Isotopic fingerprinting of atmospheric nitrogen and sulfur using lichens (Cladia retipora) in Tasmania, Australia

Abstract

Increases in global anthropogenic emissions are far reaching, and are a concern even in remote areas. Tasmania, Australia is an island state that hosts the only Southern Hemisphere premier Baseline Air Pollution Station as part of the World Meteorological Organization-Global Atmosphere Watch network. Despite Tasmania's importance as a baseline location, little is known about atmospheric nitrogen (N) and sulfur (S) deposition and sources across the state. Here we investigate total N and S content and isotopic compositions (δ15N, δ34S) in the lichen Cladia retipora as a bio-indicator to identify whether atmospheric N and S deposition in Tasmania is affected by anthropogenic pollution. Both TN and TS were extremely low in all 66 samples collected across the state, averaging 0.29 ± 0.28% and 0.03 ± 0.05%, respectively. The average δ15N value was −2.8 ± 1.9‰ and there was no correlation with TN, but values were highest towards the denser populated SE of Tasmania. Lichens collected from sites within 500 m of salt marshes revealed a strong local source of microbially-reduced S as indicated by δ34S values as low as −21.9‰. All other lichen samples had a mean value of δ34S value of 13.7 ± 2.2‰, indicating mixing of marine biogenic S and anthropogenic S. This study represents the first baseline study of atmospheric N and S in C. retipora across Tasmania, and demonstrates the suitability of lichen bio-monitoring for future studies in this region.