Kakadu freshwater floodplains to disappear in a century due to sea-level rise

  Last updated December 4, 2017 at 4:51 pm

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The freshwater floodplains that make up 20% of the landscape of Kakadu National Park are likely to disappear within a century, according to new CSIRO research published today.


Kakadu National Park (Image: Chris Ford)


These vulnerable areas are already at risk today from invasive species like feral pigs, buffalo and the relatively recent colonisation by cane toads. Pigs wreck floodplain habitats, making life difficult for the native species that call them home.  By rooting around in the soil they destroy native plant biodiversity and make it easier for weeds to invade.  They also compete for food with native species such as Magpie Geese. Fast growing aquatic weeks such as para grass also threaten freshwater habitats.


In this study, researchers developed a model to see what would happen to biodiversity, cultural activities such as traditional hunting and fishing and economic activities including tourism under different sea-level rise scenarios.


They concluded that by 2070, with a 0.7m predicted sea-level rise, 60% of freshwater foodplains will be lost. This jumps to 78% by 2100 with a rise of 1.1m. By 2132, with a sea-level rise of 2.15m, there would be a total loss of all freshwater floodplains.


Even if we acted now to stabilise climate change, sea levels will keep rising, because there is such a time lag in the system. The researchers predict that the breaking point will happen sometime between 2030 and 2070, after which there’s no turning back. The system will switch from freshwater ecology to marine in a matter of decades.


Predicted high-tide mark today (dark blue, left) and in 2100 with predicted sea-level rise of 0.7m. Generated using Coastal Risk Australia.


The model takes into account stressors to the system including invasive species such as feral pigs and para grass and how they may affect key species such as the Magpie Goose. This is seen as an indicator species because it lives in the susceptible floodplain regions, competes with feral pigs for food, and has significant cultural importance to Aboriginal communities.


The risk in the 2100 scenario from invasive species is substantially lower, but only because of the loss of the freshwater ecology they depend and thrive in.


Under the scenarios considered, new freshwater habitats will created further inland, but they are predicted to be much less extensive than those that currently exist.


While there is little that can be done to change the overall course of the changes, the model developed in this study can help decision-makers identify areas which now seem a low priority or too costly, as important places to target for protection and mangagement of invasive species. They could be future sites for smaller, but very valuable freshwater refuge areas.


The economic costs are complex. The model predicts a loss in tourism revenue, valued currently at at least $15 million, which will be felt in fewer job opportunities and business development for Indigenous communities.


The complexity of the risks “becomes more diabolical over longer time frames” in the words of the authors, because the benefits of investing in control of invasive species eventually cease to exist due to the eventual predicted loss of the entire freshwater ecosystem.


Kakadu in 2100 will look “very different” and traditional management systems will not work. At least tools like this one allow us to time travel out to longer time frames, to see how we can better plan to adapt to the changes that sea-level rise will bring to this unique and precious ecosystem.


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Lisa Bailey