Speed Presentation 2024 Australian Marine Sciences Association Annual Meeting combined with NZMSS

Using oxygenation to remediate an anthropogenically altered fjord-like estuary (#59)

James A Hortle 1 , D. Jeff Ross 1
  1. Institute for Marine and Antarctic Studies, Taroona, TAS, Australia

Oxygen depletion is an increasing feature in coastal waters globally, altering ecosystem structure and function. To combat this, artificial aeration and oxygenation methods are sometimes implemented. Macquarie Harbour on Tasmania's West coast naturally has low oxygen concentrations in its bottom waters due to its unique hydrology, extreme stratification, and shallow sill, but recently levels have dropped further. Salmon farming, altered hydro flows, and a climate change driven increase in water temperatures are considered the likely drivers. In response to this recent drop in oxygen, an oxygenation system was trialled to determine; a) the effectiveness and scalability of various injection methods, b) the potential to offset oxygen demand from salmon aquaculture, and c) its contribution to broader ecosystem remediation. We undertook a sediment and water column monitoring program to compare pre, during and post oxygenation conditions. Bacterial eDNA, video surveys and benthic grabs were used to assess community responses, while sensor networks, nutrient and metals analysis, and sound surveys were used to assess physical changes. We will present the initial results and discuss changes in physical parameters, associated ecological responses both good and bad, and ultimately what this means for safety and feasibility of upscaling oxygenation in Macquarie Harbour.