Browsing Faculty of Science by Title
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Ketshajwang, K.K.; Holmback, J.; Yeboah, S.O. (AOCS Press. http://www.springerlink.com/content/120382/, NaN, 1998)[more][less]
Abstract: Seed oils were extracted with n-hexane from three edible Leguminosae seeds: Tylosema esculentum, Xanthocercis zambesiaca, and Bauhinia petersiana, giving yields of 48.2, 17.6, and 20.8% (w/w), respectively. Some physical and chemical parameters were determined to ascertain the general characteristics of the oils. The saponification and iodine values indicated that all three oil samples could be classified among the olive group of oils. This inference was supported by the results of the detailed fatty acid composition of the oils as determined by capillary gas chromatography. The ratio of total unsaturated to total saturated fatty acids in all three oil samples was approximately 70:30, with either oleic or linoleic acid being the dominant fatty acid. These results were in agreement with a proton nuclear magnetic resonance analysis of the fatty acid classes in the seed oils. Thus, the analysis served to justify the use of the three Leguminosae seed oils in food preparations. The work has further indicated that, with their attractive properties, the seed oils from T. esculentum, X. zambesiaca, and B. petersiana are good candidates for further studies to evaluate their future commercial prospects in the Southern African region. URI: http://hdl.handle.net/10311/304 Files in this item: 1
quality and compositional.pdf (1.683Mb) -
Moges, S.A.; Alemaw, B.F.; Chaoka, T.R.; Kachroo, R.K. (Elsevier, www.elsevier.com/locate/pce, NaN, 2007)[more][less]
Abstract: This paper is aimed at developing a geostatistical model to improve interpolated annual and monthly rainfall variation using remotely- sensed cold cloud duration (CCD) data as a background image. The data set consists of rainfall data from a network of 704 rain gauges in the Rufiji drainage basin in Tanzania. We found ordinary kriging to be a robust estimator due mainly to its inherent nature of including the non-stationary local mean during estimation. Parameter sensitivity analysis and examination of the residuals revealed that the parameter values of the variogram viz., the nugget effect, the range, sill value and maximum direction of continuity, as long as they are in acceptable ranges, and any different combination of these parameters, have low effect on model efficiency and accuracy. Rather, the use of remotely-sensed CCD data as a background image is found to improve the interpolation as compared to the estimation based on observed point rainfall data alone. The study revealed the improvement in terms of Nash–Sutcliffe model performance index (R2) by using CCD as external drift with kriging provided an R2 of 64.5% compared to the simple kriging and ordinary kriging, which performed with efficiency of 60.0% and 61.4%, respectively. For each case, parameter sensitivity analysis was conducted to investigate the effect of the change in the parameters on the model performance and the spatio-temporal interpolation results. URI: http://hdl.handle.net/10311/500 Files in this item: 1
MOGES2007Rainfall interpolation.pdf (1.188Mb) -
Magwaza, A.O.; Meijboom, R.; Muller, A.; Mavunkal, I.J. (Elsevier B.V. www.elsevier.com/locate/ica, NaN, 2008)[more][less]
Abstract: Mono- and bis-substituted phosphite complexes [Ru3(CO)12 x Lx] (L = tris(2,4-di-tert-butylphenyl) phosphite; x = 1, 2) were synthesized by simple substitution reactions, and were characterized by spectroscopic methods. The monosubstituted ruthenium complex disproportionates in acetone producing a mononuclear ruthenium complex as one of the decomposition products. Single crystal X-ray diffraction analysis established the molecular structure of this new compound. URI: http://hdl.handle.net/10311/259 Files in this item: 2
license.txt (1.998Kb) -
Majinda, R.R.T; Abegaz, B.M.; Bezabih, M.; Ngadjui, B.T; Wanjala, C.C.W.; Mdee, L.K.; Bojase, G.; Silayo, A.; Masesane, I.; Yeboah, S.O. (IUPAC. http://www.iupac.org/publications/pac/, NaN, 2001)[more][less]
Abstract: Marketed plants are very important items of trade in many parts of the world. The community uses these for a variety of purposes such as foods, cosmetics, flavors, spices, and medicines. It seems that plants that are used for medicinal purposes form the most common category. Four plants used for treatment of microbial infections, viz., Bolusanthus speciosus, Erythrina latissima, Crotalaria podocarpa, and Elephantorrhiza goetzei, were investigated, and these yielded several known and novel structures, some with appreciable antibiotic activity against the test organisms. The activity of some of the isolated plants and the parts of the plant from which these were obtained lend support to their traditional use. Bulbine abyssinica and B. capitata yielded phenylanthraquinones, some of which were shown to possess strong antiplasmodial activity. In addition, these yielded isofuranonaphthoquinones, which were also found to be weakly antiplasmodial and antioxidant. Scilla nervosa yielded several known and novel homoisoflavoinds of the 3-benzylchroman-4-ones and 3-benzylidinechroman- 4-one type, as well as some stilbenoids. The homoisoflavonoids showed strong antitumor activity against various cancer cell lines. Rhus pyroides gave a novel bichalcone, which showed weak antifeedant activity, consistent with the observation by farmers that the plant was avoided by corn cricket. Results from investigated Dorstenia species originating from Cameroon, Ethiopia, and Tanzania yielded styrenes, coumarins, chalcones, and flavonoids. The chalcones and flavonoids showed various levels of prenylation or geranylation, and an observation made so far is that prenylated flavonoids are only found in Dorstenia species of African origin. The only example of a bis-geranylated chalcone is found in Dorstenia. URI: http://hdl.handle.net/10311/308 Files in this item: 1
Recent results from.pdf (4.630Mb) -
Jain, P.K.; Lungu, E.M.; Mogotsi, B. (Elsevier Science Ltd. http://www.sciencedirect.com/science/journal/09601481, January NaN, 2002)[more][less]
Abstract: Lack of trained manpower for repair and maintenance of solar energy devices in Botswana has resulted in failure of devices, loss of revenue, and dwindling of consumer faith in solar technologies. The government of Botswana commissioned a study to assess the needs for trained manpower in New and Renewable Sources of Energy (NRSE) technologies, to identify the required training programs and their levels, and the facilities that need to be upgraded and/or created for the implementation of such training programs at the existing technical and educational institutions within the country. The paper presents the findings of the study, and the recommendations made. The study proposed seven training programs at progressively increasing skills and expertise levels that include two certificate courses in each of the solar water heating and photovoltaic technologies for maintenance personnel, a national craft certificate program in solar energy technologies, a higher diploma in energy technologies for supervisory personnel, and a short course for upper management personnel in decision-making positions in order to raise their skills in the procurement of equipment and services, and to provide overall effective leadership. A short course to upgrade the skills of the present maintenance personnel to alleviate the immediate problems is also proposed. Required upgrading of existing technical training facilities, the creation of new facilities and estimated budgetary requirements constitute some of the recommendations. The recommendations have gone through various channels of discussions, and have been accepted in principle. The report is currently under consideration for implementation by relevant government departments. URI: http://hdl.handle.net/10311/137 Files in this item: 2
license.txt (1.998Kb) -
Mpoloka, S.W. (Academic Journals, www.academicjournals.org, August 18, 2010)[more][less]
Abstract: Residual long-term effects of increased UV-B radiation were investigated in an indigenous plant species, Dimorphotheca sinuata, by analysing photosynthetic gene expression. Reductions were observed in the amount of the rbcL and psbA mRNA expressed in progeny of plants that were previously subjected to enhanced UV-B levels. However, observed reductions did not attain statistical significance. This could explain the reduction in net biomass and physiological and biochemical parameters observed by other researchers as a result of UV-B exposure. Results from this study with plants grown in the absence of UV-B point to changes in the regulation of photosynthetic genes and such mutations due to raised UV-B levels could cause permanent changes in plant populations. URI: http://hdl.handle.net/10311/1011 Files in this item: 1
Mpoloka SRE 2010.pdf (122.9Kb) -
Moleele, N.M.; Mainah, J. (Elsevier http://www.linkinghub.elsevier.com/retrieve/pii/S0140196302910992, NaN, 2003)[more][less]
Abstract: The Kalahari ecosystem is characterized by natural resource conflicts and land-use pressure resulting from intensification of human activities. This paper addresses three issues of concern associated with the Kalahari ecosystem resource management: (i) the major land-use/land cover shifts in the Kalahari ecosystem since 1970 and the resulting pattern in vegetation species composition, cover and density; (ii) the possible explanations for the observed shifts; and (iii) the possible resource conflicts likely to arise. Data collection involved the comparison of two sets of panchromatic photographs along two transects (Hukunsti–Ngwatle and Tshane–Tsabong) to study land-use/cover shifts that have occurred in the Kalahari ecosystem between 1971 and 1986. Secondly, the nature of possible conflicts resulting from population pressure and associated patterns of land-use was investigated by making observations on selected environmental variables along a 300km transect with diverse environments comprising different-sized settlements, vegetation communities and land-uses. Land-use/land cover shifts have occurred within the Kalahari ecosystem as evidenced by the two transects analysed in this paper. The main changes are the retreat of grass cover up to 18 kms from settlements and the increase in thorny and non-thorny woody encroachers closer to the settlements. In the Matsheng area, land-use/land cover gradients reflect marked differences in human pressure. For instance, while settlements (kraals/households) and fields around Tshane (smaller and dwindling settlement) have declined to 5% at the 4 km distance in 1986, these landuses account for 22?3% of land cover at 4 km around Hukuntsi (bigger and expanding village). Five major vegetation communities were identified using key plant species during the dry season. However, these communities do not have distinct land-use activities associated with them. Cattle densities were higher in communities found far away from settlements and water points where the grass cover was abundant. Cattle graze far from settlements to obtain quality fodder and trek to the water points around village pans or at cattle posts. There are no definite boundaries between vegetation communities and land-use activities, hence a lot of interaction between activities of these zones depends on the dispersion of resources. Shifts in land-use/cover changes can be accounted for by anthropogenic activities (arable agriculture, livestock grazing and human settlements) enhanced by natural factors like seasonal variations and prolonged droughts of the mid-1980s. It is argued in this paper that potential remedial measures include biosphere conservation areas, resource zoning and resource modeling plans to determine land suitability. URI: http://hdl.handle.net/10311/411 Files in this item: 1
Moleele_JAE_2003.pdf (1.813Mb) -
Hamandawana, H.; Chanda, R.; Eckardt, F. (Taylor & Francis, http://www.tandf.co.uk/journals/titles/00207233.asp, NaN, 2007)[more][less]
Abstract: This paper draws on archival information, anecdotal evidence from local communities, in situ observations during field investigation and multi-date remotely sensed satellite imagery. The authors investigated the role of human factors in the degradation of natural resources in and around the Okavango Delta. Their study concerned a period slightly in excess of 140 years between 1860 and 2001. Environmental changes in this sub-region appear to be the convergent outcome of interaction between natural and non-natural factors. A sustained decrease in rainfall appears to have instigated downward trends from a wide range of factors whose adverse effects were aggravated by human agency. The evidence points to progressive deterioration in the form of sustained contraction of surface water sources and grazing resources. Mistakes of the past need to be avoided by formulating appropriately informed human response and adaptation strategies. URI: http://hdl.handle.net/10311/279 Files in this item: 1
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Ngandeu, F.; Bezabih, M.; Ngamga, D.; Tchinda, A.; Ngadjui, B.; Abegaz, B.; Dufat, H.; Tillequin, F. (Elsevier Ltd. www.elsevier.com/locate/phytochem, NaN, 2007)[more][less]
Abstract: Three prenylated rotenoids, elliptol, 12-deoxo-12a-methoxyelliptone and 6-methoxy-6a,12a-dehydrodeguelin were isolated from the twigs of Millettia duchesnei, together with the known compounds, 6a,12a-dehydrodeguelin, 6-hydroxy-6a,12a-dehydrodeguelin, 6-oxo- 6a,12a-dehydrodeguelin, elliptone, 12a-hydroxyelliptone and eriodictyol. Their structures were elucidated on the basis of spectral data and comparison with information reported in the literature and with authentic specimens for some known compounds. The full NMR data of 6-oxo-6a,12a-dehydrodeguelin and 6-hydroxy-6a,12a-dehydrodeguelin are reported here for the first time. URI: http://hdl.handle.net/10311/243 Files in this item: 2
license.txt (1.998Kb) -
Massamba, F. (Birkhäuser Basel. http://www.springerlink.com/content/110963/?p=c42ba01ff0bd482b81a3ebdf3b649c9a&pi=0, NaN, 2009)[more][less]
Abstract: We investigate lightlike hypersurfaces of indefinite Sasakian manifolds, tangent to the structure vector field and whose screen distribution is integrable. We prove some results on parallel vector fields and on a leaf of the integrable distribution D0? h i of this class. A theorem on a geometrical configuration of the screen distribution is obtained. We show that any totally contact umbilical leaf of a screen integrable distribution of a lightlike hypersurface is an extrinsic sphere. Description: The mathematical symbols may not come as they are in the abstract. URI: http://hdl.handle.net/10311/689 Files in this item: 1
Screen Integrable Lightlike.pdf (1.251Mb) -
Kampunzu, A.B.; Cailteux, J.L.H.; Kamona, A.F.; Intiomale, M.M.; Melcher, F. (Elsevier www.elsevier.com/locate/oregeorev, NaN, 2009)[more][less]
Abstract: Stratabound epigenetic sulphide Zn–Pb–Cu ore deposits of the Central African Copperbelt in the Democratic Republic of Congo and Zambia are mostly hosted in deformed shallow marine platform carbonates and associated sedimentary rocks of the Neoproterozoic Katanga Supergroup. Economic orebodies, that also contain variable amounts of minor Cd, Co, Ge, Ag, Re, As, Mo, Ga, and V, occur mainly as irregular pipe-like bodies associated with collapse breccias and faults as well as lenticular bodies subparallel to bedding. Kipushi and Kabwe in the Democratic Republic of the Congo and Zambia, respectively, are the major examples of carbonate-hosted Zn–Pb–Cu mined deposits with important by-products of Ge, Cd, Ag and V in the Lufilian Arc, a major metallogenic province famous for its world-class sediment-hosted stratiform Cu–Co deposits. The carbonate-hosted deposits range in age from Neoproterozoic to early Palaeozoic (680 to 450 Ma). The formation of the relatively older Neoproterozoic deposits is probably related to early collision events during the Lufilian Orogeny, whereas the younger Palaeozoic deposits may be related to post-collisional processes of ore formation. Fluid inclusion and stable isotope data indicate that hydrothermal metal-bearing fluids evolved from formation brines during basin evolution and later tectonogenesis. Ore fluid migration occurred mainly along major thrust zones and other structural discontinuities such as karsts, breccias and faults within the Katangan cover rocks, resulting in ore deposition within favourable structures and reactive carbonates of the Katangan Supergroup. URI: http://hdl.handle.net/10311/380 Files in this item: 1
Kampunzu2009Sediment-hosted Zn.pdf (4.792Mb) -
Ringrose, S.; Huntsman-Mapila, P.; Kampunzu, A.B.; Downey, W.; Coetzee, S.; Vink, B.W.; Matheson, W.; Vanderpost, C. (Elsevier www.elsevier.com/locate/palaeo, NaN, 2005)[more][less]
Abstract: This work considers new evidence for palaeo environmental change taking place during the Pleistocene in northern Botswana. Duricrusted strandlines along the northeastern margin of Sua Pan provide palaeo-environmental data pertaining to the Makgadikgadi subbasin (MSB) with inferences regarding the larger Makgadikgadi–Okavango–Zambezi (MOZ) rift depression. Field, XRD and geochemical data show that MSB strandlines comprise calcretes (LU1 type), MgO-rich calcretes with silica (LU2 type), sil-calcrete (LU3 type) and silcrete (LU4 type). Early freshwater episodes appear to have been followed by calcrete-dominated drying phases interspersed with repeated silcretisation. Calcretisation through pan littoral sediments may have been both biogenically and environmentally induced. Calcite precipitation was in part controlled by the Mg/Ca ratio of pore water in the pan littoral zone suggesting closed basin type evaporative conditions, which were followed by a major desiccation interval. Phases of silcrete precipitation appear to be related to periods when the geochemistry of the lake littoral more closely resembled present-day Na–CO3–SO4–Cl-type brines. Silica saturated acidic, moderately saline groundwater preceded Si precipitation which took place as the pH reduced. Si mobilisation occurred (inter alia) as a result of quartz grain dissolution enhanced by diatoms, bacteria and algal growth in the moist pan littoral. SiO2-rich pore waters migrated through cracked and desiccated calcrete into areas of lower salinity and lower pH resulting in preferential calcite removal and silcrete precipitation. Approximate TL dates imply that exposed littoral sand underwent calcretisation during the drying phases of extensive palaeo-lakes which occurred prior to 110 ka, 80–90 ka and 41–43 ka. These wet periods compare fairly well with Vostok core chronologies for southern Africa. URI: http://hdl.handle.net/10311/794 Files in this item: 1
Kampunzu2006Sedimentological.pdf (3.498Mb) -
Nsinamwa, M.; Sebego, R.J. (Botswana College of Agriculture, http://www.bca.bw/Research/bojaasBca/InstructionToAuthors.htm, NaN, 2007)[more][less]
Abstract: Grasses and forbs in Southern Africa have been understudied in terms of species richness and factor that affect diversity patterns. To gain a better understanding of factors affecting patterns of herbaceous plant species seedbank around water points, six boreholes ( three in each land zone) were randomly selected for sampling. Top soil layers of 20cm depth were sampled from six boreholes at distances of 50, 100, 200, 400, 800, 1500, and 3000m ( the Piosphere approach) in fenced and unfenced plots to determine the density and composition of the seedbank. The samples were allowed to germinate in the growth tray (10 x 15 x 8cm³) under controlled conditions (temperature, moisture) in a green house followed by daily counting of seedlings. Herbaceous plant species diversity was analyzed by using Simpson's diversity index. Analysis of varience on herbaceous species diversity was determined using the SAS software. Herbaceous plant community clustering was determined by using TWINSPAN, a FORTRAN programme. Significant (p=0.0001) germination variants were observed along the distance from livestock watering points. Most grass seedlings recorded germinated from soil samples obtained from from fenced plots, while less than 40% of the forb seedlings were. Most of the forbs species were recorded within 400m from the water points and that soils closer to water points also contained grass seeds despite the level of degradation and /or trampling. URI: http://hdl.handle.net/10311/313 Files in this item: 1
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Laletsang, K.; Modisi, M.P.; Shemang, E.M.; Moffat, L.; Moagi, O.R. (Elsevier www.elsevier.com/locate/jafrearsci, NaN, 2007)[more][less]
Abstract: A seismic refraction analysis was carried out on data acquired on an 8.5 km profile at Lake Ngami, NW Botswana, to determine the structure and stratigraphy underlying the lake. The seismic spread comprised a 48-channel seismograph with a 9.5 m receiver and source spacing. The seismic source comprised 10 hammer blows on an aluminum plate, from which a vertical stack was recorded. The data were processed with WinSismTM version 10 program using the intercept time method. A total field magnetic survey was also carried out along the same line. The seismic refraction profile shows a low velocity layer (400–1600 m/s) extending from the surface at the southern end of the line to a maximum depth of 30 m in the middle of the profile, returning to a depth of 20 m from 4.5 km to the northern end of the line. The low velocity layer consists of the unconsolidated sediments and is underlain by more compact and saturated material with seismic velocities of 1600–3600 m/s. This material is interpreted to comprise semi- to fully consolidated sandstone. The base of these sandstones, however, could only be mapped near the southern end of the line out to 2 km. High seismic velocity rocks (3600–5000 m/s), interpreted to be weathered to fresh basement, were mapped below the sandstones at the southern end of the line. The magnetic profile shows a high at the beginning of the line which progressively declines to a low at 3 km. The field strength increases rapidly over the next 1.5 km to reach a plateau level at 4.5 km. The magnetic high at the beginning of the line corresponds to shallow basement which is mapped in the refraction profile. The magnetic low at 3 km is indicative of a thickened sediment section at this location. The southern end of the line with high seismic velocities comprises basement rocks located in the footwall block of the Kunyere Border Fault of the Okavango Rift. The step-wise downthrown hanging wall block consists of the low to intermediate velocity basin deposits in the northern part of the profile. URI: http://hdl.handle.net/10311/376 Files in this item: 1
Modisi2007ShallowSeismic.pdf (656.3Kb) -
Masale, M. (Elsevier Science Ltd. http://www.elsevier.com/locate/physb, NaN, 2004)[more][less]
Abstract: The energy spectrum of an electron confined near a current-carrying core is obtained as a function of the azimuthal applied magnetic field within the effective-mass approximation. The double degeneracy of the non-zero electron's axial wave number (kz) states is lifted by the current-induced magnetic field while that of the non-zero azimuthal quantum number (m) states is preserved. A further analysis is the evaluations of the oscillator strengths for optical transitions involving the lowest-order pair of the electron's energy subbands within the dipole approximation. The radiation field is taken as that of elliptically polarized light incident along the core axis. In this polarization and within the dipole approximation, the allowed transitions are only those governed by the following specific selection rules. The azimuthal quantum numbers of the initial and final states must differ by unity while the electron's axial wave number is conserved. The azimuthal magnetic field is also found to lift the multiple degeneracies of the kz=0 interaction integrals as well as those of the oscillator strengths for optical transitions. URI: http://hdl.handle.net/10311/244 Files in this item: 2
license.txt (1.998Kb)Masale_PB_2004.pdf (1.197Mb) -
Mbaiwa, J.E. (Channel view publications, http://www.multilingual-matters.net/jtc/default.htm, NaN, 2004)[more][less]
Abstract: The objective of this article is to assess the socio-cultural impacts of tourism development in the Okavango Delta, Botswana. This paper largely relied on the research work and reports by the author in the Okavango Delta from 1998 to 2004. In all instances, both primary and secondary data sources were used. However, much of the paper is based on the results of a survey carried out between April 2001 and July 2002. Findings indicate that tourism development in the Okavango Delta has both positive and negative socio-cultural impacts. Some of the positive socio-cultural impacts include income generation and employment opportunities from both community-based tourism projects and safari companies, infrastructure development such as airport and airstrips, tarred roads, hotels, lodges and camps, the improvement of social services such as banking, health, telecommunications and access to electricity. The negative socio-cultural impacts include enclave tourism, racism, relocation of traditional communities, breaking up of the traditional family structure, increase in crime, prostitution, the adoption of the Western safari style of dressing and a traditionally unacceptable ‘vulgar’ language by young people. This article argues that tourism needs to be sensitive to local cultural norms and beliefs for it to be accepted by local people and promote sustainable development. This is possible if all the stakeholders (government, operators and local people) collaborate in policy formulation, implementation and monitoring. This can minimise the negative cultural impacts and instead promote the positive. URI: http://hdl.handle.net/10311/311 Files in this item: 1
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Shaikh, M.; Moleele, N.; Ekosse, G.I.E.; Totolo, O.; Atlhopheng, J. (JASEM http://www.ajol.info/index.php/jasem/article/view/43693/27216, June NaN, 2006)[more][less]
Abstract: Since 1988 Botswana has been experiencing an unprecedented increase in vehicular traffic which is suspected to be having contamination effects on soils along heavily used roads in the country. This study aimed at understanding the contamination trends of heavy metals on soils due to vehicular emissions. The soil physicochemistry (bulk density, particle size distribution, pH, electrical conductivity and cation exchange capacity), mineralogy (using x-ray diffraction techniques) and heavy metals (Cd, Pb, Cu and Zn) concentrations were determined for soil samples obtained along the roadside at 2m, 4m, 6m and 100 m of the Gaborone – Tlokweng Emigration/Immigration Boarder Post Road, which is one of the busiest in the country. Bulk density of soil samples were from 1.19 to 1.4; and sand, loamy sand and sandy loam textural classes constituted the soil samples. The soil pH was from 5.09 to 8.57; the EC ranged from 6.27 μS cm-1to 20.3 27 μS cm-1 and the CEC values were from 10.2 meq100g-1 to 27.2 meq100g-1. Clay minerals were identified in the samples as well as feldspar and quartz. The concentration levels for Pb were from 0 mgkg-1 to 71 mgkg-1; Zn were from 5.23 mgkg-1 to 51.26 mgkg-1 ; Cu were from 0.3 mgkg-1 to 18.1 mgkg-1 and Cd 0 mgkg-1 to 2.4 mgkg-1 . The interplay of soil physico-chemistry and mineralogy on heavy metals concentrations is discussed. Although levels of heavy metals concentrations fell below normal ranges, the values obtained were generally higher than those from some developed and developing countries. URI: http://hdl.handle.net/10311/361 Files in this item: 1
Shaikh_JASEM_2006.pdf (1.018Mb) -
Bonyongo, M.C.; Mubyana, T. (South African Journal of Science, http://www.sajs.co.za/, NaN, 2004)[more][less]
Abstract: WETLANDS SUCH AS THE OKAVANGO Delta, located in semi-arid regions, are of great ecological, environmental and socio-economic importance. In most cases, however, few data exist on nutrient cycling in these areas. This paper presents preliminary results of an ongoing study, which investigates the influence of seasonal flooding on soil nutrient status in the different vegetation communities of the delta. Soil K, Na, and pH significantly increased with a decrease in soil moisture, with the values increasing from the primary floodplains to the islands communities. Available P, Ca and Mg decreased as the elevation gradient increased from the riverbed. Although nutrient status generally was highest in the floodplain vegetation areas adjacent to the riverbed, there was no significant difference in available P, Ca and Mg within the vegetation communities. Calcium levels in the different vegetation zones were more influenced by rainfall than floodplain vegetation community. Higher soil Ca was observed in the rainy season, while elevated Mg was recorded after the rains. Overall, these results indicate that flooding is an essential aspect of the Okavango Delta as it may be a primary source of some of the soil nutrients that support the high diversity of plants sustaining the delta’s ecosystem. URI: http://hdl.handle.net/10311/401 Files in this item: 1
Soil nutrient status.pdf (1.635Mb) -
Mosweu, S. (Academic Journals, http://www.academicjournals.org/SRE, NaN, 2008)[more][less]
Abstract: The distribution of selected soil properties, selected woody vegetation properties, and land use in a lunette dune-pan system were investigated in the Sekoma area, which is located within the IGBP Kalahari Transect (KT) in Botswana. KT was established by the IGBP for studies focusing on both regional and global environmental changes. The study showed that the lunette dune-pan system exhibited substantial spatial heterogeneity in the distribution of the selected soil attributes. This limited the extent to which variation in the investigated vegetation characteristics could be explained on the basis of soil resources distribution. Encroacher plant species were found to be prevalent in the sites that were subjected to higher land use pressure. The study concluded that land use, particularly browsing, was the principal environmental driver and had precedence over the distribution of the selected soil attributes in relation to woody plant properties in the lunette dune-pan system. URI: http://hdl.handle.net/10311/964 Files in this item: 1
Mosweu_SRE_2008.pdf (783.3Kb) -
Wright, C.; Kgaswane, E.M.; Kwadiba, M.T.O.; Simon, R.E.; Nguuri, T.K.; McRae-Samuel, R. (Elsevier Science Ltd. www.elsevier.com/locate/lithos, NaN, 2003)[more][less]
Abstract: Events induced by deep gold-mining activity on the edge of the Witwatersrand basin dominate the seismicity of South Africa. The deployment of 54 broad-band seismic stations at 84 separate locations across southern Africa between April 1997 and April 1999 (Kaapvaal network) enabled the seismicity of South Africa to be better defined over a 2-year period. Seismic events located by the South African national network, and by localized seismic networks deployed in mines or across goldmining areas, were used to evaluate earthquake location procedures and to show that the Kaapvaal network locates mininginduced tremors with an average error of 1.56 ± 0.10 km compared with 9.50 ± 0.36 km for the South African network. Travel times of seismic events from the mines recorded at the Kaapvaal network indicate regional variations in the thickness of the crust but no clearly resolved variations in seismic wavespeeds in the uppermost mantle. Greater average crustal thicknesses (48–50 km compared with 41–43 km) are observed in the northern parts of the Kaapvaal craton that were affected by the Bushveld magmatism at 2.05 Ga. Estimates of average crustal thickness for the southern part of the Kaapvaal craton from receiver functions (38 km) agree well with those from refracted arrivals from mining-induced earthquakes if the crustal thicknesses below the sources are assumed to be 40–43 km. In contrast, the average crustal thickness inferred from refracted arrivals for the northern part of the Kaapvaal craton is larger by about 7 km (51 km) than that inferred from receiver functions (44 km), suggesting a thick mafic lower crust of variable seismic properties due to variations in composition and metamorphic grade. Pn wavespeeds are high (8.3–8.4 km/s), indicating the presence of highly depleted magnesium-rich peridotite throughout the uppermost mantle of the craton. Seismic Pg and Sg phases indicate that the upper crust around the Witwatersrand basin is comparatively uniform in composition when averaged over several kilometres. URI: http://hdl.handle.net/10311/280 Files in this item: 1
Wright_L71_2003.pdf (3.483Mb)