Lichens as indicators of atmospheric pollution in urban ecosystems

Modern methods of lichen indication allow assessing the impact of climate change and air pollution on ecosystem health. The purpose of this study was to evaluate the general state of atmospheric air in urban ecosystems of cities and towns using lichen indication methods. The objectives of the study included identifying lichen indicator species, as well as assessing the response of these species to various pollutants (e.g., lead, iron, manganese). The study was conducted in 2017 in the Bryansk region of the Russian Federation (9 settlements in total) and the Oryol region (1 settlement – the city of Oryol). Four hundred samples belonging to epiphytic lichens were collected. Additional 300 and 137 samples of epiphytic lichens were used for chemical and toxicological analyses, respectively. The following two generally accepted lichen indicator indices were calculated: poleotolerance index (PI) and atmospheric purity index (API). When calculating the latter, the lichen species Xanthoria parietina was used as the baseline. Epiphytic lichens in small settlements were represented by 50 species (28 genera, 8 families). In large cities, 55 (Bryansk) and 53 (Oryol) species of epiphytic lichens were detected. The number of species in small settlements was 1.5 times lower than that of large cities. There were 8-15 and 25-32 species of epiphytic lichens in the central region and in the periphery of Bryansk, respectively. The number of epiphytic lichen species detected in the parks was 41. Within the territory of large cities, 17 species of lichens were identified as potential indicators, since they were found in every second or fourth sample. Maximum concentrations of lead were recorded in industrial areas of cities, as well as near major roads with traffic intersection and bridges and in some dormitory suburbs. This is a distinctive feature of large cities – the predominance of lead in lichen thalli, which is primarily associated with vehicles. In small cities in which there are no specific industrial enterprises (metallurgical plants, etc.), other heavy metals – manganese and iron – prevail in the thalli of lichens. In this work, new methods are adopted – mapping pollution with the use of nitrophilous epiphytic lichens that reflect the ongoing macro processes of nitrification in urban areas. The authors have proposed and tested the following lichen indicator methods: the use of indicator species (epiphytes-nitrophytes) of various sensitivities and the study of their distribution within the territory. The mapping method has been substantiated, which takes into account the API and zoning of territories according to the level of general pollution. Among the indicator species, Xanthoria parietina turned out to be the most suitable one.