Mercury in an Australian sclerophyll Eucalyptus forest and emissions from fuel reduction prescribed burning

Environmental context: Understanding how mercury cycles through the environment is crucial for protecting ecosystems and human health. Our study is among the first to measure mercury concentrations in Eucalyptus forest soils and litter and estimate emissions from prescribed burns, addressing a significant gap in current knowledge. These new data enhance our understanding of mercury cycling in Australia and contribute to the global information on the biogeochemical cycle of mercury.

Rationale: Research on mercury in Australian soils and litter is sparse. This study aims to address this knowledge gap by investigating mercury pools in soil and litter in a eucalypt forest in Victoria, Australia.

Methodology: We analysed total mercury concentrations in O and A horizon soils, and twig, bark and leaf litter. Soil samples were collected from an area affected by a prescribed burn and unburned areas. Additionally, soil samples from the base of tree stems were taken in unburned areas. The organic matter content of all soil samples was also assessed.

Results: In unburned soils, mean mercury concentrations at the base of tree stems, in the O-horizon and A horizon were 143 ± 61, 112 ± 71 and 56 ± 30 ng g−1 respectively. In burned soils, mean mercury concentrations in the O and A horizons were 91 ± 63 and 46 ± 19 ng g−1 respectively. Mercury concentrations in leaf, bark and twig litter averaged 71 ± 11, 21 ± 13 and 8 ± 4 ng g−1 respectively. The emission factor was estimated as 0.247 g Hg ha−1.

Discussion: The studied sclerophyll forest represents a significant mercury reservoir. Burning did not significantly alter the mercury burden in soil; however, emissions of mercury from litter did occur. This finding underscores the need for more comprehensive research into mercury cycling in Australia and suggests that prescribed burning practices should account for potential mercury emissions.