Abstract
Agriculture is responsible for 98% of atmospheric ammonia (NH3) in Ireland, of which pigs and poultry produce 7%; with laying hens specifically contributing 0.6%. Though a small proportion of the national NH3 total emissions, the ecological impacts on sensitive sites attributed to laying hen farms can be substantial. NH3 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.
Highlights
Egg production in the Republic of Ireland accounts for €49 million of agricultural output per annum, with c. 250 producers employing 800 people (Department of Agriculture Food and the Marine, 2015)
Though not directly comparable to monitoring conducted in this study due to different housing types, monitored spring emissions were higher than those observed from the battery cage at 0.20 g bird-1 day-1 and lower than summer emissions from the deep pit at 0.29 g bird-1 day-1
This shows a significant diversity of emission rates for battery cages within different countries, battery cages are currently illegal throughout Europe under Council Directive (1999/74/EC)(European Comission, 1999)
Summary
Egg production in the Republic of Ireland accounts for €49 million of agricultural output per annum, with c. 250 producers employing 800 people (Department of Agriculture Food and the Marine, 2015). The majority of ammonia emissions (91%) is generated from more diffuse sources such as cattle, slurry spreading and synthetic fertilisers (European Environment Agency, 2017). As these are diffuse sources, there is a lower risk for high ammonia concentrations; though their contribution to impacts should not be discounted. In line with the Industrial Emissions Directive (2010/75/EU) (European Union, 2010), European BAT (Best Available Technology) reference documents recommend a number of systems in which laying hens should be housed These include aviaries, deep litter with a manure pit, and enriched cage systems. A number of approaches are recommended for deep litter systems, which generally have much higher emission rates than caged or aviary systems (Hayes et al, 2006; Starmans and Van Der Hoek, 2007; Hill et al, 2014); including forced air drying of manure, enhanced ventilation, air blowing from below via a perforated floor, etc.
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