Riparian vegetation consisted of woody weeds over introduced grasses
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 a few sensitive and flow-dependent macroinvertebrates.
Findings
A moderately diverse community of at least 36 species of macroinvertebrates was collected or seen from the river (22 species in autumn and 24 in spring), nearly 4 m wide and more than 70 cm deep, in autumn and spring 2016. The creek was a slow-flowing connected channel during both sampling seasons. The community comprised large numbers of amphipods (Austrochiltonia) and low to moderate numbers of introduced snails (Physiella), mites, the amphipod Talitridae, shrimp, springtails, beetles, biting midges, chironomids (including Rheotanytarsus), mayflies (Offadens and Thraulophlebia inconspicua), waterbugs, and leptocerid caddisflies. Yabby holes were also seen along the wet banks of the stream during both seasons. The majority of species collected were tolerant and generalist species that have a wide distribution in the region and the rest of the State, with few sensitive or flow-dependent species collected.
The water was fresh (salinity ranged from 371-981 mg/L), well oxygenated (83-113% saturation), turbid and slightly coloured in autumn but clear in spring, and with moderate to high concentrations of nutrients such as phosphorus (0.03-0.09 mg/L) and nitrogen (0.40-0.88 mg/L). Small patches of oils were also noticed on the edge of the creek in spring.
The sediments were dominated by sand and clay, and algae in spring with smaller amounts of cobble, pebble, silt and detritus also present. Samples taken from below the surface were mostly grey clays 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. More than 5 cm of silt has been deposited in the creek bed, possibly from the eroded banks or sourced from the large catchment upstream. The only animal droppings seen in the vicinity of the site were from ducks that congregate on the water’s edge.
A large amount of filamentous algae (Cladophora) was present and extended over more than 65% of the site in spring but only a small amount of phytoplankton (chlorophyll a ranged from 0.34-2.8 μg/L) was detected during 2016. Less than 35% of the channel was covered by sedges (Cyperus), reeds (Phragmites) and dock (Rumex). The riparian zone consisted of exotic grasses, castor oil plants and bamboo. The surrounding vegetation beyond 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, mayflies and chironomids. It has also provided habitat for stoneflies in the past.
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.
Wastewater discharges to the creek, adding excessive nutrients and organic matter (potentially leading to excess algal growth and aquatic weeds)
SA Water Wastewater Treatment Plant at 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.
Livestock having direct access at the site and 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 (e.g., stream and creek) and wetland fencing to exclude or limit stock from entering riparian zones.
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.
Observed Condition
Expected Condition
