Research Articles (Earth Sciences)

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3D static modeling and CO2 static storage estimation of the hydrocarbon-depleted charis beservoir, Bredasdorp basin, South Africa
(Natural Resources Research, 2023) Afolayan, Blessing Ayotomiwa; Opuwari, Mimonitu; Mackay, Eric
An essential greenhouse gas effect mitigation technology is carbon capture, utilization and storage, with carbon dioxide (CO2) injection into underground geological formations as a core of carbon sequestration. Developing a robust 3D static model of the formation of interest for CO2 storage is paramount to deduce its facies changes and petrophysical properties. This study investigates a depleted oilfield reservoir within the Bredasdorp Basin, offshore South Africa. It is a sandstone reservoir with effective porosity mean of 13.92% and dominant permeability values of 100–560 mD (1 mD = 9.869233 × 10–16 m2). The petrophysical properties are facies controlled, as the southwestern area with siltstone and shale facies has reduced porosity and permeability. The volume of shale model shows that the reservoir is composed of clean sands, and water saturation is 10–90%, hence suitable for CO2 storage based on petrophysical characteristics. Static storage capacity of the reservoir as virgin aquifer and virgin oilfield estimates sequestration of 0.71 Mt (million tons) and 1.62 Mt of CO2, respectively. Sensitivity studies showed reservoir depletion at bubble point pressure increased storage capacity more than twice the depletion at initial reservoir pressure. Reservoir pressure below bubble point with the presence of gas cap also increased storage capacity markedly.
A MeerKAT polarization survey of southern calibration sources
(2024) Taylor, A.R; Legodi, L.S
We report on full-Stokes L-band observations of 98 MeerKAT calibration sources. Linear polarization is detected in 71 objects above a fractional level of 0.2%. We identify ten sources with strong fractional linear polarization and low Faraday rotation measure that could be suitable for wide-band absolute polarization calibration. We detect significant circular polarization from 24% of the sample down to a detection level of 0.07%. Circularly polarized emission is seen only for flat spectrum sources α>−0.5. We compare our polarized intensities and Faraday synthesis results to data from the NVSS at 1400 MHz and the ATCA SPASS survey at 2300 MHz. NVSS data exist for 54 of our sources and SPASS data for 20 sources. The percent polarization and rotation measures from both surveys agree well with our results. The residual instrumental linear polarization for these observations is measured at 0.16%, and the residual instrumental circular polarization is measured at 0.05%. These levels may reflect either instabilities in the relative bandpass between the two polarization channels with either time or antenna orientation, or atmospheric/ionospheric variations with pointing direction. Tracking of the hourly gain solutions on J0408-6545 after transfer of the primary gain solutions suggests a deterioration of the gain stability by a factor of several starting about 2 hr after sunrise. This suggests that observing during the nighttime could dramatically improve the precision of polarization calibration.
Advancements in satellite remote sensing for mapping and monitoring ofalien invasive plant species (AIPs)
(Elsevier, 2019) Royimani, Lwando; Mutanga, Onisimo; Dube, Timothy
Detecting and mapping the occurrence, spatial distribution and abundance of Alien Invasive Plants (AIPs) have recently gained substantial attention, globally. This work, therefore, provides an overview of advancements in satellite remote sensing for mapping and monitoring of AIPs and associated challenges and opportunities. Satellite remote sensing techniques have been successful in detecting and mapping the spatial and temporal distribution of AIPs in rangeland ecosystems. Also, the launch of high spatial resolution and hyperspectral remote sensing sensors marked a major breakthrough to precise characterization of earth surface feature as well as optimal resource monitoring. Although essential, the improvements in spatial and spectral properties of remote sensing sensors presented a number of challenges including the excessive acquisition and limited temporal resolution. Therefore, the use of high spatial and hyperspectral datasets is not a plausible alternative to continued and operational scale earth observation, especially in financially constrained countries. On the other hand, literature shows that image classification algorithms have been instrumental in compensating the poor spatial and spectral resolution of remote sensing sensors. Furthermore, the emergence of robust and advanced non-parametric image classification algorithms have been a major development in image classification algorithms.
Advancements in the satellite sensing of the impacts of climate and variability on bush encroachment in savannah rangelands
(Elsevier, 2022) Maphanga, Thabang; Dube, Timothy; Shoko, Cletah
An increase in shrubs or woody species is likely, directly or indirectly, to significantly affect rural livelihoods, wildlife/livestock productivity and conservation efforts. Poor and inappropriate land use management practices have resulted in rangeland degradation, particularly in semi-arid regions, and this has amplified the bush encroachment rate in many African countries, particularly in key savannah rangelands. The rate of encroachment is also perceived to be connected to other environmental factors, such as climate change, fire and rainfall variability, which may influence the structure and density of the shrubs (woody plants), when compared to uncontrolled grazing. Remote sensing has provided robust data for global studies on both bush encroachment and climate variability over multiple decades, and these data have complemented the local and regional evidence and process studies. This paper thus provides a detailed review of the advancements in the use of remote sensing for the monitoring of bush encroachment on the African continent, which is fuelled by climate variability in the rangeland areas.
Advances in satellite remote sensing of the wetland ecosystems in Sub-Saharan Africa
(Taylor and Francis Group, 2022) Thamaga, Kgabo Humphrey; Dube, Timothy; Shoko, Cletah
Wetlands are highly productive systems that act as habitats for avariety of fauna andflora. Despite their ecohydrological signifi-cance, wetland ecosystems are severely under threat from globalenvironmental changes as well as pressure from anthropogenicactivities. Such changes results in severe disturbances of plantspecies composition, spatial distribution, productivity, diversity,and their ability to offer critical ecosystem goods and services .However, wetland degradation varies considerably from place toplace with severe degradation in developing countries, especiallyin sub-Saharan Africa due to poor management practices thatleads to underutilization and over reliance on them for liveli-hoods. The lack of monitoring and assessment in this region hastherefore led to the lack of consolidated detailed understandingon the rate of wetland loss.
Analysis of the fragmented legal regime pertaining to rehabilitation measures for wetlands: A South African perspective – part 1
(WIT Press, 2022) Lemine, Bramley Jemain; Kanyerere, Thokozani
Wetlands are disappearing and it is an international dilemma. Many efforts have been made to ensure its protection and conservation, including rehabilitation. Rehabilitation measures have been adopted in policies of various jurisdictions. In South Africa, the wetlands legislative framework is fragmented. It was submitted that a wetlands policy is in the pipeline for South Africa. As opposed to the research on the general protection of this resources, Part 1 of this research aimed, by way of a documentary analysis of the legislative wetland framework, journal articles, books and case law, to provide what the extent of the fragmentation, specifically, rehabilitation measures were, as well as the effect thereof. Part 2 of this research explicitly focused on rehabilitation measures taken by three other jurisdictions, as well as a design for such in South Africa’s envisaged policy.
Antimicrobial resistance screening and profiles: A glimpse from the South African perspective
(IWA Publishing, 2020) Genthe, Bettina; Ndlela, L.; Madlala, T.
According to the Centre for Disease Dynamics Economics and Policy, South Africa represents a paradox of antibiotic management similar to other developing countries, with both overuse and underuse (resulting from lack of access) of antibiotics. In addition, wastewater reuse may contribute towards antibiotic resistance through selective pressure that increases resistance in native bacteria and on clinically relevant bacteria, increasing resistance profiles of the common pathogens. Sediments of surface water bodies and wastewater sludge provide a place where antibiotic resistance genes are transferred to other bacteria. Crop irrigation is thought to be a potential source of exposure to antibiotic-resistant bacteria through the transfer from the water or sludge into crops. The objectives of this study were to examine the antibiotic-resistance profiles of Escherishia coli from three agricultural locations in the Western Cape, South Africa. Using a classical microbiology culture approach, the resistance profiles of E. coli species isolated from river water and sediments, farm dams and their sediments and a passive algal wastewater treatment ponds and sediment used for crop irrigation were assessed for resistance to 13 commonly used antibiotics. Randomly selected E. coli isolates from the sediment and water were tested for resistance.
Application of multi‑method approach to assess groundwater–surface water interactions, for catchment management
(Springer, 2018) Madlala, T.; Kanyerere, Thokozani; Oberholster, P.; Xu, Y.
Globally, the dependence of river systems to delayed discharge of subsurface water to augment flows during dry seasons is well documented. Discharge of fresh subsurface water can dilute concentrated river flow quality during reduced flow. Observed and reported results on the Berg River’s declining water quantity and quality are a concern to the regions socio-economic growth and environmental integrity. Understanding the role of subsurface water discharges on the quantity and quality of receiving surface water courses can improve their management during dry periods. A case study was designed and implemented in the upper Berg River catchment in the Western Cape Province of South Africa to assess the influence of groundwater–surface water interaction on water quantity and quality. This study aimed to quantify and characterize the quality of subsurface water available in the upper catchment to improve observed declining water quality downstream. Hydrograph separation provided estimates of water fluxes during 2012–2014 low and high flow periods, while hydrochemical analysis provided insights on impacts of major land use activity in this catchment on water resources. Hydrograph separation analysis indicated that the Berg River is 37.9% dependent on subsurface water discharges annually. Dominant Na–Cl-type water indicates the quality of water from the upper Berg River is largely affected by natural processes including short residence times of aquifer water, rock–water interactions and atmospheric deposition of NaCl ions. These results provide insights for suggesting management options to be implemented to protect subsurface water for continued dilution and water resources management in the lower catchments.
Application of seismic stratigraphy in reservoir characterisation: A case study of the passive margin deposits of the northern Orange Basin, South Africa
(Springer Nature, 2020) Samakinde, Chris Adesola; Van Bever Donker, Jan M.; Durrheim, Raymond J.
The Barremian-Cenozoic depositional sequences in the northern Orange Basin, SW, South Africa, were investigated using the principles of seismic stratigraphy to understand the interplay of tectonics and sedimentary processes in the distribution of potential hydrocarbon reservoirs. A seismic stratigraphic workflow (seismic sequence, seismic facies and lithofacies analysis) was completed by utilising three seismic lines (L1, L2 and L3) tied to Wireline data (gamma, checkshots and sonic) in two exploration wells (A1 and A2). Seven depositional sequences were mapped followed by the creation of lithofacies log interpreted from the gamma-ray log (GR) by setting maximum GR value at 60 API for Sandstone, 60–100 API for Siltstone and above 100 API for Shale. Six seismic facies units are recognised based on internal geometry and configurations of the seismic reflectors; Tangential-Oblique (SF1), Hummocky (SF2), Wavy-Parallel (SF3), Chaotic (SF4), Sub-parallel/parallel (SF5) and Divergent (SF6). SF4 is dominant within the Barremian-Aptian sequence and expressed in an incised valley fill, suggesting mass transport deposition accompanied by strong hydrodynamic conditions.
Application of the rainfall infiltration breakthrough (RIB) model for groundwater recharge estimation in west coastal South Africa
(Water Research Commission, 2013) Xianfeng, Sun; Jovanovic, Nebo Z.; Kapangaziwiri, Evison; Brendonck, Luc; Bugan, Richard Domain Hunter
Recharge estimation in arid and semi-arid areas is very challenging. The chloride mass balance method applied in western South Africa fails to provide reliable recharge estimates near coastal areas. A relationship between rainfall events and water level fluctuations (WLF) on a monthly basis was proposed in the rainfall infiltration breakthrough (RIB) model for the purpose of groundwater recharge estimation. In this paper, the physical meaning of parameters in the CRD and previous RIB models is clarified, and the RIB model is reviewed with the algorithm improved to accommodate various time scales, namely, daily, monthly and annual scales. Recharge estimates on a daily and monthly basis using the revised RIB approach in 2 study areas, one in a sandy alluvial aquifer (Riverlands) and the other in the Table Mountain Group (TMG) shallow unconfined aquifer (Oudebosch), are presented, followed by sensitivity analysis. Correlation analysis between rainfall and observed WLF data at daily scale and monthly scale, together with recharge estimates obtained from other methods, demonstrates that the RIB results using monthly data are more realistic than those for daily data, when using long time series. Scenarios using the data from Oudebosch with different rainfall and groundwater abstraction inputs are simulated to explore individual effects on water levels as well as recharge rate estimated on a daily basis. The sensitivity analysis showed that the recharge rate by the RIB model is specifically sensitive to the parameter of specific yield; therefore, the accurate representative specific yield of the aquifer needs to be selected with caution. The RIB model demonstrated in these two cases can be used to estimate groundwater recharge with sufficiently long time series of groundwater level and rainfall available in similar regions. In summary, the RIB model is best suited for shallow unconfined aquifers with relatively lower transmissiv - ity; the utility of the RIB model for application in different climatic areas under different hydrogeological conditions needs to be further explored.
Application of the standardised streamflow index for hydrological drought monitoring in the Western Cape Province, South Africa: a case study in the Berg River catchment.
(Multidisciplinary Digital Publishing Institute (MDPI), 2023) Mukhawana, Mxolisi Blessing; Kanyerere, Thokozani; Kahler, David
In many regions around the world, drought has been recurrent, more frequent, and more intense over time. Hence, scientific research on drought monitoring has become more urgent in recent years. The aim of this study was to test the applicability of the Standardised Streamflow Index (SSI) for hydrological drought monitoring in the Berg River catchment (BRC), Western Cape (WC) province, South Africa (SA). Using various methods described in this study, the sensitivity of the SSI to the commonly used Gamma, Log-normal, Log-logistic, Pearson Type III, and Weibull Probability Distribution Functions (PDFs) was tested. This study has found that all the tested PDFs produced comparable results for mild to severe drought conditions. The SSI calculated using the Gamma, Log-Normal, and Weibull PDFs is recommended for the BRC because it consistently identified extreme drought conditions during the 1990–2022 study period and identified the 2015–2018 droughts as the worst during the study period. Although more studies are required to test other PDFs not considered, this study has shown that the SSI can be applicable in the BRC. This study has provided a foundation for more research on the application of the SSI in the BRC and other catchments in SA.
Assessing edge effect on the spatial distribution of selected forest biochemical properties derived using the worldview data in Dukuduku forests, South Africa
(Wiley, 2019) Mutanga, Onisimo; Dube, Timothy; Omer, Galal
This work explores the potential of the high‐resolution WorldView‐2 sensor in quan‐tifying edge effects on the spatial distribution of selected forest biochemical proper‐ties in fragmented Dukuduku forest in KwaZulu‐Natal, South Africa. Specifically, we sought to map fragmented patches within forested areas in Dukuduku area, using very high spatial resolution WorldView‐2 remotely sensed data and to statistically determine the effect of these fragmented patches on the spatial distribution of se‐lected forest biochemical properties.
Assessing the adverse effects of a mixture of AMD and sewage effluent on a sub-tropical dam situated in a nature conservation area using a modified pollution index
(Springer Nature, 2021) Oberholster, P.F; Goldin, J; Xu, Y
Currently water resources in nature conservation areas are under severe pressure due to external drivers of anthropogenic pollution. There is a lack of monitoring tools to determine water quality status of dams situated in nature reserves receiving a mixture of pollutants over space and time. The present study was conducted over a 12-month period with the aim of applying a modified pollution index (PILD) to determine the water quality and phytoplankton status of the Loskop Dam situated in the Loskop nature reserve, South Africa. From the data generated in the current study, it was evident that the PILD effectively determined nutrient enrichment and heavy metal pollution in the dam. Furthermore, the study showed that the most pollution tolerant phytoplankton species was the diatom Melosira varians followed by the dinoflagellate Ceratuim hirundinella and the cyanobacteria Microcystis aeruginosa. Chemical variables during the sampling period that exceeded the limits of the South African, Canadian, Australia and New Zealand guideline levels were Zn, TP, Cl, Fe, Mn and NH4. The occurrence of concentrations of Cl above the target water quality range for aquatic ecosystems (5 µgl−1) over the entire sampling period, may have been related to point source sewage pollution in the upper catchment. The PILD showed poor water quality conditions during the months of September and October during the dam’s destratification (lake overturn).
Assessing the Effects of Land Use on Surface Water Quality in the Lower uMfolozi Floodplain System, South Africa
(International Journal of Environmental Research and Public Health, 2021-01-11) Chirima, George; Dlamini, Mandla; Jovanovic, Nebo; Adam, Elhadi
This study investigated the impacts of cultivation on water and soil quality in the lower uMfolozi floodplain system in KwaZulu-Natal province, South Africa. We did this by assessing seasonal variations in purposefully selected water and soil properties in these two land-use systems. The observed values were statistically analysed by performing Student’s paired t-tests to determine seasonal trends in these variables. Results revealed significant seasonal differences in chloride and sodium concentrations and electrical conductivity (EC) and the sodium adsorption ratio (SAR) with cultivated sites exhibiting higher values. Most of the analyzed chemical parameters were within acceptable limits specified by the South African agricultural-water-quality (SAWQ) water quality guidelines for irrigation except for sodium adsorption ratio (SAR), chloride, sodium and EC. EC, pH and nitrate content which were higher than the specified SAWQ limits in cultivated sites. Quantities of glyphosate, ametryn and imidacloprid could not be measured because they were below detectable limits. The study concludes that most water quality parameters met SAWQ’s standards. These results argue for concerted efforts to systematically monitor water and soil quality characteristics in this environment to enhance sustainability by providing timely information for management purposes.
Assessing the effects of non-stationarity on reservoir yield estimations: A case study of the Southern Okavango integrated water development system in Botswana
(John Wiley and Sons Ltd, 2024) Mazvimavi, Dominic; Kapangaziwiri, Evison; Gumbo, Anesu Dion
Streamflow data used for water resources planning should ideally be stationary, and any non-stationary behaviour is taken into account. However, with limited time series data, the influence of non-stationarity is often hidden and can result in unreliable estimates. This paper examines the impact of non-stationarity on the Southern Okavango Integrated Water Development (SOIWD) project that was carried out with streamflow collected between 1969 and 1989 against an extended time series from 1990 to 2019. To achieve this, (a) the statistics of these inflows and (b) the reliability of satisfying water demands from the proposed reservoirs were tested based on the two periods (1969–1989 and 1990–2019). The results show that average monthly flows for July, August and September significantly change when peak outflows from the delta occur. Given the expected variability of the flow regime, an uncertainty approach utilising flow perturbation from ±5% to ±90% was also used to investigate the system's response to changes in the driving flow conditions. The increasing availability of flow data from 1990 to 2019 has shown that the SOIWD system would not have satisfied the water demand as it would not be operationally viable. This confirms the importance of accounting for non-stationarity in reservoir yield estimation and reemphasises its importance in hydrological studies
Assessing the relationship between youth capabilities and food security: A case study of a rainwater harvesting project in South Africa
(AJOL, 2015) Germaine, Owen; Goldin, Jacqueline
Rainwater harvesting presents a viable option for securing water availability in order to increase food production. The study focuses on rural youth in Luphisi and Dwaleni villages in the Mpumalanga Province and considers the relationship between youth capabilities and food security. The study uses qualitative data collected from focus group discussions and quantitative data from a baseline survey within the context of an integrated rainwater harvesting project. The indicators tapped into attributes related to trust, social cohesion, inclusion and sociability, and examined these within the context of the ‘capability approach’, to consider whether and in what ways these attributes can be linked to food security. Results show that youth have high levels of certain capabilities such as trust, social cohesion and inclusion, co-operation, self-esteem, and meaning.
Assessing the role of water resources protection practice for sustainable water resources management: A review
(MDPI, 2022) Makanda, Koleka; Nzama, Stanley; Kanyerere, Thokozani
Water resource protection is central to sustainable water supply management for human wellbeing and for the ecological ecosystem to flourish. This review paper focuses on highlighting the role of groundwater and surface water protection practice to improve their sustainable utilization in South Africa. Using an integrative approach, this paper initially reflects on the history of water resources utilization, and it examines what is understood by the term “water resources protection”. This review paper then continues by providing an analysis of the current practice at global and local levels. The study found evidence of water resource utilization in the ancient times with limited challenges despite unavailability of regulation mechanisms. However, in recent times water resource availability challenges linked to water availability and water quality deterioration are evident globally despite having policies and regulation in place.
Assessing the surface material quality of unpaved rural roads to understand susceptibility to surface deterioration. A case study of four rural areas in KwaZulu-Natal, South Africa
(Elsevier, 2019) Nkomo, Lucky S'phumelele; Desai, Sumaiya Amod; Dube, Timothy
Road surface deterioration is one of the most common problems of unpaved road networks worldwide. It is areduction in the performance of a road due to a decline in road surface material quality. Accumulated damagefrom vehicles, environmental and physical effects may contribute to a decline in the surface material quality andhence deterioration on an unpaved road surface. This study assesses the surface material quality of unpaved ruralroads in four rural areas in the KwaZulu-Natal Province, South Africa in order to understand susceptibility tosurface deterioration. The study further establishes other possible factors such as slope gradient and rainfall, thatcould determine the surface material quality. Soil samples were collected from R3, R4, and R5 road classes infour rural areas which are: Emazabekweni, Dukuza, Mkhunya and Mhlwazini Area. Laboratory analyses wereconducted in order to determine the performance of the material as potential wearing course. Material per-formance was then determined using the Standard Methods of Testing Road Construction Materials (TMH1:1976) classification method. The results obtained imply that there is a need for better material selection duringthe construction of unpaved road networks. All road classes in Mkhunya, Emazabekweni and Mhlwazini areasexhibited grading coefficient (Gc) values less than 16 and some of the shrinkage product (Sp) values in excess of365, corresponding to a classification of Class D, A and B. These results indicate material that is susceptible toslippery conditions, easily erodible and prone to the formation of ravels and corrugations. Correlation analysisresults conducted to assess the individual relationship between measured rainfall and slope with field shrinkageproduct and grading coefficient values in each area indicated that variation in slope better explains shrinkageproduct values in each area with an R2of 0.62 when compared to rainfall producing a lower R2of 0.57. Forgrading coefficient, slope and rainfall produced similar R2of 0.65 and 0.67, respectively.
Assessing the variation of river channel reach inflows on transmission losses
(World Water Policy, 2022) Mazvimavi, Dominic; Mujere, Never; Masocha, Mhosisi; Makurira, Hodson
Arid and semi-arid regions are characterized by limited water availability throughout the year and highly variable streamflows. River channel transmission losses add another uncertainty to the complex flow regimes. However, the contribution of different factors influencing to transmission losses is poorly understood. In this work we determined whether variations in river channel transmission losses along five reaches of varying lengths could be related to reach inflows in Runde River catchment in Zimbabwe. We directly estimated transmission losses as the difference between reach inflow and outflow discharges. Using simple bivariate regression equations, channel transmission losses were modelled as response variables while reach inflows were the predictor variables. Our results indicate statistically significant positive relationships (p = .000, R2 > 0.05) between inflows and transmission losses for all minor, moderate, and major flow events. This simple approach can be applied in similar settings to understand the variations in transmission losses
Assessment of catchment scale groundwater-surface water interaction in a non-perennial river system, heuningnes catchment, South Africa
(Scientific African, 2023) Banda, Vincent Dzulani; Mengistu, Haile; Kanyerere, Thokozani
A significant proportion of the world's river networks are non-perennial rivers that are characterized by segments of dry, standing, and flowing water. However, the role of groundwater and the controlling elements governing the flow processes in these rivers is not widely documented. In this study, aquifer-river interaction was assessed using a combo of geological, hydrological, environmental stable isotope, and hydrochemical data in the Heuningnes catchment, South Africa. Results showed the depth to groundwater levels ranging from 3 to 10 m below ground level and aquifer transmissivity values of 0.17 to 1.74 m2/day. The analytical data indicated that Na-Cl type water dominates most groundwater and river water samples. Environmental stable isotope data of river samples in upstream areas showed depleted δ18O (-4.3 to -5.12 ‰) and δ2H (-22.9 to -19.3 ‰) signatures similar to the groundwater data, indicating a continuous influx of groundwater into the river water. Conversely, high evaporative enrichment of δ18O (1.13 to 7.08 ‰) and δ2H (38.8 to 7.5 ‰) were evident in downstream river samples. It is evident from the local geological structures that the fault in the north-eastern part of the study area passing Boskloof most likely acts as a conduit to groundwater flow in the NE-SW direction thereby supplying water to upstream river flow, while the Bredasdorpberge fault likely impedes groundwater flow resulting in hydraulic discontinuity between upstream and downstream areas. Relatively low conductive formation coupled with an average hydraulic gradient of 8.4 × 10−4 suggests a slow flow rate resulting in less flushing and high salinization of groundwater in downstream areas. The results underscore the significance of using various data sets in understanding groundwater-river interaction thereby providing a relevant water management platform for managing non-perennial river systems in water-stressed regions. Overall, the study provides important insights into the need for maintaining moderately high groundwater levels in shallow and local groundwater systems for sustaining the ecological integrity of non-perennial rivers.