- Title
- The Algoa Bay region groundwater cycle – linking source to coast
- Creator
- Dodd, Carla
- Subject
- Ecohydrology
- Subject
- Hydrology
- Subject
- Groundwater -- Management
- Date Issued
- 2024-04
- Date
- 2024-04
- Type
- Master's theses
- Type
- text
- Identifier
- http://hdl.handle.net/10948/63722
- Identifier
- vital:73592
- Description
- Groundwater is a crucial component of freshwater supply globally, especially in water-scarce regions such as semi-arid climatic areas where surface water resources are climatically limited and further constrained during droughts. Groundwater resources are also important from an ecological perspective as they support numerous surface ecosystems including wetlands and rivers. Coastal groundwater discharge along the South African coast sustains supratidal spring-fed living microbialite ecosystems (SSLiME). These systems act as potential analogues for Earth’s earliest ecosystems and are therefore useful from a palaeoscientific and evolutionary perspective. The Southern Cape coast of South Africa is characterised by both fractured and intergranular aquifers and hosts the most extensive network of SSLiME reported globally. However, the region is frequently affected by water scarcity crises and consequently groundwater development and usage has increased. Yet, it is unclear to what extent coastal discharge is linked to inland aquifers and whether anthropogenic activities influence the quantity and quality of groundwater that flows into SSLiME. This thesis aims to assess the groundwater cycle of the Algoa Bay region along the Southern Cape coast by means of a multi-tracer study. Specifically, it endeavours to develop a better understanding of the hydrogeochemical connectivity between inland groundwater resources and coastal microbialite ecosystems. To achieve this, four groups of hydrochemical tracers were used: H- and O-isotope ratios, major cations and anions, organic micropollutants and macronutrients. Sampling strategies included monthly precipitation collection over twelve months (stable water isotopes), once-off groundwater collection from boreholes, inland springs and coastal discharge (all tracers). In addition, coastal groundwater discharge was sampled during a once-off repeat campaign (all tracers) and seasonally at selected sites (macronutrients). A local meteoric water line (LMWL) for the region was established and compared to the isotopic signature of groundwater. The results indicate that groundwater is likely recharged directly and with little evaporation. Furthermore, similarities in isotopic signatures between inland and coastal aquifer systems suggest some level of hydrogeological connectivity or similar environmental drivers of recharge, such as precipitation amount and moisture source. This is also supported by the physico-chemistry and major ionic composition of the groundwater samples. However, the major ion composition of groundwater is variable and, although it predominantly reflects the sodium-chloride nature of precipitation, lithological and spatial trends are apparent. For example, coastward trends such as increasing conductivity, calcium, total alkalinity, and nitrogen is evident. While isotopes and major ions inform on the environmental drivers and geogenic influence on groundwater recharge, the organic micropollutants and macronutrients provide insight into the nature of anthropogenic impacts on groundwater quality. Micropollutants quantified in the groundwater samples included artificial sweeteners, pharmaceuticals, a biocide, and an illicit drug. These compounds are mostly classed as wastewater indicators and indicate aquifer contamination from leaking reticulation systems and septic tanks. The highest concentrations are associated with the urban and coastal peri-urban areas, while groundwater from rural areas is often devoid of any micropollutants except sulfamic acid, which may be introduced during recharge from precipitation. Furthermore, the presence of selected compounds in groundwater discharge signifies that at least a component of the groundwater is derived from recent infiltration. Similarly, the macronutrient content of groundwater reflects the proximal land use. As such, coastal groundwater discharge sites adjacent to coastal villages reflect higher concentrations compared to rural sites. In addition, the nutrient load supplied to and discharged from SSLiME systems is quantified and the nutrient attenuation is estimated. This thesis contributes recent hydrogeochemical information for a structurally complex semi-arid area under both natural (drought conditions) and human (increased water use, degradation of aquifers) pressures. Collectively, the results indicate that coastal groundwater discharge is likely a mixture of both the intergranular and fractured aquifers and that anthropogenic activities in the hinterland is contaminating the groundwater. This study is an important addition to the baseline hydrological information available for the region and may be useful in terms of sustainable groundwater management strategies and development toward a socio-ecological optimum, especially as related to coastal microbialite system.
- Description
- Thesis (PhD) -- Faculty of Science, School of Environmental Sciences, 2024
- Format
- computer
- Format
- online resource
- Format
- application/pdf
- Format
- 1 online resource (xiv, 206 pages)
- Format
- Publisher
- Nelson Mandela University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- Nelson Mandela University
- Rights
- All Rights Reserved
- Rights
- Open Access
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | SOURCE1 | Dodd, C.pdf | 10 MB | Adobe Acrobat PDF | View Details Download |