Bushfires are often important in maintaining many natural Australian environments, influencing the ecology, hydrology, and geomorphology of landscapes. However, bushfires also have the potential to cause large-scale impacts on terrestrial and aquatic ecosystems. The 2019/2020 Black Summer bushfire season (July 2019 – March 2020) was the worst recorded fire season in New South Wales’ history with >5.3 million hectares of forest burnt across the state and >23,000 km2 of directly impacted waterways across >90% of coastal catchments within which bushfires occurred.
Impacts on waterways generally stem from the mass movement and deposition of sediments and debris from forested areas during the initial rainfall events occurring after bushfires and the subsequent release of associated nutrients and contaminants into aquatic environments. To date many studies have not assessed the long-term impacts to water quality or ecosystem health, or the potential influence of fire extent and severity on such impacts.
In response to the NSW Government’s inquiry into the 2019/2020 bushfire season, this study has combined historical and recently collected water quality data to delineate and assess acute and chronic bushfire-related impacts in different estuary types across the state of NSW. Nutrients, suspended sediment, dissolved oxygen, salinity, chlorophyll-a, phycocyanin, and fluorescent dissolved organic matter data have been considered, with distinct differences observed between open systems (e.g. wave dominated estuaries) and intermittently closed systems (e.g. coastal lakes). Generally, acute effects to dissolved oxygen levels were observed during and immediately following the 2019/2020 bushfire season, whereas impacts to turbidity, nitrogen, phosphorus, and chlorophyll-a persisted months later. These findings have been used to develop an interim conceptual model which: