Metal and nutrient dynamics on an aged intensive green roof.

Runoff and rainfall quality was compared between an aged intensive green roof and an adjacent conventional roof surface. Nutrient concentrations in the runoff were generally below Environmental Quality Standard (EQS) values and the green roof exhibited NO3(-) retention. Cu, Pb and Zn concentrations were in excess of EQS values for the protection of surface water. Green roof runoff was also significantly higher in Fe and Pb than on the bare roof and in rainfall. Input-output fluxes revealed the green roof to be a potential source of Pb. High concentrations of Pb within the green roof soil and bare roof dusts provide a potential source of Pb in runoff. The origin of the Pb is likely from historic urban atmospheric deposition. Aged green roofs may therefore act as a source of legacy metal pollution. This needs to be considered when constructing green roofs with the aim of improving pollution remediation.

Rainwater runoff retention on an aged intensive green roof.

Urban areas are characterised by large proportions of impervious surfaces which increases rainwater runoff and the potential for surface water flooding. Increased precipitation is predicted under current climate change projections, which will put further pressure on urban populations and infrastructure. Roof greening can be used within flood mitigation schemes to restore the urban hydrological balance of cities. Intensive green roofs, with their deeper substrates and higher plant biomass, are able to retain greater quantities of runoff, and there is a need for more studies on this less common type of green roof which also investigate the effect of factors such as age and vegetation composition. Runoff quantities from an aged intensive green roof in Manchester, UK, were analysed for 69 rainfall events, and compared to those on an adjacent paved roof. Average retention was 65.7% on the green roof and 33.6% on the bare roof. A comprehensive soil classification revealed the substrate, a mineral soil, to be in good general condition and also high in organic matter content which can increase the water holding capacity of soils. Large variation in the retention data made the use of predictive regression models unfeasible. This variation arose from complex interactions between Antecedant Dry Weather Period (ADWP), season, monthly weather trends, and rainfall duration, quantity and peak intensity. However, significantly lower retention was seen for high rainfall events, and in autumn, which had above average rainfall. The study period only covers one unusually wet year, so a longer study may uncover relationships to factors which can be applied to intensive roofs elsewhere. Annual rainfall retention for Manchester city centre could be increased by 2.3% by a 10% increase in intensive green roof construction. The results of this study will be of particular interest to practitioners implementing greenspace adaptation in temperate and cool maritime climates.

What lies beneath?--issues in the representation of air quality management data for public consumption.

Policy developments in the UK and the European Union (EU) now require local authorities to engage the general public within the whole process of local air quality management (AQM). Indeed, this is considered to be one of the means by which air quality issues can gain public support and help ensure future improvements. One of the outcomes of this is that data sets associated with air quality management must now be disseminated to nonscientific audiences. This is a problematic task for a number of reasons. One of these relates to the fact that air quality data are complex and variable, yet the public demand representations that are clear and unambiguous. Another important issue is associated with the increasing use of geographical information systems (GIS) and mapping tools, which allow data to be generated and summarised in many different ways without due regard to the effects that the choice of methodology can have on the way data are interpreted. The variation in information obtained using different techniques can represent a problem, but is also an opportunity to further explore data sets and to draw out specific information for complementary air quality management tasks. However, at present, the lack of a well-grounded methodology and guidance for handling and representing the spatial aspects of data sets means that consistency between areas and authorities is not maintained. Such a situation fosters ambiguity at several levels, from the individual's perception of public health-related information to an Authority's rationale for the selection of air quality management areas (AQMAs). This paper investigates a number of issues relating to spatial data generation and representation in the field of air quality management, particularly in relation to emissions inventory data. The examples are UK based, but the issues raised are applicable to other examples and areas. One case study examines the difference in information gained through a number of common mapping techniques and shows how different 'problems' can be identified merely as an artefact of the dissemination technique itself. To further illustrate the difficulties and conflicts faced in representing and explaining these data in a practical context, reference is then also made to the methods recently considered by an example London authority. The paper concludes with a call for the development of a more standardised method for representing different types of air quality management-related data, which may help to overcome these problems in the future.