Parachilna Creek, Mt Mary
2012 Aquatic Ecosystem Condition Report
- Permanent stream comprising pools and flowing water habitats in autumn and spring 2012
- Diverse macroinvertebrate community with rare, sensitive, flow-dependent, generalists and tolerant species present
- Water was fresh, clear, and low in nutrients but showing signs of enrichment by the extent of filamentous algae in both seasons sampled
- Riparian vegetation consisted of native trees and shrubs
About the location
Parachilna Creek rises as Blinman and Wockerawirra creeks around Mount Emily and they flow for about 20 km westwards where they merge, and then it flows through the ABC and Heysen ranges before eventually discharging into Commodore Swamp and the plains on the eastern side of Lake Torrens. The major land use in the 37,142 hectare catchment, upstream from the site sampled, is grazing natural vegetation (98%) with minor areas also used for residential living, transport and communications, and nature conservation. The monitoring site was located off the Parachilna to Oratunga Road, about 10.5 km south-west from Oratunga and 11 km east from Parachilna in the Northern Flinders Ranges.
The creek was given a Good rating because the site sampled showed evidence of relatively minor changes in ecosystem structure and function. There was evidence of human disturbance including nutrient enrichment, sheep accessing the banks and the presence of an aquatic weed but the stream supports one of the most diverse assemblages of aquatic macroinvertebrates and plants in the Flinders Ranges.
A diverse community of at least 47 species of macroinvertebrates was collected from the creek, 1.1-17.5 m wide and up to 25 cm deep, in autumn and spring 2012. The creek consisted of shallow pools connected by fast flowing riffles in both seasons sampled; the riffles were more extensive in spring compared to autumn. The community was dominated by baetid mayflies (Cloeon), chironomids (Procladius, Ablabesmyia, Paramerina, Larsia, Corynoneura, Cricotopus, Tanytarsus, Chironomus and Polypedilum), biting midges (Bezzia, Culicoides and Dasyhelea) and mosquitoes (Anopheles) in the pools and caddisflies (Cheumatopsyche) and blackflies (Simulium ornatipes) in the riffles. It also included smaller numbers of flatworms, worms, mites (Piona), melitid amphipods, beetles (Hyphydrus, Allodessus, Sternopriscus, Necterosoma, Platynectes, Eretes, Macrogyrus and Scirtidae), march-flies, soldierflies, chironomids (Rheotanytarsus and Cryptochironomus), caenid mayflies (Tasmanocoenis tillyardi), waterbugs (Microvelia, Agraptocorixa, Micronecta, Enithares and Anisops), odonates (Ischnura, Xanthagrion, Hemianax, Diplacodes and Orthetrum) and caddisflies (Hellyethira simplex, Hydroptila calcara, Hydroptila scamandra and Triplectides australis). The community included rare (Melitid amphipods and Pionid mite), flow sensitive (blackflies, Cheumatopsyche, Platynectes beetle and Rheotanytarsus midge) and widely found sensitive species (Cloeon and Tasmanocoenis tillyardi), as well as many generalist and tolerant insect groups. The shallow habitats at the site sampled would not favour snails, yabbies or fish, and probably contributed towards their absence in 2012. A number of tadpoles and small froglets (probably Crinia riparia) were the only other aquatic animals seen at the site.
The water was generally fresh (salinity ranged from 818-1,147 mg/L), well oxygenated (99-127% saturation), clear, and with low concentrations of nutrients such as phosphorus (0.01-0.02 mg/L) and nitrogen (0.24-0.35 mg/L).
The sediments were dominated by pebble, algae and gravel, with smaller amounts of boulder, cobble, sand, silt and detritus also present; samples taken from below the surface were well-aerated sands in autumn but they turned sulphidic in spring, indicating that the sediments lacked oxygen during the warmer months when microbial decay processes would be expected to be very active. No significant deposit of fine sediment was recorded during the year and only minor areas of flood damage were noted over less than 10 m of bank in spring. Deposits of sheep and kangaroo faeces were observed from the edges of the water and on the banks during the spring period, presumably when animals visited the creek to drink during the hotter months of the year.
A small amount of phytoplankton was present (chlorophyll a ranged from 0.5-1.1 Âµg/L) but filamentous algae (Cladophora and Spirogyra) was very extensive and covered over 35% of the site during the year. Another 10% of the channel was covered by aquatic plants, including submerged charophytes (Chara) and patches of several emergent species (Cyperus, Juncus, Typha and the introduced weed Watercress Rorippa). The riparian vegetation was dominated by River Red Gums and acacias over a largely native understorey on the poorly vegetated banks (25-49% vegetative cover). The surrounding vegetation at the site comprised a similar assemblage of River Red Gums and acacias.
Special environmental features
Parachilna Creek maintains permanently flowing habitats that sustain a diverse range of rare, sensitive, flow-dependent and pool generalists from the region. These conditions have ensured that the creek is one of the most biologically significant streams in the Flinders Ranges.
Pressures and management responses
|Feral goats, donkeys and rabbits are exerting excessive grazing pressure on vegetation, causing erosion and adding excessive nutrients to the watercourse.||The SA Arid Lands Natural Resources Management Board provides technical advice and incentives for the management of introduced weeds and feral pest animals, as funding permits. Pest management efforts are guided by a region-wide strategy, based on risk assessment, to determine priority locations and species. Funding is actively sought from a number of sources to support region-wide integrated management.|
|Livestock have direct access at the site and upstream in the catchment 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.|