Creek comprised isolated pools in autumn and a connected non-flowing channel in spring 2016
Sparse macroinvertebrate community with no rare, sensitive or flow-dependent species present
Water was moderately fresh, clear but coloured, and enriched with nutrients
Riparian vegetation consisted of a scattered River Red Gums over introduced grasses, weeds, and a few rushes
Area map
About the location
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 monitoring site was located in the upper catchment upstream from Glen Devon Road, about 1 km north from Mount Pleasant. The major land use in the 1,539 hectare catchment was stock grazing (74%), with smaller areas used for irrigated horticulture, plantation forestry, other minimal uses, dams and residential living.
The river was given a Poor rating because the site sampled showed evidence of major changes in ecosystem structure and function. There was evidence of human disturbance due significant nutrient enrichment of the stream and riparian understorey vegetation was dominated by weeds, but the creek still supported a range of tolerant and generalist aquatic macroinvertebrates.
Findings
A sparse community of at least 26 species of macroinvertebrates was collected or seen from the river (6 species in autumn and 25 in spring), 5 m wide and up to 50 cm deep, in autumn and spring 2016. The river consisted of isolated pools in autumn and a connected, non-flowing channel in spring. The community was dominated by large numbers of mites and backswimmers, and included low to moderate numbers of native and introduced snails, amphipods, springtails, beetles, mosquitoes, chironomids, mayflies, water boatmen, dragonflies and caddisflies. All were common generalist and opportunistic species that are well adapted to tolerate organically polluted streams. No rare, sensitive or flow-dependent species were seen during 2016.
The water was generally moderately fresh (salinity ranged from 1,075-1,535 mg/L), with occasionally low oxygen levels (26-89% saturation), and was clear but strongly coloured, and with very high concentrations of nutrients such as phosphorus (0.05-0.25 mg/L) and nitrogen (1.5-2.9 mg/L). Small patches of oil were noticed on the edge of the water during both sampling events.
The sediments were dominated by detritus and silt with smaller amounts of coarser substrates also present. Samples taken from below the surface were grey sands that had an anaerobic odour in spring, indicating the sediments lack oxygen on occasion. There was no evidence of bank erosion. No stock had accessed the stream in recent times based on the lack of any droppings near the river.
There was a moderate amount of phytoplankton recorded (chlorophyll a ranged from 0.68-1.63 μg/L) but no filamentous algae was seen at the site in either season sampled. Over 10% of the channel was covered by several types of aquatic plants, including cumbungi (Typha), sedges (Cyperus, Eleocharis and Isolepis), rush (Juncus), creeping monkey-flower (Mimulus), star-wort (Callitriche) and dock (Rumex). The riparian zone extended more than 10 m wide in places and was dominated by scattered River Red Gums over introduced grasses, weeds, and a few rushes. The surrounding vegetation comprised cattle grazing paddocks with a few large gums in the local landscape.
Special environmental features
None identified.
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.
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. The Board also partner with local government to deliver a number of watercourse revegetation projects across the region.
Nutrient inputs to the creek from numerous diffuse sources (potentially leading to excess growth of algae and aquatic weeds)
The Adelaide and Mount Lofty Ranges NRM Board land management program encourages and promotes managing land to improve water quality. This includes working with industry and landholders to ensure efficient use of fertilisers and discuss ways to reduce runoff of nutrients into waterways.
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.
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Observed Condition
Expected Condition
