Torrens River, north from Mount Pleasant (WAP site 1)
2011 Aquatic Ecosystem Condition Report
- Permanently wet, slightly flowing, moderately freshwater stream in autumn and spring 2011
- Moderately diverse macroinvertebrate community with no rare or sensitive species
- Obvious signs of moderate to gross nutrient enrichment
- Riparian vegetation dominated by introduced grasses.
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 near a track off Glen Devon Road, about 1 km north from Mount Pleasant. The major land use in the 1,536 km catchment is stock grazing, with smaller areas used for recreation, remnant native vegetation, forestry and irrigated cropping.
The river 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 vegetation and fine sediment deposition in the channel. The site sampled supported a wide range of macroinvertebrate species which contributed towards its assigned rating, however, the level of disturbance was significant and the site could arguably have been rated in an even worse condition.
A moderately diverse community of at least 31 species of macroinvertebrates was collected from the river, 3.1 m wide and up to 63 cm deep, in autumn and spring 2011. The river consisted of a still to slow-flowing channel in both seasons sampled. The community was dominated by generalists and species tolerant to poor water quality such as mites, chironomids and amphipods (Austrochiltonia). It also included smaller numbers of limpets, native and introduced snails, worms, freshwater shrimp, springtails, beetles, dixids, soldierflies, mayflies, waterbugs, odonates and caddisflies. No sensitive or rare species were collected and the only flow-dependent macroinvertebrate collected was a dytiscid beetle (Platynectes). The only fish seen at the site was an introduced pest called Mosquitofish (Gambusia).
The water was moderately fresh (salinity ranged from 1,240-1,508 mg/L), well oxygenated (62-71% saturated), clear and slightly coloured, and with moderate to high concentrations of nutrients such as nitrogen (1.14-1.33 mg/L) and phosphorus (0.03-0.06 mg/L).
The sediments were dominated by detritus and algae, with bedrock, pebble, sand and silt also present. Samples taken from below the surface were blackened and sulphidic, indicating that the sediments were anaerobic and lacked oxygen. A large deposit of fine silt, 1-5 cm deep, covered the streambed in places but there was no evidence of any significant areas of bank erosion at the site in 2011.
Over 35% of the channel was covered by filamentous algae (including Cladophora and Spirogyra) and a similar area was covered by aquatic plants. Extensive growths of submerged pondweed (Stuckenia) were recorded as well as patches of several types of emergent plants (Bolboschoenus, Cyperus, Juncus, Eleocharis, Rumex, Schoenoplectus and Typha). The riparian vegetation was dominated by introduced grasses under isolated River Red Gums, tea trees, paperbarks and wattles. The surrounding vegetation was cleared cropping and grazing land with a few scattered gum trees remaining in the local landscape.
Special environmental features
The site sampled from the Torrens River near Mount Pleasant provided permanently wet, freshwater habitat that supported a wide range of aquatic macroinvertebrates, including at least one flow-dependent species.
Pressures and 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.|
|Livestock having direct access to the creek 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.