Dr Caroline Chiquet successfully defended her thesis on The biodiversity and wider environmental value of green walls
A study of 2 types of living walls (green façades and living wall systems), looking at birds and invertebrates on green façades compared with bare walls and at invertebrates on a range of living wall systems.
The following PhD Projects are currently underway in the Green Wall Centre
The biodiversity & environmental value of urban hedges
GIS/field study of distribution, species, management, density of urban hedges. Their biodiversity value (birds & invertebrates). Comparative value of species as particulate traps.
Particulate pollution mitigation by urban hedges and green screens
Detailed observational and manipulative studies of the ability of green screens (range of species types and combinations) and hedges to capture particulates in urban areas.
Particulate pollution mitigation using green walls
Detailed studies of the ability of green screens, green façades and living walls to capture particulates in urban areas.
Indoor plants and living walls: air quality and rhizosphere interactions
Investigations of the microbial communities active in VOC detoxification in living walls and whether the communities supported by single plants are antagonistic, synergistic, or do not interact when the plants are grown together.
The biodiversity and wider environmental value of green walls
Dr. Caroline Chiquet studied green façades and living wall systems, supervised by Professor John Dover and Dr. Paul Mitchell.
The term “Green walls” (GW) refers to vertical greening systems, i.e. to vegetation growing on or against vertical surfaces. Green façades (i.e. walls covered with climbers or wall shrubs) are familiar features on buildings and walls in urban areas, whilst living walls (i.e. artificial structures made of continuous or modular units, with plants rooted into, attached to the wall with a built-in irrigation system) are more unusual. However, both are a potential way to improve the quality of life in the urban environment through the many ecosystem services they provide.
A common perception is that walls are not considered as a valuable habitat - sometimes not even as habitat at all - and even less as a potential refuge for wildlife in urban areas. As such, they are relatively unexplored at the ecosystem level. However, when vegetation is allowed to grow and develop on them, it uses largely underexploited vertical space and allows an additional type of ecosystem to be incorporated into the urban fabric.
This project aimed to fill the lack of information on the animal population using green walls in the urban environment. Surveys were carried out on the bird, snail, spider and insect communities in green walls of Stoke-on-Trent, Birmingham and London, UK. The green walls were green façades and living walls either new or well-established walls, on new buildings or as retrofitted features. After determining the animal populations, the study focused on the effects of varying characteristics of green walls (e.g. vegetation surface area, plant density and richness, botanical composition, type of foliage) on these communities and also investigated if the local environment (e.g. pedestrian and vehicle traffic volumes, abundance of nearby vegetation) influenced the use of green walls by animals. The results showed that animal groups respond differently to the characteristics of green walls and the surrounding features. Importantly, the design and the maintenance interventions of green walls influence their use by animals and, as such, it is possible to modify these environments to make them more attractive to certain animal communities. Whether growing on independent self-supporting structures or directly on or in buildings, plants can use largely underexploited vertical space allowing an additional type of ecosystem to be incorporated into the urban environment.
Another project looking at the photo-synthetic activity and the thermal mitigation of the heat island effect is currently on-going
The Biodiversity and Environmental Value of Urban Hedges
Elle Atkins is studying urban hedges. Her project is supervised by Professor John Dover, Dr. Ruth Swetnam and Graham Smith.
It is generally well known that hedges provide valuable habitats for wildlife and offer many other benefits to agricultural landscapes such as wind breaks and barriers to pollution due to their ability to alter airflow and to restrict the spread of pesticides and fertilisers. They are also perceived as an attractive element to the British landscape. Hedges are also present within urban areas but surprisingly little is known about the benefits they offer. It is likely that there are many differences in the structure and species composition of urban hedgerows compared to hedges in rural areas as many will be planted as boundary markers such as surrounding houses, parks or commercial areas and will be planted with species that will provide year round screening such as Laylandii, Privet or Laurel rather than the more traditional Hawthorn dominated rural hedgerow. Some of these ‘traditional’ hedgerows exist within urban areas as they have been surrounded with the expansion of the town or city. Urban hedgerows will still offer habitats for wildlife but the extent to which they do this is not well known. Urban greenery such as green walls, parks and urban trees offer many benefits to humans, these are termed ecosystem services and are likely to include pollution capture, increased drainage, a cooling effect in hot weather and an insulating effect in cold periods and also an increased sense of wellbeing.
This project aims to locate and map urban hedgerows in 3 different urban areas using false colour aerial photography. This will then be used to look at the spatial information and connectivity of urban hedgerows. Another string to this project is to investigate the potential of urban hedgerows to offer ecosystem services focusing on their ability to trap particulates from pollutions which are responsible for thousands of premature deaths in Europe. A number of studies will be conducted using an Environmental Scanning Electron Microscope to count the particulates captured on the leaves and branches of different species of hedge plants. Measurements of the structure of the hedge will be taken to aid in providing an estimation of the ability of the hedge as a whole in capturing particulate pollution.
The biodiversity of urban hedges will also be studied and will focus on the use of hedges within urban areas by birds and invertebrates. This will be linked to the species, quality and management of the hedges.
Particulate Pollution Mitigation by Urban Hedges and Green Screens
Simon Phillips is studying particulate pollution mitigation using green screens and urban hedges, supervised by Professor John Dover and Dr. Ruth Swetnam.
A growing world population has led to an increasing number of people now living in urban areas and this is expected to rise to 60% of the world population by 2030, with a further expected increase to 70% by 2050. Due to population growth urban areas have higher levels of air pollution when compared to rural areas.
One of the most dangerous types of air pollution is airborne particulate matter. There are two main ranges of particulate matter: coarse particulate matter which covers particle sizes of 10 µm (PM10) and smaller, and fine particulate matter which covers particles smaller than 2.5 µm (PM2.5) . Particle size indicates how far a particle will penetrate into the lungs and whether it will pass from the lungs into the bloodstream, therefore being detrimental to human health causing respiratory and cardiovascular disease.
Studies have shown that vegetation can mitigate the effects of particulate pollution especially PM10 and PM2.5, however these studies have mainly focussed on trees. Climbers such as Ivy (Hedera helix) can remove pollutants from the immediate environment where pollution is generated. A number of studies have demonstrated that plants such as Ivy can act as particulate traps removing not only carbon particles, but also a range of metal particles.
This study aims to look at the potential of planted Ivy green screens in reducing particulate pollution in urban areas. Experiments will look at their potential for increasing their impact as particulate traps by planting in multiple rows and looking at different species combinations.
The approach will use an Environmental Scanning Electron Microscope (ESEM) to quantify the different particulate sizes deposited on plant material and inorganic substrates will be used as particulate traps to quantify the particulates removed by the green screen.
The elemental make-up of particulates will be examined using Energy Dispersive X-ray Spectrometry analysis on the ESEM. The experimental results will be used in a Geographic Information System environment to evaluate the impact of green screens on particulate matter reduction under different scenarios.
The PhD is being part-sponsored by Mobilane UK.
Particulate Pollution Mitigation Using Green Walls
Udeshika Weerakoddy is studying particulate pollution mitigation using green walls, supervised by Professor John Dover and Dr. Paul Mitchell.
The increasing complexity and magnitude of the problem of urban air pollution have resulted in a growing need for the services of disciplines in modern engineering technology where we need more research. Emission of Particulate Matter (PM) comprises a considerable fraction of this pollution. Serious health issues are caused by PM10 and and PM2.5 ultra-fine particles are known to be a major cause of premature death of urban dwellers. Interventions are being tried worldwide to determine the role of green infrastructure in minimizing the Particulate Matter, but some aspects are overlooked.
As an advanced green structure with complex species composition, the PM trapping capacity and magnitude of Living Walls is not well understood and has rarely been researched. The current research project explores the best species composition and optimal conditions of living walls in the context of PM trapping, thereby ensuring the maximum benefits of green walls to meet global air quality standards.
This project particularly aims to study the specific characteristics of the plants including leaf surface characteristics, foliage density and dimensions, and planting densities which could enhance the efficiency and the efficacy of trapping particulates while considering site-specific variations and seasonal influences. The work will employ the Environmental Scanning Electron Microscope (ESEM) and Energy Dispersive X-ray (EDX) to quantify the abundance of different particle size ranges on plants and to study their elemental composition respectively.
This study would result in a feasible solution to the problem of urban particulate pollution while enhancing urban greening without much land space utilization.
Indoor plants and living walls: air quality and rhizosphere interactions
Dilhani di Silva is studying air quality and rhizosphere interactions in indoor plants and living walls, supervised by Dr. Dan Tonge and Dr. Peter Gowland.
Indoor air quality (IAQ) directly affects human health since poor or polluted air may cause problems such as dry eye, nose and throat, headache, nausea, fatigue, respiratory difficulties and stress, the classic symptoms of “sick building syndrome”. High concentrations or long-term exposure to indoor pollutants may lead to more serious conditions, including asthma and heart disease, and impact liver, kidney or nervous system function. Volatile Organic Compounds (VOCs) are important air pollutants and are typically found at higher concentrations indoors compared with outdoors. They are commonly emitted from everyday items including electric and electronic equipment, cosmetics, perfumes, paints, furniture, fabrics, detergents, printers and glues, carpets, ceiling tiles and compressed wood products. Of the more than 350 indoor VOCs that have been identified from indoor air, formaldehyde, benzene, toluene, xylene and tetrachloroethene are the most common.
Potted plants such as Peace Lily, Kentia Palm, Janet Craig, Spider Plant and Rubber Trees have been shown to reduce VOCs in indoor environments. The microbes in the root zone of these plants, the “rhizosphere”, have been identified as the organisms responsible for the detoxification process. So a comprehensive understanding of the association and the mechanism of rhizosphere microorganisms with plants is very important in the optimisation of VOC reduction, hence improving IAQ.
In this project, we will employ soil metagenomic analyses. This involves the characterisation and quantification of the microbial communities active in the rhizosphere of potted plants. Work on VOC/rhizosphere interactions has typically been carried out with single plants. With the advent of new green wall technologies we have the opportunity to increase the density of plants in the office environment without losing large areas of floor space. However, we do not know how the microbes in the rhizosphere of plants will interact in multi-species plantings and our project will attempt to determine whether interactions are mutualistic, antagonistic or neutral in terms of VOC reduction. Genomic analyses of the rhizosphere microbial community will be carried out by performing Next Generation Sequencing (NGS) and we expect to identify the functional and structural genes related with VOCs detoxification in indoor air.
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