Browsing by Author "Mazvimavi, D"

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    An assessment of the contribution of surface and subsurface flows to river flows of the Sandspruit in the Berg River Catchment, South Africa.
    (University of the Western Cape, 2018) Damons, Matthew; Mazvimavi, D
    Studies have shown that the primary origin of salinity in river flows of the Sandspruit in the Berg Catchment located in the Western Cape Province of South Africa was mainly a result of atmospheric deposition of salts. The salts are transported to rivers through surface runoff and subsurface flow (i.e. through flow and groundwater flow). The purpose of this study was to determine the contributions of subsurface and surface flows to the total flows in the Sandspruit, Berg Catchment. Three rain events were studied. Water samples for two rain events were analysed for environmental tracers ?18O, Silica or Silicon dioxide (SiO2), Calcium (Ca2+) and Magnesium (Mg2+). Tracers used for two component hydrograph separation were ?18O and SiO2. The tracers, Ca2+ and Mg2+, revealed inconsistent contributions of both subsurface flow and surface flow. Two component hydrograph separations indicated is that groundwater is the dominant contributor to flow, while surface runoff mainly contributes during the onset of the storm event. Groundwater response to precipitation input indicated that boreholes near the river have a quicker response than boreholes further away from the river. Boreholes nearer to the river also indicate higher water levels in response to precipitation, in comparison to boreholes further from the river.
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    Contribution of understorey vegetation to evapotranspiration partitioning in apple orchards under Mediterranean climatic conditions in South Africa
    (Elsevier, 2021) Ntshidi, Z; Dzikiti, S; Mazvimavi, D
    Orchard evapotranspiration (ET) is a complex flux which has been the subject of many studies. It often includes transpiration from the trees, cover crops and weeds, evaporation from the soil, mulches and other orchard artefacts. In this study we investigated the contribution of the orchard floor evaporative fluxes to whole orchard ET focusing on the transpiration dynamics of understorey vegetation which is currently not well known. Data on the partitioning of ET into its constituent components were collected in apple (Malus Domestica Bork) orchards with varying fractional canopy cover. The study orchards were in the prime apple growing regions in South Africa. The orchards were planted to the Golden Delicious/Reinders and the red cultivars (i.e. Cripps’ Pink/ Royal Gala/Fuji). Tree transpiration was quantified using the heat ratio method and the thermal dissipation sap flow techniques. Understorey transpiration was measured at selected intervals using micro stem heat balance sap flow gauges calibrated against infrared gas analyser readings. Orchard ET was measured using an open path eddy covariance system while the microclimate, radiation interception, and soil evaporation were also monitored. Orchard floor evaporative fluxes accounted for as much as 80% of the measured ET in young orchards with dense understorey vegetation that covered most of the orchard floor.
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    Water use of selected cover crop species commonly grown in South African fruit orchards and their response to drought stress
    (Elsevier, 2021) Mazvimavi, D; Ntshidi, Z; Dzikiti, S; Mkunyana, Y
    Cover crops are widely planted in orchards for a variety of reasons. These include suppressing soil erosion, nutrient cycling, phytosanitary purposes, general orchard aesthetics etc. However, there is need to balance these benefits against use of scarce resources such as water and nutrients. Currently no information exists on how different cover crop species use water in orchards and how they cope with drought stress. The aim of this study was therefore to compare the transpiration dynamics of various cover crop types in order to identify species with conservative water use rates. Studied species included: 1) two exotic legumes i.e. Lupine (Lupinus albus L.), and Common vetch (Vicia sativa), 2) three exotic grasses i.e. Tall fescue (Festuca arundinacea), Rye grass (Lolium perenne), and Kikuyu grass (Pennisetum clandestium) and; 3) grasses that are indigenous to sub-Saharan Africa i.e. African Lovegrass (Eragrostis capensis) and Rhodes grass (Chloris gayana). The crops were planted in pots under controlled greenhouse conditions. Transpiration rates were quantified using miniature stem heat balance sap flow gauges and by manual weighing. Drought stress was imposed by withholding irrigation at selected intervals and the responses were quantified through changes in the water relations of the plants. The study showed that exotic legumes had the highest daily water use which peaked at about 2.4 L per square metre of leaf area per day, followed by exotic grasses at 1.5–2.0 L/m2/d. The indigenous grasses used the least water ranging from 0.8 to 1.2 L/m2/d. The indigenous grasses largely displayed an isohydric response to drought stress by maintaining their leaf water status with increasing soil water deficit. The exotic species, on the other hand, showed risk taking behaviour (anisohydry) wherein both the transpiration and leaf water status decreased sharply as drought stress increased. Consequently, some exotic species failed to recover when stress was relieved. From a water use perspective, this study demonstrates that indigenous grass species are more appropriate as cover crops in South African orchards because of their low transpiration rates and the ability to cope with extended periods of water deficit. © 2021 Elsevier Ltd
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    Water use productivity of the rooibos tea crop in the winter rainfall region, Western Cape, South Africa
    (University of the Western Cape, 2023) Mkhanzi, Wasanga; Mazvimavi, D
    Aspalathus linearis, commonly known as rooibos or red tea, is one of the well-known herbal tea beverages in South Africa. A. linearis is known for its medicinal, economic, traditional and ecological values. This leguminous shrub is endemic to the greater Cederberg Region of the Western Cape Province, South Africa. The area receives winter rainfall. With the Western Cape Province predicted to get drier in future with increasing temperatures and heat waves, the sustainability of range restricted species like A. linearis may be negatively affected by climate change. Given the value of the rooibos crop, there is a need to establish the sustainability of rooibos production to mediate the effects of climate change. Henceforth, this study seeks to determine the water use and yield patterns of rain-fed rooibos crops. In addition, the study sought to test how environmental conditions affect rooibos production and estimate the water use efficiency of A. linearis under present-day (May 2019-June 2020) conditions in a prime rooibos growing area in Porterville in the Western Cape Province. The study's objectives were achieved by determining the micro-climate, soil physical properties, plant attributes and the water use dynamics of cultivated A.linearis. Weather data were obtained from an automatic weather station (AWS). The field leaf area index (LAI) was measured using a LAI-2000 leaf area meter. Plant growth was determined by measuring plant height, width and breath. Soil samples were collected to determine the type and physical properties of the soil at the rooibos field, while soil moisture content was determined in the field using soil moisture probes at 20, 40, 60, 80 and 100 cm depths. Water use of the rooibos crop was quantified using various methods such as micro-stem heat balance sap flow sensors, Penman Montheith equation, open path eddy covariance, FruitLook and the soil water balance method. Lastly, to assess the potential impact of climate change on the rooibos crop, ETo was estimated using two Shared Socioeconomic Pathways (SSPs): SSP1-2.6 and SSP5-8.5. The results show that the study area is dominated by sandy soils, characterised by a low water holding capacity. The rooibos crop's average growth ranged from 1.0 cm in winter to 12cm in spring. LAI increased steadily from 0.28 in June and reached its peak at 1.56 in December.