Masters Degrees (Earth Sciences)
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- ItemCharacterising southern ocean phytoplankton community variability and environmental coupling: zonal, sectoral, and seasonal perspectives(Stellenbosch : Stellenbosch University, 2024-03) Quinlan, Liam Bodley; Fietz, Susanne; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.ENGLISH ABSTRACT: Marine phytoplankton communities vary in functional groups prevalence across the Southern Ocean. The variability of phytoplankton groups, some drivers of important biogeochemical processes, is intricately linked to their adaptation to specific environmental conditions. Community group composition will thus vary as the surface water environment does. In the southern Ocean, different latitudes (ocean zones), longitudes (ocean sectors), and times of year (seasons) support distinct community profiles. In characterising the relationships that exist between specific phytoplankton groups and major environmental drivers, we can contribute to the baseline understanding of the Southern Ocean ecosystem, with implications for the biogeochemical processes its phytoplankton support and the trophic food web these primary producers underpin. Phytoplankton community structure was determined by chemotaxonomic pigment reconstruction (CHEMTAX) for historically under-surveyed austral spring and winter voyages to the Indian and Atlantic Ocean sectors of the Southern Ocean. Complimented by ship-board environmental monitoring of the physical sea surface environment (temperature, salinity, and light) and macronutrient parameters (nitrate, phosphate, silicate), the relationships between phytoplankton groups and major environmental drivers were explored using Canonical Correlation Analysis (CCA). From this analysis we determined group-environment associations that promote similar community structures three broad zonal regions: northernmost temperate, transitional sub-Antarctic, and southernmost polar. Phytoplankton communities across these regions appear to become increasingly dominated by fewer groups placing greater importance on key functional groups further south. Some group-environments associations appear independent of ocean zone, sector, or season, emphasizing the coupling between major groups components of Southern Ocean phytoplankton communities and their environment. The consistency of positive coupling relationships falls within two classifications: physical environment associated groups (phaeocystis cryptophytes, chlorophytes, coccolithophores, cyanobacteria, and pelagophytes) and nutrient associated groups (diatoms, dinoflagellates, and prasinophytes). These relationships suggest that changes to the Southern Ocean physical environment and nutrient regimes will drive group-specific community restructuring to either favor or hinder some groups over others, with knock-on consequences for the biogeochemical processes those groups drive and the trophic chains they support.
- ItemDeveloping a cost-effective method to characterise regional aquifer vulnerability in the Cape Flats(Stellenbosch : Stellenbosch University, 2024-03) Hunink, Brynn Matthew; Chow, Reynold; Woehling, Thomas; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.ENGLISH ABSTRACT: Aquifer vulnerability assessments are important tools in avoiding aquifer deterioration as they indicate how likely an aquifer is to be adversely affected by land-based, anthropogenic activities.” The aim of this study is to develop a simple, cost-effective method to characterise aquifer vulnerability by combining and modifying existing methods. These methods are then applied in the same study area to validate the cost-effective method. The Cape Flats Aquifer (CFA), located in the Western Cape, South Africa, is used as a case study due to concerns over the deterioration of groundwater quality to the well-utilised aquifer during the past decade. Assessment of aquifer vulnerability in the CFA is achieved through a combination of DRASTIC-L aquifer vulnerability mapping and wellhead protection area (WPA) delineation. DRASTIC-L is used to identify areas that are most vulnerable to contamination. Steady-state wellhead protection areas are delineated using finite difference numerical modelling (MODFLOW) and reverse particle tracking (MODPATH) to determine the capture zones for major abstraction wells. However, the complex, expensive, and time-consuming nature of numerical modelling highlights the need for simplified, cost-effective methods that can be applied across South Africa. Inherent limitations and redundancies with the DRASTIC-L method that were identified by previous studies and within this study resulted in the development of the modified DRASTL method. Additionally, a new method for cost-effective capture zone delineation using a combination of GIS and analytical equations is evaluated. The results of DRASTL and the newly developed method for wellhead protection area delineation are combined to cost-effectively characterise aquifer vulnerability in the CFA, which is referred to as the DRASTL-WPA method. Results from DRASTIC-L indicate that the CFA is very vulnerable. The DRASTL method shows a similar spatial trend to DRASTIC-L; however, DRASTL is associated with a higher average vulnerability but a lower tendency for very low or very high vulnerabilities. It can be seen that a very similar output can be produced with fewer input parameters; however, validation is required to evaluate the accuracy of the methods for the study area. The cost-effective WPA delineation method yielded an intersection of greater than 70% with the results from MODPATH given that an abstraction well is ~8 km away from a bedrock outcrop, and ~12 km away from the combined effects of bedrock outcrops and river boundaries. This is likely due to the inability of GIS software to simulate complex hydrogeological boundary conditions, as well as limiting assumptions of homogeneity and isotropy. Additionally, one can expect an average 3.7 times overprediction of the capture zone size. Several capture zones in the CFA correspond with the highest aquifer vulnerability highlighted by the results of DRASTIC-L and DRASTL. Thus, it is suggested that land use practices are monitored or restricted within these capture zones. Additionally, the capture zones delineated by the numerical model or DRASTL-WPA can be used to define areas where in-situ remediation or beneficial management practices should be implemented. Moreover, the numerical model can help with groundwater management planning in the CFA to ensure the sustainable use of groundwater resources.
- ItemCharacterisation of regional strains in the western Saldania Belt and implications for the structural evolution of Pan-African Rocks in the Western Cape, South Africa(Stellenbosch : Stellenbosch University, 2024-03) Rheeder, Christie George; Kisters, Alexander; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.ENGLISH ABSTRACT: The western Saldania Belt records the closure of the Adamastor Ocean and the amalgamation of southwest Gondwana during the late Neoproterozoic and early Phanerozoic. Still, uncertainties regarding its geodynamic setting and tectonic evolution remain. The lack of outcrop and deceptive monotony of the belt added to the uncertainty about the Saldania Belt and has seen the belt linked to the well-understood northern Pan-African belts. Structural mapping included numerous type localities, made up of widespread surface mapping and 3D exposures in quarries throughout the region, together with historical data, which formed an integrated regional geodatabase to reveal the juxtaposition of structural domains characterised by distinct fabric development and kinematics. Two structurally overlying domains, namely an upper and a lower domain, form the main regions within the study area. The rocks in the upper domain exhibit transpressional strain partitioning into (1) broad regions of north to northwesterly-trending folds (F2) indicating horizontal, mainly coaxial, east-northeast to west-southwest-directed shortening at high angles to the continental margin, and (2) margin-parallel, non-coaxial deformation along the sinistral strike-slip Colenso Fault Zone (ca. 555 and 520 Ma). Non-coaxial strain was further promoted by strain localisation into synkinematic plutons of the Cape Granite Suite. Structures within the belt record Pan-African strains and signify sinistral transpression dominated by strike-slip motion during southeast-directed subduction and convergence at shallow angles to the continental margin (< 20°). In contrast, lower domain rocks present a pervasively transposed, mélange-like sequence that documents episodes of vertical, coaxial shortening alternating with non-coaxial top-to-the-west and -northwest thrusting. The coaxial shortening strains are linked to the thickening and gravitational loading of the succession in response to thrusting and tectonic underplating. In contrast, non-coaxial strains signify episodes of seismic slip during underthrusting. The distinct differences in the fabrics observed in the contrasting domains represent a deformed fore- arc region, made-up of a deeper-level accretionary prism (lower domain), overlain by a folded fore- arc basin fil (upper domain). The transfer of lower-domain phyllites, utilising thrusts, into the overlying fore-arc sequence is indicated by regional-scale klippen structures. The proposed fore-arc setting of the Saldania Belt suggests the subduction of the Adamastor Ocean beneath the leading edge of the Kalahari Craton, challenging pre-existing stratigraphic and structural correlations.
- ItemEvaluating sources and environmental risk of pesticide pollution in Western Cape rivers(Stellenbosch : Stellenbosch University, 2023-12) Davies, Emma Jane; Chow, Reynold; Stamm, Christian; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.ENGLISH ABSTRACT: Agriculture is key to South Africa’s economy which has led to the country becoming a leading pesticide user in Sub-Saharan Africa. The Western Cape is a dominant agricultural region in South Africa, making it particularly vulnerable to pesticide pollution. After application, pesticides can be transported away from the designated site, potentially causing adverse health effects to non-target organisms. Therefore, the risk of pesticide pollution must be better understood. This research deployed passive samplers in rivers for two-week intervals every month from February 2022 - March 2023 in the agricultural catchments Grabouw, Hex River Valley, and Piketberg. This expands on a previous campaign from 2017-2019. 44 pesticides were measured using Liquid Chromatography Mass Spectrometry. The original aspects of this study include the expansion of the sampling list to include the fungicide dimethomorph and a suite of drugs. 22 (out of 44) pesticides and seven (out of 20) drugs were detected above the limit of quantification. Piketberg had high drug concentrations and detection frequencies which correlated with pesticide concentrations, whereas Grabouw and Hex River Valley did not. This suggests that pesticide pollution in Piketberg is likely sourced from both wastewater treatment plants and agriculture, whereas the absence of drugs in Grabouw and Hex River Valley suggests that pesticide contamination is more likely sourced from agriculture. This is particularly true for terbuthylazine and carbendazim because their concentrations correlated with cumulative drug concentrations (R²=0.47 and 0.77, respectively). Five pesticides were detected in control samples deployed in Jonkershoek Nature Reserve. While detections could be from neighbouring agricultural catchments via atmospheric transport, they also indicate non-agricultural sources of herbicides (e.g., atrazine and terbuthylazine from trail maintenance or invasive plant control). A few compounds typically contributed to majority of the detected concentrations, specifically, imidacloprid (54%) and dimethomorph (22%) in Hex River Valley, imidacloprid (46%) and chlorantraniliprole (38%) in Grabouw and imidacloprid (22%) and terbuthylazine (27%) in Piketberg. The newly measured fungicide, dimethomorph, had high concentrations up to 80 ng/L and detection frequencies in Hex River Valley (96%) and Piketberg (25%). Pesticides with high detection frequencies were not applied year-round but have high Groundwater Ubiquity Scores (GUS), suggesting a high leaching potential into groundwater. Environmental risk was evaluated by comparing concentrations to European Environmental Quality Standards (EQS). Four compounds exceeded EQS values, namely the insecticides imidacloprid and chlorpyrifos, the herbicide terbuthylazine, and the fungicide spiroxamine. Exceedances for chlorpyrifos, spiroxamine, and terbuthylazine coincide with application events and rainfall. All compounds that exceeded in 2022/2023 (except for spiroxamine) also exceeded during the 2017-2019 campaign, indicating high persistence and continual exposure risk to aquatic life. Assessment of pesticide mixtures suggests that certain combinations (e.g., imidacloprid and chlorantraniliprole) can have increased toxicity effects on organisms, and almost occur year-round. Hydrological and concentration patterns suggest that increased detections are mainly driven by rainfall in winter, pesticide application in summer and constant input from wastewater treatment plants or groundwater transport. Future research should prioritize sampling of groundwater, wastewater influent and effluent and soils to improve our understanding of pesticide transport pathways.
- ItemPlio-pleistocene palaeoenvironment of the south western continental shelf of South Africa: a foraminiferal perspective(Stellenbosch : Stellenbosch University, 2023-12) Walsh, Jared Tanner; Fietz, Susanne; Bergh, Eugene; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.ENGLISH ABSTRACT: The oceanography and ecology on the western continental shelf of South Africa (Orange Shelf) were highly influenced by the initiation and intensification of the Benguela Up- welling System (BUS) during the Plio-Pleistocene. On the Orange Shelf, literature sub- stantiating the e↵ect of the Plio-Pleistocene climate transition on foraminiferal assemblages is sparse. Foraminifera proved reliable as palaeo-proxies, and by assessing the response of foraminifera to the Plio-Pleistocene climate transition, a new perspective emerges for the changing oceanography in the BUS during this time. Furthermore, interpolations from the well-studied Namibian shelf and slope are often relied upon to interpret the palaeoceano- graphic conditions in the BUS, therefore supporting the need for new foraminifera-based palaeoceanographic studies from South Africa. Sediments and microfossil foraminifera from vibracores on the inner and outer Orange Shelf (200–400 meters below sea level) were anal- ysed using faunal analyses, foraminiferal biostratigraphy, and Strontium Isotope Stratigra- phy. The dating methods used provided conflicting results for various components. For example, in one unit, phosphorite was dated to 5.70–5.98 Ma, but Pleistocene indicator species Globorotalia truncatulinoides yielded ages approximately 2.58 Ma from its first ap- pearance. This study observed sediment reworking within Plio-Pleistocene sediment and, to a lesser extent, foraminiferal assemblages across the continental shelf. The cooling of sea surface temperatures (SST) in the BUS following the initiation of Northern Hemisphere glaciation during the Plio-Pleistocene transition was observed by the increase of temperate SST indicators Globigerina bulloides and Globoconella inflata, and the subpolar SST indi- cator Neogloboquadrina pachyderma. The influence of Agulhas leakage was prevalent on the outer shelf, and to a lesser extent on the inner shelf during the Pliocene, and was inferred from high abundances of Orbulina universa and trace abundances of Globorotalia menardii and Globigerinoides ruber. Regarding primary productivity, planktic indicators Globigerina bulloides and Neogloboquadrina pachyderma decline with the onset of the Pleistocene on both the inner and outer shelf. The inner shelf seemed to undergo less drastic changes in terms of primary productivity than the outer shelf during this time. This study suggests an external nutrient influx with increasing proximity to the coast, supporting the persistence of planktic primary productivity during the Pleistocene and the decline in upwelling intensity. Benthic primary productivity indicator Uvigerina peregrina increased during the Pleistocene. While upwelling intensity appears to decrease over the Plio-Pleistocene transition, the influx of nutrient-rich bottom water to benthic foraminifera on the outer shelf remained sufficient to support primary productivity. This study contributes to a greater understanding of the relationship between productivity, nutrient supply, and the upwelling intensification of BUS in the context of foraminifera assemblages on the Orange Shelf over the Plio-Pleistocene.