Effects of air pollution on natural ecosystems: science and evidence publications

NIEA Natural Environment Division has been leading on a work programme to evaluate and mitigate impacts of elevated ammonia concentrations and nitrogen deposition on on sensitive ecosystems.

The work is undertaken in collaboration with the UK Centre for Ecology & Hydrology (UKCEH), Ulster Wildlife, Monaghan County Council and National Trust. The latest reports to come out of the work programme are listed below and further reports will be added as they are published.

Monitoring Reports – Key Findings

Reports have been prepared that present the outcomes of ongoing monitoring and assessment at eight Special Areas of Conservation (SACs). The reports can be accessed here. A summary of the findings is listed below:

  • The eight designated sites studied are Peatlands Park, Garry Bog, Turmennan, Moneygal Bog, Curran Bog, Ballynahone Bog, Slieve Beagh and Cuilcagh Mountain.
  • These sites contain peatland habitats with an annual critical level1 for ammonia concentrations of 1 µg m-3. This is the level above which ecological damage is expected to occur.
  • The results show an exceedance of the annual critical level for ammonia of 1 µg m-3 at six out of the eight SACs. The only two sites not exceeding the recommended critical level are upland sites: Cuilcagh Mountain and Slieve Beagh. The mean annual concentration of ammonia at these sites has been measured at just below the 1µg m-3 annual critical level for ammonia.
  • The magnitude and temporal profile of measured ammonia concentrations at each site is dependent upon the proximity and type of farming practices in the local area. The largest concentrations and measured gradients occur where emission sources exist close to monitoring sites near SAC site boundaries.
  • Seasonal patterns are observed across all sites. Land-spreading of slurries and manures causes an increase in measured concentrations at all sites (including upland sites), with a dominant peak in March/April and smaller secondary peaks in the autumn at some sites.
  • Measured concentrations can be elevated over the summer months when ammonia emissions increase with warmer and drier conditions. Measured concentrations are generally lower during winter, which correlates with cooler, wetter conditions, and the closed spreading season under the Nutrients Action Programme Regulations.
  • Across the eight SACs, measured annual average ammonia concentrations are showing broad alignment with the modelled values for site concentrations.  However, annual average values conceal the seasonal peaks and concentration gradients that can cause acute habitat damage. It is therefore important to assess both annual average concentrations (for comparison with the critical levels) and higher resolution temporal and spatial patterns, to get a complete understanding of the local and regional sources impacting a site.
  • A weather station placed on Ballynahone Bog SAC clearly shows the influence of meteorological conditions on measured ammonia concentrations. Local prevailing wind patterns play a key role in atmospheric nitrogen input to protected sites.
  • Vegetation analysis was undertaken at several sites to investigate levels of nitrogen present in the tissue of sensitive plant species (bog mosses). Where measured ammonia concentrations in the air are elevated, levels of nitrogen in plant cells are also elevated, indicating ecological harm and habitat enrichment. 
  • Levels of nitrogen in plants sampled from Cuilcagh Mountain SAC were elevated despite ammonia concentrations in the air being just below the 1µg m-3 annual critical level. This requires further investigation but may be due to additional nitrogen deposition in rainfall, fog or snow (wet deposition) and nitrogen accumulation over time.

Modelling reports

Two modelling reports describe national estimates of nitrogen deposition across the total land area of Northern Ireland and the import/export of atmospheric nitrogen deposition across the UK. The newer report supersedes the earlier one, with more recent model outputs. The reports can be accessed here. A summary of report findings is listed below:

  • The total amount of atmospheric nitrogen pollution deposited in Northern (NI) is estimated at 11.7 kt N yr-1.
  • Of this 11.7 kt N yr-1, 6.3 kt N originate from NI sources and the remaining 5.4 kt N originate from UK and EU sources. This includes 1.9 kt N from the Republic of Ireland (ROI).
  • NI exports ammonia through atmospheric dispersion and transport, and sources in NI contribute 5.4 kt to N deposition in Scotland, 1.8 kt N to England and 0.5 kt N to Wales, per year (data from 2018).
  • NI exports more nitrogen deposition to the rest of the UK than it receives from the UK and elsewhere.
  • This assessment provided estimates of NI contributions to elsewhere in the UK but did not include NI contributions to ROI and Europe. This may form part of a future assessment.
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