An iconic wetland at risk from sea level rise

Originally published in the Adelaide Advertiser, 1 degree series, August 2007 – updated with hyperlinks

A RICH diversity of unique plant and animal species live in World Heritage Listed Kakadu National Park. These include vast flocks of magpie geese, which congregate in millions to feed on water chestnuts growing on the floodplain of the South Alligator River. Unfortunately, this pristine northern Australian wetland now faces severe threats from climate change, feral animals and invasive weeds.

The Kakadu wetlands formed about 6000 years ago. This occurred after sea levels had stabilised, following an earlier rise of 120m at the end of the last ice age. Ironically, it could be further sea level rise that spells the end of these wetlands. Among the many effects of human-induced climate change are rising sea levels and more intense cyclones in the tropics.

About 20cm of sea level rise occurred during the 20th century. At least double that amount – and perhaps much more – is predicted for the 21st century. Both sea level rise and more intense storm surges act to increase the regularity and severity with which seawater washes through the low-lying freshwater wetlands. At the Mary River mouth, extensive earthen barrages have been built already in an attempt to hold the burgeoning tides at bay.

If emissions of greenhouse gases are not curtailed quickly and substantially, by the end of this century, the sea level rise caused by global warming will have inundated extensive tracts of Kakadu. What remains will be isolated patches of freshwater wetlands within a mire of brackish swamps and saltwater mangroves. Stripped of their prime habitat, the spectacular aggregations of magpie geese will decline and fragment. They will become an occasionally spotted curiosity, rather than a tourism mainstay.

Indigenous people will be robbed of a traditional bush food. Many other species of birds, as well as frogs, water snakes and freshwater fish will also retreat or disappear. One of Australia’s natural jewels will have lost its lustre. (Prof. Ross Garnaut, in his draft report on the economic impacts of climate change on Australia, pinpoints Kakadu as one of the areas most under threat)

NOTE: I have written a more detailed outlook on this problem for Australasian Science magazine. You can download a PDF of the article for free, here.

By Barry Brook

Barry Brook is an ARC Laureate Fellow and Chair of Environmental Sustainability at the University of Tasmania. He researches global change, ecology and energy.

8 replies on “An iconic wetland at risk from sea level rise”

To quote me, from the above piece:
“Unfortunately, this pristine northern Australian wetland now faces severe threats from climate change, feral animals and invasive weeds.”

They are one of the feral animals.


And what do the the feral buffalo have to do with sea-level rise? They were introduced over one hundred years ago, and have been almost wiped out anyway.


At the Mary River mouth, extensive earthen barrages have been built already in an attempt to hold the burgeoning tides at bay.

Really? According to the Australian Government Greenhouse Office:

This booklet gives an overview of a study undertaken to evaluate the cost and benefits
of options to prevent the intrusion of salt water upon the Mary River Wetlands in the
Northern Territory, Australia. Since the 1940s, this highly significant freshwater wetland
has been subject to approximately 240 km2 of salt water inundation, resulting in the
loss of salt-sensitive vegetation and significant impacts on the area’s environmental
and economic values.

Whilst the salt water inundation in the Mary River is not a result of climate change,
it provides an opportunity to undertake research in circumstances similar to those
projected to occur due to global warming.

So according to the AGGO, the existing earthen barrages were not built to hold the “burgeoning tides [due to GHG-indeced sea-level rise] at bay”

Another alarmist lie to add to my collection.


Ah, no. Feral buffalo exist in the hundreds of thousands in the NT, and are causing untold damage to tropical ecosystems. Between 3000-5000 head are harvested annually from Bulman (Arnhem Land) alone each year. The Brucellosis-Tuberculosis Eradication Campaign (BTEC) only removed them from Kakadu National Park and westward, but the main base in Arnhem Land was left alone and the remnant population has now spread progressively westward to establish pre-BTEC numbers in many areas. I have been to Arnhem Land many times and personally observed individual groups numbering in the hundreds (i.e., spread that around several 10s of thousands of square kilometres).


Gorman JT, Saalfeld K, Griffiths AD. 2007. Population estimate of Asian water buffalo and
wild cattle in the Arafura Swamp, central Arnhem Land. 19: 1-8

Koenig J, Griffiths AD, Godjuwa C, Camion O. 2003. Aerial survey of vertebrates in the Mann river district, central Arnhem Land. Northern Territory Naturalist 17:7–19

Petty, A.M., Werner, P.A., Lehmann, C.E.R., Riley, J.E., Banfai, D.S., Elliot, L.P., 2007. Savanna responses to feral buffalo in Kakadu National Park, Australia. Ecological Monographs 77, 441-463

Buffalo were responsible for increasing saltwater intrusion to freshwater wetlands, so the increasing salt intrusion from sea level rise coupled with channel-opening by rising buffalo densities will damage greater and greater areas of freshwater wetlands in Kakadu and adjacent areas. Add invasive weeds (e.g., Mimosa sp.), and you have a lethal cocktail of environmental degradation. It’s happening now, and Kakadu is in serious trouble.


[deleted pointless attack on my moderation principles]

Anyway Corey, I got my information from this 2004 Department of Environment publication:

Water buffalos were imported to Australia in the 19th century to supply meat to remote northern settlements. The settlements and their buffalos were abandoned in 1949 and, despite harvesting for meat, hides and as hunters’ trophies, feral buffalos spread across the northern floodplains. By the 1970s, feral buffalo numbers were so high that they were destroying wetlands and harbouring diseases that could affect native species and livestock. The Brucellosis and Tuberculosis Eradication Campaign, developed to protect the meat export industry, has all but eradicated feral buffalos from the wild. The challenge will be to ensure that feral buffalo populations do not rebuild.

Maybe the challenge was not met.


So according to the AGGO, the existing earthen barrages were not built to hold the “burgeoning tides [due to GHG-indeced (sic) sea-level rise] at bay”

Mugwump, your insertion of “[due to GHG-indeced (sic) sea-level rise]” is a mendacious confabulation. Barry did not say that the tidal damage, that the barrages were built in reponse to, was a result of climate change. As Cory explained, buffalo were primarily responsible or tidal intrusion into the wetlands, and Barry explicitly mentioned feral in his opening paragraph.

Perhaps he could have been a bit more explicit in explaining how past pressures have and future pressures will act, but all he said really was that the barrages were a response to burgeoning tidal action. This is true. Go to the Mary River and see for yourself it you dispute this.

Ferals and weeds are profoundly threatening Kakadu – climate change will greatly exacerbate this.

Your little bit of editing is another Denialist misrepresentation to add to the list.


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