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The diatom record: Reconstructing historically recent environmental change in the Knysna estuary
Estuaries 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...
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| Format: | Thesis |
| Language: | English |
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Department of Environmental and Geographical Science
2023
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| _version_ | 1867613272820154368 |
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| access_status_str | Open Access |
| author | Antonopoulos, Helen Grace |
| author2 | Meadows, Michael Edward |
| author_browse | Antonopoulos, Helen Grace Meadows, Michael Edward |
| author_facet | Meadows, Michael Edward Antonopoulos, Helen Grace |
| author_sort | Antonopoulos, Helen Grace |
| collection | Thesis |
| description | Estuaries 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. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/37014 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:33:31.121Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2023 |
| publishDateRange | 2023 |
| publishDateSort | 2023 |
| publisher | Department of Environmental and Geographical Science |
| publisherStr | Department of Environmental and Geographical Science |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/37014 The diatom record: Reconstructing historically recent environmental change in the Knysna estuary Antonopoulos, Helen Grace Meadows, Michael Edward Kirsten, Kelly L Diatoms estuaries historically recent change Little Ice Age land use change anthropogenic impact Estuaries 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. 2023-02-23T10:10:44Z 2023-02-23T10:10:44Z 2022 2023-02-20T12:12:28Z Master Thesis Masters MSc http://hdl.handle.net/11427/37014 eng application/pdf Department of Environmental and Geographical Science Faculty of Science |
| spellingShingle | Diatoms estuaries historically recent change Little Ice Age land use change anthropogenic impact Antonopoulos, Helen Grace The diatom record: Reconstructing historically recent environmental change in the Knysna estuary |
| thesis_degree_str | Master's |
| title | The diatom record: Reconstructing historically recent environmental change in the Knysna estuary |
| title_full | The diatom record: Reconstructing historically recent environmental change in the Knysna estuary |
| title_fullStr | The diatom record: Reconstructing historically recent environmental change in the Knysna estuary |
| title_full_unstemmed | The diatom record: Reconstructing historically recent environmental change in the Knysna estuary |
| title_short | The diatom record: Reconstructing historically recent environmental change in the Knysna estuary |
| title_sort | diatom record reconstructing historically recent environmental change in the knysna estuary |
| topic | Diatoms estuaries historically recent change Little Ice Age land use change anthropogenic impact |
| url | http://hdl.handle.net/11427/37014 |
| work_keys_str_mv | AT antonopouloshelengrace thediatomrecordreconstructinghistoricallyrecentenvironmentalchangeintheknysnaestuary AT antonopouloshelengrace diatomrecordreconstructinghistoricallyrecentenvironmentalchangeintheknysnaestuary |