Corticolous lichen diversity, a potential indicator for monitoring air pollution in tropics

As information on lichen diversity and air quality in tropical ecosystems are limited, attempts were made in this study to correlate the distribution and diversity of corticolous (tree bark colonizing) lichens in the Western Province of Sri Lanka. The major source of air pollution in the study area was vehicular emissions. Thirty one sites located on six transects diverging from the Colombo City were selected for this purpose. Eight trees representing three species (Cocos nucifera, Mangifera indica and Artocarpus heterophyllus) within each site (1 km2) were chosen for the study. The coverage and frequency of corticolous lichens found on the selected trees were recorded by using 250 cm2 grids. After studying their morphology, anatomy, reproductive structures and chemistry, the lichens were identified using taxonomic keys. In addition, land use pattern, traffic density, pH of the substrates and exposure levels of the bark of these trees to light were also recorded. Ambient SO2 and NO2 levels at each site were determined using passive samplers having filter pads coated with the absorbing reagents ethylene glycol and acetone for SO2, and NaI, NaOH and ethylene glycol for NO2. Data were analyzed statistically using the mean comparison, correlation coefficient and principal component analysis to investigate the relationship between the diversity of lichens and environmental parameters. Lichen diversity data collected on selected trees were used to formulate the index of atmospheric purity (IAP). A negative correlation was found to exist between the lichen diversity expressed as IAP and the concentrations of SO2 and NO2 levels in the study sites. These results revealed that corticolous lichens have the potential to be used as indicators of air quality monitoring in a tropical environment as well.

DOI: http://dx.doi.org/10.4038/jnsfsr.v41i2.5707

J.Natn.Sci.Foundation Sri Lanka 2013 41(2):131-140