Savaria - A Vas Megyei Múzeumok értesítője 15. (1981) (Szombathely, 1988)

Természettudomány - M. R. D. Seaward: A zuzmók alkalmazása a levegő szennyezettségének indikálására

techniques can be applied to determine the histological, morphological and ecological responses of lichens to particular pollution levels; many of these involve the transplantation of lichen thalli in order to equate a species performance to the effects of a new environmental regime (e.g. BRODO 1967, SEAWARD 1976), but those most widely, and satisfactorily, employed involve either a.) mapping generalized zones based upon total number and/or diversity of species (e.g. GILBERT 1970, HAWKSWORTH and ROSE 1970, SEAWARD 1975), or b.) spatial mapping over a number of years of one or more particular species (e.g. SEAWARD 1976). The first technique a.) is less satisfactory for monitoring decreasing S0

2 levels ; successful on-going monitoring of ameliorating environments, such as those experiencing the implementation of clean air policy, can best be pursued by the second technique b.) which involves the detailed investigation of a single species (HENDERSON-SELLERS and SEAWARD 1979, SEAWARD 1982). Lichens have been employed in a bionindicational role to monitor the extent or spread of pollutants associated with urban and industrial complexes. The atmosphere of such complexes i laden with contaminants in the form of gases (e.g. S0

2

, CO, C0

2

, NO

x

, hidrocarbons), smoke dust, aerosols, heavy metals, etc., mainly contained within an "urban climate", the physical and chemical components of which may act independently or synergistically to create conditions that are detrimental to lichens. Although field and laboratory investigations have shown S0

2 to be the major detrimental factor influencing lichen distribution, other pollutants, extremes of temperature and water supply, and substrate availability also play an important role. The decline in the urban lichen flora along transects towards the centre of urban and industrial areas has been investigated in many countries throughout the world. Although urban areas normally have a poor lichen flora, the few species to be found can be used to good effect, the species composition being related to a mean annual or winter S0

2 level. In conditions of reasonably stable pollution there is a clearly defined negative relationship between species diversity of lichens and S0

2 concentration. It is possible, with caution, to use graphs derived from such analyses to predict the S0

2 level from a straightforward species count at a site. It would appear that lichens respond relatively quickly to a rise in S0

2 concentration and can therefore de satisfactorily employed to monitor ambient levels ; however, in areas experiencing a fall in S0

2 concentration, the use of lichens as bioindicators is less straightforward and often it is difficult to demonstrate any relationship between species diversity and air pollution level (SEAWARD 1976a). The rate at which lichens reinvade cleaned-up areas is enormously variable, and successful esteblishment if invading lichen propagules may well be influenced by complex factors, particularly the nature of the substrate (SEAWARD 1982). Nevertheless, a species-diversity count, based on field records of reasonably identifiable lichens which occur frequently within a defined area and are not restricted to a microhabitat, can be useful for evaulating the general level of air pollution, particularly in respect of transects radiating from urban and/or industrial complexes; furthermore, amelioration of the atmosphere of such areas can be effectively demonstrated by a comparison transect data (SEAWARD 1981). Urban reinvasion of the saxicolous lichen Lecanora muralis (Schreber) Rabenh, over the past fourteen years has been monitored in order to identify the environmental parameters of greatest importance to this species and to determine its value in on-going pollution monitoring. L. muralis is a particularly suitable lichen since it adapts preferentially to a range of natural and manmade substrates according to the amient air pollution level; the inner urban limits on the different substrates are quite clearly defined and a bioindicational scale based on its ecological performance can be used to monitor both 46