INVESTIGATION OF LICHEN DIVERSITY AND DENSITY WITH SO2 CONCENTRATIONS IN SELECTED LOCATIONS IN COLOMBO DISTRICT

Abstract

Lichens have been used as a bioindicator to determine the air quality worldwide and corticolous lichens have gained much attention in studies carried out in urban areas. The study was carried out to investigate the changes in diversity and density of corticolous lichens from August to November 2016 in ten sites along the Highlevel road starting from University of Colombo to Awissawella. The density, diversity of lichens were studied using a 450 cm2 transparent grid fixed on host trees. The lichens were identified using the taxonomic keys. In addition, the SO2 concentrations during morning, afternoon, evening were obtained in each site at each sampling day of the study site. The traffic data too was obtained. Data were analyzed statistically using regression analysis and correlation analysis. Altogether, 45 lichen species were found in this study. Sulphur dioxide concentrations varied from 1.64 mg/m3 (University of Colombo) to 0.16 mg/m3 (Labugama). A strong significant negative correlation was found between distance and the afternoon concentration of SO2 (r = -0.838, P-value = 0.002), indicating that the SO2 levels in the atmosphere decrease when moving away from Colombo Fort. A strong significant negative correlation was found between lichen diversity (r = -0.711, P-value = 0.021), density (r = -0.655, P-value = 0.040) and the SO2 concentration. The results of this study indicate that from the city (University of Colombo, with the highest SO2 concentration recorded) towards Seethawaka (final study site), the SO2 concentration has decreased mainly due to the changes in vehicular emissions. Accordingly, both the density and diversity of lichens were found to be correlated negatively with elevated SO2 concentrations.