Hookina Creek, Mayo Gorge Waterhole
2012 Aquatic Ecosystem Condition Report
- Permanent stream comprising isolated pools in autumn and spring 2012
- Sparse macroinvertebrate community with no rare or significant species other than a commonly occurring mayfly
- Water was moderately fresh to saline, clear and enriched with nutrients
- Riparian vegetation consisted of native shrubs over weeds and rushes
About the location
Hookina Creek rises north from Cradock in the Southern Flinders Ranges as tributaries of Wonoka Creek, which flow northwards where they merge with Mernmerna Creek south from the Elder Range to form Hookina Creek, which heads north-west where it eventually discharges onto the plains surrounding the eastern side of Lake Torrens. The major land uses in the 129,541 hectare catchment, upstream from the site sampled, are grazing natural vegetation (54%) and grazing modified pastures (31%); only 2% of the catchment is used for nature conservation. The monitoring site was located off a track to Mount Little from the Hawker-Parachilna Road, about 20 km north-north-east from Hawker.
The creek was given a Fair rating because the site sampled showed evidence of moderate changes in ecosystem structure, and some changes to the way the ecosystem functions. There was evidence of human disturbance including nutrient enrichment, fine sediment deposition and weeds dominating the understorey vegetation on the banks but the stream still provided habitat for a range of commonly occurring macroinvertebrates and three types of aquatic plants.
A sparse community of at least 17 species of macroinvertebrates was collected from the creek, 15-20 m wide and up to 20 cm deep, in autumn and spring 2012. The creek consisted of shallow, isolated pools in both seasons sampled. The community was dominated by large numbers of waterbugs (Micronecta and Anisops) but included smaller numbers of beetles (Necterosoma and Ochthebius), craneflies, biting midges (Nilobezzia), march-flies, chironomids (Procladius, Corynoneura, Chironomus, Polypedilum and Cryptochironomus), mayflies (Cloeon), waterbugs (Agraptocorixa), odonates (Ischnura and Hemianax) and caddisflies (Triplectides australis). All were mobile, aerial dispersing insect groups that are commonly found from non-flowing pool habitats in the region. The mayfly was the only sensitive species collected, although it has a widespread distribution from the more permanent freshwater streams in the Flinders Ranges and Far North of the State. No rare or habitat specialist species were collected. A few yabby holes were also seen on the edges of the stream, indicating that this burrowing species also inhabits the creek. No fish were seen at the site during 2012.
The water was moderately fresh to saline (salinity ranged from 2,314 mg/L in autumn to 4,527 mg/L in spring), well oxygenated (100-141% saturation), clear, and with generally moderate to high concentrations of nutrients such as phosphorus (0.01-0.08 mg/L) and nitrogen (0.31-0.79 mg/L).
The sediments were dominated by clay, detritus and silt, with smaller amounts of cobble and sand also present; samples taken from below the surface were sulphidic grey and black silts, indicating that the sediments were anaerobic, or lacking in oxygen. Over 10 cm of silt covered the streambed in spring, which would have contributed to the poor condition of the underlying sediments. No evidence of any significant bank erosion was recorded but kangaroo and sheep faeces were recorded from the edges of the creek in spring.
A large amount of phytoplankton was present in spring (chlorophyll a 17 Âµg/L) when a very small amount of blue-green algae or cyanobacteria was also recorded (chlorophyll b 0.78 Âµg/L). No sign of any filamentous algae was noted during either survey in 2012. Over 10% of the channel was covered by emergent plants, including sedges (Cyperus), rushes (Juncus) and cumbungi (Typha). The riparian vegetation was dominated by patches of gums and acacias over weeds (e.g. Castor Oil Plants) and rushes on the poorly vegetated banks (25-49% vegetative cover). The surrounding vegetation at the site comprised sheoaks and saltbush.
Special environmental features
Hookina Creek is part of a large stream system in the Southern Flinders Ranges that drains onto the plains surrounding Lake Torrens. In the past, the stream supported a wider range of species when pools were connected by flowing riffle habitats. A range of common, flow-dependent species were recorded from riffles in 1994-95 (e.g. biting midge Dasyhelea, blackfly Simulium ornatipes and caddisfly Cheumatopsyche), indicating that these insect groups can colonise the site when flowing habitats are present. A range of snails and flatworms were also collected from the slower-flowing channel and pools during the same period. However, it is clear that only a generalist assemblage of aquatic species inhabit this creek when it dries to isolated pools.
Pressures and management responses
|Livestock and feral animals in the catchment are exerting excessive grazing pressure on vegetation, causing sediment erosion and adding excessive nutrients to the watercourse.||The SA Arid Lands Natural Resources Management Board recognizes that both direct and diffuse impacts on aquatic ecosystem condition can occur through direct stock access and excessive grazing pressure from stock and feral herbivores. Technical advice and incentives are offered to land managers in the region, as funding permits, to address these impacts through appropriate activities suitable for the context. In addition, projects are underway across the region to identify, prioritise and address impacts at key aquatic sites.|