Impact Type: Deposition of pollutant
Key Concerns:
While very large concentrations of SO2 may negatively affect grass growth, studies have shown that agricultural grasses may evolve a tolerance to high SO2 levels (Ayazloo and Bell 1981, UKCLAG 1996). In the case of arable crops, this would require the specific planting of SO2 tolerant seeds.
However, SO2 emissions have been reduced dramatically over the last decade so that currently no direct negative impacts of SO2 would be expected on arable crops in the UK. Background concentrations are often below 2 ug m-3. By contrast, in this agricultural situation, crop removal depletes soil sulphur levels, so that croplands may be short of sulphur. In this case S may need to be added as part of the fertiliser supply.
Additional Comments:
The present shortage of 'sulphur fertilisation' of agricultural land has sometimes led to the suggestion that the SO2 pollution in the atmosphere was a good thing. In the past S was free, but now it must be added as part of the mineral fertiliser supply. Additionally, it can also be argued that the present situation of having to add mineral fertiliser, focuses the S where it is needed, and avoids unwanted exposure and damage to semi-natural vegetation and freshwater.
| 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). |
809 |