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An investigation into using stable water isotopes to determine the dependency of vegetation on groundwater at Cape Point Nature Reserve
We hypothesized that rainwater had a different and distinct isotopic signal to groundwater, and thus plants growing on groundwater-fed areas would have a unique and distinct isotopic composition compared to plants growing on freely-drained soils. We studied two groundwater-fed areas and adjacent fre...
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| Format: | Thesis |
| Language: | English |
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Department of Biological Sciences
2017
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| _version_ | 1867613148061630464 |
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| access_status_str | Open Access |
| author | Taylor, Robert |
| author2 | Bond, William J |
| author_browse | Bond, William J Taylor, Robert |
| author_facet | Bond, William J Taylor, Robert |
| author_sort | Taylor, Robert |
| collection | Thesis |
| description | We hypothesized that rainwater had a different and distinct isotopic signal to groundwater, and thus plants growing on groundwater-fed areas would have a unique and distinct isotopic composition compared to plants growing on freely-drained soils. We studied two groundwater-fed areas and adjacent freely-drained areas in the Cape Point Nature Reserve, Cape Peninsula. We sampled groundwater and analyzed the isotopic composition and compared this to the isotope composition of rainfall. We found that δ¹⁸O and oD values of rainwater (δ¹⁸O = O%o to -5.6%o and oD = +11 %o to -22%o) overlapped the isotopic composition of groundwater (δ¹⁸O = -4.2%o to -4.5%o and oD = -11.9%o to -13.2%o). Thus isotopic analysis could not determine which areas were groundwater-fed and which were rain-fed. We also sampled xylem water from five species, namely Leucadendron laureolum and Metalasia muricata (both of which grew on both dry and wetland areas), Mimetes hirtus (wetland only), Erica labialis (dry area only), and Erica multumbellifera (wet area orily). Our results suggest that both of L. laureolum and Metalasia muricata had access to groundwater on both groundwater-fed sites and the free-drained site. E. multumbellifera at a groundwater-fed marsh was likely also using groundwater, however on the adjacent freely drained site E. labialis was likely using rainwater. M. hirtus had a much more positive isotopic composition (δ¹⁸O = -1.5 ±1.2%o and δD = 5.1 ± 18.0%o) than either groundwater or rainwater, indicating that it was using evaporated water, which suggests the species were very shallow rooted. Thus M. hirtus would be very sensitive to drying out of the soil. This study has demonstrated that stable water isotopes cannot clearly distinguish rainwater and groundwater and we may have use other methods such as thermal imagery, chemical analysis, and xylem pressure potentials to determine the degree of dependency of vegetation on groundwater. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/25993 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:31:31.816Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2017 |
| publishDateRange | 2017 |
| publishDateSort | 2017 |
| publisher | Department of Biological Sciences |
| publisherStr | Department of Biological Sciences |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/25993 An investigation into using stable water isotopes to determine the dependency of vegetation on groundwater at Cape Point Nature Reserve Taylor, Robert Bond, William J Botany Biological Conservation Plant Ecology We hypothesized that rainwater had a different and distinct isotopic signal to groundwater, and thus plants growing on groundwater-fed areas would have a unique and distinct isotopic composition compared to plants growing on freely-drained soils. We studied two groundwater-fed areas and adjacent freely-drained areas in the Cape Point Nature Reserve, Cape Peninsula. We sampled groundwater and analyzed the isotopic composition and compared this to the isotope composition of rainfall. We found that δ¹⁸O and oD values of rainwater (δ¹⁸O = O%o to -5.6%o and oD = +11 %o to -22%o) overlapped the isotopic composition of groundwater (δ¹⁸O = -4.2%o to -4.5%o and oD = -11.9%o to -13.2%o). Thus isotopic analysis could not determine which areas were groundwater-fed and which were rain-fed. We also sampled xylem water from five species, namely Leucadendron laureolum and Metalasia muricata (both of which grew on both dry and wetland areas), Mimetes hirtus (wetland only), Erica labialis (dry area only), and Erica multumbellifera (wet area orily). Our results suggest that both of L. laureolum and Metalasia muricata had access to groundwater on both groundwater-fed sites and the free-drained site. E. multumbellifera at a groundwater-fed marsh was likely also using groundwater, however on the adjacent freely drained site E. labialis was likely using rainwater. M. hirtus had a much more positive isotopic composition (δ¹⁸O = -1.5 ±1.2%o and δD = 5.1 ± 18.0%o) than either groundwater or rainwater, indicating that it was using evaporated water, which suggests the species were very shallow rooted. Thus M. hirtus would be very sensitive to drying out of the soil. This study has demonstrated that stable water isotopes cannot clearly distinguish rainwater and groundwater and we may have use other methods such as thermal imagery, chemical analysis, and xylem pressure potentials to determine the degree of dependency of vegetation on groundwater. 2017-11-01T08:47:23Z 2017-11-01T08:47:23Z 2003 2017-02-14T10:25:17Z Bachelor Thesis Honours BSc (Hons) http://hdl.handle.net/11427/25993 eng application/pdf Department of Biological Sciences Faculty of Science University of Cape Town |
| spellingShingle | Botany Biological Conservation Plant Ecology Taylor, Robert An investigation into using stable water isotopes to determine the dependency of vegetation on groundwater at Cape Point Nature Reserve |
| thesis_degree_str | Bachelor's / Honours |
| title | An investigation into using stable water isotopes to determine the dependency of vegetation on groundwater at Cape Point Nature Reserve |
| title_full | An investigation into using stable water isotopes to determine the dependency of vegetation on groundwater at Cape Point Nature Reserve |
| title_fullStr | An investigation into using stable water isotopes to determine the dependency of vegetation on groundwater at Cape Point Nature Reserve |
| title_full_unstemmed | An investigation into using stable water isotopes to determine the dependency of vegetation on groundwater at Cape Point Nature Reserve |
| title_short | An investigation into using stable water isotopes to determine the dependency of vegetation on groundwater at Cape Point Nature Reserve |
| title_sort | investigation into using stable water isotopes to determine the dependency of vegetation on groundwater at cape point nature reserve |
| topic | Botany Biological Conservation Plant Ecology |
| url | http://hdl.handle.net/11427/25993 |
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