Contamination of Sydney’s water supplies by nutrients after the bushfires

Within the last month The Sydney Morning Herald (SMH) has published two articles (December 13th and January 14th) on the concern for the health of Sydney’s drinking water reservoirs after the unprecedented bush fire season.

Within the last month The Sydney Morning Herald (SMH) has published two articles (December 13th and January 14th) on the concern for the health of Sydney’s drinking water reservoirs after the unprecedented bush fire season.

The Bureau of Meteorology has forecast upcoming heavy rainfall for the Sydney catchment area. This news comes as a welcomed relief for fire fighters and the general community after months of devastating drought and bush fires resulting in many people losing their homes, properties and lives. PET extends our sympathies to all those affected by these devastating fires.

The rain, of course, is to be celebrated, however it also comes with concerns that nutrients released during the fire season will be washed from catchments into Sydney’s drinking water reservoirs.

The SMH article published on December 13th highlighted the extent of the land that has been burnt around Sydney’s drinking water reservoirs and the effect it may have on the city:

“The Green Wattle Creek fire has burnt about 120,000 hectares around Lake Burragorang, which supplies about 80 per cent of the city's water behind Warragamba Dam.

“The resulting bushfire ash contains organic material and concentrated nutrients such as phosphorous and nitrogen. While the ash acts like a sponge, if sufficient rain falls in a short time that material could be pushed into the dam, triggering a range of water treatment challenges.”

The article published in the SMH on January 14th stated that there is currently a plan to try to mitigate against the flow of ash into the dams: 

"Silt curtains and floating barriers help to mitigate the inflow of ash into dams, reducing additional pressure on water treatment plants. WaterNSW has an additional 1000 metres of silt curtains in case they are needed in either Nepean or Tallowa dams."

However if the ash does enter the dams in runoff from the predicted heavy rainfall events, the large amounts of nutrients, combined with the warm weather of the summer season, could create a “perfect storm” situation for the growth of blue green algal blooms.

Blue green algae (cyanobacteria) will thrive in water containing nitrogen and phosphorus as a food source. Once phosphorus enters the water body, it remains in the water column or is stored in the sediment for future use by algal cells. The only way to break the nutrient pollution of water bodies is to remove or bind the phosphate, rendering it unavailable for algal cells to feed on.

One of Australia leading molecular algal biologist was quoted as saying:

“Of greater worry would be if the species of any algal outbreak turned out to contain toxins. The 2007 bloom was non-toxic but others may not be so benign, Brett Neilan, a molecular biologist at Newcastle University said.”

"Some blue-green algae can contain liver toxins at certain times of the year, or neuro-toxins that can lead to paralysis," Professor Neilan said, adding "we also have the world's worst algae".”

WaterNSW has assured that:

Scientists will continue to monitor water quality in major water supply areas around the clock.”

Phoslock is an Australian product owned by Phoslock Environmental Technologies (PET). It is used to bind excess dissolved phosphorus in water bodies that, if left untreated, leads to algal blooms that can be toxic to humans and animals that come into contact with the water. Phoslock is one of the measures used by water body managers as a tool to improve water quality by controlling nuisance algal blooms.

The Sydney Morning Herald articles referred to in the blog can be found at: https://www.smh.com.au/national/nsw/sydney-s-water-supply-faces-contamination-if-heavy-rainfall-arrives-20191213-p53jkv.html and https://www.smh.com.au/environment/weather/government-looks-at-protecting-state-s-drinking-water-with-heavy-rain-forecast-20200114-p53rf9.html