Date of Award

2013

Degree Type

Thesis

Degree Name

Doctor of Philosophy

School

School of Natural Sciences

Faculty

Faculty of Health, Engineering and Science

First Advisor

Professor William Stock

Second Advisor

Associate Professor Andrea Hinwood

Abstract

During the last few decades, various techniques for using lichens as biomonitors have been developed for monitoring air pollution and forest ecosystem health. Lichens have been used effectively to determine the dispersion of heavy metals emitted by industrial point-sources; however the approach has not been commonly used in Australia. This thesis aimed to determine the effectiveness of using a lichen biomonitoring approach to measure the heavy metal pollutants emitted from coal-fired power stations and related industries in Collie, south-western Australia, an area with concern over poor air quality. Three different approaches to lichen biomonitoring were investigated. The first explored lichen community composition patterns in thirty-six study sites across an identified pollution gradient in the jarrah forest ecosystems of Collie. The second measured in situ Usnea inermis lichens for heavy metals, across wet and dry seasons in Collie. The third approach used lichen transplant bags of Usnea inermis to determine seasonal heavy metal accumulation patterns. Because the gaseous pollutants NO2 and SO2 are known to have a significant effect on lichen vitality and distribution, they were monitored by means of a direct measurement approach using Radiello® passive air samplers, to determine any confounding effects. A total of twenty lichen taxa were recorded in the lichen community study, with an average species diversity of ten per site. The lichens Usnea inermis and Cladonia rigida occurred at all thirty-six study sites. High lichen diversity and abundance values were recorded from control sites, and crustose and squamulose species were more abundant across all study sites. The grouping of lichen communities into pollution-tolerant classes, based on information from other studies, showed that the jarrah forests surrounding the industries in Collie were dominated by pollution-tolerant lichen species, while sensitive species were infrequent and rare. Spatial distribution maps of lichen diversity indices showed areas with low diversity values downwind from the coal mines and coal-fired power stations and near an alumina refinery, indicating a possible influence from these point-sources on lichen community composition. Pollution effects on lichen communities were observed with little influence from forest management practices, demonstrating the effectiveness of this method for monitoring air pollution influences in managed jarrah forests. The study also identified Usnea inermis as a suitable species for both the in situ and transplant lichen biomonitoring experiments to explore heavy metal pollution in the area, because of its widespread distribution across the pollution gradient. Low concentrations of NO2 and SO2 were recorded by Radiello® passive samplers, suggesting that these pollutants had very little confounding influence on lichen community composition and heavy metal accumulation patterns. However, seasonal differences in the dispersion of gaseous pollutants were observed, particularly in the summer season. The areas influenced by gaseous pollutants were also found to be those with low lichen diversity, suggesting that although low in concentration, the gaseous pollutants were having a demonstrable influence on the lichens in the jarrah forests in Collie. Mean concentrations for the metals As, Cd, Cr, Cu, Pb, Mn, Hg, Ni and Zn were low for in situ Usnea inermis lichens; however elevated concentrations of some metals were recorded at certain locations. Arsenic concentrations in spring were high from sites close to the coal mines and Mn was elevated in both seasons from sites near an alumina refinery. Higher metal concentrations were recorded in the higher rainfall autumn season compared with spring for most metals. The fallout patterns of heavy metals were explained by a power curve showing exponential decreases in concentrations, with very low concentrations found beyond the 8 - 10 km distance range from the closest pollution source. Spatial dispersion maps showed interpolated concentrations consistent with that expected if point-sources were responsible for the generation of high atmospheric heavy metal concentrations. Transplanted Usnea inermis lichens did not show elevated metal concentrations, however seasonal variations were observed, with the highest concentrations recorded in the wet winter season. Metal uptake in both the in situ and transplanted lichen studies was favoured by low temperature and high rainfall, suggesting that metal uptake was promoted during periods of wet deposition. This highlights the importance of season of sampling if lichen biomonitoring studies are to be deployed in WA. The wetter and cooler winter season with more consistent rainfall patterns is recommended as optimal for conducting lichen biomonitoring studies in Collie. The transplants exposed over a 48 week period recorded the highest concentrations for most metals, however they also showed a loss of metal accumulation ability at the high exposure sites. Exposure periods of 24 – 32 weeks (6 – 8 months) are recommended for more reliable results when using lichen transplants. The transplant study also identified that the control sites were affected by industrial emissions, suggesting that reference sites should be located at distances greater than those used in this study. The results from all three biomonitoring approaches identified pollution dispersion patterns associated with industrial point-sources, and also identified a pollution influence at the control sites, an area previously considered to be unaffected by industrial pollution. Findings from this study support the idea that a lichen biomonitoring approach can be used as an effective tool for monitoring heavy metal air pollution in Western Australia and if used correctly it could replace the more expensive active sampling techniques. The study also provided essential baseline information for future studies on the effect of industrial pollution on lichen communities in WA.

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