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Sewage, salt, and sediments: water-quality assessment of the lower Vaal-Orange River system
Thesis (MScConEcol)--Stellenbosch University, 2025.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867613747210616832 |
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| access_status_str | Open Access |
| author | Bekker, Frederik Jacobus |
| author2 | Esler, Karen J. |
| author_browse | Bekker, Frederik Jacobus Esler, Karen J. |
| author_facet | Esler, Karen J. Bekker, Frederik Jacobus |
| author_sort | Bekker, Frederik Jacobus |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MScConEcol)--Stellenbosch University, 2025. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/134511 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:41:01.634Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/134511 Sewage, salt, and sediments: water-quality assessment of the lower Vaal-Orange River system Bekker, Frederik Jacobus Esler, Karen J. Strydom, Matthys Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology & Entomology. Water quality -- South Africa -- Vaal River Water quality -- South Africa -- Orange River Water -- Pollution -- South Africa -- Management Sewage -- Environmental aspects -- South Africa Water salinization -- South Africa -- Vaal River Watershed Trace elements -- Environmental aspects -- South Africa UCTD Thesis (MScConEcol)--Stellenbosch University, 2025. Bekker, F. J. 2025. Sewage, salt, and sediments: water-quality assessment of the lower Vaal-Orange River system. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/0cae9c94-0945-42ee-bbc0-0a690b2b4b0d ENGLISH ABSTRACT: Water users in the lower Vaal-Orange River system are subjected to chemicals and pathogens from sources over which they have little control. These sources include raw sewage from dysfunctional wastewater-treatment works, saline irrigation return flows and upstream discharges from the industrialised upper Vaal River region. For this thesis, water-quality impacts on users in the lower Vaal-Orange River system were examined. It was found that sewage, salt, sediments, and high-flow events are the main vectors of poor water quality. The main sources of water pollution were found to be untreated sewage discharges, irrigation return flows and the first flush of high flow from the Vaal River. A stressor assessment was performed using international water-quality guidelines and the water-quality database of the civil society organisation Gariep Watch. It showed microbial contamination of potable and irrigation water as the main risk to water users. This is caused by the deteriorating state and maladministration at municipal sewage-treatment works in the study area and in the Vaal River catchment area. Untreated sewage and irrigation return flows contribute to available plant nutrients in the lower Vaal-Orange River system. It was found that nitrogen, phosphate, and potassium levels in the irrigation water should be accounted for to prevent over-fertilisation of crops. Farmers may thus achieve substantial savings by lowering fertilisation rates. Moreover, plant-nutrient concentrations in irrigation return flows can be lowered, reducing eutrophication and other harmful effects on aquatic ecosystems. Raised salinity was pronounced in the study area. Over five years, 91.6% of the Vaal River’s salt (calculated salt load) going into the lower Orange River originated upstream of the study area. The salt is mainly conveyed downstream when flows are high. The sulphate-dominant salt load from the Vaal River dictates the chemical composition of the lower Orange River and suggests mine-related sources in the upper Vaal River catchment. Trace-metal concentrations were raised in the study area, with untreated sewage water found to be the main source. Iron and manganese were at concentrations that exceed international guidelines for potable use. The high aluminium, mercury, and iron levels may be toxic to aquatic biota. These trace metals correlate well with flow and total suspended solids, illustrating their association with river sediments. The good linear correlations between flow and pathogens, flow and salinity, flow and trace metals and suspended solids and trace metals can be used by water users as forewarnings. These correlations show the link between field-measurable indicators, such as sudden increases in salinity or visible sediments, and harm arising from pathogens and trace metals. Water-quality risks are expected to increase with the 2030 commissioning of phase 2 of the Lesotho Highlands Water Project. This transfer of water to the industrialised upper Vaal River will increase discharges of polluted water and lower downstream flow. This, with acid mine drainage, untreated sewage discharges and climate change, could end this river’s capacity to sustain life. Nonetheless, a window of opportunity is present by which the adverse effects of the water-quality issues identified in this thesis could be averted or mitigated. AFRIKAANSE OPSOMMING: Watergebruikers in die laer Vaal- en Oranjeriviere word tans blootgestel aan chemiese stowwe en patogene organismes wat afkomstig is van bronne waaroor hulle geen beheer het nie. Hierdie bronne sluit in ongesuiwerde rioolwater vanaf disfunksionele rioolsuiweringswerke, versoute landbou-dreineringswater en stroom-op loslatings vanaf die geindustrialiseerde bo-Vaalrivier. Die impak van watergehalte op watergebruikers in die laer Vaal-Oranjerivierstelsel word ondersoek in hierdie proefskrif. Daar is bevind dat riool, sout, riviersedimente en periodes van hoogvloei faktore is wat swak watergehalte beinvloed. Die hoofbronne van besoedeling is ongesuiwerde rioolwater, landbou-dreineringswater en die eerste afloop van hoogvloei vanaf die Vaalrivier. ‘n Stressor-assessering is gedoen met behulp van internasionale watergehalteriglyne waarmee die nie-regeringsorganisasie Gariep Watch se watergehaltedatabasis ge-evalueer is. Hierdie studie het gewys dat die mikrobiese kontaminasie van drink- en besproeiingswater die grootste risiko vir waterverbruikers inhou. Dit word veroorsaak deur die agteruitgang en wanbestuur van munisipale rioolsuiweringswerke in die studiegebied asook in die Vaalrivier opvanggebied. Ongesuiwerde rioolwater en landbou-dreineringswater dra by tot die beskikbare konsentrasies plantnutriënte in die laer Vaal-Oranjerivierstelsel. Daar is bevind dat die stikstof, fosfaat en kaliumkonsentrasies in die besproeiingswater in berekening gebring moet word om die oorbemesting van gewasse te voorkom. Landbouprodusente mag aansienlike besparings realiseer deur die hoeveelheid bemestingstowwe te verminder. Deur plantnutriëntkonsentrasies in die landbou-dreineringswater te verminder, kan eutrofikasie asook die nadelige effekte op akwatiese ekosisteme ook verminder word. Verhoogde soutkonsentrasies is gevind in die studiegebied. Oor ‘n vyf-jaar studieperiode was 91.6% van die Vaalrivier se sout (berekende soutlading) na die laer Oranjerivier, afkomstig vanaf die Vaalrivier stroom-op van die studiegebied. Hierdie sout bereik die Oranjerivier hoofsaaklik tydens periodes van hoogvloei. Die sulfaat-dominante soutlading vanaf die Vaalrivier dikteer die chemiese samestelling in die laer Oranjerivier en dui op mynverwante bronne in die bo-Vaal opvanggebied. Swaarmetaalkonsentrasies was hoog in die studiegebied en daar is bevind dat ongesuiwerde rioolwater ‘n hoofbron hiervan is. Die yster en mangaankonsentrasies het die internasionale riglyne vir drinkbare gebuik oorskrei. Hoë aluminium, kwik en ysterkonsentrasies mag ook toksies wees vir akwatiese biota. Die goeie korrelasie tussen swaarmetale en riviervloei asook met totale gesuspendeerde stowwe illustreer ‘n verwantskap tussen die metale en riviersedimente. Verder kan die goeie liniêre korrelasies tussen riviervloei en mikrobiese patogene, vloei en soute, vloei en swaarmetale asook gesuspendeerde stowwe en swaarmetale goed gebruik word as vroeë waarskuwing van verhoogde besoedeling. Hierdie korrelasies demonstreer dus die skakel tussen veld-moniteerbare inikatore soos ‘n skielike toename in soutkonsentrasie of sigbare partikels in die water en skadelike gevolge as gevolg van patogene en swaarmetale. Daar kan verwag word dat die watergehalterisiko’s sal toeneem met die 2030 ingebruikneming van fase 2 van die Lesotho Hoogland Waterprojek. Hierdie oordrag van water na die geindustrialiseerde bo-Vaalrivier sal ‘n toename in besoedelde vrylatings asook laer stroom-af vloei veroorsaak. Dit, tesame met suurmynwater, ongesuiwerde rioolwater en klimaatsverandering, mag die einde van hierdie rivier se vermoë om lewe te onderhou beteken. Nietemin, daar is steeds ‘n venster van geleentheid waarin die nadelige gevolge van die watergehalte-aspekte wat in hierdie verhandeling geidentifiseer is, voorkom of versag kan word. Masters 2025-12-11T12:48:58Z 2025-12-11T12:48:58Z 2025-12 Thesis https://scholar.sun.ac.za/handle/10019.1/134511 en Stellenbosch University xxvii, 234 pages : illustrations, maps application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Water quality -- South Africa -- Vaal River Water quality -- South Africa -- Orange River Water -- Pollution -- South Africa -- Management Sewage -- Environmental aspects -- South Africa Water salinization -- South Africa -- Vaal River Watershed Trace elements -- Environmental aspects -- South Africa UCTD Bekker, Frederik Jacobus Sewage, salt, and sediments: water-quality assessment of the lower Vaal-Orange River system |
| title | Sewage, salt, and sediments: water-quality assessment of the lower Vaal-Orange River system |
| title_full | Sewage, salt, and sediments: water-quality assessment of the lower Vaal-Orange River system |
| title_fullStr | Sewage, salt, and sediments: water-quality assessment of the lower Vaal-Orange River system |
| title_full_unstemmed | Sewage, salt, and sediments: water-quality assessment of the lower Vaal-Orange River system |
| title_short | Sewage, salt, and sediments: water-quality assessment of the lower Vaal-Orange River system |
| title_sort | sewage salt and sediments water quality assessment of the lower vaal orange river system |
| topic | Water quality -- South Africa -- Vaal River Water quality -- South Africa -- Orange River Water -- Pollution -- South Africa -- Management Sewage -- Environmental aspects -- South Africa Water salinization -- South Africa -- Vaal River Watershed Trace elements -- Environmental aspects -- South Africa UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/134511 |
| work_keys_str_mv | AT bekkerfrederikjacobus sewagesaltandsedimentswaterqualityassessmentofthelowervaalorangeriversystem |