A project to boost oxygen levels in Tasmania’s Macquarie Harbour has reached a significant milestone, with early trials showing positive results.
The initiative, led by marine ecologists at the University of Tasmania’s Institute for Marine and Antarctic Studies (IMAS), aims to improve the habitat of the endangered Maugean skate.
IMAS Associate Professor Jeff Ross said the harbour is naturally a low dissolved oxygen environment, with levels declining from 2009 to 2013 due to factors such as salmonid aquaculture, river flows and climate change.
“The Macquarie Harbour Oxygenation Project (MHOP) is designed to evaluate the feasibility, scalability and environmental efficacy of mechanical oxygenation as a tool to help increase the levels of dissolved oxygen,” he said.
“We know similar approaches have been successful overseas at increasing levels of dissolved oxygen in water, but Macquarie Harbour is quite unique, so a staged approach is critical.”
Monitoring has confirmed that the preliminary trials have been successful, demonstrating that oxygen is delivered and retained at depth with no adverse ecological effects.
“In February, we began cautiously with a one-week trial that delivered 500–700 kg of oxygen a day. Based on positive results, we then transitioned to a six-week trial from April through to June,” Ross said.
“For this trial, we progressively increased oxygen loads from 1,000–3,000 kg a day over six weeks, with a detailed examination of nutrient and heavy metal concentrations before, during and after the trial and found that the microbial community and sediment health showed no adverse environmental effects.”
The third trial began in early August, with the project team aiming to increase the oxygen load delivered daily to 5,000 kg.
“The loads and scale of delivery and effect are now quite significant, especially in the context of potentially improving bottom-water dissolved oxygen levels in target areas that are important Maugean skate habitat and for offsetting the estimated demands of salmon aquaculture,” Ross said.
He added that an important focus of the project is to improve energy efficiency in running the oxygenation plant, particularly if the system is scaled up and used on an ongoing basis.
“As the oxygenation load has increased for each phase, we have seen a five-fold decrease in the energy requirements for every kilogram of oxygen delivered and achieving more energy efficiency gains is the focus of our engineering team as we continue to increase and assess the scalability of the system,” he said.
