Tributary of Oratunga Creek, Snob's Hut Spring
2012 Aquatic Ecosystem Condition Report
- Discontinuous flowing spring habitats present in autumn but only a small trickling pool remaining in spring 2012
- Moderately diverse macroinvertebrate community with regionally significant, rare, sensitive and flow-dependent species present
- Water was fresh, clear and high in nitrogen sourced from groundwater baseflow to the spring
- Riparian vegetation consisted of native shrubs and trees over sedges
About the location
The Tributary of Oratunga Creek where Snob’s Hut Spring is located, rises south from Mount Samuel in the Northern Flinders Ranges and flows in an easterly direction for about 5 km before discharging into Oratunga Creek, about 3 km downstream from Oratunga. This stream eventually discharges into Parachilna Creek during exceptionally wet years. The only land use in the 3,000 hectare catchment, upstream from the site sampled, is grazing natural vegetation. The monitoring site was located off the Parachilna to Oratunga Road, about 12.5 km north-west from Blinman
The creek was given a Very Good rating because the site sampled showed evidence of very little changes in ecosystem structure and function, with many rare and sensitive macroinvertebrate species present. There was evidence of minor human disturbance due to nutrient enrichment but the stream provided habitat for a near natural range of the expected aquatic macroinvertebrates and plants from the region.
A moderately diverse community of at least 26 species of macroinvertebrates was collected from the creek that comprised a discontinuous but flowing spring, 0.5-1 m wide and up to 5 cm deep, in autumn; a small pool was present among bedrock in spring 2012 but it was too small to sample for aquatic life. The community was dominated by blackflies (Simulium ornatipes) and scirtid beetles from the extensive areas of fast-flowing riffles present in autumn but the pools were not dominated by any species. A wide range of species were collected in small numbers, including mites (Limnesiidae and Hygrobatidae), melitid amphipods, beetles (Allodessus, Platynectes andHydraena), craneflies, biting midges (Bezzia and Nilobezzia), soldierflies, chironomids (Ablabesmyia, Corynoneura, Cricotopus, Paratanytarsus, Chironomus and Polypedilum), waterbugs (Microvelia), baetid mayflies (Cloeon), dragonflies (Hemicordulia) and caddisflies (Hellyethira simplex, Hydroptila scamandra, Cheumatopsyche, Lectrides varians and Triplectides australis). The regionally endemic blind amphipod from the Family Melitidae was present from the flowing habitat at the site, and the site was also notable due to the presence of two rarely collected mites, a sensitive but widely distributed mayfly and several flow-dependent species (e.g. blackflies, dytiscid beetle Platynectes larvae and caddisfly Cheumatopsyche). Most species collected were, however, insect groups capable of aerial dispersal and the mites and amphipods are probably able to shelter in wet sub-surface sediments if the spring dries. A number of unidentified frogs and tadpoles were also recorded from the site, indicating that the reach either remains permanently wet in places or only dries for brief periods of the year.
The water was fresh (salinity ranged from 566-663 mg/L), generally well oxygenated except when the stream was drying (30-90% saturation), clear to slightly coloured, and with low to moderate concentrations of phosphorus (0.008-0.03 mg/L) and high concentrations of nitrogen (1-2.38 mg/L); the latter was due to the large inflow of oxidised nitrogen from the groundwater baseflow to the spring (e.g. NOx ranged from 0.71-2 mg/L).
The sediments were dominated by gravel and sand, with smaller amounts of boulder, cobble, pebble, filamentous algae, bedrock and silt also present; samples taken from below the surface were grey silts and sands and showed no indications that the sediments were anaerobic, or lacking in oxygen. No evidence of any significant erosion was seen and the only sign of any animal visitation to the site was the presence of kangaroo and emu faeces in the channel and on the banks of the stream.
Only a small amount of phytoplankton was present in autumn (chlorophyll a 1.6 Âµg/L) when a filamentous alga (Cladophora) covered over 10% of the site. The presence of small growths of filamentous algae around groundwater upwelling sites is well known in the region but should not extend across in-stream pools unless additional nutrient inputs are occurring to the stream from its’ catchment. About 10% of the site was also covered by an aquatic plant (sedge Cyperus gymnocaulos). The riparian vegetation was dominated by White Cypress Pine and wild rosemary over sedges and grasses on the well vegetated banks (>80% vegetative cover).
Special environmental features
Oratunga Creek is an ephemeral stream in a lightly grazed catchment that had regionally significant, rare and sensitive species present at the Snob’s Hut Spring tributary in 2012, along with several flow-dependent species and a wide range of caddisflies and other insects.
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 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.|