Impact Type: Direct exposure to pollutant
Enhanced ammonia concentrations (e.g. in the vicinity of intensive poultry farms) have been shown to have negative effects on bryophyte diversity (Pitcairn 1998). Although not studied the known sensitivity of Sphagnum to nitrogen deposition (Gunnarsson & Rydin 2000, Williams et al. 1999, Baxter1992) suggests that this genus will also be affected in such situations.
A critical level for NH3 exposure has been set (Ashmore & Wilson 1994) although Burkhardt et al. (1998) have shown that in general critical loads for nitrogen deposition are already exceeded at NH3 concentrations less then the critical level. Another factor which can influence the impact of NH3 deposition is drainage. Williams et al (1999) showed that drainage of peatlands can reduce the capture by Sphagna of inorganic nitrogen. A new field study (Sheppard pers comm.) is examining the impact of NH3 along a transect for a range of sphagnum species. Bleaching has been observed in S. papillosum, but so far the long term implications remain to be seen. Effects are likely to be strongly linked to the critical level
|Habitat/ Ecosystem Type||Critical Load/ Level||Status||Indication of exceedance||Reference|
3 µg NH3 m-3 annual mean (uncertainty of 2-4 µg NH3 m-3)
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.