Diamantina River

• Category: Inland Aquatic Biomes.
• Geographic Location: Australia.
• Summary: An extensive ecosystem depends on this frequently and erratically flooding river; the diverse plant, fish, and animal species here have adapted to the extreme weather regime.

The Diamantina River flows through Queensland and South Australia, draining into Lake Eyre, the lowest point in Australia. The Diamantina begins in the Swords Range northwest of Longreach, and flows southwest to form the Warburton River at its confluence with the Georgina River. The river reaches as far as Lake Eyre only during wet years. At 560 miles (901 kilometers) in length, nearly all the Diamantina River lies in a basin used as agricultural land, especially for the grazing of cattle and sheep. It is, with Cooper Creek and the Georgina River, one of the three principal rivers of the Australian Outback's Channel Country.

The river basin is quite flat, ranging from Lake Eyre's 52 feet (16 meters) below sea level to a high point in the northeast of about 1,600 feet (488 meters). Most of the rivers in this basin flow toward the cattle country of Birdsville in the southwest. The Diamantina River flows sluggishly and has a series of wide shallow channels with no main channel for much of its length. The climate is hot and arid, settling in around 100 degrees F (38 degrees C) on summer days, with summer night averages of 75 degrees F (24 degrees C) and winter temperatures of 52–77 degrees F (11–25 degrees C). Parts of the basin sometimes see frost.

Rainfall here is concentrated in the wet season, from December to March (Australian summer), with significant rainfall exceptionally rare the rest of the year. The basin always has been subject to both erratic floods and catastrophic droughts, and in wet years, rainfall totals almost four times higher (43 inches or 1,092 millimeters) than average (12 inches or 305 millimeters) have been reported in the wettest areas. During floods, the river has reached widths of nearly 20 miles (32 kilometers). In dry years, on the other hand, total rainfall tends to be less than four inches (101 millimeters) for nearly the entire river basin.

Soils in the Diamantina River region have low phosphate content, but adequate levels of other nutrients; they are mainly brown and gray vertisols (moisture-sensitive clays), with some fluvents (flood deposits). Grasses flourish in the rainy season.

Biodiversity

Floods along the Diamantina River leave behind scattered seasonal waterholes upon which numerous plants and animals depend. The bilby (Macrotis lagotis) and other small animals frequently depend on waterholes to tide them over until the next unpredictable major rainfall event. Another of the animals that depend on these waterholes is the endangered dusky hopping mouse (Notomys fuscus), a nocturnal rodent a few inches (millimeters) long that makes its home in dunes, drinking from waterholes and eating seeds, small plants, and insects. Overgrazing and predation from feral cats have jeopardized the hopping mouse, along with competition with the more recently introduced house mouse and rabbit. The plains rat (Pseudomys australis), about twice the size of the hopping mouse, is likewise dependent on waterholes and also endangered as a result of habitat loss and predation by feral cats. Plains rats live in complex but shallow burrow systems in the soft soil around low shrubs. They don't drink from waterholes generally, but obtain their moisture by eating many of the small animals that do drink from them.

The Diamantina River floodplain has been designated an Important Bird Area by Birdlife International. When flooded, the river supports approximately 500,000 waterbirds. It is home to, or supports for a period of migration, significant numbers of the Nankeen night-heron, royal spoonbill, little curlew, Australian bustard, grey grasswren, inland dotterel, cinnamon quail-thrust, and pied honeyeater.

The desert gobi fish is found throughout the small ponds and creeks of the Lake Eyre basin, including the banks of the Diamantina. Rabbits are a serious threat to many of the endemic species of water-dependent plants alongside these riverbanks, which are in great jeopardy as soil erosion becomes more likely when the rabbits overgraze.

In and around the water, the environments that are home to freshwater fish, small mammals, and migratory birds are particularly vulnerable to climate change. At stake is habitat loss or fragmentation; the spread of alien species is another vector generally driven by global warming. Many of Australia's freshwater fish have historically adapted to variable or unpredictable water flow conditions; they may continue to do so. However, the rate and magnitude of projected change could outpace their ability to adapt. This is especially true for species with limited ranges or unusual habitat requirements.

Among the plant communities here, the invasive gum arabic tree (Acacianilotica), a spinescent woody legume, was introduced decades ago for ornamental purposes and has since become aggressively invasive. It has been spreading almost unchecked, in part because of grazing cattle that consume the plant's nutritious pods and essentially reseed the land with their waste.

Protected Areas

Halfway between Winton and Birdsville is Diamantina National Park. It was established in 1993 and received a 2007 award from the World Wildlife Fund for its work as a nature reserve over the course of the decade, particularly in protecting the bilby, a nocturnal omnivore endemic to Australia and a threatened species. It is related to the lesser bilby (Macrotis leucura), which did become extinct in the 1950s.

Bilbies are about the size of rabbits, 1 to 2 feet (0.3 to 0.6 meters) long, and live in extensive burrows and tunnels. Though they do not need to drink water, they do well in riverside areas where the food sources that provide their necessary moisture thrive, including spiders, fruit, fungi, small birds and mammals, and larvae. They compete with rabbits for many of their staple food sources—and they are preyed upon by the feral cats of the region.

Diamantina National Park supports large bird populations of such species as the plains-wanderer, straw-necked ibis, white-necked heron, Bourke's parrot, black honeyeater, gibberbird, Hall's babbler, chestnut-breasted quail thrush, spinifexbird, and the critically endangered night parrot.

Climate Change

Climate change is expected to significantly alter Australia's rivers, including the Diamantina. During the period of time from 2020 to 2070, reduced stream flow due to global warming is expected to change the physical structure of the country's rivers, reducing the amount of water and nutrients and increasing the amount of sediment. This will determine how the rivers may be used. Rises in temperature couold also increase evaporation rates, causing changes to the waterholes many animals of the area depend on. Reduced water is also expected to expand Australia's deserts.

Bibliography

Bull, L. J., and M. J. Kirby, editors. Dryland Rivers: Hydrology and Geomorphology of Semi-Arid Channels. Wiley, 2002.

Kingsford, Richard. Ecology of Desert Rivers. Cambridge University Press, 2006.

Larkin, Zacchary, et al. "Australia's Inland Rivers Are the Pulse of the Outback. By 2070, They'll Be Unrecognisable." The Conversation, 20 Apr. 2020, theconversation.com/australias-inland-rivers-are-the-pulse-of-the-outback-by-2070-theyll-be-unrecognisable-136492. Accessed 31 Oct. 2024.

Shanafield, Margaret, et al. "Australian Non-Perennial Rivers: Global Lessons and Research Opportunities." Journal of Hydrology, vol. 634, 2024, doi.org/10.1016/j.jhydrol.2024.130939. Accessed 31 Oct. 2024.

Walker, K. F., et al. "A Perspective on Dryland River Ecosystems." Regulated Rivers: Research and Management, vol. 11, no. 1, 1995, pp. 85-104.