The first-of-its-kind trial for Australia, delivered by Unitywater in partnership with University of the Sunshine Coast (UniSC), OzFish and Healthy Land and Water, has indicated the effectiveness of shellfish in reducing nutrients from waterways.
Unitywater Executive Manager Sustainable Infrastructure Solutions, Mike Basterfield, said the trial was developed to test the value of shellfish reefs in abating nutrients downstream from its Murrumba Downs Wastewater Treatment Plant, potentially shaping future investment in nature-based solutions.
“The shellfish reefs are made up of durable oyster baskets developed by OzFish volunteers, each filled with around 18 kilograms of recycled oyster shells sourced from restaurants and commercial shucking operations,” Mr Basterfield said.
“The shells are then laid in the sun for 12 months to remove sand, grit and other impurities, preparing them for oyster spat before their final installation.”
Mr Basterfield said once installed, results are measured by sampling the shellfish’ flesh and quantifying how much nitrogen has been absorbed, how much of it settles into surrounding sediment and how much is naturally removed from the water using well-established scientific methods.
“In the first six months of measuring results, the shellfish reefs achieved a total reduction of 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 in its body tissue to help them grow, ensuring the nutrients don’t re-enter the waterways.”
“These early results suggest that installing approximately 154 reefs, made up of 6,500 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 a team of 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.
“Our team has used a range of techniques, including testing the nitrogen content of both the shellfish flesh and the sediment underneath and around the reefs, to understand how well these reefs are working,” he said.
Unitywater Executive Manager Sustainable Infrastructure Solutions, Mike Basterfield, said the trial will expand to include two additional reefs in the North Pine River between Lawnton and Murrumba Downs, following development approval from the State Assessment Referral Agency (SARA).
“Unitywater’s commitment to net zero includes an ambitious goal of ensuring all nutrients from wastewater are diverted or offset from waterways by 2040 and this is one of the innovative nature-based solutions we are trialling to bring us closer to this target.”
“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.
To learn more about sustainability at Unitywater, head to www.unitywater.com/sustainability
