Browsing Okavango Research Institute (ORI) by Title
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Bartsch, A.; Wagner, W.; Scipal, K.; Sabel, D.; Wolski, P. (Elsevier, March 17, 2008)[more][less]
Abstract: This paper elaborates on recent advances in the use of ScanSAR technologies for wetland-related research. Applications of active satellite radar systems include the monitoring of inundation dynamics as well as time series analyses of surface soil wetness. For management purposes many wetlands, especially those in dry regions, need to be monitored for short and long-term changes. Another application of these technologies is monitoring the impact of climate change in permafrost transition zones where peatlands form one of the major land cover types. Therefore, examples from boreal and subtropical environments are presented using the analysed ENVISAT ASAR Global mode (GM, 1 km resolution) data acquired in 2005 and 2006. In the case of the ENVISAT ASAR instrument, data availability of the rather coarse Global Mode depends on request priorities of other competing modes, but acquisition frequency may still be on average fortnightly to monthly depending on latitude. Peatland types covering varying permafrost regimes of the West Siberian Lowlands can be distinguished from each other and other land cover by multitemporal analyses. Up to 75% of oligotrophic bogs can be identified in the seasonal permafrost zone in both years. The high seasonal and interannual dynamics of the subtropic Okavango Delta can also be captured by GM time series. Response to increased precipitation in 2006 differsfrom flood propagation patterns. In addition, relative soil moisture maps may provide a valuable data source in order to account for external hydrological factors of such complex wetland ecosystems. URI: http://hdl.handle.net/10311/767 Files in this item: 1
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Bonyongo, M.C.; Harris, S. (Willey Blackwell Publishing http://eu.wiley.com/WileyCDA/Brand/id-35.html, NaN, 2007)[more][less]
Abstract: We used body weight ratio to determine the degree of species-packing of the Okavango Delta (22,000 km2) grazers and compared it to that of four conservation areas of similar sizes but varying in the diversity of habitat types. They are Etosha National Park (23,175 km2) in Namibia, Hwange National Park (14,621 km2) in Zimbabwe, Kafue National Park (24,000 km2) in Zambia and Kruger National Park (19,633 km2) in South Africa. We considered possible ecological explanations for existing gaps within the assemblage. The weight ratio (measure of the degree of species-packing) of the grazers of the Okavango Delta was 1.25, with a total of 27 species which was far less than the theoretically expected 2.0. One-way analysis of covariance (ANCOVA) showed that there were significant differences in the degree of species-packing between the Okavango Delta and other conservation areas of similar size in southern Africa (F1,5 ¼ 166, P < 0.001). Regressing habitat heterogeneity (expressed as number of different habitat types) on species-packing of the five conservation areas yielded a positive linear relationship with R2 ¼ 0.76 implying that 76% of the variation in the degree of speciespacking in the five conservation areas is explained by variation in habitat heterogeneity. We conclude that size ratios are useful descriptors of animal communities and it is a useful measure of species diversity, which can be used for monitoring purposes. Imbalances in weight ratios provide a measure of identifying perturbations due to species loss or arrival of new species within a natural ecosystem. URI: http://hdl.handle.net/10311/608 Files in this item: 1
Bonyongo_AJE_2007.pdf (1.153Mb) -
Sajidu, S.M.I.; Masamba, W.R.L.; Thole, B.; Mwatseteza, J.F. (Academic Journals, http://www.academicjournals.org/ijps, NaN, 2008)[more][less]
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VanderPost, C.; McFarlane, M. (Elsevier www.elsevier.com/locate/jag, NaN, 2007)[more][less]
Abstract: Locating additional long-term groundwater resources in semi-arid regions of developing countries with growing populations is an expensive undertaking. Simple geographic information system (GIS) techniques can be utilised to facilitate efficient application of expensive geophysical techniques and test-drilling by functioning as an interdisciplinary integration and decision-making tool, especially in data-poor and poorly mapped environments where more sophisticated GIS techniques are not applicable. The paper demonstrates this in the context of the search for groundwater alternatives to the dwindling river water supply in the Boteti area of the Kalahari region in Botswana. URI: http://hdl.handle.net/10311/573 Files in this item: 1
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Bonyongo, C.M. (Botswana Society, NaN, 2005)[more][less]
Abstract: This paper presents preliminary results from a long-term study on the ecology of large herbivores in the Okavango Delta. The paper evaluates habitat selection and utilization by impala (Aepyceros melampus) at the various habitat scales. Impala, the most abundant and widely distributed mammal species in the Delta, showed seasonality in habitat use and habitat selection. In all seasons impala used mixed open woodlands more than any other habitat type. Open grasslands and upper floodplains are also key habitats for impala. As a mixed feeder, impala are able to use a wide range of habitats. URI: http://hdl.handle.net/10311/931 Files in this item: 1
Bonyongo 2005 Habitat.pdf (1.198Mb) -
Ngwenya, B.N.; Kgathi, D.L. (Elsevier Ltd; www.elsevier.com/locate/pce, NaN, 2006)[more][less]
Abstract: This case study investigates access to potable water in HIV/AIDS related home-based care households in five rural communities in Ngamiland, Botswana. Primary data collected from five villages, consisted of two parts. The first survey collected household data on demographic and rural livelihood features and impacts of HIV/AIDS. A total of 129 households were selected using a two-stage stratified random sampling method. In the second survey, a total of 39 family primary and community care givers of continuously ill, bed-ridden or non-bed-ridden HIV/AIDS patients were interviewed. A detailed questionnaire, with closed and open-ended questions, was used to collect household data. In addition to using the questionnaire, data was also collected through participant observation, informal interviews and secondary sources. The study revealed that there are several sources of water for communities in Ngamiland such as off-plot, outdoor (communal) and on-plot outdoor and/or indoor (private) water connections, as well as other sources such as bowsed water, well-points, boreholes and open perennial/ephemeral water from river channels and pans. There was a serious problem unreliable water supply caused by, among other things, the breakdown of diesel-powered water pumps, high frequency of HIV/AIDS related absenteeism, and the failure of timely delivery of diesel fuel. Some villages experienced chronic supply disruptions while others experienced seasonal or occasional water shortages. Strategies for coping with unreliability of water supply included economizing on water, reserve storage, buying water, and collection from river/dug wells or other alternative sources such as rain harvesting tanks in government institutions. The unreliability of water supply resulted in an increase in the use of water of poor quality and other practices of poor hygiene as well as a high opportunity cost of water collection. In such instances, bathing of patients was cut from twice daily to once or not at all. Depending on the severity of HIV/AIDS related symptoms, e.g. diarrhoea, 20-80 additional litres of water could be required daily. The case study demonstrates that, at individual level, access to water is an integral element of the patient's holistic healing process and psychosocial well being. At household and community levels, access to sufficient supplies of potable water when and where it is needed is central to mitigation of HIV/AIDS impacts. Access to water should therefore not be treated strictly as an economic good due to its importance as a basic human need, a social good and indeed a human right. URI: http://hdl.handle.net/10311/172 Files in this item: 2
license.txt (1.998Kb)ngwenya_kgathi_PCE_06.pdf (4.416Mb) -
Ngwenya, B.N.; Mosepele, K. (Elsevier www.elsevier.com/locate/pce, NaN, 2007)[more][less]
Abstract: Generally, rural households pursue all year round natural and non-natural resource-based livelihood systems to diversify these options in order to cope with risks emanating from a range of shocks and stressors. Artisanal fishing in the Delta is not only a major livelihood option but also a source of food security. This paper is based on analysis of primary data collected from a survey of 248 subsistence fishers’ households through simple random sampling in 22 villages in the Delta. The overall objectives of the survey were to assess the general prevalence of HIV/AIDS in the Ngamiland district of Botswana, to investigate potential effects of AIDS-related stressors, particularly chronic illness on artisanal fishing activities, and to assess implications towards food security. Results from this study indicate that HIV prevalence rates for pregnant women attending antenatal clinics in the Delta are approximately 30% and are related to factors such as marriage, education, and employment. Despite this relatively high prevalence percentage, most of the affected households do not have adequate access to HIV/AIDS support facilities. Support services are provided on the basis of population size and/or status of the settlement (i.e. urban, urban village, rural or remote). Therefore, since about 50% of the Delta’s population lives in settlements of less than 500 people, they receive health services indirectly through major population centres whose capacity to deliver timely HIV/AIDS services is limited. This disproportionate access to HIV/AIDS services disadvantages the majority of fishing communities in the Delta, and may affect their ability to fish. Moreover, about 53% of sampled households had cared for a continuously ill person/s (CIP’s) in the last 5 years, out of which approximately 29% felt that this seriously impacted fishing activities. These serious impacts included sale of family assets, depletion of savings, and switching or abandoning fishing activities. Subsequently, household food security is seriously affected because fish provides a significant proportion of food to CIP households where approximately 55% of households get their food from fish products. During food shortages, CIP households resorted to a hierarchy of strategies which included cutting down on meals or reducing meal portions, looking for paid work, gathering wild fruit, asking for food from relatives, selling livestock, and getting social assistance. In conclusion, artisanal fishing is a natural safety net which constitutes an important buffer for households affected by HIV/ AIDS-related stressors in the Okavango Delta. Access to fish helps these households mitigate potentially adverse impacts such as deterioration into chronic poverty. URI: http://hdl.handle.net/10311/572 Files in this item: 1
NGWENYA2007Okavango.pdf (1.602Mb) -
Phorano, O.M.; Nthomang, K.; Ngwenya, B.N. (Botswana Society, NaN, 2005)[more][less]
Abstract: Batswana have been hard-hit by the HIV/AIDS pandemic. The Botswana government has initiated the Community Home-Based Care programme to provide material support for HIV/AIDS patients cared for at home by family members and relatives. This paper identifies and explores emerging home care issues and pays specific attention to potential risks related to poorly managed clinical human and solid waste disposal generated through home-based care of HIV/AIDS patients in Ngamiland and Kweneng Districts in Botswana. Data were collected through focus group discussion with care-givers, discursive interviews with professional service providers, and participant observation. The results of the study indicate that the majority of care givers received material benefits provided through the CHBC programme. However, it was clear that CHBC did not have the capacity to address other critical needs for the proper care of patients in the home. Most households studied are very poor and lack basic facilities such as toilets, basic waste receptacles and regular collection of solid waste. Access to these facilities is important for disposing of both clinical and ordinary human and solid waste from HBC patients. Poor sanitation facilities - especially the improper handling of soiled laundry and inadequate ventilation - increase risks of infection. The study recommends the formation of care-giver support groups to reduce risks associated with poorly managed clinical solid waste disposal generated from home care-giving of HIV/AIDS patients. URI: http://hdl.handle.net/10311/952 Files in this item: 1
Phorano 2005 HIV.pdf (2.631Mb) -
Ngwenya, B.N.; Butale, B.M. (Botswana Society, NaN, 2005)[more][less]
Abstract: Home care involves the transfer of a patient’s medical supervision from a formal institution to a family setting in the context of a community. The aim of this paper is to assess the resource capacity of families to provide immediate home care to HIV/AIDS related chronically or terminally ill member/s in Maun in Ngamiland District. Data for the study was obtained through cross-sectional interviews with 61 care-givers. Ethnographic methods were also used: these included informal interviews with key informants, unobtrusive participant observation, and narratives of individual and family life experiences. Data collection focused on assessing family resource capacity to access three forms of capital, namely social, productive and produced. Issue focus analysis on qualitative data, and descriptive frequencies and cross-tabulations on quantitative data were carried out. Generally, care-givers reported receiving non-material support from multiple sources. These included moral support from close family members, especially their own children, siblings, parents and spouses, and less from parents’ in-law and their extended family. The threshold of care-giving resource demands could either fragment the family unit, on precipitate ‘enclave-like’ or ‘disengaged’ co-existence or passive aggression. On the other hand, caregiving resource demands may enhance mutual obligation and shared responsibility among family members. A high level of tolerability tends to reduce vulnerability and facilitate pooling limited resources in ways that enhance family capacity. Conversely, adversarial intra-family relations compromise the ability of a family to mobilize its resources. About 70% of care-givers were dependent on non-farming activities as their source of livelihood. Care-giving depletes family resources, including the abandonment of income generating activities. About 81% of care-givers said that they could not do anything to recover or reverse the loss. Access to produced capital such as telecommunication infrastructure is important in terms of the dissemination of public education information aimed at helping reduce risks and the prevention of infection. A significant proportion of care-givers had access to a radio (60%) and cell-phone (48%). The paper ends with some policy recommendations. URI: http://hdl.handle.net/10311/953 Files in this item: 1
Ngwenya 2005 AIDS.pdf (3.334Mb) -
Mmopelwa, G.; Kgathi, D.L.; Masamba, W.R.L.; Thukuza, A. (Botswana Society, NaN, 2005)[more][less]
Abstract: Water supply in Maun is unreliable and unpredictable, and most households experience water shortage all year round. Coping strategies for households include water storage in tanks. Water quality is also poor due to its salty taste, presence of sediments and colour. The majority of households have henceforth embarked on coping strategies such as buying bottled water. On average, households spend about P71 per month as avoidance cost. A contingent valuation method assessment was carried out and it was found that the mean maximum household’s willingness to pay for a water quality improvement fund was P55 per month. Chemical analysis carried out on water samples from the study area confirm that the water has high electrical conductivity, sediments, colour, and iron and manganese levels. URI: http://hdl.handle.net/10311/938 Files in this item: 1
Mmopelwa 2005 House.pdf (1.540Mb) -
Kurugundla, C.N.; Bonyongo, M.C.; Serumola, O. (Taylor & Francis, December 22, 2010)[more][less]
Abstract: The risk and effect of the insecticide deltamethrin, applied aerially in Botswana to control and eradicate tsetse fly, was studied on the non-target weevil Cyrtobagous salviniae, a biocontrol agent of the aquatic weed Salvinia molesta. Environmentally-simulated short-term toxicity bioassay used open iron cages and closed plastic basins containing weevils and salvinia placed in riverine water bodies, where they were exposed to the aerial applications of deltamethrin over the Kwando–Linyanti system in 2006. Control samples were placed 40 km outside the sprayed area. Weevil mortality, determined at 12, 36 and 60 hours after the aerial application, reached a maximum of 27%. No significant difference in mortalities was observed between the closed basins and the open cages. The amount of deltamethrin deposited at ground level was between 1.2 and 6.4 μg m–2 and the insecticide toxicity was related to the weevil mortality. Simultaneous field monitoring through five spray applications showed that weevil abundance declined in late winter. Deltamethrin had a negligible impact on the weevil’s ability to control salvinia under field conditions, probably due to the weevils’ protective mechanism and because vegetation could act as a barrier, preventing the insecticide from reaching the weevils. Minimum impacts of deltamethrin on the weevils in the present study and their recovery in the field are consistent with those of earlier spray applications in the Okavango Delta, Botswana. URI: http://hdl.handle.net/10311/808 Files in this item: 1
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Magole, L.; Thapelo, K. (Botswana Society, NaN, 2005)[more][less]
Abstract: This paper presents the results of a study carried out on the impact of the recent (2004) severe flooding of the Okavango River on the livelihood of the molapo (flood recession) farming community of Tubu village in Ngamiland sub-district. Government and NGO disaster relief organisations responded to the floods in panic and desperation while affected communities appeared calm and laid-back. To the extent that they (communities) refused to evacuate flood plains and island settlements to make way for the considerably high and potentially dangerous flood of 2004; the communities' reaction was surprising as the floods were so severe upstream, that they caused damage to property, threatened lives and reduced yields significantly. However, studying the farming community of Tubu revealed that community members have other considerations which make them perceive the inherent risk differently from outsiders. Communities view flooding (whether severe or normal) more as part of the biodiversity production system and a source of livelihood than a destructive force. It was found regarding molapo farming that, first, even under hazardous flooding conditions crop yields are still better compared to those under alternative dryland farming. Secondly, destructive floods occur at 10- to 20-year intervals, making the gamble worthwhile because over time the flood-related benefits outweigh the risks. Thirdly, because the molapo farming communities are poor, other sources of livelihood are not adequately developed to take over from molapo farming. Fourth, the system has evolved into an old tradition which the farmers are not willing to part with. Hence the farmers are adamant that abandoning the production system is not, as yet, an option for them. URI: http://hdl.handle.net/10311/949 Files in this item: 1
Magole 2005 Impact of.pdf (1.900Mb) -
Impact on water quality of land uses along Thamalakane-Boteti River: an outlet of the Okavango DeltaMasamba, W.R.L.; Mazvimavi, D. (Elsevier, July 8, 2008)[more][less]
Abstract: Botswana is a semiarid country and yet has one of the world’s famous wetlands: the Okavango Delta. The Thamalakane- Boteti River is one of the Delta’s outlets. The water quality of the Thamalakane-Boteti River was determined and related to its utilisation. The major land uses along the Thamalakane River within Maun are residential areas, lodges, hotels, and grazing by cattle and donkeys. The water is used as a source of water for livestock, wildlife in a game park, horticulture and domestic applications including drinking. The river is also used for fishing. To check whether these activities negatively impact on the water quality, pH, electrical conductivity, dissolved oxygen, temperature, total dissolved nitrogen and phosphorus, Faecal coliforms and Faecal streptococci and selected metals were determined from July 2005 to January 2006. The pH was near neutral except for the southern most sampling sites where values of up to 10.3 were determined. Dissolved oxygen varied from 2 mg/l to 8 mg/l. Sodium (range 0.6–3.2 mg/l), K (0.3–3.6 mg/l), Fe (1.6–6.9 mg/l) conductivity (56–430 lS/cm) and Mg (0.2–6.7 mg/l) increased with increased distance from the Delta, whereas lead showed a slight decline. Total dissolved phosphorus was low (up to 0.02 mg/l) whereas total dissolved nitrogen was in the range 0.08–1.5 mg/l. Faecal coliform (range 0–48 CFU/100 ml) and Faecal streptococci (40–260 CFU/100 ml) were low for open waters with multiple uses. The results indicate that there is possibility of pollution with organic matter and nitrogen. It is recommended that more monitoring of water quality needs to be done and the sources of pollution identified. URI: http://hdl.handle.net/10311/740 Files in this item: 1
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Aranibar, J.N.; Anderson, I.C.; Ringrose, S.; Macko, S.A. (Elsvier, www.elsevier.com, NaN, 2003)[more][less]
Abstract: Cyanobacterial soil crusts may be important in arid and semi-arid ecosystems because of their ability to fix atmospheric nitrogen (N2). These crusts are very sensitive to trampling by animals, and their destruction can decrease ecosystem N inputs, affecting the productivity of the region. The objective of this study was to quantify the nitrogen-fixing activity in soil crusts during the wet season in southern African ecosystems using in situ acetylene reduction assays. The average acetylene reduction rates for each site ranged from 88 to 535 nmol m-2 h-1, were highly variable, and were lower than previously reported for other arid areas. All soil samples showed acetylene reduction activity; however, soils with crusts supported higher rates than did "non-crusty" soils under litter, moss, or sand. High values of 15N natural abundance (delta15N) indicated that processes other than N fixation were more important in the crusts than N fixation. For example, coupled and ammonia volatilization or atmospheric deposition of 15N-enriched nitrate or ammonium may have caused shifts in delta15N within the soil crusts. The estimated annual N fixation rates ranged from 8 to 44 g N ha-1 year-1, orders of magnitude lower than values estimated in other studies. The anomalous wet conditions experienced during the year of the study may have increased the temporal availability of soil mineral N and decreased N fixation rates. However, the presence of N fixation activity in all crusts analysed and their ability to survive at high temperature and after long dry periods may provide ecosystem resilience, facilitating ecosystem recovery after severe droughts. URI: http://hdl.handle.net/10311/983 Files in this item: 1
Ringrose_Importance_of_Nitrogen_2003.pdf (2.069Mb) -
Kiker, G.; Munoz-Carpena, R.; Wolski, P.; Cathey, A.; Gaughan, A.; Kim, J. (Inderscience, http://www.inderscience.com, NaN, 2008)[more][less]
Abstract: In this paper, we present a review and conceptual design to integrate hydrological/ecological models, global uncertainty and sensitivity analysis, integrative modelling and decision analysis for complex and adaptive transboundary challenges. The research uses the transboundary issues within the Okavango River basin, a shared water resource among the nations of Angola, Namibia and Botswana, as an example for constructing these integrated tools. The objective of this paper is to present a design that integrates a set of tools that builds systematically on past basin modelling research to incorporate the inherent uncertainty within the system and its application for answering practical management questions. URI: http://hdl.handle.net/10311/864 Files in this item: 1
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Ringrose, S.; Vanderpost, C.; Matheson, W.; Wolski, P.; Huntsman-Mapila, P.; Murray-Hudson, M.; Jellema, A. (Elsevier Ltd; www.elsevier.com/locate/jaridenv, January NaN, 2007)[more][less]
Abstract: This work seeks to determine whether riparian woody plant variables respond to drying and salinity regimes in the semi-arid distal Okavango Delta, northern Botswana. Structural and compositional variables were obtained from 47 field sites. Mapping using satellite imagery illustrated differences in the character of riparian zones in terms of species composition and provided data on flood frequency. Salinity data plots show increases downstream. Results imply that woody plant variables respond to desiccation-driven change due to water-table lowering (reduced recharge) and increased salinization through distinct changes in tree and shrub height, plant density and species richness. In the wetter, intermediate distributaries, key biotic indicators of ecosystem change comprise structural variables such as decreases in canopy cover per cent and tree height and increases of shrub height, which are indicative of mainly ground-water declines. Biotic indicators in the less frequently flooded receiver channels comprise plant density and species richness increases involving mainly brackish ground-water-tolerant and dryland species which are indicative of both ground-water declines and/or salinization. These indicators could provide useful parameters for use in long- and short-term monitoring aimed at assessing desiccation-driven change in different parts of the Okavango Delta and possibly other semi-arid wetlands. The indicators are important as a less-expensive alternative to drilling as a means of verifying ground-water declines and/or salinization. URI: http://hdl.handle.net/10311/161 Files in this item: 2
license.txt (1.998Kb)Ringrose_et_al_JAE_07.pdf (1.322Mb) -
Mubyana, T.; Krah, M.; Totolo, O.; Bonyongo, M. (Journal of Arid Environments. http://www.elsevier.com/wps/find/journaldescription.cws_home/622855/description#description, NaN, 2003)[more][less]
Abstract: The effect of flooding on soil total nitrogen, phosphorus and microbial population in different vegetation zones (floodplain, island and woodland) and profile depth (0?1, 0?5, 2?0, 3?0, 4?0 and 5?0m) of the Okavango Delta was studied from February to July 1999. Total nitrogen significantly differed with soil profile depth, moisture regime and months. In the woodlands, insignificant total nitrogen was detected at all depths except at 0?1m, where 0?03% and 1?17% were detected in February and March, respectively. In the island samples, only 0?05% was detected at 4m in February. Nitrogen in the floodplain samples was concentrated in the A1 horizon where 0?12%, 0?61% and 0?03% were detected in February, March, and May, respectively. Organic phosphorus significantly differed with vegetation zone but not with months and depth. Although organic phosphorus was low (0?02–0?52%) at all sites, it was liberally distributed throughout the profiles. On the island, actinomycetes were only detected up to 2m in February and up to 3m in July. Fungi concentrated in the top 0?5m (103–105). In both the floodplain and island samples, bacteria concentrated in the upper 3m. However, after May, populations decreased significantly. In the floodplain, significant actinomycetes populations were only detected in the upper 0?5m. Generally, organic phosphorus showed positive correlations with fungal populations. This study indicates that these soils are low in total nitrogen and phosphorus. URI: http://hdl.handle.net/10311/293 Files in this item: 1
Influence of seasonal flooding.pdf (3.953Mb) -
Heinl, M.; Neuenschwander, A.; Sliva, J.; Vanderpost, C. (Springer: http://www.springerlink.com, NaN, 2006)[more][less]
Abstract: A series of 98 satellite images was analysed to reconstruct the fire and flood history of a floodplain system in southern Africa(Okavango Delta, Botswana). The data was used to investigate interactions between fire and flooding, and to determine the relevance of rainfall and flood-events for fire occurrences on floodplains and on drylands. The aims of the study are (1) to analyse and compare the fire frequency on floodplains and on adjacent drylands, (2) to investigate the influence of rainfall and flooding on the fire occurrence and (3) to determine correlations between fire frequency and flood frequency. The analyses show higher fire frequencies on floodplains than on drylands because of higher biomass production and fuel loads. The fire occurrence on drylands shows a correlation with annual rainfall events, while the fire frequency on floodplains is in principle determined by the flood frequency. Between floodplain types, clear differences in the susceptibility to fire where shown by analysing flood frequency vs. fire frequency. Here, the highest potential to burn was found for floodplains that get flooded about every second year. By calculating mean fire return intervals, the potential to burn could be specified for the different floodplain types. URI: http://hdl.handle.net/10311/792 Files in this item: 1
Heinl_Michael_LE_2006.pdf (1.827Mb) -
Wolski, P.; Murry-Hudson, M.; Fernkvist, P.; Liden, A.; Huntsman-Mapila, P.; Ramberg, L. (Botswana Society, NaN, 2005)[more][less]
Abstract: Groundwater under islands in the Okavango Delta is a known sink of inorganic dissolved minerals, preventing salinisation of this virtually enclosed evaporation-dominated hydrological system. The Okavango Delta is an oligotrophic, yet very productive system, and it is important to understand sources, pathways and recycling of nutrients in order to fully comprehend its ecology. In order to investigate the role of islands as nutrient sinks, concentrations of nitrogen and phosphorus, as well as major inorganic ions were measured in island and floodplain groundwater. The electrical conductivity was found to be up to 50 times higher in the island centre groundwater than in the surrounding floodplain groundwater. The amount of total phosphorus was found to be up to 400 times higher and total nitrogen up to five times higher in the interior of the island than in the surrounding floodplain. These show that major nutrients are, like other inorganic ions, accumulated under islands. Importantly, the ratio of nitrogen to phosphorus was 5:1 in floodplain water and water in island fringe soils, but 1:4 in island centres. his indicates an intensive removal of nitrogen along the floodplain-island groundwater flow path by the floodplain fringe and riparian biota, resulting in a relative enrichment in P. URI: http://hdl.handle.net/10311/950 Files in this item: 1
Wolski 2005 Islands.pdf (1.469Mb) -
Chimbari, M.J.; Shiff, C.J. (Taylor & Francis, May 5, 2008)[more][less]
Abstract: Preliminary laboratory studies were conducted to determine the molluscicidal potency of Jatropha curcas, the physic nut. Biomphalaria glabrata and Bulinus globosus snails were exposed to varying concentrations of aqueous extracts of crushed J. curcas seeds from unripe, ripe and overripe fruits collected from two geographically different sites, (Bindura and Kariba, Zimbabwe). Snail mortalities were compared between different developmental stages of J. curcas and between seed collection areas, and LC50 and LC90 values for the different extracts tested were computed. Biomphalaria glabrata was most susceptible to unripe fruit seed extract (with LC50 values of 282 and 389 mg l-1 being recorded for Kariba-origin and Bindura-origin plants, respectively) and least susceptible to ripe fruit seed extracts (with LC50 values of 605 and 708 mg l-1 being recorded for Kariba-origin and Bindura-origin plants, respectively). Bulinus globosus was most susceptible to overripe fruit seed extract (Kariba-origin plants: LC50, 389 mg l-1) and least susceptible to unripe fruit seed extract (Kariba-origin plants: LC50, 687 mg l-1). The area from which fruits were collected did not influence the potency of J. curcas. The potency of J. curcas depends on both the developmental stage of the fruit and the species of the target snail. In view of its many other uses, besides as a molluscicide, we recommend further studies on J. curcas. URI: http://hdl.handle.net/10311/809 Files in this item: 1