Environmental Engineering Reference
In-Depth Information
shrubby beard-like lichens were most sensitive to SO
2
and crustose lichens least
sensitive. In 1972, 15 000 school children across the UK used a simplified
version of Gilbert's scale which involved observing lichens on trees, stone and
concrete. They found a link between pollution dominated by sulphur dioxide
and the presence or absence of selected species (Gilbert
1974
; Mabey
1974
). The
simple scale compared favourably with the more sophisticated scales based
on correlations between epiphytic lichen diversity and winter mean average
SO
2
concentrations in lowland England and Wales (Hawksworth & Rose
1970
).
Around the same time in London, Jack Laundon produced maps showing
Xanthoria parietina limits in London related to sulphur dioxide levels (Laundon
1967
,
1970
). These were probably the first such maps ever with isopleths and
dots (David Hawksworth, personal communication). Mark Seaward studied
distribution patterns of Lecanora muralis on roofing tiles (asbestos cement tile
and sheet, concrete and mortar tiles and siliceous wall capstone) in relation to
distance from Leeds city centre, substrate mean daily SO
2
concentrations and
rainwater pH. His research indicated 'substrate switches' indicative of environ-
mental change and the existence of an urban ecotype (Seaward
1976
). At the
end of the 1960s, a quantitative recording method, the Index of Atmospheric
Purity (IAP) was developed by De Sloover and LeBlanc for quantifying environ-
mental conditions using lichens as bioindicators (Kricke & Loppi
2002
). The IAP
considers the number of species at each monitoring site and their sensitivity
towards environmental stressors, primarily air pollution, and was applied
particularly in Switzerland and Germany.
Interest in problems associated with air pollution, lichens and the First
International Mycological Congress held at Exeter in 1971 provided the impe-
tus for publication of the first book devoted to air pollution and lichens
(Ferry et al.
1973
). At that time, it was recognised that air pollutants which
influence lichens include heavy metals, radionuclides, dusts, fertilisers, fungi-
cidal sprays and selective weed killers in addition to HF and SO
2
( James
1973
).
The concept of excess levels of air pollutant concentrations leading to adverse
effects on organisms was considered early in vascular plants (Nash
1973
),
and standards for sulphur dioxide air quality in Europe were later produced
(Farmer
1995
). Ozone was recognized in the late 1950s as the principal
phytotoxic component of photochemical smog and by the 1970s considered
by many to be one of the most important air pollutants in the world (Nash
1973
). Widely regarded as the probable cause of lichen decline in southern
California (Sigal & Nash
1983
) where O
3
also caused considerable damage to
agricultural crops and pine (Ashmore
2002
). Recent experimental research calls
the influence of O
3
on lichens into question (Riddell et al.
2008
).
Critical levels of SO
2
for the especially sensitive cyanobacterial lichens
(10
m
gm
3
yr
1
), were established (UNECE
2004
). Much literature followed,
totalling over 1500 papers (Nash & Wirth
1988
; Nimis et al.
2002
) and topics
