Algae specialist suspects old tip leachate and fertiliser

Blue-green algae specialist Dr Guastaaf Hallegraeff has said leachate from the old Woy Woy tip and the use of fertiliser on nearby playing surfaces could both be contributing factors to ongoing bird deaths at Blackwall.

The former Woy Woy tip is located under the James Brown playing surfaces behind the Peninsula Leisure Centre.

Council has said the tip was correctly remediated and capped to manage any potential leachate but Dr Hallegraeff has said the former dump could be a potential source of blue-green algae.

He said fertiliser run off is another common cause.

"Blue-green blooms tend to be driven by high nutrients (notably phosphate) and high temperature," Dr Hallagraeff said.

He urged Council to check its use of fertiliser on the James Brown playing fields.

In terms of whether toxins such as microcystin would have an even greater impact on the health or Brisbane Water than the bird mortality, he said: "Microcystin from freshwater run-off is known to occasionally accumulate in coastal oysters."

The Environmental Protection Authority has written to the Central Coast Council advising it to put risk mitigation measures in place.

In Dr Hallagraeff's opinion, the two key measures that the Central Coast Council should use are to reduce the use of nutrient fertiliser and increase the monitoring for microcystin.

Gross pollution traps, such as those installed around Tuggerah Lakes in recent years, would only prevent future bird deaths and related issues if they stopped the nutrient leaching.

Dr Hallagraeff said he would have to physically inspect the traps to draw any conclusions about their appropriateness for the location, and optimal cleaning and maintenance.

Email, 12 Oct 2016

Gustaaf Hallagraeff, University of Tasmania