Lichens and industrial pollution - Ecology of Industrial Pollution - page 57

et al. 2008 ). In the Los Angeles air basin, nitrogen dry deposition rates in forests
downwind of the urban areas can reach 35 40 kg ha 1 year 1 ), roughly equiva-
lent to the amount of N used to fertilise agricultural fields. Laboratory fumiga-
tions and field transplant experiments of Ramalina menziesii suggest
that gaseous HNO 3 , not O 3 , may be responsible for the impoverishment of
lichen communities in these semi-arid regions, where it is a major component
of air pollution during ambient summer conditions in the Los Angeles air
basin (Riddell et al. 2008 ).

Lichen biodiversity in metal-enriched environments
Waste dump and metalliferous habitats contribute to the world's industrial
and mineralogical heritage, e.g., the World Heritage Site, Falun Mine, Sweden
(Lindestrom 2002 ). They also provide important refuges for biodiversity, includ-
ing rare 'metallophyte' lichens restricted to particular chemical environments.
The preservation of biodiversity was highlighted in the Convention on Bio-
diversity (CBD) held in Rio de Janeiro in 1993. The Robert Brooks Memorial
Workshop on Metal-tolerant Plants supported by Rio Tinto and the Royal
Botanic Gardens, Kew, held in July 2001 identified geobotanical exploration/
field surveys and the establishment of collections from mineralised areas prior
to mining activities as key priorities (Whiting et al. 2004 , 2005 ). Metal-tolerant
plants stabilise surfaces and are particularly useful for land restoration, e.g.,
following mine closure. Vascular plant species which 'hyperaccumulate' metals
to concentrations in excess of those found in many ores are increasingly used
in 'phytomining' (particularly nickel) and in remediation (Callahan et al. 2006 ).
But lichens grow too slowly and are too challenging to grow under these
conditions to have direct application.
There has been a long tradition of studying lichens found on metalliferous
spoil heaps and naturally mineralised rocks especially in Central Europe
(Hilitzer 1923 ; Schade 1933 ; Poelt 1955 ; Lange & Ziegler 1963 ; Noeske et al.
1970 ; Wirth 1972 ; James et al. 1977 ; Purvis 1985 ; Purvis & James 1985 ; Purvis &
Halls 1996 ; Huneck 2006 ). Poelt and Ullrich ( 1964 ) introduced the term
'chalcophile' (greek chalcos ore) to describe lichens more-or-less restricted

to metalliferous rocks and slags and ores. Acarospora sinopica, a rust-coloured
species occurs on highly mineralised weathered rocks containing iron and
copper sulphide minerals ( Fig. 3.1 ). Volkmar Wirth was the first to suggest that
it was the low pH rather than the high concentrations of iron and other metals
that was responsible for their development (Wirth 1972 ). Sulphide minerals
are the principal acid-forming constituents of mine spoils which liberate
dilute sulphuric acid as a result of bacterially assisted oxidative weathering
and which leads to 'acid mine drainage', a major source of metal contamin-
ation ( Jenkins et al. 2000 ). A role for lichen substances has also been suggested
(Hauck et al. 2007 ).

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