LICHENS AS BIOINDICATORS OF AIR QUALITY IN DIMITROVGRAD ( SOUTH-EASTERN SERBIA ) 1

Air pollution detection in Dimitrovgrad has not been done yet. In this work different lichen have been used as a bioindication to establish different air pollution levels. At 18 investigated points 22 lichen taxa have been found. Using the Index of Atmospheric Purity (IAP) it has been found that there are 3 different air pollution zones in Dimitrovgrad: “lichen desert”, “transitional” and “normal zone”. The most sensitive lichen taxa in Dimitrovgrad are Evernia prunastra, Ochrolechia pallescens, Parmelia sulcata, and Physcia tenella and the most tolerant are Phaeophyscia orbicularis, Physcia adscendens, Physconia distorta, Physconia grisea, and Xanthoria parietina.


INTRODUCTION
The quality of air quality is getting worse all over the world.The presence and absence of lichens and different species around different pollution sources has been used for problems connected to air pollution.Many scientists have been dealing with this problem (Henderson, 1991, Henderson, 1993, Henderson, 1994, Nali et al., 2007, Jovan, 2008).Interest in this type of investigation started in Serbia in last decade of 20 th century ( Cvijan, Stamenkovic, 1996, Savić, 1998, Savić, Tibell, 2006, Stamenković, 1997).Bioindication of air pollution by using lichens has not been done in Dimitrovgrad until now.Dimitrovgrad is an urban settlement in southeastern Serbia, near the border with the Republic of Bulgaria.It has a population of around 8 000.The climate of this city is moderate continental.The mean annual air temperature is 9.7 o C, the mean annual air humidity is 72% and the mean annual rainfall is only 581.2 mm.(Fig. 1) The most frequent winds in Dimitrovgrad are southeasterly and easterly (Figure 2) Industry in Dimitrovgrad is not well developed and traffic has a relatively high intensity.

MATERIALS AND METHODS
Lichen samples in Dimitrovgrad were collected from 13 points.The investigated points are located in the urban part of Dimitrovgrad, starting from the center of town towards the last houses in the outskirts.Samples were collected from the bard of the tree species Acer negundo L., Juglans regia L., Prunus domestica L., Tilia platyphyllos Scop.Determination of the collected lichen species was done using so-called identification books (Wirth, 1995, Dobson, 2005, Jahns and Masselink, 1982, Murati, 1992, Murati, 1993, Boqueras, 2000).In this research, we have used the numeric method of the Index of Atmospheric Purity (IAP) (Loppi et al., 1997, Kricke andLoppi, 2002).

IAP = Σf
where: f is the coefficient representing the frequency and occupancy of each species at the site.
By marking the researched points on a city map and joining the points with the same or similar values of the IAP we obtained a picture of the zones with different air pollution in Dimitrovgrad, using lichens as bioindicators (Figure 3).
According to the calculated IAP values, we obtained a picture of the zones of different air pollution levels throughout Dimitrovgrad (Figure 3).A small area of the town, along the main city street, and forming a belt in a SW-NE direction, was characterized as a "lichen desert".Around this area there is a zone that belongs to the "transitional zone".This zone covers most of Dimitrovgrad (around 75-80%).
Points 6, 7, 8, and 10 have the highest IAP values.These points are located in the east part of the town and belong to a zone with lower air pollution level ("lichen normal zone").
According to the IAP values a small area in Dimitrovgrad is located in a "lichen desert" (A).Further investigation of this zone could transform it into a "transitional zone" due to the presence of some species (Candellariela xanthostigma, Lecanora pulicaris and Lecidella elaeochroma) which are moderately tolerant, and even sensitive, to air pollution.This fact suggests the possibility of an air improvement process with the consequence of lichen recolonization.Nontheless, this presumption should be verified by further monitoring.
Such a picture of the different air pollution levels in Dimitrovgrad is a logical consequence of air pollution and the mixed influence of microclimate, substrate and geo-physical features, as well as the distribution of "green" areas and objects.
According to the qualitative lichen characteristics and calculated IAP values, a qualitative / assessment of lichen sensibility to air pollution has been made.

CONCLUSIONS
Dimitrovgrad is an urban settlement and without much large industry and traffic.
A bioindication and physical-chemical investigation of air pollution in Dimitrovgrad has not been carried out.
According to the calculated IAP (Index of Atmospheric Purity) values we created a picture of the zones of different air pollution levels spreading over Dimitrovgrad.
The zone with the highest air pollution level ("lichen desert") is located in the central and southwestern part of Dimitrovgrad, in the form of thin and long belt.Almost all of the rest of the the town is in a lichen "transitional zone".In this area, the air is moderately polluted.A small part of Dimitrovgrad, on east side, belongs to the lichen "normal zone", with the lowest air pollution level.
By qualitative lichen sensitivity it was found that most sensitive lichen species are from the following genera: Candelariella, Evernia, Ochrolechia, Parmelia; less

Fig. 1 .
Fig. 1.Climate diagram for Dimitrovgrad (according to data of the Serbian Hydro Meteorological Service)

Fig. 3 .
Fig. 3. Investigated points and different air pollution zones in Dimitrovgrad