Impact Type: Direct exposure to pollutant
The virtual absence of Sphagnum species from the blanket bogs of the southern Pennines has been attributed to high SO2 pollution (Ferguson & Lee 1983a,b). Of the 18 species of Sphagnum reported in the area in 1913, only 5 were recorded in 1964 (Tallis 1964) and of those only S. recurvum is common today (Press et al. 1983).
Fumigation experiments by Ferguson et al. (1978) have shown that SO2 can severely inhibit the growth of ombrotrophic species of Sphagna (i.e. S. imbricatum and S. tenellum) at 131µg m-3 SO2, while minerotrophic species of Sphagna (i.e. S. recuvum) are more tolerant of sulphur (Lee et al. 1993).
It is not clear to what extent the effects on the Southern Pennines were a result of high SO2 concentrations or high S deposition.
Although SO2 concentrations declined steeply in the 1950s-1970s, no marked recovery of Sphagnum cover occurred in the southern Pennines due to increasing concentrations of nitrogen pollutants which thus assumed the dominant role in determining poor growth of Sphagnum species in the 1980s and 1990s.
|Habitat/ Ecosystem Type||Critical Load/ Level||Status||Reliability||Indication of exceedance||Reference|
|Forests and semi-natural vegetation||
20 µg SO2 m-3 annual mean and half-year(Oct-March) mean
|UNECE, 2004||quite reliable i.e. the results of some studies are comparable||
Low temperature appears to enhance the negative effects of SO2, and the lower critical level of 15 µg SO2 m-3 is used where the effective temperature sum (ETS) (i.e. the sum of temperatures) above 5oC is below 1000 degree days (d.d) (Ashmore et al., 1994).