Aroona Creek, downstream from Aroona Dam
2012 Aquatic Ecosystem Condition Report
- Permanent stream comprising isolated pools in autumn and spring 2012
- Diverse macroinvertebrate community with two sensitive but ubiquitous species collected
- Water was moderately fresh to saline, clear and only moderately enriched with nutrients
- Riparian vegetation consisted of native trees and shrubs over a largely native understorey
About the location
Aroona Creek rises as Windy and Emu creeks in the Northern Flinders Ranges and they flow westwards and eventually merge to form Aroona Creek, which ultimately flows into Aroona Dam near Leigh Creek South. The major land use in the 69,244 hectare catchment, upstream from the site sampled, is grazing natural vegetation (96%), with minor areas used for managed resource protection, nature conservation, mining and residential living. The monitoring site was located off a track from Aroona Dam Road, about 4 km west from Leigh Creek South.
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 caused by nutrient enrichment but the stream still provided habitat for a wide range of aquatic macroinvertebrates and plants.
A diverse community of at least 32 species of macroinvertebrates was collected from the creek, 8-8.8 m wide and up to 68 cm deep, in autumn and spring 2012. The creek consisted of quite deep, isolated pools in both seasons sampled. The community was dominated by large numbers of baetid mayflies (Cloeon) and chironomids (Procladius, Larsia, Cricotopus, Cladotanytarsus, Tanytarsus, Chironomus, Dicrotendipes and Polypedilum) but included smaller numbers of flatworms, yabbies (Cherax destructor), beetles (Allodessus, Sternopriscus, Necterosoma penicillatus and Necterosoma dispar, Platynectes, Eretes, Macrogyrus and hydrophilid larvae), craneflies, mosquitoes (Anopheles), biting midges (Bezzia), caenid mayflies (Tasmanocoenis), waterbugs (Microvelia, Agraptocorixa, Micronecta and Anisops), odonates (Diplacodes and Hemicordulia) and caddisflies (Hellyethira simplex, Ecnomus cygnitus and Triplectides australis). All were widely distributed species that are often found from non-flowing pool habitats in the region. The most significant result was the presence of the two sensitive but ubiquitous mayflies from the Flinders Ranges in both seasons sampled. The site also supported a wide range of beetles and chironomids, and included two uncommonly collected caddisflies from the region (H. simplex and E. cygnitus). Most species were mobile insect groups but a few flatworms from the Class Temnocephala and yabbies, their probable host, were also collected in spring. No fish were seen but a large tortoise was seen and numerous frogs were heard calling during the 2012 surveys.
The water was moderately fresh (salinity ranged from 1,231-1,457 mg/L), well oxygenated (73-109% saturation), clear, and with generally only moderate to high concentrations of nutrients such as phosphorus (0.03 mg/L) and nitrogen (0.25-0.69 mg/L).
The sediments were dominated by boulder, cobble, pebble and algae, with smaller amounts of bedrock, gravel, sand, silt and detritus also present; samples taken from below the surface were well-aerated sands and rocks, and showed no evidence that the sediments were anaerobic, or lacking in oxygen. About 10 m of bank showed evidence of erosion caused by past flood damage but there was no signs of any additional erosion caused by feral animals accessing the stream at the site.
A small amount of phytoplankton was present during the year (chlorophyll a ranged from 0.5-1.6 Âµg/L) but filamentous algae (Cladophora and Spirogyra) extended over 10% of the site during both seasons sampled. A few types of aquatic plants also covered less than 10% of the reach, including sedges (Cyperus), rushes (Juncus) and cumbungi (Typha). The riparian vegetation was dominated by gums, acacias and paperbarks over patches of sedges and rushes on the poorly vegetated banks (25-49% vegetative cover). The surrounding vegetation at the site comprised low woodland dominated by gums, acacias, paperbarks and native pine over a largely native understorey.
Special environmental features
Aroona Creek supports a wide range of commonly found aquatic species but no rare or sensitive habitat specialists were recorded at the site in 2012. However, previous sampling of the same location during the mid 1990’s did record several flow-dependent species (e.g. blackflies Simulium ornatipes, biting midge Dasyhelea and caddisfly Cheumatopsyche), mites and a wider range of insect species when the stream was flowing in spring.
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 NaturalResources 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.|