Browsing by Author "Mazvimavi, D."

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    A comparative assessment of the quantity and sources of water used by alien invasive prosopis spp and indigenous Acacia karroo in the Northern Cape Province
    (University of the Western Cape, 2015) Ntshidi, Zanele; Mazvimavi, D.; Dzikiti, S.
    Invasive alien plants (IAPs) are often reported to use more water than indigenous plants. Inaddition, IAPs have an ability to adapt to harsh environmental conditions and they tend to spread at rapid rates, thereby threatening the country’s water resources, agricultural land, and biodiversity. Much of South Africa is expected to get drier in future due to climate change and the new climatic conditions are also predicted to accelerate the rate at which alien plants will spread. Approximately 10 million hectares are currently estimated to have been invaded by alien plants in South Africa, with an estimated average annual rate of spread of more than 5%. The first objective of this study was to compare the water use by deep rooted tree species which include invasive alien Prosopis (sp) trees and the co-occurring indigenous A. karroo. These trees are growing in a flood plain of a groundwater dependent catchment in the Northern Cape Province. Both species are dependent on groundwater and thus compete with local communities for this resource. The second objective was to determine the sources of water that the trees were using in order to understand the impacts of each species on groundwater resources. Transpiration was measured using the heat ratio method of the heat pulse velocity sap flow technique while the volumetric soil water content was monitored at several depths down the soil profile using automated capacitance soil water content probes. Weather data was collected using an automatic weather station. Stable isotopes of oxygen and hydrogen from plant, soil and groundwater samples were analysed to determine the sources of water used by the trees. Average tree density was approximately 613 stems per hectare for Prosopis compared to about 100 stems per hectare for A. karroo. Comparative measurements of water use shows that the annual stand level transpiration from Prosopis invasions was approximately 353 mm/year while that from A. karroo was only about 137 mm/year. Differences in stand transpiration were a result of the higher plant density for Prosopis than A. karroo. There were no significant differences in the transpiration rates of the two species for trees with a similar transpiring leaf area. Application of a two compartment linear mixing model for the oxygen isotope ratio during the peak transpiration period in summer showedthat Prosopis derived 23% of its water from the unsaturated zone and 77% from the saturated zone. A. karroo on the other hand derived 53% of its water from the unsaturated zone and47% from the saturated zone. Diurnal fluctuations in groundwater levels were strongly related to the transpiration dynamics of both species. This supports the observation that these deep rooted trees have substantial impacts on groundwater at the study site. Root sap flow patterns of Prosopis showed evidence of hydraulic redistribution wherein the groundwater abstracted by the tap roots was deposited in the shallow soil layers by lateral roots. However, the root sap flow patterns of A. karroo growing adjacent to the Prosopis did not show this phenomenon.
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    Factors influencing sustainability of communally-managed waterfacilities in rural areas of Zimbabwe
    (Elsevier, 2017) Kativhu, T.; Mazvimavi, D.; Tevera, D.
    Sustainability of point water facilities is a major development challenge in many rural settings ofdeveloping countries not sparing those in the Sub-Saharan Africa region. This study was done inZimbabwe to investigate the factors influencing sustainability of rural water supply systems. A total of399 water points were studied in Nyanga, Chivi and Gwanda districts. Data was collected using aquestionnaire, observation checklist and key informant interview guide. Multi-Criteria analysis was usedto assess the sustainability of water points and inferential statistical analysis such as Chi square tests andAnalysis of Variance (ANOVA) were used to determine if there were significant differences on selectedvariables across districts and types of lifting devices used in the study area. The thematic approach wasused to analyze qualitative data. Results show that most water points were not functional and only 17%across the districts were found to be sustainable. A fusion of social, technical,financial, environmentaland institutional factors was found to be influencing sustainability. On technical factors the ANOVAresults show that the type of lifting devicefitted at a water point significantly influences sustainability(F¼37.4, p<0.01). Availability of spare parts at community level was found to be determining thedowntime period of different lifting devices in the studied wards. Absence of user committees was foundto be central in influencing sustainability as water points that did not have user committees were notsustainable and most of them were not functional during the time of the survey.
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    The influence of canopy cover and cultivar on rates of water use in apple orchards in the Western Cape Province, South Africa
    (University of the Western Cape, 2020) Mobe, Nompumelelo Thelma; Mazvimavi, D.
    Water availability and climate related issues are some of the greatest crop production risks to irrigated agriculture in arid regions. In South Africa, for example, the increasing frequency and severity of droughts related to climate change and the growing competition for limited water resources among different users threaten the sustainability and growth of irrigated agriculture, especially the water-intensive fruit industry. Major fruit such as apples (Malus domestica Borkh) are produced entirely under irrigation in South Africa. As a result, there has been considerable research to accurately quantify the water requirements of fruit tree orchards in order to maximize water productivity.
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    Influences of river flows on recruitment success of Fynbos riparian vegetation along selected high gradient streams in the Western Cape, South Africa
    (University of the Western Cape, 2014) Magoba, Rozwivhona Faith; Mazvimavi, D.; Brown, C. A.
    Riparian vegetation occurs in two distinct zones, the wet bank and the dry bank. Knowledge on how the flow regime influences the zonal structure of riparian vegetation is required to mitigate the adverse effects of water resource utilization on riparian vegetation. The first objective of this study was to determine whether flow exerts a physical influence on zonal structure pre- or post-recruitment. An examination of the survival of seedlings and saplings was conducted along Western Cape rivers to investigate seedling persistence and survival on lateral zones. A comparison of the ratios of seedlings, saplings and adults in different riparian zones for the years, 2004, 2011 and 2013, was carried out. The results suggest that in general seeds are deposited randomly on the banks, where they germinate and become seedlings. Seedlings that become established at locations unsuitable for their persistence into adulthood are removed either by high flows or perish during dry conditions. Thus, lateral zonation eventually develops due to species differences in tolerance to conditions at different positions on the banks. The second objective was to explore the effects of the reduction in dry season low flows on the recruitment success of riparian species at sites upstream and downstream of abstraction points. At most sites plants were arranged into different lateral zones and the numbers of species between upstream and downstream sites were not significantly different. There were significant differences in the abundances between up- and downstream sites, with the loss of herbaceous plants and sedges at downstream sites, both of which favour moist conditions. Also, in the absence of dry season flows, the seedlings of dry bank tree species recruited closer to the channel than those at the sites with summer flows. The shifting of the dry bank into the channel narrows the channel, which may affect the hydraulic pressures exerted during floods. The spatial arrangement in the riparian zone has as much to do with flow conditions post recruitment as it does with conditions during recruitment. This shows that the structure of riparian plants is determined not only by whether or not the minimum flows are met, this points to the need to reinstate the naturally variable flow and adopting a holistic approach for the understanding and management of aquatic systems.