Australia-first trial in Moreton Bay

Above: Unitywater, UniSC, OzFish, and Healthy Land staff installing the shellfish reefs in Pine River.

“Promising results” are being reported from a unique trial in Pine River trial using shellfish reefs to improve water quality.

The first-of-its-kind trial for Australia has already indicated the effectiveness of shellfish in reducing nutrients from waterways.

Unitywater has partnered with University of the Sunshine Coast (UniSC), OzFish and Healthy Land and Water for the investigation.

The trial is testing the value of shellfish reefs in reducing nutrients downstream from Unitywater’s Murrumba Downs Wastewater Treatment Plant.

A decision on whether this will shape future investment in nature-based solutions will be made once final results are in.

“Shellfish reefs are made up of durable oyster baskets developed by OzFish volunteers,” Unitywater Executive Manager Sustainable Infrastructure Solutions Mike Basterfield said.

“Each is filled with around 18 kilograms of recycled oyster shells sourced from restaurants and commercial shucking operations.

“The shells are laid in the sun for 12 months to remove sand, grit and other impurities, preparing them for oyster spat before their final installation.”

Shellfish flesh is used to see how much nitrogen has been absorbed, how much settles into surrounding sediment and how much is naturally removed from the water.

“In the first six months, the shellfish reefs achieved a total reduction off 7.24 kilograms of nitrogen in the waterway,” Mr Basterfield said.

“This is thanks to their unique ability to filter water, separating organic material for food and storing nutrients to help them grow, ensuring the nutrients don’t re-enter the waterways.

“These early results suggest installing approximately 154 reefs, made up of 6500 baskets and covering an area approximately the size of two rugby league football fields, could completely offset the nitrogen discharged from a treatment plant servicing 10,000 people.”

Reef monitoring was conducted by researchers led by UniSC marine ecology expert Associate Professor Ben Gilby, who said more than 95 per cent of shellfish reefs have disappeared along Australia’s coastline.

“Shellfish have historically played a large role in nutrient removal, but overharvesting and other human activity has led their numbers to reduce drastically nation-wide,” Dr Gilby said.

“Findings gathered from this trial show the reef is filtering the water and improving its quality and storing nutrients within the shellfish tissue and reef structure itself. This is a significant finding for future restoration projects.”

The trial will expand to include two reefs in the North Pine River between Lawnton and Murrumba Downs, following approval from the State Assessment Referral Agency (SARA).

“These new sites will help us test reef performance under different conditions, like depth and salinity, and give us a clearer picture of how to scale this solution,” Mr Basterfield said.

For more about Unitywater’s sustainability projects visit www.unitywater.com/sustainability