Cockatoo Creek, south from Kalbeeba
2011 Aquatic Ecosystem Condition Report
- Permanently wet, flowing, moderately fresh creek in autumn and spring 2011
- Diverse macroinvertebrate community with a few rare and flow-dependent species
- Obvious signs of moderate to gross nutrient enrichment
- Riparian vegetation consists of scattered gums over sedges, rushes and weeds.
About the location
Cockatoo Creek is a moderately sized stream in the Southern Mount Lofty Ranges that rises west from Williamstown and flows in a westerly direction into the South Para River near Gawler. The monitoring site was located on a track off Allendale Road, just before the junction with the South Para River and about 4 km east from Evanston Park. The major land uses in the 31,596 hectare catchment are stock grazing and remnant native vegetation, with smaller areas used for cereal cropping, orchards, rural residential living, water supply and quarries.
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, degraded riparian habitats, bank erosion and fine sediment deposited in the creek. Despite this the stream still provided habitat for a wide range of macroinvertebrate species.
A diverse community of at least 50 species of macroinvertebrates was collected from the flowing creek, 0.6-3.2 m wide and up to 20 cm deep, in autumn and spring 2011. Large areas of shallow, fast-flowing riffle habitat were present in autumn but were limited to only a few metres of slower-flowing habitat in spring. The community was dominated by large numbers of amphipods and blackflies, species tolerant to poor water quality and moderate salinity levels. It also included smaller numbers of flatworms, introduced and native snails, limpets, leeches, worms, isopods, springtails, beetles, craneflies, dixids, mosquitoes, biting midges, soldierflies, sciomyzids, chironomids, mayflies, waterbugs, odonates and caddisflies. Several species normally associated with flowing water were collected, including blackflies (Simulium ornatipes), hydropsychid caddisflies (Cheumatopsyche sp. 2) and dytiscid beetles (Platynectes decempunctatus). The only rare species collected were two chironomids in autumn (Harrissius and Harnischia) but no typically sensitive species were recorded from this site. No fish were seen at the site in 2011.
The water was moderately fresh (salinity ranged from 2,337-2,637 mg/L), well oxygenated (90-137% saturated), clear, and with low nutrient concentrations in autumn and moderate to high concentrations in spring (nitrogen 0.27-0.76 mg/L and phosphorus <0.005-0.02 mg/L).
The sediments were dominated by detritus, cobble and algae, with boulder, silt, sand and clay also present. Samples taken from below the surface were black, anaerobic and sulfidic, indicating that the sediments lacked oxygen and were a harsh environment for most burrowing species to live in. Over 5 cm of silt covered the creekbed in spring and more than 10 m of bank showed evidence of erosion caused by cattle accessing and damaging the edges of the stream.
Small amount amounts of filamentous algae were recorded in autumn but larger growths extended over 35% of the channel in spring. A similar area was covered by a range of submerged (Chara) and emergent aquatic plants (Juncus, Cyperus, Isolepis, Typha and Bolboschoenus).The narrow riparian zone was comprised a few gum trees over rushes, sedges and various weed species (e.g. artichokes and soursobs). The surrounding vegetation was cleared cattle grazing land with only a few scattered gums remaining in the local landscape.
Special environmental features
The presence of permanently flowing habitats that support a wide range of aquatic species, including a few rare and flow-dependent species, were significant features of this site on Cockatoo Creek.
Pressures and management responses
|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.|
|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.|
|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.