Murray River ecosystem

• Category: Inland Aquatic Biomes.
• Geographic Location: Australia.
• Summary: The Murray River supports many rich habitats in a variety of climate and elevation zones, but is under great stress from human activity.

The Murray River is the largest of three rivers in the Murray-Darling Basin, and among the longest in Australia, at 1,565 miles (2,520 kilometers). The climate and habitats along the Murray River change considerably, beginning as subtropical in the far north; changing to cool and humid in the eastern uplands, Snowy Mountains, and temperate southeast; and ending as semiarid to arid in the western plains. The Murray begins in the Australian Alps, drains the western side of the range, then meanders northwest over the inland plains as the border between Victoria and New South Wales, finally turning south for 310 miles (500 kilometers) to Lake Alexandrina and the ocean.

The Murray-Darling river system drains inland Victoria, New South Wales, and southern Queensland. The system as a whole extends 2,330 miles (3,750 kilometers). The prehistoric Lake Bungunia formerly was the terminus of the Murray River; at maximum, it stretched over 13,000 square miles (33,000 square kilometers). But the lake long ago drained, as the wet period of the Murray-Darling Basin ended a half-million years ago. Since then, the region has been mostly arid, and species long ago common to the Murray are now restricted to Queensland.

The Murray’s volume of water is minuscule compared to other rivers of its length in the world. On rare occasions, extreme drought has dried up the river entirely. The river system as of 2010 received 58 percent of its natural flow; the region is Australia’s breadbasket and the river is heavily drawn upon. Irrigation using the Murray’s waters began in the 1850s, with the first large pumping station built in 1887, allowing farming along the river to rapidly expand. In the 20th century, the river was the site of four reservoirs, as well as locks and weirs for a proposed but obsolete system for river traffic.

Biodiversity

Notable flora in the Murray River basin encompasses one of the world’s largest river red gum forests, a flood-fed, wetland-type ecosystem. One 70-mile (112-kilometer) segment of the river features the Barmah Forest, a Ramsar-recognized Wetland of International Importance, along one bank, and the Millewa Forest on the other. Forests of red gum appear both upland and right along the river fringe. These river red gum forests are a product of the Cadell Fault, which altered the route of the Murray 25,000 years ago.

These river red gum forest floodplains are vital because of their ability to support a broad range of threatened and vulnerable species of every type. Observers here have documented the Barmah-Millewah’s value to such species as the flowering slender darling pea, Mueller daisy, and Moira grass among flora; the trout cod, silver perch, southern bell frog, giant banjo frog, inland carpet python, broad-shelled turtle, and squirrel glider among terrestrial and aquatic fauna; and the intermediate egret, plumed egret, blue-billed duck, superb parrot, and white-bellied sea-eagle among avians.

The Murray River basin as a whole is home to identified endangered fauna including at least 35 bird species, 16 mammal species, and 35 native fish species. With some 30,000 wetlands, about 7 percent of the Murray River basin has been set aside in reserves particularly to support migratory birds.

Fish species that are relatively widespread here include the Murray cod, trout cod, golden perch, silver perch, Australian smelt, and the eel-tailed catfish. The Murray short-necked turtle and Murray River crayfish are among the species unique to the river, but it also has species that appear elsewhere in the southeast, including long-necked turtles, and varieties of shrimp, rat, and platypus.

Threats

River regulation since Europeans settled the area has adversely affected native fish and aquatic life, causing some species to decline until they become endangered or rare. The Murray’s natural flow changed, benefiting agriculture but disrupting ecosystems inside and outside the river. Agricultural runoff and pest species have also damaged the river, and increased salinity of both the water and the land, potentially making it unusable in the medium to long term. The last major flood of the Murray was in 1956; it left river towns under water for longer than six months. However, because of heavy rains and storms caused by climate change, the Murray River has flooded more often. It has flooded in 2016 and again in 2022 and 2023.

Weirs and dams negatively impact the river biome. They prevent migrations of fish and have in many cases displaced the river-adapted Murray crayfish with a floodplain species, the yabbie. Dams and weirs alter seasonal flood cycles, disrupting recruitment and spawning. Since 1950, the endemic Murray cod and river blackfish have declined as water control systems have proliferated. Human-built fishways along the Murray, in some cases, are poorly designed and tend to inhibit the seasonal movement of such species as golden perch, Australian bass, and barramundi.

Water removal from the Murray River takes up to 80 percent of the available flows, resulting in insufficient water for habitats at most segments, including its estuary and the floodplain forests. The Murray system includes several lakes whose salinity now varies, although until recently they were commonly fresh. This may be the result of human-created changes in the environment. Droughts in 2000–07 stressed the red gum forests, raising concern about their survival. Increased droughts in Australia, thought to be the result of climate change, are likely to continue to stress the red gum forests. Reduced rainfall and increased evaporation as a result of higher temperatures caused by climate change are also likely to place undue stress on the environment.

Bibliography

Crawford, Jack. "How Capitalism Is Killing the Murray-Darling River Basin." Redflag, 19 July 2021, redflag.org.au/article/how-capitalism-killing-murray-darling-basin. Accessed 18 Nov. 2024

Mallen-Cooper, Martin. Fishways and Freshwater Fish Migration on South-Eastern Australia. Sydney, Australia: University of Technology Sydney, 1996.

Pittock, Jamie. “Challenges of Freshwater Protected Areas.” World Wildlife Federation. www.panda.org/es/?17772/Challenges-of-freshwater-protected-areas#:~:text=Some%20rivers%20no%20longer%20reach,and%20afflicted%20by%20invasive%20species. Accessed 18 Nov. 2024.

Roberts, Nick, et al. 13 Thirsty Species. Victoria, Australia: Victorian National Parks Association and Environment Victoria, 2010.

Weir, Jessica K. Murray River Country: An Ecological Dialogue With Traditional Owners. Brisbane: Australian Institute of Aboriginal and Torres Studies Press, 2009.

Willis, Belinda. "Flooding Plains as River Murray Hits Six-Year Flow Peak." In Daily, 22 Aug. 2022, indaily.com.au/news/2022/08/22/flooding-plains-as-river-murray-hits-six-year-flow-peak/. Accessed 18 Nov. 2024.