Oxygen depletion is an increasing feature in coastal waters globally, altering ecosystem structure and function. To combat this, artificial aeration and oxygenation methods have sometimes been implemented. The form and scale of these methods is variable, ranging from direct injection of gas in the form of fine bubbles to mechanical mixing at the water/air interface. Literature concerning the efficacy of these devices is limited and tends to focus on freshwater systems. It also largely fails to compare different methods and the effects at an ecosystem level.
Macquarie Harbour on Tasmania's west coast naturally has low oxygen concentrations in its bottom waters due to its unique hydrology and shallow sill, but recently levels have dropped further. Salmon farming, altered hydro flows, and increased water temperatures are considered the likely drivers. In response to this recent drop in oxygen, the salmon industry and government aim to trial an oxygenation system to offset a portion of the salmon farming induced oxygen demand. This provides an ideal opportunity to contrast oxygenation methodologies in a large-scale, real-world trial. Additionally, this project will aim to assess the performance of these methods not simply on volume of oxygen injected but in more ecologically relevant measures, e.g., how much oxygen is retained in the system? What are the ecological consequences, both positive and negative? Does the receiving environment use oxygen at a consistent rate spatially and over time and what does this mean for scalability?
This project will aim to answer these questions by monitoring the environment around the proposed oxygenation system to spatially map the extent of the oxygenation and assess any interactions between oxygenated water and the ecosystem. This will include monitoring water column and benthic chemistry, bacterial and macrofaunal communities. Furthermore, laboratory experiments will aim to build understanding of the mechanisms behind observed data.
For more information on the broader Macquarie Harbour Oxygenation Project, visit the project page here.
