Fifth Creek, near Black Hill
2012 Aquatic Ecosystem Condition Report
Ephemeral freshwater creek which was flowing in spring 2011 but dry in autumn 2012
Diverse macroinvertebrate community with many rare, sensitive and flow-dependent species when wet
Obvious signs of nutrient enrichment
Riparian vegetation consisted of mostly weeds with native scrubland beyond
About the location
Fifth Creek is a small stream in the Mount Lofty Ranges which rises near Montacute Heights and flows in a north-westerly direction before discharging into the Torrens River at Paradise. The major land uses in the 950 hectare catchment are native vegetation (41%) and conservation park (32%). The monitoring site was located just off Montacute Road, about 2 kilometres upstream from Athelstone, Adelaide.
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 and weedy riparian zones but the stream still provides habitat for several rare and sensitive species of macroinvertebrates.
A diverse community of at least 47 species of macroinvertebrates was collected from this flowing creek, 1.4 m wide and 15 cm deep in spring 2011. However, the site was dry in autumn 2012. The community was dominated by species tolerant to pollution such as worms, mites, snails from the family Hydrobiidae and a non-biting midge (Cricotopus). Other species were collected in smaller numbers and included a range of generalist and pollution tolerant species such as four species of snails, the isopod Heterias, springtails, a beetle (Platynectes), biting midges, mothfly larvae, dance fly larvae, bush fly larvae, non-biting midges, two types of waterbugs, two dragonflies and three caddisflies. Many sensitive and rare species were also found, including two species of the flow-dependent blackfly larvae (Austrosimulium and Simulium), a rare species of fly larvae (Austrothaumalea), two stoneflies (Dinotoperla and Austrocerca) and the caddisfly Taschorema. Two species of frog (Crinia signifera and Limnodynastes dumerilli) were heard calling and yabbies, unidentified larval fish and two introduced snails (Potamopyrgus and Physiella) were also seen in the creek.
The sediments were dominated by cobbles and detritus in the flowing sections, while silt and detritus dominated the pools. Samples taken from below the surface were grey in colour and that released sulfide when tested, indicating that the sediments were anaerobic and lacked oxygen. Minor silt deposits were noted in the pool habitat and more than 10 m of bank showed signs of erosion due to seasonal higher flows down the creek.
A moderate amount of phytoplankton (chlorophyll a 5.64 µg/L) was recorded in spring 2011 and over 35% of the channel was covered by filamentous algae (Cladophora) and more than 65% was covered by aquatic plants including the emergent plants Cyperus, Polygonum, Phragmites, Rorrippa and Rumex. Mint and arum lilies were also present at the site. The riparian zone comprised of mainly introduced grasses and weeds such as bamboo, sweet pea, blue periwinkle and ivy, with some Phragmites also present on the banks. The surrounding vegetation was native scrubland.
Special environmental values
Fifth Creek provides habitat for many species sensitive to pollution including some flow-dependent species, even though the creek was dry in autumn 2012.
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