Nitrogen impacts on a national scale

Everyday living results in nitrogen compounds being released into the atmosphere – everything from switching on a light (oxides of nitrogen released from fossil fuel power stations) to having cottage Greater Knapweed Centaurea scabiosa is a positive site condition indicator of a lowland calcareous grassland community © J.F. Gaffardpie for dinner (ammonia released from livestock production) can have an impact.  These reactive compounds dissolve in rain, or are deposited directly onto the ground or vegetation, and can adversely affect many sensitive habitats. These impacts have been confirmed by new analysis funded by JNCC, Defra and the country conservation bodies.


The analysis is the largest of its kind and examines four widespread habitats - calcareous and acid grasslands, heathlands, and bogs. Each was examined for evidence of vegetation change caused by nitrogen deposition after accounting for other factors that could have had an impact. Data from the Vascular Plant Database (1930-1969 and 1987-1999), BSBI Local Change Survey (1987-1988 and 2003-2004), British Bryological Society, British Lichen Society, Plantlife Common Plant Survey and three country grassland datasets were used to support the analysis.


A significant response in 91 plant and lichen species and other ecosystem properties indicate changes in ecosystem structure and function at a national scale.  Species that showed decline included the BAP priority species Annual Knawel, three species/species groups protected under the Habitats Directive and many positive indicator species for condition of protected sites.  The results confirm that species are being impacted once the nitrogen ‘critical load’ (a threshold, set by scientists, below which there should be no harm to the ecosystem) is exceeded. For some species in acid and calcareous grasslands and heathlands, changes are even being seen below the set critical load.


The study highlights the serious challenge of nitrogen deposition and its implications for meeting the UK’s conservation commitments. The challenge also applies to other European countries, with more than 60% of the European Union’s Natura 2000 sites subject to aerial nitrogen pollution inputs above sustainable levels.  

Nitrogen deposition and Natura 2000 book cover


Alongside the analysis of UK vegetation data, JNCC organised a European workshop Nitrogen Deposition and Natura 2000, in collaboration with the Stockholm Environment Institute and Centre for Ecology & Hydrology. The workshop brought scientists, policymakers and conservation practitioners together to review new science of nitrogen deposition on biodiversity, and to compare approaches to assessing nitrogen impacts in relation to the requirements of the Habitats Directive. The proceedings, including best practice recommendations, have recently been published, and a summary leaflet is available.


JNCC is now working with the country agencies and Government to explore the implications of the new evidence of nitrogen impacts for country biodiversity strategies and air pollution policies.


The reports from the study are available on the JNCC website.


Contact File


Clare Whitfield, Air Pollution Adviser

Tel: +44 (0)1733 866804

Anna Robinson, Biodiversity Information Officer 

Tel: +44 (0) 1733 866851


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