Willochra Creek, downstream from junction with Castle Springs
2012 Aquatic Ecosystem Condition Report
- Permanent stream comprising pools and riffles in autumn and a non-flowing channel in spring 2012
- Sparse macroinvertebrate community with one rarely collected beetle recorded
- Water was saline, clear and enriched with nutrients
- Riparian vegetation consisted of samphire and the creek was covered by large amounts of filamentous algae
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 425,154 hectare catchment, upstream from the site sampled, are grazing modified pastures and cropping, with minor areas used for grazing natural vegetation and nature conservation. The monitoring site was located off a track to Castle Springs from the Quorn to Hawker Road, about 8 km south-south-west from Simmonston and 9 km north-north-west from Willochra.
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 the presence of pest fish but the stream still provided habitat for some saline tolerant macroinvertebrates and plants.
A sparse community of at least 11 species of macroinvertebrates was collected from the creek, 12.5-17.2 m wide and up to 24 cm deep, in autumn and spring 2012. The creek consisted of still to slow-flowing pools connected by small areas of flowing riffle habitats in autumn but contracted to a non-flowing channel in spring. The community was dominated by moderate numbers of dytiscid beetle larvae (Necterosoma) in autumn and amphipod crustaceans (Austrochiltonia) in spring. It also included a mite (Arrenurus), beetles (Necterosoma penicillatus, Necterosoma regulare and Enochrus), biting midges (Nilobezzia), soldierflies, chironomids (Procladius and Tanytarsus barbitarsus), pyralid caterpillars and dragonflies (Austrolestes). All were saline tolerant species but no rare or sensitive habitat specialists were collected apart from a rarely collected dytiscid beetle (Necterosoma regulare). The site did not support any of the commonly occurring flow-dependent species found in the region, despite the presence of riffles in autumn. A number of common Flinders Ranges groups were absent from the site including flatworms, snails, yabbies, scirtid beetles, mayflies, waterbugs and caddisflies; high salinity, lack of persistent and extensive areas 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 native hardyhead fish (Craterocephalus eyresii) were seen and collected during both surveys in 2012.
The water was saline (salinity ranged from 22,275-30,515 mg/L), well oxygenated (120-126% saturation), clear, and with generally high concentrations of nutrients such as phosphorus (0.04-0.08 mg/L) and nitrogen (1.21-4.94 mg/L).
The sediments were dominated by detritus with smaller amounts of cobble, pebble, boulder, algae, gravel, sand, silt 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. A light cover of silt covered the streambed, 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, apart from kangaroo droppings, were recorded from the edges of the creek.
A moderate amount of phytoplankton was present (chlorophyll a ranged from 2.7-6 Âµg/L) and filamentous algae (Cladophora and Spirogyra) covered over 35% of the creek during the year. About 10% of the channel was also covered by two types of submerged aquatic plants (Ruppia and charophytes). The riparian vegetation was dominated by a low shrubland comprising samphire, saltbush and a few scattered gum trees 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 few species of saline tolerant 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 and feral animals have direct access at the site and upstream, exerting excessive grazing pressure, 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:
|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.|