Fires impact water quality long after quenched

Leading research into the impact of the 2003 Alpine bushfires on water quality suggests the trouble is far from over when the fires are finally out.

In the past, the impact of fires on water catchments could only be estimated, as the unpredictable nature of fires left very little possibility for collecting strong data.

When two catchments being used for long-term water quality research were burnt during the 2003 Alpine fires, Dr Patrick Lane, Dr Gary Sheridan and a team of researchers took the opportunity to measure the impact of fire on water yield and quality.

They were funded in the project by research and development corporation Land & Water Australia and the Victorian Department of Sustainability and Environment.

“This research is extremely valuable for reporting future water yields and managing the effects of fires in catchments. The team are commended for their contribution to understanding sediment and nutrient yields and helping to close a significant knowledge gap in Australian contaminants research,” said Dr Stuart Pearson of Land & Water Australia, who supervised the project.

Lane explained how fires affect water quality and yield: “If a severe fire is followed by substantial rainfall, the sediment and nutrient run-off can pollute water supplies. Nutrients attach to the sediment particles, so when the sediment settles in reservoirs, the nutrients do too. This can lead to algal blooms. The Gippsland Lakes, for example, have had significant algal blooms since the 2007 bushfires.

“Also, the amount of rainfall ending up in streams increased in our research catchments by 70% after fires. The main reason for this is the loss of vegetation, which means there is much less interception of rainfall by the leaves, and much less transpiration by trees. With sizeable rainfall, flooding like that after the 2007 fires can result — that’s also a risk bushfire-affected regions face.

“After the initial increase in run-off, which peaks in the first 1–3 years and then steadily declines, the vigorous regrowth forest absorbs more rainfall than the old one, especially in forests of ash like those around Kinglake and Marysville, meaning less water for catchments in the long term. We’re now investigating strategies to reduce such losses.”

Lane and other researchers are helping authorities predict the possible fall-out from the Black Saturday fires for long-term water impacts.

In anticipation of rainfall, water is being moved from storage areas in burnt catchments to safe catchments. The research from this project is providing a springboard for further research.