Brownhill Creek is made up of a network of three small streams flowing through steeply-sided, well-vegetated valleys in the foothills of the southern Mount Lofty Ranges at Mitcham. The dominant land uses in the catchment upstream from the site sampled included native vegetation (57%), urban and rural residential areas (18%) and grazing (10%). The monitoring site was located on the main channel off Brownhill Creek Road near the junction with Tilley’s Hill Road.
The creek was given a Good rating because the site sampled showed evidence of relatively minor changes in ecosystem structure and function. There was minor evidence of human disturbance due to the presence of filamentous algae and a degraded riparian zone but the stream provides habitat for a large number of rare, sensitive and flow-dependent species of macroinvertebrates.
Findings
A diverse community of at least 45 species of macroinvertebrates was collected from the creek (31 species in autumn and 30 in spring), 1.3-2.3 m wide and up to 65 cm deep, in autumn and spring 2016. The creek consisted of mostly fast-flowing riffles (80-90%) connecting slow-flowing to still pools (10-20%). The community was dominated by amphipods (autumn only) and moderate numbers of hydrobiid snails blackflies and chironomids. Other macroinvertebrates recorded in low to moderate numbers included worms, isopods, shrimp, yabbies, beetles, biting midges, danceflies, stoneflies, mayflies (3 families), dragonflies (3 families) and caddisflies (5 families). Numerous rare, sensitive and/or flow-dependent species were also collected, including blackflies (Austrosimulium furiosum, Simulium melatum and Simulium ornatipes), craneflies (Family Empididae), mayflies (Offadens sp. 5, Atalophlebia australasica and Thraulophlebia inconspicua), gomphid dragonfly (Hemigomphus gouldii), stoneflies (Illiesoperla mayii and Dinotoperla evansi) and caddisflies (Taschorema evansi, Taschorema complex, Ulmerochorema membrum, Cheumatopsyche sp. 2, Triplectides similis and Triplexa species).
The water was fresh (salinity ranged from 427-536 mg/L), well oxygenated (87-89% saturation), clear, and with moderately high concentrations of nutrients such as phosphorus (0.01-0.05 mg/L) and nitrogen (0.36-0.42 mg/L).
The sediments were dominated by detritus with coarse cobbles, pebbles, gravel and algae extensive in riffles and fine silt and clay in the pools; samples taken from below the surface were mostly grey clay and silt that released sulfide when tested in both seasons sampled, indicating that the sediments were anaerobic and lacked oxygen. There was no evidence of any significant areas of bank erosion and no animal droppings were seen in the vicinity of the creek.
Only a small to moderate amount of phytoplankton was recorded during the year (chlorophyll a ranged from 0.34-2.45 μg/L) but a filamentous alga (Cladophora) covered over 10% of the creek in spring. A similar area was also covered by aquatic plants, including knotweed (Persicaria), reeds (Phragmites), cumbungi (Typha) and introduced weeds such as watercress (Rorippa), dock (Rumex), blackberries and wild celery. The riparian zone was dominated by woody weeds such as willows and blackberries with a few native gums and wattles over an understorey mostly comprising various weeds, ivy and sedges. The surrounding vegetation near the site was mostly native eucalypt woodland with a weedy understorey, and further upstream the landscape comprised more cleared grazing land.
Special environmental features
The site provides an important habitat for a rich diversity of macroinvertebrates, including many rare and sensitive species.
Pressures and management responses
Pressures
Management responses
Widespread introduced weeds in the riparian zone at the site and upstream
The Adelaide and Mount Lofty Ranges NRM Board has several pest plant (weed) mitigation and control programs. They work closely with landholders to control weeds on their property and to help stop the spread to other properties and waterways.
This aquatic ecosystem condition report is based on monitoring data collected by the EPA. It was prepared with and co-funded by the Adelaide and Mount Lofty Ranges NRM Board.
Observed Condition
Expected Condition
