Assessing soil carbon and carbon dioxide effluxes under different vegetation cover conditions in the Eastern Cape Province, South Africa
- Authors: Zengeni, Rebecca
- Date: 2013
- Subjects: Soils -- Carbon content -- Measurement , Carbon dioxide mitigation -- South Africa , Greenhouse gas mitigation -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10665 , http://hdl.handle.net/10948/d1018676
- Description: Albany thicket is prevalent in the Eastern Cape Province of South Africa. Its spread has diminished through overgrazing and heavy browsing by animals, land clearance and urban expansion. The result is highly degraded land characterized by invasion of alien species. There is a wealth of documented evidence on the high carbon sequestration ability of thicket biome, but not much has been done to assess its effect on carbon dioxide emissions from the soil. Given that the concentration of atmospheric greenhouse gases has been constantly rising since the industrial era, it is imperative to assess the influence of thicket biome as a source or sink of these gases. There is evidence of shifts in the climate in southern Africa as reflected by changes in rainfall patterns, increased temperatures, recurrent droughts and fires. As such, the historical rainfall variability in an Albany thicket region and its interaction with the temporal land use / cover changes was studied. This served to give some background information about the study area for more detailed study on C and carbon dioxide effluxes in thicket vegetation under different levels of degradation. This study thus aimed to determine the influence of thicket vegetation at various levels of degradation on soil carbon and carbon dioxide fluxes. The impact of plant photosynthetic pathway on soil C residence time and gas effluxes were analysed to elucidate on the land-use and cover patterns occurring in the area. All this was done to shed some light on the role of soil and thicket vegetation on carbon dioxide emissions and C storage in the spectrum of a shifting climate. The main area of research was Amakhala reserve in an Albany thicket in Eastern Cape Province; and it concentrated on three land cover types namely intact thicket, degraded thicket and grassland. The objectives mentioned above were achieved by assessing historical rainfall variability from 1970 to 2010 through trend and time series analysis at nine rainfall stations located at Amakhala reserve, Grahamstown, Bathurst, Port Alfred, Uitenhage and Port Elizabeth. The land use changes that have occurred in the Albany thicket region covering Amakhala reserve, Grahamstown, Bathurst and Port Alfred were also assessed for 1989, 1999 and 2009 through satellite image analysis with Idrisi Andes GIS software; then their interaction with rainfall variability were determined. To elucidate on the vegetation species composition and land use / cover changes that have occurred in the study area, plant biomass as well carbon (C) and nitrogen (N) isotope measurements were done. Plant biomass was assessed for the dominant species through use of pre-existing allometric equations that required data on plant basal diameter, canopy area, stem numbers and height. The plant carbon was then estimated through use of a conversion factor of 0.48 on above-ground biomass, while soil organic C was determined through the modified Walkely - Black method. Carbon and N isotope ratios were determined from the foliar material of three replicate samples of dominant plant species then analyzed through mass spectrometry. Soil carbon dioxide effluxes were then monitored in each of the intact thicket (IT), degraded thicket (DT) and grassland (G) over a 10 month period; by measuring the net carbon dioxide exchange rate (NCER) through the dynamic chamber method. An automated carbon dioxide exchange analyzer, coupled to a soil temperature probe and photosynthetic active radiation (PAR) sensor was used; with NCER measurements taken every 20-30 days. Soil temperature, moisture, penetration resistance and PAR readings were taken during each assay and later used to interpret the NCER. Results showed that long term variability in annual rainfall had a declining trend at Grahamstown (r = -0.59), Uitenhage and Bathurst stations (r = -0.32 at both stations), but was not significant at Amakhala, Port Alfred and Port Elizabeth stations. Most reductions in rainfall occurred in the 1980s and 1990s with the autumn, winter and summer rainfalls, the daily rainfall index and the daily rainfall subclasses of 10 mm and above showing a similar trend. The land use change detection gave a significant increase in proportion of degraded and transformed (moderately degraded) land between 1989 and 2009 with most of the increases occurring from 1989 to 1999, while farmland area decreased by 1.8 percent over the years. Thus the Albany region had over 30 percent of its land occupied by transformed vegetation, with heavy browsing and uncontrolled grazing being attributed to the destruction of pristine vegetation. Land-use change to game ranching and goat pastoralism was attributed to the reduction in farmland. Rainfall variability – land use change linkages were most significant in 1999 that recorded the least rainfall and had the lowest mean, maximum and sum of the NDVI. Grahamstown had the most significant rainfall-NDVI trends as it had the lowest NDVIs in 1999 when rainfall was lowest, the highest NDVI in 1989 when rainfall was highest and moderate NDVIs in 2009 when rainfall was moderate. Vegetation at the IT was characterized by a dense thicket with diverse growth forms of canopy trees, woody shrubs, succulent shrubs and ephemerals which mostly had the C3 type of pathway. This was in contrast with the IT soil isotopy that showed more positive C isotope ratios, indicating a switch between C3 and CAM photosynthesis in original vegetation. Most of the canopy trees had disappeared in the DT to be replaced by herbs, shrubs and grasses. As such, there was a huge difference in isotope ratios between DT plants and soils with the plants having mostly C3 metabolism while the soil showed a predominance of CAM plants in previous vegetation, indicating significant changes in land cover. The G site mostly comprised the grasses Themeda triandra and Panicum maximum and a few herbs. It maintained a dominance of C4 metabolism in both plants and soils showing very little change in species composition over the years. Because of the higher species diversity at IT, its soil organic C was quite high reaching levels of 3.4 percent (i.e. 3.4 t C / ha) in the top 10 cm then decreasing with depth (p < 0.001); but was moderate at DT (1.1-1.3 percent) and very low at G ( 0.5 percent C) (p < 0.001). In the same manner above-ground biomass was highest at IT i.e. 330 000 kg/ha; but was only 22 000 kg/ha in DT and as low as 6 700 kg/ha in G vegetation. High biomass at IT was mostly attributed to the succulent shrub Portulacaria afra and the canopy trees Euclea undulate, Rhus longispina and Schotia afra. This above-ground biomass translated to biomass C amounts of 158 000 kg/ha at IT, 10 600 kg/ha at DT and 3 200 kg/ha at G. Thus the IT had the highest while G the least and DT moderate plant and soil C sequestration ability. In all, the conversion of IT to DT led to a net loss of 147 000 Kg of biomass C / ha and 12 000kg less organic C / ha of land. Soil carbon dioxide effluxes were however variable between seasons as they were affected by differences in soil properties and seasonal weather patterns. High soil moisture levels (up to 16 percent gravimetric moisture) resulted in reduced soil penetration resistance (1 to 4 Kg/cm2) which raised effluxes at G and DT sites (up to 1.2 μmols m-2 sec-1) in winter, while low moisture (2 percent) resulted in hard dry soil (14 Kgm-2 penetration resistance) with suppressed CO2 effluxes in spring (0.2 μmols m-2 sec-1) especially in DT and G soils. Rising temperature generally caused accelerated gas emissions but only when moisture was not limiting (as was the case in IT). Thus the high summer temperatures (up to 40oC) gave lower effluxes especially in DT and G (< 1 μm-2sec-1) due to limited moisture supply (< 10 percent); while the Autumn period that had very high temperature (up to 48 oC) and good moisture (up to 16 percent) saw accelerated soil CO2 emissions (averaging 2 μmols m-2 sec-1) from all cover types. The high biomass and litter fall at IT served as ready substrate for soil respiration as long as moisture was not limiting and temperatures were favourable, while reduced cover at DT resulted in poor moisture conservation and creation of hard dry soils in spring and summer with reduced respiration. It was concluded that the DT had high CO2 effluxes in winter and reduced emissions in summer; while the opposite was true for the IT. All the cover types had minimal CO2 effluxes in spring and accelerated emissions in autumn. The grassland on the other hand was a fairly moderate source or sink of CO2 in most seasons compared with the other two covers. It was observed that an environment of good moisture and low-moderate temperatures (such as that in the winter) minimises effluxes while maintaining good plant productivity. It was concluded that thicket vegetation is a good sink of carbon that should be preserved in its natural condition to optimize its carbon sequestration potential. All three land covers served as sources or sinks of CO2 depending on soil and seasonal conditions. Thus high moisture and low penetration resistance generally increased effluxes of thicket ecosystems. The effect of increasing temperature on effluxes was only significant when moisture was not limiting. Conditions of good moisture and low-moderate temperatures gave reasonable amounts of effluxes while maintaining good plant productivity. Though the dry soil conditions significantly reduced effluxes in all land covers; they were not desirable since they decreased plant productivity and ultimately its C sequestration potential. Moreover, prolonged dry conditions only serve to exacerbate recovery of thicket plants as they increase mortality of canopy species in degraded and transformed areas in comparison with intact thicket.
- Full Text:
- Date Issued: 2013
- Authors: Zengeni, Rebecca
- Date: 2013
- Subjects: Soils -- Carbon content -- Measurement , Carbon dioxide mitigation -- South Africa , Greenhouse gas mitigation -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10665 , http://hdl.handle.net/10948/d1018676
- Description: Albany thicket is prevalent in the Eastern Cape Province of South Africa. Its spread has diminished through overgrazing and heavy browsing by animals, land clearance and urban expansion. The result is highly degraded land characterized by invasion of alien species. There is a wealth of documented evidence on the high carbon sequestration ability of thicket biome, but not much has been done to assess its effect on carbon dioxide emissions from the soil. Given that the concentration of atmospheric greenhouse gases has been constantly rising since the industrial era, it is imperative to assess the influence of thicket biome as a source or sink of these gases. There is evidence of shifts in the climate in southern Africa as reflected by changes in rainfall patterns, increased temperatures, recurrent droughts and fires. As such, the historical rainfall variability in an Albany thicket region and its interaction with the temporal land use / cover changes was studied. This served to give some background information about the study area for more detailed study on C and carbon dioxide effluxes in thicket vegetation under different levels of degradation. This study thus aimed to determine the influence of thicket vegetation at various levels of degradation on soil carbon and carbon dioxide fluxes. The impact of plant photosynthetic pathway on soil C residence time and gas effluxes were analysed to elucidate on the land-use and cover patterns occurring in the area. All this was done to shed some light on the role of soil and thicket vegetation on carbon dioxide emissions and C storage in the spectrum of a shifting climate. The main area of research was Amakhala reserve in an Albany thicket in Eastern Cape Province; and it concentrated on three land cover types namely intact thicket, degraded thicket and grassland. The objectives mentioned above were achieved by assessing historical rainfall variability from 1970 to 2010 through trend and time series analysis at nine rainfall stations located at Amakhala reserve, Grahamstown, Bathurst, Port Alfred, Uitenhage and Port Elizabeth. The land use changes that have occurred in the Albany thicket region covering Amakhala reserve, Grahamstown, Bathurst and Port Alfred were also assessed for 1989, 1999 and 2009 through satellite image analysis with Idrisi Andes GIS software; then their interaction with rainfall variability were determined. To elucidate on the vegetation species composition and land use / cover changes that have occurred in the study area, plant biomass as well carbon (C) and nitrogen (N) isotope measurements were done. Plant biomass was assessed for the dominant species through use of pre-existing allometric equations that required data on plant basal diameter, canopy area, stem numbers and height. The plant carbon was then estimated through use of a conversion factor of 0.48 on above-ground biomass, while soil organic C was determined through the modified Walkely - Black method. Carbon and N isotope ratios were determined from the foliar material of three replicate samples of dominant plant species then analyzed through mass spectrometry. Soil carbon dioxide effluxes were then monitored in each of the intact thicket (IT), degraded thicket (DT) and grassland (G) over a 10 month period; by measuring the net carbon dioxide exchange rate (NCER) through the dynamic chamber method. An automated carbon dioxide exchange analyzer, coupled to a soil temperature probe and photosynthetic active radiation (PAR) sensor was used; with NCER measurements taken every 20-30 days. Soil temperature, moisture, penetration resistance and PAR readings were taken during each assay and later used to interpret the NCER. Results showed that long term variability in annual rainfall had a declining trend at Grahamstown (r = -0.59), Uitenhage and Bathurst stations (r = -0.32 at both stations), but was not significant at Amakhala, Port Alfred and Port Elizabeth stations. Most reductions in rainfall occurred in the 1980s and 1990s with the autumn, winter and summer rainfalls, the daily rainfall index and the daily rainfall subclasses of 10 mm and above showing a similar trend. The land use change detection gave a significant increase in proportion of degraded and transformed (moderately degraded) land between 1989 and 2009 with most of the increases occurring from 1989 to 1999, while farmland area decreased by 1.8 percent over the years. Thus the Albany region had over 30 percent of its land occupied by transformed vegetation, with heavy browsing and uncontrolled grazing being attributed to the destruction of pristine vegetation. Land-use change to game ranching and goat pastoralism was attributed to the reduction in farmland. Rainfall variability – land use change linkages were most significant in 1999 that recorded the least rainfall and had the lowest mean, maximum and sum of the NDVI. Grahamstown had the most significant rainfall-NDVI trends as it had the lowest NDVIs in 1999 when rainfall was lowest, the highest NDVI in 1989 when rainfall was highest and moderate NDVIs in 2009 when rainfall was moderate. Vegetation at the IT was characterized by a dense thicket with diverse growth forms of canopy trees, woody shrubs, succulent shrubs and ephemerals which mostly had the C3 type of pathway. This was in contrast with the IT soil isotopy that showed more positive C isotope ratios, indicating a switch between C3 and CAM photosynthesis in original vegetation. Most of the canopy trees had disappeared in the DT to be replaced by herbs, shrubs and grasses. As such, there was a huge difference in isotope ratios between DT plants and soils with the plants having mostly C3 metabolism while the soil showed a predominance of CAM plants in previous vegetation, indicating significant changes in land cover. The G site mostly comprised the grasses Themeda triandra and Panicum maximum and a few herbs. It maintained a dominance of C4 metabolism in both plants and soils showing very little change in species composition over the years. Because of the higher species diversity at IT, its soil organic C was quite high reaching levels of 3.4 percent (i.e. 3.4 t C / ha) in the top 10 cm then decreasing with depth (p < 0.001); but was moderate at DT (1.1-1.3 percent) and very low at G ( 0.5 percent C) (p < 0.001). In the same manner above-ground biomass was highest at IT i.e. 330 000 kg/ha; but was only 22 000 kg/ha in DT and as low as 6 700 kg/ha in G vegetation. High biomass at IT was mostly attributed to the succulent shrub Portulacaria afra and the canopy trees Euclea undulate, Rhus longispina and Schotia afra. This above-ground biomass translated to biomass C amounts of 158 000 kg/ha at IT, 10 600 kg/ha at DT and 3 200 kg/ha at G. Thus the IT had the highest while G the least and DT moderate plant and soil C sequestration ability. In all, the conversion of IT to DT led to a net loss of 147 000 Kg of biomass C / ha and 12 000kg less organic C / ha of land. Soil carbon dioxide effluxes were however variable between seasons as they were affected by differences in soil properties and seasonal weather patterns. High soil moisture levels (up to 16 percent gravimetric moisture) resulted in reduced soil penetration resistance (1 to 4 Kg/cm2) which raised effluxes at G and DT sites (up to 1.2 μmols m-2 sec-1) in winter, while low moisture (2 percent) resulted in hard dry soil (14 Kgm-2 penetration resistance) with suppressed CO2 effluxes in spring (0.2 μmols m-2 sec-1) especially in DT and G soils. Rising temperature generally caused accelerated gas emissions but only when moisture was not limiting (as was the case in IT). Thus the high summer temperatures (up to 40oC) gave lower effluxes especially in DT and G (< 1 μm-2sec-1) due to limited moisture supply (< 10 percent); while the Autumn period that had very high temperature (up to 48 oC) and good moisture (up to 16 percent) saw accelerated soil CO2 emissions (averaging 2 μmols m-2 sec-1) from all cover types. The high biomass and litter fall at IT served as ready substrate for soil respiration as long as moisture was not limiting and temperatures were favourable, while reduced cover at DT resulted in poor moisture conservation and creation of hard dry soils in spring and summer with reduced respiration. It was concluded that the DT had high CO2 effluxes in winter and reduced emissions in summer; while the opposite was true for the IT. All the cover types had minimal CO2 effluxes in spring and accelerated emissions in autumn. The grassland on the other hand was a fairly moderate source or sink of CO2 in most seasons compared with the other two covers. It was observed that an environment of good moisture and low-moderate temperatures (such as that in the winter) minimises effluxes while maintaining good plant productivity. It was concluded that thicket vegetation is a good sink of carbon that should be preserved in its natural condition to optimize its carbon sequestration potential. All three land covers served as sources or sinks of CO2 depending on soil and seasonal conditions. Thus high moisture and low penetration resistance generally increased effluxes of thicket ecosystems. The effect of increasing temperature on effluxes was only significant when moisture was not limiting. Conditions of good moisture and low-moderate temperatures gave reasonable amounts of effluxes while maintaining good plant productivity. Though the dry soil conditions significantly reduced effluxes in all land covers; they were not desirable since they decreased plant productivity and ultimately its C sequestration potential. Moreover, prolonged dry conditions only serve to exacerbate recovery of thicket plants as they increase mortality of canopy species in degraded and transformed areas in comparison with intact thicket.
- Full Text:
- Date Issued: 2013
Assessment of the incidence of E.coli in Tyume and Buffalo rivers in the Eastern Cape Province of South Africa
- Authors: Koba, Siziwe
- Date: 2013
- Language: English
- Type: Thesis , Doctoral , PhD (Microbiology)
- Identifier: vital:11272 , http://hdl.handle.net/10353/d1006889
- Description: Waterborne diseases are among the leading causes of morbidity and mortality in developing countries and every year around 2.2 million people die due to basic hygiene related diseases like coliform diarrhoea. Universal access to safe drinking water and sanitation has been promoted as an essential step in reducing these preventable diseases (Tambekar and Banginwar, 2005; Patil, 2004; Charan, 2004). Diarrheagenic Escherichia coli are one of the most important etiologic agents of acute diarrhea and represent a major public health problem in developing countries like South Africa The present study was conducted between August 2010 and July 2011 to investigate the prevalence and distribution of virulent E. coli strains from water samples collected from Tyume and Buffalo River, located in Eastern Cape Province of South Africa using conventional microbiological methods and PCR analysis. Twelve Water samples were collected from three different sites of the rivers, viz; upstream, middle stream and the downstream of the dam. E.coli was isolated by the membrane filtration method on mFC. A total of 374 isolates from both rivers were identified by convenctional microbiological techniques. For both Buffalo and Tyume River, A large proportion (87 and 114, respectively) of the isolates from the mid stream samples satisfied the identification characteristics for E. coli (blue colonies on MFC agar and violet/purple colonies on Chromocult agar) and thus revealing high levels contamination when compared to isolates from the downstream (55 and 47) and the upstream (30 and 31) All the isolates that satisfied the primary identification stage were subjected to PCR. DNA was extracted using the boiling method and then the DNA was used as a template for PCR. Specific PCR analysis was performed on all E. coli isolates to amplify the alr gene that codes for alanine racemase Out and of the 202 isolates amplified for Tyume river, 70 (35 percent) were positively identified as E. coli since they possessed the alr gene fragment. and out of the 172 isolates amplified from Buffalo River, 80(47 percent) were also positively identified as E. coli. For both Tyume and Buffalo River, the highest prevalence was observed midstream (39 percent and 56 pecent respectively). The identified E. coli were further characterized into different pathotypes. Amplification of the shig gene, LT gene, EaeA gene, Eagg gene and the ST gene were used to detect pathogenic E.coli. In Tyume River, Genes of ETEC (lt or st) were detected in 21/70 (30 percent); Gene of EPEC (eae) was detected in 14/70 specimens (35 percent); Genes of EAEC (Eagg) was detected in 14/70(35 percent) and genes of EIEC (shig) were detected in 11/70(16 percent). In Buffalo River, no DEC was recovered upstream and downstream of the river. EAEC (8 percent) was the only pathotypes recovered midstream of the river. Strains of all five E. coli categories showed high-level resistance to ampicillin, tetracycline, cotrimoxazole, and chloramphenicol but were highly susceptible to quinolones, aminoglycosides, and novobiocin. The highest resistance (100 percent) amongst the isolates was observed to ampicillin by EAEC, Heat Labile (ETEC) and EIEC, followed by 87.5 percent by EAEC to carbenicillin. The highest susceptibility was to quinolones (100 percent) by all the four categories of E.coli. The screening for antibiotic resistance genes revealed the absence of SHV, CTMX and TetC genes as they were not detected in any of the E.coli isolates. However, TEM genes were observed in 80 percent of the isolates. Integron conserved segment was detected in these same organisms in the same proportion as TEM
- Full Text:
- Date Issued: 2013
- Authors: Koba, Siziwe
- Date: 2013
- Language: English
- Type: Thesis , Doctoral , PhD (Microbiology)
- Identifier: vital:11272 , http://hdl.handle.net/10353/d1006889
- Description: Waterborne diseases are among the leading causes of morbidity and mortality in developing countries and every year around 2.2 million people die due to basic hygiene related diseases like coliform diarrhoea. Universal access to safe drinking water and sanitation has been promoted as an essential step in reducing these preventable diseases (Tambekar and Banginwar, 2005; Patil, 2004; Charan, 2004). Diarrheagenic Escherichia coli are one of the most important etiologic agents of acute diarrhea and represent a major public health problem in developing countries like South Africa The present study was conducted between August 2010 and July 2011 to investigate the prevalence and distribution of virulent E. coli strains from water samples collected from Tyume and Buffalo River, located in Eastern Cape Province of South Africa using conventional microbiological methods and PCR analysis. Twelve Water samples were collected from three different sites of the rivers, viz; upstream, middle stream and the downstream of the dam. E.coli was isolated by the membrane filtration method on mFC. A total of 374 isolates from both rivers were identified by convenctional microbiological techniques. For both Buffalo and Tyume River, A large proportion (87 and 114, respectively) of the isolates from the mid stream samples satisfied the identification characteristics for E. coli (blue colonies on MFC agar and violet/purple colonies on Chromocult agar) and thus revealing high levels contamination when compared to isolates from the downstream (55 and 47) and the upstream (30 and 31) All the isolates that satisfied the primary identification stage were subjected to PCR. DNA was extracted using the boiling method and then the DNA was used as a template for PCR. Specific PCR analysis was performed on all E. coli isolates to amplify the alr gene that codes for alanine racemase Out and of the 202 isolates amplified for Tyume river, 70 (35 percent) were positively identified as E. coli since they possessed the alr gene fragment. and out of the 172 isolates amplified from Buffalo River, 80(47 percent) were also positively identified as E. coli. For both Tyume and Buffalo River, the highest prevalence was observed midstream (39 percent and 56 pecent respectively). The identified E. coli were further characterized into different pathotypes. Amplification of the shig gene, LT gene, EaeA gene, Eagg gene and the ST gene were used to detect pathogenic E.coli. In Tyume River, Genes of ETEC (lt or st) were detected in 21/70 (30 percent); Gene of EPEC (eae) was detected in 14/70 specimens (35 percent); Genes of EAEC (Eagg) was detected in 14/70(35 percent) and genes of EIEC (shig) were detected in 11/70(16 percent). In Buffalo River, no DEC was recovered upstream and downstream of the river. EAEC (8 percent) was the only pathotypes recovered midstream of the river. Strains of all five E. coli categories showed high-level resistance to ampicillin, tetracycline, cotrimoxazole, and chloramphenicol but were highly susceptible to quinolones, aminoglycosides, and novobiocin. The highest resistance (100 percent) amongst the isolates was observed to ampicillin by EAEC, Heat Labile (ETEC) and EIEC, followed by 87.5 percent by EAEC to carbenicillin. The highest susceptibility was to quinolones (100 percent) by all the four categories of E.coli. The screening for antibiotic resistance genes revealed the absence of SHV, CTMX and TetC genes as they were not detected in any of the E.coli isolates. However, TEM genes were observed in 80 percent of the isolates. Integron conserved segment was detected in these same organisms in the same proportion as TEM
- Full Text:
- Date Issued: 2013
Atmospheric pressure metal-organic vapour phase epitaxial growth of InAs/GaSb strained layer superlattices
- Authors: Miya, Senzo Simo
- Date: 2013
- Subjects: Gallium arsenide semiconductors , Organometallic compounds , Compound semiconductors , Metal organic chemical vapor deposition , Superlattices as materials , Epitaxy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10557 , http://hdl.handle.net/10948/d1020866
- Description: The importance of infrared (IR) technology (for detection in the 3-5 μm and 8-14 μm atmospheric windows) has spread from military applications to civilian applications since World War II. The commercial IR detector market in these wavelength ranges is dominated by mercury cadmium telluride (MCT) alloys. The use of these alloys has, however, been faced with technological difficulties. One of the materials that have been tipped to be suitable to replace MCT is InAs/InxGa1-xSb strained layer superlattices (SLS’s). Atmospheric pressure metal-organic vapour phase epitaxy (MOVPE) has been used to grow InAs/GaSb strained layer superlattices (SLS’s) at 510 °C in this study. This is a starting point towards the development of MOVPE InAs/InxGa1-xSb SLS’s using the same system. Before the SLS’s could be attempted, the growth parameters for GaSb were optimised. Growth parameters for InAs were taken from reports on previous studies conducted using the same reactor. Initially, trimethylgallium, a source that has been used extensively in the same growth system for the growth of GaSb and InxGa1-xSb was intended to be used for gallium species. The high growth rates yielded by this source were too large for the growth of SLS structures, however. Thus, triethylgallium (rarely used for atmospheric pressure MOVPE) was utilized. GaSb layers (between 1 and 2 μm thick) were grown at two different temperatures (550 °C and 510 °C) with a varying V/III ratio. A V/III ratio of 1.5 was found to be optimal at 550 °C. However, the low incorporation efficiency of indium into GaSb at this temperature was inadequate to obtain InxGa1-xSb with an indium mole fraction (x) of around 0.3, which had previously been reported to be optimal for the performance of InAs/InxGa1-xSb SLS’s, due to the maximum splitting of the valence mini bands for this composition. The growth temperature was thus lowered to 510 °C. This resulted in an increase in the optimum V/III ratio to 1.75 for GaSb and yielded much higher incorporation efficiencies of indium in InxGa1-xSb. However, this lower growth temperature also produced poorer surface morphologies for both the binary and ternary layers, due to the reduced surface diffusion of the adsorbed species. An interface control study during the growth of InAs/GaSb SLS’s was subsequently conducted, by investigating the influence of different gas switching sequences on the interface type and quality. It was noted that the growth of SLS’s without any growth interruptions at the interfaces leads to tensile strained SLS’s (GaAs-like interfaces) with a rather large lattice mismatch. A 5 second flow of TMSb over the InAs surface and a flow of H2 over GaSb surface yielded compressively strained SLS’s. Flowing TMIn for 1 second and following by a flow of TMSb for 4 seconds over the GaSb surface, while flowing H2 for 5 seconds over the InAs surface, resulted in SLS’s with GaAs-like interfacial layers and a reduced lattice mismatch. Temperature gradients across the surface of the susceptor led to SLS’s with different structural quality. High resolution x-ray diffraction (HRXRD) was used to determine the thicknesses as well as the type of interfacial layers. The physical parameters of the SLS’s obtained from simulating the HRXRD spectra were comparable to the parameters obtained from cross sectional transmission electron microscopy (XTEM) images. The thicknesses of the layers and the interface type played a major role in determining the cut-off wavelength of the SLS’s.
- Full Text:
- Date Issued: 2013
- Authors: Miya, Senzo Simo
- Date: 2013
- Subjects: Gallium arsenide semiconductors , Organometallic compounds , Compound semiconductors , Metal organic chemical vapor deposition , Superlattices as materials , Epitaxy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10557 , http://hdl.handle.net/10948/d1020866
- Description: The importance of infrared (IR) technology (for detection in the 3-5 μm and 8-14 μm atmospheric windows) has spread from military applications to civilian applications since World War II. The commercial IR detector market in these wavelength ranges is dominated by mercury cadmium telluride (MCT) alloys. The use of these alloys has, however, been faced with technological difficulties. One of the materials that have been tipped to be suitable to replace MCT is InAs/InxGa1-xSb strained layer superlattices (SLS’s). Atmospheric pressure metal-organic vapour phase epitaxy (MOVPE) has been used to grow InAs/GaSb strained layer superlattices (SLS’s) at 510 °C in this study. This is a starting point towards the development of MOVPE InAs/InxGa1-xSb SLS’s using the same system. Before the SLS’s could be attempted, the growth parameters for GaSb were optimised. Growth parameters for InAs were taken from reports on previous studies conducted using the same reactor. Initially, trimethylgallium, a source that has been used extensively in the same growth system for the growth of GaSb and InxGa1-xSb was intended to be used for gallium species. The high growth rates yielded by this source were too large for the growth of SLS structures, however. Thus, triethylgallium (rarely used for atmospheric pressure MOVPE) was utilized. GaSb layers (between 1 and 2 μm thick) were grown at two different temperatures (550 °C and 510 °C) with a varying V/III ratio. A V/III ratio of 1.5 was found to be optimal at 550 °C. However, the low incorporation efficiency of indium into GaSb at this temperature was inadequate to obtain InxGa1-xSb with an indium mole fraction (x) of around 0.3, which had previously been reported to be optimal for the performance of InAs/InxGa1-xSb SLS’s, due to the maximum splitting of the valence mini bands for this composition. The growth temperature was thus lowered to 510 °C. This resulted in an increase in the optimum V/III ratio to 1.75 for GaSb and yielded much higher incorporation efficiencies of indium in InxGa1-xSb. However, this lower growth temperature also produced poorer surface morphologies for both the binary and ternary layers, due to the reduced surface diffusion of the adsorbed species. An interface control study during the growth of InAs/GaSb SLS’s was subsequently conducted, by investigating the influence of different gas switching sequences on the interface type and quality. It was noted that the growth of SLS’s without any growth interruptions at the interfaces leads to tensile strained SLS’s (GaAs-like interfaces) with a rather large lattice mismatch. A 5 second flow of TMSb over the InAs surface and a flow of H2 over GaSb surface yielded compressively strained SLS’s. Flowing TMIn for 1 second and following by a flow of TMSb for 4 seconds over the GaSb surface, while flowing H2 for 5 seconds over the InAs surface, resulted in SLS’s with GaAs-like interfacial layers and a reduced lattice mismatch. Temperature gradients across the surface of the susceptor led to SLS’s with different structural quality. High resolution x-ray diffraction (HRXRD) was used to determine the thicknesses as well as the type of interfacial layers. The physical parameters of the SLS’s obtained from simulating the HRXRD spectra were comparable to the parameters obtained from cross sectional transmission electron microscopy (XTEM) images. The thicknesses of the layers and the interface type played a major role in determining the cut-off wavelength of the SLS’s.
- Full Text:
- Date Issued: 2013
Characterisation and biotic classification of Eastern Cape mixed substrate shores
- Authors: Garner, Cornelia Johanna
- Date: 2013
- Subjects: Coastal sediments -- South Africa -- Eastern Cape , Coastal biodiversity --- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10641 , http://hdl.handle.net/10948/d1020825
- Description: A significant proportion of the South African coastline is composed of both soft (mostly sand) and hard (mostly bedrock) substrata, i.e. “mixed”. This study described and classified macrobenthic assemblages of 20 Eastern Cape mixed substrate shores that differed in shore topography and the extent and position of intertidal rock and sand. A stratified random approach was used. Species richness, composition, abundance and environmental variables were determined. Commonly used beach indices were calculated. A total of 78 macrofaunal and 172 macroalgal species from rock substrate assemblages and 205 macrofauna species from sediment were recorded. Total species richness and richness per substratum exceeded that of sandy beaches devoid of rock and rocky shores with no sand. Rhodophyta were the most diverse and abundant algae, dominating all low-elevation rock surfaces as midlittoral and infralittoral turfs. Chlorophyta diversity was higher than at rocky shores, contributing more to cover-abundance at study sites and in microhabitats with an increased sand load. Sessile macrofauna species richness and abundance was lower than that of rocky shores. Polychaetes and crustaceans were the most diverse and abundant beach infauna. Species richness of both substrates declined from the low shore towards the high shore, but abundance trends varied substantially. The presence and extent of an intertidal biotope/subzone at either substrate depended on substrate availability.The supralittoral fringe in both substrate types was most often affected. Zonal overlap was evident on rock substrate: assemblages of raised midlittoral rock surfaces were enriched by species from lower surfaces sometimes leading to elimination of character taxa. Classification and ordination identified three potential mixed substrate shore biotic types: Biotic type A (Jania-Corallina- Polysiphonia turf) was characterised by robustly-textured algal turfs, a lowered predominance and diversity of polychaetes and an increase in crustacean abundance and diversity in sediment. Biotic type B (Polysiphonia-Tayloriella-Caulacanthus turf) had intermediately and biotic type C (Arthrocardia-Laurencia turf) the most sheltered eulittoral zones and beaches. DCCA identified the major environmental parameters affecting the macrobiota as: the level of wave energy, geological control of waves by hard substrate, sediment grain size and sediment inundation. A strong cross-shore wave attenuation results in sheltered sediments and midshore rock surfaces. Beach macrofauna were highly variable and diverse, which directly opposes previous perceptions about the sediment-bound biota of mixed substrate shores. The hierarchical cluster analysis produced a biotic classification of mixed substrate shores that was indicative of a biotic response to the total effects of leading environmental parameters. Macrobenthos of rock surfaces and sediment therefore showed potential to be used as an alternative or complementary to physical characteristics in classifying mixed substrate shores.
- Full Text:
- Date Issued: 2013
- Authors: Garner, Cornelia Johanna
- Date: 2013
- Subjects: Coastal sediments -- South Africa -- Eastern Cape , Coastal biodiversity --- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10641 , http://hdl.handle.net/10948/d1020825
- Description: A significant proportion of the South African coastline is composed of both soft (mostly sand) and hard (mostly bedrock) substrata, i.e. “mixed”. This study described and classified macrobenthic assemblages of 20 Eastern Cape mixed substrate shores that differed in shore topography and the extent and position of intertidal rock and sand. A stratified random approach was used. Species richness, composition, abundance and environmental variables were determined. Commonly used beach indices were calculated. A total of 78 macrofaunal and 172 macroalgal species from rock substrate assemblages and 205 macrofauna species from sediment were recorded. Total species richness and richness per substratum exceeded that of sandy beaches devoid of rock and rocky shores with no sand. Rhodophyta were the most diverse and abundant algae, dominating all low-elevation rock surfaces as midlittoral and infralittoral turfs. Chlorophyta diversity was higher than at rocky shores, contributing more to cover-abundance at study sites and in microhabitats with an increased sand load. Sessile macrofauna species richness and abundance was lower than that of rocky shores. Polychaetes and crustaceans were the most diverse and abundant beach infauna. Species richness of both substrates declined from the low shore towards the high shore, but abundance trends varied substantially. The presence and extent of an intertidal biotope/subzone at either substrate depended on substrate availability.The supralittoral fringe in both substrate types was most often affected. Zonal overlap was evident on rock substrate: assemblages of raised midlittoral rock surfaces were enriched by species from lower surfaces sometimes leading to elimination of character taxa. Classification and ordination identified three potential mixed substrate shore biotic types: Biotic type A (Jania-Corallina- Polysiphonia turf) was characterised by robustly-textured algal turfs, a lowered predominance and diversity of polychaetes and an increase in crustacean abundance and diversity in sediment. Biotic type B (Polysiphonia-Tayloriella-Caulacanthus turf) had intermediately and biotic type C (Arthrocardia-Laurencia turf) the most sheltered eulittoral zones and beaches. DCCA identified the major environmental parameters affecting the macrobiota as: the level of wave energy, geological control of waves by hard substrate, sediment grain size and sediment inundation. A strong cross-shore wave attenuation results in sheltered sediments and midshore rock surfaces. Beach macrofauna were highly variable and diverse, which directly opposes previous perceptions about the sediment-bound biota of mixed substrate shores. The hierarchical cluster analysis produced a biotic classification of mixed substrate shores that was indicative of a biotic response to the total effects of leading environmental parameters. Macrobenthos of rock surfaces and sediment therefore showed potential to be used as an alternative or complementary to physical characteristics in classifying mixed substrate shores.
- Full Text:
- Date Issued: 2013
Characterisation of surfaces modified through self-assembled monolayers and click chemistry
- Authors: Coates, Megan Patricia
- Date: 2013
- Subjects: Monomolecular films Gold Adsorption Nanotubes Self-assembly (Chemistry) Self-assembly (Chemistry) Scanning electrochemical microscopy X-ray photoelectron spectroscopy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4277 , http://hdl.handle.net/10962/d1001684
- Description: Different approaches to surface modification were investigated in this work on gold, glassy carbon, multi-walled carbon nanotube paper and on single-walled carbon nanotubes adsorbed on glassy carbon. These approaches include electrochemical grafting, electropolymerisation, click chemistry, axial ligation, adsorption and self-assembled monolayers. The modified surfaces were characterised using a variety of techniques; predominantly electrochemistry, scanning electrochemical microscopy and X-ray photoelectron spectroscopy. For the formation of self-assembled monolayers on gold, four new manganese(III) phthalocyanines (1a-d), octa-substituted at the peripheral position with pentylthio, decylthio, benzylthio, and phenylthio groups were synthesized and characterised. X-ray photoelectron spectroscopy was used to show the formation of a sulphur-gold bond. A number of approaches using 4-azidoaniline (2a) combined with azide-alkyne click chemistry and electrochemistry were also used to anchor ferrocene and pyridine moieties on to the carbon surfaces, including direct in situ diazotation and grafting, electropolymerisation, and the synthesis of the diazonium salt followed by grafting. Iron phthalocyanine was linked to the pyridine-clicked surfaces through axial ligation, where the strong axial bond formed by the interaction between the central metal and the lone pair of the nitrogen in the pyridine group resulted in stable modified electrodes. The potential of these surfaces for the detection of analytes such as thiocyanate, hydrazine and sulphite are briefly shown as well. This work also describes for the first time the possibility of performing local micro-electrochemical grafting of a gold substrate by 4-azidobenzenediazonium (2b) using scanning electrochemical microscopy in a single and simple one step approach, without complications from adsorption.
- Full Text:
- Date Issued: 2013
- Authors: Coates, Megan Patricia
- Date: 2013
- Subjects: Monomolecular films Gold Adsorption Nanotubes Self-assembly (Chemistry) Self-assembly (Chemistry) Scanning electrochemical microscopy X-ray photoelectron spectroscopy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4277 , http://hdl.handle.net/10962/d1001684
- Description: Different approaches to surface modification were investigated in this work on gold, glassy carbon, multi-walled carbon nanotube paper and on single-walled carbon nanotubes adsorbed on glassy carbon. These approaches include electrochemical grafting, electropolymerisation, click chemistry, axial ligation, adsorption and self-assembled monolayers. The modified surfaces were characterised using a variety of techniques; predominantly electrochemistry, scanning electrochemical microscopy and X-ray photoelectron spectroscopy. For the formation of self-assembled monolayers on gold, four new manganese(III) phthalocyanines (1a-d), octa-substituted at the peripheral position with pentylthio, decylthio, benzylthio, and phenylthio groups were synthesized and characterised. X-ray photoelectron spectroscopy was used to show the formation of a sulphur-gold bond. A number of approaches using 4-azidoaniline (2a) combined with azide-alkyne click chemistry and electrochemistry were also used to anchor ferrocene and pyridine moieties on to the carbon surfaces, including direct in situ diazotation and grafting, electropolymerisation, and the synthesis of the diazonium salt followed by grafting. Iron phthalocyanine was linked to the pyridine-clicked surfaces through axial ligation, where the strong axial bond formed by the interaction between the central metal and the lone pair of the nitrogen in the pyridine group resulted in stable modified electrodes. The potential of these surfaces for the detection of analytes such as thiocyanate, hydrazine and sulphite are briefly shown as well. This work also describes for the first time the possibility of performing local micro-electrochemical grafting of a gold substrate by 4-azidobenzenediazonium (2b) using scanning electrochemical microscopy in a single and simple one step approach, without complications from adsorption.
- Full Text:
- Date Issued: 2013
Climate change mitigation strategies and its effect on economic change
- Authors: Roux, Louis Johannes
- Date: 2013
- Subjects: Climatic changes -- Economic aspects , Climate change mitigation , Global warming -- Economic aspects
- Language: English
- Type: Thesis , Doctoral , DBA
- Identifier: vital:8889 , http://hdl.handle.net/10948/d1020816
- Description: Scientists started to study the relationship between changing weather patterns and the emission of carbon dioxide (CO2) and other harmful gasses. They soon discovered compelling evidence that CO2 concentration and other gases have been increasing and it was causing temperatures to increase in certain areas on the earth, which disturb historic weather patterns. Climate change has become a very popular field of study in the modern science. Europe first introduced measures to reduce carbon emissions but it was the Kyoto in 1997 where global leaders were asked to participate in a joint protocol to reduce greenhouse gases. South Africa responded to climate change challenges in 2008 with the Long term Mitigation Scenarios (LTMS). The Integrated Resource Plan for electricity to 2030 was developed from the LTMS scenarios and after some major amendments it was accepted and promulgated by Government and has recently been included in the National Development Plan to 2030 (NDP). There are concerns about the achievability of some of the objectives listed in the NDP and this study explored the IRP2010 as the proposed strategy to meet energy demand and reduce emissions. The purpose for this study was to answer this question: Is there an optimum climate change mitigation strategy for South Africa and how can the effect thereof be simulated on economic growth? Through primary and secondary research during the study it was possible to define some 32 categories of energy producing assets that are commercially active or nearly market-ready. The characteristics of the various assets and the relevant fuel are defined in mathematical equations. It was found that the three portfolios that matched the 450TWh electricity requirement would perform substantially better than the NDP portfolio in terms of cost and similar on emissions with marginally fewer employment opportunities created. The proposed electricity strategy in this study was 390TWh and 33.5 Million tonnes of oil consumption by 2030. This strategy was substantially more affordable than the 450TWh strategy. Trends in the Supply and Use tables since 1993 were studied and then forecasted to 2030 to determine consumption levels on electricity and liquid fuel into the future. It was found that electricity demand is seriously overestimated and South Africa would end up with large excess capacity in electricity infrastructures if the NDP energy strategy (IRP2010) is implemented. It is concluded that the NDP energy strategy to 2030 is based on an incorrect electricity demand forecast. It would lead to excessive investment in an electricity infrastructure. Government has confirmed that part of the new infrastructure would be nuclear. It is also found that NDP has not clearly supported nuclear as part of the strategy. Nuclear is partly the reason why the capital requirement of the NDP portfolio is so much higher than the other portfolios. It is the conclusion of this study that South Africa do not need to invest in a nuclear build programme as the electricity demand would be adequately covered by adding the new Medupi and Kusile power stations, Ingula pump storage scheme, some wind and solar renewables, electricity from cogeneration, biogas, biomass, small hydro and imported hydro from neighbour countries. To invest in electricity capacity to generate 450TWh annually by 2030 would result in excessive energy cost, GDP growth could be up to 1% lower due to underperforming capital investments in the electricity infrastructure and higher energy cost would lead to a decline in global competitiveness.
- Full Text:
- Date Issued: 2013
- Authors: Roux, Louis Johannes
- Date: 2013
- Subjects: Climatic changes -- Economic aspects , Climate change mitigation , Global warming -- Economic aspects
- Language: English
- Type: Thesis , Doctoral , DBA
- Identifier: vital:8889 , http://hdl.handle.net/10948/d1020816
- Description: Scientists started to study the relationship between changing weather patterns and the emission of carbon dioxide (CO2) and other harmful gasses. They soon discovered compelling evidence that CO2 concentration and other gases have been increasing and it was causing temperatures to increase in certain areas on the earth, which disturb historic weather patterns. Climate change has become a very popular field of study in the modern science. Europe first introduced measures to reduce carbon emissions but it was the Kyoto in 1997 where global leaders were asked to participate in a joint protocol to reduce greenhouse gases. South Africa responded to climate change challenges in 2008 with the Long term Mitigation Scenarios (LTMS). The Integrated Resource Plan for electricity to 2030 was developed from the LTMS scenarios and after some major amendments it was accepted and promulgated by Government and has recently been included in the National Development Plan to 2030 (NDP). There are concerns about the achievability of some of the objectives listed in the NDP and this study explored the IRP2010 as the proposed strategy to meet energy demand and reduce emissions. The purpose for this study was to answer this question: Is there an optimum climate change mitigation strategy for South Africa and how can the effect thereof be simulated on economic growth? Through primary and secondary research during the study it was possible to define some 32 categories of energy producing assets that are commercially active or nearly market-ready. The characteristics of the various assets and the relevant fuel are defined in mathematical equations. It was found that the three portfolios that matched the 450TWh electricity requirement would perform substantially better than the NDP portfolio in terms of cost and similar on emissions with marginally fewer employment opportunities created. The proposed electricity strategy in this study was 390TWh and 33.5 Million tonnes of oil consumption by 2030. This strategy was substantially more affordable than the 450TWh strategy. Trends in the Supply and Use tables since 1993 were studied and then forecasted to 2030 to determine consumption levels on electricity and liquid fuel into the future. It was found that electricity demand is seriously overestimated and South Africa would end up with large excess capacity in electricity infrastructures if the NDP energy strategy (IRP2010) is implemented. It is concluded that the NDP energy strategy to 2030 is based on an incorrect electricity demand forecast. It would lead to excessive investment in an electricity infrastructure. Government has confirmed that part of the new infrastructure would be nuclear. It is also found that NDP has not clearly supported nuclear as part of the strategy. Nuclear is partly the reason why the capital requirement of the NDP portfolio is so much higher than the other portfolios. It is the conclusion of this study that South Africa do not need to invest in a nuclear build programme as the electricity demand would be adequately covered by adding the new Medupi and Kusile power stations, Ingula pump storage scheme, some wind and solar renewables, electricity from cogeneration, biogas, biomass, small hydro and imported hydro from neighbour countries. To invest in electricity capacity to generate 450TWh annually by 2030 would result in excessive energy cost, GDP growth could be up to 1% lower due to underperforming capital investments in the electricity infrastructure and higher energy cost would lead to a decline in global competitiveness.
- Full Text:
- Date Issued: 2013
Climate variability and climate change in water resources management of the Zambezi River basin
- Authors: Tirivarombo, Sithabile
- Date: 2013
- Subjects: Water resources development -- Zambezi River Watershed Climatic changes -- Zambezi River Watershed Water-supply -- Zambezi River Watershed Water-supply -- Political aspects -- Africa, Southern Water rights -- Africa, Southern Water security -- Africa, Southern Rain and rainfall -- Africa, Southern Rainfall probabilities -- Africa, Southern Food security -- Africa, Southern Drought forecasting -- Africa, Southern Watersheds -- Africa, Southern Water supply -- Measurement -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:6024 , http://hdl.handle.net/10962/d1002955
- Description: Water is recognised as a key driver for social and economic development in the Zambezi basin. The basin is riparian to eight southern African countries and the transboundary nature of the basin’s water resources can be viewed as an agent of cooperation between the basin countries. It is possible, however, that the same water resource can lead to conflicts between water users. The southern African Water Vision for ‘equitable and sustainable utilisation of water for social, environmental justice and economic benefits for the present and future generations’ calls for an integrated and efficient management of water resources within the basin. Ensuring water and food security in the Zambezi basin is, however, faced with challenges due to high variability in climate and the available water resources. Water resources are under continuous threat from pollution, increased population growth, development and urbanisation as well as global climate change. These factors increase the demand for freshwater resources and have resulted in water being one of the major driving forces for development. The basin is also vulnerable due to lack of adequate financial resources and appropriate water resources infrastructure to enable viable, equitable and sustainable distribution of the water resources. This is in addition to the fact that the basin’s economic mainstay and social well-being are largely dependent on rainfed agriculture. There is also competition among the different water users and this has the potential to generate conflicts, which further hinder the development of water resources in the basin. This thesis has focused on the Zambezi River basin emphasising climate variability and climate change. It is now considered common knowledge that the global climate is changing and that many of the impacts will be felt through water resources. If these predictions are correct then the Zambezi basin is most likely to suffer under such impacts since its economic mainstay is largely determined by the availability of rainfall. It is the belief of this study that in order to ascertain the impacts of climate change, there should be a basis against which this change is evaluated. If we do not know the historical patterns of variability it may be difficult to predict changes in the future climate and in the hydrological resources and it will certainly be difficult to develop appropriate management strategies. Reliable quantitative estimates of water availability are a prerequisite for successful water resource plans. However, such initiatives have been hindered by paucity in data especially in a basin where gauging networks are inadequate and some of them have deteriorated. This is further compounded by shortages in resources, both human and financial, to ensure adequate monitoring. To address the data problems, this study largely relied on global data sets and the CRU TS2.1 rainfall grids were used for a large part of this study. The study starts by assessing the historical variability of rainfall and streamflow in the Zambezi basin and the results are used to inform the prediction of change in the future. Various methods of assessing historical trends were employed and regional drought indices were generated and evaluated against the historical rainfall trends. The study clearly demonstrates that the basin has a high degree of temporal and spatial variability in rainfall and streamflow at inter-annual and multi-decadal scales. The Standardised Precipitation Index, a rainfall based drought index, is used to assess historical drought events in the basin and it is shown that most of the droughts that have occurred were influenced by climatic and hydrological variability. It is concluded, through the evaluation of agricultural maize yields, that the basin’s food security is mostly constrained by the availability of rainfall. Comparing the viability of using a rainfall based index to a soil moisture based index as an agricultural drought indicator, this study concluded that a soil moisture based index is a better indicator since all of the water balance components are considered in the generation of the index. This index presents the actual amount of water available for the plant unlike purely rainfall based indices, that do not account for other components of the water budget that cause water losses. A number of challenges were, however, faced in assessing the variability and historical drought conditions, mainly due to the fact that most parts of the Zambezi basin are ungauged and available data are sparse, short and not continuous (with missing gaps). Hydrological modelling is frequently used to bridge the data gap and to facilitate the quantification of a basin’s hydrology for both gauged and ungauged catchments. The trend has been to use various methods of regionalisation to transfer information from gauged basins, or from basins with adequate physical basin data, to ungauged basins. All this is done to ensure that water resources are accounted for and that the future can be well planned. A number of approaches leading to the evaluation of the basin’s hydrological response to future climate change scenarios are taken. The Pitman rainfall-runoff model has enjoyed wide use as a water resources estimation tool in southern Africa. The model has been calibrated for the Zambezi basin but it should be acknowledged that any hydrological modelling process is characterised by many uncertainties arising from limitations in input data and inherent model structural uncertainty. The calibration process is thus carried out in a manner that embraces some of the uncertainties. Initial ranges of parameter values (maximum and minimum) that incorporate the possible parameter uncertainties are assigned in relation to physical basin properties. These parameter sets are used as input to the uncertainty version of the model to generate behavioural parameter space which is then further modified through manual calibration. The use of parameter ranges initially guided by the basin physical properties generates streamflows that adequately represent the historically observed amounts. This study concludes that the uncertainty framework and the Pitman model perform quite well in the Zambezi basin. Based on assumptions of an intensifying hydrological cycle, climate changes are frequently expected to result in negative impacts on water resources. However, it is important that basin scale assessments are undertaken so that appropriate future management strategies can be developed. To assess the likely changes in the Zambezi basin, the calibrated Pitman model was forced with downscaled and bias corrected GCM data. Three GCMs were used for this study, namely; ECHAM, GFDL and IPSL. The general observation made in this study is that the near future (2046-2065) conditions of the Zambezi basin are expected to remain within the ranges of historically observed variability. The differences between the predictions for the three GCMs are an indication of the uncertainties in the future and it has not been possible to make any firm conclusions about directions of change. It is therefore recommended that future water resources management strategies account for historical patterns of variability, but also for increased uncertainty. Any management strategies that are able to satisfactorily deal with the large variability that is evident from the historical data should be robust enough to account for the near future patterns of water availability predicted by this study. However, the uncertainties in these predictions suggest that improved monitoring systems are required to provide additional data against which future model outputs can be assessed.
- Full Text:
- Date Issued: 2013
- Authors: Tirivarombo, Sithabile
- Date: 2013
- Subjects: Water resources development -- Zambezi River Watershed Climatic changes -- Zambezi River Watershed Water-supply -- Zambezi River Watershed Water-supply -- Political aspects -- Africa, Southern Water rights -- Africa, Southern Water security -- Africa, Southern Rain and rainfall -- Africa, Southern Rainfall probabilities -- Africa, Southern Food security -- Africa, Southern Drought forecasting -- Africa, Southern Watersheds -- Africa, Southern Water supply -- Measurement -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:6024 , http://hdl.handle.net/10962/d1002955
- Description: Water is recognised as a key driver for social and economic development in the Zambezi basin. The basin is riparian to eight southern African countries and the transboundary nature of the basin’s water resources can be viewed as an agent of cooperation between the basin countries. It is possible, however, that the same water resource can lead to conflicts between water users. The southern African Water Vision for ‘equitable and sustainable utilisation of water for social, environmental justice and economic benefits for the present and future generations’ calls for an integrated and efficient management of water resources within the basin. Ensuring water and food security in the Zambezi basin is, however, faced with challenges due to high variability in climate and the available water resources. Water resources are under continuous threat from pollution, increased population growth, development and urbanisation as well as global climate change. These factors increase the demand for freshwater resources and have resulted in water being one of the major driving forces for development. The basin is also vulnerable due to lack of adequate financial resources and appropriate water resources infrastructure to enable viable, equitable and sustainable distribution of the water resources. This is in addition to the fact that the basin’s economic mainstay and social well-being are largely dependent on rainfed agriculture. There is also competition among the different water users and this has the potential to generate conflicts, which further hinder the development of water resources in the basin. This thesis has focused on the Zambezi River basin emphasising climate variability and climate change. It is now considered common knowledge that the global climate is changing and that many of the impacts will be felt through water resources. If these predictions are correct then the Zambezi basin is most likely to suffer under such impacts since its economic mainstay is largely determined by the availability of rainfall. It is the belief of this study that in order to ascertain the impacts of climate change, there should be a basis against which this change is evaluated. If we do not know the historical patterns of variability it may be difficult to predict changes in the future climate and in the hydrological resources and it will certainly be difficult to develop appropriate management strategies. Reliable quantitative estimates of water availability are a prerequisite for successful water resource plans. However, such initiatives have been hindered by paucity in data especially in a basin where gauging networks are inadequate and some of them have deteriorated. This is further compounded by shortages in resources, both human and financial, to ensure adequate monitoring. To address the data problems, this study largely relied on global data sets and the CRU TS2.1 rainfall grids were used for a large part of this study. The study starts by assessing the historical variability of rainfall and streamflow in the Zambezi basin and the results are used to inform the prediction of change in the future. Various methods of assessing historical trends were employed and regional drought indices were generated and evaluated against the historical rainfall trends. The study clearly demonstrates that the basin has a high degree of temporal and spatial variability in rainfall and streamflow at inter-annual and multi-decadal scales. The Standardised Precipitation Index, a rainfall based drought index, is used to assess historical drought events in the basin and it is shown that most of the droughts that have occurred were influenced by climatic and hydrological variability. It is concluded, through the evaluation of agricultural maize yields, that the basin’s food security is mostly constrained by the availability of rainfall. Comparing the viability of using a rainfall based index to a soil moisture based index as an agricultural drought indicator, this study concluded that a soil moisture based index is a better indicator since all of the water balance components are considered in the generation of the index. This index presents the actual amount of water available for the plant unlike purely rainfall based indices, that do not account for other components of the water budget that cause water losses. A number of challenges were, however, faced in assessing the variability and historical drought conditions, mainly due to the fact that most parts of the Zambezi basin are ungauged and available data are sparse, short and not continuous (with missing gaps). Hydrological modelling is frequently used to bridge the data gap and to facilitate the quantification of a basin’s hydrology for both gauged and ungauged catchments. The trend has been to use various methods of regionalisation to transfer information from gauged basins, or from basins with adequate physical basin data, to ungauged basins. All this is done to ensure that water resources are accounted for and that the future can be well planned. A number of approaches leading to the evaluation of the basin’s hydrological response to future climate change scenarios are taken. The Pitman rainfall-runoff model has enjoyed wide use as a water resources estimation tool in southern Africa. The model has been calibrated for the Zambezi basin but it should be acknowledged that any hydrological modelling process is characterised by many uncertainties arising from limitations in input data and inherent model structural uncertainty. The calibration process is thus carried out in a manner that embraces some of the uncertainties. Initial ranges of parameter values (maximum and minimum) that incorporate the possible parameter uncertainties are assigned in relation to physical basin properties. These parameter sets are used as input to the uncertainty version of the model to generate behavioural parameter space which is then further modified through manual calibration. The use of parameter ranges initially guided by the basin physical properties generates streamflows that adequately represent the historically observed amounts. This study concludes that the uncertainty framework and the Pitman model perform quite well in the Zambezi basin. Based on assumptions of an intensifying hydrological cycle, climate changes are frequently expected to result in negative impacts on water resources. However, it is important that basin scale assessments are undertaken so that appropriate future management strategies can be developed. To assess the likely changes in the Zambezi basin, the calibrated Pitman model was forced with downscaled and bias corrected GCM data. Three GCMs were used for this study, namely; ECHAM, GFDL and IPSL. The general observation made in this study is that the near future (2046-2065) conditions of the Zambezi basin are expected to remain within the ranges of historically observed variability. The differences between the predictions for the three GCMs are an indication of the uncertainties in the future and it has not been possible to make any firm conclusions about directions of change. It is therefore recommended that future water resources management strategies account for historical patterns of variability, but also for increased uncertainty. Any management strategies that are able to satisfactorily deal with the large variability that is evident from the historical data should be robust enough to account for the near future patterns of water availability predicted by this study. However, the uncertainties in these predictions suggest that improved monitoring systems are required to provide additional data against which future model outputs can be assessed.
- Full Text:
- Date Issued: 2013
Competitive strategy implementation in microfinance organisations in Kenya
- Authors: Waweru, Ruth Wambui
- Date: 2013
- Subjects: Microfinance -- Kenya , Financial institutions -- Kenya
- Language: English
- Type: Thesis , Doctoral , DBA
- Identifier: vital:8888 , http://hdl.handle.net/10948/d1020815
- Description: Poverty is a major challenge in most developing countries. Key challenges of the government are to alleviate poverty and propel citizens toward wealth creation through development of enterprises across all sectors and to address the problem of unemployment. In Kenya, the SME sector comprises of about 99% of private sector enterprises and is prolific in employment and wealth creation. Despite this critical role played by SMEs in growing the economy, they remain outside the formal banking sector, especially in Africa. Although the number of MFOs since the 1980s has increased, the demand for financial services is largely unmet. However, MFOs are increasingly experiencing competition from new entrants and commercial banks that have developed financial models to target SMEs. MFOs are required to formulate and implement competitive strategies to enable them achieve sustainable growth and compete with commercial banks. However, strategy implementation is generally accepted as a challenge across organisations and it is often easier to formulate strategies than implementing it. Despite the need to address strategy implementation challenges across organisations, there is a greater focus by practitioners and researchers regarding strategy formulation than implementation. Consequently, this study aimed at assessing the level of strategy implementation in MFOs and factors that affect strategy implementation in MFOs. The ultimate objective was to develop a hypothetical model that could be used to improve strategy implementation in microfinance organisations in Kenya. This quantitative study used purposive sampling to select MFOs that are members of the Association of Microfinance Institutions (AMFI) in Kenya, completing a selfadministered structured questionnaire. In total, 135 MFOs were involved in this study and a total sample size of 300 managers was used in this study. This study considered fourteen factors to have an influence on the level of strategy implementation of MFOs in Kenya and hence fourteen null-hypotheses were formulated and tested. The content factors included stakeholder involvement in strategy development and the quality of strategies. The context factors included organisational structure and culture, strategic leadership and alignment of strategy to market conditions. The operational process factors included operational planning, monitoring and review of progress, teamwork, resources allocation, people-strategy fit, effective communication, strategic and management control systems and information resources. It is assumed that if all these critical strategy implementation factors are addressed, MFOs should be able improve their level of strategy implementation, ultimately leading to improved performance. The outcome factors considered were improved financial sustainability and outreach of MFOs. Advanced statistical analyses were used to analyse the data, such as factor analysis, regression and correlation analysis to assess the hypothesised relationship between the dependent and independent variables of this study. The empirical results revealed that the level of strategy implementation in MFOs in Kenya is moderate to high and content, context and operational factors do have an influence on the level of strategy implementation. However, operational factors have a more significant positive linear relationship with level of strategy implementation than the other two factors. There is also a positive relationship between the level of strategy implementation and financial sustainability and outreach by MFOs. This study has contributed to the existing body of knowledge by developing a hypothetical model that can be utilised by MFOs as well as other organisations to improve the level of strategy implementation resulting in better performance. The findings of the study can also inform strategy formulation and implementation of MFOs in Kenya, but also in other developing countries, to become more competitive. This study could also help MFOs and other organisations to put in place structures, systems, people and other resources required to attain a high level of strategy implementation. This study provides useful and practical guidelines in dealing with content, context and operational factors affecting strategy implementation in any organisational setting.
- Full Text:
- Date Issued: 2013
- Authors: Waweru, Ruth Wambui
- Date: 2013
- Subjects: Microfinance -- Kenya , Financial institutions -- Kenya
- Language: English
- Type: Thesis , Doctoral , DBA
- Identifier: vital:8888 , http://hdl.handle.net/10948/d1020815
- Description: Poverty is a major challenge in most developing countries. Key challenges of the government are to alleviate poverty and propel citizens toward wealth creation through development of enterprises across all sectors and to address the problem of unemployment. In Kenya, the SME sector comprises of about 99% of private sector enterprises and is prolific in employment and wealth creation. Despite this critical role played by SMEs in growing the economy, they remain outside the formal banking sector, especially in Africa. Although the number of MFOs since the 1980s has increased, the demand for financial services is largely unmet. However, MFOs are increasingly experiencing competition from new entrants and commercial banks that have developed financial models to target SMEs. MFOs are required to formulate and implement competitive strategies to enable them achieve sustainable growth and compete with commercial banks. However, strategy implementation is generally accepted as a challenge across organisations and it is often easier to formulate strategies than implementing it. Despite the need to address strategy implementation challenges across organisations, there is a greater focus by practitioners and researchers regarding strategy formulation than implementation. Consequently, this study aimed at assessing the level of strategy implementation in MFOs and factors that affect strategy implementation in MFOs. The ultimate objective was to develop a hypothetical model that could be used to improve strategy implementation in microfinance organisations in Kenya. This quantitative study used purposive sampling to select MFOs that are members of the Association of Microfinance Institutions (AMFI) in Kenya, completing a selfadministered structured questionnaire. In total, 135 MFOs were involved in this study and a total sample size of 300 managers was used in this study. This study considered fourteen factors to have an influence on the level of strategy implementation of MFOs in Kenya and hence fourteen null-hypotheses were formulated and tested. The content factors included stakeholder involvement in strategy development and the quality of strategies. The context factors included organisational structure and culture, strategic leadership and alignment of strategy to market conditions. The operational process factors included operational planning, monitoring and review of progress, teamwork, resources allocation, people-strategy fit, effective communication, strategic and management control systems and information resources. It is assumed that if all these critical strategy implementation factors are addressed, MFOs should be able improve their level of strategy implementation, ultimately leading to improved performance. The outcome factors considered were improved financial sustainability and outreach of MFOs. Advanced statistical analyses were used to analyse the data, such as factor analysis, regression and correlation analysis to assess the hypothesised relationship between the dependent and independent variables of this study. The empirical results revealed that the level of strategy implementation in MFOs in Kenya is moderate to high and content, context and operational factors do have an influence on the level of strategy implementation. However, operational factors have a more significant positive linear relationship with level of strategy implementation than the other two factors. There is also a positive relationship between the level of strategy implementation and financial sustainability and outreach by MFOs. This study has contributed to the existing body of knowledge by developing a hypothetical model that can be utilised by MFOs as well as other organisations to improve the level of strategy implementation resulting in better performance. The findings of the study can also inform strategy formulation and implementation of MFOs in Kenya, but also in other developing countries, to become more competitive. This study could also help MFOs and other organisations to put in place structures, systems, people and other resources required to attain a high level of strategy implementation. This study provides useful and practical guidelines in dealing with content, context and operational factors affecting strategy implementation in any organisational setting.
- Full Text:
- Date Issued: 2013
Coping with HIV and AIDS in marginal communities: a case study of Chivanhu Settlement in Nemanwa, Masvingo, Zimbabwe
- Authors: Makonese, Loveness
- Date: 2013
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3337 , http://hdl.handle.net/10962/d1003744
- Description: This thesis seeks to understand and analyse HIV and AIDS and rural livelihoods in Zimbabwe with particular reference to an isolated and marginalised informal settlement called Chivanhu in Masvingo Province. The focus is specifically on questions around HIV susceptibility, AIDS vulnerability and household resilience. In this regard, it is important to recognise that HIV and AIDS cannot be lumped together as one medical or social condition. Rather, there is a progression from HIV infection to AIDS-related chronic illnesses to possible death, and livelihood strategies often alter along this HIV and AIDS time-line. Zimbabwe for over a decade now has gone through a series of economic and political crises which have impacted detrimentally on both urban and rural livelihoods, even for those households which are not directly affected by the HIV and AIDS pandemic. With the economy in free-fall, households have had to pursue a range of livelihood strategies in order to sustain themselves. These socio-economic conditions have in many ways facilitated susceptibility to HIV infection and vulnerability to AIDS. Many studies have examined this in relation to wellentrenched and stable communities in rural Zimbabwe. But the livelihood dynamics for such communities are significantly different to more unstable and informal settlements like Chivanhu, as thesis seeks to show. At the same time, the thesis offers a longitudinal study which is able to map the changes to the livelihoods of infected and affected households in Chivanhu. Though recognising the debilitating effects of the pandemic on these households, it also raises questions about the possible resilience of certain households despite great adversity. In doing so, it goes beyond the individual and household levels of analysis to consider the role of clusters (or groups of households) in responding to the impacts of HIV and AIDS. In this regard, particular emphasis is placed on gender and orphanhood. In the end, the thesis offers a nuanced analysis of the everyday complexities and challenges for affected households in a marginalised and informal rural community in Zimbabwe and thereby makes a contribution to re-theorising HIV and AIDS and rural livelihoods more broadly.
- Full Text:
- Date Issued: 2013
- Authors: Makonese, Loveness
- Date: 2013
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3337 , http://hdl.handle.net/10962/d1003744
- Description: This thesis seeks to understand and analyse HIV and AIDS and rural livelihoods in Zimbabwe with particular reference to an isolated and marginalised informal settlement called Chivanhu in Masvingo Province. The focus is specifically on questions around HIV susceptibility, AIDS vulnerability and household resilience. In this regard, it is important to recognise that HIV and AIDS cannot be lumped together as one medical or social condition. Rather, there is a progression from HIV infection to AIDS-related chronic illnesses to possible death, and livelihood strategies often alter along this HIV and AIDS time-line. Zimbabwe for over a decade now has gone through a series of economic and political crises which have impacted detrimentally on both urban and rural livelihoods, even for those households which are not directly affected by the HIV and AIDS pandemic. With the economy in free-fall, households have had to pursue a range of livelihood strategies in order to sustain themselves. These socio-economic conditions have in many ways facilitated susceptibility to HIV infection and vulnerability to AIDS. Many studies have examined this in relation to wellentrenched and stable communities in rural Zimbabwe. But the livelihood dynamics for such communities are significantly different to more unstable and informal settlements like Chivanhu, as thesis seeks to show. At the same time, the thesis offers a longitudinal study which is able to map the changes to the livelihoods of infected and affected households in Chivanhu. Though recognising the debilitating effects of the pandemic on these households, it also raises questions about the possible resilience of certain households despite great adversity. In doing so, it goes beyond the individual and household levels of analysis to consider the role of clusters (or groups of households) in responding to the impacts of HIV and AIDS. In this regard, particular emphasis is placed on gender and orphanhood. In the end, the thesis offers a nuanced analysis of the everyday complexities and challenges for affected households in a marginalised and informal rural community in Zimbabwe and thereby makes a contribution to re-theorising HIV and AIDS and rural livelihoods more broadly.
- Full Text:
- Date Issued: 2013
Critical core competencies for effective strategic leadership in project management
- Authors: Jowah, Enoch Larry
- Date: 2013
- Subjects: Leadership -- Psychological aspects , Project management , Core competencies , Leadership
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: vital:9305 , http://hdl.handle.net/10948/d1017230
- Description: Project management is undeniably the fastest growing discipline as organizations move into the euphoria of projectification of their operations. Though projects have been a part of human life since time immemorial, there is a sudden realisation of the effectiveness of the methods used in project management. The enrolment of students studying for project management in tertiary institutions has shown tremendous increase. Yet the project execution process is mired by high failure rates and absence of clarity on the necessary skills required for effective project execution. The authority-gap in project management presents political and operational conflicts, and new innovative ways of authority-gap reduction need to be identified and taught in training programs. Simultaneously there is a realisation by both academics and practitioners that there is a difference between managers and leaders. Extensive studies on leadership have not allowed for a one-stop-leadership-style to be used in leadership of any form, let alone project leadership. In fact there is no standard definition of leadership as this has been heavily contextualized and thereby disallowing the creation of a universal definition. No cast-in-stone leadership styles are known and thereby leaving the research on leadership to concentrate on critical competencies required for effective leadership of projects. This study seeks to establish the core competencies needed by the project leaders and other practitioners to reduce the failure rate and maximise the benefits currently sought after by organisations. Studies have shown that the matrix structure within which the embedded projects work is a contributing factor to the failure of projects. Because projects are executed by people, it would be the proper utilisation of people’s talents and competencies that are expected to yield favourable results. Thus, whilst the matrix structure creates the authority-gap that presents a problem for effective project execution, management-by-projects still remains the best way known to add economic value to performance and productivity. The study therefore focuses on those characteristics of project leaders that will most likely make the difference in the way people perform in the workplace. The research findings emphasised the importance of empowerment of project managers and the development of their interpersonal skills of the project leader with special emphasis on extroversion, genuineness of senior management, and the responsiveness of the project leaders as important requirements for effective authority- gap reduction. These critical competencies will therefore facilitate the project execution process and enhance the empowered project leader’s ability to reduce the high project failure rate and high cost overruns. These competencies apply specifically to the human element as it relates to the role of the project leader and the interaction with the team members, this new knowledge needs to be introduced into training programs and project practitioners.
- Full Text:
- Date Issued: 2013
- Authors: Jowah, Enoch Larry
- Date: 2013
- Subjects: Leadership -- Psychological aspects , Project management , Core competencies , Leadership
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: vital:9305 , http://hdl.handle.net/10948/d1017230
- Description: Project management is undeniably the fastest growing discipline as organizations move into the euphoria of projectification of their operations. Though projects have been a part of human life since time immemorial, there is a sudden realisation of the effectiveness of the methods used in project management. The enrolment of students studying for project management in tertiary institutions has shown tremendous increase. Yet the project execution process is mired by high failure rates and absence of clarity on the necessary skills required for effective project execution. The authority-gap in project management presents political and operational conflicts, and new innovative ways of authority-gap reduction need to be identified and taught in training programs. Simultaneously there is a realisation by both academics and practitioners that there is a difference between managers and leaders. Extensive studies on leadership have not allowed for a one-stop-leadership-style to be used in leadership of any form, let alone project leadership. In fact there is no standard definition of leadership as this has been heavily contextualized and thereby disallowing the creation of a universal definition. No cast-in-stone leadership styles are known and thereby leaving the research on leadership to concentrate on critical competencies required for effective leadership of projects. This study seeks to establish the core competencies needed by the project leaders and other practitioners to reduce the failure rate and maximise the benefits currently sought after by organisations. Studies have shown that the matrix structure within which the embedded projects work is a contributing factor to the failure of projects. Because projects are executed by people, it would be the proper utilisation of people’s talents and competencies that are expected to yield favourable results. Thus, whilst the matrix structure creates the authority-gap that presents a problem for effective project execution, management-by-projects still remains the best way known to add economic value to performance and productivity. The study therefore focuses on those characteristics of project leaders that will most likely make the difference in the way people perform in the workplace. The research findings emphasised the importance of empowerment of project managers and the development of their interpersonal skills of the project leader with special emphasis on extroversion, genuineness of senior management, and the responsiveness of the project leaders as important requirements for effective authority- gap reduction. These critical competencies will therefore facilitate the project execution process and enhance the empowered project leader’s ability to reduce the high project failure rate and high cost overruns. These competencies apply specifically to the human element as it relates to the role of the project leader and the interaction with the team members, this new knowledge needs to be introduced into training programs and project practitioners.
- Full Text:
- Date Issued: 2013
Critical studies in carbon electrode materials with applications in the electroanalysis of the mycotoxin citrinin
- Authors: Niland, Michael John
- Date: 2013
- Subjects: Electrodes, Carbon , Mycotoxins
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4555 , http://hdl.handle.net/10962/d1018256
- Description: Guided by increasing legislation, the analysis of food borne toxins, including mycotoxins, seeks to address market related demands for the development of analytical systems to monitor this threat to food security and human health. This Thesis is directed at the assessment of the application of electrochemistry for direct electroanalysis and characterisation of the mycotoxin citrinin (CIT) in aqueous media as well as fundamental investigations of the surface of polished and oxidised glassy carbon electrodes (GCE). This study provides the first known account of CIT detection through electrochemical methods. Although electrochemically active, CIT current responses (Ip) were highly irreproducible at polished GCE with a coefficient of variation (C.V.) of 20.16 %. As stability of Ip across multiple electrode preparations is a key requirement in electroanalysis, investigations were directed at attaining stability in CIT Ip. Achieving stability in CIT Ip was investigated via two approaches, including: accounting for Ip variability between electrode preparations as a result of variable GCE surface conditions as a post-data-acquisition analysis and secondly, removing Ip variability through modification of GCE. Accounting for variability in Ip was investigated through the application of double layer capacitance as an indicator of the activity of an electrode, and in so doing serving as a relative mediator of Ip responses between electrodes. Application of this procedure dropped CIT C.V. to a third of starting value across polished GCE (C.V. = 7.18 %), chemically oxidised GCE (Pi-GCE, C.V = 8.47 %) and functionalised multi-walled carbon nanotube modified GCE (fMWCNT, C.V. = 25.79 %) and was effective with analysis of structurally distinct molecules, 2,4-dimethylaniline (2,4-DMA) and 1,2,4-trihydroxybenzene (Triol). Furthermore, it afforded the ability to determine discreet solution overlapping data sets of Ip. Stabilising Ip through GCE surface modification was achieved by anodic electro-oxidation of GCE and allowed for direct electroanalysis of CIT and subsequent characterisation and analysis of CIT in complex media as it reduced C.V. of CIT Ip to 0.73 %. Fundamental investigations of the electrode surface condition are described such that the source of variability could be identified and the interactions of CIT with the electrode understood. Two surface oxidation techniques were applied in modification of GCE; anodic electro-oxidation (EOx GCE) and chemical oxidation using piranha solution (Pi-GCE), analysis of which has previously not been reported. Fundamental analyses to determine surface morphology and chemistry of Pi-GCE, EOx-GCE and polished GCE were conducted using high resolution scanning electron microscopy (HRSEM), scanning electrochemical microscopy (SECM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR) and via electroanalytical methods. These studies showed that both oxidation procedures introduced a variety of oxide species at GCE surface, and further that the extent of those species was similar with total % O being 27.67 % and 33.47 % at Pi-GCE and EOx-GCE respectively. Although chemically similar, each surface was morphologically distinct. Electrochemical analyses at the surfaces revealed Pi-GCE to behave more similarly to polished GCE than EOx-GCE. As CIT responses were found to be stable at EOx-GCE (C.V. = 0.73 %) as opposed to Pi-GCE (C.V. = 22.87 %), stability of CIT Ip was likely to be as a result of a physical interaction with electrode morphology rather than interaction on a chemical basis. Morphological analyses revealed polished GCE and Pi-GCE to be highly morphologically irregular at the micro-scale. Although comparatively smooth, the surface morphology of EOx-GCE does not account for the stability of Ip. This study thus proposed a theory to describe the mechanism by which the limited conductivity and porosity of EOx-GCE allow for it to provide a relatively stable surface area within the oxide layer, adjacent to the electrode surface, and thus provided a stable platform for electroanalysis. Voltammetric characterization of CIT at EOx-GCE revealed that anodic oxidation in aqueous media involved an uneven number of electrons to protons via an ECE mechanism. This was illustrated to be nt = 2e- accompanied by the transfer of 1H⁺ per molecule oxidised. A proposed reaction scheme for the initial stages of CIT oxidation was suggested to involve both hydroxyl and carboxyl moieties of the CIT molecule. CIT oxidation was shown to arise as a result of a relatively complex mass transport regime which included both adsorptive and diffusive derived Ip₁. The LOD in buffered aqueous media was found to be 16 nM, a highly competitive result in relation to chromatographic techniques. Further application of EOx-GCE in complex media illustrated that CIT associates non-specifically with the components of food samples, primarily proteins. As a result of this, extraction of CIT from such media is mandatory. Liquid-liquid extraction illustrated a recovery in CIT Ip₁ and in so doing provided a means of accurately and sensitively detecting CIT from food samples with an LOD of 20 nM. These responses were corroborated by HPLC analyses on the same extractions and illustrate the applicability of electroanalysis as an analytical technique.
- Full Text:
- Date Issued: 2013
- Authors: Niland, Michael John
- Date: 2013
- Subjects: Electrodes, Carbon , Mycotoxins
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4555 , http://hdl.handle.net/10962/d1018256
- Description: Guided by increasing legislation, the analysis of food borne toxins, including mycotoxins, seeks to address market related demands for the development of analytical systems to monitor this threat to food security and human health. This Thesis is directed at the assessment of the application of electrochemistry for direct electroanalysis and characterisation of the mycotoxin citrinin (CIT) in aqueous media as well as fundamental investigations of the surface of polished and oxidised glassy carbon electrodes (GCE). This study provides the first known account of CIT detection through electrochemical methods. Although electrochemically active, CIT current responses (Ip) were highly irreproducible at polished GCE with a coefficient of variation (C.V.) of 20.16 %. As stability of Ip across multiple electrode preparations is a key requirement in electroanalysis, investigations were directed at attaining stability in CIT Ip. Achieving stability in CIT Ip was investigated via two approaches, including: accounting for Ip variability between electrode preparations as a result of variable GCE surface conditions as a post-data-acquisition analysis and secondly, removing Ip variability through modification of GCE. Accounting for variability in Ip was investigated through the application of double layer capacitance as an indicator of the activity of an electrode, and in so doing serving as a relative mediator of Ip responses between electrodes. Application of this procedure dropped CIT C.V. to a third of starting value across polished GCE (C.V. = 7.18 %), chemically oxidised GCE (Pi-GCE, C.V = 8.47 %) and functionalised multi-walled carbon nanotube modified GCE (fMWCNT, C.V. = 25.79 %) and was effective with analysis of structurally distinct molecules, 2,4-dimethylaniline (2,4-DMA) and 1,2,4-trihydroxybenzene (Triol). Furthermore, it afforded the ability to determine discreet solution overlapping data sets of Ip. Stabilising Ip through GCE surface modification was achieved by anodic electro-oxidation of GCE and allowed for direct electroanalysis of CIT and subsequent characterisation and analysis of CIT in complex media as it reduced C.V. of CIT Ip to 0.73 %. Fundamental investigations of the electrode surface condition are described such that the source of variability could be identified and the interactions of CIT with the electrode understood. Two surface oxidation techniques were applied in modification of GCE; anodic electro-oxidation (EOx GCE) and chemical oxidation using piranha solution (Pi-GCE), analysis of which has previously not been reported. Fundamental analyses to determine surface morphology and chemistry of Pi-GCE, EOx-GCE and polished GCE were conducted using high resolution scanning electron microscopy (HRSEM), scanning electrochemical microscopy (SECM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR) and via electroanalytical methods. These studies showed that both oxidation procedures introduced a variety of oxide species at GCE surface, and further that the extent of those species was similar with total % O being 27.67 % and 33.47 % at Pi-GCE and EOx-GCE respectively. Although chemically similar, each surface was morphologically distinct. Electrochemical analyses at the surfaces revealed Pi-GCE to behave more similarly to polished GCE than EOx-GCE. As CIT responses were found to be stable at EOx-GCE (C.V. = 0.73 %) as opposed to Pi-GCE (C.V. = 22.87 %), stability of CIT Ip was likely to be as a result of a physical interaction with electrode morphology rather than interaction on a chemical basis. Morphological analyses revealed polished GCE and Pi-GCE to be highly morphologically irregular at the micro-scale. Although comparatively smooth, the surface morphology of EOx-GCE does not account for the stability of Ip. This study thus proposed a theory to describe the mechanism by which the limited conductivity and porosity of EOx-GCE allow for it to provide a relatively stable surface area within the oxide layer, adjacent to the electrode surface, and thus provided a stable platform for electroanalysis. Voltammetric characterization of CIT at EOx-GCE revealed that anodic oxidation in aqueous media involved an uneven number of electrons to protons via an ECE mechanism. This was illustrated to be nt = 2e- accompanied by the transfer of 1H⁺ per molecule oxidised. A proposed reaction scheme for the initial stages of CIT oxidation was suggested to involve both hydroxyl and carboxyl moieties of the CIT molecule. CIT oxidation was shown to arise as a result of a relatively complex mass transport regime which included both adsorptive and diffusive derived Ip₁. The LOD in buffered aqueous media was found to be 16 nM, a highly competitive result in relation to chromatographic techniques. Further application of EOx-GCE in complex media illustrated that CIT associates non-specifically with the components of food samples, primarily proteins. As a result of this, extraction of CIT from such media is mandatory. Liquid-liquid extraction illustrated a recovery in CIT Ip₁ and in so doing provided a means of accurately and sensitively detecting CIT from food samples with an LOD of 20 nM. These responses were corroborated by HPLC analyses on the same extractions and illustrate the applicability of electroanalysis as an analytical technique.
- Full Text:
- Date Issued: 2013
Design, implementation and evaluation of a directly water cooled photovoltaic- thermal system
- Authors: Mtunzi, Busiso
- Date: 2013
- Subjects: Sensitivity analysis -- Photovoltaic thermal system (PV/T) , Solar utilization -- Carbon emission
- Language: English
- Type: Thesis , Doctoral , PhD (Physics)
- Identifier: vital:11597 , http://hdl.handle.net/10353/d1016198 , Sensitivity analysis -- Photovoltaic thermal system (PV/T) , Solar utilization -- Carbon emission
- Description: This research project was based on the Design, Implementation and Evaluation of a Photovoltaic Water heating system in South Africa, Eastern Cape Province. The purpose of the study was to design and investigate the scientific and economic contribution of direct water cooling on the photovoltaic module. The method involved performance comparison of two photovoltaic modules, one naturally cooled (M1) and the other, direct water cooled module (M2). Module M2 was used to produce warm water and electricity, hence, a hybrid system. The study focused on comparing the modules’ efficiency, power output and their performance. The temperatures attained by water through cooling the module were monitored as well as the electrical energy generated. A data logger and a low cost I/V characteristic system were used for data collection for a full year. The data were then used for performance analysis of the modules. The results of the study revealed that the directly water cooled module could operate at a higher electrical efficiency for 87% of the day and initially produced 3.63% more electrical energy each day. This was found to be true for the first three months after installation. In the remaining months to the end of the year M2 was found to have more losses as compared to M1 as evidenced by the modules’ performance ratios. The directly water cooled module also showed an energy saving efficiency of 61%. A solar utilization of 47.93% was found for M2 while 8.77% was found for M1. Economically, the project was found to be viable and the payback period of the directly cooled module (M2) system was found to be 9.8 years. Energy economics showed that the system was more sensitive to the price changes and to the energy output as compared to other inputs such as operation and maintenance and years of operation. A generation cost of R0.84/kWh from the system was found and when compared to the potential revenue of R1.18 per kWh, the system was found to enable households to make a profit of 40.5 %. Use of such a system was also found to be able to contribute 9.55% towards carbon emission reduction each year. From these results, it was concluded that a directly cooled photovoltaic/thermal heating (PV/T) system is possible and that it can be of much help in terms of warm water and electricity provision.
- Full Text:
- Date Issued: 2013
- Authors: Mtunzi, Busiso
- Date: 2013
- Subjects: Sensitivity analysis -- Photovoltaic thermal system (PV/T) , Solar utilization -- Carbon emission
- Language: English
- Type: Thesis , Doctoral , PhD (Physics)
- Identifier: vital:11597 , http://hdl.handle.net/10353/d1016198 , Sensitivity analysis -- Photovoltaic thermal system (PV/T) , Solar utilization -- Carbon emission
- Description: This research project was based on the Design, Implementation and Evaluation of a Photovoltaic Water heating system in South Africa, Eastern Cape Province. The purpose of the study was to design and investigate the scientific and economic contribution of direct water cooling on the photovoltaic module. The method involved performance comparison of two photovoltaic modules, one naturally cooled (M1) and the other, direct water cooled module (M2). Module M2 was used to produce warm water and electricity, hence, a hybrid system. The study focused on comparing the modules’ efficiency, power output and their performance. The temperatures attained by water through cooling the module were monitored as well as the electrical energy generated. A data logger and a low cost I/V characteristic system were used for data collection for a full year. The data were then used for performance analysis of the modules. The results of the study revealed that the directly water cooled module could operate at a higher electrical efficiency for 87% of the day and initially produced 3.63% more electrical energy each day. This was found to be true for the first three months after installation. In the remaining months to the end of the year M2 was found to have more losses as compared to M1 as evidenced by the modules’ performance ratios. The directly water cooled module also showed an energy saving efficiency of 61%. A solar utilization of 47.93% was found for M2 while 8.77% was found for M1. Economically, the project was found to be viable and the payback period of the directly cooled module (M2) system was found to be 9.8 years. Energy economics showed that the system was more sensitive to the price changes and to the energy output as compared to other inputs such as operation and maintenance and years of operation. A generation cost of R0.84/kWh from the system was found and when compared to the potential revenue of R1.18 per kWh, the system was found to enable households to make a profit of 40.5 %. Use of such a system was also found to be able to contribute 9.55% towards carbon emission reduction each year. From these results, it was concluded that a directly cooled photovoltaic/thermal heating (PV/T) system is possible and that it can be of much help in terms of warm water and electricity provision.
- Full Text:
- Date Issued: 2013
Developing teaching and learning skills at a Higher education institution: a collaborative action research study
- Authors: Mokhele, Paul Rampaola
- Date: 2013
- Subjects: Learning -- Study and teaching (Tertiary) -- South Africa
- Language: English
- Type: Thesis , Doctoral , D Ed
- Identifier: vital:18456 , http://hdl.handle.net/11260/d1007960
- Description: The thesis which was originally undertaken to improve my teaching skills and determine ways of allowing me space to live my academic values also turned out to become the enquiry to investigate students’ learning and study skills. Students and I collaborated in a year-long self-study action research where we were trying different teaching-learning strategies in order to improve our practice(s). Throughout the study I kept a reflective journal and students also reflected in a portfolio of learning their impressions about the new teaching-learning strategies. In addition to these data gathering methods data from students were gathered using chats, observation, and open-ended questionnaire. Data was analysed using a narrative method, reflexivity principle, and grounded theory. There are two major steps I followed in this study which are aimed at improving students’ basic study and learning skills, and my teaching skills. The first relates to action research into student learning at the school of Mathematics Science and Technology (MSTE) at a rural university. The study reveals that: Students have their own different and unique styles of learning, implementing various learning styles afford students an opportunity to find a style that matches their own. The second action step relates to my own self-study research trying different teaching methods based on my academic and personal values. Here, the study reveals that: The best teaching-learning practice is the one developed and agreed upon between the teacher educator and his or her students. These ‘action’ steps were not mutually exclusive – they were conducted in parallel. After the description of developing student learning skills at undergraduate level my reflections on the study followed in relation to theories and methods of teaching-learning and further revealed that what works with one group of students will not necessarily work with another group. The best teacher educator is constantly seeking ways of improving the learning experience of his or her students. The recommendations that teacher educators should become self reflective practitioners and improve their professions using self-study collaborative approach will benefit other teacher educators who are keen to study and improve their practice.
- Full Text:
- Date Issued: 2013
- Authors: Mokhele, Paul Rampaola
- Date: 2013
- Subjects: Learning -- Study and teaching (Tertiary) -- South Africa
- Language: English
- Type: Thesis , Doctoral , D Ed
- Identifier: vital:18456 , http://hdl.handle.net/11260/d1007960
- Description: The thesis which was originally undertaken to improve my teaching skills and determine ways of allowing me space to live my academic values also turned out to become the enquiry to investigate students’ learning and study skills. Students and I collaborated in a year-long self-study action research where we were trying different teaching-learning strategies in order to improve our practice(s). Throughout the study I kept a reflective journal and students also reflected in a portfolio of learning their impressions about the new teaching-learning strategies. In addition to these data gathering methods data from students were gathered using chats, observation, and open-ended questionnaire. Data was analysed using a narrative method, reflexivity principle, and grounded theory. There are two major steps I followed in this study which are aimed at improving students’ basic study and learning skills, and my teaching skills. The first relates to action research into student learning at the school of Mathematics Science and Technology (MSTE) at a rural university. The study reveals that: Students have their own different and unique styles of learning, implementing various learning styles afford students an opportunity to find a style that matches their own. The second action step relates to my own self-study research trying different teaching methods based on my academic and personal values. Here, the study reveals that: The best teaching-learning practice is the one developed and agreed upon between the teacher educator and his or her students. These ‘action’ steps were not mutually exclusive – they were conducted in parallel. After the description of developing student learning skills at undergraduate level my reflections on the study followed in relation to theories and methods of teaching-learning and further revealed that what works with one group of students will not necessarily work with another group. The best teacher educator is constantly seeking ways of improving the learning experience of his or her students. The recommendations that teacher educators should become self reflective practitioners and improve their professions using self-study collaborative approach will benefit other teacher educators who are keen to study and improve their practice.
- Full Text:
- Date Issued: 2013
Development of a creep sample retrieval technique and friction weld site repair procedure
- Authors: Wedderburn, Ian Norman
- Date: 2013
- Subjects: Friction welding
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: vital:9635 , http://hdl.handle.net/10948/d1020116
- Description: The remnant life monitoring of creep loaded high temperature and pressure components in power stations is critical to ensuring their safe and cost effective operation as failures can have severe consequences. Effective creep life condition monitoring allows for optimising component life predictions and subsequent plant maintenance decisions. In South Africa many power generation stations have been in operation well beyond their 30 year design service life, as such knowledge of the remnant creep life of high temperature and pressure components, such as steam pipelines, becomes of utmost importance. Techniques for the remnant creep life assessments of critical high temperature and pressure components must therefore be as effective as possible. The common and well accepted in-situ inspection technique for assessing creep damage in steam pipes is by the metallographic replication technique. The technique is however limited to the outer surface of the pipe, without information on damage within the wall. This research will illustrate a means of obtaining a sample for creep life analysis with depth through the wall of a pipe, as wells as an alternative technique for the repair of the sample retrieval site. A sample retrieval technique was developed that would retrieve a small diameter cylindrical sample from a cored blind hole for creep analysis by visual creep void assessment or by the small punch creep test. The small punch creep test requires only a small diameter thin disc of material for testing for which its results are comparable with conventional uniaxial creep testing which requires a much larger sample of material. The smaller sample requirement of the small punch creep test therefore allows for a vastly reduced invasive sample retrieval operation and consequently smaller repair size area. Also the fact that the sample is retrieved from a blind hole is advantageous since the pipe wall is not penetrated which would require full plant shutdown. A friction welding technique was identified as an alternative to traditional arc fusion welding for the repair of the sample retrieval site, this technique being the Friction Hydro Pillar Processing technique. Friction Hydro Pillar Processing is a solid-state welding technique and as such has a number of inherent benefits over arc fusion welding as the weld is performed below the melting temperature of the material. From a process point of view Friction Hydro Pillar Processing is ideally suited for automation, has virtually no fumes generated, minimal distortion is experienced and no spatter has to be removed afterwards. The technique has yet to see industrial application and as such development of suitable process parameters was undertaken. Finally, to apply the sample retrieval and repair operations in-situ to a steam pipe in a power plant suitable equipment was developed. Existing friction welding equipment is generally bulky workshop based equipment and is unsuitable for on-site work due to its size and weight. Therefore development of dedicated equipment was required to enable Friction Hydro Pillar Processing to be applied to steam pipes within a power plant environment.
- Full Text:
- Date Issued: 2013
- Authors: Wedderburn, Ian Norman
- Date: 2013
- Subjects: Friction welding
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: vital:9635 , http://hdl.handle.net/10948/d1020116
- Description: The remnant life monitoring of creep loaded high temperature and pressure components in power stations is critical to ensuring their safe and cost effective operation as failures can have severe consequences. Effective creep life condition monitoring allows for optimising component life predictions and subsequent plant maintenance decisions. In South Africa many power generation stations have been in operation well beyond their 30 year design service life, as such knowledge of the remnant creep life of high temperature and pressure components, such as steam pipelines, becomes of utmost importance. Techniques for the remnant creep life assessments of critical high temperature and pressure components must therefore be as effective as possible. The common and well accepted in-situ inspection technique for assessing creep damage in steam pipes is by the metallographic replication technique. The technique is however limited to the outer surface of the pipe, without information on damage within the wall. This research will illustrate a means of obtaining a sample for creep life analysis with depth through the wall of a pipe, as wells as an alternative technique for the repair of the sample retrieval site. A sample retrieval technique was developed that would retrieve a small diameter cylindrical sample from a cored blind hole for creep analysis by visual creep void assessment or by the small punch creep test. The small punch creep test requires only a small diameter thin disc of material for testing for which its results are comparable with conventional uniaxial creep testing which requires a much larger sample of material. The smaller sample requirement of the small punch creep test therefore allows for a vastly reduced invasive sample retrieval operation and consequently smaller repair size area. Also the fact that the sample is retrieved from a blind hole is advantageous since the pipe wall is not penetrated which would require full plant shutdown. A friction welding technique was identified as an alternative to traditional arc fusion welding for the repair of the sample retrieval site, this technique being the Friction Hydro Pillar Processing technique. Friction Hydro Pillar Processing is a solid-state welding technique and as such has a number of inherent benefits over arc fusion welding as the weld is performed below the melting temperature of the material. From a process point of view Friction Hydro Pillar Processing is ideally suited for automation, has virtually no fumes generated, minimal distortion is experienced and no spatter has to be removed afterwards. The technique has yet to see industrial application and as such development of suitable process parameters was undertaken. Finally, to apply the sample retrieval and repair operations in-situ to a steam pipe in a power plant suitable equipment was developed. Existing friction welding equipment is generally bulky workshop based equipment and is unsuitable for on-site work due to its size and weight. Therefore development of dedicated equipment was required to enable Friction Hydro Pillar Processing to be applied to steam pipes within a power plant environment.
- Full Text:
- Date Issued: 2013
Drivers of macrophyte assemblages in South African freshwater systems
- Authors: Martin, Grant Douglas
- Date: 2013
- Subjects: Freshwater plants -- South Africa Aquatic weeds -- South Africa Invasive plants -- South Africa Freshwater ecology -- South Africa Biotic communities -- South Africa Maximum entropy method Lagarosiphon major -- South Africa Phytophagous insects -- South Africa Hydrellia -- South Africa Parasitoids -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5621 , http://hdl.handle.net/10962/d1004127
- Description: Potentially damaging submerged invasive freshwater macrophytes have been identified in South African freshwater systems, but have received less attention than their floating counterparts. To ascertain the changes and effects that these species may have on macrophyte ecology, an understanding of the drivers of macrophyte assemblages is essential. The aims of this thesis were to investigate select abiotic and biotic factors driving introduction, establishment and spread of submerged macrophytes in South Africa. Surveys on the status of submerged plant species in South Africa were conducted to find out the distribution and diversity of the species present, imported to, and traded in South Africa. Numerous submerged indigenous and invasive macrophyte locality records were collected during field surveys, of which many were first time records. Pet stores and aquarist trading activities were identified as potential vectors for the spread of submerged macrophytes through online surveys and personal interviews. These results highlighted the potential these species have for continuing to enter, and spread within South African water bodies. Maximum Entropy (MAXENT) is a general-purpose method used to predict or infer distributions from incomplete information, and was used here to predict areas suitable for the establishment of five of these invasive macrophytes. Many systems throughout South Africa, particularly those in the subtropical coastal regions, were found to be climatically suitable for the establishment of Elodea canadensis Michx., Egeria densa Planch., Hydrilla verticillata (L.f.) Royle (all Hydrocharitaceae), Myriophyllum spicatum L. (Haloragaceae), and Cabomba caroliniana Gray (Cabombaceae). Despite the high probability of invasion, facilitated by vectors and suitable climate, South Africa’s rich indigenous submerged aquatic flora may be preventing the establishment of these submerged invasive species. Studies on the competitive interactions between a common indigenous submerged macrophytes, Lagarosiphon major (Roxb.) (Hydrocharitaceae) and M.spicatum, an invasive native to Eurasia, were conducted to ascertain which conditions influence competitive superiority. High sediment nutrient conditions significantly increased the growth rate and competitive ability of both species, while clay sediments significantly increased the competitive ability of L. major over M. spicatum, but sandy sediments improved the competitive ability of M. spicatum. These results highlighted the dynamic changes in competition between submerged species driven by abiotic factors, but did not take into consideration the effect that herbivory, a biotic factor, could have on competition between the two species. The effect of herbivory by phytophagous insects of submerged plant species has been regarded as negligible. To find out what this effect is, multiple field surveys were undertaken throughout South Africa to find natural enemies of indigenous Lagarosiphon species with the aim of identifying such species, and quantifying their influence on plant growth dynamics. Several new phytophagous species were recorded for the first time. An ephydrid fly, Hydrellia lagarosiphon Deeming (Diptera: Ephydridae) was ascertained to be the most ubiquitous and abundant species associated with L. major in South Africa. The influence of herbivory by this fly on the competitive ability of L. major in the presence of M. spicatum was investigated using an inverse linear model, which showed that herbivory by H. lagarosiphon reduced the competitive ability of L. major by approximately five times in favour of M. spicatum. This study served to highlight the importance of herbivory as a driver of submerged aquatic plant dynamics. Current ecological theory emphasises the importance of investigating beyond plant-herbivore interactions, by including multitrophic interactions in community dynamics. Therefore, the potential of parasitism by a parasitoid wasp, Chaenusa luteostigma sp. n. Achterberg (Hymenoptera: Braconidae: Alysiinae) on H. lagarosiphon to shift the competitive interactions between the two plant species was also examined. The addition of the parasitoid reduced the effect of herbivory by the fly on L. major by half, thereby shifting the competitive balance in favour of L. major over M. spicatum. This study provides valuable insight into a selection of drivers of submerged macrophyte assemblages of South Africa. It highlights the precarious position of South African freshwater systems with regard to the potential invasion by damaging submerged invasive species. It also provides interesting insights into the effect of competition, herbivory and parasitism on the establishment and spread of species within submerged freshwater systems. Understanding the different influences could assist managers and policy makers to make validated decisions ensuring the integrity of South African freshwater systems.
- Full Text:
- Date Issued: 2013
- Authors: Martin, Grant Douglas
- Date: 2013
- Subjects: Freshwater plants -- South Africa Aquatic weeds -- South Africa Invasive plants -- South Africa Freshwater ecology -- South Africa Biotic communities -- South Africa Maximum entropy method Lagarosiphon major -- South Africa Phytophagous insects -- South Africa Hydrellia -- South Africa Parasitoids -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5621 , http://hdl.handle.net/10962/d1004127
- Description: Potentially damaging submerged invasive freshwater macrophytes have been identified in South African freshwater systems, but have received less attention than their floating counterparts. To ascertain the changes and effects that these species may have on macrophyte ecology, an understanding of the drivers of macrophyte assemblages is essential. The aims of this thesis were to investigate select abiotic and biotic factors driving introduction, establishment and spread of submerged macrophytes in South Africa. Surveys on the status of submerged plant species in South Africa were conducted to find out the distribution and diversity of the species present, imported to, and traded in South Africa. Numerous submerged indigenous and invasive macrophyte locality records were collected during field surveys, of which many were first time records. Pet stores and aquarist trading activities were identified as potential vectors for the spread of submerged macrophytes through online surveys and personal interviews. These results highlighted the potential these species have for continuing to enter, and spread within South African water bodies. Maximum Entropy (MAXENT) is a general-purpose method used to predict or infer distributions from incomplete information, and was used here to predict areas suitable for the establishment of five of these invasive macrophytes. Many systems throughout South Africa, particularly those in the subtropical coastal regions, were found to be climatically suitable for the establishment of Elodea canadensis Michx., Egeria densa Planch., Hydrilla verticillata (L.f.) Royle (all Hydrocharitaceae), Myriophyllum spicatum L. (Haloragaceae), and Cabomba caroliniana Gray (Cabombaceae). Despite the high probability of invasion, facilitated by vectors and suitable climate, South Africa’s rich indigenous submerged aquatic flora may be preventing the establishment of these submerged invasive species. Studies on the competitive interactions between a common indigenous submerged macrophytes, Lagarosiphon major (Roxb.) (Hydrocharitaceae) and M.spicatum, an invasive native to Eurasia, were conducted to ascertain which conditions influence competitive superiority. High sediment nutrient conditions significantly increased the growth rate and competitive ability of both species, while clay sediments significantly increased the competitive ability of L. major over M. spicatum, but sandy sediments improved the competitive ability of M. spicatum. These results highlighted the dynamic changes in competition between submerged species driven by abiotic factors, but did not take into consideration the effect that herbivory, a biotic factor, could have on competition between the two species. The effect of herbivory by phytophagous insects of submerged plant species has been regarded as negligible. To find out what this effect is, multiple field surveys were undertaken throughout South Africa to find natural enemies of indigenous Lagarosiphon species with the aim of identifying such species, and quantifying their influence on plant growth dynamics. Several new phytophagous species were recorded for the first time. An ephydrid fly, Hydrellia lagarosiphon Deeming (Diptera: Ephydridae) was ascertained to be the most ubiquitous and abundant species associated with L. major in South Africa. The influence of herbivory by this fly on the competitive ability of L. major in the presence of M. spicatum was investigated using an inverse linear model, which showed that herbivory by H. lagarosiphon reduced the competitive ability of L. major by approximately five times in favour of M. spicatum. This study served to highlight the importance of herbivory as a driver of submerged aquatic plant dynamics. Current ecological theory emphasises the importance of investigating beyond plant-herbivore interactions, by including multitrophic interactions in community dynamics. Therefore, the potential of parasitism by a parasitoid wasp, Chaenusa luteostigma sp. n. Achterberg (Hymenoptera: Braconidae: Alysiinae) on H. lagarosiphon to shift the competitive interactions between the two plant species was also examined. The addition of the parasitoid reduced the effect of herbivory by the fly on L. major by half, thereby shifting the competitive balance in favour of L. major over M. spicatum. This study provides valuable insight into a selection of drivers of submerged macrophyte assemblages of South Africa. It highlights the precarious position of South African freshwater systems with regard to the potential invasion by damaging submerged invasive species. It also provides interesting insights into the effect of competition, herbivory and parasitism on the establishment and spread of species within submerged freshwater systems. Understanding the different influences could assist managers and policy makers to make validated decisions ensuring the integrity of South African freshwater systems.
- Full Text:
- Date Issued: 2013
Education District Office support for teaching and learning in schools: the case of two districts in the Eastern Cape
- Authors: Mavuso, Mzuyanda Percival
- Date: 2013
- Subjects: Schools -- Development -- South Africa -- Eastern Cape , School management and organization -- South Africa -- Eastern Cape , Educational change -- South Africa -- Eastern Cape , School management teams -- South Africa -- Eastern Cape , School administrators -- South Africa -- Eastern Cape , School supervision -- South Africa -- Eastern Cape , School improvement programs -- South Africa -- Eastern Cape , Educational leadership -- South Africa -- Eastern Cape , Educational evaluation -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD (Education)
- Identifier: vital:16194 , http://hdl.handle.net/10353/d1006259 , Schools -- Development -- South Africa -- Eastern Cape , School management and organization -- South Africa -- Eastern Cape , Educational change -- South Africa -- Eastern Cape , School management teams -- South Africa -- Eastern Cape , School administrators -- South Africa -- Eastern Cape , School supervision -- South Africa -- Eastern Cape , School improvement programs -- South Africa -- Eastern Cape , Educational leadership -- South Africa -- Eastern Cape , Educational evaluation -- South Africa -- Eastern Cape
- Description: The idea of district support for schools is based on the view that local education offices are best placed to play a critical role in the promotion of quality teaching and learning. In performing this mandate whose characterisation has, over time, moved away from ‘inspection’ and ‘supervision’ both of which are seen as old fashioned and undemocratic, to support, which is seen as developmental. The aim of this study was to understand how three categories of district based officers, Subject Advisors, Integrated Quality Management System Coordinators and Education Development Officers support teaching and learning in schools. This was a case study of two districts in the Eastern Cape Province of South Africa. A total of six district officials and four school based officials participated in this study. In-depth interviews and document analysis were carried out. There were four main findings. First, support for schools by three district based officials was understood and practiced as administrative tasks, mainly consisting of monitoring policy implementation and monitoring resource provision to schools. School Management Teams saw district officers’ visits as focussing on compliance rather than support. Second, some pedagogical support was given by Subject Advisors through training teachers in subject content and methods of teaching that subject. This was done through workshops and demonstration lessons. However Subject Advisors did not at any time observe actual classroom teaching to see if teachers were implementing what they had learnt at workshops. Third, none of the officers mentioned direct support for teaching and learning at classroom level. Visits by officials were not directly linked to influencing teaching and learning classroom level. Fourth, schools saw district officials as working in separate pockets and sometimes sending different signals to them, despite claims by district officials that inter-disciplinary meetings were held among district officials, however, the nature of the coordination and the use to which it is put remains unclear. There were three main conclusions, first that although the district officials’ visits to schools were described as support, they exhibited the trappings of technicism of inspection; supervision and control; and appeared to neglect the developmental aspects implied in the notion of support. Second, the conception and practice of support visits by district officials were characterised by tension between support and control. Third, at district level support to schools lacked coordination among the three categories of officers who visit schools. This has implications for quality management in schools. Given the findings and conclusions of this study; it is recommended that the issue of support for schools be the focus of a survey research for which a probability sample must be drawn in order to generate findings that are generalisable across the participating target population. Other research could focus on investigating mechanisms by which the tension between support and control can be resolved. To improve practice of a framework for the development of a coordinated district support focusing on the core business of teaching and learning is suggested.
- Full Text:
- Date Issued: 2013
- Authors: Mavuso, Mzuyanda Percival
- Date: 2013
- Subjects: Schools -- Development -- South Africa -- Eastern Cape , School management and organization -- South Africa -- Eastern Cape , Educational change -- South Africa -- Eastern Cape , School management teams -- South Africa -- Eastern Cape , School administrators -- South Africa -- Eastern Cape , School supervision -- South Africa -- Eastern Cape , School improvement programs -- South Africa -- Eastern Cape , Educational leadership -- South Africa -- Eastern Cape , Educational evaluation -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD (Education)
- Identifier: vital:16194 , http://hdl.handle.net/10353/d1006259 , Schools -- Development -- South Africa -- Eastern Cape , School management and organization -- South Africa -- Eastern Cape , Educational change -- South Africa -- Eastern Cape , School management teams -- South Africa -- Eastern Cape , School administrators -- South Africa -- Eastern Cape , School supervision -- South Africa -- Eastern Cape , School improvement programs -- South Africa -- Eastern Cape , Educational leadership -- South Africa -- Eastern Cape , Educational evaluation -- South Africa -- Eastern Cape
- Description: The idea of district support for schools is based on the view that local education offices are best placed to play a critical role in the promotion of quality teaching and learning. In performing this mandate whose characterisation has, over time, moved away from ‘inspection’ and ‘supervision’ both of which are seen as old fashioned and undemocratic, to support, which is seen as developmental. The aim of this study was to understand how three categories of district based officers, Subject Advisors, Integrated Quality Management System Coordinators and Education Development Officers support teaching and learning in schools. This was a case study of two districts in the Eastern Cape Province of South Africa. A total of six district officials and four school based officials participated in this study. In-depth interviews and document analysis were carried out. There were four main findings. First, support for schools by three district based officials was understood and practiced as administrative tasks, mainly consisting of monitoring policy implementation and monitoring resource provision to schools. School Management Teams saw district officers’ visits as focussing on compliance rather than support. Second, some pedagogical support was given by Subject Advisors through training teachers in subject content and methods of teaching that subject. This was done through workshops and demonstration lessons. However Subject Advisors did not at any time observe actual classroom teaching to see if teachers were implementing what they had learnt at workshops. Third, none of the officers mentioned direct support for teaching and learning at classroom level. Visits by officials were not directly linked to influencing teaching and learning classroom level. Fourth, schools saw district officials as working in separate pockets and sometimes sending different signals to them, despite claims by district officials that inter-disciplinary meetings were held among district officials, however, the nature of the coordination and the use to which it is put remains unclear. There were three main conclusions, first that although the district officials’ visits to schools were described as support, they exhibited the trappings of technicism of inspection; supervision and control; and appeared to neglect the developmental aspects implied in the notion of support. Second, the conception and practice of support visits by district officials were characterised by tension between support and control. Third, at district level support to schools lacked coordination among the three categories of officers who visit schools. This has implications for quality management in schools. Given the findings and conclusions of this study; it is recommended that the issue of support for schools be the focus of a survey research for which a probability sample must be drawn in order to generate findings that are generalisable across the participating target population. Other research could focus on investigating mechanisms by which the tension between support and control can be resolved. To improve practice of a framework for the development of a coordinated district support focusing on the core business of teaching and learning is suggested.
- Full Text:
- Date Issued: 2013
Effectiveness of irrigation water management institutions in Zimbabwe: a new institutional economics theory approach
- Authors: Nhundu, Kenneth
- Date: 2013
- Language: English
- Type: Thesis , Doctoral , PhD (Agricultural Economics)
- Identifier: vital:11195 , http://hdl.handle.net/10353/d1006784
- Description: Despite considerable advances in technology across the world, some scholars (Bratton, 1987; Namara et al., 2010) have argued that declining agricultural productivity among smallholder farmers in Africa remains a major bottleneck in the development of the continent. Unganai (1993) indicates that about 60% of the southern African region is semi-arid or arid and suffers from periodic droughts. In addition, World Bank (2003) notes that agricultural production is dominated by rain-fed agriculture and irrigation systems are limited. This is compounded by the scarcity and poor management of irrigation water resources. Water scarcity in agriculture has large impacts on the population, especially in rural areas, where more than 60 percent of the population are engaged in agriculture which represents their main source of food and income (FAO, 2008). On the macroeconomic level, agricultural share of the GDP is about 37 percent and 75 percent of the export value is generated from the agricultural sector globally. To this effect, management of agricultural water particularly in rain-fed systems remains imperative for improved farm level yields because the bulk of the food comes from rain-fed agriculture (FAO, 2008; Namara et al., 2010). However, increasing water scarcity and poor accessibility may become a limiting factor not only for agricultural production and the welfare of rural population but also for the entire economy. Improving the management of water resources and an efficient use of water by all sectors, including agricultural production, are therefore important if the welfare and health of the population, particularly in rural areas, are to be maintained and improved (Nyong & Kanaroglou, 1999).
- Full Text:
- Date Issued: 2013
- Authors: Nhundu, Kenneth
- Date: 2013
- Language: English
- Type: Thesis , Doctoral , PhD (Agricultural Economics)
- Identifier: vital:11195 , http://hdl.handle.net/10353/d1006784
- Description: Despite considerable advances in technology across the world, some scholars (Bratton, 1987; Namara et al., 2010) have argued that declining agricultural productivity among smallholder farmers in Africa remains a major bottleneck in the development of the continent. Unganai (1993) indicates that about 60% of the southern African region is semi-arid or arid and suffers from periodic droughts. In addition, World Bank (2003) notes that agricultural production is dominated by rain-fed agriculture and irrigation systems are limited. This is compounded by the scarcity and poor management of irrigation water resources. Water scarcity in agriculture has large impacts on the population, especially in rural areas, where more than 60 percent of the population are engaged in agriculture which represents their main source of food and income (FAO, 2008). On the macroeconomic level, agricultural share of the GDP is about 37 percent and 75 percent of the export value is generated from the agricultural sector globally. To this effect, management of agricultural water particularly in rain-fed systems remains imperative for improved farm level yields because the bulk of the food comes from rain-fed agriculture (FAO, 2008; Namara et al., 2010). However, increasing water scarcity and poor accessibility may become a limiting factor not only for agricultural production and the welfare of rural population but also for the entire economy. Improving the management of water resources and an efficient use of water by all sectors, including agricultural production, are therefore important if the welfare and health of the population, particularly in rural areas, are to be maintained and improved (Nyong & Kanaroglou, 1999).
- Full Text:
- Date Issued: 2013
Electricity generation, transmission and distribution policy: a comparative study of Nigeria (1960-2011) and South Africa (1960-2011)
- Authors: Okafor, Chukwuemeka
- Date: 2013
- Subjects: Electric power distribution -- Nigeria , Electric power distribution -- South Africa , Electric power consumption -- Nigeria , Electric power consumption -- South Africa , Electric power production -- Nigeria , Electric power production -- South Africa , Electric power transmission -- Nigeria , Electric power transmission -- South Africa , Electricity
- Language: English
- Type: Thesis , Doctoral , PhD (in Public Administration)
- Identifier: vital:11660 , http://hdl.handle.net/10353/d1007049 , Electric power distribution -- Nigeria , Electric power distribution -- South Africa , Electric power consumption -- Nigeria , Electric power consumption -- South Africa , Electric power production -- Nigeria , Electric power production -- South Africa , Electric power transmission -- Nigeria , Electric power transmission -- South Africa , Electricity
- Description: The electric power policies in Nigeria and South Africa are considered the governments’ intention to provide quality and affordable electricity to the people. A comparative study on the electric power policies focuses on the similarities and differences in the policy approaches, the policy issues that affect electrification, and the impact of the policy issues in achieving the goal of universal access to quality and affordable electricity power in both countries. The methodological approach allows for an in depth textual study on the electric power policy documents in both countries. In Nigeria, the government intends to address the massive demand-supply imbalance and achieve the goal of electrification through reforms that focus on private sector-led growth in the sub-sector. In South Africa, the identification of electrification as a public problem by the post apartheid government leads to an integrated policy framework that focuses on balancing economic concerns with social and environmental considerations. The study identifies electricity provision as a social welfare responsibility of the governments in both countries and examines the policy issues in the context of public welfare. In Nigeria, the policy issues are found to be self serving and not in line with sustainable public interest, given the socio-economic challenges. As a result they, exert less impact on achieving the goal of universal access to quality and affordable electricity in the country. In South Africa, good governance in the sub-sector has enabled the identification of policy issues in line with sustainable public interests of social equity, poverty alleviation and environmental sustainability; and government using public administration agencies to play a key role in service delivery. Recommendations of the study mainly derive from the South African experience on electrification, and are intended to offer some policy-lessons to Nigeria in the sub-sector. The study contributes to new knowledge in the discipline of public administration by opening up new vistas for a comparative analysis of electric power policy issues in both countries in the context of public welfare. Besides, a comparative study on electrification in Nigeria and South Africa from a policy angle contributes to the existing knowledge base in the discipline.
- Full Text:
- Date Issued: 2013
- Authors: Okafor, Chukwuemeka
- Date: 2013
- Subjects: Electric power distribution -- Nigeria , Electric power distribution -- South Africa , Electric power consumption -- Nigeria , Electric power consumption -- South Africa , Electric power production -- Nigeria , Electric power production -- South Africa , Electric power transmission -- Nigeria , Electric power transmission -- South Africa , Electricity
- Language: English
- Type: Thesis , Doctoral , PhD (in Public Administration)
- Identifier: vital:11660 , http://hdl.handle.net/10353/d1007049 , Electric power distribution -- Nigeria , Electric power distribution -- South Africa , Electric power consumption -- Nigeria , Electric power consumption -- South Africa , Electric power production -- Nigeria , Electric power production -- South Africa , Electric power transmission -- Nigeria , Electric power transmission -- South Africa , Electricity
- Description: The electric power policies in Nigeria and South Africa are considered the governments’ intention to provide quality and affordable electricity to the people. A comparative study on the electric power policies focuses on the similarities and differences in the policy approaches, the policy issues that affect electrification, and the impact of the policy issues in achieving the goal of universal access to quality and affordable electricity power in both countries. The methodological approach allows for an in depth textual study on the electric power policy documents in both countries. In Nigeria, the government intends to address the massive demand-supply imbalance and achieve the goal of electrification through reforms that focus on private sector-led growth in the sub-sector. In South Africa, the identification of electrification as a public problem by the post apartheid government leads to an integrated policy framework that focuses on balancing economic concerns with social and environmental considerations. The study identifies electricity provision as a social welfare responsibility of the governments in both countries and examines the policy issues in the context of public welfare. In Nigeria, the policy issues are found to be self serving and not in line with sustainable public interest, given the socio-economic challenges. As a result they, exert less impact on achieving the goal of universal access to quality and affordable electricity in the country. In South Africa, good governance in the sub-sector has enabled the identification of policy issues in line with sustainable public interests of social equity, poverty alleviation and environmental sustainability; and government using public administration agencies to play a key role in service delivery. Recommendations of the study mainly derive from the South African experience on electrification, and are intended to offer some policy-lessons to Nigeria in the sub-sector. The study contributes to new knowledge in the discipline of public administration by opening up new vistas for a comparative analysis of electric power policy issues in both countries in the context of public welfare. Besides, a comparative study on electrification in Nigeria and South Africa from a policy angle contributes to the existing knowledge base in the discipline.
- Full Text:
- Date Issued: 2013
Electrocatalytic detection of pesticides with electrodes modified with nanoparticles of phthalocyanines and multiwalled carbon nanotubes
- Authors: Siswana, Msimelelo Patrick
- Date: 2013
- Subjects: Phthalocyanines Pesticides Electrocatalysis Electrochemistry Nanotubes Nanoparticles Transmission electron microscopy Scanning electron microscopy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4282 , http://hdl.handle.net/10962/d1002613
- Description: Three types of electrodes: carbon paste electrodes modified with nanoparticles of metallophthalocyanines (MPcNP-CPEs, M = Mn, Fe, Ni, Co), basal plane pyrolytic graphite electrodes modified with iron or nickel phthalocyanine nanoparticles and multiwalled carbon nanotube composites (FePcNP/MWCNT-BPPGE or NiPcNP/MWCNT-BPPGE),and basal plane pyrolytic graphite electrodes modified with multiwalled carbon nanotubes and electropolymerized metal tetra-aminophthalocyanines (poly-MTAPc-MWCNT-BPPGE), where M is Mn, Fe, Ni or Co, were prepared. Electrochemical characterizations showed that faster electron transfer kinetics occurred at the NiPcNP/MWCNT-BPPGE than at the FePcNP/MWCNT-BPPGE surface. SEM and electrochemical characterizations of poly-MTAPc-MWCNT-BPPGE showed that MTAPc had been deposited on the MWCNTBPPGE surface, and that the poly-CoTAPc-MWCNT-BPPGE exhibited the fastest electron transfer kinetics of all the poly-MTAPc-MWCNT-BPPGEs. Using amitrole and asulam as test analytes, electrochemical experiments showed that, amongst the CPEs, the FePcNP-CPE and NiPcNP-CPE displayed the most electrocatalytic behavior towards amitrole and asulam oxidation, respectively, and further experiments were done to obtain the electrochemical parameters associated with these electrodes and the corresponding analytes. Although, the FePcNP/MWCNT- BPPGE displayed electrocatalytic behavior towards amitrole oxidation in comparison with the bare BPPGE, it was less electrocatalytic than the FePcNP-CPE in terms of detection potential. The NiPcNP/MWCNT-BPPGE displayed the same detection potential as the NiPcNP-CPE. The poly-FeTAPc-MWCNT-BPPGE exhibited the most electrocatalytic behavior towards amitrole, of all the electrodes investigated, and the poly-CoTAPc-MWCNT-BPPGE displayed the best electrocatalytic behavior towards asulam, amongst the poly-MTAPc-MWCNT-BPPGEs.
- Full Text:
- Date Issued: 2013
- Authors: Siswana, Msimelelo Patrick
- Date: 2013
- Subjects: Phthalocyanines Pesticides Electrocatalysis Electrochemistry Nanotubes Nanoparticles Transmission electron microscopy Scanning electron microscopy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4282 , http://hdl.handle.net/10962/d1002613
- Description: Three types of electrodes: carbon paste electrodes modified with nanoparticles of metallophthalocyanines (MPcNP-CPEs, M = Mn, Fe, Ni, Co), basal plane pyrolytic graphite electrodes modified with iron or nickel phthalocyanine nanoparticles and multiwalled carbon nanotube composites (FePcNP/MWCNT-BPPGE or NiPcNP/MWCNT-BPPGE),and basal plane pyrolytic graphite electrodes modified with multiwalled carbon nanotubes and electropolymerized metal tetra-aminophthalocyanines (poly-MTAPc-MWCNT-BPPGE), where M is Mn, Fe, Ni or Co, were prepared. Electrochemical characterizations showed that faster electron transfer kinetics occurred at the NiPcNP/MWCNT-BPPGE than at the FePcNP/MWCNT-BPPGE surface. SEM and electrochemical characterizations of poly-MTAPc-MWCNT-BPPGE showed that MTAPc had been deposited on the MWCNTBPPGE surface, and that the poly-CoTAPc-MWCNT-BPPGE exhibited the fastest electron transfer kinetics of all the poly-MTAPc-MWCNT-BPPGEs. Using amitrole and asulam as test analytes, electrochemical experiments showed that, amongst the CPEs, the FePcNP-CPE and NiPcNP-CPE displayed the most electrocatalytic behavior towards amitrole and asulam oxidation, respectively, and further experiments were done to obtain the electrochemical parameters associated with these electrodes and the corresponding analytes. Although, the FePcNP/MWCNT- BPPGE displayed electrocatalytic behavior towards amitrole oxidation in comparison with the bare BPPGE, it was less electrocatalytic than the FePcNP-CPE in terms of detection potential. The NiPcNP/MWCNT-BPPGE displayed the same detection potential as the NiPcNP-CPE. The poly-FeTAPc-MWCNT-BPPGE exhibited the most electrocatalytic behavior towards amitrole, of all the electrodes investigated, and the poly-CoTAPc-MWCNT-BPPGE displayed the best electrocatalytic behavior towards asulam, amongst the poly-MTAPc-MWCNT-BPPGEs.
- Full Text:
- Date Issued: 2013
Environmental water quality management of glyphosate-based herbicides in South Africa
- Authors: Mensah, Paul Kojo
- Date: 2013
- Subjects: Water quality management -- South Africa Water quality management -- Environmental Aspects -- South Africa Herbicides -- Environmental aspects -- South Africa Herbicides -- Toxicology -- South Africa Water -- Glyphosate content -- South Africa Water -- Pollution -- South Africa Water quality -- Measurement -- South Africa Water -- Analysis -- South Africa Freshwater ecology -- South Africa Integrated water development -- South Africa Caridina -- Effect of pollution on -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:6023 , http://hdl.handle.net/10962/d1001987
- Description: Although the use of pesticides is necessary to meet the socio-economic needs of many developing countries, especially in Africa, side effects of these bio-active chemicals have contributed to contaminating aquatic and terrestrial ecosystems. Environmental water quality degradation by pesticides interferes with ecosystem health and poses numerous risks to aquatic life. In South Africa, glyphosate-based herbicides are frequently used to control weeds and invading alien plants, but ultimately end up in freshwater ecosystems. However, there are no South African-based environmental water quality management strategies to regulate these bio-active chemicals. Therefore, this study sought to provide a sound scientific background for the environmental water quality management of glyphosate-based herbicides in South Africa, by conducting both laboratory and field investigations. In the laboratory investigations, aquatic ecotoxicological methods were used to evaluate responses of the freshwater aquatic shrimp Caridina nilotica exposed to Roundup® at different biological system scales, and the responses of multiple South African aquatic species exposed to Roundup® through species sensitivity distribution (SSD). In the field investigations, the effect of Kilo Max WSG on the physicochemical and biological conditions of three selected sites in the Swartkops River before and after a spray episode by Working for Water were evaluated through biomonitoring, using the South African Scoring System version 5 (SASS5) as a sampling protocol. Both Roundup® and Kilo Max WSG are glyphosate-based herbicides. All the data were subjected to relevant statistical analyses. Findings of this study revealed that Roundup® elicited responses at different biological system scales in C. nilotica, while SSD estimates were used to derive proposed water quality guidelines for glyphosate-based herbicides in South Africa. The biomonitoring revealed that using glyphosate-based herbicides to control water hyacinth within the Swartkops River had a negligible impact on the physicochemical and biological conditions. Based on these findings, a conceptual framework that can be used for the integrated environmental water quality management of glyphosate-based herbicides in South Africa was developed as part of integrated water resource management (IWRM). The combined data sets contribute to a sound scientific basis for the environmental water quality management of glyphosate-based herbicides in South Africa.
- Full Text:
- Date Issued: 2013
- Authors: Mensah, Paul Kojo
- Date: 2013
- Subjects: Water quality management -- South Africa Water quality management -- Environmental Aspects -- South Africa Herbicides -- Environmental aspects -- South Africa Herbicides -- Toxicology -- South Africa Water -- Glyphosate content -- South Africa Water -- Pollution -- South Africa Water quality -- Measurement -- South Africa Water -- Analysis -- South Africa Freshwater ecology -- South Africa Integrated water development -- South Africa Caridina -- Effect of pollution on -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:6023 , http://hdl.handle.net/10962/d1001987
- Description: Although the use of pesticides is necessary to meet the socio-economic needs of many developing countries, especially in Africa, side effects of these bio-active chemicals have contributed to contaminating aquatic and terrestrial ecosystems. Environmental water quality degradation by pesticides interferes with ecosystem health and poses numerous risks to aquatic life. In South Africa, glyphosate-based herbicides are frequently used to control weeds and invading alien plants, but ultimately end up in freshwater ecosystems. However, there are no South African-based environmental water quality management strategies to regulate these bio-active chemicals. Therefore, this study sought to provide a sound scientific background for the environmental water quality management of glyphosate-based herbicides in South Africa, by conducting both laboratory and field investigations. In the laboratory investigations, aquatic ecotoxicological methods were used to evaluate responses of the freshwater aquatic shrimp Caridina nilotica exposed to Roundup® at different biological system scales, and the responses of multiple South African aquatic species exposed to Roundup® through species sensitivity distribution (SSD). In the field investigations, the effect of Kilo Max WSG on the physicochemical and biological conditions of three selected sites in the Swartkops River before and after a spray episode by Working for Water were evaluated through biomonitoring, using the South African Scoring System version 5 (SASS5) as a sampling protocol. Both Roundup® and Kilo Max WSG are glyphosate-based herbicides. All the data were subjected to relevant statistical analyses. Findings of this study revealed that Roundup® elicited responses at different biological system scales in C. nilotica, while SSD estimates were used to derive proposed water quality guidelines for glyphosate-based herbicides in South Africa. The biomonitoring revealed that using glyphosate-based herbicides to control water hyacinth within the Swartkops River had a negligible impact on the physicochemical and biological conditions. Based on these findings, a conceptual framework that can be used for the integrated environmental water quality management of glyphosate-based herbicides in South Africa was developed as part of integrated water resource management (IWRM). The combined data sets contribute to a sound scientific basis for the environmental water quality management of glyphosate-based herbicides in South Africa.
- Full Text:
- Date Issued: 2013