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How bushfires and rain turned Australia's waterways into ‘cake mix’, and what we can do about it by Paul McInerney, Anu Kumar, Gavin Rees, Klaus Joehnk, Tapas Kumar Biswas September 14,2020   |  Source: DTE

As the world watched the Black Summer bushfires in horror, we warned that when it did finally rain, our aquatic ecosystems would be devastated.

Following bushfires, rainfall can wash huge volumes of ash and debris from burnt vegetation and exposed soil into rivers. Fires can also lead to soil “hydrophobia”, where soil refuses to absorb water, which can generate more runoff at higher intensity. Ash and contaminants from the fire, including toxic metals, carbon and fire retardants, can also threaten biodiversity in streams.

As expected, when heavy rains eventually extinguished many fires, it turned high quality water in our rivers to sludge with the consistency of cake mix.

In the weeks following the first rains, we sampled from these rivers.

Of particular concern was the upper Murray River on the border between Victoria and NSW, which is critical for water supply. There, the bushfires were particularly intense.

When long-awaited rain eventually came to the upper Murray River catchment, it was in the form of large localised storms. Tonnes of ash, sediment and debris were washed into creeks and the Murray River. Steep terrain within burnt regions of the upper Murray catchment generated a large volume of fast flowing runoff that carried with it sediment and

 

© Down To Earth 2019

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