Optimization of flexible spectrum in optical transport networks
- Boiyo, Duncan Kiboi, Gamatham, Romeo
- Authors: Boiyo, Duncan Kiboi , Gamatham, Romeo
- Date: 2017
- Subjects: Digital communications Optical fiber communication , Optical communications Fiber optics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/14609 , vital:27803
- Description: The ever-increasing demand for broadband services by end-user devices utilising 3G/4G/LTE and the projected 5G in the last mile will require sustaining broadband supply from fibre-linked terminals. The eventual outcome of the high demand for broadband is strained optical and electronic devices. The backbone optical fibre transport systems and techniques such as dense wavelength division multiplexing (DWDM), higher modulation formats, coherent detection and signal amplification have increased both fibre capacity and spectrum efficiency. A major challenge to fibre capacity and spectrum efficiency is fibre-faults and optical impairments, network management, routing and wavelength assignment (RWA). In this study, DWDM and flexible spectrum techniques such as wavelength assignment and adjustment, wavelength conversion and switching, optical add and drop multiplexing (OADM) and bitrate variable transmission have been experimentally optimized in a laboratory testbed for short- and long-haul optical fibre networks. This work starts by experimentally optimising different transmitters, fibre-types and receivers suitable for implementing cost effective and energy efficient flexible spectrum networks. Vertical cavity surface-emitting lasers (VCSELs) and distributed feedback (DFB) lasers have been studied to provide up to 10 Gb/s per channel in 1310 nm and 1550 nm transmission windows. VCSELs provide wavelength assignment and adjustment. This work utilises the non-return-to-zero (NRZ) on-off keying (OOK) modulation technique and direct detection due to their cost and simplicity. By using positive intrinsic negative (PIN) photo-receivers with error-free BER sensitivity of -18±1 dBm at the acceptable 10-9-bit error rate (BER) threshold level, unamplified transmission distances between 6 km and 76 km have been demonstrated using G.652 and G.655 single mode fibres (SMFs). For the first time, an all optical VCSEL to VCSEL wavelength conversion, switching, transmission at the 1550 nm window and BER evaluation of a NRZ data signal is experimentally demonstrated. With VCSEL wavelength conversion and switching, wavelength adjustments to a spectrum width of 4.8 nm (600 GHz) can be achieved to provide alternative routes to signals when fibre-cuts and wavelength collision occurs therefore enhancing signal continuity. This work also demonstrates a technique of removing and adding a wavelength in a bundle of DWDM and flexible channels using an OADM. This has been implemented using a VCSEL and a fibre Bragg grating (FBG) providing a wavelength isolation ratio of 31.4 dB and ~0.3 𝑑𝐵 add/drop penalty of 8.5 Gb/s signal. As a result, an OADM improves spectrum efficiency by offering wavelength re-use. Optical impairments such as crosstalk, chromatic dispersion (CD) and effects of polarization mode dispersion (PMD) have been experimentally investigated and mitigated. This work showed that crosstalk penalty increased with fibre-length, bitrate, interfering signal power and reduced channel spacing and as a result, a crosstalk-penalty trade-off is required. Effects of CD on a transmitted 10 Gb/s signal were also investigated and its mitigation techniques used to increase the fibre-reach. This work uses the negative dispersion fibres to mitigate the accumulated dispersion over the distance of transmission. A 5 dB sensitivity improvement is reported for an unamplified 76 km using DFB transmitters and combination of NZDSF true-wave reduced slope (TW-RS) and submarine reduced slope (TW-SRS) with + and – dispersion coefficients respectively. We have also demonstrated up to 52 km 10 Gb/s per channel VCSEL-based transmission and reduced net dispersion. Experimental demonstration of forward Raman amplification has achieved a 4.7 dB on-off gain distributed over a 4.8 nm spectral width and a 1.7 dB improvement of receiver sensitivity in Raman-aided 10 Gb/s per wavelength VCSEL transmission. Finally, 4.25-10 Gb/s PON-based point to point (P2P) and point to multipoint (P2MP) broadcast transmission have been experimentally demonstrated. A 10 Gb/s with a 1:8 passive splitter incurred a 3.7 dB penalty for a 24.7 km fibre-link. In summary, this work has demonstrated cost effective and energy efficient potential flexible spectrum techniques for high speed signal transmission. With the optimized network parameters, flexible spectrum is therefore relevant in short-reach, metro-access and long-haul applications for national broadband networks and the Square Kilometre Array (SKA) fibre-based signal and data transmission.
- Full Text:
- Date Issued: 2017
- Authors: Boiyo, Duncan Kiboi , Gamatham, Romeo
- Date: 2017
- Subjects: Digital communications Optical fiber communication , Optical communications Fiber optics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/14609 , vital:27803
- Description: The ever-increasing demand for broadband services by end-user devices utilising 3G/4G/LTE and the projected 5G in the last mile will require sustaining broadband supply from fibre-linked terminals. The eventual outcome of the high demand for broadband is strained optical and electronic devices. The backbone optical fibre transport systems and techniques such as dense wavelength division multiplexing (DWDM), higher modulation formats, coherent detection and signal amplification have increased both fibre capacity and spectrum efficiency. A major challenge to fibre capacity and spectrum efficiency is fibre-faults and optical impairments, network management, routing and wavelength assignment (RWA). In this study, DWDM and flexible spectrum techniques such as wavelength assignment and adjustment, wavelength conversion and switching, optical add and drop multiplexing (OADM) and bitrate variable transmission have been experimentally optimized in a laboratory testbed for short- and long-haul optical fibre networks. This work starts by experimentally optimising different transmitters, fibre-types and receivers suitable for implementing cost effective and energy efficient flexible spectrum networks. Vertical cavity surface-emitting lasers (VCSELs) and distributed feedback (DFB) lasers have been studied to provide up to 10 Gb/s per channel in 1310 nm and 1550 nm transmission windows. VCSELs provide wavelength assignment and adjustment. This work utilises the non-return-to-zero (NRZ) on-off keying (OOK) modulation technique and direct detection due to their cost and simplicity. By using positive intrinsic negative (PIN) photo-receivers with error-free BER sensitivity of -18±1 dBm at the acceptable 10-9-bit error rate (BER) threshold level, unamplified transmission distances between 6 km and 76 km have been demonstrated using G.652 and G.655 single mode fibres (SMFs). For the first time, an all optical VCSEL to VCSEL wavelength conversion, switching, transmission at the 1550 nm window and BER evaluation of a NRZ data signal is experimentally demonstrated. With VCSEL wavelength conversion and switching, wavelength adjustments to a spectrum width of 4.8 nm (600 GHz) can be achieved to provide alternative routes to signals when fibre-cuts and wavelength collision occurs therefore enhancing signal continuity. This work also demonstrates a technique of removing and adding a wavelength in a bundle of DWDM and flexible channels using an OADM. This has been implemented using a VCSEL and a fibre Bragg grating (FBG) providing a wavelength isolation ratio of 31.4 dB and ~0.3 𝑑𝐵 add/drop penalty of 8.5 Gb/s signal. As a result, an OADM improves spectrum efficiency by offering wavelength re-use. Optical impairments such as crosstalk, chromatic dispersion (CD) and effects of polarization mode dispersion (PMD) have been experimentally investigated and mitigated. This work showed that crosstalk penalty increased with fibre-length, bitrate, interfering signal power and reduced channel spacing and as a result, a crosstalk-penalty trade-off is required. Effects of CD on a transmitted 10 Gb/s signal were also investigated and its mitigation techniques used to increase the fibre-reach. This work uses the negative dispersion fibres to mitigate the accumulated dispersion over the distance of transmission. A 5 dB sensitivity improvement is reported for an unamplified 76 km using DFB transmitters and combination of NZDSF true-wave reduced slope (TW-RS) and submarine reduced slope (TW-SRS) with + and – dispersion coefficients respectively. We have also demonstrated up to 52 km 10 Gb/s per channel VCSEL-based transmission and reduced net dispersion. Experimental demonstration of forward Raman amplification has achieved a 4.7 dB on-off gain distributed over a 4.8 nm spectral width and a 1.7 dB improvement of receiver sensitivity in Raman-aided 10 Gb/s per wavelength VCSEL transmission. Finally, 4.25-10 Gb/s PON-based point to point (P2P) and point to multipoint (P2MP) broadcast transmission have been experimentally demonstrated. A 10 Gb/s with a 1:8 passive splitter incurred a 3.7 dB penalty for a 24.7 km fibre-link. In summary, this work has demonstrated cost effective and energy efficient potential flexible spectrum techniques for high speed signal transmission. With the optimized network parameters, flexible spectrum is therefore relevant in short-reach, metro-access and long-haul applications for national broadband networks and the Square Kilometre Array (SKA) fibre-based signal and data transmission.
- Full Text:
- Date Issued: 2017
Efficiency evaluation of South African water service provision
- Authors: Brettenny, Warren James
- Date: 2017
- Subjects: Water-supply -- South Africa Municipal water supply -- South Africa , Municipal water supply -- South Africa -- Management Benchmarking (Management) -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/14741 , vital:27835
- Description: In recent years South Africa has experienced numerous service delivery protests. These protests are a result of the lack of delivery of basic services such as water and sanitation (amongst others). To address this, local governments have taken part in benchmarking initiatives (National Benchmarking Initiative, Municipal Benchmarking Initiative) and regulation programmes (BlueDrop,GreenDrop) in an effort to improve the quality of potable water and sanitation services. The latter of these focuses on the quality of the water services delivered and neither focus on the efficiency with which this delivery is achieved. This study uses both nonparametric (data envelopment analysis) aswell as parametric (stochastic frontier) methods to assess the efficiency of water service provision in South Africa over a six year period from 2005 to 2010. Subsequently, the method which is most suited for use in the South African context is proposed. In addition, this study demonstrates how these methods can be used to determine the effectiveness of benchmarking initiatives, namely the National Benchmarking Initiative, in improving the efficiency of water service provision. Furthermore, additional insight into the selection ofm in them out of n bootstrap procedure for efficiency evaluations is established through a simulation study. The inclusion of efficiency evaluations into South African benchmarking initiatives provides new and important insight into the standard of water service delivery. As such, the techniques used in this study illustrate how efficiency analysis can enhance benchmarking initiatives in South Africa.
- Full Text:
- Date Issued: 2017
- Authors: Brettenny, Warren James
- Date: 2017
- Subjects: Water-supply -- South Africa Municipal water supply -- South Africa , Municipal water supply -- South Africa -- Management Benchmarking (Management) -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/14741 , vital:27835
- Description: In recent years South Africa has experienced numerous service delivery protests. These protests are a result of the lack of delivery of basic services such as water and sanitation (amongst others). To address this, local governments have taken part in benchmarking initiatives (National Benchmarking Initiative, Municipal Benchmarking Initiative) and regulation programmes (BlueDrop,GreenDrop) in an effort to improve the quality of potable water and sanitation services. The latter of these focuses on the quality of the water services delivered and neither focus on the efficiency with which this delivery is achieved. This study uses both nonparametric (data envelopment analysis) aswell as parametric (stochastic frontier) methods to assess the efficiency of water service provision in South Africa over a six year period from 2005 to 2010. Subsequently, the method which is most suited for use in the South African context is proposed. In addition, this study demonstrates how these methods can be used to determine the effectiveness of benchmarking initiatives, namely the National Benchmarking Initiative, in improving the efficiency of water service provision. Furthermore, additional insight into the selection ofm in them out of n bootstrap procedure for efficiency evaluations is established through a simulation study. The inclusion of efficiency evaluations into South African benchmarking initiatives provides new and important insight into the standard of water service delivery. As such, the techniques used in this study illustrate how efficiency analysis can enhance benchmarking initiatives in South Africa.
- Full Text:
- Date Issued: 2017
A new synthetic approach for preparation of Efavirenz
- Authors: Chada, Sravanthi
- Date: 2017
- Subjects: Antiretroviral agents , Asymmetric synthesis , Enzyme inhibitors , HIV (Viruses) -- Enzymes
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/15512 , vital:28265
- Description: Efavirenz, a drug that is still inaccessible to millions of people worldwide, is potent non nucleoside reverse transcriptase inhibitor (NNRTI), is one of the preferred agents used in combination therapy for first-line treatment of the human immunodeficiency virus (HIV). NNRTIs attach to and block an HIV enzyme called reverse transcriptase, by blocking reverse transcriptase; NNRTIs prevent HIV from multiplying and can reduce the amount of HIV in the body. Efavirenz can't cure HIV/AIDS, but taken in combination with other HIV medicines (called an HIV regimen) every day helps people with HIV live longer healthier lives. Efavirenz also reduces the risk of HIV transmission and can be used by children who are suffering from HIV/AIDS. All the above therapeutic uses of efavirenz prompted us to identify the novel and hopefully cost efficient synthetic methodology for the preparation of efavirenz. In this thesis a new synthetic method for asymmetric synthesis of efavirenz is described. This route started from commercially available starting materials and it is first established in traditional batch chemistry and further the parameters transferred to a semi continuous flow protocol for optimization.
- Full Text:
- Date Issued: 2017
- Authors: Chada, Sravanthi
- Date: 2017
- Subjects: Antiretroviral agents , Asymmetric synthesis , Enzyme inhibitors , HIV (Viruses) -- Enzymes
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/15512 , vital:28265
- Description: Efavirenz, a drug that is still inaccessible to millions of people worldwide, is potent non nucleoside reverse transcriptase inhibitor (NNRTI), is one of the preferred agents used in combination therapy for first-line treatment of the human immunodeficiency virus (HIV). NNRTIs attach to and block an HIV enzyme called reverse transcriptase, by blocking reverse transcriptase; NNRTIs prevent HIV from multiplying and can reduce the amount of HIV in the body. Efavirenz can't cure HIV/AIDS, but taken in combination with other HIV medicines (called an HIV regimen) every day helps people with HIV live longer healthier lives. Efavirenz also reduces the risk of HIV transmission and can be used by children who are suffering from HIV/AIDS. All the above therapeutic uses of efavirenz prompted us to identify the novel and hopefully cost efficient synthetic methodology for the preparation of efavirenz. In this thesis a new synthetic method for asymmetric synthesis of efavirenz is described. This route started from commercially available starting materials and it is first established in traditional batch chemistry and further the parameters transferred to a semi continuous flow protocol for optimization.
- Full Text:
- Date Issued: 2017
The design and testing of a national estuarine monitoring prgramme for South Africa
- Authors: Cilliers, Gerhard Jordaan
- Date: 2017
- Subjects: Estuaries -- South Africa Berg Estuary (South Africa)
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/15490 , vital:28258
- Description: Adaptive water resource management requires sound scientific based decisions, emanating from robust scientific data. The Department of Environmental Affairs are mandated for collaborative management of the South African coast, including estuaries, through the Integrated Coastal Management Act (Act no 24 of 2008) (ICMA). The Department Water and Sanitation is mandated through the National Water Act (Act no 36 of 1998) (NWA) to design, test and implement monitoring programmes to provide water resource data. Extensive freshwater monitoring programmes exist in South Africa but there is no standard long-term monitoring programme for estuaries. This study designed and tested a National Estuarine Monitoring Programme (NESMP) that is anchored in the NWA and the ICMA. The design was based on a review of international estuary monitoring programmes, consultation with relevant role players and five decades experience in the design, testing and implementation of water resource monitoring programmes by DWS. The main objective of this thesis is 1) to design a national estuarine monitoring programme 2) test the design of the programme for practical implementation by reflecting on collected data from case studies, and 3) design a Decision Support System to translate complex monitoring data into management information. The main objective of the NESMP is 1) to collect long-term data to determine trends in the condition of estuaries in South Africa and 2) to provide management orientated information for effective estuary management. The National Estuary Monitoring programme consists of three tiers. Tier 1 focuses on basic data including system variables and nutrient data. Tier 2 collects data required for the determination of the Ecological Water Requirements (EWR) of estuaries in accordance with a standardised method used by DWS. A tailor made monitoring programme addressing specific issues including pollution incidents and localised development pressure, making use of a combination of Tier 1 and Tier 2 components, forms Tier 3 of the NESMP. This study tested the Tier 1 components of the programme on 28 estuaries across the South African coast since 2012. However, due to space constraints, the data reflected on in this thesis, is only for case studies on the Berg and Breede estuaries between 2012 and 2016. The results indicate that the establishment and operation of the NESMP on South African estuaries making use of monthly surveys, and the deployment of permanent water quality loggers, in line with the proposed protocol, are possible. This does however require collaboration with other role players in order to share responsibility and associated resources. A tiered management structure ensures national, regional and local level implementation takes place seamlessly. A decision support system (DSS) was also designed as part of this thesis to assist with data interpretation and the creation of management orientated information. This DSS includes a measurement of the percentage exceedance of the Threshold of Potential Concern (TPC), which acts as an early warning system for water resource deterioration. This study showed that effective collaboration will ensure the sustainability of the NESMP. Implementation of the more complex and resource intensive Tier 2 and Tier 3 sampling will however need to be investigated to establish the overall success of the NESMP.
- Full Text:
- Date Issued: 2017
- Authors: Cilliers, Gerhard Jordaan
- Date: 2017
- Subjects: Estuaries -- South Africa Berg Estuary (South Africa)
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/15490 , vital:28258
- Description: Adaptive water resource management requires sound scientific based decisions, emanating from robust scientific data. The Department of Environmental Affairs are mandated for collaborative management of the South African coast, including estuaries, through the Integrated Coastal Management Act (Act no 24 of 2008) (ICMA). The Department Water and Sanitation is mandated through the National Water Act (Act no 36 of 1998) (NWA) to design, test and implement monitoring programmes to provide water resource data. Extensive freshwater monitoring programmes exist in South Africa but there is no standard long-term monitoring programme for estuaries. This study designed and tested a National Estuarine Monitoring Programme (NESMP) that is anchored in the NWA and the ICMA. The design was based on a review of international estuary monitoring programmes, consultation with relevant role players and five decades experience in the design, testing and implementation of water resource monitoring programmes by DWS. The main objective of this thesis is 1) to design a national estuarine monitoring programme 2) test the design of the programme for practical implementation by reflecting on collected data from case studies, and 3) design a Decision Support System to translate complex monitoring data into management information. The main objective of the NESMP is 1) to collect long-term data to determine trends in the condition of estuaries in South Africa and 2) to provide management orientated information for effective estuary management. The National Estuary Monitoring programme consists of three tiers. Tier 1 focuses on basic data including system variables and nutrient data. Tier 2 collects data required for the determination of the Ecological Water Requirements (EWR) of estuaries in accordance with a standardised method used by DWS. A tailor made monitoring programme addressing specific issues including pollution incidents and localised development pressure, making use of a combination of Tier 1 and Tier 2 components, forms Tier 3 of the NESMP. This study tested the Tier 1 components of the programme on 28 estuaries across the South African coast since 2012. However, due to space constraints, the data reflected on in this thesis, is only for case studies on the Berg and Breede estuaries between 2012 and 2016. The results indicate that the establishment and operation of the NESMP on South African estuaries making use of monthly surveys, and the deployment of permanent water quality loggers, in line with the proposed protocol, are possible. This does however require collaboration with other role players in order to share responsibility and associated resources. A tiered management structure ensures national, regional and local level implementation takes place seamlessly. A decision support system (DSS) was also designed as part of this thesis to assist with data interpretation and the creation of management orientated information. This DSS includes a measurement of the percentage exceedance of the Threshold of Potential Concern (TPC), which acts as an early warning system for water resource deterioration. This study showed that effective collaboration will ensure the sustainability of the NESMP. Implementation of the more complex and resource intensive Tier 2 and Tier 3 sampling will however need to be investigated to establish the overall success of the NESMP.
- Full Text:
- Date Issued: 2017
Statistical viability assessment of a photovoltaic system in the presence of data uncertainty
- Authors: Clohessy, Chantelle May
- Date: 2017
- Subjects: Bayesian field theory , Photovoltaic power systems
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/15655 , vital:28280
- Description: This thesis investigates statistical techniques that can be used to improve estimates and methods in feasibility assessments of photovoltaic (PV) systems. The use of these techniques are illustrated for a case study of a 1MW PV system proposed for the Nelson Mandela Metropolitan University South Campus in Port Elizabeth, South Africa. The results from the study provide strong support for the use of multivariate profile analysis and interval estimate plots for the assessment of solar resource data. A unique view to manufacturing process control in the generation of energy from a PV system is identified. This link between PV energy generation and process control is lacking in the literature and exploited in this study. Variance component models are used to model power output and energy yield estimates of the proposed PV system. The variance components are simulated using Bayesian simulation techniques. Bayesian tolerance intervals are derived from the variance components and are used to determine what percentage of future power output and energy yield values fall within an interval with a certain probability. The results from the estimated tolerance intervals were informative and provided expected power outputs and energy yields for a given month and specific season. The methods improve on current techniques used to assess the energy output of a system.
- Full Text:
- Date Issued: 2017
- Authors: Clohessy, Chantelle May
- Date: 2017
- Subjects: Bayesian field theory , Photovoltaic power systems
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/15655 , vital:28280
- Description: This thesis investigates statistical techniques that can be used to improve estimates and methods in feasibility assessments of photovoltaic (PV) systems. The use of these techniques are illustrated for a case study of a 1MW PV system proposed for the Nelson Mandela Metropolitan University South Campus in Port Elizabeth, South Africa. The results from the study provide strong support for the use of multivariate profile analysis and interval estimate plots for the assessment of solar resource data. A unique view to manufacturing process control in the generation of energy from a PV system is identified. This link between PV energy generation and process control is lacking in the literature and exploited in this study. Variance component models are used to model power output and energy yield estimates of the proposed PV system. The variance components are simulated using Bayesian simulation techniques. Bayesian tolerance intervals are derived from the variance components and are used to determine what percentage of future power output and energy yield values fall within an interval with a certain probability. The results from the estimated tolerance intervals were informative and provided expected power outputs and energy yields for a given month and specific season. The methods improve on current techniques used to assess the energy output of a system.
- Full Text:
- Date Issued: 2017
The Grootfontein aquifer at Mahikeng, South Africa as hydro-social system
- Authors: Cobbing, Jude Edmund
- Date: 2017
- Subjects: Groundwater -- South Africa -- Mahikeng Hydrogeology -- South Africa -- Mahikeng
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/21351 , vital:29484
- Description: The Grootfontein aquifer is located about 20 km south east of Mahikeng, North West Province, South Africa, and currently supplies about 20% of Mahikeng’s water. Formed in weathered Malmani Subgroup dolomites, the aquifer contains good quality groundwater that could potentially supply more of Mahikeng’s water, as well as provide a strategic reserve of water for use during droughts. Over-abstraction of groundwater from the aquifer, mainly by irrigating farmers but also by the boreholes supplying Mahikeng, has caused the natural groundwater level to drop at a rate of about 0.4 m per year since the 1970s, leading to water level declines of as much as 28 m in parts of the aquifer. Although the Grootfontein aquifer is one of the best studied aquifers in South Africa hydrogeologically, efforts to address these declines since the 1970s have largely failed. This research combines hydrogeological evidence with social research (interviews and participant-observation) and the principles of Earth Stewardship Science to argue that the aquifer functions as a hydro-social system, and that institutional characteristics are the root cause of a collective inability to restore the aquifer to its full potential as a water resource. A sub-optimal and undesirable Nash equilibrium prevails, in which major groundwater users are unable or unwilling to reduce abstraction. The situation has significant cost and risk implications for the environmental, economic and social sectors, and contributes to insecurity, pessimism, inequality and mistrust. An effective local forum with appropriate powers, supported and mandated by the Department of Water and Sanitation, is needed to begin the work of dismantling the sub-optimal equilibrium to realise the potential of the Grootfontein aquifer. Such a forum would require a shared understanding of the hydrogeological mechanisms of the aquifer as well as its social and institutional functioning, since these influence each other in complex ways.
- Full Text:
- Date Issued: 2017
- Authors: Cobbing, Jude Edmund
- Date: 2017
- Subjects: Groundwater -- South Africa -- Mahikeng Hydrogeology -- South Africa -- Mahikeng
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/21351 , vital:29484
- Description: The Grootfontein aquifer is located about 20 km south east of Mahikeng, North West Province, South Africa, and currently supplies about 20% of Mahikeng’s water. Formed in weathered Malmani Subgroup dolomites, the aquifer contains good quality groundwater that could potentially supply more of Mahikeng’s water, as well as provide a strategic reserve of water for use during droughts. Over-abstraction of groundwater from the aquifer, mainly by irrigating farmers but also by the boreholes supplying Mahikeng, has caused the natural groundwater level to drop at a rate of about 0.4 m per year since the 1970s, leading to water level declines of as much as 28 m in parts of the aquifer. Although the Grootfontein aquifer is one of the best studied aquifers in South Africa hydrogeologically, efforts to address these declines since the 1970s have largely failed. This research combines hydrogeological evidence with social research (interviews and participant-observation) and the principles of Earth Stewardship Science to argue that the aquifer functions as a hydro-social system, and that institutional characteristics are the root cause of a collective inability to restore the aquifer to its full potential as a water resource. A sub-optimal and undesirable Nash equilibrium prevails, in which major groundwater users are unable or unwilling to reduce abstraction. The situation has significant cost and risk implications for the environmental, economic and social sectors, and contributes to insecurity, pessimism, inequality and mistrust. An effective local forum with appropriate powers, supported and mandated by the Department of Water and Sanitation, is needed to begin the work of dismantling the sub-optimal equilibrium to realise the potential of the Grootfontein aquifer. Such a forum would require a shared understanding of the hydrogeological mechanisms of the aquifer as well as its social and institutional functioning, since these influence each other in complex ways.
- Full Text:
- Date Issued: 2017
The effect of synthetically-derived xanthone compounds on the suppression of the progression of breast cancer and the associated complications
- Authors: Davison, Candace
- Date: 2017
- Subjects: Breast -- Cancer -- Chemotherapy Breast -- Cancer -- Prevention , Antibacterial agents -- Therapeutic use
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/13889 , vital:27354
- Description: Breast cancer is the most frequently diagnosed cancer in women worldwide.A treatment regime, both effective and safe and can only be achieved once more effective chemotherapeutic agents are discovered or identified. These “drugs” must selectively induce cell death such as apoptosis or necroptosis in the cancer cells. Apoptotic cell death allows a cell to “commit suicide” in genetically- controlled or programmed mechanism(s). The microenvironment of the tumour is important since a nurturing malignant environment is required for tumour maintenance, progression and ultimately the development of metastasis. Due to the correlation of the tumour microenvironment to aggressive tumour progression, emphasis should be placed on the constituents of the tumour’s microenvironment. In recent years, the understanding of intracellular pathways in cancer cells has increased rapidly, contributing to the development of drugs with more specific targets such as growth factors, signalling molecules, cell adhesion proteins, proteases, cell-cycle proteins, modulators of apoptosis and molecules that promote angiogenesis and metastasis. The main aim of this study was thus to identify a few potential or active compounds from a library of synthetically-derived compounds as possible alternative breast cancer treatment candidates.
- Full Text:
- Date Issued: 2017
- Authors: Davison, Candace
- Date: 2017
- Subjects: Breast -- Cancer -- Chemotherapy Breast -- Cancer -- Prevention , Antibacterial agents -- Therapeutic use
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/13889 , vital:27354
- Description: Breast cancer is the most frequently diagnosed cancer in women worldwide.A treatment regime, both effective and safe and can only be achieved once more effective chemotherapeutic agents are discovered or identified. These “drugs” must selectively induce cell death such as apoptosis or necroptosis in the cancer cells. Apoptotic cell death allows a cell to “commit suicide” in genetically- controlled or programmed mechanism(s). The microenvironment of the tumour is important since a nurturing malignant environment is required for tumour maintenance, progression and ultimately the development of metastasis. Due to the correlation of the tumour microenvironment to aggressive tumour progression, emphasis should be placed on the constituents of the tumour’s microenvironment. In recent years, the understanding of intracellular pathways in cancer cells has increased rapidly, contributing to the development of drugs with more specific targets such as growth factors, signalling molecules, cell adhesion proteins, proteases, cell-cycle proteins, modulators of apoptosis and molecules that promote angiogenesis and metastasis. The main aim of this study was thus to identify a few potential or active compounds from a library of synthetically-derived compounds as possible alternative breast cancer treatment candidates.
- Full Text:
- Date Issued: 2017
Ecophysiology and nutrient uptake mechanisms facilitating the prolonged bloom persistence by Cyanothece sp. in Lake St Lucia, South Africa
- Authors: Du Plooy, Schalk Jacobus
- Date: 2017
- Subjects: Cyanobacterial blooms , Cyanobacteria -- Physiology , Cyanobacteria
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/7344 , vital:21324
- Description: Cyanobacterial blooms are becoming more frequent worldwide, with possible negative effects on human health. The effects of climate change and eutrophication have been associated with persistent cyanobacterial blooms becoming more frequent. Altered water characteristics, salinity in particular, influence ecosystem dynamics that may lead to conditions conducive to cyanobacterial blooms. The occurrence of an 18-month long Cyanothece sp. bloom (the longest for any cyanobacterium recorded so far worldwide and the first of the genus) from June 2009 to December 2010 in Africa’s largest estuarine lake, St Lucia, highlighted the susceptibility of ecosystems to anthropogenic alterations. This study investigated the long-term survival and physiological adaptations of Cyanothece sp. to various and dynamic environmental conditions that contributed towards its bloom persistence. The main findings are the high salinities at which Cyanothece sp. could perform important physiological processes such as N uptake, N2 fixation and photosynthesis. Nutrient uptake (both nitrogen and phosphorus) was observed over the full experimental salinity range (0-300) while N2 fixation was only observed up to a salinity of 120. Nutrient uptake rates significantly decreased at this threshold salinity of 120. Interestingly, photosystem II activity was not observed in Cyanothece sp. during this study, but photosystem I activity was robust. Salinity had a minor influence on electron transport rates by photosystem I, high temperature (> 30°C) did however increase electron transport rates. Rapid responses to hypo-osmotic shock (i.e. osmotic downshift during freshening events) by Cyanothece sp. cells also helped minimize cell rupture due to high turgor pressure. Zooplankton abundance within the St Lucia system was negatively correlated with salinity, while grazing experiments indicated that the typical estuarine zooplankton species are able to graze on Cyanothece sp. cells. Therefore, the disappearance of zooplankton at salinities above 60 must have been an important factor in the bloom persistence. Apart from the ecological factors that were at play in St Lucia during the bloom period, the persistence of the Cyanothece sp. bloom can be attributed to the robust nature of their nutrient uptake, nitrogen fixation and photosynthetic systems to maintain activity despite extreme hypersalinity levels.
- Full Text:
- Date Issued: 2017
- Authors: Du Plooy, Schalk Jacobus
- Date: 2017
- Subjects: Cyanobacterial blooms , Cyanobacteria -- Physiology , Cyanobacteria
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/7344 , vital:21324
- Description: Cyanobacterial blooms are becoming more frequent worldwide, with possible negative effects on human health. The effects of climate change and eutrophication have been associated with persistent cyanobacterial blooms becoming more frequent. Altered water characteristics, salinity in particular, influence ecosystem dynamics that may lead to conditions conducive to cyanobacterial blooms. The occurrence of an 18-month long Cyanothece sp. bloom (the longest for any cyanobacterium recorded so far worldwide and the first of the genus) from June 2009 to December 2010 in Africa’s largest estuarine lake, St Lucia, highlighted the susceptibility of ecosystems to anthropogenic alterations. This study investigated the long-term survival and physiological adaptations of Cyanothece sp. to various and dynamic environmental conditions that contributed towards its bloom persistence. The main findings are the high salinities at which Cyanothece sp. could perform important physiological processes such as N uptake, N2 fixation and photosynthesis. Nutrient uptake (both nitrogen and phosphorus) was observed over the full experimental salinity range (0-300) while N2 fixation was only observed up to a salinity of 120. Nutrient uptake rates significantly decreased at this threshold salinity of 120. Interestingly, photosystem II activity was not observed in Cyanothece sp. during this study, but photosystem I activity was robust. Salinity had a minor influence on electron transport rates by photosystem I, high temperature (> 30°C) did however increase electron transport rates. Rapid responses to hypo-osmotic shock (i.e. osmotic downshift during freshening events) by Cyanothece sp. cells also helped minimize cell rupture due to high turgor pressure. Zooplankton abundance within the St Lucia system was negatively correlated with salinity, while grazing experiments indicated that the typical estuarine zooplankton species are able to graze on Cyanothece sp. cells. Therefore, the disappearance of zooplankton at salinities above 60 must have been an important factor in the bloom persistence. Apart from the ecological factors that were at play in St Lucia during the bloom period, the persistence of the Cyanothece sp. bloom can be attributed to the robust nature of their nutrient uptake, nitrogen fixation and photosynthetic systems to maintain activity despite extreme hypersalinity levels.
- Full Text:
- Date Issued: 2017
Foraging ecology of gentoo penguins pygoscelis papua at the Falkland Islands
- Authors: Handley, Jonathan Murray
- Date: 2017
- Subjects: Gentoo penguin -- Food -- Falkland Islands Gentoo penguin -- Ecology
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/14113 , vital:27431
- Description: Marine top predators often occupy broad geographical ranges that encompass varied habitats. Therefore, a pre-requisite towards conserving these animals is to determine the components of their realized niche, and investigate whether a species is a specialist or a generalist. For generalist species, it is also necessary to understand if local specialisation occurs. Uncovering these components can allow us to build models of a species realized niche that may then be used to infer habitat use in unsampled locations. However, fully understanding the components of a marine top predators realized niche is challenging owing to the limited opportunity for in situ observations. Overcoming these limitations is a key step in marine top predator research. It will enhance our understanding of trophic coupling in marine systems, and aid in the development of tools to better study these predators in their dynamic environment. Seabirds, penguins (Spheniscids) in particular, are a group of animals for which investigating their realized niche is of vital importance. This is because numerous species face growing uncertainty in the Anthropocene, and in a time of rapid environmental change there is furthermore a need to better understand the potential use of these birds as indicators of ecosystem health. The aim of this thesis, therefore, is to investigate the foraging ecology of gentoo penguins (Pygoscelis papua) at the Falkland Islands. At the Falkland Islands, limited historical information exists regarding this species foraging ecology, with most information coming from a single location at the Falklands. As the Falkland Islands have the world’s largest population of gentoo penguins, elucidating factors influencing this population will have global relevance. Furthermore, historical information indicated potential competition with fisheries, and with prospecting for hydrocarbons and an inshore fishery, there is a need to understand the distribution of these birds across the islands. Penguins are also well suited to carry biologging devices allowing for in situ observations of inter and intraspecific interactions, as well as habitat specific interactions. In this study, I sampled birds over three breeding seasons, from four breeding colonies - chosen for their varied surrounding at sea habitat - across the Falkland Islands. I investigated the diet with stomach content and stable isotope analysis, the at-sea distribution with GPS and time depth recorders, and how these birds behaved at sea using custom made animal-borne camera loggers. Furthermore, I developed a method to recognise prey encounter events from back mounted accelerometers, using a supervised machine learning approach. As part of the first species specific description of diet at this scale for the Falklands, I revealed six key prey items for the birds: rock cod (Patagonotothen spp.), lobster krill (Munida spp.), Falkland herring (Sprattus fuegensis), Patagonian squid (Doryteuthis gahi), juvenile fish (likely all nototheniids), and southern blue whiting (Micromesistius australis). The use of animal-borne camera loggers verified that not only do gentoo penguins consume a diverse array of prey items, but they adopted various methods to capture and pursue prey, with evidence of birds following optimal foraging theory. Prey composition varied significantly between study sites with the at-sea distribution and habitat use of penguins reflecting that of local prey. Birds from colonies close to gently sloping, shallow waters, foraged primarily in a benthic manner and had larger niche widths. However, those at a colony surrounded by steeply sloping, deeper waters, typically foraged in a pelagic manner. Contrasting diet patterns were also prevalent from stable isotope data, and the niche widths of birds relating to both stomach content and stable isotope data were larger at colonies where benthic foraging was prevalent. Therefore, it was clear that surrounding bathymetry played a key role in shaping this species’ foraging ecology, and that at the population level at the Falkland Islands birds are generalists. However, at individual colonies some specialisation occurs to take advantage of locally available prey. I developed habitat distribution models - via boosted regression trees – which transferred well in time but poorly across space. Reasons for poor model transfer might relate to the generalist foraging nature of these birds and the reduced availability of environmental predictors owing to the limited range of these birds. I furthermore developed a method to identify prey encounter events that can also, to a degree, distinguish between prey items. This method will be a promising approach to refine habitat distribution models in future. These habitat distribution models could potentially contribute to marine spatial planning at the Falkland Islands. Footage from animal-borne camera loggers clearly showed that prey behaviour can significantly influence trophic coupling in marine systems and should be accounted for in studies using marine top predators as samplers of mid to lower trophic level species. Ultimately, flexibility in foraging strategies and inter-colony variation will play a critical role when assessing factors such as interspecific competition or overlap with anthropogenic activities.
- Full Text:
- Date Issued: 2017
- Authors: Handley, Jonathan Murray
- Date: 2017
- Subjects: Gentoo penguin -- Food -- Falkland Islands Gentoo penguin -- Ecology
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/14113 , vital:27431
- Description: Marine top predators often occupy broad geographical ranges that encompass varied habitats. Therefore, a pre-requisite towards conserving these animals is to determine the components of their realized niche, and investigate whether a species is a specialist or a generalist. For generalist species, it is also necessary to understand if local specialisation occurs. Uncovering these components can allow us to build models of a species realized niche that may then be used to infer habitat use in unsampled locations. However, fully understanding the components of a marine top predators realized niche is challenging owing to the limited opportunity for in situ observations. Overcoming these limitations is a key step in marine top predator research. It will enhance our understanding of trophic coupling in marine systems, and aid in the development of tools to better study these predators in their dynamic environment. Seabirds, penguins (Spheniscids) in particular, are a group of animals for which investigating their realized niche is of vital importance. This is because numerous species face growing uncertainty in the Anthropocene, and in a time of rapid environmental change there is furthermore a need to better understand the potential use of these birds as indicators of ecosystem health. The aim of this thesis, therefore, is to investigate the foraging ecology of gentoo penguins (Pygoscelis papua) at the Falkland Islands. At the Falkland Islands, limited historical information exists regarding this species foraging ecology, with most information coming from a single location at the Falklands. As the Falkland Islands have the world’s largest population of gentoo penguins, elucidating factors influencing this population will have global relevance. Furthermore, historical information indicated potential competition with fisheries, and with prospecting for hydrocarbons and an inshore fishery, there is a need to understand the distribution of these birds across the islands. Penguins are also well suited to carry biologging devices allowing for in situ observations of inter and intraspecific interactions, as well as habitat specific interactions. In this study, I sampled birds over three breeding seasons, from four breeding colonies - chosen for their varied surrounding at sea habitat - across the Falkland Islands. I investigated the diet with stomach content and stable isotope analysis, the at-sea distribution with GPS and time depth recorders, and how these birds behaved at sea using custom made animal-borne camera loggers. Furthermore, I developed a method to recognise prey encounter events from back mounted accelerometers, using a supervised machine learning approach. As part of the first species specific description of diet at this scale for the Falklands, I revealed six key prey items for the birds: rock cod (Patagonotothen spp.), lobster krill (Munida spp.), Falkland herring (Sprattus fuegensis), Patagonian squid (Doryteuthis gahi), juvenile fish (likely all nototheniids), and southern blue whiting (Micromesistius australis). The use of animal-borne camera loggers verified that not only do gentoo penguins consume a diverse array of prey items, but they adopted various methods to capture and pursue prey, with evidence of birds following optimal foraging theory. Prey composition varied significantly between study sites with the at-sea distribution and habitat use of penguins reflecting that of local prey. Birds from colonies close to gently sloping, shallow waters, foraged primarily in a benthic manner and had larger niche widths. However, those at a colony surrounded by steeply sloping, deeper waters, typically foraged in a pelagic manner. Contrasting diet patterns were also prevalent from stable isotope data, and the niche widths of birds relating to both stomach content and stable isotope data were larger at colonies where benthic foraging was prevalent. Therefore, it was clear that surrounding bathymetry played a key role in shaping this species’ foraging ecology, and that at the population level at the Falkland Islands birds are generalists. However, at individual colonies some specialisation occurs to take advantage of locally available prey. I developed habitat distribution models - via boosted regression trees – which transferred well in time but poorly across space. Reasons for poor model transfer might relate to the generalist foraging nature of these birds and the reduced availability of environmental predictors owing to the limited range of these birds. I furthermore developed a method to identify prey encounter events that can also, to a degree, distinguish between prey items. This method will be a promising approach to refine habitat distribution models in future. These habitat distribution models could potentially contribute to marine spatial planning at the Falkland Islands. Footage from animal-borne camera loggers clearly showed that prey behaviour can significantly influence trophic coupling in marine systems and should be accounted for in studies using marine top predators as samplers of mid to lower trophic level species. Ultimately, flexibility in foraging strategies and inter-colony variation will play a critical role when assessing factors such as interspecific competition or overlap with anthropogenic activities.
- Full Text:
- Date Issued: 2017
Agribusiness challenges to effectiveness of contract farming in commercialisation of small-scale vegetable farmers
- Authors: Khapayi, Musa
- Date: 2017
- Subjects: Farms, Small -- South Africa -- Eastern Cape , Agriculture -- Economic aspects -- South Africa -- Eastern Cape , Agricultural industries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: http://hdl.handle.net/10948/13981 , vital:27363
- Description: The spread of contract farming in South Africa in recent years has provoked an ideological debate in literature. Linking small-scale vegetable farmers with lucrative agricultural markets through agribusiness value chains is seen as one of the foremost emerging agricultural practices to develop the subsistence farming sector into a mainstream economic sector – thereby revitalising the rural economy and alleviating poverty levels in the developing rural areas of South Africa. However, the challenges agribusiness and small-scale farmers experience in contract farming engagement and the prospects for enhancing the inclusion of small-scale farmers into modern value chains remain open to debate – two decades after transition to democracy. Yet the factors and mechanisms influencing the effective application of contract farming in the transition to commercial farming by small-scale farmers have not been thoroughly explored in South African research. Despite the efforts and the substantial investments made and the various policies and initiatives instigated to fast-track the linkages of small-scale farmers into high-value markets, the success stories of previously disadvantaged farmers operating in commercial agri-food chains are rare. Given the millions of small-scale farmers in former homelands alone, the negligible number of small-scale farmers successfully operating in commercial agri-food chains shows that the objectives to enable small-scale farmers to improve their livelihoods through participation in commercial agri-food chains have not yet been met. The broad objectives of the study were therefore to investigate the agribusiness challenges inherent in contract farming and the conditions and incentives required by agribusiness firms to engage small-scale vegetable farmers in contract farming programmes. Furthermore, the study examined the role played by the South African government to reduce the high transaction costs incurred by agribusinesses when engaging small-scale farmers in contractual arrangements. The Amathole and Sarah Baartman (formerly Cacadu) district municipalities in the Eastern Cape Province of South Africa were chosen as the composite survey area for this study. A predominantly qualitative research approach was applied to gather data on the phenomena under study. The following methodologies and research instruments and tools were selected. Firstly – as the secondary component of the research – a systematic review of literature to date was conducted to guide the empirical research and primary methodology. Secondly, the empirical component of the study comprised a questionnaire survey, unstructured interviews and focus group discussions. The questionnaire survey was used to collect data from the agribusiness firms in the area surveyed concerning the following aspects: the significant determinants of contract farming, the incentives required by the agribusiness firms to engage small-scale vegetable farmers in their contract farming programmes and the challenges faced by agribusiness firms in their interaction with small-scale farmers in contractual arrangements. Unstructured interviews were used to gather data from officials at each of the three levels of government – the Department of Rural Development and Land Reform nationally, Department of Agriculture and Land Reform provincially and (at local government level) two district municipalities – on the role played by government to reduce the high transaction costs incurred by agri-firms when procuring agricultural raw materials from small-scale vegetable farmers. Focus group discussions were conducted with small-scale farmers regarding their perspective on working with agribusiness firms and to establish the distinguishing characteristics of small-scale farmers in the area surveyed. Relevant policy documents collected from two of the three representative groups of the study population, i.e. agribusiness personnel and government officials, provided the essential context. The study revealed a limited number of contract farming business linkages between small-scale vegetable farmers and agribusiness firms in the survey area. Those that do exist are problematic to both the agribusiness firms and the small-scale farmers. It emerged that the contract farming environment in the area surveyed is highly polarised and characterised by a fundamental conflict of interest between agribusiness and farmer. Among the divergent key factors inhibiting contract farming engagement were a lack in terms of quality seeds, trust, entrepreneurial skills and formal contract agreements. Asset endowment (both land and non-land assets) was found to be significant pre-selection determinants in the farmer’s capacity to be contracted. Access to innovative technology, as well as government incentives such as production inputs, were found to be critical to agribusiness firms to engage smallscale farmers in their contract farming programmes. Government assistance in terms of high transaction costs to agribusiness firms working with large groups of small-scale farmers was found to be essential but inadequate under current policy. This impacts directly on the effectiveness and promotion of contract farming. Furthermore, the current results corroborate the findings of numerous South African studies in the vast body of worldwide research. Firstly, lack of land and non-land assets continue to be major impediments to the direct participa-tion of small-scale farmers in contract farming programmes and, secondly, the transaction and market information costs incurred by agribusiness prevent the participation of less endowed farmers in contract farming programmes. Conducted within the interpretivist paradigm, the explorative research identified wide-ranging challenges in the relationship between agri-business and small-scale farmers which directly impact the effective-ness of contract farming as a development and agrarian reform strategy. Despite their problematic relationship, however, agribusiness and small-scale contract farmers were in agreement that the government needs to expand its support for agri-firms to incentivise greater numbers of small-scale farmers having the opportunity to achieve commercial status through contract farming. The study therefore recommends a collaborative partnership between private firms and government, with state support through revised policies and development programmes. These amendments are crucial to enhancing the engagement of small-scale vegetable farmers in lucrative agri-food chains.
- Full Text:
- Date Issued: 2017
- Authors: Khapayi, Musa
- Date: 2017
- Subjects: Farms, Small -- South Africa -- Eastern Cape , Agriculture -- Economic aspects -- South Africa -- Eastern Cape , Agricultural industries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: http://hdl.handle.net/10948/13981 , vital:27363
- Description: The spread of contract farming in South Africa in recent years has provoked an ideological debate in literature. Linking small-scale vegetable farmers with lucrative agricultural markets through agribusiness value chains is seen as one of the foremost emerging agricultural practices to develop the subsistence farming sector into a mainstream economic sector – thereby revitalising the rural economy and alleviating poverty levels in the developing rural areas of South Africa. However, the challenges agribusiness and small-scale farmers experience in contract farming engagement and the prospects for enhancing the inclusion of small-scale farmers into modern value chains remain open to debate – two decades after transition to democracy. Yet the factors and mechanisms influencing the effective application of contract farming in the transition to commercial farming by small-scale farmers have not been thoroughly explored in South African research. Despite the efforts and the substantial investments made and the various policies and initiatives instigated to fast-track the linkages of small-scale farmers into high-value markets, the success stories of previously disadvantaged farmers operating in commercial agri-food chains are rare. Given the millions of small-scale farmers in former homelands alone, the negligible number of small-scale farmers successfully operating in commercial agri-food chains shows that the objectives to enable small-scale farmers to improve their livelihoods through participation in commercial agri-food chains have not yet been met. The broad objectives of the study were therefore to investigate the agribusiness challenges inherent in contract farming and the conditions and incentives required by agribusiness firms to engage small-scale vegetable farmers in contract farming programmes. Furthermore, the study examined the role played by the South African government to reduce the high transaction costs incurred by agribusinesses when engaging small-scale farmers in contractual arrangements. The Amathole and Sarah Baartman (formerly Cacadu) district municipalities in the Eastern Cape Province of South Africa were chosen as the composite survey area for this study. A predominantly qualitative research approach was applied to gather data on the phenomena under study. The following methodologies and research instruments and tools were selected. Firstly – as the secondary component of the research – a systematic review of literature to date was conducted to guide the empirical research and primary methodology. Secondly, the empirical component of the study comprised a questionnaire survey, unstructured interviews and focus group discussions. The questionnaire survey was used to collect data from the agribusiness firms in the area surveyed concerning the following aspects: the significant determinants of contract farming, the incentives required by the agribusiness firms to engage small-scale vegetable farmers in their contract farming programmes and the challenges faced by agribusiness firms in their interaction with small-scale farmers in contractual arrangements. Unstructured interviews were used to gather data from officials at each of the three levels of government – the Department of Rural Development and Land Reform nationally, Department of Agriculture and Land Reform provincially and (at local government level) two district municipalities – on the role played by government to reduce the high transaction costs incurred by agri-firms when procuring agricultural raw materials from small-scale vegetable farmers. Focus group discussions were conducted with small-scale farmers regarding their perspective on working with agribusiness firms and to establish the distinguishing characteristics of small-scale farmers in the area surveyed. Relevant policy documents collected from two of the three representative groups of the study population, i.e. agribusiness personnel and government officials, provided the essential context. The study revealed a limited number of contract farming business linkages between small-scale vegetable farmers and agribusiness firms in the survey area. Those that do exist are problematic to both the agribusiness firms and the small-scale farmers. It emerged that the contract farming environment in the area surveyed is highly polarised and characterised by a fundamental conflict of interest between agribusiness and farmer. Among the divergent key factors inhibiting contract farming engagement were a lack in terms of quality seeds, trust, entrepreneurial skills and formal contract agreements. Asset endowment (both land and non-land assets) was found to be significant pre-selection determinants in the farmer’s capacity to be contracted. Access to innovative technology, as well as government incentives such as production inputs, were found to be critical to agribusiness firms to engage smallscale farmers in their contract farming programmes. Government assistance in terms of high transaction costs to agribusiness firms working with large groups of small-scale farmers was found to be essential but inadequate under current policy. This impacts directly on the effectiveness and promotion of contract farming. Furthermore, the current results corroborate the findings of numerous South African studies in the vast body of worldwide research. Firstly, lack of land and non-land assets continue to be major impediments to the direct participa-tion of small-scale farmers in contract farming programmes and, secondly, the transaction and market information costs incurred by agribusiness prevent the participation of less endowed farmers in contract farming programmes. Conducted within the interpretivist paradigm, the explorative research identified wide-ranging challenges in the relationship between agri-business and small-scale farmers which directly impact the effective-ness of contract farming as a development and agrarian reform strategy. Despite their problematic relationship, however, agribusiness and small-scale contract farmers were in agreement that the government needs to expand its support for agri-firms to incentivise greater numbers of small-scale farmers having the opportunity to achieve commercial status through contract farming. The study therefore recommends a collaborative partnership between private firms and government, with state support through revised policies and development programmes. These amendments are crucial to enhancing the engagement of small-scale vegetable farmers in lucrative agri-food chains.
- Full Text:
- Date Issued: 2017
Freshwater invertebrate assemblages of the Eastern Cape Karoo region (South Africa) earmarked for shale gas exploration
- Authors: Mabidi, Annah
- Date: 2017
- Subjects: Invertebrates -- South Africa -- Karoo , Shale gas -- Conservation -- South Africa -- Karoo Freshwater animals -- South Africa -- Karoo Stream ecology -- South Africa -- Karoo
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/13713 , vital:27301
- Description: The Eastern Cape Karoo region is semi-arid with highly variable rainfall. This variability in rainfall sustains a mosaic of surface freshwater bodies that range from permanently to temporarily inundated. These waterbodies provide habitats for diverse invertebrate assemblages. The imminent hydraulic fracturing for shale gas has a potential to modify the water regime, with particular risk of salinisation. Accumulation of salts in freshwater wetlands results in loss of biodiversity, as invertebrate species shift from salt intolerant to salt tolerant species. This study therefore aims to expand on existing knowledge and provide new information on the distribution, diversity and structure of macroinvertebrate assemblages associated with various freshwater bodies in the region prior to shale gas exploration. Limnological and ecological aspects of thirty-three waterbodies (rivers, dams and depression wetlands) were investigated between November 2014 and March 2016. An experimental study on the effects of salinity on hatching success of branchiopod resting eggs was also included in the research. Rivers were characterised by high conductivity and depression wetlands by high turbidity, while dams had relatively higher pH than the other two waterbody types. In terms of global phosphorus interpretation guidelines, the results indicate that freshwater systems in the study region are predominantly eutrophic, indicating that agricultural run-off, particularly from livestock dung (goats, cattle and sheep), is an important source of phosphorus in the freshwater systems studied. Our results revealed new distribution records for branchiopod crustaceans in the Eastern Cape region, including the first record of Laevicaudata. Results showed that the sampled variables were unable to explain the variation in physicochemistry and invertebrate assemblage of several sites. Waterbody type, whether a depression wetland or a river, was the only factor that consistently showed an effect on the composition of both physicochemical data and invertebrate data. Depression wetlands ranged from completely bare to being extensively covered by macrophytes. Therefore, the effect of macrophyte cover in structuring macroinvertebrate assemblages was the focus of further investigation. The results indicated that the macrophyte cover gradient had little influence on the structure of the invertebrate assemblages in the depression wetlands, while only the presence/absence of vegetation significantly influenced the structure of the invertebrate assemblages in these systems. Surface area, dissolved inorganic nitrogen and pelagic chlorophyll-a were the environmental variables that best explained the variation in the macroinvertebrate assemblages among the sites. However, the differences in macroinvertebrate richness, abundance and distribution patterns among sites were only weakly influenced by local and regional environmental factors. These findings suggest that invertebrate in temporary wetland systems are adapted to the highly variable nature of temporary habitats, thus the influence of local variables is negligible. Results of the experimental study, on the effect of salinity on hatching success of branchiopod resting eggs, revealed that hatchling abundance and diversity of large branchiopods was significantly reduced at salinities of 2.5 g L−1 and above. Salt-tolerant taxa such as Copepoda and Ostracoda were the only ones to emerge in the highest salinity of 10 g L−1. Thus, should the region continue to experience increasing aridity and possible shale gas development, which all aggravate the salinisation problem, severe loss of branchiopod diversity (Anostraca, Laevicaudata, Spinicaudata and Notostraca) is likely to occur. This may lead to considerable decline in invertebrate diversity in the region, with cascading effects on food webs and ecosystem functions. The findings of this study can potentially be used in comparative studies on wetland invertebrate ecology in other semi-arid regions and in the formulation of policy and strategies for biodiversity conservation.
- Full Text:
- Date Issued: 2017
- Authors: Mabidi, Annah
- Date: 2017
- Subjects: Invertebrates -- South Africa -- Karoo , Shale gas -- Conservation -- South Africa -- Karoo Freshwater animals -- South Africa -- Karoo Stream ecology -- South Africa -- Karoo
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/13713 , vital:27301
- Description: The Eastern Cape Karoo region is semi-arid with highly variable rainfall. This variability in rainfall sustains a mosaic of surface freshwater bodies that range from permanently to temporarily inundated. These waterbodies provide habitats for diverse invertebrate assemblages. The imminent hydraulic fracturing for shale gas has a potential to modify the water regime, with particular risk of salinisation. Accumulation of salts in freshwater wetlands results in loss of biodiversity, as invertebrate species shift from salt intolerant to salt tolerant species. This study therefore aims to expand on existing knowledge and provide new information on the distribution, diversity and structure of macroinvertebrate assemblages associated with various freshwater bodies in the region prior to shale gas exploration. Limnological and ecological aspects of thirty-three waterbodies (rivers, dams and depression wetlands) were investigated between November 2014 and March 2016. An experimental study on the effects of salinity on hatching success of branchiopod resting eggs was also included in the research. Rivers were characterised by high conductivity and depression wetlands by high turbidity, while dams had relatively higher pH than the other two waterbody types. In terms of global phosphorus interpretation guidelines, the results indicate that freshwater systems in the study region are predominantly eutrophic, indicating that agricultural run-off, particularly from livestock dung (goats, cattle and sheep), is an important source of phosphorus in the freshwater systems studied. Our results revealed new distribution records for branchiopod crustaceans in the Eastern Cape region, including the first record of Laevicaudata. Results showed that the sampled variables were unable to explain the variation in physicochemistry and invertebrate assemblage of several sites. Waterbody type, whether a depression wetland or a river, was the only factor that consistently showed an effect on the composition of both physicochemical data and invertebrate data. Depression wetlands ranged from completely bare to being extensively covered by macrophytes. Therefore, the effect of macrophyte cover in structuring macroinvertebrate assemblages was the focus of further investigation. The results indicated that the macrophyte cover gradient had little influence on the structure of the invertebrate assemblages in the depression wetlands, while only the presence/absence of vegetation significantly influenced the structure of the invertebrate assemblages in these systems. Surface area, dissolved inorganic nitrogen and pelagic chlorophyll-a were the environmental variables that best explained the variation in the macroinvertebrate assemblages among the sites. However, the differences in macroinvertebrate richness, abundance and distribution patterns among sites were only weakly influenced by local and regional environmental factors. These findings suggest that invertebrate in temporary wetland systems are adapted to the highly variable nature of temporary habitats, thus the influence of local variables is negligible. Results of the experimental study, on the effect of salinity on hatching success of branchiopod resting eggs, revealed that hatchling abundance and diversity of large branchiopods was significantly reduced at salinities of 2.5 g L−1 and above. Salt-tolerant taxa such as Copepoda and Ostracoda were the only ones to emerge in the highest salinity of 10 g L−1. Thus, should the region continue to experience increasing aridity and possible shale gas development, which all aggravate the salinisation problem, severe loss of branchiopod diversity (Anostraca, Laevicaudata, Spinicaudata and Notostraca) is likely to occur. This may lead to considerable decline in invertebrate diversity in the region, with cascading effects on food webs and ecosystem functions. The findings of this study can potentially be used in comparative studies on wetland invertebrate ecology in other semi-arid regions and in the formulation of policy and strategies for biodiversity conservation.
- Full Text:
- Date Issued: 2017
Tree toppling by elephants and its consequences in thicket mosaic vegetation of Addo Elephant National Park
- Authors: Mgqatsa, Nokubonga
- Date: 2017
- Subjects: Elephants -- Behavior -- South Africa -- Addo Elephant National Park Woody plants -- South Africa -- Addo Elephant National Park
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/19365 , vital:28859
- Description: This study explored the extent of elephant tree toppling and possible cascading effects in Karoo Thicket Mosaic habitat in the Eastern Cape Province, South Africa. While the notion that elephants topple trees is well recognised, little is known about their indirect effects and the possible influence on several trophic levels. Changes brought about by elephants have the potential to influence microclimatic conditions, soil litter processes, plant community composition and other animals. Therefore, this study determined the impacts of elephants on tree toppling, and hence the production of coarse woody debris and the Coarse Woody Debris Profile. Additionally, I explored the consequences of elephant tree toppling on the plant community, small mammals and seed removal. Furthermore, I explored the potential factors facilitating the coexistence of woody plants and elephants. I compared coarse woody debris production and the Coarse Woody Debris Profile between sites with and without elephants. Further, I assessed the consequences of tree toppling in the elephant present site at a patch scale to explore the possible cascading effects of elephants. Firstly, I showed that elephants impacted woody plants through branch/stem breakages and toppling of trees, but that effects vary for different categories of the Coarse Woody Debris Profile. This result confirms the most recent findings that woody plants are at risk from elephant herbivory in Karoo Thicket Mosaic habitat. The elephant toppling effect on these landscapes is largely influenced by plant growth form, with woody trees suffering high levels of elephant toppling than shrubs of comparable size. However, toppled Pappea capensis is able to persist from being toppled by elephants, either through coppicing or resprouting. Additionally, I showed that toppled trees form discrete patches on the landscape, with altered microclimate and browsing pressures. While I detected no significant effect of these changes on plant composition and abundance within these patches, these findings indicate the possible influence of elephants on facilitating plant recruitment and altering plant communities of thicket through toppling of trees. Moreover, I showed that elephant toppling of trees provide habitat patches for small mammals, thus affecting seed removal by vertebrates within patches. These changes had no discernable effect on soil seed banks. However, they highlight the need to better understand the temporal dynamics of these patches and implications for seed dynamics and plant communities on the landscape. The results show the patterns of elephant impacts on woody plants and possible cascading effects in the presence of elephants. Therefore, the study advances our understanding of top-down effects of elephants and shows the relevance of understanding these effects in order to effectively manage elephant impacts in different systems.
- Full Text:
- Date Issued: 2017
- Authors: Mgqatsa, Nokubonga
- Date: 2017
- Subjects: Elephants -- Behavior -- South Africa -- Addo Elephant National Park Woody plants -- South Africa -- Addo Elephant National Park
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/19365 , vital:28859
- Description: This study explored the extent of elephant tree toppling and possible cascading effects in Karoo Thicket Mosaic habitat in the Eastern Cape Province, South Africa. While the notion that elephants topple trees is well recognised, little is known about their indirect effects and the possible influence on several trophic levels. Changes brought about by elephants have the potential to influence microclimatic conditions, soil litter processes, plant community composition and other animals. Therefore, this study determined the impacts of elephants on tree toppling, and hence the production of coarse woody debris and the Coarse Woody Debris Profile. Additionally, I explored the consequences of elephant tree toppling on the plant community, small mammals and seed removal. Furthermore, I explored the potential factors facilitating the coexistence of woody plants and elephants. I compared coarse woody debris production and the Coarse Woody Debris Profile between sites with and without elephants. Further, I assessed the consequences of tree toppling in the elephant present site at a patch scale to explore the possible cascading effects of elephants. Firstly, I showed that elephants impacted woody plants through branch/stem breakages and toppling of trees, but that effects vary for different categories of the Coarse Woody Debris Profile. This result confirms the most recent findings that woody plants are at risk from elephant herbivory in Karoo Thicket Mosaic habitat. The elephant toppling effect on these landscapes is largely influenced by plant growth form, with woody trees suffering high levels of elephant toppling than shrubs of comparable size. However, toppled Pappea capensis is able to persist from being toppled by elephants, either through coppicing or resprouting. Additionally, I showed that toppled trees form discrete patches on the landscape, with altered microclimate and browsing pressures. While I detected no significant effect of these changes on plant composition and abundance within these patches, these findings indicate the possible influence of elephants on facilitating plant recruitment and altering plant communities of thicket through toppling of trees. Moreover, I showed that elephant toppling of trees provide habitat patches for small mammals, thus affecting seed removal by vertebrates within patches. These changes had no discernable effect on soil seed banks. However, they highlight the need to better understand the temporal dynamics of these patches and implications for seed dynamics and plant communities on the landscape. The results show the patterns of elephant impacts on woody plants and possible cascading effects in the presence of elephants. Therefore, the study advances our understanding of top-down effects of elephants and shows the relevance of understanding these effects in order to effectively manage elephant impacts in different systems.
- Full Text:
- Date Issued: 2017
Studies on acoustic properties of non-woven fabrics
- Authors: Mvubu, Mlando Basel
- Date: 2017
- Subjects: Needlepunch (Nonwoven fabric) Nonwoven fabrics , Textile fabrics
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/19387 , vital:28866
- Description: This study is divided in to two main parts. The first part deals with the optimization of process parameters of needle-punched non-woven fabrics for achieving maximum sound absorption by employing a Box-Behnken factorial design. The influence of fibre type, depth of needle penetration and stroke frequency on sound absorption properties were studied. These parameters were varied at three levels during experimental trials. From multiple regression analysis, it was observed that the depth of needle penetration alone was the most dominant factor among the selected parameters, which was followed by the interaction between depth of needle penetration and stroke frequency. Fibre type was the least dominant parameter affecting sound absorption. A maximum sound absorption coefficient of 47% (0.47) was obtained from the selected parameters. The results showed that for a process such as needle-punching, which is influenced by multiple variables, it is important to also study the interactive effects of process parameters for achieving optimum sound absorption. The second part of the study deals with the effect of type of natural fibre (fineness), and the blending ratio (with PET fibres) on the air permeability of the needle-punched non-woven fabrics and then it proceeds to study the effect of the air-gap, type of natural fibre (fineness) and blending ratio (with PET fibres) on sound absorption of needle-punched non-woven fabrics. These parameters are tested individually and their two way interaction (synergy) effect using ANOVA. The air-gap was varied from 0mm to 25mm with 5mm increments, three natural fibre types were used and all were blended with polyester fibres at three blending ratios for each natural fibre type. The Univariate Tests of Significance shows that all three parameters have a significant effect on sound absorption together with two two-way interactions, with the exception of the Blend Ratio × Air Gap two-way interaction which was not significant. It was found that the sound absorption improves with the increase in the air-gap size up to 15mm after which sound absorption decreased slightly with the further increase in the air-gap up to 25mm.
- Full Text:
- Date Issued: 2017
- Authors: Mvubu, Mlando Basel
- Date: 2017
- Subjects: Needlepunch (Nonwoven fabric) Nonwoven fabrics , Textile fabrics
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/19387 , vital:28866
- Description: This study is divided in to two main parts. The first part deals with the optimization of process parameters of needle-punched non-woven fabrics for achieving maximum sound absorption by employing a Box-Behnken factorial design. The influence of fibre type, depth of needle penetration and stroke frequency on sound absorption properties were studied. These parameters were varied at three levels during experimental trials. From multiple regression analysis, it was observed that the depth of needle penetration alone was the most dominant factor among the selected parameters, which was followed by the interaction between depth of needle penetration and stroke frequency. Fibre type was the least dominant parameter affecting sound absorption. A maximum sound absorption coefficient of 47% (0.47) was obtained from the selected parameters. The results showed that for a process such as needle-punching, which is influenced by multiple variables, it is important to also study the interactive effects of process parameters for achieving optimum sound absorption. The second part of the study deals with the effect of type of natural fibre (fineness), and the blending ratio (with PET fibres) on the air permeability of the needle-punched non-woven fabrics and then it proceeds to study the effect of the air-gap, type of natural fibre (fineness) and blending ratio (with PET fibres) on sound absorption of needle-punched non-woven fabrics. These parameters are tested individually and their two way interaction (synergy) effect using ANOVA. The air-gap was varied from 0mm to 25mm with 5mm increments, three natural fibre types were used and all were blended with polyester fibres at three blending ratios for each natural fibre type. The Univariate Tests of Significance shows that all three parameters have a significant effect on sound absorption together with two two-way interactions, with the exception of the Blend Ratio × Air Gap two-way interaction which was not significant. It was found that the sound absorption improves with the increase in the air-gap size up to 15mm after which sound absorption decreased slightly with the further increase in the air-gap up to 25mm.
- Full Text:
- Date Issued: 2017
Synthesis and investigation of the chemosensing properties of novel fluorescent triazolyl coumarin-based polymers
- Ngororabanga, Jean Marie Vianney
- Authors: Ngororabanga, Jean Marie Vianney
- Date: 2017
- Subjects: Fluorescent polymers Chemical detectors
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/20110 , vital:29120
- Description: Environmental pollution by ionic species has become one of the greatest challenges to the sustainable development of communities. Increasing amounts of these ionic species in the environment is associated with several detrimental effects to human health and ecological systems. Proper detection and monitoring of these ionic species is essential. Considering the diversity of the ions and the fact that the available sensors are limited, it is clear that there is need for a rapid and low-cost method for recognition and monitoring of these ions. Fluorescence based methods are ranked among the most powerful transduction systems to signal chemical recognition events. Fluorescent polymers containing triazolyl coumarin units in the polymer backbone or as pendant groups were therefore designed and investigated as potential sensors for these ions. Three methods were used to incorporate triazolyl coumarin units into the polymers. The first method involved polymerization of the vinyl monomer containing the triazolyl coumarin unit. The second method involved AA-BB step-grow click polymerization of diazide and dialkyne-functionalized monomers. The third method involved post-polymerization functionalization of an azide-functionalized polymer with an alkyne functionalized coumarin derivative. In each method, formation of the triazole ring was achieved using a Cu(I)-catalyzed 1,3-dipolar cycloaddition (CuAAC) reaction. The photophysical properties of the polymers and their starting monomers were investigated and compared. Polymers with triazolyl coumarin units in the backbone or as pendant groups were found to have higher absorption and emission intensities than their corresponding monomers while polymers resulting from functionalization of azide-functionalized polymer were found to exhibit improved photophysical properties compared to the starting azide-functionalized polymer. The chemosensing potential of the polymers was investigated through absorption and emission. The polymers were found to be selective towards different metal ions (Fe3+, Hg2+ and Al3+) and anions (-OH and F-). The mechanisms of interaction between the polymers and ions were investigated by comparing the absorption and emission spectra of the polymers to those of their monomers in the presence of an ion of interest. In some cases the mechanism of interaction was supported by 1H NMR and FT-IR.
- Full Text:
- Date Issued: 2017
- Authors: Ngororabanga, Jean Marie Vianney
- Date: 2017
- Subjects: Fluorescent polymers Chemical detectors
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/20110 , vital:29120
- Description: Environmental pollution by ionic species has become one of the greatest challenges to the sustainable development of communities. Increasing amounts of these ionic species in the environment is associated with several detrimental effects to human health and ecological systems. Proper detection and monitoring of these ionic species is essential. Considering the diversity of the ions and the fact that the available sensors are limited, it is clear that there is need for a rapid and low-cost method for recognition and monitoring of these ions. Fluorescence based methods are ranked among the most powerful transduction systems to signal chemical recognition events. Fluorescent polymers containing triazolyl coumarin units in the polymer backbone or as pendant groups were therefore designed and investigated as potential sensors for these ions. Three methods were used to incorporate triazolyl coumarin units into the polymers. The first method involved polymerization of the vinyl monomer containing the triazolyl coumarin unit. The second method involved AA-BB step-grow click polymerization of diazide and dialkyne-functionalized monomers. The third method involved post-polymerization functionalization of an azide-functionalized polymer with an alkyne functionalized coumarin derivative. In each method, formation of the triazole ring was achieved using a Cu(I)-catalyzed 1,3-dipolar cycloaddition (CuAAC) reaction. The photophysical properties of the polymers and their starting monomers were investigated and compared. Polymers with triazolyl coumarin units in the backbone or as pendant groups were found to have higher absorption and emission intensities than their corresponding monomers while polymers resulting from functionalization of azide-functionalized polymer were found to exhibit improved photophysical properties compared to the starting azide-functionalized polymer. The chemosensing potential of the polymers was investigated through absorption and emission. The polymers were found to be selective towards different metal ions (Fe3+, Hg2+ and Al3+) and anions (-OH and F-). The mechanisms of interaction between the polymers and ions were investigated by comparing the absorption and emission spectra of the polymers to those of their monomers in the presence of an ion of interest. In some cases the mechanism of interaction was supported by 1H NMR and FT-IR.
- Full Text:
- Date Issued: 2017
A technical and economic evaluation of a passive underground mine-water purification system (PUMPS): a geothermally powered geo-engineering system designed for in-situ bio-remediation of acid mine water
- Ntholi, Thakane Thato Prudence
- Authors: Ntholi, Thakane Thato Prudence
- Date: 2017
- Subjects: Water -- Purification -- South Africa Water -- Purification -- Biological treatment , Mine water -- South Africa -- Evaluation Acid mine drainage -- South Africa Environmental geochemistry -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/19586 , vital:28900
- Description: PUMPS mimics natural geothermal vents as a conceptual model designed for the remediation of acid mine water (AMW) in voids of abandoned gold mines of the Witwatersrand Basin in South Africa. In this system, a reaction chamber containing Desulfotomaculum kuznetsovii sulfate reducing bacteria will be set at the bottom of a 3-4 km deep mine that will be flooded. A geothermal system with at least one (1) doublet will be drilled from the bottom of the mine to the depth of 8km, where the temperatures are sufficient for geothermal energy harvesting. AMW, used as a geothermal fluid, will be pumped down the injection well and circulate through hot rock. The hot water is then used to generate electricity and then channelled into the reaction chamber to undergo bio-remediation. Following treatment, the water flows back into the mine voids where it will improve the quality of untreated AMW through dilution. Eventually, the mine will be flooded with clean water that can be stored underground and/or pumped up to surface for social and ecosystem services. Following an introduction and proof of concept for the PUMPS, the research builds further on the technical and economic evaluation of the PUMPS in order to assert its viability and sustainability. The technical viability includes testing the ability for Desulfotomaculum kuznetsovii to survive in high pressure condition; quantifying the amount of energy that can be drawn from the geothermal reservoir; determining the placement and scheme of the geothermal wells; and, finally, developing a robust economic model of the system. Experiments show that Desulfotomaculum Kuznetsovii can tolerate high pressure conditions in of at least 100bar at their ideal sulfate reducing temperature of 63°C. Geochemical modelling shows that AMW can be used effectively as a geothermal fluid for PUMPS. To achieve highest efficiency and minimal fluid loss, the geothermal wells should be placed along the SSE-NNW direction, based on the known stress field across the Witwatersrand Basin. With a flow rate of 30l/s the energy drawn from the geothermal reservoir is sufficient to drive PUMPS and the surplus energy is determined by the volume of AMW treated per day. All results indicate that the PUMPS is technically and economically viable. The economic model shows that the value and viability of the PUMPS is best reflected with a comprehensive inclusion of potential revenue (for example from chemical solution mining of deep seated gold) and financial/environmental incentives.
- Full Text:
- Date Issued: 2017
- Authors: Ntholi, Thakane Thato Prudence
- Date: 2017
- Subjects: Water -- Purification -- South Africa Water -- Purification -- Biological treatment , Mine water -- South Africa -- Evaluation Acid mine drainage -- South Africa Environmental geochemistry -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/19586 , vital:28900
- Description: PUMPS mimics natural geothermal vents as a conceptual model designed for the remediation of acid mine water (AMW) in voids of abandoned gold mines of the Witwatersrand Basin in South Africa. In this system, a reaction chamber containing Desulfotomaculum kuznetsovii sulfate reducing bacteria will be set at the bottom of a 3-4 km deep mine that will be flooded. A geothermal system with at least one (1) doublet will be drilled from the bottom of the mine to the depth of 8km, where the temperatures are sufficient for geothermal energy harvesting. AMW, used as a geothermal fluid, will be pumped down the injection well and circulate through hot rock. The hot water is then used to generate electricity and then channelled into the reaction chamber to undergo bio-remediation. Following treatment, the water flows back into the mine voids where it will improve the quality of untreated AMW through dilution. Eventually, the mine will be flooded with clean water that can be stored underground and/or pumped up to surface for social and ecosystem services. Following an introduction and proof of concept for the PUMPS, the research builds further on the technical and economic evaluation of the PUMPS in order to assert its viability and sustainability. The technical viability includes testing the ability for Desulfotomaculum kuznetsovii to survive in high pressure condition; quantifying the amount of energy that can be drawn from the geothermal reservoir; determining the placement and scheme of the geothermal wells; and, finally, developing a robust economic model of the system. Experiments show that Desulfotomaculum Kuznetsovii can tolerate high pressure conditions in of at least 100bar at their ideal sulfate reducing temperature of 63°C. Geochemical modelling shows that AMW can be used effectively as a geothermal fluid for PUMPS. To achieve highest efficiency and minimal fluid loss, the geothermal wells should be placed along the SSE-NNW direction, based on the known stress field across the Witwatersrand Basin. With a flow rate of 30l/s the energy drawn from the geothermal reservoir is sufficient to drive PUMPS and the surplus energy is determined by the volume of AMW treated per day. All results indicate that the PUMPS is technically and economically viable. The economic model shows that the value and viability of the PUMPS is best reflected with a comprehensive inclusion of potential revenue (for example from chemical solution mining of deep seated gold) and financial/environmental incentives.
- Full Text:
- Date Issued: 2017
Characterisation of photovoltaic devices using large area light beam induced current measurements
- Okullo, Michael, Van Dyk, Ernes, Okullo, W
- Authors: Okullo, Michael , Van Dyk, Ernes , Okullo, W
- Date: 2017
- Subjects: Photovoltaic cells Photovoltaic power generation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/20526 , vital:29314
- Description: Photovoltaic (PV) modules are made by connecting PV cells in series in order to generate a reasonable voltage that can be used for any productive work. Inaccuracy in cell sorting during crystalline silicon module construction, or non-uniform deposition of PV material and laser scribing during thin _lm module construction, may introduce current mismatch in the module. Current mismatch is a consequence of connecting module cells which have non-identical electrical characteristics. When current mismatch occurs in a module, it is the cell generating the lowest current that determines the module output current and this leads to a decrease in the output power and lifespan of the module. Investigation of current uniformity and the different current reducing features in PV modules, which are potential sources of current mismatch, is therefore critical in optimising the performance of PV modules. In this study, a large area light beam induced current (LA-LBIC) measurement system was developed. This non-destructive technique was used to characterise crystalline silicon PV modules (mono-crystalline and multi-crystalline), thin _lm PV modules (amorphous silicon and copper indium diselenide) and a combined concentrator photovoltaic (CPV) module. A light source mounted onto a motorised x-y scanning stage was used to illuminate a PV module, or the Fresnel lens of a CPV module, point-by-point, while measuring the module output current. The measured current was mapped as a function of position and presented as an LBIC image. The point-illuminated circuit model of a PV module was designed and used to explain the variation in current between and within module cells in the LA-LBIC maps. Application of the model to crystalline silicon modules attributes the variation in photo-generated current between cells mainly to current mismatch between series connected cells. Current variation within cells is attributed to individual cell shunts. In the thin _lm modules, the model attributes the variation in photo-generated current mainly to differences in local cell shunts and series resistances originating from the scribing procedure during cell formation in the manufacturing process. In the PV modules studied, variation in photo-generated current was found to exist both between and within cells. The variation was more pronounced between cells than within cells. Module point I-V curves at different points of the module were measured in order to extract short circuit current, to quantify the variations between and within cells. A striation ring defect, causing a drop in short circuit current of 38%, was detected in the mono-crystalline module. Investigation of the striation ring defect indicated that the defect is active in the bulk (p-type) but inactive in the top (n-type) layer. Further characterisation of the defect revealed that a higher percentage loss in short circuit current occurs at lower light intensities. In the multi-crystalline silicon module, cracks were detected and found to electrically isolate the module cells into two parts, causing them to operate in parallel and consequently introducing current mismatch in the module. The I-V curve of the module at standard test condition (STC) revealed a step below the knee, which is a manifestation of current mismatch in the module. High currents, as a consequence of diffuse reflection, leading to multiple reflections by the top glass were also observed at localised points on the bus bar and cell separations. In the a-Si module, the variation in photo-current within some cells, was found to be substantial. In the copper indium diselenide (CIS) module, an electrical disconnection across the module cells was identified. A disconnection in the form of a triangular shape was also identified in this module, which completely disconnected the front contact of this area from the module. This unique disconnection feature caused current in the module to follow in a reverse direction when the light spot was incident within the boundary of the disconnection. Scans performed under different forward voltage biases were useful in identifying severely shunted module cells. A severely shunted cell was found to generate a higher photo-current than a good cell at the same forward bias voltage. This unique observation was explored further using point-illuminated module I-V measurements, and was found to be due to the crossing over of the I-V curves of the two cells. In order to explore the relationship between cell photo-current and cell shunt resistance, a method to determine the shunt resistances of the cells in an encapsulated module was devised. The method involves measuring the I-V curves of a fully illuminated module and a partially illuminated module when one of its cells is shaded and the I-V curves used to determine the short circuit current and the shunt resistance of the shaded cell. A strong correlation was found to exist between the short circuit current of the shaded cell and the cell shunt resistance, as well as between the short circuit current of the shaded cell and dark LBIC. The LA-LBIC technique was further applied to characterise a combine CPV module. Results showed that the Fresnel lens facets close to the centre generate a higher photo-current at the receiver than those towards the edges. The reduced photo-current towards the edges was attributed to losses due to di_raction, dielectric reflection and internal re_ection. About 65% of the area of the Fresnel lenses were found to be e_ective in light collection in terms of the photo-current generated at the receiver. Abrasions and scratches on the Fresnel lenses were identi_ed as some of the current limiting features in a CPV module. The LA-LBIC technique used in this study has demonstrated the potential to investigate current mismatch, current limiting and current enhancing features in PV modules. The capacity to further characterise current limiting features in order to investigate their effects on photo-current under different wavelengths and light intensities was also demonstrated. Extending the LA-LBIC technique to characterise a combined CPV module is a great achievement of this work.
- Full Text:
- Date Issued: 2017
- Authors: Okullo, Michael , Van Dyk, Ernes , Okullo, W
- Date: 2017
- Subjects: Photovoltaic cells Photovoltaic power generation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/20526 , vital:29314
- Description: Photovoltaic (PV) modules are made by connecting PV cells in series in order to generate a reasonable voltage that can be used for any productive work. Inaccuracy in cell sorting during crystalline silicon module construction, or non-uniform deposition of PV material and laser scribing during thin _lm module construction, may introduce current mismatch in the module. Current mismatch is a consequence of connecting module cells which have non-identical electrical characteristics. When current mismatch occurs in a module, it is the cell generating the lowest current that determines the module output current and this leads to a decrease in the output power and lifespan of the module. Investigation of current uniformity and the different current reducing features in PV modules, which are potential sources of current mismatch, is therefore critical in optimising the performance of PV modules. In this study, a large area light beam induced current (LA-LBIC) measurement system was developed. This non-destructive technique was used to characterise crystalline silicon PV modules (mono-crystalline and multi-crystalline), thin _lm PV modules (amorphous silicon and copper indium diselenide) and a combined concentrator photovoltaic (CPV) module. A light source mounted onto a motorised x-y scanning stage was used to illuminate a PV module, or the Fresnel lens of a CPV module, point-by-point, while measuring the module output current. The measured current was mapped as a function of position and presented as an LBIC image. The point-illuminated circuit model of a PV module was designed and used to explain the variation in current between and within module cells in the LA-LBIC maps. Application of the model to crystalline silicon modules attributes the variation in photo-generated current between cells mainly to current mismatch between series connected cells. Current variation within cells is attributed to individual cell shunts. In the thin _lm modules, the model attributes the variation in photo-generated current mainly to differences in local cell shunts and series resistances originating from the scribing procedure during cell formation in the manufacturing process. In the PV modules studied, variation in photo-generated current was found to exist both between and within cells. The variation was more pronounced between cells than within cells. Module point I-V curves at different points of the module were measured in order to extract short circuit current, to quantify the variations between and within cells. A striation ring defect, causing a drop in short circuit current of 38%, was detected in the mono-crystalline module. Investigation of the striation ring defect indicated that the defect is active in the bulk (p-type) but inactive in the top (n-type) layer. Further characterisation of the defect revealed that a higher percentage loss in short circuit current occurs at lower light intensities. In the multi-crystalline silicon module, cracks were detected and found to electrically isolate the module cells into two parts, causing them to operate in parallel and consequently introducing current mismatch in the module. The I-V curve of the module at standard test condition (STC) revealed a step below the knee, which is a manifestation of current mismatch in the module. High currents, as a consequence of diffuse reflection, leading to multiple reflections by the top glass were also observed at localised points on the bus bar and cell separations. In the a-Si module, the variation in photo-current within some cells, was found to be substantial. In the copper indium diselenide (CIS) module, an electrical disconnection across the module cells was identified. A disconnection in the form of a triangular shape was also identified in this module, which completely disconnected the front contact of this area from the module. This unique disconnection feature caused current in the module to follow in a reverse direction when the light spot was incident within the boundary of the disconnection. Scans performed under different forward voltage biases were useful in identifying severely shunted module cells. A severely shunted cell was found to generate a higher photo-current than a good cell at the same forward bias voltage. This unique observation was explored further using point-illuminated module I-V measurements, and was found to be due to the crossing over of the I-V curves of the two cells. In order to explore the relationship between cell photo-current and cell shunt resistance, a method to determine the shunt resistances of the cells in an encapsulated module was devised. The method involves measuring the I-V curves of a fully illuminated module and a partially illuminated module when one of its cells is shaded and the I-V curves used to determine the short circuit current and the shunt resistance of the shaded cell. A strong correlation was found to exist between the short circuit current of the shaded cell and the cell shunt resistance, as well as between the short circuit current of the shaded cell and dark LBIC. The LA-LBIC technique was further applied to characterise a combine CPV module. Results showed that the Fresnel lens facets close to the centre generate a higher photo-current at the receiver than those towards the edges. The reduced photo-current towards the edges was attributed to losses due to di_raction, dielectric reflection and internal re_ection. About 65% of the area of the Fresnel lenses were found to be e_ective in light collection in terms of the photo-current generated at the receiver. Abrasions and scratches on the Fresnel lenses were identi_ed as some of the current limiting features in a CPV module. The LA-LBIC technique used in this study has demonstrated the potential to investigate current mismatch, current limiting and current enhancing features in PV modules. The capacity to further characterise current limiting features in order to investigate their effects on photo-current under different wavelengths and light intensities was also demonstrated. Extending the LA-LBIC technique to characterise a combined CPV module is a great achievement of this work.
- Full Text:
- Date Issued: 2017
An in vitro evaluation of anti-breast cancer activity of novel, heterocyclic aromatic compounds in combination with curcumin
- Authors: Pereira, Melanie Claire
- Date: 2017
- Subjects: Breast -- Cancer Heterocyclic compounds
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/20416 , vital:29284
- Description: Nearly two thirds of breast cancers are classified as estrogen receptor positive. Estrogen receptor (+) breast cancer is usually treated with anti-estrogen therapy, using Tamoxifen as the primary standard of treatment. Unfortunately, resistance to Tamoxifen is known to occur after 1 to 3 years of Tamoxifen therapy. For this reason, improved treatment strategies for ER (+) breast cancer are urgently needed. The general toxicity exerted by most anti-cancer drugs on proliferating cells, as well as some normal cells, restricts their therapeutic use. Novel cytotoxic agents developed with unique mechanisms of action have not been therapeutically suitable, since many of these compounds lack tumour selectivity. The adverse effects and the inefficacies of most chemotherapeutic therapies have motivated extensive investigations of alternatives. Numerous studies have demonstrated the advantages of using combination therapy with naturally-derived agents as an alternative, due to the higher therapeutic efficacy; with the added benefit of lower drug usage and reduction in drug-resistance development. An excellent example of a naturally derived and common dietary agent is curcumin, the active constituent of turmeric. Curcumin is known to modulate several signalling pathways in addition to displaying a diverse range of anti-tumour activities against a number of cancer cells. Several reports point to curcumin being beneficial if used in addition to chemotherapeutic drugs. In this study, synthetic aminonaphthoquinone derivatives (coded Rau 008, Rau 010, Rau 015 and Rau 018) were tested individually and in combination with curcumin for the potential as anti-breast cancer agents in different tumour cell lines. Notably, the aminonaphthoquinone class of compounds have shown potential as anti-cancer agents in various tumour cell lines. This study was thus aimed at screening the Rau compounds (and selected combinations with curcumin) for anti-cancer activity using a range of in vitro biological assays, and was not mechanistic in nature. The IC50 values of the individual and combined drugs were determined from dose-response curves using non-linear regression analyses. Synergistic, additive and antagonistic drug interactions were assessed using combination index and isobologram approaches. Based on these interactions, selected drug combinations were then further analysed for their potential anti-estrogenic, cytotoxic, anti-angiogenic and anti-metastatic effects against the ER(-) MDA-MB-231 and ER(+) MCF-7 breast cancer cell lines. The potential anti-cancer effects of the selected drug combinations on other estrogen-responsive models, such as the osteosarcoma (MG-63) and endometrial cancer (HEC-1A) cell lines, were also investigated. Overall, the findings of this study indicated that the sensitivity of the tumour cells to the various test compounds was significantly enhanced when combined with curcumin. For instance, in the presence of curcumin, Rau 008 or Rau 010 reduced the metastatic capability of ER(-) breast cancer cells significantly. The anti-proliferative effect of the Rau 015+curcumin combination was enhanced in ER(+) and ER(-) breast cancer, including oteosarcoma cells, while a combination of Rau 015 and curcumin induced a significant cytotoxic effect in ER(-) breast cancer and endometrial cancer-derived cells. A combination of Rau 018 and curcumin inhibited the proliferation of ER(+) breast cancer, and the combined effect was significantly more enhanced compared to individual treatment. A similar effect was noted in osteosarcoma-derived cells. Further, the Rau 018+curcumin combination exerted a marked cytotoxic and anti-angiogenic effect in ER(-) breast cancer, osteosarcoma and endometrial cancer in addition to inhibiting the attachment of ER(-) breast cancer cells to collagen. Notably, curcumin enhanced the anti-proliferative effect of Tamoxifen in breast cancer (MCF-7 and MDA-MB-231), osteosarcoma and endometrial cancer, and also induced a significant cytotoxic effect against ER(+) breast cancer and osteosarcoma, whilst also reducing the invasive potential of ER(-) breast cancer. A combination of 17β-estradiol and curcumin induced a marked anti-proliferative effect in ER(+) and ER(-) breast cancer, reduced the adhesion of ER(-) breast cancer to laminin, and elicited a significant cytotoxic and anti-angiogenic effect against endometrial cancer. Notably all the selected combinations (except Rau 018 and curcumin) inhibited bone mineralization. These findings point to the vital influence of curcumin in the responsiveness of ER(+) and ER(-) tumours towards the relative test agents. Further, among the Rau+curcumin combinations tested in this study, the anti-cancer activity of Rau 015+curcumin and Rau 018+curcumin appeared to be the most effective in the different cell lines tested. Nonetheless, it appears that a combination of 30 μM Rau 018 with 100 μM curcumin may be more promising as an anti-breast cancer agent against ER(+) and perhaps triple negative breast cancer, and warrants further investigation.
- Full Text:
- Date Issued: 2017
- Authors: Pereira, Melanie Claire
- Date: 2017
- Subjects: Breast -- Cancer Heterocyclic compounds
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/20416 , vital:29284
- Description: Nearly two thirds of breast cancers are classified as estrogen receptor positive. Estrogen receptor (+) breast cancer is usually treated with anti-estrogen therapy, using Tamoxifen as the primary standard of treatment. Unfortunately, resistance to Tamoxifen is known to occur after 1 to 3 years of Tamoxifen therapy. For this reason, improved treatment strategies for ER (+) breast cancer are urgently needed. The general toxicity exerted by most anti-cancer drugs on proliferating cells, as well as some normal cells, restricts their therapeutic use. Novel cytotoxic agents developed with unique mechanisms of action have not been therapeutically suitable, since many of these compounds lack tumour selectivity. The adverse effects and the inefficacies of most chemotherapeutic therapies have motivated extensive investigations of alternatives. Numerous studies have demonstrated the advantages of using combination therapy with naturally-derived agents as an alternative, due to the higher therapeutic efficacy; with the added benefit of lower drug usage and reduction in drug-resistance development. An excellent example of a naturally derived and common dietary agent is curcumin, the active constituent of turmeric. Curcumin is known to modulate several signalling pathways in addition to displaying a diverse range of anti-tumour activities against a number of cancer cells. Several reports point to curcumin being beneficial if used in addition to chemotherapeutic drugs. In this study, synthetic aminonaphthoquinone derivatives (coded Rau 008, Rau 010, Rau 015 and Rau 018) were tested individually and in combination with curcumin for the potential as anti-breast cancer agents in different tumour cell lines. Notably, the aminonaphthoquinone class of compounds have shown potential as anti-cancer agents in various tumour cell lines. This study was thus aimed at screening the Rau compounds (and selected combinations with curcumin) for anti-cancer activity using a range of in vitro biological assays, and was not mechanistic in nature. The IC50 values of the individual and combined drugs were determined from dose-response curves using non-linear regression analyses. Synergistic, additive and antagonistic drug interactions were assessed using combination index and isobologram approaches. Based on these interactions, selected drug combinations were then further analysed for their potential anti-estrogenic, cytotoxic, anti-angiogenic and anti-metastatic effects against the ER(-) MDA-MB-231 and ER(+) MCF-7 breast cancer cell lines. The potential anti-cancer effects of the selected drug combinations on other estrogen-responsive models, such as the osteosarcoma (MG-63) and endometrial cancer (HEC-1A) cell lines, were also investigated. Overall, the findings of this study indicated that the sensitivity of the tumour cells to the various test compounds was significantly enhanced when combined with curcumin. For instance, in the presence of curcumin, Rau 008 or Rau 010 reduced the metastatic capability of ER(-) breast cancer cells significantly. The anti-proliferative effect of the Rau 015+curcumin combination was enhanced in ER(+) and ER(-) breast cancer, including oteosarcoma cells, while a combination of Rau 015 and curcumin induced a significant cytotoxic effect in ER(-) breast cancer and endometrial cancer-derived cells. A combination of Rau 018 and curcumin inhibited the proliferation of ER(+) breast cancer, and the combined effect was significantly more enhanced compared to individual treatment. A similar effect was noted in osteosarcoma-derived cells. Further, the Rau 018+curcumin combination exerted a marked cytotoxic and anti-angiogenic effect in ER(-) breast cancer, osteosarcoma and endometrial cancer in addition to inhibiting the attachment of ER(-) breast cancer cells to collagen. Notably, curcumin enhanced the anti-proliferative effect of Tamoxifen in breast cancer (MCF-7 and MDA-MB-231), osteosarcoma and endometrial cancer, and also induced a significant cytotoxic effect against ER(+) breast cancer and osteosarcoma, whilst also reducing the invasive potential of ER(-) breast cancer. A combination of 17β-estradiol and curcumin induced a marked anti-proliferative effect in ER(+) and ER(-) breast cancer, reduced the adhesion of ER(-) breast cancer to laminin, and elicited a significant cytotoxic and anti-angiogenic effect against endometrial cancer. Notably all the selected combinations (except Rau 018 and curcumin) inhibited bone mineralization. These findings point to the vital influence of curcumin in the responsiveness of ER(+) and ER(-) tumours towards the relative test agents. Further, among the Rau+curcumin combinations tested in this study, the anti-cancer activity of Rau 015+curcumin and Rau 018+curcumin appeared to be the most effective in the different cell lines tested. Nonetheless, it appears that a combination of 30 μM Rau 018 with 100 μM curcumin may be more promising as an anti-breast cancer agent against ER(+) and perhaps triple negative breast cancer, and warrants further investigation.
- Full Text:
- Date Issued: 2017
Ecology of key cerithioidean gastropods in the mangroves of the iSimangaliso Wetland Park, KwaZulu-Natal South Africa
- Authors: Raw, Jacqueline Leoni
- Date: 2017
- Subjects: Gastropoda -- South Africa -- KwaZulu-Natal Mangrove ecology -- South Africa -- KwaZulu-Natal
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/11942 , vital:27009
- Description: Gastropods are one of the most diverse species groups in mangrove habitats, however, many of their specific roles in relation to ecological patterns and processes are currently largely unknown. The overall aim of this research project was to provide basic ecological information for key gastropod species from subtropical mangroves within a protected area. South African mangroves cover relatively small areas and are restricted to estuaries, these habitats therefore present unique opportunities and challenges to the species that occur in them. Three gastropod species, Terebralia palustris, Cerithidea decollata, and Melanoides tuberculata, all occur at their natural southernmost range limit within South Africa and were selected based on their prominence and occurrence in mangrove habitats of the iSimangaliso Wetland Park, a UNESCO World Heritage Site. Trophic linkages and resource partitioning, resource utilization rates, and ecological resilience were investigated respectively using: 1) a stable isotope (δ15N and δ13C) approach; 2) an experimental approach to quantify feeding dynamics (ingestion rate, consumption/digestion efficiency and grazing impact); and 3) a mixed-effects modelling approach to relate population responses to environmental variables. The diet of T. palustris was seasonally variable and a number of sources were incorporated by different sized snails, but their grazing impact on microphytobenthos was not significant. The results also indicated an ontogenetic shift in the dietary niche for T. palustris through robust partitioning of resources between different size classes. The diets of C. decollata and M. tuberculata were dominated by different primary resources as a function of where they occurred in the mangroves. Melanoides tuberculata consumed a wide variety of primary resources, a typical trait of an opportunistic generalist species. The ingestion rate of M. tuberculata was not dependent on the availability of microphytobenthos, and was highest when conditions were oligotrophic. The resilience of C. decollata was related to the tree-climbing behaviour of this species and its occurrence was best explained by sediment conductivity. These responses were considered in conjunction to what has previously been reported on the resilience of the mangrove trees. The results of this research project have provided new basic ecological information for all three gastropod species in this data-deficient subtropical region. This information can potentially be used in comparative studies for these species in other regions or in broader scale ecological studies. Terebralia palustris has recently experienced a range contraction along the South African coastline. This research project has shown that the diet of this species is highly variable and that food limitation and competition for resources should be considered as potential drivers of the local decline. Cerithidea decollata has in contrast expanded its distributional range in this region. This research project has shown that this species has a generalist diet and exhibits traits in relation to tolerance that are expected to have facilitated its expansion into temperate saltmarsh habitats that occur in dynamic estuaries. Melanoides tuberculata is a globally invasive species, and as South African populations are within its native range, ecological information from this region is valuable as it can be used to investigate the potential ecological effects following introduction into new habitats beyond the native range. Biological drivers have a significant impact on mangrove ecosystem functioning, particularly in relation to recycling and the retention of organic carbon generated through primary productivity. Understanding the ecological linkages that maintain ecological functioning and stability is therefore an important step towards conserving and sustainably managing threatened ecosystems such as mangrove forests.
- Full Text:
- Date Issued: 2017
- Authors: Raw, Jacqueline Leoni
- Date: 2017
- Subjects: Gastropoda -- South Africa -- KwaZulu-Natal Mangrove ecology -- South Africa -- KwaZulu-Natal
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/11942 , vital:27009
- Description: Gastropods are one of the most diverse species groups in mangrove habitats, however, many of their specific roles in relation to ecological patterns and processes are currently largely unknown. The overall aim of this research project was to provide basic ecological information for key gastropod species from subtropical mangroves within a protected area. South African mangroves cover relatively small areas and are restricted to estuaries, these habitats therefore present unique opportunities and challenges to the species that occur in them. Three gastropod species, Terebralia palustris, Cerithidea decollata, and Melanoides tuberculata, all occur at their natural southernmost range limit within South Africa and were selected based on their prominence and occurrence in mangrove habitats of the iSimangaliso Wetland Park, a UNESCO World Heritage Site. Trophic linkages and resource partitioning, resource utilization rates, and ecological resilience were investigated respectively using: 1) a stable isotope (δ15N and δ13C) approach; 2) an experimental approach to quantify feeding dynamics (ingestion rate, consumption/digestion efficiency and grazing impact); and 3) a mixed-effects modelling approach to relate population responses to environmental variables. The diet of T. palustris was seasonally variable and a number of sources were incorporated by different sized snails, but their grazing impact on microphytobenthos was not significant. The results also indicated an ontogenetic shift in the dietary niche for T. palustris through robust partitioning of resources between different size classes. The diets of C. decollata and M. tuberculata were dominated by different primary resources as a function of where they occurred in the mangroves. Melanoides tuberculata consumed a wide variety of primary resources, a typical trait of an opportunistic generalist species. The ingestion rate of M. tuberculata was not dependent on the availability of microphytobenthos, and was highest when conditions were oligotrophic. The resilience of C. decollata was related to the tree-climbing behaviour of this species and its occurrence was best explained by sediment conductivity. These responses were considered in conjunction to what has previously been reported on the resilience of the mangrove trees. The results of this research project have provided new basic ecological information for all three gastropod species in this data-deficient subtropical region. This information can potentially be used in comparative studies for these species in other regions or in broader scale ecological studies. Terebralia palustris has recently experienced a range contraction along the South African coastline. This research project has shown that the diet of this species is highly variable and that food limitation and competition for resources should be considered as potential drivers of the local decline. Cerithidea decollata has in contrast expanded its distributional range in this region. This research project has shown that this species has a generalist diet and exhibits traits in relation to tolerance that are expected to have facilitated its expansion into temperate saltmarsh habitats that occur in dynamic estuaries. Melanoides tuberculata is a globally invasive species, and as South African populations are within its native range, ecological information from this region is valuable as it can be used to investigate the potential ecological effects following introduction into new habitats beyond the native range. Biological drivers have a significant impact on mangrove ecosystem functioning, particularly in relation to recycling and the retention of organic carbon generated through primary productivity. Understanding the ecological linkages that maintain ecological functioning and stability is therefore an important step towards conserving and sustainably managing threatened ecosystems such as mangrove forests.
- Full Text:
- Date Issued: 2017
Community structure and trophic relations in marine tufa stromatolite pools of the Eastern Cape
- Authors: Rishworth, Gavin Midgley
- Date: 2017
- Subjects: Bioturbation -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/7116 , vital:21236
- Description: Microbialites were the dominant life-form of most shallow oceans during the Precambrian. These structures are formed by the deposition of calcium carbonate by cyanobacteria as well as the binding and trapping of sediment by these and other microalgae. In modern environments they are scarce due to several factors, including grazing pressures by metazoans, altered calcium carbonate saturation states of seawater and competition with macroalgae. The recent discovery of an extensive network of actively accreting layered microbialites (stromatolites) along the South African coastline is potentially informative from this perspective. These stromatolites form within the peritidal zone, at the interface of groundwater seepage and periodic marine incursion, forming pools trapped by the accreting fabric. The aim of this thesis was to characterise the ecosystem dynamics of a representative selection of the South African locations. During a comprehensive monthly assessment over an annual cycle, as well as for additional seasonal collections, physico-chemical measurements were monitored together with biological components such as benthic and pelagic microalgae as well as the invertebrate fauna inhabiting the stromatolite pools. These components were then assessed in terms of the potential physical and biological drivers which might explain patterns of variability. Finally, to link all of the ecosystem components, a food-web analysis was conducted, to determine the trophic linkages and, importantly, the reliance by the various consumer organisms on the stromatolite material as a food resource. Results show that the stromatolite pools are driven by a regular interplay between freshwater and marine salinity states, this being determined by tidal amplitude and ocean storm cycles. Furthermore, marine incursion represents the primary source of phosphorus for the stromatolite pools, while available nitrogen is consistently provided by the freshwater inlet stream at each site. This results in an optimum zone of primary biomass within the main stromatolite pool supported by nutrient conditions, while the shifts in salinity state occurring over a weekly tidal schedule likely exclude organisms and macrophytes that are not halotolerant. This is reflected in the benthic microalgae that form the stromatolite accretions in that they are primarily driven by salinity conditions, in addition to seasonal patterns. Interestingly, the variable nutrient conditions, both between sites and temporally, did not contribute as an important driver of the benthic microalgae but did significantly relate to the pelagic microalgae (phytoplankton). This, together with the higher biomass of benthic microalgae compared to its pelagic counterpart, suggests that the stromatolite pools are a benthic-driven system. The short duration of water retention within the stromatolite pools as a result of the constant freshwater inflow, likely also precludes nutrient build-up and favours the benthic, sessile ecosystem component, especially the stromatolite-forming microalgae. In terms of the metazoan infauna, the South African stromatolite pools support a persistent assemblage. This might be surprising given the apparently destructive influence of grazing and burrowing animals on microbial mats in terms of restricting the formation of layered accretions. However, metazoans that burrow within the stromatolite fabric were observed to coexist with clear, layered accretions. This supports the observations in some other modern microbialite habitats to suggest that metazoan disruption is clearly not the only or primary factor responsible for modern microbialite scarcity. When assessing the possible drivers of the metazoan community occupying the stromatolite matrix, both salinity patterns and resource conditions in terms of nutrient supply and macroalgal cover were consistently best related to infaunal abundance and presence/absence. This further demonstrates the role of salinity conditions in terms of providing a habitat that is restrictive to most metazoan organisms, while also suggesting that the metazoans are responding to macroalgal rather than the stromatolite microalgal conditions. To further develop this observation, the results from the stable isotope work clearly reflect a dominance of pool macroalgae in the diets of invertebrate consumers, with little to no stromatolite material consumed. This suggests that there is limited apparent destructive grazing influence by the metazoans on the stromatolite matrix, in addition to the burrowing bioturbation mentioned previously. Furthermore, the metazoan grazers may be indirectly benefitting the stromatolites by restricting macroalgal biomass, which might otherwise outcompete its microalgal counterpart. This study provides a valuable understanding of benthic-driven peritidal stromatolite ecosystems, and also, from a geological perspective of past stromatolite habitats, suggests some of the mechanisms as to why metazoans may be able to coexist with layered microbialites. Given the threats to similar habitats globally, especially in terms of water resources, management measures necessary to ensure stromatolite persistence in modern environments such as these are proposed. The possible ecological role of peritidal stromatolite habitats within the broader environment, as well as recommendations for future work, is also contextualised.
- Full Text:
- Date Issued: 2017
- Authors: Rishworth, Gavin Midgley
- Date: 2017
- Subjects: Bioturbation -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/7116 , vital:21236
- Description: Microbialites were the dominant life-form of most shallow oceans during the Precambrian. These structures are formed by the deposition of calcium carbonate by cyanobacteria as well as the binding and trapping of sediment by these and other microalgae. In modern environments they are scarce due to several factors, including grazing pressures by metazoans, altered calcium carbonate saturation states of seawater and competition with macroalgae. The recent discovery of an extensive network of actively accreting layered microbialites (stromatolites) along the South African coastline is potentially informative from this perspective. These stromatolites form within the peritidal zone, at the interface of groundwater seepage and periodic marine incursion, forming pools trapped by the accreting fabric. The aim of this thesis was to characterise the ecosystem dynamics of a representative selection of the South African locations. During a comprehensive monthly assessment over an annual cycle, as well as for additional seasonal collections, physico-chemical measurements were monitored together with biological components such as benthic and pelagic microalgae as well as the invertebrate fauna inhabiting the stromatolite pools. These components were then assessed in terms of the potential physical and biological drivers which might explain patterns of variability. Finally, to link all of the ecosystem components, a food-web analysis was conducted, to determine the trophic linkages and, importantly, the reliance by the various consumer organisms on the stromatolite material as a food resource. Results show that the stromatolite pools are driven by a regular interplay between freshwater and marine salinity states, this being determined by tidal amplitude and ocean storm cycles. Furthermore, marine incursion represents the primary source of phosphorus for the stromatolite pools, while available nitrogen is consistently provided by the freshwater inlet stream at each site. This results in an optimum zone of primary biomass within the main stromatolite pool supported by nutrient conditions, while the shifts in salinity state occurring over a weekly tidal schedule likely exclude organisms and macrophytes that are not halotolerant. This is reflected in the benthic microalgae that form the stromatolite accretions in that they are primarily driven by salinity conditions, in addition to seasonal patterns. Interestingly, the variable nutrient conditions, both between sites and temporally, did not contribute as an important driver of the benthic microalgae but did significantly relate to the pelagic microalgae (phytoplankton). This, together with the higher biomass of benthic microalgae compared to its pelagic counterpart, suggests that the stromatolite pools are a benthic-driven system. The short duration of water retention within the stromatolite pools as a result of the constant freshwater inflow, likely also precludes nutrient build-up and favours the benthic, sessile ecosystem component, especially the stromatolite-forming microalgae. In terms of the metazoan infauna, the South African stromatolite pools support a persistent assemblage. This might be surprising given the apparently destructive influence of grazing and burrowing animals on microbial mats in terms of restricting the formation of layered accretions. However, metazoans that burrow within the stromatolite fabric were observed to coexist with clear, layered accretions. This supports the observations in some other modern microbialite habitats to suggest that metazoan disruption is clearly not the only or primary factor responsible for modern microbialite scarcity. When assessing the possible drivers of the metazoan community occupying the stromatolite matrix, both salinity patterns and resource conditions in terms of nutrient supply and macroalgal cover were consistently best related to infaunal abundance and presence/absence. This further demonstrates the role of salinity conditions in terms of providing a habitat that is restrictive to most metazoan organisms, while also suggesting that the metazoans are responding to macroalgal rather than the stromatolite microalgal conditions. To further develop this observation, the results from the stable isotope work clearly reflect a dominance of pool macroalgae in the diets of invertebrate consumers, with little to no stromatolite material consumed. This suggests that there is limited apparent destructive grazing influence by the metazoans on the stromatolite matrix, in addition to the burrowing bioturbation mentioned previously. Furthermore, the metazoan grazers may be indirectly benefitting the stromatolites by restricting macroalgal biomass, which might otherwise outcompete its microalgal counterpart. This study provides a valuable understanding of benthic-driven peritidal stromatolite ecosystems, and also, from a geological perspective of past stromatolite habitats, suggests some of the mechanisms as to why metazoans may be able to coexist with layered microbialites. Given the threats to similar habitats globally, especially in terms of water resources, management measures necessary to ensure stromatolite persistence in modern environments such as these are proposed. The possible ecological role of peritidal stromatolite habitats within the broader environment, as well as recommendations for future work, is also contextualised.
- Full Text:
- Date Issued: 2017
Cape gannets in contrasting environments: ehaviour, demographics and indicators of environmental change
- Authors: Ryklief, Rabiah
- Date: 2017
- Subjects: Endemic birds -- South Africa Marine pollution -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/21167 , vital:29452
- Description: Marine communities represent biological networks, where physical and chemical changes in the marine environment can influence the physiology and behaviour of marine organisms. Stochastic marine conditions can alter key biological interactions and thus, influence the mechanisms that underpin population demography and phenotypic plasticity. Marine top predators, such as seabirds, are often controlled by bottom-up processes and their ability to cope with variable ocean conditions lies in their physiological and behavioural response to such perturbations. Seabirds are central-place foragers during the breeding season making them particularly vulnerable to environmental fluctuations as they face constrains associated with reproductive effort in addition to self-maintenance. The Cape gannet Morus capensis is a medium-sized pelagic seabird that is endemic to southern Africa. The Cape gannet has experienced considerable change in population distribution and abundance over the past 50 years. These changes have been linked to a combination of fishing pressure and climate-mediated regime shifts of their preferred prey, i.e. sardine Sardinops sagax and anchovy ngraulis encrasicolus. Historically, Malgas Island was the largest Cape gannet colony in South Africa. However, it is now in a state of population decline, despite its occurrence within one of the most productive upwelling systems in the world, the Benguela Current. At present, Bird Island is the largest Cape gannet colony and has recently stabilised, despite regular immigration of gannets from the west coast. Furthermore, Bird Island lies within the Agulhas bioregion and is subject to low levels of productivity from the nutrient-poor Agulhas current. Malgas and Bird islands are the two most populous of the six extant Cape gannet colonies. Birds at these colonies provided a natural experiment due to the contrasting population trajectories and environmental conditions at their colonies. The foraging ecology and behaviour of Cape gannets were studied during the breeding season to assess the mechanistic links connecting climate and fisheries to population demography. Cape gannets displayed considerable inter-annual variation in foraging effort and distribution across a five-year period. This highlights the importance of long-term datasets to contextualise the degree of natural variation within a species, as well as considerations for conservation management. For the first time, oceanographic variables such as sea surface temperature and chlorophyll-a, indices that reflect marine productivity, were used to predict Cape gannet foraging distribution. Furthermore, Cape gannets at Bird Island had an energy budget deficit in a year when foraging effort was much higher in comparison to what was observed at Malgas Island. This in turn was linked to the first identification of nutritional stress in a Sulid species. Reasons for this include a combination of higher intra-specific competition in conjunction with a lower energetic content of referential prey species at Bird Island. Foraging effort showed more variability at Malgas Island in comparison to Bird Island, likely due to Malgas Island gannets often taking two short foraging trips a day, whereas Bird Island gannets often spent the night at sea. Some degree of phenotypic plasticity was evidenced by substantial variations across breeding seasons and ocean basins in foraging effort and behaviour.
- Full Text:
- Date Issued: 2017
- Authors: Ryklief, Rabiah
- Date: 2017
- Subjects: Endemic birds -- South Africa Marine pollution -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/21167 , vital:29452
- Description: Marine communities represent biological networks, where physical and chemical changes in the marine environment can influence the physiology and behaviour of marine organisms. Stochastic marine conditions can alter key biological interactions and thus, influence the mechanisms that underpin population demography and phenotypic plasticity. Marine top predators, such as seabirds, are often controlled by bottom-up processes and their ability to cope with variable ocean conditions lies in their physiological and behavioural response to such perturbations. Seabirds are central-place foragers during the breeding season making them particularly vulnerable to environmental fluctuations as they face constrains associated with reproductive effort in addition to self-maintenance. The Cape gannet Morus capensis is a medium-sized pelagic seabird that is endemic to southern Africa. The Cape gannet has experienced considerable change in population distribution and abundance over the past 50 years. These changes have been linked to a combination of fishing pressure and climate-mediated regime shifts of their preferred prey, i.e. sardine Sardinops sagax and anchovy ngraulis encrasicolus. Historically, Malgas Island was the largest Cape gannet colony in South Africa. However, it is now in a state of population decline, despite its occurrence within one of the most productive upwelling systems in the world, the Benguela Current. At present, Bird Island is the largest Cape gannet colony and has recently stabilised, despite regular immigration of gannets from the west coast. Furthermore, Bird Island lies within the Agulhas bioregion and is subject to low levels of productivity from the nutrient-poor Agulhas current. Malgas and Bird islands are the two most populous of the six extant Cape gannet colonies. Birds at these colonies provided a natural experiment due to the contrasting population trajectories and environmental conditions at their colonies. The foraging ecology and behaviour of Cape gannets were studied during the breeding season to assess the mechanistic links connecting climate and fisheries to population demography. Cape gannets displayed considerable inter-annual variation in foraging effort and distribution across a five-year period. This highlights the importance of long-term datasets to contextualise the degree of natural variation within a species, as well as considerations for conservation management. For the first time, oceanographic variables such as sea surface temperature and chlorophyll-a, indices that reflect marine productivity, were used to predict Cape gannet foraging distribution. Furthermore, Cape gannets at Bird Island had an energy budget deficit in a year when foraging effort was much higher in comparison to what was observed at Malgas Island. This in turn was linked to the first identification of nutritional stress in a Sulid species. Reasons for this include a combination of higher intra-specific competition in conjunction with a lower energetic content of referential prey species at Bird Island. Foraging effort showed more variability at Malgas Island in comparison to Bird Island, likely due to Malgas Island gannets often taking two short foraging trips a day, whereas Bird Island gannets often spent the night at sea. Some degree of phenotypic plasticity was evidenced by substantial variations across breeding seasons and ocean basins in foraging effort and behaviour.
- Full Text:
- Date Issued: 2017