Effects of air pollution on natural ecosystems
Introduction
As well as having effects on human health, air pollution can also be harmful to our natural environment. Pollutants in the air can be toxic to sensitive plants and trees, while pollutants in rainfall damage habitats by depositing acid or excess nutrients. Water bodies such as rivers and lakes are also susceptible to the effects of air pollution.
The most significant air pollution for our natural environment occurs when reactive nitrogen compounds, such as ammonia and nitrogen oxides, are deposited to sensitive sites. Deposition can be through direct contact between polluted air and plants. This type of deposition is called ‘dry deposition’ and it mostly happens close to pollution sources.
Deposition also occurs when pollution is dissolved in precipitation (rain and snow), which falls onto sensitive sites. We call this ‘wet deposition’ and it can happen at long distances away from the pollution source.
Ammonia is by far the biggest contributor to nitrogen deposition and comes from agricultural activities such as livestock housing, slurry/manure storage and spreading and fertiliser use. Please visit the Ammonia emissions in Northern Ireland page for more information.
Another source of nitrogen deposition is from nitrogen oxides, which are produced from road transport (petrol and diesel engines) and some types of industry.
Sulphur dioxide is another air pollutant that has harmful effects on vegetation and it is produced from burning fuels, in particular coal.
The above diagram shows the Nitrogen Cycle. Emission Ammonia (NH3) + nitrous oxide (N₂O) + NOx etc. enter the air as gasses where further reactions occur. They are Dispersed and can be transported great distances in the atmosphere. Eventually dry NH3 is deposited onto the land and NH4+ and NOx are deposited through precipitation. These, along with runoff from farms & fields can leach into water sources.
Air Pollution at Designated Sites
Northern Ireland has 294 Areas of Special Scientific Interest, 54 Special areas of Conservation and 16 Special Protection Areas that have been designated as needing protection because of the importance of the species and habitats that they support. Sites include peatlands, native woodlands, species-rich grasslands and freshwater & coastal habitats.
In Northern Ireland, ammonia is the air pollutant of primary concern for its effects on designated sites.
Ammonia can have a directly toxic effect on sensitive vegetation, like lichen and mosses. Ammonia and nitrogen deposition reduce plant species richness and diversity, favouring species that are tolerant to excess nutrients. This leads to changes in plant and animal communities within our habitats and can also alter their ecosystem function. For example, peatlands sequester carbon and are therefore crucial in the fight against climate change. If peatlands are being damaged by ammonia and nitrogen deposition, they will not be able to store carbon as effectively.
DAERA monitors the condition of designated sites, and assessments can help to identify where damage from air pollution is a contributing factor to habitat damage and species loss.
Monitoring Air Pollution at Designated Sites
In collaboration with partners UK Centre for Ecology and Hydrology, Ulster Wildlife and the National Trust, NIEA’s Air Quality and Biodiversity Unit delivers a programme of monitoring and evidence work. The work aims to identify and quantify sources of atmospheric nitrogen input to the NI designated site network, to inform mitigation strategies and to evaluate how these naturally N-poor ecosystems are affected by the addition of nitrogen.
Concentrations of ammonia have been monitored at Ballynahone Bog since September 2014. Ammonia monitoring has been ongoing since June 2020 on an additional seven SACs (Curran Bog, Garry Bog, Moneygal, Peatlands Park, Sliabh Beagh, Cuilcagh Mountain and Turmennan). At Cuilcagh SAC and Ballynahone Bog, ammonia monitoring is accompanied by wet deposition monitoring. As of July 2022, ammonia monitoring has also been initiated at Murlough SAC.
The map above shows NI Ammonia monitoring sites:
- ALPHA — Garry Bog, Curran Bog, Moneygal Bog, Peatlands Park, Turmeannan and Slieve Beagh
- ALPHA & wet deposition — Cuilcagh Mountain
- ALPHA, DELTA, wet deopsition, NO2 — Ballynahone Bog
- A 10km square Boundary is drawn around Ballynahone Bog
Most ammonia air pollution samplers are exchanged at monthly intervals. This monitoring aligns with the UK National Ammonia Monitoring Network (ongoing since the 1990s) in addition to a network of 25 rural location sites run by AFBI.
Modelling provides estimates of annual mean concentrations for NH3 and NOx right across NI, as well the amount of nitrogen deposited in rainfall. These estimates are used to make comparisons with the Critical Levels that have been calculated for NH3 and NOx and the Critical Loads for nitrogen deposition.
Image right shows a wet deposition monitor at Ballynahone Bog: rainfall is collected and then samples taken each month to be analysed for the presence of nitrogen pollution.
Ballynahone Bog
Biomonitoring is also carried out at a number of sites to determine the effect of nitrogen on vegetation. Samples for foliar analysis are collected in winter or spring, before temperatures rise and growing commences.
Local prevailing wind patterns play a key role in atmospheric nitrogen pollution input to designated sites, in terms of local ammonia concentrations and N deposition originating from local, regional and transboundary sources. To investigate local wind patterns and their temporal variability with locally measured weather data, and to analyse these data in conjunction with NH3 measurements, meteorological data is collected at Ballynahone Bog and Peatlands Park.
Statutory Planning Advice
As the Statutory Nature Conservation Body, NIEA is consulted on planning proposals to identify any possible risks to the natural environment. Through this process, potential impacts from air pollution to protected sites can be identified. Standing Advice is available here.
UK Air Pollution Assessment System (APAS) – Air Quality Assessment Tool
A new integrated air pollution assessment tool, UK APAS, is currently in development. The project is being led by JNCC, with funding from DEFRA and DAERA. Find out more here.
Science and evidence publications
NIEA commissions and carries out research into the effects of air pollution on sensitive sites here. To find out more click here.
Atmospheric Nitrogen Impact on NI Ecosystems
NIEA Natural Environment Division has been leading on an evidence programme to evaluate and mitigate ammonia and nitrogen (N) deposition impacts on Northern Ireland’s natural ecosystems. This work is in conjunction with the UK Centre for Ecology and Hydrology (UKCEH) and project partners: Ulster Wildlife, National Trust, Monaghan County Council and Fermanagh and Omagh District Council.
To find out more, watch the joint DAERA – UKCEH webinar hosted on the 15th June 2023 for Clean Air Day: