UWCScholar :: Browsing by Author "Grenfell, Michael"

Browsing by Author "Grenfell, Michael"

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Effects of catchment management on physical river condition, chemistry, hydrogeomorphology and ecosystem service provision in small coastal rivers of the Western Cape
(University of the Western Cape, 2019) Petersen, Chantel R.; Grenfell, Michael; Jovanovic, Nebojsa
River systems are by nature complex and dynamic systems, which vary in structure and therefore function, and are closely connected to their landscapes. The primary aim of this thesis was to develop a systems operational understanding of how river patterns and processes (geomorphology and hydrology) link to aquatic and riparian systems and biodiversity (ecology) in a framework of evolving land cover/use and management. This illustrated the hydrogeomorphic controls regulating the structure and functioning of rivers in the provision of goods and services that vegetation, especially riparian vegetation, perform as ecological infrastructure, with a focus on the Duiwe River catchment. This study used a combination of desktop and field analysis. The desktop analysis followed the spatial and temporal historical land use change detection of river sub-catchments to assess the influence on water quality and river flow. It included historical water quality, flow records, rainfall data and aerial photograph time series analysis for trend detection, which were linked to changes in land use activities. The field surveys included cross-section surveys, physical and chemical sediment analysis, vegetation distribution, ground-water depth surveys and instream biological surveys of aquatic bioindicators. The study illustrated a correlation between land cover/use, water quality and river ecological integrity. When spatial heterogeneity of the catchments was altered by human or natural events, it was reflected by changes in the water quality. The linkages between the land cover/use and ecological integrity were examined using macroinvertebrates and algae. Macroinvertebrates were indicative of habitat integrity and river condition, while the benthic filamentous algae were indicative of increased nutrients and alkalinity. Results indicated that the full consortium of algae and macroinvertebrates be used as bioindicators for ecological integrity assessments in these short, coastal rivers. The influence of riparian vegetation and its effectiveness in providing regulating (retaining sediment and nutrients) and provisioning (good water quality for humans and the aquatic environment) services was examined by relating contrasting land uses, riparian vegetation, nutrient dynamics and water quality. The land covers generated different runoff volumes, water quality parameter concentrations and associated nutrient loads. Agriculture and alien Acacia mearnsii trees had the greatest impact on nutrient loads. However, a decreasing trend in nutrient concentrations was observed in the cross-section from the pastures to the riparian zones to the river at all sites. The key findings from this study were formulated into a conceptual framework flow-chain model demonstrating the linkages between river pattern, processes and ecology in the provision of ecosystem services. This interdisciplinary investigation demonstrated strong links between climate, topography, hydrogeomorphology, land cover/use, human activities and their influence on ecological river integrity. The developed framework provides a hierarchical model to link the different disciplines. It illustrates the top-down constraints provided by the system controllers and habitat drivers, coupled with the anthropogenic impacts as controllers to determine the response of biological entities (riparian vegetation and aquatic biota) at different scales, to ultimately provide ecosystem services. It provides the basis for an understanding of the linkages, processes and interactions that allows, prevents or alters ecosystem service provision by river ecosystems and in the study context, by riparian buffer zones.
Effects of land use change on streamflow and stream water quality of a coastal catchment
(South African Water Research Commission, 2017) Petersen, C.R.; Jovanovic, Nebo Z.; Le Maitre, D.C.; Grenfell, Michael
This study aimed to link land cover/use change to water quality in an important water supply coastal catchment. The approach followed a spatial and temporal analysis of historical catchment land use change to assess how changes influenced water quality and river flow in the Touws and Duiwe Rivers, southwestern Cape, South Africa. Each sub-catchment has unique characteristics which influence land use and water quality and the purpose was to analyse each one separately. Historical water quality and flow analysis were based on the records available (Duiwe River: 1998-2013; Touws River: 1980-2013) together with rainfall data. Records were analysed to detect trends over time, which were linked to changes in land use activities. Agriculture intensified rapidly in the Duiwe River catchment with most arable land cultivated by 1960 and water storage as farm dams escalating. Concentrations of nutrients and electrical conductivity were higher in the Duiwe River than in the more natural Touws River, and were positively correlated to river flows. Mean values for total nitrogen and electrical conductivity were 0.03 mg/L and 16.7 mg/L, respectively, in the Touws River and 0.25 mg/L and 127 mg/L, respectively, in the Duiwe River. Nutrient concentrations decreased in the Duiwe River after 2006 as fertilizer applications to pastures were reduced. The South African Target Water Quality Ranges were exceeded at times and in the Touws catchment this appears to have been due to extensive fires. For instance, sodium concentrations reached a maximum of 1 874.5 mg/L in 1996 compared to a usual average concentration of 20.8 mg/L where the guidelines are between 0 and100 mg/L. The link between land cover/use and water quality was demonstrated and when spatial heterogeneity of the catchments was altered by human or natural events, this was reflected in changes in the water quality.
Environmental modelling of wetland distribution in the Western Cape, South Africa: A climate change perspective
(University of Western Cape, 2021) Mohanlal, Shanice; Rivers-Moore, Nicholas A.; Grenfell, Michael
Wetlands have been recognised as one of the most intrinsically valuable and threatened ecosystems in the world. Global estimates indicate that wetlands are being lost or transformed at a rapid rate, exacerbated by projected climate change impacts. This has prompted the need to improve wetland mapping to address the conservation and management of these ecosystems effectively. However, this remains a challenge. Current mapping approaches estimates of wetland extent vastly underestimate the true extent. Ancillary data has been acknowledged to improve the accuracy of mapping the distribution of wetlands.
Hydrogeomorphic controls on the longitudinal distribution and dynamics of reed beds in non-perennial river systems, Western Cape, South Africa.
(University of the Western Cape, 2019) Makhonco, Nomanesi; Grenfell, Michael
There has been a growing interest in the role of interactions between vegetation and geomorphology in shaping fluvial environments, from evolutionary to modern-process timescales. However, much of this work has mainly been done in perennial systems (e.g. Corenblit et al., 2016; Gibling and Davies, 2012; Gran et al., 2015; Surian et al., 2015). These interactions have also been to some degree highlighted in dryland rivers (e.g. Grenfell et al., 2014; Kotschy et al 2008; Tooth and McCarthy, 2007; Tooth et al., 2014; Tooth, 2018). One of the key ways in which vegetation and geomorphology interact is through the interplay between channel competence and capacity (Corenblit et al., 2016). This interplay can be exemplified by reed bed wetland environments. For example, when a dense stand of reeds is established within a channel, roughness and sediment trapping efficiency are greatly increased, and this can result in flow diversion, and channel abandonment and infilling (Tooth et al., 2014).
Influence of landscape moisture sources and topography on rock weathering patterns associated with wildfire
(Wiley, 2022) Mol, Lisa; Grenfell, Michael
From 9 March 2015, a wildfire burned an area of 25.7 km2, or approximately half of the Jonkershoek catchment (Western Cape, South Africa), over the course of 3 days. During this period, large areas of fynbos and commercial forest plantations were razed, and rocks, including boulders and smaller rocks, were exposed to high temperatures. While a substantial body of work has been carried out to investigate the effects of wildfire on landscape development, less is known about the effect of wildfire on rock weathering within a landscape. Previous studies have reported the overall effect of wildfire on rock deterioration, but the effect of intra-fire temperature differences associated with heat behaviour on a slope has not been sufficiently addressed. In this study we investigate the effects of topography and proximity to moisture on rock deterioration processes.
Investigating associations between fluvial style and the characteristics and distribution of geomorphic units in non-perennial rivers
(University of the Western Cape, 2019) Grootboom, Curtis Renatius; Grenfell, Michael
Although non-perennial rivers are the most dominant river type in arid and semi-arid areas, far outnumbering perennial rivers, recent reviews have shown that the knowledge base supporting non-perennial river research is still in its infancy. This is a cause for concern as non-perennial rivers are increasing in number due to climate and other environmental change, and over-exploitation of catchment water resources. Thus more research is needed to improve decision support in the management of non-perennial systems. This thesis examines key geomorphic units found in non-perennial reaches with contrasting fluvial styles in the Touws and Prins Rivers, semi-arid Little Karoo, Western Cape. The study analyses the different types of bar located within these characterised fluvial styles, as the building blocks of physical habitat suitability and diversity. Few studies have assessed and investigated the physical characteristics of non-perennial rivers, and this knowledge gap provided the opportunity to examine and explain the associations between fluvial style, and the characteristics and distribution of geomorphic units. In this research, a procedure to observe and measure the characteristics of morphologic features was developed and applied. The approach was based on identifying and describing the morphometric characteristics of channel and floodplain features identified by aerial image analysis and field survey.
Spectral classification, mapping and physical habitat implications of a riparian invasion by Tamarix ramosissima Ledeb. in the Touws River, Klein Karoo, South Africa
(Taylor and Francis Group, 2022) Grenfell, Michael; Dube, Timothy
This paper investigates the invasion of a reach of the Touws River by the deciduous alien tree Tamarix ramosissima Ledeb. (Pink Tamarisk, Saltcedar). The objectives of the paper were to investigate the utility of a delta-normalised difference vegetation index (dNDVI) in evaluating the status, pattern and process of invasion, and to evaluate the implications of the invasion for riverscape morphodynamics and physical habitat structure and function. The spectral classification developed had an overall accuracy of 59.89%, omission error of 28.25%, and commission error of 11.86%. The classification of vegetation was used to quantify the aerial extent and pattern of invasion (currently at least 65.50% of the valley floor vegetation cover). Field observations and existing knowledge of seed dispersal mechanisms and germination constraints of the invasive tree were compared with those of the indigenous sweet thorn Vachellia karroo, to provide insight into invasion patterns and processes within the reach. The linear channel-flanking distribution of the invasion has the potential to alter reach hydrology and morphodynamics, which are key building blocks of physical habitat structure and function. The spectral classification approach demonstrated is relatively simple, has a strong biophysical basis in that it exploits a known, predictable and observable seasonal vegetation response that produces a clear spectral signature, and can be applied to long reaches of rivers impacted by alien vegetation invasions
Understanding spatial patterns of dispersal and deposition of fine sediment and adsorbed phosphates in the Wiesdrift Wetland on the Nuwejaars River, Cape Agulhas
(University of the Western Cape, 2021) Jagganath, Tashveera; Grenfell, Michael
River catchments in agricultural areas are strongly influenced by runoff from cultivated or grazed fields, and nutrient loading of these fields can result in large quantities of nitrates and phosphates being transported to rivers in surface runoff. In intensively farmed areas, nutrient loading is often so high that large quantities of nitrates and phosphates are transported to streams in surface runoff. Within these areas, strips of natural riparian vegetation and wetlands are critical in providing nutrient uptake functions that can reduce the load entering streams. A wetland can be a source, sink or transformer of nutrients, where fine sediments such as silt and clay have the ability to store and trap considerable amounts of phosphorus through adsorption and precipitation processes. Therefore, the determination of phosphorus adsorbed to fine sediment is important in understanding the role and value of wetlands in agricultural landscapes, and is the main focus of this study. The aim of the study is to evaluate an indicator-based approach, WET-EcoServices, to assess wetland sediment and phosphate trapping, through comparison with field survey data. The study focuses on spatial analysis and field survey of three Hydrogeomorphological (HGM) units classified for the Wiesdrift wetland on the Nuwejaars River, Cape Agulhas. The three HGM units are classified as: a floodplain wetland at the inlet of the system, a channelled valley-bottom wetland towards the middle part of the system and a floodplain wetland towards the outlet of the system. In-field observations were recorded for hydrogeomorphic and vegetation characteristics for each HGM Unit. AstroTurf mat sediment samples, grabbed channel bed and floodplain sediment samples were analysed for particle size and orthophosphate concentrations, while suspended sediment masses were recorded from three pairs of time-integrated sediment samplers located near the inlet, near the middle, and near the outlet of the wetland. Statistical analysis showed that orthophosphate concentrations are associated with fine sediment. Thus, the orthophosphate concentrations follow the distribution of silt on the Wiesdrift wetland. The dominant vegetation along transect 2, at which the highest concentrations of orthophosphate was found, is occupied by Typha capensis and Cyperus textilis. The percentage of fine sediment (silt) ranged between 0-37%, where the remaining percentage was sand. There was also a significant positive correlation between orthophosphate concentration and silt (Spearman’s rank-order correlation: rs = 0.692, N = 70, P < .001). The largest total sediment amount was found at Outlet 1 and Outlet 2 in the HGM unit 3 of the Wiesdrift wetland, with a value of 0.653 g. Overall, orthophosphate concentrations ranged between 0 mg/kg and 31320 mg/kg within the Wiesdrift wetland. WET-EcoServices determines an average score for phosphate trapping from on-site indicators such as hydrological zones, vegetation structure and soil texture/permeability. The dispersal of fine sediment and associated adsorbed phosphate is more complex than can be determined by a tool like WET-EcoServices because the tool captures the long-term mean conditions of a wetland system that determines the overall uptake of phosphates over extended time periods, thus future wetland assessments is recommended to take place over a longer period than this study. However, the field results of orthophosphate distribution are generally consistent with the findings from WET-EcoServices, further motivating for the use of the tool in wetland management applications.
Using cloud computing techniques to monitor long-term variations in ecohydrological dynamics of small seasonally-flooded wetlands in semi-arid South Africa.
(Journal of Hydrology, 2022) Gxokwe, Siyamthanda; Dube, Timothy; Mazvimavi, Dominic; Grenfell, Michael
Wetlands in drylands have high inter- and intra-annual ecohydrological variations that are driven to a great extent by climate variability and anthropogenic influences. The Ramsar Convention on Wetlands encourages the development of frameworks for national action and international cooperation for ensuring conservation and wise use of wetlands and their resources at local, national and regional scales. However, the implementation of these frameworks remains a challenge. This is mainly due to limited availability of high-resolution data and suitable big data processing techniques for assessing and monitoring wetland ecohydrological dynamics at large spatial scales, particularly in the sub-Saharan African region. The availability of cloud computing platforms such as Google Earth Engine (GEE) offers unique big data handling and processing opportunities to address some of these challenges. In this study, we applied the GEE cloud computing platform to monitor the long-term ecohydrological dynamics of a seasonally flooded part of the Nylsvley floodplain wetland complex in north-eastern South Africa over a 20-year period (2000–2020).
Wetlands in drylands: Diverse perspectives for dynamic landscapes
(Springer, 2022) Grenfell, Suzanne; Grenfell, Michael; Tooth, Stephen
The United Nations Environment Programme (UNEP 1997) classifes global drylands according to an Aridity Index (AI), defned as the ratio between mean annual precipitation (MAP) and potential evapotranspiration (PET). Drylands are areas where AI is <0.65, collectively incorporating subhumid, semiarid, arid and hyperarid settings (UNEP 1997; see Fig. 1). Wetlands in drylands (hereafter WiDs) have distinctive hydrogeomorphological, biogeochemical, ecological, and social-ecological features, and as a result, they require carefully tailored research and management strategies.
Will a rising sea sink some estuarine wetland ecosystems?
(Elsevier, 2016) Callaway, R.M.; Bertelli, C.M.; Mendzil, A.F.; Tew, I.; Grenfell, Suzanne; Grenfell, Michael
Sea-level rise associatedwith climate change presents amajor challenge to plant diversity and ecosystemservice provision in coastal wetlands. In this study,we investigate the effect of sea-level rise on benthos, vegetation, and ecosystem diversity in a tidal wetland in westWales, the UK. Present relationships between plant communities and environmental variableswere investigated through 50 plots atwhich vegetation (species and coverage), hydrological (surface or groundwater depth, conductivity) and soil (matrix chroma, presence or absence ofmottles, organic content, particle size) data were collected. Benthic communities were sampled at intervals along a continuum from saline to freshwater. To ascertain future changes to the wetlands' hydrology, a GIS-based empirical model was developed. Using a LiDAR derived land surface, the relative effect of peat accumulation and rising sea levels were modelled over 200 years to determine how frequently portions of the wetland will be inundated by mean sea level, mean high water spring and mean high water neap conditions. The model takes into account changing extents of peat accumulation as hydrological conditions alter. Model results show that changes to the wetland hydrology will initially be slow. However, changes in frequency and extent of inundation reach a tipping point 125 to 175 years from2010 due to the extremely low slope of the wetland. From then onwards, large portions of the wetland become flooded at every flood tide and saltwater intrusion becomes more common. This will result in a reduction in marsh biodiversity with plant communities switching toward less diverse and occasionally monospecific communities that are more salt tolerant.

Browsing by Author "Grenfell, Michael"

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