1,721,262 research outputs found
Monitoring water quality with riparian trees along the Berg River, Western Cape
Full text linkMagister Scientiae (Biodiversity and Conservation Biology) - MSc (Biodiv and Cons Biol)Heavy metals and nutrients have long been regarded as pollutants to freshwater ecosystems. These elements have a detrimental effect on plants, animals and the water quality of rivers in South Africa. The Berg River flows from the mountains of Franschhoek to the West Coast of the Western Cape. It is an important river in Cape Town, as it is essential for water distribution to town, for agriculture and industry and also supports a rich diversity of organisms in the ecosystem. Along the river, many farms and towns are situated and many tributaries enter the river. The Berg River dam provides for a water supply during the drier periods of the year. Therefore it is crucial to maintain a good water quality. The study was driven by the need to increase the knowledge of water quality in the upper Berg River after the construction of a new major Berg River dam, constructed in 2007. This study investigated oxygen, water temperature, electrical conductivity, pH, ammonium, nitrate, nitrite in the water and cadmium, copper, lead, iron, zinc, potassium, sodium, calcium, magnesium and phosphorus found in water, sediment and three plant species at ten sites along the upper Berg River, Western Cape. The results showed that the electrical conductivity, pH and the concentrations of nitrate, calcium and magnesium increased downstream, whereas the water temperature decreased downstream. Nitrate, cadmium, copper, potassium, sodium, calcium and magnesium displayed a general increase towards the colder period in the water. Seasonally, copper and magnesium showed significant winter increase within the sediment. Nitrogen, iron and calcium levels within Salix sp., Acacia mearnsii and Brabejum stellatifolium increased downstream. Nitrogen, cadmium, copper, potassium, calcium, magnesium and phosphorus in the three species were higher in the warmer seasons and decreased in the colder. Sources of pollution stem from the Franschhoek and Dwars tributaries, urban and farm runoff
The ecohydrology of the Fransehoek Trust Wetland: water, soils and vegetation.
Full text link>Magister Scientiae - MScThe research was driven by a need to increase the knowledge base concerning wetland ecological
responses, as well as to identify and evaluate the factors driving the functioning of the
Franschhoek Trust Wetland.
An ecohydrological study was undertaken in which vegetation cover, depth to groundwater,
water and soil chemistry were monitored at 14 sites along three transects for a 12 month period.
The parameters used include temperature, pH, electrical conductivity (EC), sodium, potassium,
magnesium, calcium, iron, chloride, bicarbonate, sulphate, total nitrogen, ammonia, nitrate,
nitrite and phosphorus. T-tests and Principal Component Analysis (PCA) were used to analyze
trends and to express the relationship between abiotic factors and vegetation.
Results reflect the strong influence of hydrology, microtopography and nutrient availability in
structuring vegetation composition in the wetland. The wetland has been classified as a
palustrine valley bottom with channel wetland, which is predominantly groundwater-fed
(phreatrotropic), but receives surface water inputs as well. Small scale gradients of
microtopography allow for differences in flooding frequency and duration resulting in
hydrologically distinct sites which differ chemically. Three zones were distinguished in the
wetland. Hollows or low sites were characterized by intermittent flooding and drying and higher
nutrient concentrations in soil and groundwater. High sites which were rarely or never flooded
exhibited higher groundwater temperature and ammonia as well as iron in soils and groundwater.
The inundated sites remained flooded throughout the year and were characterized by high nitrate
and nitrite in soil as well as high EC, magnesium, bicarbonate, sulphate and phosphorus in
groundwater. The limited availability of nitrogen in the wetland favoured plant types Typha
capensis, Paspalum urvillei and Juncus .kraussii which are able to either fix nitrogen or store
nitrogen during more favorable conditions. The main chemical concentration changes take place
between summer and winter. The Principal Component Analyses suggest that sodium, chloride,
potassium, ammonia and phosphorus are the dominant ions determining the chemistry of
groundwater. Increased abstraction from the table mountain aquifer to supplement human
demand may put the wetland at risk of degradation. Intensified agriculture and other land use in
the area are likely to increase pollution loads into the wetland causing shifts in nutrient
availability and vegetation composition. Continued and long term monitoring is essential to
ensure effective management of the wetland and is highly recommended. Closer partnerships
between wetland managers and scientists as well as community awareness and involvement
through a volunteer monitoring programme should be encourage
Phyllosphere bacteria in greenhouses and their use in biocontrol
No full textAbstract: We depend on plant protection products to secure food production. However, current use of these products threatens human and environmental health and their efficacy is decreasing as pathogens acquire resistance. Therefore, regulations on pesticide use are becoming more stringent and consumers are demanding cleaner produce. Thus, novel solutions to protect our crops are needed to safeguard food production. In this thesis, we looked at the never-ending arms race between microbes to find these solutions. First, known mechanisms by which bacteria on the phyllosphere, the above-ground parts of plants, protect plants against diseases were described, also called biocontrol. Secondly, we moved toward greenhouses and investigated the phyllosphere bacteria in these ecosystems. Greenhouses are highly effective environments but, prone to diseases. We characterized that leaves of greenhouse crops show reduced diversity. Interestingly, bumblebees and predatory mites, introduced for pollination and pest control, were important bacterial sources and vectors. These results open up possibilities for using these introduced bumblebees and mites to enrich the greenhouse microbiome, which is further explored in this thesis. To select the beneficial bacteria for such greenhouse enrichment, a large number of bacteria were isolated and characterized. First, compost teas were examined as underexplored microbe-based solutions. However, long-term storage of commercial compost teas impacts the viability of microbes and insufficient numbers of interesting lactic acid bacteria were isolated. Therefore, subsequent efforts in this thesis were directed toward more defined formulations, using well-characterized bacterial strains that were isolated from the phyllosphere. Specifically lactobacilli were targeted in the screening for putative biocontrol agents because they are known for their non-toxic and even beneficial interactions with humans and insects. Moreover, they were detected in several phyllosphere and bumblebee samples from the greenhouses sampled in this thesis. Yet, their applications in biocontrol have not been widely explored. First, the novel species Latilactobacillus fragifolii was characterized This species produces a carotenoid, an uncommon trait that has shown to be associated with flower or phyllosphere adaptation. Moreover, the novel species could protect seedlings from disease caused by a model pathogen, Pseudomonas syringae DC3000. The second strain of interest was Lactiplantibacillus plantarum AMBP214, a biocontrol agent that was shown to be dispersable via bumblebees after spray-drying. Effective and timely dispersal of biocontrol agents is not straightforward in greenhouses. Here, we showed that the dispersal of AMP214 onto flowers via bumblebees was consistent and abundant, in numbers up to 105 CFUs per flower, i.e. exceeding previous reports
Leaf-accumulated particulate matter of perennial urban plant species in relation to their morphological and anatomical leaf traits
No full textAbstract: The importance of urban forests in reducing particulate matter (PM) has been widely established. The foliage of plants provide a natural surface for PM deposition. Past studies have shown the effectiveness of plant species in PM accumulation either based on their leaf longevity (i.e., deciduous/evergreen) or sampled in distinct urban environments. Nonetheless, several factors but not limited to including leaf longevity and the distance from emission source may contribute towards the differences in PM exposure time. Accordingly, PM accumulation patterns between plant species may vary. Therefore, to identify the effective plant species for PM mitigation while maintaining impartiality, we set up a common garden at a background location away from a direct pollution. Ninety-six plant species were selected, with each plant species having 5 replicates each which were bought from one nursery. A total of 480 plants were potted and placed in the common garden. The plants consisted of 45 deciduous broadleaf/needle-like trees, 32 deciduous broadleaf shrubs, 12 evergreen needle/scale-like trees, 5 evergreen broadleaf trees, and 2 climber species belonging to 29 distinct families and 5 functional plant types. The atmospheric metal PM was assessed using Saturation isothermal remanent magnetization (SIRM) while the morphological and anatomical leaf traits such as leaf area, leaf shape, leaf wettability, trichome and stomatal density were examined quantitatively to determine the importance of leaf traits in PM accumulation and immobilization. Throughout this PhD research, we investigated the differences between plant species and their effective leaf traits in (i) net particle accumulation (SIRMU) (ii) particle immobilization (SIRMW), (iii) particle density, (iv) determine the relationship between SIRMU and SIRMW, (v) the temporal dynamics of magnetic PM accumulation and immobilization to recognize the contribution of leaf traits and/or atmospheric conditions in PM accumulation on leaf surfaces. Besides, the association between leaf traits such as epicuticular wax structure (EWS) types and leaf wettability was also investigated. The outcomes of this research illustrated that plant species with high leaf trichome density and high leaf wettability were effective in PM accumulation and PM immobilization. The PM immobilization on leaf surfaces was in proportion to the net accumulated PM. Plant species with trichomes showed a high (70 %) immobilized fraction compared to plant species with no trichomes (48 %) suggesting that for the same amount of accumulated PM, a larger amount is retained by the leaf due to the presence of trichomes. Similarly, when analyzing particle density using scanning electron microscopy (SEM) on leaves of investigated plant species, a high particle density was observed on leaves of plant species with high trichome density. A thorough examination of SEM images illustrated that micro-protuberances such as raised stomata, epicuticular wax crystals trichomes and convex epidermal cells contributed in the edge enhancement effects which warrants for within-session successive repeated measurements when analyzing particle density on leaves with complex micro-morphology using SEM. Concerning the association between leaf traits, a significant association between the EWS types and leaf wettability was indicated. However, the different EWS types cannot be identified using drop contact angle (DCA) measurements due to the overlapping intervals in DCA of distinct EWS types. The effects of leaf traits were observed throughout this research but the assessment of magnetic PM accumulation at temporal scale indicated the effect of meteorological conditions. The PM accumulation was influenced by precipitation, wind speed (negatively) and by relative humidity, ambient PM2.5 concentrations (positively). Thus, concluding that PM accumulation on leaf surfaces is influenced by both leaf traits and meteorological conditions. Based on the results of this research we suggest that plant species such as T. cordata, T. platyphyllos, A. incana, A. campestre and P. abies as effective plant species for PM mitigation in urban environments considering both their ecosystem services and ecosystem disservices
The ecohydrology of the Fransehoek Trust Wetland: water, soils and vegetation.
No full text>Magister Scientiae - MScThe research was driven by a need to increase the knowledge base concerning wetland ecological
responses, as well as to identify and evaluate the factors driving the functioning of the
Franschhoek Trust Wetland.
An ecohydrological study was undertaken in which vegetation cover, depth to groundwater,
water and soil chemistry were monitored at 14 sites along three transects for a 12 month period.
The parameters used include temperature, pH, electrical conductivity (EC), sodium, potassium,
magnesium, calcium, iron, chloride, bicarbonate, sulphate, total nitrogen, ammonia, nitrate,
nitrite and phosphorus. T-tests and Principal Component Analysis (PCA) were used to analyze
trends and to express the relationship between abiotic factors and vegetation.
Results reflect the strong influence of hydrology, microtopography and nutrient availability in
structuring vegetation composition in the wetland. The wetland has been classified as a
palustrine valley bottom with channel wetland, which is predominantly groundwater-fed
(phreatrotropic), but receives surface water inputs as well. Small scale gradients of
microtopography allow for differences in flooding frequency and duration resulting in
hydrologically distinct sites which differ chemically. Three zones were distinguished in the
wetland. Hollows or low sites were characterized by intermittent flooding and drying and higher
nutrient concentrations in soil and groundwater. High sites which were rarely or never flooded
exhibited higher groundwater temperature and ammonia as well as iron in soils and groundwater.
The inundated sites remained flooded throughout the year and were characterized by high nitrate
and nitrite in soil as well as high EC, magnesium, bicarbonate, sulphate and phosphorus in
groundwater. The limited availability of nitrogen in the wetland favoured plant types Typha
capensis, Paspalum urvillei and Juncus .kraussii which are able to either fix nitrogen or store
nitrogen during more favorable conditions. The main chemical concentration changes take place
between summer and winter. The Principal Component Analyses suggest that sodium, chloride,
potassium, ammonia and phosphorus are the dominant ions determining the chemistry of
groundwater. Increased abstraction from the table mountain aquifer to supplement human
demand may put the wetland at risk of degradation. Intensified agriculture and other land use in
the area are likely to increase pollution loads into the wetland causing shifts in nutrient
availability and vegetation composition. Continued and long term monitoring is essential to
ensure effective management of the wetland and is highly recommended. Closer partnerships
between wetland managers and scientists as well as community awareness and involvement
through a volunteer monitoring programme should be encourage
The inorganic pollution of the Franschhoek River : sources and solutions
No full textThe aim of the study was to quantify the extent of inorganic chemical pollution of the Franschhoek River and draw relationships between contaminants in water, sediment and plants. The invasive Acacia mearnsii and Salix babylonica and indigenous Brabejum stellatifolium species were chosen as biomonitors due to their wide spread distribution along the river and their apparent ability to accumulate heavy metals. The sites chosen allowed for comparison of the river quality upstream with that of the river further down stream as it meandered through residential, agricultural and recreational areas, until it joined with the Berg River further downstream. The general aim of the study was to assess the degree of inorganic pollution in the Franschhoek River to evaluate its contribution to pollution of the Berg River, of which it is an important tributary. Also understanding the sources of the pollution would contribute to the ability to reduce pollution
Monitoring water quality with riparian trees along the Berg River, Western Cape
No full textMagister Scientiae (Biodiversity and Conservation Biology) - MSc (Biodiv and Cons Biol)Heavy metals and nutrients have long been regarded as pollutants to freshwater ecosystems. These elements have a detrimental effect on plants, animals and the water quality of rivers in South Africa. The Berg River flows from the mountains of Franschhoek to the West Coast of the Western Cape. It is an important river in Cape Town, as it is essential for water distribution to town, for agriculture and industry and also supports a rich diversity of organisms in the ecosystem. Along the river, many farms and towns are situated and many tributaries enter the river. The Berg River dam provides for a water supply during the drier periods of the year. Therefore it is crucial to maintain a good water quality. The study was driven by the need to increase the knowledge of water quality in the upper Berg River after the construction of a new major Berg River dam, constructed in 2007. This study investigated oxygen, water temperature, electrical conductivity, pH, ammonium, nitrate, nitrite in the water and cadmium, copper, lead, iron, zinc, potassium, sodium, calcium, magnesium and phosphorus found in water, sediment and three plant species at ten sites along the upper Berg River, Western Cape. The results showed that the electrical conductivity, pH and the concentrations of nitrate, calcium and magnesium increased downstream, whereas the water temperature decreased downstream. Nitrate, cadmium, copper, potassium, sodium, calcium and magnesium displayed a general increase towards the colder period in the water. Seasonally, copper and magnesium showed significant winter increase within the sediment. Nitrogen, iron and calcium levels within Salix sp., Acacia mearnsii and Brabejum stellatifolium increased downstream. Nitrogen, cadmium, copper, potassium, calcium, magnesium and phosphorus in the three species were higher in the warmer seasons and decreased in the colder. Sources of pollution stem from the Franschhoek and Dwars tributaries, urban and farm runoff
Modelling and experimental validation of deposition on vegetation to facilitate urban particulate matter mitigation
No full textAbstract: Exposure to air pollution, such as particulate matter (PM), causes adverse health effects, particularly to the respiratory tract and cardiovascular system. PM is the collective name for all kinds of particles ranging from small particles and liquid droplets, which contain organic compounds, acids and metals, to soil or dust particles. One distinguishes PM10, PM2.5 and PM0.1, which have aerodynamic particle sizes smaller than 10, 2.5 and 0.1 \ub5m, respectively. It is mainly the latter that is the most harmful, as PM0.1 penetrates deep into the respiratory system and carries relatively more toxic substances than the other PM fractions. Over a 15-year period, PM concentrations in European member states have fallen by about 30%. Nevertheless, the World Health Organisation (WHO) air quality guidelines, which became stricter in 2021, are exceeded in most places around the world. Particularly in cities, excessive levels of PM are measured and it is here that PM mitigation should be investigated. For this, the implementation of urban green infrastructure, including trees, shrubs, green roofs and green walls, is being looked at. Plants hinder airflow and remove PM from the air by deposition on their leaves and branches. This process is known as dry deposition. Plants can capture PM very efficiently, due to their complex structure of leaves and branches. Green walls offer significant advantages over other types of urban green infrastructure because they can grow on the huge available wall area and, because they do not hinder air circulation, as we sometimes see with trees. Green walls are believed to have a much greater, untapped potential to reduce PM pollution. However, a literature review showed that we do not know the quantitative impact of green walls and lack the tools and/or general methodology to do so. The objective of this thesis is therefore to develop a method for assessing PM removal by green walls, based on predictive models and based on relevant parameters that are experimentally determined. Computational fluid dynamics (CFD) is a numerical method to simulate airflow in complex environments such as cities. These models can also simulate the vegetation-wind interaction in detail and are interesting tools to assess the effect of green walls on PM concentrations in real environments. It is important to first study the aerodynamic effect of green walls and parameterise it correctly in CFD models. Plants decrease the wind speed and create turbulence through a combination of viscous and form drag, which are determined by the permeability (K) and drag coefficient (Cd), respectively. Wind tunnel experiments were conducted with three commonly found climbers (Hedera helix, Parthenocissus tricuspidata and Parthenocissus quinquefolia) and the variation of leaf area density was investigated for two of them. It was observed that the air resistance depended on plant species, leaf area density and wind speed. The difference between the plant species was assigned to the functional leaf size (FLS), the ratio of the largest circle within the boundaries of the leaf to the total leaf area. FLS is likely associated with other morphological characteristics of plants that, when considered collectively, provide a more comprehensive representation of leaf complexity. The pressure and velocity measurements obtained were used to optimise the permeability and drag coefficient in a CFD model. At wind speeds below 0.6 m s-1, the resistance was mainly determined by viscous drag and a larger leaf size resulted in a higher viscous drag. At wind speeds above 1.5 m s-1, form drag was dominant and the parameterised Cd decreased with increasing wind speed due to the sheltering effect of successive plant elements. The leaf area density had a significant effect on K and Cd and, is therefore an important plant parameters in CFD models. The main conclusion here is that the common practice of using a constant Cd to model the influence of plants on the air flow leads to deviations from reality. Wind tunnels are highly suitable to study the impact of green walls on PM concentration under controlled environmental conditions. For this purpose, a new wind tunnel setup was built and great attention was paid to obtaining a uniform air flow. Thus, based on CFD models, appropriate flow controllers were chosen, consisting of honeycombs and screens with different mesh sizes. New PM generation devices and measuring equipment were installed and set up appropriately. Devices were available for generating and measuring ultrafine dust ( 0.03 \ub5m. On the other hand, relative humidity and the type of PM (soot or dust) did not significantly affect the collection efficiency. The main objective of this study was to obtain an optimised size-resolved deposition model. Dry deposition occurs through several mechanisms, in particular gravity, diffusion, impaction and interception, and the subsequent resuspension of deposited PM back to the environment. The modelling of these mechanisms was described by \citet{Zhang2001} and \citet{Petroff2010}. The data obtained from the wind tunnel experiments allowed validating these deposition models. It was for the first time that deposition of real PM on green walls was studied. The different PM deposition mechanisms were found to be strongly dependent on particle size and wind speed. The models of \citet{Zhang2001} and \citet{Petroff2010} each matched PM concentration measurements for only certain particle sizes. Therefore, a combination of the two models was investigated and the root mean square error was lower by on average 3.5% (PM 0.03 \ub5m) compared to the original models at wind speeds greater than 1.5 m s-1. For wind speeds less than 1.5 m s-1, the optimised model did not differ from the original models. The optimised model was able to meet the imposed criteria for air quality models, where a correct model exhibits low deviation from measurements ('normalised mean square error' < 1.5), low bias ('fractional bias' between -0.3 and 0.3) and high R2. In comparison, the R of the optimised model was 0.57, while that of Zhang et al. (2001) and Petroff et al. (2010) was 0.23 and 0.31, respectively. The optimised model was however characterised by a high scatter, with the fraction of modeled results located within a factor of two of the measurements being lower than 50. A model study with a green fa\ue7ade oriented parallel to the incoming airflow showed that deposition by interception and impaction reduced remarkably, but that the orientation had no effect on deposition by Brownian diffusion. A promising green wall form for PM mitigation is the living wall system (LWS). LWS consist of supporting structures with substrate to grow plants in and can be planted with a variety of plant species. This allows to select plant species with optimal characteristics to achieve PM deposition. These characteristics refer to the macro- and microstructure of the leaves, and research has been conducted mainly on these. On the other hand, the influence of the supporting structure and substrate on PM concentrations has rarely been studied. With the new wind tunnel setup, LWS from different manufacturers were tested for their ability to capture PM. The setups were subjected for three hours to an air flow with a low PM concentration (resuspension phase) and then for three hours to an air flow to which additional PM was added (deposition phase). Some setups were able to decrease the PM concentration during both phases, while others just caused the concentration to increase. Some systems were able to reduce particulate matter concentration during both phases, namely LWS consisting of planters (-2% and -4% for PM0.1 and PM2.5, respectively) and textile cloths (-23% and -5% for PM0.1 and PM2.5, respectively). While other systems actually resulted in an increase in concentration especially LWS existing textile fabrics consisting of geotextiles (+11% for both PM fractions) and with moss as substrate (+2% and +5% for PM0.1 and PM2.5, respectively). This highlights the importance of careful selection of suspension systems to reduce particulate matter concentrations. Further research is therefore needed on the materials used in these systems in relation to their particulate content, as well as on plant development in these systems. In addition to air measurements, measurements were taken of the amount of PM deposited on the leaves and suspension system of LWS. This allowed the difference in PM resuspension and deposition between plant species to be investigated. The amount of deposited particulate matter was determined based on 'saturation isothermal remanent magnetisation' (SIRM), a measure of magnetisable particulate matter. This was possible because the added 'Arizona fine test dust' contained iron oxide. However, no significant difference was observed between the SIRM values measured before the wind tunnel experiment, after resuspension and after deposition. This suggested that the iron oxide content in the Arizona fine test dust was too low to measure a significant difference in the SIRM values on leaves after three hours. The plant species did give rise to different SIRM values ranging between 5 and 260 \ub5 A. In particular, SIRM values above 26 \ub5 A were observed for the plant species that were grouped due to their significantly higher accumulation of PM. 'Specific leaf area' (SLA), specifically the ratio of the one-sided 'fresh' leaf area to its dry mass, was the significant leaf characteristic. SLA correlated with leaf complexity. In particular, plant species with elongated leaves were characterized by low SLA, high FLS and high complexity and showed significantly higher SIRM values. Finally, the optimised size-resolved deposition model was also tested in an urban model to get an idea of the impact of a green wall on PM concentrations in a so-called 'street canyon'. These are narrow streets with high buildings on both sides, making air pollution more persistent. To this end, an ideal scenario was tested in which a green wall was introduced along both sides of the street over a length of about 270 m. The model result showed a decrease in PM2.5 and PM10 of 46 \ub1 12% and 52 \ub1 14%. This result is of course for a very optimal scenario where the green wall covers the entire building fa\ue7ades. Since this is not feasible in reality, other ways of promoting contact between green walls and polluted air can be explored. The insights obtained illustrate that the use of climbing plants can be a cost-effective and environmentally friendly solution to reduce PM concentrations. Moreover, the findings showed that models can be used to investigate the impact of green walls on PM levels. These findings fit within the broader context of designing healthy and sustainable urban environments and developing innovative solutions based on solid scientific knowledge
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