Kakadu wetlands

• Category: Inland Aquatic Biomes.
• Geographic Location: Australia.
• Summary: Kakadu contains more than 10,000 insect species, an excess of 280 bird species, 117 kinds of reptiles, 60 mammals, 53 freshwater fish, and more than 1,700 plant types.

The Kakadu Wetlands has been called a climate change hot spot. Situated in the Alligator Rivers region of Australia’s Northern Territory, the Kakadu Wetlands has a tropical monsoonal climate. Humidity is low and rain is rare in the dry season (April to September). Build-up or transition months include high temperatures and high humidity, with violent lightning storms. The rainy season is from January to March and sometimes April; it is both warm and wet. Rainfall in Kakadu averages 51–61 inches (1,300–1,565 millimeters) per year.

The Kakadu Wetlands biome is part of an extensive network of habitats that feature stone plateaus and escarpments, floodplains and billabongs, tidal flats, monsoonal rainforests, and coastal beaches.

Kakadu has nearly 310 square miles (500 square kilometers) of coast and estuary lined mostly with mangrove forest. Creeks and rivers influenced by tides can extend 62 miles (100 kilometers) inland. The estuaries and tidal flats grow in the dry season and erode during flood season, which also moves silt out to sea, making the waters along the Kakadu coast muddy. Estuaries and tidal flats are home to animals and plants that have adapted to oxygen-deficient salt mud.

Biota

Of the known plant types in Kakadu, 67 species are rare or vulnerable. While certainly not unaffected by invasive flora, Kakadu is one of the most weed-free areas of the country, with only 5.7 percent of known plants here classed as weeds. Unlike most of Australia, Kakadu has largely avoided both plant and animal extinctions, with a few exceptions.

Floodplains plant communities here feature spike rush and other sedges, freshwater mangrove, paperbark, pandanus, and water lilies. Mangroves are also found in the estuaries and tidal flats; they stabilize the coastline while offering feeding and breeding areas for many species of fish. Tidal flats behind the mangroves—including the isolated patches of freshwater monsoon forest of mangrove, fig, and kapok—support grasses, sedges, and hardy succulents.

Mangrove swamps and glasswort flats are most common, but coastal and riverbank freshwater springs allow pockets of coastal monsoon rainforest. Birds are plentiful in both, as are flying foxes—and the crocodiles that feast on fallen flying foxes. Beaches and the coastal area are home to turtles, snakes, and a variety of sea cow.

Other wetlands and floodplains here are noted for their extreme seasonal changes. Floodplains that are wet for two to six months support grasses, sedges, and mangroves, while floodplains under water for six to nine months produce varieties of water lilies. The creek banks and permanent waterholes (billabongs) support paperbark trees as well as mangroves and water pandanus.

Wet season rains create a shallow freshwater sea that extends far over the plains. When the water recedes, life concentrates in the remaining pools and wet areas. Among such species are reptiles, including varieties of turtles, snakes, and both fresh- and saltwater crocodiles. The area also is home to wallabies and a wide variety of birds. Monsoon pockets are home to different avian varieties—figs, rainbow pittas, and the like—than those of the other areas.

The floodwaters provide nutrients to the floodplains, which in combination with abundant sunlight and groundwater make these habitats naturally abundant in animal and plant life. When the dry season reduces water to billabongs, creeks, and rivers, the floodplains remain vital feeding grounds and refuges for waterbirds. Some waterbirds abundant in Kakadu cluster in a narrow band along the northern coast of Australia, among them the magpie goose, green pygmy goose, wandering whistling duck, and Burdekin duck. Commonly seen in the area, too, are the comb-crested jacana (lotus bird), cormorant, egret, heron, and ibis. About 30 species of migratory birds from the Northern Hemisphere visit these wetlands each wet season.

Kakadu boasts more than 280 bird species, some of which range across habitats, while others are unique to only one. The birds spotted in Kakadu constitute about one-third of Australia’s bird species. Over 6,835 square miles (11,000 square kilometers) of the savanna here is home to endangered or restricted range species.

The region’s mammal population includes rare, endemic (found only here), vulnerable, and endangered species. Time of day or time of year affects the activity of many Kakadu mammals. Sixty species of placental mammals and marsupials are known to inhabit the park; mostly they are forest and woodland types, either nocturnal or active mainly in the cooler parts of the day. Nearly all mammal species here are considered to be in decline, although in Kakadu they have found an ideal environment to make their stand.

Kakadu also has 25 species of frog, 117 different kinds of reptile, 32 types of fish in a single creek system, and 10,000 species of insect. Because of the intense daytime heat, most snakes are active only at night. The crocodile population of Kakadu is tremendous, and the saltwater varieties are found in most Kakadu waterways. Accordingly, swimming is discouraged but not prohibited in plunge pools and gorge areas.

Pressures and Preservation

Reptile populations have tumbled since the introduction of the cane toad, and once common lizards and snakes are now rare. Invasive species include the water buffalo; wild pig; cane toad; giant sensitive tree (Mimosa pigra); and para grass, a weed that is taking over areas once covered with legumes, grasses, and other food for the native birds. Feral introduced animals, such as donkeys, cats, dogs, and mice present a similar problem exacerbated by their breeding in the park, growing their numbers. Similarly aggressive nonnative vegetable species have corrupted parts of the floodplain and water systems.

Climate change also is impacting the area, with a greater incidence of cyclones that periodically devastate the environment (as well as local businesses, including tourism). More erratic and intense rains are expected to disrupt tourism in Kakadu National Park; the potential impact and mitigating actions are being studied. In addition, the woody component of the savannas has thickened, possibly as a result of elevated atmospheric carbon dioxide, which favors the growth of some species, while others have declined due to increased fire frequency. Saltwater intrusion in the wetlands is a growing risk as sea levels rise. Climate change may also be blamed for the spread of fire-prone weeds such as gamba grass.

Since 1992, Kakadu National Park has been a World Heritage Area, a United Nations Educational, Scientific and Cultural Organization (UNESCO) site. Listed for both its natural and cultural heritage, the park’s nearly 1.7 million acres (683,000 hectares) have been designated a Ramsar-protected Wetlands of International Importance, covered under the 1971 convention that identified 1,950 such sites around the world as needing conservation attention. Although savanna woodlands cover 80 percent of the park, the wetlands are of paramount interest.

The park’s South Alligator River is thought to be the only large riverine system in the world to be contained and protected entirely within a national park, and Kakadu may be the only national park in the world containing a full river system catchment area.

Bibliography

Australian Government. “Floodplains and Billabongs.” Department of Sustainability, Environment, Water, Population and Communities, 2012. . Accessed 12 Nov. 2024.

Finlayson, C. Max and Isabell von Oertzen, eds. Landscape and Vegetation Ecology of the Kakadu Region, Northern Australia. Dordrecht, Netherlands: Kluwer Academic Publishers, 1996.

Florin, Anna, Andrew Fairbairn, and Chris Clarkson. "65,000 Years of Food Scraps Found at Kakadu Tell a Story of Resilience Amid Changing Climate Sea Levels and Vegetation." The Conversation, 4 May 2022, theconversation.com/65-000-years-of-food-scraps-found-at-kakadu-tell-a-story-of-resilience-amid-changing-climate-sea-levels-and-vegetation-181240. Accessed 12 Nov. 2024.

“Kakadu: Vulnerability to Climate Change Impacts.” Australian Government, 2011, www.dcceew.gov.au/sites/default/files/documents/kakadu-coast.pdf. Accessed 12 Nov. 2024.

Steffen, Will. Australia’s Biodiversity and Climate Change. Colingswood, Australia: Csiro Publishing, 2009.