Environmental Engineering Reference
In-Depth Information
diversity, are important. Biomonitoring, therefore, has a practical role to assess
London's air quality under changing atmospheric conditions (Davies et al.
2007
;
Larsen et al.
2007
).
The Natural History Museum wildlife garden is located at a very busy road
junction in central London. Located within the garden is an automated urban
roadside monitoring station, 4m from the roadside where sulphur dioxide,
nitric oxide, nitrogen dioxide, carbonmonoxide and PM
10
are measured. Lichen
diversity has changed significantly with many species recorded (and some
imported) when the garden was established now dying out (as in the case of
the 'Pollution Lichen' and new species recolonising (Honey et al.
1998
; Leigh &
Ware
2003
; Bell et al.
2004
). Lichen transplants were introduced into the garden
alongside temporary gauges in order to evaluate the impact of urban air pollu-
tion on different lichen species. Digital photography and chlorophyll fluores-
cence confirmed that the healthiest lichens were those transplanted adjacent to
the road where peak NO, NO
2
,NO
x
and VOC air concentrations were recorded
(DEFRA
2002
; Bell et al.
2004
). Further experiments are required under different
climatic conditions and pollution gradients. Trees are now developing a flora
characterised by increasing numbers of nitrogen and particle-tolerant species,
including those not formerly recorded in urban areas. If, as predicted, air quality
continues to improve given recent advances in 'clean vehicle technologies',
we may expect an increase in lichen diversity here (Leigh & Ware
2003
).
Early studies carried out under a high SO
2
pollution climate indicated
that shrubby lichens were most sensitive to pollution and crustose species
least. Usnea species were absent from an area 48 km south from the centre of
London (Rose
1973
). Usnea spp., at one time widespread and luxuriant, almost
entirely disappeared from a major area of England and Wales covering at least
68 000 km
2
and at least 6 000 km
2
of lowland Scotland, mainly as a result of the
increase in atmospheric pollution (Seaward
1998
)(
Fig. 3.2a
). Linda Davies and
the author visited Regent's Park, central London on 1 June 2007 to monitor
Usnea sp. on Tilia sp. she discovered during her earlier study (Davies
2005
).
Whilst the return of Usnea to central London is encouraging, thalli are small
10 km
grid squares it has returned to has increased by more than 55% within the past
lem of recolonisation by selected genotypes remains. This is graphically illus-
trated by a pioneering study of 231 specimens of Parmelia sulcata which showed
there were three rRNA genotypes, but only one was found to be recolonising
London (Crespo et al.
1999
).
