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Event- and seasonal-scale sedimentation patterns within a clastic discontinuous valley-bottom wetland: Implications for phosphate retention.
Thesis (MSc)--Stellenbosch University, 2022.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2022
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| _version_ | 1867613964390629376 |
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| access_status_str | Open Access |
| author | De Freitas, Cathrine-Rose |
| author2 | Grenfell, Suzanne |
| author_browse | De Freitas, Cathrine-Rose Grenfell, Suzanne |
| author_facet | Grenfell, Suzanne De Freitas, Cathrine-Rose |
| author_sort | De Freitas, Cathrine-Rose |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MSc)--Stellenbosch University, 2022. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/126360 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:44:30.757Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2022 |
| publishDateRange | 2022 |
| publishDateSort | 2022 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/126360 Event- and seasonal-scale sedimentation patterns within a clastic discontinuous valley-bottom wetland: Implications for phosphate retention. De Freitas, Cathrine-Rose Grenfell, Suzanne Stellenbosch University. Faculty of Arts and Social Sciences. Dept. of Geography and Environmental Studies. Anions Soil absorption and adsorption Phosphates --Absorption and adsorption Nutrient cycles Sedimentation and deposition Suspended sediments Wetland -- Management Wetland -- Ecology UCTD Thesis (MSc)--Stellenbosch University, 2022. ENGLISH ABSTRACT: Globally, the consideration of wetlands as sediment and nutrient sinks has been well supported by various studies. However, this has not been as thoroughly investigated in clastic discontinuous valley-bottom wetlands. As a result, very little to no data are presently available on the short-term sedimentation patterns and associated phosphate retention within valley-bottom wetlands. This project evaluated event-based and seasonal sedimentation patterns in a select valley-bottom wetland and determined their impact on sediment-attached phosphate retention. To determine variation in suspended sediment flux at the event scale, and to document changes to vegetation cover throughout the season, two approaches were used. Firstly, sediment suspended within surface water was sampled at eight locations within the wetland on the Groot Phesantekraal farm immediately after seven rainfall events, which exceeded 10 mm, when the entire wetland was connected hydrologically. Two time-averaged suspended sediment samplers were installed, one at the wetland head, and a second at the downstream channel of the wetland toe. Vegetation and surface morphology changes after each rainfall event were determined using Manning’s roughness coefficients calculated for each sampling site. In addition, three cores were taken longitudinally down Floodout C to establish variation in total P, bioavailable P and sediment characteristics with depth. Surface samples were used to provide insight into surface variability in total P and associated sediments i.e. clay and silt. The results suggest that fluxes in sediment and total P within the wetland are determined by areas of high and low flow velocities attributed to repeated cut-and-fill cycles evident in Floodouts A, B and C, as well as seasonal vegetation growth towards the end of August 2021. Downstream increases in total P concentrations on the surface of Floodout C were closely linked to surface sediment fining. High total P concentrations were also present within a buried clay layer in all of the cores, indicating legacy sediments and possibly the location of the previous valley floor where accretion occurred prior to the formation of Floodout C. Bioavailable P was only high within the cores at levels where P uptake by roots could occur and remained very low deeper in all cores. This study found that the wetland was a net sediment exporter for the year 2021, whereby 71% more sediment exited the downstream reach in the re-forming channel than was supplied to the upstream inlet channel. Despite this, the wetland retained 37% of the total P supplied to the upstream reach, suggesting that the wetland is a site of nutrient exchange rather than only a sediment sink. The findings from this study determined that considering system geomorphology, catchment land use and vegetation is essential when assessing phosphate and sediment retention capabilities of discontinuous valley-bottom wetlands. AFRIKAANSE OPSOMMING: Wêreldwyd is die oorweging van vleilande as sediment- en voedingsgatte goed deur verskeie studies ondersteun. Dit is egter nie so deeglik in klastiese onderbroke vallei-bodemvleilande ondersoek nie. As gevolg hiervan, is daar tans baie min of geen data op die korttermyn sedimentasiepatrone en gepaardgaande fosfaatretensie binne vallei-bodem vleilande beskikbaar. Hierdie projek het gebeurtenisgebaseerde en seisoenale sedimentasiepatrone in ‘n spesifieke vallei-bodem vlei geëvalueer en die impak daarvan op sediment-aangehegte fosfaatretensie bepaal. Om variasie in opgeskorte sedimentvloei op die gebeurtenisskaal te bepaal, en om veranderinge aan plantegroeibedekking deur die seisoen te dokumenteer, is twee benaderings gebruik. Eerstens is sediment wat binne oppervlakwater opgeskort is, op agt plekke in die vleiland op Groot Phesantekraal plaas na sewe reënvalgebeurtenisse wat 10 mm oorskry het, toe die hele vleiland hidrologies verbind is, onmiddellik gemonster. Twee tydgemiddelde opgeskorte sedimentmonsters is geïnstalleer, een by die vleilandkop, en 'n tweede by die stroomafkanaal van die vleilandtoon. Plantegroei- en oppervlakmorfologieseveranderinge na elke reënvalgebeurtenis is bepaal met behulp van Manning se ruheidskoëffisiënte wat vir elke monsternemingsterrein bereken is. Daarbenewens is drie sedimentkerne in die lengte van Floodout C geneem om variasie in totale P, biobeskikbare P en sedimentkenmerke met diepte te vestig. Oppervlakmonsters is gebruik om insig te gee in oppervlakveranderlikheid in totale P en gepaardgaande sedimente d.w.s. klei en slik. Die resultate dui daarop dat variasies in sediment en totale P in die vleiland word deur gebiede van hoë en lae vloeisnelheid bepaal, wat verband hou met Floodouts A, B en C, asook seisoenale plantegroeigroei teen die einde van Augustus 2021. Stroomaf toename van totale P konsentrasies op die oppervlak van Floodout C was gekoppel aan die vining van sedimente in die boonste gedeeltes van die kerne, na die distale punt van Floodout C. Hoë totale P konsentrasies was ook binne 'n begrawe klei laag in al die kerne gevind, wat dui op nalatenskap sedimente en moontlik die vallei vloer waar akkresie plaasgevind het voor die vorming van Floodout C. Biobeskikbare P was net hoog binne die kerne op vlakke waar P opname deur wortels kon voorkom en gebly baie laag dieper in alle kerne. Hierdie studie het bevind dat die vleiland 'n bron van sediment vir die jaar 2021 was. Die vleiland bydra tot 70% van stroomaf sediment. totale P is egter steeds in die vleiland behou, terwyl voordelige persentasies N en C stroomaf vrygestel is wat aandui dat die vleiland 'n terrein van voedingsuitruiling is eerder as 'n sedimentsinkgat. Die resultate van hierdie studie het bepaal dat die stelselgeomorfologie, opvanggebiedgrondgebruik en plantegroei noodsaaklik is vir die beoordeling van fosfaat- en sedimentretensievermoëns van onderbroke vallei-bodemvleilande. Masters 2022-11-23T17:02:46Z 2023-01-23T06:53:59Z 2022-11-23T17:02:46Z 2022-12 Thesis http://hdl.handle.net/10019.1/126360 en Stellenbosch University xv, 90 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Anions Soil absorption and adsorption Phosphates --Absorption and adsorption Nutrient cycles Sedimentation and deposition Suspended sediments Wetland -- Management Wetland -- Ecology UCTD De Freitas, Cathrine-Rose Event- and seasonal-scale sedimentation patterns within a clastic discontinuous valley-bottom wetland: Implications for phosphate retention. |
| title | Event- and seasonal-scale sedimentation patterns within a clastic discontinuous valley-bottom wetland: Implications for phosphate retention. |
| title_full | Event- and seasonal-scale sedimentation patterns within a clastic discontinuous valley-bottom wetland: Implications for phosphate retention. |
| title_fullStr | Event- and seasonal-scale sedimentation patterns within a clastic discontinuous valley-bottom wetland: Implications for phosphate retention. |
| title_full_unstemmed | Event- and seasonal-scale sedimentation patterns within a clastic discontinuous valley-bottom wetland: Implications for phosphate retention. |
| title_short | Event- and seasonal-scale sedimentation patterns within a clastic discontinuous valley-bottom wetland: Implications for phosphate retention. |
| title_sort | event and seasonal scale sedimentation patterns within a clastic discontinuous valley bottom wetland implications for phosphate retention |
| topic | Anions Soil absorption and adsorption Phosphates --Absorption and adsorption Nutrient cycles Sedimentation and deposition Suspended sediments Wetland -- Management Wetland -- Ecology UCTD |
| url | http://hdl.handle.net/10019.1/126360 |
| work_keys_str_mv | AT defreitascathrinerose eventandseasonalscalesedimentationpatternswithinaclasticdiscontinuousvalleybottomwetlandimplicationsforphosphateretention |