Do bushfires boost aquatic systems by adding nutrients to the water? This is among the questions being asked by Australian Nuclear Science and
Technology Organisation (ANSTO) environmental scientists Dr John Ferris, Dr Paul Brown and Dr Scott Markich, who have put the microscope to some aquatic life in the Woronora River, which runs through one of the areas of bushland most severely burnt by the Christmas bushfires.
According to ANSTO Environmental Scientist Dr John Ferris, it is pretty well known that a fire can bring a nutrient boost to nearby waters, but the studies would look at answering the more detailed questions of how big a boost and identify which organisms in the aquatic community benefit.
Working in conjunction with students Katherine Pulling and Neil Keyzer from the Environmental Science Unit of the University of Wollongong, a baseline picture was established in 2001 of the water quality and how it related to the microscopic plants known as diatoms. These diatoms help form the building blocks of life in aquatic environments, and are considered excellent indicators of the health of rivers and streams.
"Diatoms have exquisitely patterned glass shells up to about 200 millionths of a metre long. Their status as photosynthetic food producers gives them an important role in freshwater and marine ecology," Dr Ferris said. "The protected upper catchment, the large area controlled by the military, and ANSTO's buffer zone have all helped to protect the Woronora River from the effects of urban encroachment, making it probably one of the cleaner streams this close to suburban Sydney," he said.
"Prior to the bushfires, Katherine Pulling found around 80 species of diatoms in what is a relatively well-protected and healthy river. One of these species has only recently been named by colleagues in Belgium and we believe it is unique to this part of the world - it actually appears to prefer the quite acid conditions that can occur naturally on the Sydney sandstone," Dr Ferris said.
"Given the baseline we had, we were in a fairly good position to see what effects the intense fire had had on the water quality and the diatom populations in the freshwater reaches of the Woronora. So, we took the opportunity of revisiting the river to see what had changed after the rains in February."
"Both phosphorus and nitrogen had increased by an average of two to four times above the baseline data from 2001. In fact, there was up to ten times the nitrogen concentrations at a couple of sites but the phosphorus increases were more modest,"Dr Ferris said.
Phosphorus levels tend to be very low in a stream like the Woronora and so the fire and rain will have been at least a temporary bonus for many diatoms and other algae in the river, as well as to the animals that feed on them.
"Katherine has full-time work now, but she is identifying and counting diatoms in her spare time and we will have some interesting data to analyse soon. After that it's time to publish the story. We'll also have contributed to ANSTO's understanding of biodiversity in its buffer zone, and that's a bonus for us," said Dr Ferris.