The Torrens River is a large stream in the Southern Mount Lofty Ranges that rises a few kilometres north from Mount Pleasant and drains in a south-westerly direction where it discharges into Gulf St Vincent at Breakout Creek. The major land uses in the 20,722 hectare catchment are grazing pastures (65%) and irrigated horticulture (8%). The monitoring site was located off of Banks Road near Cudlee Creek.
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 fine sediment deposition. The stream provided habitat for only one sensitive macroinvertebrate species.
Findings
A moderately diverse community of at least 29 species of macroinvertebrates was collected from this site, approximately 4.5 m wide and 45 cm deep, in autumn and spring 2015. The creek consisted of slow-flowing connected pools in autumn 2015 but had ceased to flow by spring. The site was dominated by mites, amphipods, non-biting midges and water boatmen. Other species collected in smaller numbers included a range of generalist and pollution tolerant species, such as beetles, mayflies, waterbugs, and caddisflies. The mayfly Atalophlebia was the only sensitive species collected from this site. Introduced fauna such as the snail Physiella and mosquito fish were seen at the site and yabby holes were noticed in the river bed.
The water was fresh (salinity ranged from 506-628 mg/L), well oxygenated (81-84% saturation) and slightly turbid, with moderate to high concentrations of nutrients such as nitrogen (0.86-0.93 mg/L) and phosphorus (0.026-0.042 mg/L). Small patches of oil and froth were seen on the edges of the river in spring.
The sediments were dominated by boulders, cobbles and silt with some detritus also present. Samples taken from below the surface were sandy grey and showed no evidence of being anaerobic, or lacking oxygen. Small deposits of silt covered the streambed to a depth of between 1 and 5 cm in places and no significant areas of bank erosion were seen.
A small amount of phytoplankton (chlorophyll a ranged from 5.99-14.5 µg/L) which included a moderate amount of cyanobacteria or blue-green algae (chlorophyll b <0.1-1.01 µg/L) and small amounts (<35%) of the filamentous algae (Spirogyra) were recorded from the site. More than 10% of site was covered by a range of emergent plants such as Cyperus, Isolepis, Juncus, Polygonum, Phragmites, and Typha. The riparian zone consisted mainly of native shrubs with some weeds and the surrounding vegetation was rural gardens with exotic trees, gums, broom and exotic grasses.
Special environmental features
Torrens River provides habitat for the mayfly Atalophlebia.
Pressures and management responses
Pressures
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.
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.
Observed Condition
Expected Condition
