Nitrogen depositions ‘reducing UK biodiversity’

Report from Centre for Ecology & Hydrology offers ‘first’ detailed analysis of UK air pollutants since 2001, writes Amy North

The diversity of plant species in the UK is at risk from nitrogen deposition, according to a new report by the Centre for Ecology & Hydrology, a public sector research centre.

However the study found that European policy measures have had a positive effect on the emissions of sulphur, nitrogen and the precursors of ground level ozone which continue to decline.

The report is the first detailed analysis of transboundary air pollutants in the UK for over a decade

In addition, it found that due to the decline of sulphur emissions rain is no longer acidic allowing soils and freshwaters to recover.

The report – Review of Transboundary Air Pollution: Eutrophication, Ground Level Ozone and Heavy Metals in the UK — was funded by the Department of Environment, Food and Rural Affairs (Defra), the Natural Environment Research Council and the UK’s Devolved Administrations. It is the first detailed analysis of air pollution in the UK since 2001.

It looks at the current state of rural air pollution in the UK whilst evaluating the measurements of atmospheric pollutants and their effects. Research for the report involved 60 scientists and reviewers over a period of three years.

The report says that there is ‘strong evidence’ to suggest that deposited nitrogen has reduced the diversity of plant species in a range of sensitive habitats across the UK.

However the study found that nitrogen is not the only element having a negative effect on wildlife in the UK. ‘Critical levels’ of ozone for agricultural crops, forests and semi-natural vegetation is exceeded over much of the UK. This means that exposure to a typical summer’s concentration of ozone can reduce wheat and potato yields by 7% and 2% respectively.


Commenting on the findings, Professor Martin Williams, from King’s College London, said: “Policies to control ground level ozone have been useful in reducing peak ozone concentrations, with significant benefits for air quality. But a steady growth in background ozone, as a consequence of ozone precursor emissions throughout the northern hemisphere, has eroded these benefits and as a result ground level ozone remains a threat. Ozone will only be mitigated effectively through hemispheric scale controls, which are now an urgent priority.”

Professor David Fowler, from the centre for Ecology and Hydrology, added: “We found that the policies to control acidification in the UK have been a considerable success, mainly due to the very large reduction in sulphur emissions from combustion gases. Ecosystems are recovering as a consequence of these controls. However, policies to control eutrophication by nitrogen compounds have been less effective, mainly because emissions of a major contributor to nitrogen deposition, ammonia, have not been significantly reduced, and remains a priority for control measures.”


While the 316-page report covers a broad range of areas key findings include:

  • Emissions of sulphur dioxide have decreased by 94% between 1970 and 2010;
  • Emissions of nitrogen oxides in recent years have not been reduced by as much as policy-makers intended, decreasing by 58% between 1970 and 2010;
  • Concentrations of sulphur dioxide in UK surface air have declined to values which no longer pose a direct threat to sensitive plant species;
  • Soil acidity has declined widely in the UK in response to reduced acid deposition;
  • Critical levels of ozone for agricultural crops, forests and semi-natural vegetation are exceeded over much of the UK.


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