Permanently flowing stream in autumn and spring 2016
Diverse macroinvertebrate community with many rare, sensitive and flow-dependent species recorded
Water was fresh, clear and generally low in nutrients
Riparian vegetation consisted of weedy trees and grasses
Area map
About the location
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, grazing and rural residential housing. The monitoring site was located on the main channel at the ford on the CFS track, accessed from Brownhill Creek Road and about 1.4 km upstream from 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 a degraded riparian zone and filamentous algae in autumn but the stream provides habitat for a 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 (32 species in autumn and 32 in spring), 1.3-2.5 m wide and up to 23 cm deep, in autumn and spring 2016. The creek consisted of mostly fast-flowing riffles (80%) and slow-flowing to still pools (20%) in autumn, but pools (60%) dominated riffle (40%) habitats in spring. The community was dominated by moderate numbers of mostly tolerant and generalist species such as introduced snails (Potamopyrgus and Physiella), chironomids, and caddisflies (Lectrides). It also included smaller numbers of flatworms, bivalves, worms, mites, amphipods, beetles, biting midges, blackflies, soldierflies, baetid and caenid mayflies, waterbugs, dragonflies, stoneflies and caddisflies. A number of rare, sensitive and/or flow-dependent species were collected, including blackflies (Austrosimulium and Simulium), a chironomid (Rheotanytarsus), mayflies (Atalophlebia australasica and Thraulophlebia), dragonflies (Hemigomphus and Synthemis), stoneflies (Illiesoperla and Dinotoperla), and caddisflies (Taschorema evansi, Taschorema complex, Ulmerochorema, Cheumatopsyche and Lingora).
The water was fresh (salinity ranged from 340-436 mg/L), well oxygenated only in autumn (28-76% saturation), clear, and with generally low to moderate concentrations of nutrients such as phosphorus (0.02-0.05 mg/L) and nitrogen (0.16-0.25 mg/L).
The sediments were dominated by silt, detritus, pebble and cobble; samples taken from below the surface were mostly grey clay and silt that did not release any sulfide when tested, indicating that the sediments were well oxygenated. However, the underside of rocks buried in the sediments were black, which indicates that they have occasionally lacked oxygen for at least part of the year. There was no evidence of any bank erosion and no animal droppings were seen in the vicinity of the creek. But fine sediment does accumulate in pools on occasion because silt covered most rocks in the channel during the autumn survey; none was seen in spring, presumably due to its mobilisation further downstream during winter flooding.
Only a small amount of phytoplankton was recorded (chlorophyll a ranged from 0.14-0.49 μg/L) and a filamentous alga (Spirogyra) was only seen in autumn, when it extended over nearly 10% of the creek. A similar area was also covered by aquatic plants, including sedges (Cyperus) and rushes (Juncus). The narrow riparian zone was dominated by introduced grasses under woody weeds such as willows and ash trees. The surrounding terrestrial vegetation was a dense eucalypt woodland with a weedy understorey dominated by grasses.
Special environmental features
The site supported a significant number of mayflies, stoneflies, caddisflies, blackflies and a dragonfly and chironomid, as well as a range of other more generalist and tolerant species of macroinvertebrates. The nutrient concentrations recorded in 2016 were among the lowest recorded from the region, although the presence of filamentous algae in autumn indicates that the stream may be affected by excess nutrients some of the time.
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.
Insufficient natural water flows in the creek resulting from water extraction and climate variability
Through water allocation planning the Adelaide and Mount Lofty Ranges NRM Board seeks to manage a sustainable water supply for the region so that there is enough water available for everyone (including the environment) even in drought conditions.
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
