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With growing global demand for food, the agriculture sector worldwide is under pressure to intensify and expand, risking acceleration of existing negative biodiversity impacts. Agriculture is the dominant source of ammonia (NH 3) emissions, which can impact biodiversity directly through dry deposition as NH 3 and by wet deposition following conversion to ammonium (NH 4) in the atmosphere. Nitrogen deposition is one of the leading causes of global decline in biodiversity alongside changing land use and climate. Natura 2000 sites which are intended to protect important habitats and species across Europe, require strict levels of protection to ensure designated features achieve favourable conservation status. Many of these sites are nitrogen-limited, and/or contain sensitive species such as lichens or mosses. This project carried out ambient NH 3 monitoring on selected Irish Natura 2000 sites, in order to establish potential impacts from agricultural NH 3. Monitoring on twelve Natura 2000 sites observed concentrations ranging from 0.47 to 4.59 μg NH 3 m−3, from which dry deposition was calculated to be 1.22–11.92 kg N ha−1 yr−1. European Monitoring and Evaluation Programme (EMEP) was used to quantify wet deposited NH 4 and nitrogen oxides (NOx), in addition to dry deposited NOx on monitored sites. Estimated total nitrogen deposition ranged between 5.93 and 17.78 kg N ha−1 yr−1. On average across all monitored sites, deposition was comprised of 50.4%, 31.7%, 7.5%, and 10.3% dry NH 3 , wet NH 4 , dry NOx and wet NOx respectively. Implications for Irish agriculture are discussed in the light of both this monitoring and the European Commission Dutch Nitrogen Case (C 293/17 & C 294/17), highlighting a number of recommendations to aid compliance with the EU Habitats Directive (92/43/EEC). [Display omitted] • Ambient ammonia across twelve Natura 2000 sites was 0.47–4.59 μg NH 3 m−3. • Nitrogen deposition across twelve Natura 2000 sites was 5.93–17.78 kg N ha−1 yr−1. • Average nitrogen deposition comprised of 50.4% dry NH 3 & 31.7% wet NH 4. • Average nitrogen deposition comprised of 7.5% dry NOx & 10.3% wet NOx. • Agriculture is the primary source of biodiversity impacts from the more harmful NH 3. [ABSTRACT FROM AUTHOR]

Agriculture is responsible for 98% of atmospheric ammonia (NH 3) in Ireland, of which pigs and poultry produce 7%; with laying hens specifically contributing 0.6%. Though a small proportion of the national NH 3 total emissions, the ecological impacts on sensitive sites attributed to laying hen farms can be substantial. NH 3 emission monitoring was conducted in Spring (February to March) and Summer (July to August) 2016 to account for seasonal variation. The total average emission and ventilation rate was 0.25 g bird−1 day−1 and 931 cm3 s−1 bird−1. This is lower than the previously used emission factor for the Irish national inventory of 0.5 g bird−1 day−1, but broadly similar to factors reported in the United Kingdom (UK) and the European Union (EU). Dispersion modelling using monitored data indicated potentially acute effects within 84 m, critical level exceedance within 312 m and exceedance of 0.3 kg N ha−1 year−1 deposition within 2.9–5.2 km. The sensitivity of the model was tested using SCAIL-Agriculture emission and ventilation rates which showed P-values for one tailed critical level below 0.01 for all models, indicating that when normalised the maximum extents modelled by AERMOD were significantly different. This analysis showed emission rate having more influence than ventilation rate. Both parameters combined had the greatest increase in dispersion extent, on average 55.8% greater than the use of monitored rates. A deposition rate of 0.3 kg N ha−1 year−1 was modelled to occur within 5.1–7.7 km when using SCAIL-Agriculture rates. Indicating that the use of SCAIL-Agriculture recommended emission and ventilation rates would have been sufficiently precautionary to assess negative ecological effects on a Natura 2000 site under the Habitats Directive (92/43/EEC). In relation to Appropriate Assessment (AA) screening, the use of any contribution from a source within a set distance may be an appropriate full AA trigger. Image 1 • Monitored average NH 3 emission rate of 0.25 g bird−1 day−1. • Monitored average ventilation rate of 931 cm3 s−1 bird−1. • Potential critical level exceedance within 312 m of farm border from source alone. • 0.3 kg N ha−1 year−1 exceeded within 2.9–5.2 km of farm border from source alone. • Modelled dispersion using SCAIL-Agriculture rates was 55.8% greater than monitored. [ABSTRACT FROM AUTHOR]