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Environmental concentrations, characteristics and risk assessment of microplastics in the Olifants and Breede Catchments, Estuaries and Coastal Areas, Western Cape, South Afric

Thu, 01 Jan 2026 00:00:00 GMT

Title: Environmental concentrations, characteristics and risk assessment of microplastics in the Olifants and Breede Catchments, Estuaries and Coastal Areas, Western Cape, South Afric Authors: Esau, Aldean Carmen Abstract: Microplastic (< 5 mm) contamination is increasingly being reported from South African aquatic environments but few studies have been done from catchment-to-coast. Thus, the aim of this study was to determine the concentrations, characteristics and risk assessment of microplastics in the Olifants and Breede River catchments, estuaries and coastal areas in the Western Cape, South Africa. Surface water and sediment were collected and analysed for microplastics in the wet and the dry season in relation to disturbances acting on these systems. Microplastics were extracted and identified using microscopy and Fourier-transform infrared spectroscopy (FTIR) analyses. Average microplastic concentrations ranged from 0.24 ± 0.01 particles/L to 0.26 ± 0.02 particles/L in water and 48.30 ± 3.95 particles/kg dry weight to 43.65 ± 2.71 particles/kg dry weight in sediment of the Olifants and Breede systems, respectively. Microplastics were mainly black/grey fibres, 500 – 1000 μm in size and polyethylene terephthalate was the dominant polymer recorded for both systems. Pollution load indices indicated that pollution was present (< 1) across the different regions and seasons of each system for water and sediment. Polymer risk indices in water ranged from low (7.50) to very high (1658.20) and low (4.00) to high (942.20) in the Olifants and Breede systems, respectively, while in sediment, indices ranged from low (6.60) to moderate (47.30) in the Olifants system and low (4.00) to moderate (57.70) in the Breede system. Spatially, in the Olifants system, pollution risk indices in water was categorised as dangerous in the catchment (3190.50), estuary (5748.60) and coast (6943.30) during the wet season, while moderate in sediment along the coast (198.50) during the dry season. In the Breede system, pollution risk indices in water was categorised as dangerous in the catchment (6790.5) during the wet season and along the coast during the wet (2746.40) and the dry season (3136.10), while high in sediment in the estuary (421.80) during the wet season. Seasonally, in the Olifants system, pollution risk indices in water was categorised as dangerous during the wet season (– 63 μm: 11864.3 & 250 μm: 9278.20) and very high during the dry season (63 μm: 1095.20 & 250 μm: 1102.01), while moderate in sediment during the wet (197.30) and the dry (251.30) season. In the Breede system, pollution risk indices in water was categorised as dangerous during the wet season (63 μm: 1223.30 & 250 μm: 9605.10) and the dry season (3273.20), while ranging from high to low in sediment during the wet (703.20) and the dry (104.40) season, respectively. The results from this study serves a baseline for future reaserch and to inform policy makers that govern the protection of these systems so they may be able to develop and implement the necessary mitigation measures to reduce contamination within these systems. The Olifants and Breede systems are ecological important systems. However, the results from the risk assessment indicates that the polymers that accumulate in these system during the wet season pose a threat to the overall health and functioning of these systems from catchment-to-coast. Thus, regular monitoring of these system are crucial. Description: Thesis (Master of Marine Science)--Cape Peninsula University of Technology, 2026

Physical and biological processes that control the distributions of carbonate chemistry across the ACC domains and the marginal ice zone in the Southern Atlantic sector of the Southern Ocean

Mon, 01 Jan 2024 00:00:00 GMT

Title: Physical and biological processes that control the distributions of carbonate chemistry across the ACC domains and the marginal ice zone in the Southern Atlantic sector of the Southern Ocean Authors: Jabulani, Christopher Nkosinathi Abstract: The Southern Ocean plays an important role in global climate systems as a major sink of atmospheric carbon dioxide through the biological and physical pumps that are responsible for absorbing atmospheric carbon dioxide, storing heat, storing freshwater (sea ice) and transporting carbon to the deep ocean. The Southern Ocean is the least sampled ocean region, due to its remote location, cold, windy, and rough weather conditions. The number of available in-situ carbonate chemistry observations are seasonally biased because they are largely done in the summer season, and few have been reported for the winter to spring period. This has hampered our understanding of the full seasonal biogeochemical cycle of carbonate chemistry in this important ocean region. Furthermore, it is not well understood how models respond to these gaps due to the lack of in-situ observations. To close these gaps and improve our understanding of the spatial and temporal variability of the carbonate system in the Southern Ocean, seawater samples for carbonate chemistry (Dissolved Inorganic Carbons and Total Alkalinity) and macronutrients were collected along the GEOTRACES transect (GT) and the marginal ice zone during the Southern oCean seAsonaL Experiment (SCALE) cruise in October 2019. In this thesis, the distributions of the carbonate system variables and the associated physical and biological processes that control its distributions across the different Antarctic Circumpolar Current domains (Subtropical, Subantarctic and Antarctic domains) are described and presented. The dataset collected was grouped into two transects, namely the open ocean GEOTRACES transect and the Marginal Ice Zones and used to characterise the distribution of dissolved inorganic carbon and total alkalinity in the south Atlantic sector of the Southern Ocean. The water column distributions of dissolved inorganic carbon and TA concentrations, along both transects, showed low concentrations at the surface waters that increased with depth. The northward decrease in DIC in the AAIW indicates the northward transport of anthropogenic CO2 captured in the Southern Ocean. The Subtropical domain and the Subantarctic domain had the lowest Dissolved Inorganic Carbon concentration with slightly higher Total Alkalinity concentrations at the surface compared to the Antarctic domain. The intermediate waters (Subtropical domain: 748 m to 1251 m; Subantarctic domain: 6 m to 748 m) had slightly higher Dissolved Inorganic Carbon concentrations and lower Total Alkalinity concentrations while the deeper waters had high Dissolved Inorganic Carbon and Total Alkalinity. The main processes that controlled the carbonate chemistry across these domains were different. The dissolution of CaCO3 minerals dominated the Antarctic and Subantarctic domains whereas the processes of CO2 release by the ocean, photosynthesis and to a lesser extent, the dissolution of CaCO3 dominated the Subtropical domain. Description: Thesis (Master of Marine Science)--Cape Peninsula University of Technology, 2024

Ecosystem service evaluation of the Zandvlei Estuary Nature Reserve, Cape Town, South Africa

Mon, 01 Jan 2024 00:00:00 GMT

Title: Ecosystem service evaluation of the Zandvlei Estuary Nature Reserve, Cape Town, South Africa Authors: Little, Nicole Monique Abstract: Ecosystem services, encompassing both tangible and intangible benefits derived from natural processes, play a vital role in enhancing human well-being and environmental sustainability. Estuaries and wetlands, particularly those found in peri-urban areas, offer a unique blend of ecological services and are of paramount importance to our society. However, these crucial ecosystems face escalating threats due to urban expansion, resource exploitation, and pollution, underscoring the urgency for innovative management strategies. Ecosystem-based management (EBM) presents a holistic approach that integrates both ecological and human needs into decision-making processes. Valuing ecosystem services is pivotal in guiding sustainable resource management and making informed policy decisions. Traditional valuation methods have predominantly relied on quantifying economic values, often neglecting the less tangible social and environmental dimensions of ecosystem services. This partial assessment fails to capture the comprehensive worth of ecosystems and their services, leaving a gap in our understanding of their true value to society. This study investigated aspects of three ecosystem services of the Zandvlei Estuary Nature Reserve (ZENR): 1) Recreational Value: A comprehensive questionnaire survey, employing a travel-cost methodology, reveals that ZENR users contribute significantly to the local economy through expenditures on travel and recreational equipment and fees. Moreover, the study sheds light on the pivotal role that ZENR plays in enhancing the social and cultural well-being of its users, with a notable 95% of respondents acknowledging its value. Additionally, over half (56%) of respondents highlight the importance of ZENR to their livelihoods. Litter management emerges as a prominent concern, with 26% of respondents expressing apprehension. The user base varies, encompassing a wide range of activities from walkers and bird watchers to on-water enthusiasts like fishers, rowers, and canoeists. Notably, walking stands as the most popular activity, while picnicking ranks the least frequented. Walkers and picnickers tend to spend less, whereas yachters and fishers are the highest spenders. A majority of respondents reside in neighbouring areas such as Marina da Gama, Muizenberg, and Lakeside, but ZENR draws visitors from across the Cape Town metropole. 2) Water Purification Service: The study delves into the regulatory ecosystem service of water purification which occurs via the natural filtration processes within the Zandvlei Estuary, where pollutants and excess nutrients are absorbed and broken down by aquatic vegetation, sediments, and microbial communities, thereby enhancing water quality and supporting the overall health of the ecosystem. This analysis was performed utilizing data from monthly water quality tests conducted by the City of Cape Town over a decade (2009 to 2018). The analysis uncovers spatial and seasonal trends, shedding light on the estuary's vital role in reducing concentrations of pollutants such as nitrogen, phosphorus, and E. coli, particularly in the aftermath of events like sewage spills. However, some chemical and biological pollutants have shown an increasing trend over the years, potentially jeopardizing the estuary's health and its capacity to provide safe recreational waters. The study pinpoints the river inlets, especially the Sand River Canal, as critical areas of concern due to reduced dilution capacity, canalization, and exposure to pollutants from industrial, agricultural, and residential sources. Stormwater drains further exacerbate the contamination issue, emphasizing the need for the rehabilitation and protection of these inlets. 3) Aesthetic Value: An assessment of property values in six areas surrounding ZENR provides insights into the cultural service of the estuary's aesthetic value using hedonic pricing methodology and general regression analyses. The findings highlight the positive influence of ZENR on the surrounding property market, contributing significantly to its economic value. The hedonic pricing approach indicates a surplus of up to R174 million generated by ZENR between 2014 and 2018 in the residential property market. General regression analyses reveal a positive correlation between house prices and proximity to the estuary, extending beyond a 200-meter range in three of the six surrounding suburbs. However, these analyses are influenced by other factors such as proximity to the beach, railway lines, or roads. It is essential to recognize that the value of an ecosystem extends beyond its monetary contributions. Ecosystem services are interconnected, and a decline in one service can have cascading effects on others. To avoid double counting, it is imperative to distinguish final ecosystem service values from support services. Effective management is pivotal in maintaining the supply of ecosystem services, and decision-makers rely on research-based information and stakeholder engagement to make informed choices. In conclusion, this study highlights the need for comprehensive valuations of ecosystem contributions to human well-being, moving beyond conventional economic metrics and embracing holistic approaches like the System of Environmental-Economic Accounting. The ZENR case study illustrates the multi-layered benefits provided by estuarine ecosystems and the importance of sustainable management to ensure their continued provision of vital services to society. Description: Thesis (Master of Marine Science)--Cape Peninsula University of Technology, 2024

Behavioural responses of Cape fur seals (Arctocephalus pusillus) to swim-with-seal tourism activities in the Robberg Marine Protected Area in South Africa

Mon, 01 Jan 2024 00:00:00 GMT

Title: Behavioural responses of Cape fur seals (Arctocephalus pusillus) to swim-with-seal tourism activities in the Robberg Marine Protected Area in South Africa Authors: Basson, Rodashia Abstract: Marine mammal tourism is growing, and experiences that provide close-up encounters are becoming more popular. One of such activity is the swim-with-seal (SWS) activity, which occurs within two marine protected areas (MPAs) in the Western Cape Province of South Africa, namely at the Robberg MPA in Plettenberg Bay and at sites in the Table Mountain National Park MPA. Information regarding SWS activities and their impacts on Cape fur seal Arctocephalus pusillus pusillus colonies is limited. This study aimed to assess the impacts of swim-with-seal (SWS) tourism on the behaviour of seals at the seal colony in the Robberg MPA. This was conducted through a modified Before-After-Control-Impact (BACI) behavioural study designed for simultaneous observations of Impact and Control areas (site factor) Before, During and After SWS activities (phase factor). Observations were carried out from an elevation at distances from the experimental sites that precluded observer impacts, with sequential photography of the colony providing the basis for enumerating seals in different behavioural categories and comparing these between sites and between phases, as well as interactive effects of site and phase. Behavioural categories included “primary” behavioural categories (lying down, sitting, moving) and “secondary” behavioural categories (grooming, nourishing, interacting, alertness) that seals within one of the primary categories could be secondarily engaged with. Between November 2020 and October 2021, 54 SWS trips were observed. Concerning the primary behaviour categories, seals in the colony were mostly observed to be lying down (74%) in relation to sitting (23%) or moving in the colony (3%). While most seals were at rest during the tourist activity, it was clear that SWS activity and associated boat approaches brought about certain behavioural responses in the colony, as shown by changes in some behavioural categories. However, even where there were significant differences in behaviour between sites and/or phases that could be attributed to tourist activity, it was only a small proportion of animals in the study area that were affected. For example, whereas the proportion of animals sitting relative to the numbers lying down in the Impact site increased as SWS activities commenced, the numbers of animals showing a switch in this behavioural posture were only approximately 2% of the numbers of animals at the site, on average. Furthermore, although the proportion of animals in the Impact site that showed alert behaviour (a secondary behavioural category) in response to activity increased statistically compared with the earlier phases or versus the Control Site, it still represented only about half a percent of the animals at the Impact Site, on average. No extreme reactions by seals, such as stampedes, were observed throughout the study. Modelled responses of seals to the distances of the boat or swimmers to the colony, indicate that some responses (certain behavioural categories) decline with distance to the colony, suggesting that the seals respond mostly to the activity when they first become aware of the tourist presence but decline as they become used to it. Overall, the reactions of seals point to the habituation of the seals to the tourist activity. The results also attest to the efficacy of the modus operandi adopted by the tourist operator during the study period, which is informed by legislation and a voluntary Code of Conduct, with the aims of avoiding disturbance to the colony and ensuring human safety. Description: Thesis (Master of Marine Science)--Cape Peninsula University of Technology, 2024