NH3 :: Lichens (general)

Latin name: 
Lichens (general)

Impact Type: Direct exposure to pollutant

Key Concerns:

  1. Species that are sensitive to SO2 and NO2, also tend to react positively to NH3. Van Dobben & ter Braak (1998, 1999) have suggested that this is due to the effect of NH3 on bark pH rather than any toxicity.
  2. Epiphytic lichens that colonise bark, fence posts, and stones are probably more at risk than the matt forming species such as Cladonias as their habitat preferences are distant from local sources.
  3. Overgrowth by pleurococcoid algae, leading to death of lichens by light extinction, is becoming an increasing problem.
  4. Lichens where the symbiont is a blue green algae (N fixer) are likely to be most at risk.

Additional Comments:

There is increasing interest in using lichens as bioindicators of NH3 concentrations. While some species favour high NH3 levels (e.g. Xanthoria parietina) others such as Parmelia caperata and Ramalina Spp. appear to be highly sensitive to NH3 (Lallemant et al. 1996).

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
References: 
Lallemant, R.; Joslain, H.; Houssay, I.; Cyprien, A.L. 1996 The use of lichens for estimating ammonia air pollution in Western France. Report to the UPRES biocatlalyse
Van Dobben, H.J.; Ter Braak, C.J.F. 1998 Effects of atmospheric NH3 on epiphytic lichens in the Netherlands: the pitfalls of biological monitoring. Atmospheric Environment 32 551-557
Species group: 
Pollutant: