Thermal degradation of diamond compacts: a TEM investigation
- Authors: Westraadt, Johan Ewald
- Date: 2011
- Subjects: Materials -- Thermal properties Chemical weathering
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/10829 , vital:26827
- Description: Diamond compacts consist of fine diamond grains bonded together by using high pressure and high temperature. In this study transmission electron microscopy (TEM)was used to study thermal degradation of diamond compacts. Three different types of diamond compacts – namely cobalt polycrystalline diamond (PCD), calcium carbonate PCD, and diamond-SiC composites – were investigated with TEM to understand the processes that occur during synthesis. These compacts were then heated in inert atmospheres and the chemical changes studied with TEM. It was found that PCD, using cobalt as a bonding agent, will degrade after exposure to temperatures above 750ºC. The cobalt pools contain tungsten in solid solution. During heat treatment above 700ºC the solid solution tungsten combines with cobalt and dissolved carbon to form η-phase particles at the cobalt/diamond interface. At higher temperatures or insufficient tungsten levels the rate of dissolved carbon, into the cobalt pool, is too high and the excess carbon will form as graphite in the cobalt pool. Increased levels of solid solution tungsten, in the cobalt, is expected to delay the onset of graphitization in the diamond compact, thereby increasing the thermal stability of the diamond compact. Non-metallic PCD using calcium carbonate as a bonding agent was successfully sintered in this study. TEM revealed similar micro-structural features as in cobalt based PCD. No signs of thermal degradation were found after exposure to 1200ºC in vacuum for this PCD. Contaminants introduced during processing prevented a detailed study of the binder in this system. The effect of substitutional metal atoms and plastic deformation of diamond on the thermal stability of diamond-SiC composites were investigated. A piston cylinder press was developed and used to synthesize diamond-SiC composites with different levels of plastically deformed diamond. It was concluded that substitutional metal atoms and plastic deformation of diamond grains play no role in the thermal degradation of diamond compacts at 750ºC. The thermal degradation of cobalt PCD is therefore completely determined by the cobalt/diamond interaction at 750ºC.
- Full Text:
- Date Issued: 2011
- Authors: Westraadt, Johan Ewald
- Date: 2011
- Subjects: Materials -- Thermal properties Chemical weathering
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/10829 , vital:26827
- Description: Diamond compacts consist of fine diamond grains bonded together by using high pressure and high temperature. In this study transmission electron microscopy (TEM)was used to study thermal degradation of diamond compacts. Three different types of diamond compacts – namely cobalt polycrystalline diamond (PCD), calcium carbonate PCD, and diamond-SiC composites – were investigated with TEM to understand the processes that occur during synthesis. These compacts were then heated in inert atmospheres and the chemical changes studied with TEM. It was found that PCD, using cobalt as a bonding agent, will degrade after exposure to temperatures above 750ºC. The cobalt pools contain tungsten in solid solution. During heat treatment above 700ºC the solid solution tungsten combines with cobalt and dissolved carbon to form η-phase particles at the cobalt/diamond interface. At higher temperatures or insufficient tungsten levels the rate of dissolved carbon, into the cobalt pool, is too high and the excess carbon will form as graphite in the cobalt pool. Increased levels of solid solution tungsten, in the cobalt, is expected to delay the onset of graphitization in the diamond compact, thereby increasing the thermal stability of the diamond compact. Non-metallic PCD using calcium carbonate as a bonding agent was successfully sintered in this study. TEM revealed similar micro-structural features as in cobalt based PCD. No signs of thermal degradation were found after exposure to 1200ºC in vacuum for this PCD. Contaminants introduced during processing prevented a detailed study of the binder in this system. The effect of substitutional metal atoms and plastic deformation of diamond on the thermal stability of diamond-SiC composites were investigated. A piston cylinder press was developed and used to synthesize diamond-SiC composites with different levels of plastically deformed diamond. It was concluded that substitutional metal atoms and plastic deformation of diamond grains play no role in the thermal degradation of diamond compacts at 750ºC. The thermal degradation of cobalt PCD is therefore completely determined by the cobalt/diamond interaction at 750ºC.
- Full Text:
- Date Issued: 2011
The influence of genetic relatedness on sociality and demography of female African elephants
- Authors: Munishi, Linus Kasian
- Date: 2011
- Subjects: African elephant , Wildlife conservation , Elephants -- Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: vital:10711 , http://hdl.handle.net/10948/d1011612 , African elephant , Wildlife conservation , Elephants -- Africa
- Description: Many elephant populations across Africa were or are being devastated by poaching and habitat loss, making population and range size for the species important issues of conservation concern in elephant ranging areas, including Tarangire National Park (TNP). Poaching and/or overhunting are known to have direct effects on the demography of elephant populations. The current understanding of the indirect effects of poaching on the sociality and demography of elephant populations is relatively poor, both at the group and an individual level. In this thesis the importance of genetic relatedness (as influenced by poaching) on sociality and demography of the female elephants was studied, using a combination of genetic, observation of behaviour and two decades of demography data collected from the northern subpopulation of TNP. I investigated and characterized the relatedness categories within elephant groups. Using a conceptual model for group size analysis in aggregation economies, I hypothesized that elephant populations subject to social disruptions due to poaching would exhibit characteristics of the free entry model, whereas more stable, closed populations would better fit the group-controlled model. I present a rare quantitative analysis of genetic relatedness and group size patterns among groups of adult female elephants in two wild populations: one in Tarangire National Park (TNP), Tanzania, and another in Addo Elephant National Park (AENP), South Africa. I demonstrate that the group size in African elephant populations is governed by genetic relatedness, and that poaching/overhunting has a significant influence upon the apparent group formation and size in elephants. I then focused on the effect of relatedness on agonistic interactions between adult females. I hypothesized that individual-based aggressive interactions among adult female African elephants would vary according to degree of kinship, with closely related dyads showing less aggression towards each other in resource-limited environments, thereby leading to indirect fitness benefits for individuals. As predicted, females did not show agonistic interactions to their close kin most often, and the frequency and intensity of aggressive interactions was inversely related to the degree of relatedness of the interactants. The effect of group relatedness and structure on reproductive success of individual female African elephant in TNP was also investigated. Adult female reproductive success was significantly influenced by within- group relatedness and structure. Higher reproductive success (with higher frequency of calf production and survival and more female calves produced) were more evident in the closely related groups than groups with low relatedness, suggesting that females from genetically disrupted groups are less likely to be reproductive than those in closely related groups. The possibility of negative effects of poaching on the subsequent generation of poached adult females and the alternative of a positive demographic response through reduced density was assessed by analysing the demographic patterns of the first generation (F1) females of prime-aged adult female African elephants in TNP using within- group relatedness and size. I also compared vital rate (age of first birth and interbirth interval) responses of first generation (F1) cows from Tarangire (poached) elephants with other females from poached (Northern Luangwa National Park, Zambia) and unpoached (Amboseli National Park, Kenya and Addo Elephant National Park, South Africa) populations. Group relatedness had no significant effect on sex ratio of the F1 cows‟ calves. There was a significant difference between the mean age of first birth and interbirth interval of F1 cows from the two (poached, Tarangire and unpoached, Amboseli National Park) elephant populations, suggesting that elephant populations reduced by poaching to low levels show an increase vigour through release from density constraints. Based on these results, the broader implications of secondary effects of poaching on elephant populations are critically evaluated. Also the importance of understanding the consequences of these effects is highlighted in light of other elephant conservation and management approaches. This understanding is useful in making conservation and management decisions for elephants and other biodiversity.
- Full Text:
- Date Issued: 2011
- Authors: Munishi, Linus Kasian
- Date: 2011
- Subjects: African elephant , Wildlife conservation , Elephants -- Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: vital:10711 , http://hdl.handle.net/10948/d1011612 , African elephant , Wildlife conservation , Elephants -- Africa
- Description: Many elephant populations across Africa were or are being devastated by poaching and habitat loss, making population and range size for the species important issues of conservation concern in elephant ranging areas, including Tarangire National Park (TNP). Poaching and/or overhunting are known to have direct effects on the demography of elephant populations. The current understanding of the indirect effects of poaching on the sociality and demography of elephant populations is relatively poor, both at the group and an individual level. In this thesis the importance of genetic relatedness (as influenced by poaching) on sociality and demography of the female elephants was studied, using a combination of genetic, observation of behaviour and two decades of demography data collected from the northern subpopulation of TNP. I investigated and characterized the relatedness categories within elephant groups. Using a conceptual model for group size analysis in aggregation economies, I hypothesized that elephant populations subject to social disruptions due to poaching would exhibit characteristics of the free entry model, whereas more stable, closed populations would better fit the group-controlled model. I present a rare quantitative analysis of genetic relatedness and group size patterns among groups of adult female elephants in two wild populations: one in Tarangire National Park (TNP), Tanzania, and another in Addo Elephant National Park (AENP), South Africa. I demonstrate that the group size in African elephant populations is governed by genetic relatedness, and that poaching/overhunting has a significant influence upon the apparent group formation and size in elephants. I then focused on the effect of relatedness on agonistic interactions between adult females. I hypothesized that individual-based aggressive interactions among adult female African elephants would vary according to degree of kinship, with closely related dyads showing less aggression towards each other in resource-limited environments, thereby leading to indirect fitness benefits for individuals. As predicted, females did not show agonistic interactions to their close kin most often, and the frequency and intensity of aggressive interactions was inversely related to the degree of relatedness of the interactants. The effect of group relatedness and structure on reproductive success of individual female African elephant in TNP was also investigated. Adult female reproductive success was significantly influenced by within- group relatedness and structure. Higher reproductive success (with higher frequency of calf production and survival and more female calves produced) were more evident in the closely related groups than groups with low relatedness, suggesting that females from genetically disrupted groups are less likely to be reproductive than those in closely related groups. The possibility of negative effects of poaching on the subsequent generation of poached adult females and the alternative of a positive demographic response through reduced density was assessed by analysing the demographic patterns of the first generation (F1) females of prime-aged adult female African elephants in TNP using within- group relatedness and size. I also compared vital rate (age of first birth and interbirth interval) responses of first generation (F1) cows from Tarangire (poached) elephants with other females from poached (Northern Luangwa National Park, Zambia) and unpoached (Amboseli National Park, Kenya and Addo Elephant National Park, South Africa) populations. Group relatedness had no significant effect on sex ratio of the F1 cows‟ calves. There was a significant difference between the mean age of first birth and interbirth interval of F1 cows from the two (poached, Tarangire and unpoached, Amboseli National Park) elephant populations, suggesting that elephant populations reduced by poaching to low levels show an increase vigour through release from density constraints. Based on these results, the broader implications of secondary effects of poaching on elephant populations are critically evaluated. Also the importance of understanding the consequences of these effects is highlighted in light of other elephant conservation and management approaches. This understanding is useful in making conservation and management decisions for elephants and other biodiversity.
- Full Text:
- Date Issued: 2011
An intelligent multimodal interface for in-car communication systems
- Authors: Sielinou, Patrick Tchankue
- Date: 2011
- Subjects: Automotive telematics , Automobiles -- Electronic equipment
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10461 , http://hdl.handle.net/10948/1495 , Automotive telematics , Automobiles -- Electronic equipment
- Description: In-car communication systems (ICCS) are becoming more frequently used by drivers. ICCS are used in order to minimise the driving distraction due to using a mobile phone while driving. Several usability studies of ICCS utilising speech user interfaces (SUIs) have identified usability issues that can affect the workload, performance, satisfaction and user experience of the driver. This is due to current speech technologies which can be a source of errors that may frustrate the driver and negatively affect the user experience. The aim of this research was to design a new multimodal interface that will manage the interaction between an ICCS and the driver. Unlike the current ICCS, it should make more voice input available, so as to support tasks (e.g. sending text messages; browsing the phone book, etc), which still require a cognitive workload from the driver. An adaptive multimodal interface was proposed in order to address current ICCS issues. The multimodal interface used both speech and manual input; however only the speech channel is used as output. This was done in order to minimise the visual distraction that graphical user interfaces or haptics devices can cause with current ICCS. The adaptive interface was designed to minimise the cognitive distraction of the driver. The adaptive interface ensures that whenever the distraction level of the driver is high, any information communication is postponed. After the design and the implementation of the first version of the prototype interface, called MIMI, a usability evaluation was conducted in order to identify any possible usability issues. Although voice dialling was found to be problematic, the results were encouraging in terms of performance, workload and user satisfaction. The suggestions received from the participants to improve the system usability were incorporated in the next implementation of MIMI. The adaptive module was then implemented to reduce driver distraction based on the driver‟s current context. The proposed architecture showed encouraging results in terms of usability and safety. The adaptive behaviour of MIMI significantly contributed to the reduction of cognitive distraction, because drivers received less information during difficult driving situations.
- Full Text:
- Date Issued: 2011
- Authors: Sielinou, Patrick Tchankue
- Date: 2011
- Subjects: Automotive telematics , Automobiles -- Electronic equipment
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10461 , http://hdl.handle.net/10948/1495 , Automotive telematics , Automobiles -- Electronic equipment
- Description: In-car communication systems (ICCS) are becoming more frequently used by drivers. ICCS are used in order to minimise the driving distraction due to using a mobile phone while driving. Several usability studies of ICCS utilising speech user interfaces (SUIs) have identified usability issues that can affect the workload, performance, satisfaction and user experience of the driver. This is due to current speech technologies which can be a source of errors that may frustrate the driver and negatively affect the user experience. The aim of this research was to design a new multimodal interface that will manage the interaction between an ICCS and the driver. Unlike the current ICCS, it should make more voice input available, so as to support tasks (e.g. sending text messages; browsing the phone book, etc), which still require a cognitive workload from the driver. An adaptive multimodal interface was proposed in order to address current ICCS issues. The multimodal interface used both speech and manual input; however only the speech channel is used as output. This was done in order to minimise the visual distraction that graphical user interfaces or haptics devices can cause with current ICCS. The adaptive interface was designed to minimise the cognitive distraction of the driver. The adaptive interface ensures that whenever the distraction level of the driver is high, any information communication is postponed. After the design and the implementation of the first version of the prototype interface, called MIMI, a usability evaluation was conducted in order to identify any possible usability issues. Although voice dialling was found to be problematic, the results were encouraging in terms of performance, workload and user satisfaction. The suggestions received from the participants to improve the system usability were incorporated in the next implementation of MIMI. The adaptive module was then implemented to reduce driver distraction based on the driver‟s current context. The proposed architecture showed encouraging results in terms of usability and safety. The adaptive behaviour of MIMI significantly contributed to the reduction of cognitive distraction, because drivers received less information during difficult driving situations.
- Full Text:
- Date Issued: 2011
An investigation into the effect of carbon type addictives on the negative electrode during the partial state of charge capacity cycling of lead acid batteries
- Authors: Snyders, Charmelle
- Date: 2011
- Subjects: Lead-acid batteries
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10379 , http://hdl.handle.net/10948/1494 , Lead-acid batteries
- Description: It is well known that a conventional lead acid cell that is exposed to a partial state of charge capacity cycling (PSoCCC) would experience a build-up of irreversible PbSO4 on the negative electrode. This results into a damaged negative electrode due to excessive PbSO4 formation by the typical visual “Venetian Blinds” effect of the active material. This displays the loss of adhesion of the active material with the electrode’s grids thereby making large sections of the material ineffective and reducing the cells useful capacity during high current applications. The addition of certain graphites to the negative paste mix had proven to be successful to reduce this effect. In the first part of the study, the physical and chemical properties of the various additives that are added to the negative electrode paste mix were comparatively studied. This was done to investigate any significant differences between various suppliers that could possibly influence the electrochemical characteristics of the Pb-acid battery performance. This comparative study was done by using the following analytical techniques; BET surface area, laser diffraction particle size, PXRD, TGA-MS and SEM. The study showed that there were no significant differences between the additives supplied from different suppliers except for some anomalies in the usefulness of techniques such as N2 adsorption to study the BET surface area of BaSO4. In order to reduce the sulphation effect from occurring within the Pb-acid battery a number of adjustments are made to the electrode active material. For example, Pb-acid battery manufacturers make use of an inert polymer based material, known as Polymat, to cover the electrode surfaces as part of their continuous electrode pasting process. It is made from a non woven polyester fiber that is applied to the pasted electrodes during the continuous pasting process. In this study the Polymat pasted electrodes has demonstrated a better physical adhesion of the active material to the grid support thereby maintaining the active material’s physical integrity. This however did not reduce the sulphation effect due to the high rate partial state of capacity cycling (HRPSoCCC) test but reduced the physical damage due to the irreversible active material blistering effect. The study investigated what effect the Polymat on the electrodes has on the III battery’s Cold Cranking Ability (CCA) at -18 degree C, the HRPSoCCC cycling and its active material utilization. The study showed that there was little or no differences in the CCA and HRPSoCCC capabilities of cells made with the Polymat when compared to cells without the Polymat, with significant improvement in active material’s adhesion and integrity to the grid wire. This was confirmed by PXRD and SEM analysis. Negative electrodes were made with four types of graphites (natural, flake, expanded and nano fibre) added to the negative paste mixture in order to reduce the effect of sulphation. The study looked at using statistical design of experiment (DoE) principles to investigate the variables (additives) such as different graphites, BaSO4 and Vanisperse to the negative electrode paste mixture where upon measuring the responses (electrochemical tests) a set of controlled experiments were done to study the extent of the variables interaction, dependency and independency on the cells electrochemical properties. This was especially in relation to the improvement of the battery’s ability to work under HRPSoCCC. The statistical analysis showed that there was a notable significant influence of the amounts of vanisperse, BaSO4 and their respective interactions on a number of electrochemical responses, such as the Peukert constant (n), CCA discharge time, material utilization at different discharge rates and the ability to capacity cycle under the simulated HRPSoCCC testing. The study did not suggest an optimized concentration of the additives, but did give an indication that there was a statistical significant trend in certain electrochemical responses with an interaction between the amounts of the additives BaSO4 and Vanisperse. The study also showed that the addition of a small amount of Nano carbon can significantly change the observed crystal morphology of the negative active material and that an improvement in the number of capacity cycles can be achieved during the HRPSoCCC test when compared to the other types of graphite additives.
- Full Text:
- Date Issued: 2011
- Authors: Snyders, Charmelle
- Date: 2011
- Subjects: Lead-acid batteries
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10379 , http://hdl.handle.net/10948/1494 , Lead-acid batteries
- Description: It is well known that a conventional lead acid cell that is exposed to a partial state of charge capacity cycling (PSoCCC) would experience a build-up of irreversible PbSO4 on the negative electrode. This results into a damaged negative electrode due to excessive PbSO4 formation by the typical visual “Venetian Blinds” effect of the active material. This displays the loss of adhesion of the active material with the electrode’s grids thereby making large sections of the material ineffective and reducing the cells useful capacity during high current applications. The addition of certain graphites to the negative paste mix had proven to be successful to reduce this effect. In the first part of the study, the physical and chemical properties of the various additives that are added to the negative electrode paste mix were comparatively studied. This was done to investigate any significant differences between various suppliers that could possibly influence the electrochemical characteristics of the Pb-acid battery performance. This comparative study was done by using the following analytical techniques; BET surface area, laser diffraction particle size, PXRD, TGA-MS and SEM. The study showed that there were no significant differences between the additives supplied from different suppliers except for some anomalies in the usefulness of techniques such as N2 adsorption to study the BET surface area of BaSO4. In order to reduce the sulphation effect from occurring within the Pb-acid battery a number of adjustments are made to the electrode active material. For example, Pb-acid battery manufacturers make use of an inert polymer based material, known as Polymat, to cover the electrode surfaces as part of their continuous electrode pasting process. It is made from a non woven polyester fiber that is applied to the pasted electrodes during the continuous pasting process. In this study the Polymat pasted electrodes has demonstrated a better physical adhesion of the active material to the grid support thereby maintaining the active material’s physical integrity. This however did not reduce the sulphation effect due to the high rate partial state of capacity cycling (HRPSoCCC) test but reduced the physical damage due to the irreversible active material blistering effect. The study investigated what effect the Polymat on the electrodes has on the III battery’s Cold Cranking Ability (CCA) at -18 degree C, the HRPSoCCC cycling and its active material utilization. The study showed that there was little or no differences in the CCA and HRPSoCCC capabilities of cells made with the Polymat when compared to cells without the Polymat, with significant improvement in active material’s adhesion and integrity to the grid wire. This was confirmed by PXRD and SEM analysis. Negative electrodes were made with four types of graphites (natural, flake, expanded and nano fibre) added to the negative paste mixture in order to reduce the effect of sulphation. The study looked at using statistical design of experiment (DoE) principles to investigate the variables (additives) such as different graphites, BaSO4 and Vanisperse to the negative electrode paste mixture where upon measuring the responses (electrochemical tests) a set of controlled experiments were done to study the extent of the variables interaction, dependency and independency on the cells electrochemical properties. This was especially in relation to the improvement of the battery’s ability to work under HRPSoCCC. The statistical analysis showed that there was a notable significant influence of the amounts of vanisperse, BaSO4 and their respective interactions on a number of electrochemical responses, such as the Peukert constant (n), CCA discharge time, material utilization at different discharge rates and the ability to capacity cycle under the simulated HRPSoCCC testing. The study did not suggest an optimized concentration of the additives, but did give an indication that there was a statistical significant trend in certain electrochemical responses with an interaction between the amounts of the additives BaSO4 and Vanisperse. The study also showed that the addition of a small amount of Nano carbon can significantly change the observed crystal morphology of the negative active material and that an improvement in the number of capacity cycles can be achieved during the HRPSoCCC test when compared to the other types of graphite additives.
- Full Text:
- Date Issued: 2011
Assessing the statistical methodologies of business research in the South African context
- Authors: Ndou, Aifheli Amos
- Date: 2011
- Subjects: Statistics -- South Africa , Commercial statistics -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:8631 , http://hdl.handle.net/10948/1484 , Statistics -- South Africa , Commercial statistics -- South Africa
- Description: The aim of the study is to establish an acceptable classification scheme for the statistical methods used in business research. The approach compares the statistical component of the research and evaluates how it has changed over time and across different journals. If, as expected, the statistical expertise has changed, the change would be identified with the view to recommending curriculum changes for Statistics Departments of South African tertiary institutions.
- Full Text:
- Date Issued: 2011
- Authors: Ndou, Aifheli Amos
- Date: 2011
- Subjects: Statistics -- South Africa , Commercial statistics -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:8631 , http://hdl.handle.net/10948/1484 , Statistics -- South Africa , Commercial statistics -- South Africa
- Description: The aim of the study is to establish an acceptable classification scheme for the statistical methods used in business research. The approach compares the statistical component of the research and evaluates how it has changed over time and across different journals. If, as expected, the statistical expertise has changed, the change would be identified with the view to recommending curriculum changes for Statistics Departments of South African tertiary institutions.
- Full Text:
- Date Issued: 2011
The photodecomposition of different polymorphic forms of 1,4-dihydropyridine channel blockers
- Authors: Francis, Farzaana
- Date: 2011
- Subjects: Photodegradation , Nifedipine , Nimodipine , Dihydropyridine
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10378 , http://hdl.handle.net/10948/1496 , Photodegradation , Nifedipine , Nimodipine , Dihydropyridine
- Description: 1,4-Dihydropyridines (DHPs) are a classification of compounds used as calcium channel blockers in the treatment of various conditions. These compounds readily undergo photodegradation. The degradants produced have no pharmaceutical activity and render the drugs ineffective. DHPs also exhibit polymorphism. Nifedipine and Nimodipine are two such drugs. This study aimed to monitor the photodegradation of these two drugs and to establish the effect of particle size, polymorphism and β-Cyclodextrin (β-CD) on the rate of photodegradation. Different polymorphs (namely the amorphous and stable crystalline polymorphs) of the two drugs were prepared for use in the study. Mixtures of each drug with β-CD were also prepared for photostability studies. The mixtures were prepared in a 1:1 molar ratio. The rate of photodegradation was studied with a 500 W metal halide lamp in accordance to ICH guidelines. The study employed samples on a small scale where degradation was analysed with High Performance Liquid Chromatography, and also samples on a larger scale where degradation was monitored with Powder X-ray Diffraction. The two sets of results of observing the degradation process by two analytical techniques where compared in terms of their quantification methods. The extent of photodegradation was suitably modelled and fitted using the Avrami-Erofeyev kinetic equation. Smaller particle size showed increased photodegradation for Nimodipine; the effect was insignificant for Nifedipine however. For both drugs it was found that the amorphous polymorph underwent faster photodegradation. The study showed that β-CD caused an increase in photodegradation for both drugs under these experimental conditions.
- Full Text:
- Date Issued: 2011
- Authors: Francis, Farzaana
- Date: 2011
- Subjects: Photodegradation , Nifedipine , Nimodipine , Dihydropyridine
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10378 , http://hdl.handle.net/10948/1496 , Photodegradation , Nifedipine , Nimodipine , Dihydropyridine
- Description: 1,4-Dihydropyridines (DHPs) are a classification of compounds used as calcium channel blockers in the treatment of various conditions. These compounds readily undergo photodegradation. The degradants produced have no pharmaceutical activity and render the drugs ineffective. DHPs also exhibit polymorphism. Nifedipine and Nimodipine are two such drugs. This study aimed to monitor the photodegradation of these two drugs and to establish the effect of particle size, polymorphism and β-Cyclodextrin (β-CD) on the rate of photodegradation. Different polymorphs (namely the amorphous and stable crystalline polymorphs) of the two drugs were prepared for use in the study. Mixtures of each drug with β-CD were also prepared for photostability studies. The mixtures were prepared in a 1:1 molar ratio. The rate of photodegradation was studied with a 500 W metal halide lamp in accordance to ICH guidelines. The study employed samples on a small scale where degradation was analysed with High Performance Liquid Chromatography, and also samples on a larger scale where degradation was monitored with Powder X-ray Diffraction. The two sets of results of observing the degradation process by two analytical techniques where compared in terms of their quantification methods. The extent of photodegradation was suitably modelled and fitted using the Avrami-Erofeyev kinetic equation. Smaller particle size showed increased photodegradation for Nimodipine; the effect was insignificant for Nifedipine however. For both drugs it was found that the amorphous polymorph underwent faster photodegradation. The study showed that β-CD caused an increase in photodegradation for both drugs under these experimental conditions.
- Full Text:
- Date Issued: 2011
The development of novel cancer targeting agents
- Authors: Knoetze, Steyn
- Date: 2011
- Subjects: Cancer -- Research , Cancer -- Treatment
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: vital:10397 , http://hdl.handle.net/10948/d1010636 , Cancer -- Research , Cancer -- Treatment
- Description: The search for the cure for cancer is currently a multi-billion dollar industry and the search for the elusive “magic bullet”, i.e. the perfect cancer drug that would interact therapeutically with cancerous tissues while having a minimal effect on healthy cells, is the topic of many research studies in the world today. A large number of novel drugs or drug complexes and conjugates are being synthesized and subjected to rigorous evaluation in the race to find the perfect cure. ECDG (Ethylene diCysteine DeoxyGlucose) seems to have promising cancer targeting ability. Even though this compound has been described in a few publications, we could not find any reference to the current use of ECDG in oncology clinics, either as a therapeutic agent, or as a diagnostic tool for imaging purposes. It was also not possible to purchase pure ECDG anywhere in the world. This prompted us to further investigate ECDG as a possible candidate for cancer targeting research, either as an imaging agent for cancer diagnosis or complexed with an anti-cancer agent for therapeutic purposes. Detailed investigations done in our laboratory can be divided into the following categories: - Development of a synthetic method for ECDG on a multigram scale ; - Purification of prepared ECDG not using the described dialysis method that only allows the purification of small quantities of ECDG (mg scale) ; Detailed investigation of the chemistry involved in the preparation of pure ECDG and its metal complexes ; - Investigation of the stability of ECDG and its metal complexes that is essential data required for any pharmaceutical agent ; - Preparation of ECDG complexes for use as a diagnostic tool, i.e. complexation with 99mTc ; Investigation of the bio distribution of ECDG-ReO complexes ; - Preparation of an ECDG kit as a diagnostic tool for use in oncology clinics. The development of novel aromatic ligands having similar characteristics compared to ECDG, containing an N2S2 chromophore as donor atoms, to further investigate their targeting capabilities, have also been investigated. All intermediates and final compounds were characterized mainly by ESI MS, in some cases IR and NMR whenever available. Successful preparation and purification of ECDG ands its metal complexes was achieved and extensively characterized and evaluated. Efforts directed towards the development of ECDG at NECSA, South Africa, were also rewarded with significant success. Furthermore, significant development regarding the synthesis of two novel compounds with ECDG-like characteristics was also completed.
- Full Text:
- Date Issued: 2011
- Authors: Knoetze, Steyn
- Date: 2011
- Subjects: Cancer -- Research , Cancer -- Treatment
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: vital:10397 , http://hdl.handle.net/10948/d1010636 , Cancer -- Research , Cancer -- Treatment
- Description: The search for the cure for cancer is currently a multi-billion dollar industry and the search for the elusive “magic bullet”, i.e. the perfect cancer drug that would interact therapeutically with cancerous tissues while having a minimal effect on healthy cells, is the topic of many research studies in the world today. A large number of novel drugs or drug complexes and conjugates are being synthesized and subjected to rigorous evaluation in the race to find the perfect cure. ECDG (Ethylene diCysteine DeoxyGlucose) seems to have promising cancer targeting ability. Even though this compound has been described in a few publications, we could not find any reference to the current use of ECDG in oncology clinics, either as a therapeutic agent, or as a diagnostic tool for imaging purposes. It was also not possible to purchase pure ECDG anywhere in the world. This prompted us to further investigate ECDG as a possible candidate for cancer targeting research, either as an imaging agent for cancer diagnosis or complexed with an anti-cancer agent for therapeutic purposes. Detailed investigations done in our laboratory can be divided into the following categories: - Development of a synthetic method for ECDG on a multigram scale ; - Purification of prepared ECDG not using the described dialysis method that only allows the purification of small quantities of ECDG (mg scale) ; Detailed investigation of the chemistry involved in the preparation of pure ECDG and its metal complexes ; - Investigation of the stability of ECDG and its metal complexes that is essential data required for any pharmaceutical agent ; - Preparation of ECDG complexes for use as a diagnostic tool, i.e. complexation with 99mTc ; Investigation of the bio distribution of ECDG-ReO complexes ; - Preparation of an ECDG kit as a diagnostic tool for use in oncology clinics. The development of novel aromatic ligands having similar characteristics compared to ECDG, containing an N2S2 chromophore as donor atoms, to further investigate their targeting capabilities, have also been investigated. All intermediates and final compounds were characterized mainly by ESI MS, in some cases IR and NMR whenever available. Successful preparation and purification of ECDG ands its metal complexes was achieved and extensively characterized and evaluated. Efforts directed towards the development of ECDG at NECSA, South Africa, were also rewarded with significant success. Furthermore, significant development regarding the synthesis of two novel compounds with ECDG-like characteristics was also completed.
- Full Text:
- Date Issued: 2011
Benefication of glycerol from algae and vegetable oil
- Authors: Mafu, Lubabalo Rowan
- Date: 2011
- Subjects: Glycerin -- Biotechnology , Biodiesel fuels , Renewable natural resources
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10409 , http://hdl.handle.net/10948/d1011503 , Glycerin -- Biotechnology , Biodiesel fuels , Renewable natural resources
- Description: This research has been directed at furthering the utilization of crude glycerol oversupply formed as a by-product from the biodiesel manufacturing process. Phosphorylation of hydroxyl groups is a synthetic route that was investigated for the conversion of glycerol into a glycerol-phosphate (GPE) ester mixture. The process investigated for the synthesis of a GPE product was based on phosphorylation reaction procedures that were previously reported in the literature. The reaction to convert glycerol into a GPE mixture has been thoroughly investigated and the hydrogen chloride gas formed as a reaction by-product has been optimized. The chemical properties of GPE have been studied and discussed together with a mass balance of the overall glycerol phosphorylation process. The phosphate groups contained in polyhydric phosphate molecules have a potential chelating effect on cations. There are several cations that may be chelated by the phosphate ester group of polyhydric phosphate molecules. These cations include ammonium (NH4+), Potassium (K+), Calcium (Ca2+) etc, which are essential as nutrients in plant fertilizer formulations. This research has investigated the use of a GPE synthesized from glycerol in the laboratory and the use thereof as a phosphorus containing base in the formulation and evaluation of Nitrogen, Phosphorus and Potassium (NPK) containing fertilizer solution, Ammonium-Potassium-Glycerol-Phosphate (APGP) fertilizer solution. The APGP fertilizer solution has further been evaluated by growing two week old tomato seedlings under controlled conditions. The performance of the APGP fertiliser solution has been evaluated using design of experiments by comparison with traditionally used liquidAmmonium-Potassium-Phosphate inorganic fertilizer. This fertilizer solution has been prepared in similar manner as APGP formulation with the difference between them being the source of phosphorus. The results have been evaluated using statistic analysis where a significant difference between the evaluated fertilizer formulations was found. The comparative study of these formulations was monitored by the observed plant weights. A blank treatment was used as a control to determine if a significant difference among these formulations was observed. Anova single factor and t-Test methods (Two-Samples assumed of equal variances) are statistical models that were applied to interpret the observed experimental data with respect to wet and dry weighed masses of tomato seedlings. These methods indicated a confirmed conclusion that there was a significant difference between APPO4 solution and APGP solution. The observed data have shown that the APPO4 solution provided significantly better fertigation performance than APGP solution. Consequently, further investigation has been conducted to determine the cause of the poorer performance of the APGP solution. The further study of the APGP fertilizer solution included nutrient stability testing, biological analysis and other observed physical changes of the APGP solution over time. Biological results have revealed the presence of a Fusarium fungus species that has grown and is suspended in APGP fertilizer solution. This microbe species has been observed to play a vital role in consuming fertilizer nutrients. In addition, the observed abnormal plant growth and nutrient decomposition of the APGP formulation has been proposed to be mostly a result of the pathogenicity of the fusarium fungi species that was suspended in the APGP solution. Further work has been proposed in which the effect of such biological contamination is eliminated through adequate sterilization procedures and the APGP formulation re-evaluated.
- Full Text:
- Date Issued: 2011
- Authors: Mafu, Lubabalo Rowan
- Date: 2011
- Subjects: Glycerin -- Biotechnology , Biodiesel fuels , Renewable natural resources
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10409 , http://hdl.handle.net/10948/d1011503 , Glycerin -- Biotechnology , Biodiesel fuels , Renewable natural resources
- Description: This research has been directed at furthering the utilization of crude glycerol oversupply formed as a by-product from the biodiesel manufacturing process. Phosphorylation of hydroxyl groups is a synthetic route that was investigated for the conversion of glycerol into a glycerol-phosphate (GPE) ester mixture. The process investigated for the synthesis of a GPE product was based on phosphorylation reaction procedures that were previously reported in the literature. The reaction to convert glycerol into a GPE mixture has been thoroughly investigated and the hydrogen chloride gas formed as a reaction by-product has been optimized. The chemical properties of GPE have been studied and discussed together with a mass balance of the overall glycerol phosphorylation process. The phosphate groups contained in polyhydric phosphate molecules have a potential chelating effect on cations. There are several cations that may be chelated by the phosphate ester group of polyhydric phosphate molecules. These cations include ammonium (NH4+), Potassium (K+), Calcium (Ca2+) etc, which are essential as nutrients in plant fertilizer formulations. This research has investigated the use of a GPE synthesized from glycerol in the laboratory and the use thereof as a phosphorus containing base in the formulation and evaluation of Nitrogen, Phosphorus and Potassium (NPK) containing fertilizer solution, Ammonium-Potassium-Glycerol-Phosphate (APGP) fertilizer solution. The APGP fertilizer solution has further been evaluated by growing two week old tomato seedlings under controlled conditions. The performance of the APGP fertiliser solution has been evaluated using design of experiments by comparison with traditionally used liquidAmmonium-Potassium-Phosphate inorganic fertilizer. This fertilizer solution has been prepared in similar manner as APGP formulation with the difference between them being the source of phosphorus. The results have been evaluated using statistic analysis where a significant difference between the evaluated fertilizer formulations was found. The comparative study of these formulations was monitored by the observed plant weights. A blank treatment was used as a control to determine if a significant difference among these formulations was observed. Anova single factor and t-Test methods (Two-Samples assumed of equal variances) are statistical models that were applied to interpret the observed experimental data with respect to wet and dry weighed masses of tomato seedlings. These methods indicated a confirmed conclusion that there was a significant difference between APPO4 solution and APGP solution. The observed data have shown that the APPO4 solution provided significantly better fertigation performance than APGP solution. Consequently, further investigation has been conducted to determine the cause of the poorer performance of the APGP solution. The further study of the APGP fertilizer solution included nutrient stability testing, biological analysis and other observed physical changes of the APGP solution over time. Biological results have revealed the presence of a Fusarium fungus species that has grown and is suspended in APGP fertilizer solution. This microbe species has been observed to play a vital role in consuming fertilizer nutrients. In addition, the observed abnormal plant growth and nutrient decomposition of the APGP formulation has been proposed to be mostly a result of the pathogenicity of the fusarium fungi species that was suspended in the APGP solution. Further work has been proposed in which the effect of such biological contamination is eliminated through adequate sterilization procedures and the APGP formulation re-evaluated.
- Full Text:
- Date Issued: 2011
An evaluation of UPLC technology for the simultaneous analysis of actives in a multi-active drug
- Authors: Bawjee, Janita
- Date: 2011
- Subjects: High performance liquid chromatography
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10384 , http://hdl.handle.net/10948/d1008407 , High performance liquid chromatography
- Description: The evaluation of the potential to use Ultra Performance Liquid Chromatography (UPLC) for the simultaneous quantification of all the actives in a multi-active tablet is described in this work. Part of the evaluation was to ensure that the necessary regulatory requirements were adhered to by ascertaining that an analytical method is suitable for a specific purpose through analytical method validation for the specific multi-active tablet. The UPLC method was also tested for the analysis of similar products, namely tablet formulations that contain similar active ingredients in the same proportions but with an additional active ingredient. A method for the simultaneous determination of paracetamol, caffeine and codeine phosphate was developed using UPLC technology. The UPLC developed method was more efficient than the existing in-house HPLC method. The UPLC method was then validated in accordance to ICH and USP guidelines. The application of this UPLC method for the analysis of similar products containing paracetamol, caffeine, codeine phosphate and one extra active ingredient was very challenging. The low concentration of the additional component, differences in sample matrix and differences in formulations added to the challenges. The direct application for the analysis of products Y and Z was not successful; however the method could be used as a platform for further research. A cost comparison between the UPLC and HPLC methods showed the UPLC method to be more cost effective. Thus, while maintenance costs are higher for the UPLC instrument, column costs are comparable to HPLC columns, but solvent and waste disposal charges decrease considerably due to lower solvent use. The reduction in instrument time dramatically improves the cost effectiveness of UPLC over HPLC due to a concurrent reduction in analyst time requirement. The results of this study show that the analytical costs associated with the analysis of multi-active drugs using HPLC procedures can be reduced substantially by the CONFIDENTIAL INTELLECTUAL PROPERTY OF ASPEN PHARMACARE implementation of UPLC technology. The hypothesis that the enhanced chromatographic power of UPLC can be leveraged to provide faster analysis times hence increased product throughput rates, and lower operating costs for the analysis of multi-active drugs was accepted. These advantages were achieved whilst meeting all regulatory requirements for analytical methods as required by regulatory bodies.
- Full Text:
- Date Issued: 2011
- Authors: Bawjee, Janita
- Date: 2011
- Subjects: High performance liquid chromatography
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10384 , http://hdl.handle.net/10948/d1008407 , High performance liquid chromatography
- Description: The evaluation of the potential to use Ultra Performance Liquid Chromatography (UPLC) for the simultaneous quantification of all the actives in a multi-active tablet is described in this work. Part of the evaluation was to ensure that the necessary regulatory requirements were adhered to by ascertaining that an analytical method is suitable for a specific purpose through analytical method validation for the specific multi-active tablet. The UPLC method was also tested for the analysis of similar products, namely tablet formulations that contain similar active ingredients in the same proportions but with an additional active ingredient. A method for the simultaneous determination of paracetamol, caffeine and codeine phosphate was developed using UPLC technology. The UPLC developed method was more efficient than the existing in-house HPLC method. The UPLC method was then validated in accordance to ICH and USP guidelines. The application of this UPLC method for the analysis of similar products containing paracetamol, caffeine, codeine phosphate and one extra active ingredient was very challenging. The low concentration of the additional component, differences in sample matrix and differences in formulations added to the challenges. The direct application for the analysis of products Y and Z was not successful; however the method could be used as a platform for further research. A cost comparison between the UPLC and HPLC methods showed the UPLC method to be more cost effective. Thus, while maintenance costs are higher for the UPLC instrument, column costs are comparable to HPLC columns, but solvent and waste disposal charges decrease considerably due to lower solvent use. The reduction in instrument time dramatically improves the cost effectiveness of UPLC over HPLC due to a concurrent reduction in analyst time requirement. The results of this study show that the analytical costs associated with the analysis of multi-active drugs using HPLC procedures can be reduced substantially by the CONFIDENTIAL INTELLECTUAL PROPERTY OF ASPEN PHARMACARE implementation of UPLC technology. The hypothesis that the enhanced chromatographic power of UPLC can be leveraged to provide faster analysis times hence increased product throughput rates, and lower operating costs for the analysis of multi-active drugs was accepted. These advantages were achieved whilst meeting all regulatory requirements for analytical methods as required by regulatory bodies.
- Full Text:
- Date Issued: 2011
On the design and monitoring of photovoltaic systems for rural homes
- Authors: Williams, Nathaniel John
- Date: 2011
- Subjects: Photovoltaic cells , Dwellings -- Power supply
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10516 , http://hdl.handle.net/10948/1308 , Photovoltaic cells , Dwellings -- Power supply
- Description: It is estimated that 1.6 billion people today live without access to electricity. Most of these people live in remote rural areas in developing countries. One economic solution to this problem is the deployment of small domestic photovoltaic (PV) systems called solar home systems (SHS). In order to improve the performance and reduce the life cycle cost of these systems, accurate monitoring data of real SHSs is required. To this end, two SHSs typical of those found in the field were designed and installed, one in a rural area of the Eastern Cape of South Africa and the other in the laboratory. Monitoring systems were designed to record energy ows in the system and important environmental parameters. A novel technique was developed to correct for measurement errors occurring during the utilization of pulse width modulation charge control techniques. These errors were found to be as large as 47.6 percent. Simulations show that correction techniques produce measurement errors that are up to 20 times smaller than uncorrected values, depending upon the operating conditions. As a tool to aid in the analysis of monitoring data, a PV performance model was developed. The model, used to predict the maximum power point (MPP) power of a PV array, was able to predict MPP energy production to within 0.2 percent over the course of three days. Monitoring data from the laboratory system shows that the largest sources of energy loss are charge control, module under performance relative to manufacturer specifications and operation of the PV array away from MPP. These accounted for losses of approximately 18-27 percent, 15 percent and 8-11 percent of rated PV energy under standard test conditions, respectively. Energy consumed by loads on the systems was less than 50 percent of rated PV energy for both the remote and laboratory systems. Performance ratios (PR) for the laboratory system ranged from 0.38 to 0.49 for the three monitoring periods. The remote system produced a PR of 0.46. In both systems the PV arrays appear to have been oversized. This was due to overestimation of the energy requirements of the loads on the systems. In the laboratory system, the loads consisting of three compact fluorescent lamps and one incandescent lamp, were used to simulate a typical SHS load pro le and collectively consumed only 85 percent of their rated power. The 8 predicted load profile for the remote system proved to be signi cantly overestimated. The results of the monitoring project demonstrate the importance of acquiring an accurate estimation of the energy demand from loads on the system. Overestimations result in over-sized arrays and energy lost to charge control while under-sized systems risk damaging system batteries and load shedding. Significant under-performance of the PV module used in the laboratory system, underlines the importance of measuring module IV curves and verifying manufacturer specifications before system deployment. It was also found that signi cant PV array performance gains could be obtained by the use of maximum power point tracking charge controllers. Increased PV array performance leads to smaller arrays and reduced system cost.
- Full Text:
- Date Issued: 2011
- Authors: Williams, Nathaniel John
- Date: 2011
- Subjects: Photovoltaic cells , Dwellings -- Power supply
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10516 , http://hdl.handle.net/10948/1308 , Photovoltaic cells , Dwellings -- Power supply
- Description: It is estimated that 1.6 billion people today live without access to electricity. Most of these people live in remote rural areas in developing countries. One economic solution to this problem is the deployment of small domestic photovoltaic (PV) systems called solar home systems (SHS). In order to improve the performance and reduce the life cycle cost of these systems, accurate monitoring data of real SHSs is required. To this end, two SHSs typical of those found in the field were designed and installed, one in a rural area of the Eastern Cape of South Africa and the other in the laboratory. Monitoring systems were designed to record energy ows in the system and important environmental parameters. A novel technique was developed to correct for measurement errors occurring during the utilization of pulse width modulation charge control techniques. These errors were found to be as large as 47.6 percent. Simulations show that correction techniques produce measurement errors that are up to 20 times smaller than uncorrected values, depending upon the operating conditions. As a tool to aid in the analysis of monitoring data, a PV performance model was developed. The model, used to predict the maximum power point (MPP) power of a PV array, was able to predict MPP energy production to within 0.2 percent over the course of three days. Monitoring data from the laboratory system shows that the largest sources of energy loss are charge control, module under performance relative to manufacturer specifications and operation of the PV array away from MPP. These accounted for losses of approximately 18-27 percent, 15 percent and 8-11 percent of rated PV energy under standard test conditions, respectively. Energy consumed by loads on the systems was less than 50 percent of rated PV energy for both the remote and laboratory systems. Performance ratios (PR) for the laboratory system ranged from 0.38 to 0.49 for the three monitoring periods. The remote system produced a PR of 0.46. In both systems the PV arrays appear to have been oversized. This was due to overestimation of the energy requirements of the loads on the systems. In the laboratory system, the loads consisting of three compact fluorescent lamps and one incandescent lamp, were used to simulate a typical SHS load pro le and collectively consumed only 85 percent of their rated power. The 8 predicted load profile for the remote system proved to be signi cantly overestimated. The results of the monitoring project demonstrate the importance of acquiring an accurate estimation of the energy demand from loads on the system. Overestimations result in over-sized arrays and energy lost to charge control while under-sized systems risk damaging system batteries and load shedding. Significant under-performance of the PV module used in the laboratory system, underlines the importance of measuring module IV curves and verifying manufacturer specifications before system deployment. It was also found that signi cant PV array performance gains could be obtained by the use of maximum power point tracking charge controllers. Increased PV array performance leads to smaller arrays and reduced system cost.
- Full Text:
- Date Issued: 2011
The effectiveness of livestock guarding dogs for livestock production and conservation in Namibia
- Authors: Potgieter, Gail Christine
- Date: 2011
- Subjects: Livestock protection dogs -- Namibia , Herding dogs -- Namibia , Livestock -- Predators of -- Control -- Namibia , Livestock -- Losses -- Namibia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10680 , http://hdl.handle.net/10948/1666 , Livestock protection dogs -- Namibia , Herding dogs -- Namibia , Livestock -- Predators of -- Control -- Namibia , Livestock -- Losses -- Namibia
- Description: The use of livestock guarding dogs (LGDs) to mitigate farmer-predator conflict in Namibia was evaluated. As farmer-predator conflict has two sides, LGDs were evaluated in terms of livestock production and conservation. The main objectives in terms of livestock production were to document: 1) the perceived ability of LGDs to reduce livestock losses in a cost-effective manner; 2) the farmers’ satisfaction with LGD performance; and 3) factors influencing LGD behaviour. The main objectives in terms of conservation were to record: 1) predator killing by farmers relative to LGD introduction; 2) direct impacts of LGDs on target (damage-causing) species; and 3) the impact of LGDs on non-target species. This evaluation was conducted on LGDs bred by the Cheetah Conservation Fund (CCF) and placed on farms in Namibia. The data were collected during face-to-face interviews with farmers using LGDs. Historical data from the CCF programme were used in conjunction with a complete survey of the farmers in the CCF LGD programme during 2009-2010. In terms of livestock production, 91 percent of the LGDs (n = 65) eliminated or reduced livestock losses. Subsequently, 73 percent of the farmers perceived their LGDs as economically beneficial, although a cost-benefit analysis showed that only 59 percent of the LGDs were cost-effective. Farmers were generally satisfied with the performance of their LGDs. However, farmer satisfaction was more closely linked to good LGD behaviour than the perceived reduction in livestock losses. The most commonly-reported LGD behavioural problems (n = 195) were staying at home rather than accompanying the livestock (21 percent) and chasing wildlife (19 percent). LGD staying home behaviour was linked to a lack of care on subsistence farms, as high quality dog food was not consistently provided. Care for LGDs declined with LGD age on subsistence, but not commercial, farms. In terms of conservation, predator-killing farmers killed fewer individuals in the year since LGD introduction than previously; this result was only significant for black-backed jackal Canis mesomelas. However, 37 LGDs killed jackals, nine killed baboons Papio ursinus, three killed caracals Caracal caracal and one killed a cheetah Acinonyx jubatus (n = 83). Farmers and LGDs combined killed significantly more jackals in the survey year than the same farmers (n = 36) killed before LGD introduction. Conversely, five farmers killed 3.2 ± 2.01 cheetahs each in the year before LGD introduction, whereas LGDs and these farmers combined killed only 0.2 ± 0.2 cheetahs per farm in the survey year. Only 16 LGDs (n = 83) killed non-target species. The high LGD success rate in terms of livestock production was facilitated by livestock husbandry practices in the study area. In terms of conservation, LGDs were more beneficial for apex predators than for mesopredators and had a minor impact on non-target species.
- Full Text:
- Date Issued: 2011
- Authors: Potgieter, Gail Christine
- Date: 2011
- Subjects: Livestock protection dogs -- Namibia , Herding dogs -- Namibia , Livestock -- Predators of -- Control -- Namibia , Livestock -- Losses -- Namibia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10680 , http://hdl.handle.net/10948/1666 , Livestock protection dogs -- Namibia , Herding dogs -- Namibia , Livestock -- Predators of -- Control -- Namibia , Livestock -- Losses -- Namibia
- Description: The use of livestock guarding dogs (LGDs) to mitigate farmer-predator conflict in Namibia was evaluated. As farmer-predator conflict has two sides, LGDs were evaluated in terms of livestock production and conservation. The main objectives in terms of livestock production were to document: 1) the perceived ability of LGDs to reduce livestock losses in a cost-effective manner; 2) the farmers’ satisfaction with LGD performance; and 3) factors influencing LGD behaviour. The main objectives in terms of conservation were to record: 1) predator killing by farmers relative to LGD introduction; 2) direct impacts of LGDs on target (damage-causing) species; and 3) the impact of LGDs on non-target species. This evaluation was conducted on LGDs bred by the Cheetah Conservation Fund (CCF) and placed on farms in Namibia. The data were collected during face-to-face interviews with farmers using LGDs. Historical data from the CCF programme were used in conjunction with a complete survey of the farmers in the CCF LGD programme during 2009-2010. In terms of livestock production, 91 percent of the LGDs (n = 65) eliminated or reduced livestock losses. Subsequently, 73 percent of the farmers perceived their LGDs as economically beneficial, although a cost-benefit analysis showed that only 59 percent of the LGDs were cost-effective. Farmers were generally satisfied with the performance of their LGDs. However, farmer satisfaction was more closely linked to good LGD behaviour than the perceived reduction in livestock losses. The most commonly-reported LGD behavioural problems (n = 195) were staying at home rather than accompanying the livestock (21 percent) and chasing wildlife (19 percent). LGD staying home behaviour was linked to a lack of care on subsistence farms, as high quality dog food was not consistently provided. Care for LGDs declined with LGD age on subsistence, but not commercial, farms. In terms of conservation, predator-killing farmers killed fewer individuals in the year since LGD introduction than previously; this result was only significant for black-backed jackal Canis mesomelas. However, 37 LGDs killed jackals, nine killed baboons Papio ursinus, three killed caracals Caracal caracal and one killed a cheetah Acinonyx jubatus (n = 83). Farmers and LGDs combined killed significantly more jackals in the survey year than the same farmers (n = 36) killed before LGD introduction. Conversely, five farmers killed 3.2 ± 2.01 cheetahs each in the year before LGD introduction, whereas LGDs and these farmers combined killed only 0.2 ± 0.2 cheetahs per farm in the survey year. Only 16 LGDs (n = 83) killed non-target species. The high LGD success rate in terms of livestock production was facilitated by livestock husbandry practices in the study area. In terms of conservation, LGDs were more beneficial for apex predators than for mesopredators and had a minor impact on non-target species.
- Full Text:
- Date Issued: 2011
Radiation damage in GaAs and SiC
- Authors: Janse van Vuuren, Arno
- Date: 2011
- Subjects: Gallium arsenide semiconductors
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10515 , http://hdl.handle.net/10948/1477 , Gallium arsenide semiconductors
- Description: In this dissertation the microstructure and hardness of phosphorous implanted SiC and neutron irradiated SiC and GaAs have been investigated. SiC is important due to its application as a barrier coating layer in coated particle fuel used in high temperature gas cooled reactors. The characterisation of neutron irradiated GaAs has been included in this study in order to compare the radiation damage produced by protons and neutrons since proton bombardment of SiC could in principle be used for out-of-reactor simulations of the neutron irradiation damage created in SiC during reactor operation. The following SiC and GaAs compounds were investigated: As-implanted and annealed single crystal 6H-SiC wafers and polycrystalline 3C-SiC bulk material implanted with phosphorous ions. As-irradiated and annealed polycrystalline 3C-SiC bulk material irradiated with fast neutrons. As-irradiated and annealed single crystal GaAs wafers irradiated with fast neutrons. The main techniques used for the analyses were transmission electron microscopy (TEM) and nano-indentation hardness testing. The following results were obtained for the investigation of implanted and irradiated SiC and GaAs: Phosphorous Implanted 6H-SiC and 3C-SiC The depth of the P+ ion damage was found to be in good agreement with predictions by TRIM 2010. Micro-diffraction of the damage region in P+ implanted 6H-SiC (dose 5×1016 ions/cm2) indicates that amorphization occurred and that recrystallisation of this layer occurred during annealing at 1200°C. TEM analysis revealed that the layer recrystallised in the 3C phase of SiC and twin defects also formed within the layer. Micro-diffraction of the damage region in P+ implanted 3C-SiC (dose 1×1015 ions/cm2) indicates that amorphization also occurred for this sample and that recrystallisation of this layer occurred during annealing at 800°C. Nano-hardness testing of the P+ implanted 6H-SiC indicated that the hardness of the implanted SiC was initially much lower than unimplanted SiC due to the formation of an amorphous layer during ion implantation. After annealing the implanted SiC at 800°C and 1200°C, the hardness increased due to re-crystallisation and point defect hardening. Neutron Irradiated 3C-SiC TEM investigations of neutron irradiated 3C-SiC revealed the presence dark spot defects for SiC samples irradiated to a dose of 5.9×1021 n/cm2 and 9.6×1021 n/cm2. Neutron Irradiated GaAs TEM investigation revealed a high density of dislocation loops in the unannealed neutron irradiated GaAs. The loop diameters increased after post-irradiation annealing in the range 600 to 800 °C. The dislocation loops were found to be of interstitial type lying on the {110} cleavage planes of GaAs. This finding is in agreement with earlier studies on 300 keV proton bombarded and 1 MeV electron irradiated GaAs where interstitial loops on {110} planes became visible after annealing at temperatures exceeding 500 °C. The small dislocation loops on the {110} planes of the neutron irradiated GaAs transformed to large loops and dislocations after annealing at 1000 °C.
- Full Text:
- Date Issued: 2011
- Authors: Janse van Vuuren, Arno
- Date: 2011
- Subjects: Gallium arsenide semiconductors
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10515 , http://hdl.handle.net/10948/1477 , Gallium arsenide semiconductors
- Description: In this dissertation the microstructure and hardness of phosphorous implanted SiC and neutron irradiated SiC and GaAs have been investigated. SiC is important due to its application as a barrier coating layer in coated particle fuel used in high temperature gas cooled reactors. The characterisation of neutron irradiated GaAs has been included in this study in order to compare the radiation damage produced by protons and neutrons since proton bombardment of SiC could in principle be used for out-of-reactor simulations of the neutron irradiation damage created in SiC during reactor operation. The following SiC and GaAs compounds were investigated: As-implanted and annealed single crystal 6H-SiC wafers and polycrystalline 3C-SiC bulk material implanted with phosphorous ions. As-irradiated and annealed polycrystalline 3C-SiC bulk material irradiated with fast neutrons. As-irradiated and annealed single crystal GaAs wafers irradiated with fast neutrons. The main techniques used for the analyses were transmission electron microscopy (TEM) and nano-indentation hardness testing. The following results were obtained for the investigation of implanted and irradiated SiC and GaAs: Phosphorous Implanted 6H-SiC and 3C-SiC The depth of the P+ ion damage was found to be in good agreement with predictions by TRIM 2010. Micro-diffraction of the damage region in P+ implanted 6H-SiC (dose 5×1016 ions/cm2) indicates that amorphization occurred and that recrystallisation of this layer occurred during annealing at 1200°C. TEM analysis revealed that the layer recrystallised in the 3C phase of SiC and twin defects also formed within the layer. Micro-diffraction of the damage region in P+ implanted 3C-SiC (dose 1×1015 ions/cm2) indicates that amorphization also occurred for this sample and that recrystallisation of this layer occurred during annealing at 800°C. Nano-hardness testing of the P+ implanted 6H-SiC indicated that the hardness of the implanted SiC was initially much lower than unimplanted SiC due to the formation of an amorphous layer during ion implantation. After annealing the implanted SiC at 800°C and 1200°C, the hardness increased due to re-crystallisation and point defect hardening. Neutron Irradiated 3C-SiC TEM investigations of neutron irradiated 3C-SiC revealed the presence dark spot defects for SiC samples irradiated to a dose of 5.9×1021 n/cm2 and 9.6×1021 n/cm2. Neutron Irradiated GaAs TEM investigation revealed a high density of dislocation loops in the unannealed neutron irradiated GaAs. The loop diameters increased after post-irradiation annealing in the range 600 to 800 °C. The dislocation loops were found to be of interstitial type lying on the {110} cleavage planes of GaAs. This finding is in agreement with earlier studies on 300 keV proton bombarded and 1 MeV electron irradiated GaAs where interstitial loops on {110} planes became visible after annealing at temperatures exceeding 500 °C. The small dislocation loops on the {110} planes of the neutron irradiated GaAs transformed to large loops and dislocations after annealing at 1000 °C.
- Full Text:
- Date Issued: 2011
Land use/cover change modelling and land degradation assessment in the Keiskamma catchment using remote sensing and GIS
- Authors: Mhangara, Paidamwoyo
- Date: 2011
- Subjects: Land use -- South Africa -- Eastern Cape , Land degradation -- South Africa -- Eastern Cape , Keiskamma River (South Africa)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10647 , http://hdl.handle.net/10948/1467 , Land use -- South Africa -- Eastern Cape , Land degradation -- South Africa -- Eastern Cape , Keiskamma River (South Africa)
- Description: Land degradation in most communal parts of the Keiskamma catchment has reached alarming proportions. The Keiskamma catchment is particularly predisposed to severe land degradation associated with soil erosion, thicket degradation and deteriorating riparian vegetation. There is a close coupling between land use/cover dynamics and degradation trends witnessed in the catchment. Soil erosion is prevalent in most of the communal areas in the catchment. The principal aim of this study was to investigate land use/cover trends, model the spatial patterns of soil loss and predict future land use/cover scenarios as a means of assessing land degradation in the Keiskamma catchment. Multi-temporal Landsat satellite imagery from 1972 to 2006 was used for land use/cover change analyses using object-oriented post-classification comparison. Fragmentation analysis was performed by computing and analyzing landscape metrics in the riparian and adjacent hillslope areas to determine the land cover structural changes that have occurred since 1972. The landscape function analysis was used to validate the current rangeland conditions in the communal areas and the former commercial farms. The current condition of the riparian zones and proximal hillslopes was assessed using the Rapid Appraisal of Riparian Condition and future land use/cover scenarios were simulated using the Markovcellular automata model. Spatial patterns of soil loss in the Keiskamma catchment were determined using the Sediment Assessment Tool for Effective Erosion Control (SATEEC), which is a GIS based RUSLE model that integrates sediment delivery ratios. Object oriented classification was used to map soil erosion surfaces and valley infill in ephemeral stream channels as a means of demonstrating the major sediment transfer processes operating in the Keiskamma catchment. The Mahalanobis distance method was used to compute the topographic thresholds for gully erosion. To understand the effect of soil characteristics in severe forms of erosion, laboratory analyses were undertaken to determine the physico-chemical soil properties. iv The temporal land use/cover analysis done using the post-classification change detection indicated that intact vegetation has undergone a significant decline from 1972 to 2006. The temporal changes within the intermediate years are characterized by cyclic transitions of decline and recovery of intact vegetation. An overall decline in intact vegetation cover, an increase in degraded vegetation and bare eroded soil was noted. Fragmentation analyses done in the communal villages of the central Keiskamma catchment indicated increasing vegetation fragmentation manifested by an increase in smaller and less connected vegetation patches, and a subsequent increase of bare and degraded soil patches which are much bigger and more connected. The Landscape Organisation Index revealed very low vegetation connectivity in the communal rangelands that have weak local traditional institutions. Fragmentation analyses in the riparian and proximal hillslopes revealed evidence of increasing vegetation fragmentation from 1972 to 2006. The Markov Cellular Automata simulation predicted a decline in intact vegetation and an increase in bare and degraded soil in 2019. The Keiskamma catchment was noted as experiencing high rates of soil loss that are above provincial and national averages. The classification of erosion features and valley infill showcased the vegetation enrichment in the ephemeral streams which is occurring at the expense of high soil losses from severe gully erosion on the hillslopes. This in turn has led to an inversion of grazing patterns within the catchment, such that grazing is now concentrated within the ephemeral stream channels. Soil chemical analyses revealed a high sodium content and low soluble salt concentration, which promote soil dispersion, piping and gully erosion. The presence of high amounts of illite-smectite in the catchment also accounts for the highly dispersive nature of the soil even at low SAR values. Significant amounts of swelling 2:1 silicate clays such as smectites cause cracking and contribute to the development of piping and gullying in the catchment. Given the worsening degradation trends in the communal areas, a systematic re-allocation of state land in sections of the catchment that belonged to the former commercial farms is recommended to alleviate anthropogenic pressure. Strengthening local institutions that effectively monitor and manage natural resources will be required in order to maintain v optimum flow regimes in rivers and curb thicket degradation. Measures to curb environmental degradation in the Keiskamma catchment should encompass suitable ecological interventions that are sensitive to the socio-economic challenges facing the people in communal areas.
- Full Text:
- Date Issued: 2011
- Authors: Mhangara, Paidamwoyo
- Date: 2011
- Subjects: Land use -- South Africa -- Eastern Cape , Land degradation -- South Africa -- Eastern Cape , Keiskamma River (South Africa)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10647 , http://hdl.handle.net/10948/1467 , Land use -- South Africa -- Eastern Cape , Land degradation -- South Africa -- Eastern Cape , Keiskamma River (South Africa)
- Description: Land degradation in most communal parts of the Keiskamma catchment has reached alarming proportions. The Keiskamma catchment is particularly predisposed to severe land degradation associated with soil erosion, thicket degradation and deteriorating riparian vegetation. There is a close coupling between land use/cover dynamics and degradation trends witnessed in the catchment. Soil erosion is prevalent in most of the communal areas in the catchment. The principal aim of this study was to investigate land use/cover trends, model the spatial patterns of soil loss and predict future land use/cover scenarios as a means of assessing land degradation in the Keiskamma catchment. Multi-temporal Landsat satellite imagery from 1972 to 2006 was used for land use/cover change analyses using object-oriented post-classification comparison. Fragmentation analysis was performed by computing and analyzing landscape metrics in the riparian and adjacent hillslope areas to determine the land cover structural changes that have occurred since 1972. The landscape function analysis was used to validate the current rangeland conditions in the communal areas and the former commercial farms. The current condition of the riparian zones and proximal hillslopes was assessed using the Rapid Appraisal of Riparian Condition and future land use/cover scenarios were simulated using the Markovcellular automata model. Spatial patterns of soil loss in the Keiskamma catchment were determined using the Sediment Assessment Tool for Effective Erosion Control (SATEEC), which is a GIS based RUSLE model that integrates sediment delivery ratios. Object oriented classification was used to map soil erosion surfaces and valley infill in ephemeral stream channels as a means of demonstrating the major sediment transfer processes operating in the Keiskamma catchment. The Mahalanobis distance method was used to compute the topographic thresholds for gully erosion. To understand the effect of soil characteristics in severe forms of erosion, laboratory analyses were undertaken to determine the physico-chemical soil properties. iv The temporal land use/cover analysis done using the post-classification change detection indicated that intact vegetation has undergone a significant decline from 1972 to 2006. The temporal changes within the intermediate years are characterized by cyclic transitions of decline and recovery of intact vegetation. An overall decline in intact vegetation cover, an increase in degraded vegetation and bare eroded soil was noted. Fragmentation analyses done in the communal villages of the central Keiskamma catchment indicated increasing vegetation fragmentation manifested by an increase in smaller and less connected vegetation patches, and a subsequent increase of bare and degraded soil patches which are much bigger and more connected. The Landscape Organisation Index revealed very low vegetation connectivity in the communal rangelands that have weak local traditional institutions. Fragmentation analyses in the riparian and proximal hillslopes revealed evidence of increasing vegetation fragmentation from 1972 to 2006. The Markov Cellular Automata simulation predicted a decline in intact vegetation and an increase in bare and degraded soil in 2019. The Keiskamma catchment was noted as experiencing high rates of soil loss that are above provincial and national averages. The classification of erosion features and valley infill showcased the vegetation enrichment in the ephemeral streams which is occurring at the expense of high soil losses from severe gully erosion on the hillslopes. This in turn has led to an inversion of grazing patterns within the catchment, such that grazing is now concentrated within the ephemeral stream channels. Soil chemical analyses revealed a high sodium content and low soluble salt concentration, which promote soil dispersion, piping and gully erosion. The presence of high amounts of illite-smectite in the catchment also accounts for the highly dispersive nature of the soil even at low SAR values. Significant amounts of swelling 2:1 silicate clays such as smectites cause cracking and contribute to the development of piping and gullying in the catchment. Given the worsening degradation trends in the communal areas, a systematic re-allocation of state land in sections of the catchment that belonged to the former commercial farms is recommended to alleviate anthropogenic pressure. Strengthening local institutions that effectively monitor and manage natural resources will be required in order to maintain v optimum flow regimes in rivers and curb thicket degradation. Measures to curb environmental degradation in the Keiskamma catchment should encompass suitable ecological interventions that are sensitive to the socio-economic challenges facing the people in communal areas.
- Full Text:
- Date Issued: 2011
Nearshore subtidal soft-bottom macrozoobenthic community structure in the western sector of Algoa Bay, South Africa
- Authors: Masikane, Ntuthuko Fortune
- Date: 2011
- Subjects: Benthic animals -- South Africa -- Algoa Bay , Benthos
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10684 , http://hdl.handle.net/10948/1466 , Benthic animals -- South Africa -- Algoa Bay , Benthos
- Description: The objectives of this study were to characterise macrozoobenthic community structure of the western sector of Algoa Bay, to identify the drivers of community structure and to develop a long-term monitoring framework. Data were collected from six study sites stratified along-shore. Each site comprised three stations; most sites were located in areas directly influenced by anthropogenic activities such as inflow from storm water drains and areas where dredged spoil was dumped. Other sites included areas in close proximity to estuary mouths. Physico-chemical parameters of the water column were measured with a YSI instrument, sediment for faunal and physico-chemical analyses was sampled with a Van Veen grab, and collected macrofauna were sedated and preserved pending analysis. In the laboratory, macrofauna were identified to finest taxonomic resolution possible under dissecting and compound microscopes, and enumerated. Sediment samples for physico-chemical analyses were kept frozen pending analysis. Up to 187 species belonging to 137 genera and 105 families were identified. Univariate community parameters such as abundance and number of species varied significantly along-shore, generally increasing towards less wave-exposed sites. Multivariate analyses revealed that community assemblages were heterogeneously distributed along-shore, corresponding to areas where anthropogenic influences such as effluent discharge and commercial harbour activities prevailed. During the 2008 survey, species assemblages separated into six groups corresponding to the six sites but xvii during the 2009 survey, species assemblages separated into four groups probably due to changes in environmental parameters such as the hydrodynamic regime. In both surveys the assemblage opposite a drainage canal (Papenkuils outfall) was distinct as it was dissimilar to all other assemblages. This site was also heterogeneous over relatively small spatial scales. Important physico-chemical variables influencing community structures during the 2008 survey included bottom measurements of temperature, salinity, dissolved oxygen, coarse sand and mud. During the 2009 survey, only bottom temperature and mud content were identified as important physico-chemical variables structuring community assemblages. The principal variable was probably the hydrodynamic regime, driving community structure at a larger scale in Algoa Bay. On a localised scale, communities were probably structured by other factors such as effluent discharges, influence of estuary mouths and activities associated with the harbour. With a lack of information on keystone species (regarded as good monitoring species) in Algoa Bay, it was proposed that groups that cumulatively comprise 50–75 percent of total abundance within communities be monitored annually. Included are amphipods, polychaetes, cumaceans, ostracods, tanaids and bivalves. It was also proposed that areas opposite estuary mouths, effluent outfalls and the dredged spoil dumpsite be monitored. This routine monitoring programme should be accompanied by periodic hypothesis driven research to assess the importance of stochastic events (e.g., upwelling) on macrozoobenthic community dynamics. Keywords: macrozoobenthos, soft-bottom, community assemblages, spatial distribution patterns, environmental drivers, long-term monitoring framework.
- Full Text:
- Date Issued: 2011
- Authors: Masikane, Ntuthuko Fortune
- Date: 2011
- Subjects: Benthic animals -- South Africa -- Algoa Bay , Benthos
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10684 , http://hdl.handle.net/10948/1466 , Benthic animals -- South Africa -- Algoa Bay , Benthos
- Description: The objectives of this study were to characterise macrozoobenthic community structure of the western sector of Algoa Bay, to identify the drivers of community structure and to develop a long-term monitoring framework. Data were collected from six study sites stratified along-shore. Each site comprised three stations; most sites were located in areas directly influenced by anthropogenic activities such as inflow from storm water drains and areas where dredged spoil was dumped. Other sites included areas in close proximity to estuary mouths. Physico-chemical parameters of the water column were measured with a YSI instrument, sediment for faunal and physico-chemical analyses was sampled with a Van Veen grab, and collected macrofauna were sedated and preserved pending analysis. In the laboratory, macrofauna were identified to finest taxonomic resolution possible under dissecting and compound microscopes, and enumerated. Sediment samples for physico-chemical analyses were kept frozen pending analysis. Up to 187 species belonging to 137 genera and 105 families were identified. Univariate community parameters such as abundance and number of species varied significantly along-shore, generally increasing towards less wave-exposed sites. Multivariate analyses revealed that community assemblages were heterogeneously distributed along-shore, corresponding to areas where anthropogenic influences such as effluent discharge and commercial harbour activities prevailed. During the 2008 survey, species assemblages separated into six groups corresponding to the six sites but xvii during the 2009 survey, species assemblages separated into four groups probably due to changes in environmental parameters such as the hydrodynamic regime. In both surveys the assemblage opposite a drainage canal (Papenkuils outfall) was distinct as it was dissimilar to all other assemblages. This site was also heterogeneous over relatively small spatial scales. Important physico-chemical variables influencing community structures during the 2008 survey included bottom measurements of temperature, salinity, dissolved oxygen, coarse sand and mud. During the 2009 survey, only bottom temperature and mud content were identified as important physico-chemical variables structuring community assemblages. The principal variable was probably the hydrodynamic regime, driving community structure at a larger scale in Algoa Bay. On a localised scale, communities were probably structured by other factors such as effluent discharges, influence of estuary mouths and activities associated with the harbour. With a lack of information on keystone species (regarded as good monitoring species) in Algoa Bay, it was proposed that groups that cumulatively comprise 50–75 percent of total abundance within communities be monitored annually. Included are amphipods, polychaetes, cumaceans, ostracods, tanaids and bivalves. It was also proposed that areas opposite estuary mouths, effluent outfalls and the dredged spoil dumpsite be monitored. This routine monitoring programme should be accompanied by periodic hypothesis driven research to assess the importance of stochastic events (e.g., upwelling) on macrozoobenthic community dynamics. Keywords: macrozoobenthos, soft-bottom, community assemblages, spatial distribution patterns, environmental drivers, long-term monitoring framework.
- Full Text:
- Date Issued: 2011
Land use change, landslide occurrence and livelihood strategies on Mount Elgon Slopes, Eastern Uganda
- Authors: Mugagga, Frank
- Date: 2011
- Subjects: Land use -- Uganda -- Mount Elgon National Park , Landslides -- Uganda -- Mount Elgon National Park , Land degradation -- Uganda -- Mount Elgon National Park
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10646 , http://hdl.handle.net/10948/1468 , Land use -- Uganda -- Mount Elgon National Park , Landslides -- Uganda -- Mount Elgon National Park , Land degradation -- Uganda -- Mount Elgon National Park
- Description: An investigation of the relationship between the physical, pedological and anthropogenic influences on landslide occurrence on the midslopes within and outside Mt Elgon National Park was carried out. One of the landslides occurred in a protected pristine forest environment within the Park while the other two were located at sites deforested for cultivation within and outside the National Park. Field based surveys, GIS techniques and laboratory tests were used to collect and analyze the data. A household survey was undertaken to establish the main community livelihood strategies, the drivers of land use change and implications for land degradation on the mid slopes of Mt Elgon. Aerial photographs taken in 1960 and orthophoto maps formed the benchmark for the analysis of the respective land use changes between 1995 and 2006, using 30m Landsat TM and 20m SPOT MS images in IDRISI Andes GIS environment. Landslide sites were mapped using a Magellan Professional MobileMapperTMCX and terrain parameters were derived using a 15M Digital Elevation Model. A hybrid supervised/unsupervised classification approach was employed to generate land cover maps from which the areal extent of three land cover classes (agricultural fields, woodlands and forests) was calculated. Particle size distribution and atterberg limits were used to test the hypothesis that soils at the landslide sites are inherently ‘problem soils’ where slope failure can occur even without human intervention. Shear strength parameters (internal of friction and cohesion) were used calculate the slope factor of safety to ascertain slope stability at pristine and disturbed landslide sites. Results from the socio-economic survey revealed that smallholder subsistence agriculture and encroachment on the National Park resources are the main sources of livelihoods for the communities surrounding the Park. The communities also have a strong socio-cultural attachment to the National Park, as it is the source of items used during traditional rituals like circumcision. Encroachment is driven by the high population pressure and the prevalent political climate. Farmers mainly use slash and burn technique to prepare land for cultivation and those close to the National Park are reluctant to adopt appropriate farming and soil conservation practices due to the uncertainties surrounding their future on such plots. Slash and burn iii techniques were observed to accelerate various forms of erosion including rills, gullies and sheet. Soil and water conservation techniques were mainly practiced on privately owned farms. The period 1960 and 1995 was characterized by minimal land use changes and no encroachment into the designated Mount Elgon National Park. Conversely, the period 1995 – 2006 marked a significant loss of woodlands and forest cover particularly on steep concave slopes (36º – 58º) within the National Park. The land use change trends were attributed to the prevalent land politics and exponential population growth in the region. The encroachment onto the critical slopes was noted to have induced a series of shallow and deep landslides in the area. Deforestation on Mt Elgon was reported to have both onsite and offsite climate variability and implications in the form of drought, heat waves, flash floods, economic dislocation, crop failure and associated malnutrition in surrounding low lying areas. The soils on pristine and disturbed slopes contain high amount of clay (>10 percent), are fine textured (>50 percent of the material passing the 0.075mm sieve) and highly plastic. These soil attributes imply low permeability, excessive water retention and high susceptibility to expansion and sliding. The vertic nature of soils at Nametsi was confirmed by the extremely high plasticity indices (averaging 33percent), while, high liquid limits at Buwabwala (53 percent) and Kitati (59 percent) qualified the soils as vertisols which are associated with landslides. The results point to the fact that soils at landslide sites are inherently ‘problem soils’ where slope failure can occur even without human intervention. Therefore, the hypothesis that soils at three landslide sites are inherently ‘problem soils’ where slope failure can occur even without human intervention is accepted. Notwithstanding the fact that the study was focussed on mid-altitude slopes of Mt Elgon, the results are in tandem with investigations carried out earlier on the lower densely populated slopes, thus confirming the widespread nature of problem soils on Mt Elgon. There is an urgent need to control human population growth and restore forest cover on the heavily deforested steep slopes particularly within the National Park, and restrain communities from encroaching on the pristine slopes of Mt Elgon. This will be achieved if the politicians, Park Authorities and local communities jointly participate in the design and implementation of CFMs. Future research could focus on climate change implications of deforestation of Mt Elgon environments and quantification of carbon loss related to deforestation and soil degradation in the mountain environments.
- Full Text:
- Date Issued: 2011
- Authors: Mugagga, Frank
- Date: 2011
- Subjects: Land use -- Uganda -- Mount Elgon National Park , Landslides -- Uganda -- Mount Elgon National Park , Land degradation -- Uganda -- Mount Elgon National Park
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10646 , http://hdl.handle.net/10948/1468 , Land use -- Uganda -- Mount Elgon National Park , Landslides -- Uganda -- Mount Elgon National Park , Land degradation -- Uganda -- Mount Elgon National Park
- Description: An investigation of the relationship between the physical, pedological and anthropogenic influences on landslide occurrence on the midslopes within and outside Mt Elgon National Park was carried out. One of the landslides occurred in a protected pristine forest environment within the Park while the other two were located at sites deforested for cultivation within and outside the National Park. Field based surveys, GIS techniques and laboratory tests were used to collect and analyze the data. A household survey was undertaken to establish the main community livelihood strategies, the drivers of land use change and implications for land degradation on the mid slopes of Mt Elgon. Aerial photographs taken in 1960 and orthophoto maps formed the benchmark for the analysis of the respective land use changes between 1995 and 2006, using 30m Landsat TM and 20m SPOT MS images in IDRISI Andes GIS environment. Landslide sites were mapped using a Magellan Professional MobileMapperTMCX and terrain parameters were derived using a 15M Digital Elevation Model. A hybrid supervised/unsupervised classification approach was employed to generate land cover maps from which the areal extent of three land cover classes (agricultural fields, woodlands and forests) was calculated. Particle size distribution and atterberg limits were used to test the hypothesis that soils at the landslide sites are inherently ‘problem soils’ where slope failure can occur even without human intervention. Shear strength parameters (internal of friction and cohesion) were used calculate the slope factor of safety to ascertain slope stability at pristine and disturbed landslide sites. Results from the socio-economic survey revealed that smallholder subsistence agriculture and encroachment on the National Park resources are the main sources of livelihoods for the communities surrounding the Park. The communities also have a strong socio-cultural attachment to the National Park, as it is the source of items used during traditional rituals like circumcision. Encroachment is driven by the high population pressure and the prevalent political climate. Farmers mainly use slash and burn technique to prepare land for cultivation and those close to the National Park are reluctant to adopt appropriate farming and soil conservation practices due to the uncertainties surrounding their future on such plots. Slash and burn iii techniques were observed to accelerate various forms of erosion including rills, gullies and sheet. Soil and water conservation techniques were mainly practiced on privately owned farms. The period 1960 and 1995 was characterized by minimal land use changes and no encroachment into the designated Mount Elgon National Park. Conversely, the period 1995 – 2006 marked a significant loss of woodlands and forest cover particularly on steep concave slopes (36º – 58º) within the National Park. The land use change trends were attributed to the prevalent land politics and exponential population growth in the region. The encroachment onto the critical slopes was noted to have induced a series of shallow and deep landslides in the area. Deforestation on Mt Elgon was reported to have both onsite and offsite climate variability and implications in the form of drought, heat waves, flash floods, economic dislocation, crop failure and associated malnutrition in surrounding low lying areas. The soils on pristine and disturbed slopes contain high amount of clay (>10 percent), are fine textured (>50 percent of the material passing the 0.075mm sieve) and highly plastic. These soil attributes imply low permeability, excessive water retention and high susceptibility to expansion and sliding. The vertic nature of soils at Nametsi was confirmed by the extremely high plasticity indices (averaging 33percent), while, high liquid limits at Buwabwala (53 percent) and Kitati (59 percent) qualified the soils as vertisols which are associated with landslides. The results point to the fact that soils at landslide sites are inherently ‘problem soils’ where slope failure can occur even without human intervention. Therefore, the hypothesis that soils at three landslide sites are inherently ‘problem soils’ where slope failure can occur even without human intervention is accepted. Notwithstanding the fact that the study was focussed on mid-altitude slopes of Mt Elgon, the results are in tandem with investigations carried out earlier on the lower densely populated slopes, thus confirming the widespread nature of problem soils on Mt Elgon. There is an urgent need to control human population growth and restore forest cover on the heavily deforested steep slopes particularly within the National Park, and restrain communities from encroaching on the pristine slopes of Mt Elgon. This will be achieved if the politicians, Park Authorities and local communities jointly participate in the design and implementation of CFMs. Future research could focus on climate change implications of deforestation of Mt Elgon environments and quantification of carbon loss related to deforestation and soil degradation in the mountain environments.
- Full Text:
- Date Issued: 2011
Effects of polarization in a distributed raman fibre amplifier
- Authors: Muguro, Kennedy Mwaura
- Date: 2011
- Subjects: Fiber optics , Polarization (Light) , Optical communications , Optical amplifiers , Raman effect
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10544 , http://hdl.handle.net/10948/d1014621
- Description: The need to exploit the large fibre bandwidth and increase the reach has seen the application of the Raman fibre amplifier (RFA) become indispensable in modern light wave systems. The success and resilience of RFAs in optical communication is deeply rooted in their unique optical properties and new technologies which have allowed the amplifier to come of age. However, the full potential of RFAs in optical communication and other applications are yet to be realized. More so are its polarization properties which still remain largely unexploited and have not been fully understood. In this work, fundamental issues regarding distributed RFA have been investigated with the aim of acquiring a better understanding of the amplifier polarization characteristics which have potential applications. In particular the effects of polarization mode dispersion (PMD) and polarization dependent loss (PDL) have been demonstrated both by simulation and experiment. The possibility of Raman polarization pulling in single mode fibres (SMFs) has also been addressed. Polarization sensitivity of RFA has been known for a long time but the clear manifestation of it has become evident in the advent of modern low PMD fibre. Unlike EDFAs which make use of special doped fibre, RFAs require no special fibre for operation. Besides, RFA uses a very long length of fibre and as such the fibre polarization characteristics come into play during amplification. In the demonstrations presented in this thesis a fibre of PMD coefficient < 0.05 pskm-1/2 was regarded as low PMD fibre while one having coefficient ≥ 0.05 pskm-1/2 was categorized to have high PMD unless otherwise stated. Several experiments were performed to evaluate the RFA gain characteristics with respect to fibre PMD and the system performance in the presence of noise emanating from amplified spontaneous emission (ASE). Analysis of Raman gain statistics was done for fibres of low and high PMD coefficients. The statistics of PDG and on-off gain were eventually used to demonstrate the extraction of PMD coefficients of fibres between 0.01- 0.1 pskm-1/2 using a forward pumping configuration. It was found that, at increasing pump power a linear relationship exists between forward and backward signal gain on a dB scale. The interaction of PDL and Raman PDG in the presence of PMD were observed at very fundamental level. It was found the presence of PDL serves to reduce the available on-off gain. It was also established that the presence of PMD mediates the interaction between PDG/PDL. When PMD is high it reduces PDG but the presence of PDL introduces a wavelength dependent gain tilting for WDM channels. Further analysis revealed that signal polarization is influenced by the pump SOP due to the pulling effect which is present even at moderate pump power.
- Full Text:
- Date Issued: 2011
- Authors: Muguro, Kennedy Mwaura
- Date: 2011
- Subjects: Fiber optics , Polarization (Light) , Optical communications , Optical amplifiers , Raman effect
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10544 , http://hdl.handle.net/10948/d1014621
- Description: The need to exploit the large fibre bandwidth and increase the reach has seen the application of the Raman fibre amplifier (RFA) become indispensable in modern light wave systems. The success and resilience of RFAs in optical communication is deeply rooted in their unique optical properties and new technologies which have allowed the amplifier to come of age. However, the full potential of RFAs in optical communication and other applications are yet to be realized. More so are its polarization properties which still remain largely unexploited and have not been fully understood. In this work, fundamental issues regarding distributed RFA have been investigated with the aim of acquiring a better understanding of the amplifier polarization characteristics which have potential applications. In particular the effects of polarization mode dispersion (PMD) and polarization dependent loss (PDL) have been demonstrated both by simulation and experiment. The possibility of Raman polarization pulling in single mode fibres (SMFs) has also been addressed. Polarization sensitivity of RFA has been known for a long time but the clear manifestation of it has become evident in the advent of modern low PMD fibre. Unlike EDFAs which make use of special doped fibre, RFAs require no special fibre for operation. Besides, RFA uses a very long length of fibre and as such the fibre polarization characteristics come into play during amplification. In the demonstrations presented in this thesis a fibre of PMD coefficient < 0.05 pskm-1/2 was regarded as low PMD fibre while one having coefficient ≥ 0.05 pskm-1/2 was categorized to have high PMD unless otherwise stated. Several experiments were performed to evaluate the RFA gain characteristics with respect to fibre PMD and the system performance in the presence of noise emanating from amplified spontaneous emission (ASE). Analysis of Raman gain statistics was done for fibres of low and high PMD coefficients. The statistics of PDG and on-off gain were eventually used to demonstrate the extraction of PMD coefficients of fibres between 0.01- 0.1 pskm-1/2 using a forward pumping configuration. It was found that, at increasing pump power a linear relationship exists between forward and backward signal gain on a dB scale. The interaction of PDL and Raman PDG in the presence of PMD were observed at very fundamental level. It was found the presence of PDL serves to reduce the available on-off gain. It was also established that the presence of PMD mediates the interaction between PDG/PDL. When PMD is high it reduces PDG but the presence of PDL introduces a wavelength dependent gain tilting for WDM channels. Further analysis revealed that signal polarization is influenced by the pump SOP due to the pulling effect which is present even at moderate pump power.
- Full Text:
- Date Issued: 2011
The response of microalgal biomass and community composition to environmental factors in the Sundays Estuary
- Authors: Kotsedi, Daisy
- Date: 2011
- Subjects: Algal blooms -- South Africa -- Sundays River Estuary
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10609 , http://hdl.handle.net/10948/1434 , Algal blooms -- South Africa -- Sundays River Estuary
- Description: The Sundays Estuary is permanently open to the sea and has been described as channel-like along its entire length with a narrow intertidal area (mostly less than 5 - 6 m in width). The estuary experiences regular freshwater inflow with large supplies of nutrients, derived from the Orange River transfer scheme and agricultural return flow. In particular, nitrate concentrations are high as a result of fertilisers used in the Sundays River catchment area. The objectives of this study were to measure microalgal biomass and community composition and relate to flow, water quality and other environmental variables. Surveys in August 2006, March 2007, February, June and August 2008 showed that salinity less than 10 percent mostly occurred from 12.5 km from the mouth and this was also where the highest water column chlorophyll a (>20 μg l-1) was found. Different groups of microalgae formed phytoplankton blooms for the different sampling sessions, which were correlated with high chlorophyll a. These included blooms of green algae (August 2006), flagellates (March 2007), dinoflagellates (June 2008) and diatom species (February and August 2008). The dominant diatom (Cyclotella atomus) indicated nutrient-rich conditions. Green algae and diatoms were associated with low salinity water in the upper reaches of the estuary. Flagellates were dominant throughout the estuary particularly when nutrients were low, whereas the dinoflagellate bloom in June 2008 was correlated with high ammonium and pH. Maximum benthic chlorophyll a was found at 12.5 km from the mouth in February, June and August 2008 and was correlated with high sediment organic and moisture content. Benthic diatoms were associated with high temperature whereas some species in June 2008 were associated with high ammonium concentrations. The middle reaches of the estuary characterise a zone of deposition rather than suspension which would favour benthic diatom colonization. Phytoplankton cells settling out on the sediments may account for the high benthic chlorophyll a because maximum water column chlorophyll a was also found in the REI zone (where salinity is less than 10 percent and where high biological activity occurs) in the Sundays Estuary. The estuary was sampled over five consecutive weeks from March to April 2009 to identify environmental factors that support different microalgal bloom species. Phytoplankton blooms, defined as chlorophyll a greater than 20 μg l-1, were found during Weeks 1, 4 and 5 from the middle to the upper reaches of the estuary. Diatom species (Cylindrotheca closterium, Cyclotella atomus and Cyclostephanus dubius) occurred in bloom concentrations during these weeks. These diatom species are cosmopolitan and indicate brackish nutrient-rich water. Flagellates were the dominant group in Weeks 2 to 4, but positive correlations with chlorophyll a were found during Weeks 1 and 2. During the first week of this study the conditions were warm and calm (measured as temperature and wind speed) and there was a well developed bloom (38 μg l-1). There was a strong cold front from 17 to 19 March, which mixed the water column resulting in the decrease of the chlorophyll a levels (<20 μg l-1) and the bloom collapsed during Weeks 2 and 3. However, in Weeks 4 and 5 conditions were again calm and warmer, which appeared to stimulate the phytoplankton bloom. Nanoplankton (2.7 - 20 μm) was dominant during each week sampled and contributed a considerable amount (55 - 79 percent) to the phytoplankton biomass. Once again subtidal benthic chlorophyll a and water column chlorophyll a were highest 12.5 km from the mouth. Deposition of phytoplankton cells from the water column was evident in the benthic samples. The study showed that the Sundays Estuary is eutrophic and characterised by microalgal blooms consisting of different phytoplankton groups.
- Full Text:
- Date Issued: 2011
- Authors: Kotsedi, Daisy
- Date: 2011
- Subjects: Algal blooms -- South Africa -- Sundays River Estuary
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10609 , http://hdl.handle.net/10948/1434 , Algal blooms -- South Africa -- Sundays River Estuary
- Description: The Sundays Estuary is permanently open to the sea and has been described as channel-like along its entire length with a narrow intertidal area (mostly less than 5 - 6 m in width). The estuary experiences regular freshwater inflow with large supplies of nutrients, derived from the Orange River transfer scheme and agricultural return flow. In particular, nitrate concentrations are high as a result of fertilisers used in the Sundays River catchment area. The objectives of this study were to measure microalgal biomass and community composition and relate to flow, water quality and other environmental variables. Surveys in August 2006, March 2007, February, June and August 2008 showed that salinity less than 10 percent mostly occurred from 12.5 km from the mouth and this was also where the highest water column chlorophyll a (>20 μg l-1) was found. Different groups of microalgae formed phytoplankton blooms for the different sampling sessions, which were correlated with high chlorophyll a. These included blooms of green algae (August 2006), flagellates (March 2007), dinoflagellates (June 2008) and diatom species (February and August 2008). The dominant diatom (Cyclotella atomus) indicated nutrient-rich conditions. Green algae and diatoms were associated with low salinity water in the upper reaches of the estuary. Flagellates were dominant throughout the estuary particularly when nutrients were low, whereas the dinoflagellate bloom in June 2008 was correlated with high ammonium and pH. Maximum benthic chlorophyll a was found at 12.5 km from the mouth in February, June and August 2008 and was correlated with high sediment organic and moisture content. Benthic diatoms were associated with high temperature whereas some species in June 2008 were associated with high ammonium concentrations. The middle reaches of the estuary characterise a zone of deposition rather than suspension which would favour benthic diatom colonization. Phytoplankton cells settling out on the sediments may account for the high benthic chlorophyll a because maximum water column chlorophyll a was also found in the REI zone (where salinity is less than 10 percent and where high biological activity occurs) in the Sundays Estuary. The estuary was sampled over five consecutive weeks from March to April 2009 to identify environmental factors that support different microalgal bloom species. Phytoplankton blooms, defined as chlorophyll a greater than 20 μg l-1, were found during Weeks 1, 4 and 5 from the middle to the upper reaches of the estuary. Diatom species (Cylindrotheca closterium, Cyclotella atomus and Cyclostephanus dubius) occurred in bloom concentrations during these weeks. These diatom species are cosmopolitan and indicate brackish nutrient-rich water. Flagellates were the dominant group in Weeks 2 to 4, but positive correlations with chlorophyll a were found during Weeks 1 and 2. During the first week of this study the conditions were warm and calm (measured as temperature and wind speed) and there was a well developed bloom (38 μg l-1). There was a strong cold front from 17 to 19 March, which mixed the water column resulting in the decrease of the chlorophyll a levels (<20 μg l-1) and the bloom collapsed during Weeks 2 and 3. However, in Weeks 4 and 5 conditions were again calm and warmer, which appeared to stimulate the phytoplankton bloom. Nanoplankton (2.7 - 20 μm) was dominant during each week sampled and contributed a considerable amount (55 - 79 percent) to the phytoplankton biomass. Once again subtidal benthic chlorophyll a and water column chlorophyll a were highest 12.5 km from the mouth. Deposition of phytoplankton cells from the water column was evident in the benthic samples. The study showed that the Sundays Estuary is eutrophic and characterised by microalgal blooms consisting of different phytoplankton groups.
- Full Text:
- Date Issued: 2011
Macrophytes as indicators of physico-chemical factors in South African Estuaries
- Authors: Bezuidenhout, Chantel
- Date: 2011
- Subjects: Estuarine ecology -- South Africa , Aquatic plants -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10597 , http://hdl.handle.net/10948/1387 , Estuarine ecology -- South Africa , Aquatic plants -- South Africa
- Description: This study investigated the response of macrophytes to physico-chemical factors in seven South African estuaries and showed that dominant salt marsh species that occur in different estuaries respond to the same environmental factors. The most important variables influencing distribution were elevation, water level, sediment- and groundwater electrical conductivity and depth to the water table. In permanently open estuaries (Kromme and Olifants) transect surveys identified three distinct vegetation zones i.e. submerged macrophytes, intertidal salt marsh and supratidal salt marsh. In the Kromme Estuary intertidal salt marsh (81.2 ha) covered extensive areas, whereas supratidal (143 ha) and floodplain (797.1 ha) salt marsh were dominant in the Olifants Estuary. Transect surveys identified four distinct vegetation zones (submerged macrophytes, intertidal salt marsh, supratidal salt marsh and reeds and sedges) in the temporarily open/closed estuaries (Mngazi, Great Brak, East Kleinemonde and Seekoei estuaries), although all zones did not occur in all of the estuaries sampled. In the Mngazi Estuary reeds and sedges (1.09 ha) covered extensive areas (no submerged or salt marsh vegetation was present), whereas salt marsh (Great Brak 24.45 ha, East Kleinemonde 17.44 ha and Seekoei 12.9 ha) vegetation was dominant in the other estuaries. Despite the geographic differences, environmental factors influencing macrophyte distribution were similar in all estuaries. Canonical Correspondence Analysis showed that vegetation distribution was significantly affected by elevation, groundwater and sediment electrical conductivity and depth to groundwater. Supratidal species were associated with a greater depth to groundwater (1.2 ± 0.04 m; n = 153) compared to intertidal species (0.5 ± 0.01 m; n = 361). Correlation analysis showed that water level and rainfall were correlated with groundwater electrical conductivity in the lower and upper intertidal zones for all the estuaries sampled. These data indicate the influence of the estuary channel on the physico-chemical conditions of the salt marsh. Low rainfall (16 ± 3.3 mm per annum) in the Olifants Estuary (30-100 mS cm-1) and lack of freshwater flooding in the Kromme Estuary (42-115 mS cm-1) have resulted in high sediment electrical conductivity by comparison with the other estuaries sampled. In the Orange River Estuary approximately 70 ha of salt marsh have been lost through the building of a causeway and flood control levees. Even though salt marsh vegetation can tolerate hypersaline sediments by using the less saline water table, the groundwater at the Orange River Estuary was too saline (avg. of 90.3 ± 6.55 mS cm-1, n = 38) to be of use to the dominant floodplain species, Sarcocornia pillansii. Freshwater inflow to estuaries is important in maintaining longitudinal salinity gradients and reducing hypersaline conditions. In the Olifants Estuary and the Orange River Estuary where supratidal salt marsh is dominant, freshwater inflow is important in raising the water level and maintaining the depth to groundwater and salinity. Lack of freshwater inflow to the Kromme Estuary has highlighted the importance of rainfall in maintaining sediment salinity within acceptable ranges for the salt marsh. Macrophytes are relatively good indicators of physico-chemical factors in estuaries. From an understanding of the response of specific species to environmental variables, ecological water requirements can be set and sensitive areas can be rehabilitated.
- Full Text:
- Date Issued: 2011
- Authors: Bezuidenhout, Chantel
- Date: 2011
- Subjects: Estuarine ecology -- South Africa , Aquatic plants -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10597 , http://hdl.handle.net/10948/1387 , Estuarine ecology -- South Africa , Aquatic plants -- South Africa
- Description: This study investigated the response of macrophytes to physico-chemical factors in seven South African estuaries and showed that dominant salt marsh species that occur in different estuaries respond to the same environmental factors. The most important variables influencing distribution were elevation, water level, sediment- and groundwater electrical conductivity and depth to the water table. In permanently open estuaries (Kromme and Olifants) transect surveys identified three distinct vegetation zones i.e. submerged macrophytes, intertidal salt marsh and supratidal salt marsh. In the Kromme Estuary intertidal salt marsh (81.2 ha) covered extensive areas, whereas supratidal (143 ha) and floodplain (797.1 ha) salt marsh were dominant in the Olifants Estuary. Transect surveys identified four distinct vegetation zones (submerged macrophytes, intertidal salt marsh, supratidal salt marsh and reeds and sedges) in the temporarily open/closed estuaries (Mngazi, Great Brak, East Kleinemonde and Seekoei estuaries), although all zones did not occur in all of the estuaries sampled. In the Mngazi Estuary reeds and sedges (1.09 ha) covered extensive areas (no submerged or salt marsh vegetation was present), whereas salt marsh (Great Brak 24.45 ha, East Kleinemonde 17.44 ha and Seekoei 12.9 ha) vegetation was dominant in the other estuaries. Despite the geographic differences, environmental factors influencing macrophyte distribution were similar in all estuaries. Canonical Correspondence Analysis showed that vegetation distribution was significantly affected by elevation, groundwater and sediment electrical conductivity and depth to groundwater. Supratidal species were associated with a greater depth to groundwater (1.2 ± 0.04 m; n = 153) compared to intertidal species (0.5 ± 0.01 m; n = 361). Correlation analysis showed that water level and rainfall were correlated with groundwater electrical conductivity in the lower and upper intertidal zones for all the estuaries sampled. These data indicate the influence of the estuary channel on the physico-chemical conditions of the salt marsh. Low rainfall (16 ± 3.3 mm per annum) in the Olifants Estuary (30-100 mS cm-1) and lack of freshwater flooding in the Kromme Estuary (42-115 mS cm-1) have resulted in high sediment electrical conductivity by comparison with the other estuaries sampled. In the Orange River Estuary approximately 70 ha of salt marsh have been lost through the building of a causeway and flood control levees. Even though salt marsh vegetation can tolerate hypersaline sediments by using the less saline water table, the groundwater at the Orange River Estuary was too saline (avg. of 90.3 ± 6.55 mS cm-1, n = 38) to be of use to the dominant floodplain species, Sarcocornia pillansii. Freshwater inflow to estuaries is important in maintaining longitudinal salinity gradients and reducing hypersaline conditions. In the Olifants Estuary and the Orange River Estuary where supratidal salt marsh is dominant, freshwater inflow is important in raising the water level and maintaining the depth to groundwater and salinity. Lack of freshwater inflow to the Kromme Estuary has highlighted the importance of rainfall in maintaining sediment salinity within acceptable ranges for the salt marsh. Macrophytes are relatively good indicators of physico-chemical factors in estuaries. From an understanding of the response of specific species to environmental variables, ecological water requirements can be set and sensitive areas can be rehabilitated.
- Full Text:
- Date Issued: 2011
Restoring the biodiversity of canopy species within degraded spekboom thicket
- Van der Vyver, Marius Lodewyk
- Authors: Van der Vyver, Marius Lodewyk
- Date: 2011
- Subjects: Plant diversity , Biodiversity
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10602 , http://hdl.handle.net/10948/1564 , Plant diversity , Biodiversity
- Description: I investigated the return of plant canopy diversity to degraded spekboom thicket landscapes under restoration treatment. I attempted the reintroduction of five nursery propagated and naturally-occurring plant species in severely degraded Portulacaria afra Jacq. (spekboom) dominated thickets that have been subjected to a restoration method involving the planting of dense rows of P. afra truncheons for various time periods and also in degraded and intact thickets. I also planted nursery propagated P. afra cuttings. An average of 30 propagules of each species, were planted in each of the chosen areas in two distinct seasons that exhibited distinct rainfall peaks. Sixteen propagules of P. afra were also planted in each treatment only once. Propagules of the two thicket woody canopy species (S. longispina and P. capensis) showed a total survival of 1% and 9%, respectively. Survival of L. ferocissimum and R. obovatum was 19% and 70% and all propagules of P. afra survived. Analyses showed that survival is primarily tied to a species effect, with R. obovatum and P. afra showing significantly better survival than the other species. Within the other surviving few species a significant preference for overhanging canopy cover was observed. The results show little significance of restoration treatment for propagule survival, suggesting that a range of conditions is needed for the successful establishment of canopy species that likely involves a microclimate and suitable substrate created by canopy cover and litter fall, combined with an exceptional series of rainfall events. I found that the high costs involved with a biodiversity planting endeavour, and the low survival of propagules of thicket canopy plant species (P. afra excepted), renders the proposed biodiversity planting restoration protocol both ecologically and economically inefficient. Restoration success involves the autogenic regeneration of key species or functional groups within the degraded ecosystem. Heavily degraded spekboom-dominated thicket does not spontaneously regenerate its former canopy species composition and this state of affairs was interpreted in terms of a state-and-transition conceptual model. Floristic analyses of degraded, intact and a range of stands under restoration treatment for varying time periods at two locations in Sundays Spekboomveld revealed that the stands under restoration are progressively regenerating canopy species biodiversity with increasing restoration age, and that intact sites are still the most diverse. The high total carbon content (TCC) measured within the older restored stands Rhinosterhoek (241 t C ha-1 after 50 years at a depth of 50 cm) rivals that recorded for intact spekboom thickets, and the number of recruits found within older restored sites rivals intact sites sampled. 2 The changes recorded in the above- and belowground environments potentially identify P. afra as an ecosystem engineer within spekboom dominated thickets that facillitates the build-up of carbon above- and belowground and the accompanying changes in soil quality and the unique microclimate aboveground, which enables the hypothetical threshold of the degraded state to be transcended. This restoration methodology is accordingly considered efficient and autogenic canopy species return was found to be prominent after a period of 35-50 years of restoration treatment.
- Full Text:
- Date Issued: 2011
- Authors: Van der Vyver, Marius Lodewyk
- Date: 2011
- Subjects: Plant diversity , Biodiversity
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10602 , http://hdl.handle.net/10948/1564 , Plant diversity , Biodiversity
- Description: I investigated the return of plant canopy diversity to degraded spekboom thicket landscapes under restoration treatment. I attempted the reintroduction of five nursery propagated and naturally-occurring plant species in severely degraded Portulacaria afra Jacq. (spekboom) dominated thickets that have been subjected to a restoration method involving the planting of dense rows of P. afra truncheons for various time periods and also in degraded and intact thickets. I also planted nursery propagated P. afra cuttings. An average of 30 propagules of each species, were planted in each of the chosen areas in two distinct seasons that exhibited distinct rainfall peaks. Sixteen propagules of P. afra were also planted in each treatment only once. Propagules of the two thicket woody canopy species (S. longispina and P. capensis) showed a total survival of 1% and 9%, respectively. Survival of L. ferocissimum and R. obovatum was 19% and 70% and all propagules of P. afra survived. Analyses showed that survival is primarily tied to a species effect, with R. obovatum and P. afra showing significantly better survival than the other species. Within the other surviving few species a significant preference for overhanging canopy cover was observed. The results show little significance of restoration treatment for propagule survival, suggesting that a range of conditions is needed for the successful establishment of canopy species that likely involves a microclimate and suitable substrate created by canopy cover and litter fall, combined with an exceptional series of rainfall events. I found that the high costs involved with a biodiversity planting endeavour, and the low survival of propagules of thicket canopy plant species (P. afra excepted), renders the proposed biodiversity planting restoration protocol both ecologically and economically inefficient. Restoration success involves the autogenic regeneration of key species or functional groups within the degraded ecosystem. Heavily degraded spekboom-dominated thicket does not spontaneously regenerate its former canopy species composition and this state of affairs was interpreted in terms of a state-and-transition conceptual model. Floristic analyses of degraded, intact and a range of stands under restoration treatment for varying time periods at two locations in Sundays Spekboomveld revealed that the stands under restoration are progressively regenerating canopy species biodiversity with increasing restoration age, and that intact sites are still the most diverse. The high total carbon content (TCC) measured within the older restored stands Rhinosterhoek (241 t C ha-1 after 50 years at a depth of 50 cm) rivals that recorded for intact spekboom thickets, and the number of recruits found within older restored sites rivals intact sites sampled. 2 The changes recorded in the above- and belowground environments potentially identify P. afra as an ecosystem engineer within spekboom dominated thickets that facillitates the build-up of carbon above- and belowground and the accompanying changes in soil quality and the unique microclimate aboveground, which enables the hypothetical threshold of the degraded state to be transcended. This restoration methodology is accordingly considered efficient and autogenic canopy species return was found to be prominent after a period of 35-50 years of restoration treatment.
- Full Text:
- Date Issued: 2011
Oorsaaipraktyke en vestiging van eenjarige raaigras in lusernweiding
- Authors: Badenhorst, Daniël
- Date: 2011
- Subjects: Alfalfa Alfalfa -- Irrigation
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/11792 , vital:26969
- Description: Die Eden- en Overbergdistrik in die Suid-Kaap vorm die mees suidelike substreke van die winterreëngebied. Dit is geleë tussen 33° 45‟ en 34° 50‟ suiderbreedte en tussen 19° 0‟ en 23° 45‟ oosterlengte. Die westelike grens van die substreek word gevorm deur die Villiersdorp-Botrivier-gebied. Aan die noordekant word die substreek begrens deur die Sonderend-, Lange- en Outeniquabergreekse. Die oostelike grens word gevorm deur die Bloukransrivier. Die Indiese Oseaankuslyn vanaf Nature‟s Valley in die ooste tot by Kleinmond in die weste vorm die suidelike grens. In die Suidkusstreek word 54.5% van die Wes-Kaapse melkproduksie en 24% van Suid-Afrika se melkproduksie deur 1900 melkprodusente geproduseer (Dowrey 2005). Ses en dertig persent van die bruto jaarlikse veeproduk is afkomstig vanaf suiwelprodukte wat hoofsaaklik vanaf aangeplante weiding geproduseer word. Aangeplante weiding beslaan 37.7% van die totale oppervlakte van die vee- en saaigebiede van die Suidkusstreek (Botha 2003). Weens beperkte, skaars besproeiingswater in groot dele van die Suid-Kaap, word heelwat weiding slegs aanvullend besproei (Protopapas 2004). Voervloeiprogramme vir melkproduksie onder aanvullende besproeiing bestaan hoofsaaklik uit kikoejoe (Pennisetum clandestinum) en lusern (Medicago sativa) (Botha 2003). Die droëmateriaalproduksie en weikapasiteit van lusern volg, soos kikoejoe, „n baie sterk seisoenale tendens met „n piek in die somer / herfs en „n laagtepunt in die winter (Durand 1993; Botha 1998; Botha 2003). Voervloeiprogramme met lusern of kikoejoe as hoofkomponente het gewoonlik voertekorte gedurende die winter tot gevolg. Hoofsaaklik om dié rede het boere uit die lusernproduserende gebiede van Heidelberg, Riversdal, Herbertsdale en Mosselbaai, deur hul onderskeie boereverenigings, „n versoek aan Outeniqua Navorsingsplaas gerig om ondersoek in te stel na moontlike oorsaaipraktyke wat die droëmateriaalproduksie van lusernstelsels gedurende die winter kan verhoog. Kikoejoeweiding word reeds die afgelope aantal jare suksesvol met Westerworldsraaigrasse oorgesaai vir beter herfs-, winter- en lenteproduksie. Anders as by kikoejoeweidings bestaan daar huidiglik geen beproefde oorsaaipraktyke wat die produksiepotensiaal van lusern in die winter en vroeë lente kan verhoog nie (Anoniem 2002).
- Full Text:
- Date Issued: 2011
- Authors: Badenhorst, Daniël
- Date: 2011
- Subjects: Alfalfa Alfalfa -- Irrigation
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/11792 , vital:26969
- Description: Die Eden- en Overbergdistrik in die Suid-Kaap vorm die mees suidelike substreke van die winterreëngebied. Dit is geleë tussen 33° 45‟ en 34° 50‟ suiderbreedte en tussen 19° 0‟ en 23° 45‟ oosterlengte. Die westelike grens van die substreek word gevorm deur die Villiersdorp-Botrivier-gebied. Aan die noordekant word die substreek begrens deur die Sonderend-, Lange- en Outeniquabergreekse. Die oostelike grens word gevorm deur die Bloukransrivier. Die Indiese Oseaankuslyn vanaf Nature‟s Valley in die ooste tot by Kleinmond in die weste vorm die suidelike grens. In die Suidkusstreek word 54.5% van die Wes-Kaapse melkproduksie en 24% van Suid-Afrika se melkproduksie deur 1900 melkprodusente geproduseer (Dowrey 2005). Ses en dertig persent van die bruto jaarlikse veeproduk is afkomstig vanaf suiwelprodukte wat hoofsaaklik vanaf aangeplante weiding geproduseer word. Aangeplante weiding beslaan 37.7% van die totale oppervlakte van die vee- en saaigebiede van die Suidkusstreek (Botha 2003). Weens beperkte, skaars besproeiingswater in groot dele van die Suid-Kaap, word heelwat weiding slegs aanvullend besproei (Protopapas 2004). Voervloeiprogramme vir melkproduksie onder aanvullende besproeiing bestaan hoofsaaklik uit kikoejoe (Pennisetum clandestinum) en lusern (Medicago sativa) (Botha 2003). Die droëmateriaalproduksie en weikapasiteit van lusern volg, soos kikoejoe, „n baie sterk seisoenale tendens met „n piek in die somer / herfs en „n laagtepunt in die winter (Durand 1993; Botha 1998; Botha 2003). Voervloeiprogramme met lusern of kikoejoe as hoofkomponente het gewoonlik voertekorte gedurende die winter tot gevolg. Hoofsaaklik om dié rede het boere uit die lusernproduserende gebiede van Heidelberg, Riversdal, Herbertsdale en Mosselbaai, deur hul onderskeie boereverenigings, „n versoek aan Outeniqua Navorsingsplaas gerig om ondersoek in te stel na moontlike oorsaaipraktyke wat die droëmateriaalproduksie van lusernstelsels gedurende die winter kan verhoog. Kikoejoeweiding word reeds die afgelope aantal jare suksesvol met Westerworldsraaigrasse oorgesaai vir beter herfs-, winter- en lenteproduksie. Anders as by kikoejoeweidings bestaan daar huidiglik geen beproefde oorsaaipraktyke wat die produksiepotensiaal van lusern in die winter en vroeë lente kan verhoog nie (Anoniem 2002).
- Full Text:
- Date Issued: 2011