The regeneration of palmiet (prionium serratum) following hydrogeomorphic disturbance: a case study of the Kromme River wetland
- Authors: Van Eck, Caydon Daniël
- Date: 2022-10-14
- Subjects: Biogeomorphology South Africa Kromme Estuary (Eastern Cape) , Wetland ecology , Prionium serratum Regeneration , Fluvial geomorphology , River channels
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/365555 , vital:65759
- Description: The Kromme River wetland in the Eastern Cape of South Africa occupies a broad valley (up to 350 m wide) with a gentle longitudinal slope of less than 2 % that has been formed by cut-and-fill cycles that are initiated by trunk-tributary interactions. These hydrogeomorphic disturbance events trigger gully erosion and generate sediments, the coarse fraction of which is deposited less than 2 km downstream, leading to depositional floodout features that fill gullies headwards. This process has been occurring at intervals for at least 10 000 years, and as such pre-dates the introduction of European farming practices in the area. Plants that regenerate by colonising these features are thought to have evolved adaptions necessary to colonise intermittently produced bare sandy sediments. This study aimed to examine the regeneration ecology of palmiet (Prionium serratum), the dominant vegetation community within these cut-and-fill wetlands, by relating its regeneration characteristics to environmental factors in a reach of the Kromme River wetland that has experienced a recent hydrogeomorphic disturbance event (approximately 10 years before the commencement of this study). Palmiet was found to be regenerating on sedimentary deposits on beds of gullies and on depositional bars on the margins of gully beds. The large depositional floodout downstream of a large gully also favoured palmiet regeneration, where it was found to be regenerating along not only the active channel, but also along old abandoned flow paths and sometimes areas well elevated above the channel. The geomorphic features that favoured palmiet regeneration were characterised by coarse-grained sediments (mean particle size approximately 310 μm) with low organic matter content (0.61 %), a low depth to the water table and low elevation above the thalweg (mean depth to water table is approximately 0.6 m), and a relatively close distance to the thalweg (< 10 m). This understanding of palmiet’s regeneration characteristics was viewed in relation to existing literature on undisturbed palmiet wetland plant communities and its reported contribution to conditions that favour wetland formation through gully filling, which allowed for the creation of a conceptual model of palmiet regeneration, colonisation and long-term persistence. This model was based on the Fluvial Biogeomorphic Succession concept. It suggests that palmiet’s interaction with the hydrogeomorphic environment throughout the different stages of its life cycle results in self-organising biogeomorphic landforms. Over hundreds of years, the reciprocal interactions between palmiet, sediments and water, fills gullies and restores valley bottoms, ultimately leading to the formation of a wetland landform. It is further proposed that through continued accretion, the geomorphic wetland landscape becomes more and more disconnected from the hydrogeomorphic dynamics of the fluvial system, such that the prevailing conditions begin to favour fynbos establishment, which may outcompete palmiet. , Thesis (MSc) -- Faculty of Science, Geography, 2022
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- Date Issued: 2022-10-14
A classification of large wetlands in Africa’s elevated drylands based on their formation, structure, and hydrological functioning using Earth Observation (EO) data and Geographic Information System (GIS)
- Authors: Lidzhegu, Zwidofhelangani
- Date: 2020
- Subjects: Wetlands -- Africa -- Classification , Wetlands -- Africa -- Research , Wetlands -- Africa -- Monitoring , Topographical surveying -- Africa , Hydrological surveys == Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/142668 , vital:38100
- Description: Due to wetland inaccessibility and limited wetland geomorphological studies, there is limited information on the geomorphological origin and hydrological functioning of different types of wetlands in Africa’s elevated drylands. As a result, there is limited information for the development of a comprehensive wetland classification system that classifies wetlands based on long-term geomorphic processes that determine their formation and shape, their structure and hydrological functioning. Therefore, the current study was designed to classify large wetlands in Africa’s elevated drylands based on processes that determine their formation, and shape their structure and hydrological functioning using remote sensing and Geographic Information System (GIS) techniques. Although wetlands perform a number of hydrological functions including groundwater recharge and water purification, the current study focuses mainly on their flood attenuation function. Detailed analysis of topographic information was undertaken using Shuttle Radar Topographic Mission (SRTM) elevations measured at the scale of 30 m x 30 m. LandsatLook and Google Earth images, tectonic as well as geological data were used as supplementary data for developing an understanding of the origin, structure and hydrological characteristics of wetlands. The Principal Component Analysis (PCA) of wetland environmental variables was used to identify and explain wetland heterogeneity. The results of the study showed that fluvial processes, tectonic history and the evolution of Africa’s landscape played a fundamental role in the formation and evolution of wetlands. This study demonstrates a wide range of processes that contribute to wetland formation, structure and functioning. At one extreme it is clear that tectonic processes may be primarily responsible for the creation of basins that host wetlands. At another extreme, wetlands may be structured primarily by fluvial processes. At a third extreme are wetlands that superficially appear to be structured by fluvial processes, but which have their structures modified by gradual rising of the base level at their distal ends, either through marginal uplift adjacent to rift valleys, or through aggradation of a floodplain that blocks a tributary valley. Overall, the classification of wetlands considered in this study can be summarised into four distinct groupings, with two of these divided further into two groupings each: (1) Tectonic basins with little or no indication of fluvial development (Bahi and Wembere wetlands), (2) Tectonic basins evolving towards a wetland with a structure increasingly shaped by fluvial characteristics (Usangu wetland), (3) Fluvially modified valleys with a local base level at the toe of the wetland such as a resistant lithology or a tectonic control that limits the rate of incision of easily weathered and eroded lithologies, leading to valley widening and longitudinal slope reduction, which are of two distinct types: (a) With a catchment on Kalahari Group sediment that is transported fluvially as bedload, and therefore with no prominent alluvial ridge or backwater depressions (Upper Zambezi and Barotse wetlands), (b) With a catchment that produces abundant fine sediment that is deposited as overbank sediments, leading to channel migration via meandering and to the construction of an elevated alluvial ridge (Lufira wetland), (4) Fluvially modified basins with evidence of gradual elevation of the base level at the toe of the wetland, which are of two types: (a) Tectonic marginal rift valley uplift such that they behave more as depression wetlands rather than as wetlands shaped by fluvial processes (Kafue and Luapula wetlands), (b) Tributary valley wetlands blocked by aggradation of the trunk valley (Lukanga wetland). In conclusion, although few geomorphological studies have been conducted on southern African wetlands because of their inaccessibility, Africa’s surface topography and its historical evolution, as well as aridity, provide an opportunity for illustrating the important role that the long-term tectonic, geological and geomorphological processes play in determining wetland origin, structure and dynamics. GIS methodology and Earth Observation (EO) data on the other hand, provide a practical means for acquiring information on inaccessible and hard to traverse wetland systems. A novel cut-and-fill approach for delineating wetlands from a Digital Elevation Model (DEM) was presented as another way in which GIS methodology and Earth Observation (EO) data can provide practical means for assessing inaccessible and hard to traverse wetland systems.
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- Date Issued: 2020
An assessment of the effectiveness of the Crossways Farm Village constructed wetland in the treatment of domestic wastewater
- Authors: Silbernagl, Ryan
- Date: 2020
- Subjects: Crossways Farm Village FWS wetland (South Africa)-- Management , Sewage -- Purification -- South Africa , Wetland management -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/145011 , vital:38400
- Description: A mass balance study was conducted comparing inflowing and outflowing solute loads in order to calculate the treatment efficiency of a free water surface (FWS) constructed wetland used to treat domestic wastewater following primary treatment in an anaerobic reactor and oxidation in a rotating biological contractor. Water samples were taken at six locations down the length of the treatment system and analysed for nitrate nitrogen (NO3-N), nitrite nitrogen (NO2-N), ammonia nitrogen (NH4-N) and phosphorus as phosphate (PO4-P). Flow was determined using two V notch weirs combined with pressure transducers based on an empirically derived stage-discharge relationship. The concentration of each solute (g.m-3) multiplied by flow (m3.day-1) provides a measurement of the mass of each solute entering and leaving the treatment wetland such that the difference (inflow – outflow) indicates the nett storage in, or loss from, the wetland. In order to determine the water balance, apart from measuring surface inflows and outflows, rainfall was measured using an onsite rain gauge. Evapotranspirational losses were determined using the Penman-Monteith equation based on weather data collected at an onsite weather station. Other than water that entered the wetland via the primary water treatment works, surface inflows could be ignored as the wetland was sealed with a plastic liner, which also prevented groundwater inflow and outflow. Wetland outputs via surface outflow and evapotranspiration were then subtracted from wetland inputs to determine the water balance over the study period. Approximately 10.5% of water inputs into the hydrological mass balance calculation was not accounted for, which is considered to be accounted for by inaccuracy associated with the estimation of evapotranspiration and possibly by differences in water levels in the wetland at the start and end of the experiment. Total input, output and storage of NO3-N, NO2-N, NH4-N and PO4-P was calculated from April 2016 to September 2016 to give the treatment efficiency of the FWS wetland system. Results showed a 91.5% reduction in NO3-N, 76.6% reduction in NH4-N, and 88.8% reduction in PO4P between the inflow and outflow. Wetland sediment and vegetation (Typha capensis) samples were also analysed for nitrogen and phosphorus content to give an estimate of nutrient stocks/storage accumulated in plant tissues and sediments over the lifespan of the wetland. Standing stock calculations showed that a total of 450.1kg of nitrogen is stored in the wetlands, of which 69.3kg is stored in wetland sediments. Wetland phosphorus retention was found to be significantly lower with a total of 57.1kg of phosphorus, of which 77.4% was stored in sediments, indicating that wetland sediments comprise the largest store and therefore removal pathway of nutrients in the Crossways Farm Village FWS wetland.
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- Date Issued: 2020
Spatial variation in modelled hydrodynamic characteristics associated with valley confinement in the Krom River wetland: implications for the initiation of erosional gullies
- Authors: Schlegel, Philippa Kirsten
- Date: 2018
- Subjects: Soil erosion South Africa Eastern Cape , Wetland management South Africa Kromme River (Eastern Cape) , Wetland conservation South Africa Kromme River (Eastern Cape)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/58684 , vital:27356
- Description: Gully erosion is a significant and widespread feature of southern African wetlands, including the wetlands of the Krom River, Eastern Cape. Gully erosion in wetlands is consistently being viewed as a major contributing factor to wetland degradation and eventual collapse. Many gullies exist in the Krom River and Working for Wetlands has spent large sums of money to stabilise head-cuts with the expectation that further erosion would be halted and possibly avoided altogether. Observations in the Krom River wetlands have revealed that most gullies in the wetland are initiated where the width of the trunk valley has been reduced as a consequence of deposition by tributary alluvial fans that impinge on the trunk valley and reduce its width. The aim of this study was to examine variation in hydrodynamic characteristics for a range of discharges, as flow in the broad Kompanjiesdrif basin (~250 meters wide) is confined in a downstream direction to a width of less than 50 meters by a combination of a large impinging left bank tributary alluvial fan that coincides with a resistant bedrock lithology. The study was done by collecting topographical survey data using a Differential Global Positioning System in order to create a Digital Terrain Model with a suitable resolution. Flow was recorded using a Marsh-McBirney Model 2000 Flo-Mate as well as recording the flood extent for each flow condition; this was used in the calibration process of the model. Vegetation measurements were conducted in order to calculate a roughness value across the valley floor. A two-dimensional raster based flood inundation model, CAESAR-Lisflood and a one-dimensional hydraulic analysis model, HEC-RAS, were then used to simulate different parameters associated with variation in discharge, including flow velocity, water depth and stream power, thereby creating a better understanding of the hydraulic characteristics that may promote the formation of gullies in the wetland. Based on these hydraulic analyses it is evident that the effect of impinging alluvial fans on hydraulic characteristics such as flow velocity, water depth and stream power, may lead to the initiation of gullies within the Krom River wetland. This work improves understanding of the collapse of palmiet wetlands in steep-sided valleys within the Cape Fold Mountains of South Africa, and can aid in wetland management.
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- Date Issued: 2018
Linking satellite and point micrometeorological data to estimate : distributed evapotranspiration modelling based on MODIS LAI, Penman-Monteith and functional convergence theory
- Authors: Weideman, Craig Ivan
- Date: 2014
- Subjects: Plants -- Water requirements -- South Africa , Evaporation (Meteorology) -- Measurement , Satellite meteorology , Micrometeorology , Evapotranspiration , MODIS (Spectroradiometer)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4779 , http://hdl.handle.net/10962/d1012078 , Plants -- Water requirements -- South Africa , Evaporation (Meteorology) -- Measurement , Satellite meteorology , Micrometeorology , Evapotranspiration , MODIS (Spectroradiometer)
- Description: Recent advances in satellite sensor technology and micrometeorological instrumentation for water flux measurement, coupled with the expansion of automatic weather station networks that provide routine measurements of near-surface climate variables, present new opportunities for combining satellite and ground-based instrumentation to obtain distributed estimates of vegetation water use over wide areas in South Africa. In this study, a novel approach is tested, which uses satellite leaf area index (LAI) data retrieved by the Moderate Resolution Imaging Spectroradiometer (MODIS) to inform the FAO-56 Penman-Monteith equation for calculating reference evaporation (ET₀) of vegetation phenological activity. The model (ETMODIS) was validated at four sites in three different ecosystems across the country, including semi-arid savanna near Skukuza, mixed community grassland at Bellevue, near Pietermaritzburg, and Groenkop, a mixed evergreen indigenous forest near George, to determine potential for application over wider areas of the South African land surface towards meeting water resource management objectives. At Skukuza, evaluated against 170 days of flux data measured at a permanent eddy covariance (EC) flux tower in 2007, the model (ETMODIS) predicted 194.8 mm evapotranspiration relative to 148.9 mm measured fluxes, an overestimate of 31.7 %, (r² = 0.67). At an adjacent site, evaluated against flux data measured on two discrete periods of seven and eight days in February and May of 2005 using a large aperture scintillometer (SLS), ETMODIS predicted 27.4 mm and 6.7 mm evapotranspiration respectively, relative to measured fluxes of 32.5 and 8.2 mm, underestimates of 15.7 % and 18.3 % in each case (r² = 0.67 and 0.34, respectively). At Bellevue, evaluated against 235 days of evapotranspiration data measured using a surface layer scintillometer (SLS) in 2003, ETMODIS predicted 266.9 mm evapotranspiration relative to 460.2 mm measured fluxes, an underestimate of 42 % (r² = 0.67). At Groenkop, evaluated against data measured using a SLS over three discrete periods of four, seven and seven days in February, June and September/October respectively, ETMODIS predicted 9.7 mm, 10.3 mm and 17.0 mm evapotranspiration, relative to measured fluxes of 10.9 mm, 14.6 mm and 23. 9 mm, underestimates of 22.4 %, 11.2 % and 24.1 % in each case (r² = 0.98, 0.43 and 0.80, respectively). Total measured evapotranspiration exceeded total modelled evapotranspiration in all cases, with the exception of the flux tower site at Skukuza, where evapotranspiration was overestimated by ETMODIS by 31.7 % relative to measured (EC) values for the 170 days in 2007 where corresponding modelled and measured data were available. The most significant differences in measured versus predicted data were recorded at the Skukuza flux tower site in 2007 (31.7 % overestimate), and the Bellevue SLS flux site in 2003 (42 % underestimate); coefficients of determination, a measure of the extent to which modelled data are able to explain observed data at validation periods, with just two exceptions, were within a range of 0.67 – 0.98. Several sources of error and uncertainty were identified, relating predominantly to uncertainties in measured flux data used to evaluate ETMODIS, uncertainties in MODIS LAI submitted to ETMODIS, and uncertainties in ETMODIS itself, including model assumptions, and specific uncertainties relating to various inputs; further application of the model is required to test these uncertainties however, and establish confidence limits in performance. Nevertheless, the results of this study suggest that the technique is generally able to produce estimates of vegetation water use to within reasonably close approximations of measurements acquired using micrometeorological instruments, with r² values within the range of other peer-reviewed satellite remote sensing-based approaches.
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- Date Issued: 2014
Economic consequences of ecological change: restoration options for the Mfolozi floodplain and implications for Lake St. Lucia, South Africa
- Authors: Collings, Sandy Lyn
- Date: 2010
- Subjects: Lake ecology -- South Africa -- Saint Lucia, Lake , Ecology -- Economic aspects -- South Africa -- Kwazulu-Natal , Wetland ecology -- South Africa -- Kwazulu-Natal , Ecosystem services -- South Africa -- Kwazulu-Natal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4744 , http://hdl.handle.net/10962/d1006950 , Lake ecology -- South Africa -- Saint Lucia, Lake , Ecology -- Economic aspects -- South Africa -- Kwazulu-Natal , Wetland ecology -- South Africa -- Kwazulu-Natal , Ecosystem services -- South Africa -- Kwazulu-Natal
- Description: Lake St Lucia in northern KwaZulu-Natal, South Africa, experiences severe ecological stress during dry periods largely as a result of diminishing freshwater supplies and conditions of hypersalinity. Possible intervention involves diverting the Mfolozi River to the St Lucia Lake system. However, due to high sediment loading, water from the Mfolozi river requires considerable filtration before a link can be established. A suggested option considered in this study is to restore the existing sugarcane farmlands on the Mfolozi Floodplain (~20 800 ha) to previous wetland conditions to reinstate a sediment removal function amongst other benefits. Proposed restoration will have a direct impact on the industries currently supported by the iSimangaliso Wetland Park and the Mfolozi Floodplain (tourism, sugar, conservation). to understand a measure of such impacts, ecosystem services for both Lake St Lucia and the Mfolozi Floodplain were analysed (flood alleviation, water provision, water purification, sediment regulation, tourism, fisheries, vegetation for harvest, existence, cultural and research). Annual economic values for each ecosystem service were determined by means of valuation methods that included benefit transfer and replacement cost. Results showed a current annual minimum value of the Mfolozi Floodplain and Lake St Lucia as greater than R21 million and R1.1 billion respectively. Partial restoration of the floodplain (~6 000 ha) is expected to increase the sum of all ecosystem services values by approximately 26% for the Mfolozi Floodplain and by 23% for the St Lucia System. Full restoration (~20 800 ha) increases the total ecosystem services value by 88% and 50% for the Mfolozi Floodplain and St Lucia System respectively. Results showed that economic values for existence, fisheries, tourism and water provision increase by the greatest percentage for the St Lucia System under both restoration scenarios. Partial and full restoration of the floodplain will result in the greatest increases in economic value for the services existence, tourism, fisheries and the harvesting of vegetation on the Mfolozi Floodplain.
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- Date Issued: 2010