Ammonia :: Montane Habitats

Effects and implications

[Ammonia is one of the key pollutants that contribute to nitrogen deposition. Please read the Nitrogen deposition - Montane Habitats  record to understand the full impacts effects of nitrogen deposition including ammonia.]

Direct impacts of ammonia on montane habitats is likely to be restricted due to no local sources at such elevations. However, if exposed the following  changes would be expected based on a studies of similar species on bog habitats (Leith et al 2004; Sheppard et al 2008, 2011).

  • Direct damage to sensitive species, e.g. bleaching and leaf discoloration, observed in Cladonia lichens e.g. Cladonia portentosa at high concentrations. Subtle changes in plant morphology, physiology and biochemistry which not only increases growth, but also increases sensitivity to environmental factors such as wind, frost, drought and pests (e.g. increased tissue N concentrations can predispose plants to insect attack).

Overview: evidence, processes and main impacts

There are unlikely to be  local sources of ammonia that are large enough to cause elevated ammonia concentrations which will directly affect these montane habitats  There have been no in situ studies of ammonia effects.

Pollutant deposition type and Risk areas

Type of N deposition

Form of N

Risk areas

Dry deposition



Few, since there are no significant ammonia sources in these areas.

Indicators of NH3 impact

These depend on the extent of the deposition and level of NH3 exposure and there is too little information available to address this.

Evidence of species specific responses

None for montane ecosystem

What factors modify NH3 deposition impacts?

  • Climate: It is possible that the extreme climate, heat and cold will both exacerbate NH3 effects if they limit C assimilation and growth, the ability of plants to use the additional N. NH3 increases risk of damage from droughts and winter desiccation in Calluna dominated heath (Sheppard et al 2008). It is also likely that with higher wind speeds any ammonia present will be so well mixed the concentrations will be too low to have a detrimental impact.
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.

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.

Leith, I.D.; Sheppard, L.J.; Fowler, D.; Cape, J.N.; Jones, M.R. ; Crossley, A.; Hargreaves, K.J.; Tang, Y.S.; Theobald, M.R.; Sutton, M.A. 2004 Quantifying dry NH3 release system to ombrotrophic bog from an automated NH3 field release system Water, Air, and Soil Pollution: Focus 4 207-218.
Sheppard, L.J.; Leith, I.D.; Crossley, A.; Dijk, N.; Fowler, D.; Sutton, M.A.; Woods, C. 2008 Stress responses of Calluna vulgaris to reduced and oxidised N applied under 'real world conditions' Environmental Pollution 154 404-413
Sheppard, L.J.; Leith, I.D.; Mizunuma, T. ; Cape, J.N.; Crossley, A.; S., Leeson ; Sutton, M.A.; Fowler, D.; Dijk, N. 2011 Dry deposition of ammonia gas drives species change faster than wet deposition of ammonium ions: evidence from a long-term field manipulation Global Change Biology 17 (12) 3589-3607

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