Macrobenthic community structure across an inter- and subtidal gradient in a mangrove estuary
- Authors: Groenewald, Christoff J
- Date: 2010
- Subjects: Mangrove ecology -- South Africa -- Mngazana Estuary , Estuarine ecology -- South Africa -- Mngazana Estuary , Benthos -- South Africa -- Mngazana Estuary
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10695 , http://hdl.handle.net/10948/1240 , Mangrove ecology -- South Africa -- Mngazana Estuary , Estuarine ecology -- South Africa -- Mngazana Estuary , Benthos -- South Africa -- Mngazana Estuary
- Description: Macrozoobenthic community structure and composition was investigated along a subtidal-intertidal gradient in the Mngazana Estuary. Six transects were sampled between the spring high water mark (HWST) and the bottom of the river channel in the lower estuary. Fifteen replicate samples were collected along each transect using a Van Veen type grab (211 cm2 bite) during each of three sampling sessions. Samples were sieved through a 500 μm mesh bag and the invertebrates stored in bottles for further analysis in the laboratory. Additional grab samples were collected for sediment particle size analysis and organic matter. Physical variables measured at each transect included: salinity, temperature, dissolved oxygen, depth, pH, percentage mud, organic content and turbidity. Sediment compactness was measured at all intertidal transects and additional sediment samples were collected at mid shore and high shore transects for percentage water content analysis. A total of 104 species were recorded along the intertidal-subtidal gradient in the sampling area. Species richness was higher in the subtidal zone compared to the intertidal zone and polychaetes numerically dominated the macrozoobenthic community at most transects, during all three sessions. At high shore transects the community was characterised by having fewer species, consisting mostly of brachyurans, polychaetes and gastropods. Shannon diversity index (H’) was generally higher for subtidal transects (x¯ = 2.3; range: 2.8 to 1) than for intertidal transects (x¯ = 1.4; range: 2.2 to 0.6) indicating that the distribution of individuals among species in the intertidal zone experienced greater variability. Results for Hill’s numbers followed the same trend as Shannon diversity with subtidal communities mostly consisting of abundant species followed by very abundant species. Intertidal communities generally exhibited lower numbers of abundant and very abundant species. Sedimentary characteristics played a major role in structuring benthic communities in comparison to other physico-chemical variables. Organic content and mud content of the substrate were identified as important factors influencing community patterns observed along the subtidal-intertidal gradient. In addition, sediment compactness and water content of the substrate was found to influence intertidal community structure. Subtidal community structure possibly had a greater dependence on seasonal variations in abiotic and/or biotic factors. Cluster dendrograms used in conjunction with MDS ordination mapping revealed that macrozoobenthic communities were generally distinct between high shore intertidal transects iii and subtidal transects. Most species exhibited a broad spatial distribution along the subtidal-intertidal gradient with mid and high shore transects being the exception. Most species also exhibited marked shifts in abundance and this was especially noticeable at the transition between the subtidal and intertidal zone. Two polychaete species, Prionospio sexoculata and Capitella capitata, were very abundant species and featured amongst the most numerically dominant species collected during each sampling session.
- Full Text:
- Date Issued: 2010
- Authors: Groenewald, Christoff J
- Date: 2010
- Subjects: Mangrove ecology -- South Africa -- Mngazana Estuary , Estuarine ecology -- South Africa -- Mngazana Estuary , Benthos -- South Africa -- Mngazana Estuary
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10695 , http://hdl.handle.net/10948/1240 , Mangrove ecology -- South Africa -- Mngazana Estuary , Estuarine ecology -- South Africa -- Mngazana Estuary , Benthos -- South Africa -- Mngazana Estuary
- Description: Macrozoobenthic community structure and composition was investigated along a subtidal-intertidal gradient in the Mngazana Estuary. Six transects were sampled between the spring high water mark (HWST) and the bottom of the river channel in the lower estuary. Fifteen replicate samples were collected along each transect using a Van Veen type grab (211 cm2 bite) during each of three sampling sessions. Samples were sieved through a 500 μm mesh bag and the invertebrates stored in bottles for further analysis in the laboratory. Additional grab samples were collected for sediment particle size analysis and organic matter. Physical variables measured at each transect included: salinity, temperature, dissolved oxygen, depth, pH, percentage mud, organic content and turbidity. Sediment compactness was measured at all intertidal transects and additional sediment samples were collected at mid shore and high shore transects for percentage water content analysis. A total of 104 species were recorded along the intertidal-subtidal gradient in the sampling area. Species richness was higher in the subtidal zone compared to the intertidal zone and polychaetes numerically dominated the macrozoobenthic community at most transects, during all three sessions. At high shore transects the community was characterised by having fewer species, consisting mostly of brachyurans, polychaetes and gastropods. Shannon diversity index (H’) was generally higher for subtidal transects (x¯ = 2.3; range: 2.8 to 1) than for intertidal transects (x¯ = 1.4; range: 2.2 to 0.6) indicating that the distribution of individuals among species in the intertidal zone experienced greater variability. Results for Hill’s numbers followed the same trend as Shannon diversity with subtidal communities mostly consisting of abundant species followed by very abundant species. Intertidal communities generally exhibited lower numbers of abundant and very abundant species. Sedimentary characteristics played a major role in structuring benthic communities in comparison to other physico-chemical variables. Organic content and mud content of the substrate were identified as important factors influencing community patterns observed along the subtidal-intertidal gradient. In addition, sediment compactness and water content of the substrate was found to influence intertidal community structure. Subtidal community structure possibly had a greater dependence on seasonal variations in abiotic and/or biotic factors. Cluster dendrograms used in conjunction with MDS ordination mapping revealed that macrozoobenthic communities were generally distinct between high shore intertidal transects iii and subtidal transects. Most species exhibited a broad spatial distribution along the subtidal-intertidal gradient with mid and high shore transects being the exception. Most species also exhibited marked shifts in abundance and this was especially noticeable at the transition between the subtidal and intertidal zone. Two polychaete species, Prionospio sexoculata and Capitella capitata, were very abundant species and featured amongst the most numerically dominant species collected during each sampling session.
- Full Text:
- Date Issued: 2010
Macrophyte phenology in a temporarily open/closed Estuary compared with a permanently open Estuary
- Authors: Vromans, Deborah Claire
- Date: 2010
- Subjects: Estuarine ecology -- South Africa -- East Kleinemonde Estuary , Aquatic plants -- South Africa -- East Kleinemonde Estuary
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10612 , http://hdl.handle.net/10948/1393 , Estuarine ecology -- South Africa -- East Kleinemonde Estuary , Aquatic plants -- South Africa -- East Kleinemonde Estuary
- Description: Temporarily open/closed estuaries (TOCEs) are unpredictable environments that change in response to mouth condition, which is influenced by freshwater flooding or sea storm surges. The aim of the study was to determine whether macrophyte phenology in a TOCE was event driven rather than cyclically predictable and if it differed from permanently open estuaries (POEs). Macrophyte growth and flowering phenology in response to environmental conditions was investigated in the East Kleinemonde Estuary (TOCE) and the Kowie Estuary (POE) along the eastern coastline of South Africa. The lack of freshwater flooding due to low rainfall coupled with several overwash events resulted in a prolonged period of mouth closure from September 2008 to the end of this study period in 2010. This in turn caused the inundation of the supratidal and intertidal habitats, high water level (> 1.57 m amsl) and high salinity (30 - 42 ppt) in the TOCE. Principle Components Analysis showed that high water level and reduced sediments were the most significant environmental factors affecting macrophyte phenology. Macrophyte phenology in the POE was primarily driven by temperature, sediment redox potential and salinity. The saline high water level and reduced sediment significantly reduced macrophyte cover in all habitats in the TOCE. Macrophytes in the POE maintained high cover abundance due to seasonal re-growth compared to the TOCE where cover declined over the sampling period due to the high water level. Subsequent to water level dropping by as little as 11 - 20 cm in the TOCE, the intertidal species Sarcocornia tegetaria and Salicornia meyeriana completed their life-cycles and produced viable seeds within four and three months of germinating respectively. In contrast, the Sarcocornia hybrid and S. meyeriana in the POE took longer to complete their life-cycles, namely seven and nine months respectively, while S. tegataria did not germinate in situ but reproduced vegetatively despite producing seed. In the TOCE, the submerged species Ruppia cirrhosa and Chara vulgaris completed their life-cycles within five and three months and produced a maximum of 26 242 and 196 998 seeds m-2 respectively. Due to high water level and prolonged inundation, the reproductive periods were shorter for the intertidal and reed and sedge species in the TOCE compared to the POE. Seed output during the two reproduction periods varied between the two estuaries. Sarcocornia decumbens and S. tegetaria produced a substantially higher number of seeds in the TOCE compared to the POE, namely 0 - 102 847 versus 20 661 - 48 576 seeds m-²; and 7 001 - 45 542 versus 1 587 – 16 958 seeds m-² respectively. Seed output in the TOCE was significantly higher in S. tegetaria during the second reproduction period despite the significantly lower plant cover, which may be a function of the stressful environment in the TOCE. Seed production of S. meyeriana was significantly higher in the POE compared to the TOCE, with 264 224 - 640 292 compared with 24 050 - 27 643 seeds m-², due to higher plant cover in the POE. The research suggests that macrophyte phenology in the TOCE was significantly influenced by mouth condition. Further, macrophytes were able to demonstrate considerable phenotypic plasticity in response to changing and unfavourable environmental conditions. These data can be used in mouth management plans and freshwater requirement studies in TOCEs to ensure that macrophytes can complete their life-cycles and produce viable seeds for the safeguarding of habitat persistence and ecological processes. In impacted estuaries where artificial mouth opening is practised and the macrophytes have been severely degraded or extirpated, management should ensure that the intertidal and supratidal habitats are not inundated during peak flowering and seed production periods i.e. late spring to early autumn (November to March).
- Full Text:
- Date Issued: 2010
- Authors: Vromans, Deborah Claire
- Date: 2010
- Subjects: Estuarine ecology -- South Africa -- East Kleinemonde Estuary , Aquatic plants -- South Africa -- East Kleinemonde Estuary
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10612 , http://hdl.handle.net/10948/1393 , Estuarine ecology -- South Africa -- East Kleinemonde Estuary , Aquatic plants -- South Africa -- East Kleinemonde Estuary
- Description: Temporarily open/closed estuaries (TOCEs) are unpredictable environments that change in response to mouth condition, which is influenced by freshwater flooding or sea storm surges. The aim of the study was to determine whether macrophyte phenology in a TOCE was event driven rather than cyclically predictable and if it differed from permanently open estuaries (POEs). Macrophyte growth and flowering phenology in response to environmental conditions was investigated in the East Kleinemonde Estuary (TOCE) and the Kowie Estuary (POE) along the eastern coastline of South Africa. The lack of freshwater flooding due to low rainfall coupled with several overwash events resulted in a prolonged period of mouth closure from September 2008 to the end of this study period in 2010. This in turn caused the inundation of the supratidal and intertidal habitats, high water level (> 1.57 m amsl) and high salinity (30 - 42 ppt) in the TOCE. Principle Components Analysis showed that high water level and reduced sediments were the most significant environmental factors affecting macrophyte phenology. Macrophyte phenology in the POE was primarily driven by temperature, sediment redox potential and salinity. The saline high water level and reduced sediment significantly reduced macrophyte cover in all habitats in the TOCE. Macrophytes in the POE maintained high cover abundance due to seasonal re-growth compared to the TOCE where cover declined over the sampling period due to the high water level. Subsequent to water level dropping by as little as 11 - 20 cm in the TOCE, the intertidal species Sarcocornia tegetaria and Salicornia meyeriana completed their life-cycles and produced viable seeds within four and three months of germinating respectively. In contrast, the Sarcocornia hybrid and S. meyeriana in the POE took longer to complete their life-cycles, namely seven and nine months respectively, while S. tegataria did not germinate in situ but reproduced vegetatively despite producing seed. In the TOCE, the submerged species Ruppia cirrhosa and Chara vulgaris completed their life-cycles within five and three months and produced a maximum of 26 242 and 196 998 seeds m-2 respectively. Due to high water level and prolonged inundation, the reproductive periods were shorter for the intertidal and reed and sedge species in the TOCE compared to the POE. Seed output during the two reproduction periods varied between the two estuaries. Sarcocornia decumbens and S. tegetaria produced a substantially higher number of seeds in the TOCE compared to the POE, namely 0 - 102 847 versus 20 661 - 48 576 seeds m-²; and 7 001 - 45 542 versus 1 587 – 16 958 seeds m-² respectively. Seed output in the TOCE was significantly higher in S. tegetaria during the second reproduction period despite the significantly lower plant cover, which may be a function of the stressful environment in the TOCE. Seed production of S. meyeriana was significantly higher in the POE compared to the TOCE, with 264 224 - 640 292 compared with 24 050 - 27 643 seeds m-², due to higher plant cover in the POE. The research suggests that macrophyte phenology in the TOCE was significantly influenced by mouth condition. Further, macrophytes were able to demonstrate considerable phenotypic plasticity in response to changing and unfavourable environmental conditions. These data can be used in mouth management plans and freshwater requirement studies in TOCEs to ensure that macrophytes can complete their life-cycles and produce viable seeds for the safeguarding of habitat persistence and ecological processes. In impacted estuaries where artificial mouth opening is practised and the macrophytes have been severely degraded or extirpated, management should ensure that the intertidal and supratidal habitats are not inundated during peak flowering and seed production periods i.e. late spring to early autumn (November to March).
- Full Text:
- Date Issued: 2010
Metabolic energy relations in the Eastern Cape Angulate Tortoise (Chersina Anguluta)
- Authors: Setlalekgomo, Mpho Rinah
- Date: 2010
- Subjects: Eastern Cape angulate Tortoise , Oxygen consumption (Physiology)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10690 , http://hdl.handle.net/10948/1400 , Eastern Cape angulate Tortoise , Oxygen consumption (Physiology)
- Description: The daily oxygen consumption (VO2) pattern, the effects of varying ambient temperatures, season and mass on the resting oxygen consumption (RVO2) of Chersina angulata of the Eastern Cape were investigated. The RVO2 was measured using flow-through respirometry and specific resting oxygen consumption (sRVO2) calculated. To determine the daily pattern in the VO2 of C. angulata, the tortoises were acclimated in an environmentally controlled room (ECR) to an ambient temperature of 26 ± 1°C and a light regime of 14 hours of light and 10 hours of darkness (14L:10D) for at least a week prior to the RVO2 measurements. The RVO2 was measured at a constant temperature of 26 ± 1°C, and at three different light regimes, namely: 14L:10D, constant darkness (DD) and constant light (LL). There were no significant effects of mass or gender on the sRVO2 of the tortoises used. Rhythms in the sRVO2 were detected under all three light regimes. The amplitudes of the rhythm were largest at 14L:10D, followed by DD and smallest at LL regime. The persistence of the rhythmic pattern under constant conditions suggests the existence of an endogenous circadian rhythm in the sRVO2 for adult C. angulata. To test for the effect of ambient temperature on the sRVO2 of adult C. angulata, the tortoises were acclimated to 22 ± 1°C and a 14L:10D light regime prior to the RVO2 measurements. RVO2 was measured at eight experimental temperatures; 14°C, 18°C, 22°C, 26°C, 30°C, 35°C, 38°C and 40°C. The sRVO2 was not influenced by gender and increased with experimental temperatures, but this did not happen consistently over the whole range of temperatures tested. A plateau, possibly a thermal preferendum zone, was detected within the temperature range of 26 - 38°C. Determination of seasonal effect on the sRVO2 of adult C. angulata was accomplished by acclimating tortoises to standard summer and winter conditions. Seasonal effects were tested in the appropriate seasons. Winter experiments were conducted in winter and summer experiments conducted in summer. The RVO2 was measured at experimental temperature 14°C, 18°C and 22°C. In addition RVO2 of iv winter-acclimated tortoises was also measured at 10°C. The sRVO2 increased significantly with increasing temperature within the temperature range tested. No distinct pattern was observed in the seasonal acclimation of adult C. angulata. The metabolic rate-temperature curves of the summer and the winter-acclimated tortoises cross each other. Season and temperature had no significant effects on the mass-scaling exponent of the sRVO2. The exponent ranged from 0.48 to 0.73 within the temperature range of 22 - 38°C. Below and above this temperature range, the exponent ranged from 1.47 to 1.67. An inverse relationship was observed between sRVO2 and body mass over the temperature range of 22 - 38°C. At 14°C and 18°C, sRVO2 increased with body mass, while at 10°C and at 40°C the slope was 1.01.
- Full Text:
- Date Issued: 2010
- Authors: Setlalekgomo, Mpho Rinah
- Date: 2010
- Subjects: Eastern Cape angulate Tortoise , Oxygen consumption (Physiology)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10690 , http://hdl.handle.net/10948/1400 , Eastern Cape angulate Tortoise , Oxygen consumption (Physiology)
- Description: The daily oxygen consumption (VO2) pattern, the effects of varying ambient temperatures, season and mass on the resting oxygen consumption (RVO2) of Chersina angulata of the Eastern Cape were investigated. The RVO2 was measured using flow-through respirometry and specific resting oxygen consumption (sRVO2) calculated. To determine the daily pattern in the VO2 of C. angulata, the tortoises were acclimated in an environmentally controlled room (ECR) to an ambient temperature of 26 ± 1°C and a light regime of 14 hours of light and 10 hours of darkness (14L:10D) for at least a week prior to the RVO2 measurements. The RVO2 was measured at a constant temperature of 26 ± 1°C, and at three different light regimes, namely: 14L:10D, constant darkness (DD) and constant light (LL). There were no significant effects of mass or gender on the sRVO2 of the tortoises used. Rhythms in the sRVO2 were detected under all three light regimes. The amplitudes of the rhythm were largest at 14L:10D, followed by DD and smallest at LL regime. The persistence of the rhythmic pattern under constant conditions suggests the existence of an endogenous circadian rhythm in the sRVO2 for adult C. angulata. To test for the effect of ambient temperature on the sRVO2 of adult C. angulata, the tortoises were acclimated to 22 ± 1°C and a 14L:10D light regime prior to the RVO2 measurements. RVO2 was measured at eight experimental temperatures; 14°C, 18°C, 22°C, 26°C, 30°C, 35°C, 38°C and 40°C. The sRVO2 was not influenced by gender and increased with experimental temperatures, but this did not happen consistently over the whole range of temperatures tested. A plateau, possibly a thermal preferendum zone, was detected within the temperature range of 26 - 38°C. Determination of seasonal effect on the sRVO2 of adult C. angulata was accomplished by acclimating tortoises to standard summer and winter conditions. Seasonal effects were tested in the appropriate seasons. Winter experiments were conducted in winter and summer experiments conducted in summer. The RVO2 was measured at experimental temperature 14°C, 18°C and 22°C. In addition RVO2 of iv winter-acclimated tortoises was also measured at 10°C. The sRVO2 increased significantly with increasing temperature within the temperature range tested. No distinct pattern was observed in the seasonal acclimation of adult C. angulata. The metabolic rate-temperature curves of the summer and the winter-acclimated tortoises cross each other. Season and temperature had no significant effects on the mass-scaling exponent of the sRVO2. The exponent ranged from 0.48 to 0.73 within the temperature range of 22 - 38°C. Below and above this temperature range, the exponent ranged from 1.47 to 1.67. An inverse relationship was observed between sRVO2 and body mass over the temperature range of 22 - 38°C. At 14°C and 18°C, sRVO2 increased with body mass, while at 10°C and at 40°C the slope was 1.01.
- Full Text:
- Date Issued: 2010
Microalgal biomass and distribution in the Mngazi and Mngazana Estuaries
- Ngesi, Hlekani Ntombizakithi
- Authors: Ngesi, Hlekani Ntombizakithi
- Date: 2010
- Subjects: Microalgae -- South Africa -- Mngazi Estuary , Algae -- South Africa -- Mngazi Estuary , Algae -- South Africa -- Mngazana Estuary , Estuarine ecology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10610 , http://hdl.handle.net/10948/1591 , Microalgae -- South Africa -- Mngazi Estuary , Algae -- South Africa -- Mngazi Estuary , Algae -- South Africa -- Mngazana Estuary , Estuarine ecology -- South Africa
- Description: The present study was undertaken in the temporarily open/closed Mngazi and permanently open Mngazana estuaries, located on the subtropical east coast of South Africa. The results from this research will assist decision makers in the freshwater management of these systems. Intertidal and subtidal benthic chlorophyll a concentrations, water column chlorophyll a, nutrients and several physico-chemical parameters were measured between June 2002 and November 2003. The objective of this study was to determine if the presence of freshwater in the estuaries had an effect on the microalgae of both estuaries. Five sites were sampled in the Mngazi Estuary and 14 sites were sampled in the Mngazana Estuary. The average water column chlorophyll a was significantly higher (p<0.05) in the Mngazana Estuary (surface 7.8 ± 0.7 μg.l-1, bottom 6.4 ± 0.7 μg.l-1) compared to the Mngazi Estuary (surface 4.9 ± 1.2 μg.l-1, bottom 7.3 ± 1.5 μg.l-1). There was no evidence of an REI (river-estuary interface) zone in areas where the water column chlorophyll a concentrations were high even during open mouth conditions in the Mngazi Estuary. The REI is that area where salinity is less than 10 ppt and is characterized by high water column productivity. Even though both systems received some freshwater during the summer periods, this was not enough to stimulate phytoplankton growth and nutrient availability seems to be the major factor limiting phytoplankton in these systems. Flagellates and diatoms were the dominant phytoplankton groups in both estuaries during the entire sampling session. The relative abundance of the different phytoplankton groups did not show differences between sites. The relative abundance of flagellates was in most cases greater than 60% and diatoms made up the remainder. The average benthic chlorophyll a was higher in the Mngazana Estuary (intertidal 24 ± 6 μg.g-1 subtidal 15.2 ± 3 μg.g-1) compared to the Mngazi Estuary (intertidal 15.3 ± 4.3 μg.g-1 subtidal 5.4 ± 1.6 μg.g-1). Regions with high benthic chlorophyll a concentrations had high sediment organic content. Sediment organic content was higher in the Mngazana Estuary (1 percent - 8 percent) compared to the Mngazi Estuary (4 percent – 6.8 percent). The sites situated on the Main Channel had on average significantly higher (p<0.05) benthic chlorophyll a biomass compared to Creek 1 and Creek 2 in the Mngazana Estuary. Peaks in benthic chlorophyll a concentrations occurred in the intertidal sediments in Creek 1 (50.4 ± 13.4 μg.g-1) and Creek 2 (57.4 ± 1.4 μg.g-1) in the Mngazana Estuary, the peaks occurred in winter during a period of low freshwater inflow into the estuary. Microphytobenthic biomass measured in the Mngazi Estuary is among the lowest values reported in the literature for temporarily open/closed estuaries. Statistical 4 analysis showed no significant difference between benthic chlorophyll a during the different mouth conditions and sampling sessions in the Mngazi Estuary. Microalgal responses in the Mngazana Estuary were similar to those observed in other permanently open marine dominated estuaries. In the temporarily open/closed Mngazi Estuary microalgal characteristics were different to that of other temporarily open/closed estuaries probably because the estuary was only sampled in the open and semi-closed state.
- Full Text:
- Date Issued: 2010
- Authors: Ngesi, Hlekani Ntombizakithi
- Date: 2010
- Subjects: Microalgae -- South Africa -- Mngazi Estuary , Algae -- South Africa -- Mngazi Estuary , Algae -- South Africa -- Mngazana Estuary , Estuarine ecology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10610 , http://hdl.handle.net/10948/1591 , Microalgae -- South Africa -- Mngazi Estuary , Algae -- South Africa -- Mngazi Estuary , Algae -- South Africa -- Mngazana Estuary , Estuarine ecology -- South Africa
- Description: The present study was undertaken in the temporarily open/closed Mngazi and permanently open Mngazana estuaries, located on the subtropical east coast of South Africa. The results from this research will assist decision makers in the freshwater management of these systems. Intertidal and subtidal benthic chlorophyll a concentrations, water column chlorophyll a, nutrients and several physico-chemical parameters were measured between June 2002 and November 2003. The objective of this study was to determine if the presence of freshwater in the estuaries had an effect on the microalgae of both estuaries. Five sites were sampled in the Mngazi Estuary and 14 sites were sampled in the Mngazana Estuary. The average water column chlorophyll a was significantly higher (p<0.05) in the Mngazana Estuary (surface 7.8 ± 0.7 μg.l-1, bottom 6.4 ± 0.7 μg.l-1) compared to the Mngazi Estuary (surface 4.9 ± 1.2 μg.l-1, bottom 7.3 ± 1.5 μg.l-1). There was no evidence of an REI (river-estuary interface) zone in areas where the water column chlorophyll a concentrations were high even during open mouth conditions in the Mngazi Estuary. The REI is that area where salinity is less than 10 ppt and is characterized by high water column productivity. Even though both systems received some freshwater during the summer periods, this was not enough to stimulate phytoplankton growth and nutrient availability seems to be the major factor limiting phytoplankton in these systems. Flagellates and diatoms were the dominant phytoplankton groups in both estuaries during the entire sampling session. The relative abundance of the different phytoplankton groups did not show differences between sites. The relative abundance of flagellates was in most cases greater than 60% and diatoms made up the remainder. The average benthic chlorophyll a was higher in the Mngazana Estuary (intertidal 24 ± 6 μg.g-1 subtidal 15.2 ± 3 μg.g-1) compared to the Mngazi Estuary (intertidal 15.3 ± 4.3 μg.g-1 subtidal 5.4 ± 1.6 μg.g-1). Regions with high benthic chlorophyll a concentrations had high sediment organic content. Sediment organic content was higher in the Mngazana Estuary (1 percent - 8 percent) compared to the Mngazi Estuary (4 percent – 6.8 percent). The sites situated on the Main Channel had on average significantly higher (p<0.05) benthic chlorophyll a biomass compared to Creek 1 and Creek 2 in the Mngazana Estuary. Peaks in benthic chlorophyll a concentrations occurred in the intertidal sediments in Creek 1 (50.4 ± 13.4 μg.g-1) and Creek 2 (57.4 ± 1.4 μg.g-1) in the Mngazana Estuary, the peaks occurred in winter during a period of low freshwater inflow into the estuary. Microphytobenthic biomass measured in the Mngazi Estuary is among the lowest values reported in the literature for temporarily open/closed estuaries. Statistical 4 analysis showed no significant difference between benthic chlorophyll a during the different mouth conditions and sampling sessions in the Mngazi Estuary. Microalgal responses in the Mngazana Estuary were similar to those observed in other permanently open marine dominated estuaries. In the temporarily open/closed Mngazi Estuary microalgal characteristics were different to that of other temporarily open/closed estuaries probably because the estuary was only sampled in the open and semi-closed state.
- Full Text:
- Date Issued: 2010
Modeling of arsenic removal from aqueous media using selected coagulants
- Authors: Majavu, Avela
- Date: 2010
- Subjects: Arsenic wastes , Water -- Purification -- Arsenic removal , Coagulation
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10426 , http://hdl.handle.net/10948/d1017100
- Description: The waste water from the industrial production of the herbicide monosodium methyl arsenate was treated using coagulation. The coagulation process as developed in this research proved to be suitable for arsenic removal in aqueous media using chromium (III), calcium (II), and combination of calcium (II) and chromium (III), and magnesium (II). The results obtained suggest that the coagulation process can be used for the treatment of the waste water from the monosodium methyl arsenate production. Response surface methodology was used to study the effects of the various parameters, namely pH, mole ratios (Cr:As, Ca:As, and Mg:As), concentration of flocculent and initial arsenic concentration. To optimize the process conditions for the maximum removal of arsenic. Central composite and factorial designs were used to study the effects of these variables and to predict the effect of each. ANOVA was used to identify those factors which had significant effects on model quality and performance. The initial arsenic concentration appeared to be the only significant factor. These models were statistically tested and verified by confirmation experiments.
- Full Text:
- Date Issued: 2010
- Authors: Majavu, Avela
- Date: 2010
- Subjects: Arsenic wastes , Water -- Purification -- Arsenic removal , Coagulation
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10426 , http://hdl.handle.net/10948/d1017100
- Description: The waste water from the industrial production of the herbicide monosodium methyl arsenate was treated using coagulation. The coagulation process as developed in this research proved to be suitable for arsenic removal in aqueous media using chromium (III), calcium (II), and combination of calcium (II) and chromium (III), and magnesium (II). The results obtained suggest that the coagulation process can be used for the treatment of the waste water from the monosodium methyl arsenate production. Response surface methodology was used to study the effects of the various parameters, namely pH, mole ratios (Cr:As, Ca:As, and Mg:As), concentration of flocculent and initial arsenic concentration. To optimize the process conditions for the maximum removal of arsenic. Central composite and factorial designs were used to study the effects of these variables and to predict the effect of each. ANOVA was used to identify those factors which had significant effects on model quality and performance. The initial arsenic concentration appeared to be the only significant factor. These models were statistically tested and verified by confirmation experiments.
- Full Text:
- Date Issued: 2010
Molecular and cellular analysis of the interaction between soluble CD23 and CD11/CD18 integrins
- Authors: Daniels, Brodie Belinda
- Date: 2010
- Subjects: CD23 antigen , Immune response -- Regulation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10303 , http://hdl.handle.net/10948/1217 , CD23 antigen , Immune response -- Regulation
- Description: The low affinity IgE receptor, CD23, is expressed by a wide variety of cells and cleaved from its original 45 kDa size to several smaller soluble CD23 proteins. Soluble CD23 function depends on the form of the protein and its interaction with various ligands. CD23 is believed to play an important role in regulating allergic responses and in inflammation, amongst others. β2 integrins are important in a variety of cell-adhesion reactions during immune-inflammatory mechanisms and the binding of their natural ligands generates outside-in cellular signalling, leading to cell activation. Although the binding of CD23 to β2 integrins contributes to this signalling in monocytes, the interaction site for CD23 is unknown. This study focused on the interaction of three soluble CD23 proteins with the β2 integrins CD11b/CD18 and CD11c/CD18. Differentiated HL60, THP1 and U937 monocytic cells were used to demonstrate the binding of three recombinant CD23 constructs (corresponding to 16, 25 and 33 kDa human soluble CD23) to upregulated CD11b/CD18 and CD11c/CD18. This binding was partially blocked by an antibody specific for the CD11b/CD18 αI domain, demonstrating that αI domains are involved in binding to CD23. Recombinant αI domain proteins of CD11b and CD11c were demonstrated to bind CD23 using ELISA and in surface plasmon resonance spectroscopy. The dissociation constants for CD23-CD11b/CD18 and CD23-CD11c/CD18 are comparable to other integrin ligands. This study has shown that CD23 interacts directly with the αI domains of β2 integrins and that the interaction surface likely spans the lectin domain as well as either the stalk and/or C-terminal tail of CD23. This study also looked at the effect that soluble CD23 proteins had on monocyte biology. It appears that iv sCD23 proteins have little effect on the phagocytic or chemotactic ability of monocytes, while an increase in oxidative burst was shown with the 16 kDa and 25 kDa CD23 proteins. Signalling pathways for the production of reactive oxygen species were investigated and it appears that the CD23 proteins signal mainly through the phosphoinositide-3 kinase pathway, although the mitogen activated protein kinase and Src kinase pathways may also play a role. These data suggest that sCD23 proteins induce outside-in signalling of β2 integrins and are able to change the activation state of CD11b/CD11c by stimulating oxidative burst. This needs to be further investigated by determining how the three sCD23 proteins are binding the CD11 proteins and investigating further leukocyte function and inflammatory responses by the cells.
- Full Text:
- Date Issued: 2010
- Authors: Daniels, Brodie Belinda
- Date: 2010
- Subjects: CD23 antigen , Immune response -- Regulation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10303 , http://hdl.handle.net/10948/1217 , CD23 antigen , Immune response -- Regulation
- Description: The low affinity IgE receptor, CD23, is expressed by a wide variety of cells and cleaved from its original 45 kDa size to several smaller soluble CD23 proteins. Soluble CD23 function depends on the form of the protein and its interaction with various ligands. CD23 is believed to play an important role in regulating allergic responses and in inflammation, amongst others. β2 integrins are important in a variety of cell-adhesion reactions during immune-inflammatory mechanisms and the binding of their natural ligands generates outside-in cellular signalling, leading to cell activation. Although the binding of CD23 to β2 integrins contributes to this signalling in monocytes, the interaction site for CD23 is unknown. This study focused on the interaction of three soluble CD23 proteins with the β2 integrins CD11b/CD18 and CD11c/CD18. Differentiated HL60, THP1 and U937 monocytic cells were used to demonstrate the binding of three recombinant CD23 constructs (corresponding to 16, 25 and 33 kDa human soluble CD23) to upregulated CD11b/CD18 and CD11c/CD18. This binding was partially blocked by an antibody specific for the CD11b/CD18 αI domain, demonstrating that αI domains are involved in binding to CD23. Recombinant αI domain proteins of CD11b and CD11c were demonstrated to bind CD23 using ELISA and in surface plasmon resonance spectroscopy. The dissociation constants for CD23-CD11b/CD18 and CD23-CD11c/CD18 are comparable to other integrin ligands. This study has shown that CD23 interacts directly with the αI domains of β2 integrins and that the interaction surface likely spans the lectin domain as well as either the stalk and/or C-terminal tail of CD23. This study also looked at the effect that soluble CD23 proteins had on monocyte biology. It appears that iv sCD23 proteins have little effect on the phagocytic or chemotactic ability of monocytes, while an increase in oxidative burst was shown with the 16 kDa and 25 kDa CD23 proteins. Signalling pathways for the production of reactive oxygen species were investigated and it appears that the CD23 proteins signal mainly through the phosphoinositide-3 kinase pathway, although the mitogen activated protein kinase and Src kinase pathways may also play a role. These data suggest that sCD23 proteins induce outside-in signalling of β2 integrins and are able to change the activation state of CD11b/CD11c by stimulating oxidative burst. This needs to be further investigated by determining how the three sCD23 proteins are binding the CD11 proteins and investigating further leukocyte function and inflammatory responses by the cells.
- Full Text:
- Date Issued: 2010
Nest site fidelity and nest site selection of loggerhead, Caretta Caretta, and leatherback, dermochelys coriacea, turtles in KwaZulu-Natal, South Africa
- Authors: Botha, Marié
- Date: 2010
- Subjects: Sea turtles -- South Africa -- KwaZulu-Natal , Loggerhead turtle -- South Africa -- KwaZulu-Natal , Leatherback turtle -- South Africa -- KwaZulu-Natal , Nest building , Turtles -- Habitat
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10696 , http://hdl.handle.net/10948/1233 , Sea turtles -- South Africa -- KwaZulu-Natal , Loggerhead turtle -- South Africa -- KwaZulu-Natal , Leatherback turtle -- South Africa -- KwaZulu-Natal , Nest building , Turtles -- Habitat
- Description: Loggerhead and leatherback sea turtles nest on the beaches of the north-eastern portion of Kwazulu-Natal within the iSimangaliso Wetland Park. Loggerheads place ~60 percent of all nests within an 8 km stretch of beach, whereas leatherbacks tend to space their nests more evenly along the entire length of the monitoring area. The study aimed to determine nest site fidelity of loggerheads and leatherbacks (using four decades of nesting data housed by Ezemvelo KZN Wildlife) and the factors that influence nest site selection of both species within the 56 km of turtle monitoring area (32N to 100S) and the 5 km area of high-density loggerhead nesting (0N to 12N). The effectiveness of nest site selection was then determined through the hatching success of loggerheads over the 5km area (0N to 12N). Results showed that loggerheads show a high degree of nest site fidelity (~3 km) with nest site fidelity of individuals increasing over subsequent seasons of nesting, as well as these individuals using the same stretches of beach for nesting (the most popular area being 1N to 4N for repeat nesters). Leatherbacks displayed nest site fidelity of ~9 km and this did not increase over successive seasons of nesting. In terms of nest site selection, loggerheads and leatherbacks both avoided areas where low shore rock was present, whereas both species preferred nesting on beaches of intermediate morphodynamic state. Leatherback nesting was significantly higher in areas with wider surf zones. Both species were able to surpass the high water mark when nesting as nests below this point would be almost certainly doomed. Hatching success of loggerheads was comparative to high (83 %) relative to other studies, however, nest success varied across the beach from beacon 1N to 12N. Areas where highest nest success was observed were not areas of highest nest density presumably due to artificial lighting. Results from this study increase our understanding of the evolutionary biology of loggerhead and leatherback turtles in South Africa and the effectiveness of loggerhead nest site selection through hatching success.
- Full Text:
- Date Issued: 2010
- Authors: Botha, Marié
- Date: 2010
- Subjects: Sea turtles -- South Africa -- KwaZulu-Natal , Loggerhead turtle -- South Africa -- KwaZulu-Natal , Leatherback turtle -- South Africa -- KwaZulu-Natal , Nest building , Turtles -- Habitat
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10696 , http://hdl.handle.net/10948/1233 , Sea turtles -- South Africa -- KwaZulu-Natal , Loggerhead turtle -- South Africa -- KwaZulu-Natal , Leatherback turtle -- South Africa -- KwaZulu-Natal , Nest building , Turtles -- Habitat
- Description: Loggerhead and leatherback sea turtles nest on the beaches of the north-eastern portion of Kwazulu-Natal within the iSimangaliso Wetland Park. Loggerheads place ~60 percent of all nests within an 8 km stretch of beach, whereas leatherbacks tend to space their nests more evenly along the entire length of the monitoring area. The study aimed to determine nest site fidelity of loggerheads and leatherbacks (using four decades of nesting data housed by Ezemvelo KZN Wildlife) and the factors that influence nest site selection of both species within the 56 km of turtle monitoring area (32N to 100S) and the 5 km area of high-density loggerhead nesting (0N to 12N). The effectiveness of nest site selection was then determined through the hatching success of loggerheads over the 5km area (0N to 12N). Results showed that loggerheads show a high degree of nest site fidelity (~3 km) with nest site fidelity of individuals increasing over subsequent seasons of nesting, as well as these individuals using the same stretches of beach for nesting (the most popular area being 1N to 4N for repeat nesters). Leatherbacks displayed nest site fidelity of ~9 km and this did not increase over successive seasons of nesting. In terms of nest site selection, loggerheads and leatherbacks both avoided areas where low shore rock was present, whereas both species preferred nesting on beaches of intermediate morphodynamic state. Leatherback nesting was significantly higher in areas with wider surf zones. Both species were able to surpass the high water mark when nesting as nests below this point would be almost certainly doomed. Hatching success of loggerheads was comparative to high (83 %) relative to other studies, however, nest success varied across the beach from beacon 1N to 12N. Areas where highest nest success was observed were not areas of highest nest density presumably due to artificial lighting. Results from this study increase our understanding of the evolutionary biology of loggerhead and leatherback turtles in South Africa and the effectiveness of loggerhead nest site selection through hatching success.
- Full Text:
- Date Issued: 2010
New platinum and palladium complexes: their anticancer application
- Authors: Louw, Marissa
- Date: 2010
- Subjects: Complex compounds -- Synthesis , Ligands (Biochemistry) , Antineoplastic antibiotics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10424 , http://hdl.handle.net/10948/d1016218
- Description: Novel non-leaving groups were employed in this dissertation to synthesize platinum complexes which can assist in the understanding or improvement of anticancer action. Emphasis was placed on (NS)-chelate and (NN)-chelate platinum complexes. Bidentate (NS)-donor ligands were used as non-leaving ligands in the synthesis of platinum(II) complexes with iodo, chloro, bromo and oxalato groups as leaving groups. These complexes were synthesized and studied since many questions regarding the interaction of sulfur-donors and platinum still exist. These relate to thermodynamic and kinetic factors and their influence on anticancer action. In this dissertation the properties of novel platinum(II) complexes of a bidentate ligand having an aromatic nitrogen-donor atom in combination with a thioethereal sulfur atom capable of forming a five-membered ring with platinum(II) were studied. The general structure of the (NS)-ligands used was 2-((alkylthio)methyl)pyridine. Alkyl groups used were methyl, ethyl, propyl, benzyl and phenyl. Amine complexes of platinum have been studied extensively in the past. However, attention was given to novel aspects of substituted pyridine and imidazole ligands and their corresponding complexes. Amongst these are 2-(2-methylaminoethyl)pyridine, 1-methyl-2-methylaminoethylimidazole and 1-methyl-2-methylaminobenzylimidazole. The leaving groups included chloro, bromo and oxalato. Mononitroplatinum(IV) complexes were prepared using novel synthetic methods. Selected platinum(II) amine complexes were used as starting materials for this synthesis. Some of these compounds exhibit promising anticancer behaviour. (Trans-(R,R)-1,2-diaminocyclohexane)(oxalato)(mononitrochloro)platinum(IV) is a particularly good anticancer agent and has been patented internationally. All these complexes were characterized using mass spectrometry, chromatography, thermogravimetric analysis, kinetic aspects such as ligand exchange rates and finally their anticancer action against three different cancer cell lines was evaluated via cytotoxicity assays. Some of the compounds exhibited particularly good anticancer potential.
- Full Text:
- Date Issued: 2010
- Authors: Louw, Marissa
- Date: 2010
- Subjects: Complex compounds -- Synthesis , Ligands (Biochemistry) , Antineoplastic antibiotics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10424 , http://hdl.handle.net/10948/d1016218
- Description: Novel non-leaving groups were employed in this dissertation to synthesize platinum complexes which can assist in the understanding or improvement of anticancer action. Emphasis was placed on (NS)-chelate and (NN)-chelate platinum complexes. Bidentate (NS)-donor ligands were used as non-leaving ligands in the synthesis of platinum(II) complexes with iodo, chloro, bromo and oxalato groups as leaving groups. These complexes were synthesized and studied since many questions regarding the interaction of sulfur-donors and platinum still exist. These relate to thermodynamic and kinetic factors and their influence on anticancer action. In this dissertation the properties of novel platinum(II) complexes of a bidentate ligand having an aromatic nitrogen-donor atom in combination with a thioethereal sulfur atom capable of forming a five-membered ring with platinum(II) were studied. The general structure of the (NS)-ligands used was 2-((alkylthio)methyl)pyridine. Alkyl groups used were methyl, ethyl, propyl, benzyl and phenyl. Amine complexes of platinum have been studied extensively in the past. However, attention was given to novel aspects of substituted pyridine and imidazole ligands and their corresponding complexes. Amongst these are 2-(2-methylaminoethyl)pyridine, 1-methyl-2-methylaminoethylimidazole and 1-methyl-2-methylaminobenzylimidazole. The leaving groups included chloro, bromo and oxalato. Mononitroplatinum(IV) complexes were prepared using novel synthetic methods. Selected platinum(II) amine complexes were used as starting materials for this synthesis. Some of these compounds exhibit promising anticancer behaviour. (Trans-(R,R)-1,2-diaminocyclohexane)(oxalato)(mononitrochloro)platinum(IV) is a particularly good anticancer agent and has been patented internationally. All these complexes were characterized using mass spectrometry, chromatography, thermogravimetric analysis, kinetic aspects such as ligand exchange rates and finally their anticancer action against three different cancer cell lines was evaluated via cytotoxicity assays. Some of the compounds exhibited particularly good anticancer potential.
- Full Text:
- Date Issued: 2010
Photoluminescence study of ZnO doped with nitrogen and arsenic
- Authors: Dangbegnon, Julien Kouadio
- Date: 2010
- Subjects: Photoluminescence , Zinc oxide , Nitrogen , Arsenic
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10518 , http://hdl.handle.net/10948/1216 , Photoluminescence , Zinc oxide , Nitrogen , Arsenic
- Description: In this work, the optical properties of ZnO doped with arsenic and nitrogen were studied. The ZnO samples were grown by Metalorganic Chemical Vapor Deposition (MOCVD). The solubility of nitrogen in the ZnO films, as well as its activation upon annealing, was also investigated. Hydrogen is known as a major source for passivation of the acceptors in ZnO:N. Therefore, it is crucial to dissociate the complex(es) formed by nitrogen and hydrogen and diffuse out the hydrogen in order to prevent the reformation of such complexes. High temperatures (≥ 600 C) are required for these purposes. In order to effectively remove the hydrogen impurities from the sample, it is important to know the optical fingerprints of hydrogen and its thermal stability. Therefore, the effects of annealing and hydrogen plasma treatment on bulk ZnO (hydrothermally grown) were first studied. The use of bulk material for this purpose was motivated by the well-resolved photoluminescence (PL) lines observed for bulk ZnO, which allow the identification of the different lines related to hydrogen after plasma treatment. Annealing at 850 C was effective for the removal of most of the hydrogen related transitions in the near-band-edge emission. Also, additional transitions at ~3.364 eV and ~3.361 eV were observed after hydrogen plasma treatment, which were ascribed to hydrogen-Zn vacancy complexes. In this work, a comparative study of the annealing ambient and temperature on ZnO films grown on GaAs substrate, using diethyl zinc (DEZn) and tertiary butanol (TBOH), showed that arsenic diffuses in the ZnO films and gives a shallow level in the band gap, which is involved in an acceptor-bound exciton line at 3.35 eV. This shallow level is visible when annealing is performed in oxygen, but not when annealing is performed in nitrogen, and indeed only for annealing temperatures around 550 C. However, annealing in either ambient also causes zinc to diffuse from the ZnO films into the GaAs substrate, rendering the electrical properties deduced from Hall measurements ambiguous. For ZnO:N, NO was used as both oxygen and nitrogen sources. Monitoring the concentration of nitrogen, carbon and hydrogen in the ZnO films, the formation of different complexes from these impurities were deduced. Furthermore, an investigation of the effect of annealing on the concentrations of impurities showed that their out- diffusion was strongly dependent on the crystalline quality of the ZnO films. For porous ZnO films, obtained at low growth temperatures (≤310 C), the out-diffusion of impurities was efficient, whereas for films grown at higher temperatures, which have improved crystalline quality, the out-diffusion was practically nonexistent. The out-diffusion of unwanted impurities may activate the nitrogen dopant in the ZnO films, as was confirmed by the PL measurements on the different samples grown at different temperatures. PL transitions at ~3.24 eV and ~3.17 eV were related to substitutional NO. These transitions were more dominant in the spectra of samples grown at low temperatures. An additional transition at ~3.1 eV was assigned to a donor-acceptor pair transition involving VZn, instead of NO, as previously reported.
- Full Text:
- Date Issued: 2010
- Authors: Dangbegnon, Julien Kouadio
- Date: 2010
- Subjects: Photoluminescence , Zinc oxide , Nitrogen , Arsenic
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10518 , http://hdl.handle.net/10948/1216 , Photoluminescence , Zinc oxide , Nitrogen , Arsenic
- Description: In this work, the optical properties of ZnO doped with arsenic and nitrogen were studied. The ZnO samples were grown by Metalorganic Chemical Vapor Deposition (MOCVD). The solubility of nitrogen in the ZnO films, as well as its activation upon annealing, was also investigated. Hydrogen is known as a major source for passivation of the acceptors in ZnO:N. Therefore, it is crucial to dissociate the complex(es) formed by nitrogen and hydrogen and diffuse out the hydrogen in order to prevent the reformation of such complexes. High temperatures (≥ 600 C) are required for these purposes. In order to effectively remove the hydrogen impurities from the sample, it is important to know the optical fingerprints of hydrogen and its thermal stability. Therefore, the effects of annealing and hydrogen plasma treatment on bulk ZnO (hydrothermally grown) were first studied. The use of bulk material for this purpose was motivated by the well-resolved photoluminescence (PL) lines observed for bulk ZnO, which allow the identification of the different lines related to hydrogen after plasma treatment. Annealing at 850 C was effective for the removal of most of the hydrogen related transitions in the near-band-edge emission. Also, additional transitions at ~3.364 eV and ~3.361 eV were observed after hydrogen plasma treatment, which were ascribed to hydrogen-Zn vacancy complexes. In this work, a comparative study of the annealing ambient and temperature on ZnO films grown on GaAs substrate, using diethyl zinc (DEZn) and tertiary butanol (TBOH), showed that arsenic diffuses in the ZnO films and gives a shallow level in the band gap, which is involved in an acceptor-bound exciton line at 3.35 eV. This shallow level is visible when annealing is performed in oxygen, but not when annealing is performed in nitrogen, and indeed only for annealing temperatures around 550 C. However, annealing in either ambient also causes zinc to diffuse from the ZnO films into the GaAs substrate, rendering the electrical properties deduced from Hall measurements ambiguous. For ZnO:N, NO was used as both oxygen and nitrogen sources. Monitoring the concentration of nitrogen, carbon and hydrogen in the ZnO films, the formation of different complexes from these impurities were deduced. Furthermore, an investigation of the effect of annealing on the concentrations of impurities showed that their out- diffusion was strongly dependent on the crystalline quality of the ZnO films. For porous ZnO films, obtained at low growth temperatures (≤310 C), the out-diffusion of impurities was efficient, whereas for films grown at higher temperatures, which have improved crystalline quality, the out-diffusion was practically nonexistent. The out-diffusion of unwanted impurities may activate the nitrogen dopant in the ZnO films, as was confirmed by the PL measurements on the different samples grown at different temperatures. PL transitions at ~3.24 eV and ~3.17 eV were related to substitutional NO. These transitions were more dominant in the spectra of samples grown at low temperatures. An additional transition at ~3.1 eV was assigned to a donor-acceptor pair transition involving VZn, instead of NO, as previously reported.
- Full Text:
- Date Issued: 2010
Quantification of greenhouse gas fluxes from soil in agricultural fields
- Authors: Nkongolo, Nsalambi Vakanda
- Date: 2010
- Subjects: Greenhouse gases -- Environmental aspects
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: vital:10645 , http://hdl.handle.net/10948/1474 , Greenhouse gases -- Environmental aspects
- Description: Field studies were conducted at Lincoln University of Missouri (USA) and Hokkaido University (Japan) to: (i) study the relationships between greenhouse gases emissions and soil properties, (ii) assess the influence of agricultural practices on greenhouse gas fluxes and soil properties and (iii) improve the quantification of greenhouse gases from soil in agricultural fields using geospatial technologies. Results showed that besides soil temperature (T), soil thermal properties such as thermal conductivity (K), resistivity (R) and diffusivity (D) and soil pore spaces indices such as the pore tortuosity factor and the relative gas diffusion coefficient (Ds/Do) are controlling factors for greenhouse gases emissions. Soil thermal properties correlated with greenhouse gases emissions when soil temperature could not. The study has found that predicted Ds/Do and correlate with greenhouse gas fluxes even when the air-filled porosity and the total porosity from which they are predicted did not. We have also showed that Ds/Do and can be predicted quickly from routine measurements of soil water and air and existing diffusivity models found in the literature. Agricultural practices do seriously impact greenhouse gases emissions as showed by the effect of mechanized tillage operations on soil physical properties and greenhouse gas fluxes in a corn and soybean fields. In fact, our results showed that tractor compaction increased soil resistance to penetration, water, bulk density and pore tortuosity while reducing air-filled porosity, total pore space and the soil gas diffusion coefficient. Changes in soil properties resulted in increased CO2, NO and N2O emissions. Finally, our results also confirmed that greenhouse gas fluxes vary tremendously in space and time. As estimates of greenhouse gas emissions are influenced by the data processing approach, differences between the different calculation approaches leads to uncertainty. Thus, techniques for developing better estimates are needed. We have showed that Geographic Information Systems (GIS), Global Positioning System (GPS), computer mapping and geo-statistics are technologies that can be used to better understand systems containing large amounts of spatial and temporal variability. Our GIS-based approach for quantifying CO2, CH4 and N2O fluxes from soil in agricultural fields showed that estimating (extrapolating) total greenhouse gas fluxes using the “standard” approach – multiplying the average flux value by the total field area – results in biased predictions of field total greenhouse gases emissions. In contrast, the GIS-based approach we developed produces an interpolated map portraying the spatial distribution of gas fluxes across the field from point measurements and later process the interpolated map produced to determine flux zones. Furthermore, processing, classification and modeling enables the computation of field total fluxes as the sum of fluxes in different zones, therefore taking into account the spatial variability of greenhouse gas fluxes.
- Full Text:
- Date Issued: 2010
- Authors: Nkongolo, Nsalambi Vakanda
- Date: 2010
- Subjects: Greenhouse gases -- Environmental aspects
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: vital:10645 , http://hdl.handle.net/10948/1474 , Greenhouse gases -- Environmental aspects
- Description: Field studies were conducted at Lincoln University of Missouri (USA) and Hokkaido University (Japan) to: (i) study the relationships between greenhouse gases emissions and soil properties, (ii) assess the influence of agricultural practices on greenhouse gas fluxes and soil properties and (iii) improve the quantification of greenhouse gases from soil in agricultural fields using geospatial technologies. Results showed that besides soil temperature (T), soil thermal properties such as thermal conductivity (K), resistivity (R) and diffusivity (D) and soil pore spaces indices such as the pore tortuosity factor and the relative gas diffusion coefficient (Ds/Do) are controlling factors for greenhouse gases emissions. Soil thermal properties correlated with greenhouse gases emissions when soil temperature could not. The study has found that predicted Ds/Do and correlate with greenhouse gas fluxes even when the air-filled porosity and the total porosity from which they are predicted did not. We have also showed that Ds/Do and can be predicted quickly from routine measurements of soil water and air and existing diffusivity models found in the literature. Agricultural practices do seriously impact greenhouse gases emissions as showed by the effect of mechanized tillage operations on soil physical properties and greenhouse gas fluxes in a corn and soybean fields. In fact, our results showed that tractor compaction increased soil resistance to penetration, water, bulk density and pore tortuosity while reducing air-filled porosity, total pore space and the soil gas diffusion coefficient. Changes in soil properties resulted in increased CO2, NO and N2O emissions. Finally, our results also confirmed that greenhouse gas fluxes vary tremendously in space and time. As estimates of greenhouse gas emissions are influenced by the data processing approach, differences between the different calculation approaches leads to uncertainty. Thus, techniques for developing better estimates are needed. We have showed that Geographic Information Systems (GIS), Global Positioning System (GPS), computer mapping and geo-statistics are technologies that can be used to better understand systems containing large amounts of spatial and temporal variability. Our GIS-based approach for quantifying CO2, CH4 and N2O fluxes from soil in agricultural fields showed that estimating (extrapolating) total greenhouse gas fluxes using the “standard” approach – multiplying the average flux value by the total field area – results in biased predictions of field total greenhouse gases emissions. In contrast, the GIS-based approach we developed produces an interpolated map portraying the spatial distribution of gas fluxes across the field from point measurements and later process the interpolated map produced to determine flux zones. Furthermore, processing, classification and modeling enables the computation of field total fluxes as the sum of fluxes in different zones, therefore taking into account the spatial variability of greenhouse gas fluxes.
- Full Text:
- Date Issued: 2010
Reactivity of Rhenium (iii) and Rhenium (V) with multidentate NN-and no-donor ligands
- Yumata, Nonzaliseko Christine
- Authors: Yumata, Nonzaliseko Christine
- Date: 2010
- Subjects: Rhenium , Ligands
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10373 , http://hdl.handle.net/10948/1085 , Rhenium , Ligands
- Description: The reaction of the potentially tridentate Schiff-base chelate Hhaep [Haep = N’-(1- (2-hydroxyphenyl)ethylidene)benzohydrazide] with [ReCl3(benzil)(PPh3)] and trans-[ReOCl3(PPh3)2] produced the neutral oxorhenium(V) complexes cis- [ReOCl2(mep)] [Hmep = 2-(1-iminoethyl)phenol] and cis-[ReOCI2(meb)(PPh3)] [Hmeb = N’-(propan-2-ylidene)benzohydrazide] in ethanol and acetone respectively. In both reactions the Hhaep molecule cleaves to give different coordinated bidentate NO-donor chelates coordinated to the rhenium(V) centers. The X-ray studies reveal that mep is present as a bidentate, monoanionic Schiffbase coordinating through the neutral imino nitrogen and the deprotonated phenolate oxygen in cis-[ReOCl2(mep)]. The bond distances and angles in cis- [ReOCI2(meb)(PPh3)] confirm that meb coordinates to the metal in the enolate form. The distorted octahedral complex fac-[ReCl3(dpa)(PPh3)] was prepared by the reaction of trans-[ReCl3(MeCN)(PPh3)2] with a twofold molar excess of dpa in acetonitrile under a nitrogen atmosphere. The compound dpa.HCl.2H2O was obtained as a by-product in the reaction of dpa with trans-[ReCI3(MeCN)(PPh3)2] in acetonitrile. The reaction of trans-[ReCl3(MeCN)(PPh3)2] with a twofold molar excess of 6- amino-3-methyl-1-phenyl-4-azahept-2-ene-1-one (Hamp) in acetonitrile led to the isolation of cis-[ReCl2(bat)(PPh3)2]. On complexation to the metal center Hamp decomposed to give the coordinated benzoylacetone (bat). Bat is present as a monoanionic bidentate chelate. The complexes [ReVOCI(had)] and [ReIVCl(had)(PPh3)](ReO4) were prepared from the reaction of trans-[ReCl3(MeCN)(PPh3)2] with N,N-bis((2-hydroxybenzyl)-2- aminoethyl)dimethylamine (H2had) in ethanol under various reaction conditions. The treatment of [ReCl3(benzil)(PPh3)] with 2-[((2- pyridinylmethyl)amino)methyl]phenol (Hham) in a 2:1 molar ratio in acetonitrile led to the isolation of the hydrogen-bonded dimer [ReOCl2(ham)]2. The distorted octahedral complex [ReOCl(hap)] [H2hap = N,N-bis(2- hydroxybenzyl)aminomethylpyridine] was prepared from the reaction of trans- [ReCl3(MeCN)(PPh3)2] with a twofold molar excess of H2hap in acetonitrile. The X-ray crystal structure analysis shows that the chloride is coordinated trans to the tripodal tertiary amino nitrogen, with a phenolate oxygen trans to the oxo oxygen.
- Full Text:
- Date Issued: 2010
- Authors: Yumata, Nonzaliseko Christine
- Date: 2010
- Subjects: Rhenium , Ligands
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10373 , http://hdl.handle.net/10948/1085 , Rhenium , Ligands
- Description: The reaction of the potentially tridentate Schiff-base chelate Hhaep [Haep = N’-(1- (2-hydroxyphenyl)ethylidene)benzohydrazide] with [ReCl3(benzil)(PPh3)] and trans-[ReOCl3(PPh3)2] produced the neutral oxorhenium(V) complexes cis- [ReOCl2(mep)] [Hmep = 2-(1-iminoethyl)phenol] and cis-[ReOCI2(meb)(PPh3)] [Hmeb = N’-(propan-2-ylidene)benzohydrazide] in ethanol and acetone respectively. In both reactions the Hhaep molecule cleaves to give different coordinated bidentate NO-donor chelates coordinated to the rhenium(V) centers. The X-ray studies reveal that mep is present as a bidentate, monoanionic Schiffbase coordinating through the neutral imino nitrogen and the deprotonated phenolate oxygen in cis-[ReOCl2(mep)]. The bond distances and angles in cis- [ReOCI2(meb)(PPh3)] confirm that meb coordinates to the metal in the enolate form. The distorted octahedral complex fac-[ReCl3(dpa)(PPh3)] was prepared by the reaction of trans-[ReCl3(MeCN)(PPh3)2] with a twofold molar excess of dpa in acetonitrile under a nitrogen atmosphere. The compound dpa.HCl.2H2O was obtained as a by-product in the reaction of dpa with trans-[ReCI3(MeCN)(PPh3)2] in acetonitrile. The reaction of trans-[ReCl3(MeCN)(PPh3)2] with a twofold molar excess of 6- amino-3-methyl-1-phenyl-4-azahept-2-ene-1-one (Hamp) in acetonitrile led to the isolation of cis-[ReCl2(bat)(PPh3)2]. On complexation to the metal center Hamp decomposed to give the coordinated benzoylacetone (bat). Bat is present as a monoanionic bidentate chelate. The complexes [ReVOCI(had)] and [ReIVCl(had)(PPh3)](ReO4) were prepared from the reaction of trans-[ReCl3(MeCN)(PPh3)2] with N,N-bis((2-hydroxybenzyl)-2- aminoethyl)dimethylamine (H2had) in ethanol under various reaction conditions. The treatment of [ReCl3(benzil)(PPh3)] with 2-[((2- pyridinylmethyl)amino)methyl]phenol (Hham) in a 2:1 molar ratio in acetonitrile led to the isolation of the hydrogen-bonded dimer [ReOCl2(ham)]2. The distorted octahedral complex [ReOCl(hap)] [H2hap = N,N-bis(2- hydroxybenzyl)aminomethylpyridine] was prepared from the reaction of trans- [ReCl3(MeCN)(PPh3)2] with a twofold molar excess of H2hap in acetonitrile. The X-ray crystal structure analysis shows that the chloride is coordinated trans to the tripodal tertiary amino nitrogen, with a phenolate oxygen trans to the oxo oxygen.
- Full Text:
- Date Issued: 2010
Sandy beach food webs and trophic linkages with estuaries: a stable light isotope approach
- Authors: Bezuidenhout, Karien
- Date: 2010
- Subjects: Stable isotopes in ecological research -- South Africa -- Eastern Cape , Food chains (Ecology) -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10694 , http://hdl.handle.net/10948/1269 , Stable isotopes in ecological research -- South Africa -- Eastern Cape , Food chains (Ecology) -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape
- Description: Two pocket sandy beaches, Eastern Cape, South Africa, were investigated, to determine whether these beaches were subsidised by an adjacent mangrove estuary, by using stable light isotope (δ 13C and δ 15N) analyses. The trophodynamics and macrofaunal food webs of these two beaches, situated between the Mgazi and Mgazana estuaries (in a warm-temperate/subtropical transition zone,), were described. Two to 2.5 trophic levels were identified for the macrobenthic community, with suspension feeders and omnivorous scavengers as the primary consumers, and carnivores as the secondary consumers. Mangrove material and terrigenous inputs were not driving the sandy beach food webs. Instead, marine allochthonous inputs (carrion, macroalgae), possibly phytoplankton, sediment organic matter, and resident macroinfauna were the dominant food sources. Cattle dung could have been the only important terrigenous food source utilised by the beach benthos. The macroinfauna displayed generalist/omnivorous feeding strategies, but within the limits of predominantly marine food sources. There was evidence that carnivores actively preyed on resident beach fauna. Omnivory and intraguild feeding might also be important biological processes in these communities. Seasonal and spatial variability in stable isotope composition of the fauna was observed, but few patterns were evident. There was a general trend of more enriched δ 15N and δ 13C composition of animal tissues in summer as opposed to winter. This was accompanied by a general decrease in C:N ratios in summer. It was hypothesised that these isotopic and biochemical changes were in response to increased food availability during summer. Although mangrove material appeared not to play an important role in the nutrition of these sandy beach communities, it was suggested that a high retention time of particles in the bay could enhance bacterial decay of particulate mangrove material, which could then act as fine, bacterial-enriched particulate food to the macrobenthos. This remains to be tested.
- Full Text:
- Date Issued: 2010
- Authors: Bezuidenhout, Karien
- Date: 2010
- Subjects: Stable isotopes in ecological research -- South Africa -- Eastern Cape , Food chains (Ecology) -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10694 , http://hdl.handle.net/10948/1269 , Stable isotopes in ecological research -- South Africa -- Eastern Cape , Food chains (Ecology) -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape
- Description: Two pocket sandy beaches, Eastern Cape, South Africa, were investigated, to determine whether these beaches were subsidised by an adjacent mangrove estuary, by using stable light isotope (δ 13C and δ 15N) analyses. The trophodynamics and macrofaunal food webs of these two beaches, situated between the Mgazi and Mgazana estuaries (in a warm-temperate/subtropical transition zone,), were described. Two to 2.5 trophic levels were identified for the macrobenthic community, with suspension feeders and omnivorous scavengers as the primary consumers, and carnivores as the secondary consumers. Mangrove material and terrigenous inputs were not driving the sandy beach food webs. Instead, marine allochthonous inputs (carrion, macroalgae), possibly phytoplankton, sediment organic matter, and resident macroinfauna were the dominant food sources. Cattle dung could have been the only important terrigenous food source utilised by the beach benthos. The macroinfauna displayed generalist/omnivorous feeding strategies, but within the limits of predominantly marine food sources. There was evidence that carnivores actively preyed on resident beach fauna. Omnivory and intraguild feeding might also be important biological processes in these communities. Seasonal and spatial variability in stable isotope composition of the fauna was observed, but few patterns were evident. There was a general trend of more enriched δ 15N and δ 13C composition of animal tissues in summer as opposed to winter. This was accompanied by a general decrease in C:N ratios in summer. It was hypothesised that these isotopic and biochemical changes were in response to increased food availability during summer. Although mangrove material appeared not to play an important role in the nutrition of these sandy beach communities, it was suggested that a high retention time of particles in the bay could enhance bacterial decay of particulate mangrove material, which could then act as fine, bacterial-enriched particulate food to the macrobenthos. This remains to be tested.
- Full Text:
- Date Issued: 2010
Social sustainability of biogas production in Sogwala village, lower Gweru district, Zimbabwe
- Authors: Dhliwayo, Nyaradzo
- Date: 2010
- Subjects: Biogas -- Zimbabwe , Biogas -- Developing countries , Sustainability -- Zimbabwe
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:10648 , http://hdl.handle.net/10948/1459 , Biogas -- Zimbabwe , Biogas -- Developing countries , Sustainability -- Zimbabwe
- Description: The study has explored the social sustainability of biogas production in a local village of Sogwala which is located in the Lower Gweru District of Zimbabwe. The social sustainability assessment was based on the two concepts of social sustainability, namely human capital and social capital with particular emphasis on their respective elements and aspects. Qualitative and quantitative research methodology methods were used on a sample of 100 households using biogas and some key informants. Analysis of the variance was used to determine whether biogas production could account for any effects on the social and human capital elements of the Sogwala community. An overview and descriptive statistics analysis of the findings from the study have been provided where the biogas users’ experiences, perspectives are discussed and results were assessed. For instance, effects on the aspects of social capital elements which include increases in the social group membership of households after the introduction of biogas production the village; the performance of biogas energy as compared with other fuel sources in terms of accessibility, efficiency and the degree of labour needed for continual production of biogas. In view of the human capital element, assessment is done on the economic status per household before and after the production of biogas, where emphasis is placed on the aspects of employment, education and health indicators within the social sustainability context. The fundamental benefits from biogas production are considered and discussed with the technical issues surrounding biogas production also being presented. This is not just a technical unit for providing alternative energy supply, but it requires management, labour and knowledge, skills to operate on a daily basis for it to have an impact that can bring positive change to the daily social lives of both the young and old.
- Full Text:
- Date Issued: 2010
- Authors: Dhliwayo, Nyaradzo
- Date: 2010
- Subjects: Biogas -- Zimbabwe , Biogas -- Developing countries , Sustainability -- Zimbabwe
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:10648 , http://hdl.handle.net/10948/1459 , Biogas -- Zimbabwe , Biogas -- Developing countries , Sustainability -- Zimbabwe
- Description: The study has explored the social sustainability of biogas production in a local village of Sogwala which is located in the Lower Gweru District of Zimbabwe. The social sustainability assessment was based on the two concepts of social sustainability, namely human capital and social capital with particular emphasis on their respective elements and aspects. Qualitative and quantitative research methodology methods were used on a sample of 100 households using biogas and some key informants. Analysis of the variance was used to determine whether biogas production could account for any effects on the social and human capital elements of the Sogwala community. An overview and descriptive statistics analysis of the findings from the study have been provided where the biogas users’ experiences, perspectives are discussed and results were assessed. For instance, effects on the aspects of social capital elements which include increases in the social group membership of households after the introduction of biogas production the village; the performance of biogas energy as compared with other fuel sources in terms of accessibility, efficiency and the degree of labour needed for continual production of biogas. In view of the human capital element, assessment is done on the economic status per household before and after the production of biogas, where emphasis is placed on the aspects of employment, education and health indicators within the social sustainability context. The fundamental benefits from biogas production are considered and discussed with the technical issues surrounding biogas production also being presented. This is not just a technical unit for providing alternative energy supply, but it requires management, labour and knowledge, skills to operate on a daily basis for it to have an impact that can bring positive change to the daily social lives of both the young and old.
- Full Text:
- Date Issued: 2010
Spatially resolved opto-electric measurements of photovoltaic materials and devices
- Authors: Thantsha, Nicolas Matome
- Date: 2010
- Subjects: Photovoltaic cells , Photovoltaic power systems , Photovoltaic power generation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10520 , http://hdl.handle.net/10948/1123 , Photovoltaic cells , Photovoltaic power systems , Photovoltaic power generation
- Description: The objective of this study is to characterize and analyse defects in solar cell devices. Materials used to fabricate solar cells are not defects free and therefore, there is a need to investigate defects in cells. To investigate this, a topographical technique was developed and employed which uses a non-destructive methodology to analyse solar cells. A system was built which uses a technique based on a laser beam induced current (LBIC). LBIC technique involves focusing light on to a surface of a solar cell device in order to create a photo-generated current that can be measured in the external circuit for analyses. The advantage of this technique is that it allows parameter extraction. Parameters that can be extracted include short-circuit current, carrier lifetime and also the external and internal quantum efficiency of a solar cell. In this thesis, LBIC measurements in the form of picture maps are used to indicate the distribution of the localized beam induced current within solar cells. Areas with low minority carrier lifetime in solar cells are made visible by LBIC mapping. Surface reflection intensity measurements of cells can also be mapped using the LBIC system developed in this study. The system is also capable of mapping photo-generated current of a cell below and above room temperature. This thesis also presents an assessment procedure capable of assessing the device and performance parameters with reference to I-V measurements. The dark and illuminated I-V characteristics of solar cells were investigated. The illuminated I-V characteristics of solar cells were obtained using a defocused laser beam. Dark I-V measurements were performed by applying voltage across the cell in the dark and measuring a current through it. The device parameters which describe the behaviour of I-V characteristic were extracted from the I-V data using Particle Swarm Optimization (PSO) method based on a one-and two-diode solar cell models. Solar cells of different technologies were analysed, namely, single-crystalline (c-Si) and multicrystalline (mc-Si) silicon, Edge-defined Film-fed Growth Si (EFG-Si) and Cu(In,Ga)(Se,S)2 (CIGSS) thin film based cells. The LBIC results illustrated the effect of surface reflection features and material defects in the solar cell investigated. IQE at a wavelength of 660 nm were measured on these cells and the results in general emphasised the importance of correcting optical losses, i.e. reflection loss, when characterizing different types of defects. The agreement between the IQE measurements and I-V characteristics of a cell showed that the differences in crystal grains influence the performance of a mc-Si cell. The temperature-dependence of I-V characteristics of a CIGSS solar cell was investigated. The results showed that, for this material, the photo response is reduced at elevated temperatures. In addition to LBIC using a laser beam, solar spectral radiation was employed to obtained device performance parameters. The results emphasised the effect of grain boundaries as a recombination centres for photo-generated hole-pairs. Lastly, mesa diode characterizations of solar cells were investigated. Mesa diodes are achieved by etching down a solar cell so that the plateau regions are formed. Mesa diodes expose the p-n junction, and therefore mesa diode analysis provides a better way of determining and revealing the fundamental current conduction mechanism at the junction. Mesa diodes avoid possible edge effects. This study showed that mesa diodes can be used to characterize spatial non-uniformities in solar cells. The results obtained in this study indicate that LBIC is a useful tool for defect characterization in solar cells. Also LBIC complements other characterization techniques such as I-V characterization.
- Full Text:
- Date Issued: 2010
- Authors: Thantsha, Nicolas Matome
- Date: 2010
- Subjects: Photovoltaic cells , Photovoltaic power systems , Photovoltaic power generation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10520 , http://hdl.handle.net/10948/1123 , Photovoltaic cells , Photovoltaic power systems , Photovoltaic power generation
- Description: The objective of this study is to characterize and analyse defects in solar cell devices. Materials used to fabricate solar cells are not defects free and therefore, there is a need to investigate defects in cells. To investigate this, a topographical technique was developed and employed which uses a non-destructive methodology to analyse solar cells. A system was built which uses a technique based on a laser beam induced current (LBIC). LBIC technique involves focusing light on to a surface of a solar cell device in order to create a photo-generated current that can be measured in the external circuit for analyses. The advantage of this technique is that it allows parameter extraction. Parameters that can be extracted include short-circuit current, carrier lifetime and also the external and internal quantum efficiency of a solar cell. In this thesis, LBIC measurements in the form of picture maps are used to indicate the distribution of the localized beam induced current within solar cells. Areas with low minority carrier lifetime in solar cells are made visible by LBIC mapping. Surface reflection intensity measurements of cells can also be mapped using the LBIC system developed in this study. The system is also capable of mapping photo-generated current of a cell below and above room temperature. This thesis also presents an assessment procedure capable of assessing the device and performance parameters with reference to I-V measurements. The dark and illuminated I-V characteristics of solar cells were investigated. The illuminated I-V characteristics of solar cells were obtained using a defocused laser beam. Dark I-V measurements were performed by applying voltage across the cell in the dark and measuring a current through it. The device parameters which describe the behaviour of I-V characteristic were extracted from the I-V data using Particle Swarm Optimization (PSO) method based on a one-and two-diode solar cell models. Solar cells of different technologies were analysed, namely, single-crystalline (c-Si) and multicrystalline (mc-Si) silicon, Edge-defined Film-fed Growth Si (EFG-Si) and Cu(In,Ga)(Se,S)2 (CIGSS) thin film based cells. The LBIC results illustrated the effect of surface reflection features and material defects in the solar cell investigated. IQE at a wavelength of 660 nm were measured on these cells and the results in general emphasised the importance of correcting optical losses, i.e. reflection loss, when characterizing different types of defects. The agreement between the IQE measurements and I-V characteristics of a cell showed that the differences in crystal grains influence the performance of a mc-Si cell. The temperature-dependence of I-V characteristics of a CIGSS solar cell was investigated. The results showed that, for this material, the photo response is reduced at elevated temperatures. In addition to LBIC using a laser beam, solar spectral radiation was employed to obtained device performance parameters. The results emphasised the effect of grain boundaries as a recombination centres for photo-generated hole-pairs. Lastly, mesa diode characterizations of solar cells were investigated. Mesa diodes are achieved by etching down a solar cell so that the plateau regions are formed. Mesa diodes expose the p-n junction, and therefore mesa diode analysis provides a better way of determining and revealing the fundamental current conduction mechanism at the junction. Mesa diodes avoid possible edge effects. This study showed that mesa diodes can be used to characterize spatial non-uniformities in solar cells. The results obtained in this study indicate that LBIC is a useful tool for defect characterization in solar cells. Also LBIC complements other characterization techniques such as I-V characterization.
- Full Text:
- Date Issued: 2010
Synthesis, characterization and reactions of novel ferrocenylimidazoles as donor ligands
- Authors: Onyancha, Douglas Okerio
- Date: 2010
- Subjects: Ferrocene
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10390 , http://hdl.handle.net/10948/1150 , Ferrocene
- Description: In this project a series of ferrocenylimidazole derivatives were successfully prepared and characterized using an array of analytical techniques. Reactions of ferrocenylcarbinols with N,N′-thiocarbonyldiimidazole under both solvent-free conditions and in dichloromethane are described. The reaction of ferrocenylmethanol afforded S,S-bis(ferrocenylmethyl)dithiocarbonate, the reaction of α-substituted ferrocenylcarbinols provided ferrocenylalkylimidazolides, while ω-ferrocenylcarbinols yielded ferrocenylimidazolecarbothioates. The reactions were carried out under solvent-free conditions, consistent with the principles of Green Chemistry. Ferrocenyl benzyl ethers were successfully prepared by reacting 4-ferrocenylbenzyl-1Hcarboxylate with a series of primary alcohols under catalytic condition and under a catalyst– free environment. Refluxing a mixture of alcohol-water and 4-ferrocenylbenzyl-1Hcarboxylate provided the corresponding ethers in modest yields. The same ethers were obtained at room temperature by employing potassium tetrachloroplatinate or hydrochloric acid as catalyst. Ferrocenyl-1H-imidazole, 4-ferrocenylphenyl-1H-imidazole and their corresponding ferrocenyl-3-subsitituted imidazolium salts have been successfully synthesized. The compounds were characterized and the electrochemical properties of selected imidazolium salts were examined by cyclic voltammetry. Additionally, X-ray structures of two of the imidazolium salts were determined. The imidazolium salts were found to be good catalysts for the Heck and Suzuki cross-coupling reactions.
- Full Text:
- Date Issued: 2010
- Authors: Onyancha, Douglas Okerio
- Date: 2010
- Subjects: Ferrocene
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10390 , http://hdl.handle.net/10948/1150 , Ferrocene
- Description: In this project a series of ferrocenylimidazole derivatives were successfully prepared and characterized using an array of analytical techniques. Reactions of ferrocenylcarbinols with N,N′-thiocarbonyldiimidazole under both solvent-free conditions and in dichloromethane are described. The reaction of ferrocenylmethanol afforded S,S-bis(ferrocenylmethyl)dithiocarbonate, the reaction of α-substituted ferrocenylcarbinols provided ferrocenylalkylimidazolides, while ω-ferrocenylcarbinols yielded ferrocenylimidazolecarbothioates. The reactions were carried out under solvent-free conditions, consistent with the principles of Green Chemistry. Ferrocenyl benzyl ethers were successfully prepared by reacting 4-ferrocenylbenzyl-1Hcarboxylate with a series of primary alcohols under catalytic condition and under a catalyst– free environment. Refluxing a mixture of alcohol-water and 4-ferrocenylbenzyl-1Hcarboxylate provided the corresponding ethers in modest yields. The same ethers were obtained at room temperature by employing potassium tetrachloroplatinate or hydrochloric acid as catalyst. Ferrocenyl-1H-imidazole, 4-ferrocenylphenyl-1H-imidazole and their corresponding ferrocenyl-3-subsitituted imidazolium salts have been successfully synthesized. The compounds were characterized and the electrochemical properties of selected imidazolium salts were examined by cyclic voltammetry. Additionally, X-ray structures of two of the imidazolium salts were determined. The imidazolium salts were found to be good catalysts for the Heck and Suzuki cross-coupling reactions.
- Full Text:
- Date Issued: 2010
The anticancer activity of Cyathula prostrata on two malignant cell lines
- Authors: Schnablegger, Gerald
- Date: 2010
- Subjects: Medicinal plants
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10309 , http://hdl.handle.net/10948/1563 , Medicinal plants
- Description: Plants have always been a source of medicine and are still being used by traditional healers in the rural part of Africa, Asia and India to treat a range of illnesses including cancer. The in vitro anticancer activity of an 80 percent ethanol extract of Cyathula prostrata, an annual branching shrub used by traditional healers in Nigeria to treat cancer was investigated. No previous studies have outlined the possible pathways and mechanisms used by cancer cells when treated with C. prostrata. Dose response analysis was performed to determine the effective cytotoxic concentrations of C. prostrata on HeLa (cervical cancer cell line) and U937 (myelo-monocytic cell line). The IC50 values were 100.8 μg/ml and 64.4 μg/ml for HeLa and U937 cells, respectively. All further experiments were performed using 125 μg/ml C. prostrata extract and 50 μM cisplatin as positive control. With the use of the fluorescent DNA binding dye propidium iodide, the induction of tumour cell death by C. prostrata extract has been linked to cell cycle arrest in the G1 phase at 24 and 48 h. In both cell lines, more than 80 percent of the C. prostrata treated cells were found in the G1 phase after 48 hours of treatment. The annexin V-FITC/PI assay revealed an increase in the percentage apoptotic cells from 4.9 percent to 53.1 percent at 24 h and 8.3 percent to 50.3 percent at 48 h. Since apoptosis induction can occur via a number of different pathways, distinct features were used as markers to investigate the mode of action of this C. prostrata extract. Markers such as activated caspase-8, p21 and cyt-c, were investigated with the aid of fluorescently labelled (FITC) antibodies with analysis using flow cytometry. No change in p21 levels was observed in response to treatment with the extract for up to 48 h. Cell cycle arrest in G1 was therefore not induced by this cyclin-CDK inhibitor. Increase in caspase-8 activation was observed in response to treatment with the extract with no cyt-c release from the mitochondria. The lack of cyt-c release was due to no change in mitochondrial membrane potential, which was investigated with the aid of fluorescent mitochondrial dyes and flow cytometric techniques. Caspase-8 activation is unique to the extrinsic apoptotic pathway. The results from this study therefore show that C. prostrata extract induces apoptosis via the extrinsic pathway and that this activation in independent of the mitochondria. The levels of hTERT, the catalytic subunit of telomerase, were investigated as an additional molecular target for C. prostrata. This was also investigated using FITC labelled antibodies and flow cytometry. A decrease in hTERT levels was observed following C. prostrata treatment. The findings from this study suggest that the extract acts through multiple targets, by inducing: cell cycle arrest in the G1 phase through an unknown mechanism; apoptosis through an extrinsic death receptor pathway and replicative senescence through inhibition of telomerase.
- Full Text:
- Date Issued: 2010
- Authors: Schnablegger, Gerald
- Date: 2010
- Subjects: Medicinal plants
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10309 , http://hdl.handle.net/10948/1563 , Medicinal plants
- Description: Plants have always been a source of medicine and are still being used by traditional healers in the rural part of Africa, Asia and India to treat a range of illnesses including cancer. The in vitro anticancer activity of an 80 percent ethanol extract of Cyathula prostrata, an annual branching shrub used by traditional healers in Nigeria to treat cancer was investigated. No previous studies have outlined the possible pathways and mechanisms used by cancer cells when treated with C. prostrata. Dose response analysis was performed to determine the effective cytotoxic concentrations of C. prostrata on HeLa (cervical cancer cell line) and U937 (myelo-monocytic cell line). The IC50 values were 100.8 μg/ml and 64.4 μg/ml for HeLa and U937 cells, respectively. All further experiments were performed using 125 μg/ml C. prostrata extract and 50 μM cisplatin as positive control. With the use of the fluorescent DNA binding dye propidium iodide, the induction of tumour cell death by C. prostrata extract has been linked to cell cycle arrest in the G1 phase at 24 and 48 h. In both cell lines, more than 80 percent of the C. prostrata treated cells were found in the G1 phase after 48 hours of treatment. The annexin V-FITC/PI assay revealed an increase in the percentage apoptotic cells from 4.9 percent to 53.1 percent at 24 h and 8.3 percent to 50.3 percent at 48 h. Since apoptosis induction can occur via a number of different pathways, distinct features were used as markers to investigate the mode of action of this C. prostrata extract. Markers such as activated caspase-8, p21 and cyt-c, were investigated with the aid of fluorescently labelled (FITC) antibodies with analysis using flow cytometry. No change in p21 levels was observed in response to treatment with the extract for up to 48 h. Cell cycle arrest in G1 was therefore not induced by this cyclin-CDK inhibitor. Increase in caspase-8 activation was observed in response to treatment with the extract with no cyt-c release from the mitochondria. The lack of cyt-c release was due to no change in mitochondrial membrane potential, which was investigated with the aid of fluorescent mitochondrial dyes and flow cytometric techniques. Caspase-8 activation is unique to the extrinsic apoptotic pathway. The results from this study therefore show that C. prostrata extract induces apoptosis via the extrinsic pathway and that this activation in independent of the mitochondria. The levels of hTERT, the catalytic subunit of telomerase, were investigated as an additional molecular target for C. prostrata. This was also investigated using FITC labelled antibodies and flow cytometry. A decrease in hTERT levels was observed following C. prostrata treatment. The findings from this study suggest that the extract acts through multiple targets, by inducing: cell cycle arrest in the G1 phase through an unknown mechanism; apoptosis through an extrinsic death receptor pathway and replicative senescence through inhibition of telomerase.
- Full Text:
- Date Issued: 2010
The botanical importance and health of the Bushmans estuary, Eastern Cape, South Africa
- Authors: Jafta, Nolusindiso
- Date: 2010
- Subjects: Estuaries -- South Africa , Bushmans river estuary , Estuarine ecology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10614 , http://hdl.handle.net/10948/1255 , Estuaries -- South Africa , Bushmans river estuary , Estuarine ecology -- South Africa
- Description: The Bushmans Estuary is one of the few permanently open estuaries in the Eastern Cape that is characterized by large intertidal salt marshes. Freshwater inflow to the estuary has decreased as a result of abstraction by more than 30 weirs and farm dams in the catchment. The mean annual run-off is naturally low (38 x 106 m3 y-1) and thus abstraction and reduction of freshwater inflow to the estuary is expected to cause a number of changes. The aims of this study were to determine the current health/status of the estuary based on the macrophytes and microalgae and identify monitoring indicators for the East London Department of Water Affairs, River Health Programme. Changes in the estuary over time were determined from available historical data which were compared with present data. This analysis showed that under normal average conditions freshwater inflow to the estuary is very low, less that 0.02 m3 s-1 most of the time. Under these conditions the estuary is in a homogenous marine state. Vertical and horizontal salinity gradients only form when high rainfall and run-off occurs (> 5 m3.s-1). Salinity gradients from 30.1 PSU at the mouth to 2.2 PSU in the upper reaches were measured in 2006 after a high flow event. However the estuary quickly reverted back to its homogenous condition within weeks after this flood. This study showed that freshwater inflow increased nutrient input to the estuary. Total oxidised nitrogen (TOxN) and soluble reactive phosphorus (SRP) concentrations were higher in August 2006, after the flood, than during the other low flow sampling sessions. TOxN decreased from a mean concentration of 21.6 μM in 2006 to 1.93 μM in February 2009. SRP decreased from 55.3 μM to 0.2 μM respectively. With the increased nutrient availability, the response in the estuary was an increase in phytoplankton biomass. After the 2006 floods the average water column chlorophyll-a was 9.0 μg l-1, while in the low freshwater inflow years it ranged from 2.1 to 4.8 μg l-1. The composition of the phytoplankton community was always dominated by flagellates and then diatoms, with higher cell numbers in the nutrient-enriched 2006 period. Although the water column nutrient data indicated that the estuary was oligotrophic, benthic microalgal biomass (11.9-16.1 μg.g-1) in the intertidal zone was comparable with nutrient rich estuaries. Benthic species indicative of polluted conditions were found (Nitzschia frustulum, Navicula gregaria, Navicula cryptotenelloides). These benthic species were found at the sites where wastewater / sewage seepage had occurred. Benthic diatom species also indicated freshwater inflow. During the high flow period in 2006 the dominant diatoms were fresh to brackish species that were strongly associated with the high concentrations of TOxN and SRP (Tryblionella constricta, Diploneis smithii, Hippodonta cf. gremainii, and Navicula species). During the freshwater limited period of 2008 and 2009 the benthic diatom species shifted to a group responding to the high salinity, ammonium and silicate concentrations. The species in this group were Nitzschia flexa, Navicula tenneloides, Diploneis elliptica, Amphora subacutiuscula and Nitzschia coarctata. Ordination results showed that the epiphytic diatom species responded to different environmental variables in the different years. Most of the species in 2008/2009 were associated with high salinity, temperature, dissolved oxygen, ammonium and silicate concentrations while the response was towards TOxN and SRP in 2006. The dominant species were Cocconeis placentula v euglyphyta in 2006; Nitzschia frustulum in 2008; and Synedra spp in 2009. The average biomass of the epiphytes was significantly lower in May 2008 than in both August 2006 and February 2009; 88.0 + 17.7 mg.m-2, 1.7 + 0.8 mg.m-2, and 61.8 + 14.4 mg.m-2 respectively. GIS mapping of past and present aerial photographs showed that submerged macrophyte (Zostera capensis) cover in 1966 and 1973 was less than that mapped for 2004. Salt marsh also increased its cover over time, from 86.9 ha in 1966 to 126 ha in 2004, colonizing what were bare sandy areas. Long-term monitoring of the health of the Bushmans Estuary should focus on salinity (as an indicator of inflow or deprivation of freshwater), benthic diatom identification and macrophyte distribution and composition (for the detection of pollution input), and bathymetric surveys (for shallowing of the estuary due to sedimentation).
- Full Text:
- Date Issued: 2010
- Authors: Jafta, Nolusindiso
- Date: 2010
- Subjects: Estuaries -- South Africa , Bushmans river estuary , Estuarine ecology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10614 , http://hdl.handle.net/10948/1255 , Estuaries -- South Africa , Bushmans river estuary , Estuarine ecology -- South Africa
- Description: The Bushmans Estuary is one of the few permanently open estuaries in the Eastern Cape that is characterized by large intertidal salt marshes. Freshwater inflow to the estuary has decreased as a result of abstraction by more than 30 weirs and farm dams in the catchment. The mean annual run-off is naturally low (38 x 106 m3 y-1) and thus abstraction and reduction of freshwater inflow to the estuary is expected to cause a number of changes. The aims of this study were to determine the current health/status of the estuary based on the macrophytes and microalgae and identify monitoring indicators for the East London Department of Water Affairs, River Health Programme. Changes in the estuary over time were determined from available historical data which were compared with present data. This analysis showed that under normal average conditions freshwater inflow to the estuary is very low, less that 0.02 m3 s-1 most of the time. Under these conditions the estuary is in a homogenous marine state. Vertical and horizontal salinity gradients only form when high rainfall and run-off occurs (> 5 m3.s-1). Salinity gradients from 30.1 PSU at the mouth to 2.2 PSU in the upper reaches were measured in 2006 after a high flow event. However the estuary quickly reverted back to its homogenous condition within weeks after this flood. This study showed that freshwater inflow increased nutrient input to the estuary. Total oxidised nitrogen (TOxN) and soluble reactive phosphorus (SRP) concentrations were higher in August 2006, after the flood, than during the other low flow sampling sessions. TOxN decreased from a mean concentration of 21.6 μM in 2006 to 1.93 μM in February 2009. SRP decreased from 55.3 μM to 0.2 μM respectively. With the increased nutrient availability, the response in the estuary was an increase in phytoplankton biomass. After the 2006 floods the average water column chlorophyll-a was 9.0 μg l-1, while in the low freshwater inflow years it ranged from 2.1 to 4.8 μg l-1. The composition of the phytoplankton community was always dominated by flagellates and then diatoms, with higher cell numbers in the nutrient-enriched 2006 period. Although the water column nutrient data indicated that the estuary was oligotrophic, benthic microalgal biomass (11.9-16.1 μg.g-1) in the intertidal zone was comparable with nutrient rich estuaries. Benthic species indicative of polluted conditions were found (Nitzschia frustulum, Navicula gregaria, Navicula cryptotenelloides). These benthic species were found at the sites where wastewater / sewage seepage had occurred. Benthic diatom species also indicated freshwater inflow. During the high flow period in 2006 the dominant diatoms were fresh to brackish species that were strongly associated with the high concentrations of TOxN and SRP (Tryblionella constricta, Diploneis smithii, Hippodonta cf. gremainii, and Navicula species). During the freshwater limited period of 2008 and 2009 the benthic diatom species shifted to a group responding to the high salinity, ammonium and silicate concentrations. The species in this group were Nitzschia flexa, Navicula tenneloides, Diploneis elliptica, Amphora subacutiuscula and Nitzschia coarctata. Ordination results showed that the epiphytic diatom species responded to different environmental variables in the different years. Most of the species in 2008/2009 were associated with high salinity, temperature, dissolved oxygen, ammonium and silicate concentrations while the response was towards TOxN and SRP in 2006. The dominant species were Cocconeis placentula v euglyphyta in 2006; Nitzschia frustulum in 2008; and Synedra spp in 2009. The average biomass of the epiphytes was significantly lower in May 2008 than in both August 2006 and February 2009; 88.0 + 17.7 mg.m-2, 1.7 + 0.8 mg.m-2, and 61.8 + 14.4 mg.m-2 respectively. GIS mapping of past and present aerial photographs showed that submerged macrophyte (Zostera capensis) cover in 1966 and 1973 was less than that mapped for 2004. Salt marsh also increased its cover over time, from 86.9 ha in 1966 to 126 ha in 2004, colonizing what were bare sandy areas. Long-term monitoring of the health of the Bushmans Estuary should focus on salinity (as an indicator of inflow or deprivation of freshwater), benthic diatom identification and macrophyte distribution and composition (for the detection of pollution input), and bathymetric surveys (for shallowing of the estuary due to sedimentation).
- Full Text:
- Date Issued: 2010
The dynamics of Larval fish and Zooplankton assemblages in the Sundays Estuary, South Africa
- Authors: Sutherland, Kate
- Date: 2010
- Subjects: Marine zooplankton -- South Africa , Zooplankton -- South Africa , Fishes -- Larvae -- South Africa , Estuarine ecology -- South Africa , Estuaries -- South Africa -- Management , Environmental monitoring -- South Africa , Coastal zone management -- South Africa , Estuarine area conservation -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10697 , http://hdl.handle.net/10948/1119 , Marine zooplankton -- South Africa , Zooplankton -- South Africa , Fishes -- Larvae -- South Africa , Estuarine ecology -- South Africa , Estuaries -- South Africa -- Management , Environmental monitoring -- South Africa , Coastal zone management -- South Africa , Estuarine area conservation -- South Africa
- Description: The larval fish and zooplankton assemblages were studied in the permanently open Sundays Estuary on the south-east coast of South Africa, using standard boat-based plankton towing methods. A total of 8174 larval and early juvenile fishes were caught, representing 12 families and 23 taxa. The Clupeidae, Gobiidae and Blenniidae were the dominant fish families. Common species included Gilchristella aestuaria, Caffrogobius gilchristi, Omobranchus woodi, Liza dumerilii, Glossogobius callidus and Myxus capensis. Estuarine resident species (Category I) predominantly in the preflexion developmental stage, dominated the system. A total of 19 zooplankton taxa were recorded. Copepoda dominated the zooplankton community. Dominant species included Pseudodiaptomus hessei, Acartia longipatella, Halicyclops sp., Mesopodopsis wooldridgei, and the larvae of Paratylodiplax edwardsii and Hymenosoma orbiculare. Mean larval fish density showed similar trends seasonally, spatially and across salinity zones, with mean zooplankton density in the Sundays Estuary. Gut content analysis of five larval fish species: Gilchristella aestuaria, Pomadasys commersonnii, Monodactylus falciformis, Myxus capensis and Rhabdosargus holubi, revealed species specific diet and prey selection. Although larval fish diet contained a variety of prey items, guts were dominated by P. hessei, chironomid larvae, Corophium triaenonyx, copepod eggs and insect larvae. Physico-chemical drivers and the interactions between these two plankton communities provide information that enables a more holistic view of the dynamics occurring in the Sundays Estuary planktonic ecosystem.
- Full Text:
- Date Issued: 2010
- Authors: Sutherland, Kate
- Date: 2010
- Subjects: Marine zooplankton -- South Africa , Zooplankton -- South Africa , Fishes -- Larvae -- South Africa , Estuarine ecology -- South Africa , Estuaries -- South Africa -- Management , Environmental monitoring -- South Africa , Coastal zone management -- South Africa , Estuarine area conservation -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10697 , http://hdl.handle.net/10948/1119 , Marine zooplankton -- South Africa , Zooplankton -- South Africa , Fishes -- Larvae -- South Africa , Estuarine ecology -- South Africa , Estuaries -- South Africa -- Management , Environmental monitoring -- South Africa , Coastal zone management -- South Africa , Estuarine area conservation -- South Africa
- Description: The larval fish and zooplankton assemblages were studied in the permanently open Sundays Estuary on the south-east coast of South Africa, using standard boat-based plankton towing methods. A total of 8174 larval and early juvenile fishes were caught, representing 12 families and 23 taxa. The Clupeidae, Gobiidae and Blenniidae were the dominant fish families. Common species included Gilchristella aestuaria, Caffrogobius gilchristi, Omobranchus woodi, Liza dumerilii, Glossogobius callidus and Myxus capensis. Estuarine resident species (Category I) predominantly in the preflexion developmental stage, dominated the system. A total of 19 zooplankton taxa were recorded. Copepoda dominated the zooplankton community. Dominant species included Pseudodiaptomus hessei, Acartia longipatella, Halicyclops sp., Mesopodopsis wooldridgei, and the larvae of Paratylodiplax edwardsii and Hymenosoma orbiculare. Mean larval fish density showed similar trends seasonally, spatially and across salinity zones, with mean zooplankton density in the Sundays Estuary. Gut content analysis of five larval fish species: Gilchristella aestuaria, Pomadasys commersonnii, Monodactylus falciformis, Myxus capensis and Rhabdosargus holubi, revealed species specific diet and prey selection. Although larval fish diet contained a variety of prey items, guts were dominated by P. hessei, chironomid larvae, Corophium triaenonyx, copepod eggs and insect larvae. Physico-chemical drivers and the interactions between these two plankton communities provide information that enables a more holistic view of the dynamics occurring in the Sundays Estuary planktonic ecosystem.
- Full Text:
- Date Issued: 2010
The geology of the Witteberg group, Cape supergroup, with specific focus on the Perdepoort member as a potential silica source
- Authors: Olivier, Wernich Corné
- Date: 2010
- Subjects: Geology -- South Africa -- Witteberg Group , Stratiography -- South Africa -- Witteberg Group , Silicate minerals -- South Africa -- Witteberg Group
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10660 , http://hdl.handle.net/10948/1386 , http://hdl.handle.net/10948/d1012889 , Geology -- South Africa -- Witteberg Group , Stratiography -- South Africa -- Witteberg Group , Silicate minerals -- South Africa -- Witteberg Group
- Description: Selected outcrops of the Upper Devonian to Lower Carboniferous, Witteberg Group, Cape Supergroup were mineralogically and structurally analyzed. The study area is located approximately 30km northwest of Kirkwood and 10km south of Darlington Dam, Eastern Cape, South Africa. Strata predominantly consist of arenaceous Witpoort Formation, which includes the Perdepoort, and Rooirand Members. The Perdepoort Member is a thinly bedded quartzite also known as the "white streak". The Rooirand Member quartzite is a highly iron stained red-brown quartzite. The dark-grey, pyritic rich shales of the Kweekvlei Formation overlie the Witpoort Formation in the southern half of the study site. These shales are highly deformed and display closely spaced thrust faults and close folds. The study area encapsulates a range of folding from tight to open folds. Faulting consists of low angle north verging thrust fault, south verging back thrusts, south and north dipping normal faults, and strike-slip faults. Closely spaced, fore-land verging thrusts faults predominate over hinterland verging back thrusts. Normal faulting post-dates thrust faulting and utilized weaknesses in axial planar cleavage and in certain instances existing thrust fault planes. Strike-slip faulting post-dates thrusting and has in places reactivated pre-existing thrust fault planes. Macro scale folding includes overturned synclines and large anticlines which have been eroded, exposing older strata. Fold axes plunge at low to moderate angles west-southwest. This correlates with tension gashes which indicate north westward directed forces. Eastward directed forces are confirmed by the presence of tension gashes and strike-slip movement. The local geology displays north westward directed compression followed by strike-slip movement. Normal faulting post-dates all other structures and is associated with the Mesozoic break-up of Gondwana. The Perdepoort Member was sampled along strike, at different outcrop latitudes. Seven samples were selected for scanning electron microscope analysis. Samples are composed almost entirely of quartz; accessories include, biotite, muscovite, sericite, baryte, and apatite. Epigenetic hematite is present along cracks within certain samples Epigenetic hematite occur along cracks with oxides and phosphates in the form of rutile, apatite and monazite present in a number of samples. When compared to other silica extraction operations the Perdepoort Member appears viable for explotation. However, for the solar cell industry the purity of this horizon is clearly far below that required for industy.
- Full Text:
- Date Issued: 2010
- Authors: Olivier, Wernich Corné
- Date: 2010
- Subjects: Geology -- South Africa -- Witteberg Group , Stratiography -- South Africa -- Witteberg Group , Silicate minerals -- South Africa -- Witteberg Group
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10660 , http://hdl.handle.net/10948/1386 , http://hdl.handle.net/10948/d1012889 , Geology -- South Africa -- Witteberg Group , Stratiography -- South Africa -- Witteberg Group , Silicate minerals -- South Africa -- Witteberg Group
- Description: Selected outcrops of the Upper Devonian to Lower Carboniferous, Witteberg Group, Cape Supergroup were mineralogically and structurally analyzed. The study area is located approximately 30km northwest of Kirkwood and 10km south of Darlington Dam, Eastern Cape, South Africa. Strata predominantly consist of arenaceous Witpoort Formation, which includes the Perdepoort, and Rooirand Members. The Perdepoort Member is a thinly bedded quartzite also known as the "white streak". The Rooirand Member quartzite is a highly iron stained red-brown quartzite. The dark-grey, pyritic rich shales of the Kweekvlei Formation overlie the Witpoort Formation in the southern half of the study site. These shales are highly deformed and display closely spaced thrust faults and close folds. The study area encapsulates a range of folding from tight to open folds. Faulting consists of low angle north verging thrust fault, south verging back thrusts, south and north dipping normal faults, and strike-slip faults. Closely spaced, fore-land verging thrusts faults predominate over hinterland verging back thrusts. Normal faulting post-dates thrust faulting and utilized weaknesses in axial planar cleavage and in certain instances existing thrust fault planes. Strike-slip faulting post-dates thrusting and has in places reactivated pre-existing thrust fault planes. Macro scale folding includes overturned synclines and large anticlines which have been eroded, exposing older strata. Fold axes plunge at low to moderate angles west-southwest. This correlates with tension gashes which indicate north westward directed forces. Eastward directed forces are confirmed by the presence of tension gashes and strike-slip movement. The local geology displays north westward directed compression followed by strike-slip movement. Normal faulting post-dates all other structures and is associated with the Mesozoic break-up of Gondwana. The Perdepoort Member was sampled along strike, at different outcrop latitudes. Seven samples were selected for scanning electron microscope analysis. Samples are composed almost entirely of quartz; accessories include, biotite, muscovite, sericite, baryte, and apatite. Epigenetic hematite is present along cracks within certain samples Epigenetic hematite occur along cracks with oxides and phosphates in the form of rutile, apatite and monazite present in a number of samples. When compared to other silica extraction operations the Perdepoort Member appears viable for explotation. However, for the solar cell industry the purity of this horizon is clearly far below that required for industy.
- Full Text:
- Date Issued: 2010
The importance of estuarine head waters for fishes in selected Eastern Cape systems, with particular emphasis on the influence of freshwater inflow, migration barriers and non-native predators on the juvenile and small fish component
- Authors: Wasserman, Ryan
- Date: 2010
- Subjects: Estuaries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10685 , http://hdl.handle.net/10948/1457 , Estuaries -- South Africa -- Eastern Cape
- Description: The utilisation of estuary headwater environments by young estuary- and marine-spawned fish species was investigated together with the effects of riverflow alteration, in-stream barrier effects and non-native ichthyofauna on the nursery function of these habitats. The distribution and abundance of young estuary- and marine-spawned fish were sampled using seine and fyke nets in the headwater environments of four permanently open Eastern Cape systems, namely the Great Fish, Kowie, Kariega and Sundays Estuaries. Within the suite of study systems, the first of two case studies focussed on barrier effects of in-stream structures on fish migration. This was undertaken in the Sundays River. In the second case study, predation and competition dynamics of the non-native piscivorous Micropterus salmoides on estuary-dependent fish was investigated in the estuary headwater regions of the Kowie River system. In all four estuaries, young estuary-spawned fish species dominated the ichthyofaunal community followed by marine-spawned species, despite varied freshwater inflow resulting in headwaters varying in salinity from fresh to hypersaline. Fish community structure however, differed largely between estuaries, with both freshwater abstraction and unnatural elevation of freshwater into estuaries, as a result of inter-basin transfers, affecting these communities. In-stream structures were found to effect upstream movement of fish in two ways, dependent on the type of barrier. Partial (size-dependent) and complete (species-dependent) restriction to upstream migration of fish by causeway-type instream structures were observed. Weir-type in-stream structures acted as a complete barrier to most species, regardless of fish size. Predation of estuary- and marine-spawned fish species by large sized M. salmoides was recorded, although these fish did not contribute significantly to their diet during this study. However, the main dietary components found in smaller sized M. salmoides stomachs overlap with those of juvenile estuary- and marinespawned fish species, suggesting feeding competition between the juveniles of indigenous and non-native fish species.
- Full Text:
- Date Issued: 2010
- Authors: Wasserman, Ryan
- Date: 2010
- Subjects: Estuaries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10685 , http://hdl.handle.net/10948/1457 , Estuaries -- South Africa -- Eastern Cape
- Description: The utilisation of estuary headwater environments by young estuary- and marine-spawned fish species was investigated together with the effects of riverflow alteration, in-stream barrier effects and non-native ichthyofauna on the nursery function of these habitats. The distribution and abundance of young estuary- and marine-spawned fish were sampled using seine and fyke nets in the headwater environments of four permanently open Eastern Cape systems, namely the Great Fish, Kowie, Kariega and Sundays Estuaries. Within the suite of study systems, the first of two case studies focussed on barrier effects of in-stream structures on fish migration. This was undertaken in the Sundays River. In the second case study, predation and competition dynamics of the non-native piscivorous Micropterus salmoides on estuary-dependent fish was investigated in the estuary headwater regions of the Kowie River system. In all four estuaries, young estuary-spawned fish species dominated the ichthyofaunal community followed by marine-spawned species, despite varied freshwater inflow resulting in headwaters varying in salinity from fresh to hypersaline. Fish community structure however, differed largely between estuaries, with both freshwater abstraction and unnatural elevation of freshwater into estuaries, as a result of inter-basin transfers, affecting these communities. In-stream structures were found to effect upstream movement of fish in two ways, dependent on the type of barrier. Partial (size-dependent) and complete (species-dependent) restriction to upstream migration of fish by causeway-type instream structures were observed. Weir-type in-stream structures acted as a complete barrier to most species, regardless of fish size. Predation of estuary- and marine-spawned fish species by large sized M. salmoides was recorded, although these fish did not contribute significantly to their diet during this study. However, the main dietary components found in smaller sized M. salmoides stomachs overlap with those of juvenile estuary- and marinespawned fish species, suggesting feeding competition between the juveniles of indigenous and non-native fish species.
- Full Text:
- Date Issued: 2010