Brachina Creek, Brachina Gorge
2012 Aquatic Ecosystem Condition Report
- Permanent stream comprising pools and flowing water habitats in autumn and spring 2012
- Diverse macroinvertebrate community with two sensitive but commonly occurring mayflies, a rare beetle from the region and several flow-dependent species
- Water was moderately fresh, clear, and low in nutrients but showing signs of enrichment due to the extent of algal and plant growths recorded in spring
- Riparian vegetation consisted of native trees and shrubs
About the location
Brachina Creek rises off the western side of Trezona Range in the Northern Flinders Ranges and flows south-west and then west, where it passes through Brachina Gorge and discharges onto the plains surrounding the eastern side of Lake Torrens. The major land use in the 20,513 hectare catchment, upstream from the site sampled, is nature conservation (99%), with minor areas also used for grazing natural vegetation and transport and communications. The monitoring site was located downstream from ‘Lubra Waters’ on Brachina Gorge Road, about 22 km north from Wilpena.
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 possible human disturbance due to some nutrient enrichment effects but the stream provides habitat for several rare, sensitive and flow-dependent species of macroinvertebrates.
A diverse community of at least 37 species of macroinvertebrates was collected from the creek, 3.3-4.5 m wide and up to 11 cm deep, in autumn and spring 2012. The creek consisted of shallow pools connected by large areas of fast-flowing riffles in autumn but it had contracted to less extensive pools connected by small riffles in spring. The community was dominated by caenid mayflies (Tasmanocoenis tillyardi), chironomids (Procladius, Paramerina, Corynoneura, Cricotopus, Chironomus and Polypedilum), mites (Koenikea) and mosquitoes (Aedes) in the pools and blackflies (Simulium ornatipes) and caddisflies (Cheumatopsyche) in the riffles. It also included smaller numbers of flatworms, beetles (Hyphydrus, Allodessus, Sternopriscus, Megaporus, Platynectes , Hydraena and Necterosoma regulare,), mosquitoes (Anopheles), biting midges (Nilobezzia), soldierflies, baetid mayflies (probably Cloeon), waterbugs (Hydrometra, Microvelia species, Agraptocorixa, Micronecta and Anisops), dragonflies (Hemianax, Orthetrum and Hemicordulia) and caddisflies (Hellyethira simplex, Hydroptila calcara, Oecetis and Triplectides australis). The community included a rarely collected beetle (Necterosoma regulare), both of the sensitive but ubiquitous mayflies from the region, a rich range of beetles, waterbugs, caddisflies and chironomids, and several flow-dependent species (e.g. Simulium, Cheumatopsyche and Platynectes). The shallow habitats at the site sampled would not favour snails, yabbies or fish, and probably contributed towards their absence during 2012.
The water was moderately fresh (salinity ranged from 1,021-1,529 mg/L), well oxygenated (73-146% saturation), clear, and with generally only low concentrations of nutrients such as phosphorus (0.03-0.04 mg/L) and nitrogen (0.18-0.28 mg/L).
The sediments were dominated by pebble, cobble, algae and gravel, with smaller amounts of bedrock, boulder, sand, silt and detritus also present; samples taken from below the surface were well-aerated grey gravels and pebbles in autumn but they changed later in the year when the sediments became dominated by anaerobic, sulphidic black silts, indicating that they lacked oxygen when flows reduced in spring. Over 10 m of bank showed evidence of erosion caused by past flood damage during the autumn survey but no significant areas of erosion were noted in spring.
A small amount of phytoplankton was present during the year (chlorophyll a ranged from 0.5-2.3 Âµg/L) but filamentous algae (Cladophora and Spirogyra) extended over 35% of the site during the spring survey. A similar area was also covered by a submerged aquatic plant (Chara), indicating that both plants and algae were significant nutrient sinks for the creek. The riparian vegetation was dominated by gums and acacias on the moderately well vegetated banks (50-79% vegetative cover). The surrounding vegetation at the site comprised low woodland dominated by White Cypress Pines and acacias.
Special environmental features
Brachina Creek lies within the Flinders Ranges National Parks and supports a diverse range of aquatic species from the region, including several flow-dependent species and some commonly occurring mayflies and caddisflies. It was one of the few sites sampled in 2012 that provided sufficient habitat diversity to sustain flow-dependent species throughout the year. Combined with previous sampling of the site dating back to the mid 1990’s when a similar assemblage of species was recorded, Brachina Creek provides an important refuge for aquatic life 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.|