Air Pollution Symposium


Proceedings from the JNCC Air Pollution and Ecosystem Change Symposium

A symposium held on 28-29 October 2003, in Caernarfon, North Wales.
Workshop objectives and background


Setting the Scene

Air pollution and ecosystems in the United Kingdom
Professor David Fowler, Centre for Ecology and Hydrology
(PDF, 2.27MB)
Evidence of change - findings of CS2000 and New Plant Atlas
Dr. Trevor Dines, Plantlife
(PDF, 314KB)
Air pollution policy and implications
Dr. Alison Vipond, Department of Environment, Food and Rural Affairs
Abstract Presentation
(PDF, 612KB)

Research update

Nitrogen effects and fate in ecosystems
Dr. Bridget Emmett, Centre for Ecology and Hydrology
(PDF, 115KB)
Woodland monitoring in the UK
Dr. Mark Broadmeadow, Forest Research
Abstract Presentation
(PDF, 981KB)
Development and application of empirical critical loads for nitrogen
Professor Mike Ashmore, Bradford University
Abstract Presentation
(PDF, 354KB)
Air pollution monitoring in the UK
Dr. Brian Reynolds, Centre for Ecology and Hydrology
Abstract Presentation
(PDF, 1.77MB)

Air Pollution Assessment

Determining impacts and risk – information requirements of the pollution regulators
Dr. Jon Foot, Scottish Environment Protection Agency and
Mr. Jim Storey, Environment Agency
Abstract Presentation
(PDF, 1MB)
Bio-indicator methods for monitoring of nitrogen impacts on statutory nature conservation sites
Dr Mark Sutton, Centre for Ecology and Hydrology
Abstract Presentation
(PDF, 288KB)
Atmospheric nitrogen pollution impacts on biodiversity
Dr. Jane Goodwin, Department for Environment, Food and Rural Affairs
Abstract Presentation
(PDF, 234KB)
Workshop – Understanding the impacts of air pollution on the SSSI series
The workshop session required groups to consider the options for assessing the impacts of air pollution on the SSSI series.
Background and Objectives
The conservation agencies were involved in the membership of Defra's recent National Expert Group on Transboundary Air Pollution (NEGTAP). The NEGTAP report provides an assessment of air pollution effects from acidification, eutrophication and ground level ozone. Forecasts of the situation in 2010 are also made, a date when all existing air pollution legislation and scheduled emission reductions will be in place.
The report concludes that many of our most valuable habitats will still be suffering the adverse impacts of excess pollution from sulphur and nitrogen compounds, in combination with increasing background levels of ground level ozone. For example, in 2010 critical loads for acidification will be exceeded in nearly half of UK ecosystems, while critical loads for eutrophication will be exceeded in 40% of UK 1km x 1km grid squares with heathland and 20% with sensitive grassland. This is clearly at variance with the UK Government's domestic and international responsibilities to protect these sites from harm.
The conservation agencies, as advisers to the Government and its devolved administrations, have a vital role to play in advising on pollution reductions necessary to protect the natural environment. In order to fulfil this responsibility the conservation agencies will need to better understand the impacts of air pollution on national and international wildlife sites, and the wider countryside.
One of NEGTAP's key recommendations was to provide site-specific links between the pollution field and what we observe on the ground. This presents the conservation agencies with a major challenge and we must make every effort to articulate the condition of our designated sites in the context of air pollution. This information will be required to inform JNCC's advocacy for further and more targeted cuts in emissions of air pollutants. It is also required in order to better inform our staff with regards the threats of air pollution and how this might interrelate with the conservation objectives, monitoring and management of sites, and to inform our advice on air pollution related casework.
The Air Pollution and Ecosystem Change Symposium is being run jointly by the Air Pollution and Uplands Lead Co-ordination Networks. It will bring together habitat specialists from the conservation agencies, external air pollution experts and policy and practitioners from Government and Government agencies.
The objectives of the symposium are:-
  1. To raise awareness amongst conservation agency staff of air pollution issues and their relevance to nature conservation and site protection.
  2. To consider how we can better understand the impact of air pollution on the condition of statutory sites and what role the conservation agencies play.


The need for the symposium is drawn out of the recommendations of NEGTAP and also the need to address these issues in order to influence subsequent rounds of domestic and international air pollution policy. NEGTAP identified nitrogen compounds as one of the greatest threats to the integrity of ecosystems. This fact together with the wider countryside enrichment observed in CS2000 and the New Plant Atlas for British and Irish Flora suggest that the main emphasis of the symposium should be on nitrogen pollution, though acidification and ozone will be covered briefly.

Air Pollution Policy and Implications

Dr. Alison Vipond
Air and Environment Quality Division
Department for Environment, Food and Rural Affairs
The sources of air pollution are many and varied, ranging from industrial, agricultural and road transport to domestic and natural sources. It is recognised that air pollution can adversely affect health, materials and vegetation. Air pollutants can travel through the atmosphere over long distances, their effects being experienced over a range of scales – local, national, continental and even hemispheric, for some pollutants. Good progress in controlling many emissions is being made. For example, UK emissions of sulphur dioxide have been cut by 80% since their peak in the 1970s, and emissions of nitrogen oxides have nearly halved since the early 1990s, bringing significant improvements in air quality.
Reducing the adverse effects on vegetation from acid and nitrogen deposition and from ground-level ozone, continues to be a major driver of international agreements on emission reductions. The EC National Emissions Ceilings Directive (NECD) and the UNECE Gothenburg Protocol are the two most recent agreements to curb emissions, aiming to reduce acidification, eutrophication and ground-level ozone. An effects-based approach to identify possible emission reduction scenarios and their costs and environmental benefits was used to inform the negotiations. The agreements set emission ceilings (upper limits) for sulphur dioxide, nitrogen oxides, ammonia and volatile organic compounds, to be achieved from 2010 onwards. Notably, they are the first agreements to contain an emission target for ammonia, a pollutant mainly derived from livestock where little emission control has been required to date.
Preparations are underway for the international review of the NECD and Gothenburg Protocol in 2004/5. This will involve the assessment of what current policies are expected to deliver and what more needs to be done to minimise adverse effects of air pollution on human health and the environment. The increased understanding of the role of global air pollution, particularly contributing to increasing levels of ground-level ozone, will also have a bearing on international air pollution policy.
On the national scale, the Government's air quality policies are set out in detail in the Air Quality Strategy for England, Scotland, Wales and Northern Ireland (AQS). The Strategy describes plans to improve and protect air quality in the UK in the medium-term, addressing the main air pollutants. The Strategy's objectives focus on achieving concentrations to avoid damage to human health. There are also two objectives aimed at achieving levels of nitrogen oxides and sulphur dioxide to avoid damage to vegetation. The current AQS objectives for ecosystems are met, but the problems are not solved. Defra is examining the potential to strengthen the objectives to ensure protection of Sites of Special Scientific Interest, compatible with the Habitats Directive and its own Public Service Agreement.
The conservation agencies have a significant role in developing our understanding of the impact of air pollution on conservation sites, and in guiding the future development of policy on emissions. In particular, an assessment of the current status of conservation areas, with respect to damage or risks from air pollution, is urgently required. This will raise the profile and understanding of a potentially serious issue, and also help to identify targets for ecosystem protection to guide air quality policies. In addition, site management can be crucial to prevent or slow damage or to speed up recovery, particularly where sites have been polluted by years of historic deposition and are now showing signs of change. Protecting our valuable habitats from air pollution requires a combination of both management at the local level, and action to reduce emissions at a range of scales, from local to global. There is a growing need to fortify links between the conservations agencies and Defra in this area.

Woodland monitoring in the UK

Mark Broadmeadow
Environmental Research Branch,
Forest Research, Alice Holt Lodge, Farnham, Surrey, GU10 4LH
A number of monitoring schemes are operated by Forest Research which provide information on the state or condition of woodland ecosystems at a national level. The Condition Survey of Non-woodland Trees and the National Inventory of Woodland and Trees were not designed to provide information on air quality, but both include an assessment of a number of indicators of the general state of trees or woodland. Furthermore, the range of attributes assessed in the latter scheme, together with its scale (40 000 ground truthing plots) provides a potentially valuable resource for air pollution studies. In contrast to these two general woodland condition monitoring schemes, the Environmental Change Network, the Forest Condition Survey (formerly the Forest Health Survey: Level I) and the Intensive Forest Health Monitoring Network (Level II) were all established to monitor the effects of air pollution, and in the case of the last of them, to identify cause-effect relationships.
The Forest Condition Survey is an annual assessment of crown transparency and growth, together with a number of other measures of state, on more than 300 plots covering five species – oak, beech, Scots pine, Norway spruce and Sitka spruce. Inter-annual variation is evident, particularly in Sitka spruce and beech as a result of insect defoliation and seed production, respectively. No long-term trends are apparent with the possible exception of a limited deterioration in oak, which may be an artefact of initial survey design. Spatial variation in condition has been investigated, and relationships are evident between both needle retention and insect damage in Scots pine and mapped nitrogen deposition. An extension study also revealed a weak relationship between the nitrogen status of the ground vegetation and distance to the woodland edge in a sample of the beech plots.
Wider comparisons and analyses within Europe also are possible through involvement with the European Large-scale Forest Condition Survey, in which over 6000 plots are assessed. The Intensive Forest Health Monitoring Programme is a second pan-European Programme, involving over 500 sites across Europe of which twenty are located in the UK. More detailed information is provided on the physical environment, enabling trends and cause effect relationships to be elucidated. A comparison of two Scots pine plots demonstrates contrasting responses. Recovery from past acid deposition is evident at a site in the English Midlands, while soil acidification and the effects of excess nitrogen deposition are now becoming apparent at a plot in Thetford forest, an area of intensive animal husbandry where deposition is dominated by reduced nitrogen. Concern is now focussing on the current and future effects of tropospheric ozone pollution which presents difficulties in its analysis and interpretation for forest ecosystems. Routine monitoring has indicated limited damage to trees in the UK, but the use of bio-indicators in the form of shrub species may prove to be a more suitable approach.
An overall assessment of the condition of British forest based on the available monitoring information is that they are generally in a favourable condition with no long-term trends apparent and that air pollution is not currently affecting the health of trees to a significant extent. Climatic events in individual years together with the effects of insect pests and pathogens are more important determinants of forest condition than the air pollution environment, and this position is likely to continue given the predictions of climate change. However, when the wider forest ecosystem is assessed, some detrimental effects of enhanced nitrogen deposition are apparent, although not to the extent that might be expected given the scale of nutrient nitrogen critical load exceedance.

Development and application of empirical critical loads for nitrogen

Professor Mike Ashmore
Department of Geography and Environmental Science
University of Bradford
The critical load concept was first developed in the context of European scale negotiations on reductions of sulphur and nitrogen emissions that were based on reduced the environmental impacts of these pollutants most effectively (by minimising critical load exceedance). The critical load of nitrogen deposition is that below which harmful effects on ecosystem structure and function do not occur according to current knowledge; in the case of empirical critical loads for nitrogen, these are based on a qualitative assessment of field and experimental evidence, rather than mass balance calculations. New critical loads for use in European scale evaluations were agreed at a workshop held in Berne, in November 2002.
But how useful are these critical loads for assessing the impacts of nitrogen deposition in the U.K.? This paper will briefly consider three important issues related to this question , focussing primarily on grasslands, heathlands and bogs and mires:-
  1. How have the Berne workshop recommendations been used to develop maps of critical loads and their exceedance for the UK?
  2. Is the fact that significant areas of the UK receive nitrogen deposition above the critical load for that ecosystem consistent with the field and experimental evidence in this country?
  3. Can critical loads be used reliably in risk assessment for specific sites?


I conclude that the national maps of critical loads and their exceedance are broadly consistent with the rather limited evidence that we have available on the ecological impacts of nitrogen deposition in the UK, and are valuable in the context of broad national policy development. However, a critical question for interpretation of the field data, and for predicting the consequences of reductions in nitrogen deposition, is the timescale of response, which in terms of effects on community composition of vascular plants, but not lichens and bryophytes, may be decades. Furthermore, there are major limitations in applying the critical load values in assessments of individual sites with their specific deposition and management histories, and nutrient status.


Air Pollution Monitoring in the UK

Dr. Brian Reynolds
Centre for Ecology and Hydrology
The UK monitoring networks relevant to acidification, nitrogen deposition and ozone are reviewed. The atmospheric deposition / air quality monitoring networks are probably adequate to define broad spatial patterns and changes in the pollution climate of the UK. Their usefulness for site specific assessments is limited by factors such as the relatively coarse resolution of the mapping and within grid cell variability. Point source emissions and the effects of complex terrain on wet deposition contribute significantly to the latter. The core monitoring network of freshwater sites (the UK Acid Waters Monitoring Network) is providing evidence of recovery from acidification and a basis for predictive modelling. Additional sites operated by individual research organisations provide complimentary data in acid sensitive areas of Scotland, the Lake District and Wales. In contrast, but with the exception of forestry, monitoring data for semi-natural systems and soils are dispersed and disparate with no networks specifically targeted at monitoring acidification / nitrogen impacts. Relevant information can be gathered from networks such as the ECN and from repeated surveys such as CS2000. However our ability to assess the effectiveness of emissions control policies and predict future responses for semi-natural systems is inhibited by the lack of a co-ordinated monitoring network.

Determining Impacts and Risks - Information Requirements of the Pollution

Dr. Jonathan Foot, Scottish Environment Protection Agency
Mr. Jim Storey, Environment Agency
There are nearly 800 candidate SACs and over 200 SPAs in the UK. The Habitats Directive requires 'measures taken...shall be designed to maintain or to restore, at a favourable conservation status, natural habitats and species of wild fauna and flora of community interest.' Competent Authorities must review the effects of existing permissions, alone and in combination with other permissions, in light of conservation objectives for SACs/SPAs. Depending on the likely effect the permission may be having, they must confirm, amend or revoke the permission.
There have been significant reductions of sulphur dioxide and oxides of nitrogen emissions but a number of these internationally protected habitats will remain in areas where the effects of air pollution will exceed environmental standards. Also, unfortunately, there has probably been little reduction in the releases of ammonia to atmosphere. Around 70% of terrestrial habitats and 25% of freshwater sites are under threat from acidification. Eutrophication is likely to be adversely affecting 65% of ecosystem areas.
SEPA and the Environment Agency have embarked on an assessment of the impacts of critical load and critical level exceedance to the habitats and species at each site. The regulators have agreed to follow a 4 stage procedure, the first two steps of which is to screen out industrial processes which have no relevance or no likely significant effect on individual sites. Recently, SEPA, the Environment Agency and the NI Environmental Heritage Service have embarked on a major screening exercise to utilise Defra's recent remodelling of acid and nutrient nitrogen deposition for the UK. The deposition from major industrial sources is being added onto this "background" data and compared to critical loads for the features and habitats of sites.
If the process does not fail the relevance and significance tests then an appropriate assessment of its effects must be made. If a likely significant effect is found then the regulator must investigate and implement options to improve the status of the site, including requiring the process to close down.
The conservation agencies have an essential role in this work and it is very important that they help ground truth the various stages and ensure the assessment is carried out against the correct features and habitats. It is also crucial that they provide information on other aspects which may be affecting the integrity of the sites.

Bio-indicator methods for monitoring of nitrogen impacts on statutory nature conservation sites

M.A. Suttona, I.D. Leitha, C.E.R. Pitcairna, Netty van Dijka, Lucy Shepparda,
Sim Tanga, R. Mitchellb, S. Smartc, D. Fowlera
Centre for Ecology and Hydrology: aEdinburgh, bBanchory and cMerlewood
Pat Wolseley, William Purvis and Peter James
Natural History Museum, London
Atmospheric nitrogen deposition represents a threat to naturally nutrient-poor plant communities, leading to a loss of conservation value in of importance for statutory nature conservation sites. Until now, the regulatory assessment of these impacts has been focused on the critical loads approach, where estimated atmospheric deposition loads are compared with 'critical loads' to estimate the occurrence and extent of 'critical load exceedance'. This provides a risk assessment that indicates the likelihood of future change. However, it does not indicate whether changes are already occurring on a site or provide a means to monitor the extent of actual change.
Bio-monitoring complements the critical loads approach in that it provides information on the actual condition of the sites of interest. The range of bio-monitoring techniques for nitrogen includes: a) biochemical measures of nitrogen accumulation, b) measures of species composition of different components and c) methods involving the transplanting of live plant material. The different techniques are variously suited to act as bio-indicators of atmospheric deposition, air concentrations of reactive nitrogen compounds and/or ecological change, and may be applied by spatial comparisons at a single point in time or for bio-monitoring over periods of several weeks to many decades. A very wide range of potential methods is available, and these vary in robustness, potential artefacts, characteristic response time, technical requirements and costs. This presentation reports ongoing work commissioned by JNCC and the UK conservation agencies to review, test and refine the most cost-effective bio-monitoring techniques for application at statutory nature conservation sites.
Of the biochemical methods, the tissue nitrogen concentration of bryophytes and Calluna is without doubt the best-characterized parameter to indicate atmospheric nitrogen deposition. While a range of responses has been observed in the past, standardized protocols are a key to obtaining consistent results. Although there is uncertainty regarding the level of tissue nitrogen at which plant community changes will occur, the method can be used (with confidence limits) to estimate whether atmospheric deposition is significantly above or below the critical load. A similar principle applies to the measurement of foliar amino acids and two more recently recognized parameters: soluble foliar ('substrate') nitrogen and foliar ammonium. Recent data show that the smaller the pool size, the larger the nitrogen response: over a local gradient of ammonia deposition, the foliar concentrations of total N, soluble N and ammonium increased by factors of 3, 5 and 20, respectively. The latter technique, in particular, appears to be sensitive, fast response and low-cost and is being tested further.
Species composition methods, by definition, represent the changes of most interest for conservation agencies. In approaches applying the Ellenberg nitrogen scale, each higher plant and bryophyte species is assigned a nitrogen preference score, allowing habitat-weighted values to be calculated. As a simple bio-indicator technique for regional spatial comparison, the method has severe limitations since many other factors affect species composition. However, the method is well suited to assess local spatial changes near sources, as well as to long-term bio-monitoring at fixed locations. The assessment of lichen floral composition provides a particularly sensitive approach to indicate atmospheric nitrogen exposure. However, while the responses to gaseous ammonia are well characterized, there is more debate regarding the effects of nitrogen oxides or total nitrogen deposition. The ammonia response is, to a large extent, mediated by an increase in bark pH, which selects against "acidophyte" species and favours "nitrophyte" species. The most sensitive specialist scoring system follows that of van Herk, while there is also potential to refine a simplified "Ellenberg"-type approach for use by non-specialists. Lichens on twigs are found to be particularly sensitive to ammonia due to their naturally higher bark pH than trunks of trees.
Plant transplant methods can be used both to monitor atmospheric nitrogen deposition and its impacts. The setting out of standardized grass plants provides a rapid and graphic demonstration of atmospheric nitrogen impacts for local site assessments. For example, plants were shown to grow twice as fast in the immediate vicinity of a poultry farm compared with 300 m distant. While shading may affect growth rate and dilution by the plant, the total N inventory of the plant gives a robust indication of atmospheric inputs, including the potential to estimate the saturation of dry deposition rates. Native plant species may also be transplanted reciprocally between high and low N sites, with measurement of growth rates and foliar N levels. While further work is required to improve the approaches for higher plants and lichens, particular success has been had with bryophytes. The method is labour intensive, but it has the advantage that, where transplanting to clean conditions leads to plant recovery, the case for pollution abatement of an existing source is substantially strengthened.
It is clear that there are limitations to each of the approaches for bio-monitoring of reactive atmospheric nitrogen. However, a number of techniques are now available to indicate different aspects, such as concentrations, deposition and impacts of different components of atmospheric nitrogen over different timescales. Used in conjunction with the classical critical loads assessment, bio-monitoring therefore provides a practical approach to demonstrate nitrogen exposure and impacts on statutory nature conservation sites.
Atmospheric nitrogen pollution impacts on biodiversity:Phase 1 - Model development and testing
Dr. Jane Goodwin, Land Use and Rural Affairs Science Unit, Biodiversity and Landscape Branch Defra
Emission of pollutants to the atmosphere (e.g. oxides of nitrogen and ammonia) can lead to levels of nitrogen enrichment which have adverse effects on vegetation and ecosystem function. Semi-natural habitats are known to be particularly vulnerable. Two recently published national monitoring studies have detected signs of widespread nitrogen enrichment in the British countryside, and an inter-agency expert panel has highlighted nitrogen enrichment as a key threat to UK vegetation composition. This work is therefore being commissioned to investigate the implications of atmospheric nitrogen deposition on biodiversity. The overall aim is to develop and test sophisticated analytical techniques in order to assess the importance of this factor with specific reference to the delivery of PSA targets for achieving favourable condition on SSSIs and to Biodiversity Action Plan targets for priority habitats and species.
This research project aims to build on the results of the earlier work in order to improve our understanding of nitrogen pollution impacts on biodiversity. It is anticipated that the work will proceed in two distinct phases. Phase 1 will include information review, model developments and testing of the applicability and validity of the approaches developed. Phase 2 is likely to proceed according to the relative merits of the work delivered under Phase 1. The objectives for Phase 1 are:
  1. Review the current knowledge base for atmospheric nitrogen pollution impacts on biodiversity.
  2. Further develop and test modelling techniques to help quantify the impacts of atmospheric nitrogen deposition on biodiversity nationally.
  3. Apply the modelling techniques to a sample of habitats and sites to examine current and projected levels of the nitrogen threat (from atmospheric and other sources) to habitats and sites of high nature conservation importance.
  4. Provide a preliminary interpretation of the results with respect to achievement of: (i) the Public Service Agreement (PSA) target for achieving favourable condition on SSSIs; and, (ii) Biodiversity Action Plan targets for priority habitats and species and related indicators of biodiversity (e.g. Country Biodiversity Strategy indicators).
  5. Develop proposals for Phase 2 of this work which should allow for a wider geographical application of the models.


The project is in the process of being let as of 23rd October and if negotiations are successful it should commence by the end of 2003 and run for approximately 18 months. A steering group will be formed to guide the project.