gqukunqa River catchment respectively. NDVI was explored as a proxy for vegetation cover to extrapolate across the catchments and monitoring period. NDVI was found to have a weak positive relationship with vegetation cover and biomass (R2 values ranged from 0,04 to 0,525). Mean monthly catchment NDVI values, biomass and vegetation cover increased throughout the wet season of 2018-2019 in both catchments. Mean monthly NDVI values increased from 0,26 to 0,55 in the Little Pot River catchment and from 0,29 to 0,53 in the Gqukunqa River catchment over the course of the 2018-2019 wet season. NDVI, biomass and vegetation cover was found to be higher on south-facing slopes than north-facing slopes in both catchments for the majority of the wet season. The Gqukunqa River has significantly higher daily sediment fluxes than the Little Pot River despite similar NDVI and rainfall intensities which is owed to the dispersive soils in the Gqukunqa River catchment. Soil surface hardness results were inconclusive due to rainfall before or during every field trip which changed the properties of the soil. The largest erosive rainfall, daily rainfall and daily sediment events occurred from January to March each wet season in both catchments. Rainfall intensity and sediment fluxes were found to have a weak relationship, however, there was a stronger relationship found between antecedent rainfall and sediment flux. The larger daily sediment fluxes in each catchment often did not result from an erosive rainfall event on the same day but rather from multiple days of rainfall which can result in saturated soils and runoff leading to surface and sub-surface erosion. The possibility of sub-surface erosion via chemical processes contributing to the larger sediment events was also explored to explain the stronger relationship between antecedent rainfall and daily sediment flux.
- Full Text:
- Date Issued: 2020
- Authors: Herd-Hoare, Sean
- Date: 2020
- Subjects: Land degradation -- Control -- South Africa -- Eastern Cape , Vegetation mapping -- South Africa -- Eastern Cape , Rain and rainfall -- South Africa -- Eastern Cape , Gqukunqa River catchment (South Africa) , Little Pot River catchment (South Africa) , Tsitsa River catchment (South Africa)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/146288 , vital:38512
- Description: Natural rangelands provide a variety of ecosystem services including livestock production which occurs on land under freehold land tenure and on land under communal tenure. There is an ongoing debate around the extent to which land degradation is occurring on these rangelands under different land management and land tenure systems and what the main degradation drivers are. Over-grazing, rainfall and soil type are key drivers of rangeland dynamics and the resultant sediment yield in the river systems, however, over-grazing is an outcome of land management while rainfall and soil type are natural drivers. This study explores the relationship between rainfall and daily sediment flux as well as the seasonal trends of vegetation cover and the study is part of a greater research effort called the Tsitsa Project which is based in the Tsitsa River catchment (near Maclear, Eastern Cape, South Africa). The Tsitsa Project aims at developing and managing both land and water in a sustainable way by improving the land, water and lives of people living in the Tsitsa River catchment. The restoration efforts of the Tstisa Project will aid in extending the lifespan of both the proposed dams on the Tsitsa River. The Tsitsa River catchment is characterised by grasslands, steep topography, highly erodible soils with many large gullies present and a very high sediment yield in the Tsitsa River which allowed for the exploration of some of the system drivers of sediment yield in this catchment. The study involved two sub-catchments of the Upper Tsitsa River catchment of different land management strategies: one dominated by commercial livestock farms (Little Pot River catchment) and one dominated by communal rangelands (Gqukunqa River catchment). The aim of this study was to determine the seasonal trends of rainfall intensity, ground cover and sediment dynamics in the Little Pot River and Gqukunqa River catchments. The purpose of the findings was to improve management strategies in degraded areas and catchments. In order to achieve this aim a variety of field and desktop methods were used. Field methods involved measuring variables including: vegetation biomass, vegetation cover, soil surface hardness, biocrust cover and slope angle for a range of Normalized Difference Vegetation Index (NDVI) values from the Sentinel-2A sensor. The study assessed the system response of the field variables in both catchments over one rainfall season (2018-2019). Desktop methods included various NDVI analyses as well as analyses of trends and relationships between vegetation dynamics, rainfall and sediment. The relationship between erosive rainfall events, daily rainfall, antecedent rainfall and daily sediment flux was explored over the time period of January 2016 to January 2019 and October 2015 to January 2019 for the Little Pot River catchment and the Gqukunqa River catchment respectively. NDVI was explored as a proxy for vegetation cover to extrapolate across the catchments and monitoring period. NDVI was found to have a weak positive relationship with vegetation cover and biomass (R2 values ranged from 0,04 to 0,525). Mean monthly catchment NDVI values, biomass and vegetation cover increased throughout the wet season of 2018-2019 in both catchments. Mean monthly NDVI values increased from 0,26 to 0,55 in the Little Pot River catchment and from 0,29 to 0,53 in the Gqukunqa River catchment over the course of the 2018-2019 wet season. NDVI, biomass and vegetation cover was found to be higher on south-facing slopes than north-facing slopes in both catchments for the majority of the wet season. The Gqukunqa River has significantly higher daily sediment fluxes than the Little Pot River despite similar NDVI and rainfall intensities which is owed to the dispersive soils in the Gqukunqa River catchment. Soil surface hardness results were inconclusive due to rainfall before or during every field trip which changed the properties of the soil. The largest erosive rainfall, daily rainfall and daily sediment events occurred from January to March each wet season in both catchments. Rainfall intensity and sediment fluxes were found to have a weak relationship, however, there was a stronger relationship found between antecedent rainfall and sediment flux. The larger daily sediment fluxes in each catchment often did not result from an erosive rainfall event on the same day but rather from multiple days of rainfall which can result in saturated soils and runoff leading to surface and sub-surface erosion. The possibility of sub-surface erosion via chemical processes contributing to the larger sediment events was also explored to explain the stronger relationship between antecedent rainfall and daily sediment flux.
- Full Text:
- Date Issued: 2020
Sexual attraction and mating compatibility between Thaumatotibia leucotreta populations and implications for semiochemical dependent technologies
- Authors: Upfold, Jennifer Kate
- Date: 2020
- Subjects: Cryptophlebia leucotreta -- South Africa , Cryptophlebia leucotreta -- Reproduction , Citrus -- Disease and pests -- Control -- South Africa , Insect sterilization -- South Africa , Pheromones , Pheromone traps
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/148526 , vital:38747
- Description: False codling moth (FCM), Thaumatotibia leucotreta (Meyrick), is the most important pest for the cultivation of citrus in South Africa. False codling moth is indigenous to southern Africa and is a regulated pest of many international markets for phytosanitary concerns. Considerable research efforts have been invested in the past decades to develop semiochemcial technologies, such as monitoring with sex pheromones, attract-and-kill, mating disruption and the sterile insect technique. One of the potential obstacles identified with semiochemical control is the differences in the ratio of the compounds comprising the sex pheromone at different geographical locations, resulting in what is known as regional attraction. This has been identified in FCM populations from three different countries, however, regional attraction within South African FCM populations was unknown. Therefore, the study assessed the genetic integrity of five laboratory-reared FCM populations originating from geographically isolated populations in South Africa using the AFLP technique in order to assess regional attractiveness within the country. The results found isolated populations from Addo, Citrusdal, Marble Hall, Nelspruit and a fifth group found to be closely related to Addo and Citrusdal called the ‘Old’ colony. These five genetically isolated populations as well as a population from Xsit (Pty) Ltd, used for the sterile insect technique (SIT), were used in regional attractiveness trials. Males were significantly (P = <0.05) more attracted to females originating from the same population. No significant attraction could be determined from the sterile males, as the recapture rates in the trap were too low. Furthermore, regional attractiveness was assessed through choice/ no-choice mating compatibility trials. Significant sexual isolation (ISI) occurred between mating combinations Addo × Nelspruit (ISI = 0,13; t2 = 6.23; p = 0.02), Addo × Marble Hall (ISI = 0,11; t2 = 4.72; p = 0.04), Citrusdal × Nelspruit (ISI = 0,11; t2 = 4.95; p = 0.04), and Citrusdal × Marble Hall (ISI = 0,12; t2 = 4.31; p = 0.04). In these combinations, Addo and Citrusdal males were found to have outcompeted Nelspruit and Marble Hall males for more mating events. Significant sexual isolation was also recorded for Sterile × Marble Hall (ISI = 0.12; t2 = 4.98; p =0.01) and Sterile × Citrusdal (ISI = 0.13; t2 = 3.96; p = 0.01) populations. The male relative performance index was significant in both combinations, indicating that non-sterile laboratory males outcompeted the sterile males in these two combinations. When given no choice, evaluated as spermatophore transfer/ female/ 48h, all males (including sterile) were successful in transferring spermatophores to all FCM populations, with no significant differences. These results indicate that there may be incipient pre-isolation mechanisms affected by local natural selection, resulting in localised sexual attraction via differences in the sex pheromone ratios. These findings provide important information for semiochemical technologies and the implication of these results with regard to monitoring with sex pheromones, attract-and-kill, mating disruption and sterile insect technique are discussed.
- Full Text:
- Date Issued: 2020
- Authors: Upfold, Jennifer Kate
- Date: 2020
- Subjects: Cryptophlebia leucotreta -- South Africa , Cryptophlebia leucotreta -- Reproduction , Citrus -- Disease and pests -- Control -- South Africa , Insect sterilization -- South Africa , Pheromones , Pheromone traps
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/148526 , vital:38747
- Description: False codling moth (FCM), Thaumatotibia leucotreta (Meyrick), is the most important pest for the cultivation of citrus in South Africa. False codling moth is indigenous to southern Africa and is a regulated pest of many international markets for phytosanitary concerns. Considerable research efforts have been invested in the past decades to develop semiochemcial technologies, such as monitoring with sex pheromones, attract-and-kill, mating disruption and the sterile insect technique. One of the potential obstacles identified with semiochemical control is the differences in the ratio of the compounds comprising the sex pheromone at different geographical locations, resulting in what is known as regional attraction. This has been identified in FCM populations from three different countries, however, regional attraction within South African FCM populations was unknown. Therefore, the study assessed the genetic integrity of five laboratory-reared FCM populations originating from geographically isolated populations in South Africa using the AFLP technique in order to assess regional attractiveness within the country. The results found isolated populations from Addo, Citrusdal, Marble Hall, Nelspruit and a fifth group found to be closely related to Addo and Citrusdal called the ‘Old’ colony. These five genetically isolated populations as well as a population from Xsit (Pty) Ltd, used for the sterile insect technique (SIT), were used in regional attractiveness trials. Males were significantly (P = <0.05) more attracted to females originating from the same population. No significant attraction could be determined from the sterile males, as the recapture rates in the trap were too low. Furthermore, regional attractiveness was assessed through choice/ no-choice mating compatibility trials. Significant sexual isolation (ISI) occurred between mating combinations Addo × Nelspruit (ISI = 0,13; t2 = 6.23; p = 0.02), Addo × Marble Hall (ISI = 0,11; t2 = 4.72; p = 0.04), Citrusdal × Nelspruit (ISI = 0,11; t2 = 4.95; p = 0.04), and Citrusdal × Marble Hall (ISI = 0,12; t2 = 4.31; p = 0.04). In these combinations, Addo and Citrusdal males were found to have outcompeted Nelspruit and Marble Hall males for more mating events. Significant sexual isolation was also recorded for Sterile × Marble Hall (ISI = 0.12; t2 = 4.98; p =0.01) and Sterile × Citrusdal (ISI = 0.13; t2 = 3.96; p = 0.01) populations. The male relative performance index was significant in both combinations, indicating that non-sterile laboratory males outcompeted the sterile males in these two combinations. When given no choice, evaluated as spermatophore transfer/ female/ 48h, all males (including sterile) were successful in transferring spermatophores to all FCM populations, with no significant differences. These results indicate that there may be incipient pre-isolation mechanisms affected by local natural selection, resulting in localised sexual attraction via differences in the sex pheromone ratios. These findings provide important information for semiochemical technologies and the implication of these results with regard to monitoring with sex pheromones, attract-and-kill, mating disruption and sterile insect technique are discussed.
- Full Text:
- Date Issued: 2020