Tributary of the Torrens River, 3 km south-west from Gumeracha
2011 Aquatic Ecosystem Condition Report
- Permanently wet, freshwater creek with fast-flowing habitats in autumn but only a slow-flowing channel present in spring
- Moderately diverse macroinvertebrate community with some rare, sensitive and flow-dependent species
- Obvious signs of moderate nutrient enrichment
- Riparian vegetation dominated by willows and other introduced weeds and grasses
- Large silt deposits present throughout the channel.
About the location
This creek is a small stream in the Southern Mount Lofty Ranges that rises about 1 km south-west from Gumeracha near ‘Avro’ and flows in a westerly direction into the Torrens River about 1.5 km downstream from Gumeracha Weir. The monitoring site was located on a track off Retreat Valley Road, about 3 km south-west from Gumeracha. The major land use in the 441 hectare catchment is stock grazing, with smaller areas of remnant native vegetation, forestry, irrigated cropping 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 degraded riparian habitats, large deposits of fine sediment in the creek and some emerging signs of nutrient enrichment.
A moderately diverse community of at least 31 species of macroinvertebrates was collected from the flowing creek, 1-3.5 m wide and up to 120 cm deep, in autumn and spring 2011. About 20% of the site consisted of fast-flowing riffle habitat in autumn but only about 3% comprised slower-flowing riffles in spring. The community was dominated by generalists and species tolerant to poor water quality such as chironomids, mites, blackfly larvae, introduced snails (Physa) and amphipods; more sensitive stoneflies were also commonly collected from the edges of pools during the spring survey. Other types of macroinvertebrates found in much lower numbers included flatworms, native snails, worms, springtails, beetles, dixids, soldierflies, sciomyzids, waterbugs, odonates and caddisflies. The only sensitive and rare species collected were two stoneflies (Austrocerca tasmanica and small specimens from the Family Gripopterygidae), a blackfly (Austrosimulium furiosum) and chironomid (Podonomopsis). The site also provided habitat for a few species normally associated with flowing water, including another type of blackfly (Simulium ornatipes) and the above-listed rare and sensitive species. No fish was seen at the site in 2011.
The water was fresh (salinity ranged from 423-559 mg/L), generally well oxygenated (50-63% saturated), clear and slightly coloured, and with moderately high concentrations of nutrients such as nitrogen (0.39-0.45 mg/L) and phosphorus (0.02-0.03 mg/L).
The sediments were dominated by detritus, silt and clay. Samples taken from below the surface were black in colour and anaerobic in autumn but the sediments appeared well oxygenated in spring. A large deposit of over 10 cm of silt covered the creekbed in autumn and spring. No significant areas of bank erosion were noted during either survey in 2011.
Over 10% of the channel was covered by filamentous algae (including Cladophora) in autumn but it was not detected again in spring. Aquatic plants covered about 10% of the site in both seasons sampled, comprising a range of emergent species (Hydrocotyle, Isolepis, Juncus, Persicaria, Phragmites, Ranunculus, Rumex and introduced Rorippa). The riparian zone consisted of a dense growth of woody weeds such as willows, gorse and blackberries over introduced grasses. The surrounding vegetation was dominated by vineyards and included cleared paddocks used for cattle grazing.
Special environmental features
The permanently flowing, freshwater habitats support a small number of rare, sensitive and flow-dependent species.
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 trees and 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.