ASSESSMENT OF AIR POLLUTION USING LICHEN-BASED BIOINDICATOR TO ENSURE SUSTAINABLE ENVIRONMENTS AND CROP PRODUCTION

Abstract

Air pollution poses a growing threat to the environment and agriculture sector, particularly in transitional
landscapes. The present study investigates the potential of lichen genera as bioindicators to comparatively assess
air pollution across the pollution gradient in the Gampaha district, Sri Lanka. Lichens, known for their sensitivity
to atmospheric pollutants, were surveyed across three zones with distinguishable pollution levels: the
Muthurajawela wetland (low pollution), Gampaha town (intermediate pollution), and the Ekala industrial zone
(high pollution). Corticolous lichen samples were counted from Cocos nucifera trees using transparent quadrats in
three randomly selected subsampling locations per site. Species diversity and Evenness were quantified using the
Shannon-Wiener diversity index (H’), and Pielou’s species evenness index, respectively. Four dominant genera—
Chrysothrix, Pyxine, Graphis, and Dirinaria—were identified, with the highest diversity (H′ = 1.2589) and
evenness (E = 0.9081) observed in the low-pollution Muthurajawela wetland. Diversity and evenness declined with
increasing pollution levels: Gampaha town (H′ = 0.9797, E = 0.8917) and the Ekala industrial zone (H′ = 0.4614,
E = 0.6657). The absence of Chrysothrix in Gampaha and both Chrysothrix and Dirinaria in Ekala with the lowest
diversity and evenness indicates their vulnerability to air pollutants, while Pyxine, a pollution-tolerant genus, was
most dominant in Ekala. These findings emphasize the efficacy of lichen-based monitoring as a cost-effective and
ecologically meaningful approach to assess air pollution gradients while promoting sustainable agriculture in the
country.
Keywords: Lichen bioindicators, Air pollution, Shannon-Wiener index, Pielou’s Evenness Index