Heathfield Creek is a small stream in the central Mount Lofty Ranges, which rises at Heathfield and flows into the Sturt River about two kilometres downstream. Near its headwaters, it receives a continuous discharge from the Heathfield Wastewater Treatment Plant (WWTP). Most of the upstream catchment is covered with remnant native vegetation (68%) but there are also some areas used for livestock grazing (25%) and urban development (5%).
The site selected for monitoring was located about 150 metres downstream from where the treated wastewater is discharged into the creek.
The creek was given a Very Poor rating at this site because the ecosystem showed evidence of major changes to both the animal and plant life, and a significant breakdown in the way the ecosystem functions because of human impact. The WWTP has contributed to significant nutrient enrichment and changes to natural flow patterns in the creek.
Findings
Slow-flowing riffle habitats up to 50 cm deep formed the creek at this site when it was sampled in October 2008.
The riffles provided habitat for about 18 macroinvertebrate species, which were present in only low numbers. The community was dominated by species which mostly feed on decaying organic material, including chironomids (Thienemaniella, Parakiefferiella, Rheotanytarsus and Polypedilum), worms and blackfly larvae (Austrosimulium furiosum). The only caddisflies collected were commonly found species tolerant of pollution, such as Lectrides varians and Triplectides australicus. No sensitive species were found.
Water quality was clearly influenced by discharges from the WWTP. While the water was fresh (salinity of 480 mg/L) and well oxygenated (91% saturation), it was very cloudy, or turbid, and contained very high concentrations of nutrients such as nitrogen (11.3 mg/L), phosphorus (1.1 mg/L) and oxidised nitrogen (8.9 mg/L). It was also more alkaline (pH 8.05) than expected for a stream in the region.
Despite the high nutrient levels no phytoplankton or green filamentous algae were found growing in the water. This was most likely because of the permanent water flow in this part of the creek, and the dense shade provided by the surrounding vegetation.
The sediments were mostly detritus, silt and clay; below the surface they were well aerated as a result of the continuous flows from the WWTP.
There was a high abundance of weedy plants such as Watercress (Rorippa nasturtium-aquaticum), knotweed (Persicaria) and dock (Rumex) growing along the edges of the creek.
Vegetation in the riparian zone was mostly eucalypt (box) woodland, with scattered River Red Gums growing over a range of woody and herbaceous weeds such as broom, blackberries, bamboo, watsonia, thistles and kikuyu. Bracken and small patches of sedge (Carex) also grew in places.
Native woodland with gums and acacias covered much of the surrounding area.
Special environmental features
None identified.
Pressures and management responses
Pressures
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.
Extensive weed growth 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 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.
Wastewater discharge, adding excessive nutrients and organic matter (leading to algal growth and aquatic weeds).
SA Water Heathfield Wastewater Treatment Plant
SA Water assess and undertake scheduled process improvement actions at the wastewater treatment plant, 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 and prepared in conjunction with the Adelaide and Mount Lofty Ranges NRM Board.
Observed Condition
Expected Condition
