Impact Type: Deposition of pollutant
Key Concerns:
Studies suggest that atmospheric SO2 and NO2 are the two most important factors in determining levels of lichen biodiversity (Hawksworth & Rose 1970a,b, Richardson 1988, van Dobben et al. 2000). Species that are sensitive to SO2 and NO2, also tend to react negatively to NH3, due to the effect of NH3 on bark pH rather that any toxicity (van Dobben & ter Braak 1998, 1999).
Lichens with N fixing cyanobacteria symbionts are particularly sensitive to acid deposition: H2SO4 caused a 30% reduction in photosynthesis at pH3 whereas HNO3 was necessary for the symbiosis in Peltigera aphthosa (Hallingbäck and Kellner 1992). Swedish studies suggest that in response to a reduction in S dominated acid deposition, problems of Pleurococcoid algae overgrowing epiphytic lichens are increasing (Dudley & Stolton 1996).
Additional Comments:
Cation ratios in Cladonia portentosa are considered to be good biomarkers for wet-deposited acidity (Hyvarinen & Crittenden 1998).
| Critical Load/ Level |
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No estimate available |