Roebuck Bay study finds treated wastewater is not causing algal blooms

A study to trace the source of nitrogen levels in seagrass growing in Roebuck Bay has found the element was either naturally occurring or came from synthetic fertilisers - not treated wastewater.

Edith Cowan University (ECU) was commissioned by Water Corporation to undertake the study and used stable isotope signatures to trace sources of nutrients that could be entering Roebuck Bay.

Water Corporation North West Regional Manager Rino Trolio said at certain times of the year, Roebuck Bay was impacted by blue green algae (Lyngbya), which required nutrients, such as nitrogen, to bloom.

“However the study, which followed widely accepted methods to trace pollutants in waterways, found no evidence at all of treated wastewater contributing to nitrogen in seagrass in the bay,” Mr Trolio said.

There are a number of known contributors to nutrients in Roebuck Bay including agriculture, farming, septic tanks and fertiliser run off in stormwater.

Mr Trolio said Water Corporation had also taken steps to reduce any further likelihood of the Broome South Wastewater Treatment Plant (WWTP) contributing nutrients to Roebuck Bay.

“This included the completion of a project to deepen and line the unlined overflow holding pond at Broome South WWTP and reduce the overall number of treatment ponds at the plant,” Mr Trolio said.

“We have also significantly reduced flows to the wastewater treatment plant, due to the construction of a second wastewater treatment plant in Broome in 2012, and the redirection of flows from a major pump station to the new plant,” Mr Trolio said.

Water Corporation will continue to undertake additional environmental investigations and monitoring of the plant, as required by the Department of Water and Environmental Regulation, concluding in late 2018.