Use of corticolous lichens for the assessment of ambient air quality along rural-urban ecosystems of tropics: a study in Sri Lanka.

ABSTRACT

Monitoring of air quality using lichens as bioindicators on the basis of lichen diversity and frequency is limited along rural-urban ecosystems in tropics. This study attempted to assess and correlate the use of corticolous lichens with atmospheric SO2 and NO2 in such an ecosystem in Sabaragamuwa Province in Sri Lanka. Nine sampling locations, each having three subsampling sites with 162 Mangifera indica and Cocos nucifera trees, were selected for the study. The coverage and frequency of lichens found on selected trees were recorded by 400-cm2 grids and identified using taxonomic keys. SO2 and NO2 levels at each site were determined by "Ogawa" passive air samplers. Data of lichen diversity were used to formulate the index of atmospheric purity (IAP). The environmental parameters related to lichen colonization were measured using standard methods. Data were analyzed using MINITAB 17. The mapping of spatial distribution of lichens and air pollutants were done using inverse distance weighting surface interpolation of geographical information system based on IAP values. A negative correlation was observed between IAP and SO2 and NO2 levels. The presence of the genus Pyxine in almost all urban sites indicated that it could be used as a reliable pollutant tolerant indicator in urban ecosystems. In addition, the index-based mapping techniques could be used successfully to see the effect of atmospheric pollution in urban ecosystems. These results conclude that corticolous lichens have the potential to be used as bioindicators of air quality monitoring along rural-urban ecosystems of tropics.