Ammonia :: Dunes, Shingle & Machair

Effects and implications

[Ammonia is one of the key pollutants that contribute to nitrogen deposition. Please read the Nitrogen deposition - Dunes, Shingle & Machair record to understand the full impacts effects of nitrogen deposition including ammonia.]

• These systems are adapted to low levels of mineral N availability, increasing the availability of N will threaten the competitive balance between species leading to changes in composition and loss of habitat species constants.
• Flowering plants show changes in growth at low ammonia concentration.

Overview: evidence, processes and main impacts

Sand dune habitats are one of the most natural remaining vegetation types in the UK, supporting over 70 nationally rare or red-data book species. Pressures threatening their existence include: sea-level rise, climate change, agricultural improvement, recreational use, lack of management, over-stabilisation and N deposition. They are generally infertile and thus sensitive to N deposition.

Very few studies have explicitly looked at ammonia impacts on dunes, as opposed to nitrogen deposition. A single study (Jones et al. 2013) assessed impacts both experimentally and adjacent to a poultry unit.. Where the NH₃ critical level of 1 ug m^-3 was exceeded, within 800 m upwind of the poultry unit, growth of plants like Dactylis glomerata, Plantago lanceolata and Achillea millefolia were increased. Tissue N concentrations in Dactylis glomerata, Festuca rubra, Leontodon hispidus and Achillea millefolia were increased by exposure to ammonia concentrations above 1 ug m^-3.

There may also be a risk of elevated ammonia concentrations from natural point sources such as wild animal and bird colonies e.g. seals, seabirds, geese etc where they occur on or sufficiently close to dune systems. 

Pollutant deposition type and risk areas

Indicators of NH₃-N enrichment

• Change in species composition due to eutrophication, and shading of the lower storey vegetation, mosses, lichens and forbs, by taller faster growing species e.g. graminoids and sometimes sedges.
• Increased moss and lichen tissue N content.
• Acceleration of soil development and the natural chronosequence of plants and selective loss and replacement of N fixing forbs.
• Increased pests and grazers.

Below ground

• Increase in soil C:N ratios despite poor N retention. 
• Increased N leaching and increase in groundwater DON concentrations.

Example evidence of species specific responses

Some examples of specific responses are given in the table below. This does not represent a comprehensive review of all species impacts. 

What factors modify ammonia impacts?

• Dune systems on the west coast where rainfall is higher and surface wetness increases NH₃ deposition.
• pH: acid dunes ecosystems are more sensitive than calcareous ones.
• Dune systems were historically managed by grazing (sheep, horses, cattle) which help remove nutrients, but can accelerate N cycling and cause damage by trampling and overgrazing.