Hahndorf Creek rises near Hahndorf in the central Mount Lofty Ranges, and flows through a small catchment area into the Onkaparinga River just south of Verdun, near the South Eastern Freeway. Livestock grazing (57%) is the main land use but there are also extensive areas of urban development (26%) and some dairying (5%). The Hahndorf Wastewater Treatment Plant regularly discharges chlorinated effluent into the stream. The site selected for monitoring was located downstream of the treatment plant, off Main Road, on the eastern boundary of Hahndorf.
The creek was given a Poor rating because the site sampled showed evidence of major changes in ecosystem structure, and moderate changes to the way the ecosystem functions. There was considerable evidence of human disturbance including nutrient enrichment, degraded riparian vegetation and fine sediment deposition in the channel.
Findings
A sparse community of at least 27 species of macroinvertebrates was collected from the creek, 2.2-2.7 m wide and up to 47 cm deep, in autumn and spring 2011. The creek consisted of a narrow, slightly flowing channel in both seasons sampled. The community was dominated by generalists and species tolerant to poor water quality such as amphipods, corixid waterbugs and chironomids. It also included smaller numbers of limpets, introduced snails (Potamopyrgus and Physa), leeches, freshwater shrimp, yabbies, beetles, mosquitoes, mayflies, waterbugs, odonates and caddisflies. No rare or sensitive species were collected and the only flow-dependent species recorded was a chironomid (Rheotanytarsus) and dytiscid beetle (Platynectes). The only fish seen at the site was an introduced pest species called Mosquitofish (Gambusia).
The water was fresh (salinity ranged from 598-968 mg/L), well oxygenated (74-89% saturated), turbid, and with high concentrations of nutrients such as nitrogen (1.32-1.89 mg/L) and phosphorus (0.07-0.1 mg/L).
The sediments were dominated by detritus, silt and gravel. Samples taken from below the surface were blackened and sulfidic, indicating that the sediments were anaerobic and lacked oxygen. Large deposits of fine silt, 5-10 cm deep, covered the streambed in places but no significant areas of bank erosion were noted at the site in 2011.
About 10% of the creek was covered by filamentous algae (mostly Cladophora and Spirogyra) and over 10% of the site was covered by aquatic plants, including floating (Spirodela), submerged (Crassula) and emergent species (Rumex and introduced watercress Rorippa). The narrow riparian zone consisted of introduced trees (poplars and pines) and gums over extensive growths of weeds that included blackberries and Blue Periwinkle. The surrounding vegetation was a rural garden and its' associated plantings.
Special environmental features
Hahndorf Creek provides permanently flowing, freshwater habitats that support a few flow-dependent species.
Pressures and management responses
Pressures
Management responses
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 and wetland fencing to exclude or limit stock from entering riparian zones.
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.
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.
Wastewater discharges to the creek, adding excessive nutrients and organic matter (leading to algal growth and aquatic weeds).
SA Water Wastewater Treatment Plant at Hahndorf
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.
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Observed Condition
Expected Condition
