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Response of the Coorong ecosystem to the impacts of the 2022–23 flood and high flows.
Australia’s Murray-Darling Basin is one of the most heavily regulated river systems in the world, however we still do not know the full impact of altered river flows on the receiving estuarine and lagoon environment during times of flood. Flow volumes, land use and water extraction in the Murray-Darling Basin effect the quantity and quality of water reaching the Murray Mouth and Coorong lagoons, with potentially cascading impacts of eutrophication and salination on the estuarine and lagoon ecosystem.
Understanding how high flows affect the environmental conditions of the Coorong lagoons, and the response of species to these changing conditions is critical to inform future water management and delivery to the region in the future. Research activities for this project focussed on:
1. Impacts on the Coorong ecosystem – Response of Coorong nutrient store and dynamics
2. Impacts on the Coorong ecosystem – Response of Coorong food web
3. On-ground ecological restoration actions – Macroinvertebrate translocations
The 2022-2023 River Murray flood event in South Australia was the third largest flood event in recorded history. It resulted in wide ranging, short term changes in the environment, which impacted on the animals and plants living in the river and its associated floodplains and wetlands.
The immediate environmental response in the Katarapko and Pike floodplain areas included reduced shallow groundwater salinities, with some saline groundwater discharging from the floodplains into the river at specific locations. Dissolved oxygen levels did not reduce to critical levels and any low oxygen events that did occur came into South Australia from further upstream.
In the Coorong, major short-term changes associated with the large volume of fresh water passing through the barrages increased water levels and lagoon connectivity, and reduced salinity. Away from the immediate flow over the barrages, nutrients reduced and sediment quality improved. The flood event produced both positive and negative environmental responses:
Positive environmental outcomes in the Coorong following the 2022-2023 flood event:
Reduced salinity enabled increased productivity of fish and invertebrates and aquatic plants.
A greater biodiversity of plants, fish and invertebrates was found throughout the Coorong and many species became more widespread.
Large numbers of formerly widespread species also returned to the Coorong South Lagoon as connectivity and moderate conditions influenced the South Lagoon.
Negative environmental outcomes in the Coorong following the 2022-2023 flood event the direct impact of physical scouring, high water levels and changing water chemistry lead to the loss of some ecosystem functions.
During periods where salinity change was dramatic, some species were not able to survive the reduction to much lower salinities, changing the composition of species in these areas with saline tolerant species being replaced by species able to tolerate much lower salinities.
What can we expect in the future?
Climate change is expected to result in increased frequency and duration of extreme weather events. Understanding how the South Australian Lower River Murray responded to the third highest river flows on record has been critical to help plan for an uncertain future under climate change.
Based on the observed responses to the 2022-2023 flood event, further positive responses to the Coorong ecosystem can be expected if the region experiences further moderate to good freshwater flows from the River Murray in the next couple of years.
The positive environmental responses to the flood event shows that the Coorong ecosystem does have signs of resilience. However, the short-term nature of these positive environmental responses highlight the need for ongoing freshwater flows entering the Coorong.
For more detailed information on the environmental response to the 2022-2023 River Murray flood event please view the fact sheets, report and Story Map.
Story Map – Environmental responses to a significant River Murray flood
For further information on the Health Coorong, Healthy Basin Program please visit the Department for Environment and Water website here.
Outcomes from the project provide valuable insights into the health and functioning of the Coorong ecosystem, enabling effective management and conservation strategies. This includes but is not limited to:
