Lichens and industrial pollution - Ecology of Industrial Pollution - page 55

Branquino 2008 ; Sutton et al. 2008 ). Further research in the Netherlands
also demonstrated that an increase in nitrophytes was correlated with increasing
bark pH. Long distance nitrogen deposition was affecting sensitive lichen
communities across Europe (Van Herk 2001 , 2003 ). Pioneering research in Pem-
brokeshire confirms the value of new growth of lichens on twigs as sensitive
indicators of environmental change and that indicator species can be used
to detect trends towards acidification or eutrophication (Wolseley & Pryor 1999 ;
Larsen-Vilsholm et al. 2009). The frequency of lichens on both twigs and trunks of
standard oak trees was tested across known gradients in NH 3 concentrations and
in different climatic regions in 'continental' Norfolk and 'oceanic' Devon. At
mean NH 3 concentrations > 2 m gm 3 , trunks continued to carry relict lichen
communities due to either a legacy of previous acidification or ecological con-
tinuity. A loss of 'acidophytes' occurred prior to the establishment of 'nitro-
phytes', indicating the importance of establishing levels of ammonia at which
sensitive communities are at risk (DEFRA 2002 ;Wolseleyet al. 2006 ; Larsen-
Vilsholm et al. 2009). Field measurements at the farm, landscape and national
scales in the vicinity of the UK National Ammonia Monitoring Network confirm
the value of distinguishing particular lichens either as 'acidophyte' and 'nitro-
phyte' (Sutton et al. 2004 ; Leith et al. 2005 ; Sutton et al. 2009 ). Data indicate that
twig lichens are even more sensitive to ammonia than lichens on trunks, have a
faster turnover and may respond more rapidly to pollution changes. As suggested
by Van Herk ( 1999 ), 'acidophytes' avoid a high supply of reactive nitrogen and
'nitrophytes' prefer it (Sutton et al. 2008).
A new method focusing on more-easy-to-identify macrolichens on trunks and
twigs has been developed (Sutton et al. 2009 ; Wolseley et al. 2009). An overall
nitrogen index (LAN) is calculated: LAN ¼ LA LN, where LA ¼ acidophyte index

and LN nitrophyte index.

A positive value indicates a site with lower NH 3 concentrations dominated
by acidophyte lichen species, and a negative value indicates a site with higher
NH 3 concentrations dominated by nitrophytes. LAN correlates with NH 3 con-
centrations across the UK, thus providing a new method to determine NH 3 in
regions where monitoring stations are absent (Wolseley et al. 2009 ).
Using the data, a critical level was derived, as the NH 3 concentration at
which the observed LAN value is significantly lower than the LAN value for
background NH 3 concentrations (Sutton et al. 2008). Expressed graphically
( Fig. 3.4 ) as the point at which the least-squares regression best-fit line shows
a value of LAN which is smaller than the minimum confidence interval for
LAN at the cleanest study location. Ammonia concentrations are highly vari-
able, and regional background values far from sources are of the order of
0.03 0.3 m gm 3 according to the time of the year. In the Netherlands, 'back-
ground' concentrations are typically larger than 3 m gm 3 , and thus this
approach would not be applicable in this and other regions with high

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