FACTORS causing the toxic blue-green algae Lyngbya majuscula to bloom in the Ramsar-listed Roebuck Bay have been investigated by scientists and Broome volunteers. Project leader and UWA hydrogeologist Ryan Vogwill… says Lyngbya can be hazardous for marine life.
“It can actually kill quite a lot of smaller animals,” Prof Vogwill says.
“Larger animals including humans can have bad skin irritations and really quite serious health effects from it.”
He says while Lyngbya occurs naturally at low levels in tropical and sub-tropical waters throughout the world, nutrients from Broome’s sewerage system tend to stimulate blooms.
He says the 20th Century had had no recorded blooms at Roebuck Bay, but in 2000 a massive bloom occurred after cyclone Rosita caused Broome’s wastewater treatment facility to overflow.
With help from volunteers and Indigenous rangers, his PhD student ecohydrologist Gayan Gunaratne analysed the effects of Broome’s stormwater during the wet seasons of 2011-12 and 2012-13.
“We collected stormwater samples for nutrient analysis and also we measured the amount of water going into the bay,” Mr Gunaratne says.
“I discovered a lot of nutrients coming from old Broome town.
“Sometimes the seasonal first flush, that means the first couple of rains, provide more than 50 per cent of the nutrients.”
He says this “shock loading” of nutrients seems to be the problem, as the bay’s annual average nutrient loading is not particularly high, compared to similar coastal areas that do not have bad Lyngbya blooms.
They also noticed Lyngbya blooms starting just before the first rains, suspecting groundwater nutrients as the cause.
Groundwater sampling indicates nutrient zones
As the Broome Peninsula’s groundwater is known to flow southward into the bay, Prof Vogwill directed honours students Nick Wright and Daniel Hearn to sample groundwater from purpose-made monitoring wells and existing shire bores.
He says they found elevated nutrient levels in the groundwater at old Broome.
Mr Gunaratne found much lower nutrient concentrations in stormwater runoff from newer parts of Broome, east of the airport.
“The new developments all have more engineered drainage design structures that do a lot of sediment retention,” Prof Vogwill says.
As a consequence they seem to be holding back a lot more nutrients.
While it is probably impossible to eradicate Lyngbya, he says controlling the available nutrients would starve it back to harmless levels.
Further research is being carried out by Gayan Gunaratne under the supervision of Prof Vogwill, Assoc Prof Matt Hipsey and Prof Ryan Lowe.
The project is funded by The University of Western Australia (UWA) and Rangelands NRM WA and the field work was done with the in-kind support of Roebuck Bay Working Group, Department of Parks and Wildlife (DPaW) and the DPaW/ Yawuru joint management team.
The research group lead by Prof Vogwill won the 2013 Southseas Oceans Hero Award for bringing together the community to discover the role of nutrient inputs in the proliferation of algae in Roebuck Bay.
Geoff Vivian, Science Network West Australia
View original article at: Science and community pinpoint algal bloom causes