Tributary of Oratunga Creek, Third Spring
2012 Aquatic Ecosystem Condition Report
- Permanent isolated pool habitats present in autumn and spring 2012
- Moderately diverse macroinvertebrate community with several rare, uncommon and sensitive species collected
- Water was mostly fresh, clear and enriched with nitrogen sourced from the inflow of groundwater to the spring
- Riparian vegetation consisted of native gums and shrubs over a native understorey
About the location
Third Spring is a small tributary of Oratunga Creek in the Northern Flinders Ranges that rises north from Breakneck Gorge and flows for about 4 km in a north-north-westerly direction before discharging into Oratunga Creek about 2 km upstream from Oratunga. The only land use in the 2,700 hectare catchment, upstream from the site sampled, is grazing natural vegetation. The monitoring site was located off Glass Gorge Road, about 12 km north-west from Blinman.
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 the presence of an aquatic weed but the stream still provided habitat for some rare and sensitive macroinvertebrate species.
A moderately diverse community of at least 22 species of macroinvertebrates was collected from the creek, 6-10 m wide and up to 60 cm deep, in autumn and spring 2012. The creek consisted of isolated pools in both seasons sampled, with more extensive and deeper habitats present in autumn compared to those present in spring. The community was dominated by moderate numbers of mites (Limnesia) and scirtid beetles in spring but no species collected in autumn was particularly abundant. The community included low numbers of mites from the Family Oxidae, beetles (Hyphydrus, Allodessus, Necterosoma dispar, Platynectes, Rhantus, Berosus discolour, Enochrus and Limnoxenus), mosquitoes (Anopheles), biting midges (Culicoides), soldierflies, chironomids (Procladius, Paramerina, Chironomus and Paratendipes), baetid mayflies (Cloeon), waterbugs (Microvelia), dragonflies (Hemianax) and caddisflies (Triplectides). A number of significant species were collected including the two mite families, which are rare in the region, the rich assemblage of beetles that included uncommon species such as B. discolour and Hyphydrus, and the presence of a widely distributed but sensitive mayfly genus. The only flow-dependent macroinvertebrates collected were adult Platynectes beetles, although the larvae are more typically associated with flowing water compared to the adults that can also occur in still-water habitats. The site was, however, probably more notable by the absence of many groups, including molluscs, crustaceans, worms, chironomids from the sub-family Orthocladiinae and caenid mayflies, and also by the limited number of waterbugs, odonates and caddisflies found in 2012. This may indicate that the spring may be too ephemeral or limited in extent to sustain a richer community of aquatic macroinvertebrates. The only other aquatic animals seen at the site were large numbers of tadpoles that were recorded during both seasons sampled.
The water was fresh to moderately fresh (salinity ranged from 907-1,053 mg/L), generally well oxygenated (58-88% saturation), clear but slightly coloured in spring, and with very low concentrations of phosphorus (0.01 mg/L) but high concentrations of nitrogen (2.1-2.2 mg/L); most of the latter occurred as oxidised nitrogen, which is typically associated with the inflow of groundwater seeps and springs to the surface waters of creeks in the Flinders Ranges.
The sediments were dominated by filamentous algae, detritus, pebble and gravel, with smaller amounts of bedrock, boulder, cobble, sand and silt also present. Samples taken from below the surface were grey gravels and pebbles and showed no signs that the sediments were anaerobic, or lacking in oxygen. No sign of any significant bank erosion was recorded and there was only a small amount of silt deposited on the bottom of the pools in the creek. The only animal faeces noted around the site were from kangaroos visiting the creek in spring.
Only a small amount of phytoplankton was recorded during the year (chlorophyll a 0.7-1.4 Âµg/L) and over 10% of the site was covered by filamentous algae (Spirogyra and Cladophora). Note that this amount of filamentous algae commonly occurs near up-welling zones in Flinders creeks in response to the high oxidised nitrogen levels but would not be expected to extend over a larger area without the addition of further inputs from stock, feral animals or other types of agricultural run-off. Over 35% of the spring was covered by aquatic plants, including native sedge (Cyperus) and introduced Watercress (Rorippa). The riparian vegetation was dominated by River Red Gums, acacias and paperbarks over sedges on the moderately well vegetated banks (50-79% vegetative cover). The surrounding vegetation at the site comprised low acacia scrub and grasslands.
Special environmental features
Third Spring lies on a permanent to semi-permanent tributary of Oratunga Creek and supported several rare and uncommonly collected macroinvertebrates from the region when it was sampled in 2012. A richer assemblage of species would be expected if small areas of flowing riffle habitat were to establish but this probably only occurs during extended wet periods.
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 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.|