Nitrogen deposition in Northern Ireland and import/export of N deposition across the UK.

Atmospheric nitrogen (N) deposition represents a significant threat to sensitive habitats and species in the United Kingdom, with excessive N supply leading to declines in many important species of high conservation value, at the expense of fast-growing species that can exploit the additional nitrogen supply. Atmospheric N is produced from emissions of ammonia (NH3, mainly from agricultural sources) and nitrogen oxides (NOx, mainly from transport, industry, power generation and other combustion sources). This report aims to quantify and compare N deposition to land in NI from sources within NI and overseas (in the UK, Republic of Ireland, Shipping and the rest of Europe) to the amount of N deposition produced from NI sources that is deposited overseas. Estimating the likely source of N deposition received by NI will allow enable policy makers to assess how effective national N mitigation measures are likely to be. This study shows that Northern Ireland exports more atmospheric N deposition to the rest of the UK than it receives (from the UK and elsewhere). The amount of N originating from sources within NI and deposited within NI is mostly from NH3 emission sources (92%), with only 8% due to NOx emissions. These atmospheric N inputs produced within the country are the fraction that can be tackled with NI-internal policy development. When taking into account atmospheric N input from all sources (NI-internal and beyond), a substantial proportion of the NHx deposition is from sources within NI, while NOx deposition may be harder to tackle with a substantial proportion coming from the UK, Republic of Ireland and the rest of Europe, including shipping.