Impact Type: Direct exposure to pollutant
Key Concerns:
There have been a number of papers published on the effects of O3 on Sphagnum spp. (Gagnon & Karnosky 1992, Lee et al. 1998, Potter et al. 1996a,b). Most of these are based on fumigation experiments either in controlled-environment chambers or open-top chambers.
In all, seven species of Sphagnum have been investigated: S. magellanicum, S. rubellum, S. flexuosum, S. capillifolium, S. cuspidatum, S. papillosum and S. recurvum. Of these, damage due to O3 has been reported for S. magellanicum, and S. flexuosum (Gagnon & Karnosky 1992) and S. recurvum (Potter et al. 1996a,b). The damage reported has been: reduced photosynthesis, slower growth (Gagnon & Karnosky 1992) or increased membrane leakage (Potter et al. 1996a,b). In none of the experiments has death or signs of visible damage been found, and the damage to S. recurvum has only been found to occur at low temperatures. Gagnon & Karnosky (1992) reported an increase in the growth of S. rubellum.
Experiments so far published have only been carried out on common and abundant species. It is therefore possible that the rare Atlantic species might be at risk (Potter et al 1996b).
Additional Comments:
The magnitude of O3 impacts on bryophytes in the UK is currently very uncertain. The largest O3 concentrations occur at high altitude sites, and the most severe bryophyte impacts are therefore expected for species at Scottish mountain sites. However, with the exception of the experimental studies of Potter et al. (1996a,b) and others, there has been little demonstration of actual species responses in the field.
| Habitat/ Ecosystem Type | Critical Load/ Level | Status | Reliability | Indication of exceedance | Reference |
|---|---|---|---|---|---|
| Semi-natural vegetation |
AOT40 3000ppb hours over 3 months or AOT40 5000ppb over 6 months |
UNECE, 2010 | expert judgement i.e. only limited or no data are avaliable for this type of receptor |
AOT40 is the Accumulated concentration Over a Threshold of 40 ppb. If an hourly average ozone concentration exceeds 40 ppb the difference between the concentration and 40 ppb is added to a running total. The units are therefore ppb multiplied by hours. For natural vegetation, the AOT40 is summed for the daylight hours for a period of three months. Daylight hours are defined as when solar radiation exceeds 50 W m-2. The daylight hours are when plant stomata are normally open. Flux-based critical levels, based on biomass reduction, are also available for local and regional assessment but are not yet incorporated into APIS. See critical levels chapter of the UNECE Mapping Manual. |
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