Territory Environments

Arid Wetlands

Most people do not associate the term 'wetland' with the dry inland areas of the continent, yet there is a great variety of 'desert wetlands'. These environments support distinctive vegetation and provide habitat for many wetland dependant animal species. There is great diversity in the range of desert wetland environments and the plants and animals they support but all have a common attribute: at least occasional abundance of water.

Shallow water in Lake Bennett and fringing salt tolerant grasses and succulents (A. Duguid)
Shallow water in Lake Bennett and fringing salt tolerant grasses and succulents (A. Duguid)

The definition of what is a wetland is based on an international agreement and includes waterholes, temporary rivers, swamps, clay pans, salt lakes and springs. It also includes artificial wetlands such as dams, sewerage ponds and associated swamps. Wetlands in the arid part of the Northern Territory range enormously in size from vast salt lakes to small spring fed pools. A few hold permanent water but most of the wetlands are dry most of the time. One of the distinguishing features is that following rain, wetlands continue to hold water after the surrounding landscape has dried out; either above the ground or in waterlogged soil. To be considered a wetland, an area must at least occasionally be wet for long enough that it is used by plants and animals that require waterlogging or inundation during their lifecycles and are visible to the naked eye. Even if they are only filled once every few decades they may still be important for species conservation.

Claypan with Canegrass (Eragrostis australasica) (A. Duguid)
Claypan with Canegrass
(Eragrostis australasica) (A. Duguid)

Another relatively large wetland type is Bluebush Swamp. These are dominated by Northern Bluebush (Chenopodium auricomum) and occur widely in the arid and semi-arid NT, including parts of the Simpson Desert, Barkly Tableland and southern Tanami Desert. Another shrub that is common in Australian wetlands is Lignum (Muehlenbeckia florulenta). It dominates large swamp areas on the semi-arid Barkly Tableland. In the arid NT it is wide spread but rarely dominates large areas.

A variety of habitats can be grouped as a wetland type called open fresh water basins. It includes lakes, claypans and other freshwater bodies with very little emergent vegetation. There is a broad range in depth and size and also in the amount of vegetation that will grow across the basin floor when temporary waters have receded. Soils are typically clayey and prevent water draining into the sub-soil. A typical claypan has hard-setting clay that is bare of vegetation except at the fringes, but many variations occur.

Another distinctive wetland type is wooded swamps. These are areas that hold water for many months and have an emergent woodland of Coolabah trees (Eucalyptus coolabah subsp. Arida and Eucalyptus victrix). The density and height of the woodland is very variable and a great many ground-storey species grow on the swamp floor as water levels drop. Most wooded swamps area associated with the floodouts of large rivers, but they also occur adjacent to some rivers where water may be held in the 'backswamps' adjacent to the main channel.

Coolabah (Eucalyptus victrix) wooded swamp (A. Duguid)
Coolabah (Eucalyptus victrix) wooded
swamp (A. Duguid)

Waterhole in the Davenport Ranges with
an aquatic plant (Myriophyllum verrucosum)
(A. Duguid)

Large sandy rivers are also wetlands and even though surface water is relatively short lasting, they have a distinctive wetland vegetation, typified by River Red Gums (Eucalyptus camaldulensis). Red Gums typically form a woodland along the banks and sometimes scattered across the river bed. These trees are important for the shelter they provided for many birds and animals.

River Red Gum in a running sandy creek (D. Albrecht)
River Red Gum in a running sandy
creek (D. Albrecht)

The only permanent natural wetlands are deep waterholes in rivers and wetlands created by permanent springs: waterholes, swamps and cascades. There are also a great many temporary springs that only flow after periods of sustained rainfall. Permanent and semi-permanent waterholes are virtually restricted to the mountain ranges: West MacDonnells, Davenport, Murchison and Dulcie ranges. The major exception is a few large semi-permanent waterholes in the Georgina River, on the southern part of the Barkly Tableland.

The permanent waterholes are extremely important as drought refuges for native fishes. In the Finke River system there 9 species, of which at least 3 are unique to that river.

The main threat to the desert wetlands of the arid NT is from introduced grasses and other weeds. These displace native species and create a greatly increased fuel load for wildfires. The problem is most extreme along the rivers, but weeds are also encroaching on swamps, including 2 of only 8 known locations for the endangered sedge Eleocharis papillosa.

Image of AUSLIG 1:250,000 topographic map depicting wetlands of the Western Plateau and Lake Eyre Basin drainage divisions
Many arid NT wetlands are very small
and cannot be depicted at the scale
of this map but have great importance
for biodiversity

Many arid NT wetlands are very small and cannot be depicted at the scale of this map but have great importance for biodiversity. The map is based on AUSLIG 1:250,000 topographic maps and depicts wetlands of the Western Plateau and Lake Eyre Basin drainage divisions. These cover all of the arid NT and the most similar parts of the semi-arid NT. Major rivers, lakes and swamps are dark blue. Small waterbodies and swamps are depicted by pale blue points.

Prepared by Angus Duguid and Bretan Clifford. 2nd September 2002

Nature of the NT

Territory Environments

Arid Wetlands

Further reading