Browsing by Author "Kirsten, Kelly"

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    Holocene environmental change at Groenvlei, Knysna, South Africa : evidence from diatoms
    (2008) Kirsten, Kelly; Meadows, Michael E
    This study demonstrates that diatom analysis of lake sediment can provide very detailed information on long and short term climate change, hampered only by inconsistent sediment accumulation at Groenvlei. Further work may provide insight to periods which were not covered in this study.
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    Late Holocene diatom community responses to climate variability along the southern Cape coastal plain, South Africa
    (2014) Kirsten, Kelly; Meadows, Michael E
    In recent decades an emphasis on understanding the long-term variability of ecosystems and their responses to environmental changes has been undertaken. This has mainly been achieved through the identification and analysis of fossil material in lake sediments. In the South Africa, the relative paucity of available sites and the semi-arid nature of the region have led to incomplete or discontinuous palaeoclimatic records. However, lakes along the southern Cape coastal plain have shown promise. With this in mind palaeo-records from neighbouring rainfall regimes were used to evaluate the spatial and temporal patterns of climatic fluctuations during the late Holocene. Diatom analysis was conducted on sediment cores retrieved from coastal lakes at two localities, namely the Wilderness Lake Complex, near Knysna, as a representative of the year-round rainfall zone, and Princessvlei on the Cape Flats, as a representative of the winter rainfall zone of the southern African coastal zone. Additionally, oxygen isotopic analysis was performed on the silicate frustules from Princessvlei. On the basis of this evidence, it can be stated with some confidence that salinity is the driving mechanism governing the state of the Wilderness lake systems, which in turn is a response to sea level changes and climatic fluctuations, in particular moisture availability. Alternatively, the Princessvlei system is governed by changes in nutrients and water turbidity, which have been shown to be proxies for moisture availability and wind. This makes moisture availability a primary controlling factor over the environment along the southern coastal plain, with shifts between wet and dry periods occurring rapidly. Notable shifts in precipitation coincide with global climatic phenomena, including the Medieval Climate Anomaly (~1200 - 700 cal yrs BP) and the Little Ice Age (~700 - 125 cal yrs BP). Marine transgressions during the late Holocene are also recorded in the diatom assemblage particularly in the Wilderness region, as is the system’s recovery during the subsequent regressions. However, anthropogenic forcings during the last few centuries have resulted in considerable modifications in the natural functioning of all systems, altering flow dynamics and nutrient influx. The outcome of this study shows that diatom analysis is a powerful tool in the reconstruction of past environments under conditions wherein other typical palaeoenvironmental proxies may be less adequately represented.
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    Princess Vlei : what diatoms can tell us about spatial and temporal heterogeneity in an urban wetland
    (2010) Cowan, Oliver; Meadows, Michael E; Kirsten, Kelly
    Globally, wetlands are being degraded and destroyed largely as a result of anthropogenic activity. Monitoring and assessment are required to maintain functional ecosystems and the valuable services they provide. Surface sediment cores were taken from 4 points around an urban wetland (Princess Vlei) on the Cape Flats, Cape Town, South Africa. Diatoms were and used as a proxy for water quality variables to determine whether the diatom flora preserved in organic sediments accumulating in and around an urban wetland is a useful tool in determining the changes in water quality over time. In addition, the project attempts to establish whether there are spatial patterns in diatom flora within a small lake. Diatoms from three depths from each of the four sites were identified, counted and analyzed according to their trophic preferences and pollution tolerances which were acquired from a variety of resources. Results showed clear spatial differences between sites as a result of positioning in relation to effluent input, output and specific site characteristics such as reed stands. Differences between depths were evident although no significant trends were observed. In summation; spatial heterogeneity in the diatom assemblage of an urban wetland reveal that diatoms are suitable indicators of water quality, even within a small system, due to their niche specificity. The project also shows that Princess Vlei remains a eutrophic and polluted wetland, although not uniformly so. Continual monitoring is required to prevent the vlei from becoming a health hazard for the surrounding community and to maintain its ability to act as a buffering zone to protect the Rondevlei nature reserve, as well as acting as a functional ecosystem in an area threatened by urbanization.