Brownhill Creek, Brownhill Creek Recreation 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 and sensitive species
Emerging signs of nutrient enrichment
Riparian vegetation comprised of mainly introduced trees and understorey plants, with native vegetation beyond
About the location
Brownhill Creek is a stream in the Mount Lofty Ranges that rises near Crafers West and flows in a north-westerly direction through metropolitan Adelaide before discharging into the Patawalonga Lake. The major land uses in the 537 hectare catchment upstream of the site sampled were native vegetation (57%), urban residential (11%) and grazing pastures (10%). The monitoring site was located at the upper end of the Brownhill Creek Recreation Park, about 3 kilometres upstream from Mitcham.
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 provides habitat for several rare and sensitive species of macroinvertebrates.
A diverse community of at least 75 species of macroinvertebrates was collected from this flowing creek, approximately 3.5 m wide and up to 54 cm deep in spring 2011 and autumn 2012. The creek consisted of slow-flowing pools with fast-flowing riffle sections between the pools, often occurring over willow roots. The community was dominated by snails (including the introduced Potamopyrgus) with low numbers of a range of sensitive, generalist and pollution tolerant species also present. Seven different types of mites were collected from this site and at least 19 different species of non-biting midges were present, including some rare species such as Stictocladius and Riethia. Other rare and sensitive species identified included three different species of blackfly (Austrosimulium, Simulium and Paracnephia), four stoneflies (Dinotoperla, Illiesoperla, Newmanoperla and Austrocerca), two mayflies (Atalophlebia and Thraulophlebia), the dragonfly Synthemis eustalacta, and four caddisflies (Taschorema, Ulmerochorema, Cheumatopsyche and Lingora). Yabbies and fish larvae were also seen in the creek. Some uncommon macroinvertebrate species were collected in previous years from a site on Brownhill Creek just downstream, including a riffle beetle (Simsonia), a non-biting midge (Botryocladius) and a caddisfly (Apsilochorema). The native fish Mountain Galaxias (Galaxias olidus), has also been found in this section of Brownhill Creek in the past.
The water was fresh (salinity of 455 mg/L), well oxygenated (94% saturation) and clear, with low to moderate concentrations of nutrients such as nitrogen (0.21-0.25 mg/L) and phosphorus (0.02-0.03 mg/L).
The sediments were dominated by detritus with some silt, sand and clay also present. Samples taken from below the surface were brown clays and silts and were sulphidic in spring. 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 0.78-1.67 µg/L) was recorded and small amounts of filamentous green algae (Cladophora) were noted at the site in spring 2011. More than 10% of the site was covered by a range of aquatic plants, including floating (Spirodella) and emergent species (Isolepis, Rorrippa and Rumex). The riparian zone comprised introduced trees (such as poplar, willow, fig and ash trees) with a weedy undergrowth, including sweet pea, blue periwinkle and introduced grasses. The surrounding vegetation at the site was native scrubland.
Special environmental values
The cool, flowing waters of Brownhill Creek provides important habitat for a diverse assemblage of non-biting midges and many rare and sensitive species including stoneflies, mayflies, caddisflies, one species of dragonfly and a threatened native fish species.
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