Breakneck River, Kangaroo Island
2013 Aquatic Ecosystem Condition Report
- Permanent flowing stream in autumn and spring 2013
- Moderately diverse macroinvertebrate community with several rare, sensitive and flow-dependent species
- Water was fresh, clear and high in nitrogen
- Riparian vegetation comprised native vegetation with no weeds
About the location
Breakneck River is a moderately sized stream within Flinders Chase National Park, located on the western end of Kangaroo Island. The river rises at an elevation of about 285 m south from the Playford Highway, and flows in a south-westerly direction for nearly 30 km before discharging into the Southern Ocean north from Cape Bedout. The major land use in the 8,817 hectare catchment upstream from the site sampled was nature conservation (99%), with minor areas of wetland and roads also present. The site sampled was located off West Bay Road, about 11.5 km north-west from the Department for Environment, Water and Natural Resources office and Flinders Chase Visitor Centre.
The river was given a Very Good rating because the site sampled showed no evidence of any significant changes in ecosystem structure and function. There was evidence of human disturbance due to nitrogen enrichment and road runoff from the unsealed West Bay Road depositing fine sediment into the river; it is likely that the elevated nitrogen levels in the stream represents a legacy effect from a bushfire that burnt most of the upstream catchment in 2008.
A moderately diverse community of at least 22 species of macroinvertebrates was collected or seen from the river (8 species in autumn and 19 species in spring), 1.5-4.4 m wide and up to 49 cm deep, in autumn and spring 2013. The river consisted of still to slow-flowing pools connected by faster-flowing, shallower riffle habitats in both seasons sampled; riffle extent at the site ranged from 10% in autumn to 50% of the river in spring. The community was dominated by moderate numbers of blackflies in the riffle habitats and chironomids in the edges, and included smaller numbers of worms, mites, yabbies, amphipods, beetles, craneflies, mosquitoes, biting midges, mayflies, stoneflies and caddisflies. A number of rare, sensitive and/or flow dependent species were recorded including a mite (Procorticacarus), blackflies (Austrosimulium furiosum and Simulium melatum), chironomid (Rheotanytarsus), mayflies (Atalophlebia australasica and Thraulophlebia inconspicua), stoneflies (Illiesoperla mayii and Newmanoperla thoreyi), and caddisflies (Taschorema evansi and Oxyethira columba). The only fish seen at the site were several native galaxiids in autumn (probably Common Galaxias).
The water was fresh (salinity ranged from 270-303 mg/L), well oxygenated (76-91% saturation), alkaline in autumn and slightly acidic in spring (pH ranged from 6.48-7.05), clear and slightly coloured, and with low concentrations of phosphorus (0.01-0.02 mg/L) but high nitrogen concentrations (0.55-0.67 mg/L).
The sediments were dominated by detritus, sand and clay, with smaller amounts of gravel and silt also present. Samples taken from below the surface were grey and black sands and showed no evidence that the sediments were anaerobic or lacking in oxygen. There was no evidence of any erosion at the site and the only animal droppings seen in the vicinity of the river were from kangaroos.
There were no significant growths of phytoplankton or filamentous algae detected in 2014. Less than 10% of the river was covered by a few aquatic plants, including rushes (Juncus), Water Ribbons (Triglochin procerum) and a sedge (Isolepis). The riparian zone was dominated by gum trees over tea-tree and native understorey, and the surrounding vegetation near the river comprised dense eucalypt woodland within the Flinders Chase National Park.
Special environmental features
Breakneck River provides a permanently flowing, freshwater habitat with a catchment fully contained within a national park. It supports a significant community of rare, sensitive, flow-dependent and generalist aquatic macroinvertebrates and provides conditions that allow a few species of native aquatic plants to grow and at least one native fish species to inhabit. The natural features of this river make it one of the few ‘wild rivers’ on the island and within the wetter part of South Australia.
Pressures and management responses
|Runoff from unsealed roads during high rainfall periods leading to fine sediments discharging into the creek (increasing turbidity and smothering habitat)||This information is not available at the moment but it will be updated as soon as possible.|