Ammonia from a poultry unit can be detected 2.8km upwind, according to a new study in the UK.

In the journal, Environmental Pollution, L. Jones of the Environment Centre Wales and co-authors at Countryside Council for Wales, the National University of Malaysia and the University of Bangor explained that the ammonia exceeded critical levels 800 metres and critical loads 2.8km upwind.

The group reported that dune grassland species utilised ammonia as a nutrient source, and that plant biomass increased at low levels of ammonia and total nitrogen deposition.

Finally, Jones and co-authors predicted that soil carbon pools will increase by nine per cent over 50 years due to the excess ammonia.

Commenting on the study, the Science for Environment Policy group of the European Commission says that intensive livestock operations, such as poultry farms, are significant point sources of ammonia pollution. Ammonia is a form of nitrogen and is easily deposited onto soil and plants. Sensitive habitats, such as sand dunes containing mats of lichens and mosses, can be damaged by high ammonia levels.

In the study, the researchers investigated the impact on a Natura 2000 site of ammonia emitted by an intensive poultry farm. The Natura 2000 site is situated upwind of the farm, and consists of coastal sand dunes with grasses, lichens and bryophytes (e.g. mosses). Over 12 months, the researchers measured deposition of ammonia in and around the farm at eight points upwind to a distance of 2,800 metres away, within the Natura 2000 site.

Ammonia concentrations were greatest (60.1 micrograms per cubic metre) closest to the poultry farm and dropped sharply further away from the farm. Concentrations were 6.3μg per cubic metre at 300 metres upwind, 1.2μg per cubic metre at 800 metres upwind, inside the Natura 2000 site, and 0.9μg per cubic metre at the furthest point, 2,800 metres upwind and also within the Natura site boundary.

Levels of ammonia at the different sampling sites rose and fell in cycles with peaks that coincided with ammonia emission peaks at the poultry farm. They were not linked to lower ammonia emissions that came from a nearby sewage treatment plant or grazing livestock farm, which were the only other potential sources of the pollutant in the area.

The average annual background concentration of ammonia was estimated to be 0.6μg per cubic metre, suggesting that ammonia emissions from the poultry farm contributed an additional 0.6μg per cubic metre to the 1.2μg per cubic metre measured at the 800 metre upwind sampling point. This level exceeds the critical threshold of 1.0μg per cubic metre for bryophytes and lichens under the Gothenburg Protocol.

Atmospheric ammonia concentrations above this threshold are considered damaging to these groups of species.

Furthermore, at the 800-metre sampling point, ammonia emissions accounted for 44 per cent of the total amount of nitrogen deposited from all sources (11.1kg of nitrogen per hectare per year), which exceeds the lower bound of the critical load range for fixed dunes with herbaceous vegetation of between 8 and 15kg nitrogen per hectare per year.

Further experiments revealed that the sand dune plants were affected by these concentrations of ammonia.

Plant tissues showed higher concentrations of nitrogen, indicating they were using ammonia as a source of nitrogen for plant growth. For example, orchard grass (Dactylis glomerata) and ribwort plantain (Plantago lanceolata), which are both nitrogen-loving species, showed significant increases in growth as a result of the deposition of ammonia. Faster growth of these species may allow them to out-compete other sand dune plants of higher conservation value, and reduce the extent of bare sand on which many rare insects depend.

The European Commission report concludes the results suggest that ammonia emitted at these levels is likely to alter the composition and functioning of the sand dune habitats.

Reference

Jones, L., Nizam, M.S., Reynolds, B. et al. 2013. Upwind impacts of ammonia from an intensive poultry unit. Environmental Pollution. 180: 221-228. DOI:10.1016/j.envpol.2013.05.012

December 2013