Bushfires play a fundamental role in shaping many Australian landscapes. They can also have significant impacts on terrestrial and aquatic ecosystems, particularly when there is an increase in sediment, nutrients, and contaminants entering waterways from fire-impacted areas.
Potential source-pathway-ecosystem relationships
Below is a conceptual model of bushfire impacts on estuarine receiving environments. This model explains the connectivity between catchments and waterways, and how the potential effects of bushfires on water quality and aquatic ecosystems.
Initial findings on water quality Impacts from NSW bushfires
1. Background
An assessment of water quality data collected before, during, and after the 2019-2020 bushfires is underway by the Department of Planning and Environment’s Estuaries and Catchments Team. Below are some key findings emerging from this assessment.
2. Indicators of bushfire impacts on aquatic systems
Short-term decrease in dissolved oxygen levels, lasting from days to weeks. This is attributed to elevated levels of organic matter decomposition in waterways post-bushfires. Reduced oxygen can stress and threaten aquatic organisms, potentially leading to mortality events such as fish kills.
Elevated turbidity and reduced clarity caused by higher sediment and debris input from burned, eroding catchments. Increased turbidity levels can impede photosynthesis due to reduced light penetration through the water column, obstruct fish gills, and smother sediment ecosystems.
Increased levels of nitrogen and phosphorus in estuaries originating from burned soils and vegetation washed into waterways. These can trigger the formation of potentially harmful algal blooms.
Increased levels of chlorophyll-a and blue-green algae pigments, likely due to nutrient driven algal blooms. These blooms can pose risks to aquatic life and human health.
3. What do these findings tell us so far?
The data collected in estuaries before, during, and after the 2019-20 Black Summer bushfires along the NSW South Coast has provided valuable insights into the short, medium, and long-term water quality impacts. Early findings suggest that water quality changes observed in intermittently closed and open lakes and lagoons (ICOLLs) are more pronounced compared to open estuaries like rivers. This is attributed to the relatively higher rate and amount of water exchanged with the ocean in open estuaries. ICOLLs will still exchange water with the ocean, and their entrances stay open for the longest when they open naturally rather than when artificially opened.