Standard Presentation 2024 Australian Marine Sciences Association Annual Meeting combined with NZMSS

The impacts of bioactive megafire aerosols on estuarine microbes (#324)

Raissa L Gill 1 , Robert Fleck 2 , Alivia Price 1 , Chris Songsomboon 1 , Callum Muir 3 , Ky Chau 2 , Mika T Westerhausen 4 , Thomas E Lockwood 4 , Jake P Violi 5 , Colin Johnson 3 , Aaron T Wright 3 , Peter J Irga 6 , Fraser R Torpy 2 , Martina Doblin 1 7
  1. Climate Change Cluster, University of Technology Sydney, Ultimo, NSW, Australia
  2. School of Life Sciences, University of Technology Sydney, Ultimo, NSW, Australia
  3. New South Wales Department of Planning and Environment, New South Wales Government, Sydney, NSW, Australia
  4. School of Mathematical and Physical Sciences, University of Technology Sydney, Ultimo, NSW, Australia
  5. School of Chemistry, University of New South Wales, Sydney, NSW, Australia
  6. School of Civil and Environmental Engineering, University of Technology Sydney, Ultimo, NSW, Australia
  7. Sydney Institute of Marine Science, Sydney, NSW, Australia

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. Building HVAC sampling revealed finer particles (0.9 vs 1.5 µm) enriched with potentially toxic (Cl-, Co, F-, Mn, NO3-, Sb, SO42-) and nutritional (Ca, Ca2+, Co, Fe, Mg, Mg2+, Mn, NO3-, Si, SO42-) elements. This material displayed enhanced solubility of mercury (12.1 vs 1.0%), three nutrients (Ca, N, Si), and more variable metal solubility (Cd, Hg, Mn). Bottle incubation experiments revealed dynamic responses of NSW estuarine microbes to wildfire particle additions. Under the average 24-hour scenario for dry deposition, responses varied by estuary, including heterotrophic, phototrophic, or no response. Under an extreme scenario, all systems veered towards heterotrophy, with an increase in metabolically active heterotrophs, and decrease in phytoplankton and their pigments. Detailed analyses of Clyde River revealed dose-dependent responses that varied temporally over 5 days, with heterotrophic bacteria dominating growth in the first 24 hours (0.5-fold increase), and photosynthetic bacteria and eukaryotes thereafter (up to 125-fold increase). Additionally, synechococcus was differentially inhibited (0.9-fold decrease). This work highlights the complexity of gauging estuarine responses post-wildfire with implications for monitoring Australia's fire-prone future.