Erin Ingrid Walsh, Tim Stevenson, Richard NL Terrett, Cathy Banwell, Stewart Sutherland, Aparna Lal

There is a growing body of evidence surrounding the implications of uncontrolled bushfires and wildfires on water. This topic has importance from an ecological perspective, and significance for human health as it has consequences for drinking water quality and supply. Against the backdrop of climate change, it is especially important to holistically understand the impact of fire on water. This review took a systematic approach to establish a comprehensive overview of the changes occurring in freshwater systems following uncontrolled wildfires and bushfires. Screening of 16,551 results obtained from Web of Science, PubMed, and MEDLINE resulted in 111 manuscripts suitable for inclusion. The impact of fire across a wide range of water quality indicators either relative to pre-fire measurements or reference sites was examined qualitatively (increase/decrease) and where possible quantitatively (% change or difference). Factors included biomass, indicator species and species diversity, metals, nutrients, salts, polycyclic aromatic hydrocarbons, particulates and turbidity, pH, conductivity, temperature, and water course morphology. Evidence focused largely on short to medium term impacts (e.g. within 2 years of the fire event), with only a subset of studies reporting on longer term changes in response to fire. We found that bushfire has acute and long-lasting effects on water in terms of physical (e.g. decreased suspended particle size), chemical (e.g. increased nutrient concentration), and biological (e.g. decreased species diversity) characteristics. There was also evidence of resilience and recovery. We urge future work to consider measures that will fulfil both environmental and human health considerations, to allow more integrated insight into the impacts of fire on water.