Willochra Creek, Partacoona
2012 Aquatic Ecosystem Condition Report
- Permanent stream comprising a slow-flowing channel in autumn and isolated pools in spring 2012
- Sparse macroinvertebrate community with no rare or significant species collected
- Water was saline, clear and enriched with nutrients
- Riparian vegetation consisted of samphire and the channel was covered by moderate growths of filamentous algae and submerged aquatic plants
About the location
Willochra Creek is a large stream in the Southern Flinders Ranges that rises south and east from Melrose as Wild Dog Creek/Rotten Creek and Booleroo Creek, flows northwards across the Willochra Plain where it eventually turns west and discharges into the southern part of Lake Torrens during exceptionally wet years. The major land uses in the 458,000 hectare catchment, upstream from the site sampled, are grazing modified pastures and cropping. The monitoring site was located off the Simmonston to Quorn Road, about 1 km west from Simmonston.
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 and fine sediment deposition but the stream still provided habitat for some saline tolerant aquatic macroinvertebrates and plants.
A sparse community of at least 16 species of macroinvertebrates was collected from the creek, 7-16 m wide and up to 58 cm deep, in autumn and spring 2012. The creek consisted of a still to slow-flowing channel in autumn but contracted to isolated pools in spring. The community was dominated by moderate numbers of mites (Koenikea and Arrenurus), amphipod crustaceans (Austrochiltonia), dytiscid beetles (Necterosoma penicillatus) and chironomids (Procladius and Tanytarsus) and included smaller numbers of beetles (Rhantus, Eretes and Berosus australie), biting midges (Nilobezzia), pyralid caterpillars and odonates (Ischnura, Austrolestes, Hemianax, Diplacodes and Hemicordulia). All were saline tolerant species but no rare or sensitive habitat specialists were collected. A number of commonly found groups from the region were absent including flatworms, snails, yabbies, scirtid beetles, mayflies, waterbugs and caddisflies; high salinity, lack of flowing habitats and fish predation were probably responsible for the absence of many of these species from the lower reaches of Willochra Creek. Introduced mosquitofish (Gambusia) and a native fish called Lake Eyre Hardyhead (Craterocephalus eyresii) were collected during both surveys in 2012.
The water was saline (salinity ranged from 13,313-30,072 mg/L), well oxygenated (92-107% saturation), clear, and with generally high concentrations of nutrients such as phosphorus (0.02 mg/L in autumn and 0.17 mg/L in spring) and nitrogen (1.11-1.87 mg/L).
The sediments were dominated by detritus, sand, silt and cobble, with smaller amounts of boulder, algae, gravel, and clay also present; samples taken from below the surface were well-aerated grey sands and rocks in autumn when the stream was flowing slightly but in spring when the stream ceased flowing the sediments were blackened and sulphidic, indicating that they were anaerobic, or lacking in oxygen. Over 5 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 or sign of any animal faeces were recorded from the edges of the creek.
A large amount of phytoplankton was present in spring (chlorophyll a 24 Âµg/L) when a small amount of blue-green algae or cyanobacteria was also recorded (chlorophyll b 1.4 Âµg/L). A filamentous alga (Cladophora) was only recorded in autumn when it covered over 10% of the channel. A similar area was also covered by a few types of aquatic plants, including submerged (Ruppia and charophytes) and emergent species (Phragmites). The riparian vegetation was dominated by a low shrubland comprising samphire on the moderately well vegetated banks (50-79% vegetative cover). The surrounding vegetation at the site comprised saltbush country that was grazed by sheep.
Special environmental values
Willochra Creek is the largest stream system in the Southern Flinders Ranges that drains into Lake Torrens. Some of its tributary streams that rise in the Mount Remarkable National Park are intermittent freshwater creeks that support a few regionally rare and significant species. Further downstream on the Willochra Plain, the Willochra Creek consists of a salinised stream that only supports a saline tolerant range of plants and animals. The only significant species recorded from the site was the Lake Eyre Hardyhead, an endemic fish species found from the Lake Torrens and Lake Eyre Basin in South Australia.
Pressures and management responses
|Livestock in the catchment exerting excessive grazing pressure on vegetation, causing sediment erosion and adding excessive nutrients to the watercourse.||
The Northern and Yorke Regional NRM Plan has the following Resource Condition Targets:
Natural Resources (Northern and Yorke) has also been updating its understanding and management of the Willochra Catchment:
|Broad acre cropping in the catchment, adding excessive nutrients to the watercourse.|
|Highly saline soils in the catchment.||The EPA in collaboration with the Department for Environment, Water and Natural Resources is anticipating a study program to investigate the source(s) of high salinity in this region and its role in shaping aquatic ecosystems. This will assist in future condition assessments of highly saline waterways and clarify whether remediation efforts are warranted.|