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Investigating regional recharge dynamics through the use of tritium and radiocarbon isotopes to assess the hydrological resilience of groundwater in southern Africa
Thesis (PhD)--Stellenbosch University, 2021.
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| Format: | Thesis |
| Language: | en_ZA en_ZA |
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Stellenbosch : Stellenbosch University
2021
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| _version_ | 1867614064704749568 |
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| access_status_str | Open Access |
| author | Van Rooyen, Jared |
| author2 | Miller, Jodie A. |
| author_browse | Miller, Jodie A. Van Rooyen, Jared |
| author_facet | Miller, Jodie A. Van Rooyen, Jared |
| author_sort | Van Rooyen, Jared |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (PhD)--Stellenbosch University, 2021. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/109868 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA en_ZA |
| last_indexed | 2026-06-10T12:46:06.004Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2021 |
| publishDateRange | 2021 |
| publishDateSort | 2021 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/109868 Investigating regional recharge dynamics through the use of tritium and radiocarbon isotopes to assess the hydrological resilience of groundwater in southern Africa Van Rooyen, Jared Miller, Jodie A. Stellenbosch University. Faculty of Science. Dept. of Earth Sciences. Groundwater -- Africa, Southern -- Management Tritium dating Carbon -- Isotopes Groundwater recharge Water resources development -- South Africa UCTD Thesis (PhD)--Stellenbosch University, 2021. ENGLISH ABSTRACT: Water resources are integral in the global pursuit of equitable growth and sustainability. Although groundwater is the most abundant freshwater resource accessible to humans and the environment, it is often underrepresented in water management strategies and policy. Furthermore, groundwater reservoirs are not only vulnerable to contamination, but to depletion through climate change, land use change and increased water demand. As groundwater monitoring in southern Africa is sparse and long-term records are rarely available, it is difficult to constrain the groundwater system on a regional scale. Radioactive isotope tracers have proven effective in estimating recharge and residence times of groundwater over a local to global scale and could provide insight to regional groundwater vulnerability in an otherwise data poor region. The use of tritium (3H) and radiocarbon (14C) isotopes requires a comprehensive understanding of initial tracer abundance in recharge as well as subsurface physiochemical processes that affect the accuracy of predicted recharge rates and residence times. The release of 3H and 14C from thermo-nuclear bomb tests during the 1950’s and 1960’s changed the applications of these tracers in hydrology. However, the ‘bomb peak’ has been mostly attenuated in modern times and the return of atmospheric tracers to background levels presents new challenges and applications in hydrological studies. To constrain the natural variability of 3H in South African rainfall, backward trajectories of ‘water parcels’ that produced sampled rainfall events were modelled to assess the controls of water mass origin on 3H activity. It was found that ~90% of 3H variability could be completely or partially explained by the origin of the water mass. By understanding the variability of 3H in South African rainfall, the theoretical activity of 3H in groundwater can be predicted through lumped parameter models. When combined with 14C theoretical abundances, measured tracer abundance can be assessed as the proportion of modern groundwater and age of the fossil component in major aquifers across southern Africa. It was found that aquifers across southern Africa have diverse proportions of mixed groundwater (0.6 - 100%) that are mixed within a wide range of older groundwater, that range in calculated ages (105 – 59400 years) and mean residence times for each aquifer system (4698 - 27841 years). The distribution of 3H activity in groundwater across South Africa was modelled using geostatistics that evaluated the effects of 3H variability in precipitation and unsaturated zone travel time. The predicted 3H surface agrees well to expected controls, with proximal (<100km) coastal regions, winter rainfall zones and deeper depth to groundwater predicted to have lower 3H activities. Conversely, inland localities with shallower depth to groundwater and/or summer rainfall are predicted to have elevated 3H activities. The predictive surface was then included as a recharge indicator in a novel groundwater vulnerability assessment, that incorporates both the risk of reducing groundwater quantity but also a deterioration in quality through modern contamination and sustained salinization. The assessment found that large portions of South Africa (22.4%) have a very high vulnerability to depletion in quantity and deterioration in quality, adding that this will likely increase (+3-6%) in the next 50 years as a result of climate change. This thesis outlines the need for an improved understanding of the vulnerability, sustainability and resilience of South Africa’s groundwater resources and offers insight through an investigation to the efficacy of 3H and 14C as tracers of regional recharge dynamics. AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar. Doctoral 2021-02-18T09:47:59Z 2021-04-21T14:29:34Z 2021-02-18T09:47:59Z 2021-04-21T14:29:34Z 2021-03 Thesis http://hdl.handle.net/10019.1/109868 en_ZA en_ZA Stellenbosch University xiii, 133 pages : color illustrations, maps application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Groundwater -- Africa, Southern -- Management Tritium dating Carbon -- Isotopes Groundwater recharge Water resources development -- South Africa UCTD Van Rooyen, Jared Investigating regional recharge dynamics through the use of tritium and radiocarbon isotopes to assess the hydrological resilience of groundwater in southern Africa |
| title | Investigating regional recharge dynamics through the use of tritium and radiocarbon isotopes to assess the hydrological resilience of groundwater in southern Africa |
| title_full | Investigating regional recharge dynamics through the use of tritium and radiocarbon isotopes to assess the hydrological resilience of groundwater in southern Africa |
| title_fullStr | Investigating regional recharge dynamics through the use of tritium and radiocarbon isotopes to assess the hydrological resilience of groundwater in southern Africa |
| title_full_unstemmed | Investigating regional recharge dynamics through the use of tritium and radiocarbon isotopes to assess the hydrological resilience of groundwater in southern Africa |
| title_short | Investigating regional recharge dynamics through the use of tritium and radiocarbon isotopes to assess the hydrological resilience of groundwater in southern Africa |
| title_sort | investigating regional recharge dynamics through the use of tritium and radiocarbon isotopes to assess the hydrological resilience of groundwater in southern africa |
| topic | Groundwater -- Africa, Southern -- Management Tritium dating Carbon -- Isotopes Groundwater recharge Water resources development -- South Africa UCTD |
| url | http://hdl.handle.net/10019.1/109868 |
| work_keys_str_mv | AT vanrooyenjared investigatingregionalrechargedynamicsthroughtheuseoftritiumandradiocarbonisotopestoassessthehydrologicalresilienceofgroundwaterinsouthernafrica |