Browsing by Author "Meadows, Michael Edward"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
- ItemOpen AccessAn Assessment of Heavy Metal Concentrations in Surface Sediments from the Knysna Estuary(2022) Armitage, Michael Philip Anthony; Meadows, Michael EdwardThis research presents an analysis of surficial sediment samples in respect of total heavy metal concentrations, sediment grain size, and total organic carbon within 36 surface sediment samples from the Ashmead Channel in the Knysna Estuary. 15 surface sediment samples were also analysed from Chongming Island in the Yangtze Estuary of the People's Republic of China, and the results compared between the two systems, in addition to other South African and global estuaries with similar characteristics to Knysna. Metals analysed were Cr, Cd, Cu, Zn, Hg, As, and Al. Statistical analyses, including Pearson's Product–Moment correlation, enrichment factor analysis, and the assessment of heavy metal contamination were conducted between the variables to determine patterns of difference and similarity between the sites, as well as to determine the degree of contamination in the Knysna sediments. Results from Knysna were also compared to those from previous studies in the area. This study found that the Knysna sediments are not highly contaminated with heavy metals in relation to South African Revised National Action List levels, however, the degree of enrichment in the sediment has increased by a substantial margin over the past 20 years. Mean metal concentrations in Knysna are Cr: 7.37mg/kg, Cd: 1mg/kg, Cu: 6.43mg/kg, Pb: 7.43mg/kg, Zn: 57.4mg/kg, Hg:< 1 mg/kg, As: < 1mg/kg, and Al: 2138mg/kg. Mean enrichment factor classes of the concerning metals are Cr: 1.69, Zn: 3.89, Pb: 2.56, and Cu: 2.33. Upon comparison with sediments from Chongming Island, it was noted that the sediment in the Yangtze has much higher background heavy metal concentrations than Knysna. The study also found that the degree of enrichment in relation to background concentrations for the sediment sites in Knysna was surprisingly similar to that seen in the Yangtze estuary for select metals, despite the Yangtze being a highly polluted system. It must be noted that the results from the Ashmead Channel likely indicate greater contamination than what is present in the entire Knysna Estuary, due to the close proximity of a number of contaminant sources, as well as flow restrictions. The Yangtze also experiences much higher sediment accumulation rates, therefore reducing the degree of enrichment. This study, therefore, shows the value of frequent contaminant monitoring in the Knysna Estuary and recommends that additional work be conducted in the system to develop the picture of heavy metal contamination, in addition to other pollutant enrichment, in the system. Furthermore, this study demonstrates that the comparison of different estuarine environments can be a useful tool for understanding the severity of heavy metal contamination in these systems.
- ItemOpen AccessLand Use Change in The Knysna River Catchment and Its Impacts on the Geomorphological Characteristics of the Estuary between 1984 and 2019(2022) Taylor, Salwah; Meadows, Michael EdwardThe Knysna catchment and estuary are recognized in South Africa for their conservation significance as a sanctuary for marine species and biodiversity alike. The economy of the area which is dependent on tourism of the Knysna Estuary and catchment. The services obtained from the ecosystem include integral biodiversity value and is of significant importance for residents and tourists. Land use and land use cover dynamics remain some of the most crucial and obvious changes that has happened in the Knysna Estuary and catchment. Such changes severely affect ecosystems health, catchment areas, estuaries and the degradation of nature reserves. A ‘cloud-based platform for scientific analysis and visualization of geospatial datasets.' (Liu et al., 2020) method namely Google Earth Engine (GEE) is applied utilizing multi-temporal satellite imagery and Sentinel as interpretation to understand land use change over 35 years. A timeseries associated with land use changes and biodiversity loss were considered between the years 1984 and 2019. Additionally, Normalized Difference Vegetation Index (NDVI) and Supervised classification were performed using GEE software and Arc Geographical information systems (GIS) to identify land cover dynamics. The images are classified into three major land use classes, waterbodies, urban areas and vegetation. Vegetation is further classified into various classes namely fynbos, thicket, plantation forestry, salt marsh and agriculture. An accuracy assessment together with ground truthing, were conducted to verify and assess the overall classification accuracy of the results. The results indicated that over the study period urban growth and cultivated land makes up the most common land use category to have impacted the Knysna Estuary. Urban areas have increased significantly in reaction to the rapid increase in population ranging from 2.5% - 2.8% during the years 1984-1992, which reached to 2.9% - 4.1% during the years 1993-2007, and finally augmented to 4.3% to 6.3% during the years 2008-2019. The major reason behind the altering in the land use and geomorphology based on the research of the Knysna Estuary is human activities that have led to key determinantal impacts on surface runoff and land degradation. Overall, the noticeable changes in surface runoff and land degradation are strongly related to land use/land cover changes brought about by human impacts.
- ItemOpen AccessLate Holocene environmental and climate dynamics along the southern Cape coast of South Africa: high resolution multi-proxy records from the wilderness embayment(2021) du Plessis, Nadia; Meadows, Michael EdwardIt is well documented that the South African palaeoenvironmental record is relatively limited in terms of both quantity and quality. This is mainly due to the region's highly seasonal rainfall regimes and generally arid to semi-arid environments which are not conducive to the preservation of sedimentary sequences and associated proxy records. The climate along the southern Cape coast is influenced by both tropical and temperate climate systems, and the region hosts highly diverse vegetation including fynbos and thicket elements and includes the Knysna Afrotemperate Region – the most extensive forest complex in southern Africa. The mechanisms controlling these tropical and temperate systems have responded to changing global boundary conditions and these changes have significantly impacted the regional vegetation mosaic. This ephemeral nature of the region's climate and vegetation suggests it is particularly sensitive to climate change, making it an ideal area to evaluate changes in these systems and how they interact over time. For this study, four sets of records were produced from three wetlands along the southern Cape coast. The Eilandvlei palynological and microcharcoal records span the last ~3000 years with the pollen and microcharcoal records from adjacent Bo Langvlei covering the last ~1300 years. The most outstanding feature in these records are the time periods covering the Medieval Climate Anomaly (MCA; c. AD 950 – 1250) and the Little Ice Age (LIA; c. AD 1300 – 1850). The evidence indicates that conditions in the region during the MCA chronozone were relatively dry and perhaps slightly cooler than present. The most durable phase of forest expansion, and likely more humid conditions, occurred during the transition between the MCA and core cooling of the LIA with the LIA clearly identified as a period of cool, dry conditions between c. AD 1600 to c. AD 1850. In addition, the Eilandvlei pollen record demonstrates the effects of external physiographic dynamics on pollen accumulation and deposition within the lake basin. A complementary set of geochemical and sedimentological records have been generated for Bo Langvlei incorporating the last ~4200 years. These records suggest that the late Holocene evolutionary history of Bo Langvlei comprised of three phases: a marine/lagoonal phase extending until c. 1270 cal yr BP, a short transitional phase between c. 1270 and 1200 cal yr BP, and IV the more recent lacustrine phase. A ~650 year pollen and microcharcoal record have been obtained from nearby Vankervelsvlei. Although discontinuous, this is the first palynological record from this unique waterbody covering this period. In terms of climate, the mechanisms driving the observed changes in the records taken as a whole appear to relate to changes in temperature and dynamics in the influence of tropical systems, perhaps transmitted at least in part via the Agulhas Current and the development of localised precipitation systems. The findings further reinforce the proposed importance of summer rainfall in regulating moisture availability along the south coast of South Africa. The records also highlight the significant impacts of fluctuating sea levels and changes in dune morphology in shaping the embayment, and more recently, the effects of accelerated anthropogenic activities in the area
- ItemOpen AccessNatural and anthropogenic influences on recent sediment characteristics in the Knysna Estuary, South Africa and Yangtze River Estuary, China(2022) Dubazana, Yakhuluntu; Meadows, Michael EdwardEstuaries and tidal wetlands situated at the nexus of fluvial, marine and terrestrial conditions is highly dynamic and complex system. Despite strong hydrodynamics, estuarine tidal flats are preferential sites for the accumulation of fine-grained sediment, organic matter and metals from various marine and terrestrial sources including those of natural and anthropogenic origin. The coastal zone performs many key ecosystem service functions for sustainable development, thus making them valuable ecological entities. In this study, the Chongming Island tidal flats of the Yangtze River Estuary in China and the Knysna Estuary in South Africa are selected as case studies. The objective of this study is to investigate the recent distribution and abundance of sediment characteristics, organic matter, and modern major and trace elements in sediments through space and time. Physically speaking, the two estuaries are very different. Three sediment cores taken from the Knysna Estuary and two sediment cores taken from the Chongming Island of the Yangtze River Estuary in 2019 were analysed to document grain size distribution using Malvern Mastersizer, geochemical signatures including major elements (Al, Fe, K, Ti, and Ca) and trace elements (Ni, Cr, Mn, Sr, Rb, Cu, Pb, Zn and Zr) via XRF, loss-on-ignition and magnetic susceptibility. The cores were divided into three zones based on the approximated time periods. Our results show that the introduction of European land-use and human impacts in the Knysna Estuary resulted in an increase in SARs to be at least three times higher than pre-European SAR values. The widespread deforestation coupled with intense farming exerted significant controls on the quantity of sediment transported downstream and increased erosion within the Knysna Estuary. Agriculture intensification increased the terrigenous input of Al, K, Ca, Ti and Cu levels. In Unit I (ca. 1960s-Present), the heavy metals Fe, Mn, Pb, Zn and Cu escalated in concentration indicating anthropogenic input due to urbanization and infrastructure development in the Knysna Estuary. In Chongming Island, Mg, Al, K, Ti, Mn, Fe, Cu, Zn, Rb, Pb and magnetic susceptibility values in the cores all show increasing trends relative to the pre-1950s and post 2002 units. This is consistent with the significantly increasing trends in the total energy consumption for the industrial development in China and the heavy metal input from the Yangtze River. Post 2002 (Unit I), the same elements exhibited a decreasing trend and their mean concentrations (mg kg-1) is the lowest of all the three units. This is attributed to the improvement in environmental protections and regulatory control of atmospheric pollution and a shift in the consumption of energy from the industrial period in the 1950s to 2000s. Coastal zone research tend to view estuaries and tidal wetlands as an independent and isolated system from any global estuary. A benchmarking case study would provide the opportunity to examine coherence, differences and similarity of coastal behavior across two different biographic regions.
- ItemOpen AccessThe diatom record: Reconstructing historically recent environmental change in the Knysna estuary(2022) Antonopoulos, Helen Grace; Meadows, Michael Edward; Kirsten, Kelly LEstuaries are highly productive systems responsible for many vital ecosystem goods and services. Therefore, it is not surprising that the diversity and abundance of exploitable estuarine resources have attracted human settlers for centuries. Increased anthropogenic pressures have placed much stress on estuarine and coastal ecosystems. This is the case of the Knysna Estuary, which is South Africa's highestrated estuary in terms of biodiversity and conservation importance. This study represents the first highresolution diatom record from the Knysna Estuary encompassing the last ∼680 years. Diatom analysis was employed to reconstruct salinity, nutrients, and saprobity variables in addition to inferring community structure and trophic status over time by creating an age-depth model based on a combination of ²¹⁰Pb and radiocarbon dates. The record is divided into three distinctive phases, namely the Pre-Colonial (∼610 to ∼200 cal BP), Colonial (∼200 cal BP to ∼1900 CE), and Anthropogenically Impacted Lagoon Phase (∼1900 CE to Present). These phases correspond with the Little Ice Age (LIA), the arrival of colonialists, and anthropogenic impacts linked to rapid population growth and land use change. More specifically, the dominance of marine species illustrate that the first phase of the LIA is associated with drier conditions, whereas a growing dilute and eutrophic assemblage reveals a wetter second phase of the LIA coinciding with the arrival of colonialists in the 1700s. Consequently, it is challenging to disentangle natural climate change with the effects of deforestation and agriculture during the Colonial Phase. A shift towards an increasingly fresh, hypertrophic, and polysaprobic diatom assemblage is indicative of the intensification of agricultural practices in the catchment from ∼1900 CE to present, stormwater inflow, the inefficiency of the Knysna Waste Water Treatment Works (WWTW), and sewage entering the estuary via streams during the final phase of the estuary's development. This high-resolution record is of vital importance, as it is one of a few palaeoestuarine studies in the Southern Hemisphere to illuminate the effects of natural climate change and human-induced impacts on an estuarine system. Despite the limitations, this study illustrates that diatoms are a useful tool for tracking environmental change in estuaries.