Unnamed creek, flows into the northern part of Millbrook Reservoir
2011 Aquatic Ecosystem Condition Report
- Permanently wet, freshwater creek with fast-flowing habitats in autumn and slow-flowing channel in spring
- Highly diverse macroinvertebrate community with several rare, sensitive and flow-dependent species
- Obvious signs of moderate nutrient enrichment
- Riparian vegetation consists of native trees over a range of native plants and weeds
About the location
This creek is a small stream in the Southern Mount Lofty Ranges that rises north from Millbrook Reservoir and flows southwards for over 2 km before it discharges into the reservoir. The monitoring site was located off the Adelaide-Mannum Road, about 1.5 km north-east from Chain of Ponds. The major land use in the 253 hectare catchment is stock grazing, with smaller areas used for water supply (Millbrook Reservoir), roads, irrigated cropping, hay production, remnant native vegetation and rural residential living.
The creek was given a Fair rating because the site sampled showed evidence of moderate changes in ecosystem structure, and some changes to the way the ecosystem functions. There was evidence of human disturbance including nutrient enrichment and woody weeds that occurred in the riparian zone. The extent of nutrient damage at the site was considered too significant to assign this creek a better rating.
A diverse community of at least 57 species of macroinvertebrates was collected from the flowing creek, 0.8-2.3 m wide and up to 29 cm deep, in autumn and spring 2011. The creek was strongly flowing in autumn but consisted of a slow-flowing channel with small areas of fast-flowing riffles in spring. The community was dominated by species tolerant to poor water quality and some sensitive macroinvertebrates. The most abundant species collected from riffle habitats were stoneflies whereas the slow-flowing pool and channel habitats supported large numbers of baetid mayflies, chironomids, dytiscid beetles and mosquitoes. The community also included smaller numbers of limpets, native snails, worms, mites, amphipods, other beetles, craneflies, dixids, blackflies, leptophlebiid mayflies, waterbugs, odonates and caddisflies. Several sensitive or rare species were collected from the site, including mayflies (Thraulophlebia inconspicua and Atalophlebia australis), stoneflies (Austrocerca tasmanica and small specimens from the Family Gripopterygidae), caddisflies (Taschorema evansi and Leptorussa), and a blackfly (Austrosimulium furiosum) and chironomid (Podonomopsis). The site also supported a range of species normally associated with flowing water, including another blackfly (Simulium ornatipes), a caddisfly (Cheumatopsyche) and many of the above-listed rare and sensitive species. The only fish seen at the site were introduced Redfin Perch.
The water was fresh (salinity ranged from 363-497 mg/L), generally well oxygenated (51-66% saturated), slightly turbid and coloured, and with moderate to high concentrations of nutrients such as nitrogen (0.92-1.25 mg/L) and phosphorus (0.06-0.07 mg/L).
The sediments were dominated by detritus, sand, silt and cobble in the slower-flowing pools whereas the riffles mostly consisted of cobble, silt and detritus. Samples taken from below the surface were grey in colour and showed no evidence that the sediments were anaerobic or lacked oxygen. A deposit of 1-5 cm of silt covered the creekbed in autumn but only about 1 cm was evident in spring. A small amount of bank erosion extended over about 10 m of the site in spring, presumably caused by recent winter floods that transported most of the fine sediment further downstream into the reservoir.
Large growths of filamentous algae (including Cladophora) covered over 65% of the channel in autumn but none was detected in spring. Aquatic plants covered over 10% of the site and comprised both submerged (Nitella and Callitriche) and emergent species (Bolboschoenus, Cyperus, Hydrocotyle, Juncus, Rumex and Ranunculus). The narrow riparian zone consisted of a native overstorey of gums and wattles, a shrub layer of tea tree and woody weeds (broom, gorse and blackberries), and an understorey of introduced grasses, rushes and dock. The surrounding vegetation at the site was native woodland, with introduced grasses dominating the understorey.
Special environmental features
The creek supports a wide range of aquatic animals and plants, including several rare, sensitive and flow-dependent macroinvertebrate species. The permanently flowing, freshwater habitats provided by this Unnamed Creek are significant natural resource assets in the region.
Pressures and management responses
|Livestock having direct access at the site and upstream (causing sediment erosion and adding excessive nutrients).||The Adelaide and Mount Lofty Ranges NRM Board’s land management program encourages and promotes managing land to improve water quality. This includes incentives for waterway and wetland fencing to exclude or limit stock from entering riparian zones.|
|Widespread introduced weeds in the riparian zone at the site and upstream (reducing habitat quality).||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.|
|Limited riparian zone vegetation at the creek and upstream (reducing habitat quality, increasing sediment erosion).||The Adelaide and Mount Lofty Ranges NRM Board’s land management program encourages and promotes managing land to improve water quality. This includes incentives for revegetation programs around waterways and wetlands and stock exclusion as well as educating landholders about the importance of riparian vegetation in managing soil erosion.|
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.