Browsing by Author "Everson, Colin Stuart."

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Assessing the effects of site preparation treatments on erosion processes and sediment yield on a commercial Eucalyptus plantation: case study at Two Streams, KwaZulu-Natal.
(2020) Bull, Jordan Michael.; Hill, Trevor Raymond.; Everson, Colin Stuart.
Soil erosion monitoring and modelling is critical in the face of climate change, as erosion is detrimental to environmental and human health. It reduces soil productivity through degradation, compromises water quality through nutrient loading freshwater sources, and decreases reservoir capacity through sedimentation. This is a global challenge which is being amplified by increased levels of soil erosion on cultivated lands (e.g. commercial forestry), the combined effects of which hinder the success of several United Nations Sustainable Development Goals. However, commercial forestry is essential for human survival, providing a host of resources for human consumption, and expanding in its global coverage each year; although, this expanding need for commercial forestry creates a paradox, as it has the potential to damage environmental health and biodiversity (systems which humans rely on for survival), particularly through soil erosion and sedimentation of freshwater systems. Afforestation of plantations has been widely considered a land-use activity which reduces soil erosion; although, this is dependent on the management of the commercial plantations, where certain commercial forestry management techniques exacerbate soil erosion, such as the well-used site preparation technique of burning. Therefore, an investigation into the effect of commercial forestry site preparation techniques such as burning (at different severities) and mulching on soil erosion and the modelling thereof is required, as only a paucity of research has reported on this. Soil erosion measurements were conducted on a newly planted Eucalyptus dunnii stand, which consisted of three different site preparation techniques, namely a hot burn, a cold burn and a mulch treatment, in the Two Streams catchment, Kwa-Zulu Natal, South Africa. Micro-runoff and runoff plots were used to respectively measure splash and rill erosion of sediment, nitrogen, phosphorous, dissolved organic carbon, particulate organic carbon loss and runoff on each treatment at different slopes. In addition, soil erosion and runoff of this catchment and treatments were modelled using the ArcSWAT model, and the observations were used to validate the simulated outputs. The mulch treatment had the most consistent reduction in runoff and erosion, while the burn treatments of different severities generated greater respective runoff and erosion quantities through different erosional processes (splash vs rill). The ArcSWAT model over-simulated runoff on the hot burn and mulch treatment, while under-simulating on the cold burn treatment; however, the model consistently over-simulated sediment and nutrient loss on all treatments, indicating the model’s inability to simulate soil erosion on the defined land-use treatments. The reduced runoff and erosion produced by the mulch treatment is attributed to the protection that the mulch provides to the soil from splash erosion and the resistance posed to overland flow reducing rill erosion. The burn treatments generating more erosion and runoff through different erosional processes was attributed to the differing nature of debris produced by each burn severity. This research will contribute towards the data sets necessary to refine the land-use management tools of the ArcSWAT model to better model soil erosion on different land-use treatments. Furthermore, this research demonstrates the erosion processes that differing site preparation treatments are susceptible to, and what this means for future research and protecting soil and downstream water quality in the face of climate change.
An assessment of the water use of indigenous and introduced tree SPP. and varying land uses around Vasi Pan, Maputaland, KwaZulu-Natal.
(2017) Pearton, Tracy Ann.; Everson, Colin Stuart.; Chetty, Kershani Tinisha.
Abstract available in PDF file.
Comparison between satellite-based and cosmic ray probe soil moisture estimates : a case study in the Cathedral Peak catchment.
(2015) Vather, Thigesh.; Chetty, Kershani Tinisha.; Mengistu, Michael Ghebrekidan.; Everson, Colin Stuart.
Abstract available in PDF file.
Ecological effects of fire in the montane grasslands of Natal.
(1985) Everson, Colin Stuart.; Tainton, Neil M.
Although controlled burning has been used to manage Highland Sourveld grasslands, little was known of its effects on the vegetation. This study examined the effects of past fire treatments on veld condition,species composition, dry matter production, quality and canopy recovery growth rates of these grasslands. Also, six techniques of estimating the species composition of grasslands were compared in order to decide on a standard technique for monitoring these grasslands. From this work it was concluded that the wheel point method is the most satisfactory. Veld condition scores were significantly lower in grassland protected from fire than where veld had been burnt or burnt and grazed at regular intervals. Frequent defoliation was found to maintain the grassland composition largely unchanged over a period of 30 years. Individual species were, however, found to react strongly to defoliation frequency. Plant demographic studies were therefore carried out to explain this differential response to burning. Three Decreaser and two Increaser I species were studied. In all species examined, recruitment of secondary tillers was stimulated by regular burning, each species being well adapted to a regular fire regime. Differential responses to burning were best explained by the combined effects of the different reproductive capacities and mortality rates of tillers of these species. A biennial spring burning regime was shown to be most suitable for maintaining the most important grass species at their present levels of abundance. Annual winter and biennial spring burning did not result in significant differences in dry matter production. Maximum net roductivity was approximately 230 g/m² in both treatments, placing them amongst the more productive areas of Southern Africa. Examination of canopy recovery growth rates showed that there is little difference in the percentage canopy cover at the end of the growing season when veld is burnt annually in winter or biennially in spring. However, differences in season of burn resulted in exposure to erosive forces at different times of the year. The results of this investigation have highlighted the importance of regular burning during the dormant period in the montane grasslands of Natal.
Productivity and water use of commercial forestry species and their potential impact on surface water resources in two forestry areas of KwaZulu-Natal, South Africa.
(2023) Kaptein, Nkosinathi David.; Clulow, Alistair David.; Toucher, Michelle Lynn.; Everson, Colin Stuart.; Germishuizen, Ilaria.
Abstract available in PDF.
Quantification of the water-use dynamics of the dominant plant communities of the Eastern Shores in the iSimangaliso Wetland Park for improved water resource management.
(2015) Clulow, Alistair David.; Everson, Colin Stuart.; Price, Jonathan.; Jewitt, Graham Paul Wyndham.
No abstract available.
The use of environmental isotopes, soil water measurements and soil water modelling to understand tree water use of an Acacia mearnsii (Black wattle) stand in KwaZulu-Natal.
(2015) Watson, Andrew.; Everson, Colin Stuart.; Clulow, Alistair David.; Bulcock, Hartley Hugh.
In Southern Africa commercial afforestation is an important agricultural activity and accounts for a large portion of the gross agricultural production, However, there are concerns regarding its possible detrimental impact on the hydrological system. Previous research in the Two Streams catchment by Clulow et al. (2011) showed that a commercial forestry species (Acacia mearnsii) was using more water than available through precipitation over a 30-month period (total evaporation was greater than rainfall) and they concluded that the trees were drawing water from another source. In this study, field measurements of stable isotopes of rainfall, soil water, stream water and groundwater were collected and analysed in order to understand the deficit in the water balance identified by Clulow et al. (2011). Experimental apparatus was used to extract isotopes from soil water. Automated rainfall and streamflow samples were used to sample rainfall and stream water (evaporation seals were designed to prevent fractionation). A specific set of criteria was used to program the automated rainfall sampler to better differentiate between event samples. HYDRUS 1-D model outputs of simulated total evaporation and soil water fluxes were verified from total evaporation and soil water measurements at the site. Rainfall varied in isotope signature throughout the year ranging from -150 to -15 permil (δ2H) and -20 to 2 permil (δ18O), these values were largely dependent on rainfall volume. Groundwater isotope composition signature changed only slightly throughout the year ranging from -12 to -5 permil (δ2H) and -4 to -1.5 permil (δ18O), with seasonality being the driving variable. The results from the isotope signatures showed that the main contributor to streamflow (-15 to -1.5 permil (δ2H) and -4.5 to -1.5 permil (δ18O)) was groundwater. Soil isotope signatures varied with depth and season, ranging from -25 to -8 permil (δ2H) and - 1.5 to 4 permil (δ18O). Groundwater signatures were evident on three occasions within the soil horizon (2.0 m and 2.4 m on 23/08/2013 and 1.6 m on 13/0/2013), where water was moved by hydraulic lift or capillary rise and made available for uptake by rooting systems. This was confirmed by Watermark and TDR-100 measurements, where there were upward fluxes of deep soil water during the dry season. HYDRUS-1D results suggested that simulated total evaporation (1052 mm) was similar to measured actual evaporation (1095 mm) during the wet season and dry season. The results conclude that the Acacia mearnsii trees extracted soil water or deep groundwater during the dry season, which allows for continuous growth throughout the year. This supports the conclusion of Clulow et al. 2011 and confirms that commercial forestry could have significant long-term impacts on catchment hydrology, particularly in dry season low flows.
The use of infrared thermometry for irrigation scheduling of cereal rye (Secale cereale L.) and annual ryegrass (Lolium multiflorum Lam.)
(2003) Mengistu, Michael Ghebrekidan.; Savage, Michael John.; Everson, Colin Stuart.
Limited water supplies are available to satisfy the increasing demands of crop production. It is therefore very important to conserve the water, which comes as rainfall, and water, which is used in irrigation. A proper irrigation water management system requires accurate, simple, automated, non-destructive method to schedule irrigations. Utilization of infrared thermometry to assess plant water stress provides a rapid, nondestructive, reliable estimate of plant water status which would be amenable to larger scale applications and would over-reach some of the sampling problems associated with point measurements. Several indices have been developed to time irrigation. The most useful is the crop water stress index (CWSI), which normalizes canopy to aIr temperature differential measurements, to atmospheric water vapour pressure deficit. A field experiment was conducted at Cedara, KwaZulu-Natal, South Africa, to determine the non-water-stressed baselines, and CWSI of cereal rye (Secale cereale L.) from 22 July to 26 September 2002, and aImual (Italian) ryegrass (Lolium multiflorum Lam.) from October 8 to December 4, 2002, when the crops completely covered the soil. An accurate measurement of canopy to air temperature differential is crucial for the determination of CWSI using the empirical (Idso et al., 1981) and theoretical (Jackson et al., 1981) methods. Calibrations of infrared thermometers, a Vaisala CS500 air temperature and relative humidity sensor and thermocouples were performed, and the reliability of the measured weather data were analysed. The Everest and Apogee infrared thermometers require correction for temperatures less than 15 QC and greater than 35 QC. Although the calibration relationships were highly linearly significant the slopes and intercepts should be corrected for greater accuracy. Since the slopes of the thermocouples and Vaisala CS500 air temperature sensor were statistically different from 1, multipliers were used to correct the readings. The relative humidity sensor needs to be calibrated for RH values less than 25 % and greater than 75 %. The integrity of weather data showed that solar irradiance, net irradiance, wind speed and vapour pressure deficit were measured accurately. Calculated soil heat flux was underestimated and the calculated surface temperature was underestimated for most of the experimental period compared to measured canopy temperature. The CWSI was determined using the empirical and theoretical methods. An investigation was made to determine if the CWSI could be used to schedule irrigation in cereal rye and annual rye grass to prevent water stress. Both the empirical and theoretical methods require an estimate or measurement of the canopy to air temperature differential, the non-waterstressed baseline, and the non-transpiring canopy to air temperature differential. The upper (stressed) and lower (non- stressed) baselines were calculated to quantify and monitor crop water stress for cereal rye and annual ryegrass. The non-water-stressed baselines were described by the linear equations Te - Ta = 2.0404 - 2.0424 * VPD for cereal rye and Te - Ta = 2.7377 - 1.2524 * VP D for annual ryegrass. The theoretical CWSI was greater than the empirical CWSI for most of the experimental days for both cereal rye and annual ryegrass. Variability of empirical (CWSI)E and theoretical (CWSI)T values followed soil water content as would be expected. The CWSI values responded predictably to rainfall and irrigation. CWSI values of 0.24 for cereal rye and 0.29 for annual ryegrass were found from this study, which can be used for timing irrigations to alleviate water stress and avoid excess irrigation water. The non-water-stressed baseline can also be used alone if the aim of the irrigator is to obtain maximum yields. However the non-water-stressed baseline determined using the empirical method cannot be applied to another location and is only valid for clear sky conditions. And the non-water-stressed baseline determined using theoretical method requires computation of aerodynamic resistance and canopy resistances, as the knowledge of canopy resistance, however the values it can assume throughout the day is still scarce. The baseline was then determined using a new method by Alves and Pereira (2000), which overcomes these problems. This method evaluated the infrared surface temperature as a wet bulb temperature for cereal rye and annual ryegrass. From this study, it is concluded that the infrared surface temperature of fully irrigated cereal rye and annual ryegrass can be regarded as a surface wet bulb temperature. The value of infrared surface temperature can be computed from measured or estimated values of net irradiance, aerodynamic resistance and air temperature. The non-water-stressed baseline is a useful concept that can effectively guide the irrigator to obtain maximum yields and to schedule irrigation. Surface temperature can be used to monitor the crop water status at any time of the day even on cloudy days, which may greatly ease the task of the irrigator.
Water-use dynamics of alien plant invaded riparian forests in South Africa.
(2018) Scott-Shaw, Bruce Charles.; Everson, Colin Stuart.
In South Africa the invasion of riparian forests by alien trees has the potential to affect the country’s limited water resources. It is difficult for government initiatives, such as the Working for Water (WfW) alien clearing programmes, to justify alien tree removal and implement rehabilitation unless a known hydrological benefit can be seen. Consequently water-use within riparian forests at three climate diverse research catchments within South Africa were monitored using the heat ratio method. The use of the Soil Water Assessment Tool (SWAT) and a Sequential Uncertainty Fitting (SUFI-2) algorithm allowed for the auto-calibration of the SWAT model at each research site using measured water-use data. Within the winter rainfall region of the Western Cape the alien stand used nearly six times more water per unit area than the indigenous stand annually. The combined accumulated daily sap flow over a two year period for three Vepris lanceolata and three Acacia mearnsii trees was 36 000 L and 55 700 L respectively, clearly demonstrating the higher water-use of the alien A. mearnsii trees. In contrast, the water-use of alien species within the summer rainfall region of KwaZulu-Natal was double that of the indigenous species. The accumulated seasonal water-use was the least in the indigenous Searsia (~2 100 L), moderate in the indigenous Maytenus (~7 100 L) and high in the alien A. mearnsii (~15 900 L) trees. The spatial distribution of water-use within northern Zululand showed that the commercial forestry areas were the dominant water-users in the catchment. These findings indicate that there would be a hydrological gain if the alien species are removed from riparian forests and rehabilitated back to their natural state. The use of the SWAT model provided substantial insights into the spatial distribution of total evaporation (ET) throughout the selected catchment areas and is a suitable hydrological model for examining the impacts of different land-uses in catchments in South Africa. Given the quantified hydrological benefit, indigenous trees should be promoted for use in rehabilitation programmes where the natural vegetation is or was forests. This is especially relevant in light of South Africa’s limited water resources.
Water-use of commercial bamboo species in KwaZulu-Natal, South Africa.
(2020) Gumede, Mxolisi Percyval.; Clulow, Alistair David.; Everson, Colin Stuart.; Everson, Theresa Mary.
Abstract available in pdf.
Web-based teaching, learning and research using real-time data from field-based agrometeorological measurement systems.
(2014) Savage, Michael John.; Everson, Colin Stuart.
Abstract available in PDF file.