The use of insecticides and cultural control for the management of soil-borne pests during plantation establishment
- Authors: Siwela, Evidence Miyelani
- Date: 2019
- Subjects: Insecticides , Plant diseases Pests -- Control Pesticides
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43446 , vital:36882
- Description: Over the past decades, the productivity of South African forestry plantations has been negatively impacted by abiotic (fire, hail, wind, frost, drought etc.) and biotic factors (pests and diseases). The biotic component of insect pests and pathogens cause significant loss to the forestry industry and this affects the productivity, financial viability and long-term sustainability of plantations. Common establishment insect pests and diseases in South Africa include the pine bark beetle (Hylastes angustatus), cutworms (Agrotis spp), white grubs (Scarabaeidae larvae), rhizina root rot (Rhizina undulata), fusarium pitch canker (Fusarium circinatum), and pine dieback (Diplodia pinea). Soil-borne pests, mainly white grubs and cutworms can contribute to high seedling mortality following the re-establishment of eucalypts and wattle. Synthetic insecticides used for their control include alpha-cypermethrin, deltamethrin, and imidacloprid. However, all these insecticides are considered highly hazardous to the environment and/or human health and can no longer be considered for use in South African plantations. A need has therefore arisen to find and screen alternative products (synthetic and/or natural), that are not only environmentally safe for use, but also effective for the control of soil-borne pests during plantation establishment. In addition, these products can then be combined with other control mechanisms (such as cultural and biological control) to form an integrated pest management strategy. To address the above, a series of research trials were implemented with the outcomes discussed below. Two trials were implemented in KwaZulu-Natal (Demagtenberg) and Mpumalanga (Klipkraal) to determine if seedling size in combination with, or without an insecticide would result in improved survival of Pinus Patula. The main factors tested were Root Plug Volume (36 cm3 versus 103 cm3), Seedling Age (Standard [smaller] versus Older [larger]), and Pesticide application (untreated versus treated). Seedling quality was assessed in terms of Shoot:Root ratio, optimum Height (Ht in cm), and root collar diameter (Rcd in mm) before planting, with tree growth variates measured at planting, and then at regular intervals. The final measurements were taken at 7 years and 2 months for Demagtenberg and 5 years and 1 month for Klipkraal. For both trials, the Root Growth Potential (RGP) and total Plant Quality Index (PQI) indicated that Root Plug Volume 36 cm3 and Seedling Age (SA)_Standard (smaller) had a better Sturdiness ratio and Shoot:Root ratio compared to that of Root Plug Volume 103 cm3 and Seedling Age (SA)_Older (larger), with these benefits translated into improved field performance. The diameter at breast height (Dbh), Basal area (BA), Stocking and Volume indicated that SA_Standard and Root Plug Volume 36 cm3 resulted in better survival and growth than that of SA_Older (larger) seedlings and Root Plug Volume 103 cm3. The application of a Pesticide resulted in improved survival and growth at Klipkraal, but not at Demagtenberg. This indicated the presence of soil-borne pests at this site. In addition, the interaction between Pesticide application and SA_Standard resulted in a significantly larger BA than all other treatments only at Klipkraal, which indicates that both improved seedling quality and pesticides contributed to improved performance. One trial was established to Eucalyptus dunnii William Dunn at Umvoti North to investigate the effectiveness of the synthetic insecticides (deltamethrin, clothianidin, imidacloprid, imidacloprid + fertilizer, imidacloprid + clothianidin + fertilizer) and two natural products (azadirachtin and potassium silicate) for the control of soil-borne pests following planting. Groundline diameter (Gld), Height (Ht) and survival were assessed over a six-month period. Despite the selection of a site known to have a high incidence of soil-borne pests, few soil-borne pest were detected on the site for the trial duration, with no treatment differences observed for any of the tree growth variates. Significant differences were observed for foliar discolouration (possible phytotoxicity), however, these results were inconclusive as majority of the affected treatments (those that survived) showed full recovery. Three-month results from 12 eucalypt trials in KwaZulu-Natal, South Africa were compared to determine the benefits (including costs) of insecticides for the control of soil-borne pests. The 12 trials were selected to represent different physiographic regions, mainly within the warm temperate regions where white grubs and cutworms are likely to occur. Data for the trials were obtained from previous management research (published documents) and included six where mortality was the only variate assessed, with the Ht and Gld also assessed in the remaining six trials. There was a ≥ 2.5% increase in survival in seven of the 12 trials through the use of insecticides relative to the control, although only four of these seven were statistically significant. Of the 12 trials, the use of insecticides resulted in > 90% survival compared to the control at Mistley (93 versus 83%), Bloemendal (96 versus 62%) and Enon (burn) (96 versus 89%). At Garfield, Vulindlela, and Baynesfield, survival in both the treated and untreated treatments was below 90%, whereas both the treated and untreated treatments were above 90% at Rustig, Greenhill, Enon (slash), Umvoti, Dargle and Umvoti North. This data indicates that where soil-borne pests are present, the application of an insecticide is beneficial. Due to the costs associated with insecticide application, the challenge will be to determine which are high-risk sites that require treatment with an insecticide. Results from these trials indicate that on sites where soil-borne pests are present (and active), the application of insecticides is beneficial. However, even if present, the level of impact is less obvious, and possibly influenced by life cycle stage, site management and climate. The testing of alternative and less highly hazardous insecticides indicated the potential future use of insecticides in terms of limited seedling phytotoxicity (some of the products tested). To understand more fully the extent of their efficacy, these products would need to be re-tested again on sites where soil-borne pests are active. Optimum establishment practices, together with the planting of quality seedlings and application of an approved insecticide, will all contribute to improved survival and growth. Perhaps the biggest challenge will be the determination of soil pest activity, such that the application of pesticides can be limited to those sites where control is necessary..
- Full Text:
- Date Issued: 2019
- Authors: Siwela, Evidence Miyelani
- Date: 2019
- Subjects: Insecticides , Plant diseases Pests -- Control Pesticides
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43446 , vital:36882
- Description: Over the past decades, the productivity of South African forestry plantations has been negatively impacted by abiotic (fire, hail, wind, frost, drought etc.) and biotic factors (pests and diseases). The biotic component of insect pests and pathogens cause significant loss to the forestry industry and this affects the productivity, financial viability and long-term sustainability of plantations. Common establishment insect pests and diseases in South Africa include the pine bark beetle (Hylastes angustatus), cutworms (Agrotis spp), white grubs (Scarabaeidae larvae), rhizina root rot (Rhizina undulata), fusarium pitch canker (Fusarium circinatum), and pine dieback (Diplodia pinea). Soil-borne pests, mainly white grubs and cutworms can contribute to high seedling mortality following the re-establishment of eucalypts and wattle. Synthetic insecticides used for their control include alpha-cypermethrin, deltamethrin, and imidacloprid. However, all these insecticides are considered highly hazardous to the environment and/or human health and can no longer be considered for use in South African plantations. A need has therefore arisen to find and screen alternative products (synthetic and/or natural), that are not only environmentally safe for use, but also effective for the control of soil-borne pests during plantation establishment. In addition, these products can then be combined with other control mechanisms (such as cultural and biological control) to form an integrated pest management strategy. To address the above, a series of research trials were implemented with the outcomes discussed below. Two trials were implemented in KwaZulu-Natal (Demagtenberg) and Mpumalanga (Klipkraal) to determine if seedling size in combination with, or without an insecticide would result in improved survival of Pinus Patula. The main factors tested were Root Plug Volume (36 cm3 versus 103 cm3), Seedling Age (Standard [smaller] versus Older [larger]), and Pesticide application (untreated versus treated). Seedling quality was assessed in terms of Shoot:Root ratio, optimum Height (Ht in cm), and root collar diameter (Rcd in mm) before planting, with tree growth variates measured at planting, and then at regular intervals. The final measurements were taken at 7 years and 2 months for Demagtenberg and 5 years and 1 month for Klipkraal. For both trials, the Root Growth Potential (RGP) and total Plant Quality Index (PQI) indicated that Root Plug Volume 36 cm3 and Seedling Age (SA)_Standard (smaller) had a better Sturdiness ratio and Shoot:Root ratio compared to that of Root Plug Volume 103 cm3 and Seedling Age (SA)_Older (larger), with these benefits translated into improved field performance. The diameter at breast height (Dbh), Basal area (BA), Stocking and Volume indicated that SA_Standard and Root Plug Volume 36 cm3 resulted in better survival and growth than that of SA_Older (larger) seedlings and Root Plug Volume 103 cm3. The application of a Pesticide resulted in improved survival and growth at Klipkraal, but not at Demagtenberg. This indicated the presence of soil-borne pests at this site. In addition, the interaction between Pesticide application and SA_Standard resulted in a significantly larger BA than all other treatments only at Klipkraal, which indicates that both improved seedling quality and pesticides contributed to improved performance. One trial was established to Eucalyptus dunnii William Dunn at Umvoti North to investigate the effectiveness of the synthetic insecticides (deltamethrin, clothianidin, imidacloprid, imidacloprid + fertilizer, imidacloprid + clothianidin + fertilizer) and two natural products (azadirachtin and potassium silicate) for the control of soil-borne pests following planting. Groundline diameter (Gld), Height (Ht) and survival were assessed over a six-month period. Despite the selection of a site known to have a high incidence of soil-borne pests, few soil-borne pest were detected on the site for the trial duration, with no treatment differences observed for any of the tree growth variates. Significant differences were observed for foliar discolouration (possible phytotoxicity), however, these results were inconclusive as majority of the affected treatments (those that survived) showed full recovery. Three-month results from 12 eucalypt trials in KwaZulu-Natal, South Africa were compared to determine the benefits (including costs) of insecticides for the control of soil-borne pests. The 12 trials were selected to represent different physiographic regions, mainly within the warm temperate regions where white grubs and cutworms are likely to occur. Data for the trials were obtained from previous management research (published documents) and included six where mortality was the only variate assessed, with the Ht and Gld also assessed in the remaining six trials. There was a ≥ 2.5% increase in survival in seven of the 12 trials through the use of insecticides relative to the control, although only four of these seven were statistically significant. Of the 12 trials, the use of insecticides resulted in > 90% survival compared to the control at Mistley (93 versus 83%), Bloemendal (96 versus 62%) and Enon (burn) (96 versus 89%). At Garfield, Vulindlela, and Baynesfield, survival in both the treated and untreated treatments was below 90%, whereas both the treated and untreated treatments were above 90% at Rustig, Greenhill, Enon (slash), Umvoti, Dargle and Umvoti North. This data indicates that where soil-borne pests are present, the application of an insecticide is beneficial. Due to the costs associated with insecticide application, the challenge will be to determine which are high-risk sites that require treatment with an insecticide. Results from these trials indicate that on sites where soil-borne pests are present (and active), the application of insecticides is beneficial. However, even if present, the level of impact is less obvious, and possibly influenced by life cycle stage, site management and climate. The testing of alternative and less highly hazardous insecticides indicated the potential future use of insecticides in terms of limited seedling phytotoxicity (some of the products tested). To understand more fully the extent of their efficacy, these products would need to be re-tested again on sites where soil-borne pests are active. Optimum establishment practices, together with the planting of quality seedlings and application of an approved insecticide, will all contribute to improved survival and growth. Perhaps the biggest challenge will be the determination of soil pest activity, such that the application of pesticides can be limited to those sites where control is necessary..
- Full Text:
- Date Issued: 2019
Top-soil water retention in organic and conventional farming systems in South Africa’s Southern Cape
- Authors: Eckert, Catherine Jessica
- Date: 2019
- Subjects: Water harvesting , Soil moisture conservation Organic farming Sustainable agriculture
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/39885 , vital:35500
- Description: With the world’s growing population and limited natural resources, there is a need to produce more food using less inputs. A major limiting factor to meeting the agricultural production needs of the growing population is fresh water. Water is a critical resource in agriculture and may be more of a limiting factor than other crop growth requirements in some areas. Furthermore, water availability is being impacted by climate change and competition from other industries. Methods of improving crop water use efficiency through conservation of water and the enhancement of crop growth need to be employed to meet the growing demand sustainably. The purpose of the research was to assess the differences in soil water status between organically farmed crops with a grass mulch and conventionally farmed crops without mulch, with a view to making more efficient use of the water resource. This research was conducted at the Mandela long term organic farming systems research trial site at Nelson Mandela University, George campus in the southern Cape, South Africa. It is part of a larger research project (the Mandela Trials) in which various researchers have been involved in different aspects of this trial including agronomy, microbiology and pest and disease control. This research took place over two seasons, namely, 2016-2017 season and 2017-2018 season. The soil water content (SWC) of organic and conventional plots were measured using fixed capacitance probes that recorded continuous data, every half hour, at depths of 10, 30 and 50 cm. A handheld theta probe was also used to measure the SWC in the top 6 cm of the soil at 7 to14 day intervals. The organic treatment had a significantly higher SWC than the conventional treatment over the two seasons in which this research was conducted. In addition, soil carbon was significantly higher in the organic treatment, than the conventional. Organic farming methods preserve and promote an increase in soil organic matter, thus improving the soil structure and increasing the soil’s water holding capacity. From this research, it is concluded that organic farming practices can be used to help conserve SWC, keeping it available to crops for longer and helping farmers make more efficient use of this scarce resource. This is especially relevant for low rainfall areas which are affected by water shortages. The improved SWC availability should be coupled with good agronomic practices to increase productive water losses and the conversion of water to yields, thus increasing water use efficiency. In addition, adding organic matter to the soil will improve resilience of the soil and help sequester carbon and thus help in mitigating climate change.
- Full Text:
- Date Issued: 2019
Top-soil water retention in organic and conventional farming systems in South Africa’s Southern Cape
- Authors: Eckert, Catherine Jessica
- Date: 2019
- Subjects: Water harvesting , Soil moisture conservation Organic farming Sustainable agriculture
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/39885 , vital:35500
- Description: With the world’s growing population and limited natural resources, there is a need to produce more food using less inputs. A major limiting factor to meeting the agricultural production needs of the growing population is fresh water. Water is a critical resource in agriculture and may be more of a limiting factor than other crop growth requirements in some areas. Furthermore, water availability is being impacted by climate change and competition from other industries. Methods of improving crop water use efficiency through conservation of water and the enhancement of crop growth need to be employed to meet the growing demand sustainably. The purpose of the research was to assess the differences in soil water status between organically farmed crops with a grass mulch and conventionally farmed crops without mulch, with a view to making more efficient use of the water resource. This research was conducted at the Mandela long term organic farming systems research trial site at Nelson Mandela University, George campus in the southern Cape, South Africa. It is part of a larger research project (the Mandela Trials) in which various researchers have been involved in different aspects of this trial including agronomy, microbiology and pest and disease control. This research took place over two seasons, namely, 2016-2017 season and 2017-2018 season. The soil water content (SWC) of organic and conventional plots were measured using fixed capacitance probes that recorded continuous data, every half hour, at depths of 10, 30 and 50 cm. A handheld theta probe was also used to measure the SWC in the top 6 cm of the soil at 7 to14 day intervals. The organic treatment had a significantly higher SWC than the conventional treatment over the two seasons in which this research was conducted. In addition, soil carbon was significantly higher in the organic treatment, than the conventional. Organic farming methods preserve and promote an increase in soil organic matter, thus improving the soil structure and increasing the soil’s water holding capacity. From this research, it is concluded that organic farming practices can be used to help conserve SWC, keeping it available to crops for longer and helping farmers make more efficient use of this scarce resource. This is especially relevant for low rainfall areas which are affected by water shortages. The improved SWC availability should be coupled with good agronomic practices to increase productive water losses and the conversion of water to yields, thus increasing water use efficiency. In addition, adding organic matter to the soil will improve resilience of the soil and help sequester carbon and thus help in mitigating climate change.
- Full Text:
- Date Issued: 2019
Triggering biodegradation of low-density polyethylene films containing biobased additives for ecological applications
- Authors: Gada, Abongile
- Date: 2019
- Subjects: Refuse and refuse disposal , Plastics industry and trade -- Waste disposal Polyethylene Polyurethanes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/39796 , vital:35460
- Description: The aims of the present study are focused on the investigation of low-density polyethylene (LDPE) films that contain biobased pro-oxidizing additives (CSIR1% and CSIR3% (w/w)) for environmental degradation in different abiotic and biotic conditions in comparison to non-biodegradable commercially available Pick n Pay (PnP) PE grocery bags. In this project, a biobased pro-oxidant additive master batch was prepared in a heat kneader mixer. A mixture of biobased radical reaction initiators and natural polymers were melt processed as a master batch. The biobased pro-oxidant additive master batch CSIR1% and CSIR3% and LDPE components were melt-extruded to form biobased pro-oxidant additive LDPE pellets using a twin screw melt extruder. The pelletized biobased pro-oxidant additive LDPE was blown into a 25 -27 μm thick film using a melt blower machine. The LDPE containing biobased pro-oxidant additive CSIR 1% and 3% test samples and the PnP polyethylene carrier bags were submitted to thermal oxidizing test conditions in a 70°C air ventilated oven and direct sunlight (photo oxidation) for a period of six months (180 days). The thermal and photo-oxidized LDPE film test samples were further subjected to biotic degradation tests in aqueous, soil and compost environments for varying periods of 180 days to 263 days in biodegradation evaluation studies. The oxidation degradation rates of the test samples were monitored and determined by evaluating carbonyl index (COi) using FT-IR spectroscopy; molecular weight determination and distribution of the test materials were analyzed by Gel Permeation Chromatography (GPC); compounds analysis was done by GC-MS; percentage crystallinity (Xc%) was quantified by DSC; thermal stability by TGA and morphological surfaces were examined by SEM analytical techniques. Biodegradation tests simulating marine salt water, burial in soil and compost conditioning methods were used to determine the “potential biodegradability” of the thermally and photo-oxidized test samples after the oxidation period. The oxidation extent and rate of LDPE films containing CSIR3% biobased additives was higher than that of LDPE films containing CSIR1% biobased additives. GPC molecular weight determination and distribution results showed a decrease for all the test samples exposed to oxidation. The molecular weight of LDPE films containing CSIR1% biobased additives decreased from 404K Mw to 111K Mw for sunlight oxidized samples and to 16KMw for the thermally oxidized LDPE samples after 200 days of oxidation exposure. Molecular weight of LDPE films containing CSIR3% biobased additives showed the most reduction from 293K Mw to 22K Mw for sunlight oxidized samples and to 2K Mw for thermally oxidized samples after 100 days of oxidation exposure. DSC analysis showed that crystallinity degree decreased after exposure to thermal and photo-oxidation. TGA results showed a reduction of initial degradation temperature by almost half compared to zero-days untreated CSIR3% samples, with higher degree temperatures observed in samples exposed to thermal oxidation than those exposed to photo-oxidation. GC-MS revealed peaks of carbonyls such as alcohols, aldehydes, ketones, carboxylic and anionic acids, and very short chain alkenes and alkanes. The SEM showed heterogeneous morphological modifications in surfaces of samples even though they were not severe. After 172 days the oxidized LDPE samples containing CSIR3% biobased additives, were investigated for potential biodegradation in aqueous, soil and composting environments. Thermally oxidized and photo-oxidized CSIR3% samples showed a mineralization degree of 10.4% and 10.7% respectively, when oxidized in 181 days aqueous biodegradation, 20% and 7.7% respectively, when oxidized in 233 days of soil burial, and 52.6% and 62% respectively, oxidized in 263 days of compost. The obtained results confirmed the abiotic oxidation step as the initiation step for PE degradation, succeeded by assimilation, by action of microorganisms (ultimate biodegradation), of lower weight molecular compounds of oxidized LDPE samples in aqueous medium, soil and composting conditions to final end products of CO2, H2O and new microbial cell biomass.
- Full Text:
- Date Issued: 2019
- Authors: Gada, Abongile
- Date: 2019
- Subjects: Refuse and refuse disposal , Plastics industry and trade -- Waste disposal Polyethylene Polyurethanes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/39796 , vital:35460
- Description: The aims of the present study are focused on the investigation of low-density polyethylene (LDPE) films that contain biobased pro-oxidizing additives (CSIR1% and CSIR3% (w/w)) for environmental degradation in different abiotic and biotic conditions in comparison to non-biodegradable commercially available Pick n Pay (PnP) PE grocery bags. In this project, a biobased pro-oxidant additive master batch was prepared in a heat kneader mixer. A mixture of biobased radical reaction initiators and natural polymers were melt processed as a master batch. The biobased pro-oxidant additive master batch CSIR1% and CSIR3% and LDPE components were melt-extruded to form biobased pro-oxidant additive LDPE pellets using a twin screw melt extruder. The pelletized biobased pro-oxidant additive LDPE was blown into a 25 -27 μm thick film using a melt blower machine. The LDPE containing biobased pro-oxidant additive CSIR 1% and 3% test samples and the PnP polyethylene carrier bags were submitted to thermal oxidizing test conditions in a 70°C air ventilated oven and direct sunlight (photo oxidation) for a period of six months (180 days). The thermal and photo-oxidized LDPE film test samples were further subjected to biotic degradation tests in aqueous, soil and compost environments for varying periods of 180 days to 263 days in biodegradation evaluation studies. The oxidation degradation rates of the test samples were monitored and determined by evaluating carbonyl index (COi) using FT-IR spectroscopy; molecular weight determination and distribution of the test materials were analyzed by Gel Permeation Chromatography (GPC); compounds analysis was done by GC-MS; percentage crystallinity (Xc%) was quantified by DSC; thermal stability by TGA and morphological surfaces were examined by SEM analytical techniques. Biodegradation tests simulating marine salt water, burial in soil and compost conditioning methods were used to determine the “potential biodegradability” of the thermally and photo-oxidized test samples after the oxidation period. The oxidation extent and rate of LDPE films containing CSIR3% biobased additives was higher than that of LDPE films containing CSIR1% biobased additives. GPC molecular weight determination and distribution results showed a decrease for all the test samples exposed to oxidation. The molecular weight of LDPE films containing CSIR1% biobased additives decreased from 404K Mw to 111K Mw for sunlight oxidized samples and to 16KMw for the thermally oxidized LDPE samples after 200 days of oxidation exposure. Molecular weight of LDPE films containing CSIR3% biobased additives showed the most reduction from 293K Mw to 22K Mw for sunlight oxidized samples and to 2K Mw for thermally oxidized samples after 100 days of oxidation exposure. DSC analysis showed that crystallinity degree decreased after exposure to thermal and photo-oxidation. TGA results showed a reduction of initial degradation temperature by almost half compared to zero-days untreated CSIR3% samples, with higher degree temperatures observed in samples exposed to thermal oxidation than those exposed to photo-oxidation. GC-MS revealed peaks of carbonyls such as alcohols, aldehydes, ketones, carboxylic and anionic acids, and very short chain alkenes and alkanes. The SEM showed heterogeneous morphological modifications in surfaces of samples even though they were not severe. After 172 days the oxidized LDPE samples containing CSIR3% biobased additives, were investigated for potential biodegradation in aqueous, soil and composting environments. Thermally oxidized and photo-oxidized CSIR3% samples showed a mineralization degree of 10.4% and 10.7% respectively, when oxidized in 181 days aqueous biodegradation, 20% and 7.7% respectively, when oxidized in 233 days of soil burial, and 52.6% and 62% respectively, oxidized in 263 days of compost. The obtained results confirmed the abiotic oxidation step as the initiation step for PE degradation, succeeded by assimilation, by action of microorganisms (ultimate biodegradation), of lower weight molecular compounds of oxidized LDPE samples in aqueous medium, soil and composting conditions to final end products of CO2, H2O and new microbial cell biomass.
- Full Text:
- Date Issued: 2019
Vulnerability in surf tourism: surf break decline and its impact on Herold's Bay, South Africa
- Authors: Schröder, Klaus
- Date: 2019
- Subjects: Surfing -- South Africa , Tourism -- Environmental aspects Climatic changes -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43501 , vital:36900
- Description: Surfing has increasingly become a mainstream and demographically diverse activity that holds substantial economic worth. It also holds substantial social, cultural and spiritual value for participants and related communities. It is therefore not surprising that the maintenance of surf breaks has become an important element of coastal tourism, and that tourism management has had a growing concern with anthropogenic impacts on the shoreline. In line with these developments, this study investigates the vulnerability of surf tourism given the general consensus that there has been a human-induced decline of the river-mouth surf break in Herold’s Bay. An adapted ecological services model is used, and in line with such models, the status of the three types of capital (natural (physical) capital, climatic capital, and built capital) and their effect on recreation capital (surfing’s participation, market, and non-market values) over a twenty-year period is tracked. The findings identified alterations to the river bed morphology, beach morphology, wind direction, and swell intensity and frequency as the main determinants in surf break decline. The corresponding increase in vulnerability of Herold’s Bay’s surf tourism industry is also given as having negative socio-economic impacts. This study has underlined both the potential and the imperative to conserve, utilise and develop surf breaks and the surf tourism industry within South Africa.
- Full Text:
- Date Issued: 2019
- Authors: Schröder, Klaus
- Date: 2019
- Subjects: Surfing -- South Africa , Tourism -- Environmental aspects Climatic changes -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43501 , vital:36900
- Description: Surfing has increasingly become a mainstream and demographically diverse activity that holds substantial economic worth. It also holds substantial social, cultural and spiritual value for participants and related communities. It is therefore not surprising that the maintenance of surf breaks has become an important element of coastal tourism, and that tourism management has had a growing concern with anthropogenic impacts on the shoreline. In line with these developments, this study investigates the vulnerability of surf tourism given the general consensus that there has been a human-induced decline of the river-mouth surf break in Herold’s Bay. An adapted ecological services model is used, and in line with such models, the status of the three types of capital (natural (physical) capital, climatic capital, and built capital) and their effect on recreation capital (surfing’s participation, market, and non-market values) over a twenty-year period is tracked. The findings identified alterations to the river bed morphology, beach morphology, wind direction, and swell intensity and frequency as the main determinants in surf break decline. The corresponding increase in vulnerability of Herold’s Bay’s surf tourism industry is also given as having negative socio-economic impacts. This study has underlined both the potential and the imperative to conserve, utilise and develop surf breaks and the surf tourism industry within South Africa.
- Full Text:
- Date Issued: 2019
Zoning the Southwestern Indian Ocean to mitigate impacts from ocean-based hydrocarbon exploration and production on sea turtles
- Authors: Pretorius, Dirk
- Date: 2019
- Subjects: Ocean zoning , Marine ecology -- Indian Ocean Sea turtles -- Indian Ocean Marine animals -- Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43303 , vital:36787
- Description: The conflict between sea turtles and the numerous socio-economic developments in the Southwestern Indian Ocean (SWIO) are set to intensify as countries are looking to develop their ocean-based economies. The Hydrocarbon Exploration and Production (HEP) industry is of particular importance, since many of the SWIO governments view it as catalyst for development. This has raised concerns about potentially significant environmental impacts from the HEP industry, to sea turtles and their habitats, based on international examples where sea turtles have been severely negatively impacted upon, like the Deepwater Horizon spill in the Gulf of Mexico. Given that the four sea turtles species in the SWIO are listed on the IUCN Red List of threatened species, the aim of this study was to derive priority areas for sea turtles in the face of HEP, that could be used in an ocean zoning strategy for sustainable economic development of HEP in the SWIO region. To achieve this, the study spatially represented the main life-history stages of sea turtles, i.e. the breeding, migrating and foraging areas of Caretta caretta (loggerhead turtles), Dermochelys coriacea (leatherback turtles), Chelonia mydas (green turtles) and Eretmochelys imbricata (hawksbill turtles), within a telemetry derived distribution for each species. This spatial representation was used to quantify the extent of Marine Protected Areas (MPAs) conserving sea turtles in the SWIO, which revealed that sea turtle breeding areas were well represented in MPAs, including C. caretta (~40 %), C. mydas (~53 %), E. imbricata (~59 %) and D. coriacea (~22 %), the latter being least protected by MPAs during breeding, possibly due to a far greater extent of their internesting areas than the other three species. MPA coverage of breeding areas could be positively correlated to the increasing population trends of C. caretta and C. mydas in the SWIO, and therefore the assumption was made that increasing population trends of sea turtles are in part related to MPA protection of their breeding areas. In addition, the potential impacts on sea turtles from existing and proposed HEP developments were assessed and mapped by using a novel, species-specific rating index. The results revealed the extensive nature of potential water pollution impacts on sea turtles, constituting 16 of the top 28 most significant impacts from HEP on sea turtles. Other significant impacts on sea turtles associated with the HEP industry, included habitat destruction, light pollution and noise pollution. Importantly, this study found that ~70 % of all potential HEP impacts (irrespective of significance) on adult nesting sea turtles could be avoided if seasonal sea turtle movement during critical life stages are included as species-specific HEP mitigation measures. The data and maps on the main life-history stages of sea turtles, and the potential cumulative impacts from the HEP industry, were used in a Systematic Conservation Planning process, to derive a concept ocean zoning. As final outcome of this study, the concept ocean zoning highlighted areas where increased protection to sea turtles, and management of the conflict between sea turtles and the HEP industry, will be required if the HEP industry is to develop in a sustainable manner in the SWIO.
- Full Text:
- Date Issued: 2019
- Authors: Pretorius, Dirk
- Date: 2019
- Subjects: Ocean zoning , Marine ecology -- Indian Ocean Sea turtles -- Indian Ocean Marine animals -- Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43303 , vital:36787
- Description: The conflict between sea turtles and the numerous socio-economic developments in the Southwestern Indian Ocean (SWIO) are set to intensify as countries are looking to develop their ocean-based economies. The Hydrocarbon Exploration and Production (HEP) industry is of particular importance, since many of the SWIO governments view it as catalyst for development. This has raised concerns about potentially significant environmental impacts from the HEP industry, to sea turtles and their habitats, based on international examples where sea turtles have been severely negatively impacted upon, like the Deepwater Horizon spill in the Gulf of Mexico. Given that the four sea turtles species in the SWIO are listed on the IUCN Red List of threatened species, the aim of this study was to derive priority areas for sea turtles in the face of HEP, that could be used in an ocean zoning strategy for sustainable economic development of HEP in the SWIO region. To achieve this, the study spatially represented the main life-history stages of sea turtles, i.e. the breeding, migrating and foraging areas of Caretta caretta (loggerhead turtles), Dermochelys coriacea (leatherback turtles), Chelonia mydas (green turtles) and Eretmochelys imbricata (hawksbill turtles), within a telemetry derived distribution for each species. This spatial representation was used to quantify the extent of Marine Protected Areas (MPAs) conserving sea turtles in the SWIO, which revealed that sea turtle breeding areas were well represented in MPAs, including C. caretta (~40 %), C. mydas (~53 %), E. imbricata (~59 %) and D. coriacea (~22 %), the latter being least protected by MPAs during breeding, possibly due to a far greater extent of their internesting areas than the other three species. MPA coverage of breeding areas could be positively correlated to the increasing population trends of C. caretta and C. mydas in the SWIO, and therefore the assumption was made that increasing population trends of sea turtles are in part related to MPA protection of their breeding areas. In addition, the potential impacts on sea turtles from existing and proposed HEP developments were assessed and mapped by using a novel, species-specific rating index. The results revealed the extensive nature of potential water pollution impacts on sea turtles, constituting 16 of the top 28 most significant impacts from HEP on sea turtles. Other significant impacts on sea turtles associated with the HEP industry, included habitat destruction, light pollution and noise pollution. Importantly, this study found that ~70 % of all potential HEP impacts (irrespective of significance) on adult nesting sea turtles could be avoided if seasonal sea turtle movement during critical life stages are included as species-specific HEP mitigation measures. The data and maps on the main life-history stages of sea turtles, and the potential cumulative impacts from the HEP industry, were used in a Systematic Conservation Planning process, to derive a concept ocean zoning. As final outcome of this study, the concept ocean zoning highlighted areas where increased protection to sea turtles, and management of the conflict between sea turtles and the HEP industry, will be required if the HEP industry is to develop in a sustainable manner in the SWIO.
- Full Text:
- Date Issued: 2019
β-N-Methylamino-L-Alanine is a developmental neurotoxin
- Authors: Scott, Laura Louise
- Date: 2019
- Subjects: Neurotoxic agents , Nervous system -- Diseases
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/43633 , vital:36949
- Description: β-N-methylamino-L-alanine (BMAA) has been implicated in the development of the neurodegenerative diseases Amyotrophic Lateral Sclerosis/Parkinsonism Dementia Complex (ALS/PDC), Amyotrophic Lateral Sclerosis (ALS) and Alzheimer’s Disease (AD), but to date no animal model has adequately substantiated this link at environmentally relevant or even exaggerated BMAA exposure levels. The resulting controversy over a possible role for BMAA in neurodegenerative diseases was further hampered by a lack of evidence for mechanistic explanation for the disease pathology associated with these diseases However, the different responses to BMAA that have been observed in neonatal compared to adult rats, together with the findings of epidemiological studies that exposure to environmental factors in utero or in the early stages of life may be important for the development of ALS several years later, suggested that age of exposure might be the determining factor of BMAA neurotoxicity. This study therefore specifically addresses the developmental nature of BMAA as a neurotoxin, and investigates the pathology and progressive nature of that pathology after exposure to the toxin at the most susceptible age. This study demonstrated the importance of BMAA exposure age over total BMAA dose by showing that the administration of a single neonatal dose of BMAA to rodents on postnatal day (PND) 3, 4 and 5, and not prenatally or on PND 6, 7 and 10, caused behavioural, locomotor, emotional and long-term cognitive deficits, clinical symptoms of neurodegeneration as well as pathological hallmarks of AD, PD and ALS in the central nervous system. Furthermore, the observed behavioural deficits and distribution of neuronal loss and proteinopathies in the rodent central nervous system following exposure to BMAA on PND 3, 4 and 5 (corresponding to the developing age of an infant during the third trimester of pregnancy) is consistent with that typically associated with the disruption of normal dopamine and/or serotonin signaling in the brain and the consequent alteration in normal hippocampal and striatal neurogenesis that is modulated, in part, by dopamine. The pattern of spread and rate of propagation of pathology in this neonatal rat BMAA model provided further evidence that BMAA potentially exerts its effect by acting on neurotransmitter signaling. The observed late onset of typical ALS symptoms and pathology suggest that in this BMAA model AD and/or PD related symptoms develop first, followed by the start of ALS symptoms only after the AD and/or PD neuropathological deficits have severely progressed. This study also demonstrated that BMAA exposure at different doses and at different developmental ages resulted in the development of different combinations of either AD and/or PD and/or ALS pathology and/or symptoms in rats, and it is therefore feasible that in humans the age and/or frequency of exposure as well as the BMAA dose might similarly be a major determinant of the variant of AD, PD and/or ALS that might develop in adulthood. Based on the low BMAA dose that was able to cause AD and/or PD-like neuropathological abnormalities in rats in this study, it is feasible that a pregnant human could over the course of her pregnancy, and specifically during the third trimester of pregnancy, consume sufficient BMAA to result in her unborn child developing AD and/or PD and/or ALS up to 30-50 years later. This neonatal BMAA model is the only non-transgenic rodent model that reproduces the behavioural deficits, neuropathology and clinical symptoms that are typically associated with AD, PD and ALS in humans and that, more importantly, mimics the delayed onset of disease symptoms and typical slow progression of these neurodegenerative diseases with age. It now seems very likely that BMAA is a developmental neurotoxin that, as a result of perinatal, but probably prenatal exposure, causes or contributes significantly to the development of neurodegenerative diseases in humans.
- Full Text:
- Date Issued: 2019
- Authors: Scott, Laura Louise
- Date: 2019
- Subjects: Neurotoxic agents , Nervous system -- Diseases
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/43633 , vital:36949
- Description: β-N-methylamino-L-alanine (BMAA) has been implicated in the development of the neurodegenerative diseases Amyotrophic Lateral Sclerosis/Parkinsonism Dementia Complex (ALS/PDC), Amyotrophic Lateral Sclerosis (ALS) and Alzheimer’s Disease (AD), but to date no animal model has adequately substantiated this link at environmentally relevant or even exaggerated BMAA exposure levels. The resulting controversy over a possible role for BMAA in neurodegenerative diseases was further hampered by a lack of evidence for mechanistic explanation for the disease pathology associated with these diseases However, the different responses to BMAA that have been observed in neonatal compared to adult rats, together with the findings of epidemiological studies that exposure to environmental factors in utero or in the early stages of life may be important for the development of ALS several years later, suggested that age of exposure might be the determining factor of BMAA neurotoxicity. This study therefore specifically addresses the developmental nature of BMAA as a neurotoxin, and investigates the pathology and progressive nature of that pathology after exposure to the toxin at the most susceptible age. This study demonstrated the importance of BMAA exposure age over total BMAA dose by showing that the administration of a single neonatal dose of BMAA to rodents on postnatal day (PND) 3, 4 and 5, and not prenatally or on PND 6, 7 and 10, caused behavioural, locomotor, emotional and long-term cognitive deficits, clinical symptoms of neurodegeneration as well as pathological hallmarks of AD, PD and ALS in the central nervous system. Furthermore, the observed behavioural deficits and distribution of neuronal loss and proteinopathies in the rodent central nervous system following exposure to BMAA on PND 3, 4 and 5 (corresponding to the developing age of an infant during the third trimester of pregnancy) is consistent with that typically associated with the disruption of normal dopamine and/or serotonin signaling in the brain and the consequent alteration in normal hippocampal and striatal neurogenesis that is modulated, in part, by dopamine. The pattern of spread and rate of propagation of pathology in this neonatal rat BMAA model provided further evidence that BMAA potentially exerts its effect by acting on neurotransmitter signaling. The observed late onset of typical ALS symptoms and pathology suggest that in this BMAA model AD and/or PD related symptoms develop first, followed by the start of ALS symptoms only after the AD and/or PD neuropathological deficits have severely progressed. This study also demonstrated that BMAA exposure at different doses and at different developmental ages resulted in the development of different combinations of either AD and/or PD and/or ALS pathology and/or symptoms in rats, and it is therefore feasible that in humans the age and/or frequency of exposure as well as the BMAA dose might similarly be a major determinant of the variant of AD, PD and/or ALS that might develop in adulthood. Based on the low BMAA dose that was able to cause AD and/or PD-like neuropathological abnormalities in rats in this study, it is feasible that a pregnant human could over the course of her pregnancy, and specifically during the third trimester of pregnancy, consume sufficient BMAA to result in her unborn child developing AD and/or PD and/or ALS up to 30-50 years later. This neonatal BMAA model is the only non-transgenic rodent model that reproduces the behavioural deficits, neuropathology and clinical symptoms that are typically associated with AD, PD and ALS in humans and that, more importantly, mimics the delayed onset of disease symptoms and typical slow progression of these neurodegenerative diseases with age. It now seems very likely that BMAA is a developmental neurotoxin that, as a result of perinatal, but probably prenatal exposure, causes or contributes significantly to the development of neurodegenerative diseases in humans.
- Full Text:
- Date Issued: 2019
A characterization of landslide occurrence in the Kigezi Highlands of South Western Uganda
- Authors: Nseka, Denis
- Date: 2018
- Subjects: Landslides -- Uganda , Land degradation -- Uganda Earth movements
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/33791 , vital:33029
- Description: The frequency and magnitude of landslide occurrence in the Kigezi highlands of South Western Uganda has increased, but the key underpinnings of the occurrences are yet to be understood. The overall aim of this study was to characterize the parameters underpinning landslide occurrence in the Kigezi highlands. This information is important for predicting or identifying actual and potential landslide sites. This should inform policy, particularly in terms of developing early warning systems to landslide hazards in these highlands. The present study analysed the area’s topography, soil properties as well as land use and cover changes underpinning the spatialtemporal distribution of landslide occurrence in the region. The present study focussed on selected topographic parameters including slope gradient, profile curvature, Topographic Wetness Index (TWI), Stream Power Index (SPI), and Topographic Position Index (TPI). These factors were parameterized in the field and GIS environment using a 10 m Digital Elevation Model. Sixty five landslide features were surveyed and mapped. Soil properties were characterised in relation to slope position. Onsite soil property analysis was conducted within the landslide scars, auger holes and full profile representative sites. Furthermore, soil infiltration and strength tests, as well as clay mineralogy analyses were also conducted. An analysis of the spatial-temporal land use and cover changes was undertaken using satellite imagery spanning the period between 1985 and 2015. Landslides were noted to concentrate along topographic hollows in the landscape. The occurrence is dominant where slope gradient is between 25˚ and 35˚, profile curvature between 0.1 and 5, TWI between 8 and 18, SPI >10 and TPI between -1 and 1. Landslides are less pronounced on slope zones where slope gradient is <15˚ and >45˚, profile curvature <0, TWI <8 and >18, SPI <10 and TPI >1. Deep soil profiles ranging between 2.5 and 7 meters are a major characteristic of the study area. Soils are characterized by clay pans at a depth ranging between 0.75 and 3 meters within the profiles. The study area is dominated by clay texture, except for the uppermost surface horizons, which are loamy sand. All surface horizons analysed had the percentage of sand, silt and clay ranging from 33 to 55%, 22 to 40% and 10 to 30% respectively. In the deeper horizons, sand was observed to reduce drastically to less than 23%, while clay increased to greater than 50%. The clay content is very high in the deeper horizons exceeding 35%. By implication, such soils with a very high clay content and plasticity index are considered as Vertisols, with a profound influence in the occurrence of landslides. The top soil predominantly contains more quartz, while subsurface horizons have considerable amounts of illite/muscovite as the dominant clay minerals, ranging from 43% to 47 %. The liquid limit, plasticity index, computed weighted plasticity index (PIw), expansiveness (ɛex) and dispersion ranging from 50, 22, 17, 10 and 23 to 66, 44,34,54 and 64, respectively also have strong implications for landslide occurrence. Landslides are not normally experienced during or immediately after extreme rainfall events but occur later in the rainfall season. By implication, this time lag in landslide occurrence and rainfall distribution, is due to the initial infiltration through quartz dominated upper soil layers, before illite/muscovite clays in the lower soil horizons get saturated. Whereas forest cover reduced from 40 % in 1985 to 8% in 2015, cultivated land and settlements increased from 16% and 11% to 52% and 25% respectively during the same period. The distribution of cultivated land decreased in lower slope sections within gradient group < 15˚ by 59%. It however increased in upper sections within gradient cluster 25˚ to 35˚ by over 85% during the study period. There is a shift of cultivated land to the steeper sensitive upper slope elements associated with landslides in the study area. More than 50% of the landslides are occurring on cultivated land, 20% on settlements while less than 15 % and 10% are occurring on grassland and forests with degraded areas respectively. Landslides in Kigezi highlands are triggered by a complex interaction of multiple- factors, including dynamic triggers and ground condition variables. Topographic hollows are convergence zones within the landscape where all the parameters interact to cause landslides. Topographic hollows are therefore potential and actual landslide sites in the study area. Characterized by deep soil horizons with high clay content dominated by illite/muscovite minerals in the sub soils and profile concave forms with moderately steep slopes, topographic hollows are the most vulnerable slope elements to landslide occurrence. The spatial temporal patterns of landslide occurrence in the study area has changed due to increased cultivation of steep middle and upper slopes. Characterized by deep soil horizons with high clay content dominated by illite/muscovite minerals in the sub soils and profile concave forms with moderately steep slopes, topographic hollows are the most vulnerable slope elements to landslide occurrence. The spatial-temporal patterns of landslide occurrence in the study area has changed due to increased cultivation of steep middle and upper slopes. A close spatial and temporal correlation between land use/cover changes and landslide occurrence is discernible. The understanding of these topographical, pedological and land use/cover parameters and their influence on landslide occurrence is important in land management. It is now possible to identify and predict actual and potential landslide zones, and also demarcate safer zones for community activities. The information generated about the area’s topographic, pedological and land cover characteristics should help in vulnerability mitigation and enhance community resilience to landslide hazards in this fragile highland ecosystem. This can be done through designating zones for community activities while avoiding potential landslide zones. It is also recommended that, tree cover restoration be done in the highlands and the farmers encouraged to re-establish terrace farming while avoiding cultivation of sensitive steep middle and upper slope sections.
- Full Text:
- Date Issued: 2018
- Authors: Nseka, Denis
- Date: 2018
- Subjects: Landslides -- Uganda , Land degradation -- Uganda Earth movements
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/33791 , vital:33029
- Description: The frequency and magnitude of landslide occurrence in the Kigezi highlands of South Western Uganda has increased, but the key underpinnings of the occurrences are yet to be understood. The overall aim of this study was to characterize the parameters underpinning landslide occurrence in the Kigezi highlands. This information is important for predicting or identifying actual and potential landslide sites. This should inform policy, particularly in terms of developing early warning systems to landslide hazards in these highlands. The present study analysed the area’s topography, soil properties as well as land use and cover changes underpinning the spatialtemporal distribution of landslide occurrence in the region. The present study focussed on selected topographic parameters including slope gradient, profile curvature, Topographic Wetness Index (TWI), Stream Power Index (SPI), and Topographic Position Index (TPI). These factors were parameterized in the field and GIS environment using a 10 m Digital Elevation Model. Sixty five landslide features were surveyed and mapped. Soil properties were characterised in relation to slope position. Onsite soil property analysis was conducted within the landslide scars, auger holes and full profile representative sites. Furthermore, soil infiltration and strength tests, as well as clay mineralogy analyses were also conducted. An analysis of the spatial-temporal land use and cover changes was undertaken using satellite imagery spanning the period between 1985 and 2015. Landslides were noted to concentrate along topographic hollows in the landscape. The occurrence is dominant where slope gradient is between 25˚ and 35˚, profile curvature between 0.1 and 5, TWI between 8 and 18, SPI >10 and TPI between -1 and 1. Landslides are less pronounced on slope zones where slope gradient is <15˚ and >45˚, profile curvature <0, TWI <8 and >18, SPI <10 and TPI >1. Deep soil profiles ranging between 2.5 and 7 meters are a major characteristic of the study area. Soils are characterized by clay pans at a depth ranging between 0.75 and 3 meters within the profiles. The study area is dominated by clay texture, except for the uppermost surface horizons, which are loamy sand. All surface horizons analysed had the percentage of sand, silt and clay ranging from 33 to 55%, 22 to 40% and 10 to 30% respectively. In the deeper horizons, sand was observed to reduce drastically to less than 23%, while clay increased to greater than 50%. The clay content is very high in the deeper horizons exceeding 35%. By implication, such soils with a very high clay content and plasticity index are considered as Vertisols, with a profound influence in the occurrence of landslides. The top soil predominantly contains more quartz, while subsurface horizons have considerable amounts of illite/muscovite as the dominant clay minerals, ranging from 43% to 47 %. The liquid limit, plasticity index, computed weighted plasticity index (PIw), expansiveness (ɛex) and dispersion ranging from 50, 22, 17, 10 and 23 to 66, 44,34,54 and 64, respectively also have strong implications for landslide occurrence. Landslides are not normally experienced during or immediately after extreme rainfall events but occur later in the rainfall season. By implication, this time lag in landslide occurrence and rainfall distribution, is due to the initial infiltration through quartz dominated upper soil layers, before illite/muscovite clays in the lower soil horizons get saturated. Whereas forest cover reduced from 40 % in 1985 to 8% in 2015, cultivated land and settlements increased from 16% and 11% to 52% and 25% respectively during the same period. The distribution of cultivated land decreased in lower slope sections within gradient group < 15˚ by 59%. It however increased in upper sections within gradient cluster 25˚ to 35˚ by over 85% during the study period. There is a shift of cultivated land to the steeper sensitive upper slope elements associated with landslides in the study area. More than 50% of the landslides are occurring on cultivated land, 20% on settlements while less than 15 % and 10% are occurring on grassland and forests with degraded areas respectively. Landslides in Kigezi highlands are triggered by a complex interaction of multiple- factors, including dynamic triggers and ground condition variables. Topographic hollows are convergence zones within the landscape where all the parameters interact to cause landslides. Topographic hollows are therefore potential and actual landslide sites in the study area. Characterized by deep soil horizons with high clay content dominated by illite/muscovite minerals in the sub soils and profile concave forms with moderately steep slopes, topographic hollows are the most vulnerable slope elements to landslide occurrence. The spatial temporal patterns of landslide occurrence in the study area has changed due to increased cultivation of steep middle and upper slopes. Characterized by deep soil horizons with high clay content dominated by illite/muscovite minerals in the sub soils and profile concave forms with moderately steep slopes, topographic hollows are the most vulnerable slope elements to landslide occurrence. The spatial-temporal patterns of landslide occurrence in the study area has changed due to increased cultivation of steep middle and upper slopes. A close spatial and temporal correlation between land use/cover changes and landslide occurrence is discernible. The understanding of these topographical, pedological and land use/cover parameters and their influence on landslide occurrence is important in land management. It is now possible to identify and predict actual and potential landslide zones, and also demarcate safer zones for community activities. The information generated about the area’s topographic, pedological and land cover characteristics should help in vulnerability mitigation and enhance community resilience to landslide hazards in this fragile highland ecosystem. This can be done through designating zones for community activities while avoiding potential landslide zones. It is also recommended that, tree cover restoration be done in the highlands and the farmers encouraged to re-establish terrace farming while avoiding cultivation of sensitive steep middle and upper slope sections.
- Full Text:
- Date Issued: 2018
A comparison of conventional and ultrasonic seams in swimwear
- Authors: Tyalana, Nommiselo
- Date: 2018
- Subjects: Textile finishing , Textile finishing agents Seams (Sewing) Textile fabrics Textile fibers Textile design
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/36727 , vital:34048
- Description: Ultrasonic welding technology is a relatively new technology in apparel construction, this research forms part of a study to assess its effectiveness as a joining technology that can be used in ladies swimwear. The ultimate aim was to determine whether the ultrasonic welding joining technique could be successfully used in assembling ladies swimwear garments, comprising only synthetic fibres, namely polyester/Lycra, polyamide/Lycra, polyamide/Lycra power-net and polyamide/Lycra mesh warp knitted fabrics. These specific swimwear fabrics were selected since they comprise 100% thermoplastic synthetic fibres, considered ideal for ultrasonic welding. This study essentially compares and contrasts the performance of two seam joining techniques: namely conventional sewing and ultrasonic welding, in terms of seam strength, when used in the above mentioned four fabrics. Conventionally sewn and ultrasonically welded seams were produced, straight and curved, in both the wale and course directions of the fabrics. The conventionally sewn seams were produced using two sewing machines; namely an overlocker, also known as a mock safety sewing machine, and a cover seam machines. All conventionally sewn seams were stitched and tested under similar conditions. The ultrasonic welded seams were produced using three different wheels, a Medium Male Knurled pattern wheel, a Staggered Triple Stitch pattern wheel and a Single Stitch pattern wheel. The amplitude and speed of the welding machine, during the ultrasonic seaming, were kept constant, except when welding the polyamide/Lycra power-net and the polyamide/Lycra mesh fabrics when the pressure had to be drastically reduced in order to avoid excessively softened seams. The results of the study are presented in the form of line charts, scatter charts and tables. The ultrasonic welded seams, joined with the Medium Male Knurled wheel, exhibited surface waviness, as opposed to those joined with the Staggered Triple Stitch wheel which were smooth. It was found that, in terms of seam strength, the ultrasonic seams produced with the Single Stitch and Medium Male Knurled pattern wheels out performed those produced with the Staggered Triple Stitch wheels. The polyester/Lycra fabric was found easier to handle during the ultrasonic seaming process than the polyamide/Lycra fabric, although the strength of the ultrasonic seams in the polyester/Lycra fabric did not differ consistently from those of the polyamide/Lycra fabric. It was found that the conventional sewn seams were consistently stronger, and had a better appearance, than the ultrasonic welded seams. Although some promising results were obtained, in terms of the strength of the ultrasonic welded seams, the results overall were far too variable, inconsistent and unsatisfactory for this technique of seaming to be recommended at this stage for any of the swimwear fabrics covered. Further, more in depth, studies are required in order to gain a better understating of the effect of the various ultrasonic seaming parameters, as well as fabric parameters on ultrasonic seam strength and consistency.
- Full Text:
- Date Issued: 2018
- Authors: Tyalana, Nommiselo
- Date: 2018
- Subjects: Textile finishing , Textile finishing agents Seams (Sewing) Textile fabrics Textile fibers Textile design
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/36727 , vital:34048
- Description: Ultrasonic welding technology is a relatively new technology in apparel construction, this research forms part of a study to assess its effectiveness as a joining technology that can be used in ladies swimwear. The ultimate aim was to determine whether the ultrasonic welding joining technique could be successfully used in assembling ladies swimwear garments, comprising only synthetic fibres, namely polyester/Lycra, polyamide/Lycra, polyamide/Lycra power-net and polyamide/Lycra mesh warp knitted fabrics. These specific swimwear fabrics were selected since they comprise 100% thermoplastic synthetic fibres, considered ideal for ultrasonic welding. This study essentially compares and contrasts the performance of two seam joining techniques: namely conventional sewing and ultrasonic welding, in terms of seam strength, when used in the above mentioned four fabrics. Conventionally sewn and ultrasonically welded seams were produced, straight and curved, in both the wale and course directions of the fabrics. The conventionally sewn seams were produced using two sewing machines; namely an overlocker, also known as a mock safety sewing machine, and a cover seam machines. All conventionally sewn seams were stitched and tested under similar conditions. The ultrasonic welded seams were produced using three different wheels, a Medium Male Knurled pattern wheel, a Staggered Triple Stitch pattern wheel and a Single Stitch pattern wheel. The amplitude and speed of the welding machine, during the ultrasonic seaming, were kept constant, except when welding the polyamide/Lycra power-net and the polyamide/Lycra mesh fabrics when the pressure had to be drastically reduced in order to avoid excessively softened seams. The results of the study are presented in the form of line charts, scatter charts and tables. The ultrasonic welded seams, joined with the Medium Male Knurled wheel, exhibited surface waviness, as opposed to those joined with the Staggered Triple Stitch wheel which were smooth. It was found that, in terms of seam strength, the ultrasonic seams produced with the Single Stitch and Medium Male Knurled pattern wheels out performed those produced with the Staggered Triple Stitch wheels. The polyester/Lycra fabric was found easier to handle during the ultrasonic seaming process than the polyamide/Lycra fabric, although the strength of the ultrasonic seams in the polyester/Lycra fabric did not differ consistently from those of the polyamide/Lycra fabric. It was found that the conventional sewn seams were consistently stronger, and had a better appearance, than the ultrasonic welded seams. Although some promising results were obtained, in terms of the strength of the ultrasonic welded seams, the results overall were far too variable, inconsistent and unsatisfactory for this technique of seaming to be recommended at this stage for any of the swimwear fabrics covered. Further, more in depth, studies are required in order to gain a better understating of the effect of the various ultrasonic seaming parameters, as well as fabric parameters on ultrasonic seam strength and consistency.
- Full Text:
- Date Issued: 2018
A congestion aware ant colony optimisation-based routing and wavelength assignment algorithm for transparent flexi-grid optical burst switched networks
- Authors: Oladipo, Joshua Femi
- Date: 2018
- Subjects: Ants -- Behavior -- Mathematical models , Distributed algorithms
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/34733 , vital:33432
- Description: Optical Burst Switching (OBS) over transparent exi-grid optical networks, is considered a potential solution to the increasing pressure on backbone networks due to the increase in internet use and widespread adoption of various high bandwidth applications. Both technologies allow for more e cient usage of a networks resources. However, transmissions over exi-grid networks are more susceptible to optical impairments than transmissions made over xed-grid networks, and OBS suers from high burst loss due to contention. These issues need to be solved in order to reap the full benets of both technologies. An open issue for OBS whose solution would mitigate both issues is the Routing and Wavelength Assignment (RWA) algorithm. Ant Colony Optimisation (ACO) is a method of interest for solving the RWA problem on OBS networks. This study aims to improve on current dynamic ACO-based solutions to the Routing and Wavelength Assignment problem on transparent exi-grid Optical Burst Switched networks.
- Full Text:
- Date Issued: 2018
- Authors: Oladipo, Joshua Femi
- Date: 2018
- Subjects: Ants -- Behavior -- Mathematical models , Distributed algorithms
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/34733 , vital:33432
- Description: Optical Burst Switching (OBS) over transparent exi-grid optical networks, is considered a potential solution to the increasing pressure on backbone networks due to the increase in internet use and widespread adoption of various high bandwidth applications. Both technologies allow for more e cient usage of a networks resources. However, transmissions over exi-grid networks are more susceptible to optical impairments than transmissions made over xed-grid networks, and OBS suers from high burst loss due to contention. These issues need to be solved in order to reap the full benets of both technologies. An open issue for OBS whose solution would mitigate both issues is the Routing and Wavelength Assignment (RWA) algorithm. Ant Colony Optimisation (ACO) is a method of interest for solving the RWA problem on OBS networks. This study aims to improve on current dynamic ACO-based solutions to the Routing and Wavelength Assignment problem on transparent exi-grid Optical Burst Switched networks.
- Full Text:
- Date Issued: 2018
A framework for designing ambient assisted living services for disabled individuals
- Authors: Kyazze, Michael
- Date: 2018
- Subjects: Assistive computer technology , Computers and people with disabilities Self-help devices for people with disabilities People with disabilities -- Means of communication -- Technological innovations Communication devices for people with disabilities
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/31240 , vital:31347
- Description: Physically disabled individuals face a number of challenges when carrying out their everyday activities such as moving around, communicating with others, and their personal care. One way of overcoming these challenges is by using personal assistants. An alternative is to enable independence through assistive technology. This research aimed to investigate how physically disabled individuals experience these challenges, and how assistive technology can enable them to be more independent. In order to achieve the goal of this research, existing literature was reviewed on disability, assisted living, and interaction techniques. The literature study on disability identified some of the challenges faced by disabled individuals in their daily lives. In order to contextualize these challenges, interview studies with eighteen disabled individuals, and twelve personal assistants were carried out in Kampala, Uganda and Port Elizabeth, South Africa. The participants from both Uganda and South Africa were limited to those living in urban areas. The Ugandan participants noted that, whereas technology may assist their daily lives, their most essential needs are basic disability support aids such as wheelchairs and better long canes. This was in contrast with the South African participants, who have access to basic disability support aids. The South African participants identified their key needs as controlling an electronic environment without assistance, e.g. house lights, using a mobile phone, and using a computer without assistance. The interviews narrowed down the scope to focus on individuals with quadriplegia, specifically individuals who have limited hand use, but can comfortably speak and move their heads, and make gestures such as head shake and nod. Literature on assisted living technologies and frameworks, provided the technical foundation for the research. The literature review of interaction techniques identified a number of possible ways in which individuals with quadriplegia can interact with technology. An appropriate set of interaction techniques, namely head shake and nod, voice, and facial feature tracking were identified. Evaluations of the interaction techniques excluded head shake and nod, because of an inconsistency in detecting an individual’s head pose in different lighting conditions, when using a Microsoft Kinect. Voice and facial feature tracking using a standard computer camera were identified as the most suitable interaction techniques for this study. A framework for designing assisted living software services was developed. The framework allows disability researchers and solution developers to understand the needs of a given disability group, and design relevant solutions. To demonstrate that the proposed framework iii | P a g e addresses the main aim of this research, a prototype was developed that enables users to control smart lights (Phillips hue), a Smart TV (Samsung), and carry out basic navigation and webbrowsing on a computer. Users could interact with the software using voice and facial feature commands. A usability study was carried out with fifteen physically disabled individuals in Port Elizabeth, South Africa. The results of the evaluation study were highly positive. The successful evaluation of the prototype provided empirical evidence that the proposed framework does assist in the design of relevant and useful software services, to meet the unique needs of physically disabled individuals.
- Full Text:
- Date Issued: 2018
- Authors: Kyazze, Michael
- Date: 2018
- Subjects: Assistive computer technology , Computers and people with disabilities Self-help devices for people with disabilities People with disabilities -- Means of communication -- Technological innovations Communication devices for people with disabilities
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/31240 , vital:31347
- Description: Physically disabled individuals face a number of challenges when carrying out their everyday activities such as moving around, communicating with others, and their personal care. One way of overcoming these challenges is by using personal assistants. An alternative is to enable independence through assistive technology. This research aimed to investigate how physically disabled individuals experience these challenges, and how assistive technology can enable them to be more independent. In order to achieve the goal of this research, existing literature was reviewed on disability, assisted living, and interaction techniques. The literature study on disability identified some of the challenges faced by disabled individuals in their daily lives. In order to contextualize these challenges, interview studies with eighteen disabled individuals, and twelve personal assistants were carried out in Kampala, Uganda and Port Elizabeth, South Africa. The participants from both Uganda and South Africa were limited to those living in urban areas. The Ugandan participants noted that, whereas technology may assist their daily lives, their most essential needs are basic disability support aids such as wheelchairs and better long canes. This was in contrast with the South African participants, who have access to basic disability support aids. The South African participants identified their key needs as controlling an electronic environment without assistance, e.g. house lights, using a mobile phone, and using a computer without assistance. The interviews narrowed down the scope to focus on individuals with quadriplegia, specifically individuals who have limited hand use, but can comfortably speak and move their heads, and make gestures such as head shake and nod. Literature on assisted living technologies and frameworks, provided the technical foundation for the research. The literature review of interaction techniques identified a number of possible ways in which individuals with quadriplegia can interact with technology. An appropriate set of interaction techniques, namely head shake and nod, voice, and facial feature tracking were identified. Evaluations of the interaction techniques excluded head shake and nod, because of an inconsistency in detecting an individual’s head pose in different lighting conditions, when using a Microsoft Kinect. Voice and facial feature tracking using a standard computer camera were identified as the most suitable interaction techniques for this study. A framework for designing assisted living software services was developed. The framework allows disability researchers and solution developers to understand the needs of a given disability group, and design relevant solutions. To demonstrate that the proposed framework iii | P a g e addresses the main aim of this research, a prototype was developed that enables users to control smart lights (Phillips hue), a Smart TV (Samsung), and carry out basic navigation and webbrowsing on a computer. Users could interact with the software using voice and facial feature commands. A usability study was carried out with fifteen physically disabled individuals in Port Elizabeth, South Africa. The results of the evaluation study were highly positive. The successful evaluation of the prototype provided empirical evidence that the proposed framework does assist in the design of relevant and useful software services, to meet the unique needs of physically disabled individuals.
- Full Text:
- Date Issued: 2018
A seismic characterization of the crustal structure underlying the offshore Natal valley within the south-west Indian Ocean
- Authors: Moorcroft, David
- Date: 2018
- Subjects: Seismology , Seismology -- Kwa Zulu Natal -- Research Coasts -- Kwa Zulu Natal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/22387 , vital:29965
- Description: The Natal Valley is a ~1000 km long, elongated depression in the seafloor, located within the south-west Indian Ocean, between the coastline of south-east Africa and the offshore aseismic Mozambique Ridge. Knowledge of its present-day crustal structure is important to reconstruct the Gondwana supercontinent break-up history and the concurrent opening of the Indian Ocean, which started during the Jurassic, some ~180 – 150 million years ago. Major geological events relating to this supercontinent break-up including continental rifting, magmatism, the emplacement of extensive oceanic flood basalt as submarine plateaus, vertical processes associated with tectonic uplift, flexural subsidence of the margin and relative global sea-level change are recorded within the crust underlying the south-west Indian Ocean. Although these events have been well modelled, fundamental questions remain regarding the nature and tectonic structure of the crust. Today, the Natal Valley region represents a frontier for geophysical exploration. Early attempts at imaging the crust beneath the seafloor within the south-west Indian Ocean made use of now primitive seismic reflection data acquisition and processing techniques available to them at the time (1960’s - 1970’s). Considering the advancements made in marine seismic reflection imaging, these vintage datasets lacked the horizontal and vertical resolution necessary to most accurately account for and describe features of the upper crust underlying the northern Natal Valley. This study is based on the acquisition, processing and preliminary interpretation of a newly acquired, regional seismic reflection profile, Profile Mz5-007, acquired across the northernmost region of the Natal Valley during the PAMELA-Moz5 cruise in 2016. The methods of marine seismic reflection data acquisition, processing and interpretation are described. The seismic reflection data presented in this dissertation provides a regional-scaled appraisal of the upper crust underlying the northern Natal Valley for the first time. The imagery allows a comprehensive description of crustal structures and features from the very northern Natal Valley, close to the Mozambique coastline, southwards into the southern Natal Valley offshore of Durban. The findings presented here support the notion that the crust underlying the northern Natal Valley experienced roughly N-S orientated trans-tensional stresses in relation to the breakup of West Gondwana. At least two major phases of volcanism are imaged within the seismic stratigraphy. The lower-most event underlies the Limpopo Fan in the northernmost regions of the Natal Valley at a depth of 2 seconds TWT and is interpreted as a seismic expression of the upper surface of the Lower – Middle Jurassic Karoo LIP. The progressive disappearance of this horizon towards the south coincides with the emergence of a second, overlying, as yet unreported volcanic horizon, which extends southwards throughout the Natal Valley. On the basis of its regional distribution, spatial relationship with the underlying event boundary and its deformation history, this volcanic horizon is interpreted to represent a series of basaltic lava outpourings during the Lower Cretaceous, initiated in response to trans-tensional crustal deformation associated with the breakup of West Gondwana. In addition to these two major phases of flood basalt outpouring, a number of localized volcanic flows are imaged throughout the stratigraphy, most notably over the Central Terrace. In addition, at least four major unconformities are identified, all of which are well developed within the Limpopo Fan. One of these is interpreted to represent the well-developed Mid-Cretaceous hiatus in sedimentation, providing a relative seismo-stratigraphic constraint to overlying and underlying seismic units. A review of the structural elements of the crust reveals how the northern Natal Valley is partitioned into two sub-basins separated by a prominent basement high, the Central Terrace, imaged across the central portions of Profile Mz5-007. To the north of the Central Terrace, structural deformation appears largely extensional, characterized by a large (~37 km wide) asymmetrical depression directly to the north of the Central Terrace and only minor structural faulting. To the south of the Central Terrace, trans-tensional stresses associated with withdrawal of the Falkland Malvinas Plateau have deformed the upper crust into a series of apparently southwards tilted crustal blocks, producing a series of deep (3.5 s TWT) half graben-like structures, within which syn-rift fill has an apparent dip towards the south. There is evidence to suggest ongoing reactivation of these fault structures. This zone of deformation is shown to bear resemblances to the faulting mapped onshore of the Kwa-Zulu Natal coastline, providing reason to consider the two regions as a continuous zone of deformation associated with the withdrawal of the Falkland-Malvinas Plateau during the breakup of West Gondwana. Furthermore, a number of post-sedimentary intrusive features are imaged, the largest of which is the Naude Ridge; a large pinnacle-like feature which has penetrated the upper crust towards the southern limit of the profile. This feature corresponds to an abrupt change in seafloor depth and upper crustal structure, suggesting that this feature may mark the transition between subsided continental crust interpreted to underlie the northern Natal Valley to the north and oceanic crust known to underlie the southern Natal Valley to the south.
- Full Text:
- Date Issued: 2018
- Authors: Moorcroft, David
- Date: 2018
- Subjects: Seismology , Seismology -- Kwa Zulu Natal -- Research Coasts -- Kwa Zulu Natal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/22387 , vital:29965
- Description: The Natal Valley is a ~1000 km long, elongated depression in the seafloor, located within the south-west Indian Ocean, between the coastline of south-east Africa and the offshore aseismic Mozambique Ridge. Knowledge of its present-day crustal structure is important to reconstruct the Gondwana supercontinent break-up history and the concurrent opening of the Indian Ocean, which started during the Jurassic, some ~180 – 150 million years ago. Major geological events relating to this supercontinent break-up including continental rifting, magmatism, the emplacement of extensive oceanic flood basalt as submarine plateaus, vertical processes associated with tectonic uplift, flexural subsidence of the margin and relative global sea-level change are recorded within the crust underlying the south-west Indian Ocean. Although these events have been well modelled, fundamental questions remain regarding the nature and tectonic structure of the crust. Today, the Natal Valley region represents a frontier for geophysical exploration. Early attempts at imaging the crust beneath the seafloor within the south-west Indian Ocean made use of now primitive seismic reflection data acquisition and processing techniques available to them at the time (1960’s - 1970’s). Considering the advancements made in marine seismic reflection imaging, these vintage datasets lacked the horizontal and vertical resolution necessary to most accurately account for and describe features of the upper crust underlying the northern Natal Valley. This study is based on the acquisition, processing and preliminary interpretation of a newly acquired, regional seismic reflection profile, Profile Mz5-007, acquired across the northernmost region of the Natal Valley during the PAMELA-Moz5 cruise in 2016. The methods of marine seismic reflection data acquisition, processing and interpretation are described. The seismic reflection data presented in this dissertation provides a regional-scaled appraisal of the upper crust underlying the northern Natal Valley for the first time. The imagery allows a comprehensive description of crustal structures and features from the very northern Natal Valley, close to the Mozambique coastline, southwards into the southern Natal Valley offshore of Durban. The findings presented here support the notion that the crust underlying the northern Natal Valley experienced roughly N-S orientated trans-tensional stresses in relation to the breakup of West Gondwana. At least two major phases of volcanism are imaged within the seismic stratigraphy. The lower-most event underlies the Limpopo Fan in the northernmost regions of the Natal Valley at a depth of 2 seconds TWT and is interpreted as a seismic expression of the upper surface of the Lower – Middle Jurassic Karoo LIP. The progressive disappearance of this horizon towards the south coincides with the emergence of a second, overlying, as yet unreported volcanic horizon, which extends southwards throughout the Natal Valley. On the basis of its regional distribution, spatial relationship with the underlying event boundary and its deformation history, this volcanic horizon is interpreted to represent a series of basaltic lava outpourings during the Lower Cretaceous, initiated in response to trans-tensional crustal deformation associated with the breakup of West Gondwana. In addition to these two major phases of flood basalt outpouring, a number of localized volcanic flows are imaged throughout the stratigraphy, most notably over the Central Terrace. In addition, at least four major unconformities are identified, all of which are well developed within the Limpopo Fan. One of these is interpreted to represent the well-developed Mid-Cretaceous hiatus in sedimentation, providing a relative seismo-stratigraphic constraint to overlying and underlying seismic units. A review of the structural elements of the crust reveals how the northern Natal Valley is partitioned into two sub-basins separated by a prominent basement high, the Central Terrace, imaged across the central portions of Profile Mz5-007. To the north of the Central Terrace, structural deformation appears largely extensional, characterized by a large (~37 km wide) asymmetrical depression directly to the north of the Central Terrace and only minor structural faulting. To the south of the Central Terrace, trans-tensional stresses associated with withdrawal of the Falkland Malvinas Plateau have deformed the upper crust into a series of apparently southwards tilted crustal blocks, producing a series of deep (3.5 s TWT) half graben-like structures, within which syn-rift fill has an apparent dip towards the south. There is evidence to suggest ongoing reactivation of these fault structures. This zone of deformation is shown to bear resemblances to the faulting mapped onshore of the Kwa-Zulu Natal coastline, providing reason to consider the two regions as a continuous zone of deformation associated with the withdrawal of the Falkland-Malvinas Plateau during the breakup of West Gondwana. Furthermore, a number of post-sedimentary intrusive features are imaged, the largest of which is the Naude Ridge; a large pinnacle-like feature which has penetrated the upper crust towards the southern limit of the profile. This feature corresponds to an abrupt change in seafloor depth and upper crustal structure, suggesting that this feature may mark the transition between subsided continental crust interpreted to underlie the northern Natal Valley to the north and oceanic crust known to underlie the southern Natal Valley to the south.
- Full Text:
- Date Issued: 2018
A social media model for public participation in a South African municipality
- Authors: Fashoro, Ifeoluwapo
- Date: 2018
- Subjects: Information technology -- Social aspects -- South Africa , Social media -- South Africa Political participation -- Technological innovations -- South Africa Municipal government -- South Africa -- Citizen participation
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/29851 , vital:30786
- Description: Social media have become the preferred method of communication for individuals, organisations and even governments. These technologies have become ingrained in our everyday lives and have changed the way we communicate, collaborate are informed of recent happenings around the world. Social media websites are reported to be the most popular around the world. In the government sphere, social media is purported as a technology that will revolutionise citizen participation, service delivery and government-citizen interactions. Accordingly, governments around the world are steadily implementing social media in a bid to meet citizens’ demand for immediate and constant access to information, as well as increased opportunities to participate in government. Public participation has become an important focus area for government which could be used to effectively engage citizens and foster citizen trust. The United Nation’s E-government survey reports the presence of 125 countries on social media platforms. Despite the increased use of social media by governments, consensus among researchers is that governments need guidance on how to use social media effectively to achieve the potential benefits proposed by these technologies. Many social media adoptions by governments have been deemed as experimental; no formal action plan was designed, and many government employees are expected to learn social media use on-the-job. The aim of this research was to investigate and propose a social media model for public participation to leverage the opportunities provided by social media and present an effective and structured approach towards public participation. The research was designed as a mixed methods research using a case study based in the Eastern Cape Province of South Africa. The research involved a survey of citizens in the selected municipality based on the Uses and Gratifications Theory, interviews with employees responsible for social media in said municipality and a contents analysis of the existing social media pages of the municipality. The model was developed from the findings of the survey, interviews and existing literature. The implementation of the model was done in the Nelson Mandela Bay Municipality. The municipality appointed a social media champion responsible for obtaining support from top management and politicians within the municipality. Additional staff were added to the social media team and formal social media training was provided to the team. An official social media strategy was drafted and at the time of writing, needed to be approved by top management. The proposed model was operationalised within the Nelson Mandela Bay Municipality. This research makes several contributions to the E-government and social media fields in South Africa. The major contribution is the provision of guidance for South African municipalities to implement and use social media in an effective manner to achieve public participation. The research provided a phased approach to social media implementation that eliminates ad hoc experimentation and ensures the municipality’s social media activities are effective. The development of the model was based on the characteristics of the municipality and its citizens derived from the interviews and survey carried out. There are five phases in the model; Initialisation, Setup, Organisation, Institutionalisation and Maintenance. The model can be thought of as a guideline, and as such municipalities should adapt the implementation of the model to fit their organisational characteristics. The social media model will assist municipalities to determine the resources, tools and tactics to enable them to implement social media effectively, which will result in an improved engagement and participation process with citizens, and thereby foster trust.
- Full Text:
- Date Issued: 2018
- Authors: Fashoro, Ifeoluwapo
- Date: 2018
- Subjects: Information technology -- Social aspects -- South Africa , Social media -- South Africa Political participation -- Technological innovations -- South Africa Municipal government -- South Africa -- Citizen participation
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/29851 , vital:30786
- Description: Social media have become the preferred method of communication for individuals, organisations and even governments. These technologies have become ingrained in our everyday lives and have changed the way we communicate, collaborate are informed of recent happenings around the world. Social media websites are reported to be the most popular around the world. In the government sphere, social media is purported as a technology that will revolutionise citizen participation, service delivery and government-citizen interactions. Accordingly, governments around the world are steadily implementing social media in a bid to meet citizens’ demand for immediate and constant access to information, as well as increased opportunities to participate in government. Public participation has become an important focus area for government which could be used to effectively engage citizens and foster citizen trust. The United Nation’s E-government survey reports the presence of 125 countries on social media platforms. Despite the increased use of social media by governments, consensus among researchers is that governments need guidance on how to use social media effectively to achieve the potential benefits proposed by these technologies. Many social media adoptions by governments have been deemed as experimental; no formal action plan was designed, and many government employees are expected to learn social media use on-the-job. The aim of this research was to investigate and propose a social media model for public participation to leverage the opportunities provided by social media and present an effective and structured approach towards public participation. The research was designed as a mixed methods research using a case study based in the Eastern Cape Province of South Africa. The research involved a survey of citizens in the selected municipality based on the Uses and Gratifications Theory, interviews with employees responsible for social media in said municipality and a contents analysis of the existing social media pages of the municipality. The model was developed from the findings of the survey, interviews and existing literature. The implementation of the model was done in the Nelson Mandela Bay Municipality. The municipality appointed a social media champion responsible for obtaining support from top management and politicians within the municipality. Additional staff were added to the social media team and formal social media training was provided to the team. An official social media strategy was drafted and at the time of writing, needed to be approved by top management. The proposed model was operationalised within the Nelson Mandela Bay Municipality. This research makes several contributions to the E-government and social media fields in South Africa. The major contribution is the provision of guidance for South African municipalities to implement and use social media in an effective manner to achieve public participation. The research provided a phased approach to social media implementation that eliminates ad hoc experimentation and ensures the municipality’s social media activities are effective. The development of the model was based on the characteristics of the municipality and its citizens derived from the interviews and survey carried out. There are five phases in the model; Initialisation, Setup, Organisation, Institutionalisation and Maintenance. The model can be thought of as a guideline, and as such municipalities should adapt the implementation of the model to fit their organisational characteristics. The social media model will assist municipalities to determine the resources, tools and tactics to enable them to implement social media effectively, which will result in an improved engagement and participation process with citizens, and thereby foster trust.
- Full Text:
- Date Issued: 2018
Advanced high speed data and clock transmission over optical fibre for square kilometre telescope array
- Authors: Isoe, George Mosoti
- Date: 2018
- Subjects: Very large array telescopes -- South Africa , Semiconductor lasers Optical communications Optical amplifiers
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/30375 , vital:30935
- Description: There is an ever present need from Internet users for more bandwidth. This is manifested by continuous increase in bandwidth demanding applications such as 5G wireless, new end user consumer links like thunderbolt, video conferencing, high definition video-on-demand transmitted over the Internet and massive data transfers required with and within data centres for backup, storage and data processing in cloud computing. Fibre optic communications technologies are playing a pivotal role in communication, being a major enabling technology in our increasingly Internet-centric society. As network services continue to become more dynamic and diverse, Internet service providers are faced with a challenge of cost reduction in the transmission network, power and spectral efficiency as well as scalability of the optical network infrastructure to support incremental expansions and virtual machines. Intelligent design of terrestrial optical networks to allow for simultaneous signal transmission through shared network infrastructure, and the use of low cost, power efficient, high bandwidth transmitters such as vertical surface emitting lasers (VCSELs) as well as exploitation of spectral efficient in-complex advanced modulation formats is a viable approach to this situation. In this study, techniques for spectral efficiency upgrade and simultaneous transmission of data signal, reference frequency (RF) clock signal and pulse-per-second (PPS) over shared infrastructure have experimentally been optimized in a laboratory environment for adoption in next-generation telescope array networks such as the Square Kilometre Array (SKA), time keeping systems such as banking systems, Coordinated Universal Time(UTC) timing and Global Positioning Systems (GPS), as well as high capacity spectral efficient short reach optical fibre networks such as data centres. This work starts by experimentally optimizing VCSEL technology for simultaneous transmission of 10 Gbps data and 1.712 GHz RF clock signal over a single G. 655 optical fibre of length 24.75 Km at different channel spacing and different propagation direction for implementation in a cost effective next-generation telescope array network. The wavelength tuneability property of VCSEL transmitters allows for wavelength adjustment, a key requirement for simultaneous data and RF clock signal transmission over a single optical fibre. A receiver sensitivity of -19.19 dBm was experimentally achieved at back-to-back analysis. A 24.75 Km of simultaneous data and RF clock signal transmission performed at 0.4 nm channel spacing introduced a transmission penalty of 1.07 dB and 1.63 dB for counter and co-propagation scheme respectively. This work mainly utilized direct modulation and direct detection using a positive intrinsic negative (PIN) due to its simplicity and cost effectiveness. A novel modulation technique for simultaneous data and polarization-based pulse-per-second timing clock signal transmission using a single VCSEL carrier is experimentally demonstrated. Two signal types, a directly modulated 10 Gbps data signal and a polarization-based pulse per second (PPS) clock signal are modulated onto a single mode 10 GHz bandwidth VCSEL carrier at 1310 nm. Spectral efficiency is maximized by exploiting the inherent orthogonal polarization switching of the xiv VCSEL with changing bias in transmission of the PPS signal. A 10 Gbps VCSEL transmission with PPS over 11 Km of G.652 fibre introduced a transmission penalty of 0.52 dB. The contribution of PPS clock signal to this penalty was found to be 0.08 dB. A technique for simultaneous directly modulated data and phase modulated reference clock signal transmission over a signal channel in wavelength division multiplexing (WDM) solutions is experimentally demonstrated. This is to prepare solutions to the ever-increasing demand over gigabit/s, terabit/s and gigahertz capacities in WDM-based terrestrial optical fibre transmission systems such as telescope array networks. a total capacity of 30 Gbps (310 Gbps) data and 12 GHz ( 4 3 GHz) reference clock signal are multiplexed at a channel spacing of 100 GHz and simultaneously transmitted over a single mode G.655 fibre of length 24.73 Km. The recovery of the phase modulated RF clock signal using a differential delay line interferometry technique is experimentally demonstrated. A 625 Gbps (2525 Gbps) DWDM data transmission system is further implemented in simulation by multiplexing 25 channels at 25 Gbps per channel using 50 GHz channel spacing. A four level pulse amplitude modulation (4-PAM) data modulation format employing VCSELs is experimentally demonstrated for adoption in high bitrate networks such as big data science projects and data centre networks. 4-PAM offers a good trade-off between complexity, efficiency, reach, and sensitivity. A software defined digital signal processing (DSP) receiver is designed and implemented in MATLAB to recover the transmitted 4-PAM data signal cost effectively without the necessity of costly receiver hardware. A novel technique for maximizing carrier spectral efficiency through simultaneous 20 Gbps 4-PAM data and phase modulated 2 GHz RF clock signal transmission on a single mode 10 GHz bandwidth VCSEL carrier at 1310 nm is experimentally demonstrated for the first time to the best of our knowledge. Data transmission and clock stability performance of the designed high spectral efficient VCSEL-based link network is evaluated through BER curve plots, phase noise measurements and Allan variance analysis respectively. VCSEL-based Raman amplification is experimentally demonstrated as a viable approach for RF clock signal distribution in extended reach astronomical telescope array networks and other extended reach terrestrial optical fibre network application. This is achieved by adopting two pumping techniques namely forward pumping and backward pumping. A maximum on off gain of 5.7 dB and 1.5 dB was experimentally attained for forward pumping and backward pumping at 24 dBm pump power respectively, while a maximum 100.8 Km fibre transmission achieved experimentally. In summary, this study has successfully demonstrated in-complex, spectral efficient, low cost and power efficient simultaneous data signal, reference frequency (RF) clock signal and pulse-per-second (PPS) transmission techniques over shared network infrastructure. Simultaneous transmission of data, RF clock and PPS timing signal is relevant in nextgeneration telescope array networks such as the Square Kilometre Array (SKA), time keeping systems such as banking systems, Coordinated Universal Time (UTC) timing and Global Positioning Systems (GPS), as well as high capacity spectral efficient short reach optical fibre networks such as data centres.
- Full Text:
- Date Issued: 2018
- Authors: Isoe, George Mosoti
- Date: 2018
- Subjects: Very large array telescopes -- South Africa , Semiconductor lasers Optical communications Optical amplifiers
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/30375 , vital:30935
- Description: There is an ever present need from Internet users for more bandwidth. This is manifested by continuous increase in bandwidth demanding applications such as 5G wireless, new end user consumer links like thunderbolt, video conferencing, high definition video-on-demand transmitted over the Internet and massive data transfers required with and within data centres for backup, storage and data processing in cloud computing. Fibre optic communications technologies are playing a pivotal role in communication, being a major enabling technology in our increasingly Internet-centric society. As network services continue to become more dynamic and diverse, Internet service providers are faced with a challenge of cost reduction in the transmission network, power and spectral efficiency as well as scalability of the optical network infrastructure to support incremental expansions and virtual machines. Intelligent design of terrestrial optical networks to allow for simultaneous signal transmission through shared network infrastructure, and the use of low cost, power efficient, high bandwidth transmitters such as vertical surface emitting lasers (VCSELs) as well as exploitation of spectral efficient in-complex advanced modulation formats is a viable approach to this situation. In this study, techniques for spectral efficiency upgrade and simultaneous transmission of data signal, reference frequency (RF) clock signal and pulse-per-second (PPS) over shared infrastructure have experimentally been optimized in a laboratory environment for adoption in next-generation telescope array networks such as the Square Kilometre Array (SKA), time keeping systems such as banking systems, Coordinated Universal Time(UTC) timing and Global Positioning Systems (GPS), as well as high capacity spectral efficient short reach optical fibre networks such as data centres. This work starts by experimentally optimizing VCSEL technology for simultaneous transmission of 10 Gbps data and 1.712 GHz RF clock signal over a single G. 655 optical fibre of length 24.75 Km at different channel spacing and different propagation direction for implementation in a cost effective next-generation telescope array network. The wavelength tuneability property of VCSEL transmitters allows for wavelength adjustment, a key requirement for simultaneous data and RF clock signal transmission over a single optical fibre. A receiver sensitivity of -19.19 dBm was experimentally achieved at back-to-back analysis. A 24.75 Km of simultaneous data and RF clock signal transmission performed at 0.4 nm channel spacing introduced a transmission penalty of 1.07 dB and 1.63 dB for counter and co-propagation scheme respectively. This work mainly utilized direct modulation and direct detection using a positive intrinsic negative (PIN) due to its simplicity and cost effectiveness. A novel modulation technique for simultaneous data and polarization-based pulse-per-second timing clock signal transmission using a single VCSEL carrier is experimentally demonstrated. Two signal types, a directly modulated 10 Gbps data signal and a polarization-based pulse per second (PPS) clock signal are modulated onto a single mode 10 GHz bandwidth VCSEL carrier at 1310 nm. Spectral efficiency is maximized by exploiting the inherent orthogonal polarization switching of the xiv VCSEL with changing bias in transmission of the PPS signal. A 10 Gbps VCSEL transmission with PPS over 11 Km of G.652 fibre introduced a transmission penalty of 0.52 dB. The contribution of PPS clock signal to this penalty was found to be 0.08 dB. A technique for simultaneous directly modulated data and phase modulated reference clock signal transmission over a signal channel in wavelength division multiplexing (WDM) solutions is experimentally demonstrated. This is to prepare solutions to the ever-increasing demand over gigabit/s, terabit/s and gigahertz capacities in WDM-based terrestrial optical fibre transmission systems such as telescope array networks. a total capacity of 30 Gbps (310 Gbps) data and 12 GHz ( 4 3 GHz) reference clock signal are multiplexed at a channel spacing of 100 GHz and simultaneously transmitted over a single mode G.655 fibre of length 24.73 Km. The recovery of the phase modulated RF clock signal using a differential delay line interferometry technique is experimentally demonstrated. A 625 Gbps (2525 Gbps) DWDM data transmission system is further implemented in simulation by multiplexing 25 channels at 25 Gbps per channel using 50 GHz channel spacing. A four level pulse amplitude modulation (4-PAM) data modulation format employing VCSELs is experimentally demonstrated for adoption in high bitrate networks such as big data science projects and data centre networks. 4-PAM offers a good trade-off between complexity, efficiency, reach, and sensitivity. A software defined digital signal processing (DSP) receiver is designed and implemented in MATLAB to recover the transmitted 4-PAM data signal cost effectively without the necessity of costly receiver hardware. A novel technique for maximizing carrier spectral efficiency through simultaneous 20 Gbps 4-PAM data and phase modulated 2 GHz RF clock signal transmission on a single mode 10 GHz bandwidth VCSEL carrier at 1310 nm is experimentally demonstrated for the first time to the best of our knowledge. Data transmission and clock stability performance of the designed high spectral efficient VCSEL-based link network is evaluated through BER curve plots, phase noise measurements and Allan variance analysis respectively. VCSEL-based Raman amplification is experimentally demonstrated as a viable approach for RF clock signal distribution in extended reach astronomical telescope array networks and other extended reach terrestrial optical fibre network application. This is achieved by adopting two pumping techniques namely forward pumping and backward pumping. A maximum on off gain of 5.7 dB and 1.5 dB was experimentally attained for forward pumping and backward pumping at 24 dBm pump power respectively, while a maximum 100.8 Km fibre transmission achieved experimentally. In summary, this study has successfully demonstrated in-complex, spectral efficient, low cost and power efficient simultaneous data signal, reference frequency (RF) clock signal and pulse-per-second (PPS) transmission techniques over shared network infrastructure. Simultaneous transmission of data, RF clock and PPS timing signal is relevant in nextgeneration telescope array networks such as the Square Kilometre Array (SKA), time keeping systems such as banking systems, Coordinated Universal Time (UTC) timing and Global Positioning Systems (GPS), as well as high capacity spectral efficient short reach optical fibre networks such as data centres.
- Full Text:
- Date Issued: 2018
An appraisal of warm temperate mangrove estuaries as food patches using zooplankton and RNA: DNA ratios of Gilchristella aestuaria larvae as indicators
- Authors: Bornman, Eugin
- Date: 2018
- Subjects: Mangrove swamps Fishes -- Larvae , Mangrove ecology , Zooplankton
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/17908 , vital:28481
- Description: Mangrove habitats are considered as the ideal fish nursery as they are known to increase the growth and survival of juvenile fishes by providing enhanced food availability and protection. However, most studies have focused on tropical mangroves with a few recent warm temperate studies finding conflicting results. Furthermore, the nursery value of South African mangroves to fishes remain understudied in subtropical areas, while warm temperate mangroves are yet to be evaluated. This study aimed to assess whether mangrove presence leads to any advantage to the larvae of an important estuarine resident fish species, Gilchristella aestuaria, by comparing the food patch quality of South African warm temperate mangrove and non-mangrove estuaries. Results indicate that larvae fed primarily on the dominant prey species, Pseudodiaptomus hessei, Paracrtia longipatella, and Acartiella natalensis. However, postflexion larvae consumed more of the larger species, P. hessei, within the two mangrove estuaries (16.09 %V in Nahoon and 13.79 %V in Xhora) than the two nonmangrove estuaries (12.20 %V in Gonubie and 7.05 %V in Qora), despite other prey species occurring at similar densities. Results indicate that mangrove habitats acted as sediment sinks, slightly reducing the turbidity of these estuaries which resulted in postflexion larvae actively selecting larger, more nutritious prey, which in turn, significantly increased their individual instantaneous growth rates (0.11 ± 0.21 Gi) when compared to postflexion larvae in non-mangrove estuaries (0.09 ± 0.12 Gi). This study found that mangrove presence was significantly related to postflexion larval densities when coupled with abiotic (such as temperature and turbidity) and biotic factors (such as predator-prey interactions). Understanding the spatial and temporal dynamics, predator-prey interactions as well as the growth and survival of G. aestuaria is particularly important as they are key zooplanktivores that are prey to other species in estuarine food webs.
- Full Text:
- Date Issued: 2018
- Authors: Bornman, Eugin
- Date: 2018
- Subjects: Mangrove swamps Fishes -- Larvae , Mangrove ecology , Zooplankton
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/17908 , vital:28481
- Description: Mangrove habitats are considered as the ideal fish nursery as they are known to increase the growth and survival of juvenile fishes by providing enhanced food availability and protection. However, most studies have focused on tropical mangroves with a few recent warm temperate studies finding conflicting results. Furthermore, the nursery value of South African mangroves to fishes remain understudied in subtropical areas, while warm temperate mangroves are yet to be evaluated. This study aimed to assess whether mangrove presence leads to any advantage to the larvae of an important estuarine resident fish species, Gilchristella aestuaria, by comparing the food patch quality of South African warm temperate mangrove and non-mangrove estuaries. Results indicate that larvae fed primarily on the dominant prey species, Pseudodiaptomus hessei, Paracrtia longipatella, and Acartiella natalensis. However, postflexion larvae consumed more of the larger species, P. hessei, within the two mangrove estuaries (16.09 %V in Nahoon and 13.79 %V in Xhora) than the two nonmangrove estuaries (12.20 %V in Gonubie and 7.05 %V in Qora), despite other prey species occurring at similar densities. Results indicate that mangrove habitats acted as sediment sinks, slightly reducing the turbidity of these estuaries which resulted in postflexion larvae actively selecting larger, more nutritious prey, which in turn, significantly increased their individual instantaneous growth rates (0.11 ± 0.21 Gi) when compared to postflexion larvae in non-mangrove estuaries (0.09 ± 0.12 Gi). This study found that mangrove presence was significantly related to postflexion larval densities when coupled with abiotic (such as temperature and turbidity) and biotic factors (such as predator-prey interactions). Understanding the spatial and temporal dynamics, predator-prey interactions as well as the growth and survival of G. aestuaria is particularly important as they are key zooplanktivores that are prey to other species in estuarine food webs.
- Full Text:
- Date Issued: 2018
An investigation of the combustion kinetics of coal-microalgae composite
- Ejesieme, Obialo Vitus, Dugmore, Gary
- Authors: Ejesieme, Obialo Vitus , Dugmore, Gary
- Date: 2018
- Subjects: Microalgae -- Biotechnology , Biomass energy -- South Africa Coal -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/34777 , vital:33447
- Description: Coal mining and handling generate sizeable quantities of ultra-fine coal particles which are heaped as discard material. Use of the ultra-fine coal for co-firing with microalgae biomass appears to be a promising option that would improve combustion of the discard. There is no available traditional biomass binder that can be used to agglomerate, reclaim, and co-fire the discard ultra-fine coal to generate heat. In a recent research, microalgae biomass was identified as an effective natural binder for discard ultra-fine coal. Biomass is a renewable resource, and many have been co-fired on a large scale except microalgae biomass. Researchers have studied co-firing of dry mixed coal-microalgae, however, the kinetics of a wet mix of microalgae biomass and ultra-fine coal, “Coalgae®” patented recently by the Nelson Mandela University needs to be explored. The study aimed at investigating in some detail the oxidation mechanism of coal-microalgae composites. The objective is to understand the impact of microalgae on the kinetic properties of coal which will inform on the application of “Coalgae®”. It involves correlating the small and large-scale combustion properties that will establish the co-firing option on an industrial scenario. The goal is to utilize all grades of discard ultra-fine resource using microalgae biomass as binder and a renewable component which enhances the combustion of coal to supply heat and electricity. The use of microalgae for fuel preparation and upgrading is on the increase due to its high growth potential, reactivity, and ability to store energy more than other biomasses. This research hypothesized that blending of discard ultra-fine coal with live microalgae biomass would improve the kinetic properties of the coal more than expected from linear combination of the dry materials. Thermogravimetric combustion of “Coalgae®” was studied under non-isothermal conditions from 40 °C to 900°C at a heating rate of 15 °C/min and air flow rate of 20 ml/min. The thermogravimetric combustion properties i.e. small-scale was related to the large-scale, John Thompson’s fixed-bed reactor under the above condition. Thermal profiles were transformed into a differential function to reveal overlapped combustion events. The Coat-Redferns kinetic model was applied on the non-de-Ejesieme, O.V. PhD Chemistry (Research), Nelson Mandela Univ. Email: ejevit@yahoo.com , s211266744@live.nmmu.ac.za convoluted reactions set to obtain some of kinetic parameters. The Fraser-Suzuki equation was used to de-convolute the overlapped combustion. Then, rate law combined with Arrhenius equation was used to derive the activation energy E a and pre-exponential factor A, while the integral form of solid states reaction model, g (∝) was applied to deduce the oxidation mechanism. The composite formed a strong and partly renewable blend under controlled temperature conditions, unlike assorted dried biomass mixed with coal. Microalgae biomass upgraded the fuel and kinetics properties of ultra-fine coal more than what was expected from a linear combination. It released heat that promoted the oxidation mechanism of the discard coal. The main effect is that the “Coalgae®” is significantly (p = 0.0570) more reactive than the coal. The co-firing approach is partly renewable and contributes to the utilization of high and low-quality available discard ultra-fine coal. It advances the combustion of coal resources and reduces carbon dioxide, CO2 emission attributed to global warming as well as preserves the natural biomass sources. The combustion of “Coalgae® “will improve economy, environment, and health, heat, and electricity supply to the society.
- Full Text:
- Date Issued: 2018
- Authors: Ejesieme, Obialo Vitus , Dugmore, Gary
- Date: 2018
- Subjects: Microalgae -- Biotechnology , Biomass energy -- South Africa Coal -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/34777 , vital:33447
- Description: Coal mining and handling generate sizeable quantities of ultra-fine coal particles which are heaped as discard material. Use of the ultra-fine coal for co-firing with microalgae biomass appears to be a promising option that would improve combustion of the discard. There is no available traditional biomass binder that can be used to agglomerate, reclaim, and co-fire the discard ultra-fine coal to generate heat. In a recent research, microalgae biomass was identified as an effective natural binder for discard ultra-fine coal. Biomass is a renewable resource, and many have been co-fired on a large scale except microalgae biomass. Researchers have studied co-firing of dry mixed coal-microalgae, however, the kinetics of a wet mix of microalgae biomass and ultra-fine coal, “Coalgae®” patented recently by the Nelson Mandela University needs to be explored. The study aimed at investigating in some detail the oxidation mechanism of coal-microalgae composites. The objective is to understand the impact of microalgae on the kinetic properties of coal which will inform on the application of “Coalgae®”. It involves correlating the small and large-scale combustion properties that will establish the co-firing option on an industrial scenario. The goal is to utilize all grades of discard ultra-fine resource using microalgae biomass as binder and a renewable component which enhances the combustion of coal to supply heat and electricity. The use of microalgae for fuel preparation and upgrading is on the increase due to its high growth potential, reactivity, and ability to store energy more than other biomasses. This research hypothesized that blending of discard ultra-fine coal with live microalgae biomass would improve the kinetic properties of the coal more than expected from linear combination of the dry materials. Thermogravimetric combustion of “Coalgae®” was studied under non-isothermal conditions from 40 °C to 900°C at a heating rate of 15 °C/min and air flow rate of 20 ml/min. The thermogravimetric combustion properties i.e. small-scale was related to the large-scale, John Thompson’s fixed-bed reactor under the above condition. Thermal profiles were transformed into a differential function to reveal overlapped combustion events. The Coat-Redferns kinetic model was applied on the non-de-Ejesieme, O.V. PhD Chemistry (Research), Nelson Mandela Univ. Email: ejevit@yahoo.com , s211266744@live.nmmu.ac.za convoluted reactions set to obtain some of kinetic parameters. The Fraser-Suzuki equation was used to de-convolute the overlapped combustion. Then, rate law combined with Arrhenius equation was used to derive the activation energy E a and pre-exponential factor A, while the integral form of solid states reaction model, g (∝) was applied to deduce the oxidation mechanism. The composite formed a strong and partly renewable blend under controlled temperature conditions, unlike assorted dried biomass mixed with coal. Microalgae biomass upgraded the fuel and kinetics properties of ultra-fine coal more than what was expected from a linear combination. It released heat that promoted the oxidation mechanism of the discard coal. The main effect is that the “Coalgae®” is significantly (p = 0.0570) more reactive than the coal. The co-firing approach is partly renewable and contributes to the utilization of high and low-quality available discard ultra-fine coal. It advances the combustion of coal resources and reduces carbon dioxide, CO2 emission attributed to global warming as well as preserves the natural biomass sources. The combustion of “Coalgae® “will improve economy, environment, and health, heat, and electricity supply to the society.
- Full Text:
- Date Issued: 2018
An investigation of the movement of sediment through the Noordhoek headland bypass dunefield system at Cape Recife, South Africa
- Authors: Goosen, Gerrit Pieter
- Date: 2018
- Subjects: Sedimentation and deposition , Fluvial geomorphology Geomorphology Sand dunes -- Environmental aspects
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/22101 , vital:29840
- Description: A detailed study of the movement of sediment across the Cape Recife headland via the Noordhoek headland bypass dunefield was conducted. The Noordhoek HBD is important because of the environmental impacts anticipated on the sewerage works, settling ponds, and road to the Cape Recife lighthouse situated in the migration path of the dunefield to the ENE of its active boundary. The primary objective of the study was to investigate the movement of sediment in and through the Noordhoek HBD system. This study has provided sand transportation and dune migration rates by making use of various dune monitoring techniques. In doing so, useful predictions have been made as to when the settling ponds and the road to the lighthouse will be inundated. An indication has also been given as to how much sand moves through the system. Some key findings from this research included: the net migration direction of the Noordhoek HBD was found to be towards the east-north-east; the wind environment at the study area was classified as a high energy wind environment; this study has highlighted that various climatic factors such as rainfall and temperature influence the movement of sediment through dune systems; sediment transport was found to be directly related to the source area and topography; the central zone of the dunefield proved to be a groundwater recharge zone for the western and eastern zones; and the leading lobes of the migrating Noordhoek dunefield are gradually covering stabilising vegetation by pulses of dunes moving through. In this study, it was calculated that presently a total volume of about 26 000 m3 of sand is migrating into the vegetation at the leading lobes annually. If the Noordhoek HBD is left to run its natural course and migrate across the Cape Recife headland to the downwind beach, an approximate volume of 26 000 m3 of sand could be supplied to the downwind beach by this system. In doing so, it has the potential to play a role in replenishing some of the sand to Port Elizabeth’s eroded southern beaches via a natural process.
- Full Text:
- Date Issued: 2018
- Authors: Goosen, Gerrit Pieter
- Date: 2018
- Subjects: Sedimentation and deposition , Fluvial geomorphology Geomorphology Sand dunes -- Environmental aspects
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/22101 , vital:29840
- Description: A detailed study of the movement of sediment across the Cape Recife headland via the Noordhoek headland bypass dunefield was conducted. The Noordhoek HBD is important because of the environmental impacts anticipated on the sewerage works, settling ponds, and road to the Cape Recife lighthouse situated in the migration path of the dunefield to the ENE of its active boundary. The primary objective of the study was to investigate the movement of sediment in and through the Noordhoek HBD system. This study has provided sand transportation and dune migration rates by making use of various dune monitoring techniques. In doing so, useful predictions have been made as to when the settling ponds and the road to the lighthouse will be inundated. An indication has also been given as to how much sand moves through the system. Some key findings from this research included: the net migration direction of the Noordhoek HBD was found to be towards the east-north-east; the wind environment at the study area was classified as a high energy wind environment; this study has highlighted that various climatic factors such as rainfall and temperature influence the movement of sediment through dune systems; sediment transport was found to be directly related to the source area and topography; the central zone of the dunefield proved to be a groundwater recharge zone for the western and eastern zones; and the leading lobes of the migrating Noordhoek dunefield are gradually covering stabilising vegetation by pulses of dunes moving through. In this study, it was calculated that presently a total volume of about 26 000 m3 of sand is migrating into the vegetation at the leading lobes annually. If the Noordhoek HBD is left to run its natural course and migrate across the Cape Recife headland to the downwind beach, an approximate volume of 26 000 m3 of sand could be supplied to the downwind beach by this system. In doing so, it has the potential to play a role in replenishing some of the sand to Port Elizabeth’s eroded southern beaches via a natural process.
- Full Text:
- Date Issued: 2018
AP-MOVPE growth and characterisation of GaSb/GaAs quantum dots
- Authors: Tile, Ngcali
- Date: 2018
- Subjects: Quantum theory , Quantum electronics Quantum dots Semiconductors
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/36716 , vital:34047
- Description: GaSb/GaAs quantum dots (QD) were grown by atmospheric pressure (AP) metal-organic vapour phase epitaxy (MOVPE) using triethylgallium (TEGa), tertiarybutylarsine (tBAs) and trimethylantimony (TMSb) as gallium (Ga), arsenic (As) and (Sb) sources, respectively. The effect of AP-MOVPE growth parameters on the formation of GaSb QD structures on GaAs was studied. The formation of small, coherent GaSb dots on GaAs improved with decreasing V/III ratios, which were controlled through changing either the TMSb/TEGa ratio at a constant growth temperature or changing the growth temperature at a constant TMSb/TEGa ratio. The maximum effective V/III ratio for dot formation was 0.175. The dot density was more sensitive to growth time than to source mole fraction in the reactor, since time determines the amount of deposited material. The dot density increased with increasing growth time, while the shape and size of the dots were more sensitive to the source vapour mole fraction, which controls the growth rate. Lower mole fractions resulted in smaller sized dots with a more uniform distribution compared to higher mole fractions. Dome-shaped dots with densities as high as 4×1010 cm-2, average base length of 35 nm and average height of 5 nm were achieved. Capping of GaSb QDs at high temperatures caused flattening and the formation of a thin, inhomogeneous GaSb layer inside GaAs. No obvious QD photoluminescence (PL) peak was detected for these samples. A two stage process for capping the dots (involving growth of a low temperature GaAs cap, followed by a high temperature cap) led to the retention of the dot-like features in/on a wetting layer (WL) of GaSb and distinct PL peaks for both the QDs and WL. An increase in excitation power during PL measurements for this particular sample caused the QD and WL peaks to shift to higher energies. This is attributed to electrostatic band bending, leading to triangular potential wells, typical for type II band alignment between GaAs and strained GaSb. Variable temperature PL measurements showed the decrease in the intensity of the WL peak to be faster than that of the QD peak as the measurement temperature increased. A detailed high resolution transmission electron microscopy analysis was performed to study the morphology and chemical interaction between GaAs and GaSb regions for capped GaSb/GaAs QDs. The capped dots had dimensions similar to those of uncapped dots and had a higher concentration of Sb at their center, with the periphery being intermixed with GaAs. Measurement of lattice strain performed inside these dots revealed the strain to be distributed inhomogenously throughout the dot area. The effect of GaAs host matrix on excitonic behaviour in AP-MOVPE grown GaSb/GaAs quantum dots was investigated. Room temperature (RT) PL emission was achieved from a single layer of quantum dots by controlling the GaAs host matrix growth temperature. These samples were prepared using a GaSb dot growth temperature of 530 °C, followed by growth of a thin GaAs ‘cold’ cap, before depositing the final part of the GaAs capping layer at either 550 °C, 600 °C or 650 °C. PL measurements at 10 K revealed QD emission peaks for all the samples at around 1.1 eV. However, variable temperature PL revealed different thermal quenching rates of the emission, with the rates of quenching reduced with increasing GaAs growth temperature. This was ascribed to reduced defect densities in GaAs grown at higher temperature, which resulted in QD emission even at RT. This RT emission peaked at approximately 1 eV. The hole localisation energy determined for these samples at RT was approximately 470 meV.
- Full Text:
- Date Issued: 2018
- Authors: Tile, Ngcali
- Date: 2018
- Subjects: Quantum theory , Quantum electronics Quantum dots Semiconductors
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/36716 , vital:34047
- Description: GaSb/GaAs quantum dots (QD) were grown by atmospheric pressure (AP) metal-organic vapour phase epitaxy (MOVPE) using triethylgallium (TEGa), tertiarybutylarsine (tBAs) and trimethylantimony (TMSb) as gallium (Ga), arsenic (As) and (Sb) sources, respectively. The effect of AP-MOVPE growth parameters on the formation of GaSb QD structures on GaAs was studied. The formation of small, coherent GaSb dots on GaAs improved with decreasing V/III ratios, which were controlled through changing either the TMSb/TEGa ratio at a constant growth temperature or changing the growth temperature at a constant TMSb/TEGa ratio. The maximum effective V/III ratio for dot formation was 0.175. The dot density was more sensitive to growth time than to source mole fraction in the reactor, since time determines the amount of deposited material. The dot density increased with increasing growth time, while the shape and size of the dots were more sensitive to the source vapour mole fraction, which controls the growth rate. Lower mole fractions resulted in smaller sized dots with a more uniform distribution compared to higher mole fractions. Dome-shaped dots with densities as high as 4×1010 cm-2, average base length of 35 nm and average height of 5 nm were achieved. Capping of GaSb QDs at high temperatures caused flattening and the formation of a thin, inhomogeneous GaSb layer inside GaAs. No obvious QD photoluminescence (PL) peak was detected for these samples. A two stage process for capping the dots (involving growth of a low temperature GaAs cap, followed by a high temperature cap) led to the retention of the dot-like features in/on a wetting layer (WL) of GaSb and distinct PL peaks for both the QDs and WL. An increase in excitation power during PL measurements for this particular sample caused the QD and WL peaks to shift to higher energies. This is attributed to electrostatic band bending, leading to triangular potential wells, typical for type II band alignment between GaAs and strained GaSb. Variable temperature PL measurements showed the decrease in the intensity of the WL peak to be faster than that of the QD peak as the measurement temperature increased. A detailed high resolution transmission electron microscopy analysis was performed to study the morphology and chemical interaction between GaAs and GaSb regions for capped GaSb/GaAs QDs. The capped dots had dimensions similar to those of uncapped dots and had a higher concentration of Sb at their center, with the periphery being intermixed with GaAs. Measurement of lattice strain performed inside these dots revealed the strain to be distributed inhomogenously throughout the dot area. The effect of GaAs host matrix on excitonic behaviour in AP-MOVPE grown GaSb/GaAs quantum dots was investigated. Room temperature (RT) PL emission was achieved from a single layer of quantum dots by controlling the GaAs host matrix growth temperature. These samples were prepared using a GaSb dot growth temperature of 530 °C, followed by growth of a thin GaAs ‘cold’ cap, before depositing the final part of the GaAs capping layer at either 550 °C, 600 °C or 650 °C. PL measurements at 10 K revealed QD emission peaks for all the samples at around 1.1 eV. However, variable temperature PL revealed different thermal quenching rates of the emission, with the rates of quenching reduced with increasing GaAs growth temperature. This was ascribed to reduced defect densities in GaAs grown at higher temperature, which resulted in QD emission even at RT. This RT emission peaked at approximately 1 eV. The hole localisation energy determined for these samples at RT was approximately 470 meV.
- Full Text:
- Date Issued: 2018
Application of hidden Markov models and their extensions to animal movement data
- Authors: Van Niekerk, Bracken
- Date: 2018
- Subjects: Markov processes Animal locomotion Time-series analysis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/23835 , vital:30624
- Description: Hidden Markov Models (HMMs) have become increasingly popular in animal movement studies as they provide a flexible modelling approach and take the correlation between successive observations into account. They can segment the movement paths into latent states, which can be considered as rough proxies for the behaviours of the animals. This study comprises of two sections, both involving the application of HMMs to large terrestrial mammal movement data. Usually step lengths representing the displacement distances between successive observations, turning angles measuring the tortuosity, or a bivariate input of both variables are used as inputs in the models. It has been found in the literature that the turning angle is either included in the modelling process or it is excluded without much justification for doing so. The first part of this study investigates the nfluence of the turning angle on the model output and resultant interpretations of the HMMs when modelling the trajectories of large terrestrial mammals in southern Africa. Results revealed at different time scales, and for both predator and herbivore species in this study, that the turning angle does not influence the state allocation of the HMMs, which is the main output in terms of interpreting the behaviours of the animals. It is thought in most cases that the inclusion of the turning angle overcomplicates the models unnecessarily without contributing any additional information in terms of the behavioural interpretations or improving the overall fit of the models. This was found for the variety of movements of the species under observation in this study. The second part of this study attempts to validate the state allocation of the HMMs fitted to eland trajectories in the Greater Addo Elephant National Park in the Eastern Cape, with the use of camera trap data. This presented a unique opportunity as this type of data is mainly used for abundance or capture-recapture studies, and the HMMs are rarely validated as the true behaviours of the animals are seldom known. Results revealed that the same diel patterns were detected by the HMMs that were shown by the classified camera trap data. Direct comparisons of the observations where the dates and times matched for the telemetry and camera trap data could be done in several rare instances, which revealed many similarities. Although it was not an ideal comparison, the camera trap data provided a rough validation of the state allocation of the HMMs used in the study.
- Full Text:
- Date Issued: 2018
- Authors: Van Niekerk, Bracken
- Date: 2018
- Subjects: Markov processes Animal locomotion Time-series analysis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/23835 , vital:30624
- Description: Hidden Markov Models (HMMs) have become increasingly popular in animal movement studies as they provide a flexible modelling approach and take the correlation between successive observations into account. They can segment the movement paths into latent states, which can be considered as rough proxies for the behaviours of the animals. This study comprises of two sections, both involving the application of HMMs to large terrestrial mammal movement data. Usually step lengths representing the displacement distances between successive observations, turning angles measuring the tortuosity, or a bivariate input of both variables are used as inputs in the models. It has been found in the literature that the turning angle is either included in the modelling process or it is excluded without much justification for doing so. The first part of this study investigates the nfluence of the turning angle on the model output and resultant interpretations of the HMMs when modelling the trajectories of large terrestrial mammals in southern Africa. Results revealed at different time scales, and for both predator and herbivore species in this study, that the turning angle does not influence the state allocation of the HMMs, which is the main output in terms of interpreting the behaviours of the animals. It is thought in most cases that the inclusion of the turning angle overcomplicates the models unnecessarily without contributing any additional information in terms of the behavioural interpretations or improving the overall fit of the models. This was found for the variety of movements of the species under observation in this study. The second part of this study attempts to validate the state allocation of the HMMs fitted to eland trajectories in the Greater Addo Elephant National Park in the Eastern Cape, with the use of camera trap data. This presented a unique opportunity as this type of data is mainly used for abundance or capture-recapture studies, and the HMMs are rarely validated as the true behaviours of the animals are seldom known. Results revealed that the same diel patterns were detected by the HMMs that were shown by the classified camera trap data. Direct comparisons of the observations where the dates and times matched for the telemetry and camera trap data could be done in several rare instances, which revealed many similarities. Although it was not an ideal comparison, the camera trap data provided a rough validation of the state allocation of the HMMs used in the study.
- Full Text:
- Date Issued: 2018
Approaches to detecting and assessing patterns, processes and responses to change in South African estuaries
- Authors: Van Niekerk, Lara
- Date: 2018
- Subjects: Estuaries -- South Africa , Climatic changes -- South Africa
- Language: English
- Type: Thesis , Doctoral , PHD
- Identifier: http://hdl.handle.net/10948/45491 , vital:38621
- Description: The research presented indicates deep knowledge of estuary pattern-process-function across a broad range of estuary types. This study successfully developed and applied approaches to detect change at varying temporal and spatial scales in South African estuaries. This assessment was based on the physical characteristics of estuaries and predicted or measured change in the drivers of estuary health. This is the first study in the country to review and synthesise the vulnerability of South African estuaries to Climate Change on a regional scale. Through sound scientific approaches this research has advanced our knowledge on complex estuarine systems and made a significant contribution globally to approaches for the conservation and management of estuaries.
- Full Text:
- Date Issued: 2018
- Authors: Van Niekerk, Lara
- Date: 2018
- Subjects: Estuaries -- South Africa , Climatic changes -- South Africa
- Language: English
- Type: Thesis , Doctoral , PHD
- Identifier: http://hdl.handle.net/10948/45491 , vital:38621
- Description: The research presented indicates deep knowledge of estuary pattern-process-function across a broad range of estuary types. This study successfully developed and applied approaches to detect change at varying temporal and spatial scales in South African estuaries. This assessment was based on the physical characteristics of estuaries and predicted or measured change in the drivers of estuary health. This is the first study in the country to review and synthesise the vulnerability of South African estuaries to Climate Change on a regional scale. Through sound scientific approaches this research has advanced our knowledge on complex estuarine systems and made a significant contribution globally to approaches for the conservation and management of estuaries.
- Full Text:
- Date Issued: 2018
Assessing growth response patterns of microalgae to varying environmental conditions using sediments from ephemeral wetlands
- Authors: Mazwane, Sixolile
- Date: 2018
- Subjects: Microalgae -- South Africa , Wetland conservation -- South Africa Landscape ecology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/22398 , vital:29966
- Description: Ephemeral wetlands serve as habitats for different fauna and flora. Microalgae make up a bulk of primary production in newly inundated wetlands and have a big influence on the aquatic community structure. As ephemeral wetlands have cyclical drying and wetting phases, algal species found in these habitats have evolved adaptations (i.e. dormancy and cysts) to survive during dry periods and become productive upon inundation. Algae have been used as ecological indicators in many aquatic ecosystems including wetlands, particularly associated with water quality and with varying inundation states. Whilst temperature and water level have been shown to affect microalgal biomass independently, this study aims to assess the effects of these two factors simultaneously on microalgal biomass, species diversity and community changes. The aim of the study was to investigate microalgal dynamics using two ephemeral wetlands in the Nelson Mandela Bay Municipality. The growth response patterns of microalgal communities to varying temperatures and inundation levels through experiments using dry temporary wetland sediments was also assessed. Dry sediments were collected from two depression wetlands with different sediment characteristics (1592 and Elephant Wallow (EW)). The study consisted of replicated treatments with three different surface area: volume ratios (SA:V) (Low surface area: volume (LSAV), Medium (MSAV) and High (HSAV)), inundated with distilled water. The microcosms were placed inside a Conviron environmental growth chamber and illuminated at between 106 to 138 μmol.m-2s-1, with a 12:12 light-dark cycle at constant temperatures of 12 °C (mean winter) and 22 °C (mean summer). Physicochemical data were recorded, and biological samples were collected every 4 days over a 28-day inundation period. In the field, Electrical conductivity (EC) and pH showed a gradual increase over the inundation period. The systems were well oxygenated (6-10 mg L-1). Overall, phytoplankton biomass in the field was ~10 μg L-1 whereas benthic biomass (MPB) was significantly higher 10 – 300 mg L-1. Within the experiments, the phytoplankton biomass showed a pattern while MPB biomass increased gradually for both experiments. There were no significant (p>0.05) differences between the 1592 and EW phytoplankton biomass. However, the MPB biomass showed significant (p<0.05) differences between the two sediments (EW high, 1592 low) and the experiments, respectively. In the winter experiment, the 1592 sediment had high phytoplankton biomass compared to EW, the reverse was observed for the MPB biomass. In summer experiment, similar results were observed in terms of phytoplankton biomass. For the MPBs, 1592 had greater biomass for all treatments compared to EW. The phytoplankton community for both field samples and experiments was dominated by chlorophytes (>50 %), followed by cyanophytes and euglenophytes (with cryptophytes in summer experiment) for both field and experiments. The MPB community was dominated by bacillariophytes (55 %) and chlorophytes (25 %) in the 1592 sediments and this was also the case with EW sediments bacillariophytes (70 %), although cyanophytes (15 %) made up the remainder of the MPB community. The 1592 sediments supported higher diatom abundances under the HSAV compared to the same treatment from the EW wetland suggesting that possibly grain size or texture might be responsible. In contrast, sediments from EW under LSAV conditions showed higher diatom cell numbers possibly indicating that increased water depth has the propensity to support greater diatom assemblages compared with the same water level for sediments from 1592. The results indicate that microalgae community is influenced by sediment type more than it is by water level. From this study it was also established that microalgae were able to reemerge from their dormancy state upon inundation and that tank experiments were successful in simulating natural ephemeral wetland conditions. The findings from this study will add to the available baseline data on microalgal dynamics in the ephemeral wetlands in South Africa, especially in semi-arid areas. This information can be valuable in enhancing our understanding regarding the role of microalgae in ephemeral wetlands in order to conserve them.
- Full Text:
- Date Issued: 2018
- Authors: Mazwane, Sixolile
- Date: 2018
- Subjects: Microalgae -- South Africa , Wetland conservation -- South Africa Landscape ecology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/22398 , vital:29966
- Description: Ephemeral wetlands serve as habitats for different fauna and flora. Microalgae make up a bulk of primary production in newly inundated wetlands and have a big influence on the aquatic community structure. As ephemeral wetlands have cyclical drying and wetting phases, algal species found in these habitats have evolved adaptations (i.e. dormancy and cysts) to survive during dry periods and become productive upon inundation. Algae have been used as ecological indicators in many aquatic ecosystems including wetlands, particularly associated with water quality and with varying inundation states. Whilst temperature and water level have been shown to affect microalgal biomass independently, this study aims to assess the effects of these two factors simultaneously on microalgal biomass, species diversity and community changes. The aim of the study was to investigate microalgal dynamics using two ephemeral wetlands in the Nelson Mandela Bay Municipality. The growth response patterns of microalgal communities to varying temperatures and inundation levels through experiments using dry temporary wetland sediments was also assessed. Dry sediments were collected from two depression wetlands with different sediment characteristics (1592 and Elephant Wallow (EW)). The study consisted of replicated treatments with three different surface area: volume ratios (SA:V) (Low surface area: volume (LSAV), Medium (MSAV) and High (HSAV)), inundated with distilled water. The microcosms were placed inside a Conviron environmental growth chamber and illuminated at between 106 to 138 μmol.m-2s-1, with a 12:12 light-dark cycle at constant temperatures of 12 °C (mean winter) and 22 °C (mean summer). Physicochemical data were recorded, and biological samples were collected every 4 days over a 28-day inundation period. In the field, Electrical conductivity (EC) and pH showed a gradual increase over the inundation period. The systems were well oxygenated (6-10 mg L-1). Overall, phytoplankton biomass in the field was ~10 μg L-1 whereas benthic biomass (MPB) was significantly higher 10 – 300 mg L-1. Within the experiments, the phytoplankton biomass showed a pattern while MPB biomass increased gradually for both experiments. There were no significant (p>0.05) differences between the 1592 and EW phytoplankton biomass. However, the MPB biomass showed significant (p<0.05) differences between the two sediments (EW high, 1592 low) and the experiments, respectively. In the winter experiment, the 1592 sediment had high phytoplankton biomass compared to EW, the reverse was observed for the MPB biomass. In summer experiment, similar results were observed in terms of phytoplankton biomass. For the MPBs, 1592 had greater biomass for all treatments compared to EW. The phytoplankton community for both field samples and experiments was dominated by chlorophytes (>50 %), followed by cyanophytes and euglenophytes (with cryptophytes in summer experiment) for both field and experiments. The MPB community was dominated by bacillariophytes (55 %) and chlorophytes (25 %) in the 1592 sediments and this was also the case with EW sediments bacillariophytes (70 %), although cyanophytes (15 %) made up the remainder of the MPB community. The 1592 sediments supported higher diatom abundances under the HSAV compared to the same treatment from the EW wetland suggesting that possibly grain size or texture might be responsible. In contrast, sediments from EW under LSAV conditions showed higher diatom cell numbers possibly indicating that increased water depth has the propensity to support greater diatom assemblages compared with the same water level for sediments from 1592. The results indicate that microalgae community is influenced by sediment type more than it is by water level. From this study it was also established that microalgae were able to reemerge from their dormancy state upon inundation and that tank experiments were successful in simulating natural ephemeral wetland conditions. The findings from this study will add to the available baseline data on microalgal dynamics in the ephemeral wetlands in South Africa, especially in semi-arid areas. This information can be valuable in enhancing our understanding regarding the role of microalgae in ephemeral wetlands in order to conserve them.
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- Date Issued: 2018