Tributary of Sixth Creek, near Montacute Conservation Park
2012 Aquatic Ecosystem Condition Report
Permanently wet freshwater creek which was flowing in spring 2011 and autumn 2012
Diverse macroinvertebrate community with many rare, sensitive and flow-dependent species
Emerging signs of nutrient enrichment
Riparian vegetation consists of mostly introduced species with native vegetation beyond
About the location
Tributary of Sixth Creek is a small stream in the Mount Lofty Ranges that rises near Stringybark and flows in a westerly direction to Sixth Creek and then discharges into the Torrens River, near Castambul. The major land uses in the 713 hectare catchment are native vegetation (55%) and grazing pastures (28%). The monitoring site was located immediately downstream of Montacute Conservation Park on Valley Road, about 2 kilometres from Castambul.
The creek was given a Very Good rating because the site sampled showed evidence of only minor changes in ecosystem structure and function, with many rare and sensitive macroinvertebrate species present. There were emerging signs of human disturbance including nutrient enrichment and the presence of weeds in the riparian zones but the stream provided an important refuge for many macroinvertebrate species in the region.
A highly diverse community of at least 77 species of macroinvertebrates was collected from this flowing creek, approximately 2 m wide and 44 cm deep, in spring 2011 and autumn 2012. The creek consisted of slow-flowing pools with fast-flowing riffle sections between the pools in spring 2011 but only had slower flowing water in autumn 2012. The site was dominated by Hydrobiidae snails and blackfly larvae (Simulium sp.). Other species collected in smaller numbers included a range of generalist and pollution tolerant species, such as worms, snails, beetles, nine different families of fly larvae including a diverse range of non-biting midges, mayflies, waterbugs, stoneflies, dragonflies and caddisflies. Some sensitive and rare species, as well as flow-dependent species, were also collected, including the riffle beetle Simsonia leai, three different types of blackfly larvae (Austrosimulium, Simulium and Paracnephia), a fly larva (Austrothaumalea), mayflies (Offadens, Atalophlebia and Thraulophlebia), stoneflies (Dinotoperla, Illiesoperla and Austrocerca), the dragonfly Austrogomphus and the caddisflies Taschorema, and Lingora. Introduced fauna such as trout and the snails Potamopyrgus and Physiella were seen in the creek. The frog Crinia signifera was heard calling and yabbies were also seen in the creek.
The water was fresh (salinity ranged from 401-607 mg/L), well oxygenated (46-77% saturation) and clear, with low concentrations of nutrients such as nitrogen (0.14-0.16 mg/L) and phosphorus (0.009-0.02 mg/L).
The sediments were dominated by cobbles and pebbles with some detritus also present. Samples taken from below the surface were sandy grey with clay and some silt present and showed no evidence of being anaerobic, or lacking oxygen. Only small deposits of silt covered the streambed to a depth of about 1 cm in places and no significant areas of bank erosion were seen.
A small amount of phytoplankton (chlorophyll a ranged from 0.34-0.44 µg/L) and small amounts of filamentous algae (<10%) were recorded from the site. More than 10% of site was covered by a range of aquatic plants, including the submerged plant Chara, and several emergent plants (Cyperus, Isolepis, Juncus articulatus, Polygonum, Rorrippa, Triglochin and Typha). The riparian zone consisted of a few exotic trees with an understorey of native bracken and weeds such as fennel, mint and blue periwinkle. The surrounding vegetation was native scrubland with eucalypts, bracken and native cherry trees present.
Special environmental values
The Tributary of Sixth Creek provides important habitat for many species sensitive to pollution and dependent on the near permanent flows that occur in this creek.
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