Browsing Okavango Research Institute (ORI) by Subject "Okavango Delta"
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Ramberg, L.; Lindholm, M.; Hessen, D.O.; Murray-Hudson, M.; Bonyongo, C.; Heinl, M.; Masamba, W.; Vanderpost, C.; Wolski, P. (Springer, http://www.springer.com, July 19, 2010)[more][less]
Abstract: The frequency of fires in the Okavango Delta seasonal floodplains peaked at an intermediate frequency of flooding. Floodplains are commonly burnt every 3–5 years. This study showed fundamental changes in ecosystem properties due to burning. A burnt seasonal floodplain in the aquatic phase had oxygen levels well above saturation, 100–200%, while the levels in the un-burnt control site were below saturation and, at night, could decline to 10–40% saturation. The total phosphorous and total nitrogen concentrations were similar on both floodplains but considerably enriched relative to inflowing water, due to nutrient release from the flooded soil-sediment and animal droppings. Zooplankton biomass was very high in both systems although the abundance of fish fry was ten times higher on the un-burnt floodplain. In a low flood year the un-burnt floodplain water had high nutrient levels, primary production, methane emission, and subsequent uptake of methane in biota, as well as a high zooplankton biomass. The very high flood the following year showed the opposite with much lower production at all levels owing primarily to greater dilution of nutrients. The abundance of fish, however, was much higher during the high flood year. Macrophytes and litter provide direct shelter for fish fry but also promote low oxygen levels when decaying. Large flooded areas result in high fish production by removing obstacles related to congestion. This interplay between hydroperiod and fire may be crucial for the maintenance of high biological productivity both in the aquatic and terrestrial phases in a very nutrient poor wetland landscape. Understanding these interactions is crucial for optimal management. URI: http://hdl.handle.net/10311/838 Files in this item: 1
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Mantlana, K.; Veenendaal, E.; Arneth, A.; Grispen, V.; Bonyongo, C.; Heitkonig, I.; Lloyd, J. (Blackwell, www.blackwell.co.uk, August NaN, 2009)[more][less]
Abstract: C4 savanna grass species, Digitaria eriantha, Eragrostis lehmanniana and Panicum repens, were grown under optimum growth conditions with the aim of characterizing their above- and below-ground biomass allocation and the response of their gas exchange to changes in light intensity, CO2 concentration and leaf-to-air vapour pressure deficit gradient (Dl). Digitaria eriantha showed the largest above- and below-ground biomass, high efficiency in carbon gain under light-limiting conditions, high water use efficiency (WUE) and strong stomatal sensitivity to Dl (P = 0.002; r2 = 0.5). Panicum repens had a high aboveground biomass and attained high light saturated photosynthetic rates (Asat, 47 μmol m−2 s−1), stomatal conductance, (gsat, 0.25 mol m−2 s−1) at relatively high WUE. Eragrostis lehmanniana had almost half the biomass of other species, and had similar Asat and gsat but were attained at lower WUE than the other species. This species also showed the weakest stomatal response to Dl (P = 0.19, r2 = 0. 1). The potential ecological significance of the contrasting patterns of biomass allocation and variations in gas exchange parameters among the species are discussed. Description: Some mathematical formulas in the title and abstract may not appear as they are in the original article URI: http://hdl.handle.net/10311/872 Files in this item: 1
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Mbaiwa, J.E. (Elsevier, September 5, 2010)[more][less]
Abstract: The Community-Based Natural Resource Management (CBNRM) program in Botswana aims at achieving conservation and rural development. In the Okavango Delta, some communities are involved in tourism through CBNRM to improve their livelihoods. However, research has not adequately analyzed changes caused by CBNRM on traditional livelihood activities and lifestyles. This study, therefore, uses modernization theory to analyze changes on traditional livelihood activities and lifestyles caused by CBNRM at Sankoyo, Mababe and Khwai villages in the Okavango Delta. Using primary and secondary data sources, results indicate that CBNRM is causing a decline in traditional livelihood activities like subsistence hunting, gathering, crop and livestock farming. As a result, a modern cash economy has emerged. New livelihood activities done by communities include: employment in CBNRM projects, the sale of crafts to tourists and thatching grass to tourism lodges. Income derived from CBNRM affords households to build modern houses, buy foreign foods and household equipment like: four-burner gas stoves, kitchen utensils, and satellite televisions. Conversely, this causes a decline in the consumption of traditional foods and the use of huts and household utensils. CBNRM is thus a modernization tool since it is causing a transformation of traditional livelihood activities and lifestyles. However, even though changes in livelihood activities and lifestyles may be an indication of the dynamism of culture in study villages, sudden change and modernization may increase livelihood insecurity. As such, tourism planning should ensure that modernization is sensitive to traditional economic systems and the need for rural livelihood sustainability. URI: http://hdl.handle.net/10311/805 Files in this item: 1
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Characterization of arsenic occurrence in the water and sediments of the Okavango Delta, NW BotswanaHuntsman-Mapila, P.; Mapila, T.; Letshwenyo, M.; Wolski, P.; Hemond, C. (Elsevier Science B.V. Amsterdam; http://www.elsevier.com/wps/find/journaldescription.cws_home/768/description#description, NaN, 2006)[more][less]
Abstract: Detailed chemical analyses were performed on surface water, groundwater and sediment samples collected from the Okavango Delta between February and November 2003 in order to examine the distribution and geochemistry of naturally occurring As in the area. Surface water in the Okavango Delta, which is neutral to slightly acidic and has high dissolved organic C (DOC), was found to be slightly enriched in As when compared to a global value for stream water. Of the 20 new borehole analyses from this project, six were found to have values exceeding 10 ug/L. the current World Health Organization provisional guideline value for As. The results from field speciation indicate that As(III) is slightly more predominant than As(V). There is a positive correlation between As and pH and between As and DOC in the groundwater samples. For the sediment samples, there is a positive correlation between As and Co. As and Fe. As and loss on ignition (LOI) and between As and the percent fines in the sample. Reductive dissolution of oxides and hydroxides in the sediments with organic C as an electron acceptor is the likely mechanism for the release of As from the sediments into the groundwater. URI: http://hdl.handle.net/10311/135 Files in this item: 2
huntsman-mapila_app_geochem.pdf (3.170Mb)license.txt (1.998Kb) -
Mmopelwa, G.; Ngwenya, B.N. (Academic Journals, December 4, 2010)[more][less]
Abstract: The Okavango Delta is the largest multi-species and multi-gear fishery in Botswana. However, there is lack of an understanding of the nature of fish market in the Delta. The objectives of the survey were (1) to identify and describe the socio economic profile of the fishers in the fishing market, (2) to describe the operations of the market and (3) to identify market constraints of fishing. A structured questionnaire was used to collect data from fishers in four study sites in the Delta. The study revealed that fishing market in the Okavango Delta is very ‘informal’ in nature, with almost no intermediaries, and catering only for the local population. Lack of preservation facilities, transport, low levels of skills and lack of access to credit are the various constraints facing fishers. URI: http://hdl.handle.net/10311/739 Files in this item: 1
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Huntsman-Mapila, P.; Kampunzu, A.B.; Vink, B.; Ringrose, S. (Elsevier; http://www.elsevier.com/wps/find/journaldescription.cws_home/503361/description#description, NaN, 2005)[more][less]
Abstract: [Please note that chemical formulae do not display properly]:The siliciclastic sediments of the Okavango inland Delta of northwest Botswana have a modal composition of quartz arenites and result from a complex history, including transport by river and deposition in a nascent rift basin located in a desert environment with input of aeolian sands. The geochemical composition of sediments from the Okavango Delta was determined in order to constrain the role of weathering at the source and the composition of the source rocks. The chemical analyses and the interelement ratios show a broad compositional range usually encompassing the PAAS composition. The chemical index of alteration (CIA) values and the A-CN-K diagram define an evolution trend which can be interpreted using a mixing model involving a strongly weathered component which corresponds to the sedimentary fraction transported by the Okavango River and a relatively immature component which corresponds to the aeolian sand component of the Okavango sediments. Field geological data supported by geochemical ratios involving elements with affinity for mafic-ultramafic and felsic rocks such as Th/Cr, Th/Sc, La/Sc, La/Co and Eu/Eu* support a source area including mafic-ultramafic and felsic rocks, with or without intermediate rocks. The relationships between certain elements (Cr-Ni, Na2O-Al2O3, K2O- Al2O3) refine the interpretation by pointing to the existence of at least three source rock end-members, including a felsic rock source and pyroxene-rich and olivine-rich mafic-ultramafic source rocks. Proterozoic granitoid-gabbro and related volcanic and ortho-metamorphic rock complexes exposed in NW Botswana and adjacent Angola and Namibia are the source rocks of the sediment component which was mixed with aeolian sand and interacted with a variable proportion of diagenetic carbonates to produce the Okavango sediments. Description: This paper was a contribution to the SAFARI 2000 Research Project. URI: http://hdl.handle.net/10311/153 Files in this item: 2
huntsman_mapila_sedgeo.pdf (6.089Mb)license.txt (1.998Kb) -
Daka, P.S.; Obuseng, V.C.; Torto, N.; Huntsman-Mapila, P. (South African Water Research Commission http://www.wrc.org.za, NaN, 2006)[more][less]
Abstract: Deltamethrin concentrations were determined in 35 sediment samples collected from three different habitats: channel, lagoon and pool sites from Xakanaxa in the Okavango Delta, NW Botswana. The samples were Soxhlet-extracted in acetone to extract deltamethrin residues and subsequently cleaned-up with silica gel 60. The final determination was carried out with a gas chromatograph equipped with an electron capture detector (GC-ECD). The sample work-up and determination gave deltamethrin recoveries of 54 to 97%, and detection limits of 0.004 mg/kg dw. The concentration of deltamethrin residues in the sediment samples collected from the three sprayed areas in the Okavango delta ranged between 0.013 and 0.291 mg/kg dw, with the highest concentrations observed in samples obtained from the pool sites. Analysis of samples for organic matter content showed percentage total organic carbon (% TOC) ranging between 0.19% and 8.21%, with samples collected from the pool having the highest total organic carbon. The concentrations of deltamethrin residues and the % TOC in sediment samples showed a similar trend with the highest levels recorded in the pool samples. These data confirmed that a simple method based on GC-ECD, after Soxhlet extraction, was robust enough to enable quantification of deltamethrin in the sediments, because comparable results were obtained with a more sophisticated system consisting of a GC coupled to a mass spectrometer with a time of flight (TOF) analyser. URI: http://hdl.handle.net/10311/650 Files in this item: 1
Daka_WSA_2006.pdf (1.231Mb) -
Mbaiwa, J.E.; Mbaiwa, O.I. (International Journal of Wilderness; http://ijw.wilderness.net/, December NaN, 2006)[more][less]
Abstract: This article examines the effects of veterinary fences on wildlife populations in the Okavango Delta, Botswana. Using data from secondary data sources, findings indicate that the existence of veterinary fences in the Okavango Delta contributes to the decline of wildlife species in Botswana. Veterinary fences are erected to control the spread of livestock diseases in order to protect the European Union beef market where Botswanaâ s beef is largely exported. Migratory wildlife species such as wildebeests, zebras, giraffes, buffalo, and tsessebes have their migratory routes blocked by veterinary fences and hence die from dehydration and entanglements in the fence. Those that get trapped by the fence often become easy kill targets for poachers. Some of the animals have been observed walking along the fence trying to cross. The erection of veterinary fences indicates that the expansion of livestock production into wildlife areas threaten the survival of wildlife in Botswana. To address the problem, an integration of wildlife production with other sectors such as agricultural development should be made a priority at national and local policy levels. This means that the principles of sustainability should be given priority in the erection of veterinary fences in wildlife areas. URI: http://hdl.handle.net/10311/28 Files in this item: 2
license.txt (1.998Kb)mbaiwa_int_j_wilderness_2006.pdf (338.1Kb) -
Mubyana-John, T.; Wutor, V.C.; Yeboah, S.O.; Ringrose, S. (Academic Journals. http://www.academicjournals.org/SRE, NaN, 2007)[more][less]
Abstract: The influence of wild fires on microbial community structure, soil organic matter, sulphur oxidising and nitrifying microbial populations in the floodplains of the Okavango Delta of Botswana was assessed. Microbial community structure was assessed by phospholipids ester-linked fatty acids (PLFA) quantification while microbial sulphur oxidisers were assessed by Most Probable Number (MPN). Community structure assessment showed that burning shifted the microbial community structure from single cellular bacteria being the dominant groups to filamentous fungi and actinomycetes being the most dominant groups. Generally burning increased the fungal component (18:2 w6) matrix from 3.40 to 8.35 while the actinomycetes and sulphur reducing bacterial (10 Me 16:0) component also increased from 1.02 to 1.70 mostly in the floodplains. Generally, the organic matter content declined with burning. However, the influence of burning on soil pH was non conclusive. Soil microbial biomass carbon increased slightly after the fire. The number of heterotrophic and nitrite-oxidizing and sulphur reducing bacteria increased. Overall, these results indicate that burning significantly alters the microbial community structure as large above ground losses of nutrients during and after burning often results in low quantities of nutrients released into the soil. URI: http://hdl.handle.net/10311/349 Files in this item: 1
Fire and.pdf (2.461Mb) -
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) -
Magole, L.; Magole, L.I. (Elsevier, July 15, 2009)[more][less]
Abstract: The Okavango Delta is amongst the largest Ramsar sites (http://www.ramsar.org/sitelist.pdf) in the world and an important wetland for community livelihoods, conservation and tourism in Botswana. Over the years, the utilization of the delta has shifted from communal use to state control, with an increased use for conservation and tourism. This increased use for conservation and tourism has manifested in the physical expansion of the conservation area – Moremi Game Reserve and the formation of Wildlife Management Areas (WMAs) around the reserve, whose primary land use is wildlife utilization. The expansion of the conservation area has translated into several practical matters, including expansion of the area for non-hunting activities or photographic areas. The livelihoods of local communities of the Okavango delta who depended on fishing, hunter-gathering, livestock rearing, rain-fed agriculture and flood recession farming have been negatively affected by the expansion of conservation and tourism in the delta. The livelihoods alternatives in the form of Community Based Natural Resource Management (CBNRM) and tourism have not provided substitutes for the people as the communities are still reliant on the same old livelihood sources as in the past, albeit within smaller and restricted areas. This paper explores the ownership of the natural resources within the Okavango Delta. It asks and attempts to answer the following questions: Who owns and controls the use of the land? Who has access to other resources there in? Who makes the decisions on how the delta resources should be managed and used? Who benefits from the delta resources? We argue firstly that ownership of the delta as defined by legal parameters and demonstrated in natural resource management practice is vested on government. Secondly, government, after assuming ownership of the delta continues to sell its stake to the international community, at the expense of local ownership and access to resources. We conclude that in the process the ability of local communities to source a livelihood out of the delta as they previously used to, is compromised. This we argue works against the goal of sustainable development for improved livelihoods as proclaimed in government policy documents. URI: http://hdl.handle.net/10311/754 Files in this item: 1
The Okavango whose delta is it.pdf (853.1Kb) -
Magole, L.; Magole, L.I. (Elsevier www.elsevier.com/locate/pce, NaN, 2009)[more][less]
Abstract: The Okavango Delta is amongst the largest Ramsar sites (http://www.ramsar.org/sitelist.pdf) in the world and an important wetland for community livelihoods, conservation and tourism in Botswana. Over the years, the utilization of the delta has shifted from communal use to state control, with an increased use for conservation and tourism. This increased use for conservation and tourism has manifested in the physical expansion of the conservation area – Moremi Game Reserve and the formation of Wildlife Management Areas (WMAs) around the reserve, whose primary land use is wildlife utilization. The expansion of the conservation area has translated into several practical matters, including expansion of the area for non-hunting activities or photographic areas. The livelihoods of local communities of the Okavango delta who depended on fishing, hunter-gathering, livestock rearing, rain-fed agriculture and flood recession farming have been negatively affected by the expansion of conservation and tourism in the delta. The livelihoods alternatives in the form of Community Based Natural Resource Management (CBNRM) and tourism have not provided substitutes for the people as the communities are still reliant on the same old livelihood sources as in the past, albeit within smaller and restricted areas. This paper explores the ownership of the natural resources within the Okavango Delta. It asks and attempts to answer the following questions: Who owns and controls the use of the land? Who has access to other resources there in? Who makes the decisions on how the delta resources should be managed and used? Who benefits from the delta resources? We argue firstly that ownership of the delta as defined by legal parameters and demonstrated in natural resource management practice is vested on government. Secondly, government, after assuming ownership of the delta continues to sell its stake to the international community, at the expense of local ownership and access to resources. We conclude that in the process the ability of local communities to source a livelihood out of the delta as they previously used to, is compromised. This we argue works against the goal of sustainable development for improved livelihoods as proclaimed in government policy documents. URI: http://hdl.handle.net/10311/746 Files in this item: 1
Magole_L_PCOE_2009.pdf (1.650Mb) -
Thakadu, O.; Irani, T.; Telg, R. (http://www.informaworld.com, April 12, 2011)[more][less]
Abstract: The present study examined the relative effectiveness of 2 public instructional communication methods in improving selected predictors of knowledge-sharing behaviors among communities in the Okavango Delta, Botswana. A total of 120 subjects took part in a quasi experimental study, with 2 experimental treatments: (a) visualized Power Point presentation and (b) verbal presentation with no visual aids. The results showed that neither method was more effective than the other. However, significant differential effects of method by grouping factor, position, were found among belief and intention measures. The study concluded that neither method was more effective, but recommended use of integrated public instructional communication methods. URI: http://hdl.handle.net/10311/778 Files in this item: 1
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Neuenschwander, A.L.; Crawford, M.M.; Ringrose, S. (Taylor & Francis; http://www.tandf.co.uk/journals/titles/01431161.asp, October NaN, 2005)[more][less]
Abstract: The Earth Observing-1 (EO-1) satellite acquired a sequence of data in 2001 and 2002 that highlighted the annual flooding of the lower Okavango Delta. The data were collected as part of the calibration/validation programme for the Advanced Land Imager (ALI) sensor on the NASA EO-1 satellite. The primary purpose of this study was to compare the capability of ALI to that of Landsat ETM+ for large-scale mapping applications in the Okavango Delta. While the extent and inaccessibility of many areas of the Delta make application of remote sensing attractive, the availability of data with adequate spatial and spectral resolution has limited the characterization of the complex patterns of land cover and geomorphology in the Delta. Initial analysis of the ALI data via supervised classification clearly showed macro-flood features, delineation of downstream channel flow areas, and lateral-downstream inundation of the floodplain. These patterns and the proportions of flooding of the channel compared to that of the floodplain (impoundment) varied annually, from the wetter seasonal swamps through the drier seasonal and occasional swamps. Consistently higher classification accuracies achieved using ALI data relative to ETM+ data are attributed to the higher signal-to-noise ratio and the increased dynamic range of the ALI data. URI: http://hdl.handle.net/10311/169 Files in this item: 2
license.txt (1.998Kb)neuenschwander_ringrose_ijrs_2005.pdf (2.296Mb) -
Mladenov, N.; McKnight, D.M.; Wolski, P.; Murray-Hudson, M. (Elsevier, www.elsevier.com/locate/ecolmodel, NaN, 2007)[more][less]
Abstract: In order to examine dissolved organic matter (DOM) fluxes in seasonal wetland systems that expand and contract seasonally, a time-variable model of dissolved organic carbon (DOC) was developed for a seasonal floodplain in the Okavango Delta of Botswana. The model simulates DOC concentrations from March 2001 to November 2002, during which time DOC concentrations varied between 8 and 31mgCL−1. The model uses a continuously stirred tank reactor (CSTR) approach to describe the hydrologic and biogeochemical controls on DOC leached from litter within the floodplain and transported into the floodplain from upstream. In 2002, a fire burned the floodplain and less litter was available for leaching than in 2001. The model was driven by observations of discharge, water temperature, upstream DOC concentrations, and DOC leaching rates from leaching experiments. Leaching experiments with sedges and grasses indicated that on average 23mgDOCg−1 were leached during the first day ofwetting and 0.6mgDOCg−1 d−1 were continuously leached afterwards. Leaching experiments also showed a decreased amount of DOC released from burned litter and soils than from unburned litter and soils. A two-pool first-order decaymodel that represents both rapidly (0.14 d−1 (at 22 ◦C)) and slowly (0.045 d−1) decaying pools of DOC provided the best representation of observed patterns in DOC concentration in 2001. The decay rate of the first pool decreased by nearly half in 2002, when an estimated 78% of litter was removed by fire. Upstream DOC transport into the floodplain was the dominant source of DOC (representing approximately 70% and 75% of the DOC input in 2001 and 2002, respectively), followed by DOC leaching from litter and DOC originating from microbial sources. In 2001, decomposition (representing approximately 36% of the DOC loss), outflow to an adjacent floodplain (36%) and infiltration (28%) were the major removal mechanisms for DOM from the study floodplain. The large amount of DOC transported by infiltration implies storage of DOC in the subsurface, whichmay influence subsurface heterotrophic activity. In light of future climate change anticipated for the region, a scenario using a 2 ◦C increase in average water temperature and 10% reduction in upstream DOC mass was performed and resulted in significant (11%) reduction in annual DOC mass within the study floodplain. URI: http://hdl.handle.net/10311/497 Files in this item: 1
Mladenov2007Simulation.pdf (2.048Mb) -
Mbaiwa, J.E. (Society of South African Geographers; http://www.journals.co.za/ej/ejour_sageo.html, NaN, 2004)[more][less]
Abstract: This paper assesses the success and sustainability of Community-Based Natural Resource Management (CBNRM) in the Okavango Delta. It does so by asking the following questions: a) to what extent has CBNRM contributed to sustainable natural resource use, rural economic development, enhanced rural livelihoods and benefit sharing? b) To what extent has power been devolved to the rural communities especially in relation to resource ownership and management? c) What are the existing and potential challenges facing the successful implementation of CBNRM in the Okavango Delta? With illustrations from the three CBNRM projects of Okavango Community Trust, Okavango Kopano Mokoro Community Trust and the Khwai Development Trust, this paper notes that local communities have successfully established community trusts as institutions to provide leadership in their participation in tourism and natural resource management. They also derive socio-economic benefits from CBNRM such as the participation in decision-making, employment and income generation. However, the lack of entrepreneurships and managerial skills, understanding of the concept of CBNRM, poor benefit sharing on CBNRM participants, and enclave tourism are some of the challenges that face CBNRM in the Okavango Delta. In the event that empowerment issues especially training and capacity building are successfully addressed, CBNRM in the Okavango Delta has the potential to be a successful model of community-based tourism. URI: http://hdl.handle.net/10311/157 Files in this item: 2
license.txt (1.998Kb)mbaiwa_sagj_2004_msm.pdf (111.4Kb) -
Black, F.J.; Bokhutlo, T.; Somoxa, A.; Maethamako, M.; Modisaemang, O.; Kemosedile, T.; Cobb-Adams, C.; Mosepele, K. (Elsevier, February 20, 2011)[more][less]
Abstract: Mercury is a neurotoxin and global pollutant, and wetlands and newly flooded areas are known to be sites of enhanced production of monomethylmercury, the form of mercury that is readily biomagnified in aquatic food chains to potentially toxic levels. The Okavango Delta in Botswana, Southern Africa, is the largest inland delta in the world and a wetland ecosystem that experiences dramatic annual flooding of large tracts of seasonal floodplains. The Delta was, therefore, expected to be home to high mercury levels in fish and to be an area where local subsistence fishing communities would be at substantial risk of mercury toxicity from fish consumption. Total mercury concentrations measured in 27 species of fish from the Okavango Delta averaged (mean±s.d., wet weight) 19±19 ng g−1 in non-piscivorous fish, and 59±53 ng g−1 in piscivorous fish. These mercury concentrations are similar to those reported for fish from lakes in other areas of tropical Africa, demonstrating that not all wetlands are sites of elevated mercury concentrations in biota. Even more intriguing is that concentrations of mercury in fish from across tropical Africa are systematically and substantially lower than those typically reported for fish from freshwater ecosystems elsewhere globally. The reasons for this apparent “African mercury anomaly” are unclear, but this finding poses a unique opportunity to improve our understanding of mercury's biogeochemical cycling in the environment. Mercury concentrations measured in human hair collected in subsistence fishing communities in the Okavango Delta were similarly low (0.21±0.22 μg g−1 dry weight) despite high levels of fish consumption, and reflect the low mercury concentrations in the fish here. URI: http://hdl.handle.net/10311/806 Files in this item: 1
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Mitsch, W.J.; Nahlik, A.; Wolski, P.; Bernal, B.; Zhang, L.; Ramberg, L. (Springer, http://www.springer.com, NaN, 2010)[more][less]
Abstract: This paper summarizes the importance of climate on tropical wetlands. Regional hydrology and carbon dynamics in many of these wetlands could shift with dramatic changes in these major carbon storages if the inter-tropical convergence zone (ITCZ) were to change in its annual patterns. The importance of seasonal pulsing hydrology on many tropical wetlands, which can be caused by watershed activities, orographic features, or monsoonal pulses from the ITCZ, is illustrated by both annual and 30-year patterns of hydrology in the Okavango Delta in southern Africa. Current studies on carbon biogeochemistry in Central America are attempting to determine the rates of carbon sequestration in tropical wetlands compared to temperate wetlands and the effects of hydrologic conditions on methane generation in these wetlands. Using the same field and lab techniques, we estimated that a humid tropical wetland in Costa Rica accumulated 255 g C m−2 year−1 in the past 42 years, 80% more than a similar temperate wetland in Ohio that accumulated 142 g C m−2 year−1 over the same period. Methane emissions averaged 1,080 mg-C m−2 day−1 in a seasonally pulsed wetland in western Costa Rica, a rate higher than methane emission rates measured over the same period from humid tropic wetlands in eastern Costa Rica (120–278 mg-C m−2 day−1). Tropical wetlands are often tuned to seasonal pulses of water caused by the seasonal movement of the ITCZ and are the most likely to be have higher fire frequency and changed methane emissions and carbon oxidation if the ITCZ were to change even slightly. Description: Some symbols may not come as they are in the abstract. URI: http://hdl.handle.net/10311/832 Files in this item: 1
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Ringrose, S.; Vanderpost, C.; Matheson, W. (Taylor & Francis; http://www.tandf.co.uk/journals/titles/01431161.asp, NaN, 1997)[more][less]
Abstract: Attention worldwide has been focused on the need to assess the appropriateness of land management strategies especially where these occur near sensitive areas of wildlife habitat. This work considers the use of mainly Thematic Mapper data in providing an assessment of the relative impact of different land management strategies on the natural vegetation cover in part of the sensitive Okavango area in Botswana. Supervised classification (maximum likelihood) techniques when used on six-band TM imagery showed that differential degradation was prevalent in land management areas, especially where these are separated by fencelines with an overall accuracy 72 per cent. Marginally more degradation is evident in a controlled hunting area adjacent to the Game Reserve, relative to a communal grazing area. Band transform analyses indicate that distinctive changes in cover type and density frequently take place over boundaries or fencelines separating land management areas. Some degradation in the controlled hunting area appears related to the influence of faultlines on the distribution of soil, hence plant community types. In other cases the pattern of degradation is distributed randomly between the Game Reserve and the cordon fence. Reasons for this unusual distribution pattern may lie in the restriction of movement of migratory wildlife species southwards by the cordon fence separating communal grazing from hunting land uses. A more appropriate management strategy may lie in the prediction of wildlife movements, prior to the erection of cordon fences URI: http://hdl.handle.net/10311/173 Files in this item: 1
ringrose_int_j_remote_sensing_1997.pdf (4.553Mb) -
Ringrose, S.; Jellema, A.; Huntsman-Mapila, P.; Baker, L.; Brubaker, K. (Taylor & Francis; http://www.tandf.co.uk/journals/titles/01431161.asp, October 10, 2005)[more][less]
Abstract: This work determines the value of remotely sensed imagery in developing drying impacts which occur as a result of internal and/or external factors in the Okavango catchment. Three sites provide a preview of the consequences of Delta margin drying as depicted over historical, intermediate and geological timescales. Initially, supervised classification resulted in the identification of sequences of islands and flood plains and their associated vegetation cover on ETM+ imagery, with a classification accuracy of 74- 77%. Comparative results, augmented by patch analysis, suggest that through time, island woody vegetation cover has invaded the flood plains and locally developed protected ecotonal areas (extensions) which are densely treed, relative to adjacent, non-protected flood plains. Over longer time periods, protected areas between extensions became infilled with woody vegetation leading to, in effect, island enlargement or agglomeration. Disadvantages of long-term Delta drying in terms of natural resource management include a reduced availability of wetland-based construction and agricultural resources. If natural regeneration (island agglomeration) is allowed to take place, these resources may ultimately be replaced by dryland timber and potential cropland. URI: http://hdl.handle.net/10311/174 Files in this item: 2
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