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

Type of N deposition

Form of N

Risk areas

Dry deposition

Gaseous

NH3

Sites in rural areas with elevated background concentrations.  Higher concentrations and dry deposition are found close to point sources e.g. intensive livestock units but also wild animal (e.g. seal and bird colonies).

Dunes with more acidic communities.

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. 

Species/group

Response

Reference

Marram grass (Ammophila arenaria

+ve, cover increased

Jones et al 2004 

 Agrostis stolonifera, Carex flacca, Holcus lanatus)

Increase cover

 

Anagallis tenella, Leontodon saxatalis, Prunella vulgaris and Plantago coronopus

Decrease cover

 

Poa pratensis  and Salix repens

Increase if sufficient P

 

Dactylis glomerata, Plantago lanceolata and Achillea millefolia 

Increased growth

Jones et al 2013

Dactylis glomerata, Festuca rubra, Leontodon hispidus and Achillea millefolia

Higher tissue N

Jones et al 2013

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.

Critical Load/Level: 

Habitat/ Ecosystem Type Critical Load/ Level Status Indication of exceedance Reference
Higher plants

3 µg NH3 m-3 annual mean (uncertainty of 2-4 µg NH3 m-3)

UNECE, 2007

Direct visible injury; species composition changes. Ecosystems where sensitive lichens and bryophytes are an important part of the ecosystem integrity, the critical level is set at 1 µg NH3 m-3.

860
Lichens and Bryophytes

1 µg NH3 m-3 annual mean

UNECE, 2007

Loss of sensitive mosses and lichens communities. Communities become dominated by nitrophiles at the expense and virtual loss of acidophytes as bark pH becomes less acidic.

860

References: 

Jones, M.L.M.; Wallace, H.L.; Norris, D.; Brittain, S.A.; Haria, S.; Jones, R.E.; Rhind, P.M.; Reynolds, B.R.; Emmett, B.A. 2004 Changes in vegetation and soil characteristics in coastal sand dunes along a gradient of atmospheric nitrogen deposition Plant Biology 6 598-605
Jones, L. ; Nizam, M.S. ; Reynolds, B.; Oxley, E.R.B.; Bareham, S. 2013 Upwind impacts of ammonia from an intensive poultry unit Environmental Pollution