Riparian vegetation consists of native shrubs and gums, and a weedy understorey with rural residential land comprising mostly grazing pastures with some scattered gums beyond
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 to nutrient and organic enrichment of the stream, and riparian understory vegetation was dominated by weedy species. Only a limited number of tolerant macroinvertebrates were recorded from the non-flowing pool habitats that were present in 2015.
Findings
A sparse community of at least 15 species of macroinvertebrates was collected from this creek, approximately 3 m wide and 25 cm deep, in autumn and spring 2015. The creek consisted of isolated pools in both autumn and spring 2015, however the pools were too small to sample for macroinvertebrates in spring. The site was dominated by amphipods. Other species collected in smaller numbers included a range of generalist and pollution tolerant species, such as snails, beetles, mosquito larvae, non-biting midges and waterbugs. No sensitive or rare species were collected from this site. The introduced snail Physiella were seen in the creek. Frogs were heard calling and tadpoles were also seen at the site in spring.
The water was fresh to saline (salinity ranged from 952-4,497 mg/L), moderately well oxygenated (44-53% saturation) and clear but strongly coloured, with high concentrations of nutrients such as nitrogen (2.87 mg/L) and phosphorus (0.53 mg/L). Small patches of oil were noticed on the water’s edge in both autumn and spring.
The sediments were dominated by sand and silt with cobbles, pebbles, gravel, bedrock and some detritus also present. Samples taken from below the surface were grey sands and showed some 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 of 2.79 µg/L) and small amounts (<10%) of the filamentous algae Spirogyra were recorded from the site. More than 35% of site was covered by a range of emergent plants (Cyperus, Eleocharis,Isolepis, Juncus, Rumex and Typha). The riparian zone consisted of native shrubs and gums with a weedy understorey. The surrounding vegetation was rural residential land consisting of mostly grazing pastures with some scattered gums present.
Special environmental features
None detected
Pressures and management responses
Pressures
Management responses
Insufficient natural water flows in the creek resulting from water extraction and climate variability (reducing ecological integrity).
Through water allocation planning the Adelaide and Mount Lofty Ranges NRM Board seeks to manage a sustainable water supply for the region so that there is enough water available for everyone (including the environment) even in drought conditions.
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.