Darling River ecosystem
The Darling River ecosystem, located in southwestern Australia, is a vital natural resource that supports both diverse wildlife and human settlements. Stretching over 1,700 miles (2,740 kilometers), it is the longest river system in Australia and plays a crucial role in the Murray-Darling Basin. This basin serves as a key water source for the state of New South Wales, but it faces significant threats from climate change, irrigation practices, and industrial development. The river's flow is characterized by high evaporation rates, particularly in its semi-arid environment, leading to challenges in maintaining water levels, especially during drought conditions.
Biodiversity within the Darling River region is notable, housing 35 endangered bird species, a variety of amphibians, reptiles, and several unique plant communities. However, environmental issues such as land degradation, water salinity, and invasive species threaten these ecosystems. Additionally, the over-extraction of water for agricultural purposes has been linked to reduced ecological health and has adversely affected the traditional lands of Indigenous communities. As climate change continues to impact rainfall patterns, the resilience of the Darling River ecosystem remains a pressing concern for conservation efforts and local communities alike.
Darling River ecosystem
- Category: Inland Aquatic Biomes.
- Geographic Location: Australia.
- Summary: The Darling River, key to natural and human life in southwestern Australia, is in jeopardy from development, irrigation extraction, changes in river flow, and global warming.
The Darling River system including its tributaries is the longest river system in Australia, at 1,700 miles (2,740 kilometers). As the northern half of the Murray-Darling River system, it is the major force watering the Australian state of New South Wales (NSW) and supporting both natural habitats and human settlements across the region. Not including the tributaries, the Darling is Australia's third-longest river. The Darling flows southwestward, with its tributaries rising in southern Queensland; it joins the Murray River at Wentworth, NSW. Downstream from the junction, the river is called the Murray as it flows into South Australia and on to the Indian Ocean.
Annual flow in the Darling is some 80 million cubic feet (2.3 million cubic meters). Much of the basin is less than 650 feet (200 meters) above sea level, making for extremely flat gradients. Rainfall in the watershed varies from 47 inches (1,200 millimeters) per year at the heights of the Great Dividing Range to less than 8 inches (200 millimeters) per year in the western reaches downstream.
The Darling River has a high level of evaporation in the largely semi-arid environment of the basin, varying from 39 inches (1,000 millimeters) per year in the eastern mountains to 79 inches (2,000 millimeters) per year in the west. Rainfall exceeds evaporation in a very small area of the catchment. With the flat gradients and high evaporation levels, several of the westward-flowing tributary rivers in the basin's center end in deltaic wetlands systems, which have environmental management significance. Because much of the Darling's course runs through extensive saltbush pastures, receiving an average of less than 10 inches (250 millimeters) of rain annually, the river often loses more water from evaporation than it gains from its tributaries—many of which from time to time fail to reach the main stream. Several of these flow into salt flats for years at a time, only to emerge as full-fledged rivers again in wet years, and rejoin the Darling as tributary streams.
Topography and Climate
The Darling riverine plains bioregion occupies most of the upper catchments of the Darling and its tributary the Barwon in northern NSW and southern Queensland. The upper-catchment landscape is a series of overlapping, low-gradient alluvial fans; the lower zone comprises more narrow floodplains confined between bedrock landscapes or by extensive sand plains and dune fields; channels cut through these areas to a considerable degree. Discharge from past and present streams control patterns of sediment deposition, soils, landscapes, and vegetation.
These Darling riverine plains lie in a semi-arid climatic zone: hot and persistently dry. This semi-arid zone also extends across most of the western arm of the Darling River biome, accompanied by small patches of either more arid or less hot semi-arid climates. Some subtropical climate crops up in the eastern, mountainous zone; subhumid areas are found in the southeast.
Thus, the Darling River biome features a range of microclimates: subtropical conditions in the far north; cool, humid eastern uplands; high alpine country in the Snowy Mountains; temperate conditions in the southeast; and hot and dry in the semi-arid and arid western plains that make up much of the basin as a whole.
Biodiversity
The Darling River and its tributary region is home to a large number of plants and animals, including 35 endangered species of birds and at least one dozen endangered mammal species. The basin also includes wetlands that are listed internationally for their importance to migratory birds that fly in from within the basin from other parts of Australia, and also from overseas.
Modern river channels in the bioregion support river red gum (Eucalyptus camaldulensis) and river cooba (Acacia stenophylla) forest communities. There are some areas of river paperbark (Melaleuca trichostachya), especially along the tributaries of the Barwon. These species grow on the channel margin in the annual flood zone. Coolabah (Eucalyptus microtheca) can be found on the northern rivers here.
The bioregion is home to at least 25 amphibian species, 104 reptile species, 319 bird species, and 58 mammal species. Records of amphibian species in the Darling Riverine Plains region include seven that are either endemic (found in no other biome on Earth) or largely restricted to this bioregion: long-thumbed frog (Limnodynastes fletcheri), giant banjo frog (Limnodynastes interioris), crucifix toad (Notaden bennettii), Crinia parinsignifera, C. sloanei,Neobatrachus sudelli, and Cyclorana verrucosa.
Reptiles here that are either endemic or largely restricted to the bioregion include: leaden delma (Delma plebia), Australian coral snake (Simoselaps australis), grey snake (Hemiaspis damelii), two-clawed worm-skink (Anomalopus leuckarti), Emydura macquarii, Ctenotus allotropis, C. brachyonyx, Egernia modesta, Pseudechis guttatus, and Anomalopus mackayi.
Waterbirds are a significant component of the Darling River fauna; a total of 35 such species in the bioregion are classified as endangered or vulnerable. Many waterbirds are known to breed here, including the freckled duck (Stictonetta naevosa). The plains along the river are a stronghold of such species as the spotted bowerbird (Chlamydera maculata), striped honeyeater (Plectorhyncha lanceolata), and plum-headed finch (Neochemia modesta).
Among the significant wetlands in the region, the Namoi River floodplain provides important habitat for the endangered bush stone curlew (Burhinus grallarius), even though its condition has been described as poor and still declining. Several vulnerable species—such as the koala (Phascolarctos cinereus), painted honeyeater (Grantiella picta), and brolga (Grus rubicundus)—have been sighted on this floodplain.
Environmental Threats
Land degradation, river-water salinity, land salinization from irrigation, water-quality problems, and loss of biodiversity are among the major environmental problems of the Darling River basin system. The prominent land-degradation problems include soil erosion, acidic soil, native-vegetation decline, and invasive weeds and noxious plants. The basin also faces the problem of biodiversity loss because of the changes in the pattern of the river flow by human actions, and due to the reduction in the volume of water flow.
Massive extractions of water for irrigation in the flatter reaches of the Darling River basin have degraded the ecological health of the river country, transforming relationships previously sustained by the seasonal flows of freshwater. An investigation in 2020 found that 20 percent of the water expected under the government's Murray-Darling Basin Plan has been stolen, most likely by farmers and agribusinesses. Some Aboriginal landowners are even experiencing the events caused by upstream overextraction of water as a contemporary dispossession of their country, so severe have some of the soil- and habitat-degradation problems become.
Climate change is expected to affect the Darling River biome with significantly reduced water availability in southern parts of the basin due to projected declines in both winter and spring rainfall, causing water scarcity to a region that is already suffering from overuse. Global warming has intensified droughts, causing the Darling River to frequently run dry. Stream flows in both snow-affected as well as snow-free stretches of the river are predicted to be altered toward potentially earlier and more intense spring events and likely drier summer and fall regimes.
Bibliography
"Climate and Climate Change." Murray-Darling Basin Authority, 17 Sept. 2024, www.mdba.gov.au/climate-and-river-health. Accessed 15 Nov. 2024.
Crawford, Jack. "How Capitalism Is Killing the Murray-Darling Basic." Red Flag, 19 July 2021, redflag.org.au/article/how-capitalism-killing-murray-darling-basin. Accessed 15 Nov. 2024.
Kearle, A., C. Gosper, H. Achurch, and T. Laity. Darling Riverine Plains Project Background Report. New South Wales National Parks and Wildlife Service, 2002.
Pittock, Jamie, et al. “A Review of the Risks to Shared Water Resources in the Murray–Darling Basin”, Australasian Journal of Water Resources, vol. 27, no. 1, 2023, pp. 1–17, doi.org/10.1080/13241583.2023.2190493. Accessed 15 Nov. 2024.
Quiggin, John. Environmental Economics and the Murray-Darling River System. Canberra: Australian National University, 2000.
Stern, H., G. de Hoedt, and J. Ernst. Objective Classification of Australian Climates. Melbourne: Australian Bureau of Meteorology, 2000.