Riparian vegetation consisted of gums and woody weeds over introduced grasses, weeds and native species
Area map
About the location
The Sturt River is a moderately sized stream in the Southern Mount Lofty Ranges that rises west from Heathfield and flows in a westerly direction to Bedford Park, where it has been channelised as it passes through the south-western suburbs and discharges into the Patawalonga. The monitoring site was located upstream from Sturt Road in Bedford Park. The major land uses in the 7,264 hectare catchment are unmapped areas of remnant native vegetation (38%), residential (16%), nature conservation (15%), and minor areas of other minimal uses, grazing pastures, roads, dams, irrigated cropping, intensive animal production and the Heathfield Wastewater Treatment Plant.
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 due to nutrient enrichment and the extent of woody weeds and other introduced plants in the riparian zone. However, the stream also provides habitat for several sensitive and flow-dependent macroinvertebrates.
Findings
A moderately diverse community of at least 28 species of macroinvertebrates was collected or seen from the river (19 species in autumn and 14 in spring), 1.3-5.4 m wide and up to 50 cm deep, in autumn and spring 2013. The river mostly consisted of still to slow -flowing pool habitats connected by small areas of faster-flowing riffle habitats in both seasons sampled. The community comprised low to moderate numbers of turbellarians, introduced snails (Potamopyrgus and Physa), worms, mites, amphipods, shrimp, springtails, beetles, blackflies (Austrosimulium furiosum and Simulium ornatipes), chironomids (including Rheotanytarsus), baetid mayflies (Cloeon), waterbugs, stoneflies (Dinotoperla evansi) and caddisflies. Yabby holes were also seen along the wet banks of the stream during each survey period. The riffles were too small to sample but provided habitat for blackflies, beetles (Platynectes), stoneflies, baetid mayflies, worms, chironomids and hydropsychid caddisflies (Cheumatopsyche). The majority of species collected were tolerant and generalist species that have a wide distribution in the region and in South Australia. No rare species were recorded and the only sensitive and/or flow-dependent species collected were the above-listed blackflies, chironomid, stonefly and caddisfly. The dytiscid beetle Platynectes is also usually associated with flowing water but may also occur in well-aerated pool habitats.
The water was fresh (salinity ranged from 759-881 mg/L), well oxygenated (77-115% saturation), clear, and with moderate to high concentrations of nutrients such as phosphorus (0.05-0.06 mg/L) and nitrogen (0.61-0.73 mg/L).
The sediments were dominated by detritus, cobble and sand, with smaller amounts of pebble, gravel, silt, clay and boulder also present; samples taken from below the surface were mostly grey sands and silts that showed no signs that the sediments had recently been anaerobic or lacking in oxygen. There was a small amount of bank erosion extending over about 10% of the site which appeared to have been caused by past flow damage. The only animal droppings seen in the vicinity of the site were from ducks that congregate on the water’s edge.
There was no sign of any filamentous algae and only a small amount of phytoplankton (chlorophylla ranged from 0.34-1.23 μg/L) present during 2013. Over 10% of the channel was covered by sedges (Cyperus) and reeds (Phragmites). The riparian zone consisted of gums and introduced Ash trees over a weedy understorey with grasses and onion grass, and a few reeds and sedges. The surrounding vegetation near the creek comprised a caravan park, which included a grassed recreational area, on one bank and a narrow strip of native vegetation surrounding a bike trail and wetland on the other bank.
Special environmental features
Sturt River provides a permanently flowing, freshwater stream that consistently supports a number of flow-dependent species, including blackflies, stoneflies, caddisflies and chironomids.
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.
Wastewater discharges to the creek, adding excessive nutrients and organic matter (leading to algal growth and aquatic weeds).
SA Water Wastewater Treatment Plants at Hahndorf and Heathfield
SA Water assess and undertake scheduled process improvement actions at wastewater treatment plants, with the aim to reduce environmental risk and ensure operations are compliant with EPA licence conditions.
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.