Composition and impact of wildfire-enriched aerosols on estuarine microbial communities : the 2019-20 Australian black summer
- Publication Type:
- Thesis
- Issue Date:
- 2026
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The Australian Black Summer megafires of 2019-20 emitted record-breaking quantities of aerosols into the atmosphere, delivering bioactive particles to ecosystems proximal and downwind of the source. High volume, heating, ventilation and air conditioning (HVAC) filters sampled in Sydney revealed finer particles (0.9 vs 1.5 µm) enriched with potentially toxic (Cl⁻, Co, F⁻, Mn, NO₃⁻, Sb, SO₄²⁻) and nutritional (Ca²⁺, Co, Fe, Mg²⁺, Mn, NO₃⁻, Si, SO₄²⁻) elements. This finer, fire-enriched material displayed higher dissolution of mercury (12.1% vs 1.0%) and three nutrients (Ca, N, Si). Bottle incubations revealed dynamic responses of NSW estuarine microbes to wildfire-enriched particle additions. Under an average 24-hour scenario for dry deposition, responses varied by estuary, including heterotrophic, phototrophic, or no response. Under an extreme scenario, all estuaries veered towards heterotrophy, with an increase in metabolically active heterotrophs, and decrease in phytoplankton abundance and pigments. Five-day incubations with Clyde River microbes showed dose-dependent growth that varied temporally, with heterotrophic bacteria dominating in the first 24 hours (0.5-fold increase), and photosynthetic bacteria and eukaryotes thereafter (up to 125-fold increase). Additionally, the cyanobacterium Synechococcus was differentially inhibited (0.9-fold decrease). This thesis highlights the complexity of gauging estuarine responses to wildfire inputs, with implications for monitoring Australia's fire-prone future.
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