Torrens River, near Gumeracha
2008 Aquatic Ecosystem Condition Report
- Affected by nutrient enrichment and pumping operations from the River Murray.
- Diverse macroinvertebrate community dominated by species tolerant of pollution.
- Riparian vegetation mostly introduced trees and weeds.
About the location
The Torrens River rises north of Mount Pleasant in the southern Mount Lofty Ranges, and flows in a westerly direction through Adelaide before discharging into Gulf St Vincent at Henley Beach. In its upper reaches, the river runs through land used mainly for livestock grazing (70%), with some horticulture (11%), and small areas of dairy farming, native vegetation and urban development.
The site selected for monitoring was located at Poplar Grove, three kilometres east of Gumeracha on the Adelaide to Mannum Road, downstream from where River Murray water is pumped into the system via a pipeline from Mannum, and upstream from where water is diverted into the reservoir network.
The river was given a Fair rating at this site because the ecosystem showed moderate changes to animal and plant life, and some changes to the way the ecosystem functions. Nutrient levels were moderately high, and the riparian zone was in poor condition.
The stream was also affected by pumping operations which created an unnaturally high flow of turbid water coming from the River Murray, altering the structure and function of the river and changing the habitat so it favoured species better able to adapt to the conditions.
A diverse community of 44 species of macroinvertebrates was identified at the edge of the pools; chironomids (Thienemanniella, Corynoneura and Cricotopus) were common. Only 29 species were found in the riffles, including large numbers of worms and mayflies (Offadens). Low numbers of only one species sensitive to high nutrient levels were collected in both habitats–a mayfly (Atalophlebia australis).
The water was fresh (salinity of 263 mg/L) and well oxygenated (103% saturation). It was very cloudy or turbid, and had moderate to high levels of nutrients such as nitrogen (0.64 mg/L) and phosphorus (0.07 mg/L).
A moderate amount of algae was found at the site, including phytoplankton and green filamentous algae (Cladophora). Up to 35% of the channel was covered with aquatic plants such as Cumbungi (Typha), spikerush (Eleocharis), rush (Juncus), Water Ribbons (Triglochin) and watermilfoil (Myriophyllum).
Sediments at the bottom of the river were made up mostly of detritus and silt, with some cobbles and pebbles in the riffles. Only small patches of fine silt from the edge of the channel showed signs of being anaerobic; the rest were aerobic and provided suitable habitat for burrowing macroinvertebrate species.
Introduced species such as Desert Ash, willows, gorse and pasture grasses dominated vegetation in the riparian zone, which included River Red Gums. The surrounding area was covered mainly with introduced pasture species, and sparse eucalypt woodland.
Special environmental features
The Torrens River at Poplar Grove provides habitat for two types of mayflies (Atalophlebia australis and Offadens). These mayflies are typically found together in the wetter parts of the Mount Lofty Ranges. Their survival is probably sustained by the artificial flows of River Murray water.
Pressures and management responses
|Livestock have direct access at the site and upstream, causing sediment erosion and adding excessive nutrients (which leads to habitat disturbance, algal growth and aquatic weeds).||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 site and upstream, providing minimal buffer protection from catchment landuses (reducing habitat quality).||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 and prepared in conjunction with the Adelaide and Mount Lofty Ranges NRM Board.