The use of mechanical oxygenation as a potential management approach for improving environmental conditions in Macquarie Harbour is the focus of the Australian Government-funded Oxygenation Offset Program in Macquarie Harbour (OOPMH). The IMAS-led Science Project component of OOPMH provides the independent scientific evidence needed to evaluate the effectiveness, efficiency and environmental safety of mechanical oxygenation strategies. Through monitoring, modelling and environmental research, this project is building the scientific knowledge needed to support future management of Macquarie Harbour’s unique ecosystem.
Macquarie Harbour is one of Australia's most unique estuarine ecosystems. Its large, deep central basins, shallow entrance to the Southern Ocean and substantial freshwater inflows from the Gordon and King Rivers create a naturally layered water column. This layering limits the mixing of oxygen-rich surface waters with deeper waters below the halocline, resulting in naturally low dissolved oxygen concentrations at depth.
Over recent decades, dissolved oxygen concentrations in the harbour's deep waters have declined further. Scientific evidence indicates that this decline has resulted from multiple interacting factors, including increased salmon farming, rising water temperatures associated with climate change, and changes in rainfall and river flows. Reduced dissolved oxygen is now recognised as one of the major environmental challenges facing Macquarie Harbour, affecting ecosystem health and the habitat of the endangered Maugean Skate.
Understanding how oxygen moves through the harbour, what drives oxygen depletion, and how different management approaches may influence oxygen conditions has become a major focus of collaborative research led by IMAS, together with CSIRO and other project partners.
Mechanical oxygenation is one potential management approach being evaluated for improving oxygen conditions in the deep waters of Macquarie Harbour. It involves dissolving oxygen into harbour waters and delivering it below the halocline, where dissolved oxygen concentrations are naturally lowest.
The role of the OOPMH Science Project is to provide the independent scientific evidence needed to evaluate the effectiveness, efficiency and environmental safety of mechanical oxygenation. This includes assessing whether oxygen can be delivered effectively and efficiently to the target depths, understanding how it moves through the harbour, and determining whether oxygenation can be undertaken without adverse environmental impacts.
This research began through the Macquarie Harbour Oxygenation Project (MHOP), a pilot-scale trial undertaken in 2024-2025, that provided the first opportunity to test mechanical oxygenation under real harbour conditions.
Key achievements of the pilot project include:
The pilot project established the scientific and engineering foundation for the OOPMH, which is evaluating mechanical oxygenation at an operational scale.
The Science Project is led by the Institute for Marine and Antarctic Studies (IMAS), in collaboration with the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and other project partners.
The OOPMH comprises two complementary projects. An oxygenation delivery project, led by Salmon Tasmania, is responsible for the design, deployment and operation of the oxygenation systems, as well as the continued oxygenation during transition from pilot to scale. The Science Project, led by IMAS, provides the independent scientific evidence needed to guide the transition from pilot- to operational-scale oxygenation.
Building on the success of the MHOP, the Science Project evaluates the effectiveness, efficiency and environmental safety of oxygenation under operational conditions. Through environmental monitoring, hydrodynamic modelling, sediment investigations, digital decision-support and environmental assessment, the project provides the evidence needed to optimise oxygen delivery, minimise environmental risks and support adaptive management as oxygenation is implemented.
Beyond evaluating oxygenation, the Science Project is advancing our understanding of oxygen dynamics and ecosystem processes in Macquarie Harbour. This knowledge will support future environmental management and provide a stronger scientific foundation for decisions about the harbour's long-term health.
The OOPMH Science Project brings together expertise in environmental monitoring, hydrodynamic modelling, sediment biogeochemistry, environmental data science and socio-economic assessment. Together, these complementary research areas provide the independent scientific evidence needed to evaluate mechanical oxygenation while advancing our understanding of oxygen dynamics and ecosystem processes in Macquarie Harbour.
A comprehensive monitoring program is evaluating the performance and environmental response of mechanical oxygenation under operational conditions. A network of fixed underwater sensor arrays continuously measures dissolved oxygen, temperature and salinity, while vessel-based surveys collect detailed water quality profiles throughout the harbour.
Baseline environmental assessments are undertaken before oxygenation begins at each new location and include water quality, sediment chemistry, benthic macrofauna, microbial communities and ecological condition. During operation, these measurements are complemented by underwater cameras and remotely operated vehicles (ROVs) to assess the response of fish and other mobile fauna. Together, these observations are used to evaluate oxygen delivery, validate model predictions, assess environmental performance and ensure oxygenation is implemented effectively, efficiently and safely.
Hydrodynamic and biogeochemical models, developed in collaboration with CSIRO, are being used to understand how oxygen moves through Macquarie Harbour and how it responds to changing environmental conditions.
Building on the successful pilot project, these models simulate the dispersal of oxygen from injection points and predict how oxygen is transported, consumed and retained throughout the harbour. By accounting for natural processes, environmental conditions and oxygen demand associated with salmon farming, the models help evaluate where, when and how oxygen can be delivered most effectively and efficiently.
At a finer scale, lease-scale modelling is being used to understand how organic matter from salmon farming is transported, deposited and broken down. This improves understanding of oxygen demand in both the water column and sediments and provides an important scientific foundation for evaluating oxygenation strategies.
Sediments play an important role in the harbour's oxygen dynamics. The Science Project is investigating how current and historical salmon farming influences sediment oxygen demand and the recovery of harbour sediments through time.
Field investigations combine sediment cores, benthic sampling, sediment oxygen demand measurements, ecological indicators and chemical tracers to distinguish aquaculture-related enrichment from natural and other human influences. These studies will improve understanding of how sediments contribute to oxygen depletion, the extent of legacy oxygen demand associated with historic farming, and how sediments recover following fallowing or cessation of farming.
Building on the mass-balance methodology developed through the MHOP, the Science Project continues to refine estimates of the oxygen demand associated with salmon farming in the harbour's deep waters.
This work improves understanding of how oxygen demand varies through time and under different production scenarios, providing the scientific basis for evaluating oxygenation requirements and supporting future management decisions.
The Science Project is developing a digital platform to support the sustainable management of Macquarie Harbour. The platform will integrate environmental monitoring, predictive modelling and operational information into a single information system, providing a shared view of harbour conditions.
By bringing together near real-time sensor observations, environmental data, hydrodynamic model outputs, river flows, weather information and operational oxygenation data, the platform will deliver evidence-based decision-support tools for planning, implementing and evaluating mechanical oxygenation while supporting the broader sustainable management of Macquarie Harbour.
The Science Project examines the broader environmental, economic and social aspects of mechanical oxygenation. This includes evaluating the costs and benefits of oxygenation strategies, understanding community perspectives, and engaging with Tasmanian Aboriginal organisations to support evidence-based decision-making for the future management of Macquarie Harbour.
The output of this project will be a turnkey methodology that can implemented on an ongoing basis to offset oxygen demand from salmon farming and to improve environmental conditions in Macquarie Harbour, that has been scientifically demonstrated to be effective, efficient and environmentally safe. Innovation in oxygenation technology and assessment frameworks will have a wide range of broader applications for environmental enhancement and remediation beyond Macquarie Harbour.
These tools will enable more responsive and informed decision-making, supporting conservation efforts for the endangered Maugean Skate and the sustainable management of the Macquarie Harbour environment.
This project is funded by the Australian Government through the Fisheries Research and Development Corporation (FRDC) and the Department of Climate Change, Energy, the Environment and Water (DCCEEW).
