ECOS 38 (2)
Excessive nitrogen in air pollution is having a devastating on fungi and plants, soils and ecosystems. Decades of scientific evidence demonstrates clear impacts of nitrogen deposition across our most diverse wildlife habitats including woodlands, grasslands, heaths and bogs.
Why aren’t we ‘talking about nitrogen’?
Nitrogen emissions rarely get a mention in the familiar list of issues affecting wildlife and habitats such as habitat loss and water pollution. When the issue is mentioned, it’s often couched as ‘nutrient enrichment’ (which sounds like a good thing) or ‘atmospheric nitrogen deposition’ (too technical for many of us).
It can also seem counter-intuitive; nitrogen is well-known as a fertiliser - good for farm crops and good for the gardener’s fruit and veg patch.
Yet many of our species-rich ecosystems – such as acid and chalk grasslands, heaths, bogs and woodlands – have evolved to thrive in low-nutrient conditions. Although 78% of the atmosphere is made up of nitrogen gas, most of it is inert. Reactive nitrogen, which is used by flora and fungi, is scarce in nature, formed only by a volcanic eruption, a lightning strike or (last but certainly not least) specialist soil bacteria.
Effects of nitrogen emissions include loss of species richness, changes in soil chemistry and habitat degradation; more than 90% of the land in Special Areas of Conservation (SACs) in England and Wales already has more nitrogen than it can tolerate (63% in the UK overall).
My organisation Plantlife has been working to raise this issue up the agenda, in collaboration with the British Ecological Society, Centre for Ecology and Hydrology, Stockholm Environment Institute and others in the Plant Link network. Since our workshop in January and the media launch of the report We need to talk about nitrogen in March 2017, the priorities for action have become clear and are discussed later in this article.
Lichens are well-known as indicators of air quality and many species are highly sensitive to nitrogen pollutants. Close to nitrogen sources, lichens such as the Eyelashes treebeard (Usnea florida, pictured) may be bleached and overgrown with algae. Photo: © David Hill/Plantlife Cymru CENNAD apprentice
Where does reactive nitrogen come from?
Mainly from agriculture. Globally, total nitrogen emissions have doubled since 1960, fuelling our growing human population and modern lifestyles.
The main sources of NOx emissions are power stations, transport and industry; these emissions are projected to stabilise by 2030 (and have already declined significantly in the UK), thanks to new technology and other measures to reduce greenhouse gas emissions and improve air quality.
Ammonia emissions, however, are expected to continue to rise globally until 2050. In the UK, there have been modest declines in recent years but levels are projected to remain stable at least until 2020.
Government air quality plans tend to focus on reducing nitrogen dioxide in urban areas to reduce the impacts on human health, while ammonia is treated as a rural farming issue. Yet the urban-rural separation in this area is not so clear. Both NOx and ammonia emissions cause the formation of Particulate Matter (PM), and both are harmful to the health of humans and ecosystems.
What’s the impact on wildlife?
Where reactive nitrogen levels are high, certain species (such as nettles) thrive but many other species of fungi, lichens and plants cannot survive – the environment is simply too fertile. In extreme cases, close to nitrogen sources, flora and fungi are directly damaged through bleaching, leaf discolouration and increased susceptibility to drought, frost and disease.
More broadly, there is a loss of biodiversity as nitrogen-loving species out-compete more sensitive species. Early evidence suggests that this may have a knock-on effect on other groups, including invertebrates and birds.
In those very places to which many rare species are now confined, such as field margins and road verges, air pollution from fertiliser spreading and traffic fumes is likely to be higher.
Over two thirds of our wild flowers, including plants like harebell (Campanula rotundifolia, pictured), require low or medium levels of nitrogen. Photo: © Beth Newman/Plantlife
Joining the dots
In January 2017, an expert workshop was held in London by Plantlife and the British Ecological Society’s Special Interest Group on Plants, Soils and Ecosystems. We heard several examples of positive action by statutory agencies, local authorities, research institutes, farming bodies and conservation groups to help mitigate nitrogen emissions and restore wildlife sites.
The focus of action is often on reducing ammonia emissions from intensive farming units, in particular to protect nearby wildlife sites and priority habitats, as this is often not covered by existing plans or strategies. There is clear evidence that farm-level actions can significantly reduce ammonia emissions through, for example, better flooring systems in livestock housing, covers for slurry stores, reducing excess fertiliser use and applying injection technology for more efficient fertiliser spreading.
Statutory agencies and local authorities in Wales and Northern Ireland are using GIS data to identify point sources of emissions and to screen planning applications for their potential impacts on wildlife-rich areas.
In England and Wales, Site Nitrogen Action Plans (SNAPs) are being developed to coordinate locally-targeted measures around particular Special Areas of Conservation (SACs), including working with local farmers, drawing parallels with the catchment management approach to reducing water pollution.
Farming sector representatives were positively engaged in the workshop, including from the Agricultural Industries Confederation, National Farmers’ Union and Ulster Farmers’ Union. Participants discussed the need for increased support and investment for farm measures through agri-environment schemes, Catchment Sensitive Farming and the Rural Development Programme.
The range of actions already underway, backed by strong evidence, is encouraging. Yet we know from the workshop – and feedback since then - that faster and coordinated action is needed at a much bigger scale.
Clear correlations have been demonstrated between rates of nitrogen deposition and species richness in a range of semi-natural habitats. Source: Field, C., et al (2014) Ecosystems 17(5): pp.864-877
There are three key areas of action that Plantlife is taking forward, in collaboration with existing partners as well as building relationships with new partners:
Raising public and political awareness
Nitrogen’s impact on fungi, lichens and plants deserves to be part of our mainstream environmental thinking and taken up by all those working in the environment, air quality and farming sectors, as well as politicians, policy-makers and budget holders in government.
We need to ‘talk about nitrogen’ - communicate the science – and get it on the agenda to prevent further long-term damage to our flora and fungi, and all the other species and ecosystems which depend upon them.
The widespread media attention given to our report launch in March helped to get that conversation off to a great start.
Since then, we’ve had feedback from those working on the issue who are pleased it’s getting well-deserved attention; and also feedback from those who work in the environment sector and were surprised that they didn’t already know about it.
Specialists from the Centre for Ecology and Hydrology, the Stockholm Environment Institute, statutory agencies and elsewhere are keen for their work to be accessed and understood by the public, politicians and others.
So there’s a great opportunity here for all of us to keep talking about nitrogen with field recording and conservation groups, campaign groups and farmers, as well as with politicians and governments.
Improving site-based assessment and management
We know that nitrogen levels are already above the defined ‘critical loads’ for our richest wildlife habitats and legally-protected areas across the UK. Yet further research is needed to improve these ‘critical load’ assessments, track emissions trends and sources, and strengthen the evidence base for policy-makers.
Critically, nitrogen levels must be factored in to the Common Standards Monitoring of Sites of Special Scientific Interest (SSSIs). Without this, it is much harder to demonstrate nitrogen impacts at particular sites and to reflect these in SSSI condition assessment and management plans in order to get the action necessary to reduce nitrogen levels and restore wildlife and its diversity.
Site-based nitrogen action plans are being developed, as mentioned above, and these processes need to have political support and funding to engage farmers and other stakeholders in practical action on the ground – at much a larger number of sites across the UK.
This needs to be accompanied by coordinated implementation plans by statutory agencies, to comply with regulations such as the 2017 Best Available Techniques for intensive pig and poultry units, and targets under the National Emissions Ceiling Directive.
Inclusion in air quality plans and new land management policy
The issue of atmospheric nitrogen deposition cuts across several policy areas, including agriculture, transport, energy, climate change, air quality, water quality. Action on nitrogen in all these areas can provide co-benefits (or win-wins) with efforts to tackle climate change, improve air and water quality, make farming more efficient and sustainable, and restore our wildlife and habitats.
As the UK prepares to leave the EU, there are many challenges and opportunities for nature conservationists. We need to send the government a clear message about the importance of maintaining and strengthening environmental legislation and equivalent new policy. In particular, this applies to land management policy developed to replace the Common Agriculture Policy (CAP) and environmental protections currently provided by EU Directives on air quality, water quality and wildlife habitats.
All of this applies to nitrogen deposition – and we need to take the opportunity to address this issue in new air quality plans, land management and farming policy and elsewhere. We can demonstrate how public money can be better used to provide public benefit, including a healthy natural environment, by setting out evidence of the cost-benefits of reduced nitrogen emissions and by developing a preferred package of measures.
To find out more, you can download our report and workshop outcomes on the Plantlife website.
You can help to monitor the impact of nitrogen on your local wildlife and improve our knowledge through citizen science, using the ‘Lichen App’ or the OPAL Air Survey