Brisbane River

• Category: Inland Aquatic Biomes.
• Geographic Location: Australia.
• Summary: Australia's Brisbane River features a variety of freshwater and estuarine habitats, which are threatened by habitat destruction and the impact of both upland and urban area dynamics.

The Brisbane River is the longest river in the northeastern Australian state of Queensland, flowing 214 miles (344 kilometers) from its source near Mount Stanley in the Great Dividing Range into Moreton Bay and the South Pacific Ocean. The lowest 50 miles (80 kilometers) form a flood-prone tidal stretch of the river. Draining a catchment of about 5,200 square miles (13,500 square kilometers), the Brisbane River ecosystem contains both freshwater and saltwater habitats. It flows through the port city of Brisbane, a fast-growing metropolitan area with the largest concentration of the catchment's one million inhabitants. Dredging and urban growth are the increasing environmental threats in downstream segments; upland concerns include clearing for agriculture, grazing, and logging. Both zones are impacted by the effects of climate change.

Vegetation Types

Overall, more than 85 percent of the Brisbane River watershed is cleared land. The farthest upland reaches of the Brisbane River watershed contain the least-disturbed native bush and forests. Alongside wild forest stands, replete with such hallmark varieties as blackbutt (Eucalyptus pilularis), forest red gum (Eucalyptus tereticornis), and tallowwood (Eucalyptus microcorys), are found such managed features as plantation forests of hoop pine (Araucaria Cunninghamii), a fine, straight-grained species cultivated for paneling and plywood use.

Middle reaches of the river system are more heavily impacted by agricultural land use. Two dams—Somerset and Wivenhoe—have also altered habitats in this area of the biome, with the trade-off being some improvement in flood control and mitigation. Farm runoff increases turbidity in tributaries and the mainstem, also challenging the nutrient balance of the river, augmenting the spread of certain bacteria and phytoplankton. Hoop pine plantation forests are still found here, but have given way to protected forest reserves in some quarters, such as the Benarkin State Forest.

In its estuarine stretch, the river winds through the heart of densely built-up Brisbane and into Moreton Bay. Here is found the Boondall Wetlands Reserve, of which a 2,500-acre (1,000-hectare) portion was recognized in 1993 as a Ramsar Wetland of International Importance. Mangroves, tea tree swamps (melaleuca wetland), salt marsh, grasslands, and open forest compose this transition area, supporting a full range of ecosystem services and a great diversity of fauna. Some characteristic plants here are the grey mangrove (Avicennia marina), swamp lily (Crinum pedunculatum), native jute (Corchorus cunninghamii), and angle-stemmed myrtle (Austromyrtus gonociada). The water hyacinth, historically introduced to the river from South America in the nineteenth century, has periodically grown out of control across the Brisbane River's surface.

Distinctive Fauna

In the mangroves and seagrass around Moreton Bay, the dugong (Dugong dugon) is a much watched-for marine grazer. Signature fish species found here and in the tidal zone of the Brisbane River include the Queensland lungfish (Neoceratodus forsteri), considered rare, and the aggressively predatory bull shark (Carcharhinus leucas), considered all too prevalent in terms of human interaction; swimming is discouraged in parts of the river where some fatalities have been ascribed to the bull in the past.

One of Australia's major populations of loggerhead turtle (Caretta caretta) is based in and around Moreton Bay. Its numbers are joined by the hawksbill (Eretmochelys imbricata) and green turtle (Chelonia mydas).

Notable extinct species of the river include the unique freshwater Brisbane River cod (genus Maccullochella), which suffered from overfishing and water quality degradation. A related sub-species of cod from the nearby Mary River (Maccullochella peelii mariensis) has been introduced in order to restock the Brisbane River. These fish are related to the largest freshwater fish in Australia, the Murray cod (Maccullochella peelii peelii).

The eel-tailed catfish (Tandanus tandanus) actually thrives in the turbid waters that deter many other species. It is also a broad feeder, consuming mollusks, shrimp, insects, and snails. The blue catfish (Arius graeffei) prefers more pristine environments; the empire gudgeon (Hypseleotris compressa) is often found in calm waters such as areas above dams.

A unique mammal in the mangrove area here is the grey-headed flying fox (Pteropus poliocephalus). Also known as fruit bats, they have thickly colonized the estuary zone of the Brisbane River. Osprey (Pandion haliaetus) nest here as well, and are commonly seen arcing over Moreton Bay, intent on their hunting missions, targeting fish that swim near the surface. Migratory wading birds such as the eastern curlew (Numenius madagascariensis) and grey-tailed tattler (Tringa brevipes) thrive here on stopover during their flights from Arctic or sub-Arctic breeding regions. The population here swells to about 50,000 during the nonbreeding season.

Human Impact

Water quality concerns in the city of Brisbane began to surface by the early twentieth century as human settlement increased both around the city and in communities much farther upstream. Quality concerns and pollution continue to be a cause of concern in the twenty-first century. Pollutants include pesticides, excess presence of hydrocarbons, bacteria, and nutrients. The river's high turbidity levels are also the result of human encroachment, the clearing of native vegetation, and the introduction of exotic species. The relationship between dredging the river for navigation and the growing turbidity of its waters led to the decision to halt dredging upstream of the city. Numerous land reclamation projects have also been instituted; the protection and replanting of native vegetation is an important component of water quality restoration initiatives because of the natural filtering role of many such species.

Global warming and climate change have caused extreme weather in Australia, such as catastrophic wildfires, flooding, and drought. In February 2022, torrential downpours caused the Brisbane River to flood. About 15,000 homes were damaged or destroyed. The "rain bomb" that occurred over several days was equal to 80 percent of Brisbane's annual rainfall. Experts noted that climate change has increased the risk of torrential downpours in Australia.

Bibliography

Davie, Peter, and Errol Stock, editors. The Brisbane River: A Source-Book for the Future. Australian Littoral Society and Queensland Museum, 1990.

Gregory, Helen. The Brisbane River Story: Meanders Through Time. Australian Marine Conservation Society, 1996.

Nock, Catherine J., et al. "Phylogenetics and Revised Taxonomy of the Australian Freshwater Cod Genus, Maccullochella(Percichthyidae)." Marine and Freshwater Research, vol. 61, no. 9, 2010, pp. 980-91.

Steele, John Gladstone. The Brisbane River. Rigby, 1975.

Zhuang, Yan. "'Rain Bomb' Hits Northeastern Australia, Killing at Least Nine." The New York Times, 27 Feb. 2022, www.nytimes.com/2022/02/27/world/australia/australia-flood-queensland.html. Accessed 28 Oct. 2024.